Method, device, and computer program for video encoding

Abstract

To disclose a method for video coding.SOLUTION: A method may include steps of: extracting a first transform coefficient of a first color component from a bitstream of a coded video; extracting a second transform coefficient of a second color component from the bitstream of the coded video; deriving an offset value based on a magnitude or sign value of the first transform coefficient; adding the offset value to a magnitude of the second transform coefficient to generate a modified second transform coefficient for the second color component; and reconstructing the coded video based on at least the first transform coefficient of the first color component and the modified second transform coefficient of the second color component.SELECTED DRAWING: Figure 16

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is based on and claims the benefit of U.S. Nonprovisional Patent Application No. 17 / 575,075, filed January 13, 2022, which claims priority to U.S. Provisional Patent Application No. 63 / 224,046, entitled “CROSS-COMPONENT TRANSFORM COEFFICIENT LEVEL RECONSTRUCTION,” filed July 21, 2021. Both applications are incorporated herein by reference in their entireties.

[0002] FIELD OF THE DISCLOSURE This disclosure relates generally to a set of advanced video coding / decoding techniques, and more specifically to cross-component methods for improving decoded transform coefficients before or after inverse quantization. [Background technology]

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

[0004] Video coding and decoding may be performed using inter-picture prediction with motion compensation. Uncompressed digital video may include a sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luma samples and associated full-sampled or sub-sampled chroma samples. The sequence of pictures may have a fixed or variable picture rate (also called frame rate), for example, 60 pictures per second or 60 frames per second. Uncompressed video has specific bitrate requirements for streaming or data processing. For example, a video with a pixel resolution of 1920x1080, a frame rate of 60 frames per 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 gigabytes of storage space.

[0005] One objective 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 employed. 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 techniques can include a technique known as intra-coding. In intra-coding, sample values ​​are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, a picture is spatially subdivided into blocks of samples. If all blocks of samples are coded in intra mode, the picture can be called an intra-picture. Intra-pictures and their derived pictures, such as independent decoder refresh pictures, can be used to reset the decoder state and thus can be used as the first picture in the coded video bitstream and video session or as still images. Samples of the block after intra prediction can then be transformed to the frequency domain, and the transform coefficients so generated can be quantized before entropy coding. Intra prediction refers to 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 the joint exploration model (JEM), versatile video coding (VVC), and benchmark sets (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 the nine predictor directions specified in the 33 possible intra predictor directions of H.265 (corresponding to the 33 angle modes of the 35 intra modes specified in H.265). The point where the arrows converge (101) represents the sample being predicted. The arrows represent the direction from which neighboring samples are used to predict sample 101. For example, arrow (102) indicates that sample (101) is predicted from one or more neighboring 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 neighboring 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 shown a square block (104) of 4×4 samples (indicated by a thick dashed line). The square block (104) contains 16 samples, each labeled with "S", its position in the Y dimension (e.g., row index), and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample (from the top) in the Y dimension and the first sample (from the left) in the X dimension. Similarly, sample S44 is the fourth sample in both the Y and X dimensions in the block (104). Since the block is 4×4 samples in size, S44 is at the bottom right. Also shown are examples of reference samples that follow a similar numbering scheme. The reference samples are labeled 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] Methods for mapping bits representing intra-prediction directions to prediction directions in a coded video bitstream can vary across video coding techniques and can range, for example, from simple direct mappings of prediction directions to intra-prediction modes to complex adaptation schemes involving codewords, most-probable modes, and similar techniques. In all cases, however, there may be certain directions of intra-prediction that are statistically less likely to occur in the video content than certain other directions. Because the goal of video compression is to reduce redundancy, in a well-designed video coding technique, those less likely directions may be represented with more bits than the more likely directions.

[0018] Inter-picture prediction, or inter-prediction, may be based on motion compensation. In motion compensation, sample data from a previously reconstructed picture or part thereof (reference picture) may be used to predict a newly reconstructed picture or picture part (e.g., block) after being spatially shifted in a direction indicated by a motion vector (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 in use (similar to the temporal dimension).

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

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

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

[0022] Aspects of the present disclosure provide a cross-component method and apparatus for improving decoded transform coefficients before or after inverse quantization in video decoding. In some exemplary implementations, a method for video decoding is disclosed. The method may include: extracting a first transform coefficient of a first color component from a bitstream of a coded video; extracting a second transform coefficient of a second color component from a bitstream of the coded video; deriving an offset value based on a magnitude or a sign value of the first transform coefficient; adding the offset value to the magnitude of the second transform coefficient to generate a modified second transform coefficient of the second color component; and reconstructing the coded video based on at least the first transform coefficient of the first color component and the modified second transform coefficient of the second color component.

[0023] In the above implementation, the first transform coefficient and the second transform coefficient are juxtaposed.

[0024] In any of the above implementations, the first color component may include one chroma component and the second color component may include another chroma component.

[0025] In some of the above implementations, the first color component may include a luma component and the second color component may include one chroma component.

[0026] In some of the above implementations, the first color component may include one chroma component and the second color component may include a luma component.

[0027] In any of the above implementations, the first transform coefficient is non-zero when quantized from the bitstream, and the second transform coefficient is zero when quantized from the bitstream.

[0028] In any of the above implementations, the first transform coefficient includes a sign value and a magnitude value, and deriving the offset value includes deriving the offset value based on the sign value of the first transform coefficient. In some implementations, adding the offset value to the magnitude of the second transform coefficient may include adding the offset value to the magnitude of the second transform coefficient after inverse quantization. In some other implementations, adding the offset value to the magnitude of the second transform coefficient may include adding the offset value to the magnitude of the second transform coefficient before inverse quantization.

[0029] In any of the above implementations, the offset value may have an opposite sign to the sign of the first transform coefficient, and adding the offset value to the magnitude of the second transform coefficient may include adding the offset value to the magnitude of the second transform coefficient after inverse quantization.

[0030] In any of the above implementations, whether the sign value of the first transform coefficient and the sign of the offset value are opposite is signaled in one of a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a frame header, a slice header, a coding tree unit header, or a tile header.

[0031] In any of the above implementations, the offset value depends on both the sign and the magnitude of the first transform coefficient. In some implementations, the magnitude of the offset value depends on the magnitude of the first transform coefficient.

[0032] In some of the above implementations, the magnitude of the offset value is predefined via a predetermined correspondence between the magnitude of the offset value and the magnitude of the transform coefficient of the first color component.

[0033] In any of the above implementations, the offset value is determined as a function of a frequency position corresponding to the first transform coefficient.

[0034] In any of the above implementations, the offset value is determined depending on the block size of the transform block to which the first transform coefficient and the second transform coefficient belong.

[0035] In any of the above implementations, the offset value is determined depending on whether the second color component is a luma component or a chroma component.

[0036] Aspects of the present disclosure also provide a video encoding or decoding device or apparatus including circuitry configured to perform any of the implementations of the above methods.

[0037] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer, cause the computer to perform a method for video decoding and / or video encoding.

