Intra prediction mode (IPM) selection with adaptive templates

Abstract

A coder (e.g., encoder or a decoder) calculates a cumulative sum of amplitudes in a first histogram of gradients (HoG) of samples in a first template of a current block and a cumulative sum of amplitudes in a second HoG of samples in a second template of the current block. The coder adaptively extends: the first template in a first direction while the cumulative sum of amplitudes in the first HoG of eligible samples of the adaptively extended first template is less than a first threshold, and the second template in a second direction while the cumulative sum of amplitudes in the second HoG of eligible samples of the adaptively extended second template is less than a second threshold. The coder determines, for coding the current block, at least one intra prediction mode (IPM) in accordance with at least the first histogram of gradients and the second histogram of gradients.

Description

Docket No.: 24-2065PCTTITLEIntra Prediction Mode (IPM) Selection with Adaptive TemplatesCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U. S. Provisional Application No. 63 / 740,919, filed December 31, 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 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).

[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 embodimentsDocket No.: 24-2065PCT

[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, 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 I PM information from a plurality of (previously reconstructed) neighboring blocks of a current block, according to some embodiments.

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

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

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

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

[0034] FIG. 25 shows an example flowchart of an intra merge mode, 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 the most dominant intra prediction (MDIP) mode.

[0037] FIG. 28A, FIG. 28B and FIG.28C illustrate examples of adaptively extended templates of a current block, in accordance with some embodiments.

[0038] FIG. 29 illustrates an example of a template adaptively extended in accordance with some embodiments.

[0039] FIG. 30A illustrates an example of incorporating the top-left template in the left template, according to some embodiments.

[0040] FIG. 30B illustrates an example of incorporating the top-left template in the top template, according to some embodiments.

[0041] FIG. 30C illustrates an example in which the top-left template is incorporated into the shorter left template, according to some embodiments.Docket No.: 24-2065PCT

[0042] FIG. 31 illustrates a flowchart for combining luma HoG with chroma HoG for generating improved chroma HoG, according to some embodiments.

[0043] FIG. 32 illustrates an example flowchart of a process for generating one or more IPM for a current block by adaptively extending one or more templates used for HoG generation while excluding regions of samples in the template from inclusion in the HoG, according to some embodiments.

[0044] FIG. 33 illustrates an example flowchart of another example process for generating one or more IPM for a current block by adaptively extending two templates used for HoG generation while excluding regions of samples in the template from inclusion in the HoG, according to some embodiments.

[0045] FIG. 34 illustrates an example flowchart of an example process for generating one or more IPM for a current block by adaptively extending a top template and a left template used for HoG generation while including the top-left template in either the top or left template, according to some embodiments.

[0046] FIG. 35 illustrates an example flowchart of an example process for generating one or more IPM for a current block by adaptively extending a template comprising chroma samples and a corresponding template comprising luma samples used for HoG generation, according to some embodiments.

[0047] FIG. 36 illustrates a block diagram of an example computer system in which embodiments of the present disclosure may be implemented.DETAILED DESCRIPTION

[0048] 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.

[0049] 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.

[0050] 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, aDocket No.: 24-2065PCTsubroutine, 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] FIG. 1 shows an example video coding / decoding system 100 in which embodiments of the present disclosure may be implemented. Video coding / decoding system 100 comprises a source device 102, a transmission medium 104, and a destination device 106. Source device 102 encodes a video sequence 108 into a bitstream 110 for more efficient storage and / or transmission. Source device 102 may store and / or send / transmit bitstream 110 to destination device 106 via transmission medium 104. Destination device 106 decodes bitstream 110 to display video sequence 108. Destination device 106 may receive bitstream 110 from source device 102 via transmission medium 104. Source device 102 and / or destination device 106 may be any of a plurality of different devices (e.g., a desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, video streaming device, etc.).

[0055] 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 generateDocket No.: 24-2065PCTvideo sequence 108 based on a capture of a natural scene and / or a synthetically generated scene. A synthetically generated scene may be a scene comprising computer generated graphics and / or screen content. Video source 112 may comprise a video capture device (e.g., a video camera), a video archive comprising previously captured natural scenes and / or synthetically generated scenes, a video feed interface to receive captured natural scenes and / or synthetically generated scenes from a video content provider, and / or a processor to generate synthetic scenes.

[0056] 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.

[0057] Encoder 114 may encode video sequence 108 into bitstream 110. Encoder 114 may apply / use (e.g., to encode video sequence 108) one or more prediction techniques to reduce redundant information in video sequence 108. Redundant information is information that may be predicted at a decoder and need not be transmitted to the decoder for accurate decoding of video sequence 108. For example, encoder 114 may apply spatial prediction (e.g., intra-frame or intra prediction), temporal prediction (e.g., inter-frame prediction or inter prediction), inter-layer prediction, and / or other prediction techniques to reduce redundant information in video sequence 108. Encoder 114 may partition pictures comprising video sequence 108 into rectangular regions referred to as blocks, for example, before applying one or more prediction techniques. Encoder 114 may then encode a block using the one or more of the prediction techniques.

[0058] 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 differenceDocket No.: 24-2065PCTbetween 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.

[0059] 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.

[0060] 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).

[0061] 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.

[0062] 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).

[0063] Decoder 120 may decode video sequence 108 from encoded bitstream 110. The decoder 120 may generate prediction blocks for pictures of video sequence 108 in a similar manner as encoder 114 and determine the prediction errors for the blocks, for example, to decode video sequence 108 Decoder 120 may generate the prediction blocks using / based on prediction types, prediction modes, and / or motion vectors received in bitstream 110. Decoder 120 mayDocket No.: 24-2065PCTdetermine the prediction errors using the transform coefficients received in bitstream 110. Decoder 120 may determine the prediction errors by weighting transform basis functions using the transform coefficients. Decoder 120 may combine the prediction blocks and the prediction errors to decode video sequence 108. Video sequence 108 at the destination device 106 may be, or may not necessarily be, the same video sequence sent, such as video sequence 108 as sent by the source device 102. Decoder 120 may decode a video sequence that approximates video sequence 108, for example, because of lossy compression of video sequence 108 by encoder 114 and / or errors introduced into encoded bitstream 110 during transmission to destination device 106.

[0064] 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.

[0065] Video coding / decoding system 100 is merely an example and video encoding / decoding systems different from the video coding / decoding system 100 and / or modified versions of the video coding / decoding system 100 may similarly perform the methods and processes as described herein. For example, the video coding / decoding system 100 may comprise other components and / or arrangements. For example, video source 112 may be external to source device 102. Similarly, video display 122 may be external to destination device 106 or omitted altogether (e.g., if video sequence 108 is intended for consumption by a machine and / or storage device). In an example, source device 102 may further comprise a video decoder and destination device 106 may further comprise a video encoder. For example, source device 102 may be configured to further receive an encoded bitstream from destination device 106 to support two-way video transmission between the devices.

[0066] 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 (WC)), the WebM VP8 and VP9 codecs, and / or AOMedia Video 1 (AV1 ), and / or any other video coding protocol).

[0067] 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, smartphone, 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.Docket No.: 24-2065PCT

[0068] 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.

[0069] Intra prediction unit 208 may perform intra prediction by forming a prediction block based on data from reconstructed neighboring samples of the block to be encoded within the same picture of video sequence 202. A reconstructed sample refers to a sample that was encoded and then decoded. Intra prediction unit 208 may exploit spatial redundancy or similarities in scene content within a picture of video sequence 202 to determine the prediction block. For example, the texture of a region of scene content in a picture may be similar to the texture in the immediate surrounding area of the region of the scene content in the same picture.

[0070] 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.

[0071] 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).

[0072] 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.

[0073] 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, constrainedDocket No.: 24-2065PCTdirectional 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.

[0074] 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, WC, VP8, VP9, AV1, and / or any other video coding standard / format.

[0075] 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.

[0076] 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 (nonbinary) 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

[0077] 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).

[0078] 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 / orDocket No.: 24-2065PCTsome 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.

[0079] Decoder 300 may comprise a decoder control unit configured to control one or more units of decoder 300. The decoder control unit may control the one or more units of decoder 300 such that bitstream 302 is decoded in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other communication protocol. For example, the decoder control unit may control the one or more units of decoder 300 such that the bitstream 302 is decoded in conformance with one or more of ITU-T H.263, AVC, HEVC, WC, VP8, VP9, AV1, and / or any other video coding standard / format.

[0080] 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.

[0081] Entropy decoding unit 306 may entropy decode the bitstream 302. For example, entropy decoding unit 306 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and syntax-based context-based binary arithmetic coding (SBAC) to decompress the prediction type used to encode a block (intra or inter prediction), prediction information of the block (intra prediction mode if intra predicted, motion vector, etc.), and transform and quantization parameters. Inverse transform and quantization unit 308 may inverse quantize and / or inverse transform the quantized transform coefficients to determine a decoded prediction error. Combiner 310 may combine the decoded prediction error with a prediction block to form a decoded block. The prediction block maybe 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.

[0082] 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 (eg., entropy decoding unit 306 and / or filters(s) 312).Docket No.: 24-2065PCT

[0083] Although not shown in FIGS.2 and 3, each of encoder 200 and decoder 300 may further comprise an intra block copy unit in addition to inter prediction and intra prediction units. The intra block copy unit may perform / operate similar to an inter prediction unit but may predict blocks within the same picture. For example, the intra block copy unit may exploit repeated patterns that appear in screen content. The screen content may include computer generated text, graphics, animation, etc.

[0084] 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.

[0085] A picture (e.g., in HEVC, or any other coding standard / format) may be partitioned into non-overlapping square blocks, which may be referred to as coding tree blocks (CTBs). The CTBs may comprise samples of a sample array. A CTB may have a size of 2nx2n samples, where n may be specified by a parameter of the encoding system. For example, n may be 4, 5, 6, or any other value. A CTB may have any other size. A CTB may be further partitioned by a recursive quadtree partitioning into coding blocks (CBs) of half vertical and half horizontal size. The CTB may form the root of the quadtree. A CB that is not split further as part of the recursive quadtree partitioning may be referred to as a leaf CB of the quadtree, and otherwise may be referred to as a non-leaf CB of the quadtree. A CB may have a minimum size specified by a parameter of the encoding system. For example, a CB may have a minimum size of 4x4, 8x8, 16x16, 32x32, 64x64 samples, or any other minimum size. A CB may be further partitioned into one or more prediction blocks (PBs) for performing inter and / or intra prediction. A PB may be a rectangular block of samples on which the same prediction type / mode may be applied. A CB may also be further partitioned into intra sub-partitions (ISP) where the reconstructed samples of each sub-partition are available to generate the prediction of the next subpartition. 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.

[0086] 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 respectively labeled 0, 5, and 6 in FIGS. 4 and 5. Finally, the non-leaf CB of the second level partitioning of CTB 400 is partitioned into four leaf CBs of half vertical and half horizontal size. The four leaf CBs are respectively labeled 1, 2, 3, and 4 in FIGS.4 and 5.

[0087] The example CTB 400 of FIG. 4 is partitioned into 10 leaf CBs respectively labeled 0-9, but may be partitioned into other quantities of leaf CBs. The 10 leaf CBs may correspond to 10 CB leaf nodes (e.g., 10 CB leaf nodes ofDocket No.: 24-2065PCTquadtree 500 as shown in FIG. 5). In other examples, a CTB may be partitioned into a different number of leaf CBs. The resulting quadtree partitioning of CTB 400 may be scanned using a z-scan (e.g., left-to-right, top-to-bottom) to form the sequence order for encoding / decoding the CB leaf nodes. A numeric label (e.g., indicator, index) of each CB leaf node in FIGS. 4 and 5 may correspond to the sequence order for encoding / decoding. For example, CB leaf node 0 may be encoded / decoded first and CB leaf node 9 may be encoded / decoded last. Although not shown in FIGS.4 and 5, each CB leaf node may comprise one or more PBs and / or TBs.

[0088] A picture, in WC (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 WC) may be further partitioned by a binary tree or ternary tree partitioning (or any other partitioning) into CBs of unequal sizes.

[0089] 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 WC) 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.

[0090] FIG. 7 A 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 the CTB 700A is merely an example and a CTB may be quadtree partitioned in a manner different from the 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.

[0091] The leaf CB 5 of FIG.4 may be partitioned into two CBs based on a vertical binary tree partitioning. The two resulting CBs may be leaf CBs respectively labeled 5 and 6 in FIGS. 7A and 7B. The leaf CB 8 of FIG. 4 may be partitioned into three CBs based on a vertical ternary tree partition. Two of the three resulting CBs may be leaf CBsDocket No.: 24-2065PCTrespectively labeled 9 and 14 in FIGS. 7 A 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 respectively labeled 11, 12, and 13 in FIGS. 7A and 7B. The leaf CB 9 of FIG.4 maybe partitioned into three CBs based on a horizontal ternary tree partition. Two of the three CBs may be leaf CBs respectively labeled 15 and 19 in FIGS.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 respectively labeled 16, 17, and 18 in FIGS. 7A and 7B.

[0092] Altogether, CTB 700A may be partitioned into 20 leaf CBs respectively labeled 0-19. The 20 leaf CBs may correspond to 20 leaf nodes (e.g., 20 leaf nodes of tree 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.

[0093] A coding standard / format (e.g., HEVC, WC, 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.

[0094] 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_S PUT allows recursive partitioning. In addition, PARTITION_VERT_4and PARTITION_HORZ_4 modes are not allowed for 8x8 or 128x128 coding blocks, and T- shaped partitioning modes are notallowed 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.

[0095] Ablockmay refertoany of a CTB, CB, PB, TB, CTU, CU, PU, and / or TU (e.g., in the context of HEVC, WC, 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, aDocket No.: 24-2065PCTmacroblock 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.

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

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

[0098] FIG. 9 shows an example set of reference samples 902 determined for intra prediction of a current block 904. Current block 904 may correspond to a block being encoded and / or decoded. Current block 904 may correspond to block 3 of partitioned CTB 700 as shown in FIG.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.

[0099] In some embodiments, reference samples 902 may include a line of samples immediately adjacent to current block 904 and include samples from a column and a row immediately adjacent to current block 904. For example, the line of samples may include reference samples to the left and / or above current block 904. In some embodiments, reference samples 902 may be obtained (or selected) from a reference line of multiple reference lines (MRL), which may include a line of samples adjacent to current block 904 and also a line of non-adjacent samples. The MRL may include reference lines identified by corresponding reference line indices that indicate an i-th line of samples adjacent to current block 904 such that the O-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 theDocket No.: 24-2065PCTcodeword to determine the MRL index that identifies a specific reference line used in intra prediction of current block 904.

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

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

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

[0103] Samples of current block 904 may be intra predicted based on reference samples 902, for example, based on (e.g., after) determination and (optionally) filtering of reference samples 902. In some examples, a filtering scheme (e.g., a filtering algorithm) may be applied to reference samples 902 to improve prediction accuracy. The filtering scheme may be one of a plurality of filter types including at least: a smoothing filter (or reference sample smoothing filter) or an interpolation filter. In some examples, if reference samples of a given block are to be filtered, only one ofDocket No.: 24-2065PCTthe plurality of filter types is selected (e.g activated) to be applied to the reference samples. For example, if the smoothing filter is selected (e.g., activated), the interpolation filter is not selected (e.g., disabled) or vice versa.

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

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

[0106] FIG. 10B shows 67 intra prediction modes, such as supported by WC. 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 WC need not be squares.

[0107] 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 around 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.Docket No.: 24-2065PCT

[0108] 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 p[x] [y], 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 I from the set of MRL 908-912, above the current block 904, may be placed in the onedimensional array re / j [x]:ref^x = p[-l + x] [- I], (x > 0). (1) The reference samples 902 belonging to reference line I, to the left of current block 904, may be placed in the onedimensional array ref2[y]:ref2[y] = PH]H + y]< (y ° (2) The variable / represents how many lines away the selected reference line is from current block. For example, if reference line #0908 is selected, then I is set to 1 to indicate the reference line adjacent to current block 904. For example, if reference line #1910 is selected, then I is set to 2. For example, if reference line #2912 is selected, then I is set to 3.

