Coding mode signal re-ordering for video coding

Abstract

A decoder determines a signaling order of a plurality of sub-modes of a coding mode for a block of a video. The decoder further parses a first flag from a bitstream and determines, based on a value of the first flag and the signaling order, a sub-mode of the plurality of sub-modes. The decoder reconstructs the block using the sub-mode.

Description

Docket No.: 24-2022PCT TITLE Coding Mode Signal Re-ordering for Video Coding CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.63 / 573,820, filed April 3, 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 embodiments.Docket No.: 24-2022PCT

[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 as described with respect to FIG.18, according to some embodiments.

[0026] FIG.21 shows an example of spatial non-adjacent neighboring blocks of a current block, according to some embodiments.

[0027] FIG. 22A shows an example of IPM information from a plurality of (previously reconstructed) neighboring blocks of a block used to determine (e.g., generating, reconstructing, predicting) the block, according to some embodiments.

[0028] FIG.22B shows an example graphical representation of combining the IPM information from the plurality of neighboring blocks of FIG.22A to generate a merged histogram of gradients (MHoG) if the block was previously coded using the MIMD mode, according to some embodiments.

[0029] FIG.22C shows an example graphical representation of combining the IPM information from the plurality of neighboring blocks of FIG.22A to generate a histogram of occurrences (HoC) if the block was previously coded using the OBIC mode, according to some embodiments.

[0030] FIG.23 shows an example flowchart of the intra Merge List mode for deriving a list of intra merge candidates, according to some embodiments.

[0031] FIG. 24 shows a flowchart of an example process for generating a history-based table of intra merge candidates, according to some embodiments.

[0032] FIG.25 illustrates a flowchart of an example of the adaptive DIMD mode signaling process based on DIMD mode activation, in accordance with some embodiments of the present disclosure.

[0033] FIG. 26 illustrates an example of a signaling tree for signaling the DIMD mode flags, in accordance with embodiments of the present disclosure.

[0034] FIG.27 illustrates another example of a signaling tree for signaling the DIMD mode flags, in accordance with embodiments of the present disclosure.

[0035] FIG.28 illustrates a flowchart of an example of the adaptive DIMD mode signaling process at the encoder based on DIMD mode activation mechanisms, in accordance with embodiments of the present disclosure.

[0036] FIG.29 illustrates a flowchart of an example of the adaptive DIMD mode signaling process at the decoder based on DIMD mode activation mechanisms, in accordance with embodiments of the present disclosure.

[0037] FIG.30A illustrates another example of a signaling tree for signaling the DIMD mode flags, in accordance with embodiments of the present disclosure.

[0038] FIG.30B shows an example of an updated signaling tree of the signaling tree shown FIG.30A after a DIMD mode is determined to be disabled or deactivated, in accordance with embodiments of the present disclosure.

[0039] FIG.31A illustrates another example of a signaling tree for signaling the DIMD mode flags, in accordance with embodiments of the present disclosure.Docket No.: 24-2022PCT

[0040] FIG.31B shows an example of an updated signaling tree of the signaling tree shown FIG.31A after a DIMD mode is determined to be disabled or deactivated, in accordance with embodiments of the present disclosure.

[0041] FIG.32 illustrates a flowchart of an example of the DIMD mode signal re-ordering process at the encoder, in accordance with some embodiments of the present disclosure.

[0042] FIG.33 illustrates a flowchart of an example of the DIMD mode signal re-ordering process at the decoder, in accordance with some embodiments of the present disclosure.

[0043] FIG.34 illustrates a flowchart of an example of combining DIMD mode signal re-ordering and mode activation at the decoder, in accordance with some embodiments of the present disclosure.

[0044] FIG.35 illustrates a flowchart of an example of the coding mode signal re-ordering process at the encoder, in accordance with some embodiments of the present disclosure.

[0045] FIG.36 illustrates a flowchart of an example of the coding mode signal re-ordering process at the decoder, in accordance with some embodiments of the present disclosure.

[0046] FIG. 37 illustrates a block diagram of an example computer system in which embodiments of the present disclosure may be implemented. DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] Also, it is noted that individual embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in a figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination can correspond to a return of the function to the calling function or the main function.Docket No.: 24-2022PCT

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.).

[0054] Source device 102 may comprise (e.g., for encoding video sequence 108 into bitstream 110) one or more of a video source 112, an encoder 114, and / or an output interface 116. Video source 112 may provide and / or generate video sequence 108 based on a capture of a natural scene and / or a synthetically generated scene. A synthetically generated scene may be a scene comprising computer generated graphics and / or screen content. Video source 112Docket No.: 24-2022PCT 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.

[0055] 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.

[0056] 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.

[0057] For temporal prediction, encoder 114 may search for a block similar to the block being encoded in another picture (e.g., referred to as a reference picture) of video sequence 108. The block determined during the search (e.g., referred to as a prediction block) may then be used to predict the block being encoded. For spatial prediction, encoder 114 may form a prediction block based on data from reconstructed neighboring samples of the block to be encoded within the same picture of video sequence 108. A reconstructed sample refers to a sample that was encoded and then decoded. Encoder 114 may determine a prediction error (e.g., also referred to as a residual) based on the difference between a block being encoded and a prediction block. The prediction error may represent non-redundant information that may be sent / transmitted to a decoder for accurate decoding of video sequence 108.Docket No.: 24-2022PCT

[0058] 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.

[0059] 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).

[0060] 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.

[0061] 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).

[0062] Decoder 120 may decode video sequence 108 from encoded bitstream 110. The decoder 120 may generate prediction blocks for pictures of video sequence 108 in a similar manner as encoder 114 and determine the prediction errors for the blocks, for example, to decode video sequence 108. Decoder 120 may generate the prediction blocks using / based on prediction types, prediction modes, and / or motion vectors received in bitstream 110. Decoder 120 may determine the prediction errors using the transform coefficients received in bitstream 110. Decoder 120 may determine the prediction errors by weighting transform basis functions using the transform coefficients. Decoder 120Docket No.: 24-2022PCT 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.

[0063] 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.

[0064] 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.

[0065] Encoder 114 and / or decoder 120 may operate according to one or more proprietary or industry video coding standards. For example, encoder 114 and / or decoder 120 may operate in accordance with one or more proprietary, open-source, and / or standardized protocols (e.g., International Telecommunications Union Telecommunication Standardization Sector (ITU-T) H.263, ITU-T H.264 and Moving Picture Expert Group (MPEG)-4 Visual (also known as Advanced Video Coding (AVC)), ITU-T H.265 and MPEG-H Part 2 (also known as High Efficiency Video Coding (HEVC)), ITU-T H.265 and MPEG-I Part 3 (also known as Versatile Video Coding (VVC)), the WebM VP8 and VP9 codecs, and / or AOMedia Video 1 (AV1), and / or any other video coding protocol).

[0066] FIG.2 shows an example encoder. Encoder 200 as shown in FIG.2 may implement one or more processes described herein. Encoder 200 may encode a video sequence 202 into a bitstream 204 for more efficient storage and / or transmission. Encoder 200 may be implemented in video coding / decoding system 100 as shown in FIG.1 (e.g., as encoder 114) or in any computing, communication, or electronic device (e.g., desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, video streaming device, etc.). Encoder 200 may comprise one or more of an inter prediction unit 206, an intra prediction unit 208, combiners 210 and 212, a transform and quantization unit (TR + Q) 214, an inverse transform and quantization unit (iTR + iQ) 216, an entropy coding unit 218, one or more filters 220, and / or a buffer 222.

[0067] 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 mayDocket No.: 24-2022PCT 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.

[0068] 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.

[0069] 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.

[0070] 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).

[0071] 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.

[0072] Inverse transform and quantization unit (iTR + iQ) 216 may inverse quantize and inverse transform the quantized transform coefficients to determine a reconstructed prediction error. Combiner 212 may combine the reconstructed prediction error with the prediction block to form a reconstructed block. Filter(s) 220 may filter the reconstructed block, for example, using a deblocking filter, a sample-adaptive offset (SAO) filter, constrained directional enhancement filters (CDEFs), and / or loop restoration (LR) filters. Buffer 222 may store the reconstructed block for prediction of one or more other blocks in the same and / or different picture of video sequence 202.

[0073] 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 moreDocket No.: 24-2022PCT units of encoder 200 such that bitstream 204 may be generated in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other video cording protocol. For example, the encoder control unit may control the one or more units of encoder 200 such that bitstream 204 may be generated in conformance with one or more of ITU-T H.263, AVC, HEVC, VVC, VP8, VP9, AV1, and / or any other video coding standard / format.

[0074] 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.

[0075] The prediction type used to encode a block (intra or inter prediction), prediction information of the block (intra prediction mode if intra predicted, motion vector, etc.), and / or transform and / or quantization parameters, may be sent to entropy coding unit 218 to be further compressed (e.g., to reduce the bitrate). For example, entropy coding unit 218 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-based context-based binary arithmetic coding (SBAC), and / or symbol-to-symbol adaptive multi-symbol (non- binary) arithmetic coding to achieve further compression. The prediction type, prediction information, and / or transform and / or quantization parameters may be packed with the prediction error to form bitstream 204.

[0076] 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).

[0077] FIG.3 shows an example decoder. A decoder 300 as shown in FIG.3 may implement one or more processes described herein. Decoder 300 may decode a bitstream 302 into a decoded video sequence 304 for display and / or some other form of consumption. Decoder 300 may be implemented in video coding / decoding system 100 in FIG.1 and / or in a computing, communication, or electronic device (e.g., desktop computer, laptop computer, tablet computer, smart phone, wearable device, television, camera, video gaming console, set-top box, and / or video streaming device). Decoder 300 may comprise an entropy decoding unit 306, an inverse transform and quantizationDocket No.: 24-2022PCT (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.

[0078] Decoder 300 may comprise a decoder control unit configured to control one or more units of decoder 300. The decoder control unit may control the one or more units of decoder 300 such that bitstream 302 is decoded in conformance with the requirements of one or more proprietary coding protocols, industry video coding standards, and / or any other communication protocol. For example, the decoder control unit may control the one or more units of decoder 300 such that the bitstream 302 is decoded in conformance with one or more of ITU-T H.263, AVC, HEVC, VVC, VP8, VP9, AV1, and / or any other video coding standard / format.

[0079] 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.

[0080] Entropy decoding unit 306 may entropy decode the bitstream 302. For example, entropy decoding unit 306 may apply context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and syntax-based context-based binary arithmetic coding (SBAC) to decompress the prediction type used to encode a block (intra or inter prediction), prediction information of the block (intra prediction mode if intra predicted, motion vector, etc.), and transform and quantization parameters. Inverse transform and quantization unit 308 may inverse quantize and / or inverse transform the quantized transform coefficients to determine a decoded prediction error. Combiner 310 may combine the decoded prediction error with a prediction block to form a decoded block. The prediction block may be generated by intra prediction unit 318 or inter prediction unit 316 (e.g., as described above with respect to encoder 200 in FIG 2). Filter(s) 312 may filter the decoded block, for example, using a deblocking filter, 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.

[0081] Decoder 300 is merely an example and decoders different from decoder 300 and / or modified versions of decoder 300 may perform the methods and processes as described herein. For example, decoder 300 may have other components and / or arrangements. One or more of the components shown in FIG.3 may be optionally included in decoder 300 (e.g., entropy decoding unit 306 and / or filters(s) 312).

[0082] 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 copyDocket No.: 24-2022PCT unit may exploit repeated patterns that appear in screen content. The screen content may include computer generated text, graphics, animation, etc.

[0083] 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.

[0084] A picture (e.g., in HEVC, or any other coding standard / format) may be partitioned into non-overlapping square blocks, which may be referred to as coding tree blocks (CTBs). The CTBs may comprise samples of a sample array. A CTB may have a size of 2nx2n samples, where n may be specified by a parameter of the encoding system. For example, n may be 4, 5, 6, or any other value. A CTB may have any other size. A CTB may be further partitioned by a recursive quadtree partitioning into coding blocks (CBs) of half vertical and half horizontal size. The CTB may form the root of the quadtree. A CB that is not split further as part of the recursive quadtree partitioning may be referred to as a leaf CB of the quadtree, and otherwise may be referred to as a non-leaf CB of the quadtree. A CB may have a minimum size specified by a parameter of the encoding system. For example, a CB may have a minimum size of 4x4, 8x8, 16x16, 32x32, 64x64 samples, or any other minimum size. A CB may be further partitioned into one or more prediction blocks (PBs) for performing inter and / or intra prediction. A PB may be a rectangular block of samples on which the same prediction type / mode may be applied. A CB may also be further partitioned into intra sub-partitions (ISP) where the reconstructed samples of each sub-partition are available to generate the prediction of the next sub- partition. For example, a CB may be split into 2 to 4 sub-partitions. For transformations, a CB may be partitioned into one or more transform blocks (TBs). A TB may be a rectangular block of samples that may determine / indicate an applied transform size.

[0085] 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.

[0086] The example CTB 400 of FIG.4 is partitioned into 10 leaf CBs respectively labeled 0-9, but may be partitioned into other quantities of leaf CBs. The 10 leaf CBs may correspond to 10 CB leaf nodes (e.g., 10 CB leaf nodes of quadtree 500 as shown in FIG.5). In other examples, a CTB may be partitioned into a different number of leaf CBs. The resulting quadtree partitioning of CTB 400 may be scanned using a z-scan (e.g., left-to-right, top-to-bottom) to form the sequence order for encoding / decoding the CB leaf nodes. A numeric label (e.g., indicator, index) of each CBDocket No.: 24-2022PCT 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.

[0087] A picture, in VVC (or in any other coding standard / format), may be partitioned in a similar manner (such as in HEVC). A picture may be first partitioned into non-overlapping square CTBs. The CTBs may then be partitioned, using a recursive quadtree partitioning, into CBs of half vertical and half horizontal size. A quadtree leaf node (e.g., in VVC) may be further partitioned by a binary tree or ternary tree partitioning (or any other partitioning) into CBs of unequal sizes.

[0088] FIG.6 shows example binary tree and ternary tree partitions. A binary tree partition may divide a parent block in half in either a vertical direction 602 or a horizontal direction 604. The resulting partitions may be half in size as compared to the parent block. In other examples, the resulting partitions may correspond to sizes that are less than and / or greater than half of the parent block size. A ternary tree partition may divide a parent block into three parts in either a vertical direction 606 or a horizontal direction 608. FIG.6 shows an example in which the middle partition may be twice as large as the other two end partitions in the ternary tree partitions. In other examples, partitions may be of other sizes relative to each other and to the parent block. Binary and ternary tree partitions are examples of multi-type tree partitioning. Multi-type tree partitions may comprise partitioning a parent block into other quantities of smaller blocks. The block partitioning strategy (e.g., in VVC) may be referred to as a combination of quadtree and multi-type tree partitioning (quadtree + multi-type tree partitioning) because of the addition of binary and / or ternary tree partitioning to quadtree partitioning.

[0089] FIG.7A shows an example of combined quadtree and multi-type tree partitioning of a CTB 700A. FIG.7B shows an example tree 700B corresponding to the combined quadtree and multi-type tree partitioning of CTB 700A shown in FIG.7A. In both FIGS.7A and 7B, quadtree splits are shown in solid lines and multi-type tree splits are shown in dashed lines. For ease of explanation, CTB 700A is shown with the same quadtree partitioning as the CTB 400 described in FIG.4, and a description of the quadtree partitioning of CTB 700A, which is similar to that for CTB 400, is omitted. The quadtree partitioning of 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.

[0090] 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 CBs respectively labeled 9 and 14 in FIGS.7A and 7B. The remaining, non-leaf CB may be partitioned first into two CBs based on a horizontal binary tree partition. One of the two CBs may be a leaf CB labeled 10. The other of the two CBs may be further partitioned into three CBs based on a vertical ternary tree partition. The resulting three CBs mayDocket No.: 24-2022PCT be leaf CBs respectively labeled 11, 12, and 13 in FIGS.7A and 7B. The leaf CB 9 of FIG.4 may be partitioned into three CBs based on a horizontal ternary tree partition. Two of the three CBs may be leaf CBs respectively labeled 15 and 19 in FIGS.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.

[0091] 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.

[0092] A coding standard / format (e.g., HEVC, VVC, or any other coding standard / format) may define various units (e.g., in addition to specifying various blocks (e.g., CTBs, CBs, PBs, TBs)). Blocks may comprise a rectangular area of samples in a sample array. Units may comprise the collocated blocks of samples from the different sample arrays (e.g., luma and chroma sample arrays) that form a picture as well as syntax elements and prediction data of the blocks. A coding tree unit (CTU) may comprise the collocated CTBs of the different sample arrays and may form a complete entity in an encoded bitstream. A coding unit (CU) may comprise the collocated CBs of the different sample arrays and syntax structures used to code the samples of the CBs. A prediction unit (PU) may comprise the collocated PBs of the different sample arrays and syntax elements used to predict the PBs. A transform unit (TU) may comprise TBs of the different samples arrays and syntax elements used to transform the TBs.

[0093] In some implementations of partitioning (e.g., AV1), a picture can be partitioned into multiple coding blocks. The largest coding blocks are also referred to as superblocks having sizes of either 128x128 or 64x64. Superblocks can be partitioned into smaller coding blocks which can be performed in nine partitioning modes. FIG.8 shows the nine partitioning modes among which only PARTITION_SPLIT allows recursive partitioning. In addition, PARTITION_VERT_4 and PARTITION_HORZ_4 modes are not allowed for 8x8 or 128x128 coding blocks, and T- shaped partitioning modes are not allowed for 8x8 coding blocks. The minimum coding block size is 4x4. Intra and inter coding blocks can be further partitioned into transform blocks and the partitioning depth is up to two levels.

[0094] A block may refer to any of a CTB, CB, PB, TB, CTU, CU, PU, and / or TU (e.g., in the context of HEVC, VVC, or any other coding format / standard). A block may be used to refer to similar data structures in the context of any video coding format / standard / protocol. For example, a block may refer to a macroblock in the AVC standard, a macroblock or a sub-block in the VP8 coding format, a superblock or a sub-block in the VP9 coding format, and / or a superblock or a sub-block (coding block or transform block) in the AV1 coding format.

[0095] 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 sample1s mayDocket No.: 24-2022PCT 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.

[0096] 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.

[0097] 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.

[0098] In some embodiments, reference samples 902 may include a line of samples immediately adjacent to current block 904 and include samples from a column and a row immediately adjacent to current block 904. For example, the line of samples may include reference samples to the left and / or above current block 904. In some embodiments, reference samples 902 may be obtained (or selected) from a reference line of multiple reference lines (MRL), which may include a line of samples adjacent to current block 904 and also a line of non-adjacent samples. The MRL may include reference lines identified by corresponding reference line indices that indicate an i-th line of samples adjacent to current block 904 such that the 0-th line indicates the reference line immediate adjacent (or closest) to current block 904 and a higher numbered i-th line indicates a line of samples further away from current block 904. An encoder may select a reference line from a set of MRL and signal an MLR index in the bitstream to indicate the selected reference line. For example, the encoder may signal a codeword encoding the MRL index. The decoder may decode the codeword to determine the MRL index that identifies a specific reference line used in intra prediction of current block 904.

