Deriving offsets in inter-component transform coefficient level restoration.

Abstract

[0001] This disclosure relates generally to video coding, and more particularly to methods and systems for deriving offsets in inter-component transform coefficient level reconstruction. An exemplary method for decoding a current video block of a video stream is disclosed. The method includes receiving a coded video bitstream, extracting first transform coefficients of a first color component for the current video block from the coded video bitstream, determining second transform coefficients of a second color component for the current video block, deriving offset values ​​based on at least one of a quantization step size or the first transform coefficients, adding the offset value to the second transform coefficients to generate modified second transform coefficients for the second color component, and decoding the current video block based on the first transform coefficients and the modified second transform coefficients of the second color component.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 250,832, filed September 30, 2021, which is incorporated by reference in its entirety. This application also claims the benefit of priority to U.S. Nonprovisional Patent Application No. 17 / 939,199, filed September 7, 2022, which is incorporated by reference in its entirety.

[0002] FIELD This disclosure relates generally to video coding / decoding, and more particularly to methods and systems for deriving offsets in inter-component transform coefficient level reconstruction. [Background technology]

[0003] The discussion of the background art provided herein is intended to provide a general context for the present disclosure. The work of the inventors named herein, to the extent that their work is described in this Background section, and aspects of the description that may not otherwise qualify as prior art at the time of the filing of this application, are not admitted, expressly or impliedly, as prior art to the present disclosure.

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

[0005] One goal of video coding and decoding may be to reduce redundancy in an uncompressed input video signal through compression. Compression can help reduce the aforementioned bandwidth and / or storage space requirements, in some cases by more than two orders of magnitude. Both lossless and lossy compression, as well as combinations thereof, may be utilized. Lossless compression refers to techniques that allow an exact copy of the original signal to be restored from the compressed original signal through the decoding process. Lossy compression refers to a coding / decoding process in which the original video information is not fully preserved during coding and cannot be fully restored during decoding. With lossy compression, the restored signal may not be identical to the original signal, but the distortion between the original and restored signals is small enough to make the restored signal useful for the intended application, even with some information loss. For video, lossy compression is widely used in many applications. The amount of acceptable distortion 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 can be selected or adjusted to reflect different distortion tolerances, and generally, higher tolerable distortion allows for coding algorithms that result in higher losses and higher compression ratios.

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

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

[0008] Conventional intra-coding, e.g., 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, e.g., obtained during the encoding and / or decoding of spatial neighbors and that precede in decoding order the block of data being intra-coded or intra-decoded. Such techniques are hereafter referred to as "intra-prediction" techniques. It should be noted that, at least in some cases, intra-prediction uses only reference data from the current picture being reconstructed and not from other reference pictures.

[0009] There may be many different forms of intra prediction. When two or more of such techniques are available in a given video coding technique, the technique in use 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 for 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 improvement by intra prediction, and therefore the entropy coding technique used to convert the codeword into a bitstream.

[0010] Certain modes of intra prediction were introduced from H.264, improved in H.265, and further improved in newer coding techniques such as Joint Search Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). In general, in intra prediction, the predictor block may be formed using neighboring sample values ​​that become available. For example, the available values ​​of a particular set of neighboring samples along a particular direction and / or line may be copied to 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, depicted at the bottom right is a subset of nine predictor directions specified among the 33 possible predictor directions of H.265 (corresponding to the 33 angle modes of the 35 intra modes specified in H.265). The point (101) where the arrows converge represents the sample being predicted. The arrows represent the direction from which neighboring samples are used to predict the sample at 101. For example, arrow (102) indicates that sample (101) is predicted from one or more neighboring samples to the 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 depicted a square block (104) of 4x4 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 4x4 samples in size, S44 is at the bottom right. Also shown is an exemplary reference sample that follows a similar numbering scheme. The reference sample is labeled R, its Y position (e.g., row index), and X position (column index) relative to the block (104). In both H.264 and H.265, predicted samples that neighbor the block being reconstructed are used.

[0013] Intra-picture prediction of block 104 can start by copying reference sample values ​​from adjacent samples according to the 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 at an angle of 45 degrees from the horizontal. In such a case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Then, sample S44 is predicted from reference sample R08.

[0014] In certain cases, 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 is increasing as video coding technology continues to develop. In H.264 (2003), for example, nine different directions are available for intra prediction. In H.265 (2013), that increases to 33, and at the time of this disclosure, JEM / VVC / BMS can support up to 65 directions. Experimental studies have been conducted to help identify the most suitable intra prediction directions, and certain techniques in entropy coding may be used to code those most suitable directions with a small number of bits, accepting a certain bit penalty for the direction. Furthermore, the direction itself can sometimes be predicted from neighboring directions used in the intra prediction of the decoded neighboring blocks.

