Selection-based intra coding using non-angular candidates

Abstract

A decoder obtains a selection indication for a current block coded using an intra-based coding mode. A histogram of intra prediction modes (IPMs) is updated based on a first block reconstructed using a non-angular mode and selected for the current block. In accordance with the obtained selection indication, the histogram is updated based on one or both of: a first set of one or more IPMs associated with the first block, or a second set of one or more IPMs associated with a second block that overlaps a reference block indicated by the non-angular mode for the first block. The decoder reconstructs the current block based on the updated histogram.

Description

Docket No.: 24-2016PCT TITLE Selection-based Intra Coding using Non-angular Candidates CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.63 / 667,780, filed July 4, 2024, which is hereby incorporated by reference in its entirety. BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Some features are shown by way of example, and not by limitation, in the accompanying drawings. In the drawings, like numerals reference similar elements.

[0003] FIG. 1 shows an example video coding / decoding system in which embodiments of the present disclosure may be implemented.

[0004] FIG. 2 shows an example encoder in which embodiments of the present disclosure may be implemented.

[0005] FIG. 3 shows an example decoder in which embodiments of the present disclosure may be implemented.

[0006] FIG.4 shows an example quadtree partitioning of a coding tree block (CTB).

[0007] FIG.5 shows an example quadtree corresponding to the example quadtree partitioning of the CTB in FIG.4.

[0008] FIG.6 show examples of binary tree and ternary tree partitions.

[0009] FIG.7 shows an example of combined quadtree and multi-type tree partitioning of a CTB.

[0010] FIG. 8 shows an example tree corresponding to the combined quadtree and multi-type tree partitioning of the CTB shown in FIG.7.

[0011] FIG.9 shows an example set of reference samples determined for intra prediction of a current block.

[0012] FIG.10A and FIG.10B show example intra prediction modes.

[0013] FIG.11 shows an example of a current block and corresponding reference samples.

[0014] FIG.12 shows an example of applying an intra prediction mode (e.g., an angular mode) for prediction of a current block.

[0015] FIG.13A shows an example of inter prediction performed for a current block in a current picture.

[0016] FIG.13B shows an example motion vector.

[0017] FIG.14 shows an example of bi-prediction performed for a current block.

[0018] FIG.15A shows example spatial candidate neighboring blocks relative to a current block being coded.

[0019] FIG.15B shows example locations of two temporal, co-located blocks relative to a current block.

[0020] FIG.16A shows an example of intra block copy (IBC).

[0021] FIG.16B shows an example of Reconstruction-Reordered Intra Block Copy (RR-IBC).Docket No.: 24-2016PCT

[0022] FIG. 17 shows an example of intra template matching prediction (IntraTMP) for predicting or determining a current block, according to some embodiments.

[0023] FIG.18 shows an example of decoder-side intra mode derivation (DIMD) for coding a current block, according to some embodiments.

[0024] FIG.19 shows an example of a template (e.g., template area) for computing a histogram of gradient (HoG) used in DIMD, according to some embodiments.

[0025] FIG.20 shows an example flowchart of the DIMD predictor derivation process, according to some embodiments.

[0026] FIG.21 shows an example of neighboring blocks of a current block used to determine a histogram, according to some embodiments.

[0027] FIG.22A shows an example flowchart of a method for determining a merged HoG (MHoG) for a current block, according to some embodiments.

[0028] FIG.22B shows an example flowchart of a method for determining a histogram of occurrences (HoC) for a current block, according to some embodiments.

[0029] FIG. 23A shows an example of IPM information from a plurality of (previously reconstructed) neighboring blocks of a current block, according to some embodiments.

[0030] FIG.23B shows an example graphical representation of combining the IPM information from the plurality of neighboring blocks of FIG.23A to generate an MHoG if the block was previously coded using the MIMD mode, according to some embodiments.

[0031] FIG.23C shows an example graphical representation of combining the IPM information from the plurality of neighboring blocks of FIG.23A to generate an HoC if the block was previously coded using the OBIC mode, according to some embodiments.

[0032] FIG.24A shows an example flowchart of the DIMD Merge List mode for deriving a list of DIMD merge candidates, according to some embodiments.

[0033] FIG.24B shows a flowchart of an example process for generating a history-based table of DIMD merge candidates, according to some embodiments.

[0034] FIG. 25 shows an example of a matrix-based intra prediction (MIP) mode, according to some embodiments.

[0035] FIG.26 shows an example of template-based intra mode derivation (TIMD) for coding a current block, according to some embodiments.

[0036] FIG.27A shows an example of a current block and neighboring blocks being coded in DIMD-based modes and non-angular modes, according to some embodiments.

[0037] FIG.27B shows an example of obtaining IPM information from neighboring blocks of a current block that are not coded using a DIMD-based mode, according to some embodiments.Docket No.: 24-2016PCT

[0038] FIG.28A shows an example of a target block overlapping a reference block indicated by a BV obtained by a non-angular mode used to code candidate block, according to some embodiments.

[0039] FIG.28B shows an example of a plurality of target blocks overlapping reference block indicated by a BV obtained by a non-angular mode, according to some embodiments.

[0040] FIG.29 shows an example of a plurality of reference blocks indicated by a plurality of respective BVs obtained by an IntraTMP mode with fusion used to code candidate block, according to some embodiments.

[0041] FIG.30 shows an example of a target block overlapping a reference block indicated by a BV obtained by a non-angular mode associated with flipping in a direction and used to code candidate block, according to some embodiments.

[0042] FIG. 31 shows a flowchart of an example method for selecting DIMD merge candidates from neighboring blocks of a current block to generate a histogram used by a DIMD-based mode to code the current block, according to some embodiments.

[0043] FIG. 32 shows a flowchart of an example method for selecting DIMD merge candidates from neighboring blocks of a current block to generate a histogram used by a DIMD-based mode to code the current block, according to some embodiments.

[0044] FIG.33A shows a flowchart of an example method for coding a current block based on an intra- based coding mode using one or more blocks coded in a non-angular (coding) mode, according to some embodiment.

[0045] FIG.33B shows a flowchart of an example method for coding a current block based on an intra- based coding mode using one or more blocks coded in a non-angular (coding) mode, according to some embodiment.

[0046] FIG.34A illustrates a flowchart of a process for, in the process of FIG.33A or FIG.33B, choosing between directly obtained intra prediction mode information associated with the blocks coded using the non- angular mode and indirectly obtained intra prediction mode, according to some embodiments.

[0047] FIG.34B, FIG.34C and FIG.34D illustrate flowcharts of processes for, in the process of FIG.33A or FIG.33B, choosing between directly obtained intra prediction mode information associated with the blocks coded using the non-angular mode and indirectly obtained intra prediction mode, according to some embodiments.

[0048] FIG.35 illustrates a block diagram of an example computer system in which embodiments of the present disclosure may be implemented. DETAILED DESCRIPTION

[0049] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. However, it will be apparent to those skilled in the art that the disclosure, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to mostDocket No.: 24-2016PCT effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the disclosure.

[0050] References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0051] Also, it is noted that individual embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in a figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination can correspond to a return of the function to the calling function or the main function.

[0052] The term “computer-readable medium” includes, but is not limited to, portable or non-portable storage devices, optical storage devices, and various other mediums capable of storing, containing, or carrying instruction(s) and / or data. A computer-readable medium may include a non-transitory medium in which data can be stored and that does not include carrier waves and / or transitory electronic signals propagating wirelessly or over wired connections. Examples of a non-transitory medium may include, but are not limited to, a magnetic disk or tape, optical storage media such as compact disk (CD) or digital versatile disk (DVD), flash memory, memory or memory devices. A computer-readable medium may have stored thereon code and / or machine-executable instructions that may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and / or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, or the like.

[0053] Furthermore, embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasksDocket No.: 24-2016PCT (e.g., a computer-program product) may be stored in a computer-readable or machine-readable medium. A processor(s) may perform the necessary tasks.

[0054] A video sequence, comprising multiple pictures / frames, may be represented in digital form for storage and / or transmission. Representing a video sequence in digital form may require a large quantity of bits. Large data sizes that may be associated with video sequences may require significant resources for storage and / or transmission. Video encoding may be used to compress a size of a video sequence for more efficient storage and / or transmission. Video decoding may be used to decompress a compressed video sequence for display and / or other forms of consumption.

[0055] FIG.1 shows an example video coding / decoding system 100 in which embodiments of the present disclosure may be implemented. Video coding / decoding system 100 comprises a source device 102, a transmission medium 104, and a destination device 106. Source device 102 encodes a video sequence 108 into a bitstream 110 for more efficient storage and / or transmission. Source device 102 may store and / or send / transmit bitstream 110 to destination device 106 via transmission medium 104. Destination device 106 decodes bitstream 110 to display video sequence 108. Destination device 106 may receive bitstream 110 from source device 102 via transmission medium 104. Source device 102 and / or destination device 106 may be any of a plurality of different devices (e.g., a desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, video streaming device, etc.).

[0056] Source device 102 may comprise (e.g., for encoding video sequence 108 into bitstream 110) one or more of a video source 112, an encoder 114, and / or an output interface 116. Video source 112 may provide and / or generate video sequence 108 based on a capture of a natural scene and / or a synthetically generated scene. A synthetically generated scene may be a scene comprising computer generated graphics and / or screen content. Video source 112 may comprise a video capture device (e.g., a video camera), a video archive comprising previously captured natural scenes and / or synthetically generated scenes, a video feed interface to receive captured natural scenes and / or synthetically generated scenes from a video content provider, and / or a processor to generate synthetic scenes.

[0057] A video sequence, such as video sequence 108, may comprise a series of pictures (also referred to as frames). A video sequence may achieve an impression of motion based on successive presentation of pictures of the video sequence using a constant time interval or variable time intervals between the pictures. A picture may comprise one or more sample arrays of intensity values. The intensity values may be taken (e.g., measured, determined, provided) at a series of regularly spaced locations within a picture. A color picture may comprise (e.g., typically comprises) a luminance sample array and two chrominance sample arrays. The luminance sample array may comprise intensity values representing the brightness (e.g., luma component, Y) of a picture. The chrominance sample arrays may comprise intensity values that respectively represent the blue and red components of a picture (e.g., chroma components, Cb and Cr) separate fromDocket No.: 24-2016PCT the brightness. Other color picture sample arrays may be possible based on different color schemes (e.g., a red, green, blue (RGB) color scheme). A pixel, in a color picture, may refer to / comprise / be associated with all intensity values (e.g., luma component, chroma components), for a given location, in the sample arrays (e.g., three sample arrays are used for one luma component and two chroma components, respectively) used to represent color pictures. A monochrome picture may comprise a single, luminance sample array. A pixel, in a monochrome picture, may refer to / comprise / be associated with the intensity value (e.g., luma component) at a given location in the single, luminance sample array used to represent monochrome pictures.

[0058] Encoder 114 may encode video sequence 108 into bitstream 110. Encoder 114 may apply / use (e.g., to encode video sequence 108) one or more prediction techniques to reduce redundant information in video sequence 108. Redundant information is information that may be predicted at a decoder and need not be transmitted to the decoder for accurate decoding of video sequence 108. For example, encoder 114 may apply spatial prediction (e.g., intra-frame or intra prediction), temporal prediction (e.g., inter-frame prediction or inter prediction), inter-layer prediction, and / or other prediction techniques to reduce redundant information in video sequence 108. Encoder 114 may partition pictures comprising video sequence 108 into rectangular regions referred to as blocks, for example, before applying one or more prediction techniques. Encoder 114 may then encode a block using the one or more of the prediction techniques.

[0059] For temporal prediction, encoder 114 may search for a block similar to the block being encoded in another picture (e.g., referred to as a reference picture) of video sequence 108. The block determined during the search (e.g., referred to as a prediction block) may then be used to predict the block being encoded. For spatial prediction, encoder 114 may form a prediction block based on data from reconstructed neighboring samples of the block to be encoded within the same picture of video sequence 108. A reconstructed sample refers to a sample that was encoded and then decoded. Encoder 114 may determine a prediction error (e.g., also referred to as a residual) based on the difference between a block being encoded and a prediction block. The prediction error may represent non-redundant information that may be sent / transmitted to a decoder for accurate decoding of video sequence 108.

[0060] Encoder 114 may apply a transform to the prediction error (e.g. using a discrete cosine transform (DCT), or any other transform) to generate transform coefficients. Encoder 114 may form bitstream 110 based on the transform coefficients and other information used to determine prediction blocks using / based on prediction types, motion vectors, and / or prediction modes. Encoder 114 may perform one or more of quantization and entropy coding of the transform coefficients and / or the other information used to determine the prediction blocks, for example, before forming bitstream 110. The quantization and / or the entropy coding may further reduce the quantity of bits needed to store and / or transmit video sequence 108.

[0061] Output interface 116 may be configured to write and / or store bitstream 110 onto transmission medium 104 for transmission to destination device 106. In addition or alternatively, output interface 116 mayDocket No.: 24-2016PCT be configured to send / transmit, upload, and / or stream bitstream 110 to destination device 106 via transmission medium 104. Output interface 116 may comprise a wired and / or a wireless transmitter configured to send / transmit, upload, and / or stream bitstream 110 in accordance with one or more proprietary, open-source, and / or standardized communication protocols (e.g., Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, 3rd Generation Partnership Project (3GPP) standards, Institute of Electrical and Electronics Engineers (IEEE) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and / or any other communication protocol).

[0062] Transmission medium 104 may comprise wireless, wired, and / or computer readable medium. For example, transmission medium 104 may comprise one or more wires, cables, air interfaces, optical discs, flash memory, and / or magnetic memory. In addition or alternatively, transmission medium 104 may comprise one or more networks (e.g., the internet) or file servers configured to store and / or send / transmit encoded video data.

[0063] Destination device 106 may decode bitstream 110 into video sequence 108 for display. Destination device 106 may comprise one or more of an input interface 118, a decoder 120, and / or a video display 122. Input interface 118 may be configured to read bitstream 110 stored on transmission medium 104 by source device 102. In addition or alternatively, input interface 118 may be configured to receive, download, and / or stream bitstream 110 from source device 102 via transmission medium 104. Input interface 118 may comprise a wired and / or a wireless receiver configured to receive, download, and / or stream bitstream 110 in accordance with one or more proprietary, open-source, standardized communication protocols, and / or any other communication protocol (e.g., such as referenced herein).

[0064] Decoder 120 may decode video sequence 108 from encoded bitstream 110. The decoder 120 may generate prediction blocks for pictures of video sequence 108 in a similar manner as encoder 114 and determine the prediction errors for the blocks, for example, to decode video sequence 108. Decoder 120 may generate the prediction blocks using / based on prediction types, prediction modes, and / or motion vectors received in bitstream 110. Decoder 120 may determine the prediction errors using the transform coefficients received in bitstream 110. Decoder 120 may determine the prediction errors by weighting transform basis functions using the transform coefficients. Decoder 120 may combine the prediction blocks and the prediction errors to decode video sequence 108. Video sequence 108 at the destination device 106 may be, or may not necessarily be, the same video sequence sent, such as video sequence 108 as sent by the source device 102. Decoder 120 may decode a video sequence that approximates video sequence 108, for example, because of lossy compression of video sequence 108 by encoder 114 and / or errors introduced into encoded bitstream 110 during transmission to destination device 106.Docket No.: 24-2016PCT

[0065] Video display 122 may display video sequence 108 to a user. Video display 122 may comprise a cathode rate tube (CRT) display, a liquid crystal display (LCD), a plasma display, a light emitting diode (LED) display, and / or any other display device suitable for displaying video sequence 108.

[0066] Video coding / decoding system 100 is merely an example and video encoding / decoding systems different from the video coding / decoding system 100 and / or modified versions of the video coding / decoding system 100 may similarly perform the methods and processes as described herein. For example, the video coding / decoding system 100 may comprise other components and / or arrangements. For example, video source 112 may be external to source device 102. Similarly, video display 122 may be external to destination device 106 or omitted altogether (e.g., if video sequence 108 is intended for consumption by a machine and / or storage device). In an example, source device 102 may further comprise a video decoder and destination device 106 may further comprise a video encoder. For example, source device 102 may be configured to further receive an encoded bitstream from destination device 106 to support two-way video transmission between the devices.

[0067] Encoder 114 and / or decoder 120 may operate according to one or more proprietary or industry video coding standards. For example, encoder 114 and / or decoder 120 may operate in accordance with one or more proprietary, open-source, and / or standardized protocols (e.g., International Telecommunications Union Telecommunication Standardization Sector (ITU-T) H.263, ITU-T H.264 and Moving Picture Expert Group (MPEG)-4 Visual (also known as Advanced Video Coding (AVC)), ITU-T H.265 and MPEG-H Part 2 (also known as High Efficiency Video Coding (HEVC)), ITU-T H.265 and MPEG-I Part 3 (also known as Versatile Video Coding (VVC)), the WebM VP8 and VP9 codecs, and / or AOMedia Video 1 (AV1), and / or any other video coding protocol).

[0068] FIG.2 shows an example encoder. Encoder 200 as shown in FIG.2 may implement one or more processes described herein. Encoder 200 may encode a video sequence 202 into a bitstream 204 for more efficient storage and / or transmission. Encoder 200 may be implemented in video coding / decoding system 100 as shown in FIG.1 (e.g., as encoder 114) or in any computing, communication, or electronic device (e.g., desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, video streaming device, etc.). Encoder 200 may comprise one or more of an inter prediction unit 206, an intra prediction unit 208, combiners 210 and 212, a transform and quantization unit (TR + Q) 214, an inverse transform and quantization unit (iTR + iQ) 216, an entropy coding unit 218, one or more filters 220, and / or a buffer 222.

[0069] Encoder 200 may partition pictures (e.g., frames) of (e.g., comprising) video sequence 202 into blocks and encode video sequence 202 on a block-by-block basis. Encoder 200 may perform / apply a prediction technique on a block being encoded using either inter prediction unit 206 or intra prediction unit 208. Inter prediction unit 206 may perform inter prediction by searching for a block similar to the block being encoded in another, reconstructed picture (e.g., a reference picture) of video sequence 202. A reconstructedDocket No.: 24-2016PCT picture refers to a picture that was encoded and then decoded. The block determined during the search (e.g., referred to as a prediction block) may then be used to predict the block being encoded to remove redundant information. Inter prediction unit 206 may exploit temporal redundancy or similarities in scene content from picture to picture in video sequence 202 to determine the prediction block. For example, scene content between pictures of video sequence 202 may be similar except for differences due to motion and / or affine transformation of the screen content over time.

[0070] Intra prediction unit 208 may perform intra prediction by forming a prediction block based on data from reconstructed neighboring samples of the block to be encoded within the same picture of video sequence 202. A reconstructed sample refers to a sample that was encoded and then decoded. Intra prediction unit 208 may exploit spatial redundancy or similarities in scene content within a picture of video sequence 202 to determine the prediction block. For example, the texture of a region of scene content in a picture may be similar to the texture in the immediate surrounding area of the region of the scene content in the same picture.

[0071] Combiner 210 may determine a prediction error (e.g., referred to as a residual) based on the difference between the block being encoded and the prediction block. The prediction error may represent non-redundant information that may be sent / transmitted to a decoder for accurate decoding of video sequence 202.

[0072] Transform and quantization unit (TR + Q) 214 may transform and quantize the prediction error. Transform and quantization unit 214 may transform the prediction error into transform coefficients by applying, for example, a DCT to reduce correlated information in the prediction error. Transform and quantization unit 214 may quantize the coefficients by mapping data of the transform coefficients to a predefined set of representative values. Transform and quantization unit 214 may quantize the coefficients to reduce irrelevant information in bitstream 204. The irrelevant information refers to information that may be removed from the coefficients without producing visible and / or perceptible distortion in video sequence 202 after decoding (e.g., at a receiving device).

[0073] Entropy coding unit 218 may apply one or more entropy coding methods to the quantized transform coefficients to further reduce the bit rate. For example, entropy coding unit 218 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and / or syntax-based context-based binary arithmetic coding (SBAC). The entropy coded coefficients may be packed to form bitstream 204.

[0074] Inverse transform and quantization unit (iTR + iQ) 216 may inverse quantize and inverse transform the quantized transform coefficients to determine a reconstructed prediction error. Combiner 212 may combine the reconstructed prediction error with the prediction block to form a reconstructed block. Filter(s) 220 may filter the reconstructed block, for example, using a deblocking filter and / or a sample-adaptive offsetDocket No.: 24-2016PCT (SAO) filter. Buffer 222 may store the reconstructed block for prediction of one or more other blocks in the same and / or different picture of video sequence 202.

[0075] Encoder 200 may further comprise an encoder control unit. The encoder control unit may be configured to control one or more units of encoder 200 as shown in FIG.2. The encoder control unit may control the one or more units of encoder 200 such that bitstream 204 may be generated in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other video cording protocol. For example, the encoder control unit may control the one or more units of encoder 200 such that bitstream 204 may be generated in conformance with one or more of ITU-T H.263, AVC, HEVC, VVC, VP8, VP9, AV1, and / or any other video coding standard / format.

[0076] The encoder control unit may be configured to attempt to minimize (or reduce) the bitrate of bitstream 204 and / or maximize (or increase) the reconstructed video quality (e.g., within the constraints of a proprietary coding protocol, industry video coding standard, and / or any other video cording protocol). For example, the encoder control unit may be configured to attempt to minimize or reduce the bitrate of bitstream 204 such that the reconstructed video quality does not fall below a certain level / threshold, and / or to maximize or increase the reconstructed video quality such that the bitrate of bitstream 204 does not exceed a certain level / threshold. The encoder control unit may determine / control one or more of: partitioning of the pictures of video sequence 202 into blocks, whether a block is inter predicted by inter prediction unit 206 or intra predicted by intra prediction unit 208, a motion vector for inter prediction of a block, an intra prediction mode among a plurality of intra prediction modes for intra prediction of a block, filtering performed by filter(s) 220, and / or one or more transform types and / or quantization parameters applied by transform and quantization unit 214. The encoder control unit may determine / control one or more of the above based on a rate-distortion measure for a block or picture being encoded. The encoder control unit may determine / control one or more of the above to reduce the rate-distortion measure for a block or picture being encoded.

[0077] The prediction type used to encode a block (intra or inter prediction), prediction information of the block (intra prediction mode if intra predicted, motion vector, etc.), and / or transform and / or quantization parameters, may be sent to entropy coding unit 218 to be further compressed (e.g., to reduce the bitrate). For example, entropy coding unit 218 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and / or syntax-based context-based binary arithmetic coding (SBAC) to achieve further compression. The prediction type, prediction information, and / or transform and / or quantization parameters may be packed with the prediction error to form bitstream 204.

[0078] Encoder 200 is merely an example and encoders different from encoder 200 and / or modified versions of encoder 200 may perform the methods and processes as described herein. For example, encoder 200 may comprise other components and / or arrangements. One or more of the components shown in FIG. 2 may be optionally included in encoder 200 (e.g., entropy coding unit 218 and / or filters(s) 220).Docket No.: 24-2016PCT

[0079] FIG.3 shows an example decoder. A decoder 300 as shown in FIG.3 may implement one or more processes described herein. Decoder 300 may decode a bitstream 302 into a decoded video sequence 304 for display and / or some other form of consumption. Decoder 300 may be implemented in video coding / decoding system 100 in FIG.1 and / or in a computing, communication, or electronic device (e.g., desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, and / or video streaming device). Decoder 300 may comprise an entropy decoding unit 306, an inverse transform and quantization (iTR + iQ) unit 308, a combiner 310, one or more filters 312, a buffer 314, an inter prediction unit 316, and / or an intra prediction unit 318.

[0080] Decoder 300 may comprise a decoder control unit configured to control one or more units of decoder 300. The decoder control unit may control the one or more units of decoder 300 such that bitstream 302 is decoded in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other communication protocol. For example, the decoder control unit may control the one or more units of decoder 300 such that the bitstream 302 is decoded in conformance with one or more of ITU-T H.263, AVC, HEVC, VVC, VP8, VP9, AV1, and / or any other video coding standard / format.

[0081] The decoder control unit may determine / control one or more of: whether a block is inter predicted by inter prediction unit 316 or intra predicted by intra prediction unit 318, a motion vector for inter prediction of a block, an intra prediction mode among a plurality of intra prediction modes for intra prediction of a block, filtering performed by filter(s) 312, and / or one or more inverse transform types and / or inverse quantization parameters to be applied by inverse transform and quantization unit 308. One or more of the control parameters used by the decoder control unit may be packed in bitstream 302.

[0082] Entropy decoding unit 306 may entropy decode the bitstream 302. For example, entropy decoding unit 306 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and syntax-based context-based binary arithmetic coding (SBAC) to decompress the prediction type used to encode a block (intra or inter prediction), prediction information of the block (intra prediction mode if intra predicted, motion vector, etc.), and transform and quantization parameters. Inverse transform and quantization unit 308 may inverse quantize and / or inverse transform the quantized transform coefficients to determine a decoded prediction error. Combiner 310 may combine the decoded prediction error with a prediction block to form a decoded block. The prediction block may be generated by intra prediction unit 318 or inter prediction unit 316 (e.g., as described above with respect to encoder 200 in FIG 2). Filter(s) 312 may filter the decoded block, for example, using a deblocking filter and / or a sample-adaptive offset (SAO) filter. Buffer 314 may store the decoded block for prediction of one or more other blocks in the same and / or different picture of the video sequence in bitstream 302. Decoded video sequence 304 may be output from filter(s) 312 as shown in FIG.3.Docket No.: 24-2016PCT

[0083] Decoder 300 is merely an example and decoders different from decoder 300 and / or modified versions of decoder 300 may perform the methods and processes as described herein. For example, decoder 300 may have other components and / or arrangements. One or more of the components shown in FIG.3 may be optionally included in decoder 300 (e.g., entropy decoding unit 306 and / or filters(s) 312).

[0084] Although not shown in FIGS.2 and 3, each of encoder 200 and decoder 300 may further comprise an intra block copy unit in addition to inter prediction and intra prediction units. The intra block copy unit may perform / operate similar to an inter prediction unit but may predict blocks within the same picture. For example, the intra block copy unit may exploit repeated patterns that appear in screen content. The screen content may include computer generated text, graphics, animation, etc.

[0085] Video encoding and / or decoding may be performed on a block-by-block basis. The process of partitioning a picture into blocks may be adaptive based on the content of the picture. For example, larger block partitions may be used in areas of a picture with higher levels of homogeneity to improve coding efficiency.

[0086] A picture (e.g., in HEVC, or any other coding standard / format) may be partitioned into non- overlapping square blocks, which may be referred to as coding tree blocks (CTBs). The CTBs may comprise samples of a sample array. A CTB may have a size of 2nx2n samples, where n may be specified by a parameter of the encoding system. For example, n may be 4, 5, 6, or any other value. A CTB may have any other size. A CTB may be further partitioned by a recursive quadtree partitioning into coding blocks (CBs) of half vertical and half horizontal size. The CTB may form the root of the quadtree. A CB that is not split further as part of the recursive quadtree partitioning may be referred to as a leaf CB of the quadtree, and otherwise may be referred to as a non-leaf CB of the quadtree. A CB may have a minimum size specified by a parameter of the encoding system. For example, a CB may have a minimum size of 4x4, 8x8, 16x16, 32x32, 64x64 samples, or any other minimum size. A CB may be further partitioned into one or more prediction blocks (PBs) for performing inter and / or intra prediction. A PB may be a rectangular block of samples on which the same prediction type / mode may be applied. A CB may also be further partitioned into intra sub-partitions (ISP) where the reconstructed samples of each sub-partition are available to generate the prediction of the next sub-partition. For example, a CB may be split into 2 to 4 sub-partitions. For transformations, a CB may be partitioned into one or more transform blocks (TBs). A TB may be a rectangular block of samples that may determine / indicate an applied transform size.

[0087] FIG.4 shows an example quadtree partitioning of a CTB 400. FIG.5 shows an example quadtree 500 corresponding to the example quadtree partitioning of CTB 400 in FIG.4. As shown in the examples of FIGS.4 and 5, CTB 400 may first be partitioned into four CBs of half vertical and half horizontal size. Three of the resulting CBs of the first level partitioning of CTB 400 are leaf CBs. The three leaf CBs of the first level partitioning of CTB 400 are respectively labeled 7, 8, and 9 in FIGS.4 and 5. The non-leaf CB of the first level partitioning of CTB 400 is partitioned into four sub-CBs of half vertical and half horizontal size. Three ofDocket No.: 24-2016PCT the resulting sub-CBs of the second level partitioning of CTB 400 are leaf CBs. The three leaf CBs of the second level partitioning of CTB 400 are respectively labeled 0, 5, and 6 in FIGS.4 and 5. Finally, The non- leaf CB of the second level partitioning of CTB 400 is partitioned into four leaf CBs of half vertical and half horizontal size. The four leaf CBs are respectively labeled 1, 2, 3, and 4 in FIGS.4 and 5.

[0088] The example CTB 400 of FIG.4 is partitioned into 10 leaf CBs respectively labeled 0-9, but may be partitioned into other quantities of leaf CBs. The 10 leaf CBs may correspond to 10 CB leaf nodes (e.g., 10 CB leaf nodes of quadtree 500 as shown in FIG.5). In other examples, a CTB may be partitioned into a different number of leaf CBs. The resulting quadtree partitioning of CTB 400 may be scanned using a z-scan (e.g., left-to-right, top-to-bottom) to form the sequence order for encoding / decoding the CB leaf nodes. A numeric label (e.g., indicator, index) of each CB leaf node in FIGS.4 and 5 may correspond to the sequence order for encoding / decoding. For example, CB leaf node 0 may be encoded / decoded first and CB leaf node 9 may be encoded / decoded last. Although not shown in FIGS.4 and 5, each CB leaf node may comprise one or more PBs and / or TBs.

[0089] A picture, in VVC (or in any other coding standard / format), may be partitioned in a similar manner (such as in HEVC). A picture may be first partitioned into non-overlapping square CTBs. The CTBs may then be partitioned, using a recursive quadtree partitioning, into CBs of half vertical and half horizontal size. A quadtree leaf node (e.g., in VVC) may be further partitioned by a binary tree or ternary tree partitioning (or any other partitioning) into CBs of unequal sizes.

[0090] FIG.6 shows example binary tree and ternary tree partitions. A binary tree partition may divide a parent block in half in either a vertical direction 602 or a horizontal direction 604. The resulting partitions may be half in size as compared to the parent block. In other examples, the resulting partitions may correspond to sizes that are less than and / or greater than half of the parent block size. A ternary tree partition may divide a parent block into three parts in either a vertical direction 606 or a horizontal direction 608. FIG.6 shows an example in which the middle partition may be twice as large as the other two end partitions in the ternary tree partitions. In other examples, partitions may be of other sizes relative to each other and to the parent block. Binary and ternary tree partitions are examples of multi-type tree partitioning. Multi-type tree partitions may comprise partitioning a parent block into other quantities of smaller blocks. The block partitioning strategy (e.g., in VVC) may be referred to as a combination of quadtree and multi-type tree partitioning (quadtree + multi-type tree partitioning) because of the addition of binary and / or ternary tree partitioning to quadtree partitioning.

