Secondary Transforms for Combined Inter-Intra Prediction Modes

Abstract

The present disclosure relates to transform configurations and signaling for a composite inter-intra prediction mode. In one example, a method for decoding a video block in a video stream is disclosed. The method may include determining that a current block is predicted under a CIIP mode, generating a set of secondary transform coefficients for the current block from a video bitstream, applying a combined inter-intra secondary transform by performing an inverse separable or non-separable secondary transform on the set of secondary transform coefficients to obtain a set of primary transform coefficients of the current block, and performing an inverse primary transform on the set of primary transform coefficients to obtain a residual block of the current block, and decoding the current block from the residual block under the CIIP mode.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Non-provisional Application No. 17 / 949,429, entitled "Secondary Transforms for Compound Inter-Intra Prediction Modes," filed September 21, 2022, which claims the benefit of priority to U.S. Provisional Application No. 63 / 251,473, entitled "Secondary Transforms for Compound Inter-Intra Prediction Modes," filed October 1, 2021, which are incorporated by reference in their entireties herein.

[0002] This disclosure relates generally to a set of advanced video coding / decoding techniques, and more specifically, to transformation techniques and configurations for mixed inter-intra prediction modes. [Background technology]

[0003] The discussion of the background art provided herein is intended to generally present the context of the present disclosure. The inventors' work is not admitted, expressly or impliedly, as prior art to the present disclosure to the extent that that work is described in this Background section, together with aspects of the description that may not otherwise be admitted as prior art at the time of filing of this application.

[0004] Video coding and decoding may be performed using inter-picture prediction with motion compensation. Uncompressed digital video may include a sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luma samples and associated full-sampled or sub-sampled chroma samples. The sequence of pictures may have a fixed or variable picture rate (also called frame rate), for example, 60 pictures per second or 60 frames per second. Uncompressed video has specific bit rate requirements for streaming or data processing. For example, a video with a pixel resolution of 1920x1080, a frame rate of 60 frames / second, and 4:2:0 chroma subsampling with 8 bits per pixel per color channel requires a bandwidth close to 1.5 Gbit / s. One hour of such video requires more than 600 GByte of storage space.

[0005] One objective of video coding and decoding may be the reduction of redundancy in an uncompressed input video signal through compression. Compression may help reduce the aforementioned bandwidth and / or storage space requirements, in some cases by more than one order of magnitude. Both lossless and lossy compression, as well as combinations thereof, may be employed. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal through a decoding process. Lossy compression refers to a coding / decoding process where the original video information is not fully preserved when coding and cannot be fully restored when decoding. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between the original and reconstructed signals is small enough to make the reconstructed signal useful for its intended application, even with some information loss. For video, lossy compression is widely adopted in many applications. The amount of distortion that can be tolerated depends on the application. For example, a user of a particular consumer video streaming application may tolerate higher distortion than a user of a movie or television broadcast application. The compression ratio achievable by a particular coding algorithm may be selected or adjusted to reflect different distortion tolerances. That is, in general, higher distortion tolerance allows for coding algorithms that result in higher losses and higher compression ratios.

[0006] Video encoders and decoders can utilize techniques from a number of broad categories and steps, including, for example, motion compensation, Fourier transform, quantization, and entropy coding.

[0007] Video codec technology can include a technique known as intra-coding. In intra-coding, sample values ​​are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, a picture is spatially subdivided into blocks of samples. If all blocks of samples are coded in intra mode, the picture can be called an intra-picture. Intra-pictures and their derived pictures, such as independent decoder refresh pictures, can be used to reset the decoder state and thus can be used as the first picture in the coded video bitstream and video session or as still images. Samples of the block after intra prediction can then be transformed to the frequency domain, and the transform coefficients so generated can be quantized before entropy coding. Intra prediction represents a technique that minimizes sample values ​​in the pre-transform domain. In some cases, the smaller the DC value after transformation and the smaller the AC coefficients, the fewer bits are needed at a given quantization step size to represent the block after entropy coding.

[0008] Conventional intra-coding, for example as known from MPEG-2 generation coding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to code / decode a block based on surrounding sample data and / or metadata that precedes in decoding order the block of data being intra-coded or intra-decoded, e.g., obtained during encoding and / or decoding of spatial neighbors. Such techniques are hereafter referred to as "intra-prediction" techniques. It should be noted that in at least some cases, intra-prediction uses reference data only from the current picture being reconstructed, and not from other reference pictures.

[0009] Intra prediction may take many different forms. If more than one of such techniques is available in a given video coding technique, the technique used may be referred to as an intra prediction mode. One or more intra prediction modes may be provided in a particular codec. In certain cases, a mode may have sub-modes and / or may be associated with various parameters, and the mode / sub-mode information and intra coding parameters of a block of video may be coded individually or collectively included in the codeword of the mode. Which codeword is used for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency gains via intra prediction, and thus may also affect the entropy coding technique used to convert the codeword into a bitstream.

[0010] Certain modes of intra prediction were introduced in H.264, improved in H.265, and further improved in newer coding techniques such as Joint Search Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). In general, in intra prediction, the predictor block may be formed using neighboring sample values ​​that become available. For example, the available values ​​of a particular neighboring sample set along a particular direction and / or line may be copied into the predictor block. The reference to the direction in use may be coded in the bitstream or may itself be predicted.

[0011] Referring to FIG. 1A, shown at the bottom right is a subset of the nine predictor directions specified in the 33 possible intra predictor directions of H.265 (corresponding to the 33 angle modes of the 35 intra modes specified in H.265). The point (101) where the arrows converge represents the sample being predicted. The arrows represent the direction from which neighboring samples are used to predict the sample at 101. For example, arrow (102) indicates that sample (101) is predicted from one or more neighboring samples to the top right at an angle of 45 degrees from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from one or more neighboring samples to the bottom left of sample (101) at an angle of 22.5 degrees from the horizontal.

[0012] 1A, at the top left is shown a square block (104) of 4×4 samples (indicated by a thick dashed line). The square block (104) contains 16 samples, each labeled with "S", its position in the Y dimension (e.g., row index), and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample (from the top) in the Y dimension and the first sample (from the left) in the X dimension. Similarly, sample S44 is the fourth sample in both the Y and X dimensions in the block (104). Since the block is 4×4 samples in size, S44 is at the bottom right. Also shown is an exemplary reference sample that follows a similar numbering scheme. The reference sample is labeled R, its Y position (e.g., row index), and X position (column index) relative to the block (104). In both H.264 and H.265, predicted samples that neighbor the block being reconstructed are used.

[0013] Intra-picture prediction of block 104 may start by copying reference sample values ​​from adjacent samples according to a signaled prediction direction. For example, assume that the coded video bitstream includes signaling for this block 104 indicating the prediction direction of the arrow (102), i.e., the sample is predicted from one or more prediction samples to the upper right and at an angle of 45 degrees from the horizontal. In such a case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Then, sample S44 is predicted from reference sample R08.

[0014] In certain cases, to calculate a reference sample, especially when the orientation is not evenly divisible by 45 degrees, the values ​​of multiple reference samples may be combined, for example by interpolation.

[0015] The number of possible directions has increased as video coding technology continues to develop. In H.264 (2003), for example, nine different directions are available for intra prediction. This increases to 33 in H.265 (2013), and JEM / VVC / BMS can support up to 65 directions at the time of this disclosure. Experimental studies have been conducted to help identify the most suitable intra prediction directions, and those most suitable directions can be encoded with a small number of bits using certain techniques of entropy coding, accepting certain bit penalties for the directions. Furthermore, the direction itself may be predicted from the neighboring directions used in the intra prediction of the decoded neighboring blocks.

[0016] FIG. 1B shows a schematic diagram (180) showing 65 intra prediction directions according to JEM to illustrate the increasing number of prediction directions in various encoding techniques that have evolved over time.

[0017] Methods for mapping bits representing intra-prediction directions in a coded video bitstream to prediction directions can vary across video coding techniques, and can range, for example, from simple direct mappings of prediction directions to intra-prediction modes to complex adaptation schemes including codewords, most probable modes, and similar techniques. In all cases, however, there may be certain directions of intra-prediction that are statistically less likely to occur in the video content than certain other directions. Because the goal of video compression is to reduce redundancy, in a well-designed video coding technique, these less likely directions may be represented with more bits than the more likely directions.

[0018] Inter-picture prediction, or inter-prediction, may be based on motion compensation. In motion compensation, sample data from a previously reconstructed picture or part thereof (reference picture) may be used to predict a newly reconstructed picture or picture part (e.g., block) after being spatially shifted in a direction indicated by a motion vector (hereinafter, MV). In some cases, the reference picture may be the same as the picture currently being reconstructed. The MV may have two dimensions X and Y, or three dimensions, with the third dimension being an indication of the reference picture in use (similar to the temporal dimension).

[0019] In some video compression techniques, a current MV applicable to a particular area of ​​sample data may be predicted from other MVs, e.g., from other MVs related to other areas of sample data that are spatially adjacent to the area being reconstructed and that precede the current MV in decoding order. Doing so may significantly reduce the overall amount of data required to code the MV by relying on the removal of redundancy in correlated MVs, thereby increasing compression efficiency. MV prediction may work effectively because, for example, when coding an input video signal derived from a camera (known as natural video), areas larger than the area to which a single MV is applicable have a statistical likelihood to move in a similar direction in the video sequence, and therefore, in some cases, can be predicted using similar motion vectors derived from MVs of neighboring areas. As a result, the actual MV of a given area is similar or identical to the MV predicted from the surrounding MVs. Such MVs may further be represented with fewer bits after entropy coding than would be used if the MVs were directly coded instead of predicted from neighboring MVs. In some cases, MV prediction may be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., sample stream). In other cases, the MV prediction itself may be non-lossy, for example due to rounding errors when computing a predictor from several surrounding MVs.

[0020] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Recommendation H.265, "High Efficiency Video Coding", December 2016). Among the many MV prediction mechanisms specified by H.265, the one described below is a technique hereafter referred to as "spatial merging".

[0021] Specifically, referring to FIG. 2, a current block (201) contains samples that are detected by the encoder during the motion search process as predictable from a spatially shifted previous block of the same size. Instead of coding its MV directly, the MV may be derived from metadata associated with one or more reference pictures, e.g., the most recent reference picture (in decoding order), using MVs associated with any one of five surrounding samples, denoted A0, A1, and B0, B1, B2 (202-206, respectively). In H.265, MV prediction may use predictors from the same reference picture that neighboring blocks are using. Summary of the Invention [Means for solving the problem]

[0022] Aspects of the present disclosure relate generally to a set of advanced video coding / decoding techniques, and more specifically, to transformation techniques and configurations for mixed inter-intra prediction modes.

[0023] In some example implementations, a method for decoding a video block in a video stream is disclosed. The method may include determining that a current block is predicted under a composite inter-intra prediction (CIIP) mode, generating a set of secondary transform coefficients for the current block from a video bitstream, applying a combined inter-intra secondary transform by performing an inverse separable or non-separable secondary transform on the set of secondary transform coefficients to obtain a set of primary transform coefficients of the current block, and performing an inverse primary transform on the set of primary transform coefficients to obtain a residual block of the current block, and decoding the current block from the residual block under the CIIP mode.

[0024] In the above implementation, the method may further include a step of determining a CIIP sub-mode of a CIIP mode for a video block from the video stream from among a set of candidate CIIP sub-modes, where the CIIP sub-mode indicates an intra prediction mode among the set of candidate intra prediction modes to be used under the CIIP mode for the video block, and a step of determining a transform kernel to use in an inverse separable or non-separable secondary transform based on the intra prediction mode.

[0025] In any one of the above implementations, the method may further include determining a transform kernel set from among a plurality of transform kernel sets based on an intra-prediction mode, extracting from the video bitstream a kernel selection indicator associated with the video block, and selecting a transform kernel from the transform kernel set based on the kernel selection indicator.

[0026] In some implementations, a video device is disclosed that can include a memory for storing computer instructions and a processing circuit configured to execute the computer instructions to perform each of the methods described above.

[0027] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer for video decoding and / or encoding, cause the computer to perform any one of the implementations of the above methods for video decoding and / or encoding.