[0099] 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 currentDocket No.: 24-2022PCT block 904, and the top left neighboring corner sample(s) extending from the i-th column and i-th row with respect to current block 904. Current block 904 may be square, such that w = h = s. In other examples, a current block need not be square, such that w ≠ h. Available samples from neighboring blocks of current block 904 may be used for constructing the set of reference samples 902. Samples may not be available for constructing the set of reference samples 902, for example, if the samples lie outside the picture of the current block, the samples are part of a different slice of the current block (e.g., if the concept of slices is used), and / or the samples belong to blocks that have been inter coded and constrained intra prediction is indicated. Intra prediction may not be dependent on inter predicted blocks, for example, if constrained intra prediction is indicated.

[0100] 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).

[0101] 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.

[0102] Samples of current block 904 may be intra predicted based on reference samples 902, for example, based on (e.g., after) determination and (optionally) filtering of reference samples 902. In some examples, a filtering scheme (e.g., a filtering algorithm) may be applied to reference samples 902 to improve prediction accuracy. The filtering scheme may be one of a plurality of filter types including at least: a smoothing filter (or reference sample smoothing filter) or an interpolation filter. In some examples, if reference samples of a given block are to be filtered, only one of the plurality of filter types is selected (e.g., activated) to be applied to the reference samples. For example, if the smoothing filter is selected (e.g., activated), the interpolation filter is not selected (e.g., disabled) or vice versa.

[0103] 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 directDocket No.: 24-2022PCT current (DC) mode, and 33 angular modes. VVC supports 67 intra prediction modes, including a planar mode, a DC mode, and 65 angular modes. Planar and DC modes may be used to predict smooth and gradually changing regions of a picture. Angular modes may be used to predict directional structures in regions of a picture. Any quantity of intra prediction modes may be supported.

[0104] 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.

[0105] FIG.10B shows 67 intra prediction modes, such as supported by VVC. The 67 intra prediction modes may be indicated / identified by indices 0 to 66. Prediction mode 0 may correspond to planar mode. Prediction mode 1 corresponds to DC mode. Prediction modes 2-66 may correspond to angular modes. Prediction modes 2-34 may be referred to as horizontal prediction modes because the principal source of prediction is in the horizontal direction. Prediction modes 35-66 may be referred to as vertical prediction modes because the principal source of prediction is in the vertical direction. Some of the intra prediction modes illustrated in FIG.10B may be adaptively replaced by wide-angle directions because blocks in VVC need not be squares.

[0106] 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.

[0107] FIG.11 shows a current block 904 and corresponding reference samples 902 from FIG.9. To further describe how intra prediction modes are applied to determine a prediction (e.g., a prediction block) of current block 904, FIG. 11 shows current block 904 and reference samples 902, from a reference line among a set of multiple reference lines (MRL) 908-912, in a two-dimensional x, y plane, where a sample may be referenced as ^[^][^]. To simplify the prediction process, reference samples 902 may be placed in two, one-dimensional arrays. The reference samplesDocket No.: 24-2022PCT 902 belonging to a reference line ^ from the set of MRL 908-912, above the current block 904, may be placed in the one-dimensional array ^^^^[^]:^^^^[^] = ^[−^ + ^][−^], (^ ≥ 0). (1)The reference samples 902 belonging to reference line l, to the left of current block 904, may be placed in the one- dimensional array ^^^^[^]:^^^^[^] = ^[−^][−^ + ^], (^ ≥ 0). (2)The variable l represents how many lines away the selected reference line is from current block. For example, if reference line #0908 is selected, then l is set to 1 to indicate the reference line adjacent to current block 904. For example, if reference line #1910 is selected, then l is set to 2. For example, if reference line #2912 is selected, then l is set to 3.

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

[0109] The prediction process may comprise determination of a predicted sample ^[^][^] (e.g., a predicted value) at a location [^][^] in current block 904. For planar mode, a sample at the location [^][^] in current block 904 may be predicted by determining / calculating the mean of two interpolated values. The first of the two interpolated values may be based on a horizontal linear interpolation at the location [^][^] in current block 904. The second of the two interpolated values may be based on a vertical linear interpolation at location [^][^] in current block 904. The predicted sample ^[^][^] in current block 904 may be determined / calculated as: 1^[^][^] = (ℎ[^][ ] [ ][ ] ) (3)2 ∙ ^ ^ + ^ ^ ^ + ^ ,whereℎ[^][^] = (^ − ^ − 1) ∙ ^^^^[^] + (^ + 1) ∙ ^^^^[^] (4)may be the horizonal linear interpolation at the location [^][^] in current block 904 and^[^][^] = (^ − ^ − 1) ∙ ^^^^[^] + (^ + 1) ∙ ^^^^[^] (5)may be the vertical linear interpolation at the location [^][^] in current block 904. ^ may be equal to a length of a side (e.g., a number of samples on a side) of the current block 904.

[0110] For DC mode, a sample at a location [^][^] in current block 904 may be predicted by the mean of the reference samples 902. The predicted sample ^[^][^] in current block 904 may be determined / calculated as: ^^^ ^^^ 1 (6)

[0111] For angular modes,the location [^][^] in a direction specified by a given angular mode to a point on the horizontal or vertical line of samples comprising reference samples 902. The sample at the location [^][^] may be predicted by interpolating between theDocket No.: 24-2022PCT two closest reference samples of the projection point if the projection does not fall directly on a reference sample. The direction specified by the angular mode may be given by an angle φ defined relative to the y-axis for vertical prediction modes (e.g., modes 19-34 in HEVC and modes 35-66 in VVC). The direction specified by the angular mode may be given by an angle φ defined relative to the x-axis for horizontal prediction modes (e.g., modes 2-18 in HEVC and modes 2-34 in VVC).

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

[0113] For horizontal prediction modes, a location [x][y] of a sample in current block 904 may be projected onto the vertical line of reference samples ^^^^[^]. A predicted sample ^[^][^ ]for horizontal prediction modes may bedetermined / calculated as:^[^][^] = (1 − %&) ∙ ^^^^[^ + %' + 1] + %& ∙ ^^^^[^ + %' + 2]. (10)%' may be the integer part of the vertical displacement of the projection point relative to the location [^][^]. %'may bedetermined / calculated as a function of the tangent of the angle φ of the horizontal prediction mode as:%' = ⌊(^ + 1) ∙ tan ,⌋. (11)%& may be the fractional part of the vertical displacement of the projection point relative to the location [^][^]. %& maybe determined / calculated as:Docket No.: 24-2022PCT %. = ((^ + 1) ∙ tan ,) − ⌊(^ + 1) ∙ tan ,⌋, (12)where ⌊ ∙ ⌋ is the integer floor function.

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

[0115] In some examples, the FIR filters may be used for predicting chroma samples and / or luma samples. For example, the two-tap interpolation FIR filter may be used for predicting chroma samples and a same and / or a different interpolation technique / filter may be used for luma samples. For example, a four-tap FIR filter may be used to determine a predicted value of a luma sample. Coefficients of the four tap FIR filter may be determined based on %&(e.g., similar to the two-tap FIR filter). For 1 / 32 sample accuracy, a set of 32 different four-tap FIR filters may comprise up to 32 different four-tap FIR filters — one for each of the 32 possible values of the fractional part of the projected displacement %&. In other examples, different levels of sample accuracy may be used. The set of four-tap FIR filters may be stored in a look-up table (LUT) and referenced based on %&. A predicted sample ^[^][^], for vertical prediction modes, may be determined based on the four-tap FIR filter as: 2 (13) ^= ^ ∙ ^^^^ + +where fT[i], i = 0...3, may be, for horizontal prediction modes, may be determined based on the four-tap FIR filter as: 2 (14) ^[^][^] = ^ ^ / [%] ∙ ^^^^[^ + %01^ + %] .' !

[0116] Supplementary reference samples may be determined / constructed if the location [^][^] of a sample in current block 904 to be predicted is projected to a negative x coordinate. The location [^][^] of a sample may be projected to a negative x coordinate, for example, if negative vertical prediction angles φ are used. The supplementary reference samples may be determined / constructed by projecting the reference samples in ^^^^[^] in the vertical line of reference samples 902 to the horizontal line of reference samples 902 using the negative vertical prediction angle φ. Supplementary reference samples may be similarly determined / constructed, for example, if the location [^][^] of a sample in current block 904 to be predicted is projected to a negative y coordinate. The location [^][^] of a sample may be projected to a negative y coordinate, for example, if negative horizontal prediction angles φ are used. TheDocket No.: 24-2022PCT supplementary reference samples may be determined / constructed by projecting the reference samples in ^^^^[^] on the horizontal line of reference samples 902 to the vertical line of reference samples 902 using the negative horizontal prediction angle φ.

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

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

[0119] The decoder may add predicted values of the samples (e.g., determined based on the intra prediction mode) of the current block to a residual of the current block to reconstruct the current block. In some examples, a decoder need not receive an indication of an angular intra prediction mode from an encoder for a current block. Instead, the decoder may determine an intra prediction mode through other decoder-side means (e.g., by applying template-based intra mode derivation (TIMD) tool / technique).Docket No.: 24-2022PCT

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

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

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

[0123] FIG.13A shows an example of inter prediction. The inter prediction may be performed for a current block 1300 in a current picture 1302 being encoded. An encoder (e.g., encoder 200 as shown in FIG.2) may perform inter prediction to determine and / or generate a reference block 1304 in a reference picture 1306. Reference block 1304 may be used to predict the current block 1300. Reference pictures (e.g., reference picture 1306) may be prior decoded pictures available at the encoder and / or a decoder. Availability of a prior decoded picture may depend / be based on whether the prior decoded picture is available in a decoded picture buffer, at the time, current block 1300 is being encoded and / or decoded. The encoder may search the one or more reference pictures 1306 for a block (e.g., a candidate reference block) that is similar (or substantially similar) to current block 1300. The encoder may determine the best matching block from the blocks (e.g., candidate reference blocks) tested during the searching process. The best matching block may be a reference block 1304. The encoder may determine that reference block 1304 is the best matching reference block based on one or more cost criteria. The one or more cost criteria may comprise a rate- distortion criterion (e.g., Lagrangian rate-distortion cost). The one or more cost criteria may be based on a differenceDocket No.: 24-2022PCT (e.g., SSD, SAD, and / or SATD) between prediction samples of reference block 1304 and original samples of current block 1300.

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

[0125] One or more reference pictures may be searched by the encoder during inter prediction to determine and / or generate the best matching reference block. The reference pictures searched by the encoder may be included in (e.g., added to) one or more reference picture lists. For example, in HEVC and VVC (and / or in one or more other communication protocols), two reference picture lists may be used (e.g., a reference picture list 0 and a reference picture list 1). A reference picture list may include one or more pictures. The reference picture 1306 of reference block 1304 may be indicated by a reference index pointing into a reference picture list comprising reference picture 1306. The reference frames can include different types of frames. For example, in some implementations (e.g., such as in AV1), up to seven frames can be used as reference frames and there are four types of frames, including LAST frame (a frame that was displayed in the near past), BWD frame ( a frame that will be displayed in the future), GOLDEN frame (a frame that was displayed in the distant past), and ARF frame (a frame from either the past or the future).

[0126] FIG.13B shows an example motion vector. A displacement between reference block 1304 and current block 1300 may be interpreted as an estimate of the motion between reference block 1304 and current block 1300 across their respective pictures. The displacement may be represented by a motion vector 1312. For example, motion vector 1312 may be indicated by a horizontal component (MVx) and a vertical component (MVy) relative to the position of current block 1300. A motion vector (e.g., motion vector 1312) may have fractional or integer resolution. A motion vector with fractional resolution may point between two samples in a reference picture to provide a better estimation of the motion of current block 1300. For example, a motion vector may have 1 / 2, 1 / 4, 1 / 8, 1 / 16, 1 / 32, or any other fractional sample resolution. Interpolation between the two samples at integer positions may be used to generate a reference block and its corresponding samples at fractional positions, for example, if a motion vector points to a non- integer sample value in the reference picture. The interpolation may be performed by a filter with two or more taps.Docket No.: 24-2022PCT

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

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

[0129] 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.

[0130] One or both of uni-prediction and bi-prediction may be available / used for performing inter prediction (e.g., at an encoder and / or at a decoder). Performing a specific type of inter prediction (e.g., uni-prediction / single reference prediction and / or bi-prediction / compound prediction) may depend on a slice type of current block. For example, for P slices, only uni-prediction may be available / used for performing inter prediction. For B slices, either uni-prediction or bi-prediction may be available / used for performing inter prediction. An encoder may determine and / or generate a reference block, for predicting a current block, from a reference picture list 0, for example, if the encoder is using uni- prediction. An encoder may determine and / or generate a first reference block, for predicting a current block, from a reference picture list 0 and determine and / or generate a second reference block, for predicting the current block, from a reference picture list 1, for example, if the encoder is using bi-prediction.

[0131] 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 oneDocket No.: 24-2022PCT 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.

[0132] A configurable weight and / or offset value may be applied to one or more inter prediction reference blocks. An encoder may enable the use of weighted prediction using a flag in a picture parameter set (PPS) 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.

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

[0134] The motion information for reference block 1402 may comprise a motion vector 1406 and / or a reference indicator / index. The reference indicator may indicate a reference picture, of the reference block 1402, in a reference picture list. In some examples, the motion information for reference block 1402 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.

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

[0136] A decoder may decode current block 1400 by determining and / or generating the reference blocks 1402 and 1404. The decoder may determine and / or generate the reference blocks 1402 and 1404, for example, based on the respective related motion information for the reference blocks 1402 and 1404. The reference blocks 1402 and 1404Docket No.: 24-2022PCT may correspond to / form (e.g., be considered as) the prediction (e.g., used to generate a prediction block) of the current block 1400. The decoder may decode the current block 1400 based on combining the prediction with the prediction errors.

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

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

[0139] The encoder may determine / select an MVP from the list of candidate MVPs. Then, the encoder may send / signal, in / via a bitstream, an indication of the selected MVP and / or a motion vector difference (MVD). The encoder may indicate the selected MVP in the bitstream using an index / indicator. The index may indicate the selected MVP in the list of candidate MVPs. The MVD may be determined / calculated based on a difference between the motion vector of the current block and the selected MVP. For example, for a motion vector (e.g., comprising a horizontal component (MVx) and a vertical component (MVy)) that indicates a position relative to a position of the current block being coded, the MVD may be represented by two components MVD^and MVD". MVD^and MVD"may be determined / calculated as:MVD^ = MV^ − MVP^ , (15)MVD" = MV" − MVP". (16)MVDx and MVDy may respectively represent horizontal and vertical components of the MVD. MVPx and MVPy may respectively represent horizontal and vertical components of the MVP.

[0140] A decoder (e.g., decoder 300 as shown in FIG.3) may decode the motion vector by adding the MVD to the MVP indicated in / via the bitstream. The decoder may decode the current block by determining and / or generating the reference block. The decoder may determine and / or generate the reference block, for example, based on the decoded motion vector. The reference block may correspond to / form (e.g., be considered as) the prediction of the current block (e.g., a prediction block). The decoder may decode the current block by combining the prediction with the prediction error.Docket No.: 24-2022PCT

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

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

[0143] An encoder (e.g., encoder 200 as shown in FIG.2) may code a motion vector using inter prediction block merging (e.g., a merge mode). For example, the encoder (e.g., using merge mode) may reuse the same motion information of a neighboring block (e.g., one of neighboring blocks A0, A1, B0, B1, and B2) for inter prediction of a current block. For example, the encoder (e.g., using merge mode) may reuse the same motion information of a temporal, co-located block (e.g., one of temporal, co-located blocks C0 and C1) for inter prediction of a current block. An MVD need not be sent (e.g., indicated, signaled) for the current block because the same motion information as that of a neighboring block or a temporal, co-located block may 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.

[0144] A list of candidate motion information for merge mode (e.g., in HEVC, VVC, or any other coding formats / standards / protocols) may comprise: up to four (or any other quantity of) spatial merge candidates derived / determined from five (or any other quantity of) spatial neighboring blocks (e.g., as shown in FIG.15A); oneDocket No.: 24-2022PCT (or any other quantity of) temporal merge candidate derived from two (or any other quantity of) temporal, co-located blocks (e.g., as shown in FIG.15B); and / or additional merge candidates comprising bi-predictive candidates and zero motion vector candidates. In some examples, the spatial neighboring blocks and the temporal, co-located blocks used for merge mode may be the same as the spatial neighboring blocks and the temporal, co-located blocks used for AMVP.

[0145] In some examples (e.g., AV1), a list of derived MV predictors may be generated by pooling the spatial and temporal MV candidates and ranking them based on weightings determined by evaluating each of the candidates. Up to four candidates may be added to the list of MV predictors, which may also be referred to as the dynamic reference list (DRL). The DRL may be used in dynamic MV prediction modes.

[0146] Inter prediction may be performed in other ways and variants than those described herein. For example, motion information prediction techniques other than AMVP and merge mode may be used. While various examples herein correspond to inter prediction modes, such as used in HEVC and VVC or AV1, the methods, devices, and systems as described herein may be applied to / used for other inter prediction modes (e.g., as used for other video coding standards / formats such as VP8, VP9, etc.). History-based motion vector prediction (HMVP), combined intra / inter prediction mode (CIIP) or compound inter-intra prediction, warped motion compensation, overlapped block motion compensation (OBMC), and / or merge mode with motion vector difference (MMVD) (e.g., as described in VVC) may be performed / used and are within the scope of the present disclosure.

[0147] 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.

[0148] 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 a displacement vector (e.g., a block vector (BV)). The BV may indicate a relative position of a reference block (e.g., in accordance with intra block compensated prediction), that best matches the current block, from a position of the current block. For example, the relative position of the reference block may be a relative position of a top-left cornerDocket No.: 24-2022PCT (or any other point / sample) of the reference block. The BV may indicate a relative displacement from the current block to the reference block that best matches the current block. The encoder may determine the best matching reference block from blocks tested during a searching process (e.g., in a manner similar to that used for inter prediction). The encoder may determine that a reference block is the best matching reference block based on one or more cost criteria. The one or more cost criteria may comprise a rate-distortion criterion (e.g., Lagrangian rate-distortion cost). The one or more cost criteria may be based on, for example, one or more differences (e.g., an SSD, an SAD, an SATD, and / or a difference determined based on a hash function) between the prediction samples of the reference block and the original samples of the current block. A reference block may correspond to / comprise prior decoded blocks of samples (e.g., reconstructed samples) of the current picture. The reference block may comprise decoded blocks of samples of the current picture prior to being processed by in-loop filtering operations (e.g., deblocking, SAO filtering, CDEFs, and / or LR filters). In some examples, the reference block may be restricted to a certain area. For example, in AV1, if the top-left pixel coordinate of a superblock is (x0, y0), IntraBC prediction is available at pixel position (x, y) only if the value of the vertical coordinate y is less than y0 and the value of the horizontal coordinate x is less x0 + 2(y0 − y). Further, due to hardware write-back delays, the immediate reconstructed area may not be accessible by IntraBC prediction.

[0149] 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.

[0150] 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).

[0151] A BV may be predictively coded (e.g., in HEVC, VVC, and / or any other coding standards / formats / protocols) before being stored and / or sent / signaled in / via a bitstream. For example, the BV for a current block may be predictively coded based on a BV of one or more blocks neighboring the current block. For example, an encoder may predictively code a BV using the merge mode (e.g., in a manner similar to as described herein for inter prediction), AMVP (e.g.,Docket No.: 24-2022PCT 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).