[0109] 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 / in Equations (1) and (2) is set to 1.

[0110] The prediction process may comprise determination of a predicted sample p [x] [y] (e.g, a predicted value) at a location [x] [y] in current block 904. For planar mode, a sample at the location [x] [y] in current block 904 may be predicted by determining / calcu lating the mean of two interpolated values. The first of the two interpolated values may be based on a horizontal linear interpolation at the location [x] [y] in current block 904. The second of the two interpolated values may be based on a vertical linear interpolation at location [x] [y] in current block 904. The predicted sample p [x] [y] in current block 904 may be determined / calculated as:1 p[x] [y] = 7 — (h[x] [y] + V[x] [y] + s), (3)2 ■ s where / i[x] [y] = (s - x - 1) ■ ref2[y] + (x + 1) ■ re[ [s] (4) may be the horizonal linear interpolation at the location [x] [y] in current block 904 andv[x][y] = (s - y - 1) ■ re / jfx] + (y + 1) ■ re2[s] (5) may be the vertical linear interpolation at the location [x] [y] in current block 904. s may be equal to a length of a side (e.g., a number of samples on a side) of the current block 904.

[0111] For DC mode, a sample at a location [x][y] in current block 904 may be predicted by the mean of the reference samples 902. The predicted sample p [x] [y] in current block 904 may be determined / calculated as:Docket No.: 24-2065PCT (s-1 s-1 \^re / i[x] + ^\ef2[y]. (6)x=0 y=0 J

[0112] For angular modes, a sample at a location [x] [y] in current block 904 may be predicted by projecting the location [x] [y] 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 [x] [y] 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 cp defined relative to the y-axis for vertical prediction modes (e.g., modes 19-34 in HEVC and modes 35-66 in WC). The direction specified by the angular mode may be given by an angle (p defined relative to the x-axis for horizontal prediction modes (e.g., modes 2-18 in HEVC and modes 2-34 in WC).

[0113] FIG. 12 showsan 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 ata location [x] [y] in current block 904 for a vertical prediction mode 906. Vertical prediction mode 906 may be given by an angle (p with respect to the vertical axis. The location [x] [y] 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 re [x]. The reference samples 902 are only partially shown in FIG. 12 and shown as being from a reference line with reference line index of 0 for ease of illustration. Reference samples 902 may be from another reference line of the set of MRL, as explained in FIG.9. As shown in FIG. 12, the projection point on the horizontal line of reference samples refk[x] may not be exactly on a reference sample. A predicted sample p [x] [y] in current block 904 may be determined / calculated by linearly interpolating between the two reference samples, for example, if the projection point falls at a fractional sample position between two reference samples. The predicted sample p [x] [y ] may be determined / calculated as:p[x][y] = (1 - if) -ref^x + i, + 1] + if- ref^x + i;+ 2], (7) i;may be the integer part of the horizontal displacement of the projection point relative to the location [x] [y ]. ifmay be determined / calculated as a function of the tangent of the angle q> of the vertical prediction mode 906 as:h = L(y + 1) ■ tan <jpj. (8) if may be the fractional part of the horizontal displacement of the projection point relative to the location [x] [y] and may be determined / calculated as:if= ((y + 1) ■ tan <p) - [(y + 1) ■ tan <pj, (9) where [ ■ J is the integer floor function.

[0114] 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 ref2[y]. A predicted sample p [x] [y]for horizontal prediction modes may be determined / calculated as:p[x][y] = (1 - if -ref2[y + it+ 1] + if-ref2\y + i, + 2], (10)Docket No.: 24-2065PCTit may be the integer part of the vertical displacement of the projection point relative to the location [x] [y] • Tmay be determined / calculated as a function of the tangent of the angle (p of the horizontal prediction mode as:<-i = K + 1) -tamjpj. (11) if may be the fractional part of the vertical displacement of the projection point relative to the location [x] [y ]. ifmay be determined / calculated as:if = ((x 4- 1) ■ tan >) - [(x + 1) ■ tan <pj, (12) where [ ■ J is the integer floor function.

[0115] The interpolation functions given by Equations (7) and (10) maybe 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 maybe implemented by finite impulse response (FIR) filters. For example, the interpolation functions may be implemented as a set of two- tap FIR filters. The coefficients of the two-tap FIR filters may be respectively given by (1-if) and if. The predicted sample p [x] [y], 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 if. In other examples, different levels of sample accuracy may be used.

[0116] In some examples, the FIR filters may be used for predicting chroma samples and / or luma samples. For example, the two-tap interpolation FIR filter may be used for predicting chroma samples and a same and / or a different interpolation technique / filter may be used for luma samples. For example, a four-tap FIR filter may be used to determine a predicted value of a luma sample. Coefficients of the four tap FIR filter may be determined based on if(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 if. 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 if. A predicted sample p [x] [y], for vertical prediction modes, may be determined based on the four-tap FIR filter as:3 (13) PMM = y fT[i] ■ re / x[x + ildx + i],i-o where fl] / ], / = 0...3, may be the filter coefficients, and Idx is integer displacement. A predicted sample p [x] [y], for horizontal prediction modes, may be determined based on the four-tap FIR filter as:3(14) p M ty] = y fT[i] ■ ref2[y + ildx + / ].i=O

[0117] Supplementary reference samples may be determined / constructed if the location [x] [y] of a sample in current block 904 to be predicted is projected to a negative x coordinate. The location [x] [y] of a sample may be projected to a negative x coordinate, for example, if negative vertical prediction angles cp are used. The supplementaryDocket No.: 24-2065PCTreference samples may be determined / constructed by projecting the reference samples in ref2[y] in the vertical line of reference samples 902 to the horizontal line of reference samples 902 using the negative vertical prediction angle (p. Supplementary reference samples may be similarly determined / constructed, for example, if the location [x] [y] of a sample in current block 904 to be predicted is projected to a negative y coordinate. The location [x] [y] of a sample may be projected to a negative y coordinate, for example, if negative horizontal prediction angles (p are used. The supplementary reference samples may be determined / constructed by projecting the reference samples in re / j [x] on the horizontal line of reference samples 902 to the vertical line of reference samples 902 using the negative horizontal prediction angle cp.

[0118] 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 WC and / or including extended intra prediction modes from WAIP for rectangular blocks. The encoder may determine, for each intra prediction mode applied, a corresponding prediction error for the current block based on a difference (e.g., sum of squared differences (SSD), sum of absolute differences (SAD), or sum of absolute transformed differences (SATD)) between the prediction samples, generated from reference samples 902 of a reference line (e.g., from a set of MRL), determined for the intra prediction mode and the original samples of the current block. The encoder may determine / select one of the intra prediction modes to encode the current block based on the determined prediction errors. For example, the encoder may determine / select one of the intra prediction modes that results in the smallest prediction error for the current block In some examples, the encoder may determine / select the intra prediction mode and the associated reference line to encode the current block based on a rate-distortion measure (e.g., Lagrangian rate-distortion cost) determined using the prediction errors. The encoder may signal, in the bitstream to a decoder for decoding of the current block, an indication of the determined / selected intra prediction mode and an indication of the associated MRL index (which may indicate a reference line index). The encoder may also signal in the bitstream to the decoder a corresponding prediction error (e.g., residual) of the intra prediction mode.

[0119] 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 / acti vated / 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.

[0120] 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 decoderDocket No.: 24-2065PCTneed 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 (eg., by applying template-based intra mode derivation (TIMD) tool / technique).

[0121] While various examples herein correspond to intra prediction modes in HEVC and WC, 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.).

[0122] Intra prediction may exploit correlations between spatially neighboring samples in the same picture of a video sequence to perform video compression. Inter prediction is another coding tool that may be used to perform video compression. Inter prediction may exploit correlations in the time domain between blocks of samples in different pictures of a video sequence. For example, an object may be seen across multiple pictures of a video sequence. The object may move (e.g., by some translation and / or affine motion) or remain stationary across the multiple pictures. A current block of samples in a current picture being encoded may have / be associated with a corresponding block of samples in a previously decoded picture. The corresponding block of samples may accurately predict the current block of samples. The corresponding block of samples may be displaced from the current block of samples, for example, due to movement of the object, represented in both blocks, across the respective pictures of the blocks. The previously decoded picture may be a reference picture. The corresponding block of samples in the reference picture may be a reference block for motion compensated prediction. An encoder may use a block matching technique to estimate the displacement (or motion) of the object and / or to determine the reference block in the reference picture.

[0123] 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.

[0124] 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 the current block 1300. Reference pictures (e.g., reference picture 1306) maybe 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 bestDocket No.: 24-2065PCTmatching reference block based on one or more cost criteria. The one or more cost criteria may comprise a ratedistortion 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.

[0125] The encoder may search for reference block 1304 within a reference region (e.g., a search range 1308). The reference region (e.g., a search range 1308) may be positioned around a collocated block (or position) 1310, of current block 1300, in reference picture 1306. Collocated block 1310 may have a same position in the reference picture 1306 as the current block 1300 in the current picture 1302. The reference region (e.g., search range 1308) may at least partially extend outside of reference picture 1306. Constant boundary extension may be used, for example, if the reference region (e.g., search range 1308) extends outside of reference picture 1306. The constant boundary extension may be used such that values of the samples in a row or a column of reference picture 1306, immediately adjacent to a portion of the reference region (e.g., search range 1308) extending outside of reference picture 1306, may be used for sample locations outside of reference picture 1306. A subset of potential positions, or all potential positions, within the reference region (e.g., search range 1308) may be searched for reference block 1304. The encoder may utilize one or more search implementations to determine and / or generate the reference block 1304. For example, the encoder may determine a set of candidate search positions based on motion information of neighboring blocks (e.g., a motion vector 1312) to the current block 1300.

[0126] 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 WC (and / or in one or more other communication protocols), two reference picture lists may be used (e.g., a reference picture list 0 and a reference picture list 1). A reference picture list may include one or more pictures. The reference picture 1306 of reference block 1304 may be indicated by a reference index pointing into a reference picture list comprising reference picture 1306. 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 ARE frame (a frame from either the past or the future).

[0127] 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 aDocket No.: 24-2065PCTreference block and its corresponding samples at fractional positions, for example, if a motion vector points to a noninteger sample value in the reference picture. The interpolation may be performed by a filter with two or more taps.

[0128] The encoder may determine a difference (e.g., a corresponding sample-by-sample difference) between reference block 1304 and current block 1300. The encoder may determine the difference between reference block 1304 and current block 1300, for example, based on / after reference block 1304 is determined and / or generated, using inter prediction, for current block 1300. The difference may be a prediction error (e.g., a residual). The encoder may store and / or send (e.g., signal), in / via a bitstream, the prediction error and / or related motion information. The prediction error and / or the related motion information may be used for decoding (e.g., decoding current block 1300) and / or other forms of consumption. The motion information may comprise the motion vector 1312 and a reference indicator / index. The reference indicator may indicate the reference picture 1306 in a reference picture list. In other examples, the motion information may comprise an indication of motion vector 1312 and / or an indication of the reference indicator / index. The reference indicator may indicate reference picture 1306 in the reference picture list comprising reference picture 1306. A decoder may decode current block 1300 by determining and / or generating the reference block 1304, which may correspond to / form (e.g., be considered as) a prediction of the current block 1300. The decoder may determine and / or generate the reference block 1304, for example, based on the related motion information. The decoder may decode current block 1300 based on combining the prediction (e.g., a reference block) with the prediction error (e.g., a residual block).

[0129] Inter prediction, as shown in FIG. 13A, maybe 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.

[0130] 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.

[0131] One or both of uni-prediction and bi-prediction may be avai lable / 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 avai lable / used for performing inter prediction. For B slices, either uni-prediction or bi-prediction may be avai lable / 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 uniprediction. 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.Docket No.: 24-2065PCT

[0132] 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 block 1400, and the reference block 1404 may be in a second picture that succeeds (e.g., in time) the current picture of current block 1400. The first picture may precede the current picture in terms of a picture order count (POC) 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.

[0133] 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.

[0134] The encoder may determine and / or generate the reference blocks 1402 and 1404 for the current block 1400 using inter prediction. The encoder may determine a difference between current block 1400 and each of reference blocks 1402 and 1404. The differences maybe 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.

[0135] The motion information for reference block 1402 may comprise a motion vector 1406 and / or a reference indicator / index. The reference indicator may indicate a reference picture, of the reference block 1402, in a reference picture list. In some examples, the motion information for reference block 1402 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.

[0136] The motion information for reference block 1404 may comprise a motion vector 1408 and / or a reference index / indicator. The reference indicator may indicate a reference picture, of the reference block 1404, in a reference picture list. The motion information for reference block 1404 may comprise an indication of motion vector 1408 and / or an indication of the reference index. The reference index may indicate the reference picture, of the reference block 1404, in the reference picture list.Docket No.: 24-2065PCT

[0137] A decoder may decode current block 1400 by determining and / or generating the reference blocks 1402 and 1404. The decoder may determine and / or generate the reference blocks 1402 and 1404, for example, based on the respective related motion information for the reference blocks 1402 and 1404. The reference blocks 1402 and 1404 may correspond to / form (e.g., be considered as) the prediction (e.g., used to generate a prediction block) of the current block 1400. The decoder may decode the current block 1400 based on combining the prediction with the prediction errors.

[0138] Motion information may be predictively coded, for example, before being stored and / or sent / signaled in / via a bit stream (e.g., in HEVC, WC, and / or other video coding standards / formats / protocols). The motion information fora 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).

[0139] 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.

[0140] 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 MVDxand MVDy. MVDXand MVDymay be determined / calculated as:MVDx= MVx- MVPx, (15) MVDy = MVy - MVPy. (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.

[0141] 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 decodedDocket No.: 24-2065PCTmotion vector. The reference block may correspond to / form (e.g., be considered as) the prediction of the current block (e.g., a prediction block). The decoder may decode the current block by combining the prediction with the prediction error.

[0142] The list of candidate MVPs (e.g., in HEVC, WC, 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.

[0143] 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 AO, A1, BO, 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 maybe CO 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.

[0144] An encoder (eg., 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 CO 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.: 24-2065PCT

[0145] 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.

[0146] 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 maybe used in dynamic MV prediction modes.

[0147] 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 WC 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 WC) may be performed / used and are within the scope of the present disclosure.

[0148] 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.

[0149] 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., 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 aDocket No.: 24-2065PCTdisplacement 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 poi nt / 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 (xO, yO), IntraBC prediction is available at pixel position (x, y) only if the value of the vertical coordinate y is less than yO and the value of the horizontal coordinate x is less xO + 2(y0 - y). Further, due to hardware write-back delays, the immediate reconstructed area may not be accessible by IntraBC prediction.

[0150] 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.

[0151] A reference block may be determined and / or generated, for a current block, using IBC. The encoder may determine a difference (e.g., a corresponding sample-by-sample difference) between the reference block and the current block. The difference may be a prediction error or residual. The encoder may store and / or send / signal, in / via a bitstream the prediction error and / or related prediction information. The prediction error and / or the related prediction information may be used for decoding and / or other forms of consumption. The prediction information may comprise a BV. The prediction information may comprise an indication of the BV. A decoder (e.g., decoder 300 as shown in FIG.3), may decode the current block by determining and / or generating the reference block. The decoder may determine and / or generate the current block, for example, based on the prediction information (e.g., the BV). The reference block may correspond to / form (e.g., be considered as) the prediction (e.g., a prediction block) of the current block. The decoder may decode the current block by combining the prediction (e.g., prediction block) with the prediction error (e.g., residual or residual block).

