Deriving coding vector candidates based on IPM-based coding mode block vector

Abstract

A video coder (encoder or decoder) derives an auto-relocated (AR) block vector prediction (BVP) candidate by applying AR BVP to a BVP candidate for a current block. The deriving comprises determining a position in a guiding reference block based on the BVP candidate, obtaining a coding BV used by an intra-prediction-mode (IPM)-based intra coding mode of a block containing the position, and deriving the AR-BVP candidate based on the coding BV and the BVP candidate. The video coder determines a list of BVP candidates based on the BVP candidate and the AR-BVP candidate, and further determines, based on the list of BVP candidates, a block vector (BV) indicating a reference block for the current block. The video coder codes (encodes or decodes) the current block based on the reference block.

Description

Docket No.: 24-2036PCT TITLE Deriving Coding Vector Candidates based on IPM-based Coding Mode Block Vector CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.63 / 678,323, filed August 1, 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.7A shows an example of combined quadtree and multi-type tree partitioning of a CTB.

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

[0011] FIG.8 shows an example of partitioning modes in AOMedia Video 1 (AV1).

[0012] FIG.9 shows an example set of reference samples determined for intra prediction of a current block.

[0013] FIG.10A, FIG.10B, and FIG.10C show example intra prediction modes.

[0014] FIG.11 shows an example of a current block and corresponding reference samples.

[0015] FIG. 12 shows an example of applying an intra prediction mode (e.g., an angular mode) for prediction of a current block.

[0016] FIG.13A shows an example of inter prediction performed for a current block in a current picture.

[0017] FIG.13B shows an example motion vector.

[0018] FIG.14 shows an example of bi-prediction performed for a current block.

[0019] FIG.15A shows example spatial candidate neighboring blocks relative to a current block being coded.

[0020] FIG.15B shows example locations of two temporal, co-located blocks relative to a current block.

[0021] FIG.16 shows an example of intra block copy (IBC).Docket No.: 24-2036PCT

[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 DIMD 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 DIMD 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 DIMD 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 the DIMD shown in FIG.18 with the reference block identified by the BV of a neighboring block, according to some embodiments.

[0035] FIGS.26A and 26B show an example of template-based intra mode derivation (TIMD) for coding a current block, according to some embodiments.

[0036] FIG.27 shows an example of Auto-relocated block vector prediction (AR-BVP) applied to IBC, according to some embodiments.

[0037] FIG.28A shows a flowchart of a method for constructing an intra block copy (IBC) merge / AMVP list for coding a current block, according to some embodiments.Docket No.: 24-2036PCT

[0038] FIG.28B shows an example of a method for constructing IntraTMP BVP candidates for coding a current block, according to some embodiments.

[0039] FIG.29 shows an example of generating an AR-BVP candidate using a BV of an intra-prediction- mode (IPM)-based intra coding mode as the reference BV, according to some embodiments.

[0040] FIG.30 shows an example flowchart illustrating a process for intra coding a current block based on an AR-BVP candidate generated using a BV of an IPM-based intra coding mode as the reference BV, according to some embodiments.

[0041] FIG. 31 shows an example of chained motion vector prediction (CMVP), according to some embodiments.

[0042] FIG.32 shows an example flowchart illustrating a process for inter coding a current block based on a vector candidate generated using a BV of an IPM-based intra coding mode as the reference BV, according to some embodiments.

[0043] FIG.33 shows an example of a method for constructing an intra block copy (IBC) merge / AMVP list by considering IPM-based intra coding block vectors (BVs) for coding a current block, according to some embodiments.

[0044] FIG.34 shows an example flowchart illustrating a process for coding a current block using IBC merge / AMVP list generated by including BVs of IPM-based intra coding modes, according to some embodiments.

[0045] FIG.35 illustrates a block diagram of an example computer system in which embodiments of the present disclosure may be implemented. DETAILED DESCRIPTION

[0046] 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 most 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.

[0047] 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.Docket No.: 24-2036PCT

[0048] 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.

[0049] 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.

[0050] 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 tasks (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.

[0051] 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.

[0052] 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, aDocket No.: 24-2036PCT 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.).

[0053] 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. The 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.

[0054] 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 from 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.

[0055] 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 informationDocket No.: 24-2036PCT 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.

[0056] 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.

[0057] 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.

[0058] 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 may 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).Docket No.: 24-2036PCT

[0059] 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.

[0060] 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).

[0061] Decoder 120 may decode video sequence 108 from encoded bitstream 110. 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 destination device 106 may be, or may not necessarily be, the same video sequence sent, such as video sequence 108 as sent by 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.

[0062] 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.

[0063] 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 decoderDocket No.: 24-2036PCT 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.

[0064] 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).

[0065] 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.

[0066] 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 reconstructed 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.

[0067] 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 videoDocket No.: 24-2036PCT 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.

[0068] 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.

[0069] 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).

[0070] 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.

[0071] 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, a sample-adaptive offset (SAO) filter, constrained directional enhancement filters (CDEFs), and / or loop restoration (LR) filters. 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.

[0072] 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.Docket No.: 24-2036PCT

[0073] 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.

[0074] 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), syntax-based context-based binary arithmetic coding (SBAC), and / or symbol-to-symbol adaptive multi-symbol (non-binary) arithmetic coding 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.

[0075] 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).

[0076] 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.Docket No.: 24-2036PCT

[0077] 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 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.

[0078] 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.

[0079] Entropy decoding unit 306 may entropy decode 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, a sample-adaptive offset (SAO) filter, constrained directional enhancement filters (CDEFs), and / or loop restoration (LR) filters. 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.

[0080] 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).

[0081] 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. ForDocket No.: 24-2036PCT 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.

[0082] 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.

[0083] 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 an 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.

[0084] 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 of 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 labeled 0, 5, and 6, respectively, 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 labeled 1, 2, 3, and 4, respectively, in FIGS.4 and 5.

[0085] The example CTB 400 of FIG.4 is partitioned into 10 leaf CBs labeled 0–9, respectively, 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 aDocket No.: 24-2036PCT 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.

[0086] 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.

[0087] 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.

[0088] FIG.7A shows an example of combined quadtree and multi-type tree partitioning of a CTB 700A. FIG. 7B shows an example tree 700B corresponding to the combined quadtree and multi-type tree partitioning of CTB 700A shown in FIG.7A. In both FIGS.7A and 7B, quadtree splits are shown in solid lines and multi-type tree splits are shown in dashed lines. For ease of explanation, CTB 700A is shown with the same quadtree partitioning as the CTB 400 described in FIG.4, and a description of the quadtree partitioning of CTB 700A, which is similar to that for CTB 400, is omitted. The quadtree partitioning of CTB 700A is merely an example and a CTB may be quadtree partitioned in a manner different from CTB 700A. Additional multi-type tree partitions of CTB 700A may be made relative to three leaf CBs shown in FIG.4. The three leaf CBs in FIG.4 that are shown in FIG.7A 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.

[0089] 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 labeled 5 and 6, respectively, in FIGS.7A and 7B. Leaf CB 8 ofDocket No.: 24-2036PCT 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 labeled 9 and 14, respectively, in FIGS.7A and 7B. 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 labeled 11, 12, and 13, respectively, in FIGS.7A and 7B. 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 labeled 15 and 19, respectively, in FIGS.7A and 7B. 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 labeled 16, 17, and 18, respectively, in FIGS.7A and 7B.

[0090] Altogether, CTB 700A may be partitioned into 20 leaf CBs labeled 0–19, respectively. The 20 leaf CBs may correspond to 20 leaf nodes (e.g., 20 leaf nodes of tree 700B shown in FIG.7B). The resulting combination of quadtree and multi-type tree partitioning of the CTB 700A 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. 7A and 7B 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.7A and 7B, it should be noted that each CB leaf node may comprise one or more PBs and / or TBs.

[0091] 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.

[0092] In some implementations of partitioning (e.g., AV1), a picture can be partitioned into multiple coding blocks. The largest coding blocks are also referred to as superblocks having sizes of either 128x128 or 64x64. Superblocks can be partitioned into smaller coding blocks which can be performed in nine partitioning modes. FIG.8 shows the nine partitioning modes among which only PARTITION_SPLIT allows recursive partitioning. In addition, PARTITION_VERT_4 and PARTITION_HORZ_4 modes are not allowed for 8x8 or 128x128 coding blocks, and T-shaped partitioning modes are not allowed for 8x8 coding blocks. The minimum coding block size is 4x4. Intra and inter coding blocks can be further partitioned into transform blocks and the partitioning depth is up to two levels.Docket No.: 24-2036PCT

[0093] 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 in 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 (coding block or transform block) in the AV1 coding format.

[0094] 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.

[0095] 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.

[0096] 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.7A. As described herein, the numeric labels 0–19 of the blocks of partitioned CTB 700A may correspond to the sequence order for encoding / decoding the blocks and may be used as such in the example of FIG.9.

[0097] 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 alsoDocket No.: 24-2036PCT 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 line 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.

[0098] 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.

[0099] 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 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).

[0100] 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 aDocket No.: 24-2036PCT 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. 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] In some implementations of intra prediction modes (e.g., as supported by AV1), the angular modes can be defined by specifying a set of nominal modes and a set of angle delta offsets can be defined aroundDocket No.: 24-2036PCT each of the nominal modes. For example, there may be eight nominal angular prediction modes each having a set of angle delta offsets indexed between -3 and +3 with the nominal angle located at 0. FIG.10C shows the eight nominal modes (in solid arrows) and the set of angle delta offsets around the D67_PRED nominal angle (in dotted arrows). The prediction angle can be derived by adding the offset to the associated nominal angle. As a result, there are 56 angular modes in AV1. Note that for small blocks, such as 4x4, 4x8, and 8x4, only nominal angular modes are applied. In addition to the 56 angular modes, there are five non- angular intra-prediction modes in AV1, including DC_PRED mode (averaging samples from reconstructed neighboring blocks), SMOOTH_V AND SMOOTH_H modes (using quadratic interpolation along the vertical and horizontal directions, respectively), SMOOTH mode (averaging the quadratic interpolation results along both directions), and Paeth mode (predicting each sample from its top, left and top left reference samples). Recursive intra-prediction modes may also be used where a coding block is divided into sub-blocks and each intra-predicted sub-block can be used to intra-predict the next sub-block.

[0106] 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 ^^^^[^]:^^^^[^] = ^[−^ + ^][−^], (^ ≥ 0). (1)Reference samples 902 belonging to reference line l, to the left of current block 904, may be placed in the one-dimensional array ^^^^[^]:^^^^[^] = ^[−^][−^ + ^], (^ ≥ 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.

[0107] 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.

[0108] 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 linearDocket No.: 24-2036PCT interpolation at location [^][^] in current block 904. The predicted sample ^[^][^] in current block 904 may be determined / calculated as: 1^[^][^] =2 ∙ ^ (ℎ[^][^] + ^[^][^] + ^), (3)whereℎ[^][^] = (^ − ^ − 1) ∙ ^^^^[^] + (^ + 1) ∙ ^^^^[^] (4)may be the horizonal linear interpolation at the location [^][^] in current block 904 and^[^][^] = (^ − ^ − 1) ∙ ^^^^[^] + (^ + 1) ∙ ^^^^[^] (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 current block 904.