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

[0017] Schemes for mapping bits representing intra-prediction directions to prediction directions in a coded video bitstream may vary from one video coding technique to another, and may range, for example, from simple direct mapping of prediction directions to intra-prediction modes to complex adaptation schemes including codewords, most probable modes, and similar techniques. In all cases, however, there may be certain directions for intra-prediction that are statistically less likely to occur in the video content than certain other directions. Because the goal of video compression is to reduce redundancy, in a well-designed video coding technique, these less likely directions may be represented by a greater number of 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 part of a picture (e.g., a block) after being spatially shifted in a direction indicated by a motion vector (hereinafter, MV). In some cases, the reference picture may be the same as the picture currently being reconstructed. The MV may have two dimensions X and Y, or three dimensions, with the third dimension being an indication of the reference picture in use (similar to the temporal dimension).

[0019] In some video compression techniques, the current MV applicable to a particular region of sample data can be predicted from other MVs, e.g., other MVs related to other regions of sample data that are spatially adjacent to the region being restored and that precede the current MV in decoding order. Doing so can significantly reduce the overall amount of data required for coding the MVs by relying on the elimination of redundancies in correlated MVs, thereby improving compression efficiency. For example, when coding an input video signal derived from a camera (known as natural video), MV prediction can work effectively because there is a statistical possibility that regions larger than the region to which a single MV is applicable move in similar directions in the video sequence, and thus, in some cases, can be predicted using similar motion vectors derived from MVs of neighboring regions. As a result, the actual MV for a given region will be similar or identical to the MV predicted from the surrounding MVs. Such MVs may then be represented after entropy coding with fewer bits than would be used if the MVs were directly coded rather than predicted from neighboring MVs. In some cases, MV prediction can be an example of lossless compression of a signal (i.e., MV) derived from the 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 Rec. H.265, "High Efficiency Video Coding", December 2016). Among the many MV prediction mechanisms specified by H.265, the one described below is a technique hereafter referred to as "spatial merging".

[0021] Specifically, referring to FIG. 2, a current block (201) contains samples that the encoder found during the motion search process to be predictable from a spatially shifted previous block of the same size. Instead of coding its MV directly, the MV can 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 can use predictors from the same reference picture used by neighboring blocks. Summary of the Invention [Means for solving the problem]

[0022] This disclosure describes various embodiments of methods, apparatus, and computer-readable storage media for deriving offsets in inter-component transform coefficient level restoration.

[0023] According to one aspect, an embodiment of the present disclosure provides a method for deriving an offset in inter-component transform coefficient level restoration. The method includes receiving, by a device, a coded video bitstream. The device includes a memory storing instructions and a processor in communication with the memory. The method also includes extracting, by the device, a first transform coefficient of a first color component for a current video block from the coded video bitstream, determining, by the device, a second transform coefficient of a second color component for the current video block, deriving, by the device, an offset value based on at least one of a quantization step size or the first transform coefficient, adding, by the device, the offset value to the second transform coefficient to generate a modified second transform coefficient for the second color component, and decoding, by the device, the current video block based on the first transform coefficient of the first color component and the modified second transform coefficient of the second color component.

[0024] According to another aspect, an embodiment of the present disclosure provides an apparatus for deriving offsets in inter-component transform coefficient level reconstruction, the apparatus including a memory storing instructions and a processor in communication with the memory, the processor being configured, when executing the instructions, to cause the apparatus to perform the above-described method for video decoding and / or encoding.

[0025] In another aspect, an embodiment of the present disclosure provides a non-transitory computer-readable medium storing instructions that, when executed by a computer for decoding and / or encoding video, cause the computer to perform the above-mentioned method for decoding and / or encoding video.

[0026] These and other aspects and their implementations are described in further detail in the drawings, specification, and claims.

[0027] 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]

[0028] [Figure 1A] FIG. 2 is a schematic diagram of an example subset of intra-prediction direction modes. [Figure 1B] FIG. 2 is a diagram of an example intra-prediction direction. [Diagram 2] FIG. 2 is a schematic diagram of a current block and its surrounding spatial merge candidates for motion vector prediction in one example. [Diagram 3] 1 is a schematic diagram of a simplified block diagram of a communication system (300) according to an exemplary embodiment. [Figure 4] 4 is a schematic diagram of a simplified block diagram of a communication system (400) according to an example embodiment. [Diagram 5] 2 is a schematic diagram of a simplified block diagram of a video decoder according to an example embodiment; [Figure 6]1 is a schematic diagram of a simplified block diagram of a video encoder according to an example embodiment; [Figure 7] 4 is a block diagram of a video encoder according to another example embodiment. [Figure 8] 4 is a block diagram of a video decoder according to another example embodiment. [Figure 9] FIG. 2 illustrates a coding block partitioning scheme according to an exemplary embodiment of the present disclosure. [Figure 10] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 11] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 12] FIG. 2 illustrates an exemplary partitioning of a base block into coding blocks according to an exemplary partitioning scheme. [Figure 13] FIG. 2 illustrates an exemplary division-of-thirds scheme. [Figure 14] FIG. 2 illustrates an exemplary quadtree / binary tree coding block partitioning scheme. [Figure 15] 4A-4C are diagrams illustrating 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 16] 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 17] FIG. 13 illustrates another scheme for splitting a coding block into multiple transform blocks, according to an exemplary embodiment of the present disclosure. [Figure 18] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 19] 1 is a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Throughout this specification and the claims, terms may have subtle meanings that are suggested or implied in the context beyond the meaning explicitly stated. The phrases "in one embodiment" or "in some embodiments" used herein do not necessarily refer to the same embodiment, and the phrases "in another embodiment" or "in other embodiments" used herein do not necessarily refer to different embodiments. Similarly, the phrases "in one implementation" or "in some implementations" used herein do not necessarily refer to the same implementation, and the phrases "in another implementation" or "in other implementations" used herein do not necessarily refer to different implementations. For example, the claimed subject matter is intended to include all or part of the exemplary embodiments / implementations.