[0038] 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]

[0039] [Figure 1A]FIG. 13 is a schematic diagram of an example subset of intra-prediction directional modes. [Figure 1B] FIG. 2 illustrates an exemplary intra-prediction direction. [Diagram 2] FIG. 2 is a schematic diagram illustrating a current block and its surrounding spatial merge candidates for motion vector prediction in one example. [Diagram 3] FIG. 3 is a schematic diagram illustrating a simplified block diagram of a communication system (300) according to an example embodiment. [Figure 4] FIG. 4 is a schematic diagram illustrating a simplified block diagram of a communication system (400) according to an example embodiment. [Diagram 5] FIG. 2 is a schematic diagram illustrating a simplified block diagram of a video decoder according to an example embodiment. [Figure 6] FIG. 1 is a schematic diagram illustrating a simplified block diagram of a video encoder according to an example 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 example embodiment. [Figure 9] FIG. 2 illustrates a coding block partitioning scheme according to an exemplary embodiment of the present disclosure. [Figure 10] FIG. 13 illustrates another scheme for coding block partitioning according to an exemplary embodiment of the present disclosure. [Figure 11] FIG. 13 illustrates another scheme for coding block partitioning according to an exemplary embodiment of the present disclosure. [Figure 12] FIG. 13 illustrates another scheme for coding block partitioning according to an exemplary embodiment of the present disclosure. [Figure 13] 2 illustrates a scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure. [Figure 14] 4A-4C are diagrams illustrating another scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure. [Figure 15] FIG. 2 illustrates another scheme for splitting a coding block into multiple transform blocks, according to an exemplary embodiment of the present disclosure. [Figure 16] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 17] FIG. 1 is a schematic diagram illustrating a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] FIG. 3 shows a simplified block diagram of a communication system (300) according to one embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) may perform unidirectional transmission of data. For example, the terminal device (310) may code video data (e.g., of a stream of video pictures captured by the terminal device (310)) for transmission to the other terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to reconstruct the video pictures, and display the video pictures according to the reconstructed video data. Unidirectional data transmission may be implemented, such as for media serving applications.

[0041] 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.

[0042] 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 (cabled) and / or wireless communication networks. The communication network (350) 9 may exchange data over circuit-switched channels, packet-switched channels, and / or other types of channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this discussion, the architecture and topology of the network (350) may not be important to the operation of the present disclosure unless explicitly described herein.

[0043] 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 applicable 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.

[0044] A video streaming system may include a video source (401) for creating a stream of uncompressed video pictures or images (402), such as a video capture subsystem (413) that may include a digital camera. In one example, the stream of video pictures (402) includes samples recorded by the digital camera of the video source 401. The stream of video pictures (402), shown as a thick line to emphasize the amount of data when compared to the encoded video data (404) (or coded video bitstream), may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or 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 retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) may include, for example, a video decoder (410) within the electronic device (430). The video decoder (410) decodes the input copy of the encoded video data (407) and creates an output stream of video pictures (411) that is uncompressed and can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). The video decoder 410 may be configured to 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.

[0045] 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).

[0046] 5 shows a block diagram of a video decoder (510) according to any of the following embodiments of the present disclosure. The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) of the example of FIG. 4.

[0047] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In the same or another embodiment, one coded video sequence may be decoded at a time, with the decoding of each coded video sequence being independent of the other coded video sequences. Each video sequence may be associated with multiple video frames or video images. The coded video sequences may be received from a channel (501), which may be a hardware / software link to a storage device that stores the encoded video data, or a streaming source that transmits the encoded video data. The receiver (531) may receive the encoded video data along with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to respective processing circuits (not shown). The receiver (531) may separate the coded video sequences from the other data. To combat network jitter, a buffer memory (515) may be placed 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 additional buffer memory (515) internal to the video decoder (510), for example to handle playback timing. When the receiver (531) is receiving data from a store / forward device of sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may not be needed 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).

[0048] The video decoder (510) may include a parser (520) to reconstruct symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and potentially information for controlling a rendering device such as a display (512) (e.g., a display screen) that may or may not be an integral part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device(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 may follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (520) may extract, from the coded video sequence, a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the subgroup. The subgroups may include groups of pictures (GOPs), pictures, tiles, slices, macroblocks, coding units (CUs), blocks, transform units (TUs), prediction units (PUs), etc. The parser (520) may also extract information from the coded video sequence, such as transform coefficients (e.g., Fourier transform coefficients), quantization parameter values, motion vectors, etc.

[0049] The parser (520) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515) to create symbols (521).

[0050] 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.

[0051] Besides the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into several functional units, as described below. In an actual implementation operating under commercial constraints, many of these functional units may closely interact with each other and may be, at least in part, integrated with each other. However, in order to clearly explain the various functions of the disclosed subject matter, the following disclosure adopts a conceptual subdivision into functional units.

[0052] The first unit may include a scalar / inverse transform unit (551), which may receive quantized transform coefficients as well as control information from the parser (520) including information indicating which type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc. The scalar / inverse transform unit (551) may output a block including sample values ​​that may be input to an aggregator (555).

[0053] In some cases, the output samples of the scaler / inverse transform (551) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may generate a block of the same size and shape as the block being reconstructed using information of surrounding blocks that have already been reconstructed and stored in the current picture buffer (558). The current picture buffer (558) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. The aggregator (555) may add, on a sample-by-sample basis, prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551), in some implementations.

[0054] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded, potentially motion-compensated block. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for inter-picture prediction. After motion compensating the fetched samples according to the symbols (521) related to the block, these samples may be added to the output of the scalar / inverse transform unit (551) by the aggregator (555) to generate output sample information (the output of unit 551 may be referred to as a residual sample or residual signal). The address in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches the prediction sample may be controlled by a motion vector, available to the motion compensated prediction unit (553) in the form of a symbol (521) 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.

[0055] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in the loop filter unit (556). Video compression techniques may include in-loop filter techniques that are controlled by parameters included in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to previously reconstructed and loop filtered sample values ​​as well as meta-information obtained during decoding of a previous portion (in decoding order) of the coded picture or coded video sequence. As described in more detail below, several types of loop filters may be included as part of the loop filter unit 556 in various orders.

[0056] 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.

[0057] Once a particular coded picture is fully reconstructed, it may be used as a reference picture for future inter-picture prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified (e.g., by the parser (520)) as a reference picture, the current picture buffer (558) may become part of the reference picture memory (557), and any unused current picture buffer may be reallocated before beginning reconstruction of the next coded picture.

[0058] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard, such as ITU-T Recommendation H.265. The coded video sequence may conform to a syntax specified by the video compression technique or standard being used, in the sense that the coded video sequence adheres to both the syntax of the video compression technique or standard and the profile documented in the video compression technique or standard. Specifically, a profile may select a particular tool from all tools available in the video compression technique or standard as the only tool that can be used under that profile. To conform to a standard, the complexity of the coded video sequence may be within a range defined by a level of the video compression technique or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. The limits set by the level may be further limited in some cases by the specification of a hypothetical reference decoder (HRD) and metadata for HRD buffer management signaled within the coded video sequence.

[0059] 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. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0060] 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.

[0061] 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).

[0062] 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 can 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 a number of separate pictures or images that give motion when viewed in sequence. The picture itself may be organized as a spatial array of pixels, each pixel may contain one or more samples depending on the sampling structure, color space, etc. being used. Those skilled in the art can easily understand the relationship between pixels and samples. The following description focuses on samples.

[0063] 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 with other appropriate functions associated with the video encoder (603) optimized for a particular system design.

[0064] In some example embodiments, the video encoder (603) may be configured to operate in a coding loop. As an oversimplified explanation, in one example, the coding loop may include a source coder (630) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to create sample data in a similar manner as a (remote) decoder would create them, even if the embedded decoder 633 processes the video stream coded by the source coder 630 without entropy coding (because 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 "sees" 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.

[0065] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. Referring also briefly to Figure 5, however, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (520) may be lossless, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633) within the encoder.

[0066] 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.

[0067] 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 the predictive reference(s) to the input picture. The terms "residue" and its adjective form "residual" may be used interchangeably.

[0068] 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, such that the reconstructed reference pictures are stored 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.