[0109] For DC mode, a sample at a location [^][^] in current block 904 may be predicted by the mean of reference samples 902. The predicted sample ^[^][^] in current block 904 may be determined / calculated as: ^^^ ^^ ^^ ^ = 1^ [][ ] ^^ ^^^^[^] + ^ ^^^^[^]#. (6)

[0110] For angular 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 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. 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).

[0111] 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 ^^^^[^]. 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 reference sample. A predicted sample ^[^][^] in current block 904 may be determined / calculated by linearly interpolating between the two reference samples, for example, if the projection point falls at aDocket No.: 24-2036PCT fractional sample position between two reference samples. The predicted sample ^[^][^] may bedetermined / calculated as:^[^][^] = (1 − %&) ∙ ^^^^[^ + %' + 1] + %& ∙ ^^^^[^ + %' + 2]. (7)In Equation (7), %'may be the integer part of the horizontal displacement of the projection point relative to the location [^]. , angle φ of vertical prediction mode 906 as:%' = ⌊(^ + 1) ∙ tan ,⌋. (8)In Equation (7), %&may be the fractional part of the horizontal displacement of the projection point relative to the location [^][^] and may be determined / calculated as:%& = ((^ + 1) ∙ tan ,) − ⌊(^ + 1) ∙ tan ,⌋, (9)where ⌊ ∙ ⌋ is the integer floor function.

[0112] 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: ^[^][^] = (1 − %&) ∙ ^^^^[^ + %' + 1] + %& ∙ ^^^^[^ + %' + 2]. (10)%' may be the integer part of the vertical displacement of the projection point relative to the location [^][^].%'may be determined / calculated as a function of the tangent of the angle φ of the horizontal prediction modeas:%' = ⌊(^ + 1) ∙ tan ,⌋. (11)%& may be the fractional part of the vertical displacement of the projection point relative to the location[^][^]. %& may be determined / calculated as:%. = ((^ + 1) ∙ tan ,) − ⌊(^ + 1) ∙ tan ,⌋, (12)where ⌊ ∙ ⌋ is the integer

[0113] 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 given by (1-%&) and %&, respectively. 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 %&. In other examples, different levels of sample accuracy may be used.

[0114] 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 sameDocket No.: 24-2036PCT 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 %&(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 %&. 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 %&. A predicted sample ^[^][^], for vertical prediction modes, may be determined based on the four-tap FIR filter as: 2 (13) ^[^][^] = ^ ^ / [%] ∙ ^^^^[^ + %01^ + %] ,where fT[i], i = 0...3,^[^][^], for horizontal2 (14) ^[^][^] = ^ ^ / [%] ∙ ^^^^[^ + %01^ + %] .

[0115] Supplementary of asample 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 samples 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.

[0116] 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),Docket No.: 24-2036PCT 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.

[0117] 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 has reference line index 0 and is immediately adjacent to the current block. In these examples, no indication of MRL index is signaled.

[0118] 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).

[0119] 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.).

[0120] 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. TheDocket No.: 24-2036PCT 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.

[0121] 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.

[0122] 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. Reference block 1304 may be used to predict 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.

[0123] 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 reference picture 1306 as current block 1300 in current picture 1302. The reference region (e.g., search range 1308) may at least partially extend outside of reference picture 1306. Constant boundaryDocket No.: 24-2036PCT 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 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 current block 1300.

[0124] 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. Reference picture 1306 of reference block 1304 may be indicated by a reference index pointing into a reference picture list comprising reference picture 1306. The reference frames can include different types of frames. For example, in some implementations (e.g., such as in AV1), up to seven frames can be used as reference frames and there are four types of frames, including LAST frame (a frame that was displayed in the near past), BWD frame (a frame that will be displayed in the future), GOLDEN frame (a frame that was displayed in the distant past), and ARF frame (a frame from either the past or the future).

[0125] 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 current 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.

[0126] 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 aDocket No.: 24-2036PCT 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 motion vector 1312 and a reference indicator / index. The reference indicator may indicate 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 reference block 1304, which may correspond to / form (e.g., be considered as) a prediction of current block 1300. The decoder may determine and / or generate 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).

[0127] 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 or single reference inter prediction.

[0128] Inter prediction of a current block, using bi-prediction or compound 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.

[0129] 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- prediction / single reference prediction and / or bi-prediction / compound 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.

[0130] FIG.14 shows an example of bi-prediction / compound prediction. Two reference blocks 1402 and 1404 may be used to predict a current block 1400. For example, 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 blockDocket No.: 24-2036PCT 1400, and 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) or a display order. The second picture may succeed the current picture in terms of the POC or the display order. In other examples, the reference pictures may both precede, or both succeed the current picture in terms of POC or the display order. 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.

[0131] 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) or a set of parameters at a similar level. 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.

[0132] The encoder may determine and / or generate reference blocks 1402 and 1404 for 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.

[0133] 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 reference block 1402, in a reference picture list. In some examples, the motion information for reference block 1402 may 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.

[0134] 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 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 reference block 1404, in the reference picture list.

[0135] A decoder may decode current block 1400 by determining and / or generating reference blocks 1402 and 1404. The decoder may determine and / or generate reference blocks 1402 and 1404, for example, based on the respective related motion information for reference blocks 1402 and 1404. Reference blocksDocket No.: 24-2036PCT 1402 and 1404 may correspond to / form (e.g., be considered as) the prediction (e.g., used to generate a prediction block) of current block 1400. The decoder may decode current block 1400 based on combining the prediction with the prediction errors.

[0136] 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).

[0137] 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.

[0138] 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 a position relative to a position of the current block being coded, the MVD may be represented by two components MVD^ and MVD". MVD^ and MVD" 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.

[0139] 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., beDocket No.: 24-2036PCT 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.

[0140] 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.

[0141] 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.

[0142] 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 be 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.Docket No.: 24-2036PCT

[0143] 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.

[0144] In some examples (e.g., AV1), a list of derived MV predictors may be generated by pooling the spatial and temporal MV candidates and ranking them based on weightings determined by evaluating each of the candidates. Up to four candidates may be added to the list of MV predictors, which may also be referred to as the dynamic reference list (DRL). The DRL may be used in dynamic MV prediction modes.

[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 or AV1, 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, etc.). History-based motion vector prediction (HMVP), combined intra / inter prediction mode (CIIP) or compound inter-intra prediction, warped motion compensation, overlapped block motion compensation (OBMC), 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) 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, AV1, and / or any other coding standards / formats / protocols) to exploit correlation between blocks of samples within a same picture (e.g.,Docket No.: 24-2036PCT of screen content videos). The prediction technique may be intra block copy (IBC or IntraBC) 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, SAO filtering, CDEFs, and / or LR filters). In some examples, the reference block may be restricted to a certain area. For example, in AV1, if the top-left pixel coordinate of a superblock is (x0, y0), IntraBC prediction is available at pixel position (x, y) only if the value of the vertical coordinate y is less than y0 and the value of the horizontal coordinate x is less x0 + 2(y0 − y). Further, due to hardware write-back delays, the immediate reconstructed area may not be accessible by IntraBC prediction.

[0148] FIG.16 shows an example of IBC (e.g., an IBC mode or an IntraBC mode). The example shown in FIG.16 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 correspondDocket No.: 24-2036PCT 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., 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 by two components BVD^and BVD". BVD^and BVD"may be determined / calculated as:BVD^ = BV^ − BVP^, (17)BVD" = BV" − BVP" . (18)In Equations (17) and (18), BVDx and BVDy may, respectively, represent horizontal and vertical components of the BVD. In Equations (17) and (18), 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).Docket No.: 24-2036PCT

[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.

[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 denoted A0, A1, B0, B1, and B2, respectively, 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 neighborDocket No.: 24-2036PCT 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 Left 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.Docket No.: 24-2036PCT 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 is 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.16, 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. 16, 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) indicating 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,Docket No.: 24-2036PCT 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., vertical 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) = ?@A^^^(B − 1 − ^, ^) (19)Reference(x, y) = ?@A^^^(^, ℎ − 1 − ^) (20)where w and h are the width and the 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, Equation (19) shows that the current block is flipped in the horizontal direction by sampling from right to left. Similarly, for vertical flipping, Equation (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] 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 some 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.

[0167] 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 toDocket No.: 24-2036PCT 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.

[0168] 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).

[0169] 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.

[0170] 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 be calculated as follows:SearchRange_w = min (64, L ∗ BlkW) (21)SearchRange_h = min (64, L ∗ 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 ofDocket No.: 24-2036PCT 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.

[0171] 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.

[0172] 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.

[0173] 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.

[0174] 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 orDocket No.: 24-2036PCT 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.

[0175] 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 candidate 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.

[0176] 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.

[0177] 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.

[0178] 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 ofDocket No.: 24-2036PCT 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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 −1Docket No.: 24-2036PCT

[0184] For each of selected reference samples (e.g., pixels) of template 1812, point-by-point multiply of each of these two matrices with a 3x3 Sobel filter window may be performed and the results are summed. 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 (]STU / ]YZU). 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)@A^^%_`1^ = |]YZU| + |]STU| 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.

[0185] 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.

[0186] 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) 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.

[0187] 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,Docket No.: 24-2036PCT weight 1828B for DIMD mode 1818B may correspond to DIMD weight 1832B (e.g., wDIMD2), which may be based on an amplitude A2, from HoG 1820, associated with DIMD mode 1818B (e.g., IPM M2) divided by the sum.

[0188] 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 f1 and f2 may be equal to 1.

[0189] 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[c^^1(^, ^) = ^dB' ∗ c^^1'(^, ^)eIn some examples, the for mode i) for DIMDmodes 1818A-B and the planar weight 1833 (wPlanar) for planar mode 1816. The weights (wi) may be constant and uniformly applied to determine each sample (x, y) 1814 of prediction block 1824. The predictor Predifor 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[c^^1(^, ^) = h∑^' ! dBf%A1' ∗ 1%A1c^^1'(^, ^)e + Bc^@[@^ ∗Note the shifting

[0190] 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.

[0191] 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,Docket No.: 24-2036PCT HoG 1819C (lmnTYZ), HoG 1819A (loZ.p), and HoG 1819B (lmnTYZqZ.p), respectively. For a directionalIPM A , l'[A] for region i (e.g., above, left, or above-left) represents the cumulative magnitude of allsamples in region i at direction (or IPM) A.

[0192] 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., 1%A1Rb1^!and 1%A1Rb1^^, respectively.

[0193] In some examples, HoGs 1819C and 1819A corresponding to histograms lmnTYZand loZ.pmay be used to determine whether 1%A1Rb1^!and / or 1%A1Rb1^^depend on a specific template region ABOVE or LEFT. In a first example, the location-dependency of 1%A1Rb1^', denoted as ^brf^^'(e.g., shown in FIG.18 as Li= L(Mi, Hleft, Habove) for DIMD mode i), can be defined as: If: (lmnTYZ[1%A1Rb1^'] > 2loZ.p[1%A1Rb1^']), then:^brf^^' = 1, that is 1%A1Rb1^' depends on region ABOVE.Else if: (loZ.p[1%A1Rb1^'] > 2lmnTYZ[1%A1Rb1^']), then:^brf^^' = 2, that is 1%A1Rb1^' depends on region LEFT.Else: ^brf^^' = 0, that is 1%A1Rb1^' is not location-dependent.

