Improvement of intra-mode coding

Abstract

To provide a method and a device for improving intra-mode decoding of a video.SOLUTION: A method includes the steps of: receiving a coded video stream including a set index and a position index for intra-prediction of a current block; determining an intra-prediction mode corresponding to at least one adjacent block of the current block in the video stream as a reference mode; determining P pieces of the previously defined intra-prediction modes into M pieces of intra-prediction mode sets, on the basis of the reference mode; identifying a target intra-prediction mode among P pieces of the previously defined intra-prediction modes; and decoding the current block of the coded video stream, on the basis of at least the target intra-prediction mode identified on the basis of the set index and the position index of the current block.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] This application is based on and claims the benefit of priority to U.S. Nonprovisional Patent Application No. 17 / 573,306, filed January 11, 2022, which claims priority to U.S. Provisional Patent Application No. 63 / 209,806, entitled "IMPROVED INTRA MODE CODING," filed June 11, 2021. Both applications are incorporated herein by reference in their entireties.

[0002] This disclosure describes a collection of modern video coding techniques. More specifically, the disclosed techniques include various schemes for intra-mode coding. [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 can be performed using inter-picture prediction with motion compensation. Uncompressed digital video can 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 can 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 bitrate 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 approaching 1.5 Gbit / s. One hour of such video requires more than 600 Gbytes of storage space.

[0005] One goal of video coding and video 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 used. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal by the 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 recovered 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 will be small enough to make the reconstructed signal useful for its intended application, even with some information loss. For video, lossy compression has been 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 can therefore be used as the first picture in a coded video bitstream and video session or as a still image. 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 the block of data being intra-coded or intra-decoded in decoding order, 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] There may be many different forms of intra-prediction. 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 separately 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 refined 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 set of neighboring samples 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 nine predictor directions specified in the 33 possible predictor directions of H.265 (corresponding to the 33 angle modes of the 35 intra modes specified in H.265). The point where the arrows converge (101) represents the sample being predicted. The arrows represent the direction from which adjacent samples are used to predict sample 101. For example, arrow (102) indicates that sample (101) is predicted from one or more adjacent samples to the upper right, at an angle of 45 degrees from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from one or more adjacent samples to the lower left of sample (101), at an angle of 22.5 degrees from the horizontal.

[0012] 1A, at the top left is depicted 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 size of the block is 4×4 samples, S44 is at the bottom right. Also shown are examples of reference samples that follow a similar numbering scheme. The reference samples are labeled with R, their 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 neighboring 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, S14 are predicted from the same reference sample R05. Then, sample S44 is predicted from reference sample R08.

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

[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 a certain bit penalty for the direction. 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] The mapping of bits representing intra-prediction directions to prediction directions in a coded video bitstream may vary across video coding techniques, and may range, for example, from simple direct mappings of prediction directions to intra-prediction modes to complex adaptation schemes involving codewords, most likely 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 properly designed video coding technique, less likely directions are represented by more bits than 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 (hereafter 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 to be used (similar to the temporal dimension).

[0019] In some video compression techniques, a current MV applicable to a particular area of ​​sample data can 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 can 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 can 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 can further be represented with fewer bits after entropy coding than would be used if the MV was directly coded instead of predicted from the neighboring MV(s). In some cases, MV prediction can be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., a 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 Rec. 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 previous block of the same size but spatially shifted. Instead of coding its MV directly, the MV can be derived from metadata associated with one or more reference pictures, e.g., from the last reference picture (in decoding order), using the MV associated with any one of the five surrounding samples represented by A0, A1, and B0, B1, B2 (202 to 206, respectively). In H.265, MV prediction can 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 provide methods and apparatus for video encoding and decoding, including various schemes for intra-mode coding.

[0023] In some example implementations, a method for performing intra prediction on a current block in a coded video stream is disclosed, which includes the steps of receiving a coded video stream including a set index and a position index for intra prediction of the current block, determining an intra prediction mode corresponding to at least one neighboring block of the current block in the video stream as a reference mode, and determining a method for dividing P predefined intra prediction modes into M intra prediction mode sets based on the reference mode, each intra prediction mode set being one of N i N position-indexed intra-prediction modes, where P and M are integers greater than 1, ithe number of prediction modes in the i-th intra-prediction mode set, where i is an integer representing an intra-prediction mode set index among the M intra-prediction mode sets; identifying a target intra-prediction mode from among the P predefined intra-prediction modes based on the received set index, position index, and splitting method; and decoding a current block of the coded video stream based at least on the target intra-prediction mode identified based on the set index and position index of the current block.

[0024] In the above implementation, N max is a power of 2, and N max is N i In some implementations, when M is greater than 2, N i is selected from the first number and the second number. In some implementations, N i is the same value for all M intra-prediction mode sets. In some implementations, one of the M intra-prediction mode sets includes the second number of intra-prediction modes and all other of the M intra-prediction mode sets include the first number of intra-prediction modes. In some implementations, M=4 and N max In some implementations, P=61, the first number is 16, and the second number is 13.

[0025] In some example implementations described above, the P predefined intra-prediction modes may include a subset of non-directional intra-prediction modes, and the relative order of the subset of non-directional intra-prediction modes within the M intra-prediction mode set is fixed regardless of the reference mode.

[0026] In some example implementations described above, the subset of non-directional intra-prediction modes is in the first intra-prediction mode set among the M intra-prediction mode sets, regardless of the reference mode.

[0027] In some example implementations described above, the non-directional subset of intra-prediction modes includes a DC prediction mode that is always arranged as the first in the order within the initially located intra-prediction mode set, regardless of the reference mode.

[0028] In some example implementations above, the intra-prediction mode based on recursive filtering is signaled as a sub-mode of the DC prediction mode.Furthermore, the subset of the non-directional intra-prediction modes may include a SMOOTH prediction mode that is always arranged as the second in the first intra-prediction mode set, regardless of the reference mode.In some implementations, the subset of the non-directional intra-prediction modes includes a SMOOTH_V prediction mode that is always arranged as the third in the first intra-prediction mode set, regardless of the reference mode.

[0029] In some example implementations described above, the subset of non-directional intra-prediction modes may include the SMOOTH_H prediction mode, which is always positioned as the fourth in order within the initially located intra-prediction mode set, regardless of the reference mode.