[0152] 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.

[0153] The encoder may send / signal, in / via a bitstream, an indication of the selected BVP and a block vector difference (BVD). The encoder may indicate the selected BVP in the bitstream using an index / indicator. The index may indicate (e.g., point to) the selected BVP in the list of candidate BVPs. The BVD may be determined / calculated based on a difference between a BV of the current block and the selected BVP. For example, for a BV (e.g., represented by a horizontal component (BVx) and a vertical component (BVy)) that indicates a position relative to a position of the current block being coded, the BVD may be represented by two components BVD^and BVD". BVD^and BVD" may be determined / calculated as:BVD^ = BV^ − BVP^ , (17)BVD" = BV" − BVP" . (18)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).

[0154] 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.

[0155] A list of candidate BVPs (e.g., in HEVC, VVC, and / or any other coding standard / format / protocol) may comprise two (or more) candidates. The candidates may comprise candidates A and B. Candidates A and B may comprise: up to two (or any other quantity of) spatial candidate BVPs determined / derived from five (or any other quantity of) spatial neighboring blocks of a current block being encoded; and / or one or more of last two (or any other quantity of) coded BVs (e.g., if spatial neighboring candidates are not available). Spatial neighboring candidates may not be available, for example, if neighboring blocks are encoded using intra prediction or inter prediction. Locations of the spatial candidate neighboring blocks, relative to a current block, being encoded using IBC may be illustrated in a manner similar to spatial candidate neighboring blocks used for coding motion vectors in inter prediction (e.g., as shown inDocket No.: 24-2022PCT FIG.15A). For example, five spatial candidate neighboring blocks of a current block being coded using IBC may be respectively denoted A0, A1, B0, B1, and B2 as shown in FIG.15A.

[0156] The most probable mode (MPM) refers to the intra prediction mode (IPM) that is most likely to be the best mode for the current block being encoded or decoded. In current intra prediction techniques, the MPM is determined by analyzing the intra prediction modes of the neighboring CUs (e.g., also referred to as blocks) of a current block (or CU) to be coded (e.g., encoded or decoded). For example, a list of 6 MPMs (referred to as the “MPM list”) may be constructed for intra prediction. The MPM list is derived from the intra prediction modes of the neighboring CUs, and is updated as the encoder progresses through the video frame. When encoding a block, the encoder may determine if the current block is a candidate for any of the MPMs in the MPM list. If it is, the encoder then compares the prediction errors of the respective MPMs to determine which MPM from the MPM list is the best mode for the current block. If the current block is not a candidate for any of the MPMs in the MPM list, the encoder may then evaluate remaining intra prediction modes (e.g., from a total of 67 intra prediction modes which may include a planar mode, a DC mode, and 65 angular directional modes) to determine the best mode for the current block.

[0157] 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.

[0158] 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}.Docket No.: 24-2022PCT

[0159] 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.

[0160] In some examples, during the 6 MPM list generation process, pruning may be used to remove duplicated intra modes so that the MPM list includes only unique intra modes. For entropy coding of the 61 non-MPM modes (that is, the 67 modes in VVC minus the 6 MPM), a truncated binary code (TBC) may be used.

[0161] In some implementations, the MPM list is extended to include 16 additional candidates, and is divided into two parts, the primary MPM (PMPM) (e.g., including 6 entries) and the secondary (SMPM) (e.g., including 16 entries). In some implementations, the first entry in the general MPM list is the planar mode. The remaining entries include the intra modes of the adjacent neighboring blocks corresponding to positions left (L), above (A), below-left (BL), above- right (AR), and above-left (AL) (e.g., shown in FIG.15A as A1, B1, A0, B0, and B2), and decoder-side intra mode derivation (DIMD) modes which are sorted in ascending order of a cost such as, for example, SAD, SSD, SATD, etc. In some examples, up to a preconfigured / predetermined number of modes (e.g., 5) with the smallest costs are added to the MPM list. The cost for a respective MPM (e.g., an IPM corresponding to an entry in the MPM list) may be computed between the prediction of the reconstructed samples of the template of the current block and the reconstructed samples. For example, the prediction may be generated by applying the respective MPM for the template. Sorted directional modes are added into the general MPM list, and then the default modes, until the general MPM list with 22 entries 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.

[0162] 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.

[0163] 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 IBCDocket No.: 24-2022PCT 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.

[0164] 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.

[0165] In an example, in the RRIBC mode, the flip direction may include one of a horizontal direction (e.g., along an x-axis) or a vertical direction (e.g., along a y-axis) for RRIBC coded blocks. In an embodiment, for a current block coded in the RRIBC mode (e.g., an IBC advanced motion vector prediction (AMVP) coded block), a first indication (e.g., a first syntax flag) may indicate / signal whether to use flipping (e.g., also referred to as mirror flipping) to encode / decode the current block. Additionally, for the current block, a second indication (e.g., a second syntax flag) may indicate / signal the direction for flipping (e.g., vertical or horizontal). For IBC merge, the flip direction may be inherited from neighboring blocks, without syntax signaling. In an example, for RRIBC, flipping of a current block (or a reference block in an alternative embodiment) in a horizontal and a vertical direction can be represented in (19) and (20), respectively:Reference(x, y) = ?@A^^^(B − 1 − ^, ^) (19)Reference(x, y) = ?@A^^^(^, ℎ − 1 − ^) (20)where w and h are the width and height of a current block, respectively. Sample(x,y) may indicate a sample value located in (x,y). Reference(x,y) may indicate a corresponding reference sample value after flipping. In other words, for horizontal flipping, (19) shows that the current block is flipped in the horizontal direction by sampling from right to left. Similarly, for vertical flipping, (20) shows that the current block is flipped in the vertical direction by sampling the current block from down to up.

[0166] 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 isDocket No.: 24-2022PCT 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.

[0167] For a current block coded in IBC mode, a BV for the current block may be constrained to indicate a relative displacement from the current block to a reference block within an IBC reference region. In 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.

[0168] FIG.17 shows an example of intra template matching prediction (IntraTMP) for predicting or determining a current block 1700, according to some embodiments. IntraTMP is an intra prediction mode that copies a reference block, from a reconstructed part of a current picture 1702 (e.g., current frame), whose template (e.g., an L-shaped template, above-only template, or left-only template) is determined to best 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.

[0169] In IntraTMP, a plurality of reference templates of respective candidate reference blocks 1714, from a predefined TMP search region 1706, are matched with current template 1708 to determine or select a reference template 1712 that best matches or is most similar to current template 1708. A reference block (RB) 1710 from the candidate reference blocks 1714 and indicated by the selected reference template 1712 may be used as a prediction block to determine or predict current block 1700. Block vector (BV) 1730 indicates a displacement from current block 1700 (e.g., the top left sample of current block 1700) to reference block 1710 (e.g., the top left sample of reference block 1710).

[0170] In some examples, TMP search region 1706 comprises a portion of a reconstructed region of current picture 1702. TMP search region 1706 indicates the regions that the encoder or decoder may search for candidate templates (such as candidate templates of candidate reference blocks 1714) to determine reference template 1712 and corresponding reference block 1710. In some examples, TMP search region 1706, may include region 1706A (R1)Docket No.: 24-2022PCT from a current CTU 1704, region 1706B (R3) including a portion of the above CTU, region 1706C (R2) including a portion of the above-left CTU, and region 1706D (R4) including a portion of the left CTU. The CTUs are a result of picture partitioning operations described above. It is to be understood that TMP search region 1706 may include other regions of reconstructed samples of current picture 1702.

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

[0172] In some examples, the candidate templates of candidate reference blocks 1714 have the same shape and size as current template 1708. In an example, the candidate templates further have the same orientation as current template 1708. In some examples, matching templates includes calculating a template matching (TM) cost between samples of a candidate reference template of a candidate RB (indicated by a respective candidate block vector) and corresponding samples of current template 1708. For example, the difference may be based on a sum of squared differences (SSD), a sum of absolute differences (SAD), a sum of absolute transformed differences (SATD), or a difference determined based on a hash function. The template matching cost represents a similarity between the templates with a smaller cost representing more similar templates.

[0173] In some examples, a position of each sample in TMP search region 1706 may be selected as a location of a candidate reference block whose respective reference template is compared against current template 1708 to determine a TM cost. The position may be indicated by a candidate block vector that represents a displacement from current block 1700 (e.g., a top-left sample of current block 1700) to the position. To speed up the template matching process, one or more of TMP search region 1706 may be subsampled by a subsampling interval (e.g., 3) such that not every position is considered as a location of a candidate reference block. After finding a set of candidates (e.g., to generate the list of candidates), a refinement process may be performed to select additional candidate block vectors. The refinement process may be performed via a second template matching search in a search region aroundDocket No.: 24-2022PCT one or more of the set of candidates. The search region may be a reduced search range associated with the subsampling interval.

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

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

[0176] In the example illustrated in FIG.17, reference template 1712 of reference block 1710 may be determined to best match current template 1708 based on the template matching cost between reference template 1712 and current template 1708 being a minimum TM cost. In another example, the encoder may select reference block 1710 as a prediction of current block 1700 and signal an index of a candidate block vector, indicating reference block 1710, in the candidate list. The decoder may generate the same 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.

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

[0178] In some examples, an encoder may determine a difference (e.g., a corresponding sample-by-sample difference) between current block 1700 and reference block 1710 used to predict current block 1700. The difference may be referred to as a prediction error or residual. The encoder may store and / or signal in a bitstream the prediction error or residual for decoding by a decoder.Docket No.: 24-2022PCT

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

[0180] 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.

[0181] 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.

[0182] In DIMD, texture gradient analysis is performed on samples in template 1812 (e.g., reference template) associated with the current block 1810 to generate a histogram of gradient (HoG) 1820. From the HoG 1820, a number (e.g., 2) of DIMD modes such as one or more of DIMD modes 1818A-B may be derived. Each entry in HoG 1820 corresponds to a respective angular intra prediction mode (IPM) with amplitudes (or magnitudes) of the entries determined based on the gradient analysis.

[0183] 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.

[0184] In some examples, the gradient analysis may be performed using edge detection filters applied to 3×3 window positions centered on the reference samples / pixels selected from template 1812. The edge detection filters can determine the amplitude and the angle of luminance direction (e.g., orientation) for each reference sample. ForDocket No.: 24-2022PCT example, the set of reference samples selected from template 1812 may include the samples in the middle line of template 1812. In some examples, the edge detection filters may include a horizontal Sobel gradient filter (Mhor) and / or a vertical Sobel gradient filter (Mver), represented by the following 3x3 matrices that will be convoluted with selected reference samples of template 1812: −1 −0 −1 −1 −2 −1RSTU = V−2 −0 −2W and RYZU = V−0 −0 −0W

[0185] For each of point multiply of each ofthese two matrices with a 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 @[\^^ = arctan (]STU / ]YZU). The calculated angle may correspond to (e.g., beconverted into) one of the angular IPMs (e.g., one of the 65 angular IPMs), and an associated amplitude (i.e., the amplitude for the window position) @A^^%_`1^ = |]YZU| + |]STU| may be added to the HoG indexed by therespective 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.

[0186] FIG.19 shows an example of a template 1812 (e.g., template area) for computing a HoG used in DIMD, according to some embodiments. Reference template 1812 (e.g., an L-shaped template) of current block 1810 is shown to be in reconstructed area 1902 (or reconstructed region) of the picture frame. Examples of HoGs for different sizes of current block 1810 are shown. For example, for a 4×4 pixel square current block 1908, a 3×3 window 1910 in the template area is shown and a corresponding HoG 1912 may be generated for current block 1908. In another example, for a rectangular current block 1904 with a 3-pixel deep template area 1906, a HoG 1914 corresponding to rectangular current block 1904 may be generated by gradient analysis of reference samples based on a filter window. As illustrated, each coordinate position on the x-axis of the illustrated HoGs is a respective IPM, and the y-axis represents the cumulative amplitude (e.g., counts) for the respective IPMs.

[0187] 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 M1and M2with the highest respective amplitudes A1and 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.

[0188] 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 beDocket No.: 24-2022PCT determined based on amplitudes (e.g., magnitudes) associated with DIMD modes 1818A-B, respectively. For example, weight 1828A for DIMD mode 1818A may correspond to DIMD weight 1832A (e.g., wDIMD1), which may be based on an amplitude A1, from HoG 1820, associated with DIMD mode 1818A (e.g., IPM M1) divided by a sum of amplitudes of DIMD modes 1818A-B. For example, weight 1828B for DIMD mode 1818B may correspond to DIMD weight 1832B (e.g., wDIMD2), which may be based on an amplitude A2, from HoG 1820, associated with DIMD mode 1818B (e.g., IPM M2) divided by the sum.

[0189] In some examples, non-angular mode 1816 (e.g., non-directional) may be, without limitation, a planar mode (or alternatively a DC mode). In other examples, non-angular mode 1816 may be a neural network-based intra prediction (NNIP) 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 / non-directional modes. Non-angular mode 1816 may have a weight 1826 corresponding to planar weight 1833 that may be a fixed weight f1(e.g., 1 / 4 or 16 / 64 in 6-bit integer precision). The remaining DIMD weights 1832A-B may include a fixed weight portion f2(e.g., 3 / 4) that is based on the fixed weight of planar weight 1833. For example, the sum of fixed weights f1and f2may be equal to 1.

[0190] DIMD predictor 1822 may be applied to template 1812 (e.g., current template) to determine a prediction block 1824 for current block 1810. For example, each sample (x,y) 1814 of prediction block 1824, denoted as fusionPred, may be determined based on applying DIMD predictor 1822 comprising a weighted average (e.g., a linear combination) of applying DIMD modes 1818A-B and non-angular mode 1816 with corresponding weights (wi) as follows: ^^`^%b[c^^1(^, ^) = ^dB' ∗ c^^1'(^, ^)eIn some examples, the weights for mode i) for DIMD modes 1818A-B and the planar weight 1833 (wPlanar) for non-angular mode 1816. The weights (wi) may be constant and uniformly applied to determine each sample (x, y) 1814 of prediction block 1824. The predictor Predifor mode i may be a DIMD mode predictor (dimdPredi) for DIMD modes 1818A-B or a planar mode predictor (dimdPlanar) for non-angular mode 1816. Accordingly, DIMD predictor 1822 may be represented and computed equivalently as follows: ^`^%b[c^^1(^, ^) = h∑^' ! dBf%A1' ∗ 1%A1c^^1'(^, ^)e + Bc^@[@^ ∗Note the shifting

[0191] 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.

[0192] 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 appliedDocket No.: 24-2022PCT to determine the impact that different template regions of template 1812 has in selecting each of the IPMs. To determine how specific samples in template 1812 contribute to inferring specific DIMD modes, template 1812 may be divided into three separate regions—including a region above current block 1810, a region to the left of current block 1810, and an above-left region of current block 1810. The gradient analysis computation may be performed separately for samples in each region, resulting in three histograms, HoG 1819C (lmnTYZ), HoG 1819A (loZ.p), and HoG 1819B (lmnTYZqZ.p), respectively. For a directional IPM A, l'[A] for region i (e.g., above, left, or above-left)represents the cumulative magnitude of all samples in region i at direction (or IPM) A.

[0193] HoG 1820, corresponding to the full histogram of gradients for the whole template 1812, may be computed as the sum of the three separate HoGs 1819A-C. In some examples, the two directional IPMs with largest and second-largest cumulative amplitude (e.g., magnitude) in HoG 1820 may be selected as main and secondary DIMD modes, e.g., 1%A1Rb1^!and 1%A1Rb1^^, respectively.

[0194] In some examples, HoGs 1819C and 1819A corresponding to histograms lmnTYZand loZ.pmay be used to determine whether 1%A1Rb1^!and / or 1%A1Rb1^^depend on a specific template region ABOVE or LEFT. In a first example, the location-dependency of 1%A1Rb1^', denoted as ^brf^^'(e.g., shown in FIG.18 as Li= L(Mi, Hleft, Habove) for DIMD mode i), can be defined as: If: (lmnTYZ[1%A1Rb1^'] > 2loZ.p[1%A1Rb1^']), then:^brf^^' = 1, that is 1%A1Rb1^' depends on region ABOVE.Else if: (loZ.p[1%A1Rb1^'] > 2lmnTYZ[1%A1Rb1^' ]), then:^brf^^' = 2, that is 1%A1Rb1^' depends on region LEFT.Else: ^brf^^' = 0, that is 1%A1Rb1^' is not location-dependent.

[0195] In a second example, the location-dependency of 1%A1Rb1^', denoted as ^brf^^'(e.g., shown in FIG. 18 as Li= L(Mi, Hleft, Habove) for DIMD mode i), can be defined as: If : (loZ.p[1%A1Rb1^' ] <average of wloZ.plmnTYZqZ.p[1%A1Rb1^']x), then:^brf^^' = 1, that is 1%A1Rb1^' depends on region ABOVE.Else if : (lmnTYZ[1%A1Rb1^'] <average of (loZ.p[1%A1Rb1^'], lmnTYZ[1%A1Rb1^'], lmnTYZqZ.p[1%A1Rb1^'])), then:^brf^^' = 2, that is 1%A1Rb1^' depends on region LEFT.Else: ^brf^^' = 0, that is 1%A1Rb1^' is not location-dependent.In this example, the indication of location-dependency may be determined based on comparing an amplitude of a HoG corresponding to a specific template portion with the average amplitude of the HoGs of all the template portions of the template.Docket No.: 24-2022PCT

[0196] Thus location-dependency in DIMD may be determined based on the analysis of HoG peaks amplitudes of the selected angular IPM. For example, location-dependency indications 1830A-B may be determined for DIMD modes 1818A-B, respectively. Location-dependency indication for DIMD mode 1816, which may be a planar mode, may be determined as a value representing that it is not location dependent or that it is diagonally dependent.

[0197] 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, 1%A1c^^1!and 1%A1c^^1^, with the Planar predictor 1%A1c^@[@^. If no DIMD mode is determined to be location-dependent (e.g., ^brf^^! == ^brf^^^ == 0), then blending / fusion withuniform weights Bf%A1!, Bf%A1^and Bc^@[@^ may be applied as explained above.

[0198] 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 (^, ^).

[0199] In some examples, if ^brf^^' ≠ 0, the sample-based weights Bzbrf^^f%A1'(^, ^) for predictor1%A1c^^1' may be computed so that the average weight used within the block is approximately equal to theuniform weight Bf%A1'with higher weights being used in the portion of the block closer to the region (e.g., ABOVE or LEFT) corresponding to ^brf^^'(e.g., indication Li). A fixed range ∆'may be determined and is predefined, (e.g.,∆'= 10) corresponding to the largest deviation of Bzbrf^^f%A1' (^, ^) from Bf%A1' . Higher values of ∆'result in a higher variation of the weights within the block. For a block of size l × }:If ^brf^^' = 1, then:^Bzbrf^^f%A1'(^, ^) = Bf%A1' + ∆' − 2∆' (l − 1)Else if ^brf^^' = 2, then:^Bzbrf^^f%A1' (^, ^) = Bf%A1' + ∆' − 2∆' (} − 1)If both DIMD modes 1818A-B (i=0 and i=1) are associated with location-dependency indications Li that indicate location dependency (i.e., ^brf^^' ≠ 0 for modes % = 0,1), then the weights Bzbrf^^f%A1'(^, ^) may be computed forboth predictors depending on the value of ^brf^^', as shown above.