[0030] Generally, terms may be understood at least in part from their usage in context. For example, terms such as "and", "or", or "and / or" as used herein may include various meanings that may depend at least in part on the context in which such terms are used. Typically, "or" when used to relate a list such as A, B, or C is intended to mean A, B, and C, which are used herein in an inclusive sense, as well as A, B, or C, which are used herein in an exclusive sense. In addition, the terms "one or more" or "at least one" as used herein may be used to describe any feature, structure, or characteristic in a singular sense, or may be used to describe a combination of features, structures, or characteristics in a plural sense, depending at least in part on the context. Similarly, terms such as "a", "an", or "the" may also be understood to convey a singular usage or a plural usage, depending at least in part on the context. In addition, the terms "based on" or "determined by" may be understood not to be necessarily intended to convey an exclusive set of factors, but instead may allow for the existence of additional factors not necessarily explicitly described, again depending at least in part on the context. FIG. 3 illustrates a simplified block diagram of a communication system (300) according to one embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) can perform unidirectional transmission of data. For example, the terminal device (310) can code video data (e.g., of a stream of video pictures captured by the terminal device (310)) for transmission to another terminal device (320) via the network (350). The coded video data can be transmitted in the form of one or more coded video bitstreams.The terminal device (320) can receive the coded video data from the network (350), decode the coded video data to recover the video picture, and display the video picture according to the recovered video data. The one-way data transmission may be implemented in a media serving application, etc.

[0031] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of coded video data, such as may be implemented during a video conferencing application. In the case of bidirectional transmission of data, in one example, each of the terminal devices (330) and (340) can code video data (e.g., of a stream of video pictures captured by the 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) can also receive coded video data transmitted by the other of the terminal devices (330) and (340), can decode the coded video data to recover the video pictures, and can display the video pictures on an accessible display device according to the recovered video data.

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

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

[0034] A video streaming system may include a video source (401) for creating a stream of uncompressed video pictures or images (402), a video capture subsystem (413) that may include, for example, a digital camera. In one example, the stream of video pictures (402) includes samples recorded by the digital camera of the video source 401. The stream of video pictures (402), depicted as a bold line to emphasize the large amount of data when compared to the encoded video data (404) (or coded video bitstream), may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), depicted as thin lines to emphasize the reduced amount of data when compared to the stream of uncompressed video pictures (402), can be stored in the streaming server (405) or directly in 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, can access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) can include, for example, a video decoder (410) in the electronic device (430). The video decoder (410) decodes an 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 depicted). 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.

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

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

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

[0038] The video decoder (510) may include a parser (520) to recover 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 device (512) (e.g., a display screen) that may or may not be an integral part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device may be in the form of a supplemental enhancement information (SEI message) or a video usability information (VUI) parameter set fragment (not depicted). 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 follow a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context dependency, etc. The parser (520) can 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 can include groups of pictures (GOPs), pictures, tiles, slices, macroblocks, coding units (CUs), blocks, transform units (TUs), prediction units (PUs), etc. The parser (520) can also extract information from the coded video sequence, such as transform coefficients (e.g., Fourier transform coefficients), quantization parameter values, motion vectors, etc.

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

[0040] The recovery of the symbols (521) may involve a number of different processing or functional units, depending on the type of coded video picture or portion thereof (such as interpicture and intrapicture, interblock and intrablock, 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 depicted for the sake of simplicity.

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

[0042] The first unit may include a scalar / inverse transform unit (551), which may receive quantized transform coefficients as well as control information from the parser (520) including information indicating which type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc., as symbols (521). The scalar / inverse transform unit (551) may output blocks containing sample values ​​that may be input to an aggregator (555).

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

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

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

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

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

[0048] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard such as ITU-T Rec. H.265. The coded video sequence may conform to the 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, the profile may select some tools from all tools available in the video compression technique or standard as the only tools available for use under that profile. To conform to a standard, the complexity of the coded video sequence may be within a range defined by the level of the video compression technique or standard. In some cases, the level limits the maximum picture size, the maximum frame rate, the maximum reconstructed sample rate (e.g., measured in megasamples per second), the 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.