[0069] The predictor (635) may perform a prediction search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or specific metadata such as reference picture motion vectors, block shapes, etc., that may serve as suitable prediction references for the new picture. The predictor (635) may operate on sample blocks by pixel blocks to find suitable prediction references. 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).

[0070] 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.

[0071] The output of all the aforementioned functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by lossless compression of the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0072] The transmitter (640) may buffer the coded video sequence created by the entropy coder (645) and prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0073] 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 technique that may be applied to the respective picture. For example, pictures may often be assigned as any of the following picture types:

[0074] An intra picture (I-picture) may be one that can be coded and decoded without using other pictures in a sequence as a source of prediction. Some video codecs allow various 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.

[0075] A predictive picture (P picture) may be a picture that can be coded and decoded using intra- or inter-prediction, which uses at most one motion vector and reference index to predict sample values ​​for each block.

[0076] A bidirectionally predicted picture (B-picture) may be a picture that can be coded and decoded using intra- or inter-prediction that uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, a multi-predicted picture may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0077] 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 they may be 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 via spatial prediction or via 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.

[0078] The video encoder (603) may perform coding operations in accordance with a given video coding technique or standard, such as ITU-T Recommendation H.265. In its operations, the video encoder (603) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0079] 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.

[0080] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits temporal or other correlation between pictures. For example, a particular picture being encoded / decoded, called the current picture, may be divided into blocks. If a block in the current picture 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.

[0081] In some exemplary embodiments, bi-prediction techniques can 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 can 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 can be jointly predicted by a combination of the first reference block and the second reference block.

[0082] Additionally, merge mode techniques may be used to improve coding efficiency in inter-picture prediction.

[0083] 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 quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels. Each of one or more of the 32×32 blocks may be further partitioned into four CUs of 16×16 pixels. In some exemplary embodiments, each CU may be analyzed during encoding to determine 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 in units of prediction blocks. 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.

[0084] 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.

[0085] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a predictive 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 a motion vector is derived from one or more motion vector predictors without the benefit of coded motion vector components outside the predictors. In some other exemplary embodiments, there may be motion vector components applicable to the current block. 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.

[0086] 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.

[0087] 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 decoding 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).

[0088] 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.

[0089] 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 a block and provides a control signal to the switch (726) based on the prediction mode. For example, if the prediction mode is an intra mode, the generic controller (721) controls the switch (726) to select an intra mode result for use by the residual calculator (723) and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream, and if the prediction mode of the block is an inter mode, the generic controller (721) controls the switch (726) to select an inter prediction result for use by the residual calculator (723) and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0090] The residual calculator (723) may be configured to calculate a difference (residual data) between a received block and a prediction result for a block selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) may be configured to encode the residual data to generate transform coefficients. For example, the residual encoder (724) may be configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various exemplary embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) may generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) may generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks may be appropriately processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols that represent syntax elements of which the coded picture is composed. Such symbols may include, for example, prediction information (e.g., intra- or inter-prediction information) that may identify the mode in which the block is coded (e.g., intra-, inter-, bi-prediction, merged or another sub-mode), certain samples or metadata used for prediction by the intra- or inter-decoder (872) or (880), residual information, for example in the form of quantized transform coefficients, etc. In one example, if the prediction mode is an inter- or bi-prediction mode, the inter-prediction information is provided to the inter-decoder (880), and if the prediction type is an intra-prediction type, the intra-prediction information is provided to the intra-decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0095] The inter decoder (880) may be configured to receive the inter prediction information and generate inter prediction results based on the inter prediction information.

[0096] The intra decoder (872) may be configured to receive intra prediction information and to generate a prediction result based on the intra prediction information.

[0097] 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).

[0098] The reconstruction module (874) may be configured to combine, in the spatial domain, the residual as output by the residual decoder (873) and the prediction result (possibly as output by an inter prediction module or an intra prediction module) to form a reconstructed block that forms part of a reconstructed picture as part of the reconstructed video. It should be noted that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0099] 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 technology. 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.

[0100] Looking at the coding block partitioning, in some example implementations, a predefined pattern may be applied. As shown in FIG. 9, an example 4-way partitioning tree may be used starting from a first predefined level (e.g., 64×64 block level) to a second predefined level (e.g., 4×4 level). For example, the base block may follow four partitioning options shown at 902, 904, 906, and 908, and the partitions represented by R may be recursively partitioned in that the same partitioning tree shown in FIG. 9 may be repeated at lower scales down to the lowest level (e.g., 4×4 level). In some implementations, additional restrictions may be applied to the partitioning scheme of FIG. 9. In the implementation of FIG. 9, rectangular partitions (e.g., 1:2 / 2:1 rectangular partitions) may be used but not repeatedly, while square partitions may be used repeatedly. Subsequent partitioning of FIG. 9 by recursion generates a final set of coding blocks, if necessary. Such a scheme may be applied to one or more of the color channels.

[0101] FIG. 10 illustrates another exemplary predefined partitioning pattern that allows for forming a partitioning tree by recursive partitioning. As illustrated in FIG. 10, an exemplary 10-way partitioning structure or pattern may be predefined. The root block may start from a predefined level (e.g., from the 128×128 level or the 64×64 level). The exemplary partitioning structure of FIG. 10 includes various 2:1 / 1:2 and 4:1 / 1:4 rectangular partitions. A partition type having three subpartitions, indicated by 1002, 1004, 1006, and 1008 in the second column of FIG. 10, may be referred to as a “T-shaped” partition. The “T-shaped” partitions 1002, 1004, 1006, and 1008 may be referred to as a left T-shaped, an upper T-shaped, a right T-shaped, and a lower T-shaped. In some implementations, none of the rectangular partitions of FIG. 10 may be further subdivided. A coding tree depth may be further defined to indicate the partitioning depth from the root node or root block. For example, the coding tree depth of the root node or root black of a 128×128 block may be set to 0, and the coding tree depth increases by 1 after the root block is further split one time following FIG. 10. In some implementations, only the all-square partitions of 1010 may allow recursive splitting to the next level of the split tree following the pattern of FIG. 10. In other words, recursive splitting is not possible for the square partitions of patterns 1002, 1004, 1006, and 1006. Subsequent splitting of FIG. 10 by recursion generates a final set of coding blocks, if necessary. Such a scheme may be applied to one or more of the color channels.

[0102] After partitioning or splitting the base block according to any of the above partitioning procedures or other procedures, a final set of partitions or coding blocks may still be obtained. Each of these partitions may be at one of various partitioning levels. Each partition may be referred to as a coding block (CB). In the various exemplary partitioning implementations above, each resulting CB may be of any of the allowed sizes and partitioning levels. They are referred to as coding blocks because they form the units for which some basic coding / decoding decisions may be made and coding / decoding parameters may be optimized, determined, and signaled in the encoded video bitstream. The highest level in the final partition represents the depth of the coding block partitioning tree. The coding block may be a luma coding block or a chroma coding block.

[0103] In some other example implementations, a quadtree structure may be used to recursively split the base luma block and the base chroma block into coding units. Such a split structure may be called a coding tree unit (CTU), and the CTU is split into coding units (CUs) by adapting the split to various local characteristics of the base CTU using the quadtree structure. In such implementations, an implicit quadtree split may be performed at the picture boundary, such that the block continues the quadtree split until its size fits into the picture boundary. The term CU is used to collectively refer to the units of luma coding block (CB) and chroma coding block (CB).