[0200] In some examples, if only one of DIMD modes 1818A-B is associated with a location dependency indication Li indicating that it is location dependent, e.g., ^brf^^' = 0 and ^brf^^(^^') ≠ 0, then the weights forBzbrf^^f%A1'(^, ^) may be computed as:Bzbrf^^f%A1(^^' (^, ^) − Bf%A1B ^ = − ) (^^')'

[0201] Bzbrf^^c^@[@^(^, ^) = 64 - ∑^' ! dBzbrf^^f%A1'(^, ^)e

[0202] 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.: 24-2022PCT ^^`^%b[c^^1(^, ^) = ~ ^dBzbrf^^f%A1'(^, ^) ∗ 1%A1c^^1'(^, ^)e^ ≫ 6In some process with a fixed. being used.

[0203] In some embodiments, based on current block 1810 being coded using DIMD, IPM information 1834 (e.g., DIMD information) may include DIMD parameters that are generated and stored in association with current block 1810. For example, the DIMD parameters may include indications of the selected DIMD modes 1818A-B (M1, M2, …, Mi), amplitudes from HoG 1820 (A1, A2, …, Ai) of the selected DIMD modes 1818A-B, and / or weights 1828A-B (w1, w2, …, wi) of the selected DIMD modes 1818A-B. For example, weights 1828A-B may be the DIMD weights 1832A-B corresponding to selected DIMD modes 1818A-B. In some examples, the DIMD parameters may further include location-dependency indications (L1, L2, …, Li) of the selected DIMD modes 1818A-B. In some examples, IPM information 1834 may include a plurality of lists (e.g., arrays) of DIMD parameters with each list corresponding to a different DIMD parameter type. For example, the plurality of lists may include a list of IPMs, a list of amplitudes, a list of weights, and / or a list of indications of location-dependency. Parameters at the same index across the plurality of lists correspond to the same DIMD mode or IPM indicated by the index to the list of IPMs.

[0204] 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.

[0205] In some examples, the BV is obtained based on performing a TMP process for current block 1810, e.g., as explained in reference to FIG.17.

[0206] In some examples, the BV may be obtained based on one of the neighboring (previously-reconstructed) blocks of current block 1810. For example, the BV may be a candidate BV obtained via the IntraTMP or IBC for coding a neighboring block. The reference block pointed to by the BV, instead of the prediction block obtained using the non- angular intra prediction mode, can be used to blend with the prediction samples of the DIMD mode(s). Other DIMD- based modes can be modified in a similar way to use the reference block pointed to by the BV of a neighboring block for blending. In some examples, a template matching (TM) cost for each candidate BV of neighboring blocks coded based on a BV may be obtained and the candidate BV with the lowest TM cost may be selected. The process for computing TM costs based on a candidate BV are described above with respect to FIG.17.

[0207] Accordingly, in some embodiments, the DIMD mode (including any of the DIMD-based modes) may adaptively select between the prediction block obtained using the non-angular intra prediction mode (e.g., planar mode, DC, NNIP, etc.) and the reference block pointed to by the BV of the neighboring block (e.g., obtained via the IntraTMP or IBC mode) to blend with the prediction samples obtained from an angular intra prediction.Docket No.: 24-2022PCT

[0208] FIG.20 shows an example flowchart 2000 of the DIMD predictor derivation process as described with respect to FIG.18, 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).

[0209] At block 2001, a histogram of intra prediction modes (IPMs) is determined for a current block (e.g., CU). The histogram is used by an intra-based coding mode for coding the current block. For example, the intra-based coding mode may be any of various DIMD related modes. For example, the intra-based coding mode may be a DIMD mode (e.g., default / regular DIMD mode), as described with respect to FIGS.18-19. For example, the intra-based coding mode may be an OBIC mode, an MIMD mode, or an intra merge mode (e.g., a DIMD Merge list mode), as further described below.

[0210] 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.

[0211] 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.

[0212] 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).

[0213] At block 2008, an indication of location dependency of each respective IPM of the selected IPMs is determined.

[0214] 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.

[0215] 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 leftDocket No.: 24-2022PCT template), then the indication of location-dependency may be set to a first value (e.g., 1) indicating vertical location- dependency; otherwise if the IPM’s amplitude in the above template portion is less than the IPM’s average amplitude among all template portions, then the indication of location-dependency may be set to a second value (e.g., 2) indicating horizontal location-dependency. As described with respect to FIG. 18, to determine the indication of location- dependency and during generation of the HoG, the amplitudes may be cumulated in separate HoGs for each of the left template portion, above template portion, and above-left template portion. The amplitudes in the separate HoGs may be summed to determine the HoG representing combined amplitudes for the entire template.

[0216] 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.

[0217] 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.

[0218] In some examples, an IPM in a range of IPMs may be determined to be non-angular. For example, the range of IPMs may be one or more predetermined IPMs that correspond to a range of angles including a diagonal direction (e.g., corresponding to Gver / Ghor being equal to or close to 1 or -1).

[0219] 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.

[0220] If at block 2016, it is determined that the number of angular IPMs to be blended is greater than 1, then at block 2020, weights of the selected IPMs are determined according to their amplitudes in the histogram. For example, a weight of a selected IPM may be based on a ratio of an amplitude of the selected IPM to amplitudes of the selected IPMs, e.g., as described with respect to FIG.18. In some examples, the planar mode can be used for the blending with, a first fixed weight, e.g., such as 1 / 4 or 16 / 64 with 6 bits integer precision. Weights of the angular IPMs may be further weighted (e.g., scaled) based on a second fixed weight. For example, the sum of the first and second fixed weights may sum to one. For example, if the first fixed weight is 1 / 4, then the second fixed weight may be set to 3 / 4 or 48 / 64 with 6 bits integer precision.

[0221] 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 non-angular mode in accordance with respective weights, as described above with respect to FIG.18.Docket No.: 24-2022PCT

[0222] 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.

[0223] At block 2024, a blending weight for each respective location dependency of a plurality of location dependencies is determined. In some examples, the plurality of location dependencies may include a horizontal location dependency, a vertical location dependency, or no location dependency. The blending weight may be a sample-based weight for a predictor (e.g., for each selected IPM) that is determined 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.

[0224] After the blending weights for each location dependency (e.g., vertical, horizontal, no 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. 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 DIMDDocket No.: 24-2022PCT 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, MPM and MRL are not signaled. The DIMD intra prediction mode described above may also referred to as the “regular DIMD intra prediction mode” or “regular DIMD mode.”

[0227] To enhance DIMD, a decoder-side technique has been proposed to merge DIMD 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).

[0228] The DIMD merge process is similar to the DIMD process described with respect to FIG.20. However, the DIMD merge process includes a set of operations replacing the operations preceding block 2010 in FIG.20. In MIMD, to code a current block, at most a predetermined number (e.g., 13) of reconstructed neighboring blocks (e.g., neighboring CU blocks of the current block) that were previously coded based on DIMD may be selected from a list of DIMD merge candidates. For example, up to the predetermined number of neighboring blocks may be selected based on being coded using DIMD and that are spatially closest to the current block.

[0229] 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 (DIMD merge candidates) may be added to the list according to an inclusion order of blocks corresponding to (e.g., including) the left sample (A1), above sample (B1), above left sample (B2), above right sample (B0), and bottom left sample (A0).

[0230] 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. For example, the merge candidates may be part of an intra merge list (e.g., DIMD merge list).

[0231] 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 secondDocket No.: 24-2022PCT block 2104 associated with (e.g., contains) sample 13, and a third block 2106 associated with (e.g., contains) sample 10 are spatial non-adjacent blocks with respect to the current block.

[0232] The IPM / DIMD information (e.g., representing the HoG or merged HoG) of each of the selected neighboring blocks (e.g., neighboring CU blocks) may be retrieved and combined to generate the MHoG. For example, amplitudes of the same IPM across IPM / DIMD information of the selected neighboring blocks may be cumulated in the MHoG. 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. 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.

[0233] 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.

[0234] In some examples, to reduce computational complexity, the IPM information (DIMD information) of the selected neighboring blocks (e.g., neighbor CUs) may be limited to storing only a predetermined number (e.g., 5) of IPMs corresponding to the highest amplitudes and storing those highest amplitudes corresponding to the IPMs. In these examples, the MHoG may be generated by combining the predetermined number of pairs (IPM, amplitude of the IPM) of each selected neighboring block. The resulting MHoG may be used to derive the prediction modes and weights as described above.

[0235] Another decoder-side technique for enhancing DIMD is based on generating a histogram of occurrences (HoC) representing sample-wise occurrences of the IPMs in the neighborhood of the current block. This enhancement is referred to as an occurrence-based intra coding (OBIC) mode and may be a sub-mode of DIMD. Similar to regular DIMD mode, the OBIC mode may blend (e.g., fuse or combine) up to a predetermined number (e.g., 5) of IPMs with highest occurrences from the HoC, along with planar mode to obtain a DIMD predictor. The weight for each mode may be determined based on amplitudes in the HoC similar to how a weight for an IPM is determined from the HoG in regular DIMD.

[0236] The OBIC process may be similar to the MIMD process (e.g., DIMD merge process) described above and, may only differ from this process by replacing the MHoG with a HoC. Accordingly, the OBIC process is similar to the DIMD process described with respect to FIG.20. However, the OBIC process includes a set of operations replacing the operations preceding block 2010 in FIG.20. In OBIC, to code a current block, at most a predetermined number (e.g., 13) of reconstructed neighboring blocks (e.g., neighboring CU blocks of the current block) that were previouslyDocket No.: 24-2022PCT coded based on DIMD may be selected from a list of intra / DIMD merge candidates. For example, up to the predetermined number of neighboring blocks may be selected based on being coded using DIMD and spatially closest to the current block. Similar to MIMD, generating the list of intra / DIMD merge candidates may include checking adjacent spatial neighboring blocks of the current block as shown in FIG.15A and non-adjacent spatial neighboring blocks as described above with respect to FIG.21.

[0237] A number (e.g., up to a predetermined number) of intra / DIMD merge candidates in the list may be selected and IPM / DIMD information of the selected intra / DIMD merge candidates may be combined into an HoC. For example, the HoC may include IPMs with cumulated sample-wise occurrences where each occurrence value for a respective IPM is calculated based on the number of samples that are coded with that IPM from the selected intra / DIMD merge candidates. For example, if a selected DIMD candidate is a neighboring block 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 is computed asℎ%^_b\^@A[0cR]+= B × ℎ. The occurrence for this specific IPM is cumulated over all considered neighboringblocks (e.g., adjacent spatial neighboring blocks and / or non-adjacent spatial neighboring blocks).

[0238] In some examples, up to a predetermined number (e.g., 5) of angular IPMs with the highest amplitudes (representing highest occurrences) in the HoC may be selected and blended together along with the planar mode to obtain an OBIC predictor (e.g. the DIMD predictor based on generating a HoC) used to generate a prediction block for coding the current block.

[0239] In some examples, some IPMs used by the neighboring blocks comprise more than one intra mode for prediction such as DIMD, using up to 5 angular modes, template-based intra mode derivation (TIMD) using up to 2 modes, spatial geometric partitioning mode (SGPM) using 2 modes, or OBIC using up to 5 angular modes. In these examples, all intra modes of such blocks are considered in the histogram generation. However, 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 HoC. In some examples, the weights used in the generation of the OBIC predictor may be computed similarly to the regular DIMD mode, and may only differ from this process by replacing gradient values from the template with occurrence values associated with the selected IPMs from the HoC. 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 OBIC predictor.

[0240] FIG. 22A shows an example of IPM information (e.g., DIMD information) from a plurality of (previously reconstructed) neighboring blocks of a block (e.g., block 0) previously used to determine (e.g., generating, reconstructing, predicting) the block, according to some embodiments. FIG.22B shows a graphical representation of combining the IPM information from the plurality of neighboring blocks to generate an MHoG if the block was coded using the MIMD mode. In contrast, FIG.22C shows a graphical representation of combining the IPM information from the plurality of neighboring blocks to generate a HoC if the block was coded using the OBIC mode.

[0241] 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 a plurality of (previously reconstructed) neighboring blocks (e.g., block 1,Docket No.: 24-2022PCT block 2, and block 3) and generates information used to generate a prediction block to code the block (e.g., block 0). For example, as shown in FIG.22A, the coder obtains first IPM information from block 1 including HoG information such as amplitudes for IPM 1, IPM 7, IPM 9, IPM 13, and IPM 17. For example, the coder obtains second IPM information from block 2 including HoG information such as amplitudes for IPM 7, IPM 9, and IPM 13. For example, the coder obtains third IPM information from block 3 including HoG information such as amplitudes for IPM 1, IPM 7, IPM 9, IPM 13, and IPM 17.

[0242] As shown in FIG.22B, if the block was 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 2202. For example, the coder determines the amplitudes of IPM 1 in the MHoG 2202 by adding all the amplitudes of IPM 1 from blocks 1-3. Also, the coder determines the amplitudes of IPM 7 in the MHoG 2202 by adding all the amplitudes of IPM 7 from blocks 1-3. Likewise, the coder determines the amplitudes of IPM 9 in the MHoG 2202 by adding all the amplitudes of IPM 9 from blocks 1-3. Also, the coder determines the amplitudes of IPM 13 in MHoG 2202 by adding all the amplitudes of IPM 13 from blocks 1-3. And, the coder determines the amplitudes of IPM 17 in MHoG 2202 by adding all the amplitudes of IPM 17 from blocks 1-3. In some implementations, using the various techniques described above (e.g., MIMD), the coder determines (e.g., generates, reconstructs, predicts) the block 0 based on the MHoG 2202. For example, a prediction block may be generated based on MHoG 2202 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.

[0243] As shown in FIG.22C, 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 2204. For example, the coder determines the amplitude (occurrence) of IPM 1 in the HoC 2204 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 2204 by adding the sizes of blocks 1, 2, and 3. Similarly, the coder determines the amplitude (occurrence) of IPM 9 in the HoC 2204 by adding the sizes of blocks 1, 2, and 3. Also, the coder determines the amplitude (occurrence) of IPM 13 in the HoC 2204 by adding the sizes of blocks 1, 2, and 3. And, the coder determines the amplitude (occurrence) of IPM 17 in the HoC 2204 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 various technique disclosed above, the coder determines (e.g., generates, reconstructs, predicts) the block 0 based on the HoC 2204.

[0244] 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 fromDocket No.: 24-2022PCT 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.

[0245] FIG.23 shows an example flowchart 2300 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 2300 includes a block 2302 in which an intra merge list is derived and a block 2304 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 2300 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.

[0246] Block 2302 may include several operations shown as blocks 2306-2314, 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.

[0247] At block 2306, 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 / DIMD merge candidate list at block 2306. 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, MIMID mode, intra merge mode (e.g., DIMD merge list mode), OBIC mode, intra prediction mode, MPM list derivation, etc.), at block 2306, no spatial adjacent candidates are added to the list of intra merge candidates.

[0248] At block 2308, 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,Docket No.: 24-2022PCT 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.

[0249] 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 2306 and thus may not be considered at block 2308. The sequence of blocks indicated by the sample locations 6-23 may be considered for inclusion of the corresponding IPM information in the list of intra merge candidates at block 2308. As shown in FIG. 21, the non-adjacent neighbor blocks corresponding to (e.g., including) sample locations 6-23 considered for inclusion in the list of intra merge candidates may be arranged in the frame along the left horizontal direction, the above vertical direction, the above left diagonal direction, the above right diagonal direction, and the below left diagonal direction.

[0250] 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, a 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 2308, no spatial non-adjacent candidates are added to the list of intra merge candidates.

[0251] At 2310, 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 history- based 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.

[0252] 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.

[0253] 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.

[0254] 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 2306 and 2308),Docket No.: 24-2022PCT 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.

[0255] In some examples, when inserting a new entry of IPM information into the history-based table, a constrained first-in-first-out (FIFO) rule may be applied where a redundancy check is first applied to determine whether there is identical IPM information in the table. If found, the entry with the identical IPM information is removed from the table and all entries following that in the table are moved forward in the FIFO order, and the new IPM information is inserted as the last entry. The table may be reset at intervals, such as, for example, at the beginning of each CTU row. Such resetting may be performed due to hardware constraints. Such resetting may also help ensure that only the most recent neighbor blocks are in the table. In some implementations, the history-based table of IPM information may be similar to the history-based table of motion vectors (HMVP) in the whole-block-based Advanced Motion Vector Predictor (AMVP) mode for inter prediction in VVC.

[0256] FIG.24 shows a flowchart 2400 of an example process for generating a history-based table of intra merge candidates, according to some embodiments. Operations of flowchart 2400 may be performed identically at the encoder (e.g., encoder 200) and the decoder (e.g., decoder 300). Flowchart 2400 starts at block 2402 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 2402, it is determined whether the IPM information (of the merge candidate) to be added already exists in the table. If, at block 2402, it is determined that the IPM information to be added is not in the table, then at block 2406, 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 2410, the IPM information of the merge candidate may be added to the history- based table.

[0257] If at block 2402, it is determined that the IPM information (e.g., DIMD information) to be added is in the table, then at block 2404, 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.

[0258] If at block 2406, it is determined that the history-based table is full, at block 2408, the oldest entry in the table is removed.

[0259] After either block 2404 or block 2408, at block 2412, the entries that follow the removed entry in the table are shifted up or moved up in sequence (e.g., in the FIFO sequence). After the rearrangement of table entries at block 2412, at block 2410, the new IPM information of the merge candidate is added as the last entry in the table.

[0260] According to the example inclusion order, intra merge candidates derived from IPM information in the history- based 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.

[0261] Returning to FIG.23, in some embodiments, at block 2312, 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)Docket No.: 24-2022PCT 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 2306-2310. 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.

[0262] 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 weights are 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.

[0263] 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.

[0264] 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.

[0265] At block 2314, a set of default intra merge candidates are added to the list of intra merge candidates, according to some embodiments.

[0266] 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)Docket No.: 24-2022PCT Blending Modes 0 (Planar) 34 (Diag) 50 (Ver) Default Mode 1 Blending Weights 16 24 24 T [IMD parameters. One or more intra merge candidates having predetermined default IPM information (e.g., the DIMD parameters specified in Table 1 above) may be added to the list of intra merge candidates as one or more default merge candidates.

[0268] 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.

[0269] Operations at block 2302, which includes blocks 2306-2314 and which generates the list of intra merge candidates, may be identical at both the encoder and decoder. After block 2302 is completed (i.e., the list of intra merge candidates is constructed), at block 2304, 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.

[0270] At the decoder, block 2304 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.

[0271] The DIMD merge mode has the benefit of the use of available neighbor information (e.g., in particular, the IPM / DIMD information derived for the spatial neighbor blocks) to better suit the signal characteristics of the current block to be predicted.