[0152] A BV may be predictively coded (e.g., in HEVC, WC, 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 beDocket No.: 24-2065PCTpredictively 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).

[0153] 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.

[0154] 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 BVDXand BVDy. BVDXand BVDymay be determined / calculated as:BVDx= BVx- BVPx, (17) BVDy = BVy - BVPy. (18) BVDx and BVDy may respectively represent horizontal and vertical components of the BVD. BVPx and BVPy may respectively represent horizontal and vertical components of the BVP. A decoder (e.g., decoder 300 as shown in FIG.3), may decode the BV by adding the BVD to the BVP indicated in / via the bitstream. The decoder may decode the current block by determining and / or generating the reference block. The decoder may determine and / or generate the reference block, for example, based on the decoded BV. The reference block may correspond to / form (e.g., be considered as) the prediction (e.g., a prediction block) of the current block. The decoder may decode the current block by combining the prediction (e.g., the prediction block) with the prediction error (e.g., residual or residual block).

[0155] 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.

[0156] A list of candidate BVPs (e.g., in HEVC, WC, 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 ofDocket No.: 24-2065PCTthe spatial candidate neighboring blocks, relative to a current block, being encoded using IBC maybe illustrated in a manner similar to spatial candidate neighboring blocks used for coding motion vectors in inter prediction (e.g., as shown in FIG. 15A). For example, five spatial candidate neighboring blocks of a current block being coded using IBC may be respectively denoted AO, A1, BO, B1, and B2 as shown in FIG. 15A.

[0157] 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”) maybe 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.

[0158] 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.

[0159] In some examples, three types of intra modes may be considered to construct the MPM list: default intra modes; neighboring intra modes; and derived intra modes. A unified 6 MPM list may be used for intra blocks irrespective of whether Multiple Reference Lines (MRL) and Intra Sub-Partitions (ISP) coding tools are applied. The MPM list for the current block is constructed based on intra modes of the left neighbor block (e.g., block corresponding to A1 in FIG. 15A) and the above neighbor block (e.g., block corresponding to B1 in FIG. 15A) of the current block. Suppose the mode of the left neighbor block is denoted as Left and the mode of the above neighbor block is denoted as Above, the unified MPM list may be constructed as follows: when a neighboring block is not available, its intra mode is set to planar mode by default; if both modes 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,Docket No.: 24-2065PCTMax - 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}.

[0160] 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.

[0161] 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 WC minus the 6 MPM), a truncated binary code (TBC) may be used.

[0162] 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), aboveright (AR), and above-left (AL) (e.g., shown in FIG.15A as A1, B1, AO, BO, 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 (eg., 5) with the smallest costs are added to the MPM list. The cost for a respective MPM (e.g., an IPM corresponding to an entry in the MPM list) may be computed between the prediction of the reconstructed samples of the template of the current block and the reconstructed samples. For example, the prediction may be generated by applying the respective MPM for the template. Sorted directional modes are added into the general MPM list, and then the default modes, until the general MPM list with 22 entries 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.

[0163] 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.Docket No.: 24-2065PCT

[0164] In some implementations, a Reconstruction-Reordered intra block copy IBC (RRIBC) mode (e.g., also referred to as IBC-Mirror Mode) is used for screen content video coding to take advantage of symmetry within video content to further improve the coding efficiency of IBC. In some examples, the RRIBC mode may be signaled based on IBC mode with an indication (or flag) indicating whether flipping is applied and if flipping is applied, further signaling an indication (or flag) indication a direction of flipping.

[0165] 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.

[0166] In an example, in the RRIBC mode, the flip direction may include one of a horizontal direction (e.g., along an x-axis) ora vertical direction (e.g., along a y-axis) for RRIBC coded blocks. In an embodiment, fora 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) = Sample(w - 1 - x,y) (19) Reference^, y) = Sample (x, h - 1 - y) (20) where w and h are the width and height of a current block, respectively. Sample(x,y) may indicate a sample value located in (x,y). Reference^, y) may indicate a corresponding reference sample value after flipping. In other words, for horizontal flipping, (19) shows that the current block is flipped in the horizontal direction by sampling from right to left. Similarly, for vertical flipping, (20) shows that the current block is flipped in the vertical direction by sampling the current block from down to up.Docket No.: 24-2065PCT

[0167] 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.

[0168] 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.

[0169] FIG. 17 shows an example of intra template matching prediction (IntraTMP) for predicting or determining a current block 1700, according to some embodiments. IntraTMP is an intra prediction mode that copies a reference block, from a reconstructed part of a current picture 1702 (e.g., current frame), whose template (e.g., an L-shaped template, above-only template, or left-only template) is determined to best match 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.

[0170] 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 oris 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 (eg., the top left sample of reference block 1710).Docket No.: 24-2065PCT

[0171] 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.

[0172] 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, a * BlkW) (21) SearchRange_h = min (64, a * BlkH) (22) a (or alpha) is a constant that controls a gain / complexity trade-off for the encoder or decoder. For example, a 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.

[0173] 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), ora 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.

[0174] 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.Docket No.: 24-2065PCT

[0175] 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.

[0176] In some examples, by performing template matching operations on candidate reference templates in TMP search regions 1706A-D, the decoder (and also encoder) may construct a candidate list of up to a predetermined maximum number (e.g., 19) of candidate block vectors (or candidate block vector predictors). These candidate block vectors may be in ascending order according to the template matching costs of respective reference templates of candidate reference blocks indicated by the candidate block vectors. In some examples, a prediction block (e.g., a predictor) of current block 1700 may be generated using one or more of the reference blocks (e.g., reference block 1710) determined using IntraTMP as well as applying one or more optional filters. For example, the following modes may be supported: single predictor, fusion of multiple predictors, sub-pel precision, and linear filter model. In the single predictor mode, a single predictor is selected from the candidate list such as selecting reference block 1710. In the fusion of multiple predictors mode, multiple predictors are blended to derive the final prediction block such as selecting two or more candidate reference blocks 1714. The blending weights may be either computed from the template matching cost of each predictor, or with a Wiener-filter based weight derivation method. In the sub-pel precision mode, when a single predictor is used, sub-pel precision can be used with 1 / 2-pel precision, 1 / 4-pel precision, or 3 / 4-pel precision, each with 8 possible directions. In the linear filter model mode, a linear filter can be learned (e.g., generated or derived) between the reference template and current template and be applied to the reference block. This mode can be used for the single predictor when sub-pel precision is not used.

[0177] In the example illustrated in FIG. 17, reference template 1712 of reference block 1710 maybe 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.

[0178] 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.

[0179] 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.

[0180] 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 currentDocket No.: 24-2065PCTblock 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 maybe determined. Because, in some examples, the reference block may be indicated by a block vector candidate with the lowest cost in the list of candidates, the decoder may obtain the block vector candidate by decoding, from the bitstream, the index of the block vector candidate in the list of candidates. The decoder may combine the residual, decoded from the bitstream, with reference block 1710 to reconstruct current block 1700. In this way, the encoder does not need to encode BV 1730 that indicates reference block 1710 in the bitstream.

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

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

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

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

[0185] In some examples, the gradient analysis may be performed using edge detection filters applied to 3x3 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 / orDocket No.: 24-2065PCTa 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 -1Mhor-2 0 2 and Mver= 0 0 0-1 0 1.. 1 2 1.

[0186] 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 and vertical direction, respectively. An angle may be calculated for the window as angle = arctan (Ghor / Gver). The calculated angle may correspond to (e.g., be converted into) one of the angular I PMs (e.g., one of the 65 angular IPMs), and an associated amplitude (i.e., the amplitude for the window position) amplitude = |Gver| + |Ghor| maybe added to the HoG indexed by the respective IPM. After an amplitude and angle for each window position in template 1812 are processed, each entry in resulting HoG 1820 represents the cumulated amplitudes for a respective IPM.

[0187] FIG. 19 shows an example of a template 1812 (e.g., template area) for computing a HoG used in DIMD, according to some embodiments. Reference template 1812 (e.g., an L-shaped template) of current block 1810 is shown to be in reconstructed area 1902 (or reconstructed region) of the picture frame. Examples of HoGs for different sizes of current block 1810 are shown. For example, for a 4x4 pixel square current block 1908, a 3x3 window 1910 in the template area is shown and a corresponding HoG 1912 may be generated for current block 1908. In another example, fora rectangular current block 1904 with a 3-pixel deep template area 1906, a HoG 1914 corresponding to rectangular current block 1904 may be generated by gradient analysis of reference samples based on a filter window. As illustrated, each coordinate position on the x-axis of the illustrated HoGs is a respective IPM, and the y-axis represents the cumulative amplitude (e.g., counts) for the respective IPMs.

[0188] Returning to FIG. 18, a number of DIMD modes 1818A-B may be determined by selecting the IPMs from HoG 1820 based on amplitudes of the IPMs. For example, IPMs Mi 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.

[0189] In some examples, a plurality of IPMs such as DIMD modes 1818A-B may be determined and combined with a non-angular 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 non-angular 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., wDIMDi), which may beDocket No.: 24-2065PCTbased on an amplitude Ai, from HoG 1820, associated with DI MD mode 1818A (e.g., I PM Mi) divided by a sum of amplitudes of DIMD modes 1818A-B. For example, weight 1828B for DIMD mode 1818B may correspond to DIMD weight 1832B (e.g., WDIMD2), which may be based on an amplitude A2, from HoG 1820, associated with DIMD mode 1818B (e.g., IPM M2) divided by the sum.

[0190] In some examples, non-angular mode 1816 may be non-directional or non-angular such as a planar mode (or alternatively a DC mode). For ease of illustration, the following descriptions may refer to non-angular mode 1816 as a planar mode, though it may be other types of non-angular modes. Non-angular mode 1816 may have a weight 1826 corresponding to planar weight 1833 that may be a fixed weight fi (e.g., 1 / 4 or 16 / 64 in 6-bit integer precision). The remaining DIMD weights 1832A-B may include a fixed weight portion (e.g., 3 / 4) that is based on the fixed weight of planar weight 1833. For example, the sum of fixed weights fi and f? may be equal to 1.

[0191] DIMD predictor 1822 maybe 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 non-angular mode 1816 with corresponding weights (w,) as follows:2fusionPred(x,y) = Σ{w_i * Pred_i(x,y)}i = OIn some examples, the weights (w,) may be the DIMD weights 1832A-B (wDimdj for mode / ) for DIMD modes 1818A- B and the planar weight 1833 (wP / anar) for non-angular mode 1816. The weights (w) maybe constant and uniformly applied to determine each sample (x, y) 1814 of prediction block 1824. The predictor Predi for mode / may be a DIMD mode predictor (dimdPredi) for DIMD modes 1818A-B or a planar mode predictor (dimdPlanar) for non-angular mode 1816. Accordingly, DIMD predictor 1822 may be represented and computed equivalently as follows:fusionPred(x,y) = (Σ{wDimd_i * dimdPredi(x,y)} + wPlanar *dimdPlanar (x,y)) » 6.Note the shifting operation is performed due to the 6-bits integer precision being used.

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

[0193] In some examples, a location-dependent DIMD mode is introduced to adjust weights 1828A-B of angular IPMs (e.g., DIMD modes 1818A-B) in DIMD. During DIMD IPM derivation, a location-dependency process is applied to determine the impact that different template regions of template 1812 has in selecting each of the IPMs. To determine how specific samples in template 1812 contribute to inferring specific DIMD modes, template 1812 may be divided into three separate regions— including a region above current block 1810, a region to the left of current block 1810, and anDocket No.: 24-2065PCTabove-left region of current block 1810. The gradient analysis computation may be performed separately for samples in each region, resulting in three histograms, HoG 1819C (Habove), HoG 1819Aand HoG 1819B (HaboveLeft), respectively. For a directional IPM m, [m] for region / (e.g., above, left, or above-left) represents the cumulative magnitude of all samples in region / at direction (or IPM) m.

[0194] HoG 1820, corresponding to the full histogram of gradients for the whole template 1812, may be computed as the sum of the three separate HoGs 1819A-C. In some examples, the two directional IPMs with largest and second- largest cumulative amplitude (e.g., magnitude) in HoG 1820 may be selected as main and secondary DIMD modes, e.g., dimdMode0and dimdMode1, respectively.

[0195] In some examples, HoGs 1819C and 1819A corresponding to histograms Haboveand Hleftmay be used to determine whether dimdMode0and / or dimdModei depend on a specific template region ABOVE or LEFT. In a first example, the location-dependency of dimdModei, denoted as locDepL(e.g., shown in FIG. 18 as L, = L(Mi, Hiett, Habove) for DIMD mode i), can be defined as:If: (Habove[dimdModei] > 2Hleft[dimdModei]), then:locDepi = 1, that is dimdModei depends on region ABOVE.Else if: Hieft[dimdModei] > 2Habove[dimdModei]), then:locDepi = 2, that is dimdModei depends on region LEFT.Else:locDepi = 0, that is dimdModei is not location-dependent.

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

[0197] Thus location-dependency in DIMD maybe 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 modesDocket No.: 24-2065PCT1818A-B, respectively. Location-dependency indication for DIMD mode 1816, which may be a planar mode, may be determined as a value representing that it is not location dependent or that it is diagonally dependent.

[0198] In some embodiments, the fusion / blending scheme by which DIMD predictor 1822 is determined may be adjusted based on the location-dependent DIMD modes. For example,.blending may be performed to fuse the main and secondary DIMD predictors, dimdPred0and dimdPred1with the Planar predictor dimdPlanar. If no DIMD mode is determined to be location-dependent (e.g., locDep0== locDep1== 0), then blending / fusion with uniform weights wDimd0, wDimd1and wPlanar may be applied as explained above.

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

[0200] In some examples, if locDepi = 0, the sample-based weights wLocDepDimdix,y') for predictor dimdPredi may be computed so that the average weight used within the block is approximately equal to the uniform weight wDimdi with higher weights being used in the portion of the block closer to the region (e.g., ABOVE or LEFT) corresponding to locDepi (eg., indication Li}. fixed range A, may be determined and is predefined, (e.g., A,= 10) corresponding to the largest deviation of wLocDepDimdi (x, y) from wDimdi ■ Higher values of Azresult in a higher variation of the weights within the block. For a block of size H x W:If locDepi = 1, then:wLocDepDimdj(x,y) = wDimdi + A, - 2A;- - - (H - 1)Else if locDepi = 2, then: wLocDepDimdi(x,y) = wDimdt+ A, - 2A;If both DIMD modes 1818A-B (i=0 and i=1) are associated with location-dependency indications that indicate location dependency (i.e., locDepi = 0 for modes i = 0,1), then the weights wLocDepDimdi (x, y) may be computed for both predictors depending on the value of locDepi, as shown above.

[0201] In some examples, if only one of DIMD modes 1818A-B is associated with a location dependency indication indicating that it is location dependent, e.g., locDepi= 0 and locDep1-i= 0, then the weights for wLocDepDimdi (x, y) may be computed as:wLocDepDimd1-i(x,y) = wDimd1-iwLocDepDimdi(x,y') = wDimdi - - -

[0202] Finally, weight 1826 for the planar predictor wLocDepPlanar(x, y) may be computed as:wLocDepPlanar(x,y) = 64 - Σ_{i=0}{wLocDepDimd_i(x,y)}

[0203] In some examples, the final location-dependent DIMD predictor 1822 may be applied to generate each sample (x,y) of prediction block 1824 as follows:Docket No.: 24-2065PCT ( 1 \^LocDepDlmd^.y) • dirndPred^.y)) ) »6+ wLocDepPlanar(x,y) * dimdPlanar(x,y) + 32 / In some examples, as explained above, non-angular mode 1816 may be systematically applied in the blending process with a fixed weight fi (e.g., % or 21 / 64). Note the shifting operation is performed due to the 6-bits integer precision being used.