[0104] In some implementations, the CB may be further divided. For example, the CB may be further divided into multiple prediction blocks (PBs) for the purpose of intra-frame or inter-frame prediction during the coding and decoding processes. In other words, the CB may be further partitioned into different sub-partitions, where individual prediction decisions / configurations may be made. In parallel, the CB may be further divided into multiple transform blocks (TBs) for the purpose of describing the level at which the transformation or inverse transformation of the video data is performed. The division scheme of the CB into PBs and TBs may be the same or different. For example, each division scheme may be performed using a unique procedure based on, for example, various characteristics of the video data. The division schemes of the PBs and TBs may be independent in some exemplary implementations. The division schemes and boundaries of the PBs and TBs may be correlated in some other exemplary implementations. In some implementations, for example, the TBs may be divided after the PB division, and in particular, each PB may be determined following the division of the coding block, and then further divided into one or more TBs. For example, in some implementations, the PB may be divided into one, two, four, or other number of TBs.

[0105] In some implementations, luma and chroma channels may be processed differently to split base blocks into coding blocks and further into predictive and / or transform blocks. For example, some implementations may allow splitting of coding blocks into predictive and / or transform blocks for a luma channel, but not for a chroma channel(s). In such implementations, transform and / or prediction of luma blocks may thus be performed only at the coding block level. In another example, the minimum transform block size of the luma channel and the chroma channel(s) may be different, e.g., a coding block of a luma channel may be allowed to be split into smaller transform and / or predictive blocks than a chroma channel. In yet another example, the maximum depth of splitting of coding blocks into transform and / or predictive blocks may be different between the luma and chroma channels, e.g., a coding block of a luma channel may be allowed to be split into deeper transform and / or predictive blocks than a chroma channel(s). As a specific example, a luma coding block may be divided into transform blocks of multiple sizes that can be represented by a recursive partitioning down by up to two levels, and transform block shapes such as square, 2:1 / 1:2, 4:1 / 1:4, etc., and transform block sizes from 4×4 to 64×64 may be allowed. However, for chroma blocks, only the largest possible transform block designated for the luma block may be allowed.

[0106] In some example implementations for partitioning a coding block into PBs, the depth, shape, and / or other characteristics of the PB partition may depend on whether the PB is intra-coded or inter-coded.

[0107] The division of the coding block (or prediction block) into transform blocks may be performed in various exemplary manners, including but not limited to quadtree division and predetermined pattern division, recursively or non-recursively, further considering the transform blocks at the boundaries of the coding block or prediction block. In general, the resulting transform blocks may be at different division levels, may not be the same size, and may not be square in shape (e.g., they may be rectangular with some allowed sizes and aspect ratios).

[0108] In some implementations, a coding partition tree scheme or structure may be used. The coding partition tree schemes used for the luma channel and the chroma channel may not be the same. In other words, the luma channel and the chroma channel may have separate coding tree structures. Furthermore, whether the luma channel and the chroma channel use the same coding partition tree structure or different coding partition tree structures, and the actual coding partition tree structure to be used, may depend on whether the slice being coded is a P slice, a B slice, or an I slice. For example, for an I slice, the chroma channel and the luma channel may have separate coding partition tree structures or coding partition tree structure modes, while for a P slice or a B slice, the luma channel and the chroma channel may share the same coding partition tree scheme. When separate coding partition tree structures or modes are applied, the luma channel may be partitioned into CB by one coding partition tree structure, and the chroma channel may be partitioned into chroma CB by another coding partition tree structure.

[0109] Specific exemplary implementations of the division of coding blocks and transform blocks are described below. In one such exemplary implementation, a base coding block may be divided into coding blocks using the recursive quadtree division described above. At each level, whether to continue further quadtree division of a particular partition may be determined by local video data characteristics. The resulting CBs may be at various quadtree division levels with various sizes. The decision of whether to code a picture area using inter-picture (temporal) prediction or intra-picture (spatial) prediction may be made at the CB level (or at the CU level in case of three color channels). Each CB may be further divided into one, two, four, or other number of PBs according to the PB division type. Within one PB, the same prediction process may be applied, and related information is sent to the decoder on a PB basis. After obtaining the residual block by applying the prediction process based on the PB division type, the CB may be divided into TBs according to another quadtree structure similar to the coding tree of the CB. In this particular implementation, the CB or TB may not be limited to a square shape. Further, in this particular example, the PB may be square or rectangular in shape for inter prediction, and only square in intra prediction. The coding block may be further divided, for example, into four square-shaped TBs. Each TB may be further divided recursively (using quad-tree partitioning) into smaller TBs called Residual Quad-Tree (RQT).

[0110] Another specific example for splitting a base coding block into CB and other PBs and / or TBs is described below. For example, instead of using multiple partition unit types as shown in FIG. 10, a quadtree with nested multi-type trees using bipartition and tripartition segmentation structures may be used. Separation of the concepts of CB, PB, and TB (i.e., splitting CB into PB and / or TB, and splitting PB into TB) may be abandoned except when necessary for CBs with sizes too large for the maximum transform length, which may require further splitting. This exemplary splitting scheme may be designed to support greater flexibility of CB splitting shapes, so that both prediction and transformation can be performed at the CB level without further splitting. In such a coding tree structure, the CB may have either a square or rectangular shape. Specifically, a coding tree block (CTB) may be first split by a quadtree structure. Then, the leaf nodes of the quadtree may be further split by a multi-type tree structure. An example of a multi-type tree structure is shown in FIG. 11. Specifically, the exemplary multi-type tree structure of FIG. 11 includes four split types: vertical bisection (SPLIT_BT_VER) (1102), horizontal bisection (SPLIT_BT_HOR) (1104), vertical trisection (SPLIT_TT_VER) (1106), and horizontal trisection (SPLIT_TT_HOR) (1108). The CB then corresponds to a leaf of the multi-type tree. In this exemplary implementation, as long as the CB is not too large relative to the maximum transform length, this segmentation is used for both prediction and transform processing without further splitting. This means that in most cases, the CB, PB, and TB have the same block size in a quadtree with a nested multi-type tree coding block structure. An exception occurs when the maximum supported transform length is smaller than the width or height of the color components of the CB.

[0111] An example of a quadtree with nested multi-type tree coding block structure of block division of one CTB is shown in FIG. 12. More specifically, FIG. 12 shows that a CTB 1200 is quadtree divided into four square partitions 1202, 1204, 1206, and 1208. A decision to further use the multi-type tree structure of FIG. 11 for division is made for each of the quadtree divided partitions. In the example of FIG. 12, partition 1204 is not further divided. Partition 1202 and partition 1208 each adopt another quadtree division. In partition 1202, the second level quadtree divided upper left partition, upper right partition, lower left partition, and lower right partition adopt the third level division of quadtree, 1104 in FIG. 11, non-partition, and 1108 in FIG. 11, respectively. Partition 1208 adopts another quadtree partitioning, and the second-level quadtree partitioned top-left partition, top-right partition, bottom-left partition, and bottom-right partition adopt the third-level partitioning of 1106 in FIG. 11, not partitioned, not partitioned, and 1104 in FIG. 11, respectively. Two of the subpartitions of the top-left partition of the third level of 1208 are further partitioned according to 1104 and 1108. Partition 1206 adopts the second-level partitioning pattern according to 1102 in FIG. 11 into two partitions, and the two partitions are further partitioned at the third level according to 1108 and 1102 in FIG. 11. A fourth-level partitioning is further applied to one of them according to 1104 in FIG. 11.

[0112] In the above specific example, the maximum luma transform size may be 64 x 64, and the maximum supported chroma transform size may also be different from the luma, e.g., 32 x 32. If the width or height of a luma coding block or a chroma coding block is larger than the maximum transform width or height, the luma coding block or the chroma coding block may be automatically split horizontally and / or vertically to meet the horizontal and / or vertical transform size constraints.