[0028] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0029] [Figure 1A] FIG. 13 is a schematic diagram of an example subset of intra-prediction directional modes. [Figure 1B] FIG. 2 illustrates an exemplary intra-prediction direction. [Diagram 2] FIG. 2 is a schematic diagram illustrating a current block and its surrounding spatial merge candidates for motion vector prediction in one example. [Diagram 3] 1 is a schematic diagram of a simplified block diagram of a communication system (300) according to an exemplary embodiment. [Figure 4] 4 is a schematic diagram of a simplified block diagram of a communication system (400) according to an exemplary embodiment. [Diagram 5] 2 is a schematic diagram of a simplified block diagram of a video decoder according to an example embodiment; [Figure 6] 1 is a schematic diagram of a simplified block diagram of a video encoder according to an example embodiment; [Figure 7] 4 is a block diagram of a video encoder according to another example embodiment. [Figure 8] 4 is a block diagram of a video decoder according to another example embodiment. [Figure 9] FIG. 2 illustrates a coding block partitioning scheme according to an exemplary embodiment of the present disclosure. [Figure 10] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 11] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 12] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 13] 4 illustrates a scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure. [Figure 14] 4A-4C are diagrams illustrating another scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an example embodiment of the present disclosure. [Figure 15]FIG. 13 illustrates another scheme for splitting a coding block into multiple transform blocks, according to an exemplary embodiment of the present disclosure. [Figure 16] FIG. 2 illustrates various reference line based intra prediction schemes according to an exemplary embodiment of the present disclosure. [Figure 17] FIG. 13 illustrates top, left, and top-left positions for PAETH modes in a block. [Figure 18] FIG. 1 illustrates an exemplary recursive intra-filtering mode. [Figure 19] FIG. 1 illustrates a planar rotation transformation according to an exemplary embodiment of the present disclosure. [Figure 20] 1A-1C are diagrams illustrating various DCT-2, DCT-4 partial butterfly lookup tables according to exemplary embodiments of the present disclosure. [Figure 21] FIG. 2 illustrates a DST-7 partial butterfly lookup table in accordance with an exemplary embodiment of the present disclosure. [Figure 22] FIG. 1 illustrates a low-frequency non-separable transformation process according to an exemplary embodiment of the present disclosure. [Figure 23] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 24] 1 is a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] FIG. 3 illustrates a simplified block diagram of a communication system (300) according to one embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) may perform unidirectional transmission of data. For example, the terminal device (310) may code video data (e.g., of a stream of video pictures captured by the terminal device (310)) for transmission to the other terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to reconstruct the video pictures, and display the video pictures according to the reconstructed video data. Unidirectional data transmission may be performed, such as for media serving applications.

[0031] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of coded video data, which may be performed, for example, during video conferencing applications. For the bidirectional transmission of data, in one example, each of the terminal devices (330) and (340) may code video data (e.g., of a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may also receive coded video data transmitted by the other of the terminal devices (330) and (340), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device according to the recovered video data.

[0032] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) may be implemented as a server, a personal computer, and a smartphone, although application of the principles underlying the present disclosure may not be so limited. The embodiments of the present disclosure may be implemented in desktop computers, laptop computers, tablet computers, media players, wearable computers, dedicated video conferencing equipment, and the like. The network (350) represents any number or type of network that conveys coded video data between the terminal devices (310), (320), (330), and (340), including, for example, wired (cabled) and / or wireless communication networks. The communication network (350) 9 may exchange data over circuit-switched channels, packet-switched channels, and / or other types of channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this description, the architecture and topology of the network (350) may not be important to the operation of the present disclosure unless expressly described herein.

[0033] 4 shows an arrangement of a video encoder and a video decoder in a video streaming environment as one example for application of the disclosed subject matter. The disclosed subject matter may be equally applicable to other video applications including, for example, video conferencing, digital television broadcasting, gaming, virtual reality, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0034] A video streaming system may include a video source (401) for creating a stream of uncompressed video pictures or images (402), a video capture subsystem (413) that may include, for example, a digital camera. In one example, the stream of video pictures (402) includes samples recorded by the digital camera of the video source 401. The stream of video pictures (402), shown as a thick line to emphasize the large amount of data when compared to the encoded video data (404) (or coded video bitstream), may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or achieve aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), shown with thin lines to emphasize its low amount of data compared to the stream of uncompressed video pictures (402), may be stored directly to the streaming server (405) or to a downstream video device (not shown) for future use. One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, may access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) may include, for example, a video decoder (410) within the electronic device (430). The video decoder (410) decodes the input copy of the encoded video data (407) and creates an output stream of video pictures (411) that is uncompressed and can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). The video decoder 410 may be configured to implement some or all of the various functions described in this disclosure.In some streaming systems, the encoded video data (404), (407), and (409) (e.g., video bitstreams) may be encoded according to a particular video coding / compression standard. Examples of such standards include ITU-T Recommendation H.265. In one example, a video coding standard under development is informally known as Versatile Video Coding (VVC). The disclosed subject matter may be used in the context of VVC, as well as other video coding standards.

[0035] It should be noted that the electronic devices (420) and (430) may include other components (not shown). For example, the electronic device (420) may include a video decoder (not shown), and the electronic device (430) may also include a video encoder (not shown).

[0036] 5 shows a block diagram of a video decoder (510) according to any of the following embodiments of the present disclosure. The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) of the example of FIG. 4.

[0037] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In the same or another embodiment, one coded video sequence may be decoded at a time, with the decoding of each coded video sequence being independent of the other coded video sequences. Each video sequence may be associated with multiple video frames or video images. The coded video sequences may be received from a channel (501), which may be a hardware / software link to a storage device that stores the encoded video data, or a streaming source that transmits the encoded video data. The receiver (531) may receive the encoded video data along with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to respective processing circuits (not shown). The receiver (531) may separate the coded video sequences from other data. To combat network jitter, a buffer memory (515) may be disposed between the receiver (531) and the entropy decoder / parser (520) (hereinafter, "parser (520)"). In certain applications, the buffer memory (515) may be implemented as part of the video decoder (510). In other applications, the buffer memory (515) may be separate and external to the video decoder (510) (not shown). In still other applications, there may be a buffer memory (not shown) external to the video decoder (510), for example to combat network jitter, and there may be another additional buffer memory (515) internal to the video decoder (510), for example to handle playback timing. When the receiver (531) is receiving data from a storage / forwarding device with sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may be unnecessary or may be small. For use with best-effort packet networks such as the Internet, a buffer memory (515) of sufficient size may be required, and its size may be relatively large.Such a buffer memory may be implemented with an adaptive size and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (510).

[0038] The video decoder (510) may include a parser (520) to reconstruct symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and potentially information for controlling a rendering device such as a display (512) (e.g., a display screen) that may or may not be an integral part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device may be in the form of a supplemental enhancement information (SEI message) or a parameter set fragment (not shown) of video usability information (VUI). The parser (520) may parse / entropy decode the coded video sequence received by the parser (520). The entropy coding of the coded video sequence may be according to a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (520) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the subgroup. The subgroups may include groups of pictures (GOPs), pictures, tiles, slices, macroblocks, coding units (CUs), blocks, transform units (TUs), prediction units (PUs), etc. The parser (520) may also extract information from the coded video sequence, such as transform coefficients (e.g., Fourier transform coefficients), quantization parameter values, motion vectors, etc.

[0039] The parser (520) can perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515) to produce symbols (521).

[0040] The reconstruction of the symbols (521) may involve a number of different processing or functional units, depending on the type of video picture or portion thereof being coded (inter-picture and intra-picture, inter-block and intra-block, etc.), as well as other factors. The units that are included and how they are included may be controlled by subgroup control information parsed from the coded video sequence by the parser (520). The flow of such subgroup control information between the parser (520) and the following processing or functional units is not shown for the sake of simplicity.

[0041] Besides the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into several functional units, as described below. In an actual implementation operating under commercial constraints, many of these functional units may interact closely with each other and may be, at least in part, integrated with each other. However, for the purpose of clearly describing the various functions of the disclosed subject matter, a conceptual subdivision into functional units is adopted in the following disclosure.

[0042] The first unit may include a scalar / inverse transform unit (551), which may receive quantized transform coefficients as well as control information from the parser (520) including information indicating which type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc. The scalar / inverse transform unit (551) may output blocks including sample values ​​that may be input to an aggregator (555).

[0043] In some cases, the output samples of the scaler / inverse transform (551) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may generate a block of the same size and shape as the block being reconstructed using information of surrounding blocks that have already been reconstructed and stored in the current picture buffer (558). The current picture buffer (558) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. In some implementations, the aggregator (555) may add, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551).

[0044] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded, potentially motion-compensated block. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for inter-picture prediction. After motion compensating the fetched samples according to the symbols (521) related to the block, these samples may be added to the output of the scalar / inverse transform unit (551) by the aggregator (555) to generate output sample information (the output of unit 551 may be referred to as a residual sample or residual signal). The address in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches the prediction sample may be controlled by a motion vector, available to the motion compensated prediction unit (553) in the form of a symbol (521), which may have, for example, an X component, a Y component (shift), and a reference picture component (time). Motion compensation may also include interpolation of sample values ​​fetched from a reference picture memory (557) when sub-sample accurate motion vectors are used, and may be associated with a motion vector prediction mechanism, etc.

[0045] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in the loop filter unit (556). Video compression techniques may include in-loop filter techniques that are controlled by parameters included in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to previously reconstructed and loop filtered sample values ​​as well as meta-information obtained during decoding of a previous portion (in decoding order) of the coded picture or coded video sequence. As described in more detail below, several types of loop filters may be included as part of the loop filter unit 556 in various orders.

[0046] The output of the loop filter unit (556) may be a sample stream that can be output to a rendering device (512) as well as stored in a reference picture memory (557) for use in future inter-picture prediction.

[0047] Once a particular coded picture is fully reconstructed, it may be used as a reference picture for future inter-picture prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified (e.g., by the parser (520)) as a reference picture, the current picture buffer (558) may become part of the reference picture memory (557), and any unused current picture buffer may be reallocated before beginning reconstruction of the next coded picture.

[0048] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard, such as ITU-T Recommendation H.265. The coded video sequence may conform to a syntax specified by the video compression technique or standard used in the sense that the coded video sequence adheres to both the syntax of the video compression technique or standard and to a profile documented in the video compression technique or standard. Specifically, a profile may select a particular tool from all tools available in the video compression technique or standard as the only tool that can be used under that profile. To conform to a standard, the complexity of the coded video sequence may be within a range defined by a level of the video compression technique or standard. In some cases, the level limits a maximum picture size, a maximum frame rate, a maximum reconstruction sample rate (e.g., measured in megasamples per second), a maximum reference picture size, etc. The limits set by the level may be further limited in some cases by a specification of a hypothetical reference decoder (HRD) and metadata for HRD buffer management signaled within the coded video sequence.

[0049] In some example embodiments, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0050] 6 shows a block diagram of a video encoder (603) according to an exemplary embodiment of the present disclosure. The video encoder (603) may be included in an electronic device (620). The electronic device (620) may further include a transmitter (640) (e.g., a transmission circuit). The video encoder (603) may be used in place of the video encoder (403) of the example of FIG.

[0051] The video encoder (603) may receive video samples from a video source (601) (which is not part of the electronic device (620) in the example of FIG. 6) that may capture video images to be coded by the video encoder (603). In another example, the video source (601) may be implemented as part of the electronic device (620).

[0052] The video source (601) may provide a source video sequence to be coded by the video encoder (603) in the form of a digital video sample stream that may be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, ...), any color space (e.g., BT.601 YCrCb, RGB, XYZ ...), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media serving system, the video source (601) may be a storage device capable of storing previously prepared video. In a video conferencing system, the video source (601) may be a camera that captures local image information as a video sequence. The video data may be provided as a number of individual pictures or images that give motion when viewed in sequence. The picture itself may be organized as a spatial array of pixels, each pixel may contain one or more samples depending on the sampling structure, color space, etc. being used. Those skilled in the art can easily understand the relationship between pixels and samples. The following description focuses on samples.

[0053] According to some example embodiments, the video encoder (603) may code and compress pictures of a source video sequence into a coded video sequence (643) in real time or under any other time constraint required by the application. Enforcing an appropriate coding rate constitutes one function of the controller (650). In some embodiments, the controller (650) may be operatively coupled to and control other functional units as described below. For simplicity, couplings are not shown. Parameters set by the controller (650) may include rate control related parameters (picture skip, quantizer, lambda value for rate distortion optimization techniques, etc.), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured to have other appropriate functions associated with the video encoder (603) optimized for a particular system design.