[0204] In some embodiments, based on current block 1810 being coded using DIMD, IPM information 1834 may include DIMD parameters that are generated and stored in association with current block 1810. For example, the DIMD parameters may include indications of the selected DIMD modes 1818A-B (Mi, M2, Mi), amplitudes from HoG 1820 (Ai, A2, Ai) of the selected DIMD modes 1818A-B, and / or weights 1828A-B (wi, W2, w,) 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 (L7, L2, Li) of the selected DIMD modes 1818A-B. In some examples, IPM information 1834 may include a plurality of lists (e.g., arrays) of DIMD parameters with each list corresponding to a different DIMD parameter type. For example, the plurality of lists may include a list of IPMs, a list of amplitudes, a list of weights, and / or a list of indications of location-dependency. Parameters at the same index across the plurality of lists correspond to the same DIMD mode or IPM indicated by the index to the list of IPMs.

[0205] In some embodiments, instead of non-angular mode 1816 being a non-angular / non-directional intra prediction mode, non-angular mode 1816 may be an intra coding mode that derives a block vector (BV) such as that obtained by the IntraTMP or IBC mode. For example, the BV may be the block vector obtained via the IntraTMP for the neighboring block. The reference block pointed by the BV, instead of the prediction block by the non-angular intra prediction 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.

[0206] Accordingly, in some embodiments, the DIMD (including any of the DIMD-based modes) may adaptively selects between the prediction block obtained using the non-angular intra prediction mode (e.g., planar mode) and the reference block pointed by the 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.

[0207] 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).

[0208] At block 2001, a histogram of intra prediction modes (IPMs) is determined fora 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 codingDocket No.: 24-2065PCTmode may be an OBIC mode, an Ml M D mode, or an intra merge mode (e.g., a DIMD Merge list mode), as further described below.

[0209] 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.

[0210] 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.

[0211] 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).

[0212] At block 2008, an indication of location dependency of each respective IPM of the selected IPMs is determined.

[0213] 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.

[0214] 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 locationdependency; 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 eachDocket No.: 24-2065PCTof 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

[0215] 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. For example, the IPM with the highest amplitude may be determined as the primary DIMD mode and selected as the DIMD predictor.

[0216] 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.

[0217] 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 Gverl Ghor being equal to or close to 1 or -1).

[0218] 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.

[0219] If at block 2016, itisdetermined 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.

[0220] 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.

[0221] 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.

[0222] 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 horizontalDocket No.: 24-2065PCTlocation 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 so 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.

[0223] 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.

[0224] 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.

[0225] In some examples, the various DIMD parameters determined / derived in flowchart 2000 may be stored as IPM information (e.g., IPM information 1834 of FIG 18) used by the current block. For example, the DIMD parameters may include selected IPMs such as from block 2012 or block 2014. For example, the DIMD parameters may include weights of selected IPMs such as those from block 2020. For example, the DIMD parameters may include amplitudes of the selected IPMs such as amplitudes obtained at block 2006 from the histogram. For example, the DIMD parameters may include indications of location dependencies of the selected IPMs such as those determined at block 2008.

[0226] 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 the MPM list is constructed The primary derived IPM of a DIMD block may be stored with a block and is used for MPM list construction of the neighboring blocks. In some examples, when DIMD is signaled,Docket No.: 24-2065PCTMPM 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.”

[0227] Various decoder-side techniques have been proposed to enhance the DIMD technique such as a Merge Intra Mode Derivation (MIMD) mode, an Occurrence-based Intra Coding (OBIC) mode, an intra merge mode, each of which are further described below.

[0228] For example, one decoder-side technique proposes to merge IPM information (e.g., IPM information 1834) from neighboring blocks of a current block to generate a prediction block for coding the current blocks. When neighboring blocks encoded with intra modes such as intra prediction mode or DIMD are available, the DIMD histograms of the selected neighboring blocks (e.g., neighboring CU blocks) are combined to form a merged histogram of gradients (MHoG) for the current block. DIMD modes and weights can be derived from this MHoG similar to how DIMD modes and weights are derived from a HoG generated for regular DIMD, as explained above with respect to FIGS. 18-20. In some examples, the HoG of the current block is not used in the construction of the MHoG. This intra mode prediction technique of generating the MHoG may be referred to as Merged Intra Mode Derivation (MIMD).

[0229] 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).

[0230] 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 intra merge candidates may be added to the list according to an inclusion order of blocks corresponding to (e.g., including) the left sample (Ai), above sample (Bi), above left sample (B2), above right sample (Bo), and bottom left sample (Ao).

[0231] FIG. 21 shows an example of neighboring blocks of a current block used to determine merge candidates for the current block or a histogram of IPMs used to code the current block, according to some embodiments. For example, the histogram may be an MHoG or an HoC described below with respect to FIGS.22A-B and 23A-B. For example, the merge candidates may be part of an intra merge list (e.g., DIMD merge list) described with respect to FIGS.24A-B or an intra merge list described with respect to FIG.25.

[0232] 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 intra merge candidates and added to the list of intra 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 (eg., contains) sample 10 are spatial non-adjacent blocks with respect to the current block.Docket No.: 24-2065PCT

[0233] 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 2200A may be performed identically at the encoder (e.g., encoder 200) and the decoder (e.g., decoder 300).

[0234] 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 intra 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 maybe selected based on being previously coded using IPM information (e.g., being coded in a DIMD, OBIC, MIMD, or intra merge mode). For example, up to the predetermined number of neighboring blocks may be selected based on being coded using IPM information and that are spatially closest to the current block.

[0235] At block 2204, IPM information of each block of the plurality of neighboring blocks are obtained (e.g., retrieved). In some examples, the IPM information of a block represents a histogram of IPMs such as the HoG, which may be an MHoG. The IPM information representing the HoG (and / or MHoG) may include DIMD parameters such as IPMs and associated parameters such as amplitudes, weights, and / or indications of location dependencies, as described with respect to FIG. 18. Depending on the intra mode (e.g., DIMD mode, MIMD mode, OBIC mode, Intra merge mode, TIMD mode, MIP mode, etc.) that was used to code a block, the IPM information of the block may be limited to storing a number (e.g., predetermined number such as 5 or 3 or 2) of IPMs and associated parameters. The number of IPMs may be dependent on the type of the intra mode and / or IPM information of the neighboring blocks used to generate the IPM information for the block. In some examples, the IPMs stored in the IPM information may be those with the highest amplitudes from a histogram that was generated for the block.

[0236] At block 2206, an MHoG is determined based on combining the IPM information of each block of the plurality of neighboring blocks according to amplitudes in (e.g., stored for respective IPM(s)) the IPM information. In some examples, the HoGs representing the IPM information of each block may be combined, e.g., based on averaging the amplitudes of the IPMs in the HoGs as follows:1NmHoGfm] = — / / oC[i][m]where N is the number of selected neighboring blocks and m is the m-th entry (or luma mode) of the HoG. As shown, the HoGs may be combined by averaging the amplitudes cumulated per IPM of the HoGs by the number N. In other words, amplitudes of the same IPM across IPM information of the selected neighboring blocks may be cumulated in the MHoG Then, amplitudes of the same IPMs across the IPM information of selected neighboring blocks may be combined. In some examples, the cumulated amplitude for an IPM may be normalized by dividing by the number N of selected neighboring blocks. The resulting MHoG may be used to derive the prediction modes and weights as described above.Docket No.: 24-2065PCT

[0237] 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.

[0238] In some examples, with respect to block 2008 in the MIMD mode, if multiple neighboring blocks are selected to determine the MHoG, the indication of location dependency may be set to a value (e.g., 0) indicating diagonal (e.g., or non-location dependent) for each of the number of selected IPMs. In an example, if only one neighboring block was selected, the indication of location dependency for each of the selected IPMs may be set to the selected IPMs' location dependency as obtained from IPM information of the neighboring block. Accordingly, a DIMD predictor may be generated from the selected IPMs of the MHoG and used to generate a prediction block for coding the current block.

[0239] 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.

[0240] 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.

[0241] The OBIC process is similar to the DIMD process described with respect to FIG. 20 exceptfor 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).

[0242] 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 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 intra merge candidates and added to the list of intra merge candidates. For example, a first block 2102 associated with (e.g., contains) sample 11, a second block 2104Docket No.: 24-2065PCTassociated 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.

[0243] FIG. 22B shows an example flowchart 2200 B 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 2200B may be performed identically at the encoder (e.g., encoder 200) and the decoder (e.g., decoder 300).

[0244] 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 maybe at most a predetermined number (e.g., 13 or 15) selected from a list of intra 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 intra merge candidates may include checking adjacent spatial neighboring blocks of the current block as shown in FIG. 15A and non-adjacent spatial neighboring blocks as described above with respect to FIG.21 In some examples, the plurality of neighboring blocks may be selected based on being previously coded using IPM information (e.g., being coded in a DIMD, OBIC, MIMD, or Intra merge mode). For example, up to the predetermined number of neighboring blocks may be selected based on being coded using IPM information and that are spatially closest to the current block.

[0245] At block 2214, IPM information of each block of the plurality of neighboring blocks are obtained (e.g., retrieved). In some examples, the IPM information of a block represents a histogram of IPMs such as the HoG, which may be an MHoG or an HoC. Block 2214 may correspond to and include similar operations as block 2204 of FIG.22A. For example, the IPM information representing the HoG (and / or MHoG) may include DIMD parameters such as IPMs and associated parameters such as amplitudes, weights, and / or indications of location dependencies, as described with respect to FIG. 18.

[0246] At block 2216, an HoC is determined based on combining the IPM information of each block of the plurality of neighboring blocks according to a size and / or dimensions of each block.

[0247] In some examples, different from generating HoG or MHoG in which amplitudes of IPMs in the IPM information are combined, the HoC may be determined to include IPMs, from the IPM information, with cumulated sample-wise occurrences where each occurrence value for a respective IPM is calculated based on the number of samples that are coded with that I PM from the selected intra merge candidates. For example, if a selected merge candidate is a neighboring block with dimensions of width w and a height h and that is coded with an intra prediction mode IPM, the occurrence of the IPM in the associated block may be computed as:histogram[IPM]+= w X h.The occurrence for this specific IPM may be cumulated over the selected plurality of neighboring blocks (e.g., including adjacent spatial neighboring blocks and / or non-adjacent spatial neighboring blocks). In other words, the sizes (e.g., width multiplied by height) of neighboring blocks with IPM information including the same IPM may beDocket No.: 24-2065PCTcumulated 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.

[0248] 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 maybe selected and blended together along with the planar mode to obtain a DI MD predictor (e.g. the DI MD predictor based on generating a HoC) used to generate a prediction block for coding the current block.

[0249] 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.

[0250] 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.

[0251] In some embodiments, the IPM information of a neighboring block may include different numbers of IPMs (e.g., angular modes) depending on the intra mode that was used to code the neighboring block. As an example, intra modes such as DIMD, OBIC, or MIMD may use to 5 IPMs, a template-based intra mode derivation (TIMD) mode may use up to 2 modes, or a spatial geometric partitioning mode (SGPM) may use up to 2 modes. In these examples, all intra modes of such blocks are considered in the histogram generation. In some examples, neighboring blocks coded using non-angular modes such as IntraTMP, IBC, or Matrix-based Intra Prediction (MIP) are not selected and are not used to generate the histogram (e.g., HoG, MHoG, or HoC).

[0252] FIG. 23A shows an example of IPM information from a plurality of (previously reconstructed) neighboring blocks of a current block, according to some embodiments. FIG. 23B shows a graphical representation of combining the IPM information from the plurality of neighboring blocks to generate an MHoG if the current block is coded using the MIMD mode. In contrast, FIG. 23C shows a graphical representation of combining the IPM information from the plurality of neighboring blocks to generate an HoC if the current block is coded using the OBIC mode.

[0253] In both the OBIC and MIMD modes, a coder (e.g., encoder in FIG. 2, decoder in FIG. 3) obtains (e.g., accesses, collects, receives) the IPM information from the plurality of (previously reconstructed) neighboring blocks (e.g., block 1, block 2, and block 3) and generates information used to generate a prediction block to code the current block. For example, as shown in FIG. 23A, the coder obtains first IPM information from block 1 including HoG information such as amplitudes for IPM 1, IPM 7, IPM 9, IPM 13, and IPM 17. For example, the coder obtains second IPM information from block 2 including HoG information such as amplitudes for IPM 7, IPM 9, and IPM 13. For example, the coder obtains third IPM information from block 3 including HoG information such as amplitudes for IPM 1, 1PM 7, IPM 9, IPM 13, and IPM 17.

[0254] As shown in FIG. 23B, if the current block is coded using MIMD mode, the coder may combine the amplitudes of like IPMs from the first IPM information, the second IPM information, and the third IPM information corresponding to respective blocks 1-3 to generate MHoG 2302. For example, the coder determines the amplitudes of IPM 1 in theDocket No.: 24-2065PCTMHoG 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.

[0255] As shown in FIG 23C, if the block was coded using OBIC mode, the coder may combine the occurrences of like IPMs from the first IPM information, the second IPM information, and the third IPM information corresponding to respective blocks 1-3 to generate HoC 2304. For example, the coder determines the amplitude (occurrence) of IPM 1 in the HoC 2304 by adding the sizes of blocks 1 and 3, each of which was coded using at least IPM 1. Similarly, the coder determines the amplitude (occurrence) of IPM 7 in the HoC 2304 by adding the sizes of blocks 1, 2, and 3. Similarly, the coder determines the amplitude (occurrence) of IPM 9 in the HoC 2304 by adding the sizes of blocks 1, 2, and 3. Also, the coder determines the amplitude (occurrence) of IPM 13 in the HoC 2304 by adding the sizes of blocks 1, 2, and 3. And, the coder determines the amplitude (occurrence) of IPM 17 in the HoC 2304 by adding the sizes of blocks 1 and 3. Here, since the second IPM information does not indicate IPM 1 and IPM17, the size of block 2 is not used for determining IPMs 1 and 17 In some examples, using the various techniques described above (e.g, OBIC), a prediction block may be generated based on HoC 2304 for coding the current block. For example, the encoder may signal, in a bitstream, a residual block indicating a difference between the prediction 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.

[0256] Another decoder-side technique for enhancing DIMD is based on using a list of merge candidates (e.g., intra merge candidates) that is identically generated at the encoder and the decoder and signaling an index that indicates one merge candidate from the list to code a current block. Each merge candidate may include IPM information from one or more of a plurality of neighboring reconstructed blocks with respect to the current block. This process is referred to as an intra merge mode or equivalent as the DIMD Merge List mode.

[0257] FIG. 24A shows an example flowchart 2400 of the intra merge mode (e.g., also referred to as an intra merge list) for deriving the list of intra merge candidates, according to some embodiments. Flowchart 2400 includes a block 2402 in which an intra merge list is derived and a block 2404 in which DIMD parameters for a selected intra 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.Docket No.: 24-2065PCT

[0258] Block 2402 may include several operations shown as blocks 2406-2414, each of which may add to the list of intra merge candidates a family of intra merge candidates obtained from spatial neighbor blocks (e.g., intra blocks) of the current block that are selected based on a different selection criterion, from combinations of IPM information already in the list, or from configured default IPM information. In example implementations, the intra merge candidates in the list of intra merge candidates is arranged as a list or table, but embodiments may not be limited by a specific arrangement structure of the intra merge candidates.