[0113] In the specific example for splitting the base coding blocks into CBs above, the coding tree scheme may support the ability for luma and chroma to have separate block tree structures. For example, for P slices and B slices, the luma CTB and chroma CTB in one CTU may share the same coding tree structure. For I slices, for example, luma and chroma may have separate coding block tree structures. When the separate block tree mode is applied, the luma CTB may be split into luma CBs by one coding tree structure, and the chroma CTB is split into chroma CBs by another coding tree structure. This means that a CU in an I slice may consist of a coding block of a luma component or a coding block of two chroma components, and a CU in a P slice or B slice always consists of coding blocks of all three color components unless the video is monochrome.

[0114] Exemplary implementations for splitting coding or predictive blocks into transform blocks and the coding order of transform blocks are described in further detail below. In some exemplary implementations, transform splitting may support transform blocks of multiple shapes, e.g., 1:1 (square), 1:2 / 2:1, and 1:4 / 4:1, with transform block sizes ranging from, e.g., 4×4 to 64×64. In some implementations, if the coding block is 64×64 or smaller, transform block splitting may be applied only to the luma component, such that for chroma blocks, the transform block size is identical to the coding block size. Otherwise, if the width or height of the coding block is greater than 64, both the luma coding block and the chroma coding block may be implicitly split into multiples of transform blocks of min(W,64)×min(H,64) and min(W,32)×min(H,32), respectively.

[0115] In some example implementations, for both intra-coded and inter-coded blocks, a coding block may be further divided into multiple transform blocks with a division depth up to a predetermined number of levels (e.g., two levels). The division depth and size of the transform block may be related. An example mapping from the transform size of the current depth to the transform size of the next depth is shown below in Table 1.

[0116] [Table 1]

[0117] According to the example mapping of Table 1, for a 1:1 square block, the next level transform split may create four 1:1 square sub-transform blocks. The transform split may stop at, for example, 4×4. Thus, a transform size of the current depth of 4×4 corresponds to the same size of 4×4 at the next depth. In the example of Table 1, for a 1:2 / 2:1 non-square block, the next level transform split creates two 1:1 square sub-transform blocks, and for a 1:4 / 4:1 non-square block, the next level transform split creates two 1:2 / 2:1 sub-transform blocks.

[0118] In some example implementations, further restrictions may be applied to the luma components of intra-coded blocks. For example, for each level of transform partitioning, all sub-transform blocks may be restricted to have equal size. For example, for a 32×16 coding block, the level 1 transform partitioning creates two 16×16 sub-transform blocks, and the level 2 transform partitioning creates eight 8×8 sub-transform blocks. In other words, to keep the transform units equal in size, the second level partitioning must be applied to all first level sub-blocks. An example of transform block partitioning for an intra-coded square block according to Table 1 is shown in FIG. 13 with the coding order indicated by the arrows. Specifically, 1302 shows a square coding block. The first level partitioning according to Table 1 into four equal-sized transform blocks is shown in 1304 with the coding order indicated by the arrows. The second level partitioning of all first level equal-sized blocks according to Table 1 into 16 equal-sized transform blocks is shown in 1306 with the coding order indicated by the arrows.

[0119] In some example implementations, the above restrictions on intra-coding may not apply to the luma components of an inter-coded block. For example, after the first level of transform partitioning, any one of the sub-transform blocks may be further partitioned independently at another level. Thus, the resulting transform blocks may or may not be of the same size. An example partitioning of an inter-coded block into transform blocks with coding order is shown in FIG. 14. In the example of FIG. 14, an inter-coded block 1402 is partitioned into transform blocks at two levels according to Table 1. At the first level, the inter-coded block is partitioned into four transform blocks of equal size. Then, only one of the four transform blocks (but not all of them) is further partitioned into four sub-transform blocks, resulting in a total of seven transform blocks with two different sizes, as shown at 1404. An example coding order of these seven transform blocks is indicated by an arrow at 1404 in FIG. 14.

[0120] In some example implementations, for the chroma component(s), some additional restrictions on the transform blocks may be applied. For example, for the chroma component(s), the transform block size may be as large as the coding block size, but cannot be smaller than a certain size, e.g., 8×8.

[0121] In some other example implementations, for coding blocks whose width (W) or height (H) is greater than 64, both the luma coding block and the chroma coding block may be implicitly divided into multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32) transform units, respectively.

[0122] Figure 15 further illustrates another alternative exemplary scheme for splitting a coding block or a predictive block into transform blocks. As illustrated in Figure 15, instead of using recursive transform splitting, a set of predetermined split types may be applied to a coding block according to the transform type of the coding block. In the particular example illustrated in Figure 15, one of six exemplary split types may be applied to split a coding block into various numbers of transform blocks. Such a scheme may be applied to either a coding block or a predictive block.

[0123] More specifically, the partitioning scheme of FIG. 15 provides up to six partitioning types for any given transform type, as shown in FIG. 15. In this scheme, every coding block or predictive block may be assigned a transform type, for example, based on a rate-distortion cost. In one example, the partitioning type assigned to a coding block or predictive block may be determined based on the transform partitioning type of the coding block or predictive block. As shown by the four partitioning types illustrated in FIG. 15, a particular partitioning type may correspond to the partitioning size and pattern (or partitioning type) of the transform block. The correspondence between various transform types and various partitioning types may be predefined. An exemplary correspondence is shown below with capitalized labels indicating the transform types that may be assigned to a coding block or predictive block based on a rate-distortion cost.

[0124] ·PARTITION_NONE: Allocate the transformation size equal to the block size.

[0125] ·PARTITION_SPLIT: Allocates a transformation size that is 1 / 2 the width and 1 / 2 the height of the block size.

[0126] ·PARTITION_HORZ: Allocates a transformation size with the same width as the block size and 1 / 2 the height of the block size.

[0127] ·PARTITION_VERT: Allocates a transformation size that is half the width of the block size and the same height as the block size.

[0128] ·PARTITION_HORZ4: Allocates a transformation size with the same width as the block size and 1 / 4 of the block size in height.

[0129] ·PARTITION_VERT4: Allocates a transformation size that is 1 / 4 the width of the block size and the same height as the block size.

[0130] In the above example, all the partition types shown in Figure 15 include uniform transform sizes for the partitioned transform blocks. This is not a limitation but merely an example. In some other implementations, mixed transform block sizes may be used for the partitioned transform blocks in a particular partition type (or pattern).

[0131] With reference to some example implementations of signaling a particular type of coding block / unit, for each intra- and inter-coding unit, a flag, i.e., skip_txfm flag, may be signaled in the coded bitstream as shown in the example syntax of Table 2 and represented by the read_skip() function to retrieve these flags from the bitstream. This flag may indicate whether the transform coefficients are all zero in the current coding unit. In some example implementations, if this flag is signaled, for example, with a value of 1, another transform coefficient related syntax, e.g., End of Block (EOB), does not need to be signaled for any of the color coding blocks in the coding unit, but can be derived as a value or data structure predefined for and associated with the zero transform coefficient block. For inter-coding blocks, as shown by the example of Table 2, this flag may be signaled after a skip mode flag indicating that the coding unit may be skipped for various reasons. If skip_mode is true, the coding unit should be skipped and there is no need to signal the skip_txfm flag and the skip_texfm flag is inferred to be 1. Otherwise, if skip_mode is false, more information about the coding unit is included in the bitstream and the skip_txfm flag is additionally signaled to indicate whether the coding unit is all zeros or not.