[0030] In some example implementations described above, the subset of non-directional intra-prediction modes may include the PAETH prediction mode, which is always positioned as the fifth in the order within the initially located intra-prediction mode set, regardless of the reference mode.

[0031] In some example implementations described above, the P predefined intra prediction modes may include an intra prediction mode based on recursive filtering, which is arranged as the first intra prediction mode set among the M intra prediction mode sets regardless of the reference mode, and which is signaled independently of the DC intra prediction mode.

[0032] In some example implementations above, if the identified target intra-prediction mode for the current block is an intra-prediction mode based on recursive filtering, the method may further include determining which of the set of intra-prediction modes based on recursive filtering is selected separately from the set index and the position index.

[0033] In some example implementations described above, the intra-prediction mode based on recursive filtering is always placed in the sixth position in the first-located intra-prediction mode set, regardless of the reference mode. The P predefined intra-prediction modes include at least one directional intra-prediction mode, at least one non-directional intra-prediction mode, and at least one luma-to-chroma intra-prediction mode.

[0034] Aspects of the present disclosure also provide an apparatus including a processing circuit configured to perform any one of the above-described method implementations for video decoding and / or encoding. 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 above-described method implementations for video decoding and / or encoding.

[0035] 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]

[0036] [Figure 1A] FIG. 2 is a schematic diagram of an example subset of intra-prediction direction 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] FIG. 1 is a schematic diagram illustrating a simplified block diagram of a communication system (300) according to an exemplary embodiment. [Figure 4] FIG. 4 is a schematic diagram illustrating a simplified block diagram of a communication system (400) according to an exemplary embodiment. [Diagram 5] FIG. 2 is a schematic diagram illustrating a simplified block diagram of a video decoder according to an exemplary embodiment. [Figure 6] FIG. 1 is a schematic diagram illustrating a simplified block diagram of a video encoder according to an exemplary embodiment. [Figure 7] FIG. 2 is a block diagram illustrating a video encoder according to another example embodiment. [Figure 8] FIG. 2 is a block diagram illustrating a video decoder according to another exemplary embodiment. [Figure 9] 1 illustrates directional intra-prediction modes according to an embodiment of the present disclosure. [Figure 10] 1 illustrates a non-directional intra-prediction mode according to an embodiment of the present disclosure. [Figure 11] 1 illustrates a recursive intra prediction mode according to an embodiment of the present disclosure. [Figure 12] 1 illustrates partitioning and scanning of transform blocks for intra-prediction blocks according to an embodiment of the present disclosure. [Figure 13] 1 illustrates partitioning and scanning of transform blocks for inter-prediction blocks according to an embodiment of the present disclosure. [Figure 14] 1 illustrates a flowchart according to an exemplary embodiment of the present disclosure. [Figure 15] FIG. 1 illustrates a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] FIG. 3 shows a simplified block diagram of a communication system (300) according to an embodiment of the present disclosure. The communication system (300) includes, for example, a plurality of terminal devices that can communicate with each other 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. One-way data transmission may be implemented, for example, for media serving applications.

[0038] 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 implemented, 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.

[0039] 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 the applicability of the principles underlying the present disclosure is not 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 (wired connection) and / or wireless communication networks. The communication network (350) 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 discussion, the architecture and topology of the network (350) may not be important to the operation of the present disclosure unless explicitly described herein.

[0040] 4 illustrates an arrangement of video encoders and video decoders in a video streaming environment as an example of an application of the disclosed subject matter. The disclosed subject matter may be equally applied to other video-enabled 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.

[0041] The video streaming system may include a video source (401), such as a video capture subsystem (413), which may include a digital camera, for creating a stream of uncompressed video pictures or images (402). 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 in bold to emphasize its high amount of data compared to the encoded video data (404) (or coded video bitstream), may be processed by an electronic device (420) including 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 implement 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 on the streaming server (405) or on 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 obtain copies (407) and (409) of the encoded video data (404). The client subsystem (406) may include a video decoder (410), for example, in 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 perform 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.

[0042] 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).

[0043] 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) can be included in an electronic device (530). The electronic device (530) can include a receiver (531) (e.g., receiving circuitry). The video decoder (510) can be used in place of the video decoder (410) in the example of FIG. 4.

[0044] 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 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) (hereafter "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 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, which may be relatively large in size. 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).

[0045] The video decoder (510) may include a parser (520) for reconstructing 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(s) may be in the form of a supplemental enhancement information (SEI message) or a video usability information (VUI) parameter set fragment (not shown). 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 according to 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.

[0046] The parser (520) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515) to produce symbols (521).

[0047] 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.

[0048] Beyond 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, in order to clearly describe the various functions of the disclosed subject matter, the following disclosure adopts a conceptual subdivision into functional units.

[0049] The first unit is a scalar / inverse transform unit (551). The scalar / inverse transform unit (551) 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 a block comprising sample values ​​that may be input to an aggregator (555).

[0050] 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 may 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 blocks of the same size and shape as the block being reconstructed using information of surrounding blocks already reconstructed and stored in a current picture buffer (558). The current picture buffer (558) buffers, for example, a partially reconstructed and / or a fully reconstructed current picture. The aggregator (555) may, in some implementations, add prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551) on a sample-by-sample basis.

[0051] 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) associated with 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) that 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.

[0052] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in the loop filter unit (556). The video compression techniques are controlled by parameters contained in the coded video sequence (also referred to as the coded video bitstream) and may include in-loop filter techniques available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to meta-information obtained during decoding of a previous portion (in decoding order) of the coded picture or coded video sequence, or to previously reconstructed, loop filtered sample values. 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.

[0053] The output of the loop filter unit (556) may be a sample stream that can be output to a rendering device (512) and also stored in a reference picture memory (557) for use in future inter-picture prediction.

[0054] Once a particular coded picture is fully reconstructed, it can 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 as a reference picture (e.g., by the parser (520)), the current picture buffer (558) can become part of the reference picture memory (557), and a new current picture buffer can be reallocated before beginning reconstruction of the next coded picture.