[0194] In a second example, the location-dependency of 1%A1Rb1^', denoted as ^brf^^'(e.g., shown in FIG.18 as Li = L(Mi, Hleft, Habove) for DIMD mode i), can be defined as: If : (loZ.p[1%A1Rb1^'] <x), then:Else if : (lmnTYZ[1%A1Rb1^'] <average of (loZ.p[1%A1Rb1^'], lmnTYZ[1%A1Rb1^'], lmnTYZqZ.p[1%A1Rb1^'])), then:^brf^^' = 2, that is 1%A1Rb1^' depends on region LEFT.Else: ^brf^^' = 0, that is 1%A1Rb1^' 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.

[0195] 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,Docket No.: 24-2036PCT 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.

[0196] 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, 1%A1c^^1! and 1%A1c^^1^, with the Planar predictor1%A1c^@[@^. If no DIMD mode is determined to be location-dependent (e.g., ^brf^^! == ^brf^^^ == 0), then blending / fusion with uniform weights Bf%A1! , Bf%A1^ and Bc^@[@^ may be applied asexplained above.

[0197] 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 (^, ^).

[0198] In some examples, if ^brf^^' ≠ 0 , the sample-based weights Bzbrf^^f%A1'(^, ^) forpredictor 1%A1c^^1'may be computed so that the average weight used within the block is approximately equal to the uniform weight Bf%A1'with higher weights being used in the portion of the block closer to the region (e.g., ABOVE or LEFT) corresponding to ^brf^^'(e.g., indication Li). A fixed range ∆'may bedetermined and is predefined, (e.g., ∆'= 10 ) corresponding to the largest deviation ofBzbrf^^f%A1'(^, ^) from Bf%A1'. Higher values of ∆' result in a higher variation of the weights withinthe block. For a block of size l × }:If ^brf^^' = 1, then:( ) ^Bzbrf^^f%A1' ^, ^ = Bf%A1' + ∆' − 2∆' −1)If both DIMD modesindications Lithatindicate location dependency (i.e., ^brf^^' ≠ 0 for modes % = 0,1), then the weightsBzbrf^^f%A1'(^, ^) may be computed for both predictors depending on the value of ^brf^^', asshown above.

[0199] 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., ^brf^^' = 0 and ^brf^^(^^') ≠ 0, then theweights for Bzbrf^^f%A1'(^, ^) may be computed as:Bzbrf^^f%A1(^^')(^, ^) − Bf%A1(^^')' = ' −

[0200] as:Bzbrf^^c^@[@^(^, ^) = 64 - ∑^' ! dBzbrf^^f%A1'(^, ^)eDocket No.: 24-2036PCT

[0201] 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: ^^`^%b[c^^1(^, ^) = ~ ^dBzbrf^^f%A1'(^, ^) ∗ 1%A1c^^1'(^, ^)e^ ≫ 6In some process. 6-bits integer precision being used.

[0202] In some embodiments, based on current block 1810 being coded using DIMD, DIMD 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, DIMD 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.

[0203] 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).

[0204] 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.

[0205] 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.: 24-2036PCT

[0206] 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.

[0207] 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).

[0208] At block 2008, an indication of location dependency of each respective IPM of the selected IPMs is determined.

[0209] 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.

[0210] 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.

[0211] 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 coding the current block.Docket No.: 24-2036PCT For example, the IPM with the highest amplitude may be determined as the primary DIMD mode and selected as the DIMD predictor.

[0212] 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.

[0213] 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 / Ghorbeing equal to or close to 1 or -1).

[0214] 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.

[0215] 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.

[0216] 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.

[0217] 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.

[0218] 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.: 24-2036PCT 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.

[0219] 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 (i.e., 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.

[0220] 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.

[0221] In some examples, the various DIMD parameters determined / derived in flowchart 2000 may be stored as DIMD information (e.g., DIMD 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.

[0222] 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 DIMD process may be performed before theDocket No.: 24-2036PCT 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.”

[0223] 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.

[0224] For example, one decoder-side technique proposes to merge DIMD information (e.g., DIMD 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).

[0225] 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).

[0226] 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).

[0227] FIG.21 shows an example 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) sample 13, and a thirdDocket No.: 24-2036PCT block 2106 associated with (e.g., contains) sample 10 are spatial non-adjacent blocks with respect to the current block.

[0228] 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).

[0229] 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 DIMD 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 DIMD information and that are spatially closest to the current block.

[0230] At block 2204, DIMD information of each block of the plurality of neighboring blocks are obtained (e.g., retrieved). In some examples, the DIMD information of a block represents a histogram of IPMs such as the HoG, which may be an MHoG. The DIMD 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 DIMD 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 DIMD information of the neighboring blocks used to generate the DIMD information for the block. In some examples, the IPMs stored in the DIMD information may be those with the highest amplitudes from a histogram that was generated for the block.

[0231] At block 2206, an MHoG is determined based on combining the DIMD information of each block of the plurality of neighboring blocks according to amplitudes in (e.g., stored for respective IPM(s)) the DIMD information. In some examples, the HoGs representing the DIMD 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 selectedentry (or luma mode) of the HoG. As shown, the HoGs may be combined by averaging the amplitudes cumulated per IPM of the HoGs by theDocket No.: 24-2036PCT number N. In other words, amplitudes of the same IPM across DIMD information of the selected neighboring blocks may be cumulated in the MHoG. Then, amplitudes of the same IPMs across the DIMD 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.

[0232] 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.

[0233] 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 DIMD 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.

[0234] 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.

[0235] 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.

[0236] 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).

[0237] 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 with respectDocket No.: 24-2036PCT 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.

[0238] 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).

[0239] 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 DIMD 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 DIMD information and that are spatially closest to the current block.

[0240] At block 2214, DIMD information of each block of the plurality of neighboring blocks are obtained (e.g., retrieved). In some examples, the DIMD 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 DIMD 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.

[0241] At block 2216, an HoC is determined based on combining the DIMD information of each block of the plurality of neighboring blocks according to a size and / or dimensions of each block.

[0242] In some examples, different from generating HoG or MHoG in which amplitudes of IPMs in the DIMD information are combined, the HoC may be determined to include IPMs, from the DIMD 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.: 24-2036PCT 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 blockmay be computed as:ℎ%^_b\^@A[0cR]+= B × 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 DIMD 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.

[0243] 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.

[0244] 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.

[0245] 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.

[0246] In some embodiments, the DIMD 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).

[0247] FIG.23A shows an example of DIMD 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 DIMD 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 DIMD information from the plurality of neighboring blocks to generate an HoC if the current block is coded using the OBIC mode.Docket No.: 24-2036PCT

[0248] 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 DIMD 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 DIMD 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 DIMD information from block 2 including HoG information such as amplitudes for IPM 7, IPM 9, and IPM 13. For example, the coder obtains third DIMD information from block 3 including HoG information such as amplitudes for IPM 1, IPM 7, IPM 9, IPM 13, and IPM 17.

[0249] 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 DIMD information, the second DIMD information, and the third DIMD 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.

[0250] 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 DIMD information, the second DIMD information, and the third DIMD 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 DIMD 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 theDocket No.: 24-2036PCT 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.

[0251] 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 DIMD 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.

[0252] 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.

[0253] 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 DIMD information already in the list, or from configured default DIMD 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.

[0254] 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 DIMD 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) DIMD informationDocket No.: 24-2036PCT derived for that block. DIMD information may be derived for a block that uses the DIMD parameters such as, for example, MIMD mode (e.g., DIMD HoG merge mode), 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.

[0255] 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.

[0256] 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 DIMD 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.

[0257] Similar to determining whether to include a spatial adjacent block in the list of DIMD merge candidates, for the DIMD 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 DIMD 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.

[0258] At 2410, a family of merge candidates from a history-based table of DIMD 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.Docket No.: 24-2036PCT For example, a predetermined number of the most recently coded blocks in the history-based table may be selected.

[0259] The history-based table may be maintained to include a predetermined number of the latest intra coded blocks that used DIMD information. In some examples, this history-based table may be updated each time an intra block (e.g., CU) is coded using the DIMD process such as when the DIMD 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 DIMD information from previously coded blocks and does not include any duplicate DIMD information.

[0260] For the DIMD 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 DIMD information derived for that block. DIMD 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 DIMD 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.

[0261] 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 DIMD 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.

[0262] In some examples, when inserting a new entry of DIMD 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 DIMD information in the table. If found, the entry with the identical DIMD information is removed from the table and all entries following that in the table are moved forward in the FIFO order, and the new DIMD 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 DIMD 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.

[0263] 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 anotherDocket No.: 24-2036PCT intra mode in which DIMD information is derived. At block 2422, it is determined whether the DIMD information (of the DIMD candidate) to be added already exists in the table. If, at block 2422, it is determined that the DIMD 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 DIMD information of the DIMD candidate may be added to the history-based table.

[0264] If at block 2422, it is determined that the DIMD information to be added is in the table, then at block 2424, the duplicate DIMD information of an existing DIMD candidate in the history-based table is already in the table and is removed from the table.

[0265] 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.

[0266] 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 DIMD information of the DIMD candidate is added as the last entry in the table.

[0267] According to the example inclusion order, DIMD merge candidates derived from DIMD 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.

[0268] 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 DIMD 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 DIMD information from the DIMD 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.

[0269] In some examples, DIMD 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 DIMD information of a new DIMD merge candidate. For example, the DIMD 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 combinedDocket No.: 24-2036PCT 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.

[0270] 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 of 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 DIMD information of all spatial adjacent blocks of the current block.

[0271] 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.

[0272] At block 2414, a set of default DIMD merge candidates are added to the list of DIMD merge candidates, according to some embodiments.

[0273] In some examples, one or more default DIMD information entries are added as DIMD merge candidates to the list of DIMD merge candidates. For example, DIMD parameters of two example default DIMD information entries are shown in Table 1 below. Blending Modes 0 (Planar) 34 (Diag) 18 (Hor) T

[0274] 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 DIMD 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.Docket No.: 24-2036PCT

[0275] 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.

[0276] In some embodiments, block 2402 may further include blocks 2416 and / or 2418. In addition to the DIMD merge candidates with DIMD 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 DIMD 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.

[0277] 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 some 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.

[0278] In some examples, the list of MHoG merge candidates may include DIMD 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 DIMD 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 DIMD information.

[0279] 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.

[0280] 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.

[0281] At block 2418, one or more DIMD merge candidates 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.Docket No.: 24-2036PCT

[0282] In some examples, the list of OBIC merge candidates may include DIMD 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 DIMD 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 DIMD information.

[0283] In some examples, a HoC may be derived from the DIMD information of two or more neighbor blocks 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.

[0284] 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.

[0285] 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.

[0286] 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.