[0091] FIG.7 shows an example of combined quadtree and multi-type tree partitioning of a CTB 700. FIG. 8 shows an example tree 800 corresponding to the combined quadtree and multi-type tree partitioning of CTB 700 shown in FIG.7. In both FIGS.7 and 8, quadtree splits are shown in solid lines and multi-type tree splits are shown in dashed lines. For ease of explanation, CTB 700 is shown with the same quadtree partitioning as the CTB 400 described in FIG.4, and a description of the quadtree partitioning of CTB 700,Docket No.: 24-2016PCT which is similar to that for CTB 400, is omitted. The quadtree partitioning of the CTB 700 is merely an example and a CTB may be quadtree partitioned in a manner different from the CTB 700. Additional multi-type tree partitions of CTB 700 may be made relative to three leaf CBs shown in FIG.4. The three leaf CBs in FIG.4 that are shown in FIG.7 as being further partitioned may be leaf CBs 5, 8, and 9. The three leaf CBs may be further partitioned using one or more binary and / or ternary tree partitions.

[0092] The leaf CB 5 of FIG.4 may be partitioned into two CBs based on a vertical binary tree partitioning. The two resulting CBs may be leaf CBs respectively labeled 5 and 6 in FIGS.7 and 8. The leaf CB 8 of FIG. 4 may be partitioned into three CBs based on a vertical ternary tree partition. Two of the three resulting CBs may be leaf CBs respectively labeled 9 and 14 in FIGS.7 and 8. The remaining, non-leaf CB may be partitioned first into two CBs based on a horizontal binary tree partition. One of the two CBs may be a leaf CB labeled 10. The other of the two CBs may be further partitioned into three CBs based on a vertical ternary tree partition. The resulting three CBs may be leaf CBs respectively labeled 11, 12, and 13 in FIGS.7 and 8. The leaf CB 9 of FIG.4 may be partitioned into three CBs based on a horizontal ternary tree partition. Two of the three CBs may be leaf CBs respectively labeled 15 and 19 in FIGS.7 and 8. The remaining, non-leaf CB may be partitioned into three CBs based on another horizontal ternary tree partition. The resulting three CBs may all be leaf CBs respectively labeled 16, 17, and 18 in FIGS.7 and 8.

[0093] Altogether, CTB 700 may be partitioned into 20 leaf CBs respectively labeled 0-19. The 20 leaf CBs may correspond to 20 leaf nodes (e.g., 20 leaf nodes of tree 800 shown in FIG.8). The resulting combination of quadtree and multi-type tree partitioning of the CTB 700 may be scanned using a z-scan (left-to-right, top- to-bottom) to form the sequence order for encoding / decoding the CB leaf nodes. A numeric label of each CB leaf node in FIGS.7 and 8 may correspond to the sequence order for encoding / decoding, with CB leaf node 0 encoded / decoded first and CB leaf node 19 encoded / decoded last. Although not shown in FIGS.7 and 8, it should be noted that each CB leaf node may comprise one or more PBs and / or TBs.

[0094] A coding standard / format (e.g., HEVC, VVC, or any other coding standard / format) may define various units (e.g., in addition to specifying various blocks (e.g., CTBs, CBs, PBs, TBs)). Blocks may comprise a rectangular area of samples in a sample array. Units may comprise the collocated blocks of samples from the different sample arrays (e.g., luma and chroma sample arrays) that form a picture as well as syntax elements and prediction data of the blocks. A coding tree unit (CTU) may comprise the collocated CTBs of the different sample arrays and may form a complete entity in an encoded bitstream. A coding unit (CU) may comprise the collocated CBs of the different sample arrays and syntax structures used to code the samples of the CBs. A prediction unit (PU) may comprise the collocated PBs of the different sample arrays and syntax elements used to predict the PBs. A transform unit (TU) may comprise TBs of the different samples arrays and syntax elements used to transform the TBs.

[0095] A block may refer to any of a CTB, CB, PB, TB, CTU, CU, PU, and / or TU (e.g., in the context of HEVC, VVC, or any other coding format / standard). A block may be used to refer to similar data structures inDocket No.: 24-2016PCT the context of any video coding format / standard / protocol. For example, a block may refer to a macroblock in the AVC standard, a macroblock or a sub-block in the VP8 coding format, a superblock or a sub-block in the VP9 coding format, and / or a superblock or a sub-block in the AV1 coding format.

[0096] In intra prediction, samples of a block to be encoded (e.g., also referred to as a current block) may be predicted from samples in a line of samples immediately adjacent to the current block. For example, the line of samples may include samples of the column immediately adjacent to the left-most column of the current block and samples of the row immediately adjacent to the top-most row of the current block. The samples from the immediately adjacent column and row may be jointly referred to as reference samples. Each sample of the current block may be predicted (e.g., in an intra prediction mode) by projecting the position of the sample in the current block in a given direction to a point along the reference samples. The sample may be predicted by interpolating between the two closest reference samples of the projection point if the projection does not fall directly on a reference sample. A prediction error (e.g., referred to as a residual) may be determined for the current block based on differences between the predicted sample values and the original sample values of the current block.

[0097] Predicting samples and determining a prediction error based on a difference between the predicted samples and original samples may be performed (e.g., at an encoder) for a plurality of different intra prediction modes (e.g., including non-directional intra prediction modes). The encoder may select one of the plurality of intra prediction modes and its corresponding prediction error to encode the current block. The encoder may send an indication of the selected prediction mode and its corresponding prediction error to a decoder for decoding of the current block. The decoder may decode the current block by predicting the samples of the current block, using the intra prediction mode indicated by the encoder, and / or combining the predicted samples with the prediction error.

[0098] FIG.9 shows an example set of reference samples 902 determined for intra prediction of a current block 904. Current block 904 may correspond to a block being encoded and / or decoded. Current block 904 may correspond to block 3 of partitioned CTB 700 as shown in FIG.7. As described herein, the numeric labels 0-19 of the blocks of partitioned CTB 700 may correspond to the sequence order for encoding / decoding the blocks and may be used as such in the example of FIG.9.

[0099] In some embodiments, reference samples 902 may include a line of samples immediately adjacent to current block 904 and include samples from a column and a row immediately adjacent to current block 904. For example, the line of samples may include reference samples to the left and / or above current block 904. In some embodiments, reference samples 902 may be obtained (or selected) from a reference line of multiple reference lines (MRL), which may include a line of samples adjacent to current block 904 and also a line of non-adjacent samples. The MRL may include reference lines identified by corresponding reference line indices that indicate an i-th line of samples adjacent to current block 904 such that the 0-th line indicates the reference line immediate adjacent (or closest) to current block 904 and a higher numbered i-th lineDocket No.: 24-2016PCT indicates a line of samples further away from current block 904. An encoder may select a reference line from a set of MRL and signal an MLR index in the bitstream to indicate the selected reference line. For example, the encoder may signal a codeword encoding the MRL index. The decoder may decode the codeword to determine the MRL index that identifies a specific reference line used in intra prediction of current block 904.

[0100] For current block 904 that is w x h samples in size, reference samples 902 may comprise: 2w samples (or any other quantity of samples) of an i-th row (e.g., indicated by an MRL index) adjacent to the top-most row of current block 904, 2h samples (or any other quantity of samples) of the i-th column adjacent to the left-most column of current block 904, and the top left neighboring corner sample(s) extending from the i-th column and i-th row with respect to current block 904. Current block 904 may be square, such that w = h = s. In other examples, a current block need not be square, such that w ≠ h. Available samples from neighboring blocks of current block 904 may be used for constructing the set of reference samples 902. Samples may not be available for constructing the set of reference samples 902, for example, if the samples lie outside the picture of the current block, the samples are part of a different slice of the current block (e.g., if the concept of slices is used), and / or the samples belong to blocks that have been inter coded and constrained intra prediction is indicated. Intra prediction may not be dependent on inter predicted blocks, for example, if constrained intra prediction is indicated.

[0101] Samples that may not be available for constructing the set of reference samples 902 may comprise samples in blocks that have not already been encoded and reconstructed at an encoder and / or decoded at a decoder based on the sequence order for encoding / decoding. Restriction of such samples from inclusion in the set of reference samples 902 may allow identical prediction results to be determined at both the encoder and decoder. In the example of FIG.9, samples from neighboring blocks 0, 1, 2, and 8 may be available to construct reference samples 902 given that these blocks are encoded and reconstructed at an encoder and decoded at a decoder prior to coding of current block 904. The samples from neighboring blocks 0, 1, 2, and 8 may be available to construct reference samples 902, for example, if there are no other issues (e.g., as mentioned above) preventing the availability of the samples from the neighboring blocks 0, 1, 2, and 8. The portion of reference samples 902 from neighboring block 6 may not be available due to the sequence order for encoding / decoding (e.g., because the block 6 may not have already been encoded and reconstructed at the encoder and / or decoded at the decoder based on the sequence order for encoding / decoding).

[0102] In some examples, unavailable samples from reference samples 902 may be filled with one or more of the available reference samples 902. For example, an unavailable reference sample may be filled with a nearest available reference sample. The nearest available reference sample may be determined by moving in a clock-wise direction through reference samples 902 from the position of the unavailable reference. The reference samples 902 may be filled with the mid-value of the dynamic range of the picture being coded, for example, if no reference samples are available.Docket No.: 24-2016PCT

[0103] Samples of current block 904 may be intra predicted based on reference samples 902, for example, based on (e.g., after) determination and (optionally) filtering of reference samples 902. In some examples, a filtering scheme (e.g., a filtering algorithm) may be applied to reference samples 902 to improve prediction accuracy. The filtering scheme may be one of a plurality of filter types including at least: a smoothing filter (or reference sample smoothing filter) or an interpolation filter. In some examples, if reference samples of a given block are to be filtered, only one of the plurality of filter types is selected (e.g., activated) to be applied to the reference samples. For example, if the smoothing filter is selected (e.g., activated), the interpolation filter is not selected (e.g., disabled) or vice versa.

[0104] Many encoders / decoders may support a plurality of intra prediction modes in accordance with one or more video coding standards. For example, HEVC supports 35 intra prediction modes, including a planar mode, a direct current (DC) mode, and 33 angular modes. VVC supports 67 intra prediction modes, including a planar mode, a DC mode, and 65 angular modes. Planar and DC modes may be used to predict smooth and gradually changing regions of a picture. Angular modes may be used to predict directional structures in regions of a picture. Any quantity of intra prediction modes may be supported.

[0105] FIGS.10A-B show example intra prediction modes. FIG.10A shows 35 intra prediction modes, such as supported by HEVC. The 35 intra prediction modes may be indicated / identified by indices 0 to 34. Prediction mode 0 may correspond to planar mode. Prediction mode 1 may correspond to DC mode. Prediction modes 2-34 may correspond to angular modes. Prediction modes 2-18 may be referred to as horizontal prediction modes because the principal source of prediction is in the horizontal direction. Prediction modes 19-34 may be referred to as vertical prediction modes because the principal source of prediction is in the vertical direction.

[0106] FIG.10B shows 67 intra prediction modes, such as supported by VVC. The 67 intra prediction modes may be indicated / identified by indices 0 to 66. Prediction mode 0 may correspond to planar mode. Prediction mode 1 corresponds to DC mode. Prediction modes 2-66 may correspond to angular modes. Prediction modes 2-34 may be referred to as horizontal prediction modes because the principal source of prediction is in the horizontal direction. Prediction modes 35-66 may be referred to as vertical prediction modes because the principal source of prediction is in the vertical direction. Some of the intra prediction modes illustrated in FIG.10B may be adaptively replaced by wide-angle directions because blocks in VVC need not be squares.

[0107] FIG.11 shows a current block 904 and corresponding reference samples 902 from FIG.9. To further describe how intra prediction modes are applied to determine a prediction (e.g., a prediction block) of current block 904, FIG.11 shows current block 904 and reference samples 902, from a reference line among a set of multiple reference lines (MRL) 908-912, in a two-dimensional x, y plane, where a sample may be referenced as ^[^][^]. To simplify the prediction process, reference samples 902 may be placed in two, one-dimensional arrays. The reference samples 902 belonging to a reference line ^ from the set of MRL 908- 912, above the current block 904, may be placed in the one-dimensional array ^^^^[^]:Docket No.: 24-2016PCT ref^[x] = p[−l + x][−l], (x ≥ 0). (1)The reference samples 902 belonging to reference line l, to the left of current block 904, may be placed in the one-dimensional array ^^^^[^]:ref^[y] = p[−l][−l + y], (y ≥ 0). (2)The variable l represents how many lines away the selected reference line is from current block. For example, if reference line #0908 is selected, then l is set to 1 to indicate the reference line adjacent to current block 904. For example, if reference line #1910 is selected, then l is set to 2. For example, if reference line #2912 is selected, then l is set to 3.

[0108] In some examples, if MRL is not activated or selected, then reference samples 902 may be from reference line #0908 that is immediately adjacent to current block 904. In this example, the variable l in Equations (1) and (2) is set to 1.

[0109] The prediction process may comprise determination of a predicted sample ^[^][^] (e.g., apredicted value) at a location [^][^] in current block 904. For planar mode, a sample at the location [^][^] in current block 904 may be predicted by determining / calculating the mean of two interpolated values. The first of the two interpolated values may be based on a horizontal linear interpolation at the location [^][^] in current block 904. The second of the two interpolated values may be based on a vertical linear interpolationat location [^][^] in current block 904. The predicted sample ^[^][^] in current block 904 may bedetermined / calculated as: p[ 1x][y] =∙ (h[x][y] + v[x][y] + s), (3)whereh[x][y] = (s − x − 1) ∙ ref^[y] + (x + 1) ∙ ref^[s] (4)may be the horizonal linear interpolation at the location [^][^] in current block 904 andv[x][y] = (s − y − 1) ∙ ref^[x] + (y + 1) ∙ ref^[s] (5)may be the vertical linear interpolation at the location [^][^] in current block 904. " may be equal to a length of a side (e.g., a number of samples on a side) of the current block 904.

[0110] For DC mode, a sample at a location [^][^] in current block 904 may be predicted by the mean ofthe reference samples 902. The predicted sample ^[^][^] in current block 904 may bedetermined / calculated as: 1 %&^ %&^ ref^[x] + $ ref^[y]+. (6) *()

[0111] For angular[^][^] in current block 904 may be predicted byprojecting the location [^][^] in a direction specified by a given angular mode to a point on the horizontal or vertical line of samples comprising reference samples 902. The sample at the location [^][^] may beDocket No.: 24-2016PCT predicted by interpolating between the two closest reference samples of the projection point if the projection does not fall directly on a reference sample. The direction specified by the angular mode may be given by an angle φ defined relative to the y-axis for vertical prediction modes (e.g., modes 19-34 in HEVC and modes 35-66 in VVC). The direction specified by the angular mode may be given by an angle φ defined relative to the x-axis for horizontal prediction modes (e.g., modes 2-18 in HEVC and modes 2-34 in VVC).

[0112] FIG.12 shows an example of applying an intra prediction mode (e.g., an angular mode such as vertical prediction mode 906) for prediction of a current block 904. FIG.12 specifically shows prediction of a sample at a location [^][^] in current block 904 for a vertical prediction mode 906. Vertical prediction mode 906 may be given by an angle φ with respect to the vertical axis. The location [^][^] in current block 904, in vertical prediction modes, may be projected to a point (e.g., referred to as a projection point) on the horizontal line of reference samples ^^^^[^]. The reference samples 902 are only partially shown in FIG.12 and shown as being from a reference line with reference line index of 0 for ease of illustration. Reference samples 902 may be from another reference line of the set of MRL, as explained in FIG.9. As shown in FIG.12, the projection point on the horizontal line of reference samples ^^^^[^] may not be exactly on a referencesample. A predicted sample ^[^][^] in current block 904 may be determined / calculated by linearlyinterpolating between the two reference samples, for example, if the projection point falls at a fractionalsample position between two reference samples. The predicted sample ^[^][^] may bedetermined / calculated as:p[x][y] = (1 − i.) ∙ ref^[x + i / + 1] + i. ∙ ref^[x + i / + 2]. (7)01 may be the integer part of the horizontal displacement of the projection point relative to the location[^][^].01 may be determined / calculated as a function of the tangent of the angle φ of the verticalprediction mode 906 as:i / = ⌊(y + 1) ∙ tan φ⌋. (8)0. may be the fractional part of the horizontal displacement of the projection point relative to the location[^][^] and may be determined / calculated as:i. = ((y + 1) ∙ tan φ) − ⌊(y + 1) ∙ tan φ⌋, (9)where ⌊ ∙ ⌋ is the integer floor function.

[0113] For horizontal prediction modes, a location [x][y] of a sample in current block 904 may be projected onto the vertical line of reference samples ^^^^[^]. A predicted sample ^[^][^] for horizontal prediction modes may be determined / calculated as: p[x][y] = (1 − i.) ∙ ref^[y + i / + 1] + i. ∙ ref^[y + i / + 2]. (10)01 may be the integer part of the vertical displacement of the projection point relative to the location[^][^].01 may be determined / calculated as a function of the tangent of the angle φ of the horizontalprediction mode as:Docket No.: 24-2016PCT i / = ⌊(x + 1) ∙ tan φ⌋. (11)0. may be the fractional part of the vertical displacement of the projection point relative to the location[^][^].0. may be determined / calculated as:i. = ((x + 1) ∙ tan φ) − ⌊(x + 1) ∙ tan φ⌋, (12)where⌊∙⌋is the integer floor function.

[0114] The interpolation functions given by Equations (7) and (10) may be implemented by an encoder and / or a decoder (e.g., encoder 200 in FIG.2 and / or decoder 300 in FIG.3). The interpolation functions may be implemented by finite impulse response (FIR) filters. For example, the interpolation functions may be implemented as a set of two-tap FIR filters. The coefficients of the two-tap FIR filters may be respectively given by (1-0.) and 0.. The predicted sample ^[^][^], in angular intra prediction, may be calculated with some predefined level of sample accuracy (e.g., 1 / 32 sample accuracy, or accuracy defined by any other metric). For 1 / 32 sample accuracy, the set of two-tap FIR interpolation filters may comprise up to 32 different two-tap FIR interpolation filters — one for each of the 32 possible values of the fractional part of the projected displacement 0.. In other examples, different levels of sample accuracy may be used.

[0115] In some examples, the FIR filters may be used for predicting chroma samples and / or luma samples. For example, the two-tap interpolation FIR filter may be used for predicting chroma samples and a same and / or a different interpolation technique / filter may be used for luma samples. For example, a four-tap FIR filter may be used to determine a predicted value of a luma sample. Coefficients of the four tap FIR filter may be determined based on 0.(e.g., similar to the two-tap FIR filter). For 1 / 32 sample accuracy, a set of 32 different four-tap FIR filters may comprise up to 32 different four-tap FIR filters — one for each of the 32 possible values of the fractional part of the projected displacement 0.. In other examples, different levels of sample accuracy may be used. The set of four-tap FIR filters may be stored in a look-up table (LUT) and referenced based on 0.. A predicted sample ^[^][^], for vertical prediction modes, may be determined based on the four-tap FIR filter as: ; (13) p[x][y] = $ fT[i] ∙ ref^[x + iIdx + i] , / ()where fT[i], i = 0...3, may be the filter coefficients, and <=^ is integer displacement. A predicted sample^[^][^], for horizontal prediction modes, may be determined based on the four-tap FIR filter as:;(14) p[x][y] = $ fT[i] ∙ ref^[y + iIdx + i] . / ()

[0116] Supplementary reference samples may be determined / constructed if the location [^][^] of a sample in current block 904 to be predicted is projected to a negative x coordinate. The location [^][^] of a sample may be projected to a negative x coordinate, for example, if negative vertical prediction angles φ are used. The supplementary reference samples may be determined / constructed by projecting the reference samplesDocket No.: 24-2016PCT in ^^^^[^] in the vertical line of reference samples 902 to the horizontal line of reference samples 902 using the negative vertical prediction angle φ. Supplementary reference samples may be similarly determined / constructed, for example, if the location [^][^] of a sample in current block 904 to be predicted is projected to a negative y coordinate. The location [^][^] of a sample may be projected to a negative y coordinate, for example, if negative horizontal prediction angles φ are used. The supplementary reference samples may be determined / constructed by projecting the reference samples in ^^^^[^] on the horizontal line of reference samples 902 to the vertical line of reference samples 902 using the negative horizontal prediction angle φ.

[0117] An encoder may determine / predict samples of a current block being encoded (e.g., current block 904) for a plurality of intra prediction modes (e.g., using one or more of the functions described herein). For example, an encoder may determine / predict samples of a current block for each of 35 intra prediction modes in HEVC and / or 67 intra prediction modes in VVC and / or including extended intra prediction modes from WAIP for rectangular blocks. The encoder may determine, for each intra prediction mode applied, a corresponding prediction error for the current block based on a difference (e.g., sum of squared differences (SSD), sum of absolute differences (SAD), or sum of absolute transformed differences (SATD)) between the prediction samples, generated from reference samples 902 of a reference line (e.g., from a set of MRL), determined for the intra prediction mode and the original samples of the current block. The encoder may determine / select one of the intra prediction modes to encode the current block based on the determined prediction errors. For example, the encoder may determine / select one of the intra prediction modes that results in the smallest prediction error for the current block. In some examples, the encoder may determine / select the intra prediction mode and the associated reference line to encode the current block based on a rate-distortion measure (e.g., Lagrangian rate-distortion cost) determined using the prediction errors. The encoder may signal, in the bitstream to a decoder for decoding of the current block, an indication of the determined / selected intra prediction mode and an indication of the associated MRL index (which may indicate a reference line index). The encoder may also signal in the bitstream to the decoder a corresponding prediction error (e.g., residual) of the intra prediction mode.

[0118] A decoder may determine / predict samples of a current block being decoded (e.g., current block 904) for an intra prediction mode. For example, a decoder may receive an indication of a reference line (e.g., a reference line index or an MRL index associated with the reference line index) and an intra prediction mode (e.g., an angular intra prediction mode) from an encoder for a current block. The decoder may retrieve a set of reference samples and perform intra prediction based on the MRL index and the intra prediction mode indicated by the encoder for the current block in a similar manner (e.g., as described above for the encoder). For example, the decoder may obtain the reference samples from a reference line indicated / identified by the decoded MRL index. In some examples, when MRL is not enabled / activated / selected, the reference line hasDocket No.: 24-2016PCT reference line index 0 and is immediately adjacent to the current block. In these examples, no indication of MRL index is signaled.

[0119] The decoder may add predicted values of the samples (e.g., determined based on the intra prediction mode) of the current block to a residual of the current block to reconstruct the current block. In some examples, a decoder need not receive an indication of an angular intra prediction mode from an encoder for a current block. Instead, the decoder may determine an intra prediction mode through other decoder-side means (e.g., by applying template-based intra mode derivation (TIMD) tool / technique).

[0120] While various examples herein correspond to intra prediction modes in HEVC and VVC, the methods, devices, and systems as described herein may be applied to / used for other intra prediction modes (e.g., as used in other video coding standards / formats, such as VP8, VP9, AV1, etc.).

[0121] Intra prediction may exploit correlations between spatially neighboring samples in the same picture of a video sequence to perform video compression. Inter prediction is another coding tool that may be used to perform video compression. Inter prediction may exploit correlations in the time domain between blocks of samples in different pictures of a video sequence. For example, an object may be seen across multiple pictures of a video sequence. The object may move (e.g., by some translation and / or affine motion) or remain stationary across the multiple pictures. A current block of samples in a current picture being encoded may have / be associated with a corresponding block of samples in a previously decoded picture. The corresponding block of samples may accurately predict the current block of samples. The corresponding block of samples may be displaced from the current block of samples, for example, due to movement of the object, represented in both blocks, across the respective pictures of the blocks. The previously decoded picture may be a reference picture. The corresponding block of samples in the reference picture may be a reference block for motion compensated prediction. An encoder may use a block matching technique to estimate the displacement (or motion) of the object and / or to determine the reference block in the reference picture.

[0122] Similar to intra prediction, an encoder may determine a difference between a current block and a prediction for a current block. An encoder may determine a difference, for example, based on / after determining / generating a prediction for a current block (e.g., using inter prediction). The difference may be a prediction error (e.g., a residual). The encoder may store and / or send (e.g., signal), in / via a bitstream, the prediction error and / or other related prediction information. The prediction error and / or other related prediction information may be used for decoding and / or other forms of consumption. A decoder may decode the current block by predicting the samples of the current block (e.g., by using the related prediction information) and combining the predicted samples with the prediction error.

[0123] FIG.13A shows an example of inter prediction. The inter prediction may be performed for a current block 1300 in a current picture 1302 being encoded. An encoder (e.g., encoder 200 as shown in FIG.2) may perform inter prediction to determine and / or generate a reference block 1304 in a reference picture 1306.Docket No.: 24-2016PCT Reference block 1304 may be used to predict the current block 1300. Reference pictures (e.g., reference picture 1306) may be prior decoded pictures available at the encoder and / or a decoder. Availability of a prior decoded picture may depend / be based on whether the prior decoded picture is available in a decoded picture buffer, at the time, current block 1300 is being encoded and / or decoded. The encoder may search the one or more reference pictures 1306 for a block (e.g., a candidate reference block) that is similar (or substantially similar) to current block 1300. The encoder may determine the best matching block from the blocks (e.g., candidate reference blocks) tested during the searching process. The best matching block may be a reference block 1304. The encoder may determine that reference block 1304 is the best matching reference block based on one or more cost criteria. The one or more cost criteria may comprise a rate-distortion criterion (e.g., Lagrangian rate-distortion cost). The one or more cost criteria may be based on a difference (e.g., SSD, SAD, and / or SATD) between prediction samples of reference block 1304 and original samples of current block 1300.

[0124] The encoder may search for reference block 1304 within a reference region (e.g., a search range 1308). The reference region (e.g., a search range 1308) may be positioned around a collocated block (or position) 1310, of current block 1300, in reference picture 1306. Collocated block 1310 may have a same position in the reference picture 1306 as the current block 1300 in the current picture 1302. The reference region (e.g., search range 1308) may at least partially extend outside of reference picture 1306. Constant boundary extension may be used, for example, if the reference region (e.g., search range 1308) extends outside of reference picture 1306. The constant boundary extension may be used such that values of the samples in a row or a column of reference picture 1306, immediately adjacent to a portion of the reference region (e.g., search range 1308) extending outside of reference picture 1306, may be used for sample locations outside of reference picture 1306. A subset of potential positions, or all potential positions, within the reference region (e.g., search range 1308) may be searched for reference block 1304. The encoder may utilize one or more search implementations to determine and / or generate the reference block 1304. For example, the encoder may determine a set of candidate search positions based on motion information of neighboring blocks (e.g., a motion vector 1312) to the current block 1300.

[0125] One or more reference pictures may be searched by the encoder during inter prediction to determine and / or generate the best matching reference block. The reference pictures searched by the encoder may be included in (e.g., added to) one or more reference picture lists. For example, in HEVC and VVC (and / or in one or more other communication protocols), two reference picture lists may be used (e.g., a reference picture list 0 and a reference picture list 1). A reference picture list may include one or more pictures. The reference picture 1306 of reference block 1304 may be indicated by a reference index pointing into a reference picture list comprising reference picture 1306.

[0126] FIG.13B shows an example motion vector. A displacement between reference block 1304 and current block 1300 may be interpreted as an estimate of the motion between reference block 1304 and currentDocket No.: 24-2016PCT block 1300 across their respective pictures. The displacement may be represented by a motion vector 1312. For example, motion vector 1312 may be indicated by a horizontal component (MVx) and a vertical component (MVy) relative to the position of current block 1300. A motion vector (e.g., motion vector 1312) may have fractional or integer resolution. A motion vector with fractional resolution may point between two samples in a reference picture to provide a better estimation of the motion of current block 1300. For example, a motion vector may have 1 / 2, 1 / 4, 1 / 8, 1 / 16, 1 / 32, or any other fractional sample resolution. Interpolation between the two samples at integer positions may be used to generate a reference block and its corresponding samples at fractional positions, for example, if a motion vector points to a non-integer sample value in the reference picture. The interpolation may be performed by a filter with two or more taps.

[0127] The encoder may determine a difference (e.g., a corresponding sample-by-sample difference) between reference block 1304 and current block 1300. The encoder may determine the difference between reference block 1304 and current block 1300, for example, based on / after reference block 1304 is determined and / or generated, using inter prediction, for current block 1300. The difference may be a prediction error (e.g., a residual). The encoder may store and / or send (e.g., signal), in / via a bitstream, the prediction error and / or related motion information. The prediction error and / or the related motion information may be used for decoding (e.g., decoding current block 1300) and / or other forms of consumption. The motion information may comprise the motion vector 1312 and a reference indicator / index. The reference indicator may indicate the reference picture 1306 in a reference picture list. In other examples, the motion information may comprise an indication of motion vector 1312 and / or an indication of the reference indicator / index. The reference indicator may indicate reference picture 1306 in the reference picture list comprising reference picture 1306. A decoder may decode current block 1300 by determining and / or generating the reference block 1304, which may correspond to / form (e.g., be considered as) a prediction of the current block 1300. The decoder may determine and / or generate the reference block 1304, for example, based on the related motion information. The decoder may decode current block 1300 based on combining the prediction (e.g., a reference block) with the prediction error (e.g., a residual block).

[0128] Inter prediction, as shown in FIG.13A, may be performed using one reference picture 1306 as a source of a prediction for current block 1300. Inter prediction based on a prediction of a current block using a single picture may be referred to as uni-prediction.

[0129] Inter prediction of a current block, using bi-prediction, may be based on two pictures (e.g., the source of prediction may be from the two pictures). Bi-prediction may be useful, for example, if a video sequence comprises fast motion, camera panning, zooming, and / or scene changes. Bi-prediction also may be useful to capture fade outs of one scene or fade outs from one scene to another, where two pictures may effectively be displayed simultaneously with different levels of intensity.

[0130] One or both of uni-prediction and bi-prediction may be available / used for performing inter prediction (e.g., at an encoder and / or at a decoder). Performing a specific type of inter prediction (e.g., uni-predictionDocket No.: 24-2016PCT and / or bi-prediction) may depend on a slice type of current block. For example, for P slices, only uni-prediction may be available / used for performing inter prediction. For B slices, either uni-prediction or bi-prediction may be available / used for performing inter prediction. An encoder may determine and / or generate a reference block, for predicting a current block, from a reference picture list 0, for example, if the encoder is using uni- prediction. An encoder may determine and / or generate a first reference block, for predicting a current block, from a reference picture list 0 and determine and / or generate a second reference block, for predicting the current block, from a reference picture list 1, for example, if the encoder is using bi-prediction.