[0054] In some example embodiments, the video encoder (603) may be configured to operate in a coding loop. As an oversimplified explanation, in one example, the coding loop may include a source coder (630) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to create sample data in a similar manner as a (remote) decoder would create them, even though the embedded decoder 633 processes the video stream coded by the source coder 630 without entropy coding (since in the video compression techniques contemplated in the disclosed subject matter, any compression between the symbols and the coded video bitstream may be lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since decoding of the symbol stream produces bit-exact results regardless of the location of the decoder (local or remote), the contents of the reference picture memory (634) are also bit-exact between the local and remote encoders. In other words, the predictive part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift when synchrony cannot be maintained, e.g., due to channel errors) is used to improve coding quality.

[0055] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. Referring also briefly to Figure 5, however, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (520) may be lossless, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633) within the encoder.

[0056] At this point, it can be said that any decoder technology, except for parsing / entropy decoding, which may only exist in the decoder, may necessarily also need to exist in the corresponding encoder in substantially the same functional form. For this reason, the disclosed subject matter may focus on the decoder operation, which is similar to the decoding part of the encoder. Thus, the description of the encoder technology may be omitted, since it is the reverse of the decoder technology described in general. Only in certain areas or aspects, a more detailed description of the encoder is provided below.

[0057] In operation, in some example implementations, the source coder (630) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from a video sequence designated as "reference pictures." In this manner, the coding engine (632) codes color channel differences (or residuals) between pixel blocks of the input picture and pixel blocks of reference pictures that may be selected as predictive references to the input picture. The terms "residual" and its adjective form "residual" may be used interchangeably.

[0058] The local video decoder (633) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols created by the source coder (630). The operation of the coding engine (632) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may typically be a replica of the source video sequence with some errors. The local video decoder (633) may replicate the decoding process that may be performed by the video decoder on the reference pictures, such that the reconstructed reference pictures are stored in the reference picture cache (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content with reconstructed reference pictures obtained by a far-end (remote) video decoder (without transmission errors).

[0059] The predictor (635) may perform a prediction search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or specific metadata such as reference picture motion vectors, block shapes, etc., that may serve as suitable prediction references for the new pixels. The predictor (635) may operate on a pixel block by pixel block basis to find a suitable prediction reference. In some cases, the input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (634), as determined by the search results obtained by the predictor (635).

[0060] The controller (650) may manage the coding operations of the source coder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0061] The output of all the aforementioned functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by lossless compression of the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0062] The transmitter (640) may buffer the coded video sequence created by the entropy coder (645) and prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0063] The controller (650) can manage the operation of the video encoder (603). During coding, the controller (650) can assign a particular coded picture type to each coded picture, which may affect the coding techniques that may be applied to the respective picture. For example, pictures may often be assigned as one of the following picture types:

[0064] An intra picture (I-picture) may be one that can be coded and decoded without using other pictures in a sequence as a source of prediction. Some video codecs allow different types of intra pictures, including, for example, independent decoder refresh ("IDR") pictures. Those skilled in the art are aware of these variations of I-pictures, as well as their respective uses and characteristics.

[0065] A predictive picture (P picture) may be a picture that can be coded and decoded using intra- or inter-prediction, which uses at most one motion vector and reference index to predict sample values ​​for each block.

[0066] A bidirectionally predicted picture (B-picture) may be a picture that can be coded and decoded using intra- or inter-prediction that uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, a multi-predicted picture may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0067] A source picture may generally be spatially subdivided into multiple sample coding blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and coded block by block. A block may be predictively coded with reference to other (already coded) blocks as determined by the coding assignment applied to the respective picture of the block. For example, a block of an I picture may be non-predictively coded or predictively coded with reference to already coded blocks of the same picture (spatial prediction or intra prediction). A pixel block of a P picture may be predictively coded via spatial prediction or via temporal prediction with reference to one previously coded reference picture. A block of a B picture may be predictively coded via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures. A source picture or an intermediate processed picture may be subdivided into other types of blocks for other purposes. The division of coding blocks and other types of blocks may or may not follow the same method, as described in more detail below.

[0068] The video encoder (603) may perform coding operations in accordance with a given video coding technique or standard, such as ITU-T Recommendation H.265. In its operations, the video encoder (603) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0069] In some example embodiments, the transmitter (640) may transmit additional data along with the encoded video. The source coder (630) may include such data as part of the coded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0070] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits temporal or other correlation between pictures. For example, a particular picture being encoded / decoded, called the current picture, may be divided into blocks. If a block in the current picture is similar to a reference block in a previously coded yet buffered reference picture in the video, it may be coded by a vector, called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0071] In some exemplary embodiments, bi-prediction techniques may be used for inter-picture prediction. According to such bi-prediction techniques, two reference pictures, such as a first reference picture and a second reference picture, are used, both of which advance the current picture in the video in decoding order (but may be in the past or future, respectively, in display order). A block in the current picture may be coded by a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. A block may be jointly predicted by a combination of the first reference block and the second reference block.

[0072] Furthermore, merge mode techniques may be used to improve coding efficiency in inter-picture prediction.

[0073] According to some exemplary embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed on a block-by-block basis. For example, a picture in a sequence of video pictures is divided into coding tree units (CTUs) for compression, and the CTUs in a picture may have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may include three parallel coding tree blocks (CTBs), i.e., one luma CTB and two chroma CTBs. Each CTU may be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels. Each of one or more of the 32×32 blocks may be further partitioned into four CUs of 16×16 pixels. In some exemplary embodiments, each CU may be analyzed during encoding to determine a prediction type for that CU from among various prediction types, such as an inter prediction type and an intra prediction type. A CU may be divided into one or more prediction units (PUs) according to temporal and / or spatial predictability. In general, each PU includes one luma prediction block (PB) and two chroma PBs. In one embodiment, prediction operations in coding (encoding / decoding) are performed in units of prediction blocks. The division of a CU into PUs (or PBs of different color channels) may be implemented in various spatial patterns. A luma PB or a chroma PB may include a matrix of sample values ​​(e.g., luma values), such as, for example, 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0074] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of the present disclosure. The video encoder (703) is configured to receive a processed block (e.g., a predictive block) of sample values ​​in a current video picture in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. The exemplary video encoder (703) can be used in place of the example video encoder (403) of FIG. 4.

[0075] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a predictive block of 8×8 samples. The video encoder (703) then determines, for example, using rate-distortion optimization (RDO), whether the processing block is best coded using intra-mode, inter-mode, or bi-predictive mode. If it is determined that the processing block is coded in intra-mode, the video encoder (703) may encode the processing block into a coded picture using intra-prediction techniques, and if it is determined that the processing block is coded in inter-mode or bi-predictive mode, the video encoder (703) may encode the processing block into a coded picture using inter-prediction techniques or bi-prediction techniques, respectively. In some exemplary embodiments, a merge mode may be used as a sub-mode of inter-picture prediction, in which a motion vector is derived from one or more motion vector predictors without the benefit of coded motion vector components outside the predictors. In some other exemplary embodiments, there may be motion vector components applicable to the current block. Thus, the video encoder (703) may include components not explicitly shown in FIG. 7, such as a mode decision module, to determine the prediction mode of a processing block.

[0076] In the example of FIG. 7, the video encoder (703) includes an inter-encoder (730), an intra-encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy encoder (725) coupled to each other as shown in the exemplary arrangement of FIG.

[0077] The inter-encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures in display order), generate inter-prediction information (e.g., a description of redundancy information, motion vectors, merge mode information according to inter-encoding techniques), and calculate an inter-prediction result (e.g., a predicted block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the encoded video information using a decoding unit 633 incorporated in the example encoder 620 of FIG. 6 (shown as residual decoder 728 of FIG. 7, as described in more detail below).

[0078] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block with already coded blocks in the same picture, generate transformed quantized coefficients, and possibly also generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). The intra encoder (722) can calculate intra prediction results (e.g., prediction blocks) based on the intra prediction information and reference blocks in the same picture.

[0079] The generic controller (721) may be configured to determine generic control data and control other components of the video encoder (703) based on the generic control data. In one example, the generic controller (721) determines a prediction mode of the block and provides a control signal to the switch (726) based on the prediction mode. For example, if the prediction mode is an intra mode, the generic controller (721) controls the switch (726) to select an intra mode result for use by the residual calculator (723) and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream, and if the prediction mode of the block is an inter mode, the generic controller (721) controls the switch (726) to select an inter prediction result for use by the residual calculator (723) and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0080] The residual calculator (723) may be configured to calculate a difference (residual data) between a received block and a prediction result for a block selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) may be configured to encode the residual data to generate transform coefficients. For example, the residual encoder (724) may be configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various exemplary embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) may generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) may generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks may be appropriately processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures.

[0081] The entropy encoder (725) may be configured to format a bitstream to include the encoded block and to perform entropy coding. The entropy encoder (725) may be configured to include various information in the bitstream. For example, the entropy encoder (725) may be configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other suitable information in the bitstream. When coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode, the residual information may not be present.

[0082] 8 shows a diagram of an example video decoder (810) according to another embodiment of the present disclosure. The video decoder (810) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In one example, the video decoder (810) can be used in place of the example video decoder (410) of FIG. 4.

[0083] In the example of FIG. 8, the video decoder (810) includes an entropy decoder (871), an inter-decoder (880), a residual decoder (873), a reconstruction module (874), and an intra-decoder (872), all coupled together as shown in the exemplary arrangement of FIG. 8.

[0084] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols that represent syntax elements of which the coded picture is composed. Such symbols may include, for example, prediction information (e.g., intra- or inter-prediction information) that may identify the mode in which the block is coded (e.g., intra-mode, inter-mode, bi-prediction mode, merged submode, or another submode), certain samples or metadata used for prediction by the intra-decoder (872) or inter-decoder (880), residual information in the form of quantized transform coefficients, etc. In one example, if the prediction mode is an inter- or bi-prediction mode, the inter-prediction information is provided to the inter-decoder (880), and if the prediction type is an intra-prediction type, the intra-prediction information is provided to the intra-decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0085] The inter decoder (880) may be configured to receive the inter prediction information and generate inter prediction results based on the inter prediction information.

[0086] The intra decoder (872) may be configured to receive intra prediction information and to generate a prediction result based on the intra prediction information.

[0087] The residual decoder (873) may be configured to perform inverse quantization to extract inverse quantized transform coefficients and process the inverse quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also utilize certain control information (to include quantizer parameters (QP)), which may be provided by the entropy decoder (871) (a data path is not shown as this may be only a small amount of control information).

[0088] The reconstruction module (874) may be configured to combine, in the spatial domain, the residual as output by the residual decoder (873) and the prediction result (possibly as output by an inter prediction module or an intra prediction module) to form a reconstructed block that forms part of a reconstructed picture as part of the reconstructed video. It should be noted that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0089] It should be noted that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using any suitable technique. In some exemplary embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (403), (603), and (603) and the video decoders (410), (510), and (810) may be implemented using one or more processors executing software instructions.

[0090] Looking at the coding block partitioning, in some exemplary implementations, a predefined pattern may be applied. As shown in FIG. 9, an exemplary four-way partitioning tree may be used starting from a first predefined level (e.g., 64×64 block level) to a second predefined level (e.g., 4×4 level). For example, the base block may follow four partitioning options illustrated by 902, 904, 906, and 908, and the partition designated as R may be recursively partitioned in that the same partitioning tree illustrated in FIG. 9 may be repeated at lower scales down to the lowest level (e.g., 4×4 level). In some implementations, additional restrictions may be added to the partitioning scheme of FIG. 9. In the implementation of FIG. 9, rectangular partitions (e.g., 1:2 / 2:1 rectangular partitions) may be allowed but not recursively, while square partitions are allowed to be recursive. Subsequent partitioning of FIG. 9 by recursion generates a final set of coding blocks, if necessary. Such a scheme may be applied to one or more of the color channels.

[0091] FIG. 10 illustrates another exemplary predefined partitioning pattern that allows recursive partitioning to form a partitioning tree. As illustrated in FIG. 10, an exemplary ten-way partitioning structure or pattern may be predefined. The root block may start from a predefined level (e.g., from the 128×128 level or the 64×64 level). The exemplary partitioning structure in FIG. 10 includes various 2:1 / 1:2 and 4:1 / 1:4 rectangular partitions. A partition type with three subpartitions, shown at 1002, 1004, 1006, and 1008 in the second column of FIG. 10, may be referred to as a “T-shaped” partition. The “T-shaped” partitions 1002, 1004, 1006, and 1008 may be referred to as a left T-shaped, an upper T-shaped, a right T-shaped, and a lower T-shaped. In some implementations, none of the rectangular partitions in FIG. 10 may be further subdivided. A coding tree depth may be further defined to indicate the partitioning depth from the root node or root block. For example, the coding tree depth of the root node or root block of a 128×128 block may be set to 0, and the coding tree depth increases by 1 after the root block is further split one time following FIG. 10. In some implementations, only the all-square partitions of 1010 may allow recursive splitting to the next level of the split tree following the pattern of FIG. 10. In other words, recursive splitting is not possible for the square partitions of patterns 1002, 1004, 1006, and 1006. Subsequent splitting of FIG. 10 by recursion generates a final set of coding blocks, if necessary. Such a scheme may be applied to one or more of the color channels.