[0049] In some exemplary embodiments, the receiver (531) can 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 recover the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

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

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

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

[0053] According to some exemplary embodiments, the video encoder (603) can 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) is functionally coupled to and can control other functional units described below. For the sake of brevity, couplings are not depicted. Parameters set by the controller (650) can include rate control related parameters (picture skip, quantizer, lambda value for rate distortion optimization techniques, ...), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) can be configured to have other appropriate functions associated with the video encoder (603) optimized for a particular system design.

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

[0055] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. However, and with brief reference again to Figure 5, 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 the parser (520), may not need to be implemented entirely within the local decoder (633) in the encoder.

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

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

[0058] The local video decoder (633) can decode coded video data of pictures that may be designated as reference pictures based on 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) can 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) can locally store copies of reconstructed reference pictures that have common content with reconstructed reference pictures obtained by a far-end (remote) video decoder (without transmission errors).

[0059] The predictor (635) may perform a prediction search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or specific metadata such as reference picture motion vectors, block shapes, etc., that may serve as suitable prediction references for the new picture. The predictor (635) may operate on sample blocks on a pixel block by pixel block basis 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).

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

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

[0062] The transmitter (640) can 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 coded video data. The transmitter (640) can merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

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

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

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

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

[0067] A source picture may be typically 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 respective picture of the block. 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 prediction 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.

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

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

[0070] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra prediction) exploits spatial correlation within 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. A block in the current picture may be coded by a vector, called a motion vector, when it resembles a reference block in a reference picture that was previously coded and is still buffered in the video. A motion vector points to a reference block in the reference picture and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0071] In some exemplary embodiments, bi-prediction techniques 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 can 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.

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

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

[0074] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of 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.

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

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

[0077] The inter encoder (730) is configured to receive a sample of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures in display order), generate inter prediction information (e.g., a description of redundancy information, motion vectors, merge mode information according to inter encoding techniques), and calculate an inter prediction result (e.g., a prediction block) based on the inter prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture decoded based on the encoded video information 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).

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

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

[0080] The residual calculator (723) may be configured to calculate a difference (residual data) between a received block and a prediction result for a block selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) may be configured to encode the residual data to generate transform coefficients. For example, the residual encoder (724) may be configured to transform the residual data from a spatial domain to a 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) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are appropriately processed to generate decoded pictures, which can be buffered in a memory circuit (not shown) and used as reference pictures.

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

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

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

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

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

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

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

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

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

[0090] Turning to block partitioning for coding and decoding, a general partitioning may start from a base block and may follow a predefined set of rules, a specific pattern, a partitioning tree, or any partitioning structure or scheme. The partitioning may be hierarchical and recursive. After isolating or dividing the base block according to any of the exemplary partitioning procedures described below or other procedures, or combinations thereof, a final set of partitions or coding blocks may be obtained. Each of these partitions may be at one of various partitioning levels in the partitioning hierarchy and may be partitions of various shapes. Each of the partitions may be referred to as a coding block (CB). In various exemplary partitioning implementations described further below, each resulting CB may be a CB of any of the allowed sizes and partitioning levels. Such partitions are referred to as coding blocks because they may form a unit for which some basic coding / decoding decisions may be made and coding / decoding parameters may be optimized, determined, and signaled in the encoded video bitstream. The highest or deepest level in the final partition represents the depth of the coding block partitioning tree structure. The coding block may be a luma coding block or a chroma coding block. The CB tree structure for each color is sometimes called a coding block tree (CBT).

[0091] The coding blocks of all color channels may be collectively referred to as a coding unit (CU). The hierarchical structure of all color channels may be collectively referred to as a coding tree unit (CTU). The partitioning pattern or partitioning structure of various color channels within a CTU may or may not be the same.

[0092] In some implementations, the partitioning tree scheme or structure used for the luma and chroma channels may not be the same. In other words, the luma and chroma channels may have separate coding tree structures or patterns. Furthermore, whether the luma and chroma channels 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 and luma channels may have separate coding partition tree structures or coding partition tree structure modes, while for a P slice or a B slice, the luma and chroma channels 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 CBs by one coding partition tree structure, and the chroma channel may be partitioned into chroma CBs by another coding partition tree structure.

[0093] In some exemplary implementations, a predefined partitioning pattern may be applied to the base block. As shown in FIG. 9, an exemplary four-way partitioning tree may start at a first predefined level (e.g., 64×64 block level or other size as the base block size), and the base block may be partitioned hierarchically down to a predefined lowest level (e.g., 4×4 level). For example, the base block may follow four predefined partitioning options or patterns shown by 902, 904, 906, and 908, and the partition designated as R is capable of recursive partitioning in that the same partitioning options 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 added to the partitioning scheme of FIG. 9. In the implementation of FIG. 9, rectangular partitions (e.g., 1:2 / 2:1 rectangular partitions) are possible, but they may not be used repeatedly, whereas square partitions may be used repeatedly. Subsequent partitioning of FIG. 9 by recursion generates a final set of coding blocks, if necessary. A coding tree depth may be further defined to indicate the division depth from a root node or root block. For example, the coding tree depth for a root node or root block of 64×64 block may be set to 0, and after the root block is further divided one time according to FIG. 9, the coding tree depth increases by 1. The maximum or deepest level from the 64×64 base block to the 4×4 minimum partition is 4 (starting from level 0) in the above scheme. Such a division scheme may be applied to one or more of the color channels. Each color channel may be divided separately according to the scheme of FIG. 9 (e.g., for each of the color channels at each hierarchical level, a division pattern or option in the predefined pattern may be determined separately). Alternatively, two or more color channels may share the same hierarchical pattern tree of FIG. 9 (e.g., for two or more color channels at each hierarchical level, the same division pattern or option in the predefined pattern may be selected).