[0272] In some examples, the intra merge mode (e.g., DIMD Merge list mode), OBIC mode, and the MIMD discussed above are designed as a DIMD sub-mode, i.e., these modes are signaled only if the DIMD feature is activated. Respectively, if one of these three modes is selected by the encoder to generate the current block prediction, the DIMD flag is activated to indicate that a DIMD mode is used. As these three modes are DIMD sub-modes whose usage depends on the activation of the DIMD mode, using basic signaling will reduce the compression efficiency. For example, one flag can be used for each sub-mode to indicate whether such a sub-mode is selected. Adding the DIMD flag, there will be four flags in total. As a result, each time one of these DIMD modes is selected, four flags will be signaled andDocket No.: 24-2022PCT decoded. These drawbacks may result in reduced coding efficiency and competitiveness of DIMD compared to other intra modes.

[0273] Embodiments of the present disclosure relate to improved signaling for DIMD mode and sub-modes. As used herein, the regular DIMD mode and the sub-modes, such as the intra merge mode (e.g., the DIMD merge list mode), OBIC mode, and the MIMD, are collectively referred to as “DIMD modes.” The improved signaling can reduce the number of bits used to signal the DIMD mode used for each block, thereby improving the coding efficiency. These and other features of the present disclosure are described further below.

[0274] Example embodiments of this disclosure provide a technique for adaptive DIMD mode signaling for a block. More specifically, the technique involves using adaptive signaling of the DIMD modes to reduce the signaling payload and improve the compression efficiency. Each DIMD sub-mode flag may be included or discarded according to a dedicated activation function for the DIMD sub-mode. The activation function can be determined based on the properties of the block, such as the availability of the neighboring blocks, the QP, the slice type of the current block. The block may be a CU block, a PB, or any coding unit used for the DIMD-related intra prediction.

[0275] FIG.25 illustrates a flowchart of an example of the adaptive DIMD mode signaling process 2500 based on DIMD mode activation mechanisms. The DIMD modes include the regular DIMD mode and one or more of DIMD sub- modes, such as one or more of the intra merge mode (e.g., the DIMD Merge list mode), OBIC mode, and MIMD mode. The method of the flowchart may include several operations such as 2502-2520, each of which may be processed to determine the DIMD mode to be used to predict or reconstruct the current block. The process 2500 may be implemented in an encoder or a decoder.

[0276] The process 2500 begins at 2502, by verifying whether the DIMD feature is enabled or activated. For the encoder, the intra prediction mode for the current block has been selected. The encoder can thus determine whether the DIMD feature is enabled based on the determination made when the intra prediction mode for the current block is selected. For the decoder, whether the DIMD feature is enabled or activated can be determined based on a high-level syntax flag, such as in the Sequence Parameter Set (SPS), that has been decoded or parsed from the video bitstream.

[0277] If it is determined at 2502 that the DIMD feature is disabled or de-activated, the DIMD modes are disabled and not used in the prediction process, and the process 2500 proceeds to 2520. If the DIMD feature is enabled or activated, the DIMD flag can be determined at 2504. For the encoder, the DIMD flag can be determined based on the selected intra prediction mode for the current block. If the selected intra prediction mode is a DIMD mode, the DIMD flag can be determined to be a value (e.g., true or 1) indicating that the DIMD mode is used; otherwise, the DIMD flag can be set to another value (e.g., false or 0) indicating the DIMD mode is not use. The determined DIMD flag can be signaled or encoded into the bitstream. For the decoder, the DIMD flag can be parsed or decoded from the bitstream.

[0278] At 2506, the value of the DIMD flag of the current block is evaluated and used to determine whether a DIMD mode is used for the current block. If the DIMD flag indicates that the current block is not using a DIMD mode, no more DIMD-related flags are encoded or parsed. The process 2500 proceeds to 2520. If the DIMD flag indicates that the current block is using a DIMD mode, the signaling for the DIMD mode is then determined.Docket No.: 24-2022PCT

[0279] To do so, at 2507, an activation status for a first DIMD sub-mode is determined. In some examples, the activation status for a DIMD sub-mode is determined via an activation function for the DIMD sub-mode. The activation function may be defined based on properties of the current block, such as the available neighboring blocks, the size of the block, the slice type of the block, and so on. Additional details regarding the activation functions will be provided later. The activation functions may be calculated by the encoder and the decoder in the same way.

[0280] Based on the activation status for the first DIMD sub-mode determined at 2507, a presence status for a first flag can be determined at 2508 to indicate whether the first flag is present or not (in order to signal the selected DIMD mode). In some examples, the first flag alone indicates whether the first DIMD sub-mode is used or not. In other examples, the first flag in combination with other one or more flags indicates whether the DIMD sub-mode is used or not. If the presence status indicates that the first flag is present, the value of the first flag is determined at 2510.

[0281] For the encoder, the first flag can be determined based on the selected DIMD mode for the block and the signaling scheme used. For instance, if the first flag alone indicates the use of the first sub-DIMD mode, the first flag can be determined based on whether the sub-DIMD mode is selected for the block or not. If not, the first flag can be determined to be “false,” “0,” or any other value agreed between the encoder and the decoder; otherwise, the first flag can be determined to be “true,” “1,” or another value. For instance, Table 1 illustrates a signaling scheme where one flag is used for each DIMD sub-mode to indicate the usage of the corresponding DIMD sub-mode. Table 1. Example DIMD Signaling Scheme Flag name DIMD mode Activation Presence Condition Value ot is is otDocket No.: 24-2022PCT

[0282] In this example, the first flag alone indicates the use of the first DIMD sub-mode for the current block. If the first DIMD sub-mode is used for the current block, the first flag has a value 1; otherwise, the first flag has a value 0. Likewise, the second flag alone indicates the use of the second DIMD sub-mode for the current block. If the second DIMD sub-mode is used for the current block, the second flag has a value 1; otherwise, the second flag has a value 0. Other flags indicate the respective DIMD sub-modes in a similar way. Note that values 0 and 1 are merely listed as example flag values and other values may be used to indicate whether a DIMD sub-mode is used or not.

[0283] FIG.26 shows an example of another signaling scheme. In this example, the flags for signaling the DIMD mode for the current block form a flag tree 2600. The root of the flag tree 2600 is the DIMD flag indicating whether a DIMD mode is used for the current block. Each leaf of the flag tree 2600 is associated with a DIMD mode decision (no DIMD mode or a particular DIMD mode). If the DIMD flag has a value 0, it means that no DIMD mode is used for the current block; if the DIMD flag has a value 1, it means that a DIMD mode is used for the current block. In the latter case, additional flags are used to signal the DIMD mode used for the current block. For example, in FIG.26, if the first flag, flag 1, has a value of 1, the first DIMD sub-mode is used. If the first flag has a value of 0, the second flag, flag 2, needs to be used to signal the DIMD mode and so on. Similar to the first flag, if flag 2, has a value 1, the second DIMD sub-mode is used. If the second flag has a value of 0, the third flag, flag 3, needs to be used to signal the DIMD mode. In this example, the first to the third flags are associated with the respective DIMD sub-modes.

[0284] FIG.27 shows an example of another signaling scheme. In this example, the flags for signaling the DIMD mode for the current block form a flag tree 2700. Similarly to the flag tree 2600, the root node is the DIMD flag, and each leaf is associated with a DIMD mode decision. Different from the flag tree 2600, two of the first to the third flags are used to identify a DIMD mode. For instance, flag 1 and flag 2 jointly determine whether the first or the second DIMD mode is used. Likewise, flag 1 and flag 3 jointly determine whether the third or the fourth DIMD mode is used. In this example, the value of the first flag can be determined based on the DIMD mode selected for the current block and the signaling scheme. For instance, according to the signaling scheme in FIG.27 and assuming the first DIMD mode is DIMD sub-mode 1, if the activation status of DIMD sub-mode 1 indicates that DIMD sub-mode 1 is activated (at 2507), it can be determined according to the signaling scheme 2700 that flag 1 is present (so that the DIMD sub-mode 1 can be signaled if used). The value of flag 1 can be determined at 2510 based on whether the DIMD sub-mode 1 is used or not by the encoder. If DIMD sub-mode 1 is used, then flag 1 has a value of 0. If the DIMD sub-mode 1 is not used and DIMD sub-mode 2 is used instead, then the value of flag 1 is also 0. In either case, additional flags (e.g., flag 2) need to be signaled to identify the used DIMD mode.

[0285] At the decoder side, the decoder can determine the value of flag 1 by parsing the bitstream.

[0286] At 2512, it is determined whether the value of first flag identifies the DIMD mode used for the current block. If so, the signaling or decoding of additional flags for the DIMD mode can be skipped, thereby reducing the number of bits used to signal the DIMD mode and increasing the coding efficiency. In the above examples, the first flag shown in Table 1 can identify the first DIMD sub-mode is used if the first flag has a value 1. Similarly, the first flag, flag 1, shownDocket No.: 24-2022PCT in FIG.26 can identify that the first DIMD sub-mode is used if the first flag has a value 1. As a result, the signaling of other flags can be skipped and the process 2500 proceeds to 2520.

[0287] If the value of the first flag does not identify the DIMD mode, additional flags may be needed. In the examples shown in Table 1 and FIG.26, if flag 1 has a value 0, then the DIMD mode used for the current block cannot be identified and the process 2500 proceeds to 2514. In the example shown in FIG.27, neither value of flag 1 can identify the DIMD mode used for the current block, and thus 2514 is performed.

[0288] At 2514, the activation status for a second DIMD sub-mode is determined. Similar to 2507, the activation status for the second DIMD sub-mode is determined via an activation function for the second DIMD sub-mode. Based on the activation status for the second DIMD sub-mode, a presence status for a second flag can be determined at 2516 to indicate whether the second flag is present or not (in order to signal the selected DIMD mode). Similar to the first flag, in some examples, the second flag alone indicates whether the second DIMD sub-mode is used or not. In other examples, the second flag in combination with other one or more flags indicates whether the second DIMD sub-mode is used or not. For example, in the examples of Table 1 and FIG.26, if the activation function for the second DIMD sub-mode shows that the second DIMD sub-mode is activated, then the second flag is present; otherwise, it is not present. In the example shown in FIG.27, if the activation function for the DIMD sub-mode 2 shows that the DIMD sub- mode 2 is activated, then flag 2 is present (because flag 2 is used to flag the DIMD sub-mode 2 in conjunction with flag 1); otherwise, it is not present.

[0289] If the presence status indicates that the second flag is present, the second flag is determined at 2518. For the encoder, the second flag can be determined based on the selected DIMD mode for the block and the signaling scheme used. For example, for the signaling schemes of Table 1 and FIG.26, if DIMD sub-mode 2 is selected by the encoder, then flag 2 can be determined to be 0; otherwise flag 2 can be determined to be 1. For the signaling scheme of FIG. 27, if DIDM sub-mode 2 is selected, then flag 2 can be determined to be 1 (and flag 1 is determined to be 0 in 2512). For the decoder, the value of flag 2 can be determined by parsing the bitstream.

[0290] If there are two DIMD sub-modes and the second flag is not present, the process 2500 proceeds to 2520 from 2516. At 2520, the current block can be encoded based on a mode that corresponds to the DIMD flag, flag 1(if present), and flag 2 (if present). For example, if the DIMD flag indicates that DIMD feature is not enabled at 2502, then an intra mode other than the DIMD modes are used to code the current block. Likewise, if the DIMD flag indicates that the DIMD mode is not used at 2506 even though it is enabled, the current block can be coded using an intra mode other than the DIMD modes. If a DIMD mode is used and the flag 1 value can identify the DIMD mode used for the current block at 2512, the current block can be coded using the identified DIMD mode. If flag 1 and flag 2 are both present, the current block can be coded using the DIMD mode identified by the combination of flag 1 and flag 2. If neither flag 1 nor flag 2 is present, a default DIMD mode, such as the regular DIMD mode, can be used to code the current block.

[0291] Note that in the example shown in Fig.25, the DIMD modes include two DIMD sub-modes and the regular DIMD mode. There can be more or fewer than two DIMD sub-modes. For example, if there are more than two DIMD sub-modes, additional operations can be performed, for example, to determine whether the value of flag 2 and flag 1Docket No.: 24-2022PCT identifies a DIMD mode, similar to 2512. If not, the activation status for another DIMD sub-mode needs to be determined. Based on the activation status, the presence status of additional flag and value of the additional flag are to be determined in a similar way as 2508-2512. If there is one DIMD sub-mode, 2512-2518 can be omitted.

[0292] It should be further noted that a DIMD sub-mode may be enabled or disabled for the whole sequence or a part of the sequence by signaling it using a high-level syntax flag in the SPS, or the PPS, or the slice header. In such scenarios, the activation status of a DIMD sub-mode is determined based on both the activation function and the high- level syntax flag.

[0293] In some implementations, each DIMD sub-mode may be one of the intra merge mode (e.g., the DIMD merge list mode), the OBIC mode, and the MIMD and different DIMD sub-modes are different.

[0294] As discussed above, at least one DIMD sub-mode may be enabled (activated) or disabled (deactivated) via an activation function that is defined based on whether the properties of the current block satisfy one or more conditions. The properties of the current block can include, for example, the CU shape or size, the characteristics of the neighboring blocks, or the QP of the current block.

[0295] In some examples, the conditions in the activation function are defined based on the block shape or size. For instance, the conditions can include one or more of whether the height or width of the block is bigger than threshold value (e.g., 32x32) or whether both the height and width are larger than or equal to a threshold value (e.g., 8 luma samples). The conditions may further include whether the width or height of the block is higher than a threshold value (e.g., 128) when the width and height are equal, whether the width or height of the block is lower or equal to a threshold value (e.g., 64) when the width and height are equal, or whether the width or height of the block is higher than a threshold value (e.g., 64) when the width and height are different.

[0296] In some implementations, the conditions may include whether the block has a specific shape. The shape may be defined based on the maximum size and / or the minimum size, such as the maximum and minimum width and / or height. The block has a specific shape if the width and / or height of the block is between the minimum and maximum values. The minimum and maximum height / width values may be transmitted in a high-level syntax, such as the SPS.

[0297] In some examples, the block shape may be defined by a minimum ratio and / or a maximum ratio between the width and height of a block. The conditions of the activation function may include whether the width-height ratio of the current block is below the minimum ratio, or above the maximum ratio, or in between the minimum and maximum ratios.

[0298] As discussed above, a DIMD sub-mode, such as the intra merge / DIMD merge list mode, OBIC mode, and the MIMD, reuses available information from neighboring blocks to build specific information (e.g., a intra merge / DIMD merge list, a histogram of occurrences, a merged histogram of gradients) which is used to derive IPM / DIMD information for predicting the current block. By merging IPM / DIMD information from multiple neighboring blocks, the derived IPM / DIMD information may be diluted and may reduce the derived prediction efficiency. Thus, it may be beneficial to adaptively enable or disable the DIMD sub-mode according to the neighborhood information of the DIMD sub-mode, such as the number of used neighboring blocks, the distance between the neighboring blocks and the current block, and so on. For example, the conditions in the activation function may include whether there are a minimal number (e.g.,Docket No.: 24-2022PCT 3) of available neighboring blocks to reuse to derive the IPM / DIMD information of the current block. If this minimal number of neighboring CU blocks is not reached, the DIMD sub-mode is not activated.

[0299] In another example, the conditions may include whether the available neighboring blocks for deriving the IPM / DIMD information of the current block are less than a maximal number (e.g., 5). If this maximal number of neighboring blocks is reached, the DIMD sub-mode is not activated.

[0300] In further examples, the conditions of the activation function can include whether the number of neighboring blocks available to derive the IPM / DIMD information for the DIMD sub-mode is higher, lower, or equal to a threshold value. For example, if the number of available neighboring blocks is larger than 3 (or lower than 6, or larger than 2 and lower than 6), the DIMD sub-mode is activated.

[0301] In some examples, the conditions of the activation function for the corresponding DIMD sub-mode may be defined based on the quantization parameter of the current block. A minimum threshold, a maximum threshold, or both a minimum threshold and a maximum threshold on the quantization parameter may be used to adaptively enable or disable the usage and the signaling of the DIMD sub-mode. As an example, if the quantization parameter of the current block is higher than the minimum threshold (e.g., 17 or 23), the DIMD sub-mode is activated. If the quantization parameter of the current block is lower than the maximum threshold (e.g., 43 or 37) the DIMD sub-mode is activated.

[0302] In some examples, the conditions of the activation function for the corresponding DIMD sub-mode may be defined based on the current slice type, such as the INTRA type, uni-directional predicted picture, or bi-directional predicted picture. As an example, if the current slice is a bi-directional predicted slice, the activation function may determine that the DIMD sub-mode is deactivated; otherwise, the DIMD sub-mode is activated.

[0303] The activation function may include one or more of the conditions discussed above. The activation function may determine the corresponding DIMD sub-mode is activated if the one or more conditions are satisfied. In other implementations, the activation function may determine the corresponding DIMD sub-mode is activated if the one or more conditions are not satisfied. In further implementations, the activation function may determine the corresponding DIMD sub-mode is activated if some of the one or more conditions are satisfied and others are not. For example, the conditions of the activation function may include multiple conditions based on the QP and the slice type. For instance, the activation function may indicate that the DIMD sub-mode is activated if the quantization parameter of the current block is larger than 13. The activation function may indicate that the DIMD sub-mode is activated if the quantization parameter of the current block is lower than 39. The activation function may indicate that the DIMD sub-mode is activated if the current block belongs to an INTRA slice or if the current block belongs to a predicted slice.

[0304] FIG.28 illustrates a flowchart 2800 of an example of the adaptive DIMD mode signaling process at the encoder based on DIMD mode activation mechanisms. The method of flowchart 2800 may include several operations such as 2802-2812, each of which may be processed to determine the signaling of the DIMD mode selected to predict the current block. The flowchart 2800 may be implemented in an encoder after the encoder determines that the DIMD is used for the current block and has selected the DIMD mode for the current block.Docket No.: 24-2022PCT

[0305] The flowchart 2800 begins at 2802, where the encoder can encode an indication of the DIMD is used to code the current block. The indication may be, for example, the DIMD flag discussed above with respect to FIG.25. At 2804, the encoder can determine the presence status of a first flag based on the indication and an activation status of a DIMD mode for the current block. In some examples, if the indication shows that DIMD is used for the current block, the activation status of the DIMD mode is determined. As discussed in more detail above with respect to FIG.25, the encoder can determine the activation status of the DIMD mode via an activation function for the DIMD mode based on the properties of the current block, such as the size and / or shape of the block, the slice type of the block, the availabilities of neighboring blocks, the QP of the block, and so on. If the activation status indicates that the DIMD mode is activated for the current block, the encoder can determine the presence status of the first flag to be “true” (or any value indicating the first flag is present); otherwise, the presence status can be determined to indicate that the first flag is not present.

[0306] At 2806, the encoder can determine whether to encode the first flag in the bitstream of the video based on the presence status of the DIMD mode. If the presence status shows that the first flag is present, the encoder can encode, at 2808, the first flag into the bitstream. The value of the first flag can be determined based on whether the selected DIMD mode for the current block is the DIMD mode currently under evaluation. For example, the value of the first flag can be set to “1” if the current DIMD mode is the selected DIMD mode for the block and to “0” otherwise. Alternatively, the value of the first flag can be set to “0” if the current DIMD mode is the selected DIMD mode for the block and to “1” otherwise. In some implementations, the value of the first flag is set according to the signaling scheme, such as the signaling scheme shown in Table 1, FIG.26, or FIG.27.