[0092] After partitioning or splitting the base block according to any of the above partitioning procedures or other procedures, a final set of partitions or coding blocks may still be obtained. Each of these partitions may be at one of various partitioning levels. Each of the partitions may be referred to as a coding block (CB). In the various exemplary partitioning implementations above, each resulting CB may be of any of the allowed sizes and partitioning levels. They are referred to as coding blocks because they may form a unit for which some basic coding / decoding decisions may be made and coding / decoding parameters may be optimized, determined, and signaled in the encoded video bitstream. The highest level in the final partition represents the depth of the coding block partitioning tree. The coding block may be a luma coding block or a chroma coding block.

[0093] In some other example implementations, a quadtree structure may be used to recursively split the base luma block and the base chroma block into coding units. Such a split structure may be called a coding tree unit (CTU), and the CTU is split into coding units (CUs) by adapting the split to various local characteristics of the base CTU using the quadtree structure. In such implementations, an implicit quadtree split may be performed at the picture boundary, such that the block continues the quadtree split until its size fits into the picture boundary. The term CU is used to collectively refer to the units of luma coding block (CB) and chroma coding block (CB).

[0094] In some implementations, the CB may be further divided. For example, the CB may be further divided into multiple prediction blocks (PBs) for the purpose of intra-frame or inter-frame prediction during the coding and decoding processes. In other words, the CB may be further partitioned into different sub-partitions, where individual prediction decisions / configurations may be made. In parallel, the CB may be further divided into multiple transform blocks (TBs) for the purpose of describing the level at which the transformation or inverse transformation of the video data is performed. The division scheme of the CB into PBs and TBs may be the same or different. For example, each division scheme may be performed using a unique procedure based on, for example, various characteristics of the video data. The division scheme of the PBs and TBs may be independent in some exemplary implementations. The division schemes and boundaries of the PBs and TBs may be correlated in some other exemplary implementations. In some implementations, for example, the TBs may be divided after the PB division, and in particular, each PB may be determined following the division of the coding block, and then further divided into one or more TBs. For example, in some implementations, the PB may be divided into one, two, four, or other number of TBs.

[0095] In some implementations, the luma and chroma channels may be processed differently to split the base blocks into coding blocks and further into predictive and / or transform blocks. For example, in some implementations, splitting of coding blocks into predictive and / or transform blocks may be allowed for the luma channel, but such splitting of coding blocks into predictive and / or transform blocks may not be allowed for the chroma channels. In such implementations, the transform and / or prediction of luma blocks may thus be performed only at the coding block level. In another example, the minimum transform block size of the luma and chroma channels may be different, e.g., the coding blocks of the luma channel may be allowed to be split into smaller transform and / or predictive blocks than the chroma channels. In yet another example, the maximum depth of the splitting of coding blocks into transform and / or predictive blocks may be different between the luma and chroma channels, e.g., the coding blocks of the luma channel may be allowed to be split into deeper transform and / or predictive blocks than the chroma channels. As a specific example, a luma coding block may be divided into transform blocks of multiple sizes that can be represented by a recursive partitioning down by up to two levels, and transform block shapes such as square, 2:1 / 1:2, and 4:1 / 1:4, as well as transform block sizes from 4×4 to 64×64 may be allowed. However, for chroma blocks, only the largest possible transform block designated for the luma block may be allowed.

[0096] In some example implementations for partitioning a coding block into PBs, the depth, shape, and / or other characteristics of the PB partition may depend on whether the PB is intra-coded or inter-coded.

[0097] The division of the coding block (or prediction block) into transform blocks may be performed in various exemplary manners, including but not limited to quadtree division and predefined pattern division, recursively or non-recursively, further considering transform blocks at the boundaries of the coding block or prediction block. In general, the resulting transform blocks may be at different division levels, may not be the same size, and need not be square in shape (e.g., they may be rectangular with some allowed size and aspect ratio).

[0098] In some implementations, a coding partition tree scheme or structure may be used. The coding partition tree schemes used for the luma channel and the chroma channel may not need to be the same. In other words, the luma channel and the chroma channel may have separate coding tree structures. Furthermore, whether the luma channel and the chroma channel use the same coding partition tree structure or different coding partition tree structures, and the actual coding partition tree structure to be used may depend on whether the slice being coded is a P slice, a B slice, or an I slice. For example, for an I slice, the chroma channel and the luma channel may have separate coding partition tree structures or coding partition tree structure modes, while for a P slice or a B slice, the luma channel and the chroma channel may share the same coding partition tree scheme. When separate coding partition tree structures or modes are applied, the luma channel may be partitioned into CB by one coding partition tree structure, and the chroma channel may be partitioned into chroma CB by another coding partition tree structure.

[0099] Specific exemplary implementations of the division of coding blocks and transform blocks are described below. In such exemplary implementations, a base coding block may be divided into coding blocks using the recursive quadtree division described above. At each level, whether to continue further quadtree division of a particular partition may be determined by local video data characteristics. The resulting CBs may be at various quadtree division levels with various sizes. The decision of whether to code a picture area using inter-picture (temporal) prediction or intra-picture (spatial) prediction may be made at the CB level (or at the CU level for all three color channels). Each CB may be further divided into one, two, four, or other number of PBs according to the PB division type. Within one PB, the same prediction process may be applied, and related information is transmitted to the decoder on a PB basis. After obtaining the residual block by applying the prediction process based on the PB division type, the CB may be divided into TBs according to another quadtree structure similar to the coding tree for CBs. In this particular implementation, the CB or TB may not be limited to a square shape. Further, in this particular example, the PB may be square or rectangular for inter prediction, and may only be square for intra prediction. The coding block may be further divided, for example, into four square TBs. Each TB may be further divided recursively (using quadtree partitioning) into smaller TBs called residual quadtrees (RQTs).

[0100] Another specific example for splitting the base coding block into CB and other PBs and / or TBs is described below. For example, instead of using multiple partition unit types as shown in FIG. 10, a quadtree with nested multi-type trees using bipartition and tripartition segmentation structures may be used. Separation of the concepts of CB, PB, and TB (i.e., splitting CB into PB and / or TB, and splitting PB into TB) may be abandoned except when necessary for CBs with sizes too large for the maximum transform length, which may require further splitting. This exemplary splitting scheme may be designed to support further flexibility on CB splitting shapes, such that prediction and transformation can both be performed at the CB level without further splitting. In such coding tree structures, CBs can have either square or rectangular shapes. Specifically, a coding tree block (CTB) may first be split by a quadtree structure. Then, the quadtree leaf nodes may be further split by a multi-type tree structure. An example of a multi-type tree structure is shown in FIG. 11. Specifically, the exemplary multi-type tree structure of FIG. 11 includes four split types called vertical bisection (SPLIT_BT_VER) (1102), horizontal bisection (SPLIT_BT_HOR) (1104), vertical trisection (SPLIT_TT_VER) (1106), and horizontal trisection (SPLIT_TT_HOR) (1108). Then, CB corresponds to a leaf of the multi-type tree. In this exemplary implementation, as long as CB is not too large for the maximum transform length, this segmentation is used for both prediction and transform processing without further splitting. This means that in most cases, CB, PB, and TB have the same block size in a quadtree with nested multi-type tree coding block structure. An exception occurs when the maximum supported transform length is smaller than the width or height of the color components of CB.

[0101] An example of a quadtree with nested multi-type tree coding block structure of block division of one CTB is shown in FIG. 12. More specifically, FIG. 12 shows that a CTB 1200 is quadtree divided into four square partitions 1202, 1204, 1206, and 1208. A decision to further use the multi-type tree structure of FIG. 11 for division is made for each of the quadtree divided partitions. In the example of FIG. 12, partition 1204 is not further divided. Partition 1202 and partition 1208 each adopt another quadtree division. In partition 1202, the second level quadtree divided upper left partition, upper right partition, lower left partition, and lower right partition adopt the third level division of quadtree, 1104 in FIG. 11, non-partition, and 1108 in FIG. 11, respectively. Partition 1208 adopts another quadtree partitioning, and the second level quadtree partitioned top-left partition, top-right partition, bottom-left partition, and bottom-right partition adopt the third level partitioning of 1106 in FIG. 11, unsplit, unsplit, and 1104 in FIG. 11, respectively. Two of the subpartitions of the top-left partition of the third level of 1208 are further split according to 1104 and 1108. Partition 1206 adopts the second level partitioning pattern according to 1102 in FIG. 11 into two partitions, and the two partitions are further split at the third level according to 1108 and 1102 in FIG. 11. A fourth level partitioning is further applied to one of them according to 1104 in FIG. 11.

[0102] In the above specific example, the maximum luma transform size may be 64 x 64, and the maximum supported chroma transform size may be different from the luma, e.g., 32 x 32. If the width or height of a luma coding block or a chroma coding block is larger than the maximum transform width or maximum transform height, the luma coding block or the chroma coding block may be automatically split horizontally and / or vertically to meet the horizontal and / or vertical transform size restrictions.

[0103] In the above specific example of splitting the base coding blocks into CBs, the coding tree scheme can support the ability for luma and chroma to have separate block tree structures. For example, for P slices and B slices, the luma CTB and chroma CTB in one CTU can share the same coding tree structure. For I slices, for example, luma and chroma may have separate coding block tree structures. When the separate block tree mode is applied, the luma CTB may be split into luma CBs by one coding tree structure, and the chroma CTB is split into chroma CBs by another coding tree structure. This means that a CU in an I slice may consist of a coding block of a luma component or a coding block of two chroma components, and a CU in a P slice or B slice is always composed of coding blocks of all three color components unless the video is monochrome.

[0104] Exemplary implementations for splitting coding or predictive blocks into transform blocks and the coding order of transform blocks are described in further detail below. In some exemplary implementations, the transform splitting can support transform blocks of multiple shapes, e.g., 1:1 (square), 1:2 / 2:1, and 1:4 / 4:1, with transform block sizes ranging from, e.g., 4×4 to 64×64. In some implementations, if the coding block is smaller than or equal to 64×64, the transform block splitting may be applied only to the luma component, such that for chroma blocks, the transform block size is identical to the coding block size. Otherwise, if the width or height of the coding block is greater than 64, both the luma coding block and the chroma coding block may be implicitly split into transform blocks that are multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32), respectively.

[0105] In some example implementations, for both intra-coded and inter-coded blocks, a coding block may be further divided into multiple transform blocks with a division depth up to a predefined number of levels (e.g., two levels). The division depth and size of the transform block may be related. An example mapping from the transform size of the current depth to the transform size of the next depth is shown below in Table 1.

[0106] [Table 1]

[0107] Based on the example mapping in Table 1, for a 1:1 square block, the next level transform split can create four 1:1 square sub-transform blocks. The transform split may stop at, for example, 4×4. Thus, a transform size of the current depth of 4×4 corresponds to the same size of 4×4 at the next depth. In the example of Table 1, for a 1:2 / 2:1 non-square block, the next level transform split creates two 1:1 square sub-transform blocks, and for a 1:4 / 4:1 non-square block, the next level transform split creates two 1:2 / 2:1 sub-transform blocks.

[0108] In some example implementations, further restrictions may be applied to the luma components of intra-coded blocks. For example, for each level of transform partitioning, all sub-transform blocks may be restricted to have equal size. For example, for a 32×16 coding block, the level 1 transform partitioning creates two 16×16 sub-transform blocks, and the level 2 transform partitioning creates eight 8×8 sub-transform blocks. In other words, to keep the transform units equal in size, the second level partitioning must be applied to all first level sub-blocks. An example of transform block partitioning for an intra-coded square block according to Table 1 is shown in FIG. 13 with the coding order indicated by the arrows. Specifically, 1302 shows a square coding block. The first level partitioning according to Table 1 into four equal-sized transform blocks is shown in 1304 with the coding order indicated by the arrows. The second level partitioning of all first level equal-sized blocks according to Table 1 into 16 equal-sized transform blocks is shown in 1306 with the coding order indicated by the arrows.