[0055] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard such as ITU-T Rec. H.265. The coded video sequence may conform to a syntax specified by the video compression technique or standard being 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 certain tools from among all tools available in the video compression technique or standard as tools dedicated to use only 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 hypothetical reference decoder (HRD) specification and metadata for HRD buffer management signaled in the coded video sequence.

[0056] In some exemplary 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(s). The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately recover 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.

[0057] 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.

[0058] 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 image(s) 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).

[0059] 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 that may store 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 multiple individual pictures or images that give motion when viewed in sequence. The picture itself may be organized as a spatial array of pixels, each of which 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.

[0060] 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 of rate distortion optimization technique, 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 related to the video encoder (603) optimized for a particular system design.

[0061] 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 creating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture(s)) 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 if 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 leads to bit-exact results regardless of the location of the decoder (local or remote), the contents in 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 will "see" when using prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift if synchrony cannot be maintained, e.g., due to channel errors) is used to improve coding quality.

[0062] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, such as the video decoder (510), described in detail above in connection 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.

[0063] At this point, it can be said that any decoder technology, except for parsing / entropy decoding, which may only exist in the decoder, may also necessarily need to exist in the corresponding encoder in substantially the same functional form. For this reason, the subject matter of the disclosure 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 given below.

[0064] 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 the reference picture(s) that may be selected as predictive reference(s) to the input picture. The terms "residue" and its adjective form "residual" may be used interchangeably.

[0065] 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 be a replica of the source video sequence, usually 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 and store the reconstructed reference pictures in a reference picture cache (634). In this way, the video encoder (603) may locally store (without transmission errors) copies of reconstructed reference pictures that have common content with reconstructed reference pictures obtained by a far-end (remote) video decoder.

[0066] The predictor (635) may perform a predictive 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 can serve as suitable prediction references for the new picture. The predictor (635) may operate on sample blocks on a pixel block by pixel block basis to find a suitable prediction reference. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (634).

[0067] 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.

[0068] The output of all the aforementioned functional units may be entropy coded 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.

[0069] The transmitter (640) may buffer the coded video sequence(s) created by the entropy coder (645) in preparation for transmission over a communication channel (660), which may be a hardware / software link to a storage device that will store 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).

[0070] The controller (650) may manage the operation of the video encoder (603). During coding, the controller (650) may 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:

[0071] An intra picture (I-picture) may be a picture that can be coded and decoded without using any other picture in a sequence as a prediction source. 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 and their respective uses and characteristics.

[0072] A predictive picture (P picture) may be a picture that can be coded and decoded using intra- or inter-prediction, which predicts the sample values ​​of each block using at most one motion vector and reference index.

[0073] A bidirectionally predicted picture (B-picture) may be a picture that can be coded and decoded using intra- or inter-prediction, which predicts sample values ​​for each block using up to two motion vectors and reference indexes. Similarly, a multi-predictive picture may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0074] 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. Blocks may be predictively coded with reference to other (already coded) blocks as determined by the coding assignment applied to the block's respective picture. For example, blocks of an I picture may be non-predictively coded or predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of a P picture may be predictively coded via spatial prediction or via temporal prediction with reference to one previously coded reference picture. Blocks of a B picture may be predictively coded by spatial prediction or by temporal prediction with reference to one or two previously coded reference pictures. Source pictures or intermediate processed pictures 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.

[0075] The video encoder (603) may perform coding operations in accordance with a given video coding technique or standard, such as ITU-T Rec. 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.

[0076] 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 or slices, SEI messages, VUI parameter set fragments, etc.

[0077] Video may be captured as multiple source pictures (video pictures) in 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 resembles 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.

[0078] 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.

[0079] Additionally, merge mode techniques may be used to improve coding efficiency in inter-picture prediction.

[0080] 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), namely, one luma CTB and two chroma CTBs. Each CTU may be recursively quad-tree 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 its prediction type among various prediction types, such as inter prediction type and 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 on a prediction block basis. The division of a CU into PUs (or PBs of different color channels) may be performed 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.

[0081] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of this 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) may be used in place of the example video encoder (403) of FIG. 4.

[0082] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a prediction block of 8x8 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 motion vectors are 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. Accordingly, 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.

[0083] 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-purpose controller (721), and an entropy encoder (725), coupled to each other as shown in the exemplary configuration of FIG.

[0084] 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 an inter-encoding technique), 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 video information encoded using a decoding unit 633 incorporated in the example encoder 620 of FIG. 6 (shown as a residual decoder 728 of FIG. 7, as described in more detail below).

[0085] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block to 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) may calculate intra prediction results (e.g., predicted blocks) based on the intra prediction information and reference blocks in the same picture.

[0086] 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 predication 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.

[0087] 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 appropriately by the intra-encoder (722) and the inter-encoder (730). 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.

[0088] The entropy encoder (725) may be configured to format a bitstream to include the encoded blocks 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. Residual information may not be present when coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode.

[0089] 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) may be used in place of the example video decoder (410) of FIG. 4.

[0090] 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 configuration of FIG. 8.

[0091] The entropy decoder (871) may be configured to recover 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-mode, inter-mode, bi-predictive mode, merged submode, or another submode) that may identify the mode in which the block is coded, certain samples or metadata used for prediction by the intra-decoder (872) or inter-decoder (880), residual information, for example in the form of quantized transform coefficients, etc. In one example, if the prediction mode is an inter-mode or bi-predictive 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).

[0092] The inter decoder (880) may be configured to receive the inter prediction information and generate inter prediction results based on the inter prediction information.

[0093] The intra decoder (872) may be configured to receive intra prediction information and to generate a prediction result based on the intra prediction information.

[0094] 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 quantization parameters (QPs)), which may be provided by the entropy decoder (871) (datapath not shown as this may be only a small amount of control information).

[0095] 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 deblocking operations, may be performed to improve visual quality.

[0096] 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.

[0097] Returning to the intra prediction process, samples in a block (e.g., a luma or chroma prediction block, or a coding block if not further divided into prediction blocks) are predicted by samples from neighbors, second neighbors, or one or more other lines, or a combination 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 used to predict the samples, the direction to go in selecting a prediction sample from one or more prediction lines, and other special intra prediction modes.