[0132] [Table 2]

[0133] [Table 3]

[0134] [Table 4]

[0135] In the following example implementations, the term chroma channel may generally refer to both Cb and Cr color components (or channels), or both U and V color components (or channels). The term luma channel may include a luma component or a Y component. A luma component or channel may be referred to as a luma color component or channel. Hereinafter, Y, U, and V are used to represent the three color components. Furthermore, the terms "coded block" and "coding" block are used interchangeably to mean either a block to be coded or a block that has already been coded. These may be blocks of any of the three color components. Three corresponding color coded / coding blocks may be for a coded / coding unit.

[0136] Referring to the coding and decoding (entropy coding) of the residual transform coefficients in each color component, for each transform block, the transform coefficient coding starts with signaling of the skip code, followed by the transform kernel type and the end of block (EOB) position if the skip code is zero (indicating the presence of non-zero coefficients). Then, each coefficient value is mapped to multiple level maps (amplitude maps) and codes.

[0137] After the EOB position is coded, the low level map and the mid level map may be coded in reverse scan order, with the former indicating whether the magnitude of the coefficient is within the low level (e.g., between 0 and 2) and the latter indicating whether the range is within the mid level (e.g., between 3 and 14). The next step is to code, for example by Exp-Golomb coding, the signs of the coefficients and the residual values ​​of the coefficients greater than the high level (e.g., 14) in forward scan order.

[0138] With regard to the use of context modeling, the lower level map coding may incorporate the transform size and direction as well as up to five neighboring coefficient information, while the mid-level map coding may follow a similar approach to the low level amplitude coding, except that the number of neighboring coefficients is reduced to a smaller number (e.g., 2). Exemplary Exp-Golomb codes for the residual level and the signs of the AC coefficients are coded without a context model, and the sign of the DC coefficient is coded using the dc code of its neighboring transform block.

[0139] In some example implementations, the chroma residuals may be jointly coded. Such a coding scheme may be based on some statistical correlation between the chroma channels. For example, in many cases, the Cr and Cb chroma coefficients may be similar in amplitude and opposite in sign, and thus, for example, the transform block level at which the transform coefficients are signaled may be jointly encoded to improve coding efficiency while only introducing small color distortion. The use (activation) of the joint chroma coding mode may be indicated, for example, by a joint chroma coding flag (e.g., TU level flag tu_joint_cbcr_residual_flag), and the selected joint mode may be implicitly indicated by the chroma CBF.

[0140] Specifically, the flag tu_joint_cbcr_residual_flag may be present if either or both of the chroma CBFs of a TU (transform block) are equal to 1. In the PPS and slice header, a chroma quantization parameter (QP) offset value may be signaled for the joint chroma residual coding mode to distinguish it from the chroma QP offset value signaled for the normal chroma residual coding mode. These chroma QP offset values ​​may be used to derive the chroma QP value of those blocks coded using the joint chroma residual coding mode. When the corresponding joint chroma coding mode (mode 2 in Table 3) is active in the TU, this chroma QP offset may be added to the chroma QP of the luma derivation applied during quantization and decoding of that TU. For other modes (modes 1 and 3 in Table 3), the chroma QP may be derived in the same manner as for a conventional Cb or Cr block. The reconstruction process of the chroma residual (resCb and resCr) from the transmitted transform block is shown in Table 3. When this mode is activated (mode 2), one single joint chroma residual block (resJointC[x][y] in Table 3) may be signaled, and the residual block of Cb (resCb) and the residual block of Cr (resCr) may be derived considering information such as tu_cbf_cb, tu_cbf_cr, and CSign, which are code values ​​specified in the slice header, rather than at the transform block level. In some implementations, CSign may be -1 most of the time.

[0141] The three exemplary joint chroma coding modes mentioned above may only be supported in intra-coded CUs. For inter-coded CUs, only mode 2 may be supported. Thus, for inter-coded CUs, the syntax element tu_joint_cbcr_residual_flag is present only if both chroma CBFs are 1.

[0142] [Table 5]

[0143] The above joint chroma coding scheme assumes some correlation between transform coefficients between juxtaposed Cr and Cb transform blocks. These assumptions are usually statistical and therefore may result in distortion in some circumstances. In particular, if one of the color coefficients in a transform block is non-zero while another color component has a zero coefficient, some of the assumptions made in the joint chroma coding scheme will certainly be off, and such coding will not preserve any coded bits (because one of the chroma coefficients is zero anyway).

[0144] In the following various exemplary implementations, a coefficient-level (i.e., per transform coefficient) cross-component coding scheme is described that exploits some correlation between juxtaposed transform coefficients (juxtaposed in the frequency domain) of color components. Such a scheme is particularly useful for transform blocks (or units) where the coefficient of one color component is zero and the corresponding transform coefficient of another color component is non-zero. For these pairs of zero and non-zero color coefficients, either before or after inverse quantization, the non-zero color coefficients can be used to estimate the original small value (which may be small before quantization in the coding process but originally non-zero) of the zero-coded coefficient of the other color component, thereby restoring some information lost in the quantization process during encoding, for example, in some cases. Due to the statistically existing inter-color correlation, some lost information during quantization to zero can be restored. Such cross-component coding recovers the lost information to some extent without significant coding cost (of the zero coefficients).

[0145] In particular, a cross-component coefficient sign coding method may be implemented that utilizes the coefficient sign value of a first color component to code the coefficient sign of a second color component. In a more specific example, the sign value of a Cb transform coefficient may be used as a context for coding other Cr transform coefficients. Such cross-component coding may be implemented for transform coefficient pairs of color components on a coefficient-by-coefficient basis. The principles underlying such implementations and other implementations described in further detail below are not limited to Cr and Cb components. They are applicable between any two of the three color components. In this regard, the luma channel is considered to be one of the color components.

[0146] The following example implementations may be used separately or combined in any order. The term block size may refer to the width or height of a block, or the maximum width and height, or the minimum width and height, or the size of a region (width*height), or the aspect ratio (width:height, or height:width). The term "level value" or "level" may refer to the magnitude of a transform coefficient value.

[0147] In some example implementations, the level values ​​and / or sign values ​​of the transform coefficients of the first color component may be used to derive an offset value to be added to the transform coefficient level values ​​of the second color component.

[0148] In some further implementations, the transform coefficients of the first color component and the second color component used to generate the offset are juxtaposed (same coordinates in the frequency domain, e.g., the estimates are non-crossing frequencies).

[0149] Although the first and second color components described above may not be limited to specific color components, in some exemplary implementations, the first color component may be Cb (or Cr) and the second color component is Cr (or Cb).

[0150] In some particular example implementations, the first color component may be luma and the second color component may be one of Cb and Cr.

[0151] In some particular example implementations, the first color component may be one of Cb and Cr, and the second color component may be luma.

[0152] In some example implementations, the quantized transform coefficients of the first color component may be non-zero, and the quantized transform coefficients of the second color component may be zero. Thus, the original relatively small non-zero information of the original transform coefficients of the second component may be lost due to quantization during the encoding process, and the example implementations described herein help recover some of the lost information using the corresponding non-zero color components that may be statistically correlated with the zero-coefficient color components.

[0153] In some example implementations, the sign value of the transform coefficient of the first color component may be used to derive an offset value that is added to the dequantized transform coefficient level value of the second color component.

[0154] In some example implementations, the sign values ​​of the transform coefficients of the first color component are used to derive an offset value that is added to the transform coefficient level values ​​of the second color component before inverse quantization.