[0094] FIG. 10 illustrates another exemplary predefined partitioning pattern that allows recursive partitioning to form a partitioning tree. As illustrated in FIG. 10, an exemplary 10-way partitioning structure or pattern may be predefined. A root block may start from a predefined level (e.g., from a base block at a 128×128 level or a 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 as 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 exemplary implementations, none of the rectangular partitions of FIG. 10 may be further subdivided. A coding tree depth may be further defined to indicate a partitioning depth from a root node or root block. For example, the coding tree depth for the root node or root black of a 128x128 block may be set to 0, and after the root block is further split one time according to FIG. 10, the coding tree depth increases by 1. 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 may not be possible for the square partitions in the T-shaped patterns 1002, 1004, 1006, and 1008. The splitting procedure following 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. In some implementations, more flexibility may be added to the use of partitions less than 8x8 levels. For example, in some cases, 2x2 chroma inter prediction may be used.

[0095] In some other example implementations of coding block partitioning, a quadtree structure may be used to partition a base block or an intermediate block into quadtree partitions. Such quadtree partitioning may be applied hierarchically and recursively to any square partition. Whether a base block or intermediate block or partition is further quadtree partitioned may be adapted to various local characteristics of the base block or intermediate block / partition. The quadtree partitioning at the picture boundary may be further adapted. For example, an implicit quadtree partitioning may be performed at the picture boundary such that a block continues to be quadtree partitioned until its size fits into the picture boundary.

[0096] In some other example implementations, a hierarchical binary split from the base block may be used. For such a scheme, the base block or mid-level block may be split into two partitions. The bisection may be either horizontal or vertical. For example, a horizontal bisection may split the base block or mid-block into equal left and right partitions. Similarly, a vertical bisection may split the base block or mid-block into equal top and bottom partitions. Such bisection may be hierarchical and recursive. It may be determined at each of the base block or mid-block whether the bisection scheme should continue and, if the scheme continues further, whether a horizontal or vertical bisection should be used. In some implementations, further splitting may stop at a predefined minimum partition size (in one or both dimensions). Alternatively, further splitting may stop when a predefined split level or depth from the base block is reached. In some implementations, the aspect ratio of the partitions may be limited. For example, the aspect ratio of the partitions may not be smaller than 1:4 (or larger than 4:1). Therefore, a vertical strip partition, having a vertical to horizontal aspect ratio of 4:1, can only be further divided vertically into an upper and lower partition, each having a vertical to horizontal aspect ratio of 2:1.

[0097] In yet some other examples, a three-way division scheme may be used to divide the base block or any intermediate blocks, as shown in FIG. 13. The ternary pattern may be implemented vertically, as shown in 1302 of FIG. 13, or horizontally, as shown in 1304 of FIG. 13. The example division ratio of FIG. 13 is shown as 1:2:1 either vertically or horizontally, but other ratios may be predefined. In some implementations, two or more different ratios may be predefined. Such a three-way division scheme may be used to complement a quadtree or bipartition structure, in that such a ternary tree division may capture an object located at a block center in one contiguous partition, whereas quadtrees and bipartitions always divide along the block center, thus dividing the object into separate partitions. In some implementations, the width and height of the partitions of the example ternary tree are always powers of two to avoid further transformations.

[0098] The above partitioning schemes may be combined in any manner at different partitioning levels. As an example, the above-mentioned quadtree and bipartitioning schemes may be combined to partition the base block into a quadtree-bipartition (QTBT) structure. In such a scheme, the base block or intermediate blocks / partitions may be either quadtree-partitioned or bipartitioned, if specified, according to a set of predefined conditions. A particular example is shown in FIG. 14. In the example of FIG. 14, the base block is first quadtree-partitioned into four partitions, as shown by 1402, 1404, 1406, and 1408. Then, each of the resulting partitions is either quadtree-partitioned into four further partitions (such as 1408) or bipartitioned into two further partitions at the next level (e.g., either horizontally or vertically, such as 1402 or 1406, both of which are symmetric), or not partitioned (such as 1404). Bisection or quadtree partitioning may be recursively enabled for square partitions, as illustrated by the overall exemplary partitioning pattern in 1410 and the corresponding tree structure / representation in 1420, where solid lines represent quadtree partitioning and dashed lines represent bisection. A flag may be used for each bisection node (non-leaf binary partition) to indicate whether the bisection is horizontal or vertical. For example, flag "0" may represent horizontal bisection and flag "1" may represent vertical bisection, as illustrated in 1420, which matches the partitioning structure in 1410. In the case of quadtree partitioning, there is no need to specify the partition type, since quadtree partitioning always splits a block or partition both horizontally and vertically to generate four sub-blocks / partitions of equal size. In some implementations, flag "1" may represent horizontal bisection and flag "0" may represent vertical bisection.