[0098] For example, the set of intra-prediction modes (also referred to as "intra modes") may include a predefined number of directional intra-prediction modes. As described above with respect to the implementation of FIG. 1, these intra-prediction modes may correspond to a predefined number of directions to follow when selecting samples outside a particular block as destinations for samples being predicted within the particular block. In another particular implementation, eight primary directional modes corresponding to angles from 45 to 207 degrees relative to the horizontal axis may be the supported predefined modes.

[0099] In other implementations of intra prediction, the directional intra modes may be further extended to a finer set of angles to further exploit more types of spatial redundancy in the directional texture. For example, as shown in FIG. 9, the above eight angle implementation may be configured to provide eight named angles (referred to as V_PRED, H_PRED, D45_PRED, D135_PRED, D113_PRED, D157_PRED, D203_PRED and D67_PRED), and each named angle may be added with a predefined number (e.g., seven) of smaller angles. This extension results in a large 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 angles may be represented by named intra angles and associated angle deltas. In the particular example above where there are seven angular directions with small increments for each named angle, the angular increments may be from -3 to 3, with increasing step sizes in increments of 3 degrees.

[0100] In some implementations, in addition to or instead of the above directional intra modes, a number of non-directional predefined intra prediction modes may also be predefined and 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 examples of these non-directional modes is shown in FIG. 10. For example, FIG. 10 shows how a 4×4 block 1002 is predicted by samples obtained from the neighboring line above and / or the neighboring line to the left. A particular sample 1010 in block 1002 may correspond to sample 1004 directly above sample 1010 in the top neighborhood of block 1002, sample 1006 located above and to the left of sample 1010 as an intersection of the top neighborhood and the left neighborhood, and sample 1008 located directly to the left of sample 1010 in the left neighborhood of block 1002. In an example DC intra prediction mode, the average value of left neighborhood sample 1008 and top neighborhood sample 1004 may be used as the predicted value of sample 1010. In an example PAETH intra prediction mode, the top, left and top left reference samples 1004, 1008 and 1006 may be taken, 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 1010. In an example SMOOTH_V intra prediction mode, sample 1010 may be predicted by a vertical quadratic interpolation of the top-left neighbor sample 1006 and the left neighbor sample 1008. In an example SMOOTH_H intra prediction mode, sample 1010 may be predicted by a horizontal quadratic interpolation of the top-left neighbor sample 1006 and the above neighbor sample 1004. In an example SMOOTH intra prediction mode, sample 1010 may be predicted by an average of the vertical and horizontal quadratic interpolations.The above non-directional intra mode implementations are shown as non-limiting examples only: other neighboring lines, other non-directional sample selection methods, and combinations of prediction samples to predict a particular sample within a prediction block are also possible.

[0101] The bitstream may signal which intra prediction mode is selected by the encoder from the above directional and non-directional modes for various coding scales (picture, slice, block, unit, etc.). In some implementations, eight typical named directional modes may be signaled first along with five smooth modes without angles (total of 13 options). Then, if the signaled mode is one of the eight intra modes with named angles, an index indicating the selected angle step for the corresponding signaled named angle may be further signaled. In other implementations, all intra prediction modes (e.g., 56 directional modes plus five non-directional modes to obtain 61 intra prediction modes) may be indexed together for signaling.

[0102] In some implementations, the 56 or other number of directional intra-prediction mode examples may be implemented using a uniform directional predictor that projects each sample of a block to a reference subsample position and interpolates the reference sample using a 2-tap bilinear filter.

[0103] In some implementations, a further filter mode, called FILTER INTRA mode, may be designed to capture weak spatial correlation with edge references. In this mode, samples predicted within the block may be used as intra prediction reference samples for some patches within the block in addition to samples outside the block. These modes may, for example, be predefined and made available for intra prediction of at least luma blocks (or only luma blocks). A predefined number (e.g., 5) of filter intra modes may be predesigned, each of which is represented by a set of n-tap filters (e.g., 7-tap filters) that reflect the correlation between a sample in a 4×2 patch and its n neighbors. In other words, the weight coefficients of the n-tap filters may be position dependent. As shown in FIG. 11, when using an 8×8 block, a 4×2 patch, and 7-tap filtering as an example, the 8×8 block 1102 may be divided into eight 4×2 patches. In FIG. 11, these patches are indicated as B0, B1, B1, B3, B4, B5, B6, and B7. For each patch, seven neighbors of the patch (denoted R0-R7 in FIG. 11) may be used to predict samples in the target 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 predictions of the immediate neighbors are used as reference. For example, for patch B7 shown in FIG. 11, all neighbors have not been reconstructed, so the predicted samples of the neighbors are used instead.

[0104] In some implementations of intra prediction, one color component may be predicted using one or more other color components. The color components may be in any one of the YCrCb, RGB, XYZ, etc. color spaces. For example, prediction Chroma from Luma (CfL) may be performed to predict a chroma component (e.g., a chroma block) from a luma component (e.g., a luma reference sample). In some implementations, cross-color prediction is mostly only allowed from luma to chroma. For example, chroma samples in a chroma block can be modeled as a linear function of the corresponding reconstructed luma samples. CfL prediction can be performed as follows: CfL(α)=α×L AC +DC (1)

[0105] Here, L AC denotes the AC contribution of the luma component, α denotes a parameter of the linear model, and DC denotes the DC contribution of the chroma components. For example, the AC components are obtained for each sample of the block, while the DC components are obtained for the whole block. Moreover, the reconstructed luma samples may be subsampled to obtain the chroma resolution, and then the average luma value (DC of luma) may be subtracted from each luma value to generate the luma AC contribution. The luma AC contribution is then used in the linear mode of equation (1) to predict the AC values ​​of the chroma components. Instead of requiring the decoder to calculate the scaling parameters to approximate or predict the chroma AC components from the luma AC contribution, a CfL implementation may determine the parameter α based on the original chroma samples and signal this in the bitstream. This reduces the decoder complexity and provides a more accurate prediction. The DC contribution of the chroma components may be calculated using an intra DC mode in the chroma components in some implementations.