[0155] In some exemplary implementations, if the sign value of the transform coefficient of the first color component is positive (or negative), a negative (or positive) offset value is added to the dequantized transform coefficient level value of the second color component to reconstruct the transform coefficient value of the second color component. In other words, the sign value of the transform coefficient of the first color component and the sign value of the offset value added to the transform coefficient level value of the second color component have different sign values. Such implementations may be consistent with the statistical observation that two chroma components typically have opposite signs for transform coefficients.

[0156] In some example implementations, whether the sign values ​​of the transform coefficients of the first color component and the sign values ​​of the offset values ​​added to the transform coefficient level values ​​of the second color component have opposite sign values ​​is signaled in a high-level syntax, including but not limited to SPS, VPS, PPS, APS, picture header, frame header, slice header, tile header, CTU header, similar to the signaling scheme described above for the joint chroma coding scheme.

[0157] In some example implementations, the offset value added to the transform coefficient level value of the second color component may depend on both the sign and the level of the transform coefficient of the first color component.

[0158] In some example implementations, the magnitude of the offset value added to the transform coefficient level value of the second color component may depend on the transform coefficient of the first color component.

[0159] In some example implementations, the magnitude of the offset value added to the transform coefficient level value of the second color component may be predefined for each input value of the coefficient level of the transform coefficient of the first color component.

[0160] In some example implementations, the offset value added to the transform coefficient level value of the second color component may depend on the frequency that the transform coefficient is located in. For example, the offset value may be smaller for higher frequency coefficients.

[0161] In some example implementations, the offset value added to the transform coefficient level value of the second color component may depend on the block size of the block that the transform coefficient belongs to. For example, the offset value may generally be smaller for larger block sizes.

[0162] In some example implementations, the offset value added to the transform coefficient level value of the second color component may depend on whether the second component is a luma (Y) component or a chroma (Cb or Cr) component. For example, if the second color component is luma, the offset value may be smaller.

[0163] FIG. 16 shows a flowchart 1600 of an example method according to the principles underlying the above implementations for cross-component decoding. The example method flow starts at 1601. At S1610, first transform coefficients of a first color component are extracted from a bitstream of a coded video. At S1620, second transform coefficients of a second color component are extracted from a bitstream of a coded video. At S1630, offset values ​​are derived based on the magnitude or sign value of the first transform coefficients. At S1640, the offset values ​​are added to the magnitude of the second transform coefficients to generate modified second transform coefficients for the second color component. At S1650, the coded video is reconstructed based on at least the first transform coefficients of the first color component and the modified second transform coefficients of the second color component. The example method flow ends at S1699.

[0164] 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.

[0165] The techniques described above may be implemented as computer software using computer-readable instructions and physically stored on one or more computer-readable media. For example, Figure 17 illustrates a computer system (1700) suitable for implementing certain embodiments of the disclosed subject matter.

[0166] 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 via interpretation and execution of microcode, such as by one or more computer central processing units (CPUs) and / or graphics processing units (GPUs).

[0167] The instructions may be executed on various types of computers or components thereof including, for example, personal computers, tablet computers, servers, smart phones, gaming devices, Internet of Things devices, and the like.

[0168] 17 with respect to computer system (1700) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of computer system (1700).

[0169] The computer system (1700) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more human users, for example, via tactile input (e.g., keystrokes, swipes, data glove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), olfactory input (not shown). The human interface devices may be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (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.).

[0170] The input human interface devices may include one or more (only one of each) of a keyboard (1701), a mouse (1702), a trackpad (1703), a touch screen (1710), a data glove (not shown), a joystick (1705), a microphone (1706), a scanner (1707), a camera (1708).

[0171] The computer system (1700) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, for example, by haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback may be included via a touch screen (1710), data gloves (not shown), or joystick (1705), although there may also be haptic feedback devices that do not function as input devices), audio output devices (such as speakers (1709), headphones (not shown)), visual output devices (such as screens (1710), 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 be capable of two-dimensional visual output or three-dimensional or higher output via means such as stereographic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0172] The computer system (1700) may also include human-accessible storage devices and associated media, such as optical media, including CD / DVD ROM / RW (1720) with media (1721) such as CDs / DVDs, thumb drives (1722), removable hard drives or solid state drives (1723), legacy magnetic media such as tapes and floppy disks (not shown), and dedicated ROM / ASIC / PLD based devices such as security dongles (not shown).

[0173] 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.

[0174] The computer system (1700) may also include an interface (1754) to one or more communication networks (1755). The network may be, for example, wireless, wired, optical. The network may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LAN, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable television, satellite television, and terrestrial broadcast television, vehicular and industrial including CAN bus, etc. Certain networks typically require an external network interface adapter attached to a specific general-purpose data port (e.g., a USB port of the computer system (1700)) or peripheral bus (1749), while other networks are typically integrated into the core of the computer system (1700) by attaching to a system bus described below (e.g., an Ethernet interface to a PC computer system or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (1700) may communicate with other entities. Such communications may be unidirectional, receive only (e.g., broadcast TV), unidirectional transmit only (e.g., CANbus to a particular CANbus device), or bidirectional, for example to other computer systems using local or wide area digital networks. Specific protocols and protocol stacks may be used in each of these networks and network interfaces, as described above.

[0175] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to the core (1740) of the computer system (1700).

[0176] The cores (1740) may include one or more central processing units (CPUs) (1741), graphics processing units (GPUs) (1742), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (1743), hardware accelerators for specific tasks (1744), graphics adapters (1750), and the like. These devices may be connected via a system bus (1748), along with read only memory (ROM) (1745), random access memory (1746), and internal mass storage devices (1747), such as internal hard drives, SSDs, etc., that are not accessible to the user. In some computer systems, the system bus (1748) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripherals may be attached directly to the core's system bus (1748) or via a peripheral bus (1749). In one example, a screen (1710) may be connected to the graphics adapter (1750). Peripheral bus architectures include PCI, USB, and the like.

[0177] The CPU (1741), GPU (1742), FPGA (1743), and accelerator (1744) can execute certain instructions that can combine to form the above-mentioned computer code. The computer code can be stored in a ROM (1745) or a RAM (1746). Transient data can also be stored in the RAM (1746), and persistent data can be stored, for example, in an internal mass storage device (1747). Fast storage and retrieval to any of the memory devices can be enabled by the use of cache memory, which can be closely associated with one or more of the CPU (1741), GPU (1742), mass storage device (1747), ROM (1745), RAM (1746), etc.

[0178] The computer-readable medium can bear computer code for performing various computer-implemented operations. The medium and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the kind well known and available to those skilled in the computer software arts.

[0179] As a non-limiting example, a computer system (1700) having the architecture, and in particular a core (1740), may provide functionality as a result of a processor (one or more) (including a CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media may be media associated with user-accessible mass storage devices as introduced above, as well as specific storage devices of the core (1740) of a non-transitory nature, such as the core internal mass storage device (1747) or ROM (1745). Software implementing various embodiments of the present disclosure may be stored in such devices and executed by the core (2640). The computer-readable media may include one or more memory devices or chips according to specific needs. The software may cause the core (2640), and in particular the processors (including a CPU, GPU, FPGA, etc.) therein, to perform certain processes or certain parts of certain processes described herein, including defining data structures stored in RAM (2646) and modifying such data structures according to processes defined by the software. Additionally, or alternatively, the computer system may provide functionality as a result of hardwired or otherwise embodied logic in circuitry (e.g., accelerator (2644)) that may operate in place of or in conjunction with software to perform certain processes or certain portions of certain processes described herein. Where appropriate, references to software may encompass logic and vice versa. 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.

[0180] Although the present disclosure has described some 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.