[0287] The DIMD merge mode has the benefit of the use of available neighbor information (e.g., in particular, the DIMD information derived for the spatial neighbor blocks) to better suit the signal characteristics of the current block to be predicted.

[0288] The DIMD mode, MIMD mode, OBIC mode, DIMD merge mode, and any other mode derived from the DIMD mode are collectively referred to as “DIMD-based modes or sub-modes.”

[0289] In some embodiments, the DIMD (including any of the DIMD-based modes) may adaptively selects between the prediction block obtained using the planar mode and the reference block pointed by the blockDocket No.: 24-2036PCT vector (BV) of the neighboring blocks (e.g., obtained via the IntraTMP or IBC mode) to blend with the prediction samples obtained from an angular intra prediction. FIG.25 shows an example of the DIMD shown in FIG.18 with the reference block identified by the BV of a neighboring block. In this example, BV 1836 is the block vector obtained via the IntraTMP for the neighboring block. The reference block pointed by BV 1836, instead of the prediction block by the planar mode, can be used to blend with the prediction samples of the DIMD modes. Other DIMD-based modes can be modified in a similar way to use the reference block pointed by the BV of a neighboring block (instead of the prediction block by the planar mode) for blending.

[0290] FIG.26A and FIG.26B show 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(s) 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.

[0291] As shown in FIG.26A, 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 L1 and L2 samples, respectively. For example, L1 and / or L2 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.

[0292] In the TIMD mode, reference of template 2606 is 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 widthDocket No.: 24-2036PCT of template region 2604B, 2(M+L1) samples, 2(M+L1)+R1 samples, etc.). In some examples, reference of template 2606 may include 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.).

[0293] In some examples, a TIMD mode predictor may be determined using a list of candidate intra prediction modes (IPMs), such as the list of IPMs 2610 shown in FIG.26B. 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. For example, applying the candidate IPM may include interpolating the predicted samples of template 2604 from samples in reference of template 2606 according to the candidate IPM (e.g., a direction or angle corresponding to the candidate IPM), similar to the intra prediction process described above with respect to FIGS.10A-12.

[0294] 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 2612 and a second TIMD mode 2614. In an example, the first and second TIMD modes are determined as the first and second IPMs, respectively.

[0295] 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.

[0296] In some embodiments, a TIMD mode predictor 2622 may be determined based on combining (e.g., blending or fusing) the first TIMD mode 2612 and the second TIMD mode 2614. For example, the TIMD mode predictor may be a linear combination of the predictors generated by the first TIMD mode 2612 and the second TIMD mode 2614. Each weight (2628A or 2628B) of the first and second TIMD modes, in the linear combination, may be determined based on costs costMode1 and costMode2 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 2624 for current block 2602.Docket No.: 24-2036PCT

[0297] In some examples, a third TIMD mode 2616 may be selected for the current block 2602. The third TIMD mode 2616 may be a non-angular intra prediction mode (i.e. DC or Planar) with the lowest cost among the non-angular IPMs. This non-angular mode 2616 and the first two TIMD modes 2612 and 2614 may be fused to generate the prediction block 2624.

[0298] In some cases, not all three TIMD modes are used to generate the TIMD mode predictor. For example, the third TIMD mode (the non-angular intra prediction mode) is used in the fusion only when certain conditions are satisfied. For example, the conditions may include one or more of (1) the non- angular intra prediction mode being different from each of the first two TIMD modes, and (2) the cost of the third TIMD mode being smaller than a threshold. The threshold can be determined as a scaled value of the lowest cost value of the first two TIMD modes, i.e., costMode3 < L * costMode1. Here, costMode3 is the cost of third TIMD mode 2616 (the non-angular IPM) and costMode1 is the cost of the first TIMD mode 2612 (i.e., the TIMD mode having a lower cost among the first and second TIMD modes). In one example, the scaling factor L can be 1.5. If both conditions are satisfied, three TIMD modes 2612-2616 are used to generate the prediction block 2624. The weight 2628 of the i-th intra prediction mode (i=1, 2, 3) can be computed from the costs of these three modes as follows:B^%\ℎ_ = ^^^^T^p^^T^p^T^Z^ , ^`A^b^_ = ∑2' ^×^^^^T^p ^ ^ rb^_Rb1^^ .If the above the non-angular intraprediction mode) is not used in the prediction.

[0299] In further examples, the costs of the first two selected TIMD modes 2612 and 2614 are compared to determine whether the fusion is to be applied. For example, a ratio of the costs of the two TIMD modes can be compared with a threshold as follows:rb^_Rb1^2< ^.In some examples, ^ = 2. If thistwo TIMD modes 2612 and 2614 are fused togenerate the prediction block 2624 as discussed above. Otherwise, only the first TIMD mode 2612 (the mode having the lower cost) is used to generate the prediction block 2624.

[0300] With the generated TIMD prediction block 2624, an encoder may generate a residual (e.g., prediction error) based on a difference between the prediction block 2624 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.

[0301] In some examples, the TIMD modes may be stored as corresponding (refined) IPMs in DIMD information used in coding current block 2602. Additionally, the DIMD information may include parameters such as the costs and / or derived weights for the IPMs corresponding to the TIMD modes. Different from the DIMD information stored for intra coding modes such as DIMD, MIMD, OBIC, DIMD Merge List, the DIMD information stored for the TIMD mode does not include amplitudes of histograms. In some examples,Docket No.: 24-2036PCT the DIMD information may also include parameters such as indications of location-dependency, referred to as directionalities, determined for the IPMs corresponding to the TIMD modes.

[0302] 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.

[0303] 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 the TIMD mode is set to “vertical” i.e. 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 said selected predictor is set to “horizontal” i.e. 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” and neither sample-wise process is operated (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 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.

[0304] 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 second 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.Docket No.: 24-2036PCT

[0305] 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.

[0306] 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 ?^ / f^ < ^. ?^ / fq, ^brf^^' = 1Else if ?^ / fq < ^. ?^ / f^, ^brf^^' = 2Otherwise, ^brf^^' = 0

[0307] For illustrative purposes, the costs are represented as SATD costs, but other costs are possible.?^ / f^ is the SATD cost associated to a selected TIMD mode and computed in the second region (e.g.,above template). ?^ / f^is the SATD cost associated to a selected TIMD mode and computed in the first region (e.g., left template). ^brf^^'is 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.

[0308] 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.

[0309] 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 set to horizontal. If vertical planar mode has the minimum SATD among the three planar modes, location-dependency or the directionality for the planar mode may be set to vertical. Otherwise, if the original planar mode has the minimum SATD,Docket No.: 24-2036PCT 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.

[0310] Another intra mode prediction technique proposes to combine the benefits of TIMD and inter- prediction merge modes to obtain a new efficient intra-prediction mode referred to herein as the “TIMD merge mode.” For each CU predicted, TIMD merge mode includes building a list of TIMD information and selecting one to be used to reconstruct the current block. This list, referred to as “list of TIMD merge candidates,” can be built from the TIMD information from various spatial neighbors (e.g., neighboring blocks in the current frame). The TIMD information may already be available for several of the intra neighboring CUs (i.e., spatial neighboring blocks) coded in TIMD mode or non-TIMD mode as many intra coding modes require TIMD information to increase the coding speed. The TIMD information can include prediction modes, fusion flag, fusion weights, and wide-angle conditions of TIMD modes.

[0311] An initial list of TIMD merge candidates can be constructed according to a given checking order of respective TIMD merge candidate families, such as TIMD information of spatial adjacent candidates, TIMD information of spatial non-adjacent candidates as illustrated in FIG.21. The list of TIMD merge candidates may have a predetermined maximal number of TIMD merge candidates (e.g., 10), and the generation process can be stopped when the maximal number is reached (i.e., when the list is full). Moreover, the generation of the list may ensure that no TIMD merge candidates with duplicate TIMD information is added to the list.

[0312] After forming the TIMD merge list, the merge candidates are sorted based on the SATD cost over the template of the current block. For the weight calculation, the SATD costs of the pair TIMD modes may be normalized using their respective fusion weights. For example, if a merge candidate has two intra modes (IPM1, IPM2) with fusion weights (W1, W2), the candidate’s cost is calculated as: Cost = (SATD(IPM1) * W1 + SATD(IPM2) * W2) >> shift.

[0313] The template size and the template cost calculation aspects may be the same as those in the TIMD mode. After sorting the TIMD merge candidates, the two best candidates from the list are selected to be used in encoder RDO algorithm.

[0314] Usage of the mode can be signaled with a CABAC-coded CU-level flag. The TIMD merge mode may be used as a sub-mode of the TIMD tool. Moreover, when the TIMD merge mode is enabled, a CABAC-coded index can also be signaled to indicate whether the first or the second candidate is used from the merge.

[0315] The TIMD merge list can be extended to consider TIMD information of history-based spatial candidates, TIMD information of combined candidates, and default TIMD information candidates. Furthermore, the maximal number of candidates per family can be bounded.Docket No.: 24-2036PCT

[0316] The TIMD mode, the TIMD merge mode, and any other mode derived from TIMD mode may be collectively referred to as “TIMD-based modes or sub-modes.” The process involved in a TIMD-based mode or a DIMD-based mode may be referred to as the “intra coding sub-mode derivation process.”

[0317] In some embodiments, TIMD can be modified to support the use of block vectors to derive one of the intra modes. When deriving the TIMD intra modes (up to three IPMs), the IBC block vector candidates or IntraTMP block vector candidates of neighboring blocks (e.g., in the merge list) can be evaluated and considered to replace one of the TIMD intra modes such as one of TIMD modes 2616, 2612, and 2614 described above with respect to FIGS.26A-B. In some examples, a BV candidate is used to replace any one of the TIMD modes if the cost associated with the block vector candidate is lower than the cost of that TIMD mode. As a result, the reference block indicated by the BV candidate is used to replace the prediction generated by the TIMD intra mode for fusion with the predictions of remaining TIMD intra modes, if there are any. In other examples, only the third non-angular TIMD intra mode is replaced by the BV candidate if the cost associated with the block vector candidate is lower than the cost of the non-angular TIMD intra mode. The BV candidate used to replace one of the TIMD intra modes may be referred to as a “TIMD BV.”

[0318] As discussed above, some intra coding modes, such as the DIMD-based mode (DIMD, MIMD, DIMD Merge, OBIC) or the TIMD-based mode (TIMD or TIMD merge), generate a prediction of the block by combining a first prediction based on an intra prediction mode (IPM) and a second prediction based on the coding BV. These types of intra coding modes may be collectively referred to as an “IPM-based intra coding mode.”

[0319] Another technique, known as Auto-relocated block vector prediction (AR-BVP), may be used in the construction of the AMVP and / or merge list (for IBC or TMP). In some implementations, a guiding BV is selected from the BVP candidates in the AMVP and / or merge list. A BV (referred to herein as a “coding BV” or a “reference BV”) pointing to a reference block of a block containing a position derived relative to a position pointed to by the guiding BV is identified. An AR-BVP candidate can be determined as the combination of the guiding BV and the identified coding BV. For example, the coding BV may be similar to a block vector displacement (BVD) in AMVP IBC.