[0106] A transform of the residual of either the intra-predicted block or the inter-predicted block may then be performed, followed by quantization of the transform coefficients. To perform the transform, the intra-coded and inter-coded blocks may be further divided into multiple transform blocks (although the term "unit" is used in its usual usage to denote a collection of three color channels (e.g., a "coding unit" includes one luma coding block and multiple chroma coding blocks) and may be used instead as "transform unit") before the transform. In some implementations, a maximum partitioning depth of the coded block (or predictive block) may be specified (the term "coded block" may be used instead of "coding block"). For example, the partitioning may be of two or fewer levels. When partitioning the predictive block into transform blocks, intra-predicted blocks and inter-predicted blocks may be treated differently. However, in some implementations, such partitioning may be similar between intra-predicted blocks and inter-predicted blocks.

[0107] In some example implementations, for intra-coded blocks, transform partitioning may be done such that all transform blocks have the same size, and the transform blocks are coded in raster scan order. An example of such transform block partitioning of an intra-coded block is shown in Figure 12. Specifically, Figure 12 shows how a coded block 1202 is partitioned into 16 transform blocks of the same block size, indicated by 1206, via mid-level quadtree partitioning 1204. An example raster scan order for coding is indicated by the ordered arrows in Figure 12.

[0108] In some example implementations, and for inter-coded blocks, the transform unit partitioning may be done recursively up to a predetermined number of partitioning levels (e.g., two levels). As shown in FIG. 13, the partitioning may be stopped or continued recursively at any level for some subdivision. Specifically, FIG. 13 shows an example where a block 1302 is partitioned into four quadtree sub-blocks 1304, one of which is further partitioned into four second-level transform blocks, while the partitioning of the other sub-block is stopped after the first level, resulting in a total of seven transform blocks of two different sizes. FIG. 13 further shows an example of a raster scan order of coding by the sequential arrows. Although FIG. 13 shows an example of a quadtree partitioning implementation of square transform blocks up to the second level, some generating implementations may support partitioning for transforms of 1:1 (square), 1:2 / 2:1 and 1:4 / 4:1 transform block shapes and sizes ranging from 4×4 to 64×64. In some implementations, when the coding block is 64x64 or smaller, the transform block partitioning may only apply to the luma component (in other words, the chroma transform block is the same as the coding block in this situation). Otherwise, when the coding block width or height is greater than 64, both the luma coding block and the chroma coding block may be implicitly partitioned into multiples of min(W,64)xmin(H,64) and min(W,32)xmin(H,32) transform blocks, respectively.

[0109] Each of the above transform blocks may then undergo a linear transform, which effectively moves the residual of the transform block from the spatial domain to the frequency domain. Some implementations of the actual linear transform may allow multiple transform sizes (ranging from 4 points to 64 points for each of the two dimensions) and transform shapes (square, rectangular with width / height ratios of 2:1 / 1:2 and 4:1 / 1:4) to support the above extended coding block partitioning example.

[0110] Turning specifically to intra-mode coding, for a particular coding block, coding unit, predictive block, or prediction unit that is intra-coded, that intra-mode needs to be signaled by one or more syntax elements in the bitstream. As mentioned above, the number of possible intra-prediction modes can be huge. For example, in some of the implementations described above, the number of available intra-prediction modes can include 62 different modes, including, for example, 56 directional intra-prediction modes (e.g., 8 nominal directions with 7 fine angles per nominal direction), 5 non-directional modes, and one luma to chroma mode (for chroma components only). Once an intra-mode is selected during the coding process for a particular coding block, coding unit, predictive block, or prediction, signaling corresponding to the selected intra-mode needs to be included in the bitstream. The signaling syntax(es) must be able to distinguish all these 62 modes in some way. For example, these 62 modes may be signaled using a single syntax for 62 indices, each corresponding to one mode. In some other example implementations, one syntax may be signaled to indicate which nominal angle or non-directional mode is being used as the nominal mode for the current block, and then another syntax may be additionally signaled to indicate which delta angle is selected for the current block if the nominal mode for the current block is a directional mode.

[0111] Since the various syntaxes related to intra-coding usually occupy a large part of the bitstream and the selection of intra-modes needs to be signaled frequently at various coding levels, etc., reducing the number of bits used for intra-mode signaling becomes important in improving video coding efficiency. In practice, the use of various intra-prediction modes may follow certain statistical patterns, and such usage patterns can be exploited to design the intra-mode indexing and signaling syntax to increase the signaling efficiency. Furthermore, on average, there may be some correlation between intra-mode selections from block to block. Such correlations may be obtained offline based on statistics and taken into account in the design of the syntax(es) for signaling intra-mode selections. The goal is to reduce the number of bits for signaling syntax elements in the coded bitstream on average. For example, some common statistics may indicate that there may be a strong correlation between the optimal intra-prediction mode of the current block and its neighboring blocks. Such correlations can be exploited when designing the syntax(es) for intra-mode coding.

[0112] The following various exemplary implementations may be used separately or combined in any order. Furthermore, each of these implementations may be embodied as part of an encoder and / or decoder and may be implemented in either hardware or software. For example, they may be hard-coded in dedicated processing circuitry (e.g., one or more integrated circuits). In another example, they may be implemented by one or more processors executing a program stored on a non-transitory computer-readable medium.

[0113] In some example implementations, the intra-prediction modes or mode options available for a current block being coded may be divided into multiple intra-prediction mode sets. Each set may be assigned a mode set index. Each set may include an intra-mode prediction mode number. The manner in which the available intra-prediction modes are divided and ordered and the intra-prediction modes are ordered in each of the mode sets may be determined at least in part according to the intra-prediction modes used by its neighboring blocks based on the correlation between the intra-prediction modes between blocks. The intra-prediction modes used by the neighboring blocks may be referred to as "reference intra-prediction modes" or "reference modes." The intra-prediction mode for a particular unit may be determined and selected. The selection of the intra-prediction mode may be signaled. First, a mode set index may be signaled to indicate the mode set index of the intra-prediction mode set that includes the selected intra-prediction mode. Second, a mode index (alternatively referred to as a mode position index within a set) may be signaled to indicate the index of the selected intra-prediction mode within the mode set.

[0114] The general implementations of intra-prediction mode partitioning and ordering above, and the specific examples below, exploit statistical effects and neighbor correlations to dynamically index these modes so that the design of the syntax for signaling their selection within the coded video bitstream can be optimized to improve coding efficiency. For example, these implementations can help reduce the number of syntaxes for signaling and can help with more efficient context generation for entropy coding.