[0109] In some example implementations, the above restrictions on intra-coding may not apply to the luma components of an inter-coded block. For example, after the first level of transform splitting, any one of the sub-transform blocks may be further split independently at another level. Thus, the resulting transform blocks may or may not be blocks of the same size. An example splitting of an inter-coded block into transform blocks according to their coding order is shown in FIG. 14. In the example of FIG. 14, an inter-coded block 1402 is split into transform blocks at two levels according to Table 1. At the first level, the inter-coded block is split into four transform blocks of equal size. Then, only one of the four transform blocks (but not all of them) is further split into four sub-transform blocks, resulting in a total of seven transform blocks with two different sizes, as shown by 1404. An example coding order of these seven transform blocks is shown by arrows at 1404 in FIG. 14.

[0110] In some example implementations, for chroma components, some further restrictions on the transform blocks may be applied: for example, for chroma components, the transform block size may be as large as the coding block size, but cannot be smaller than a predefined size, e.g., 8×8.

[0111] In some other example implementations, for coding blocks whose either width (W) or height (H) is greater than 64, both the luma coding block and the chroma coding block may be implicitly divided into multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32), respectively.

[0112] Figure 15 further illustrates another alternative exemplary scheme for splitting a coding block or a predictive block into transform blocks. As illustrated in Figure 15, instead of using recursive transform partitioning, a set of predefined partition types may be applied to a coding block according to the transform type of the coding block. In the particular example illustrated in Figure 15, one of six exemplary partition types may be applied to split a coding block into a varying number of transform blocks. Such a scheme may be applied to either a coding block or a predictive block.

[0113] More specifically, the partitioning scheme of FIG. 15 provides up to six partition types for any given transform type, as shown in FIG. 15. In this scheme, every coding block or predictive block may be assigned a transform type based on, for example, a rate-distortion cost. In one example, the partition type assigned to a coding block or predictive block may be determined based on the transform partition type of the coding block or predictive block. As shown by the four partition types illustrated in FIG. 15, a particular partition type may correspond to the partition size and pattern (or partition type) of the transform block. The correspondence between various transform types and various partition types may be predefined. An exemplary correspondence is shown below with capitalized labels indicating the transform types that may be assigned to a coding block or predictive block based on the rate-distortion cost.

[0114] ·PARTITION_NONE: Allocate transformation size equal to block size.

[0115] ·PARTITION_SPLIT: Allocates a transformation size of 1 / 2 the block size in width and 1 / 2 the block size in height.

[0116] ·PARTITION_HORZ: Allocates a transformation size with width equal to the block size and height equal to 1 / 2 the block size.

[0117] ·PARTITION_VERT: Allocates a transformation size with a width half the block size and a height equal to the block size.

[0118] ·PARTITION_HORZ4: Allocates a transformation size with width equal to the block size and height equal to 1 / 4 of the block size.

[0119] ·PARTITION_VERT4: Allocates a transformation size with a width of 1 / 4 of the block size and a height equal to the block size.

[0120] In the above example, the partition types shown in Figure 15 all include uniform transform sizes for the partitioned transform blocks. This is not a limitation but merely an example. In some other implementations, mixed transform block sizes may be used for the partitioned transform blocks in a particular partition type (or pattern).

[0121] The PBs (or CBs, also called PBs if not further divided into predictive blocks) obtained from any of the above partitioning schemes can become individual blocks for coding via either intra-prediction or inter-prediction. For inter-prediction on the current PB, a residual between the current block and the predictive block can be generated, coded, and included in the coded bitstream.

[0122] Turning to the intra prediction process, samples in a block (e.g., luma or chroma prediction block, or coding block if not further divided into prediction blocks) are predicted by samples of adjacent, next adjacent, or other line or lines, or combinations thereof, to generate a prediction block. The residual between the actual block being coded and the prediction block may then be processed by a transform after quantization. Various intra prediction modes may be made available, and parameters related to the selection of the intra mode and other parameters may be signaled in the bitstream. The various intra prediction modes may relate, for example, to one or more line positions for predicting samples, the direction in which the prediction samples are selected from predicting one or more lines, and other special intra prediction modes.

[0123] For example, the set of intra-prediction modes (interchangeably referred to as "intra modes") may include a predefined number of directional intra-prediction modes. As described above with respect to the example implementation of FIG. 1, these intra-prediction modes may correspond to a predefined number of directions to follow when selecting a sample outside the block as a destination for a sample being predicted within a particular block. In another particular example implementation, eight main directional modes may be supported and predefined, corresponding to angles from 45 degrees to 207 degrees relative to the horizontal axis.

[0124] In some other implementations of intra prediction, the directional intra modes may be further extended to a set of angles with finer granularity to further exploit more diverse spatial redundancy in the directional texture. For example, as shown in FIG. 16, the above eight angle implementation may be configured to provide eight nominal angles (referred to as V_PRED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED, and D67_PRED), and for each nominal angle, a predefined number (e.g., seven) of finer angles may be added. Such an extension results in a larger total number of directional angles (e.g., 56 in this example) that can be used for intra prediction, which correspond to the same number of predefined directional intra modes. The prediction angle may be represented by the nominal intra angle + angle delta. In the above specific example with seven finer angle directions for each nominal angle, the angle delta may be -3 to 3 times the step size of 3 degrees.

[0125] In some implementations, instead of or in addition to the above directional intra modes, a predefined number of non-directional intra prediction modes may also be predefined and made available. For example, five non-directional intra modes called smooth intra prediction modes may be specified. These non-directional intra mode prediction modes may be specifically called DC intra mode, PAETH intra mode, SMOOTH intra mode, SMOOTH_V intra mode, and SMOOTH_H intra mode. Prediction of samples of a particular block using these exemplary non-directional modes is shown in Figure 17. As an example, Figure 17 shows how a 4x4 block 2002 is predicted by samples obtained from the neighboring line above and / or the neighboring line to the left. A particular sample 1710 in block 1702 may correspond to a sample 1704 directly above the sample 1710 in the top neighboring line of block 1702, a sample 1706 to the top left of sample 1710 as the intersection of the top neighboring line and the left neighboring line, and a sample 1708 to the direct left of sample 1710 in the left neighboring line of block 1702. In an exemplary DC intra prediction mode, an average of the left and top neighboring samples 1708 and 1704 may be used as a predictor for sample 1710. In an exemplary PAETH intra prediction mode, the top, left, and top left reference samples 1704, 1708, and 1706 may be fetched, and then any value between these three reference samples that is closest to (top+left-top left) may be set as the predicted value of sample 1710. In the exemplary SMOOTH_V intra prediction mode, sample 1710 may be predicted by a quadratic vertical interpolation of the top-left neighboring sample 1706 and the left neighboring sample 1708. In the exemplary SMOOTH_H intra prediction mode, sample 1710 may be predicted by a quadratic horizontal interpolation of the top-left neighboring sample 1706 and the above neighboring sample 1704. In the exemplary SMOOTH intra prediction mode, sample 1710 may be predicted by an average of quadratic vertical and horizontal interpolations. The above implementations of non-directional intra modes are provided merely as non-limiting examples.Other adjacent lines, and other non-directional selections of samples, and methods of combining predicted samples to predict a particular sample within a predictive block are also possible.

[0126] The selection of a particular intra-prediction mode by the encoder from the above directional or non-directional modes at various coding levels (picture, slice, block, unit, etc.) may be signaled in the bitstream. In some exemplary implementations, the eight exemplary nominal directional modes may be signaled first, along with the five smooth modes without angles (a total of 13 options). Then, if the signaled mode is one of the eight nominal angle intra-modes, an index indicating the selected angle delta for the corresponding signaled nominal angle is further signaled. In some other exemplary implementations, all intra-prediction modes may be indexed together (e.g., 56 directional modes plus 5 non-directional modes to generate 61 intra-prediction modes) for signaling.

[0127] In some example implementations, the example 56 or other number of directional intra-prediction modes may be realized with a unified directional predictor that projects each sample of a block to a reference subsample position and interpolates the reference samples by a 2-tap bilinear filter.

[0128] In some implementations, additional filter modes, called FILTER INTRA modes, can be designed to capture the reduced spatial correlation with the references on the edges. In these modes, samples predicted within the block in addition to samples outside the block may be used as intra prediction reference samples for some patches within the block. These modes may, for example, be predefined and made available for intra prediction of at least the luma block (or only the luma block). A predefined number (e.g., 5) of filter intra modes can be predesigned, each of which is represented by a set of n-tap filters (e.g., 7-tap filters) that reflects, for example, the correlation between a sample in a 4×2 patch and its adjacent n neighbors. In other words, the weight coefficients of the n-tap filters may be position dependent. As shown in FIG. 18, when using an 8×8 block, a 4×2 patch, and 7-tap filtering as an example, the 8×8 block 2002 may be divided into eight 4×2 patches. These patches are indicated in FIG. 18 as B0, B1, B1, B3, B4, B5, B6, and B7. For each patch, its seven neighbors (denoted R0-R7 in FIG. 18) may be used to predict samples in the current patch. For patch B0, all neighbors may already be reconstructed, while for other patches, some of the neighbors may not be reconstructed since they are within the current block, in which case the predicted values ​​of the immediate neighbors are used as reference. For example, patch B7 shown in FIG. 18 does not have all its neighbors reconstructed, so the predicted samples of the neighbors are used instead.

[0129] In some implementations of intra prediction, one color component may be predicted using one or more other color components. The color components may be any one of the components of YCrCb color space, RGB color space, XYZ color space, etc. For example, prediction may be performed that predicts a chroma component (e.g., a chroma block) from a luma component (e.g., a luma reference sample), called luma-to-chroma, or CfL. In some exemplary implementations, much is allowed for cross-color prediction only from luma to chroma. For example, a chroma sample in a chroma block may be modeled as a linear function of the corresponding reconstructed luma sample. CfL prediction may be performed as follows: CfL(α)=α×L AC +DC (1)

[0130] Here, L AC where α represents the AC contribution of the luma component, α represents a parameter of the linear model, and DC represents the DC contribution of the chroma component. For example, the AC components are obtained for each sample of the block, while the DC components are obtained for the entire block. Moreover, the reconstructed luma samples may be subsampled to obtain the chroma resolution, and then the average luma value (the luma DC) may be subtracted from each luma value to form the luma AC contribution. The luma AC contribution is then used in the linear mode of equation (1) to predict the AC value of the chroma component. Instead of requiring the decoder to calculate a scaling parameter to approximate or predict the chroma AC component from the luma AC contribution, an exemplary CfL implementation may determine the parameter α based on the original chroma samples and signal it in the bitstream. This reduces the decoder complexity and provides a more accurate prediction. As for the DC contribution of the chroma component, in some exemplary implementations, it may be calculated using an intra DC mode within the chroma component.

[0131] Instead of intra prediction, the PB may be inter predicted in either single reference or mixed reference inter prediction modes. In particular, in inter prediction modes, a video block may be predicted by one or more other reference blocks or inter prediction blocks from one or more other frames via either single reference or mixed reference inter prediction. To perform inter prediction, a reference block may be specified by its frame identifier (temporal location of the reference block) and a motion vector (spatial location of the reference block) indicating a spatial offset between the current block being encoded or decoded and the reference block. The reference frame identification and the motion vector may be signaled in the bitstream. The motion vector as a spatial block offset may be directly signaled or may itself be predicted by another reference motion vector or a predictor motion vector. For example, the current motion vector may be predicted directly by a reference motion vector (e.g., of a candidate neighboring block) or by a combination of the reference motion vector and the motion vector difference (MVD) between the current motion vector and the reference motion vector. The latter is sometimes referred to as merge mode with motion vector difference (MMVD). A reference motion vector may be identified in the bitstream, for example, as a pointer to a spatially adjacent block of the current block or to a temporally adjacent but spatially co-located block.

[0132] In some implementations, a composite inter-intra prediction (CIIP) mode may be implemented. In the CIIP mode, a prediction block may be derived as a combination of an intra prediction (or intra predictor) block and an inter prediction (intra predictor) block. The inter prediction block in CIIP may be derived using a single reference inter prediction with a translation operation corresponding to a motion vector, while the intra prediction block in CIIP may be determined from neighboring samples based on a subset of the intra prediction modes described above. In some example implementations, the spatial samples in the intra prediction block of the current block being predicted in the CIIP mode may be derived from intra reference line samples according to one of the subsets of intra prediction modes including the DC_PRED, V_PRED, H_PRED, and SMOOTH modes described above. The use of each of this subset of intra prediction modes to derive the intra prediction block may correspond to a CIIP submode index, as shown in Table 2.