[0320] FIG.27 shows an example of AR-BVP applied to IBC where the guiding BV (BVP-1) 2701 is a BVP candidate in the IBC list, such as an IBC merge list, according to some embodiments. The guiding BV may be used to identify a first reference block (e.g., reference PU1), and five positions of the first reference block that are aligned with the five positions of the current block 2706 are also identified. For example, a position (e.g., top-left position) of the first reference block is indicated by a position (e.g., top-left position) of the current block being displaced by the guiding BV. Each of the five positions is checked to determine if a coding block containing the sample at the position is encoded / decoded using an IBC mode or an IntraTMP mode. These positions are denoted corresponding to the center of block (CT) 2720, left-top (LT) 2721, right-top (TR) 2722, left-bottom (LB) 2723, and right-bottom (RB) 2724. In some examples, because theDocket No.: 24-2036PCT size of the current block in both horizontal and vertical positions is an even number, the center position (CT) is selected as one of the four positions near the center point of the block. In the case that AR-BVP is used in IBC and a block containing a sample at a position of at least one of the five positions (CT, LT, RT, LB, and RB) defined relative to the first reference block was encoded / decoded using IntraTMP or IBC mode, the block vector used to indicate the reference block of the first reference block is used as the coding or reference BV to combine with the guiding BV.

[0321] FIG.27 further shows one example of multiple candidate AR BVPs iteratively derived from the initial guiding BV 2701. Guiding BV 2701 points to the first reference block (PU1). The five positions of the first reference block PU1 correspond to the guiding BV 2701 applied to the five respective positions (CT, LT, RT, LB, and RB) of current block 2706. Each of the five positions of the first reference block may be checked to determine if a block at any of those positions was coded in an IBC or IntraTMP mode. For example, a block at the position CT of the first reference block may be determined to be coded using BV- CT12704. Then, BV-CT12704 may be applied to the first reference block to determine a second reference block (reference PU2), from which five positions of the second reference block may be checked to derive one or more AR-BVPs. For example, the first AR-BVP candidate (BVP-AR1) 2705 may be derived as the addition of the guiding BV 2701 and the coding BV(BV-CT1) 2704 used for the encoding / decoding of the block containing / at position CT of the first reference block. The second AR-BVP candidate, BV-AR22707, may be derived as the addition of previous AR-BVP (BVP-AR12705) and a block vector BV-LT212706 derived from a block at LT position of the second reference block (reference PU2). For example, each of the five positions of the second reference block (reference PU2) may be checked to determine if a block containing the sample at those respective positions was encoded / decoded in an IBC mode. For example, the block at the LT position may satisfy the condition and was coded using BV-LT212706, which points to a third reference block (reference PU3).

[0322] This cascading process may be iterated multiple times and referred to as a number of hops. In some examples, the cascading process may be constrained to one hop. For example, BVP-AR12705 may be added as a candidate AR BVP derived from BVP-12701, but BVP-AR22707—which corresponds to a second hop—would not be determined and added as a second candidate AR BVP. A similar process may be performed to apply the AR-BVP technique to the TMP BV candidates.

[0323] In some embodiments, the generated AR-BVP candidates may be included in the AMVP and / or merge lists after the spatial adjacent candidates. In some embodiments, AR-BVP candidates may be included in the AMVP and / or merge lists after the spatial non-adjacent candidates. In some embodiments, AR-BVP candidates may be included in the AMVP and / or merge lists after the HMVP candidates.

[0324] As discussed above, the AR-BVP techniques use a BVP candidate in the IBC list or an IntraTMP list as the guiding BV. For example, the IBC list may include the BVs of previously reconstructed blocks coded with IBC, and the IntraTMP list may include BVs of previously reconstructed blocks coded withDocket No.: 24-2036PCT IntraTMP. Similarly, the BV of an IBC or IntraTMP coded block is used as the coding BV or reference BV. However, there may be previously reconstructed coding blocks coded with other intra coding modes, such as an IPM-based intra coding mode (e.g., DIMD-based mode or a TIMD-based mode). These other intra coding modes may also have a block vector associated therewith. For example, a block may be coded with a DIMD-based mode with a BV or a TIMD-based mode with a BV. Without considering these additional block vectors, the determined AR-BVP candidates may be incomplete and may be missing candidates that lead to more accurate predictions, thereby reducing the coding efficiency.

[0325] To solve this problem, the BVs of previously reconstructed blocks (with respect to a current block) other than IBC and IntraTMP modes can be taken into account in the AR-BVP process. Considering that the AR-BVP technique uses two distinct BVs, the guiding BV and the reference / coding BV, the additional BVs can be considered as a candidate for the guiding BV and / or the reference / coding BV. For example, in addition to the BV candidates in the IBC list and the IntraTMP list, the BVs of a block coded by an IPM- based intra coding mode (e.g., a DIMD-based mode or a TIMD-based mode) can be used as the guiding BV to derive AR BVP candidates.

[0326] Further, each of the five positions of the guiding reference block can be examined to determine if a block at any of those positions was coded using an IPM-based intra coding mode with BV (e.g., DIMD- based BV and TIMD-based BV) in addition to the IBC or IntraTMP mode. If so, the BV of such an IPM- based intra coding mode can be used as the reference / coding BV to generate AR BVP candidates. In this way, the AR-BVP reference block (the block pointed by the AR BVP candidate) can better match the current block and thus the coding efficiency of the AR-BVP technique will be improved.

[0327] These and other features of the present disclosure are described further below.

[0328] FIG.28A shows a flowchart 2800A of a method for constructing an intra block copy (IBC) merge / AMVP list for coding a current block, according to some embodiments. In some implementations, the merge / AMVP candidates can be built based on the spatial candidates of the current block. In particular, the candidates may include the 5 adjacent BVs from the adjacent blocks (e.g., as shown in FIG.15A) as shown in block 2805 and multiple (e.g., 20) non-adjacent BV candidates (e.g., as shown in numbered positions of diagram in FIG.21) from the non-adjacent neighboring blocks encoded using an IBC or TMP mode as shown in block 2806. In the example shown in FIG.28A, the candidates may further include HMVP candidates (block 2807) that were used to code the blocks in the current CTU or frame before the current block is coded.

[0329] In some examples, these BVP candidates (including BVP candidates from the adjacent blocks obtained at block 2805, BVP candidates from non-adjacent blocks obtained at block 2806, and HMVP candidates obtained at block 2807) are reordered and pruned to remove duplicate BVP candidates. In some examples, the BVP candidates are ranked in an ascending order based on the associated coding costs, and the best N candidates (candidates with the lowest coding costs) are selected to generate aDocket No.: 24-2036PCT merge list. In some implementations, the merge list can be ordered ascendingly according to the coding costs of the BVP candidates.

[0330] At block 2808, AR-BVP candidates are generated from the merge or AMVP list derived above. In some examples, each candidate in the merge list is used as a guiding BV to determine one or more AR- BVP candidates as described above with respect to FIG.27. At block 2809, a final list of BVP candidates (e.g., IBC merge list or IBC AMVP list) may be generated based on the BVP candidates obtained in blocks 2805-2808, such as by removing duplicate candidates, re-ordering the candidates based on the coding costs, and pruning the candidates to the target number, and so on.

[0331] FIG.28B shows an example of a method for constructing IntraTMP BVP candidates for coding a current block, according to some embodiments. As shown in FIG.28B, an initial merge list of BVP candidates 2818 corresponding to adjacent and non-adjacent merge BVP candidates are determined as shown at blocks 2815 and 2816 of FIG.28B. In some implementations, the initial merge list of BVP candidates has a pre-determined number of BVP candidates (e.g., 10). The initial merge list 2818 can be updated based on merge AR-BVP candidates built at 2820. The merge AR-BVPs can be generated by applying AR BVP to BVP candidates in the initial merge list 2818. The initial merge list 2818 can also be updated based on sparse AR-BVP candidates generated at 2822. The sparse AR-BVPs can be generated by applying AR-BVP to BVP candidates in the sparse list 2814. For example, the merge AR-BVP candidates, and the sparse AR-BVP candidates if available (as well as other AR-BVP candidates), can be added to the initial merge list. The resulting list of candidates can be processed at 2824, including reordering (e.g. based on the template matching costs) and pruning to remove duplicates and limit the number of BVP candidates in the merge list to the pre-determined number, to generate the merge list 2826. In some examples, the initial sparse list 2814 may be used to further update the merge list 2826. For example, the BVP candidates in the merge list can be evaluated against the initial sparse list 2814 to remove (at 2829) any redundant merge BVP candidates in the updated merge list. As a result, the updated merge list 2830 may have the same or fewer number of BVP candidates than the initial merge list 2818.

[0332] The updated merge list 2830 can be used in conjunction with the initial sparse list 2814 to generate, at 2832, the updated sparse list of BVP candidates 2834. In some examples, the sparse list of BVP candidates is selected from the initial sparse list and the updated merge list by selecting those BVP candidates having lower template matching costs than remaining candidates. In some implementations, the number of candidates in the sparse list is kept the same as the number of candidates in the initial sparse list.

[0333] In some examples, generating BVP candidates for IntraTMP may further include applying a refinement process (2835) to the BVP candidates in the updated sparse list 2834. The refinement process can involve a refinement window within which additional BVP candidates may be evaluated and generated. For example, for a BVP candidate to be refined, the coder (encoder or decoder) may determine aDocket No.: 24-2036PCT refinement search window associated with the BVP candidate. The refinement search window can be determined to be at the position pointed to by the BVP candidate from the left top sample of the current block. The size of the refinement search window can be determined according to the type of the BVP candidate. For example, the search window 2838 for an AR-BVP candidate (“yes” branch at 2837 and “yes” branch at 2836) can have a first size (e.g., 3x3); the search window 2842 for a BVP candidate from the initial sparse list (“no” branch at 2837) can have a second size (e.g., 5x5); and the search window 2840 for a BVP candidate from the initial merge list (“yes” branch at 2837 and “no” branch at 2836) has a third size (e.g., 11x11). In some examples, the first size, the second size, and the third size can be different, and the first size is smaller than the second size which is smaller than the third size. Additional BVP candidates may be generated according to a sampling interval in each search window and the BVP candidates having the lowest TMP costs can be included in the refined list of BVP candidates 2844.

[0334] FIG.29 shows an example of generating an AR-BVP candidate using a BV of an IPM-based intra coding mode as the reference / coding BV, according to some embodiments. In this example, the current block 2902 has a candidate BVP 2901 associated therewith and this candidate BVP can be used as the guiding BV to derive an AR-BVP candidate. The candidate BVP 2901 may be an adjacent spatial BVP, a non-adjacent spatial BVP, or an HMVP candidate used to code a previous block as discussed above with respect to FIGS.28A and 28B. In the example shown in FIG.29, the block from which the candidate BVP 2901 is derived may be coded with IBC, IntraTMP, or an IPM-based intra coding mode (e.g., DIMD-based mode or TIMD-based mode) with a BV. The reference BVP 2903 may be a BV of a block coded using an IPM-based intra coding mode (e.g., DIMD-based mode or TIMD-based mode) and the block contains the left top position (or another position of the five positions) of the guiding reference block 2904.