[0115] In some example embodiments, the set of predefined intra-prediction modes available to the encoder may include P modes, where P may be 62 (e.g., 56 directional modes, 5 non-directional modes, and 1 luma-to-chroma mode), or any other predetermined number. The number of intra-prediction mode sets may be denoted as M, and the number of intra-prediction modes in each mode set may be N. i where i is used to denote the mode set index, for example ranging from 1 to M or from 0 to M-1. i The maximum value of N max Let us assume that.

[0116] In some example implementations, N max may be restricted to a number equal to a power of 2. For example, N max may be limited to 8, 16, or 32. Such a design may help to efficiently use signaling bits in the signaling syntax.

[0117] In some example implementations, when M is greater than 2, all N of the M mode sets are i may be restricted to have at most two distinct values. In this way, the syntax for signaling the mode index within each of the mode sets may be simplified and streamlined.

[0118] In some example implementations, the number of available intra prediction modes for the current block is N max If the number of modes in each mode set is equal, then max In other words, P is set to N max If divisible by , then each of the M mode sets will have the same N max For example, when P=64 and M=4, each mode set contains 16 (N max = 16, or 2 to the power of 4) intra prediction modes. i, ... In some example implementations, the number of available intra prediction modes for a current block (P) is N max If the number of intra-modes in a set is not equal to a multiple of N, max However, the number of intra-modes in all other mode sets is N max In other words, N i has two possible values ​​in all M mode sets. One of the values ​​is N max Other values ​​can be N max All of the M mode sets, except for one set with a smaller number of modes, can be made smaller than N max For example, P can be 62, M can be 4, and N max may be 16, three of the four mode groups may contain 16 modes each, and the other mode set may contain 14 modes. In another example, the total number of available intra-prediction modes for the luma component may be 61, with M set to 4, N0 is 13, and N1, N2, and N3 all equal to 16. Again, such an implementation may help simplify the syntax design for signaling the mode index within the M mode sets for a selected intra-prediction mode.

[0119] In some exemplary embodiments, the (relative) positions of all non-directional modes are pre-determined and fixed, regardless of the intra-prediction modes of neighboring blocks.In other words, the placement and configuration of non-directional modes into and within a mode set among all available modes may be independent of the intra-prediction modes (or reference modes) of neighboring blocks, while the placement of other intra-prediction modes into and within a mode set may depend on the reference modes.In this way, the dynamic determination of mode sets can be simplified by taking advantage of the statistics that non-directional modes may not be very correlated between neighboring blocks.

[0120] In some example implementations, regardless of the intra prediction modes of neighboring blocks, all non-directional modes of the P available modes may be placed in the first intra mode set (with the lowest mode set index).

[0121] In some example implementations, the DC prediction mode (a mode with no directionality) is always placed in the first relative position (lowest position index within the mode set) of the first intra mode set (the mode set with the lowest index), regardless of the intra prediction modes of neighboring blocks.

[0122] In some example implementations, one or more intra-prediction modes based on recursive filtering may be signaled as sub-modes of the DC prediction mode. Thus, the intra-prediction modes based on recursive filtering may be additionally signaled only if the mode set index and the position index indicate that the DC mode is selected (e.g., both the mode index and the position index are the lowest, e.g., both are equal to 0 in the previous example implementation).

[0123] In some example implementations, the SMOOTH prediction mode as described above may always be placed in the second position (second lowest position index) of the first intra mode set (the mode set with the lowest mode set index), regardless of the intra prediction modes of neighboring blocks.

[0124] In some example implementations, the SMOOTH_V prediction mode as described above may always be placed in the third position (third lowest position index) of the first intra mode set (the mode set with the lowest mode set index), regardless of the intra prediction modes of neighboring blocks.

[0125] In some example implementations, the above SMOOTH_H prediction mode may always be placed in the fourth position (fourth lowest position index) of the first intra mode set (the mode set with the lowest mode set index), regardless of the intra prediction modes of neighboring blocks.

[0126] In some example implementations, the PAETH prediction mode as described above may always be placed in the fifth position (fifth lowest position index) of the first intra mode set (the mode set with the lowest mode set index), regardless of the intra prediction modes of neighboring blocks.

[0127] In some other or further example implementations, the intra prediction mode based on recursive filtering may be signaled independently of the DC intra prediction mode, may be one of the P modes rather than a sub-mode, and may be placed in the first intra mode set (the mode set with the lowest mode set index) regardless of the intra prediction modes of neighboring blocks.

[0128] In some further example implementations, there is a set of intra-prediction modes based on recursive filtering, one of which is selected, and additional signaling can be used to indicate which recursive-based intra-prediction mode among the set of intra-prediction modes based on recursive filtering has been selected for the current block.

[0129] In some example implementations, when signaled independently of the DC intra-prediction mode, the intra-prediction mode based on recursive filtering may always be placed in the sixth position of the first intra-mode set (the mode set with the lowest mode set index), regardless of the intra-prediction modes of neighboring blocks. In this case, the DC intra-prediction mode may be placed in the lowest index position in the lowest index mode set.

[0130] FIG. 14 shows a flowchart 1400 of an exemplary method according to the principles underlying the above implementation for intra mode coding. The exemplary method flow starts at 1401. At S1410, a coded video stream is received, the coded video stream including a set index and a position index for intra prediction of a current block. At S1420, an intra prediction mode corresponding to at least one neighboring block of the current block in the video stream is determined as a reference mode. At S1430, a method for dividing the P predefined intra prediction modes into M intra prediction mode sets is determined based on the reference mode, each intra prediction mode set including Ni position-indexed intra prediction modes, where P and M are integers greater than 1, Ni is the number of prediction modes in the i-th intra prediction mode set, and i is an integer representing an intra prediction mode set index among the M intra prediction mode sets. At S1440, a target intra prediction mode is identified from among the P predefined intra prediction modes based on the received set index and position index and the division method. At S1450, the current block of the coded video stream is decoded based at least on the target intra-prediction mode identified based on the set index and position index of the current block. The exemplary method flow ends at S1499. The above method flow also applies to encoding.