[0131] FIG.14 shows an example of bi-prediction. Two reference blocks 1402 and 1404 may be used to predict a current block 1400. Reference block 1402 may be in a reference picture of one of reference picture list 0 or reference picture list 1. Reference block 1404 may be in a reference picture of another one of reference picture list 0 or reference picture list 1. As shown in FIG.14, reference block 1402 may be in a first picture that precedes (e.g., in time) a current picture of current block 1400, and the reference block 1404 may be in a second picture that succeeds (e.g., in time) the current picture of current block 1400. The first picture may precede the current picture in terms of a picture order count (POC). The second picture may succeed the current picture in terms of the POC. In other examples, the reference pictures may both precede or both succeed the current picture in terms of POC. A POC may be / indicate an order in which pictures are output (e.g., from a decoded picture buffer). A POC may be / indicate an order in which pictures are generally intended to be displayed. Pictures that are output may not necessarily be displayed but may undergo different processing and / or consumption (e.g., transcoding). The two reference blocks determined and / or generated using / for bi-prediction may correspond to (e.g., be comprised in) a same reference picture. The reference picture may be included in both the reference picture list 0 and the reference picture list 1, for example, if the two reference blocks correspond to the same reference picture.

[0132] A configurable weight and / or offset value may be applied to one or more inter prediction reference blocks. An encoder may enable the use of weighted prediction using a flag in a picture parameter set (PPS). The encoder may send / signal the weight and / or offset parameters in a slice segment header for current block 1400. Different weight and / or offset parameters may be sent / signaled for luma and / or chroma components.

[0133] The encoder may determine and / or generate the reference blocks 1402 and 1404 for the current block 1400 using inter prediction. The encoder may determine a difference between current block 1400 and each of reference blocks 1402 and 1404. The differences may be prediction errors or residuals. The encoder may store and / or send / signal, in / via a bitstream, the prediction errors and / or their respective related motion information. The prediction errors and their respective related motion information may be used for decoding and / or other forms of consumption.

[0134] The motion information for reference block 1402 may comprise a motion vector 1406 and / or a reference indicator / index. The reference indicator may indicate a reference picture, of the reference block 1402, in a reference picture list. In some examples, the motion information for reference block 1402 mayDocket No.: 24-2016PCT comprise an indication of motion vector 1406 and / or an indication of the reference index. The reference index may indicate the reference picture, of reference block 1402, in the reference picture list.

[0135] The motion information for reference block 1404 may comprise a motion vector 1408 and / or a reference index / indicator. The reference indicator may indicate a reference picture, of the reference block 1404, in a reference picture list. The motion information for reference block 1404 may comprise an indication of motion vector 1408 and / or an indication of the reference index. The reference index may indicate the reference picture, of the reference block 1404, in the reference picture list.

[0136] A decoder may decode current block 1400 by determining and / or generating the reference blocks 1402 and 1404. The decoder may determine and / or generate the reference blocks 1402 and 1404, for example, based on the respective related motion information for the reference blocks 1402 and 1404. The reference blocks 1402 and 1404 may correspond to / form (e.g., be considered as) the prediction (e.g., used to generate a prediction block) of the current block 1400. The decoder may decode the current block 1400 based on combining the prediction with the prediction errors.

[0137] Motion information may be predictively coded, for example, before being stored and / or sent / signaled in / via a bit stream (e.g., in HEVC, VVC, and / or other video coding standards / formats / protocols). The motion information for a current block may be predictively coded based on motion information of one or more blocks neighboring the current block. The motion information of the neighboring block(s) may often correlate with the motion information of the current block because the motion of an object represented in the current block is often the same as (or similar to) the motion of objects in the neighboring block(s). Motion information prediction techniques (such as those in HEVC and VVC) may comprise advanced motion vector prediction (AMVP) and / or inter prediction block merging (e.g., merge mode).

[0138] An encoder (e.g., encoder 200 as shown in FIG.2), may code a motion vector. The encoder may code the motion vector (e.g., using AMVP) as a difference between a motion vector of a current block being coded and a motion vector predictor (MVP). An encoder may determine / select the MVP from a list of candidate MVPs. The candidate MVPs may be / correspond to previously decoded motion vectors of neighboring blocks in the current picture of the current block, and / or blocks at or near the collocated position of the current block in other reference pictures. The encoder and / or a decoder may reciprocally generate and / or determine the list of candidate MVPs.

[0139] The encoder may determine / select an MVP from the list of candidate MVPs. Then, the encoder may send / signal, in / via a bitstream, an indication of the selected MVP and / or a motion vector difference (MVD). The encoder may indicate the selected MVP in the bitstream using an index / indicator. The index may indicate the selected MVP in the list of candidate MVPs. The MVD may be determined / calculated based on a difference between the motion vector of the current block and the selected MVP. For example, for a motion vector (e.g., comprising a horizontal component (MVx) and a vertical component (MVy)) that indicates aDocket No.: 24-2016PCT position relative to a position of the current block being coded, the MVD may be represented by twocomponents MVDA and MVDB. MVDA and MVDB may be determined / calculated as:MVD' = MV' − MVP', (15)MVD* = MV* − MVP*. (16)MVDx and MVDy may respectively represent horizontal and vertical components of the MVD. MVPx and MVPy may respectively represent horizontal and vertical components of the MVP.

[0140] A decoder (e.g., decoder 300 as shown in FIG.3) may decode the motion vector by adding the MVD to the MVP indicated in / via the bitstream. The decoder may decode the current block by determining and / or generating the reference block. The decoder may determine and / or generate the reference block, for example, based on the decoded motion vector. The reference block may correspond to / form (e.g., be considered as) the prediction of the current block (e.g., a prediction block). The decoder may decode the current block by combining the prediction with the prediction error.

[0141] The list of candidate MVPs (e.g., in HEVC, VVC, and / or one or more other communication protocols), for AMVP, may comprise two or more candidates (e.g., candidates A and B). Candidates A and B may comprise: up to two (or any other quantity of) spatial candidate MVPs determined / derived from five (or any other quantity of) spatial neighboring blocks of a current block being coded; one (or any other quantity of) temporal candidate MVP determined / derived from two (or any other quantity of) temporal, co-located blocks (e.g., if both of the two spatial candidate MVPs are not available or are identical); and / or zero motion vector candidate MVPs (e.g., if one or both of the spatial candidate MVPs or temporal candidate MVPs are not available). Other quantities of spatial candidate MVPs, spatial neighboring blocks, temporal candidate MVPs, and / or temporal, co-located blocks may be used for the list of candidate MVPs.

[0142] FIG.15A shows example spatial candidate neighboring blocks for a current block. For example, five (or any other quantity of) spatial candidate neighboring blocks may be located relative to a current block 1500 being encoded. The five spatial candidate neighboring blocks may be A0, A1, B0, B1, and B2. FIG.15B shows temporal, co-located blocks for the current block. For example, two (or any other quantity of) temporal, co-located blocks may be located relative to current block 1500 being coded. The two temporal, co-located blocks may be C0 and C1. The two temporal, co-located blocks may be in one or more reference pictures that may be different from the current picture of current block 1500.

[0143] An encoder (e.g., encoder 200 as shown in FIG.2) may code a motion vector using inter prediction block merging (e.g., a merge mode). For example, the encoder (e.g., using merge mode) may reuse the same motion information of a neighboring block (e.g., one of neighboring blocks A0, A1, B0, B1, and B2) for inter prediction of a current block. For example, the encoder (e.g., using merge mode) may reuse the same motion information of a temporal, co-located block (e.g., one of temporal, co-located blocks C0 and C1) for inter prediction of a current block. An MVD need not be sent (e.g., indicated, signaled) for the current block because the same motion information as that of a neighboring block or a temporal, co-located block may beDocket No.: 24-2016PCT used for the current block (e.g., at the encoder and / or a decoder). A signaling overhead for sending / signaling the motion information of the current block may be reduced because the MVD need not be indicated for the current block. The encoder and / or the decoder may reciprocally generate a candidate list of motion information from neighboring blocks or temporal, co-located blocks of the current block (e.g., in a manner similar to AMVP). The encoder may determine to use (e.g., inherit) motion information, of one neighboring block or one temporal, co-located block in the candidate list, for predicting motion information of the current block being coded. The encoder may signal / send, in / via a bitstream, an indication of the determined motion information from the candidate list. For example, the encoder may signal / send an indicator / index. The index may indicate the determined motion information in the list of candidate motion information. The encoder may signal / send the index to indicate the determined motion information.

[0144] A list of candidate motion information for merge mode (e.g., in HEVC, VVC, or any other coding formats / standards / protocols) may comprise: up to four (or any other quantity of) spatial merge candidates derived / determined from five (or any other quantity of) spatial neighboring blocks (e.g., as shown in FIG. 15A); one (or any other quantity of) temporal merge candidate derived from two (or any other quantity of) temporal, co-located blocks (e.g., as shown in FIG.15B); and / or additional merge candidates comprising bi- predictive candidates and zero motion vector candidates. In some examples, the spatial neighboring blocks and the temporal, co-located blocks used for merge mode may be the same as the spatial neighboring blocks and the temporal, co-located blocks used for AMVP.

[0145] Inter prediction may be performed in other ways and variants than those described herein. For example, motion information prediction techniques other than AMVP and merge mode may be used. While various examples herein correspond to inter prediction modes, such as used in HEVC and VVC, the methods, devices, and systems as described herein may be applied to / used for other inter prediction modes (e.g., as used for other video coding standards / formats such as VP8, VP9, AV1, etc.). History-based motion vector prediction (HMVP), combined intra / inter prediction mode (CIIP), and / or merge mode with motion vector difference (MMVD) (e.g., as described in VVC) may be performed / used and are within the scope of the present disclosure.

[0146] A block matching operation (or technique) may be applied / used (e.g., in inter prediction) to determine a reference block in a different picture than that of a current block being coded (e.g., encoded and / or decoded). A block matching operation also may be applied / used to determine a reference block in a same picture as that of a current block being coded. The reference block, in a same picture as that of the current block, as determined using block matching may often not accurately predict the current block (e.g., for camera captured videos). Prediction accuracy for screen content videos may not be similarly impacted, for example, if a reference block in the same picture as that of the current block is used for encoding. Screen content videos may comprise, for example, computer generated text, graphics, animation, etc. Screen content videos may comprise (e.g., may often comprise) repeated patterns (e.g., repeated patterns of text and / or graphics)Docket No.: 24-2016PCT within the same picture. Using a reference block (e.g., as determined using block matching), in a same picture as that of a current block being encoded, may provide efficient compression for screen content videos.

[0147] A prediction technique may be used (e.g., in HEVC, VVC, and / or any other coding standards / formats / protocols) to exploit correlation between blocks of samples within a same picture (e.g., of screen content videos). The prediction technique may be intra block copy (IBC) or current picture referencing (CPR). An encoder may apply / use a block matching technique (e.g., similar to inter prediction) to determine a displacement vector (e.g., a block vector (BV)). The BV may indicate a relative position of a reference block (e.g., in accordance with intra block compensated prediction), that best matches the current block, from a position of the current block. For example, the relative position of the reference block may be a relative position of a top-left corner (or any other point / sample) of the reference block. The BV may indicate a relative displacement from the current block to the reference block that best matches the current block. The encoder may determine the best matching reference block from blocks tested during a searching process (e.g., in a manner similar to that used for inter prediction). The encoder may determine that a reference block is the best matching reference block based on one or more cost criteria. The one or more cost criteria may comprise a rate-distortion criterion (e.g., Lagrangian rate-distortion cost). The one or more cost criteria may be based on, for example, one or more differences (e.g., an SSD, an SAD, an SATD, and / or a difference determined based on a hash function) between the prediction samples of the reference block and the original samples of the current block. A reference block may correspond to / comprise prior decoded blocks of samples (e.g., reconstructed samples) of the current picture. The reference block may comprise decoded blocks of samples of the current picture prior to being processed by in-loop filtering operations (e.g., deblocking and / or SAO filtering).

[0148] FIG.16A shows an example of IBC (e.g., an IBC mode). The example shown in FIG.16A may correspond to screen content. The rectangular portions / sections with arrows beginning at their boundaries may be the current blocks being encoded. The rectangular portions / sections that the arrows point to may be the reference blocks for predicting the respective current blocks.

[0149] A reference block may be determined and / or generated, for a current block, using IBC. The encoder may determine a difference (e.g., a corresponding sample-by-sample difference) between the reference block and the current block. The difference may be a prediction error or residual. The encoder may store and / or send / signal, in / via a bitstream the prediction error and / or related prediction information. The prediction error and / or the related prediction information may be used for decoding and / or other forms of consumption. The prediction information may comprise a BV. The prediction information may comprise an indication of the BV. A decoder (e.g., decoder 300 as shown in FIG.3), may decode the current block by determining and / or generating the reference block. The decoder may determine and / or generate the current block, for example, based on the prediction information (e.g., the BV). The reference block may correspond to / form (e.g., be considered as) the prediction (e.g., a prediction block) of the current block. The decoder may decode theDocket No.: 24-2016PCT current block by combining the prediction (e.g., prediction block) with the prediction error (e.g., residual or residual block).

[0150] A BV may be predictively coded (e.g., in HEVC, VVC, and / or any other coding standards / formats / protocols) before being stored and / or sent / signaled in / via a bitstream. For example, the BV for a current block may be predictively coded based on a BV of one or more blocks neighboring the current block. For example, an encoder may predictively code a BV using the merge mode (e.g., in a manner similar to as described herein for inter prediction), AMVP (e.g., as described herein for inter prediction), or a technique similar to AMVP. The technique similar to AMVP may be BV prediction and difference coding (or AMVP for IBC).

[0151] An encoder (e.g., encoder 200 as shown in FIG.2) performing BV prediction and coding may code a BV as a difference between the BV of a current block being coded and a block vector predictor (BVP). An encoder may select / determine the BVP from a list of candidate BVPs. The candidate BVPs may comprise / correspond to previously decoded BVs of neighboring blocks in the current picture of the current block. The encoder and / or a decoder may reciprocally generate or determine the list of candidate BVPs.

[0152] The encoder may send / signal, in / via a bitstream, an indication of the selected BVP and a block vector difference (BVD). The encoder may indicate the selected BVP in the bitstream using an index / indicator. The index may indicate (e.g., point to) the selected BVP in the list of candidate BVPs. The BVD may be determined / calculated based on a difference between a BV of the current block and the selected BVP. For example, for a BV (e.g., represented by a horizontal component (BVx) and a vertical component (BVy)) that indicates a position relative to a position of the current block being coded, the BVD may be represented bytwo components BVDA and BVDB. BVDA and BVDB may be determined / calculated as:BVD' = BV' − BVP', (17)BVD* = BV* − BVP*. (18)BVDx and BVDy may respectively represent horizontal and vertical components of the BVD. BVPx and BVPy may respectively represent horizontal and vertical components of the BVP. A decoder (e.g., decoder 300 as shown in FIG.3), may decode the BV by adding the BVD to the BVP indicated in / via the bitstream. The decoder may decode the current block by determining and / or generating the reference block. The decoder may determine and / or generate the reference block, for example, based on the decoded BV. The reference block may correspond to / form (e.g., be considered as) the prediction (e.g., a prediction block) of the current block. The decoder may decode the current block by combining the prediction (e.g., the prediction block) with the prediction error (e.g., residual or residual block).

[0153] A same BV as that of a neighboring block may be used for the current block and a BVD need not be separately signaled / sent for the current block, such as in the merge mode. A BVP (in the candidate BVPs), which may correspond to a decoded BV of the neighboring block, may itself be used as a BV for the current block. Not sending the BVD may reduce the signaling overhead.Docket No.: 24-2016PCT

[0154] A list of candidate BVPs (e.g., in HEVC, VVC, and / or any other coding standard / format / protocol) may comprise two (or more) candidates. The candidates may comprise candidates A and B. Candidates A and B may comprise: up to two (or any other quantity of) spatial candidate BVPs determined / derived from five (or any other quantity of) spatial neighboring blocks of a current block being encoded; and / or one or more of last two (or any other quantity of) coded BVs (e.g., if spatial neighboring candidates are not available). Spatial neighboring candidates may not be available, for example, if neighboring blocks are encoded using intra prediction or inter prediction. Locations of the spatial candidate neighboring blocks, relative to a current block, being encoded using IBC may be illustrated in a manner similar to spatial candidate neighboring blocks used for coding motion vectors in inter prediction (e.g., as shown in FIG.15A). For example, five spatial candidate neighboring blocks of a current block being coded using IBC may be respectively denoted A0, A1, B0, B1, and B2 as shown in FIG.15A.

[0155] The most probable mode (MPM) refers to the intra prediction mode (IPM) that is most likely to be the best mode for the current block being encoded or decoded. In current intra prediction techniques, the MPM is determined by analyzing the intra prediction modes of the neighboring CUs (e.g., also referred to as blocks) of a current block (or CU) to be coded (e.g., encoded or decoded). For example, a list of 6 MPMs (referred to as the “MPM list”) may be constructed for intra prediction. The MPM list is derived from the intra prediction modes of the neighboring CUs, and is updated as the encoder progresses through the video frame. When encoding a block, the encoder may determine if the current block is a candidate for any of the MPMs in the MPM list. If it is, the encoder then compares the prediction errors of the respective MPMs to determine which MPM from the MPM list is the best mode for the current block. If the current block is not a candidate for any of the MPMs in the MPM list, the encoder may then evaluate remaining intra prediction modes (e.g., from a total of 67 intra prediction modes which may include a planar mode, a DC mode, and 65 angular directional modes) to determine the best mode for the current block.

[0156] The use of MPMs can significantly improve the coding efficiency because the encoder does not need to explicitly signal the intra prediction mode for the current block if it is one of the MPMs. Instead, the decoder can infer the intra prediction mode for the current block from the corresponding MPM list identically generated at the decoder. Thus, signaling overhead in the bitstream may be reduced.

[0157] In some examples, three types of intra modes may be considered to construct the MPM list: default intra modes; neighboring intra modes; and derived intra modes. A unified 6 MPM list may be used for intra blocks irrespective of whether Multiple Reference Lines (MRL) and Intra Sub-Partitions (ISP) coding tools are applied. The MPM list for the current block is constructed based on intra modes of the left neighbor block (e.g., block corresponding to A1 in FIG.15A) and the above neighbor block (e.g., block corresponding to B1 in FIG.15A) of the current block. Suppose the mode of the left neighbor block is denoted as Left and the mode of the above neighbor block is denoted as Above, the unified MPM list may be constructed as follows: when a neighboring block is not available, its intra mode is set to planar mode by default; if both modes LeftDocket No.: 24-2016PCT and Above are non-angular modes, then the MPM list is set to include{planar, DC, V, H, V − 4, V + 4}, where “V” and “H” refer to vertical mode and horizontal mode, respectively; if one of modes Left and Above is an angular mode, and the other is non-angular, set a mode Max as the larger mode of Left and Above, and set MPM list to include {planar, Max, Max − 1, Max + 1, Max –– 2, Max + 2}; if Left and Above are both angular and they are different, set a mode Max and a mode Min as the larger mode in Left and Above and as the smaller mode in Left and Above, respectively, and thereafter, if Max – Min is equal to 1, then set MPM list to include {planar, Left, Above, Min – 1, Max + 1, Min – 2}, if Max – Min is greater than or equal to 62, then set MPM list to include {planar, Left, Above, Min + 1, Max – 1, Min + 2}, if Max – Min is equal to 2, set MPM list to include {planar, Left, Above, Min + 1, Min – 1, Max + 1}, or otherwise, set MPM list to include {planar, Left, Above, Min – 1, –Min + 1, Max – 1}; and if Left and Above are both angular and they are the same, set MPM list to include {planar, Left, Left − 1, Left + 1, Left – 2, Left + 2}.

[0158] The encoder may encode an MPM index in the bitstream to indicate the position of the selected intra prediction mode in the MPM list to the decoder. The encoder may represent the MPM index as a codeword and entropy encode the codeword into the bitstream. The decoder may derive the MPM list in a manner identical to the encoder, and use the MPM index obtained from the codeword decoded from bitstream to obtain the intra prediction mode from the MPM list derived at the decoder. In some instances, the first bin of codeword, representing the MPM index, is context coded using an arithmetic coder (e.g., CABAC) so as to achieve additional coding efficiencies. For example, three contexts may be used, corresponding to whether the current intra block is MRL enabled, ISP enabled, or a normal intra block.

[0159] In some examples, during the 6 MPM list generation process, pruning may be used to remove duplicated intra modes so that the MPM list includes only unique intra modes. For entropy coding of the 61 non-MPM modes (that is, the 67 modes in VVC minus the 6 MPM), a truncated binary code (TBC) may be used.

[0160] In some implementations, the MPM list is extended to include 16 additional candidates, and is divided into two parts, the primary MPM (PMPM) (e.g., including 6 entries) and the secondary (SMPM) (e.g., including 16 entries). In some implementations, the first entry in the general MPM list is the planar mode. The remaining entries include the intra modes of the adjacent neighboring blocks corresponding to positions left (L), above (A), below-left (BL), above-right (AR), and above-left (AL) (e.g., shown in FIG.15A as A1, B1, A0, B0, and B2), and decoder-side intra mode derivation (DIMD) modes which are sorted in ascending order of a cost such as, for example, SAD, SSD, SATD, etc. In some examples, up to a preconfigured / predetermined number of modes (e.g., 5) with the smallest costs are added to the MPM list. The cost for a respective MPM (e.g., an IPM corresponding to an entry in the MPM list) may be computed between the prediction of the reconstructed samples of the template of the current block and the reconstructed samples. For example, the prediction may be generated by applying the respective MPM for the template. Sorted directional modes are added into the general MPM list, and then the default modes, until the general MPM list with 22 entries isDocket No.: 24-2016PCT constructed. In some examples, if a CU block is vertically oriented, the order of neighboring blocks corresponds to A, L, BL, AR, AL; otherwise, it is L, A, AL, AR, BL.

[0161] Referring back to FIG.16A, in IBC mode applied for screen content, a reference block (RB) may be determined as a “best matching” reference block to a current block. For example, the arrows correspond to block vectors (BVs) that indicate respective displacements from respective current blocks (CBs) to respective reference blocks that best match the respective current blocks. In the examples shown in FIG.16A, the reference blocks match the respective current blocks and the calculated residuals would be small, if not zero. However, often, video content may be more efficiently encoded by considering symmetry properties. For example, it has been observed that symmetry is often present in video content, especially in text character regions and computer generated graphics in screen content video.

[0162] In some implementations, a Reconstruction-Reordered intra block copy IBC (RRIBC) mode (e.g., also referred to as IBC-Mirror Mode) is used for screen content video coding to take advantage of symmetry within video content to further improve the coding efficiency of IBC. In some examples, the RRIBC mode may be signaled based on IBC mode with an indication (or flag) indicating whether flipping is applied and if flipping is applied, further signaling an indication (or flag) indication a direction of flipping.

[0163] In some embodiments, when the RRIBC mode is indicated for encoding a current block, a residual for the current block may be calculated based on samples of a reference block (e.g., corresponding to an original reference block being encoded and decoded to form a reconstructed block) being flipped relative to the current block according to a flip direction indicated for the current block. In an example, at the encoder side, the current block (to be predicted) may be flipped before matching and residual calculation, while the reference block (used to predict the current block) may be derived without flipping. Similarly, at the decoder side, the current block (that was flipped at the encoder) may be determined based on the reference block and residual information, then flipped back to restore the original orientation of the current block before being flipped at the encoder side. In another example, instead of the current block being flipped, the reference block may be flipped instead such that the reference block is flipped to encode the current block (at the encoder) and flipped back (at the decoder) to restore the original orientation of the reference block at the encoder. As described in this specification, reference to flipping the current block may alternatively refer to flipping the reference block and not the current block such that the reference block and the current block are flipped in the direction with respect to each other.

[0164] In an example, in the RRIBC mode, the flip direction may include one of a horizontal direction (e.g., along an x-axis) or a vertical direction (e.g., along a y-axis) for RRIBC coded blocks. In an embodiment, for a current block coded in the RRIBC mode (e.g., an IBC advanced motion vector prediction (AMVP) coded block), a first indication (e.g., a first syntax flag) may indicate / signal whether to use flipping (e.g., also referred to as mirror flipping) to encode / decode the current block. Additionally, for the current block, a second indication (e.g., a second syntax flag) may indicate / signal the direction for flipping (e.g., verticalDocket No.: 24-2016PCT or horizontal). For IBC merge, the flip direction may be inherited from neighboring blocks, without syntax signaling. In an example, for RRIBC, flipping of a current block (or a reference block in an alternative embodiment) in a horizontal and a vertical direction can be represented in (19) and (20), respectively:Reference(x, y) = Sample(w − 1 − x, y) (19)Reference(x, y) = Sample(x, h − 1 − y) (20)where w and h are the width and height of a current block, respectively. Sample(x,y) may indicate a sample value located in (x,y). Reference(x,y) may indicate a corresponding reference sample value after flipping. In other words, for horizontal flipping, (19) shows that the current block is flipped in the horizontal direction by sampling from right to left. Similarly, for vertical flipping, (20) shows that the current block is flipped in the vertical direction by sampling the current block from down to up.

[0165] Considering the horizontal or vertical symmetry, the current block and the reference block are normally aligned horizontally or vertically, respectively. Therefore, in an example, based on the RRIBC mode and a flipping direction, the reference block may be determined from a reference region (including candidate reference blocks) aligned in the same flipping direction, as will be further described below. As a result, when flipping in a horizontal direction is applied / indicated, the vertical component (BVy) of the BV (indicating a displacement from the current block to the reference block) may not need to be signaled because it may be inferred to be equal to 0. Similarly, when flipping in a vertical direction is applied / indicated, the horizontal component (BVx) of the BV may not need to be signaled because it may be inferred to be equal to 0. In other words, in an example, only one component, aligned with the direction for flipping, of the BV may be encoded and signaled for the current block.

[0166] FIG.16B illustrates an example of RRIBC mode applied for screen content to utilize symmetry within text regions to increase efficiency for coding video content. Similar to an encoder described in FIG.16A (e.g., encoder 114 of FIG.1), the encoder may determine, for example, that a reference block 1604, based on applying horizontal flipping, is the best matching reference block for a current block 1602. For example, the encoder may select reference block 1604 as the “best matching” reference block based on one or more cost criterion, such as a rate-distortion criterion, as described above. The one or more cost criterion may be applied to reference block 1604 that is flipped in the horizontal direction relative to current block 1602. For example, current block 1602 may be flipped before the one or more cost criterion are applied to determine reference block 1604. Note that for flipping in the horizontal direction, reference block 1604 is located in a reference region that is in horizontal alignment with current block 1602. Therefore, a block vector (BV) 1606, indicating a displacement between current block 1602 and reference block 1604, may be represented as only a horizontal component (BVx) of BV 1606 because due to the constraints on possible locations of reference blocks, the vertical component of BV 1606 will be equal to 0 when horizontal flipping is indicated / applied.

[0167] For a current block coded in IBC mode, a BV for the current block may be constrained to indicate a relative displacement from the current block to a reference block within an IBC reference region. In someDocket No.: 24-2016PCT examples, a BVP used to predicatively code a BV may be similarly constrained. This is because a BVP may be derived from a BV of a spatially neighboring block of the current block or a prior coded BV as explained above. Based on the BVP, a BVD may be determined as a difference between the BV and the BVP. This BVD may be encoded and transmitted along with an indication of the selected BVP in a bitstream to enable decoding of the current block, as described above. With the introduction of RRIBC, a reference block (that is flipped in a direction relative to the current block) may be constrained to (i.e., selected from) an RRIBC reference region, corresponding to the direction, that is a subset or within the IBC reference region. Like in the IBC mode, the BVP may be used to predictively code a BV, for a current block, indicating a relative displacement from the current block to a reference block within the a reference region (e.g., RRIBC region). Based on the RRIBC mode being indicated and based on a direction for flipping a reference block relative to a current block, the reference region (e.g., an RRIBC reference region) can be determined that corresponds to the direction for flipping. The reference region indicates a region within a picture frame from which the reference block may be selected (e.g., after flipping of the current block).

[0168] FIG. 17 shows an example of intra template matching prediction (IntraTMP) for predicting or determining a current block 1700, according to some embodiments. IntraTMP is an intra prediction mode that copies a reference block, from a reconstructed part of a current picture 1702 (e.g., current frame), whose template (e.g., an L-shaped template, above-only template, or left-only template) is determined to best matches current template 1708 (e.g., the L-shaped template, above only template, or left-only template) of current block 1700 to predict current block 1700. Current block 1700 comprises a rectangular block of samples, in a picture or video frame of current picture 1702, to be encoded by the encoder or decoded by the decoder. Current template 1708 may be determined based on samples in a reconstructed region neighboring current block 1700. For example, current template 1708 may comprise samples that are adjacent to current block 1700 such as including one or more rows of samples above current block 1700 and / or and one or more columns of samples to the left of current block 1700. In some examples, the current template 1708 may be an L-shaped template , a top-only template, or a left-only template of the current block 1700. For example, the L-shaped template may include the top-only template and the left-only template. For example, the L-shaped template may further include an above-left template.

[0169] In IntraTMP, a plurality of reference templates of respective candidate reference blocks 1714, from a predefined TMP search region 1706, are matched with current template 1708 to determine or select a reference template 1712 that best matches or is most similar to current template 1708. A reference block (RB) 1710 from the candidate reference blocks 1714 and indicated by the selected reference template 1712 may be used as a prediction block to determine or predict current block 1700. Block vector (BV) 1730 indicates a displacement from current block 1700 (e.g., the top left sample of current block 1700) to reference block 1710 (e.g., the top left sample of reference block 1710).Docket No.: 24-2016PCT

[0170] In some examples, TMP search region 1706 comprises a portion of a reconstructed region of current picture 1702. TMP search region 1706 indicates the regions that the encoder or decoder may search for candidate templates (such as candidate templates of candidate reference blocks 1714) to determine reference template 1712 and corresponding reference block 1710. In some examples, TMP search region 1706, may include region 1706A (R1) from a current CTU 1704, region 1706B (R3) including a portion of the above CTU, region 1706C (R2) including a portion of the above-left CTU, and region 1706D (R4) including a portion of the left CTU. The CTUs are a result of picture partitioning operations described above. It is to be understood that TMP search region 1706 may include other regions of reconstructed samples of current picture 1702.

[0171] In some examples, the dimensions of TMP search region 1706 (SearchRange_w, SearchRange_h) may be set to be proportional to the dimensions of current block 1700 (BlkW, BlkH) to have a fixed number of cost comparisons (e.g., SAD) per pixel. For example, the dimensions of TMP search region 1706 may becalculated as follows:SearchRange_w = min (64, α ∗ BlkW) (21)SearchRange_h = min (64, α ∗ BlkH) (22)α (or alpha) is a constant that controls a gain / complexity trade-off for the encoder or decoder. For example, α may be equal to 5. In FIG.17, it should further be noted that the dimensions of TMP search region 1706 are illustrated by example and not by limitation. In practical implementation, for example, the dimensions of the regions may vary, and / or one or more of the regions may not be present. In the example illustrated by FIG.17, portions of reconstructed region directly above and directly left of current block 1700 may not be available for prediction or determination and may be excluded from TMP search region 1706. For example, this may be because a reference block in these portions would overlap with current block 1700, which would be an invalid location for prediction or determination of current block 1700. A similar restriction may also be based on the unavailability of samples because of the sequence order of encoding or decoding, or because the samples may be outside of TMP search region or current picture 1702.