[0307] If the encoder determines, at 2806, not to encode the first flag in the bitstream, the encoder may proceed to encode the next bit in the bitstream at 2810 without encoding the first flag. The next bit may be a next flag for signaling the DIMD mode or a bit for information unrelated to DIMD mode. At 2812, the encoder can encode the current block using the DIMD mode that corresponds to the determination of whether to encode the first flag. In other words, if it is determined that the first flag is not to be encoded in the bitstream, the DIMD mode used to encode the current block is a mode that does not need the first flag for signaling. If it is determined that the first flag is encoded in the bitstream, the DIMD mode used to encode the current block is a mode whose signaling includes the first flag.

[0308] FIG.29 illustrates a flowchart 2900 of an example of the adaptive DIMD mode signaling process at the decoder based on DIMD mode activation mechanisms. The method of flowchart 2900 may include several operations such as 2902-2912, each of which may be processed to determine the signaling of the DIMD mode selected to reconstruct the current block. Flowchart 2900 begins at 2902, where the decoder can obtain, from a bitstream of a video, an indication of the DIMD is used to encode the current block. Similar to the indication discussed above with respect to 2802 of FIG. 28, the indication may be, for example, the DIMD flag discussed above with respect to FIG.25. The decoder can determine that the DIMD is enabled for the block, and obtaining the indication can be based on determining the DIMD being enabled.

[0309] At 2904, the decoder can determine the presence status of a first flag in the bitstream based on the indication and an activation status of a DIMD mode for the current block. In some examples, if the indication shows that DIMD isDocket No.: 24-2022PCT used for the current block, the activation status of the DIMD mode is determined. As discussed above in more detail with respect to FIG.25, the decoder can determine the activation status of the DIMD mode via an activation function for the DIMD mode in a way similar to the encoder. For example, the activation function can be based on the properties of the current block, such as the size and / or shape of the block, the slice type of the block, the availabilities of neighboring blocks, the QP of the block, and so on. The decoder can determine the activation status of the DIMD mode based on determining whether the one or more properties satisfy one or more conditions for the DIMD mode. In some examples, the one or more conditions include a condition of a size of a CU containing the block being one of more of equal to, less than, or larger than a threshold CU size. The condition may further specify that the height of the CU and the width of the CU being different or same. In further examples, the one or more conditions may include the number of available neighboring blocks of the block useable for deriving IPM / DIMD information being one or more of equal to, smaller than, or larger than a neighboring block number threshold. The one or more conditions may further include a quantization parameter (QP) value of the block being one or more of equal to, less than, or larger than a threshold QP value, a slice type of the block belonging to or not belong to a set of pre-determined slice types, and so on. In some examples, determining the activation status of the DIMD mode can be further based on a syntax value for a partition of the video, the syntax value indicating the first DIMD mode being activated for the block. The partition may be a sequence, a frame, or a slice of the video and the syntax value may be in the SPS, frame header, or slice header.

[0310] If the activation status indicates that the DIMD mode is activated for the current block, the decoder can determine the presence status of the first flag to be true or another value indicating the first flag is present; otherwise, the presence status can be determined to indicate that the first flag is absent from the bitstream.

[0311] At 2906, the decoder can determine whether the first flag is in the bitstream (and thus whether to decode the first flag from the bitstream) based on the presence status of the DIMD mode. If the presence status shows that the first flag is present, the decoder can decode (or parse), at 2908, the first flag from the bitstream. The value of the first flag can be used to determine the DIMD mode used to encode the current block according to the signaling scheme. For example, if an individual flag is used to signal each DIMD mode, the value of the decoded or parsed first flag can be used to determine whether the DIMD mode signaled by the first flag is used or not. In another example, such as the signaling scheme shown in FIG.26, if the decoded first flag has a value “1” then the decoder can determine that the DIMD sub-mode 1 is used; otherwise, the decoder will need to decode (or parse) more flags from the bitstream to identify the DIMD mode used by the encoder. For the signaling scheme shown in FIG.27, the decoder will need to decode (or parse) at least one more flag from the bitstream, at 2910, in order to identify the DIMD mode used by the encoder. In some examples, the DIMD mode is associated with a plurality of DIMD modes comprising the first DIMD mode, a second DIMD mode, and a third DIMD mode. Based on the value of the first flag being a first predetermined value, the decoder can determine the DIMD mode as one of the first DIMD mode or the third DIMD mode without determining the activation status of the second DIMD mode for the block.

[0312] If it is determined at 2906 that the first flag is not present in the bitstream, the decoder may proceed to decode the next bit in the bitstream at 2910 without decoding the first flag. The next bit may be a next flag for signaling theDocket No.: 24-2022PCT DIMD mode as discussed above or a bit for information unrelated to DIMD mode. At 2912, the decoder can decode the current block using the DIMD mode that corresponds to the determination of whether to decode (or parse) the first flag. In other words, if it is determined that the first flag is not present in the bitstream, the DIMD mode is a mode that is signaled without the first flag. If it is determined that the first flag is present in the bitstream, the DIMD mode is a mode signaled by the first flag alone or in combination with other flags.

[0313] In examples where there are more flags in the signaling scheme, the decoder can determine, based on not to parse the first flag or the value of the parsed first flag being a pre-determined value, a second presence status of a second flag for the block based on the indication and a second activation status of a second DIMD mode. The decoder can determine, based on the second presence status, whether to parse the second flag from the bitstream. In these examples, the DIMD mode is determined based on the indication, the determination of whether to parse the first flag, and the determination of whether to parse the second flag.

[0314] In some signaling schemes, such as the signaling schemes shown in FIGS.26 and 27, at least one of the DIMD modes is signaled using a combination of multiple flags. This type of signaling scheme may reduce the number of bits for signaling a DIMD mode, compared with the signaling scheme shown in Table 1. For instance, in FIG.26, instead of always using four bits for signaling the DIMD mode, some DIMD modes are signaled with fewer than four bits. For example, two bits (DIMD flag and flag 1) are used to signal the DIMD sub-mode 1 and three bits (DIMD flag, flag 1, and flag 2) are used to signal the DIMD sub-mode 2. In FIG.27, three bits are used to signal each of the DIMD modes. As used herein, the flags that are used to identify the DIMD modes are referred to as “DIMD mode identifying flags.” The DIMD mode identifying flags can include the DIMD flag, flag 1, flag 2, and flag 3 shown in Table 1, FIG.26, FIG.27, as well as FIGS.30A and 31B to be discussed later.

[0315] Further, example signaling schemes may apply variable-length signaling in which one DIMD mode may be signaled using more flags (e.g., more bits) than another. If the DIMD mode that has a higher probability of being selected for a block is signaled with fewer bits than a DIMD mode that has a lower probability of being selected, the overall number of bits used to signal the DIMD modes for multiple blocks can be further reduced. However, statistics of selected DIMD modes may vary depending on the content in the video, video frame, etc. One DIMD mode that is configured to be signaled using one flag may have a lower probability of being selected for a block than another DIMD mode that is configured to be signaled using, e.g., two flags. As a result, more two-flag DIMD mode signalings may be used in the bitstream than single-flag DIMD mode signalings, leading to more bits being used for the DIMD mode signaling. As such, using a fixed signaling scheme for different videos or different frames of a video may lead to coding inefficiencies. Further because the multiple DIMD modes are exclusive in that only one DIMD mode may be selected for a block, parsing additional DIMD mode identifying flags from the bitstream after the first DIMD mode identifying flag parsed from the bitstream identify the DIMD mode used for a block increases the bitrate and the computational complexity of the decoder (and the encoder).

[0316] To solve the above problems, adaptive DIMD mode signal re-ordering is described, where the available DIMD modes are ordered adaptively for each block based on the properties of the block. In this way, the DIMD mode thatDocket No.: 24-2022PCT has a higher probability of being selected for a block is signaled with fewer bits than a DIMD mode that has a lower probability of being selected. In addition, the parsing (and encoding) of DIMD mode identifying flags can be configured to terminate after the first DIMD mode identifying flag parsed from the bitstream can identify the DIMD mode used for a block. In this way, the number of bits and computational consumptions required to signal the DIMD modes for blocks can be reduced, thereby improving the coding efficiency.

[0317] FIG.30A shows a signaling scheme similar to FIG.26 that can be used for adaptive signaling described herein. In the example shown in FIG.30A, the number of bits used to signal the DIMD mode associated with each leaf is shown. As can be seen from FIG.30A, leaf 1 uses two bits to signal the associated DIMD mode; leaf 2 uses three bits to signal the associated DIMD mode; leaf 3 and leaf 4 each uses four bits to signal the respective associated DIMD modes. As such, to reduce the number of bits for signaling the DIMD mode, the DIMD mode associated with leaf 1, the first DIMD mode, should have a higher likelihood to be selected for the block than the DIMD mode associated with leaf 2, the second DIMD mode. Likewise, the DIMD mode associated with leaf 2, the second DIMD mode, should have a higher likelihood to be selected for the block than the DIMD modes associated with leaf 3 (the third DIMD mode) and leaf 4 (the fourth DIMD mode).

[0318] In some examples, the likelihood of a DIMD mode being selected for a block may be determined based on the occurrence of individual DIMD modes observed so far in a partition containing the block, such as a sequence, a frame, or a slice. For example, the encoder or the decoder can determine a count for each DIMD mode. The count indicates the number of times the corresponding DIMD mode being used for blocks in the partition of the video that contains the block. The DIMD modes can be ordered according to a descending order of the counts of the DIMD modes.

[0319] For signaling schemes such as that shown in FIG.26 where each flag can be used to represent or otherwise be associated with a mode / sub-mode, the signaling order of the modes can be adaptively determined according to the context IDs (for context models) of the flags corresponding to these modes (e.g., DIMD flag, OBIC flag, and so on). A “context model” is a probability model for one or more bins of the binarized symbol. This model may be chosen from a selection of available models depending on the statistics of recently coded data symbols. The context model stores the probability of each bin being "1" or "0". For example, the context model of a flag can be used to estimate the conditional probabilities of the flag and may be derived using already-coded flag from neighboring blocks. For example, for a flag with four contexts models, the context ID for the flag can be a first value (e.g., 0) if none of the neighboring blocks of the current block uses this flag. In some implementations, for example, in CABAC / CAVLC, the neighboring block refers to either the above block or the left block. If the above block of the current block uses this flag, the context ID may be increased by one (e.g., 1); if the left block uses this flag, the context ID may be increased by two (e.g., 2); and if both the above and left blocks use this flag, the context ID may be increased by three (e.g., 3). Once the context ID for the flag is derived, the corresponding context model from the four context models may be selected and used to entropy code the flag representing the mode / sub-mode for the current block.

[0320] As can be seen from the above, the context ID reflects the number of neighboring blocks that use the same mode or sub-mode. As such, the context ID can be used to determine the signaling order of the flags for the modes / sub-Docket No.: 24-2022PCT modes. For example, the signaling of the modes / sub-modes can be ordered according to the order / value of the context ID. For instance, the flag of a mode / sub-mode is ordered after another flag if the context ID of the flag is smaller than the context ID of the other flag. In other examples, the signaling order is determined by a specific order of the context ID. For instance, the signaling order can be determined by a sequence of the context ID {3, 1, 2, 0}. In this example, the flag with context ID 3 is ordered before the flag with context ID 1, which is ordered before the flag with context ID 2, and so on. By determining the signaling order of the modes / sub-modes based on their context IDs, the signal reordering can be adapted to the local usage of a flag, while the occurrence-based method discussed above is based on the occurrence of the flag since the beginning of the partition (e.g., the tile or frame).

[0321] In further examples, the context-based mechanism may be combined with the occurrence-based mechanism to reorder the flags of the modes / sub-modes. When combining the two mechanisms, the relative priority between these two mechanisms can be defined. In some examples, the context-based re-ordering may have a higher priority than the occurrence-based reordering. For example, considering three modes / sub-modes: DIMD regular mode, OBIC mode, and intra merge / DIMD merge list mode, these three modes / sub-modes are ordered first based on their context IDs. If two modes / sub-modes have the same context ID, the occurrence-based reordering can be used to break the tie and to determine the signaling order. For instance, if none of the above and left neighboring blocks of the current block are coded with the DIMD regular mode or the OBIC mode, then the context ID for both of these two modes / sub-modes is zero. In this scenario, the occurrence of these two modes / sub-modes in the partition can be calculated and the mode / sub-mode with the higher occurrence can be signaled before the other mode / sub-mode. In alternative examples, the occurrence-based re-ordering may be set to have a higher priority than the context-based reordering. In these examples, the context IDs of the modes / sub-modes can be used to determine the order of the modes / sub-modes when they have the same occurrence value. Various other ways of combining the context-based mechanism with the occurrence-based mechanism to reorder the flags of the modes / sub-modes may be used.

[0322] While the above examples focus on using the context IDs of modes / sub-modes to determine the signaling order of these modes / sub-modes, the signaling order may be determined, alone or in combination with other metrics (such as the occurrence), based on the neighboring blocks coding modes. For example, instead of using the context IDs, the signaling order may be determined based on the modes / sub-modes of neighboring blocks. For instance, a first mode / sub-mode can be signaled before a second mode / sub-mode if the first mode / sub-mode is used to code N1 neighboring blocks (left or above) and the second mode / sub-mode is used to code N2neighboring blocks with N1>N2. In scenarios where N1=N2=1, the left neighboring block can be given a higher (or lower) priority than the above neighboring block. In other words, a first mode / sub-mode used to code only the left neighboring block is given a higher (or lower) priority over a second mode / sub-mode used to code only the above neighboring block.

[0323] In other examples, the signaling order of the DIMD modes may be adaptively determined based on properties of the block, such as the size or shape of the block, the QP of the block, the characteristics of the neighboring blocks, the slice type of the block, and so on. For example, the signaling order may be determined to be an order based on one or more conditions being satisfied (or not satisfied). The one or more conditions may be defined based on theDocket No.: 24-2022PCT properties of the block. The order may be a pre-determined order such as {the regular DIMD mode, the intra merge / DIMD Merge list mode, the OBIC mode, the MIMD mode}. With this order and the signaling scheme shown in FIGS.26, 27, 30A, and 31A, the first DIMD mode will be the regular DIMD mode; the second DIMD mode will be the intra merge / DIMD Merge List mode; the third DIMD mode will be the OBIC mode; and the fourth DIMD mode will be the MIMD mode.

[0324] In some implementations, the signaling order may be adapted to the size and / or shape of the current CU block. As an example, the conditions for determining the signaling order may be the width or height of the block is higher than a threshold value (e.g., 128) when the width and height are equal. If these conditions are satisfied, the signaling order may be determined as {DIMD mode, intra merge / DIMD Merge list mode, OBIC mode, MIMD mode}. In other implementations, the conditions may be the width or height of the block is lower than a threshold value (e.g., 64) when the width and height are equal. If these conditions are satisfied, the signaling order may be determined as {OBIC mode, MIMD mode, DIMD mode, intra merge / DIMD Merge list mode}. In further implementations, the conditions may be the width or height of the block is higher than a threshold value (e.g., 32) when the width and height are different. If these conditions are satisfied, the signaling order may be determined as {OBIC mode, MIMD mode, DIMD mode, intra merge / DIMD Merge list mode}.

[0325] In some examples, the signaling order may be adapted to the shape of the current block. As an example, a specific shape that corresponds to a specific signaling order for the DIMD modes may be signaled by signaling the maximum and / or minimum size (e.g., in a high-level syntax). For example, the maximum (or minimum) size may be signaled by signaling the maximum (or minimum) width and / or height measured in terms of the number of pixels. As such, the condition may be that the width of the block is between the maximum and minimum width and the height of the block is between the maximum and minimum height. If these conditions are satisfied, the signaling order may be determined as {intra merge / DIMD Merge list mode, OBIC mode, MIMD, DIMD mode}.

[0326] Likewise, the block shape may be represented by a shape ratio defined over the dimension (width or height) of the CU. For example, the shape ratio can be defined as the larger one of the width and height over the smaller one of the width and height, or vice versa. A block shape may be defined by a maximum shape ratio and / or a minimum shape ratio. For example, a block can be considered as having a specific block shape if the shape ratio of the block is lower than the maximum shape ratio or higher than the minimum ratio or falls between the maximum shape ratio and the minimum shape ratio for that block shape. In this example, a block shape that corresponds to a specific signaling order for the DIMD modes may be signaled by signaling the minimum and / or maximum shape ratio (e.g., in a high-level syntax). For example, the condition may include that the shape ratio of the block falls between the minimum shape ratio and the maximum shape ratio (or higher than the minimum shape ratio, or lower than the maximum ratio). If this condition is satisfied, the signaling order of the DIMD modes can be determined as {intra merge / DIMD Merge list mode, DIMD mode, OBIC mode, MIMD}.

[0327] In some implementations, the DIMD mode signaling order may be adapted to the characteristics of the neighboring blocks of the current block. The signaling order may be determined based on one or more of the modes ofDocket No.: 24-2022PCT the neighboring blocks, the IPM / DIMD information of the neighboring blocks, the distance (e.g., average, minimum or maximum distance) of the neighboring blocks to the current block, the area (e.g., average, minimum or maximum area) of the neighboring CU blocks, and so on.

[0328] In some implementations, the DIMD mode signaling order may be determined based on the available neighboring IPM / DIMD information for each DIMD mode. The available neighboring IPM / DIMD information may be different for different DIMD modes. Some DIMD modes may consider only the DIMD modes; some may consider all available IPM / DIMD information regardless of the neighboring block mode; and others may discard specific neighboring block modes. As an example, if the MIMD mode derives its IPM / DIMD information using N neighboring blocks (e.g., N=2, 3, or 5) and the OBIC mode derives its IPM / DIMD information using M neighboring blocks, with M < N, the MIMD may be signaled before the OBIC mode. In some implementations, the N neighboring blocks used by the MIMD mode can be blocks coded with any mode and the M neighboring blocks used by the OBIC mode can also be blocks coded with any mode. In other implementations, the N neighboring blocks used by the MIMD mode are blocks coded with the MIMD mode and the M neighboring blocks used by the OBIC mode are blocks coded with the OBIC mode.

[0329] As another example, if the intra merge / DIMD merge list mode derives its IPM / DIMD information using N neighboring blocks (e.g., N=2, 3, or 5), and the MIMD mode derives its IPM / DIMD information using M neighboring blocks, with M > N, the intra merge / DIMD merge list mode may be signaled before the MIMD mode. In some implementations, the N neighboring blocks used by the MIMD mode can be blocks coded with any mode and the M neighboring blocks used by the OBIC mode can also be blocks coded with any mode. In other implementations, the N neighboring blocks used by the intra merge / DIMD merge list mode are blocks coded with the intra merge / DIMD merge list mode and the M neighboring blocks used by the MIMD mode are blocks coded with the MIMD mode.

[0330] In some implementations, the DIMD mode signaling order may be adapted to the distance and / or the area of the available neighboring blocks of each DIMD mode. In some examples, the criteria for a neighboring block to be considered as an available neighboring block may vary for different DIMD modes. Some DIMD modes may consider only neighboring blocks coded by a DIMD mode as available neighboring blocks; some may consider neighboring blocks having IPM / DIMD information as the available neighboring blocks regardless of the modes of the neighboring blocks; others may exclude the neighboring blocks coded with at least one specific mode from being considered as available neighboring blocks. One condition for signaling order can be the average (resp. the minimum or the maximum) distance between the current block to available neighboring blocks used by a first mode is lower (or higher) than the average (resp. the minimum or the maximum) distance between the current block to available neighboring blocks used by a second mode. If the condition is satisfied, the first mode may be signaled before the second mode. In another example, the condition for the signaling order can be the average (resp. the minimum or the maximum) area of the available neighboring blocks used by one mode is lower (or higher) than that of a second mode. If the condition is satisfied, the first DIMD mode may be signaled before the second DIMD mode.