[0259] At block 2406, intra merge candidates from a family of spatial adjacent blocks are considered for adding intra merge candidates to the list of intra 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 intra merge candidates from spatial adjacent blocks can be added to the list of intra 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 intra merge candidate list at block 2406. For the IPM information of a particular spatial block to be included in the intra merge candidate list, that block must at least already have had (e.g., during the reconstruction of blocks in the current frame) IPM information derived for that block. IPM information may be derived for a block that uses the DIMD parameters such as, for example, MIMD mode (e.g., DIMD HoG merge mode), intra merge mode, DIMD mode, OBIC mode, intra prediction mode, or MPM list derivation. In some examples, a merge candidate is added to the list of intra 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, Ml Ml D mode, intra merge mode, OBIC mode, intra prediction mode, MPM list derivation, etc.), at block 2406, no spatial adjacent candidates are added to the list of intra merge candidates.

[0260] At block 2408, intra merge candidates from a family of spatial non-adjacent blocks of the current block are added to the list of intra merge candidates. The positions and inclusion order of the intra 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.

[0261] The numbers 1-5 shown in FIG.21 refer to spatially adjacent neighbors of the current block (shown shaded) in the inclusion order L, A, AR, BL, and AL, that were already added to, or otherwise considered for inclusion in, the merge candidate list at block 2406 and thus may not be considered at block 2408. The sequence of blocks indicated by the sample locations 6-24 may be considered for inclusion of the corresponding IPM information in the list of intra 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 intra merge candidates may be arranged in theDocket No.: 24-2065PCTframe 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.

[0262] Similar to determining whether to include a spatial adjacent block in the list of intra merge candidates, for the IPM information of a particular spatial non-adjacent block to be included in the list of intra merge candidates, that block must have had DIMD used for encoding / decoding or at least have had IPM information derived for that block. In some examples, an intra merge candidate is added to the list of intra 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 intra merge candidates.

[0263] At 2410, a family of merge candidates from a history-based table of IPM information is added to the list of intra merge candidates. For example, one or more intra merge candidates (e.g., a predetermined number) from the historybased table may be added to the list of intra merge candidates. For example, a predetermined number of the most recently coded blocks in the history-based table may be selected.

[0264] The history-based table may be maintained to include a predetermined number of the latest intra coded blocks that used IPM information. In some examples, this history-based table may be updated each time an intra block (e.g., CU) is coded using the DIMD process such as when the IPM information is derived (e.g., a block using the DIMD mode, or an MPM-based mode, or based on a direction derived from DIMD, or a MIMD mode, or intra merge mode, or OBIC mode). This table includes a limited number of entries of IPM information from previously coded blocks and does not include any duplicate IPM information.

[0265] For the IPM information of a particular spatial block to be included in the history-based table, that block must have had DIMD used for encoding / decoding or at least have had IPM information derived for that block. IPM information may be derived for a block for encoding / decoding based on DIMD or another intra prediction mode that uses the DIMD parameters. In some examples, an entry of IPM information is added to the history-based table only if the corresponding neighbor block was reconstructed based on DIMD or another intra prediction mode that uses the DIMD parameters.

[0266] In some embodiments, spatial adjacent blocks and spatial non-adjacent blocks of the current block may have been already considered in accordance with a predetermined inclusion order (e.g., based on blocks 2406 and 2408), only IPM information of spatial blocks that are neither spatial adjacent blocks nor spatial non-adjacent blocks according to the predetermined inclusion pattern are added to the history-based table.

[0267] In some examples, when inserting a new entry of IPM information into the history-based table, a constrained first-in-first-out (FIFO) rule may be applied where a redundancy check is first applied to determine whether there is identical IPM information in the table. If found, the entry with the identical IPM information is removed from the table and all entries following that in the table are moved forward in the FIFO order, and the new IPM information is inserted as the last entry. The table may be reset at intervals, such as, for example, at the beginning of each CTU row. Such resetting may be performed due to hardware constraints. Such resetting may also help ensure that only the mostDocket No.: 24-2065PCTrecent neighbor blocks are in the table. In some implementations, the history-based table of IPM information may be similar to the history-based table of motion vectors (HMVP) in the whole-block-based Advanced Motion Vector Predictor (AMVP) mode for inter prediction in WC.

[0268] FIG. 24B shows a flowchart 2420 of an example process for generating a history-based table of intra 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 merge candidate. The current block may be considered as a merge candidate based on the current block being coded using DIMD or another intra mode in which IPM information is derived. At block 2422, it is determined whether the IPM information (of the merge candidate) to be added already exists in the table. If, at block 2422, it is determined that the IPM information to be added is not in the table, then at block 2426, it may be determined whether the table is full. This determination may be based on a preconfigured maximum size threshold for the history-based table. If the table is not full, at block 2430, the IPM information of the merge candidate may be added to the history-based table.

[0269] If at block 2422, it is determined that the IPM information to be added is in the table, then at block 2424, the duplicate IPM information of an existing merge candidate in the history-based table is already in the table and is removed from the table.

[0270] 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.

[0271] 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 atblock 2432, at block 2430, the new IPM information of the merge candidate is added as the last entry in the table.

[0272] According to the example inclusion order, intra merge candidates derived from IPM information in the historybased table are added to the list of intra merge candidates after considering intra merge candidates derived from spatial adjacent blocks and spatial non-adjacent blocks of the current block.

[0273] Returning to FIG. 24A, in some embodiments, at block 2412, a set of combined intra merge candidates are added to the list of intra merge candidates. In some examples, one or more combined intra merge candidates may be added to the list of intra merge candidates based on existing intra merge candidates (and respective IPM information) in the list such as intra merge candidates considered and selected from one or more of the intra merge candidate families described above with respect to blocks 2406-2410. In some examples, a combined intra merge candidate may be generated based on combining IPM information from the IPM information of intra merge candidates that are already in the list of intra merge candidates. In some examples, intra merge candidates that are already in the list, but which are based on a combination of other intra merge candidates in the list, are not used to derive further combined intra merge candidates.

[0274] In some examples, IPM information corresponding to HoGs from at least two intra merge candidates in the list of intra merge candidates are combined to create a new combined HoG, from which the blending modes and weightsDocket No.: 24-2065PCTare derived to obtain the IPM information of a new intra merge candidate. For example, the IPM information (e.g., amplitudes of like IPMs) of at least two merge candidates may be averaged to generate an MHoG, and the blending modes and weights are derived from this MHoG in a manner similar to that in the blending mode derivation in DIMD and MIMD, as described, for example, in relation to FIGS. 19-20. In some examples, considering the new combined intra 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.

[0275] In some examples, a plurality of combined intra merge candidates may be derived and include two or more of the following: a candidate derived from the first and second intra merge candidates in the list of intra merge candidates; a candidate derived from the first and third intra merge candidates in the list of intra merge candidates; a candidate derived from the second and third intra merge candidates of the list of intra merge candidates; a candidate derived from the two first intra merge candidates of the list of intra merge candidates with a vertical location dependency; a candidate derived from the two first intra merge candidates of the list of intra merge candidates with a horizontal location dependency; and / or a candidate derived from combining IPM information of all spatial adjacent blocks of the current block.

[0276] In some implementations, a combined intra 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 intra merge candidates before adding combined merge candidates, the second combined candidate, derived from the first and third candidates, may be skipped as there is no third merge candidate.

[0277] At block 2414, a set of default intra merge candidates are added to the list of intra merge candidates, according to some embodiments.

[0278] In some examples, one or more default IPM information entries are added as intra merge candidates to the list of intra merge candidates. For example, DIMD parameters of two example default IPM information entries are shown in Table 1 below.Blending Modes 0 (Planar) 34 (Diag) 18 (Hor) Default Mode 0 Blending Weights 16 24 24Location Dependency 0 0 2 Blending Modes 0 (Planar) 34 (Diag) 50 (Ver) Default Mode 1 Blending Weights 16 24 24Location Dependency 0 0 1Table 1: Example default DIMD parameters

[0279] The table shows default mode 0 and default mode 1, that each specify a set of predetermined DIMD parameters. One or more intra merge candidates having predetermined default IPM information (e.g., the DIMDDocket No.: 24-2065PCTparameters specified in Table 1 above) may be added to the list of intra merge candidates as one or more default merge candidates.

[0280] In some examples, the addition, if any, of combined intra merge candidates optionally followed by the default intra merge candidates completes the addition of merge candidates to the list of intra merge candidates.

[0281] In some embodiments, block 2402 may further include blocks 2416 and / or 2418. In addition to the intra merge candidates with IPM information retrieved from previously coded (e.g., reconstructed) neighboring blocks of the current block as described with respect to blocks 2406-2414, blocks 2416-2418 may add one or more intra merge candidates that derive IPM information from neighboring spatial blocks. It should be noted that the order of blocks 2406-2418 may be different than from what is shown in FIG. 24A.

[0282] At block 2416, one or more intra merge candidate derived using the MHoG derivation process and referred to as MHoG-based candidates may be added to the list of intra 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.

[0283] In some examples, the list of MHoG merge candidates may include IPM information (e.g., DIMD parameters related to an MHoG or an HoG) of spatial neighbor blocks (e.g., CUs) of the current block such as the spatial adjacent neighbor blocks and the spatial non-adjacent blocks that was coded based on DIMD or another intra prediction mode using DIMD parameters, as described above with respect to FIG. 15Aand FIG.21. In an example, redundant IPM information is removed or not added to the list of MHoG merge candidates. In some examples, the list of MHoG merge candidates may further include one or more merge candidates from a history-based table of IPM information

[0284] In some examples, a plurality of different subsets of the list of MHoG merge candidates may be selected to generate a plurality of different intra merge candidates to add to the list of intra merge candidates.

[0285] In some examples, the one or more MHoG-based candidates are added to the list of intra 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 intra merge candidates.

[0286] At block 2418, one or more intra merge candidates derived using the OBIC derivation process and referred to as OBIC-based candidates may be added to the list of intra 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.

[0287] In some examples, the list of OBIC merge candidates may include IPM information (e.g., DIMD parameters related to an MHoG, HoG, or HoC) of spatial neighbor blocks (e.g., CUs) of the current block such as the spatial adjacent neighbor blocks and the spatial non-adjacent blocks that was coded based on DIMD or another intra prediction mode using DIMD parameters, as described above with respect to FIG. 15A and FIG.21. In an example, redundant IPM information is removed or not added to the list of OBIC merge candidates. In some examples, the listDocket No.: 24-2065PCTof OBIC merge candidates may further include one or more merge candidates from a history-based table of IPM information.

[0288] In some examples, a HoC may be derived from the IPM information of two or more neighbor blocks corresponding to the selected OBIC merge candidates. The derived HoC may be used to derive the intra merge candidate to be added to the list of intra merge candidates.

[0289] In some examples, a plurality of different subsets of the list of OBIC merge candidates may be selected to generate a plurality of different intra merge candidates to add to the list of intra merge candidates.

[0290] Operations at block 2402, which includes blocks 2406-2414 and may further include blocks 2416-2418 and which generates the list of intra merge candidates, may be identical at both the encoder and decoder. After block 2402 is completed (i.e., the list of intra merge candidates is constructed), at block 2404, blended modes, weights and location dependency are derived. At the encoder, this may include determining the best intra merge candidate in the list of intra 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 intra merge candidates starting from the top (e.g., the lowest SAD, SATD cost) of the list of intra merge candidates. The index to the position of the best (selected) intra merge candidate in the list of intra 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.

[0291] 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 intra merge candidates. The index can be used to obtain the selected intra merge candidate from which to derive the DIMD predictor.

[0292] The DIMD merge mode has the benefit of the use of available neighbor information (e.g., in particular, the IPM information derived for the spatial neighbor blocks) to better suit the signal characteristics of the current block to be predicted.

[0293] 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."

[0294] In some embodiments, the intra merge candidates may further be derived from a neighboring block coded using a template-based intra mode derivation (TIMD) mode, further described below with respect to FIGS. 26A-B.

[0295] FIG. 25 shows an example flowchart illustrating a process 2500 for coding a current block in an intra merge mode, according to some embodiments. In some examples, the intra merge mode may be implemented as a submode of DIMD. Operations of process 2500 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.

[0296] At block 2502, a coder generates a list of intra merge candidates using IPM information of a plurality of neighboring blocks of a current block. As detailed further below, the list of intra merge candidates may be generated identically at the encoder and the decoder to code (e.g., encode and decode) the current block.Docket No.: 24-2065PCT

[0297] In some examples, the plurality of neighboring blocks are coded using intra mode prediction based on being coded by any of a set of IPM-based coding modes. For example, an IPM-based intra coding mode may be a mode that generates a prediction of a block by combining a first prediction based on a first I PM and a second prediction based on a second IPM, such as a decoder-side intra mode derivation (DIMD)-based mode (e.g., DIMD, MIMD, DIMD Merge, OBIC) or a template based intra prediction (TIMD)-based mode (TIMD or TIMD merge). For example, the list of intra merge candidates may include one or more merge candidates described above with respect to FIG. 24A.

[0298] Block 2502 may include blocks 2504-2508 describing how a neighboring block of the current block is used to generate an intra merge candidate added to the list of intra merge candidates. At block 2504, the coder selects a neighboring block, of the current block, coded using intra mode prediction. For example, the neighboring block may be coded in one of an IPM-based coding mode.

[0299] At block 2506, the coder obtains one or more first IPMs used to predict / code the neighboring block. For example, the one or more first IPMs may be obtained from IPM information generated by or resulting from the IPM- based coding mode used to code the neighboring blocks.

[0300] At block 2508, the coder generates the intra merge candidate based on determining (e.g., deriving or setting) one or more second IPMs of the intra merge candidates using the one or more first IPMs. For example, determining the one or more second IPMs may include mapping first parameters of the one or more first IPMs to second parameters of the one or more second IPMs of the intra merge candidate.

[0301] In some examples, as part of generating the intra merge candidate to add to the list, a set of IPM parameters used to generate the prediction block may be stored. For example, the IPM parameters may include one or more parameters of IPM information 1834. For example, the set of parameters may include one or more of IPMs to be blended (e.g., indexes identifying the one or more IPMs), one or more corresponding weights, and / or one or more location-dependency indicators.

[0302] In some embodiments, additional neighboring blocks may be processed to add additional merge candidates until a predetermined number is reached, for example, when the list is full. An order of the plurality of neighboring blocks may be checked according to a plurality of positions defined relative to the current block such as those described with respect to FIG. 21.

[0303] In some embodiments, block 2502 further involves processing the list of intra merge candidates such as by removing duplicate candidates, reordering the candidates based on the coding costs, and pruning the candidates to a target number of candidates, and so on. For example, for each merge candidate, a template matching cost may be computed as a weighted sum of IPM template matching costs of the IPMs in the merge candidate. Then, the list may be reordered according to the template matching cost of each intra merge candidate.

[0304] At block 2510, an intra merge candidate is selected from the list to generate a prediction block for coding the current block.

[0305] For instance, at the encoder, the encoder may compute costs (eg., RDO cost) for prediction blocks generated using respective merge candidates in the list to determine an intra merge candidate associated with a lowest cost.Docket No.: 24-2065PCTThen, the encoder may signal an index in the bitstream to indicate that the intra merge candidate, in the list of intra merge candidates, is to be used to code the current block. At the decoder, the decoder may decode from the bitstream an indication (e.g., index) of the intra merge candidate in the list of intra merge candidates, and identify the intra merge candidate from the list according to the indication. The identified intra merge candidate may be used to obtain (e.g., generate) a prediction block for reconstructing the current block.

[0306] At block 2512, the coder codes the current block based on the prediction block. In some embodiments, at the encoder, the current block may be encoded by subtracting the prediction block, corresponding to the determined intra merge candidate, from the current block to determine a residual (e.g., residual block or prediction error). The residual may be encoded and signaled in the bitstream. At the decoder, the decoder may determine a prediction block for the current block by using the indicated intra merge candidate. The current block may be reconstructed (e.g., decoded) based on a residual (e.g., residual block) obtained from a bitstream and the prediction block. For example, the current block may be determined by adding the residual to the prediction block.