[0172] In some examples, the candidate templates of candidate reference blocks 1714 have the same shape and size as current template 1708. In an example, the candidate templates further have the same orientation as current template 1708. In some examples, matching templates includes calculating a template matching (TM) cost between samples of a candidate reference template of a candidate RB (indicated by a respective candidate block vector) and corresponding samples of current template 1708. For example, the difference may be based on a sum of squared differences (SSD), a sum of absolute differences (SAD), a sum of absolute transformed differences (SATD), or a difference determined based on a hash function. The template matching cost represents a similarity between the templates with a smaller cost representing more similar templates.Docket No.: 24-2016PCT

[0173] In some examples, a position of each sample in TMP search region 1706 may be selected as a location of a candidate reference block whose respective reference template is compared against current template 1708 to determine a TM cost. The position may be indicated by a candidate block vector that represents a displacement from current block 1700 (e.g., a top-left sample of current block 1700) to the position. To speed up the template matching process, one or more of TMP search region 1706 may be subsampled by a subsampling interval (e.g., 3) such that not every position is considered as a location of a candidate reference block. After finding a set of candidates (e.g., to generate the list of candidates), a refinement process may be performed to select additional candidate block vectors. The refinement process may be performed via a second template matching search in a search region around one or more of the set of candidates. The search region may be a reduced search range associated with the subsampling interval.

[0174] In some examples, based on the encoder selecting IntraTMP for coding the current block, the encoder may signal the usage of this mode, and the same prediction and matching operations are performed at the decoder.

[0175] In some examples, by performing template matching operations on candidate reference templates in TMP search regions 1706A-D, the decoder (and also encoder) may construct a candidate list of up to a predetermined maximum number (e.g., 19) of candidate block vectors (or candidate block vector predictors). These candidate block vectors may be in ascending order according to the template matching costs of respective reference templates of candidate reference blocks indicated by the candidate block vectors. In some examples, a prediction block (e.g., a predictor) of current block 1700 may be generated using one or more of the reference blocks (e.g., reference block 1710) determined using IntraTMP as well as applying one or more optional filters. For example, the following modes may be supported: single predictor, fusion of multiple predictors, sub-pel precision, and linear filter model. In the single predictor mode, a single predictor is selected from the candidate list such as selecting reference block 1710. In the fusion of multiple predictors mode, multiple predictors are blended to derive the final prediction block such as selecting two or more candidate reference blocks 1714. The blending weights may be either computed from the template matching cost of each predictor, or with a Wiener-filter based weight derivation method. In the sub-pel precision mode, when a single predictor is used, sub-pel precision can be used with 1 / 2-pel precision, 1 / 4-pel precision, or 3 / 4-pel precision, each with 8 possible directions. In the linear filter model mode, a linear filter can be learned (e.g., generated or derived) between the reference template and current template and be applied to the reference block. This mode can be used for the single predictor when sub-pel precision is not used.

[0176] In the example illustrated in FIG. 17, reference template 1712 of reference block 1710 may be determined to best match current template 1708 based on the template matching cost between reference template 1712 and current template 1708 being a minimum TM cost. In another example, the encoder may select reference block 1710 as a prediction of current block 1700 and signal an index of a candidate block vector, indicating reference block 1710, in the candidate list. The decoder may generate the same candidateDocket No.: 24-2016PCT list and determine reference block 1710 based on decoding the index from the bitstream. A block vector (BV) may indicate the displacement of a reference block (e.g., reference block 1710) relative to the current block 1700.

[0177] In some examples, the IntraTMP mode may be enabled for blocks (e.g., CUs) with a size (e.g., width times height) less than or equal to a threshold size (e.g., 64). In an example, the threshold size for IntraTMP is configurable. The IntraTMP prediction mode may be signaled at a block (e.g., per CU) level through a dedicated flag.

[0178] In some examples, an encoder may determine a difference (e.g., a corresponding sample-by-sample difference) between current block 1700 and reference block 1710 used to predict current block 1700. The difference may be referred to as a prediction error or residual. The encoder may store and / or signal in a bitstream the prediction error or residual for decoding by a decoder.

[0179] To perform TMP to code current block 1700, a decoder may perform the same operations as the encoder as described above. For example, based on receiving an indication from the encoder that IntraTMP is used to predict current block 1700 (e.g., via a flag), the decoder may similarly determine or construct current template 1708 of current block 1700. After determining or constructing current template 1708, the decoder may further similarly search TMP search region 1706 to generate a list of candidates from which reference block 1710 may be determined. Because, in some examples, the reference block may be indicated by a block vector candidate with the lowest cost in the list of candidates, the decoder may obtain the block vector candidate by decoding, from the bitstream, the index of the block vector candidate in the list of candidates. The decoder may combine the residual, decoded from the bitstream, with reference block 1710 to reconstruct current block 1700. In this way, the encoder does not need to encode BV 1730 that indicates reference block 1710 in the bitstream.

[0180] In some embodiments, similar to RRIBC for IBC, a similar flipping mode may be implemented for IntraTMP and is referred to as RR-TMP or RR-IntraTMP. In these embodiments, the encoder and / or decoder may search TMP search region 1706 for a flipped template that best matches current template 1708. In some examples, for horizontal flipping, the flipped template corresponds to current template 1708 being flipped in a horizontal direction. For example, the flipped template may match the horizontally flipped current template 1708 in shape, size, and orientation. Similarly, for vertical flipping, the flipped template corresponds to current template 1708 being flipped in a vertical direction. For example, the flipped template may match the vertically flipped current template 1708 in shape, size, and orientation. A candidate reference block of the selected flipped template may be used to code the current block. If vertical flipping were performed, the candidate reference block may be flipped in the vertical direction to determine a prediction block for coding the current block. If horizontal flipping were performed, the candidate reference block may be flipped in the horizontal direction to determine a prediction block for coding the current block. The prediction block may be used toDocket No.: 24-2016PCT encode or decode / reconstruct the current block similarly as the prediction block generated from the IntraTMP mode.

[0181] Various decoder-side techniques such as decoder-side intra mode derivation (DIMD) have been introduced. These techniques allow intra prediction of a current block to be performed without explicitly signaling any specific intra prediction modes (IPMs) in the bitstream. Such techniques are possible based on the encoder and decoder using previously encoded / decoded samples (e.g., reconstructed samples) and independently and identically deriving one or more of the same IPMs for coding the current block. Signaling of the IPMs can be omitted if the encoder and decoder identically determine / derive the same IPMs.

[0182] FIG.18 is a diagram showing an example of decoder-side intra mode derivation (DIMD) for coding a current block 1810, according to some embodiments. DIMD is an intra coding mode in which one or more IPMs used to generate a prediction block 1824 of current block 1810 are not transmitted in the bitstream. Instead, the one or more IPMs may be derived by the decoder using a gradient analysis of neighboring reconstructed pixels (or reference samples) of current block 1810. In some examples, the one or more IPMs may be determined by the encoder, for example, by a rate distortion optimization (RDO) algorithm.

[0183] In DIMD, texture gradient analysis is performed on samples in template 1812 (e.g., reference template) associated with the current block 1810 to generate a histogram of gradient (HoG) 1820. From the HoG 1820, a number (e.g., 2) of DIMD modes such as one or more of DIMD modes 1818A-B may be derived. Each entry in HoG 1820 corresponds to a respective angular intra prediction mode (IPM) with amplitudes (or magnitudes) of the entries determined based on the gradient analysis.

[0184] In some examples, to derive the DIMD modes 1818A-B (and DIMD predictor 1822) for current block 1810, template 1812 including a set of reference samples (e.g., neighboring pixels) may be selected and used to perform a gradient analysis. These reference samples are part of the reconstructed portion of the picture containing current block 1810. Template 1812 may be a 3-samples wide (in width or height) template area (composed of left, above, and above-left areas) defined relative to a position of current block 1810.

[0185] In some examples, the gradient analysis may be performed using edge detection filters applied to 3×3 window positions centered on the reference samples / pixels selected from template 1812. The edge detection filters can determine the amplitude and the angle of luminance direction (e.g., orientation) for each reference sample. For example, the set of reference samples selected from template 1812 may include the samples in the middle line of template 1812. In some examples, the edge detection filters may include a horizontal Sobel gradient filter (Mhor) and / or a vertical Sobel gradient filter (Mver), represented by the following 3x3 matrices that will be convoluted with selected reference samples of template 1812: −1 −0 −1 −1 −2 −1

[0186] For each ofby-point multiply of each of these two matrices with a 3x3 Sobel filter window may be performed and the results are summed.Docket No.: 24-2016PCT The 3x3 Sobel filter window may be centered around the current reference sample and composed of its 8 direct neighbors. Thus, two values Ghor(from the multiplication with Mhor), and Gver(from the multiplication with Mver) are obtained corresponding to the gradient intensities at the current sample, in the horizontal andvertical direction, respectively. An angle may be calculated for the window as [\]^^ = arctan (^TUV / ŶZV). The calculated angle may correspond to (e.g., be converted into) one of the angular IPMs (e.g., oneof the 65 angular IPMs), and an associated amplitude (i.e., the amplitude for the window position)[`^^0ab=^ = |^YZV| + |^TUV| may be added to the HoG indexed by the respective IPM. After anamplitude and angle for each window position in template 1812 are processed, each entry in resulting HoG 1820 represents the cumulated amplitudes for a respective IPM.

[0187] FIG.19 shows an example of a template 1812 (e.g., template area) for computing a HoG used in DIMD, according to some embodiments. Reference template 1812 (e.g., an L-shaped template) of current block 1810 is shown to be in reconstructed area 1902 (or reconstructed region) of the picture frame. Examples of HoGs for different sizes of current block 1810 are shown. For example, for a 4×4 pixel square current block 1908, a 3×3 window 1910 in the template area is shown and a corresponding HoG 1912 may be generated for current block 1908. In another example, for a rectangular current block 1904 with a 3-pixel deep template area 1906, a HoG 1914 corresponding to rectangular current block 1904 may be generated by gradient analysis of reference samples based on a filter window. As illustrated, each coordinate position on the x-axis of the illustrated HoGs is a respective IPM, and the y-axis represents the cumulative amplitude (e.g., counts) for the respective IPMs.

[0188] Returning to FIG.18, a number of DIMD modes 1818A-B may be determined by selecting the IPMs from HoG 1820 based on amplitudes of the IPMs. For example, IPMs M1 and M2 with the highest respective amplitudes A1 and A2 in HoG 1820 may be selected and used to determine DIMD modes 1818A and 1818B, respectively. For example, up to a predetermined number (e.g., 4) of angular intra modes with the highest amplitudes may be selected from HoG 1820. In some examples, the number of DIMD modes 1818A-B may be combined in a fusion / blending scheme to generate a DIMD predictor 1822.

[0189] In some examples, a plurality of IPMs such as DIMD modes 1818A-B may be determined and combined with a planar mode 1816 in the blending / fusion process corresponding to DIMD predictor 1822. DIMD predictor 1822 may comprise a linear combination (e.g., a weighted average) of DIMD modes 1818A- B and planar mode 1816 with weights 1828A-B and 1826 , respectively. In some examples, weights 1828A- B for DIMD modes 1818A-B may be determined based on amplitudes (e.g., magnitudes) associated with DIMD modes 1818A-B, respectively. For example, weight 1828A for DIMD mode 1818A may correspond to DIMD weight 1832A (e.g., wDIMD1), which may be based on an amplitude A1, from HoG 1820, associated with DIMD mode 1818A (e.g., IPM M1) divided by a sum of amplitudes of DIMD modes 1818A-B. For example, weight 1828B for DIMD mode 1818B may correspond to DIMD weight 1832B (e.g., wDIMD2), which may beDocket No.: 24-2016PCT based on an amplitude A2, from HoG 1820, associated with DIMD mode 1818B (e.g., IPM M2) divided by the sum.

[0190] In some examples, planar mode 1816 may have a weight 1826 corresponding to planar weight 1833 that may be a fixed weight f1(e.g., 1 / 4 or 16 / 64 in 6-bit integer precision). The remaining DIMD weights 1832A-B may include a fixed weight portion f2 (e.g., 3 / 4) that is based on the fixed weight of planar weight 1833. For example, the sum of fixed weights f1and f2may be equal to 1.

[0191] DIMD predictor 1822 may be applied to template 1812 (e.g., current template) to determine a prediction block 1824 for current block 1810. For example, each sample (x,y) 1814 of prediction block 1824, denoted as fusionPred, may be determined based on applying DIMD predictor 1822 comprising a weighted average (e.g., a linear combination) of applying DIMD modes 1818A-B and planar mode 1816 with corresponding weights (wi) as follows: ^^b"0d\e^^=(^, ^) = $fg1 ∗ e^^=1(^, ^)hIn some examples, the for mode i) for DIMDmodes 1818A-B and the The weights (wi) may be constant and uniformly applied to determine each sample (x, y) 1814 of prediction block 1824. The predictor Predi for mode i may be a DIMD mode predictor (dimdPredi) for DIMD modes 1818A-B or a planar mode predictor (dimdPlanar) for planar mode 1816. Accordingly, DIMD predictor 1822 may be represented and computed equivalently as follows: ^b"0d\e^^=(^, ^) = j∑^1() fgi0`=1 ∗ =0`=e^^=1(^, ^)h + ge^[\[^ ∗Note the shifting

[0192] The selection of DIMD is signaled in the bitstream for intra coded blocks using a flag. At the decoder, if the DIMD flag is true, the intra prediction mode is derived in the reconstruction process using the same previously encoded neighboring pixels. If not, the intra prediction mode is parsed from the bitstream as in classical intra coding mode.

[0193] In some examples, a location-dependent DIMD mode is introduced to adjust weights 1828A-B of angular IPMs (e.g., DIMD modes 1818A-B) in DIMD. During DIMD IPM derivation, a location-dependency process is applied to determine the impact that different template regions of template 1812 has in selecting each of the IPMs. To determine how specific samples in template 1812 contribute to inferring specific DIMD modes, template 1812 may be divided into three separate regions—including a region above current block 1810, a region to the left of current block 1810, and an above-left region of current block 1810. The gradient analysis computation may be performed separately for samples in each region, resulting in three histograms, HoG 1819C (nopUYZ), HoG 1819A (nqZrs), and HoG 1819B (nopUYZtZrs), respectively. For a directionalDocket No.: 24-2016PCTIPM ` , n1[`] for region i (e.g., above, left, or above-left) represents the cumulative magnitude of allsamples in region i at direction (or IPM) `.

[0194] HoG 1820, corresponding to the full histogram of gradients for the whole template 1812, may be computed as the sum of the three separate HoGs 1819A-C. In some examples, the two directional IPMs with largest and second-largest cumulative amplitude (e.g., magnitude) in HoG 1820 may be selected as main and secondary DIMD modes, e.g., =0`=Sd=^)and =0`=Sd=^^, respectively.

[0195] In some examples, HoGs 1819C and 1819A corresponding to histograms nopUYZand nqZrsmay be used to determine whether =0`=Sd=^)and / or =0`=Sd=^^depend on a specific template region ABOVE or LEFT. In a first example, the location-dependency of =0`=Sd=^1, denoted as ^dui^^1(e.g., shown in FIG.18 as Li = L(Mi, Hleft, Habove) for DIMD mode i), can be defined as: If: (nopUYZ[=0`=Sd=^1] > 2nqZrs[=0`=Sd=^1]), then:^dui^^1 = 1, that is =0`=Sd=^1 depends on region ABOVE.Else if: (nqZrs[=0`=Sd=^1] > 2nopUYZ[=0`=Sd=^1]), then:^dui^^1 = 2, that is =0`=Sd=^1 depends on region LEFT.Else: ^dui^^1 = 0, that is =0`=Sd=^1 is not location-dependent.

[0196] In a second example, the location-dependency of =0`=Sd=^1, denoted as ^dui^^1(e.g., shown in FIG.18 as Li= L(Mi, Hleft, Habove) for DIMD mode i), can be defined as: If : (nqZrs[=0`=Sd=^1] <Else if : (nopUYZ[=0`=Sd=^1] <average of (nqZrs[=0`=Sd=^1], nopUYZ[=0`=Sd=^1], nopUYZtZrs[=0`=Sd=^1])), then:^dui^^1 = 2, that is =0`=Sd=^1 depends on region LEFT.Else: ^dui^^1 = 0, that is =0`=Sd=^1 is not location-dependent.In this example, the indication of location-dependency may be determined based on comparing an amplitude of a HoG corresponding to a specific template portion with the average amplitude of the HoGs of all the template portions of the template.

[0197] Thus location-dependency in DIMD may be determined based on the analysis of HoG peaks amplitudes of the selected angular IPM. For example, location-dependency indications 1830A-B may be determined for DIMD modes 1818A-B, respectively. Location-dependency indication for DIMD mode 1816, which may be a planar mode, may be determined as a value representing that it is not location dependent or that it is diagonally dependent.Docket No.: 24-2016PCT

[0198] In some embodiments, the fusion / blending scheme by which DIMD predictor 1822 is determined may be adjusted based on the location-dependent DIMD modes. For example, blending may be performedto fuse the main and secondary DIMD predictors, =0`=e^^=) and =0`=e^^=^, with the Planar predictor=0`=e^[\[^. If no DIMD mode is determined to be location-dependent (e.g., ^dui^^) == ^dui^^^ == 0), then blending / fusion with uniform weights gi0`=) , gi0`=^ and ge^[\[^ may be applied asexplained above.

[0199] In some embodiments, if at least one of the DIMD modes 1818A-B is inferred to be location- dependent, then sample-based blending may be used to determine DIMD predictor 1822. A locationvarying / dependent weight may be used to blend the predictors at each location of sample (^, ^).

[0200] In some examples, if ^dui^^1 ≠ 0 , the sample-based weights g|dui^^i0`=1(^, ^) forpredictor =0`=e^^=1may be computed so that the average weight used within the block is approximately equal to the uniform weight gi0`=1with higher weights being used in the portion of the block closer to the region (e.g., ABOVE or LEFT) corresponding to ^dui^^1(e.g., indication Li). A fixed range ∆1may bedetermined and is predefined, (e.g., ∆1= 10 ) corresponding to the largest deviation ofg|dui^^i0`=1(^, ^) from gi0`=1. Higher values of ∆1 result in a higher variation of the weights withinthe block. For a block of size n × ^:If ^dui^^1 = 1, then:^g|dui^^i0`=1(^, ^) = gi0`=1 + ∆1 − 2∆1 (n − 1)g|dui^^i0`=1(^, ^) = gi0`=1 + ∆1 − 2∆1 (^ − 1)If both DIMD modes 1818A-B (i=0 and i=1) are associated with location-dependency indications Lithat indicate location dependency (i.e., ^dui^^1 ≠ 0 for modes 0 = 0,1), then the weightsg|dui^^i0`=1(^, ^) may be computed for both predictors depending on the value of ^dui^^1, asshown above.

[0201] In some examples, if only one of DIMD modes 1818A-B is associated with a location dependencyindication Li indicating that it is location dependent, e.g., ^dui^^1 = 0 and ^dui^^(^&1) ≠ 0, then theweights for g|dui^^i0`=1(^, ^) may be computed as:g|dui^^i0`= (^, ^) −g|dui^^i0`= ^, ^) = g (^& gi0`=( 1) (^&1)1 i0`=1 −2

[0202] Finally, weight 1826 for the planar predictor g|dui^^e^[\[^(^, ^) may be as:g|dui^^e^[\[^(^, ^) = 64 - ∑^1() fg|dui^^i0`=1(^, ^)h

[0203] In some examples, the final location-dependent DIMD predictor 1822 may be applied to generate each sample (x,y) of prediction block 1824 as follows:Docket No.: 24-2016PCT ^^b"0d\e^^=(^, ^) = ^ $fg|dui^^i0`=1(^, ^) ∗ =0`=e^^=1(^, ^)h^ ≫ 6In. 6-bits integer precision being used.

[0204] In some embodiments, based on current block 1810 being coded using DIMD, IPM information 1834 may include DIMD parameters that are generated and stored in association with current block 1810. For example, the DIMD parameters may include indications of the selected DIMD modes 1818A-B (M1, M2, …, Mi), amplitudes from HoG 1820 (A1, A2, …, Ai) of the selected DIMD modes 1818A-B, and / or weights 1828A- B (w1, w2, …, wi) of the selected DIMD modes 1818A-B. For example, weights 1828A-B may be the DIMD weights 1832A-B corresponding to selected DIMD modes 1818A-B. In some examples, the DIMD parameters may further include location-dependency indications (L1, L2, …, Li) of the selected DIMD modes 1818A-B. In some examples, IPM information 1834 may include a plurality of lists (e.g., arrays) of DIMD parameters with each list corresponding to a different DIMD parameter type. For example, the plurality of lists may include a list of IPMs, a list of amplitudes, a list of weights, and / or a list of indications of location-dependency. Parameters at the same index across the plurality of lists correspond to the same DIMD mode or IPM indicated by the index to the list of IPMs. IPM information when obtained in DIMD or other DIMD-based coding may be referred to as “DIMD information”.

[0205] FIG.20 shows an example flowchart 2000 of a DIMD predictor derivation process, according to some embodiments. Operations of flowchart 2000 may be performed identically at the encoder (e.g., encoder 200) and the decoder (e.g., decoder 300).

[0206] At block 2001, a histogram of intra prediction modes (IPMs) is determined for a current block (e.g., CU). The histogram is used by an intra-based coding mode for coding the current block. For example, the intra-based coding mode may be any of various DIMD related modes. For example, the intra-based coding mode may be a DIMD mode (e.g., default / regular DIMD mode), as described with respect to FIGS.18-19. For example, the intra-based coding mode may be an OBIC mode, an MIMD mode, or a DIMD Merge list mode, as further described below.

[0207] In some examples, when the intra-based coding mode is the DIMD mode, block 2001 may include blocks 2002-2004. At block 2002, neighboring samples of the current block are determined. For example, the availability of the neighboring samples may be determined based on, e.g., whether blocks (e.g., CUs) above, above right, left below, above left, and / or left of the current block have been determined or reconstructed. In some examples, the neighboring samples may be part of a template of the current block such as template 1812, as described with respect to FIGS.18-19.Docket No.: 24-2016PCT

[0208] At block 2004, the histogram is a histogram of gradients (HoG) generated for the neighboring samples, e.g., from the template of the current block. Specifically, the HoG may be generated based on available samples (e.g., from available template areas) of the template, as described with respect to FIGS.18-19.

[0209] At block 2006, a number of IPMs are selected from the histogram (e.g., the HoG) based on amplitudes of the IPMs in the histogram. In some examples, the IPMs may be selected based on having the highest amplitudes in the histogram, and thus represents the most represented IPMs. The number of selected IPMs may be up to a predetermined number (e.g., 5).

[0210] At block 2008, an indication of location dependency of each respective IPM of the selected IPMs is determined.

[0211] For example, when the intra-based coding mode is the DIMD mode and the histogram is the HoG, the indication of location dependency per selected IPM may be determined based on amplitudes of template portions (e.g., template portions or template regions) of the template. For example, the template portions may include a left template portion and a top template portion of the template. As described with respect to FIG.18, two separate HoGs may be generated corresponding to processed samples in the left template portion and the right template portion, respectively. Then, the indication of location dependency for each selected IPM may be determined based on comparing amplitudes of the selected IPM between the above and left template portions. For example, the comparison may be related to a ratio of the IPM amplitudes in the template portions.

[0212] Specifically, in some examples, the indication of the location dependency of a selected IPM may be determined as follows: by default, the indication of location dependency may be set to 0 indicating no location dependency; if the IPM’s amplitude in the left template portion is less than the IPM’s average amplitude among all template portions (e.g., among three template portions such as the left template, above template, and above left template), then the indication of location-dependency may be set to a first value (e.g., 1) indicating vertical location-dependency; otherwise if the IPM’s amplitude in the above template portion is less than the IPM’s average amplitude among all template portions, then the indication of location-dependency may be set to a second value (e.g., 2) indicating horizontal location-dependency. As described with respect to FIG.18, to determine the indication of location-dependency and during generation of the HoG, the amplitudes may be cumulated in separate HoGs for each of the left template portion, above template portion, and above-left template portion. The amplitudes in the separate HoGs may be summed to determine the HoG representing combined amplitudes for the entire template.

[0213] At block 2010, it is determined whether mode blending (e.g., also referred to as mode combination or fusion) is enabled. If mode blending is disabled, then at block 2012, one of the selected IPMs at block 2006 is determined as the DIMD predictor used to generate a prediction block for codingDocket No.: 24-2016PCT the current block. For example, the IPM with the highest amplitude may be determined as the primary DIMD mode and selected as the DIMD predictor.

[0214] If at block 2010, it is determined that mode blending is enabled, then at block 2014, the number of angular IPMs to be blended is determined. In some examples, mode blending may be enabled, for example, when the first and second selected IPMs of the selected IPMs are both angular modes.

[0215] In some examples, an IPM in a range of IPMs may be determined to be non-angular. For example, the range of IPMs may be one or more predetermined IPMs that correspond to a range of angles including a diagonal direction (e.g., corresponding to Gver / Ghor being equal to or close to 1 or -1).

[0216] At block 2016, it is determined whether the number of angular IPMs to blend is greater than 1. If the number of angular IPMs to blend is not greater than 1, then at block 2018, the DIMD predictor is obtained (e.g., determined) based on blending the one selected angular IPM with a planar mode. For example, the DIMD predictor may be determined as a linear combination of the selected angular IPM and the planar mode with each having a respective fixed weight. For example, the selected angular IPM may have a first fixed weight (e.g., 2 / 3) and the planar mode may have a second fixed weight (e.g., 1 / 3). The sum of the first and second fixed weights may be equal to one.

[0217] If at block 2016, it is determined that the number of angular IPMs to be blended is greater than 1, then at block 2020, weights of the selected IPMs are determined according to their amplitudes in the histogram. For example, a weight of a selected IPM may be based on a ratio of an amplitude of the selected IPM to amplitudes of the selected IPMs, e.g., as described with respect to FIG.18. In some examples, the planar mode can be used for the blending with, a first fixed weight, e.g., such as 1 / 4 or 16 / 64 with 6 bits integer precision. Weights of the angular IPMs may be further weighted (e.g., scaled) based on a second fixed weight. For example, the sum of the first and second fixed weights may sum to one. For example, if the first fixed weight is 1 / 4, then the second fixed weight may be set to 3 / 4 or 48 / 64 with 6 bits integer precision.

[0218] At block 2022, a DIMD predictor is obtained (e.g., generated or derived) based on blending (e.g., fusing or combining) the selected IPMs with a planar mode in accordance with respective weights, as described above with respect to FIG.18.

[0219] In some examples, the DIMD predictor may be obtained further based on using location- dependent blending modes. For example, the weights determined at block 2020 may be uniformly applied to determine all samples in the prediction block and may be referred to as uniform weights. For location- dependent blending, block 2022 may include blocks 2024-2028.

[0220] At block 2024, a blending weight for each respective location dependency of a plurality of location dependencies is determined. In some examples, the plurality of location dependencies may include a horizontal location dependency, a vertical location dependency, or no location dependency. The blending weight may be a sample-based weight for a predictor (e.g., for each selected IPM) that is determined soDocket No.: 24-2016PCT that the average weight used to generate prediction samples (of a prediction block) for the current block is approximately equal to the corresponding uniform weight (e.g., calculated at block 2020) and so that higher weights are used in the portion of the block closer to the left template region or the above template region depending on the indication of location dependency of the respective selected IPM being the horizontal or vertical location dependency, respectively. In some examples, a range used in the location- dependency blending may be a predefined value and corresponds to the maximum deviation of sample- based weights from the corresponding uniform weight. Higher values of the predefined range result in a higher variation of the weights within the prediction block.

[0221] After the blending weights for each location dependency are determined at block 2024, at block 2026, a location-dependency predictor is determined per location dependency. For example, the predictions per each location dependency are blended. For example, for each of horizontal location dependency, vertical location dependency and no location dependency (e.g., diagonal location dependency) that is used by any of the selected IPMs of the DIMD predictor, the selected IPMs having the same location dependency are blended based on their respective amplitudes.

[0222] At block 2028, the DIMD predictor may be obtained based on blending together the location- dependency predictors. For example, the location-dependency predictors may be blended in accordance with the respective sums of amplitudes of the selected IPMs in each location dependency. This may provide a directional sample-wise blending depending on location dependency and using fixed weight deviation as calculated at block 2024.

[0223] In some examples, the various DIMD parameters determined / derived in flowchart 2000 may be stored as IPM information (e.g., IPM information 1834 of FIG.18) used by the current block. For example, the DIMD parameters may include selected IPMs such as from block 2012 or block 2014. For example, the DIMD parameters may include weights of selected IPMs such as those from block 2020. For example, the DIMD parameters may include amplitudes of the selected IPMs such as amplitudes obtained at block 2006 from the histogram. For example, the DIMD parameters may include indications of location dependencies of the selected IPMs such as those determined at block 2008.

[0224] In some embodiments, a DIMD intra prediction mode (e.g., DIMD IPM), corresponding to the DIMD predictor determined at block 2022, may be added to an MPM list along with IPMs being considered for use on the current block. At the encoder, if the DIMD IPM is determined to be the best intra mode (e.g., based on a lowest RDO cost or the like), then the current block may be encoded using the DIMD IPM and only a flag indicating that the current block is encoded using DIMD is transmitted in the bitstream with the residual of the current block. The specific IPMs used in the DIMD IPM are not transmitted in the bitstream. The decoder may receive the flag indicating that DIMD is performed and perform operations of flowchart 2000 to determine DIMD predictor used to determine the prediction block for reconstructing the current block. Since derived intra modes are included into the MPM list, the DIMDDocket No.: 24-2016PCT process may be performed before the MPM list is constructed. The primary derived IPM of a DIMD block may be stored with a block and is used for MPM list construction of the neighboring blocks. In some examples, when DIMD is signaled, MPM and MRL are not signaled. The DIMD intra prediction mode described above may also referred to as the “regular DIMD intra prediction mode” or “regular DIMD mode.”

[0225] Various decoder-side technique have been proposed to enhance the DIMD technique such as a Merge Intra Mode Derivation (MIMD) mode, an Occurrence-based Intra Coding (OBIC) mode, a DIMD Merge List mode, each of which are further described below.

[0226] For example, one decoder-side technique proposes to merge IPM information (e.g., IPM information 1834) from neighboring blocks of a current block to generate a prediction block for coding the current blocks. When neighboring blocks encoded with intra modes such as intra prediction mode or DIMD are available, the DIMD histograms of the selected neighboring blocks (e.g., neighboring CU blocks) are combined to form a merged histogram of gradients (MHoG) for the current block. DIMD modes and weights can be derived from this MHoG similar to how DIMD modes and weights are derived from a HoG generated for regular DIMD, as explained above with respect to FIGS.18-20. In some examples, the HoG of the current block is not used in the construction of the MHoG. This intra mode prediction technique of generating the MHoG may be referred to as Merged Intra Mode Derivation (MIMD).