[0331] In some examples, the DIMD mode signaling order may be adapted according to the quantization parameter (QP) of the current block. A minimum threshold of quantization parameter, a maximum threshold of quantizationDocket No.: 24-2022PCT parameter, or both may be used to adaptively reorder the signaling of the DIMD modes. For example, the conditions for the signaling order can include the QP of the current block is higher than the minimum threshold (e.g., 17, or 23). The conditions can also include the QP of the current block is lower than the maximum threshold (e.g., 43 or 37). The conditions may also include the QP of the current block is higher than the minimum threshold and lower than the maximum threshold. If one or more of the conditions are satisfied, the signaling order may be a pre-determined order. Different conditions may lead to different pre-determined order. As an example, if the QP of the current block is higher than the minimal threshold, the signaling order can be {OBIC mode, intra merge / DIMD Merge list mode, regular DIMD mode, MIMD mode}. If the QP of the current block is lower than the maximal threshold, the signaling order can be {OBIC mode, MIMD mode, intra merge / DIMD Merge list mode, regular DIMD mode}.

[0332] In some examples, the DIMD mode signaling order may be adapted according to the slice type of the current block. The slice types may include, by way of example and not limitation, INTRA, uni-directional predicted picture, or bi-directional predicted picture. For example, the conditions for the signaling order can be the slice type of the current block is a specific slice type. If this condition is satisfied, the signaling order can be determined to be a certain order; otherwise, the signaling order may be determined to be another order. As an example, if the slice type of the current block is a bi-directional predicted slice, the DIMD mode signaling order can be {OBIC mode, MIMD, intra merge / DIMD Merge list mode, DIMD mode}.

[0333] It should be understood that the signaling orders listed in the above examples are for illustration only and should not be limiting. Other signaling orders may be used when the one or more conditions for signaling order are satisfied. Further, in the above examples, because the signaling order is determined adaptively to each block, the signaling order may vary from one block to another block. In some implementations, one or more DIMD modes may have a fixed position, when available, in the DIMD signaling and may not be re-ordered.

[0334] As discussed above, an activation function can be used to determine whether a DIMD mode is activated for the block or not. In addition, a high-level syntax (e.g., SPS, picture header, slice header) may also be used to disable a DIMD mode. If one or more of the DIMD modes are determined to be deactivated, the signaling scheme can be updated to reduce the number of bits used to signal the DIMD modes. FIG.30B shows an example of the updated signaling tree for the signaling tree shown in FIG.30A after the second DIMD mode is determined to be disabled or deactivated. In this example, leaf 2 (corresponding to the disabled second DIMD mode) can be removed from the signaling tree 3000A leading to the updated signaling tree 3000B. As shown in the signaling tree 3000B, in addition to leaf 2, flag 2 that is used to distinguish leaf 2 from other leaves (e.g., the last flag in a set of flags used to signal the mode associated with leaf 2) are also removed. As a result, the signaling tree 3000B only has three flags: DIMD flag, Flag 1, and Flag 3. The number of bits used to signal the third DIMD mode and the fourth DIMD mode is reduced from 4 to 3.

[0335] FIG.31A shows an example signaling tree 3100A for another signaling scheme similar to FIG.27 that can be used for adaptive signaling described herein. In FIG.31A, the number of bits used to signal the respective DIMD mode associated with each leaf in the signaling tree 3100A is shown. FIG.31B shows an example of the updated signalingDocket No.: 24-2022PCT tree for the signaling tree shown in FIG.31A after the first DIMD mode is determined to be disabled or deactivated. In this example, leaf 1 (corresponding to the disabled first DIMD mode) can be removed from the signaling tree 3100A leading to the updated signaling tree 3100B. As shown in the signaling tree 3100B, in addition to leaf 1, flag 2 that is used to distinguish leaf 1 from other leaves (e.g., the last flag in a set of flags used to signal the mode associated with leaf 1) are also removed. As a result, the signaling tree 3100B only has three flags: DIMD flag, Flag 1, and Flag 3. The number of bits used to signal the second DIMD mode is also reduced from 3 to 2. As a result, the overall number of bits used to signal the DIMD mode for the blocks of the video can be reduced, thereby improving the coding efficiency.

[0336] FIG.32 illustrates a flowchart 3200 of an example of the DIMD mode signal re-ordering process at the encoder, in accordance with some embodiments of the present disclosure. The method of flowchart 3200 may include several operations such as 3202-3212, each of which may be processed to determine the signaling of the DIMD mode selected to predict the current block. The flowchart 3200 may be implemented in an encoder after the encoder has selected the intra prediction mode for the current block.

[0337] The flowchart 3200 begins at 3202, where the encoder can determine whether the DIMD feature is used or selected. Because the encoder has selected the intra prediction mode for the current block, the encoder can thus determine whether the selected intra prediction mode is a DIMD mode. If it is determined that the DIMD mode is selected, the encoder can determine, at 3204, a signaling order for the available DIMD modes. As discussed above in more detail, the signaling order may be determined based on one or more properties of the block. The properties can include one or more of the size and / or shape of the block, the slice type of the block, characteristics of available neighboring blocks, the quantization parameter of the block, and so on. The encoder can determine the signaling order to be a pre-determined order based on one or more conditions defined on the properties of the block being satisfied or not being satisfied.

[0338] At 3206, the encoder can determine a flag for signaling the DIMD mode, based on the DIMD mode selected for the block and the signaling order determined at 3204. In some implementations, the flag determined at 3206 does not include the DIMD flag indicating whether DIMD feature is enabled. For example, if a signaling scheme is used (e.g., the signaling scheme shown in FIGS.26, 27, 30A-B, and 31A-B), the encoder can assign the DIMD modes to the leaves of the signaling tree based on the determined signaling order. The flag(s) used to signal the selected DIMD mode can be identified from the signaling tree. As an example, the signaling scheme shown in FIG.30A is used, and the signaling order is determined to be {intra merge / DIMD merge list mode, MIMD mode, regular DIMD mode, OBIC mode}. If the selected DIMD mode is the intra merge / DIMD merge list mode (the first DIMD mode), the flags used to signal this mode are “10” and the determined flag (flag 1) at 3206 has a value 0. In examples where more flags are needed to signal the selected DIMD mode, the encoder will determine more flags based on the signaling order and the signaling scheme. In the above example, if the selected DIMD mode is the OBIC mode (the fourth DIMD mode), the encoder can determine that flags for signaling this mode is “1111.” In this example, the determined flag (flag 1) at 3206 has a value “1.”

[0339] At 3208, the encoder can encode the determined flag into the bitstream of the video. At 3212, the encoder can encode the block using the selected DIMD mode into the bitstream. If, at 3202, it is determined that a DIMD modeDocket No.: 24-2022PCT is not selected for the current block, the encoder can determine the signaling flag(s) for the non-DIMD coding mode selected for the current block. In such a scenario, the block is encoded using the selected non-DIMD coding mode at 3212.

[0340] FIG.33 illustrates a flowchart 3300 of an example of the DIMD mode signal re-ordering process at the decoder, in accordance with some embodiments of the present disclosure. The method of flowchart 3300 may include several operations such as 3302-3312, each of which may be processed to determine the signaling of the DIMD mode selected to reconstruct the current block. Flowchart 3300 begins at 3302, where the decoder can determine whether a DIMD mode is used for the current block. In some examples, the decoder can obtain from a bitstream of a video an indication of the DIMD is used to encode the current block. The indication may be, for example, the DIMD flag discussed above with respect to FIG.25. The decoder can determine whether the DIMD is used for the block based on the obtained DIMD flag.

[0341] If it is determined that the DIMD mode is used for the current block, the decoder can determine, at 3304, a signaling order of the DIMD modes for the current block. Similar to the encoder, the decoder can determine the signaling order based on one or more properties of the block. The properties can include one or more of the size and / or shape of the block, the slice type of the block, characteristics of available neighboring blocks, the quantization parameter of the block, and so on. The encoder can determine the signaling order to be a pre-determined order based on one or more conditions defined on the properties of the block being satisfied or not being satisfied.

[0342] For example, the one or more conditions can include a condition of the size of the block being one or more of equal to, less than, or larger than a threshold block size. The condition may further specify that the height and the width of the block being different or the same. The one or more conditions may also include that the number of available neighboring blocks of the block useable for deriving IPM / DIMD information for a first DIMD model is one or more of equal to, smaller than, or larger than the number of available neighboring blocks of the block useable for deriving IPM / DIMD information for a second DIMD model. If the conditions are satisfied, the first DIMD mode may be ordered before the second DIMD mode.

[0343] In further examples, the one or more conditions include that the number of available neighboring blocks of the block that are coded with a first DIMD mode and are useable for deriving IPM / DIMD information for the first DIMD mode is one or more of equal to, smaller than, or larger than the number of available neighboring blocks of the block that are coded with a second DIMD tool and are useable for deriving IPM / DIMD information for the second DIMD tool. If the conditions are satisfied, the first DIMD mode may be ordered before the second DIMD mode. In other examples, the one or more conditions include that the number of available neighboring blocks of the block useable for deriving IPM / DIMD information for a first DIMD mode is one or more of equal to, smaller than, or larger than an area of available neighboring blocks of the block useable for deriving IPM / DIMD information for the second DIMD mode. If the conditions are satisfied, the first DIMD mode may be ordered before the second DIMD mode.

[0344] In some examples, the one or more conditions include the distance between the block to available neighboring blocks of the block useable for deriving IPM / DIMD information for a first DIMD mode is one or more of equal to, smallerDocket No.: 24-2022PCT than, or larger than a distance between the block to available neighboring blocks of the block useable for deriving IPM / DIMD information for the second DIMD mode. The one or more conditions may further include the quantization parameter (QP) value of the block being one or more of equal to, less than, or larger than a threshold QP value. The one or more conditions can also include the slice type of the block belonging to or not belong to a set of pre-determined slice types, such as INTRA, uni-directional predicted picture, or bi-directional predicted picture.

[0345] In alternative or additional examples, the signaling order can be determined by determining a count for each DIMD mode. The count indicates the number of times the DIMD mode is used for blocks in a partition of the video containing the block. The partition can be a sequence, a frame, or a slice. The signaling order of the DIMD modes can be determined according to a descending order of the counts of DIMD modes.

[0346] At 3306, the decoder can parse a flag from the bitstream. At 3308, the decoder can determine the DIMD mode used to code the current block based on the parsed flag and the signaling order. For example, if the signaling scheme shown in FIG.3000A is used and the parsed flag has a value of 0, the decoder can determine that the first DIMD mode is used. Based on the signaling order, the decoder can identify the DIMD mode that corresponds to the first DIMD mode. If the parsed flag cannot identify the DIMD mode, the decoder may parse more flags from the bitstream until the decoded flags leads to a leaf in the signaling tree and thus identify the DIMD mode.

[0347] At 3312, the decoder can reconstruct the current block using the identified DIMD mode. If, at 3302, it is determined that the DIMD mode is not used, the decoder can determine the non-DIMD coding mode for the current block at 3310 and reconstruct the block at 3312 using the determined coding mode.

[0348] As discussed above with respect to FIGS.30B and 31B, an activation function may be used for each block to determine whether to activate a DIMD mode which may be used in conjunction with the signaling order to achieve higher coding efficiency. FIG.34 illustrates a flowchart 3400 of an example of combining DIMD mode signal re-ordering and mode activation at the decoder, in accordance with some embodiments of the present disclosure. The method of flowchart 3400 may include several operations such as 3402-3416, each of which may be processed to determine the signaling of the DIMD mode selected to reconstruct the current block. Flowchart 3400 begins at 3402, where the decoder can obtain, from a bitstream of a video, an indication that the DIMD is used to encode the current block. The indication may be, for example, the DIMD flag discussed above with respect to FIG.25. The decoder can determine that the DIMD is enabled for the block, and obtaining the indication can be based on determining the DIMD being used.

[0349] At 3404, the decoder can determine a signaling order of the DIMD modes for the current block. As discussed in more detail above with respect to FIG.33, the decoder can determine the signaling order based on one or more properties of the block. The properties can include one or more of the size and / or shape of the block, the slice type of the block, characteristics of available neighboring blocks, the quantization parameter of the block, and so on. The encoder can determine the signaling order to be a pre-determined order based on one or more conditions defined on the properties of the block being satisfied or not being satisfied.

[0350] At 3406, the decoder can determine an activation status of the first DIMD mode according to the signaling order. As discussed above in more detail with respect to FIG.25, the decoder can determine the activation status ofDocket No.: 24-2022PCT the DIMD mode via an activation function for the DIMD mode in a way similar to the encoder. For example, the activation function can be based on the properties of the current block, such as the size and / or shape of the block, the slice type of the block, the availabilities of neighboring blocks, the QP of the block, and so on. The decoder can determine the activation status of the DIMD mode based on determining whether the one or more properties satisfy one or more conditions for the DIMD mode.

[0351] At 3408, the decoder can determine whether the flag associated with the first DIMD mode is present in the bitstream. In some examples, such as when the signaling scheme of FIG.30A is used, if the activation status of the first DIMD mode shows that the first DIMD mode is not activated, then the decoder can determine that the first flag (flag 1) is not present in the bitstream (as shown in FIG.30B). In such scenarios, the decoder can move on to determine the activation status of the next DIMD mode according to the signaling order at 3410. In other examples, such as when the signaling scheme of FIG.31A is used, if the activation status of the first DIMD mode shows that the first DIMD mode is not activated, then the decoder can determine that flag 1 is present, but flag 2 is not present (as shown in FIG.31B). Based on the activation status of a DIMD mode indicating the DIMD mode is not activated, the decoder can determine that the last flag of a set of flags used to signal the first DIMD mode is not present.

[0352] At 3412, the decoder can determine whether the flag associated with the next DIMD mode according to the signaling order is present in the bitstream. If not, the decoder can move on to examine the next DIMD mode based on the signaling order. If it is determined at 3412 that the flag associated with the next DIMD mode is present or at 3408 that the first flag associated with the first DIMD mode is present, the decoder can parse the flag from the bitstream at 3414. At 3416, the decoder can decode the current block using a DIMD mode determined based on the parsed flags. For example, if the first flag is not present in the bitstream, but the second flag is present, the DIMD mode may be determined based on the first flag being absent and the second flag being present (e.g., using an updated signaling tree similar to that shown in FIGS.30B and 31B). In some examples, additional operations may need to be performed to parse more flags in order to identify the DIMD mode.

[0353] In some examples, the flowchart in FIG.25 may be modified to include the signal ordering to further improve the coding efficiency. For example, an operation of determining the signal ordering may be added before 2507 if it is determined that the DIMD mode is used at 2506. The determined signaling order may be used to determine which mode is the first sub-mode, the second sub-mode, and so on.

[0354] It should be understood that while the above examples focus on signal re-ordering for the DIMD modes / sub- modes, the same mechanism can be applied to other types of coding modes that have multiple sub-modes. For example, the coding mode signal re-ordering described above can be applied to the TIMD modes / sub-modes. The sub- modes of the TIMD mode may include the regular TIMD mode, TIMD SAD (TIMD using SAD as the cost metric), and the TIMD merge mode.

[0355] Likewise, the coding mode signal re-ordering described above can also be applied to the extrapolation filter- based intra prediction (EIP) modes / sub-modes. In the EIP mode, the samples in a CU are predicted from the top-left position to the bottom-right position by applying an extrapolation filter to neighboring reconstructed samples or predictedDocket No.: 24-2022PCT samples. The sub-modes of the EIP mode may include the regular EIP mode, the EIP merge mode, and the multi- model EIP mode.

[0356] In another example, the coding mode signal re-ordering described above can also be applied to the intra template matching prediction (TMP) modes / sub-modes. The sub-modes of the TMP mode may include the regular TMP / Intra-TMP mode, TMP fusion mode, and the TMP LIC mode.

[0357] In a further example, the coding mode signal re-ordering described above can also be applied to the spatial geometric partitioning mode (SGPM). The sub-modes of the SGPM may include the regular SGPM and the SGPM merge mode.

[0358] The coding mode signal re-ordering presented herein can also be applied to other tools which have different derivation processes for a given tool, such as an inter prediction tool. Examples of other modes for which the adaptive signaling can be applied include, but are not limited to, the intra-block copy prediction (IBC), the merge mode inter prediction, or the adaptative motion vector prediction (AMVP).

[0359] FIG.35 illustrates a flowchart of an example of the coding mode signal re-ordering process at the encoder, in accordance with some embodiments of the present disclosure. Operations of process 3000 may be performed by an encoder, such as, for example, encoder 200 in FIG.2.

[0360] At 3502, the process 3500 involves determining a signaling order of a plurality of sub-modes of a coding mode for a block of a video. In some examples, the signaling order is determined based on one or more properties of the block. The one or more properties can include one or more of a size of the block, a shape of the block, a slice type of the block, characteristics of available neighboring blocks, a quantization parameter of the block. In some examples, determining the signaling order includes determining the signaling order to be a first order based on one or more conditions defined on the properties of the block being satisfied or not being satisfied. The one or more conditions can include a condition of a size of the block being one or more of equal to, less than, or larger than a threshold block size. The condition may further specify that a height and a width of the block being different or same.

[0361] In some examples, the coding mode is a decoder-side intra mode derivation (DIMD) mode or a template- based intra mode derivation (TIMD) mode. In some examples, the one or more conditions can include a number of available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block useable for deriving coding information for a second sub-mode. In some examples, the one or more conditions can include a number of available neighboring blocks of the block that are coded with a first sub-mode and are useable for deriving coding information for the first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block that are coded with a second sub-mode and are useable for deriving coding information for the second sub- mode. In some examples, the one or more conditions can include a number of available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block useable for deriving coding information for a second sub-mode. In some examples, the one or more conditions comprise a distance between the block to available neighboring blocks ofDocket No.: 24-2022PCT the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a distance between the block to available neighboring blocks of the block useable for deriving coding information for a second sub-mode.

[0362] In some examples, the one or more conditions comprise a quantization parameter (QP) value of the block being one or more of equal to, less than, or larger than a threshold QP value. In some examples, the one or more conditions comprise a slice type of the block belonging to or not belonging to a set of pre-determined slice types.

[0363] In further examples, determining the signaling order includes determining a count for each sub-mode of the plurality of sub-modes, the count indicating a number of times the sub-mode is used for blocks in a partition of the video containing the block, and ordering the plurality of sub-modes according to a descending order of the counts of the plurality of sub-modes. The partition can be a sequence, a frame, or a slice. In some examples, determining the signaling order can further include for each sub-mode of the plurality of sub-modes for the block determining a context ID for selecting a context model for the sub-mode and ordering the plurality of sub-modes is further based on the context IDs of the plurality of sub-modes.