[0335] Combining (e.g., adding) the guiding BVP 2901 and the reference BVP 2903 leads to the AR-BVP 2905. The AR-BVP reference block 2906 pointed to by the AR-BVP 2905 may better match the current block 2902 than other reference blocks. In this way, the prediction of the current block 2902 using the AR- BVP reference block 2906 can be generated, and the prediction error can be reduced.

[0336] FIG.30 shows an example flowchart illustrating a process 3000 for intra coding a current block based on an AR-BVP candidate generated using a BV of an IPM-based intra coding mode as the reference BV, according to some embodiments. Operations of process 3000 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.

[0337] At 3002, process 3000 involves deriving an auto-relocated (AR) block vector prediction (BVP) candidate by applying AR BVP to a BVP candidate for a current block. The BVP candidate may be a candidate from a list of BVs generated for the current block. The list may include BVs of neighboring blocks, history BVs, and others. The neighboring block may be a neighboring block adjacent to the current block or a neighboring block that is non-adjacent to the current block. The history BVs may be used for other blocks coded before the current block (previously coded / reconstructed blocks) such as the HMVPDocket No.: 24-2036PCT candidates. The list of BVs may be used to generate the IBC merge / AMVP list as discussed above with respect to FIGS.28A-B. For IntraTMP, the list of BVs may include the BVs in the initial merge list and / or the BVs in the initial sparse list. In some examples, the list of BVs from which the BVP candidate is selected may further include a block vector of an IPM-based intra coding mode of a neighboring (adjacent or non-adjacent) block of the current block. For example, the list of candidates may further include a DIMD BV and / or a TIMD BV used in coding a block (e.g., a neighboring block or a history block) before the current block.

[0338] In some examples, deriving the AR BVP candidate includes determining a position in a guiding reference block based on the BVP candidate. For example, the encoder / decoder can determine the guiding reference block as the reference block pointed to by the BVP candidate. The position may be one of a set of positions defined relative to the position indicated by the BVP candidate. The set of positions can include a center position, a left top position, a left bottom position, a right top position, or a right bottom position of the reference block as described above with respect to FIG.29 and can be determined by applying the BVP candidate to the respective positions of the current block.

[0339] Deriving the AR BVP candidate can further include obtaining a reference / coding BV used by an IPM-based intra coding mode of a block (previously reconstructed / coded block) containing the position. For example, the block containing the position can be identified and evaluated to determine whether the block is coded by an intra coding mode with a BV. For example, the encoder / decoder can determine if the block is coded by a mode in an intra coding mode list that includes the IPM-based intra coding mode. If so, the coding BV of the block (BV used by the intra coding mode used to code the block) can be used as the reference / coding BV. The AR-BVP candidate can be derived by combining (e.g., adding) the reference / coding BV with the BVP candidate.

[0340] An IPM-based intra coding mode may be a mode that generates a prediction of the block by combining a first prediction based on an intra prediction mode (IPM) and a second prediction based on the a BV, such as a decoder-side intra mode derivation (DIMD)-based mode (DIMD, MIMD, DIMD Merge, OBIC) or a template based intra prediction (TIMD)-based mode (TIMD or TIMD merge). In some examples, the intra coding mode list may further include the Intra-TMP mode and / or the intra block copy (IBC) mode.

[0341] In some embodiments, each position of the five positions may be contained by a different coding block. Accordingly, up to the number of the set of positions of new AR-BVP candidates may be determined if each of the coding blocks is coded by a mode in the intra coding mode list.

[0342] In some embodiments, the AR-BVP technique may be iteratively applied a number of times (e.g., hops) to derive additional BVP candidates. For example, the coder (encoder or decoder) may further determine a second position in a second reference block based on a combination of the reference / coding BV with the BVP candidate and obtains a second coding BV used by an IPM-based intra coding mode of a second block containing the second position. The IPM-based intra coding mode of the second block mayDocket No.: 24-2036PCT be the same or different from the IPM-based intra coding mode of the first block discussed above. In this case, deriving the AR BVP candidate includes combining the second coding BV with the combination of the reference / coding BV and the BVP candidate.

[0343] For example, the coder can further derive a second AR-BVP candidate based on the first AR-BVP candidate. The coder can determine a second reference block based on a combination of the reference / coding BV with the BVP candidate (the first AR-BVP candidate) and obtains a second coding BV used by an IPM-based intra coding mode of a second block (previously reconstructed / coded block) containing a second position within the second reference block. The IPM-based intra coding mode of the second block may be the same or different from the IPM-based intra coding mode of the first block discussed above. The coder may further combine the second coding BV with the first AR-BVP candidate to generate the second AR-BVP candidate.

[0344] At 3004, process 3000 involves determining a list of BVP candidates based on the BVP candidate and the AR-BVP candidate. For example, the list of BVP candidates may be the IBC merge / AMVP list shown in FIG.28A. As discussed with respect to FIG.28A, the IBC merge / AMVP list may be generated based on the BVP candidates obtained from BVPs of adjacent and non-adjacent neighboring blocks, HMVP candidates, AR-BVPs generated above, and so on. These BVP candidates may be processed to generate the IBC merge / AMVP list, such as by removing duplicate candidates, re-ordering the candidates based on the coding costs, and pruning the candidates to the target number, and so on.

[0345] In examples of IntraTMP (e.g., FIG.28B), the list of BVP candidates may be the updated sparse list 2834. As discussed above in detail with respect to FIG.28B, the updated sparse list 2834 may be generated by selecting candidates from the initial sparse list and updated merge list 2830 (or merge list 2826). The merge list 2826 (or the updated merge list 2830) is determined based on the merge AR-BVPs (and sparse AR-BVPs). The merge AR-BVPs (or the sparse AR-BVPs) may include the AR-BVP candidate, and the initial merge list 2818 (or the initial sparse list 2814) may include the BVP candidate.

[0346] At 3006, process 3000 involves determining, based on the list of BVP candidates, a BV indicating a reference block for the current block. For example, in IntraTMP, the list of BVP candidates may be further processed (e.g., via the refinement process in FIG.28B) to determine a refined / updated list of BVP candidates from which the BV is selected. In other modes, such as IBC mode, the list of BVP candidates can be used to select the BV for the current block. For instance, at the encoder, the encoder may compute costs (e.g., RDO cost) for reference blocks indicated by corresponding BVP candidates in the list of BVP candidates to determine a BVP candidate associated with a lowest cost. Then, the encoder may signal an index in the bitstream to indicate that BVP candidate, in the list of BVP candidates, to be used as the BV. At the decoder, the decoder may decode from the bitstream an indication (e.g., index) of the BVP candidate in the list of BVP candidates and then identify the BVP from the list according to the indication. The identified BVP may be used as the BV to obtain a reference block for reconstructing the current block.Docket No.: 24-2036PCT

[0347] At 3008, process 3000 involves coding the current block based on the reference block. In some embodiments, at the encoder, the current block may be encoded by subtracting the reference block corresponding to the determined BV from the current block to determine a residual (e.g., residual block). The residual may be encoded and signaled in the bitstream. At the decoder, the decoder may determine a predicted block for the current block by determining the reference block identified by the BV. The current block may be reconstructed (e.g., decoded) based on a residual (e.g., residual block) obtained from a bitstream and the predicted block (e.g., reference block). For example, the current block may be determined by adding the residual to the reference block identified by the BV.

[0348] In inter prediction, the chained motion vector prediction (CMVP) is introduced as an inter merge candidate list construction. CMVP candidates can be derived as the accumulation of the recursively traced motion vectors (MVs) and block vectors (BVs) based on the pre-derived MVs. FIG.31 shows an example of chained motion vector prediction (CMVP), according to some embodiments. As shown in FIG.31, when deriving a CMVP motion vector, five positions, including the center (CT), top-left (LT), top-right (RT), bottom-left (LB), and bottom-right (RB) of the reference block (corresponding to respective positions of the current block), are checked to find traced MVs or BVs.

[0349] For instance, for a current block 3106 of a current picture 3130, a guiding motion vector 3101 is applied to one of the five positions (the CT position in this example) to identify a guiding reference block 3102 in a reference picture 3131. Each of the five positions in the guiding reference block 3102 that correspond to five respective positions in the current block are evaluated to determine reference BVPs (also referred to as coding BVPs). For example, a position in the guiding reference block 3102 can be examined to determine whether a coding block (previously reconstructed block) containing the position is coded with IBC or IntraTMP. If so, the BV of the coding block can be used as a reference BV 3103 (coding BV). The reference BV 3103 can be combined with (added to) the guiding motion vector 3101 to generate a CMVP motion vector 3105 which points to a CMVP reference block 3106. The generated CMVP motion vector (along with the information of the reference picture 3131) can be added to a list of candidate MVs for the current block from which a MV is selected (e.g., based on a prediction error / cost) to inter code the current block.

[0350] In some examples, CMVP candidates are derived for each MV in a MV merge list, each reference picture list (i.e., L0 and L1), and each trace depth, and are inserted after HMVP candidates. In some implementations, the number of traced depths to derive CMVPs is restricted to one. The traceable reference pictures are only within the reference picture list.

[0351] Similar to the AR-BVP, the CMVP techniques use a BV in the IBC mode or an IntraTMP mode as the reference BV and do not consider other types of reconstructed coding blocks coded with other intra coding modes that may have a block vector, such as an IPM-based intra coding mode. WithoutDocket No.: 24-2036PCT considering these additional block vectors, the determined CMVP candidates may be incomplete and may be missing candidates that lead to more accurate predictions, thereby reducing the coding efficiency.

[0352] To improve the coding efficiency, the BVs of previously reconstructed blocks of the current blocks other than IBC and IntraTMP modes can be taken into account in the CMVP process. For example, each of the five positions of the guiding reference block can be examined to determine if a block at any of those positions was coded in an IBC or IntraTMP mode as well as other intra coding modes with a BV such as an IPM-based intra coding mode with BV. In this way, the CMVP reference block (the block pointed by the CMVP candidate) can better match the current block and thus the coding efficiency of the CMVP technique will be improved.

[0353] For instance, in the example shown in FIG.31, the coder (encoder or decoder) can determine whether the coding block containing the center position CT is coded with an intra coding mode with a BV, including IBC, IntraTMP, or an IPM-based intra coding mode with a BV (e.g., DIMD BV or TIMD BV). If so, the coder can use the BV of the coding block as the reference BV 3103 to generate the CMVP MV 3105. A similar process can be applied to other positions of the guiding reference block 3102 to determine additional CMVP candidates.

[0354] FIG.32 shows an example flowchart illustrating a process 3200 for coding a current block based on a vector candidate generated using a BV of an IPM-based intra coding mode as the reference BV, according to some embodiments. Operations of process 3200 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.

[0355] At 3202, process 3200 involves deriving a vector candidate for a current block. Deriving the vector candidate may include determining a position in a guiding reference block based on a guiding vector candidate, obtaining a coding vector used by an IPM-based intra coding mode of a block containing the position, and deriving the vector candidate based on the coding vector and the guiding vector candidate.