[0227] The DIMD merge process is similar to the DIMD process described with respect to FIG.20 except for how the histogram of IPMs is determined (e.g., constructed or generated) for the current block at block 2001. Instead of generating the histogram from neighboring samples of a current block, such as from a reference template of the current block, the histogram may be an MHoG determined from at most a predetermined number (e.g., 13) of reconstructed neighboring blocks (e.g., neighboring CU blocks of the current block).

[0228] In some examples, a neighboring block may be from a family of spatial adjacent blocks as shown in FIG.15A. For example, one or more DIMD merge candidates may be added to the list according to an inclusion order of blocks corresponding to (e.g., including) the left sample (A1), above sample (B1), above left sample (B2), above right sample (B0), and bottom left sample (A0).

[0229] FIG.21 shows an example of positions of neighboring blocks of a current block used to determine a histogram, according to some embodiments. For example, the histogram may be an MHoG. The family of spatial adjacent blocks neighboring the current block, as described with respect to FIG.15A, may correspond to sample locations 1-5 adjacent to the current block. In some examples, a neighboring block may be from a family of spatial non-adjacent neighboring blocks of the current block such as blocks corresponding to sample locations 6 and above. For example, blocks 2102-2016 may be selected as DIMD merge candidates and added to the list of DIMD merge candidates. For example, a first block 2102 associated with (e.g., contains) sample 11, a second block 2104 associated with (e.g., contains) sampleDocket No.: 24-2016PCT 13, and a third block 2106 associated with (e.g., contains) sample 10 are spatial non-adjacent blocks with respect to the current block.

[0230] FIG.22A shows an example flowchart 2200A of a method for determining an MHoG for a current block coded using, for example, an MIMD mode, according to some embodiments. Operations of flowchart 2000A may be performed identically at the encoder (e.g., encoder 200) and the decoder (e.g., decoder 300).

[0231] At block 2202, a plurality of neighboring blocks (e.g., neighboring CUs) of a current block may be selected to generate the MHoG. For example, the plurality of neighboring block may be at most a predetermined number (e.g., 3) selected from a list of DIMD merge candidates of the current block. For example, the list may include a predetermined number (e.g., 13) of spatial adjacent and / or non-adjacent blocks of the current block such as those described with respect to FIG.21. In some examples, the plurality of neighboring blocks may be selected based on being previously coded using IPM information (e.g., being coded in a DIMD, OBIC, MIMD, or DIMD Merge List mode). For example, up to the predetermined number of neighboring blocks may be selected based on being coded using IPM information and that are spatially closest to the current block.

[0232] At block 2204, IPM information of each block of the plurality of neighboring blocks are obtained (e.g., retrieved). In some examples, the IPM information of a block represents a histogram of IPMs such as the HoG, which may be an MHoG. The IPM information representing the HoG (and / or MHoG) may include DIMD parameters such as IPMs and associated parameters such as amplitudes, weights, and / or indications of location dependencies, as described with respect to FIG.18. Depending on the intra mode (e.g., DIMD mode, MIMD mode, OBIC mode, DIMD Merge List mode, TIMD mode, MIP mode, etc.) that was used to code a block, the IPM information of the block may be limited to storing a number (e.g., predetermined number such as 5 or 3 or 2) of IPMs and associated parameters. The number of IPMs may be dependent on the type of the intra mode and / or IPM information of the neighboring blocks used to generate the IPM information for the block. In some examples, the IPMs stored in the IPM information may be those with the highest amplitudes from a histogram that was generated for the block.

[0233] At block 2206, an MHoG is determined based on combining the IPM information of each block of the plurality of neighboring blocks according to amplitudes in (e.g., stored for respective IPM(s)) the IPM information. In some examples, the HoGs representing the IPM information of each block may be combined, e.g., based on averaging the amplitudes of the IPMs in the HoGs as follows: 1^where N is the number of selectedth entry (or luma mode) of the HoG. As shown, the HoGs may be combined by averaging the amplitudes cumulated per IPM of the HoGs by the number N. In other words, amplitudes of the same IPM across IPM information of the selectedDocket No.: 24-2016PCT neighboring blocks may be cumulated in the MHoG. Then, amplitudes of the same IPMs across the IPM information of selected neighboring blocks may be combined. In some examples, the cumulated amplitude for an IPM may be normalized by dividing by the number N of selected neighboring blocks. The resulting MHoG may be used to derive the prediction modes and weights as described above.

[0234] In some examples, similar to how a number of IPMs are selected based on an HoG in regular DIMD, as described with respect to FIG.18, FIG.19, and block 2006 of FIG.20, the number of IPMs (e.g., up to a predetermined number such as 5) may be similar selected from the MHoG. The number of IPMs may be selected, for example, based on the highest amplitudes in the MHoG.

[0235] In some examples, with respect to block 2008 in the MIMD mode, if multiple neighboring blocks are selected to determine the MHoG, the indication of location dependency may be set to a value (e.g., 0) indicating diagonal (e.g., or non-location dependent) for each of the number of selected IPMs. In an example, if only one neighboring block was selected, the indication of location dependency for each of the selected IPMs may be set to the selected IPMs’ location dependency as obtained from IPM information of the neighboring block. Accordingly, a DIMD predictor may be generated from the selected IPMs of the MHoG and used to generate a prediction block for coding the current block.

[0236] In some examples, if MIMD mode is selected by the encoder, the encoder may signal usage of the MIMD mode with a flag at the block or prediction unit level as a sub-mode of DIMD. The decoder may parse this flag from the bitstream and derive the DIMD predictor using the generated MHoG.

[0237] Another decoder-side technique for enhancing DIMD is based on generating a histogram of occurrences (HoC) representing sample-wise occurrences of the IPMs in the neighborhood of the current block. This technique may be referred to as an occurrence-based intra coding (OBIC) mode and may be a sub-mode of DIMD. Similar to regular DIMD mode, the OBIC mode may blend (e.g., fuse or combine) up to a predetermined number (e.g., 5) of IPMs with highest occurrences from the HoC, along with planar mode to obtain a DIMD predictor. The weight for each mode may be determined based on amplitudes in the HoC similar to how a weight for an IPM is determined from the HoG in regular DIMD.

[0238] The OBIC process is similar to the DIMD process described with respect to FIG.20 except for how the histogram of IPMs is determined (e.g., constructed or generated) for the current block at block 2001. Instead of generating the histogram from neighboring samples of a current block, such as from a reference template of the current block, the histogram may be a HoC determined from at most a predetermined number (e.g., 13) of reconstructed neighboring blocks (e.g., neighboring CU blocks of the current block).

[0239] Similar to the neighboring blocks described with respect to the MIMD mode, a neighboring block may be from a family of spatial adjacent blocks as shown and described with respect to FIG.15A. Also, FIG.21 may show examples of neighboring blocks of the current block used to determine a histogram such as the HoC. The family of spatial adjacent blocks neighboring the current block, as described withDocket No.: 24-2016PCT respect to FIG.15A, may correspond to sample locations 1-5 adjacent to the current block. In some examples, a neighboring block may be from a family of spatial non-adjacent neighboring blocks of the current block such as blocks corresponding to sample locations 6 and above. For example, blocks 2102- 2016 may be selected as DIMD merge candidates and added to the list of DIMD merge candidates. For example, a first block 2102 associated with (e.g., contains) sample 11, a second block 2104 associated with (e.g., contains) sample 13, and a third block 2106 associated with (e.g., contains) sample 10 are spatial non-adjacent blocks with respect to the current block.

[0240] FIG.22B shows an example flowchart 2200B of a method for determining an HoC for a current block coded using, for example, an OBIC mode, according to some embodiments. Operations of flowchart 2000B may be performed identically at the encoder (e.g., encoder 200) and the decoder (e.g., decoder 300).

[0241] At block 2212, a plurality of neighboring blocks (e.g., neighboring CUs) of a current block may be selected to generate the HoC. For example, the plurality of neighboring block may be at most a predetermined number (e.g., 13 or 15) selected from a list of DIMD merge candidates of the current block. For example, the list may include a predetermined number (e.g., 13) of spatial adjacent and / or non- adjacent blocks of the current block such as those described with respect to FIG.21 and block 2202 of FIG.22A. Similar to the MIMD mode, generating the list of DIMD merge candidates may include checking adjacent spatial neighboring blocks of the current block as shown in FIG.15A and non-adjacent spatial neighboring blocks as described above with respect to FIG.21 In some examples, the plurality of neighboring blocks may be selected based on being previously coded using IPM information (e.g., being coded in a DIMD, OBIC, MIMD, or DIMD Merge List mode). For example, up to the predetermined number of neighboring blocks may be selected based on being coded using IPM information and that are spatially closest to the current block.

[0242] At block 2214, IPM information of each block of the plurality of neighboring blocks are obtained (e.g., retrieved). In some examples, the IPM information of a block represents a histogram of IPMs such as the HoG, which may be an MHoG or an HoC. Block 2214 may correspond to and include similar operations as block 2204 of FIG.22A. For example, the IPM information representing the HoG (and / or MHoG) may include DIMD parameters such as IPMs and associated parameters such as amplitudes, weights, and / or indications of location dependencies, as described with respect to FIG.18.

[0243] At block 2216, an HoC is determined based on combining the IPM information of each block of the plurality of neighboring blocks according to a size and / or dimensions of each block.

[0244] In some examples, different from generating HoG or MHoG in which amplitudes of IPMs in the IPM information are combined, the HoC may be determined to include IPMs, from the IPM information, with cumulated sample-wise occurrences where each occurrence value for a respective IPM is calculated based on the number of samples that are coded with that IPM from the selected DIMD merge candidates.Docket No.: 24-2016PCT For example, if a selected DIMD candidate is a neighboring block with dimensions of width w and a height h and that is coded with an intra prediction mode IPM, the occurrence of the IPM in the associated block may be computed as:ℎ0"ad]^[`[<eS]+= g × h.The occurrence for this specific IPM may be cumulated over the selected plurality of neighboring blocks (e.g., including adjacent spatial neighboring blocks and / or non-adjacent spatial neighboring blocks). In other words, the sizes (e.g., width multiplied by height) of neighboring blocks with IPM information including the same IPM may be cumulated for that IPM in the HoC. The resulting HoC may be used to derive the prediction modes and weights as described above with respect to blocks 2006-2028.

[0245] In some examples, with respect to block 2006 of FIG.20 when in the OBIC mode, up to a predetermined number (e.g., 5) of angular IPMs with the highest amplitudes (representing highest occurrences) in the HoC may be selected and blended together along with the planar mode to obtain a DIMD predictor (e.g. the DIMD predictor based on generating a HoC) used to generate a prediction block for coding the current block.

[0246] In some examples, with respect to block 2008 when in the OBIC mode, the indication of location dependency may be set to a value (e.g., 0) indicating diagonal (e.g., or non-location dependent) for each of the number of selected IPMs.

[0247] In some examples, if OBIC mode is selected by the encoder, the encoder may signal usage of the OBIC mode with a flag at the block or prediction unit level as a sub-mode of DIMD. The decoder may parse this flag from the bitstream and derive the DIMD predictor using the generated HoC.

[0248] In some embodiments, the IPM information of a neighboring block may include different numbers of IPMs (e.g., angular modes) depending on the intra mode that was used to code the neighboring block. As an example, intra modes such as DIMD, OBIC, or MIMD may use to 5 IPMs, a template-based intra mode derivation (TIMD) mode may use up to 2 modes, or a spatial geometric partitioning mode (SGPM) may use up to 2 modes. In these examples, all intra modes of such blocks are considered in the histogram generation. In some examples, neighboring blocks coded using non-angular modes such as IntraTMP, IBC, or Matrix-based Intra Prediction (MIP) are not selected and are not used to generate the histogram (e.g., HoG, MHoG, or HoC).

[0249] FIG. 23A shows an example of IPM information from a plurality of (previously reconstructed) neighboring blocks of a current block, according to some embodiments. FIG. 23B shows a graphical representation of combining the IPM information from the plurality of neighboring blocks to generate an MHoG if the current block is coded using the MIMD mode. In contrast, FIG. 23C shows a graphical representation of combining the IPM information from the plurality of neighboring blocks to generate an HoC if the current block is coded using the OBIC mode.Docket No.: 24-2016PCT

[0250] In both the OBIC and MIMD modes, a coder (e.g., encoder in FIG.2, decoder in FIG.3) obtains (e.g., accesses, collects, receives) the IPM information from the plurality of (previously reconstructed) neighboring blocks (e.g., block 1, block 2, and block 3) and generates information used to generate a prediction block to code the current block. For example, as shown in FIG.23A, the coder obtains first IPM information from block 1 including HoG information such as amplitudes for IPM 1, IPM 7, IPM 9, IPM 13, and IPM 17. For example, the coder obtains second IPM information from block 2 including HoG information such as amplitudes for IPM 7, IPM 9, and IPM 13. For example, the coder obtains third IPM information from block 3 including HoG information such as amplitudes for IPM 1, IPM 7, IPM 9, IPM 13, and IPM 17.

[0251] As shown in FIG.23B, if the current block is coded using MIMD mode, the coder may combine the amplitudes of like IPMs from the first IPM information, the second IPM information, and the third IPM information corresponding to respective blocks 1-3 to generate MHoG 2302. For example, the coder determines the amplitudes of IPM 1 in the MHoG 2302 by adding all the amplitudes of IPM 1 from blocks 1- 3. Also, the coder determines the amplitudes of IPM 7 in the MHoG 2302 by adding all the amplitudes of IPM 7 from blocks 1-3. Likewise, the coder determines the amplitudes of IPM 9 in the MHoG 2302 by adding all the amplitudes of IPM 9 from blocks 1-3. Also, the coder determines the amplitudes of IPM 13 in MHoG 2302 by adding all the amplitudes of IPM 13 from blocks 1-3. And, the coder determines the amplitudes of IPM 17 in MHoG 2302 by adding all the amplitudes of IPM 17 from blocks 1-3. In some implementations, using the various techniques described above (e.g., MIMD), a prediction block may be generated based on MHoG 2302 for coding the current block. For example, the encoder may signal, in a bitstream, a residual block indicating a difference between the prediction block and the current block. For example, the decoder may obtain the residual block from the bitstream and combine it with the prediction block, that was identically generated as the encoder, to reconstruct the current block.

[0252] As shown in FIG.23C, if the block was coded using OBIC mode, the coder may combine the occurrences of like IPMs from the first IPM information, the second IPM information, and the third IPM information corresponding to respective blocks 1-3 to generate HoC 2304. For example, the coder determines the amplitude (occurrence) of IPM 1 in the HoC 2304 by adding the sizes of blocks 1 and 3, each of which was coded using at least IPM 1. Similarly, the coder determines the amplitude (occurrence) of IPM 7 in the HoC 2304 by adding the sizes of blocks 1, 2, and 3. Similarly, the coder determines the amplitude (occurrence) of IPM 9 in the HoC 2304 by adding the sizes of blocks 1, 2, and 3. Also, the coder determines the amplitude (occurrence) of IPM 13 in the HoC 2304 by adding the sizes of blocks 1, 2, and 3. And, the coder determines the amplitude (occurrence) of IPM 17 in the HoC 2304 by adding the sizes of blocks 1 and 3. Here, since the second IPM information does not indicate IPM 1 and IPM17, the size of block 2 is not used for determining IPMs 1 and 17. In some examples, using the various techniques described above (e.g., OBIC), a prediction block may be generated based on HoC 2304 for coding the current block. For example, the encoder may signal, in a bitstream, a residual block indicating a difference between the prediction blockDocket No.: 24-2016PCT and the current block. For example, the decoder may obtain the residual block from the bitstream and combine it with the prediction block, that was identically generated as the encoder, to reconstruct the current block.

[0253] Another decoder-side technique for enhancing DIMD is based on using a list of DIMD merge candidates that is identically generated at the encoder and the decoder and signaling an index that indicates one DIMD merge candidate from the list to code a current block. Each DIMD merge candidate may include IPM information from a plurality of neighboring reconstructed blocks with respect to the current block. This process is referred to as a DIMD Merge List mode.

[0254] FIG.24A shows an example flowchart 2400 of the DIMD Merge List mode for deriving the list of DIMD merge candidates, according to some embodiments. Flowchart 2400 includes a block 2402 in which a DIMD merge list is derived and a block 2404 in which DIMD parameters for a selected DIMD merge candidate from the list are derived. For example, these DIMD parameters may include blended modes (e.g., DIMD modes), weights, and indications of location dependency. Operations of flowchart 2400 may be performed by an encoder, such as, for example, encoder 200 in FIG.2, or by a decoder, such as, for example, decoder 300 in FIG.3.

[0255] Block 2402 may include several operations shown as blocks 2406-2414, each of which may add to the list of DIMD merge candidates a family of DIMD merge candidates obtained from spatial neighbor blocks (e.g., intra blocks) of the current block that are selected based on a different selection criterion, from combinations of IPM information already in the list, or from configured default IPM information. In example implementations, the DIMD merge candidates in the list of DIMD merge candidates is arranged as a list or table, but embodiments may not be limited by a specific arrangement structure of the DIMD merge candidates.

[0256] At block 2406, DIMD merge candidates from a family of spatial adjacent blocks are considered for adding DIMD merge candidates to the list of DIMD merge candidates. For example, as explained with respect to FIG.15A, this family of blocks may include the spatial adjacent blocks corresponding to adjacent neighbor samples of the current block. In some examples, the DIMD merge candidates from spatial adjacent blocks can be added to the list of DIMD merge candidates according to the inclusion order of blocks corresponding to left sample (L), above sample (A), above left sample (AL), above right sample (AR), and bottom left sample (BL). In some examples, another inclusion order such as, L, A, AR, BL, and AL, or yet another different inclusion order may be used. The blocks in the family of spatial adjacent blocks are also considered in the derivation of the MPM list. Between 1 and 5 (all spatial adjacent neighbors) candidates may be added to the DIMD merge candidate list at block 2406. For the IPM information of a particular spatial block to be included in the DIMD merge candidate list, that block must at least already have had (e.g., during the reconstruction of blocks in the current frame) IPM information derived for that block. IPM information may be derived for a block that uses the DIMD parameters such as, for example, MIMD mode (e.g., DIMD HoG merge mode),Docket No.: 24-2016PCT DIMD Merge List mode, DIMD mode, OBIC mode, intra prediction mode, or MPM list derivation. In some examples, a merge candidate is added to the list of DIMD merge candidates only if the corresponding neighbor block was encoded or decoded based on DIMD or another intra prediction mode that uses the DIMD parameters. In some instances, such as when none of the adjacent spatial adjacent blocks are reconstructed using a mode that uses DIMD parameters (e.g., DIMD mode, MIMID mode, DIMD Merge List mode, OBIC mode, intra prediction mode, MPM list derivation, etc.), at block 2406, no spatial adjacent candidates are added to the list of DIMD merge candidates.

[0257] At block 2408, DIMD merge candidates from a family of spatial non-adjacent blocks of the current block are added to the list of DIMD merge candidates. The positions and inclusion order of the DIMD merge candidates of non-adjacent candidates in the same frame as the current block may be in accordance with a predetermined sequence, such as that shown in FIG.21. The pattern and sequence of blocks indicated in FIG.21 is the same as that defined in some implementations for inter-merge prediction candidates.

[0258] The numbers 1-5 shown in FIG.21 refer to spatially adjacent neighbors of the current block (shown shaded) in the inclusion order L, A, AR, BL, and AL, that were already added to, or otherwise considered for inclusion in, the merge candidate list at block 2406 and thus may not be considered at block 2408. The sequence of blocks indicated by the sample locations 6-24 may be considered for inclusion of the corresponding IPM information in the list of DIMD merge candidates at block 2408. As shown in FIG.21, the non-adjacent neighbor blocks corresponding to (e.g., including) sample locations 6-24 considered for inclusion in the list of DIMD merge candidates may be arranged in the frame along the left horizontal direction, the above vertical direction, the above left diagonal direction, the above right diagonal direction, and the below left diagonal direction.

[0259] Similar to determining whether to include a spatial adjacent block in the list of DIMD merge candidates, for the IPM information of a particular spatial non-adjacent block to be included in the list of DIMD merge candidates, that block must have had DIMD used for encoding / decoding or at least have had IPM information derived for that block. In some examples, a DIMD merge candidate is added to the list of DIMD merge candidates only if the corresponding neighbor block was reconstructed based on DIMD or another intra prediction mode that uses the DIMD parameters. In some instances, such as when none of the spatial non-adjacent blocks are reconstructed using a mode that uses DIMD parameters, at block 2408, no spatial non-adjacent candidates are added to the list of DIMD merge candidates.

[0260] At 2410, a family of merge candidates from a history-based table of IPM information is added to the list of DIMD merge candidates. For example, one or more DIMD merge candidates (e.g., a predetermined number) from the history-based table may be added to the list of DIMD merge candidates. For example, a predetermined number of the most recently coded blocks in the history-based table may be selected.

[0261] The history-based table may be maintained to include a predetermined number of the latest intra coded blocks that used IPM information. In some examples, this history-based table may be updated eachDocket No.: 24-2016PCT time an intra block (e.g., CU) is coded using the DIMD process such as when the IPM information is derived (e.g., a block using the DIMD mode, or an MPM-based mode, or based on a direction derived from DIMD, or a MIMD mode, or DIMD Merge List mode, or OBIC mode). This table includes a limited number of entries of IPM information from previously coded blocks and does not include any duplicate IPM information.

[0262] For the IPM information of a particular spatial block to be included in the history-based table, that block must have had DIMD used for encoding / decoding or at least have had IPM information derived for that block. IPM information may be derived for a block for encoding / decoding based on DIMD or another intra prediction mode that uses the DIMD parameters. In some examples, an entry of IPM information is added to the history-based table only if the corresponding neighbor block was reconstructed based on DIMD or another intra prediction mode that uses the DIMD parameters.

[0263] In some embodiments, spatial adjacent blocks and spatial non-adjacent blocks of the current block may have been already considered in accordance with a predetermined inclusion order (e.g., based on blocks 2406 and 2408), only IPM information of spatial blocks that are neither spatial adjacent blocks nor spatial non-adjacent blocks according to the predetermined inclusion pattern are added to the history-based table.

[0264] In some examples, when inserting a new entry of IPM information into the history-based table, a constrained first-in-first-out (FIFO) rule may be applied where a redundancy check is first applied to determine whether there is identical IPM information in the table. If found, the entry with the identical IPM information is removed from the table and all entries following that in the table are moved forward in the FIFO order, and the new IPM information is inserted as the last entry. The table may be reset at intervals, such as, for example, at the beginning of each CTU row. Such resetting may be performed due to hardware constraints. Such resetting may also help ensure that only the most recent neighbor blocks are in the table. In some implementations, the history-based table of IPM information may be similar to the history-based table of motion vectors (HMVP) in the whole-block-based Advanced Motion Vector Predictor (AMVP) mode for inter prediction in VVC.

[0265] FIG.24B shows a flowchart 2420 of an example process for generating a history-based table of DIMD merge candidates, according to some embodiments. Operations of flowchart 2420 may be performed identically at the encoder (e.g., encoder 200) and the decoder (e.g., decoder 300). Flowchart 2420 starts at block 2422 when a current block is considered as a DIMD candidate. The current block may be considered as a DIMD candidate based on the current block being coded using DIMD or another intra mode in which IPM information is derived. At block 2422, it is determined whether the IPM information (of the DIMD candidate) to be added already exists in the table. If, at block 2422, it is determined that the IPM information to be added is not in the table, then at block 2426, it may be determined whether the table is full. This determination may be based on a preconfigured maximum size threshold for the history-based table. If the table is not full, at block 2430, the IPM information of the DIMD candidate may be added to the history-based table.Docket No.: 24-2016PCT

[0266] If at block 2422, it is determined that the IPM information to be added is in the table, then at block 2424, the duplicate IPM information of an existing DIMD candidate in the history-based table is already in the table and is removed from the table.

[0267] If at block 2426, it is determined that the history-based table is full, at block 2428, the oldest entry in the table is removed.

[0268] After either block 2424 or block 2428, at block 2432, the entries that follow the removed entry in the table are shifted up or moved up in sequence (e.g., in the FIFO sequence). After the rearrangement of table entries at block 2432, at block 2430, the new IPM information of the DIMD candidate is added as the last entry in the table.

[0269] According to the example inclusion order, DIMD merge candidates derived from IPM information in the history-based table are added to the list of DIMD merge candidates after considering DIMD merge candidates derived from spatial adjacent blocks and spatial non-adjacent blocks of the current block.

[0270] Returning to FIG. 24A, in some embodiments, at block 2412, a set of combined DIMD merge candidates are added to the list of DIMD merge candidates. In some examples, one or more combined DIMD merge candidates may be added to the list of DIMD merge candidates based on existing DIMD merge candidates (and respective IPM information) in the list such as DIMD merge candidates considered and selected from one or more of the DIMD merge candidate families described above with respect to blocks 2406-2410. In some examples, a combined DIMD merge candidate may be generated based on combining IPM information from the IPM information of DIMD merge candidates that are already in the list of DIMD merge candidates. In some examples, DIMD merge candidates that are already in the list, but which are based on a combination of other DIMD merge candidates in the list, are not used to derive further combined DIMD merge candidates.

[0271] In some examples, IPM information corresponding to HoGs from at least two DIMD merge candidates in the list of DIMD merge candidates are combined to create a new combined HoG, from which the blending modes and weights are derived to obtain the IPM information of a new DIMD merge candidate. For example, the IPM information (e.g., amplitudes of like IPMs) of at least two merge candidates may be averaged to generate an MHoG, and the blending modes and weights are derived from this MHoG in a manner similar to that in the blending mode derivation in DIMD and MIMD, as described, for example, in relation to FIGS.19-20. In some examples, considering the new combined DIMD merge candidate, location dependency may be set for example to diagonal (e.g., indicated by a predetermined value of 0) as a default value, or can be set accordingly to the blending modes, i.e., that a vertical location dependency is set for a vertical blended mode, or a horizontal location dependency is set for a horizontal blended mode.

[0272] In some examples, a plurality of combined DIMD merge candidates may be derived and include two or more of the following: a candidate derived from the first and second DIMD merge candidates in the list of DIMD merge candidates; a candidate derived from the first and third DIMD merge candidates in the list ofDocket No.: 24-2016PCT DIMD merge candidates; a candidate derived from the second and third DIMD merge candidates of the list of DIMD merge candidates; a candidate derived from the two first DIMD merge candidates of the list of DIMD merge candidates with a vertical location dependency; a candidate derived from the two first DIMD merge candidates of the list of DIMD merge candidates with a horizontal location dependency; and / or a candidate derived from combining IPM information of all spatial adjacent blocks of the current block.

[0273] In some implementations, a combined DIMD merge candidate is not added to the list if it cannot be derived. For example, if there are only two candidates in the list of DIMD merge candidates before adding combined DIMD candidates, the second combined candidate, derived from the first and third candidates, may be skipped as there is no third DIMD candidate.

[0274] At block 2414, a set of default DIMD merge candidates are added to the list of DIMD merge candidates, according to some embodiments.

[0275] In some examples, one or more default IPM information entries are added as DIMD merge candidates to the list of DIMD merge candidates. For example, DIMD parameters of two example default IPM information entries are shown in Table 1 below. Blending Modes 0 (Planar) 34 (Diag) 18 (Hor) T

[0276] The table shows default mode 0 and default mode 1, that each specify a set of predetermined DIMD parameters. One or more DIMD merge candidates having predetermined default IPM information (e.g., the DIMD parameters specified in Table 1 above) may be added to the list of DIMD merge candidates as one or more default DIMD candidates.

[0277] In some examples, the addition, if any, of combined DIMD merge candidates optionally followed by the default DIMD merge candidates completes the addition of merge candidates to the list of DIMD merge candidates.

[0278] In some embodiments, block 2402 may further include blocks 2416 and / or 2418. In addition to the DIMD merge candidates with IPM information retrieved from previously coded (e.g., reconstructed) neighboring blocks of the current block as described with respect to blocks 2406-2414, blocks 2416-2418 may add one or more DIMD merge candidates that derive IPM information from neighboring spatial blocks. It should be noted that the order of blocks 2406-2418 may be different than from what is shown in FIG.24A.

[0279] At block 2416, one or more DIMD merge candidate derived using the MHoG derivation process and referred to as MHoG-based candidates may be added to the list of DIMD merge candidates. In someDocket No.: 24-2016PCT examples, a list of MHoG merge candidates may be generated from which two or more MHoG merge candidates are selected to derive each of the one or more MHoG-based candidates. For example, the MHoG derivation process described above with respect to FIGS.21, 22A, 23A, and 23B may be applied to selected MHoG merge candidates.

[0280] In some examples, the list of MHoG merge candidates may include IPM information (e.g., DIMD parameters related to an MHoG or an HoG) of spatial neighbor blocks (e.g., CUs) of the current block such as the spatial adjacent neighbor blocks and the spatial non-adjacent blocks that was coded based on DIMD or another intra prediction mode using DIMD parameters, as described above with respect to FIG.15A and FIG.21. In an example, redundant IPM information is removed or not added to the list of MHoG merge candidates. In some examples, the list of MHoG merge candidates may further include one or more DIMD candidates from a history-based table of IPM information.

[0281] In some examples, a plurality of different subsets of the list of MHoG merge candidates may be selected to generate a plurality of different DIMD merge candidates to add to the list of DIMD merge candidates.

[0282] In some examples, the one or more MHoG-based candidates are added to the list of DIMD merge candidates before other families of merge candidates are considered. For example, the one or more MHoG- based candidates have the lowest indices in the list of DIMD merge candidates.

[0283] At block 2418, one or more DIMD merge candidate derived using the OBIC derivation process and referred to as OBIC-based candidates may be added to the list of DIMD merge candidates. In some examples, a list of OBIC merge candidates may be generated from which two or more OBIC merge candidates are selected to derive each of the one or more OBIC-based candidates. For example, the OBIC derivation process described above with respect to FIGS.21, 22B, 23A, and 23C may be applied to selected OBIC merge candidates.

[0284] In some examples, the list of OBIC merge candidates may include IPM information (e.g., DIMD parameters related to an MHoG, HoG, or HoC) of spatial neighbor blocks (e.g., CUs) of the current block such as the spatial adjacent neighbor blocks and the spatial non-adjacent blocks that was coded based on DIMD or another intra prediction mode using DIMD parameters, as described above with respect to FIG.15A and FIG.21. In an example, redundant IPM information is removed or not added to the list of OBIC merge candidates. In some examples, the list of OBIC merge candidates may further include one or more DIMD candidates from a history-based table of IPM information.

[0285] In some examples, a HoC may be derived from the IPM information of two or more neighbor block corresponding to the selected OBIC merge candidates. The derived HoC may be used to derive the DIMD merge candidate to be added to the list of DIMD merge candidates.Docket No.: 24-2016PCT

[0286] In some examples, a plurality of different subsets of the list of OBIC merge candidates may be selected to generate a plurality of different DIMD merge candidates to add to the list of DIMD merge candidates.