[0364] In some examples, determining the signaling order includes for each sub-mode of the plurality of sub-modes for the block determining a context ID for selecting a context model for the sub-mode, and ordering the plurality of sub- modes according to the context IDs of the plurality of sub-modes. In some examples, determining the signaling order can further include determining a count for each sub-mode of the plurality of sub-modes, the count indicating a number of times the sub-mode is used for blocks in a partition of the video containing the block, and ordering the plurality of sub-modes is further according to a descending order of the counts of the plurality of sub-modes. The partition can be a sequence, a frame, or a slice.

[0365] In some examples, the coding mode is a decoder-side intra mode derivation (DIMD) mode. The plurality of sub-modes of the DIMD mode includes a DIMD regular mode, intra merge / DIMD merge list mode, an occurrence-based intra coding (OBIC) mode, or a Merges Intra Mode Derivation (MIMD) mode. In other examples, the coding mode is a template-based intra mode derivation (TIMD) mode, an intra template matching prediction (TMP) mode, a spatial geometric partitioning mode (SGPM), an extrapolation filter-based intra prediction (EIP) mode, an intra-block copy prediction (IBC), a merge mode inter prediction, or an adaptative motion vector prediction (AMVP).

[0366] At 3504, the process 3500 involves determining, based on the signaling order and a sub-mode, of the plurality of sub-modes, selected for the block, a value of a first flag. At 3506, the process 3500 involves encoding the first flag into a bitstream, and at 3508, the process 3500 involves encoding the block using the sub-mode as discussed above.

[0367] FIG.36 illustrates a flowchart of an example of the coding mode signal re-ordering process at the decoder, in accordance with some embodiments of the present disclosure. Operations of process 3000 may be performed by a decoder, such as, for example, decoder 300 in FIG.3.

[0368] At 3602, the process 3600 involves determining a signaling order of a plurality of sub-modes of a coding mode for a block of a video. In some examples, the signaling order is determined based on one or more properties of the block. The one or more properties can include one or more of a size of the block, a shape of the block, a slice type ofDocket No.: 24-2022PCT the block, characteristics of available neighboring blocks, a quantization parameter of the block. In some examples, determining the signaling order includes determining the signaling order to be a first order based on one or more conditions defined on the properties of the block being satisfied or not being satisfied. The one or more conditions can include a condition of a size of the block being one or more of equal to, less than, or larger than a threshold block size. The condition may further specify that a height and a width of the block being different or same.

[0369] In some examples, the coding mode is a decoder-side intra mode derivation (DIMD) mode or a template- based intra mode derivation (TIMD) mode. In some examples, the one or more conditions can include a number of available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block useable for deriving coding information for a second sub-mode. In some examples, the one or more conditions can include a number of available neighboring blocks of the block that are coded with a first sub-mode and are useable for deriving coding information for the first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block that are coded with a second sub-mode and are useable for deriving coding information for the second sub- mode. In some examples, the one or more conditions can include a number of available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block useable for deriving coding information for a second sub-mode. In some examples, the one or more conditions comprise a distance between the block to available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a distance between the block to available neighboring blocks of the block useable for deriving coding information for a second sub-mode.

[0370] In some examples, the one or more conditions comprise a quantization parameter (QP) value of the block being one or more of equal to, less than, or larger than a threshold QP value. In some examples, the one or more conditions comprise a slice type of the block belonging to or not belonging to a set of pre-determined slice types.

[0371] In further examples, determining the signaling order includes determining a count for each sub-mode of the plurality of sub-modes, the count indicating a number of times the sub-mode is used for blocks in a partition of the video containing the block, and ordering the plurality of sub-modes according to a descending order of the counts of the plurality of sub-modes. The partition can be a sequence, a frame, or a slice. In some examples, determining the signaling order can further includes for each sub-mode of the plurality of sub-modes for the block determining a context ID for selecting a context model for the sub-mode and ordering the plurality of sub-modes is further based on the context IDs of the plurality of sub-modes.

[0372] In some examples, determining the signaling order includes for each sub-mode of the plurality of sub-modes for the block, determining a context ID for selecting a context model for the sub-mode, and ordering the plurality of sub- modes according to the context IDs of the plurality of sub-modes. In some examples, determining the signaling order can further include determining a count for each sub-mode of the plurality of sub-modes, the count indicating a number of times the sub-mode is used for blocks in a partition of the video containing the block, and ordering the plurality ofDocket No.: 24-2022PCT sub-modes is further according to a descending order of the counts of the plurality of sub-modes. The partition can be a sequence, a frame, or a slice.

[0373] In some examples, the coding mode is a decoder-side intra mode derivation (DIMD) mode. The plurality of sub-modes of the DIMD mode includes a DIMD regular mode, intra merge / DIMD merge list mode, an occurrence-based intra coding (OBIC) mode, or a Merges Intra Mode Derivation (MIMD) mode. In other examples, the coding mode is a template-based intra mode derivation (TIMD) mode, an intra template matching prediction (TMP) mode, a spatial geometric partitioning mode (SGPM), an extrapolation filter-based intra prediction (EIP) mode, an intra-block copy prediction (IBC), a merge mode inter prediction, or an adaptative motion vector prediction (AMVP).

[0374] At 3604, the process 3600 involves parsing a first flag from a bitstream. At 3606, the process 3600 involves determining, based on a value of the first flag and the signaling order, a sub-mode of the plurality of sub-modes. In some examples, based on the signaling order, the value of the first flag indicates whether a specific sub-mode is selected. For example, in FIG.26, value 1 of flag 1 can indicate that the first sub-mode in the signaling order is selected. Value 0 of flag 1 can indicate that the first sub-mode in the signaling order is not selected. In some examples, process 3600 further includes parsing a second flag from the bitstream. Based on the signaling order, at least values of the first flag and the second flag indicate whether a specific sub-mode is selected. In the example shown in FIG.26, values of the flag 1 and flag 0 can specify whether the second sub-mode according to the signaling order is selected. Value 0 of flag 1 and value 1 of flag 2 indicate that the second sub-mode is selected; value 0 of flag 1 and value 0 of flag 2 indicate that the second sub-mode is not selected. In another example, as shown in FIG.27, value 0 of flag 1 and value 0 of flag 2 indicate that the first sub-mode according to the signaling order is selected; value 0 of flag 1 and value 1 of flag 2 indicate that the second sub-mode according to the signaling order is selected.

[0375] At 3608, the process 3600 involves reconstructing the block using the sub-mode as discussed above. In some examples, process 3600 further involves determining an activation status for a sub-mode of the plurality of sub-modes. A second flag is the last flag of a set of flags used to signal the sub-mode. Based on the activation status indicating that the sub-mode is disabled for the block, the process 3600 involves reconstructing the block without parsing the second flag.

[0376] 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 3700 is shown in FIG.37. Blocks depicted in the figures above, such as the blocks in FIGS.1, 2, and 3, may execute on one or more computer systems 3700. Furthermore, each of the steps of the flowcharts depicted in this disclosure may be implemented on one or more computer systems 3700.

[0377] Computer system 3700 includes one or more processors, such as processor 3704. Processor 3704 may be, for example, a special purpose processor, general purpose processor, microprocessor, or digital signal processor. Processor 3704 may be connected to a communication infrastructure 3702 (for example, a bus or network). ComputerDocket No.: 24-2022PCT system 3700 may also include a main memory 3706, such as random-access memory (RAM), and may also include a secondary memory 3708.

[0378] Secondary memory 3708 may include, for example, a hard disk drive 3710 and / or a removable storage drive 3712, representing a magnetic tape drive, an optical disk drive, or the like. Removable storage drive 3712 may read from and / or write to a removable storage unit 3716 in a well-known manner. Removable storage unit 3716 represents a magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive 3712. As will be appreciated by persons skilled in the relevant art(s), removable storage unit 3716 includes a computer usable storage medium having stored therein computer software and / or data.

[0379] In alternative implementations, secondary memory 3708 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 3700. Such means may include, for example, a removable storage unit 3718 and an interface 3714. 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 3718 and interfaces 3714 which allow software and data to be transferred from removable storage unit 3718 to computer system 3700.

[0380] Computer system 3700 may also include a communications interface 3720. Communications interface 3720 allows software and data to be transferred between computer system 3700 and external devices. Examples of communications interface 3720 may include a modem, a network interface (such as an Ethernet card), a communications port, etc... Software and data transferred via communications interface 3720 are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface 3720. These signals are provided to communications interface 3720 via a communications path 3722. Communications path 3722 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.

[0381] 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 3716 and 3718 or a hard disk installed in hard disk drive 3710. These computer program products are means for providing software to computer system 3700. Computer programs (also called computer control logic) may be stored in main memory 3706 and / or secondary memory 3708. Computer programs may also be received via communications interface 3720. Such computer programs, when executed, enable the computer system 3700 to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor 3704 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 3700.

[0382] In another embodiment, features of the disclosure may be implemented in hardware using, for example, hardware components such as application-specific integrated circuits (ASICs) and gate arrays. Implementation of a hardware state machine to perform the functions described herein will also be apparent to persons skilled in the art.

Claims

Docket No.: 24-2022PCT CLAIMS What is claimed is:

1. A method comprising: obtaining an indication of decoder-side intra mode derivation (DIMD) being used to code a block; determining, based on the indication, a signaling order of a plurality of decoder-side intra mode derivation (DIMD) modes for the block, the plurality of DIMD modes comprising a DIMD regular mode, an occurrence- based intra coding (OBIC) mode, a Merges Intra Mode Derivation (MIMD) mode, or an Intra Merge mode; parsing a first flag from a bitstream; determining, based on a value of the first flag and the signaling order, a sub-mode of the plurality of sub- modes; and reconstructing the block using the sub-mode.

2. A method, comprising: determining a signaling order of a plurality of sub-modes of a coding mode for a block of a video; parsing a first flag from a bitstream; determining, based on a value of the first flag and the signaling order, a sub-mode of the plurality of sub- modes; and reconstructing the block using the sub-mode.

3. The method of any one of claims 1 and 2, wherein based on the signaling order, the value of the first flag indicates whether a specific sub-mode is selected.

4. The method of any one of claims 1 and 2, further comprising parsing a second flag from the bitstream, wherein based on the signaling order, at least values of the first flag and the second flag indicate whether a specific sub- mode is selected.

5. The method of any one of claims 1-4, wherein the signaling order is determined based on one or more properties of the block.

6. The method of claim 5, wherein the one or more properties comprise one or more of a size of the block, a shape of the block, a slice type of the block, characteristics of available neighboring blocks, a quantization parameter of the block.

7. The method of any one of claims 5 and 6, wherein determining the signaling order comprises determining the signaling order to be a first order based on one or more conditions defined on the properties of the block being satisfied or not being satisfied.

8. The method of claim 7, wherein the one or more conditions comprise a condition of a size of the block being one or more of equal to, less than, or larger than a threshold block size.

9. The method of claim 8, wherein the condition further specifies that a height and a width of the block being different or same.Docket No.: 24-2022PCT 10. The method of any one of claims 7-9, wherein the coding mode is a decoder-side intra mode derivation (DIMD) mode or a template-based intra mode derivation (TIMD) mode.

11. The method of claim 10, wherein the one or more conditions comprise a number of available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block useable for deriving coding information for a second sub-mode.

12. The method of any one of claims 10 and 11, wherein the one or more conditions comprise a number of available neighboring blocks of the block that are coded with a first sub-mode and are useable for deriving coding information for the first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block that are coded with a second sub-mode and are useable for deriving coding information for the second sub-mode.

13. The method of any one of claims 10-12, wherein the one or more conditions comprise a number of available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block useable for deriving coding information for a second sub-mode.

14. The method of any one of claims 10-13, wherein the one or more conditions comprise a distance between the block to available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a distance between the block to available neighboring blocks of the block useable for deriving coding information for a second sub-mode.

15. The method of any one of claims 7-14, wherein the one or more conditions comprise a quantization parameter (QP) value of the block being one or more of equal to, less than, or larger than a threshold QP value.

16. The method of any one of claims 7-15, wherein the one or more conditions comprise a slice type of the block belonging to or not belonging to a set of pre-determined slice types.

17. The method of any one of claims 1-16, wherein determining the signaling order comprises: determining a count for each sub-mode of the plurality of sub-modes, the count indicating a number of times the sub-mode is used for blocks in a partition of the video containing the block, wherein the partition is a sequence, a frame, or a slice; and ordering the plurality of sub-modes according to a descending order of the counts of the plurality of sub- modes.

18. The method of claim 17, wherein determining the signaling order comprises: for each sub-mode of the plurality of sub-modes for the block, determining a context ID for selecting a context model for the sub-mode wherein ordering the plurality of sub-modes is further based on the context IDs of the plurality of sub-modes.

19. The method of any one of claims 1-18, wherein determining the signaling order comprises:Docket No.: 24-2022PCT for each sub-mode of the plurality of sub-modes for the block, determining a context ID for selecting a context model for the sub-mode; and ordering the plurality of sub-modes according to the context IDs of the plurality of sub-modes.

20. The method of claim 19, wherein determining the signaling order further comprises: determining a count for each sub-mode of the plurality of sub-modes, the count indicating a number of times the sub-mode is used for blocks in a partition of the video containing the block, wherein the partition is a sequence, a frame, or a slice, wherein ordering the plurality of sub-modes is further according to a descending order of the counts of the plurality of sub-modes.

21. The method of any one of claims 1-20, further comprising: determining an activation status for a sub-mode of the plurality of sub-modes, wherein a second flag is a last flag of a set of flags used to signal the sub-mode; and based on the activation status indicating that the sub-mode is disabled for the block, reconstructing the block without parsing the second flag.

22. The method of any one of claims 2-21, wherein the coding mode is a decoder-side intra mode derivation (DIMD) mode.

23. The method of claim 22, wherein the plurality of sub-modes of the coding mode comprises a DIMD regular mode, an occurrence-based intra coding (OBIC) mode, a Merges Intra Mode Derivation (MIMD) mode, or an Intra Merge mode.

24. The method of any one of claims 2-21, wherein the coding mode is a template-based intra mode derivation (TIMD) mode, an intra template matching prediction (TMP) mode, a spatial geometric partitioning mode (SGPM), an extrapolation filter-based intra prediction (EIP) mode, an intra-block copy prediction (IBC), a merge mode inter prediction, or an adaptative motion vector prediction (AMVP).

25. A method comprising: obtaining, from a bitstream of a video, an indication of decoder-side intra mode derivation (DIMD) being used to code a current block; determining, based on the indication, a signaling order of a plurality of DIMD modes for the block; determining, based on an activation status of a first DIMD mode for the current block, a presence status of a first flag associated with the first DIMD mode according to the signaling order; determining, based on the presence status, whether to parse the first flag from the bitstream; and reconstructing the current block using a DIMD mode determined based, at least in part, upon the signaling order and the determination of whether to parse the first flag.

26. A method, comprising: determining a signaling order of a plurality of sub-modes of a coding mode for a block of a video; determining, based on the signaling order and a sub-mode, of the plurality of sub-modes, selected for the block, a value of a first flag;Docket No.: 24-2022PCT encoding the first flag into a bitstream; and encoding the block using the sub-mode.

27. The method of claim 26, wherein the signaling order is determined based on one or more properties of the block.

28. The method of claim 27, wherein the one or more properties comprise one or more of a size of the block, a shape of the block, a slice type of the block, characteristics of available neighboring blocks, a quantization parameter of the block.

29. The method of any one of claim 27 and 28, wherein determining the signaling order comprises determining the signaling order to be a first order based on one or more conditions defined on the properties of the block being satisfied or not being satisfied.

30. The method of claim 29, wherein the one or more conditions comprise a condition of a size of the block being one or more of equal to, less than, or larger than a threshold block size.

31. The method of claim 30, wherein the condition further specifies that a height and a width of the block being different or same.

32. The method of any one of claims 29-31, wherein the coding mode is a decoder-side intra mode derivation (DIMD) mode or a template-based intra mode derivation (TIMD) mode.

33. The method of claim 32, wherein the one or more conditions comprise a number of available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block useable for deriving coding information for a second sub-mode.

34. The method of any one of claims 32 and 33, wherein the one or more conditions comprise a number of available neighboring blocks of the block that are coded with a first sub-mode and are useable for deriving coding information for the first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block that are coded with a second sub-mode and are useable for deriving coding information for the second sub-mode.

35. The method of any one of claims 32-34, wherein the one or more conditions comprise a number of available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a number of available neighboring blocks of the block useable for deriving coding information for a second sub-mode.

36. The method of any one of claims 32-35, wherein the one or more conditions comprise a distance between the block to available neighboring blocks of the block useable for deriving coding information for a first sub-mode is one or more of equal to, smaller than, or larger than a distance between the block to available neighboring blocks of the block useable for deriving coding information for a second sub-mode.

37. The method of any one of claims 29-36, wherein the one or more conditions comprise a quantization parameter (QP) value of the block being one or more of equal to, less than, or larger than a threshold QP value.Docket No.: 24-2022PCT 38. The method of any one of claims 29-37, wherein the one or more conditions comprise a slice type of the block belonging to or not belonging to a set of pre-determined slice types.

39. The method of any one of claims 26-38, wherein determining the signaling order comprises: determining a count for each sub-mode of the plurality of sub-modes, the count indicating a number of times the sub-mode is used for blocks in a partition of the video containing the block, wherein the partition is a sequence, a frame, or a slice; and ordering the plurality of sub-modes according to a descending order of the counts of the plurality of sub- modes.

40. The method of claim 39, wherein determining the signaling order comprises: for each sub-mode of the plurality of sub-modes for the block, determining a context ID for selecting a context model for the sub-mode wherein ordering the plurality of sub-modes is further based on the context IDs of the plurality of sub-modes.

41. The method of any one of claims 26-40, wherein determining the signaling order comprises: for each sub-mode of the plurality of sub-modes for the block, determining a context ID for selecting a context model for the sub-mode; and ordering the plurality of sub-modes according to the context IDs of the plurality of sub-modes.

42. The method of claim 41, wherein determining the signaling order further comprises: determining a count for each sub-mode of the plurality of sub-modes, the count indicating a number of times the sub-mode is used for blocks in a partition of the video containing the block, wherein the partition is a sequence, a frame, or a slice, wherein ordering the plurality of sub-modes is further according to a descending order of the counts of the plurality of sub-modes.

43. The method of any one of claims 26-42, wherein the coding mode is a decoder-side intra mode derivation (DIMD) mode.

44. The method of claim 43, wherein the plurality of sub-modes of the coding mode comprises a DIMD regular mode, an occurrence-based intra coding (OBIC) mode, a Merges Intra Mode Derivation (MIMD) mode, or an Intra Merge mode.

45. The method of any one of claims 26-42, wherein the coding mode is a template-based intra mode derivation (TIMD) mode, an intra template matching prediction (TMP) mode, a spatial geometric partitioning mode (SGPM), an extrapolation filter-based intra prediction (EIP) mode, an intra-block copy prediction (IBC), a merge mode inter prediction, or an adaptative motion vector prediction (AMVP).

46. 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 1-45.

47. An encoder comprising: one or more processors; andDocket No.: 24-2022PCT memory storing instructions that, when executed by the one or more processors, cause the encoder to perform the method of any one of claim 26-45.

48. A non-transitory computer-readable recording medium storing a bitstream generated by the method for encoding a video according to any one of claims 26-45.

49. A decoder comprising: one or more processors; and memory storing instructions that, when executed by the one or more processors, cause the decoder to perform the method of any one of claims 1-25.

50. 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 1-25.

51. A bitstream generated according to any one of claims 26-45.

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