[0099] In some example implementations of QTBT, the quadtree and bisection rule sets may be represented by the following predefined parameters and their associated corresponding functions: -CTU size: quadtree root node size (base block size) -MinQTSize: The minimum allowable quadtree leaf node size. -MaxBTSize: Maximum allowable binary tree root node size -MaxBTDepth: Maximum allowed binary tree depth -MinBTSize: The minimum allowable binary tree leaf node size. In some exemplary implementations of the QTBT partitioning structure, the CTU size may be set as 128×128 luma samples with two corresponding 64×64 blocks of chroma samples (when exemplary chroma subsampling is considered and used), the MinQTSize may be set as 16×16, the MaxBTSize may be set as 64×64, the MinBTSize may be set as 4×4 (for both width and height), and the MaxBTDepth may be set as 4. A quadtree partition may be applied to the CTU first to generate quadtree leaf nodes. A quadtree leaf node may have a size from its minimum allowable size of 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If a node is 128×128, it will not be split by the binary tree first because its size exceeds MaxBTSize (i.e., 64×64). Otherwise, a node that does not exceed MaxBTSize may be split by the binary tree. In the example of FIG. 14, the base block is 128×128. The base block can only be quadtree partitioned according to a predefined set of rules. The base block has a partition depth of 0. Each of the resulting four partitions is 64×64, not exceeding MaxBTSize, and may be further quadtree or bintree partitioned at level 1. The process continues. When the bintree depth reaches MaxBTDepth (i.e., 4), no further partitions may be considered. When the width of a bintree node is equal to MinBTSize (i.e., 4), no further horizontal partitions may be considered. Similarly, when the height of a bintree node is equal to MinBTSize, no further vertical partitions may be considered.

[0100] In some example implementations, the above QTBT scheme may be configured to support flexibility for luma and chroma to have the same QTBT structure or separate QTBT structures. For example, for P slices and B slices, the luma CTB and chroma CTB in one CTU may share the same QTBT structure. However, for I slices, the luma CTB may be divided into CBs by a QTBT structure, and the chroma CTB may be divided into chroma CBs by another QTBT structure. This means that CUs may be used to refer to different color channels in an I slice, e.g., 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 may consist of coding blocks of all three color components.

[0101] In some other implementations, the QTBT scheme may be complemented with the ternary scheme described above. Such implementations may be referred to as a multi-type tree (MTT) structure. For example, in addition to the bisection of the node, one of the trisection patterns of FIG. 13 may be selected. In some implementations, only square nodes may undergo trisection. An additional flag may be used to indicate whether the trisection is horizontal or vertical.

[0102] The design of two-level or multi-level trees, such as the QTBT implementation and the QTBT implementation complemented by trisection, may be motivated primarily by reduced complexity. In theory, the complexity of traversing a tree is T D where T represents the number of split types and D is the depth of the tree. Trade-offs may be made by using multitypes (T) while reducing the depth (D).

[0103] 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 prediction or inter-frame prediction during the coding and decoding processes. In other words, the CB may be further divided 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 then be further divided into one or more TBs after being determined following the division of the coding block. For example, in some implementations, the PB may be divided into one, two, four, or other number of TBs.

[0104] In some implementations, the luma and chroma channels may be processed differently to split the base blocks into coding blocks and further into prediction and / or transform blocks. For example, in some implementations, splitting of the coding blocks into prediction and / or transform blocks may be allowed for the luma channel, but such splitting of the coding blocks into prediction and / or transform blocks may not be allowed for the chroma channel. In such implementations, the transformation and / or prediction of the luma blocks may therefore be performed only at the coding block level. In another example, the minimum transform block size for the luma and chroma channels may be different, e.g., the coding blocks for the luma channel may be allowed to be split into smaller transform and / or predictive blocks than the chroma channel. In yet another example, the maximum depth of the splitting of the coding blocks into transform and / or predictive blocks may be different between the luma and chroma channels, e.g., the coding blocks for the luma channel may be allowed to be split into deeper transform and / or predictive blocks than the chroma channel. In a specific example, a luma coding block may be partitioned into transform blocks of multiple sizes that can be represented by a recursive partitioning down to two levels, and transform block shapes such as square, 2:1 / 1:2, and 4:1 / 1:4, as well as transform block sizes from 4 x 4 to 64 x 64 may be allowed. However, for chroma blocks, only the largest possible transform block designated for the luma block may be allowed.

[0105] 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.