[0131] The embodiments 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 on a non-transitory computer-readable medium. The embodiments of the present disclosure may be applied to a luma block or a chroma block.

[0132] 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, FIG. 15 illustrates a computer system (1500) suitable for implementing certain embodiments of the disclosed subject matter.

[0133] The computer software may be coded using any suitable machine code or computer language that may undergo assembly, compilation, linking, or similar mechanisms to generate code including instructions that may be executed directly, or through interpretation and execution of microcode, such as by one or more computer central processing units (CPUs) and graphics processing units (GPUs).

[0134] The instructions may be executed in various types of computers or components thereof including, for example, a personal computer, a tablet computer, a server, a smart phone, a gaming device, an Internet of Things device, and the like.

[0135] 15 of the computer system (1500) 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, nor should the arrangement of components be interpreted as having a dependency or requirement relating to any one or combination of components illustrated in the exemplary embodiment of the computer system (1500).

[0136] The computer system (1500) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more users, such as, for example, tactile input (keystrokes, swipes, data glove movements, etc.), audio input (voice, clapping, etc.), visual input (gestures, etc.), olfactory input (not shown), etc. The human interface devices may be used to capture certain media that are not necessarily directly related to conscious human input, such as sound (speech, music, ambient sounds, etc.), images (scanned images, photographic images obtained from a still image camera, etc.), video (two-dimensional video, three-dimensional video including stereoscopic video, etc.).

[0137] The input human interface devices may include one or more of a keyboard (1501), a mouse (1502), a trackpad (1503), a touch screen (1510), a data glove (not shown), a joystick (1505), a microphone (1506), a scanner (1507), a camera (1508), etc. (only one of each is shown).

[0138] The computer system (1500) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the 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 (1510), data gloves (not shown), or joystick (1505), although there may also be haptic feedback devices that do not function as input devices), audio output devices (such as speakers (1509), headphones (not shown)), visual output devices (such as screens (1510), including CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch screen input capability, each with or without haptic feedback capability, some of which may output two-dimensional visual output or three or more dimensional output via means such as stereographic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0139] The computer system (1500) may also include human accessible storage devices and their associated media, such as optical media including CD / DVD ROM / RW (1520) along with media such as CDs / DVDs (1521), thumb drives (1522), removable hard drives or solid state drives (1523), legacy magnetic media such as tapes and floppy disks (not shown), dedicated ROM / ASIC / PLD based devices such as security dongles (not shown), etc.

[0140] Those skilled in the art should also understand that the term "computer-readable medium" as used in connection with the presently disclosed subject matter does not encompass transmission media, carrier waves, or other transitory signals.

[0141] The computer system (1500) may also include an interface (1554) to one or more communication networks (1555). The networks may be, for example, wireless, wired, optical. The networks 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, cellular networks including wireless LAN, GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable television, satellite television and terrestrial television, vehicular and industrial including CAN bus, etc. Certain networks typically require an external network interface adapter connected to a particular general-purpose data port or peripheral bus (1549) (e.g., a USB port on the computer system (1500)), while others are generally integrated into the core of the computer system (1500) by connecting to a system bus, as described below (e.g., an Ethernet interface for a PC computer system, or a cellular network interface for a smartphone computer system). Using any of these networks, the computer system (1500) may communicate with other entities. Such communications may be unidirectional, receive only (e.g., broadcast TV), unidirectional transmit only (e.g., from a CANbus to a particular CANbus device), or bidirectional, e.g., 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.

[0142] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be connected to the core (1540) of the computer system (1500).

[0143] The cores (1540) may include one or more central processing units (CPUs) (1541), graphics processing units (GPUs) (1542), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (1543), hardware accelerators for specific tasks (1544), graphics adapters (1550), etc. These devices may be connected via a system bus (1548), along with read only memory (ROM) (1545), random access memory (1546), internal mass storage devices (1547) such as internal hard drives, SSDs, etc. that are not accessible to the user. In some computer systems, the system bus (1548) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripherals may be connected directly to the core's system bus (1548) or via a peripheral bus (1549). In one example, a screen (1510) may be connected to the graphics adapter (1550). Peripheral bus architectures include PCI, USB, and the like.

[0144] The CPU (1541), GPU (1542), FPGA (1543), and accelerator (1544) can execute certain instructions that, in combination, can constitute the aforementioned computer code. The computer code can be stored in a ROM (1545) or a RAM (1546). Transient data can also be stored in the RAM (1546), and persistent data can be stored, for example, in internal mass storage (1547). The use of cache memory allows for quick storage and retrieval in any memory device, and can be closely associated with one or more of the CPU (1541), GPU (1542), mass storage device (1547), ROM (1545), RAM (1546), etc.

[0145] The computer-readable medium may 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 kind well known and available to those skilled in the computer software arts.

[0146] As a non-limiting example, the computer system (1500) having the architecture, and in particular the core (1540), may provide functionality as a result of the processor(s) (including CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media may be the user-accessible mass storage devices introduced above, as well as media associated with the specific storage of the core (1540) that is non-transitory in nature, such as the core internal mass storage (1547) or ROM (1545). Software implementing various embodiments of the present disclosure may be stored in such devices and executed by the core (1540). The computer-readable media may include one or more memory devices or chips according to specific needs. The software may cause the core (1540) and in particular the processors therein (including CPU, GPU, FPGA, etc.) to perform certain processes or certain portions of certain processes described herein, including the definition of data structures stored in RAM (1546) and modifying such data structures according to the software-defined processes. Additionally or alternatively, the computer system may provide functionality as a result of logic hardwired or otherwise embedded in circuitry (e.g., accelerator (1544)) that may operate in place of or together with software to perform certain processes or portions of certain processes described herein. References to software may include logic, and vice versa, where appropriate. Where appropriate, references to computer-readable media may encompass circuitry (such as an integrated circuit (IC)) that stores software for execution, circuitry that embodies logic for execution, or both. The present disclosure encompasses any suitable combination of hardware and software.