[0287] Operations at block 2402, which includes blocks 2406-2414 and may further include blocks 2416- 2418 and which generates the list of DIMD merge candidates, may be identical at both the encoder and decoder. After block 2402 is completed (i.e., the list of DIMD merge candidates is constructed), at block 2404, blended modes, weights and location dependency are derived. At the encoder, this may include determining the best DIMD merge candidate in the list of DIMD merge candidates based on a cost (e.g., SAD, SATD, etc.) difference between a predicted block obtained using the DIMD predictor and the current block and / or based on rate distortion optimization (RDO cost) of each of the DIMD merge candidates starting from the top (e.g., the lowest SAD, SATD cost) of the list of DIMD merge candidates. The index to the position of the best (selected) DIMD merge candidate in the list of DIMD merge candidates is determined. Subsequently, in some examples, the selected predictor may be added to the MPM list. If the current block is predicted by the DIMD predictor and encoded for transmission based on the DIMD prediction, then a DIMD enabled flag and the index can be transmitted in the bitstream.

[0288] At the decoder, block 2404 may include parsing the bitstream for one or both of a DIMD enabled flag or index to the list of DIMD merge candidates. The index can be used to obtain the selected DIMD merge candidate from which to derive the DIMD predictor.

[0289] The DIMD merge mode has the benefit of the use of available neighbor information (e.g., in particular, the IPM information derived for the spatial neighbor blocks) to better suit the signal characteristics of the current block to be predicted.

[0290] FIG. 25 shows an example of matrix-based intra prediction (MIP) 2500, according to some embodiments. MIP 2500 may be performed by an encoder (e.g., encoder 200 in FIG.2) and / or a decoder (e.g., decoder 300 in FIG. 3). MIP 2500 may include one or more operations such as one or more of downsampling 2505, matrix-vector multiplication 2510, upsampling 2515, and / or any other additional steps / processes. In some examples, downsampling 2505 and / or upsampling 2515 may be omitted.

[0291] Samples of a current block 2502 to be coded (e.g., encoded or decoded) may be predicted from reference samples (e.g., samples previously encoded and reconstructed at an encoder, and decoded at a decoder) taken from a column to the left of current block 2502 (e.g., the column immediately adjacent to the left-most column of current block 2502) and / or reference samples taken from a row above current block 2502 (e.g., the row immediately adjacent to the top-most row of current block 2502). The samples from the column to the left of current block 2502 may be left reference samples (e.g., refL) and the samples from the row above current block 2502 may be top reference samples (e.g., refT). Current block 2502 may be W x H samples in size. The top reference samples refT may extend over W samples of the row above current block 2502 and / or the left reference samples refL may extend over H samples of the column to the left of currentDocket No.: 24-2016PCT block 2502. The top reference samples refT may extend over more or less samples of the row above current block 2502 and / or the left reference samples refL may extend over more or less samples of the column to the left of current block 2502. The dimensions W and / or H may be integer powers of two (or any other quantity). W and H may be integer powers of two (e.g., between 4 and 64, or may be any other quantity).

[0292] Samples available from neighboring blocks of current block 2502 may be used to determine / construct the left reference samples refL and / or the top reference samples refT. In some scenarios, samples may not be available for determining / constructing the left reference samples refL and the top reference samples refT. Samples may not be available for determining / constructing the left reference samples refL and the top reference samples refT, for example, if the samples lie outside the picture of current block 2502, the samples are part of a different slice or CTU of current block 2502, and / or the samples belong to blocks that have been inter coded and constrained intra prediction is indicated. Intra prediction may not be dependent on inter predicted blocks, for example, if the constrained intra prediction is indicated (e.g., configured for encoding and / or decoding). Samples that may not be available for determining and / or constructing the left reference samples refL and / or the top reference samples refT may include samples in blocks that have not already been encoded and decoded at an encoder and / or decoded at a decoder based on the sequence order for encoding / decoding. Samples available for determining / constructing the left reference samples refL and / or the top reference samples refT may be reconstructed samples. Using reconstructed samples for determining / constructing the left reference samples refL and / or the top reference samples refT may allow identical prediction results to be determined at both the encoder and the decoder.

[0293] Samples unavailable for determining / constructing the left reference samples refL and / or the top reference samples refT may be filled with available samples of the left reference samples refL and / or the top reference samples refT. Samples unavailable for determining / constructing the left reference samples refL and / or the top reference samples refT may be filled with a nearest available sample of the left reference samples refL and / or the top reference samples refT. Samples unavailable for determining / constructing the left reference samples refL and / or the top reference samples refT may be filled with a nearest available sample, of the left reference samples refL and / or the top reference samples refT, determined, for example, by moving in a clock-wise direction through the left reference samples refL and / or the top reference samples refT from the position of the unavailable sample. If no samples are available, the left reference samples refL and / or the r top reference samples refT may be filled with the mid-value of the dynamic range of the picture of current block 2502 being coded.

[0294] The encoder and / or the decoder performing the MIP 2500 may perform downsampling 2505 of the left reference samples refL and / or the top reference samples refT. The encoder and / or the decoder performing the MIP 2500 may perform downsampling of the left reference samples refL and / or the top reference samples refT, for example, after the left reference samples refL and / or the top reference samples refT are constructed / determined. Downsampling of the left reference samples refL and / or the top referenceDocket No.: 24-2016PCT samples refT may generate / determine downsampled reference samples that may be referred to as reduced left reference samples (e.g., redL) and / or reduced top reference samples (e.g., redT), respectively. The downsampling of the left reference samples refL and / or the top reference samples refT may reduce the quantity of samples in the left reference samples refL and / or the top reference samples refT. Reducing the quantity of samples may advantageously reduce the quantity of operations (e.g., multiplications) needed to perform matrix-vector multiplication 2510. The quantities of reduced left reference samples redL and / or the reduced top reference samples redT may be based on the dimensions of current block 2502. For example, the reduced left reference samples redL and / or the reduced top reference samples redT may each consist of 2 samples based on current block 2502 having dimensions W=4 and H=4. The reduced left reference samples redL and / or the reduced top reference samples redT may each consist of 4 samples. The reduced left reference samples redL and / or the reduced top reference samples redT may each consist of 4 samples, for example, based on current block 2502 having any other dimensions. The reduced left reference samples redL and / or the reduced top reference samples redT may each consist of more or less samples depending on the dimensions of current block 2502. The left reference samples refL and / or the top reference samples refT may each consist of more or less samples depending on the dimensions of current block 2502.

[0295] The encoder and / or the decoder may generate / determine the reduced left reference samples redL and / or the reduced top reference samples redT. The encoder and / or the decoder may generate / determine the reduced left reference samples redL and / or the reduced top reference samples redT, for example, by averaging sets of reference samples in the left reference samples refL and / or the top reference samplesrefT, respectively. For example, the encoder and / or the decoder may generate / determine, if current block 2502 has dimensions W=4 and H=4, the reduced left reference samples redL according to the following equation: ^refL[i ∙ 2 + j] + + 1^ ≫ 1, for 0 ≤ i < 2. (22)Otherwise, themay generate / determine the reduced left reference samples redL according to the following equation: ^^&^refL^i ∙ 2^ + j^ + + y1 ≪ (k − 1)z^ ≫ k, for 0 ≤ i < 4, (23)whereblock 2502 is given by W=4·2k. The encoder and / or the decoder may generate / determine the reduced top reference samples redT in an analogous manner to equations (22) and (23) for the reduced left reference samples redL.

[0296] The encoder and / or the decoder may concatenate the reduced left reference samples redL and the reduced top reference samples redT. The encoder and / or the decoder may concatenate the reduced left reference samples redL and the reduced top reference samples redT, for example, to generate / determine aDocket No.: 24-2016PCT concatenated vector of downsampled reference samples (e.g., pTemp = [redL, redT]). For example, for current block 2502 having dimensions W=4 and H=4, the concatenated vector of downsampled reference samples pTemp may have a size of 4. Otherwise, the concatenated vector of downsampled reference samples pTemp may have a size of 8 (or any other quantity).

[0297] The encoder and / or the decoder may perform matrix-vector multiplication 2510 to determine and / or generate a prediction of current block 2502. The prediction of the current block may be a reduced sample prediction of current block 2502 (e.g., predMIP 2520). The encoder and / or decoder may determine / generatepredMIP 2520 by determining / calculating a matrix vector product:predMIP = mWeight / ∙ pTemp, (24)where mWeighti is a weight matrix of the i-th MIP mode. For example, the weight matrix mWeighti may comprise Wred·Hred rows and a quantity of columns. The quantity of columns may be equal to 4 (e.g., if W=H=4), or 8 in all other instances. Wred and Hred may be determined / calculated as: Wred = ^4 , for max(W, H) ≤ 8min(W, 8) , for max(W, H) > 8 (25)Hred = ^4 , for max(W, H) ≤ 8min(W, 8) , for max(W, H) > 8

[0298] Each term in predMIP 2520 may be determined / generated based on a linearthe reference samples in the concatenated vector of downsampled reference samples pTemp weighted by a respective set of weights (or row of weights) in the weight matrix mWeighti. The terms in predMIP 2520 may correspond to a prediction of a respective sample of current block 2502.

[0299] The encoder and / or the decoder may select the weight matrix mWeighti from one of a plurality of sets of weight matrices. For example, the plurality of sets of weight matrices may comprises three sets of weight matrices – set S0, set S1, and set S2. The encoder and / or the decoder may select the weight matrix mWeighti based on a variable (e.g., parameter mipSizeId). The encoder and / or the decoder may determine mipSizeId. The encoder and / or the decoder may determine mipSizeId, for example, based on the dimensions W and H of current block 2502. For instance, the encoder and / or the decoder may determine / calculate the variable mipSizeId as: 0, for W = H = 4mipSizeId = ^ 1, for max(W, H) = 8 (27)2, for max(W, H) > 8

[0300] The encoder and / or the decoder may select the weight matrix mWeighti from the set S0 based on the variable mipSizeId = 0. The encoder and / or the decoder may select the weight matrix mWeighti from the set S0 based on current block 2502 having dimensions of 4x4 (e.g., W=H=4). The set S0 may comprise 16 different weight matrices mWeighti, i^{0, ..., 15} (or any other quantity of weight matrices). Each of the 16 different weight matrices mWeighti, i^{0, ..., 15} may include 16 rows and 4 columns. The encoder and / orDocket No.: 24-2016PCT the decoder may select the weight matrix mWeighti from set S1 based on the variable mipSizeId = 1 or based on current block 2502 having dimensions of 4x8, 8x4, or 8x8 (e.g., max (W, H) =8). The set S1 may comprise 8 different weight matrices mWeighti, i^{0, ..., 7} (or any other quantity of weight matrices). Each of the 8 different weight matrices mWeighti, i^ {0, ..., 7} may include 16 rows and 8 columns. The encoder and / or the decoder may select the weight matrix mWeighti from the set S2 based on the variable mipSizeId = 2 or based on current block 2502 having a width or a height greater than 8 (e.g., max (W, H) >8). The set S2 may comprise 6 different weight matrices mWeighti, i^{0, ..., 5} (or any other quantity of weight matrices). Each of the 6 different matrices mWeighti, i^{0, ..., 5} may include 64 rows and 8 columns.

[0301] The weight matrices mWeighti in the sets S0, S1, and S2 may be represented by integers (e.g., 8- bit integers) to enable a more efficient hardware implementation. The encoder and / or the decoder may replace the concatenated vector of downsampled reference samples pTemp with the vector p. The vector pmay be determined / calculated as:p[0] = 2^&^ − pTemp[0], (28)p[i] = pTemp[i] − pTemp[0], for i > 0. (29)B may be a bit depth. The encoder and / or the decoder may use the vector p in place of the concatenated vector of downsampled reference samples pTemp in equation (24) to determine / calculate predMIP 2520.

[0302] The encoder and / or the decoder may use a transpose of the weight matrix mWeighti, for example, for each of the weight matrix mWeighti in the sets S0, S1, and S2. The encoder and / or the decoder may determine / generate predMIP 2520 using the transpose of the weight matrix mWeighti. The encoder and / or the decoder may interchange the reduced left reference samples redL and the reduced top reference samples redT in the concatenation of the reduced left reference samples redL and the reduced top reference samples redT to generate / determine the concatenated vector of downsampled reference samples pTemp, and then use the transpose of the weight matrix mWeighti to determine / generate predMIP 2520 (e.g., using equation (24)).

[0303] The encoder and / or the decoder may perform upsampling 2515 on predMIP 2520 (e.g., the reduced sample prediction of current block 2502) to determine / generate a prediction of current block 2502 (e.g., predSamples 2525). The prediction of current block 2502, predSamples 2525, may comprise a predicted sample for each sample in current block 2502. The encoder and / or the decoder may determine / generate predSamples 2525, for example, based on linear interpolation from predMIP.

[0304] The encoder may predict the samples of current block 2502. The encoder may predict the samples of current block 2502 (e.g., during encoding of current block 2502) for a plurality of MIP modes i (e.g., as shown in FIG.25). The encoder may predict the samples of current block 2502, for example, for each weight matrix mWeighti of the MIP modes in one of the sets S0, S1, and S2 (e.g., including the transpose of each weight matrix mWeighti of the MIP modes in the one of the sets S0, S1, and S2). For each MIP mode applied, the encoder may determine / calculate a prediction error and / or a residual for current block 2502 based on aDocket No.: 24-2016PCT difference (e.g., SSD, SAD, SATD, and / or any other difference) between the prediction samples determined for the MIP mode and the original samples of current block 2502. The encoder may determine / select one of the MIP modes to encode current block 2502. The encoder may determine / select one of the MIP modes to encode current block 2502, for example, based on the determined prediction errors. The encoder may select an MIP mode i that results in the smallest prediction error and / or the smallest prediction residual for current block 2502. The encoder may determine / select one of the MIP modes, to encode current block 2502, based on a rate-distortion measure (e.g., Lagrangian rate-distortion cost) determined / calculated using the prediction errors and / or the residuals. The encoder may send / transmit an indication (e.g., a signal) of the selected MIP mode and its corresponding prediction error and / or residual to the decoder for decoding of current block 2502. The encoder may further send / transmit an indication (e.g., a flag) that MIP is used to predict current block 2502. This indication (e.g., a flag) may be separate from the indication (e.g., a signal) of the selected MIP mode. The encoder may send / transmit the above information in a bitstream to the decoder.

[0305] The decoder may predict the samples of current block 2502 (e.g., during decoding of current block 2502) for the selected MIP mode (e.g., as shown in FIG.25). The decoder may receive the indication (e.g., a signal) of the selected MIP mode i from the encoder for current block 2502. The decoder may perform MIP based on the MIP mode indicated / signaled by the encoder for current block 2502 and / or based on the indication (e.g., a flag) that MIP is used to predict current block 2502 (e.g., separated from the indication (e.g., a signal) of the selected MIP mode). The decoder may add the predicted values of the samples of current block 2502 (e.g., predSamples 2525) to the prediction error and / or the residual of current block 2502 received from the encoder to reconstruct current block 2502. The decoder may receive the above information in a bitstream from the encoder.

[0306] In some embodiment, in the MIP mode, a DIMD derivation process may be performed to generate an HoG used to determine (or select) a transform set from a plurality of transform sets. For example, the selected transform set may be used to transform and / or inverse transform residual coefficients generated from a prediction block of samples (e.g., predSamples 2525). In some examples, a horizontal gradient and a vertical gradient may be calculated for each of predMIP 2520 to generate HoG 2527 in a process similar to that described in FIG.19 and block 2004 of FIG.20, but generating HoG 2527 from predMIP 2520 instead of neighboring samples of current block 2502. In an example, an IPM with the highest amplitude from HoG 2527 may be used to determine (or select): a transform set (e.g., low-frequency non-separable transform (LFNST) set) from a plurality of transform sets (e.g. LFNST sets), and / or a transpose indication parameter / flag (e.g., LFNST transpose flag). A value of the transpose indication parameter may indicate whether to transpose a sample input vector used in the MIP mode.

[0307] For example, depending on the MIP mode, in some MIP modes, if the value of the transpose indication parameter is equal to 0, then the scanning order of LFNST coefficients used for the current block may be set to the horizontal scanning order; and if the value of the MIP transpose indication parameter isDocket No.: 24-2016PCT equal to 1, then the scanning order of LFNST coefficients used for the current block may be set to the vertical scanning order. Or, in some other MIP modes, if the value of the MIP transpose indication parameter is equal to 0, then the scanning order of LFNST coefficients used for the current block may be set to the vertical scanning order; and if the value of the MIP transpose indication parameter is equal to 1, then the scanning order of LFNST coefficients used for the current block may be set to the horizontal scanning order.

[0308] In some embodiments, a plurality of the highest IPMs from HoG 2527 (e.g., up to 5 IPMs) may be stored in association with current block 2502. In some examples, the plurality of amplitudes corresponding to the plurality of highest IPMs may also be stored in association with current block 2502.

[0309] FIG.26 shows an example of template-based intra mode derivation (TIMD) for coding a current block, according to some embodiments. The TIMD mode is a type of intra prediction in which an intra prediction mode (IPM) may be identically determined (e.g., independently derived) by an encoder (e.g., encoder 200) and a decoder (e.g., decoder 300) such that the IPM determined (e.g., selected) by the encoder does not need to be signaled to the decoder. Hence signaling bandwidth is reduced and TIMD may be considered as a type of decoder-side intra mode derivation process.

[0310] As shown in FIG.26, in the TIMD mode, a video coder (e.g., encoder 200 or decoder 300) may determine a template 2604 for current block 2602. Template 2604 may comprise one or more regions of samples in a reconstructed region 2608 of a current picture (or frame) of current block 2602. The one or more regions may include reconstructed samples neighboring (e.g., adjacent to) current block 2602. In some examples, the one or more regions of template 2604 may comprise a template region 2604A to the left of current block 2602 (e.g., a left template) and a template region 2604B above current block 2602 (e.g., an above template). In some examples, template 2604 may include a region that is above and to the left of current block 2602 (e.g., the region enclosed by reference of template 2606 and template regions 2604A-B). Template regions 2604A and 2604B may have a thickness (e.g., width and height respectively) of R1 and R2 samples, respectively. For example, R1 and / or R2 may be 2 samples, 4 samples, 8 samples, etc. Template region 2604A may have a height of N samples, which may be a height of current block 2602. Template region 2604B may have a width of M samples, which may be a width of current block 2602.

[0311] In TIMD mode, reference of template 2606 are used to derive a template predictor for template 2604. The video coder may determine (e.g., select and obtain) reference of template 2606 as a region of samples (in reconstructed region 2608) neighboring (e.g., adjacent to) template 2604. For example, reference of template 2606 may comprise reconstructed samples left and above template 2604. Reference of template 2606 may have a thickness to the left of template region 2604A of R1 samples and a thickness above template region 2604B of R2 samples. For example, R1 and / or R2 may be 1 sample, 2 samples, 4 samples, etc. In some examples, reference of template 2606 may include an upper region having a width greater than template region 2604B (e.g., a width that is greater or equal to twice the width of template region 2604B, 2(M+L1) samples, 2(M+L1)+R1 samples, etc.). In some examples, reference of template 2606 may includeDocket No.: 24-2016PCT a left region having a height greater than template region 2604A (e.g., a height that is greater or equal to twice the height of template region 2604A, 2(N+L1) samples, 2(N+L1)+R2 samples, etc.).

[0312] In some examples, a TIMD mode predictor may be determined using a list of candidate intra prediction modes (IPMs). For example, the list may include IPMs from a most probable mode (MPM) list. In some examples, one or more of a DC mode, a planar mode, a horizontal and / or vertical DC mode, or a horizontal and / or vertical planar, may be added to the list of candidate IPMs. A cost (e.g., SAD or SATD) for each candidate IPM in the list may be determined based on differences between reconstructed samples in template 2604 and predicted samples of template 2604 generated based on reference of template 2606 and using the candidate IPM. For example, the video coder may determine the predicted samples by applying the candidate IPM to samples of reference of template 2606.

[0313] In some examples, a first IPM and a second IPM, from the list, with the lowest costs of costs (determined for candidate IPMs in the list) are selected to determine (e.g., derive) a first TIMD mode and a second TIMD mode. In an example, the first and second TIMD modes are determined as the first and second IPMs, respectively.

[0314] In some examples, the first and second TIMD modes may be determined by refining the first and second IPMs. For example, an angular mode range may be extended from a first range of the list (e.g., 67 modes) to a second range (e.g., 131 modes) and costs of the two adjacent modes (i.e., + / -1 mode) of each selected IPM may be determined. For example, the first TIMD mode may be determined as an IPM having the smallest cost among costs of the first IPM and its two adjacent modes in the second range. The second TIMD mode may be determined as an IPM having the smallest cost among costs of the second IPM and its two adjacent modes in the second range.

[0315] In some embodiments, a TIMD mode predictor may be determined based on combining (e.g., blending or fusing) the first TIMD mode and the second TIMD mode. For example, the TIMD mode predictor may be a linear combination of the first TIMD mode and the second TIMD mode. Each weight of the first and second TIMD modes, in the linear combination, may be determined based on costs of the first and second TIMD modes, respectively. For example, a weight, for a TIMD mode, may be determined as being inversely proportional to a cost of the TIMD mode. The TIMD mode predictor may be applied to template 2604 to determine a prediction block for current block 2602. An encoder may generate a residual (e.g., prediction error) based on a difference between the prediction block and current block 2602. A decoder may reconstruct current block 2602 based on the reciprocally generated prediction block and the residual received from the encoder in a bitstream.

[0316] In some examples, the TIMD modes may be stored as corresponding (refined) IPMs in IPM information used in coding current block 2602. Additionally, the IPM information may include parameters such as the costs and / or derived weights for the IPMs corresponding to the TIMD modes. Different from the IPM information stored for intra coding modes such as DIMD, MIMD, OBIC, DIMD Merge List, the IPMDocket No.: 24-2016PCT information stored for the TIMD mode does not include amplitudes of histograms. In some examples, the IPM information may also include parameters such as indications of location-dependency, referred to as directionalities, determined for the IPMs corresponding to the TIMD modes.

[0317] In some examples, directionalities (e.g., first and second directionality) of the TIMD modes (e.g., first and second TIMD modes) may be determined based on costs of the TIMD modes. For example, a directionality or indication of location dependency may include horizontal indicating prediction samples closer to the left boundary of the current block are likely to be more spatially correlated with the parameters (e.g., weight) for the determined TIMD mode, vertical indicating prediction samples closer to the above boundary of the current block are likely to be more spatially correlated with the parameters (e.g., weight) for the determined TIMD mode, no direction, and / or diagonal indicating a combination of horizontal and vertical. In an example, no direction may correspond to and indicate the diagonal direction.

[0318] For a selected TIMD mode (e.g., a candidate minimizing SATD cost computed in the template area), the directionality (indicating location-dependency) may be determined based on which portion(s) of the current template contributes the most to the selection of the TIMD mode. There are as many location- dependency directionalities as regions of the current template. For instance, a current template may comprise a first region (e.g., template region 2604B) and a second region (e.g., template region 2604A). If it is determined that the above template is the most impactful template for the selection of the TIMD mode, the location-dependency state associated to / with the TIMD mode is set to “vertical” (e.g., indication of location- dependency may be set to vertical) such that sample-wise vertical fusion will be operated for blending this TIMD mode. If it is determined that left template is the most impactful template for the selection of the TIMD mode, the location-dependency state associated to / with the selected predictor is set to “horizontal” (e.g., indication of location-dependency may be set to horizontal) such that sample-wise horizontal fusion will be operated for blending this TIMD mode. If templates participation in the selection of the TIMD mode is balanced, the associated location-dependency state is set to “non-location-dependent” (e.g., indication of location-dependency may be set to none or non-location dependent) and neither sample-wise process is operated (e.g., meaning regular block-wise weight blending is achieved) or a sample-wise diagonal fusion will be operated for blending this TIMD mode. Thus, location-dependency state associated to / with selected TIMD mode impacts directionality of the sample-wise TIMD fusion process. In some examples, the first region and the second region do not overlap. In other examples, they may overlap.

[0319] In some examples, the directionality may be determined according to availability of template samples and / or template regions. For example, only one template region may be available at the picture border. For example, if only the first region (e.g., left template) is present or available, a first directionality may be determined (e.g., location-dependency being set to 2 indicating horizontal) corresponding to that first region. Otherwise, if only the second region (e.g., above template) is present or available, a second directionality may be determined (e.g., location-dependency being set to 1 indicating vertical) corresponding to that secondDocket No.: 24-2016PCT region. In some examples, when the location dependency is determined as being not enabled (e.g., disabled) the value may be set to, e.g., 0, which may indicate a diagonal direction.

[0320] In some examples, the impact may be determined based on comparing a first cost of the first region with a second cost of the second region. The cost may be calculated much like how TIMD costs are calculated, e.g., using SATD, SSE, or SAD. In some examples, a lower cost indicates higher impact. In some examples, a ratio may be calculated between the first cost and the second cost to determine which region has greater impact and thus determine the directionality of the TIMD mode.

[0321] For example, for the first cost for the first region (e.g., a left template region / area) and the second cost for the second region (e.g., an above template region / area), determination of the directionality of the TIMD mode may be determined as follows: If ^^^i^ < ^. ^^^it, ^dui^^1 = 1Else if ^^^it < ^. ^^^i^, ^dui^^1 = 2Otherwise, ^dui^^1 = 0

[0322] For illustrative purposes, the costs are represented as SATD costs, but other costs are possible.^^^i^ is the SATD cost associated to / with a selected TIMD mode and computed in the second region (e.g.,above template). ^^^i^is the SATD cost associated to / with a selected TIMD mode and computed in the first region (e.g., left template). ^dui^^1is the location-dependent parameter value associated with the i-th selected TIMD mode (e.g., i belongs to [0;2]). A value of 0 may indicate no location-dependency; a value of 1 may indicate vertical location-dependency of the i-th selected TIMD mode; and a value of 2 may indicate horizontal location-dependency of the i-th selected TIMD mode. ^ is a scaling factor and, e.g., may be a value less than 1. For example, ^ may be a value comprised in the range [1 / 10; 1 / 6] such as 1 / 8.

[0323] In some examples, when a candidate TIMD mode is non-angular (e.g. DC or Planar mode), the associated location-dependency state (e.g., directionality) may be set to 0 (e.g., indicating no-location- dependency) as it is expected that these “flat” modes when selected do not exhibit large differences in terms of relative template SATD. However, in other examples, a location-dependency state may be determined (e.g., derived) for the candidate non-angular TIMD mode similar to how the location-dependency state is determined for an angular TIMD mode, as described above.

[0324] In some examples, a directionality of a non-angular mode may be derived / determined based on a plurality of directional non-angular modes (e.g., directional DC, directional planar) corresponding to that non- angular mode. For example, the directionality may be determined as being corresponding to direction of the lowest cost (e.g., SATD cost) of the directional non-angular modes (e.g., among vertical, horizontal and original modes). For instance, template SATD cost may be computed for original, horizontal and vertical Planar modes. If horizontal planar mode has the minimum SATD among the three planar modes, location- dependency or the directionality for the planar mode may be to horizontal. If vertical planar mode has the minimum SATD among the three planar modes, location-dependency or the directionality for the planar modeDocket No.: 24-2016PCT may be to vertical. Otherwise, if the original planar mode has the minimum SATD, then the directionality may be set to diagonal (or possibly sample-wise fusion is deactivated). It is noted that although a directional non- angular mode has a lowest SATD, the regular original non-angular mode may be used during the fusion process.

[0325] In the various DIMD-based modes such as DIMD, OBIC, MIMD, MIMD, and DIMD Merge List described above, which are considered angular-based coding modes, neighboring blocks of a current block may be considered to generate a histogram (e.g., HoG, MHoG, or HoC) used in coding the current block. In the case of the DIMD Merge List, neighboring blocks or history-based candidate blocks may be considered to be added to a list of DIMD merge candidates or, in some examples, such blocks may be used to generate an OBIC-based candidate and / or an MIMD-based candidate. However, for these DIMD-based modes, only neighboring blocks that are coded in a DIMD-based mode are considered. In some examples, the DIMD- based mode may include DIMD, OBIC, MIMD, MIMD, or DIMD Merge List. In general, blocks that are coded using a non-angular mode such as IntraTMP, IBC, or TIMD, etc. are not considered, which may significantly limit the available neighboring blocks and hence usage of DIMD-based modes. For example, FIG.27A shows an example of a current block 2700 and neighboring blocks 2702-2708 being coded in DIMD-based modes and non-angular modes. Blocks 2702 and 2708 may be coded in an IBC mode. Blocks 2704 and 2714 may be coded in an IntraTMP mode (ITMP). Block 2706 may be coded in a DIMD-based mode and thus be associated with (e.g., having) previously derived IPM information 2701 (e.g., IPM information 1834 of FIG. 18). Block 2712 may be coded in a TIMD mode.

[0326] As shown in FIG.27A, blocks 2702-2712 may correspond to spatial adjacent neighboring blocks of current block 2700, as described with respect to FIG.15A and FIG.21. It should be understood that other types of neighboring blocks such as spatial non-adjacent neighboring blocks, as described in FIG.21, and / or a list of history-based candidate blocks may also be considered in generating a histogram for the DIMD- based mode being used to code current block 2700.

[0327] In some implementations, due to the restriction on neighboring blocks being coded in DIMD-based modes, in the example of FIG.27A, only block 2706 may be considered in coding (e.g., generating the histogram) current block 2700, which reduces the diversity of candidates and excludes useful information that may be derived from the other neighboring blocks. In fact, it has been observed in simulation that non- angular modes such as IntraTMP and IBC are selected up to 40% of the time when blocks are intra coded.

[0328] Embodiments relate to extending the types of blocks (e.g., neighboring blocks such as adjacent and / or non-adjacent neighbors of the current block) that may be used in a DIMD-based mode to code a current block. In some examples, in addition to blocks being coded in a DIMD-based mode, blocks that are coded in a non-angular mode may also be considered in the DIMD-based mode such as in generating the histogram for the DIMD-based mode or in generating one or more DIMD merge candidates in the DIMD Merge List.Docket No.: 24-2016PCT

[0329] In some examples, the non-angular mode may include TIMD, matrix-based intra prediction (MIP), IBC (e.g., regular IBC or RRIBC), IntraTMP (regular IntraTMP or RR-TMP), etc. In some examples, the non- angular mode may use (e.g., obtain or derive) a block vector that indicates a displacement from a current block to a reference block used to generate a prediction block for coding the current block. Examples of non- angular modes that have an associated block vector include the IBC and IntraTMP modes.

[0330] In some embodiments, IPM information may be obtained directly from a block coded in the non- angular mode. Though being coded in the non-angular mode, the coding of the block may include deriving one or more intra prediction modes, which may be obtained as DIMD parameters comprised in the IPM information. The DIMD parameters may be derived and stored in association with the block. For example, the non-angular mode may be TIMD, as described in FIG.26, which may derive TIMD modes corresponding to IPMs. In some examples, the IPMs and corresponding weights resulting from the TIMD mode may be obtained as DIMD parameters of the neighboring block and used to code the current block.