[0106] The division of the coding block (or prediction block) into transform blocks may be performed in various exemplary manners, including but not limited to quadtree division and predefined pattern division, recursively or non-recursively, further considering transform blocks at the boundaries of the coding block or prediction block. In general, the resulting transform blocks may be at different division levels, may not be the same size, and may not need to be square in shape (e.g., they may be rectangular with some allowed size and aspect ratio). Further examples are described in more detail below with respect to Figures 15, 16, and 17.

[0107] However, in some other implementations, the CB obtained via any of the above partitioning schemes may be used as a basic or minimum coding block for prediction and / or transformation. In other words, no further partitioning is performed for the purpose of performing inter-prediction / intra-prediction and / or for the purpose of transformation. For example, the CB obtained from the above QTBT scheme may be used as a unit for performing prediction as is. Specifically, such a QTBT structure removes the concept of multiple partition types, i.e., removes the separation of CU, PU, ​​and TU, and supports more flexibility on CU / CB partition shapes as described above. In such a QTBT block structure, the CU / CB can have either a square or rectangular shape. The leaf nodes of such a QTBT are used as units for prediction and transformation processing without further partitioning. This means that the CU, PU, ​​and TU have the same block size in such an exemplary QTBT coding block structure.

[0108] The above various CB division schemes, as well as further division of the CB into PB and / or TB (including no PB / TB division), may be combined in any manner. The following specific implementations are provided as non-limiting examples.

[0109] Specific exemplary implementations of the division of coding blocks and transform blocks are described below. In such exemplary implementations, base blocks may be divided into coding blocks using recursive quadtree division or predefined division patterns described above (such as the division patterns of Figures 9 and 10). At each level, whether further quadtree division of a particular partition should be continued may be determined by local video data characteristics. The resulting CBs may be at various quadtree division levels and of various sizes. The decision of whether to code a picture area using inter-picture (temporal) prediction or intra-picture (spatial) prediction may be made at the CB level (or at the CU level for all three color channels). Each CB may be further divided into one, two, four, or other number of PBs according to a predefined PB division type. Within one PB, the same prediction process may be applied, and related information may be transmitted to the decoder on a PB basis. After obtaining the residual blocks by applying the prediction process based on the PB division type, the CBs may be divided into TBs according to another quadtree structure similar to the coding tree for CBs. In this particular implementation, the CB or TB may be, but need not be, limited to a square shape. Furthermore, 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 quadtree partitioning) into smaller TBs called residual quadtrees (RQTs).

[0110] Another exemplary implementation for splitting a base block into CB, PB, and / or TB is further described below. For example, rather than using multiple partition unit types such as the types shown in FIG. 9 or FIG. 10, a quadtree with nested multi-type trees using bipartition and tripartition segmentation structures (e.g., QTBT or QTBT with tripartition described above) may be used. Separation 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, when such CBs require further splitting. This exemplary splitting scheme may be designed to support further flexibility on CB splitting shapes, such that prediction and transformation can both be performed at the CB level without further splitting. In such coding tree structures, CBs may have either square or rectangular shapes. Specifically, a coding tree block (CTB) may first be split by a quadtree structure. Then, the quadtree leaf nodes may be further split by a nested multi-type tree structure. An example of a nested multi-type tree structure using bisection or trisection is shown in FIG. 11. Specifically, the example multi-type tree structure in FIG. 11 includes four split types called vertical bisection (SPLIT_BT_VER) (1102), horizontal bisection (SPLIT_BT_HOR) (1104), vertical trisection (SPLIT_TT_VER) (1106), and horizontal trisection (SPLIT_TT_HOR) (1108). Then, CB corresponds to a leaf of the multi-type tree. In this example implementation, as long as CB is not too large for the maximum transform length, this segmentation is used for both prediction and transform processing without further splitting. This means that in most cases, CB, PB, and TB have the same block size in a quadtree with 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 CB.In some implementations, in addition to bisection or trisection, the nested pattern of FIG. 11 may further include a quadtree division.

[0111] One specific example of a quadtree with nested multi-type tree coding block structure of block partitioning (including quadtree partitioning, bisection, and trisection options) for one base block is shown in FIG. 12. More specifically, FIG. 12 shows that a base block 1200 is quadtree partitioned into four square partitions 1202, 1204, 1206, and 1208. A decision to further use the multi-type tree structure and quadtree of FIG. 11 for further partitioning is made for each of the quadtree partitioned partitions. In the example of FIG. 12, partition 1204 is not further partitioned. Partitions 1202 and 1208 each adopt a different quadtree partitioning. In partition 1202, the second level quadtree partitioned top left, top right, bottom left, and bottom right partitions adopt third level partitioning of quadtree, horizontal bisection 1104 of FIG. 11, non-partition, and horizontal trisection 1108 of FIG. 11, respectively. Partition 1208 adopts another quadtree division, and the second level quadtree divided top-left, top-right, bottom-left, and bottom-right partitions adopt third level division of vertical third division 1106, unsplit, unsplit, and horizontal bisection 1104 of FIG. 11, respectively. Two of the subpartitions of the top-left partition of the third level of 1208 are further divided according to horizontal bisection 1104 and horizontal third division 1108 of FIG. 11, respectively. Partition 1206 adopts a second level division pattern into two partitions following vertical bisection 1102 of FIG. 11, and the two partitions are further divided at the third level according to horizontal third division 1108 and vertical bisection 1102 of FIG. 11. A fourth level division is further applied to one of them according to horizontal bisection 1104 of 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 be different from luma, e.g., 32 x 32. Even if the above example CB of Figure 12 is not generally further divided into smaller PBs and / or TBs, when the width or height of the luma coding block or chroma coding block is larger than the maximum transform width or maximum transform height, the luma coding block or chroma coding block may be automatically divided in the horizontal and / or vertical directions to satisfy the transform size constraints in that direction.