[0356] For an intra coded current block, the vector candidate may be an AR-BVP candidate, and the guiding vector candidate may be a BVP candidate for the current block. Deriving the vector candidate may be performed via AR BVP. The BVP candidate may be a candidate from a list of BVs generated for the current block as discussed above with respect to FIG.30. In the example of deriving AR BVP candidate, determining a position in a guiding reference block based on a guiding vector candidate may include determining a position in a guiding reference block based on the BVP candidate as discussed above with respect to FIG.30. Obtaining a coding vector used by an IPM-based intra coding mode of a block containing the position can include obtaining a coding BV used by an IPM-based intra coding mode of a block (previously reconstructed / coded block) containing the position as discussed above with respect to FIG.30. Deriving the vector candidate based on the coding vector and the guiding vector candidate can include deriving the AR-BVP candidate based on the coding BV and the BVP candidate as discussed above with respect to FIG.30.Docket No.: 24-2036PCT

[0357] For an inter-coded current block, the vector candidate may be a chained motion vector prediction (CMVP) candidate and the guiding vector candidate may be a motion vector candidate for the current block. The motion vector candidate may be selected from a merge list of MV candidates for the current block. Deriving the vector candidate may be performed via CMVP as discussed above with respect to FIG. 31. In this example, the guiding vector candidate may be obtained from a reference picture of a current picture containing the current block. The reference picture may be selected from a list of reference pictures for the current picture. The vector candidate points to one reference picture in the list of reference pictures.

[0358] In some examples, obtaining the coding vector can include determining the block containing the position, determining that the block is coded via an intra coding mode in an intra coding mode list comprising an IPM-based intra coding mode, and determining a coding BV of the block as the coding vector. The IPM-based intra coding mode may be a mode that generates a prediction of the block by combining a first prediction based on an intra prediction mode (IPM) and a second prediction based on the coding BV, such as a decoder-side intra mode derivation (DIMD)-based mode (DIMD, MIMD, DIMD Merge, OBIC) or a template based intra prediction (TIMD)-based mode (TIMD or TIMD merge). In some examples, the intra coding mode list may further include the Intra-TMP mode and / or the intra block copy (IBC) mode.

[0359] The position in the guiding reference block may be one of a center position, a left top position, a left bottom position, a right top position, or a right bottom position and the position is with respect to the guiding reference block. In some embodiments, each position of the five positions may be contained by a different coding block. Accordingly, up to the number of the set of positions of new vector candidates may be determined if each of the coding blocks is coded by a mode in the intra coding mode list.

[0360] In some embodiments, the above vector candidate derivation process may be iteratively applied a number of times (e.g., hops) to derive additional vector candidates. For example, the coder (encoder or decoder) may further determine a second position in a second reference block based on a combination of the coding vector with the guiding vector candidate and obtains a second coding vector used by an IPM- based intra coding mode of a second block containing the second position. The IPM-based intra coding mode of the second block may be the same or different from the IPM-based intra coding mode of the first block discussed above. In this case, deriving the vector candidate includes combining the second coding vector with the combination of the coding vector and the guiding vector candidate.

[0361] For example, the coder can further derive a second vector candidate based on the first vector candidate. The coder can determine a second reference block based on a combination of the coding vector with the guiding vector candidate (the first vector candidate) and obtains a second coding vector used by an IPM-based intra coding mode of a second block (previously reconstructed / coded block) containing a second position within the second reference block. The IPM-based intra coding mode of the second block may be the same or different from the IPM-based intra coding mode of the first block discussed above. The coder may further combine the second coding vector with the combination of the coding vector with theDocket No.: 24-2036PCT guiding vector candidate (the first vector candidate) to generate the second vector candidate. The second coding vector may be a BV or a MV depending on the coding mode of the current block.

[0362] At 3204, process 3200 involves determining a list of vector candidates based on the guiding vector candidate and the vector candidate. For example, for intra-coded current block, the list of guiding vector candidates can be a list of BVP candidates in the IBC merge / AMVP list shown in FIG.28A or the updated sparse list 2834 for IntraTMP (e.g., FIG.28B). For inter-coded current block, the list of vector candidates may be generated by adding the generated CMVP candidates to the MV merge list.

[0363] At 3206, process 3200 involves determining, based on the list of vector candidates, a vector indicating a reference block for the current block. For intra-coded current block, the vector may be a block vector used in the intra coding as discussed above with respect to block 3006 of FIG.30. For an inter- coded current block, the vector may be a motion vector used to identify a reference block in the reference picture for coding the current block via inter prediction.

[0364] At 3208, process 3200 involves coding the current block based on the reference block. In some embodiments, at the encoder, the current block may be encoded by subtracting the reference block corresponding to the determined vector from the current block to determine a residual (e.g., residual block). The residual may be encoded and signaled in the bitstream. At the decoder, the decoder may determine a predicted block for the current block by determining the reference block identified by the vector. The current block may be reconstructed (e.g., decoded) based on a residual (e.g., residual block) obtained from a bitstream and the predicted block (e.g., reference block). For example, the current block may be determined by adding the residual to the reference block identified by the vector.

[0365] As discussed above, considering the BVs of IPM-based intra coding modes in AR-BVP and CMVP can increase the coding efficiencies of these tools because adding the BVs of IPM-based intra coding modes as additional guiding BV and / or additional reference BVs can increase the likelihood of finding a better matching reference block, thereby reducing the prediction cost / error. Likewise, the BVs of IPM- based intra coding modes can also be considered in other video coding tools to further increase the coding efficiencies of those tools. For example, the IBC coding mode can be improved by considering BVs of IPM- based intra coding modes when building the IBC merge / AMVP list. In this way, more BVP candidates may be considered to generate the IBC merge / AMVP list which leads to BVPs having smaller prediction errors to be included in the list and be used to generate the prediction. As a result, the prediction residual becomes smaller and requires fewer bits to encode.

[0366] FIG. 33 shows an example of a flowchart 3300 for constructing an intra block copy (IBC) merge / AMVP list by considering IPM-based intra coding block vectors (BVs) for coding a current block, according to some embodiments. FIG.33 is similar to FIG.28A except that in each block of FIG.33, the neighboring or history blocks with an IPM-based intra coding BV are also added as BVP candidates for generating the IBC merge / AMVP list.Docket No.: 24-2036PCT

[0367] For example, when considering the spatial candidates of the current block (3305 and 3306), the BVs of adjacent blocks and non-adjacent blocks can include IPM-based intra coding BVs. In other words, in addition to neighboring blocks that are coded using an IBC or TMP mode, neighboring blocks (adjacent and non-adjacent)) coded with an IPM-based intra coding mode having a BV are also considered and included in the adjacent BVP candidates and / or non-adjacent BVP candidates. Likewise, the HMVP candidates that were used to code the blocks in the current CTU or frame before the current block is coded can also include BVs of IPM-based intra coding modes if the history blocks are coded with an IPM-based intra coding mode.

[0368] These BVP candidates (including BVP candidates from the adjacent blocks obtained at block 3305, BVP candidates from non-adjacent blocks obtained at block 3306, and HMVP candidates obtained at block 3307, each type of candidates may include IPM-based coding mode BVs) may reordered and pruned to remove duplicate BVP candidates.

[0369] At 3308, AR-BVP candidates are generated from the merge / AMVP list derived above. The AR- BVP candidates may be generated by including IPM-based intra coding BVs (as guiding BVs and / or reference BVs) as discussed above with respect to FIGS.29-30. In other examples, the AR-BVP candidates may be generated without including IPM-based intra coding BVs (e.g., not using IPM-based coding BVs as guiding BVs and / or reference BVs) as discussed above with respect to FIG.28A. The final list of BVP candidates (e.g., IBC merge list or IBC AMVP list) may be generated at 3309 based on the BVP candidates obtained in blocks 3305-3308, such as by removing duplicate candidates, re-ordering the candidates based on the coding costs, and pruning the candidates to the target number, and so on.

[0370] While FIG.33 shows that IPM-based coding mode BVs are considered in each operation of 3305- 3307, some operations can be performed without considering the IPM-based coding mode BVs. For example, the IPM-based coding mode BVs may be considered when generating the adjacent spatial BVP, when generating the non-adjacent spatial BVP, when generating the HMVP candidates, or any combination thereof.

[0371] FIG.34 shows an example flowchart illustrating a process 3400 for coding a current block using IBC merge / AMVP list generated by including BVs of IPM-based intra coding modes, according to some embodiments. Operations of process 3400 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.

[0372] At 3402, process 3400 involves obtaining a candidate block vector (BV) used by an IPM-based intra coding mode coding a previously reconstructed block of a current block. The IPM-based intra coding mode generates a prediction of the block by combining a first prediction based on an IPM and a second prediction based on the candidate BV. The IPM-based intra coding mode may be a decoder-side intra mode derivation (DIMD)-based mode or a template based intra prediction (TIMD)-based mode. The previously reconstructed block may be a neighboring block of the current block. The neighboring blockDocket No.: 24-2036PCT may be adjacent to the current block and thus the candidate BV may be an adjacent spatial BVP. The neighboring block may be a non-adjusted to the current block and thus the candidate BV may be a non- adjacent spatial BVP. The previously reconstructed block may also be a history block and the candidate BV may be a history-based motion vector prediction (HMVP) candidate. The current block is coded using an intra block copy (IBC) mode.

[0373] At 3404, process 3400 involves generating, for the current block, a list of block vector (BV) candidates including the candidate BV. The list of BV candidates may be the IBC merge / AMVP list and generating the list of BV candidates may be performed as discussed above with respect to FIG.33. As such, the list of BV candidates may further include a candidate BV of a neighboring block of the current block coded in IBC or IntraTMP. At 3406, process 3400 involves determining, based on the list of BV candidates, a BV indicating a reference block for the current block. The BV that has the smallest matching cost in the list of BV candidates may be selected as the BV.

[0374] At 3408, process 3400 involves coding the current block based on the reference block. In some embodiments, at the encoder, the current block may be encoded by subtracting the reference block corresponding to the determined BV from the current block to determine a residual (e.g., residual block). The residual may be encoded and signaled in the bitstream. At the decoder, the decoder may determine a predicted block for the current block by determining the reference block identified by the BV. The current block may be reconstructed (e.g., decoded) based on a residual (e.g., residual block) obtained from a bitstream and the predicted block (e.g., reference block). For example, the current block may be determined by adding the residual to the reference block identified by the vector.

[0375] Embodiments of the present disclosure may be implemented in hardware using analog and / or digital circuits, in software, through the execution of instructions by one or more general purpose or special-purpose processors, or as a combination of hardware and software. Consequently, embodiments of the disclosure may be implemented in the environment of a computer system or other processing system. An example of such a computer system 3500 is shown in FIG.35. Blocks depicted in the figures above, such as the blocks in FIGS.1, 2, and 3, may execute on one or more computer systems 3500. Furthermore, each of the steps of the flowcharts depicted in this disclosure may be implemented on one or more computer systems 3500.

[0376] Computer system 3500 includes one or more processors, such as processor 3504. Processor 3504 may be, for example, a special purpose processor, general purpose processor, microprocessor, or digital signal processor. Processor 3504 may be connected to a communication infrastructure 3502 (for example, a bus or network). Computer system 3500 may also include a main memory 3506, such as random-access memory (RAM), and may also include a secondary memory 3508.