[0133] [Table 2]

[0134] The composite inter-intra prediction (or predictor) block in the current block may be generated as a sample-level weighted sum of the intra prediction block and the inter prediction block at the sample level, as derived according to the above description. Thus, the relative weight between the intra prediction block and the inter prediction block may be represented by a weight matrix. Corresponding to the various inter-intra weighting modes of the CIIP, various exemplary methods for determining the weight matrix may be implemented.

[0135] In one exemplary implementation of the weighting mode of CIIP, commonly referred to as CIIP, the elements of the inter-intra weighting matrix corresponding to samples in the current block may follow a deterministic relationship with the position of the sample. Such a deterministic relationship may depend on the intra prediction mode being used. In one particular example, the weighting applied to the intra prediction sample P0(x,y) (x and y represent the sample position in the block) may be derived as follows:

number

[0136] [Table 3]

[0137] In the above example of normal CIIP, the weighting in intra prediction generally decreases as the sample moves away from the upper left corner of the block (or away from the intra prediction reference sample), except for DC_PRED mode, and the inter prediction weighting is independent of the sample position.In other words, the implementation illustrated in Table 3 reflects a scheme in which the inter prediction weight increases as the sample position moves away from the intra reference sample.

[0138] In some other exemplary inter-intra weighting implementations in CIIP, called wedge CIIP, a set of weight patterns may be defined, and one of the set of weight patterns may be selected by the encoder for the current block. An index of the selected pattern in the set of weight patterns may be signaled in the bitstream. Such a pattern may be applied to the current block to determine a particular weight matrix used to combine / add the intra-predicted and inter-predicted blocks for each sample of the block. For example, 16 different patterns (also called wedge patterns) may be predefined and represented by indexes 0-15. In wedge CIIP, once the index of the pattern is specified, the entire weight matrix for the block is derived using the predefined lookup table in Table 3, rather than being signaled sample-by-sample as in the normal CIIP approach.

[0139] In any CIIP, once the above weighting matrix is ​​obtained and applied to combine intra-predicted and inter-predicted blocks, such combined block can be used as the actual prediction block in the current block to obtain a residual block. The residual block can then undergo a primary transformation, and optionally a second transformation, as well as the remainder of the quantization and entropy coding process, from the encoder's perspective. In the case of a decoder, the bitstream is parsed / decoded and inversely transformed to obtain the residual block. If the decoder determines from the bitstream that a CIIP is used for the current block, it can further obtain the weighting matrix of the CIIP based on the information extracted from the bitstream (either the lookup index signaled above, or the wedge pattern index signaled above). The prediction block can then be derived from the weighting matrix and the corresponding intra-predicted and inter-predicted blocks from already reconstructed samples in the current frame or reference frame. The original block can then be restored from the residual block and the prediction block.

[0140] Turning to the primary transform, an exemplary 2D transform process may involve the use of hybrid transform kernels (which may be composed of, for example, a different 1D transform for each dimension of the coded residual block) in addition to using the same transform kernel for both dimensions. Exemplary primary 1D transform kernels may include, but are not limited to, a) 4-point (4p), 8-point (8p), 16-point (16p), 32-point (32p), and 64-point (64p) DCT-2, b) 4-point, 8-point, 16-point asymmetric DST and their inverted versions, c) 4-point, 8-point, 16-point, or 32-point identity transform (DST stands for discrete sine transform). Thus, a 2D transform process may involve the use of hybrid transforms or transform kernels (different transforms for each dimension of the coded residual block), and the selection of the transform or transform kernel to be used for each dimension may be based on a rate-distortion (RD) criterion. The term transform kernel may alternatively be referred to as a transform basis function. For example, Table 4 lists basis functions for 1D DCT-2, DST-4, and DST-7 (where DCT stands for discrete cosine transform) that can be implemented as hybrids of 2D transforms.

[0141] [Table 4]

[0142] For example, DCT-2 (4p-64p), DST-4 (8p, 16p), and DST-7 (4p) transforms exhibit symmetric / anti-symmetric properties, and therefore some exemplary implementations may support "partial butterfly" implementations to reduce the (multiply, add / partial, shift) operation count. The partial butterfly implementation may involve plane rotations using trigonometric cosine and sine functions at various angles, as described in FIG. 19. Exemplary 12-bit lookup tables are shown in FIG. 20 and FIG. 21, which may be utilized to generate the trigonometric function values.

[0143] In some implementations, a secondary transform on the primary transform coefficients may be performed. For example, as shown in FIG. 22, a LFNST (low frequency separable transform), also known as a reduced secondary transform, may be applied between the forward primary transform and quantization (at the encoder) and between the inverse quantization and the inverse primary transform (at the decoder side) to further decorrelate the primary transform coefficients. In essence, the LFNST may take a portion of the primary transform coefficients, e.g., a low frequency portion (thus a "reduced" portion from the full set of primary transform coefficients of the transform block), to proceed to the secondary transform. In an exemplary LFNST, a 4×4 non-separable transform or an 8×8 non-separable transform may be applied according to the transform block size. For example, a 4×4 LFNST may be applied to small transform blocks (e.g., min(width, height)<8) and an 8×8 LFNST may be applied to large transform blocks (e.g., min(width, height)>8). For example, when an 8x8 transform block is subjected to a 4x4 LFNST, only the low frequency 4x4 portion of the 8x8 primary transform coefficients undergo a further secondary transform.

[0144] As specifically shown in FIG. 22, the transform block may be 8×8 (or 16×16). Thus, a forward primary transform 2202 of the transform block generates an 8×8 (or 16×16) primary transform coefficient matrix 2204, with each square unit representing a 2×2 (or 4×4) portion. The input to the forward LFNST may not be, for example, the entire 8×8 (or 16×16) primary transform coefficients. For example, a 4×4 (or 8×8) LFNST may be used for the secondary transform. Thus, as shown in the shaded portion (top left) 2206, only the 4×4 (or 8×8) low frequency primary transform coefficients of the primary transform coefficient matrix 2204 may be used as input to the LFNST. The remaining portion of the primary transform coefficient matrix may not undergo a secondary transform. Thus, after the secondary transform, the portions of the primary transform coefficients that are affected by the LFNST become secondary transform coefficients, while the remaining portions not affected by the LFNST (e.g., the unshaded portions of matrix 2204) retain their corresponding primary transform coefficients. In some example implementations, the remaining portions not subject to the secondary transform may be set to all zero coefficients.

[0145] An example of the application of a non-separable transform for use in LFNST is described below. To apply an example 4×4 LFNST, a 4×4 input block X (representing, for example, a 4×4 low frequency portion of a block of primary transform coefficients such as the shaded portion 2206 of the linear transform matrix 2204 in FIG. 22) can be expressed as follows:

number

[0146] This 2D input matrix is ​​first linearized or converted to a vector in the order of one example.

number

number

[0147] Next, the inseparable transformation of the 4×4 LFNST can be calculated as

Number

Number

Number

[0148] The above exemplary LFNST is based on a direct matrix multiplication approach for applying inseparable transformations and as a result is executed in a single pass without multiple iterations. In some further exemplary implementations, the dimension of the inseparable transformation matrix (T) of, for example, the 4×4 LFNST can be further reduced to minimize the computational complexity and memory space requirements for storing the transformation coefficients. Such an implementation may be referred to as a reduced inseparable transformation (RST). More specifically, the main concept of the RST is to map an N (where N is 4×4 = 16 in the above example but may also be equal to 64 for an 8×8 block) - dimensional vector to an R - dimensional vector in a different space, where N / R (R < N) represents the dimensionality reduction factor. Thus, instead of an N×N transformation matrix, the RST matrix becomes an R×N matrix as follows,

Number

[0149] Here, the R rows of the transformation matrix are a reduced R basis of the N-dimensional space. Thus, the transformation converts an input vector or N dimensions into an output vector of reduced R dimensions. Thus, as shown in Figure 22, the secondary transformation coefficients 2208 transformed from the primary coefficients 2206 are reduced in dimension by a factor or N / R. The three squares around 2208 in Figure 22 may be padded with zeros.

[0150] The inverse transform matrix of the RTS may be the transpose of its forward transform. For an example 8×8 LFNST (contrasted with the 4×4 LFNST above for more detailed explanation here), an example reduction factor of 4 may be applied, and thus the 64×64 direct non-separable transform matrix is ​​correspondingly reduced to a 16×64 direct matrix. Furthermore, in some implementations, some, but not all, of the input primary coefficients may be linearized into the input vectors of the LFNST. For example, only some of the example 8×8 input primary transform coefficients may be linearized into the X vector above. In a particular example, of the four 4×4 quadrants of the 8×8 primary transform coefficient matrix, the bottom right (high frequency coefficients) may be excluded, and only the other three quadrants are linearized into a 48×1 vector using a predefined scan order rather than a 64×1 vector. In such implementations, the non-separable transform matrix may be further reduced from 16×64 to 16×48.

[0151] Therefore, an exemplary reduced 48×16 inverse RST matrix can be used at the decoder side to generate the top-left, top-right, and bottom-left 4×4 quadrants of the 8×8 core (primary) transform coefficients. Specifically, if a further reduced 16×48 RST matrix is ​​applied instead of a 16×64 RST with the same transform set configuration, the non-separable secondary transform takes as input 48 matrix elements vectorized from the three 4×4 quadrant blocks of the 8×8 primary coefficient block, excluding the bottom-right 4×4 block. In such an implementation, the omitted bottom-right 4×4 primary transform coefficient is ignored in the secondary transform. This further reduced transform converts the 48×1 vector into a 16×1 output vector, which is scanned back to the 4×4 matrix to fill 2208 in FIG. 22. The three squares of secondary transform coefficients surrounding 2208 may be zero-padded.

[0152] With the help of such a reduction in the dimensions of the RST, the memory usage for storing all the LFNST matrices is reduced: in the above example, for example, the memory usage can be reduced from 10 KB to 8 KB with a reasonably small performance degradation compared to an implementation without dimensionality reduction.

[0153] In some implementations, to reduce complexity, LFNST may be further restricted to be applicable only if all coefficients outside the portion of primary transform coefficients subject to LFNST (e.g., outside 2206 portion of 2204 in FIG. 22) are not significant. Thus, when LFNST is applied, all primary-only transform coefficients (e.g., the unshaded portion of primary coefficient matrix 2204 in FIG. 22) may be close to zero. Such a restriction allows for adjustment of LFNST index signaling at the last significant position, thus avoiding additional coefficient scans that may be required to check for significant coefficients at certain positions when this restriction does not apply. In some implementations, the worst-case processing (in terms of multiplications per pixel) of LFNST may limit non-separable transforms of 4×4 and 8×8 blocks to 8×16 and 8×48 transforms, respectively. In such cases, for other sizes less than 16, the last significant scan position must be less than 8 when LFNST is applied. For blocks with shapes of 4×N and N×4 and N>8, the above restrictions mean that LFNST is applied only once to the top-left 4×4 region. When LFNST is applied, all primary-only coefficients are zero, so the number of operations required for the primary transform is reduced in such cases. From the encoder's perspective, quantization of coefficients may be simplified when the LFNST transform is tested. Rate-distortion optimized quantization (RDO) must be done at most for the first 16 coefficients (in scan order), and the remaining coefficients may be forced to be zero.

[0154] In some example implementations, the available RST kernels may be specified as several transform sets, with each transform set including several non-separable transform matrices. For example, there may be a total of four transform sets and two non-separable transform matrices (kernels) for each transform set used in LFNST. These kernels may be pre-trained offline and thus data driven. The offline trained transform kernels may be stored in memory or hard-coded into the encoding or decoding device for use during the encoding / decoding process. The selection of the transform set during the encoding or decoding process may be determined by the intra prediction mode. The mapping from intra prediction mode to transform sets may be predefined. An example of such a predefined mapping is shown in Table 4. For example, as shown in Table 4, if one of the three cross-component linear model (CCLM) modes (INTRA_LT_CCLM, INTRA_T_CCLM, or INTRA_L_CCLM) is used for the current block (i.e., 81<=predModeIntra<=83), transform set 0 may be selected for the current chroma block. For each transform set, the selected non-separable secondary transform candidates may be further specified by an explicitly signaled LFNST index, e.g., the index may be signaled in the bitstream once per intra CU after the transform coefficients.