[0331] In another example, the DIMD process may be used by the non-angular mode during the MPM derivation process or to, for example, select a transform such as for low-frequency non-separatable transform (LFNST) in MIP mode, as described with respect to FIG.25.

[0332] In some examples, similar to how an LFNST may be selected for the MIP mode, a transform selection process may be similarly performed for an IntraTMP coded block described with respect to FIG.17. For example, the DIMD derivation process may be applied to samples of reference block 1710 used as a prediction block for coding current block 1700. Similar to how the DIMD derivation process is applied for the MIP mode, a horizontal gradient and a vertical gradient may be calculated for each predicted sample of reference block 1710 to generate an HoG in a process similar to that described in FIG.19 and block 2004 of FIG. 20. But, the HoG may be generated from samples of reference block 1710 (e.g., determined as prediction block for current block 1700) instead of neighboring samples of current block 1700. In an example, an IPM with the highest amplitude from the HoG may be used to determine (or select): a transform set from a plurality of transform sets. In some examples, the plurality of transform sets may include a plurality of multiple transform selection (MTS) sets. In some examples, the plurality of transform sets may include an MTS transform set and an LFNST transform set. In these examples for an IntraTMP coded block, the IPM derived based on DIMD may be used to select the MTS transform set or the LFNST transform set. IPM information, including the derived IPM, may be stored and used for generating the MPM list of the neighbor intra prediction blocks. Blocks coded in non-angular modes, such as, for example, IBC, may obtain, store, and use IPM information in manners similar to IntraTMP.

[0333] In some embodiments, a plurality of the highest IPMs from the HoG (e.g., up to 5 IPMs) may be stored in association with current block 1700. In some examples, the plurality of amplitudes corresponding to the plurality of highest IPMs may also be stored in association with current block 1700.Docket No.: 24-2016PCT

[0334] In some examples, one approach for obtaining IPM information from a neighboring block coded in a non-angular mode may be to perform the DIMD process, such as that described in FIGS.18-20, on reference samples in a reference template of the neighboring block to obtain a histogram, from which IPMs may be selected. However, this approach may incur high computational costs since the DIMD process would need to be performed for each neighboring block that is coded in a non-angular mode.

[0335] In some embodiments, to limit the computation costs, IPM information may be obtained indirectly from a first block (e.g., previously reconstructed first block) coded in the non-angular mode without explicitly performing the DIMD process on the block to derive a histogram of IPMs. Specifically, IPM information may be obtained based on a block vector, used by (e.g., indicates or is associated with) the non-angular mode, that indicates a displacement from a current block to a reference block used to generate a prediction block for coding the current block. In some examples, IPM information may be obtained from a second block (e.g., previously reconstructed first block) that overlaps the reference block and used as representative IPM information for the first block. By using the technique of indirectly deriving IPM information from a given block, more neighboring blocks of the current blocks are available to be used as DIMD merge candidates for predicting the current block. Neighboring blocks, such as spatial adjacent neighbors, are likely to have more similar characteristics to the current block, so deriving and using IPM information representative of these characteristics are likely to improve prediction accuracy, leading to smaller residuals and more efficient coding.

[0336] In some examples, the second block overlapping the reference block may contain a position indicated by the block vector (e.g., the position being the top-left position / sample of the reference block). In some examples, the second block may be selected from a plurality of blocks (e.g., previously reconstructed / decoded blocks) overlapping the reference block. In some examples, the second block may be one of one or more blocks selected from the plurality of blocks.

[0337] For example, the second block may be selected based on an order of a list of blocks (e.g., in a raster scan order) containing the plurality of blocks, such as, the earliest block of the plurality of blocks in the order. For example, the second block may be selected as having the largest overlap compared with other blocks in the plurality of blocks. The largest overlap may indicate containing the most samples of the reference samples compared to other blocks in the plurality of blocks. For example, the second block may be selected as one of the plurality of blocks in which a ratio (or fraction) of the overlap to a size of a respective block is the largest.

[0338] In some examples, the IPM information may be obtained based on the block vector by weighting third blocks, selected from the plurality of blocks, according to respective overlap area of each block of the third blocks. For example, a block with a higher overlapping area with the reference block compared with that of another block is assigned a higher weight. In some examples, the third blocks may include all the plurality of blocks. In some examples, the third blocks may include blocks of the plurality of blocks that satisfy one or more conditions.Docket No.: 24-2016PCT

[0339] FIG.27B shows an example of obtaining IPM information from neighboring blocks of a current block 2700 that are not coded using a DIMD-based mode, according to some embodiments. FIG.27B shows the same neighboring blocks 2702, 2704, 2706, 2708, 2712, and 2714 as FIG.27A. The process illustrated by FIG.27B may be performed identically at the encoder (e.g., encoder 200 of FIG.2) and the decoder (e.g., decoder 300 of FIG.3).

[0340] In some examples, neighboring blocks coded in a non-angular mode (e.g., a non-DIMD mode) from which IPM information may be obtained may be considered as an available DIMD merge candidate. For example, modes such as TIMD used to code block 2712 may derive and store IPMs and / or associated weights, as described with respect to FIG. 26, that may be considered as DIMD parameters of IPM information 2713. For example, during TIMD, a DIMD process may be performed to derive the MPM list, from which DIMD parameters may be obtained.

[0341] In another example, in a non-angular mode such as MIP used to code a block, a histogram of IPMs may be derived in selecting a transform. A number of the IPMs (e.g., one or up to five) from the histogram may be stored in association with this block and subsequently obtained as DIMD parameters in IPM information for coding current block 2700.

[0342] In some examples, a first (neighboring) block coded in a non-angular mode that indicates a block vector may be considered as a candidate DIMD block for coding current block 2700. Specifically, IPM information may be obtained from a second block overlapping a reference block indicated by the block vector. For example, the block indicator may indicate a displacement from the first block (e.g., the top-left sample / position / corner of the first block) to the reference block (e.g., the top-left sample / position / corner of the reference block).

[0343] As shown in FIG.27B, the second block may contain a position indicated by the block vector. For example, block 2702 may be coded in an IBC mode that uses a reference block 2722 (IBC target), indicated by a block vector (BV) 2703, to determine a prediction of block 2702 for coding block 2702. Instead of omitting block 2702 as a candidate DIMD merge block, IPM information 2733 may be obtained from a block 2732 coded in a DIMD-based mode and that overlaps reference block 2722. Then, IPM information 2733 may be obtained as being representative of characteristics of samples of block 2702 coded in the IBC mode.

[0344] For example, block 2704 may be coded in an IntraTMP (ITMP) mode that uses a reference block 2724 (ITMP target), indicated by a BV 2705, to determine a prediction of block 2704 for coding block 2704. Instead of omitting block 2704 as a candidate DIMD merge block, IPM information 2731 may be obtained from a block 2730 coded in a DIMD-based mode and that overlaps reference block 2724. Then, IPM information 2731 may be obtained as being representative of characteristics of samples of block 2704 coded in the IntraTMP mode.

[0345] For example, block 2708 may be coded in the IBC mode that uses a reference block 2728 (IBC target), indicated by a BV 2709, to determine a prediction of block 2708 for coding block 2708. Instead ofDocket No.: 24-2016PCT omitting block 2708 as a candidate DIMD merge block, IPM information 2735 may be obtained from a block 2734 coded in a non-DIMD based mode. For example, the non-DIMD based mode may include TIMD, IBC (e.g., regular or RRIBC), IntraTMP (e.g., regular or RRTMP), or MIP, etc. IPM information 2735 may include IPMs and associated parameters (e.g., weights) derived by the non-DIMD mode. Then, IPM information 2735 may be obtained as being representative of characteristics of samples of block 2708 coded in the IBC mode.

[0346] Accordingly, compared to FIG.27A in which only one block 2706 neighboring current block 2700 qualifies as a candidate DIMD merge block for use in a DIMD-based mode, obtaining IPM information directly and / or indirectly from non-DIMD blocks (e.g., blocks coded in a non-angular mode) enables five neighboring blocks (blocks 2702, 2704, 2706, 2708, 2712) to qualify as candidate DIMD merge blocks for use in the DIMD-based mode for coding current block 2700. Although FIG.27B only shows neighboring blocks that are spatial adjacent neighbors of current block 2700, the techniques of directly and / or indirectly obtaining IPM information from neighboring blocks are also applicable to spatial non-adjacent neighbors of current block 2700 or blocks from a history-based list of (previously reconstructed) blocks.

[0347] FIG.28A shows an example of a target block 2808 overlapping a reference block 2806 indicated by a BV 2805 obtained by a non-angular mode used to code candidate block 2804, according to some embodiments. Candidate block 2804 may be neighboring block of current block 2802 (e.g., at positions 2 and 5 as described in FIG.21) that is being considered as a DIMD merge candidate for a DIMD-based mode coding current block 2802. As explained above, the non-angular mode may be an IBC mode or an IntraTMP mode. In the IBC mode, BV 2805 may be determined based on a Merge mode or an AMVP mode in which a BVD and a BVP are obtained to determine BV 2805. In the IntraTMP mode, BV 2805 may be determined based on performing template matching prediction to determine reference block 2806 with a smallest template matching cost, as described above with respect to FIG.17. As described with respect to FIG.27B, IPM information (e.g., IPM information 1834 of FIG.18 or other DIMD parameters discussed above) may be obtained (e.g., retrieved) from target block 2808 and used to represent characteristics of candidate block 2804. This process enables candidate block 2804 to be used as a candidate DIMD merge block in the DIMD- based mode.

[0348] As shown in FIG.28A, it is unlikely for target block 2808 that was previously coded to be the same as reference block 2806 defined based on samples in a reconstructed region of the current picture. Reference block 2806 was previously selected for predicting candidate block 2804 and is likely to have characteristics similar to candidate block 2804. However, target block 2808, that overlaps reference block 2806 and whose obtained IPM information is used to selected, may have a very different size than target block 2808. Larger blocks are likely to have higher amplitudes for IPMs in the histogram (e.g., HoG, MHoG, or HoC) represented by the IPM information and may lead to distorted results when combined with IPM information of other neighboring blocks selected for coding current block 2802. In some implementations, the IPM informationDocket No.: 24-2016PCT obtained from / for target block 2808 may be scaled (e.g., weighted or adjusted) based on a size of target block 2808 and a size of reference block 2806.

[0349] For example, amplitudes of IPM(s) obtained from the IPM information may be scaled (e.g., weighted) by a scaling factor (W) that is determined based on a ratio (or fraction) of a first value representing a size of (or area) of reference block 2806 to a second value representing a size (or area) of target block 2808. An example of the scaling is shown as follows, where an amplitude of each m-th IPM in the HoG represented bythe IPM information is scaled by the scaling factor W:"u[^^=nd^[`] = ^. nd^[`]

[0350] In some examples, the first and second values may be the first and second sizes of reference block 2806 and target block 2808, respectively. For example, the scaling factor may be determined as follows: ^= g^. ℎ^g^ . ℎ^where g^is the width of reference block block 2804, ℎ^is the height of referenceblock 2806 and / or candidate block 2804, g^target block 2808, ℎ^is the height of target block 2808.

[0351] In some examples, the first and second values may be the first and second sums of dimensions of reference block 2806 and target block 2808, respectively. For example, the scaling factor may be determined as follows: g+= ^ ℎ^ ^g^ + ℎ^

[0352] FIG.28B shows an example of a plurality of target blocks 2808-2812 overlapping reference block 2806 indicated by BV 2805 obtained by a non-angular mode used to code candidate block 2804, according to some embodiments. Like FIG.28A, candidate block 2804 may be a neighbor block of current block 2802 that is to be considered as a DIMD merge candidate for coding current block 2802 in a DIMD-based mode.

[0353] In the non-angular mode such as IBC or IntraTMP, reference block 2806 may be defined from samples in the reconstructed region of the current picture and may not be associated with any specific, previously-reconstructed blocks such as target blocks 2808-2812. Thus, as explained in FIG.28A, it is very unlikely for reference block 2806 to be the same as a previously-reconstructed block.

[0354] In some implementations, the plurality of target blocks 2808-2812 overlapping reference block 2806 may be determined. IPM information from one or more of target blocks 2808-2812 may be selected and / or combined to be representative of characteristics of candidate block 2804.

[0355] In some examples, one or more of target blocks 2808-2812 may be selected based on whether a target block satisfies a condition. For example, the condition may be related to whether a ratio of an amount of overlap, between the target block and reference block 2806, to a size of the target block is equal to orDocket No.: 24-2016PCT greater than a threshold value (T). For example, one or more of target blocks 2808-2812 may be considered based on satisfying the condition as follows: ^≤ g^ . ℎ^g^ . ℎ^with g^ , ℎ^ being the width and the height of the target block overlapping with referenceblock 2806, respectively; and g^ , ℎ^ beingheight of the target block, respectively. ^represents a threshold value representative of an overlapping ratio and may be a value less than or equal to 1. Depending on the threshold (T) and the amount of overlap, a target block such as target block 2812 may be discarded (omitted or not considered) because most of target block 2812 is not overlapping reference block 2806 and IPM information, if available, obtained from target block 2812 may be less likely to be representative of characteristics of reference block 2806.

[0356] In some examples, IPM information obtained from third target blocks selected from target blocks 2808-2812 may be combined (e.g., blended or fused) and represent characteristics of candidate block 2804. For example, IPM information of the third target blocks may be combined to generate an MHoG in a similar process as that described with respect to FIG.22A, FIGS. and 23A-B.

[0357] In some examples, IPM information such as amplitudes of IPMs in each IPM information of the third target blocks may be combined according to a weight determined with respect to an amount of overlap with reference block 2806. Accordingly, IPM information for a target block with a higher overlap (i.e., larger overlap area) than other target blocks may be associated with a higher weight. For example, a weight for a first target block may be determined based on a ratio of an overlap amount (of the first target block with reference block 2806) to a size of reference block 2806. In this example, IPM information (if available) of target block 2810 (if selected) may have a highest weight followed by IPM information (if available) of target block 2808 (if selected) followed by IPM information (if available) of target block 2812 (if selected).

[0358] In some embodiments, one target block may be selected from the plurality of target blocks 2808- 2812 based on one or more of the following conditions: - being the first / earliest block in a list of candidate target blocks with available IPM information. For example, respective indications (e.g., BVs) of the plurality of target blocks 2808-2812 may be stored in the list according to a raster scan order; - the target block among the plurality of target blocks with the largest overlap, i.e., contains the most samples of reference block 2806; - the target block with the highest ratio of overlap to size of the target block, as described above; and / or - the target block with the largest overlap among third blocks, of the plurality of target blocks, that satisfies a threshold, as described above.Docket No.: 24-2016PCT

[0359] FIG.29 shows an example of a plurality of reference blocks 2906A-C indicated by a plurality of respective BVs 2910A-C obtained by an IntraTMP mode with fusion used to code candidate block 2904, according to some embodiments. The IntraTMP mode with fusion may be an example of a non-angular mode used to candidate blocks. Candidate block 2904 may be a neighbor block of current block 2902 that is to be considered as a DIMD merge candidate for coding current block 2902 in a DIMD-based mode. In the IntraTMP mode with fusion, a plurality of reference blocks 2906A-C may be obtained and blended according to respective fusion weights to generate a prediction block for coding candidate block 2904. Target blocks 2908A-C that overlap reference block 2906A-C, respectively, may be obtained. For example, for a reference block, a target block may be a block that contains the top-left sample of the reference block, as described with respect to FIG.28A. For example, for a reference block, a target block may be a block that is selected from a plurality of blocks overlapping the reference block, as described with respect to FIG.28B. For example, for a reference block, a plurality of target blocks may be selected from a plurality of blocks overlapping the reference block, as described with respect to FIG.28B.

[0360] In some examples, a target block may be selected from target blocks 2908A-C based on fusion weights (determined by the IntraTMP mode with fusion) of reference blocks 2906A-C corresponding to target blocks 2908A-C, respectively. For example, the target block may be selected as the block with the highest associated fusion weight from blocks, of target blocks 2908A-C, with associated IPM information (e.g., coded in a DIMD-based mode or in a non-angular mode that derives DIMD parameters). For example, if the target block, of target blocks 2906A-C, with the highest fusion weight does not include IPM information, then a next target block of target blocks 2906A-C with the second highest fusion weight may be checked to determine if the next target block is associated with IPM information, etc. In some examples, up to a predetermined number (e.g., N = 3) of target blocks of target blocks 2908A-C, in a descending order of fusion weights, may be checked to determine if IPM information may be obtained to prevent a target block with a very low fusion weight from being considered.

[0361] In some examples, a plurality of available target blocks are selected from target blocks 2908A-C and IPM information of respective available target blocks are combined (e.g., blended) based on fusion weights of the respective available target blocks. For example, the plurality of available target blocks may be blocks, from the target blocks 2908A-C, associated with (e.g., containing or storing) IPM information. In some examples, the amplitudes of IPMs of a histogram (e.g., HoG, MHoG, HoC) represented by each IPM information of each respective available target block may be weighted according to a fusion weight of the respective available target block. For example, a scaling factor for each available target block may be determined based on a ratio of a fusion weight of the available target block to a sum of fusion weights of the plurality of reference blocks 2906A-C corresponding to target blocks 2908A-C, respectively. Accordingly, the IPM information of selected / available target blocks of target blocks 2908A-C may be combined to generate an MHoG associated with candidate block 2904, which may then be considered as a DIMD merge candidateDocket No.: 24-2016PCT for coding current block 2902 in a DIMD-based mode. For example, the MHoG (mHoG) may be generated as follows: 1^`nd^[`] =^ $ g1. nd^[0][`]with g1being the scaling factor each mode index) of the HoG associated with the i-th targetone or amplitudes of one or more respective IPMs). N may be the number of target blocks 2908A-C with IPM information.

[0362] In some examples, there may be less available target blocks with IPM information than the total number N of identified / selected target blocks. In some implementations, to account for the difference, the scaling factors or weights g1may be rescaled (e.g., normalized) so that their sum is equal to 1: ^$ g1 = 1For example, a scaling factor / weight for an block may be normalized by dividing a fusionweight, of a reference block corresponding to target block, by a sum of fusion weights of all available target blocks of the plurality of target blocks 2908A-C.

[0363] In some embodiments, a scaling factor for each available target block for a respective reference block may be further scaled according to a second scaling factor / weight that is based on a size of the available target block and a size of the reference block, as described with respect to FIG.28A.

[0364] In some examples, an available target block may be a target block that satisfies one or more overlapping conditions with respect to a reference block corresponding to the target block, as described with respect to FIG.28B.

[0365] Although, FIG.29 shows one target block 2908A-C being selected for each respective reference block of reference block 2906A-C, one or more (e.g., a plurality of) target blocks that overlap each reference block may be selected for each block, as described with respect to FIG.28B.

[0366] FIG.30 shows an example of a target block 3008 overlapping a reference block 3006 indicated by a BV 3012 obtained by a non-angular mode associated with flipping in a direction and used to code candidate block 3004, according to some embodiments. For example, candidate block 3004 may be a neighboring block (e.g., spatial neighbor) of current block 3002.

[0367] In some examples, the non-angular mode may be associated with flipping in a direction such as a horizontal or a vertical direction. In this non-angular mode, reference block 3006 is flipped in the direction to determine a prediction block for coding candidate block 3004. For example, the non-angular mode may be RR-IBC mode enabled and selected for coding / reconstructing candidate block 3004. BV 3012 may be obtained during the RR-IBC mode, as described with respect to FIG.16B, or during the RR-TMP mode, as described with respect to FIG.17.Docket No.: 24-2016PCT

[0368] Target block 3008 may be determined based on a coding block overlapping reference block 3006, as explained above with respect to FIGS.28A-B. IPM information 3010 may be obtained from target block 3008 either directly or indirectly, as explained above with respect to FIGS. 27B-28B. For example, IPM information 3010 may include DIMD parameters such as one or more IPMs and one or more corresponding amplitudes. In an example, these DIMD parameters may have been derived by a DIMD-based coding mode used to code target block 3008. In an example, these DIMD parameters may have been derived in the transform selection process of a non-angular mode used to code target block 3008. In an example, these DIMD parameters may have been derived based on a second BV indicated by a second non-angular mode coding target block 3008. For example, these DIMD parameters may be obtained from a second target block that overlaps a second reference block indicated by the second BV with respect to target block 3008.

[0369] However, based on the direction of flipping used by the non-angular mode to select / determine reference block 3006, the one or more IPMs from IPM information 3010 may be representative of characteristics of reference block 3006, but not representative of characteristics of candidate block 3004. For example, contents of candidate block 3004 may be associated with (e.g., be most represented by) a primary direction 3005. If reference block 3006 is determined based on horizontal flipping in, e.g., an RRIBC mode, contents of reference block 3006 may be associated with (e.g., be most represented by) a primary direction 3007, which is not the same as primary direction 3005 of candidate block 3004. Thus, IPM information 3010 of target block 3008, which may have similar characteristics of reference block 3006, may include an IPM corresponding to (e.g., similar to) primary direction 3007.

[0370] In some examples, to obtain accurate IPM information to associated with candidate block 3004 coded in a non-angular mode associated with flipping in a direction, a first IPM (or one or more IPMs) from IPM information 3010 may be adjusted according to the direction of flipping. For example, when the direction is horizontal, the first IPM that corresponds to a first direction may be converted to a second IPM corresponding to a second direction associated with the first direction being flipped in the direction. In other words, the second IPM may be computed from the first IPM depending on the direction represented by the first IPM. For example, the first direction may be flipped according to the vertical axis (y-axis) when the flipping direction is horizontal or flipped according to the horizontal axis (x-axis) when the flipping direction is vertical.

[0371] In some embodiments, the first IPM may be converted to the second IPM based on an IPM representing a second direction different from a first direction of flipping used by the non-angular mode. For example, the second direction may be the opposite of the first direction or may be perpendicular to the first direction. For example, the first direction may be one of the horizontal or vertical directions and the second direction may be the other of the horizontal or vertical directions.

[0372] In some examples, for angular modes in the range S ∈ ^2 ; 34^, the flipped mode (FMV) may becomputed as follows for flipping in a vertical direction:^S (0) = 2. n − S(0)Docket No.: 24-2016PCT where H = 18 (corresponding to the horizontal direction) and mode 2 is converted to 34, and reciprocally, mode 34 is converted to mode 2.

[0373] In some examples, for angular modes in the range S ∈ ^35 ; 65^, the flipped mode (FMH) iscomputed as follows for flipping in a horizontal direction:^S¢(0) = 2. £ − S(0)where H = 50 (corresponding to the vertical direction) and mode 66 is converted to 34, and reciprocally, mode 34 is converted to mode 66.

[0374] FIG.31 shows a flowchart 3100 of an example method for selecting DIMD merge candidates from neighboring blocks of a current block to generate a histogram (e.g., HoG, MHoG, or HoC) used by a DIMD- based mode to code the current block, according to some embodiments. Flowchart 3100 may be implemented by an encoder (e.g., encoder 200 of FIG.2) and / or a decoder (e.g., decoder 300 of FIG.3). Operations of flowchart 3100 may be performed identically at the encoder and the decoder to generate the same histogram without a need for the encoder to signal IPMs and respective amplitudes to construct the histogram.

[0375] In some examples, a plurality of blocks neighboring the current block may be considered to determine DIMD merge candidates from which IPM information may be combined to generate the HoG, similar to how an MHoG or an HoC may be generated, as described with respect to FIGS.22A-24. For example, the plurality of blocks may be spatial adjacent neighbors of the current block or spatial non-adjacent neighbor of the current block, as described with respect to FIG.15A and FIG.21. For example, the plurality of blocks may include neighbor blocks from a list of history-based blocks that were previously reconstructed. The list may include reconstructed blocks that have associated IPM information.

[0376] In some examples, the plurality of blocks may be considered in an order of spatially closest neighboring blocks of the current block. For example, spatial proximity between a block and the current block may be determined as a distance between the block (e.g., a top-left position / sample / corner of the block) and the current block (e.g., a top-left position / sample / corner of the block). In some examples, the distance may be a Euclidean distance or a Manhattan distance.

[0377] At block 3102, a first block neighboring a current block is obtained. For example, the first block may be a spatial adjacent or non-adjacent neighbor of the current block.

[0378] In some examples, the first block may be from the plurality of blocks determined for the current block. For example, the plurality of blocks may include a predetermined number (e.g., 13) of previously- reconstructed / decoded blocks.

[0379] At block 3104, it is determined whether the first block has associated IPM information. If the determination at block 3104 is true, flowchart 3100 proceeds to block 3106. Otherwise, flowchart 3100 proceeds to block 3110. In some examples, IPM information may be obtained for the first block based on theDocket No.: 24-2016PCT first block being coded in a DIMD-based mode such as one of modes: DIMD, OBIC, MIMD, DIMD Merge List, etc.

[0380] In some examples, IPM information may be available and obtained from the first block previously coded / reconstructed using a non-DIMD mode that derives directional (e.g., angular) information. For example, the non-DIMD mode may be a TIMD mode, an SGPM mode, a MIP mode, etc. For example, the non-DIMD mode may be a non-angular mode such as IBC mode or IntraTMP mode. However, it may be possible that no directional information was derived in the non-DIMD mode; in this case, no IPM information would be obtained.

[0381] At block 3106, it is determined whether the first block was coded by a reference block indicated by a block vector (BV) indicated by a non-angular mode coding the first block. If the determination at block 3106 is true, flowchart 3100 proceeds to block 3108. Otherwise, flowchart 3100 proceeds to block 3112.

[0382] In some examples, the non-angular mode may include, for example, the IBC mode or the IntraTMP mode. In these modes, at least one reference block is obtained for coding the current block. For example, at least one BV is associated with (e.g., indicated by) the non-angular mode to indicate the at least one reference block, respectively.

[0383] At block 3108, it is determined whether a second block, overlapping the reference block, has associated IPM information. If the determination at block 3108 is true, flowchart 3100 proceeds to block 3110. Otherwise, flowchart 3100 proceeds to block 3112.

[0384] In some examples, the determination of whether the second block has associated IPM information is similar to block 3104, in which it is determined whether the first block has associated IPM information. For example, the second block may be determined to have associated IPM information based on the second block being coded in a DIMD-based mode. In some examples, the second block may be determined to have associated IPM information based on the second block being coded in a non-DIMD mode that derives directional information, as discussed above.

[0385] In some examples, the determination of whether the second block has associated IPM information may be further based on whether the second block is in a neighboring region defined relative to the current block. For example, the neighboring region may be defined as the current CTU of the current block. For example, the neighboring region may be defined as the two previous CTU rows / lines.

[0386] In some examples, the operations of blocks 3106-3108 may be iteratively performed for a number of iterations, e.g., up to a predetermined number (e.g., 2 or 3). For example, the second block may be considered as the first block and it may be further determined whether the second block is coded by a second reference block indicated by a second block vector.

[0387] At block 3110, the first block (and associated IPM information) is added to a list of DIMD merge candidates. For example, the associated IPM information obtained from block 3108 may be added.Docket No.: 24-2016PCT

[0388] In some examples, the second block may be a block overlapping the reference block and containing a position indicated by a top-left sample / position of the first block displaced by the BV, as described above with respect to FIG.28A.

[0389] In some examples, the second block may be one of a plurality of blocks overlapping the reference block. In such examples, the associated IPM information obtained for the first block may be based on combining the IPM information of multiple blocks (including the second block) of the plurality of blocks, as described above with respect to FIG.28B.

[0390] In some examples, the first block is associated with a plurality of reference blocks including the second block, as explained with respect to FIG.29. For example, the first block may have been coded in an IntraTMP mode with fusion. In such examples, the IPM information obtained for the first block may combine IPM information of one or more blocks overlapping the plurality of reference blocks, as explained with respect to FIG.29.

[0391] In some examples, the first block may be coded in a non-angular mode that is associated with flipping in a direction. For example, the non-angular mode may be RRIBC or RRTMP. For example, the direction may be horizontal or vertical. In these examples, one or more IPMs obtained from the IPM information may be converted (e.g., transformed) according to the direction of flipping, as explained with respect to FIG.30.

[0392] At block 3112, it is determined whether to obtain a next neighboring block for the current block to determine whether to add one or more additional blocks to the list of DIMD merge candidates. For example, the next neighboring block may be next in the plurality of blocks neighboring the current block.

[0393] In some examples, up to a predetermined number (e.g., N = 3) of candidate blocks may be determined whose IPM information may be combined to determined (e.g., generate or construct) the histogram for coding the current block. For example, the predetermined number of candidate blocks may be the spatially closest blocks to the current block and having IPM information that was obtained, which may be directly or indirectly obtained from the candidate blocks. It should be noted that a spatial proximity for the first block, associated with a determined second block at block 3108, is between the first block and the current block and not between the second block and the current block.

[0394] FIG.32 shows a flowchart 3200 of an example method for selecting DIMD merge candidates from neighboring blocks of a current block to generate a histogram (e.g., HoG, MHoG, or HoC) used by a DIMD- based mode to code the current block, according to some embodiments. Flowchart 3200 may be implemented by an encoder (e.g., encoder 200 of FIG.2) and / or a decoder (e.g., decoder 300 of FIG.3). Operations of flowchart 3200 may be performed identically at the encoder and the decoder to generate the same histogram without a need for the encoder to signal IPMs and respective amplitudes to construct the histogram.

[0395] In some examples, similar to FIG.31, a plurality of blocks neighboring the current block may be considered to determine DIMD merge candidates from which IPM information may be combined to generateDocket No.: 24-2016PCT the HoG, similar to how an MHoG or an HoC may be generated, as described with respect to FIGS.22A-24. For example, the plurality of blocks may be spatial adjacent neighbors of the current block or spatial non- adjacent neighbor of the current block, as described with respect to FIG.15A and FIG.21. For example, the plurality of blocks may include neighbor blocks from a list of history-based blocks that were previously reconstructed. The list may include reconstructed blocks that have associated IPM information.

[0396] At block 3202, one or more first blocks (e.g., up to N blocks) coded in a DIMD-based mode may be selected, from the plurality of blocks neighboring the current block, for the current block. For example, N may be 3. In some examples, the N first blocks may be determined from the spatially closest blocks of the plurality of blocks to the current block and that were coded in one of DIMD-based modes. In some examples, the N first blocks may be determined from an order of the plurality of blocks and that were coded in one of DIMD- based modes. For example, the order may be identical to the one used for primary and / or secondary MPM list derivation. For example, with respect to FIG.15A, if the current block is vertically oriented, the order of neighboring blocks may be A, L, BL, AR, AL, otherwise the order may be L, A, BL, AR, AL for the current block being horizontally oriented.

[0397] For example, examples of DIMD-based modes may include DIMD, OBIC, MIMD, DIMD Merge List, etc. In some examples, the N first blocks may also include one or more blocks, from the plurality of blocks, coded in a non-DIMD based mode that derives directional (e.g., angular) information such as IPMs and / or respective weights that may be considered as DIMD parameters of IPM information.