[0147] Although the present disclosure has described several exemplary embodiments, there are modifications, permutations, and various substitute equivalents that are within the scope of the present disclosure. In the implementations and embodiments described above, any operations of the processes may be combined or configured in any quantity or order as needed. Also, two or more of the operations of the processes described above may be performed in parallel. 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 thus are within its spirit and scope. 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 Directivity 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]

[0148] 101 Samples 102 Arrow 103 Arrow 104 Square Block 201 Current Block 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 Stream 403 Video Encoder 404 Video Data, Video Bitstream 405 Streaming Server 406 Client Subsystem 407 Video data, input copy 408 Client Subsystem 409 Video data, input copy 410 Video Decoder 411 Output Stream 412 Display 413 Video Capture Subsystem 420 Electronic Devices 430 Electronic Devices 501 Channel 510 Video Decoder 512 Rendering Devices, Displays 515 Buffer Memory 520 Parser 521 Symbols 530 Electronic Devices 531 Receiver 551 Reverse conversion unit 552 Intra picture prediction unit, intra 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 Encoder 620 Electronic Devices, Encoders 630 Source Coder 632 Coding Engine 633 local decoder, decoding unit, local video decoder 634 Reference Picture Memory, Reference Picture Cache 635 Predictor 640 Transmitter 643 Video Sequences 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 1002 Block 1004 Samples 1006 Samples 1008 Sample 1010 Sample 1102 Block 1202 Block 1204 Quadtree splitting 1302 Block 1304 Quadtree Subblock 1400 Flowchart 1500 Computer System 1501 Keyboard 1502 Mouse 1503 Trackpad 1505 Joystick 1506 Mike 1507 Scanner 1508 Camera 1509 Audio Output Device Speaker 1510 Touch Screen 1521 Medium 1522 Thumb Drive 1523 Solid State Drive 1540 Core 1541 Central Processing Unit, CPU 1542 Graphics Processing Unit, GPU 1543 Field Programmable Gate Area, FPGA 1544 Hardware Accelerator 1545 Read-Only Memory, ROM 1546 Random Access Memory, RAM 1547 Core Internal Mass Storage Device, Internal Mass Storage 1548 System Bus 1549 Peripheral Bus 1550 Graphics Adapter 1554 Interface 1555 Communication Network

Claims

1. 1. A method for performing intra prediction on a current block of a coded video stream, comprising: receiving the coded video stream including a set index and a position index for intra prediction of the current block; determining an intra prediction mode corresponding to at least one neighboring block of the current block in the video stream as a reference mode; determining, based on the reference modes, how to divide the P predefined intra-prediction modes into M intra-prediction mode sets, each of which includes N i N position-indexed intra-prediction modes, where P and M are integers greater than 1, i is the number of prediction modes in the i-th intra-prediction mode set, where i is an integer representing an intra-prediction mode set index among the M intra-prediction mode sets; identifying a target intra-prediction mode from among the P predefined intra-prediction modes based on the received set index, the position index, and the partitioning method; decoding the current block of the coded video stream based at least on the target intra-prediction mode identified based on the set index and the position index of the current block; Including, A method in which N max is a power of 2 and N max is the largest value among N i .

2. The method of claim 1, wherein when M is greater than 2, N i is selected from a first number and a second number.

3. The method of claim 2, wherein N i is the same value for all M intra-prediction mode sets.

4. The method described in claim 2, wherein one of the M intra prediction mode sets includes the second number of intra prediction modes, and all other of the M intra prediction mode sets include the first number of intra prediction modes.

5. The method of claim 2, wherein M=4 and N max =16.

6. The method described in claim 5, wherein P = 61, the first number is 16, and the second number is 13.

7. The P predefined intra-prediction modes include a subset of non-directional intra-prediction modes, the relative order of the subset of non-directional intra-prediction modes within the M intra-prediction mode sets is fixed regardless of the reference mode. The method of claim 6.

8. The method described in claim 7, wherein the subset of non-directional intra prediction modes is in the first intra prediction mode set among the M intra prediction mode sets, regardless of the reference mode.

9. The method described in claim 8, wherein the subset of non-directional intra-prediction modes includes a DC prediction mode that is always arranged as the first in order within the first-located intra-prediction mode set, regardless of the reference mode.

10. The method described in claim 9, wherein an intra prediction mode based on recursive filtering is signaled as a sub-mode of the DC prediction mode.

11. The method described in claim 8, wherein the subset of non-directional intra-prediction modes includes a SMOOTH prediction mode that is always arranged second in order within the first-located intra-prediction mode set, regardless of the reference mode.

12. The method described in claim 8, wherein the subset of non-directional intra-prediction modes includes a SMOOTH_V prediction mode that is always arranged third in order within the first-located intra-prediction mode set, regardless of the reference mode.

13. The method described in claim 8, wherein the subset of non-directional intra-prediction modes includes a SMOOTH_H prediction mode that is always arranged as the fourth in order within the first-located intra-prediction mode set, regardless of the reference mode.

14. The method described in claim 8, wherein the subset of non-directional intra-prediction modes includes a PAETH prediction mode that is always arranged as the fifth in order within the first-located intra-prediction mode set, regardless of the reference mode.

15. The P predefined intra-prediction modes include an intra-prediction mode based on recursive filtering, The intra prediction mode based on the recursive filtering is arranged as the intra prediction mode set located first among the M intra prediction mode sets, regardless of the reference mode; The recursive filtering-based intra-prediction mode is signaled independently of any DC intra-prediction mode.

8. The method according to any one of claims 1 to 7.

16. The method described in claim 15, wherein if the identified target intra prediction mode for the current block is an intra prediction mode based on recursive filtering, the method further includes a step of determining which of a set of intra prediction modes based on recursive filtering is selected separately from the set index and the position index.

17. The method described in claim 15, wherein the intra-prediction mode based on the recursive filtering is always placed in the sixth position within the first-located intra-prediction mode set, regardless of the reference mode.

18. The method described in claim 15, wherein the P predefined intra-prediction modes include at least one directional intra-prediction mode, at least one non-directional intra-prediction mode, and at least one luma-to-chroma intra-prediction mode.

19. An apparatus for performing intra prediction on a current block of a coded video stream, comprising:

19. An apparatus comprising processing circuitry configured to perform the method of any one of claims 1 to 18.

20. A computer program configured, when executed by a processor, to cause the processor to perform a method according to any one of claims 1 to 18.

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