[0307] In some embodiments, the intra merge mode may include one or more types of intra merge modes (or submodes). For example, the intra merge mode may include a DIMD merge list mode, such as that described in FIG.24A, in which the plurality of neighbors considered may be those that are coded using a DIMD-based mode. For example, the intra merge mode may include a TIMD merge list mode, in which the plurality of neighbors considered may be those that are coded using a TIMD-based mode. For example, the intra merge mode may include an intra-modes merge mode, in which the plurality of neighbors considered may be those that are coded using a TIMD-based mode or a DIMD-based mode.

[0308] 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 identically by the encoder and the decoder from the intra prediction modes of the neighboring CUs, and is updated as the encoder / decoder progresses through the video frame.

[0309] 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.

[0310] 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.Docket No.: 24-2065PCT

[0311] In some examples, three types of intra modes may be considered to construct the MPM list: default intra modes; neighboring intra modes; and derived intra modes. A unified 6 MPM list may be used for intra blocks irrespective of whether Multiple Reference Lines (MRL) and Intra Sub-Partitions (ISP) coding tools are applied. The MPM list for the current block is constructed based on intra modes of the left neighbor block (e.g block corresponding to A1 in FIG. 15A) and the above neighbor block (e.g., block corresponding to B1 in FIG. 15A) of the current block. Suppose the mode of the left neighbor block is denoted as Left and the mode of the above neighbor block is denoted as Above, the unified MPM list may be constructed as follows: when a neighboring block is not available, its intra mode is set to planar mode by default; if both modes 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}.

[0312] 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.

[0313] 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 WC minus the 6 MPM), a truncated binary code (TBC) may be used.

[0314] 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), aboveright (AR), and above-left (AL) (e.g., shown in FIG.15A as A1, B1, AO, BO, 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.Docket No.: 24-2065PCTIn some examples, up to a preconfigured / predetermined number of modes (e.g., 5) with the smallest costs are added to the MPM list. The cost for a respective MPM (e.g., an IPM corresponding to an entry in the MPM list) may be computed between the prediction of the reconstructed samples of the template of the current block and the reconstructed samples. For example, the prediction may be generated by applying the respective MPM for the template. Sorted directional modes are added into the general MPM list, and then the default modes, until the general MPM list with 22 entries 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.

[0315] FIG. 26A and FIG. 26B show an example of a template-based intra mode derivation (TIMD) technique for coding a current block, according to some embodiments. The TIMD mode is a type of intra prediction in which one or more intra prediction modes (IPMs) may be identically determined (e.g., independently and identically 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.

[0316] As shown in FIG. 26A, in a 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 2104A-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.

[0317] In the TIMD mode, a 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, but not adjacent to current block 2602. For example, reference of template 2606 may comprise reconstructed samples left, above, and / or both left and above template 2604. Reference of template 2606 may have a thickness to the left of template region 2604A of R1 samples and a thickness above template region 2604B of R2 samples. For example, R1 and / or R2 may be 1 sample, 2 samples, 4 samples, etc. In some examples, reference of template 2606 may include an upper region having a width greater than template region 2604B (e.g., a width that is greater or equal to twice the width of template region 2604B, 2(M+L1) samples, 2(M+L1)+R1 samples, etc.). In some examples, reference of template 2606 may 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.).Docket No.: 24-2065PCT

[0318] In some examples, a TIMD mode predictor may be determined using a list of candidate intra prediction modes (IPMs) 2610 shown in FIG.26B. For example, list 2610 may include IPMsfrom a most probable mode (MPM) list In some examples, one or more of the following modes may be added to the list of candidate IPMs: a DC mode, a planar mode, a horizontal and / or vertical DC mode, and / or or a horizontal and / or vertical planar mode. A cost (e.g., SAD or SATD) for each candidate IPM in list 2610 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.

[0319] In some examples, a first IPM 2622 (shown as IPM_2 with Cost_2) and a second IPM 2624 (shown as IPM_k with Cost_k), from list 2610, with the lowest costs of costs determined for candidate IPMs in list 2610 are selected to determine (e.g., derive) a primary TIMD mode 2612 and a secondary TIMD mode 2614. For example, primary TIMD mode 2612 may be set to first IPM 2622 having the lowest cost of the costs, and secondary TIMD mode 2614 may be set to second IPM 2624 having the second lowest cost of the costs.

[0320] In some examples, primary TIMD mode 2612 and secondary TIMD mode 2614 may be set by refining first IPM 2622 and second IPM 2624, respectively, to determine first refined IPM 2632 and second refined IPM 2634, respectively. For example, an IPM in a first angular precision (e.g., represented by a first range of modes such as 67 modes) corresponding to IPMs in list 2610 may be converted (or mapped) to an extended IPM in a second angular precision (e.g., represented by a second range of modes such as 131 modes). The second angular precision may be associated with a second range of modes referred to as wide angles intra prediction modes. In some examples, the conversion or mapping may be performed by left shifting an index, indicating the IPM in the first angular precision, by a predetermined number (e.g., 1), which is equivalent to multiplying the index by a second predetermined number (e.g., a power of 2 such as 2). Refining the IPM may further include comparing the cost of the extended IPM (which has the same cost as the IPM) with costs of the two adjacent modes (i.e., + / -1 mode) of the selected IPM. For example, first refined IPM 2632 (shown as I PM_2* with Cost_2*) may be determined as an IPM having the smallest cost among costs of an extend first IPM (corresponding to a mapped first IPM 2622) and its two adjacent modes in the second range. For example, second refined IPM 2634 (shown as I PM_k* with Cost_k*) may be determined as an IPM having the smallest cost among costs of an extend second IPM (corresponding to a mapped second IPM 2624) and its two adjacent modes in the second range.

[0321] In some embodiments, a TIMD mode predictor 2640 may be determined based on combining (e.g., blending or fusing) the primary TIMD mode 2612 and the secondary TIMD mode 2614. For example, the TIMD mode predictor may be a linear combination of the predictors generated by the primary TIMD mode 2612 and the secondary TIMD mode 2614. Each weight (2628A or 2628B) of the first and second TIMD modes, in the linear combination, maybe determined based on costs costModel and costMode2 of the first and second TIMD modes, respectively. ForDocket No.: 24-2065PCTexample, 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 2644 for current block 2602.

[0322] 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 2644.

[0323] 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 < a * costModel. Here, costMode3 is the cost of third TIMD mode 2616 (the non-angular IPM) and costModel is the cost of the primary 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 a can be 1.5. If both conditions are satisfied, three TIMD modes 2612-2616 are used to generate the prediction block 2644. The weight 2628A-C of the / -th intra prediction mode ( / =1, 2, 3) can be computed from the costs of these three modes as follows:.,, sumCost costMode, „,...,weiqhti = -, sumCost = > costMode:.u 12xsumCost > '1If the above two conditions are not both satisfied, the third TIMD mode 2616 (i.e., the non-angular intra prediction mode) is not used in the prediction.

[0324] 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:costMode2costModel<In some examples, [3 - 2. If this condition is satisfied, the two TIMD modes 2612 and 2614 are fused to generate the prediction block 2644 as discussed above. Otherwise, only the primary TIMD mode 2612 (the mode having the lower cost) is used to generate the prediction block 2644.

[0325] With the generated TIMD prediction block 2644, an encoder may generate a residual (e.g., prediction error) based on a difference between the prediction block 2644 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.

[0326] In some examples, the TIMD modes may be stored as corresponding (refined) IPMs in IPM information 2650 used in coding current block 2602. For example, indexes / indications of refined IPMs 2632 and 2634 (Mi, M2,..., Mi) may be stored as IPM information 2650. Additionally, IPM information 2650 may include parameters such as the costsDocket No.: 24-2065PCT(Ci, C2,.... Ci) and / or derived weights (wi, W2,.... Wj) for the IPMs corresponding to the TIMD modes. Different from the IPM information stored for intra coding modes such as DIMD, MIMD, OBIC, DIMD Merge List, IPM information 2650 stored for the TIMD mode does not include amplitudes of histograms. In some examples, IPM information 2650 may also include parameters such as indications of location-dependency, (Li, L2,.... L) referred to as directionalities, determined for the IPMs corresponding to the TIMD modes.

[0327] 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.

[0328] 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 samplewise TIMD fusion process. In some examples, the first region and the second region do not overlap. In other examples, they may overlap.

[0329] 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., locationdependency 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 locationDocket No.: 24-2065PCTdependency is determined as being not enabled (e.g., disabled) the value may be set to, e.g., 0, which may indicate a diagonal direction.

[0330] 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.

[0331] 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 maybe determined as follows:If SATDA< k. SATDL, locDep = 1Else if SATDL< k. SATDA, locDepi = 2Otherwise, locDept= 0

[0332] For illustrative purposes, the costs are represented as SATD costs, but other costs are possible. SATDAis the SATD cost associated to a selected TIMD mode and computed in the second region (e.g., above template). SATDAis the SATD cost associated to a selected TIMD mode and computed in the first region (e.g., left template). locDept 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, k is a scaling factor and, e.g., may be a value less than 1. For example, k may be a value comprised in the range [1 / 10; 1 / 6] such as 1 / 8.

[0333] 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.

[0334] 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 minimumDocket No.: 24-2065PCTSATD, 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.

[0335] 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 modeornon-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.

[0336] 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.

[0337] 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(IPMi) * Wi + SATD(IPM2) ‘ W2) » shift.

[0338] The template size and the template cost calculation aspects may be the same as those in the TIMD mode. After sorting the TI D merge candidates, the two best candidates from the list are selected to be used in encoder RDO algorithm.

[0339] 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.

[0340] 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.

[0341] 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.”Docket No.: 24-2065PCT

[0342] 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 TI D 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-angularTIMD 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.”

[0343] 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 “ I PM-based intra coding mode.”

[0344] FIG. 27 shows an example of the most dominant intra prediction (MDIP) mode. The MDIP is an intra mode based on histogram of gradients (HoG) extracted from neighboring templates or template areas. As shown in FIG. 27, the template area 2704 for current block 2702 includes a left template area 2706 and an above template area 2708. The template area 2704 may also be referred to as the “L-shaped” template area. In some examples, if the block size is equal to or larger than 256, 4-line / column template areas are used as shown in FIG. 27; otherwise, the template areas are set to 3 lines / columns. In some examples, the top left area 2710 is included in the template area 2704. In other examples, the top-left area 2710 is not included in the template area 2704.

[0345] In some examples, the MDIP process selects 8 intra prediction modes with 4 intra prediction modes derived from the L-shaped template area 2704, 2 intra prediction modes derived from the left template area 2706, and 2 intra prediction modes derived from the above template area 2708. In this process, duplicate intra prediction modes can be excluded and thus, modes can be added until 8 intra prediction modes are identified.

[0346] In some examples, these 8 intra prediction modes are ordered according to their respective template matching costs. The template matching cost of an intra prediction mode may be calculated based on a cost template of the current block and the template of the cost template For example, the cost template can include multiple rows above the current block and multiple columns to the left of the current block. In some examples, the cost template may be smaller than the template area 2704. For instance, the cost template may be a subset of the template area 2704. In some examples, the intra prediction mode with the minimum template matching cost is designated as the MDIP mode.

[0347] In some examples, the MDIP mode is signaled before MPM information at each coding unit (CU) level. To avoid redundancy, the MDIP mode is excluded from MPM, secondary MPM (SMPM), and non-MPM lists. To furtherDocket No.: 24-2065PCTreduce signaling overhead, after computing the HoG, 16 improbable intra modes with small HoG amplitude are also removed from MPM, SMPM, and non-MPM lists.

[0348] As can be seen from the above, the accuracy of DIMD, MDIP, and other techniques that use HoG for deriving one or more intra prediction modes (IPM) may depend on the quality of the templates used. For example, it may be important that the collection of samples included in the templates can minimize impact of noise and adequately represent the current block. In order to address these issues, this disclosure describes techniques for adaptively enlarging the template to encompass a larger area neighboring the current block while simultaneously maintaining the total number of operations to evaluate the template at manageable levels. Techniques for further improving the quality of the HoG by considering templates of multiple types of samples (e.g., luma samples and chroma samples) in the same neighboring template areas are also provided.

[0349] One or more templates of the current block that are used for calculating HoG are adaptively extended (e.g., also referred to as adaptively grown) until the cumulative sum amplitude of samples in the template reaches a threshold number. During the adaptive enlarging of the template, regions of samples can be skipped (i,e., regions of samples not included in the HoG) so that the template can extend further while still maintaining the number of samples requiring evaluation at a manageable level.

[0350] These and other features of the present disclosure are described further below.

[0351] In current implementations of MDIP, as shown in FIG. 27, the templates used for calculating the horizontal and vertical gradients of samples for inclusion in HoG comprise a fixed number of lines above and on the left of the current block (e.g., 3 or 4). In some instances, the collection of samples available for inclusion in the HoG can be extended and / or improved to reduce noise and / or more accurately correspond to the current block.

[0352] According to some embodiments of the present disclosure, the MDIP process is modified so that an adaptive number of samples is considered to fill the HoG until the total cumulative amplitude is greater or equal than a predetermined threshold. Some embodiments provide for the cumulative sum of all amplitudes in the HoG to be computed at every Nthsample, and / or at every Mthline. If the cumulative sum is smaller than a predetermined threshold, the process continues considering the next sample / line. Otherwise, the computation of the HoG terminates. The maximal number of lines / samples may be bounded to terminate the sum regardless of the value of the cumulative sum.

[0353] FIG. 28A, FIG. 28B and FIG.28C show examples of templates being adaptively extended according to some embodiments, according to some embodiments. FIG.28A shows an example of a current block 2802 with its top template 2804 being adaptively extended. FIG. 28B shows an example of the current block with its left template 2806 being adaptively extended. FIG.28C shows a scenario in which both the top template 2804 and the left template 2806 are both adaptively extended.

[0354] After another threshold, such as the number of samples, and / or lines, the step between two samples / l ines may be increased (N > 1, and / or M > 1 ). For example, if the cumulative sum already processes the three first lines, theDocket No.: 24-2065PCTstep may be increased, and the gradients may be computed on the fifth line, while the fourth line is skipped. Then, rather than processing the samples in each row, the lines with the following offset are processed: 0, 1, 2, 4, 6,...

[0355] FIG. 29 shows an example template with some rows of pixels excluded from the HoG. The fill patterns show that rows 0-2, 4, and 7 are included in the HoG, but rows 3 and 5-6 are excluded. Thus, FIG. 29 represents an example implementation in which the template 2904 (top template or left template) is initially set to 3 lines (rows) of samples closest to the current block 2902, and it is determined that cumulative sum of amplitudes in the initial template 2904 is less than a predetermined threshold. Upon the determination that the current cumulative sum of amplitudes is less than the threshold, the template is enlarged (e.g., adaptively extended / grown) and the cumulative sum of amplitudes is calculated for samples in the enlarged template. As the template is being extended (e.g., adaptively grown), implementations may skip lines, or otherwise exclude samples of certain lines from being considered in the HoG. The exclusion of some samples (e.g., samples in one line) from the HoG permits controlling the number of operations required to evaluate the HoG at a manageable level. This process iterates until either the cumulative sum of amplitudes equals or exceeds the threshold or a maximum template height is reached.

[0356] In some examples, as shown in FIG. 29, upon determining that the initial template does not reach the threshold, the template is extended by skipping one row (that is, excluding the samples of that row from being included in the HoG) and adding another one row of which the samples are included in the HoG. For example, row 3 in FIG. 29 is indicated as being excluded from the HoG, and row 4 is shown as included. When still the cumulative sum of amplitudes is less than the threshold, the template is further extended and the further extended rows include rows of which samples are excluded from the HoG and rows of which the samples are included in the HoG. In FIG.29, in the extended template 2906, rows 5 and 6 are represented as being excluded, and row 7 is indicated as being included in the HoG.