[0155] [Table 5]

[0156] Since LFNST is restricted in the above example implementation to be applicable only when all coefficients outside the first coefficient subgroup or portion are not significant, the LFNST index coding depends on the position of the last significant coefficient. In addition, the LFNST index may be context coded, but it is independent of the intra prediction mode, and only the first bin may be context coded. Furthermore, LFNST may be applied to intra CUs in both intra and inter slices, and to both luma and chroma. If dual tree is enabled, the LFNST indexes for luma and chroma components may be signaled separately. For inter slices (dual tree is disabled), a single LFNST index is signaled and used for both luma and chroma.

[0157] In some example implementations, when an intra sub-partitioning (ISP) mode is selected, LFNST may be disabled and RST index may not be signaled because performance improvement is likely to be limited even if RST is applied to all feasible partition blocks. Furthermore, disabling RST of ISP prediction residuals may reduce encoding complexity. In some further implementations, when a multiple linear regression intra prediction (MIP) mode is selected, LFNST may also be disabled and RST index may not be signaled.

[0158] Considering that due to the existing maximum transform size limitation (e.g., 64×64), large CUs larger than 64×64 (or any other predefined size representing the maximum transform block size) are implicitly split (e.g., TU tiling), LFNST index lookup can increase data buffering by 4 times for a certain number of decoding pipeline stages. Thus, in some implementations, the maximum size allowed for LFNST may be limited, for example, to 64×64. In some implementations, LFNST may be enabled with DCT2 only as the primary transform.

[0159] In CIIP mode, both inter prediction and intra prediction need to be performed, including both primary and secondary transforms. When performing a primary transform on a block coded in CIIP mode, the primary transform (or primary transform kernel) may have to be selected from available trigonometric and identity transforms, for example, as listed in Table 4. Intra prediction in CIIP mode may be performed under one of DC_PRED, V_PRED, H_PRED, and SMOOTH modes, and the available selection may not be ideal for efficiently decorrelating the residual signal when performing intra prediction using CIIP mode. Since there are various submodes in CIIP, and CIIP modes can include normal CIIP and wedge CIIP, a mechanism for selecting a secondary transform kernel that fits a particular CIIP configuration (e.g., CIIP submode, CIIP weighting mode such as normal CIIP and wedge CIIP) is important. In this disclosure, various implementations aimed at accomplishing at least this task are described.

[0160] In this disclosure, a secondary transform set refers to a group of transform kernel (or candidate) options. A transform set may include one or more transform kernel (or candidate) options.

[0161] In this disclosure, a linear transform may refer to a combination of DCT, ADST, inverted ADST (FLIPADST), LGT, and row-column transform (RCT). For example, a DCT may be applied horizontally and an ADST may be applied vertically to a block.

[0162] In some implementations, under a CIIP mode, the secondary transform may be non-separable. Furthermore, the selection of the non-separable secondary transform may depend on the intra-prediction mode of the intra-prediction portion of the CIIP.

[0163] In some implementations, the CIIP mode may be correlated with the intra-prediction portion of the CIIP. Thus, the selection of the non-separable secondary transform may depend, directly or indirectly, on the CIIP mode.

[0164] In some implementations, when a block is predicted using a CIIP mode, the residual (or residual block, residual matrix) may be coded using a separable / non-separable linear transform, and a non-separable secondary transform, i.e., a combined inter-intra secondary transform (CIIST), may be further applied.

[0165] In some implementations, the secondary transformation may only be non-separable.

[0166] In some implementations, the secondary transformation may only be separable.

[0167] In some implementations, the secondary transformation may be separable or non-separable.

[0168] In some implementations, each intra prediction mode may map or correspond to a transform kernel set including multiple transform kernels. When performing prediction using a CIIP mode, the intra prediction mode (of the intra prediction portion of the CIIP) may be determined based on the CIIP submode. Exemplary CIIP submodes may be found in Table 2 in the previous section. As an example, each CIIP submode may be mapped to an intra prediction mode. Once the intra prediction mode is determined, a secondary transform kernel set may be derived based on the intra prediction mode. The transform kernel for the secondary transform may be determined by signaling, for example, by a signaled kernel index. The transform kernel may also be derived based on the block itself, for example, the pattern of the block.

[0169] In some implementations, the CIIP submodes may be mapped to any one of the DC_PRED, V_PRED, H_PRED, or SMOOTH_PRED modes.

[0170] In some implementations, the II_DC_PRED CIIP sub-mode may be mapped to the DC_PRED intra-prediction mode. A secondary transform kernel set that corresponds to (or is pre-associated with) the DC_PRED intra-prediction mode may be selected.

[0171] In some implementations, when the CIIP submode is II_DC_PRED, the secondary transform kernels may be pre-associated with the DC_PRED intra prediction mode.

[0172] In some implementations, the II_SMOOTH_PRED CIIP sub-mode may be mapped to the SMOOTH_PRED intra-prediction mode. A secondary transform kernel set that corresponds to (or is pre-associated with) the SMOOTH_PRED intra-prediction mode may be selected.

[0173] In some implementations, when the CIIP submode is II_SMOOTH_PRED, the secondary transform kernel may be pre-associated with the SMOOTH_PRED intra prediction mode.

[0174] In some implementations, the II_V_PRED CIIP sub-mode may be mapped to the V_PRED intra-prediction mode. A secondary transform kernel set that corresponds to (or is pre-associated with) the V_PRED intra-prediction mode may be selected.

[0175] In some implementations, when the CIIP submode is II_V_PRED, the secondary transform kernel may be pre-associated with the V_PRED intra prediction mode.

[0176] In some implementations, the II_H_PRED CIIP sub-mode may be mapped to the H_PRED intra-prediction mode. A secondary transform kernel set that corresponds to (or is pre-associated with) the H_PRED intra-prediction mode may be selected.

[0177] In some implementations, when the CIIP submode is II_H_PRED, the secondary transform kernel may be pre-associated with the H_PRED intra prediction mode. In some implementations, further restrictions or preconditions may be imposed when mapping a CIIP submode to an intra prediction mode. For example, a specific weighting mode of the CIIP (e.g., normal CIIP, wedge CIIP) may be required. In one implementation, the scheme for mapping a CIIP submode to an intra prediction mode may be applied only when the CIIP is normal CIIP. As an example normal CIIP, the intra prediction weights associated with a video block depend on the intra prediction mode and decrease along the prediction direction of the intra prediction.

[0178] In some implementations, the scheme for mapping a CIIP sub-mode to an intra-prediction mode may be applied when the CIIP is a wedge CIIP.

[0179] In some implementations, if the CIIP is a wedge CIIP, the kernel for the secondary transform may be selected from the secondary transform kernel set based on a wedge pattern (see the previous section for details on wedge patterns). As an example, the intra prediction weights associated with a video block under a CIIP mode may be characterized by a spatial weighting pattern, which is a wedge pattern.

[0180] In some implementations, if the CIIP is a wedge CIIP, the secondary transformation kernel may be determined directly based on the wedge pattern.

[0181] 23 shows a flowchart 2300 of an exemplary video decoding method according to the principles underlying the above implementation. The method 2300 may include some or all of the following steps: step 2310, determining that the current block is predicted under a CIIP mode, step 2320, generating a set of secondary transform coefficients for the current block from a video bitstream, step 2330, applying a combined inter-intra secondary transform by performing an inverse separable or non-separable secondary transform on the set of secondary transform coefficients to obtain a set of primary transform coefficients of the current block, and performing an inverse primary transform on the set of primary transform coefficients to obtain a residual block of the current block, and step 2340, decoding the current block from the residual block under a CIIP mode.

[0182] In the embodiments and implementations of the present disclosure, any steps and / or operations may be combined or arranged in any quantity or order, as desired. Two or more of the steps and / or operations may be performed in parallel. The embodiments and implementations of the present disclosure may be used separately or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored in a non-transitory computer-readable medium. The embodiments of the present disclosure may be applied to a luma block or a chroma block. The term block may be interpreted as a prediction block, a coding block, or a coding unit, i.e., a CU. The term block here may also be used to refer to a transform block. In the following items, when referring to a block size, it may refer to either the width or height of the block, or the maximum value of the width and height, or the minimum value of the width and height, or the size of the area (width*height), or the aspect ratio of the block (width:height, or height:width).

[0183] The techniques described above may be implemented as computer software using computer readable instructions and physically stored on one or more computer readable media. For example, Figure 24 illustrates a computer system (2500) suitable for implementing certain embodiments of the disclosed subject matter.

[0184] Computer software can be coded using any suitable machine code or computer language that can be amenable to mechanisms such as assembly, compilation, linking, etc. to create code including instructions that can be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc. directly, or via interpretation, microcode execution, etc.

[0185] The instructions may be executed on various types of computers or computer components including, for example, personal computers, tablet computers, servers, smart phones, gaming consoles, Internet of Things devices, and the like.

[0186] 24 for the computer system (2500) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of the computer system (2500).

[0187] The computer system (2500) may include certain human interface input devices. Such human interface input devices may respond to input by one or more human users through, for example, tactile input (keystrokes, swipes, data glove movements, etc.), audio input (voice, clapping, etc.), visual input (gestures, etc.), olfactory input (not shown). The human interface devices may also be used to capture certain media not necessarily directly associated with conscious human input, such as audio (voice, music, ambient sounds, etc.), images (scanned images, photographic images obtained from still image cameras, etc.), and video (two-dimensional video, three-dimensional video including stereoscopic video, etc.).

[0188] The input human interface devices may include one or more (only one of each shown) of a keyboard (2501), a mouse (2502), a trackpad (2503), a touch screen (2510), a data glove (not shown), a joystick (2505), a microphone (2506), a scanner (2507), and a camera (2508).

[0189] The computer system (2500) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, for example, through haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (2510), data gloves (not shown), or joystick (2505), although some haptic feedback devices may not function as input devices), audio output devices (speakers (2509), headphones (not shown), etc.), visual output devices (screens (2510), including CRT screens, LCD screens, plasma screens, OLED screens, etc., each with or without touch screen input capability, each with or without haptic feedback capability, some capable of outputting two-dimensional visual output or three or more dimensional output by means of stereographic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown), and printers (not shown).

[0190] The computer system (2500) may also include human accessible storage devices and associated media, such as optical media, including CD / DVD ROM / RW (2520) with media (2521) such as CDs / DVDs, thumb drives (2522), removable hard drives or solid state drives (2523), legacy magnetic media such as tapes and floppy disks (not shown), and dedicated ROM / ASIC / PLD based devices such as security dongles (not shown).

[0191] Those skilled in the art should also understand that the term "computer-readable medium" as used in connection with the subject matter of this disclosure does not encompass transmission media, carrier waves, or other transitory signals.

[0192] The computer system (2500) may also include an interface (2554) to one or more communication networks (2555). The network may be, for example, wireless, wired, optical. The network may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LAN, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable television, satellite television, and terrestrial broadcast television, vehicular and industrial including CAN bus, etc. Certain networks typically require an external network interface adapter attached to a particular general-purpose data port (e.g., a USB port of the computer system (2500)) or peripheral bus (2549), while other networks are typically integrated into the core of the computer system (2500) by attachment to a system bus as described below (e.g., an Ethernet interface to a PC computer system, or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (2500) can communicate with other entities. Such communications may be unidirectional, receive only (e.g., television broadcast), unidirectional transmit only (e.g., CANbus to a particular CANbus device), or bidirectional, for example, to other computer systems using local or wide area digital networks. Specific protocols and protocol stacks may be used in each of these networks and network interfaces, as described above.

[0193] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (2540) of the computer system (2500).

[0194] The cores (2540) may include one or more central processing units (CPUs) (2541), graphics processing units (GPUs) (2542), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (2543), hardware accelerators for specific tasks (2544), graphics adapters (2550), etc. These devices may be connected through a system bus (2548), along with read-only memory (ROM) (2545), random access memory (2546), internal mass storage (2547) such as an internal hard drive or SSD that is not accessible to the user. In some computer systems, the system bus (2548) is accessible in the form of one or more physical plugs, allowing expansion with additional CPUs, GPUs, etc. Peripheral devices may be attached directly to the core's system bus (2548) or through a peripheral bus (2549). In one example, a screen (2510) may be connected to the graphics adapter (2550). Architectures for peripheral buses include PCI, USB, etc.

[0195] The CPU (2541), GPU (2542), FPGA (2543), and accelerator (2544) may combine to execute certain instructions that may constitute the aforementioned computer code. The computer code may be stored in a ROM (2545) or a RAM (2546). Persistent data may be stored, for example, in an internal mass storage (2547), while transitory data may also be stored in a RAM (2546). The use of cache memory, which may be closely associated with one or more CPUs (2541), GPUs (2542), mass storage (2547), ROM (2545), RAM (2546), etc., allows for fast storage and retrieval from any memory device.