[0398] At block 3204, one or more second blocks (e.g., up to M blocks) coded in a non-DIMD based mode and having associated IPM information may be selected, from the plurality of blocks neighboring the current block, for the current block. For example, M may be 2. For example, the M second blocks may be determined from the spatially closest blocks of the plurality of blocks to the current block and that were coded in a non- angular mode that uses a reference block for coding the block, as explained with respect to FIGS.27B-30.

[0399] In some examples, the M second blocks may be determined from an order of the plurality of blocks and that were coded in one of DIMD-based modes. For example, the order may be identical to the one used for primary and / or secondary MPM list derivation. For example, with respect to FIG.15A, if the current block is vertically oriented, the order of neighboring blocks may be A, L, BL, AR, AL, otherwise the order may be L, A, BL, AR, AL for the current block being horizontally oriented.

[0400] For example, the non-angular mode may include an IntraTMP mode or an IBC mode.

[0401] At block 3206, one or more third blocks (up to T blocks), from the plurality of blocks, may be selected. The one or more third blocks include the one or more first blocks and / or the one or more second blocks. For example, T may represent a threshold number of blocks that is at least as large as N (e.g., T >= N). For example, T may represent a threshold number of blocks that is at least as large as N plus M (e.g., T > N + M). Using the examples of N and M above, T may be, for example, at least 5.Docket No.: 24-2016PCT

[0402] At block 3208, a histogram of intra prediction modes (IPMs) used by an intra-based mode coding the current block may be generated based on IPM information obtained from the one or more third blocks. For example, the intra-based mode may be an OBIC mode, an MIMD mode, or a DIMD Merge List mode.

[0403] In some examples, different from selecting a number of K closest neighboring blocks with obtainable IPM information (e.g., either directly or indirectly), as explained in FIG.31, the N one or more first blocks and the M one or more second blocks may be obtained. Then, at block 3208, the IPM information from the N one or more first blocks and the M one or more second blocks may be combined (e.g., averaged) such as in the MHoG derivation process, as described with respect to FIG.22A and FIGS.23A-B.

[0404] In some embodiments, the T one or more third blocks may be selected based on prioritizing the one or more first blocks over the one or more second blocks. For example, up to a number N of one or more first blocks may be selected with N being equal to T. In this example, the one or more third blocks may be only from the one or more first blocks if there are exactly N one or more first blocks that were determined. If less there are less than T one or more first blocks determined, then the remaining blocks of the one or more third blocks up to T may be selected from the one or more N blocks. Accordingly, in some examples, block 3204 may be dependent on whether the one or more first blocks determined at block 3202 is less than the threshold T of the one or more third blocks. Block 3204 may be performed if the number of the one or more first blocks is less than the threshold T. Otherwise, the T one or more third blocks may be selected as the N one or more first blocks.

[0405] FIG.32 above described an example process for selecting DIMD merge candidates from neighboring blocks of a current block to generate a histogram (e.g., HoG, MHoG, or HoC) used by a DIMD-based mode to code the current block. The process of FIG.32 described the use, in addition to DIMD-coded neighboring blocks, of neighboring blocks that are coded with non-angular coding (e.g., IBC, IntraTMP, TIMD, MIP) but have obtained or generated information related to IPMs in a manner similar to the IPM information obtained or generated during DIMD coding of a block.

[0406] In some examples, in a process such as the process of flowchart 3200 or some other processes for generating a histogram (e.g., HoG, MHoG, HoC) for DIMD-based coding of a current block, a second block that is coded using a non-angular mode (non DIMD-based mode) but that has directly determined (derived / obtained) IPM information during its reconstruction, may additionally have associated indirectly determined (derived / determined) IPM information obtained from a third block. The third block overlaps a reference block identified by a block vector (BV) of the second block. In such scenarios, a decision needs to be made as to which IPM information (e.g., the directly derived IPM information of the second block, or the indirectly derived IPM information from the third block) or a combination thereof is to be used in selecting the IPM for the current block.

[0407] Thus, techniques are needed for determining which of the second block’s directly obtained IPM information, the third block’s IPM information (e.g., the second block’s indirectly obtained IPM information),Docket No.: 24-2016PCT or a combination of the two IPM information is to be used as the IPM information associated with the second block for purposes of generating the histogram for DIMD-based coding of the current block.

[0408] Example embodiments provide for a non-angular candidate of a (current) block coded in a DIMD- based mode to include first IPM information directly obtained for the non-angular candidate, or second IPM information indirectly obtained from a third block overlapping a reference block indicated by a BV of the non- angular candidate. Example embodiments may include a selection indication for selecting one of the first or second IPM information, default priorities of the first or second IPM information per type of non-angular candidate, combining the first and second IPM information, etc.

[0409] FIG.33A shows a flowchart 3300 of an example method for coding a current block based on an intra- based coding mode using blocks coded in a non-angular (coding) mode, according to some embodiments. Flowchart 3300 may be implemented for coding a current block using Decoder-side Intra Mode Derivation (DIMD) or another DIMD-based process. Flowchart 3300 may be implemented by a coder such as an encoder (e.g., encoder 200 of FIG.2) or a decoder (e.g., decoder 300 of FIG.3).

[0410] At block 3302, the coder selects / determines, for the current block, a third block for generating a histogram of intra prediction modes (IPMs) used by an intra-based coding mode. Depending on the intra- based coding mode, the histogram may be a histogram of gradients (HoG) or a histogram of occurrences (HoC). For example, the histogram may be a HoG for the DIMD mode, a HoC for the OBIC mode, or a merged HoG (MHoG) for the MIMD mode. For example, the histogram may be a HoG / MHoG for an MIMD / DIMD / combined candidate determined for the DIMD Merge List mode or an HoC for an OBIC-based candidate determined for the DIMD Merge List mode.

[0411] In some examples, the intra-based coding mode may be one of: a DIMD mode, an Occurrence- based Intra Coding (OBIC) mode, a Merged Intra Mode Derivation (MIMD) mode, or a DIMD Merge List mode.

[0412] In some examples, the third block may be an adjacent neighboring block of the current block, a non- adjacent neighboring block of the current block, or a block from a list of blocks that were previously reconstructed, such as from a list of history-based candidate blocks. For example, the list of blocks may include a number of blocks most recently reconstructed using IPM information. In another example, the list of blocks may include a number of blocks that were most recently reconstructed.

[0413] In some examples, block 3302 may correspond to block 3102 of FIG.31. For example, the first block referred to in block 3302 may be an example of candidate block 2804 of FIG.28A or FIG.28B, or candidate block 2904 of FIG.29.

[0414] At block 3304, the coder determines, for the current block, a first block that has been reconstructed using a non-angular mode. The coder may determine a first set of one or more IPMs associated with the first block. For example, during the reconstruction of the first block using the non-angular mode, IPM informationDocket No.: 24-2016PCT of a set of one or more IPMs may have been generated / obtained and may be available for access by the coder for reconstructing the current block.

[0415] The IPM information of the first set of one or more IPMs may include any of, an IPM used for coding the first block, one or more IPMs determined for determining an IPM for coding the first block, amplitudes of the one or more IPMs, directionalities of the one or more IPMs, HoG of the one or more IPMs, HoC of the one or more IPMs, etc. IPM information of blocks that coded using a DIMD-based coding may be referred to as IPM information.

[0416] The determined number of IPMs, the types of IPMs, and the information relating to the IPMs may be different among the different non-angular modes. Therefore, the set of one or more IPMs associated with the first block may depend on factors such as, for example, the non-angular mode used to code the first block.

[0417] The first block may be coded using any non-angular coding mode that generates (and stores for later retrieval) IPM information during its reconstruction. In some examples, the non-angular mode may include any mode that indicates the reference block used to generate a prediction (e.g., prediction block) for coding the first block. For example, the first block that is reconstructed using this non-angular mode may include a block vector (BV) that points to the reference block with respect to a position of the first block. For example, the BV indicates a displacement from the position of first second block (e.g., top-left position / sample / corner of the first block) to a position of the reference block (e.g., top-left position / sample / corner of the reference block). Examples of the non-angular mode may include an Intra Block Copy (IBC) mode or an Intra Template Matching Prediction (IntraTMP) mode. Examples of the non-angular mode may further include an inter- prediction mode. For example, in the inter prediction mode, the BV may be a motion vector (MV) indicating the reference block in a reference picture / frame with respect to a position of the current block in a current picture / frame.

[0418] In some examples, the first block may be an adjacent neighboring block of the current block, a non- adjacent neighboring block of the current block, or a block from a list of blocks that were previously reconstructed, such as from a list of history-based candidate blocks. For example, the list of blocks may include a number of blocks most recently reconstructed using a non-angular mode that determines at least some IPM information.

[0419] In some examples, block 3302 may correspond to block 3102 of FIG.31. For example, the first block referred to in block 3304 may be an example of candidate block 2804 of FIG.28A or FIG.28B, or candidate block 2904 of FIG.29.

[0420] At block 3306, the coder determines a second block that overlaps a reference block indicated by the non-angular mode for the first block. The coder determines a second set of one or more IPMs associated with the second block.

[0421] For example, as noted above, the reference block may be indicated by a BV associated with the non-angular mode. The BV may be previously determined in the non-angular mode for coding the first block.Docket No.: 24-2016PCT

[0422] In some examples, the second block overlapping the reference block may contain a position that is displaced from the first block by the BV indicated by the non-angular mode. For example, the second block may contain the top-left sample (e.g., corner or position) of the reference block.

[0423] In some embodiments, the non-angular mode may include any mode that indicates the reference block used to generate a prediction (e.g., prediction block) for coding the first block. For example, the first block that is reconstructed using this non-angular mode may include the BV that points to the reference block with respect to a position of the first block. For example, the BV indicates a displacement from the position of the first block (e.g., top-left position / sample / corner of the first block) to a position of the reference block (e.g., top-left position / sample / corner of the reference block). Examples of the non-angular mode may include an IBC mode (e.g., regular IBC mode), an RRIBC mode, an IntraTMP mode (e.g., regular IntraTMP mode), or an RR-TMP mode. Examples of the non-angular mode may further include an inter-prediction mode. For example, in the inter prediction mode, the BV may be a motion vector (MV) indicating the reference block in a reference picture / frame with respect to a position of the current block in a current picture / frame.

[0424] In some examples, the determination of the second block may be further based on the first block being reconstructed using the non-angular mode and the first block not being reconstructed using first IPM information.

[0425] In some examples, the second block contains a top-left sample of the reference block. In other words, the second block contains a sample at a position indicated by the BV with respect to the current block.

[0426] In some examples, a plurality of blocks (e.g., previously reconstructed / decoded blocks) overlapping the reference block are determined. The second block may be selected from the plurality of blocks based on an order of the plurality of blocks, an amount of overlap between each block and the reference block, or one or more conditions, as described with respect to FIG.28B. For example, the first block may be selected based on the amount of overlap and / or a size of the second block.

[0427] In some examples, the first block and the second block are previously reconstructed blocks (e.g., previously encoded / decoded blocks).

[0428] In some examples, the second block is reconstructed using IPM information including an amplitude of an IPM. In some examples, the second block uses IPM information based on the second block being reconstructed using one of: an OBIC mode, an MIMD mode, a DIMD mode (e.g., a regular / default DIMD mode), or a DIMD Merge List mode. In some examples, the second block may be determined as using IPM information based on the third block being reconstructed using TIMD or MIP.

[0429] In some examples, the second block may be previously reconstructed / decoded using a second non- angular mode. For example, the second non-angular mode may be an IntraTMP mode, an IBC mode, TIMD, or a MIP mode. But, IPM information may still have been derived during the reconstruction process and may be retrieved by the coder as being associated with (e.g., used) for the second block.

[0430] At block 3308, a selection indication is obtained by the coder.Docket No.: 24-2016PCT

[0431] In some examples, the selection indication is a configuration setting, a flag, or an indication of a priority or priority ordering. In some examples, the selection indication may indicate what, from the first set of one or more IPMs determined at block 3304 and the second set of one or more IPMs determined at block 3306, is to be used to update the histogram at block 3310. For example, the selection indication may indicate whether it is only the IPM information of the first set of one or more IPMs, only the IPM information of the second set of one or more IPMs, or a combination of the first and second sets of IPM information is to be used for the updating of the histogram.

[0432] In some examples, the selection indication may be obtained before the coder determines the first set of one or more IPMs and / or the second set of one or more IPMs. In such examples, based on the value of the obtained selection indication (described in FIGs.34A-34D) the coder may choose to skip determining of either the first set of one or more IPMs or the second set of one or more IPMs (e.g., blocks 3304 or 3306). For example, if the selection indication indicates use of the second set of one or more IPMs, then the determining of the first set of one or more IPMs may be skipped, or if the selection indication indicates use of the first set of one or more IPMs, then the determining of the second set of one or more IPMs may be skipped.

[0433] In some examples, when the coder is an encoder, the encoder may select the selection indication based on checking the resulting prediction / predicted blocks generated based on each of the possible selections using a rate-distortion optimization (RDO) cost. For example, the encoder may set the selection indication associated with a lowest cost, e.g., an RDO cost. The encoder may signal the selection indication in a bitstream.

[0434] In some examples, when the coder is a decoder, the decoder may obtain the selection indication from the bitstream. For example, the decoder may decode the selection indication.

[0435] At block 3310, the coder updates, in accordance with the selection indication obtained at 3308, the histogram of IPMs based on IPM information of one or both the first set of one or more IPMs obtained at block 3304 and the second set of one or more IPMs obtained at block 3306.

[0436] In some examples, the histogram of IPMs (e.g., histogram noted at block 3302) may be a HoG or an MHoG. In such examples, updating the amplitude may include obtaining, from the IPM information of one or both of the first set of one or more IPMs and the second set of one or more IPMs, at least a first amplitude of the IPM obtained from the IPM information. Then, the obtained first amplitude may be added to the amplitude of the IPM in the histogram.

[0437] In some examples, the histogram of IPMs may be an HoC. In such examples, updating the amplitude may include, depending on the IPM information of one or both the first set of one or more IPMs and the second set of one or more IPMs or a combination thereof that is being used for the update, adding a value associated with a size of the second block, a size of the first block, or a combination thereof, to the amplitude of the IPM in the histogram.Docket No.: 24-2016PCT

[0438] In some examples, the coder updates, based on the second block being reconstructed using IPM information, an amplitude of an IPM, of the histogram, corresponding to an IPM obtained from the IPM information. For example, the IPM of the histogram and the IPM obtained from the IPM information may have the same IPM index.

[0439] In some examples, the IPM of the histogram may be determined based on converting (e.g., transforming) the IPM obtained from the IPM information, in which case the IPM of the histogram and the IPM from the IPM information do not have the same IPM index, as described with respect to FIG.30. In these examples, the non-angular mode may be associated with flipping in a direction such as RR-IBC or RR-TMP. For example, when the non-angular mode applies flipping in a horizontal direction, the IPM of the histogram may be determined based on converting (e.g., transforming) the IPM from the IPM information according to an IPM indicating the vertical direction. For example, when the non-angular mode applies flipping in a vertical direction, the IPM of the histogram may be determined based on converting (e.g., transforming) the IPM from the IPM information according to an IPM indicating the horizontal direction.

[0440] In some examples, more than one amplitude in the histogram may be updated. For example, a plurality of amplitudes of a plurality of IPMs, of the histogram, that correspond to a plurality of IPMs obtained from the IPM information may be updated. For example, the second block may have been reconstructed in a DIMD mode, which may result in 5 IPMs being selected and stored as IPM information (may be referred to as DIMD information when obtained in the DIMD mode). In this example, the amplitudes of 5 IPMs in the histogram that correspond (e.g., having the same respective IPM indices) to the 5 IPMs in the IPM information may be updated.

[0441] In some examples, the second block uses IPM information based on the second block being reconstructed using one of: an OBIC mode, an MIMD mode, a DIMD mode (e.g., a regular / default DIMD mode), or a DIMD Merge List mode. In some examples, the second block may be determined as using IPM information based on the second block being reconstructed using a non-angular mode such as, for example, TIMD or MIP.

[0442] In some examples, the first block may be previously reconstructed / decoded using a second non- angular mode. For example, the second non-angular mode may be an IntraTMP mode, an IBC mode, a TIMD mode, or a MIP mode. But, IPM information may still have been derived during the reconstruction process and may be retrieved by the decoder as being associated with (e.g., used) for the first block.

[0443] At block 3312, the coder codes the current block based on the updated histogram.

[0444] In some examples, one or more IPMs may be selected from IPMs of the histogram based on amplitudes of the IPMs and the one or more IPMs may be combined to derive a DIMD predictor, as described with respect to FIGS.18-20. The DIMD predictor may be used to determine (e.g., generate) a prediction block for the current block. The same prediction block may be determined by the encoder and the decoder. At the encoder, an encoder may signal, in a bitstream, a residual block (e.g., prediction error) as a differenceDocket No.: 24-2016PCT between the current block and the prediction block. At the decoder, the decoder may obtain, from the bitstream, the residual block. Then, the decoder may combine the residual block with the prediction block to reconstruct (e.g., decode) the current block.

[0445] In some examples, the intra-based coding mode used to code the current block may be a DIMD Merge List mode. For example, the histogram may be an HoC used to determine (or generate) an OBIC candidate (e.g., OBIC-based candidate) in the DIMD Merge List mode. As part of coding the current block, the coder may add the OBIC candidate to a list of DIMD merge candidates.

[0446] In some examples, the intra-based coding mode may be a DIMD Merge List mode. For example, the histogram may be a HoG or MHoG used to determine (or generate) an MIMD candidate (e.g., MIMD-based candidate) in the DIMD Merge List mode. As part of coding the current block, the coder may add the MIMD candidate to a list of DIMD merge candidates.

[0447] In some examples, the current block may be coded based on the list, which may include various types of DIMD merge candidates. When the coder is a decoder and to reconstruct the current block, the decoder may obtain, from a bitstream, an indication of a DIMD merge candidate in the list, as described with respect to FIGS.24A-B. For example, the indication may be an index pointing to that DIMD merge candidate in the list. The decoder may generate a prediction block based on the indicated DIMD merge candidate. Then, the decoder may reconstruct the current block based on the prediction block and a residual obtained from the bitstream.

[0448] In some embodiments, the process of reconstructing the current block may include selecting first IPMs with the highest amplitudes from the histogram, then applying an IPM blending (e.g., fusion / combination) process to generate a DIMD predictor. For example, the decoder may generate, based on first amplitudes of the first IPMs, first weights corresponding to the first IPMs. The DIMD predictor may be determined based on combining the first IPMs according to the first weights, and the current block may be reconstructed using the DIMD predictor.

[0449] In some examples, the determining of the third block for generating the histogram of IPMs at block 3302 may be performed when determining N first blocks of a plurality of blocks as described in block 3202. The N first blocks include the third block described at block 3302 and are coded using an intra-based coding mode. The determining of the first block reconstructed using the non-angular mode at block 3304 may be performed when determining M second blocks of the plurality of blocks as described at block 3204, The M second blocks include the first block described at block 3304 and are coded in at least one non-angular coding mode. The M fifth blocks may be determined from the spatially closest (previously-reconstructed) blocks to the current block and that were coded in a non-angular mode that uses a reference block for coding the block.

[0450] T blocks from the N first blocks and the M second blocks may be selected as described at block 3206. The selected T blocks include one or more first blocks including the third block described at block 3302,Docket No.: 24-2016PCT and / or one or more second blocks including the first block described at block 3304. The selecting of the T blocks from the N first blocks and the M second blocks may prioritize blocks from the N first blocks over blocks from the M second blocks. For example, including more first blocks than second blocks in the T blocks may enable including IPM information of more DIMD coded blocks in the histogram from which the IPM for the current block is selected.

[0451] The subsequent updating of the histogram may include updating the histogram based on the selected T blocks as described at block 3208. The updating the histogram based on the selected T blocks may include using a weighted combination of histograms of IPMs associated with the T blocks. For example, histograms of block coded using DIMD-based coding modes may be assigned a higher weight than the histograms of blocks coded using non-angular coding modes. In another example, the weights may be further be determined according to a priority ordering such as, for example, blocks coded using a DIMD coding mode having higher weights than blocks coded using other DIMD-based coding modes, and / or blocks coded using a non-angular coding mode of TIMD having higher weights than blocks coded using IBC or IntraTMP.

[0452] FIG.33B shows a flowchart 3320 of an example method for coding a current block based on an intra- based coding mode using one or more blocks coded in a non-angular (coding) mode, according to some embodiments. Flowchart 3320 may be implemented for coding a current block using Decoder-side Intra Mode Derivation (DIMD) or another DIMD-based process. Flowchart 3320 may be implemented by a coder such as an encoder (e.g., encoder 200 of FIG.2) or a decoder (e.g., decoder 300 of FIG.3).

[0453] In some examples, the method of flowchart 3320 is performed during a DIMD-based coding process of a current block. The method may be used to generate and / or update the histogram of intra prediction modes (IPMs) based on which the intra-based coding mode that is to be applied to the current block is determined. Depending on the intra-based coding mode, the histogram may be a histogram of gradients (HoG) or a histogram of occurrences (HoC). For example, the histogram may be a HoG for the DIMD mode, a HoC for the OBIC mode, or a merged HoG (MHoG) for the MIMD mode. For example, the histogram may be a HoG / MHoG for an MIMD / DIMD / combined candidate determined for the DIMD Merge List mode or an HoC for an OBIC-based candidate determined for the DIMD Merge List mode. In some examples, the intra- based coding mode applied to the current block may be one of: a DIMD mode, an Occurrence-based Intra Coding (OBIC) mode, a Merged Intra Mode Derivation (MIMD) mode, or a DIMD Merge List mode.

[0454] At block 3322, the coder obtains a selection indication for the current block coded in the intra-based coding mode.

[0455] In some examples, the selection indication is a configuration setting, a flag, or an indication of a priority or priority ordering. In some examples, the selection indication may indicate what, from a first set of one or more IPMs determined at block 3324 and a second set of one or more IPMs determined at block 3326, is to be used to update a histogram at block 3328. For example, the selection indication may indicate whether it is only the IPM information of the first set of one or more IPMs, only the IPM information of the second setDocket No.: 24-2016PCT of one or more IPMs, or a combination of the first and second sets of IPM information is to be used for the updating of the histogram.

[0456] For example, when the coder is a decoder, the decoder may obtain the selection indication from a bitstream.

[0457] At block 3328, the coder updates, in accordance with the selection indication obtained at 3322, the histogram of IPMs based on IPM information of one or both: a first set of one or more IPMs associated with a first block (which may correspond to the first block referenced in FIG.33A) reconstructed using a non- angular mode; or a second set of one or more IPMs associated with a second block (which may correspond to the second block referenced in FIG.33A) indicated by (e.g., derived from) the first block.

[0458] In some embodiments, the obtained selection indication indicates which of the first or second set of one or more IPMs are to be obtained.

[0459] In some examples, the obtained selection indication indicates that both the first and second set of one or more IPMs are obtained to update the histogram of IPMs.

[0460] As part of the updating, block 3328 may include one or both of block 3324 or block 3326. The first set of one or more IPMs are obtained at block 3324 and the second set of one or more IPMs obtained at block 3326.

[0461] In some examples, based on the obtained selection indication indicating one of the first or second set of IPMs, only the corresponding blocks 3324 or 3326, respectively, would be performed.

[0462] In some examples, based on the obtained selection indication indicating both the first or second set of IPMs, both blocks 3324 or 3326 would be ...

Claims

Docket No.: 24-2016PCT CLAIMS 1. A method comprising: obtaining a selection indication for a current block coded using an intra-based coding mode; updating a histogram of intra prediction modes (IPMs) based on a first block reconstructed using a non-angular mode and selected for the current block, wherein the histogram is updated, in accordance with the obtained selection indication, based on one or both of: a first set of one or more IPMs associated with the first block; or a second set of one or more IPMs associated with a second block that overlaps a reference block indicated by the non-angular mode for the first block; and coding the current block based on the updated histogram.

2. The method of claim 1, wherein the coding the current block comprises: selecting, based on amplitudes of IPMs in the updated histogram, a set of IPMs from the updated histogram; generating a prediction block, for coding the coding block, using the set of IPMs.

3. The method of claim 2, further comprising: determining, based on amplitudes of the set of IPMs, a set of weights corresponding to the set of IPMs, wherein the prediction block is generated using a decoder-side intra mode derivation (DIMD) predictor that combines the set of IPMs according to the set of weights.

4. The method of any one of claims 1-3, wherein the histogram is updated further based on one or more IPMs of a third block previously coded or reconstructed using one of a plurality of intra-based coding modes.

5. The method of any one of claims 1-4, wherein the histogram of IPMs is updated based on: the first set of one or more IPMs when the selection indication comprises a first value; and the second set of one or more IPMs when the selection indication comprises a second value.

6. The method of any one of claims 1-5, wherein the histogram is updated based on: a combination of the first and second sets of one or more IPMs when the selection indication comprises a third value.

7. The method of claim 6, wherein the first and second sets are combined to update the histogram based on a level of difference, between the first and second sets of one or more IPMs, exceeding a preconfigured threshold.

8. The method of any one of claims 6-7, wherein, based on a level of difference, between the first and second sets of one or more IPMs, being less than or equal to a preconfigured threshold, the combination comprises one of the first set and the second set and not the other, and the one of the first set and the second set is selected based on a priority ordering of the non-angular mode coding the first block and an intra-coding mode coding the second block.Docket No.: 24-2016PCT 9. The method of any one of claims 1-4, wherein the selection indication indicates a default prioritization, and wherein the histogram is updated based on the one or both of the first or second sets in accordance with the default prioritization.

10. The method of claim 9, wherein the default prioritization specifies a priority ordering of selecting: one of the first or second sets; or one of the first set, the second set, or the combination of the first and second sets.

11. The method of any one of claims 1-4, wherein the selection indication indicates a respective default prioritization for each of a plurality of intra coding modes comprising the non-angular mode coding the first block and an intra coding mode coding the second block, and wherein the histogram is updated based on one of the first and second sets selected in accordance with respective default prioritizations of the non-angular mode of the first block and the intra coding mode of the second block.

12. The method of any one of claims 1-4, wherein the selection indication indicates, for each of a plurality of non-angular modes, a respective default prioritization selecting one of the first and second sets or selecting one of the first set, second set, or the combination; and wherein the histogram is updated based on one or both of the first and second sets in accordance with the default prioritization of the non-angular mode of the first block.

13. The method of any one of claims 1-8, wherein the updating the histogram of IPMs comprises: when the selection indication has a first value, the histogram is updated based on the second set when the second set is available, or on the first set when the second set of one or more IPMs is not available; when the selection indication has a second value, the histogram is updated based on a combination of the first and second sets if both the first and second sets are available; and when the selection indication has a third value, the histogram is updated based on a preset default operation.

14. The method of claim 13, wherein the preset default operation specifies using: one of the first and second sets for the updating; or one of the first and second sets for the updating according to a priority ordering of a plurality of intra coding modes comprising the non-angular mode of the first block and an intra coding mode of the second block.

15. The method of any one of claims 1-14, wherein selection indication comprises a distance between the current block and the second block, and wherein the selection between the first and second sets for updating the histogram is based on the distance.

16. The method of claim 15, wherein the selection indication further comprises a distance between the current block and the first block, and the selection between the first and second sets for updating the histogram is further based on the distance between the current block and the first block.Docket No.: 24-2016PCT 17. The method of any one of claims 15-16, wherein the selection indication further comprises a block size of one or both of the first and second blocks, and wherein the selection between the first and second sets if further based on the block size of the one or both of the first and second blocks.

18. The method of any one of claims 1-17, wherein the updating the histogram comprises: adding, to the histogram, amplitudes of the one or both of the first and second set of IPMs ; or adding, to the histogram, values based on block sizes associated with the one or both of the first and second sets.

19. The method of claim 18, wherein the updating the histogram comprises the adding the values based on the block sizes, and wherein: when the first set of IPMs is selected for updating the histogram, each of the amplitudes of the first set of IPMs in the histogram is updated based on a size of the first block; and when the second set of IPMs is selected for updating the histogram, each of the amplitudes of the second set of IPMs in the histogram is updated based on a size of the second block.

20. The method of any one of claims 4-19, wherein the third block is coded using Decoder-side Intra Mode Derivation (DIMD), Template-based Intra Mode Derivation (TIMD), or Occurrence-based Intra Coding (OBIC) mode.

21. The method of any one of claims 1-20, wherein the intra-based coding mode comprises one of: an OBIC mode, a Merge Intra Mode Derivation (MIMD) mode, or a DIMD Merge List mode, and wherein the second block is reconstructed using one of an OBIC mode, an MIMD mode, a TIMD mode, a DIMD mode, or a DIMD Merge List mode.

22. The method of any one of claims 1-21, wherein the non-angular mode is an Intra Block Copy (IBC) mode, an Reordered-reconstruction IBC (RR-IBC) mode, an Intra Template Matching Prediction (IntraTMP) mode, or an RR-TMP mode.

23. The method of any one of claims 1-22, wherein the first block is selected based on being a neighboring block of the current block or from a list of previously-reconstructed blocks.

24. The method of any one of claims 1-23, wherein coding the current block comprises: determining an OBIC candidate or an MIMD candidate based on the updated histogram; and adding the OBIC candidate or the MIMD candidate to a list of merge candidates, wherein the current block is coded based on the list.

25. The method of any one of claims 1-24, wherein the coding the current block comprises: obtaining, from a bitstream, an indication of a DIMD merge candidate in the list; generating a prediction block based on the indicated DIMD merge candidate; and reconstructing the current block based on the prediction block and a residual obtained from the bitstream.Docket No.: 24-2016PCT 26. The method of any one of claims 1-25, wherein the obtaining the selection indication comprises decoding the selection indication from a bitstream, and wherein the coding the current block comprises reconstructing the current block based on the prediction block and a residual block obtained from a bitstream.

27. The method of any one of claims 1-24, wherein the coding the current block comprises: encoding, in a bitstream, the selection indication for the current block; and encoding, in a bitstream, a residual indicating a difference between the current block and the prediction block.

28. The method of any one of claims 1-24 or 27, wherein the coding the current block comprises: generating a prediction block based on a DIMD merge candidate selected from the list; encoding, in a bitstream, an indication of the selected DIMD merge candidate in the list; and encoding, in the bitstream, a residual indicating a difference between the current block and the prediction block.

29. A non-transitory computer-readable medium comprising instructions that, when executed by one or more processors of an apparatus, cause the apparatus to perform the method of any one of claims 1- 28.

30. An encoder comprising: one or more processors; and memory storing instructions that, when executed by the one or more processors, cause the encoder to perform the method of any one of claims 1-24 or 27-28.

31. A non-transitory computer-readable recording medium storing a bitstream generated by the method for encoding a video according to any one of claims 1-24 or 27-28.

32. A decoder comprising: one or more processors; and memory storing instructions that, when executed by the one or more processors, cause the decoder to perform the method of any one of claims 1-26.

33. A non-transitory computer readable medium storing a bitstream, which, when decoded by a decoder, causes the decoder to perform the method according to any one of claims 1-26.

34. A bitstream generated according to any one of claims 1-24 or 27-28.

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