[0357] In some examples, after the evaluation of the initial template, the template is extended by adding a predetermined number (e.g., one) at a time of lines of samples eligible for inclusion in the HoG. In some examples, the added number of lines of samples eligible for inclusion in the HoG may be incremented for each subsequent extending of the template. In some examples, each extending of the template, includes adding to the template a predetermined number (e.g., 1) of skipped rows of which samples are not considered in the HoG. In some examples, each subsequent extending of the template, includes adding to the template a progressively incremented number of skipped rows of which samples are not considered in the HoG.

[0358] The process of adaptively extending the template(s) may be performed independently over some or all templates in the template area of the current block, for example, over the top and left templates. The thresholds used to fill the HoG or derive the step may be determined depending on the block size, and / or on the template size.

[0359] When computing a given gradient for a reference sample, its amplitude may be scaled with a weight, which depends on the distance of the reference sample from the current block and the direction of the neighboring template sample. Thus, in some examples, the HoG provides a collection of weighted amplitudes of samples.Docket No.: 24-2065PCT

[0360] By defining a threshold to stop the cumulative sum, the process tends to uniform the size of the templates. For example, the shorter side of the template is extended further than the longer side so that both templates include a sufficient number of samples to reach the threshold cumulative sum of amplitudes.

[0361] As the process is adaptive to the content, the smallest template may be increased by considering more pixels until a given threshold is reached. Some embodiments provide for the smaller of the top template or the left template of the current block incorporate the top-left template. FIG. 30A shows an example in which the shorter left template 3006 of the current block 3002 is, as shown in the image on the right, configured to incorporate the top-left template 3008 while the top template 3004 remains the same. However, embodiments are not limited to template configurations where the top-left template is incorporated into the shorter template. For example, some embodiments may provide for the top-left template to be incorporated into the top template or the left template irrespective of which of the two is shorter. FIG.30B, for example, illustrates the top-left template 3008 being incorporated into the top template that is longer than the left template.

[0362] FIG. 30C illustrates another example in which the top-left template is incorporated into the shorter left template 3006. The extended left template area 3020 overlaps the samples that have been included in the initial left template that incorporates the top-left template due to the cumulative sum process.

[0363] In some examples, a down-sampling process can be performed on the neighboring samples of the current block before applying the process. In this case, the HoG can be computed on the down-sampled version of the reconstructed samples / pixels around the current block. The down-sampling process can reduce the number of samples involved in the process, thereby reducing computational complexity of the process.

[0364] In some examples, the down-sampling process may also be applied to increase the template area in the reconstructed samples to improve the accuracy of the process. For example, by applying a down-sampling of 2 (vertically and / or horizontally), the area of the reconstructed samples which is processed by the process can be increased by up to 4 time (up to 2 times horizontally and up to 2 times vertically), while keeping the same number of operations. Because the area covered by the template area is increased, the HoGs may be derived more accurately and thus the IPM selected (e.g., the MDIP) may be more accurate.

[0365] The down-sampling process described above may be applied to chroma block, the luma block, or both. Another variant may apply a down-sampling process on the neighboring pixel before applying the process. In this case, the HoG will be computed on a down-sampled version of the reconstructed pixels around the current block.

[0366] The down-sampling may also be applied to consider a larger area of reconstructed pixels to improve the process. For example, by applying a down-sampling of 2 (vertically and horizontally), the area of reconstructed pixels which is processed is multiplied by 4 (2x horizontally, and x2 vertically), while keeping the same number of operations.

[0367] According to some embodiments, the adaptive templates described above may be used to improve prediction of chroma components. Compared with the corresponding luma component, chroma components may have larger smooth areas, leading to flat HoGs with no peaks. To improve the HoGs for selection of IPM for chroma components, these HoGs may be combined with the HoGs derived from the corresponding luma component. For example, the HoGDocket No.: 24-2065PCTderived from the luma top (resp. left) template maybe combined with the chroma top (resp. left) template. FIG. 31 shows an example of combining the HoG of the luma component with the HoGs of the chroma component, according to some embodiment. At 3102, the luma HoGs (e.g., the HoG of the left template area and / or the HoG of the top template area) are derived. At 3104, the HoGs of the Cb component (the HoG of the left template area, the HoG of the top template area, and the HoG of the L-shaped template area) are derived. At 3106, the HoGs of the Cr component (the HoG of the left template area, the HoG of the top template area, and the HoG of the L-shaped template area) are derived. At 3110, the luma HoG(s) is combined with the HoGs of the Cb component, which is used to derive the improved Cb (e.g., Cb MDIP) at 3112. Likewise, at 3114, the luma HoG(s) is combined with the HoGs of the Cr component, which is used to derive the improved Cr (e.g., Cr MDIP) at 3116.

[0368] As shown in FIG. 31, the luma HoG(s) may optionally be scaled at 3108 before being combined with the chroma HoGs. The scaling may be performed based on a weighting factor to balance the impact of the luma HoGs. In some examples, the weighting factor may be lower than 1 to give more weight to the chroma gradients than the luma gradients. In some examples, the weighting factor may be larger than 1 to give more weight to the luma gradients than the chroma gradients. In other examples, the weighting factor is set to one. Additionally, or alternatively, the weighting factor may be adaptive (e.g., through applying a function) to the chroma gradients, the luma gradients, the difference (e.g., the absolute difference) between luma and chroma gradients, the width and height of a current block, or the chroma subsampling (4:4:4, 4:2:2, or 4:2:0). The function of deriving the weighting factor may be a linear function, a piece-wise linear function, ora non-linear function.

[0369] The HoG of the luma component and the chroma components can be obtained using adaptive templates. In some embodiments, the selection of IPM for chroma is improved by combining luma and chroma HoGs, before deriving a predetermined number of IPMs per chroma component. In one variation, the cumulative sum of amplitudes is computed by summing luma and chroma gradients. The cumulative sum may be computed by summing Y and Cb components, or and by summing Y and Cr components gradients. The threshold Thmma-cb of the Y / Cb cumulative sum may differ from the threshold T uma-cr of the Y / Cr.

[0370] In another variation, the cumulative sum process is applied independently on luma and chroma gradients, i.e., that a threshold Thm™ exists to stop the cumulative sum on the luma, another one for the Cb component Thcb, and another Thcrfor the Cr component. Thcb and Thcr may differ.

[0371] FIG. 32 shows an example flowchart illustrating a process 3200 for generating one or more IPM for a current block by adaptively extending one or more templates used for HoG generation while also excluding regions of samples in the template from inclusion in the HoG, according to some embodiments. In some examples, process 3200 may be performed by an encoder (e.g., encoder 200 of FIG. 2) or a decoder (e.g., decoder 300 of FIG.3). As described above, MDIP currently generates a plurality of IPMs for consideration to be used to encode or decode a current block based on HoG of its top template, left template, and the L-shape template. In one example embodiment, the process 3200 can be used to generate the plurality of IPMs for MDIP. However, the process 3200 may be used for generating the plurality of IPMs for many IPM-based intra coding modes such as, for example, the DIMD-basedDocket No.: 24-2065PCTmodes (DIMD, MIMD, DIMD Merge, OBIC) or the TIMD-based modes (TIMD or TIMD merge) that generate HoG from templates of the current block.

[0372] At block 3202, the process 3200 calculates a cumulative sum of amplitudes in a first histogram of gradients of samples in a first template of the current block. The first template may be the top template or the left template of the current block. For purposes of describing process 3200, the top template of the current block is considered the first template. The height or length of the first template are not limited in embodiments. In one example, the height of the initial first template is 4 lines (rows) of samples above the current block. Embodiments are not limited to the first template, used for HoG computation, being immediately adjacent to the top edge of the current block.

[0373] Texture gradient analysis is performed on samples in the first template to generate the HoG for the first template. Each entry in the HoG corresponds to a respective angular IPM with amplitudes (or magnitudes) of the entries determined based on the gradient analysis. HoG generation using a gradient analysis of neighboring reconstructed pixels of the current block is described above in more detail.

[0374] At block 3204, the process 3200 adaptively extends the first template in a first direction while the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended first template is less than a first threshold. The adaptively extending includes, at each of one or more first intervals, excluding samples in a respective region in the first template from being included in the first histogram of gradients.

[0375] For example, the process 3200 determines whether the cumulative sum of amplitudes of all the IPMs in the first template’s HoG is equal to or greater than a predetermined threshold amplitude. If yes (I,e., that the cumulative sum of amplitudes is equal to or greater than the threshold), the process exits block 3204 and proceeds to block 3206. If not (i.e., that the cumulative sum of amplitudes is less than the threshold), the process 3200 extends the first template in the height direction (direction parallel to the corresponding edge of the current block) by adding samples or lines (rows) of samples while simultaneously excluding one or more regions intermediate between the current portion of template and the newly extended portion of the template. For example, in an example where the initial first template consists of 3 lines and the process 3200 determines that the cumulative sum of amplitudes is less than the threshold, the first template may be extended by skipping the next line (i.e., excluding the samples of the next row from being considered in the HoG) and adding the line following the next line to the first template. The excluding of some samples in the extended first template from inclusion in the HoG enables controlling the increase of required operations while enabling the evaluation of samples in a larger neighborhood of the current block.

[0376] The process 3200 may perform the determination of whether the cumulative sum of amplitudes reaches the predetermined threshold amplitude at predetermined intervals. For example, the determination may be made after each line of samples for inclusion in the HoG is added. In another example, the determination is made after each extending of the first template by adding one or more lines of samples not included in the HoG and one or more lines of samples to be included in the HoG. Embodiments are not limited to any particular number of lines being added in each iteration extending the first templateDocket No.: 24-2065PCT

[0377] In some examples, in successive iterations extending the first template, an increasing step size is applied to the number of skipped lines. For example, in the first extending of the first template, one line is skipped between the current top line of the first template and the extended one or more lines of samples to be included in the HoG. In the second extending of the first template, two lines are skipped between the current top line of the first template and the extended one or more lines of samples to be included in the HoG. Alternatively, or in combination with the changing step size for skipped rows, the process 3200 may apply an increasing step size to the number of lines of samples to be included in the HoG. In some examples, the step size for skipped lines and / or added lines is maintained at the same value. In some examples, the step size for skipped lines and / or added lines decreases with each successive iteration.

[0378] In some examples, for each iteration extending the first template, another threshold specified in terms of a maximum number of lines or samples may be evaluated. If the extended first template exceeds the threshold maximum number of lines or samples, the extending of the first template is terminated even if it has not reached the threshold cumulative sum amplitude.

[0379] It should be noted that after each extending of the first template, some samples in the extended first template are ineligible for inclusion in the HoG because they belong to a skipped region (e.g., skipped line). Thus, the HoG is calculated based only on the eligible samples.

[0380] In some examples, samples for inclusion in the HoG are obtained after down sampling the first template. Down sampling enables extending the area covered by the first template while maintaining the same level of calculations required for the HoG.

[0381] In some examples, the cumulative sum of amplitudes is calculated using weighted amplitudes of the eligible samples. The amplitudes of respective samples can be weighted according to the distance from the current block to those samples.

[0382] In some examples, top-left template of the current block may be adaptively extended in combination with a selected one of the first template or the second template. For example, the samples of the top-left template may be included in the HoG of the selected one of the first template or the second template. In some examples, the selected one of the first template or the second template is the shorter template.

[0383] At block 3206, the process 3200 determines at least one I PM in accordance with at least the first histogram of gradients. In an example, the IPMs with the highest amplitudes in the HoG may be selected. In some examples, the selection of an IPM for predicting the current block from the plurality of derived IPMs may be performed in any of the manners described above in relation to the IPM-based intra prediction modes.

[0384] In some examples, before block 3206, additional operations may be performed. In one example, a second template may be used to generate a second set of IPM. For purposes of this description, since the first template is above the current block, the second template is left of the current block.Docket No.: 24-2065PCT

[0385] The second template may be adaptively extended in a manner similar to the first template. The second template, being parallel to the current block’s left edge, is also extended (I.e., grown) in its height direction The height direction of the second template is at a right angle to the height direction of the first template.

[0386] After completing the adaptive extending of the second template, an IPM can be determined in accordance with at least the first histogram of gradients and the second histogram of gradients. An example process for using first template and a second template of which one is the top template and the other is the left template of the current block is described in relation to FIG. 33.

[0387] In another example, an adaptive extending process for templates similar to that described above may be applied to a first template that comprises chroma samples and a second template that is in the same orientation as the first template and comprising luma samples, to generate improved chroma components. An example process is described in relation to FIG. 35.

[0388] The extending of the first template is described above in terms of adding one or more lines. Alternatively, the extending may be performed by adding one or more samples.

[0389] FIG. 33 illustrates an example flowchart of another example process 3300 for generating one or more IPM for a current block by adaptively extending one or more templates used for HoG generation while excluding regions of samples in the template from inclusion in the HoG, according to some embodiments. In some examples, process 3300 may be performed by an encoder (e.g., encoder 200 of FIG. 2) or a decoder (e.g., decoder 300 of FIG.3). As described above, MDIP currently generates a plurality of IPMs for consideration to be used to encode or decode a current block based on HoG of its top template, left template, and the L-shape template. In one example embodiment, the process 3300 can be used to generate the plurality of IPMs for MDIP. However, the process 3300 can also be used for generating the plurality of IPMs for many IPM-based intra coding modes such as, for example, the DIMD- based modes (DIMD, MIMD, DIMD Merge, OBIC) or the TIMD-based modes (TIMD or TIMD merge).

[0390] At block 3302 a cumulative sum of amplitudes is calculated in a first histogram of gradients of samples in a first template of the current block, and at block 3304, a cumulative sum of amplitudes is calculated in a second histogram of gradients of samples in a second template of the current block. It may be considered that the first template is above the current block and the second template is left of the current block. Calculating of the HoG may be performed in a similar manner to that described at block 3202 of FIG. 32.

[0391] At block 3306, the first template is adaptively extended (i.e., grown) in a first direction while the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended first template is less than a first threshold. The adaptively extending includes, at each of one or more first intervals, excluding samples in a respective region in the first template from being included in the first histogram of gradients. This operation may be performed in a similar manner to that described at block 3204 of FIG.32.

[0392] At block 3308, the second template is adaptively extended (i.e., grown) in a second direction while the cumulative sum of amplitudes in the second histogram of gradients of eligible samples of the adaptively extended second template is less than a second threshold. The adaptively extending includes, at each of one or more secondDocket No.: 24-2065PCTintervals, excluding samples in a respective region in the second template from being included in the second histogram of gradients. The adaptive extending of the second template may be performed in a similar manner as of the first template. The first template and the second template are both extended in their respective height direction, but the height direction of the second template is orthogonal to the height direction of the first template.

[0393] The first threshold and the second threshold may or may not be the same. The first interval and the second interval may or may not be the same. A step size of the added lines and / or skipped lines may or may not be the same between the first and second templates.

[0394] At block 3310, at least one intra prediction mode (IPM) is determined in accordance with the first histogram of gradients, the second histogram of gradients, and a third histogram of gradients, wherein the third histogram of gradients is obtained from a third template that includes the first template and the second template.

[0395] In an example, the IPM is determined in accordance with the first histogram of gradients, the second histogram of gradients and a third histogram of gradients, wherein the third histogram of gradients is obtained from a third template that includes the first template and the second template. This may include evaluating a respective plurality of IPMs from each of the first histogram of gradients, second histogram of gradients, and the third histogram of gradients, according to an IPM-based intra prediction mode, such as, for example, MDIP.

[0396] In some examples, the third template (e.g., L-shape template) includes a fourth template (e.g., top-left template) located top-left of the current block, and the third histogram of gradients comprises gradients of samples in the fourth template. In some examples, one of the first template or the second template is shorter in length than the other, and the fourth template is combined with the shorter one of the first template or the second template for purposes of adaptively extending. Alternatively, in some examples, the third template includes only the first template and the second template.