[0181] Appendix A: Acronyms JEM: Collaborative Search Model VVC: Versatile Video Coding BMS: Benchmark Set MV: Motion Vector HEVC: High Efficiency Video Coding SEI: Supplemental Extended Information VUI: Video Usability Information GOPs: Group of Pictures TUs: conversion units PUs: Prediction Units CTUs: Coding Tree Units CTBs: coding tree blocks PBs: Predicted blocks HRD: Hypothetical Reference Decoder SNR: Signal to Noise Ratio CPUs: Central Processing Units GPUs: Graphics Processing Units 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 Retrieval Team MPM: Most Probable Mode WAIP: Wide-angle Intra Prediction CU: coding unit PU: Prediction Unit TU: conversion unit CTU: Coding Tree Unit PDPC: Position-dependent prediction combination ISP: Intra Subpartition SPS: Sequence Parameter Settings PPS: Picture Parameter Set APS: Adaptive Parameter Set VPS: Video Parameter Set DPS: Decoding Parameter Set ALF: Adaptive Loop Filter SAO: Sample Adaptive Offset CC-ALF: Cross-component adaptive loop filter CDEF: Constrained Directional Enhancement Filter CCSO: Cross component sample offset LSO: Local Sample Offset LR: Loop recovery filter AV1:AOMedia Video 1 AV2:AOMedia Video 2 [Explanation of symbols]

[0182] 101 Samples 102 Arrow 103 Arrow 104 Block 180 Schematic diagram showing intra prediction direction 201 Block 202 Ambient Samples 203 Ambient Samples 204 Ambient Samples 205 Ambient Samples 206 Ambient Samples 300 Communication Systems 310 Terminal Devices 320 Terminal Devices 330 Terminal Devices 340 Terminal Devices 350 Communication Network 400 Communication Systems 401 Video Source 402 Video Picture Stream 403 Video Encoder 404 Video Data, Video Bitstream 405 Streaming Server 406 Client Subsystem 407 Input Copy 408 Client Subsystem 409 Video data, 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 Device, Display 515 Buffer Memory 520 Entropy Decoder / Parser 521 Symbols 530 Electronic Devices 531 Receiver 551 Scaler / Descaler Unit 552 Intra prediction unit, intra picture prediction unit 553 Motion Compensation Prediction Unit 555 Aggregator 556 Loop Filter Unit 557 Reference Picture Memory 558 Picture Buffer 601 Video Sources 603 Video Encoder 620 Electronic Devices, Encoders 630 Source Coder 632 Coding Engine 633 Decoder, Decoding Unit, Local Decoder 634 Reference Picture Memory 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 902 Base Block 904 Base Block 906 Base Block 908 Base Block 1002 "T-shaped" partition, pattern 1004 "T-shaped" partition, pattern 1006 "T-shaped" partition, pattern 1008 "T-shaped" partition, pattern 1102 Vertical bisection (SPLIT_BT_VER) 1104 Horizontal split into two (SPLIT_BT_HOR) 1106 Vertical third division (SPLIT_TT_VER) 1108 Horizontal third division (SPLIT_TT_HOR) 1200 CTB 1202 Square Partition 1204 Square Partition 1206 Square Partition 1208 Square Partition 1302 Square coding block 1304 First Level Split 1306 Second Level Split 1402 Inter-coded Blocks 1404 7 conversion blocks 1600 Flowchart 1700 Computer Systems 1701 Keyboard 1702 Mouse 1703 Trackpad 1705 Joystick 1706 Microphone 1707 Scanner 1708 Camera 1709 Audio Output Device Speaker 1710 Touch Screen 1720 CD / DVD ROM / RW 1721 CD / DVD and other media 1722 Thumb Drive 1723 Removable Hard Drive or Solid State Drive 1740 cores 1741 Central Processing Unit (CPU) 1742 Graphics Processing Unit (GPU) 1743 Field Programmable Gate Area (FPGA) 1744 Hardware Accelerator 1745 Read-Only Memory (ROM) 1746 Random Access Memory (RAM) 1747 Core Internal Mass Storage 1748 System Bus 1749 Peripheral bus 1750 Graphics Adapter 1754 Interface 1755 Communication Network 2640 cores 2644 Accelerator

Claims

1. 1. A method for video encoding, comprising: determining a first transform coefficient for a first color component; determining second transform coefficients for a second color component; deriving an offset value based on a magnitude or sign value of the first transform coefficient; Including, the modified second transform coefficients of the second color component are generated by adding, to the magnitudes of the second transform coefficients, offset values ​​derived based on the magnitudes or sign values ​​of the first transform coefficients. method.

2. The method of claim 1 , wherein the first transform coefficients and the second transform coefficients are juxtaposed.

3. The method of claim 1 , wherein the first color component comprises one chroma component and the second color component comprises another chroma component.

4. The method of claim 1 , wherein the first color component includes a luma component and the second color component includes one chroma component.

5. The method of claim 1 , wherein the first color component comprises one chroma component and the second color component comprises a luma component.

6. the first transform coefficient is non-zero when quantized; the second transform coefficient is zero when quantized; The method of claim 1.

7. the first transform coefficients include a sign value and a magnitude value; deriving the offset value includes deriving the offset value based on the sign value of the first transform coefficient. The method of claim 1.

8. 8. The method of claim 1, wherein adding the offset value to the magnitude of the second transform coefficient comprises adding the offset value to the magnitude of the second transform coefficient after inverse quantization.

9. 8. The method of claim 1, wherein adding the offset value to the magnitude of the second transform coefficient comprises adding the offset value to the magnitude of the second transform coefficient before inverse quantization.

10. the offset value has a sign opposite to that of the first transform coefficient; adding the offset value to the magnitude of the second transform coefficient includes adding the offset value to the magnitude of the second transform coefficient after dequantization.

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

11. whether the sign value of the first transform coefficient and the sign of the offset value are opposite to each other; Video Parameter Set (VPS), Sequence Parameter Set (SPS), Picture Parameter Set (PPS), Adaptive Parameter Set (APS), Frame header, slice header, coding tree unit header, or Tile Header 8. The method according to claim 1, wherein the signal is transmitted in one of the following ways:

12. The method of claim 1 , wherein the offset value depends on both the sign and the magnitude of the first transform coefficient.

13. The method of claim 12 , wherein the magnitude of the offset value depends on the magnitude of the first transform coefficient.

14. The method of claim 12 , wherein the magnitude of the offset value is predefined via a predetermined correspondence between the magnitude of the offset value and the magnitude of the transform coefficient of the first color component.

15. The method according to claim 1 , wherein the offset value is determined depending on a frequency position corresponding to the first transform coefficient.

16. The method according to claim 1 , wherein the offset value is determined depending on a block size of a transform block to which the first transform coefficient and the second transform coefficient belong.

17. The method of claim 1 , wherein the offset value is determined depending on whether the second color component is a luma or a chroma component.

18. A device for video encoding configured to perform a method according to any one of claims 1 to 17.

19. a quantized coefficient of the first transform coefficient is non-zero; the quantized coefficient of the second transform coefficient is zero; 19. The device of claim 18.

20. A computer program for causing a computer to execute a method according to any one of claims 1 to 17.

21. A method for transmitting a video bitstream, comprising: generating a video bitstream, determining a first transform coefficient for a first color component; determining second transform coefficients for a second color component; deriving an offset value based on a magnitude or sign value of the first transform coefficient; Including, the modified second transform coefficients of the second color component are generated by adding, to the magnitudes of the second transform coefficients, offset values ​​derived based on the magnitudes or sign values ​​of the first transform coefficients. generating a video bitstream; transmitting the video bitstream; A method comprising:

22. A computer program which, when executed by a processor, causes the processor to perform the method of claim 21.

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