[0377] Secondary memory 3508 may include, for example, a hard disk drive 3510 and / or a removable storage drive 3512, representing a magnetic tape drive, an optical disk drive, or the like. RemovableDocket No.: 24-2036PCT storage drive 3512 may read from and / or write to a removable storage unit 3516 in a well-known manner. Removable storage unit 3516 represents a magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive 3512. As will be appreciated by persons skilled in the relevant art(s), removable storage unit 3516 includes a computer usable storage medium having stored therein computer software and / or data.

[0378] In alternative implementations, secondary memory 3508 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 3500. Such means may include, for example, a removable storage unit 3518 and an interface 3514. Examples of such means may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a thumb drive and USB port, and other removable storage units 3518 and interfaces 3514 which allow software and data to be transferred from removable storage unit 3518 to computer system 3500.

[0379] Computer system 3500 may also include a communications interface 3520. Communications interface 3520 allows software and data to be transferred between computer system 3500 and external devices. Examples of communications interface 3520 may include a modem, a network interface (such as an Ethernet card), a communications port, etc... Software and data transferred via communications interface 3520 are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface 3520. These signals are provided to communications interface 3520 via a communications path 3522. Communications path 3522 carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link, and other communications channels.

[0380] As used herein, the terms “computer program medium” and “computer readable medium” are used to refer to tangible storage media, such as removable storage units 3516 and 3518 or a hard disk installed in hard disk drive 3510. These computer program products are means for providing software to computer system 3500. Computer programs (also called computer control logic) may be stored in main memory 3506 and / or secondary memory 3508. Computer programs may also be received via communications interface 3520. Such computer programs, when executed, enable the computer system 3500 to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor 3504 to implement the processes of the present disclosure, such as any of the methods described herein. Accordingly, such computer programs represent controllers of the computer system 3500.

[0381] In another embodiment, features of the disclosure may be implemented in hardware using, for example, hardware components such as application-specific integrated circuits (ASICs) and gate arrays. Implementation of a hardware state machine to perform the functions described herein will also be apparent to persons skilled in the art.

Claims

Docket No.: 24-2036PCT CLAIMS 1. A method comprising: deriving an auto-relocated (AR) block vector prediction (BVP) candidate by applying AR BVP to a BVP candidate for a current block, the deriving comprising: determining a position in a guiding reference block based on the BVP candidate; obtaining a coding BV used by an intra-prediction-mode (IPM)-based intra coding mode of a block containing the position; and deriving the AR-BVP candidate based on the coding BV and the BVP candidate; determining a list of BVP candidates based on the BVP candidate and the AR-BVP candidate; processing the list of BVP candidates to generate a second list BVP candidates; selecting, from the second list of BVP candidates, a block vector (BV) indicating a reference block for the current block; and coding the current block based on the reference block.

2. A method comprising: deriving an auto-relocated (AR) block vector prediction (BVP) candidate by applying AR BVP to a BVP candidate for a current block, the deriving comprising: determining a position in a guiding reference block based on the BVP candidate; obtaining a coding BV used by an intra-prediction-mode (IPM)-based intra coding mode of a block containing the position; and deriving the AR-BVP candidate based on the coding BV and the BVP candidate; determining a list of BVP candidates based on the BVP candidate and the AR-BVP candidate; determining, based on the list of BVP candidates, a block vector (BV) indicating a reference block for the current block; and coding the current block based on the reference block.

3. The method of any one of claims 1-2, wherein the BVP candidate is obtained from a neighboring block of the block.

4. The method of claim 3, wherein the neighboring block is adjacent to the block.

5. The method of claim 3, wherein the neighboring block is non-adjacent to the block.

6. The method of any one of claims 1-5, wherein the BVP candidate is a BV used for another block coded before the block.

7. The method of any one of claims 1-6, wherein the BVP candidate is obtained by sampling a search region according to a sampling interval and based on a template matching cost between a current template of the block and a reference template at the sampled location in the search region.Docket No.: 24-2036PCT 8. The method of any one of claims 1-7, wherein the BVP candidate is selected from a list of block vectors comprising a block vector of an IPM-based intra coding mode of a neighboring block of the current block.

9. The method of any one of claims 1-8, wherein the obtaining the coding BV comprises: determining the block containing the position; determining that the block is coded via an intra coding mode in an intra coding mode list comprising the IPM-based intra coding mode; and determining a coding BV of the block as the coding BV.

10. The method of claim 9, wherein the intra coding mode list further comprises an Intra-TMP mode or an intra block copy (IBC) mode.

11. The method of any one of claims 1-10, wherein the position is one of a center position, a left top position, a left bottom position, a right top position, or a right bottom position.

12. The method of claim 11, wherein the position is with respect to the guiding reference block.

13. The method of any one of claims 1-12, wherein the IPM-based intra coding mode generates a prediction of the block by combining a first prediction based on an IPM and a second prediction based on the coding BV.

14. The method of any one of claims 1-13, wherein the IPM-based intra coding mode is a decoder-side intra mode derivation (DIMD)-based mode or a template based intra prediction (TIMD)-based mode.

15. The method of any one of claims 1-14, wherein the determining the list of BVP candidates comprises generating the list of BVP candidates based on a second list of BVP candidates comprising the BVP candidate and the AR-BVP candidate.

16. The method of claim 15, wherein the determining, based on the list of BVP candidates, a BV comprises selecting the BV from a third list of BVP candidates generated by processing the list of BVP candidates.

17. The method of claim 16, wherein the processing the list of BVP candidates comprises refining a BVP candidate in the list of BVP candidates by searching for a refined BVP candidate, to be included in the third list of BVP candidates, in a search window surrounding the BVP candidate.

18. The method of any one of claims 1-17, wherein the deriving the AR-BVP candidate further comprises: determining a second position in a second reference block based on a combination of the coding BV with the BVP candidate; and obtaining a second coding BV used by an IPM-based intra coding mode of a second block containing the second position; and wherein the deriving the AR BVP candidate comprises combining the second coding BV with the combination of the coding BV and the BVP candidate.

19. The method of any one of claims 1-18, further comprising deriving a second AR-BVP candidate.Docket No.: 24-2036PCT 20. The method of claim 19, wherein the deriving the second AR-BVP candidate comprises: determining a second reference block based on a combination of the coding BV with the BVP candidate; obtaining a second coding BV used by an IPM-based intra coding mode of a second block containing a second position within the second reference block; and combining the second coding BV with the combination of the coding BV with the BVP candidate to generate the second AR-BVP candidate.

21. The method of claim 20, wherein the list of BVP candidates is further determined based on the second AR-BVP candidate.

22. A method comprising: deriving a vector candidate for a current block, the deriving comprising: determining a position in a guiding reference block based on a guiding vector candidate; obtaining a coding vector used by an IPM-based intra coding mode of a block containing the position; and deriving the vector candidate based on the coding vector and the guiding vector candidate; determining a list of vector candidates based on the guiding vector candidate and the derived vector candidate; determining, based on the list of vector candidates, a vector indicating a reference block for the current block; and coding the current block based on the reference block.

23. The method of claim 22, wherein the vector candidate is an auto-relocated (AR) block vector prediction (BVP) candidate and the guiding vector candidate is a BVP candidate for the current block.

24. The method of claim 23, wherein the deriving the vector candidate is performed via AR BVP.

25. The method of any one of claims 22-24, wherein the vector candidate is a chained motion vector prediction (CMVP) candidate and the guiding vector candidate is a motion vector candidate for the current block.

26. The method of claim 25, wherein the deriving the vector candidate is performed via CMVP.

27. The method of claim 26, wherein the guiding vector candidate is obtained from a reference picture of a current picture containing the current block.

28. The method of claim 27, wherein the reference picture is selected from a list of reference pictures for the current picture.

29. The method of claim 28, wherein the vector candidate points to one reference picture in the list of reference pictures.

30. The method of any one of claims 22-29, wherein the obtaining the coding vector comprises: determining the block containing the position;Docket No.: 24-2036PCT determining that the block is coded via an intra coding mode in an intra coding mode list comprising an IPM-based intra coding mode; and determining a coding BV of the block as the coding vector.

31. The method of claim 30, wherein the intra coding mode list further comprises an Intra-TMP mode or an intra block copy (IBC) mode.

32. The method of any one of claims 22-31 wherein the position is one of a center position, a left top position, a left bottom position, a right top position, or a right bottom position.

33. The method of claim 32, wherein the position is with respect to the guiding reference block.

34. The method of any one of claims 22-33, wherein the IPM-based intra coding mode generates a prediction of the block by combining a first prediction based on an IPM and a second prediction based on the coding vector.

35. The method of any one of claims 22-34, wherein the IPM-based intra coding mode is a decoder-side intra mode derivation (DIMD)-based mode or a template based intra prediction (TIMD)-based mode.

36. The method of any one of claims 22-35, wherein the deriving the vector candidate further comprises: determining a second position in a second reference block based on a combination of the coding vector with the guiding vector candidate; and obtaining a second coding vector used by an IPM-based intra coding mode of a second block containing the second position; and wherein the deriving the vector candidate comprises combining the second coding vector with the combination of the coding vector with the guiding vector candidate.

37. The method of claim 36, wherein the second coding vector is a BV or a MV.

38. A method comprising: obtaining a candidate block vector (BV) used by an intra-prediction-mode (IPM)-based intra coding mode coding a previously reconstructed block with respect to a current block, the current block being coded using an intra block copy (IBC) mode; generating, for the current block, a list of BV candidates including the candidate BV; determining, based on the list of BV candidates, a BV indicating a reference block for the current block; and coding the current block based on the reference block.

39. The method of claim 38, wherein the previously reconstructed block is a neighboring block of the current block.

40. The method of claim 39, wherein the neighboring block is adjacent to the current block.

41. The method of claim 39, wherein the neighboring block is not adjacent to the current block.

42. The method of any one of claims 38-41, wherein the candidate BV is a history-based motion vector prediction (HMVP) candidate.Docket No.: 24-2036PCT 43. The method of any one of claims 38-42, wherein the list of BV candidates further comprises a candidate BV of a neighboring block of the current block coded in IBC.

44. The method of any one of claims 38-43, wherein the IPM-based intra coding mode generates a prediction of the current block by combining a first prediction based on an IPM and a second prediction based on the candidate BV.

45. The method of any one of claims 38-44, wherein the IPM-based intra coding mode is a decoder-side intra mode derivation (DIMD)-based mode or a template based intra prediction (TIMD)-based mode.

46. The method of any one of claims 1-45, further comprising: determining a residual based on the reference block and the current block, wherein the coding the current block based on the reference block comprises encoding the residual in a bitstream.

47. The method of any one of claims 1-45, further comprising: decoding, from a bitstream, a residual of the current block, wherein the coding the current block based on the reference block comprises reconstructing the current block based on the reference block and the residual.

48. 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 1-47.

49. 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 claim 1-46.

50. A non-transitory computer-readable recording medium storing a bitstream generated by the method for encoding a video according to any one of claims 1-46.

51. 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 1-45 and 47.

52. 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 1-45 and 47.

53. A bitstream generated according to any one of claims 1-46.

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