[0196] The computer-readable medium can bear computer code for performing various computer-implemented operations. The medium and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the available kind well known to those skilled in the computer software arts.

[0197] As a non-limiting example, a computer system (2500) having an architecture, and specifically a core (2540), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be the user-accessible mass storage introduced above, as well as media associated with a particular storage of the core (2540) of a non-transitory nature, such as the core internal mass storage (2547) or ROM (2545). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (2540). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (2540), and specifically the processor therein (including a CPU, GPU, FPGA, etc.) to perform a particular process or a particular portion of a particular process described herein, including defining data structures stored in RAM (2546) and modifying such data structures according to a process defined by the software. Additionally or alternatively, the computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator (2544)), which may operate in place of or in conjunction with software to perform particular processes or particular portions of particular processes described herein. References to software may encompass logic, and vice versa, where appropriate. References to computer-readable media may encompass circuitry (such as integrated circuits (ICs)) that stores software for execution, circuitry that embodies logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0198] While this disclosure describes several exemplary embodiments, there are alterations, permutations, and various substitute equivalents that fall within the scope of this disclosure. Thus, it will be appreciated that those skilled in the art can devise numerous systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and are therefore within the spirit and scope of the present disclosure. Appendix A: Acronyms JEM: Joint Exploration Model VVC: Versatile Video Coding BMS: Benchmark Set MV: Motion Vector HEVC: High Efficiency Video Coding SEI: Supplemental Extended Information VUI: Video Usability Information GOP: Group of Pictures TU: conversion unit PU: Prediction unit CTU: Coding Tree Unit CTB: coding tree block PB: Predicted block HRD: Hypothetical Reference Decoder SNR: Signal to Noise Ratio CPU: Central Processing Unit GPU: Graphics Processing Unit CRT: cathode ray tube LCD: Liquid crystal display OLED: Organic Light Emitting Diode CD:Compact Disc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random Access Memory ASIC: Application Specific Integrated Circuit PLD: Programmable Logic Device LAN: Local Area Network GSM: Global System for Mobile Communications LTE: Long Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: Field Programmable Gate Area SSD: Solid State Drive IC: Integrated Circuit HDR: High Dynamic Range SDR: Standard Dynamic Range JVET: Joint Video Exploration Team MPM: Most Probable Mode WAIP: Wide-angle Intra Prediction CU: coding unit PU: Prediction Unit TU: conversion unit CTU: Coding Tree Unit PDPC: Position-dependent prediction combination ISP: Intra Subpartition SPS: Sequence Parameter Settings PPS: Picture Parameter Set APS: Adaptive Parameter Set VPS: Video Parameter Set DPS: Decoding Parameter Set ALF: Adaptive Loop Filter SAO: Sample Adaptive Offset CC-ALF: Cross-component adaptive loop filter CDEF: Constrained directional enhancement filter CCSO: Cross component sample offset LSO: Local Sample Offset LR: Loop recovery filter AV1:AOMedia Video 1 AV2:AOMedia Video 2 [Explanation of symbols]

[0199] 101 Point where the arrows converge, sample 102 Arrow 103 Arrow 104 Square Block 180 Schematic diagram showing intra prediction direction 201 Block 202 Surrounding Samples 203 Surrounding Samples 204 Surrounding Samples 205 Surrounding Samples 206 Surrounding Samples 300 Communication Systems 310 Terminal Devices 320 Terminal Devices 330 Terminal Devices 340 Terminal Devices 350 Communication Network 400 Communication Systems 401 Video Source 402 Video Picture Stream 403 Video Encoder 404 Encoded video data 405 Streaming Server 406 Client Subsystem 407 encoded video data 409 encoded video data 410 Video Decoder 411 Video Picture Output Stream 412 Display 413 Video Capture Subsystem 420 Electronic Devices 430 Electronic Devices 501 Channel 510 Video Decoder 512 Display, rendering device 515 Buffer Memory 520 Entropy Decoder / Parser 521 Symbols 530 Electronic Devices 531 Receiver 551 Scaler / Descaler Unit 552 Intra-picture prediction unit 553 Motion Compensation Prediction Unit 555 Aggregator 556 Loop Filter Unit 557 Reference Picture Memory 558 Picture Buffer 601 Video Sources 603 Video Coder, Video Encoder 620 Electronic Devices, Encoders 630 Source Coder 632 Coding Engine 633 Local Video Decoder, Decoding Unit 634 Reference Picture Memory, Reference Picture Cache 635 Predictor 640 Transmitter 643 coded video sequence 645 Entropy Coder 650 Controller 660 Communication Channels 703 Video Encoder 721 General-purpose controller 722 Intra Encoder 723 Residual Calculator 724 Residual Encoder 725 Entropy Encoder 726 Switch 728 Residual Decoder 730 InterEncoder 810 Video Decoder 871 Entropy Decoder 872 Intra Decoder 873 Residual Decoder 874 Reconstruction Module 880 Interdecoder 902 Base Block 904 Base Block 906 Base Block 908 Base Block 1002 "T-shaped" partition, pattern 1004 "T-shaped" partition, pattern 1006 "T-shaped" partition, pattern 1008 "T-shaped" partition, pattern 1010 Square Partition 1102 Vertical bisection (SPLIT_BT_VER) 1104 Horizontal split into two (SPLIT_BT_HOR) 1106 Vertical third division (SPLIT_TT_VER) 1108 Horizontal third division (SPLIT_TT_HOR) 1200 CTB 1202 Square Partition 1204 Square Partition 1206 Square Partition 1208 Square Partition 1302 Square coding block 1304 First Level Split 1306 Second Level Split 1402 Inter-coded Blocks 1404 Conversion Block 1702 Block 1704 Reference Sample 1706 adjacent samples 1708 Reference sample, adjacent sample 1710 Sample 2002 4x4 blocks, 8x8 blocks 2010 Sample 2202 Forward linear transformation 2204 Linear transformation coefficient matrix 2206 Shaded area, linear coefficient 2208 Secondary Conversion Coefficients 2300 Flowchart 2500 Computer System 2501 Keyboard 2502 Mouse 2503 Trackpad 2505 Joystick 2506 Microphone 2507 Scanner 2508 Camera 2509 Speaker 2510 Touch Screen 2520 CD / DVD ROM / RW 2521 CD / DVD and other media 2522 Thumb Drive 2523 Removable Hard Drive or Solid State Drive 2540 cores 2541 Central Processing Unit (CPU) 2542 Graphics Processing Unit (GPU) 2543 Field Programmable Gate Area (FPGA) 2544 Hardware Accelerator 2545 Read-Only Memory (ROM) 2546 Random Access Memory (RAM) 2547 cores internal large capacity storage 2548 System Bus 2549 Surrounding Bus 2550 Graphics Adapter 2554 Interface 2555 Communication Network

Claims

1. 1. A method for decoding a current block from a video bitstream, comprising: determining that the current block is predicted under a combined inter-intra prediction (CIIP) mode; generating a set of secondary transform coefficients for the current block from the video bitstream; performing an inverse separable or non-separable secondary transform on the set of secondary transform coefficients to obtain a set of primary transform coefficients of the current block; performing an inverse linear transform on the set of linear transform coefficients to obtain a residual block of the current block; applying a combined inter-intra quadratic transformation by decoding the current block from the residual block under the CIIP mode; A method comprising:

2. determining a CIIP sub-mode of the CIIP mode for the current block from the video bitstream among a set of candidate CIIP sub-modes, the CIIP sub-mode indicating an intra prediction mode among a set of intra prediction modes used under the CIIP mode for the current block; determining a transform kernel for use in the inverse separable or non-separable quadratic transform based on the intra-prediction mode; The method of claim 1 further comprising:

3. The step of determining the transformation kernel comprises: determining a transform kernel set from among a plurality of transform kernel sets based on the intra-prediction mode; extracting from the video bitstream a kernel selection indicator associated with the current block; selecting the transformation kernel from the set of transformation kernels based on the kernel selection indicator; 3. The method of claim 2, comprising:

4. The set of intra prediction modes is: DC_PRED mode, V_PRED mode, H_PRED mode, or SMOOTH_PRED mode 3. The method of claim 2, comprising one or more of:

5. The set of CIIP submode candidates includes: II_DC_PRED mode, II_V_PRED mode, II_H_PRED mode, or II_SMOOTH_PRED mode The method according to any one of claims 2 to 4, comprising at least one of:

6. determining, in response to the CIIP submode being the II_DC_PRED mode, that the transform kernel is pre-associated with a DC_PRED intra prediction mode; determining, in response to the CIIP submode being the II_V_PRED mode, that the transform kernel is pre-associated with a V_PRED intra prediction mode; determining, in response to the CIIP submode being the II_H_PRED mode, that the transform kernel is pre-associated with an H_PRED intra prediction mode; The method of claim 5 , further comprising: determining, in response to the CIIP submode being the II_SMOOTH_PRED mode, that the transform kernel is pre-associated with a SMOOTH_PRED intra-prediction mode.

7. 4. The method of claim 3, wherein the step of determining a transform kernel set from among a plurality of transform kernel sets based on the intra prediction mode is performed only in response to determining that intra prediction weights of samples of the current block under the CIIP mode are based on derivation of a formula from the positions of the samples.

8. The method of claim 7 , wherein the intra prediction weights of the samples of the current block depend on the intra prediction mode and decrease along a prediction direction of intra prediction.

9. The method of claim 1 , wherein the intra prediction weights associated with the current block under the CIIP mode include a spatial weighting pattern among a set of predetermined spatial weighting patterns.

10. determining a transform kernel for use in the inverse separable quadratic transform based on the spatial weighting pattern.

10. The method of claim 9, further comprising:

11. extracting from the video bitstream a spatial weighting pattern indicator indicative of the spatial weighting pattern among the set of predetermined spatial weighting patterns; determining the spatial weighting pattern according to the spatial weighting pattern indicator; 10. The method of claim 9, further comprising:

12. 1. A device for decoding a current block from a video bitstream, the device comprising: a memory for storing computer instructions; and a processor in communication with the memory, the processor, when executing the computer instructions, causing the device to: determining that the current block is predicted under a CIIP mode; generating a set of secondary transform coefficients for the current block from the video bitstream; performing an inverse separable or non-separable secondary transform on the set of secondary transform coefficients to obtain a set of primary transform coefficients of the current block; performing an inverse linear transform on the set of linear transform coefficients to obtain a residual block of the current block; applying a combined inter-intra quadratic transformation by Decoding the current block from the residual block under the CIIP mode. The device is configured to:

13. When the processor executes the computer instructions, the processor further causes the device to: determining a CIIP sub-mode of the CIIP mode for the current block from the video bitstream among a set of CIIP sub-mode candidates, the CIIP sub-mode indicating an intra prediction mode among a set of intra prediction modes used under the CIIP mode for the current block; determining a transform kernel for use in the inverse separable or non-separable secondary transform based on the intra-prediction mode; 13. The device of claim 12, configured to:

14. When the processor is configured to cause the device to determine the transformation kernel, determining a transform kernel set from among a plurality of transform kernel sets based on the intra prediction mode; extracting from the video bitstream a kernel selection indicator associated with the current block; Selecting the transformation kernel from the set of transformation kernels based on the kernel selection indicator The device of claim 13, comprising:

15. The set of intra prediction modes is: DC_PRED mode, V_PRED mode, H_PRED mode, or SMOOTH_PRED mode 14. The device of claim 13, comprising one or more of:

16. The set of CIIP submode candidates includes: II_DC_PRED mode, II_V_PRED mode, II_H_PRED mode, or II_SMOOTH_PRED mode 16. The device according to claim 13, comprising at least one of:

17. In response to the CIIP submode being the II_DC_PRED mode, the processor is configured to cause the device to determine that the transform kernel is pre-associated with a DC_PRED intra prediction mode; In response to the CIIP submode being the II_V_PRED mode, the processor is configured to cause the device to determine that the transform kernel is pre-associated with a V_PRED intra prediction mode; In response to the CIIP submode being the II_H_PRED mode, the processor is configured to cause the device to determine that the transform kernel is pre-associated with an H_PRED intra-prediction mode; 17. The device of claim 16, wherein in response to the CIIP submode being the II_SMOOTH_PRED mode, the processor is configured to cause the device to determine that the transform kernel is pre-associated with a SMOOTH_PRED intra-prediction mode.

18. 12. A program comprising computer readable instructions which, when executed by a processor, cause the processor to perform the method of any one of claims 1 to 11.

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