[0397] In some examples, one of the first template or the second template having a shorter length is configured to be adaptively extended with a larger step size of added rows than the other of the first template or the second template.

[0398] In some examples, samples for inclusion in the HoG are obtained after down sampling the first template and / or the second template. Down sampling enables extending the area covered by the templates while maintaining the same level of calculations required for the HoG.

[0399] In some examples, the cumulative sum of amplitudes is calculated using weighted amplitudes of the eligible samples. The amplitudes of respective samples can be weighted according to the distance from the current block to those samples.

[0400] FIG. 34 shows an example flowchart illustrating a process 3400 for generating one or more IPM for a current block by adaptively extending a top template and a left template used for HoG generation while including the top-left template in either the top or left template, according to some embodiments. In some examples, process 3400 may be performed by an encoder (e.g., encoder 200 of FIG. 2) or a decoder (e.g., decoder 300 of FIG. 3). As described above, MDIP currently generates a plurality of IPMs for consideration to be used to encode or decode a current block based on HoG of its top template, left template, and the L-shape template. In one example embodiment, the processDocket No.: 24-2065PCT3400 can be used to generate the plurality of IPMs for MDIP. However, the process 3400 can also be used for generating the plurality of IPMs for many IPM-based intra coding modes such as, for example, the DIMD-based modes (DIMD, MIMD, DIMD Merge, OBIC) or the TIMD-based modes (TIMD or TIMD merge).

[0401] At block 3402, a cumulative sum of amplitudes in a first histogram of gradients of samples in a top template of a current block and a cumulative sum of amplitudes in a second histogram of gradients of samples in a left template of the current block are calculated. The HoG calculation may be performed similarly to the description of 3202 or 3304.

[0402] At block 3404, the top template is adaptively extended in a first direction while the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended top template is less than a first threshold. Additionally, the left template is adaptively extended in a second direction while the cumulative sum of amplitudes in the second histogram of gradients of eligible samples of the adaptively extended left template is less than a second threshold. The adaptively extending includes extending a top-left template of the current block in correspondence with the shorter of top template or the left template.

[0403] In some examples, the first direction may be in a vertical direction away from the current block (e.g., upwards) and the second direction may be in a horizontal direction away from the current block (e.g., to the left).

[0404] The adaptive extending of the templates may be performed similarly to the process described in 3204 and / or 3306, except that the excluding of regions (e.g., lines or samples) in the templates from inclusion in HoGs performed in 3204 and / or 3306 may be optional in process 3400.

[0405] At block 3406, at least one intra prediction mode (IPM) is determined in accordance with at least the first histogram of gradients and the second histogram of gradient. This may be performed in a manner similar to that described at block 3310.

[0406] FIG. 35 shows an example flowchart illustrating a process 3500 for generating one or more IPM for a current block by adaptively extending a template comprising chroma samples and a corresponding template comprising luma samples used for HoG generation, according to some embodiments. In some examples, process 3500 may be performed by an encoder (e.g., encoder 200 of FIG. 2) or a decoder (e.g., decoder 300 of FIG. 3). As described above, MDIP currently generates a plurality of IPMs for consideration to be used to encode or decode a current block based on HoG of its top template, left template, and the L-shape template. In one example embodiment, the process 3500 can be used to generate the plurality of IPMs for MDIP. However, the process 3500 can also be used for generating the plurality of IPMs for many IPM-based intra coding modes such as, for example, the DIMD-based modes (DIMD, MIMD, DIMD Merge, OBIC) or the TIMD-based modes (TIMD or TIMD merge).

[0407] At block 3502, a cumulative sum of amplitudes in a first histogram of gradients of chroma samples in a first template of a current block and a cumulative sum of amplitudes in a second histogram of gradients of luma samples in a second template of the current block are calculated. The first and second templates are both either located above the current block or located left of the current block. This operation may be similar to 3202, 3304 or 3402.

[0408] At block 3504, the first template is adaptively extended in a first direction while the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended first template is less than aDocket No.: 24-2065PCTfirst threshold. Additionally, the second template is adaptively extended in a second direction while the cumulative sum of amplitudes in the second histogram of gradients of eligible samples of the adaptively extended second template is less than a second threshold.

[0409] In some examples, the first direction may be in a vertical direction away from the current block (e.g., upwards) and the second direction may be in a horizontal direction away from the current block (e.g., to the left).

[0410] The adaptive extending of the templates may be performed similarly to the process described in 3204 and / or 3306, except that the excluding of regions (e.g., lines or samples) in the templates from inclusion in HoGs performed in 3204 and / or 3306 may be optional in process 3500.

[0411] In an example, samples in the first template are one of Cb or Cr samples.

[0412] In an example, the first threshold is different from the second threshold. For example, the cumulative sum amplitude threshold for the chroma component and the cumulative sum amplitude threshold for the luma component are different and are applied independently in chroma and luma components.

[0413] In another example, the first threshold is equal to the second threshold. For example, the cumulative sum amplitude may be computed by summing Y and Cb components, or and by summing Y and Cr components gradients.

[0414] At 3506, at least one I PM is determined in accordance with at least the first histogram of gradients and the second histogram of gradients. This operation may be similar to 3310 or 3406.

[0415] 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 3600 is shown in FIG. 36. Blocks depicted in the figures above, such as the blocks in FIGS. 1, 2, and 3, may execute on one or more computer systems 3600. Furthermore, each of the steps of the flowcharts depicted in this disclosure may be implemented on one or more computer systems 3600.

[0416] Computer system 3600 includes one or more processors, such as processor 3604. Processor 3604 may be, for example, a special purpose processor, general purpose processor, microprocessor, or digital signal processor. Processor 3604 may be connected to a communication infrastructure 3602 (for example, a bus or network). Computer system 3600 may also include a main memory 3606, such as random-access memory (RAM), and may also include a secondary memory 3608.

[0417] Secondary memory 3608 may include, for example, a hard disk drive 3610 and / or a removable storage drive 3612, representing a magnetic tape drive, an optical disk drive, or the like. Removable storage drive 3612 may read from and / or write to a removable storage unit 3616 in a well-known manner. Removable storage unit 3616 represents a magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive 3612. As will be appreciated by persons skilled in the relevant art(s), removable storage unit 3616 includes a computer usable storage medium having stored therein computer software and / or data.Docket No.: 24-2065PCT

[0418] In alternative implementations, secondary memory 3608 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 3600. Such means may include, for example, a removable storage unit 3618 and an interface 3614. 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 3618 and interfaces 3614 which allow software and data to be transferred from removable storage unit 3618 to computer system 3600.

[0419] Computer system 3600 may also include a communications interface 3620. Communications interface 3620 allows software and data to be transferred between computer system 3600 and external devices. Examples of communications interface 3620 may include a modem, a network interface (such as an Ethernet card), a communications port, etc... Software and data transferred via communications interface 3620 are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface 3620. These signals are provided to communications interface 3620 via a communications path 3622. Communications path 3622 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.

[0420] 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 3616 and 3618 or a hard disk installed in hard disk drive 3610. These computer program products are means for providing software to computer system 3600. Computer programs (also called computer control logic) may be stored in main memory 3606 and / or secondary memory 3608. Computer programs may also be received via communications interface 3620. Such computer programs, when executed, enable the computer system 3600 to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor 3604 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 3600.

[0421] 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

1. Docket No.: 24-2065PCTCLAIMS1. A method, comprising:calculating a cumulative sum of amplitudes in a first histogram of gradients of samples in a first template of a current block and a cumulative sum of amplitudes in a second histogram of gradients of samples in a second template of the current block;adaptively extending:the first template in a first direction while the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended first template is less than a first threshold; and the second template in a second direction while the cumulative sum of amplitudes in the second histogram of gradients of eligible samples of the adaptively extended second template is less than a second threshold; anddetermining, for coding the current block, at least one intra prediction mode (I PM) in accordance with at least the first histogram of gradients and the second histogram of gradients.

2. The method of claim 1, wherein the adaptively extending includes extending a top-left template of the current block in correspondence with the shorter of first template or the second template.

3. The method of any one of claims 1-2, wherein the first template is a top template of the current block and the second template is a left template of the current block.

4. The method of any one of claims 1-3, wherein one of the first and second template comprises a top-left template of the current block.

5. A method comprising:calculating a cumulative sum of amplitudes in a first histogram of gradients of samples in a first template of a current block;adaptively extending the first template in a first direction while the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended first template is less than a first threshold, wherein the adaptively extending includes, at each of one or more first intervals, excluding samples in a respective region in the first template from being included in the first histogram of gradients; anddetermining, for coding the current block, at least one intra prediction mode (I PM) in accordance with at least the first histogram of gradients.

6. The method of claim 5, further comprising:calculating a cumulative sum of amplitudes in a second histogram of gradients of samples in a second template of the current block, wherein the first template is above the current block and the second template is left of the current block;adaptively extending the second template in a second direction while the cumulative sum of amplitudes in the second histogram of gradients of eligible samples of the adaptively extended second template is less than a secondDocket No.: 24-2065PCTthreshold, wherein the adaptively extending includes, at each of one or more second intervals, excluding samples in a respective region in the second template from being included in the second histogram of gradients; and wherein the determining an IPM in accordance with at least the first histogram of gradients comprises determining the IPM in accordance with at least the first histogram of gradients and the second histogram of gradients.

7. The method of claim 6, wherein the first template is adaptively extended at a first step size of added rows of samples and the second template is adaptively extended at a second step size of added rows, wherein the first step size is the same as the second step size.

8. The method of claim 6, wherein the first template is adaptively extended at a first step size of added rows of samples and the second template is adaptively extended at a second step size of added rows, wherein the first step size is different than the second step size.

9. The method of claim 8, wherein one of the first template or the second template having a shorter length is configured to be adaptively extended with a larger step size of added rows than the other of the first template or the second template.

10. The method of any one of claims 6-9, wherein the first interval is different from the second interval.

11. The method of any one of claims 6-9, wherein the first interval is the same as the second interval.

12. The method of any one of claims 5-11, wherein the each of one or more first intervals corresponds to a first number of consecutive one or more rows of samples added to the first template, and the respective region comprises a second number of consecutive one or more rows of samples.

13. The method of any one of claim 12, wherein the second number is incremented for each said respective region.

14. A method, comprising:calculating a cumulative sum of amplitudes in a first histogram of gradients of chroma samples in a first template of a current block and a cumulative sum of amplitudes in a second histogram of gradients of luma samples in a second template of the current block, wherein the first and second templates are both either located above the current block or located left of the current block;adaptively extending:the first template in a first direction while the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended first template is less than a first threshold; and the second template in a second direction while the cumulative sum of amplitudes in the second histogram of gradients of eligible samples of the adaptively extended second template is less than a second threshold; anddetermining, for coding the current block, at least one intra prediction mode (IPM) in accordance with at least the first histogram of gradients and the second histogram of gradients.

15. The method of claim 14, wherein samples in the first template are one of Cb or Cr samples.

16. The method of any one of claims 14-15, wherein the first threshold is different from the second threshold.Docket No.: 24-2065PCT17. The method of any one of claims 14-15, wherein the first threshold is equal to the second threshold.

18. The method of any one of claims 1-4, 6-17, wherein the determining the IPM in accordance with at least the first histogram of gradients further comprises determining the IPM in accordance with the first histogram of gradients, the second histogram of gradients, and a third histogram of gradients, wherein the third histogram of gradients is obtained from a third template that includes the first template and the second template.

19. The method of claim 18, wherein the determining the IPM in accordance with at least the first histogram of gradients further comprises evaluating a respective plurality of IPMs from each of the first histogram of gradients, second histogram of gradients, and the third histogram of gradients, according to most dominant intra prediction (MDIP).

20. The method of any one of claims 18-19, wherein the third template includes a fourth template located top-left of the current block, and the third histogram of gradients comprises gradients of samples in the fourth template.

21. The method of any one of claims 18-19, wherein the third template includes only the first template and the second template.

22. The method of any one of claims 20-21, wherein one of the first template or the second template is shorter in length than the other, and the fourth template is combined with the shorter one of the first template or the second template.

23. The method of any one of claims 1-4 or 6-22, wherein the first threshold is different from the second threshold.

24. The method of any one of claims 1-4 or 6-22, wherein the first threshold is the same as the second threshold.

25. The method of any one of claims 1-24, wherein the adaptively extending the first template in the first direction while the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended first template is less than a first threshold comprises:down sampling the first template in at least one of a horizontal direction and a vertical direction; and calculating the cumulative sum of amplitudes based on samples in the down sampled first template.

26. The method of any one of claims 1-25, wherein the cumulative sum of amplitudes comprises weighted amplitudes that are weighted according to a distance from the current block to samples associated with the weighted amplitudes.

27. The method of any one of claims 1-13 or 18-26, further comprising:calculating a cumulative sum of amplitudes in a fifth histogram of gradients of samples in a fifth template of the current block, wherein the first template and fifth template are either both above the current block or left of the current block, and wherein the samples in the first template are chroma samples and samples in the fifth template are luma samples;adaptively extending the fifth template in the first direction while the cumulative sum of amplitudes in the fifth histogram of gradients of eligible samples of the adaptively extended fifth template is less than a fifth threshold, wherein the adaptively extending includes, at each of one or more fifth intervals, excluding samples in a respective region in the fifth template from being included in the fifth histogram of gradients; andDocket No.: 24-2065PCTwherein the determining an IPM in accordance with at least the first histogram of gradients comprises determining the IPM in accordance with at least the first histogram of gradients and the second histogram of gradients.

28. The method of claim 27, wherein first threshold and the fifth threshold are different.

29. The method of any one of claim 27-28, wherein samples in the first template are one of Cb or Cr samples.

30. The method of any one of claims 1-13 or 18-29, wherein the samples in the first template are chroma samples, and wherein the adaptively extending further includes:combining the cumulative sum of amplitudes in the first histogram of gradients of eligible samples of the adaptively extended first template and a cumulative sum of amplitudes in a fifth histogram of gradients of eligible samples of an adaptively extended fifth template, wherein samples of the fifth template are luma samples; and adaptively extending the first template and the fifth template in the first direction while the combined cumulative sum of amplitudes is less than the first threshold.

31. The method of any one of claims 1-30, further comprising:determining, based on the at least one IPM, a prediction block for coding the current block;decoding, from a bitstream, a residual block for the current block; andreconstructing the current block based on combining the prediction block and the residual block.

32. The method of any one of claims 1-31, further comprising:receiving, from the bitstream, an indication of an intra-based coding mode associated with one or more histogram of gradients, wherein the calculating the cumulative sum of amplitudes in the first histogram of gradient is based on the indication.

33. The method of any one of claims 1-30, further comprising:determining, based on the at least one IPM, a prediction block for coding the current block;encoding, in a bitstream, a residual block based on a difference between the current block and the prediction block.

34. The method of any one of claims 1-30 or 33, further comprising:encoding, in the bitstream, an indication of an intra-based coding mode associated with one or more histogram of gradients, wherein the calculating the cumulative sum of amplitudes in the first histogram of gradient is based on the indication.

35. The method of any one of claims 32 or 34, wherein the intra-based coding mode comprises an MDIP mode or a decoder-side intra mode derivation (DIMD) mode.

36. 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 1-35.

37. An encoder comprising:one or more processors; andDocket No.: 24-2065PCTmemory storing instructions that, when executed by the one or more processors, cause the encoder to perform the method of any one of claim 1-30 or 33-35.

38. 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 -30 or 33-35.

39. A decoder comprising:one or more processors; andmemory storing instructions that, when executed by the one or more processors, cause the decoder to perform the method of any one of claims 1-32 or 35.

40. 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 1-32 or 35.

41. A bitstream generated according to any one of claims 1 -30 or 33-35.

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