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

[0114] When a coding block is further divided into multiple transform blocks, the transform blocks therein may be ordered in the bitstream according to various orders or scanning schemes. Exemplary implementations for dividing a coding block or a prediction block into transform blocks and the coding order of the transform blocks are described in further detail below. In some exemplary implementations, as described above, the transform division can support transform blocks of multiple shapes, e.g., 1:1 (square), 1:2 / 2:1, and 1:4 / 4:1, with transform block sizes ranging from, e.g., 4×4 to 64×64. In some implementations, when a coding block is smaller than or equal to 64×64, the transform block division 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 divided into transform blocks that are multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32), respectively.

[0115] In some example implementations of transform block partitioning, for both intra-coded and inter-coded blocks, the coding block may be further partitioned into multiple transform blocks with a partition depth up to a predefined number of levels (e.g., two levels). The partition depth and size of the transform block may be related. For some example implementations, the 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] Based on the example mapping in Table 1, for a 1:1 square block, the next level transform split can create four 1:1 square sub-transform blocks. The transform split may stop at, for example, 4×4. Thus, a transform size of the current depth of 4×4 corresponds to the same size of 4×4 of the next depth. In the example of Table 1, for a 1:2 / 2:1 non-square block, the next level transform split can create two 1:1 square sub-transform blocks, while for a 1:4 / 4:1 non-square block, the next level transform split can create two 1:2 / 2:1 sub-transform blocks.

[0118] In some example implementations, for the luma component of an intra-coded block, further restrictions may be added on the transform block partitioning. 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, a second level partitioning must be applied to all first level sub-blocks. An example of a transform block partitioning for an intra-coded square block according to Table 1 is shown in FIG. 15 with the coding order indicated by the arrows. Specifically, 1502 shows a square coding block. The first level partitioning according to Table 1 into four equal-sized transform blocks is shown in 1504 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 1506 with the coding order indicated by the arrows.

[0119] In some exemplary implementations, the above restrictions on intra-coding may not apply for the luminance component of an inter-coded block. For example, after the first level of transform division, any one of the sub-transform blocks may be further divided independently at another level. Thus, the resulting transform blocks may or may not be blocks of the same size. An exemplary division of an inter-coded block into transform blocks according to their coding order is shown in FIG. 16. In the example of FIG. 16, an inter-coded block 1602 is divided into transform blocks at two levels according to Table 1. At the first level, the inter-coded block is divided into four transform blocks of equal size. Then, only one of the four transform blocks (but not all of them) is further divided into four sub-transform blocks, resulting in a total of seven transform blocks with two different sizes, as indicated by 1604. An exemplary coding order of these seven transform blocks is indicated by arrows at 1604 in FIG. 16.

[0120] In some example implementations, for chroma components, some further restrictions on the transform blocks may be added: for example, for chroma components, the transform block size may be as large as the coding block size, but cannot be smaller than a predefined size, e.g., 8×8.

[0121] In some other example implementations, for coding blocks with either width (W) or height (H) greater than 64, both luma coding blocks and chroma coding blocks may be implicitly divided into multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32), respectively, where in this disclosure, “min(a,b)” may return the smaller value between a and b.

[0122] Figure 17 further illustrates another alternative exemplary scheme for splitting a coding block or a predictive block into transform blocks. Instead of using recursive transform partitioning as illustrated in Figure 17, a set of predefined partition types may be applied to a coding block according to the transform type of the coding block. In the particular example illustrated in Figure 17, one of six exemplary partition types may be applied to split the coding block into various numbers of transform blocks. Such a scheme for generating transform block partitions may be applied to either a coding block or a predictive block.

[0123] More specifically, the partitioning scheme of FIG. 17 provides up to six exemplary partitioning types for any given transform type (transform type refers to the type of primary transform, such as, for example, ADST). In this scheme, every coding block or predictive block may be assigned a transform partitioning type, for example, based on a rate-distortion cost. In one example, the transform partitioning type assigned to a coding block or predictive block may be determined based on the transform type of the coding block or predictive block. As illustrated by the six transform partitioning types illustrated in FIG. 17, a particular transform partitioning type may correspond to the partitioning size and pattern of the transform block. The correspondence between various transform types and various partitioning types may be predefined. An example is shown below in which capitalized labels indicate transform partitioning 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 of 1 / 2 the block size in width and 1 / 2 the block size in height.

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

[0127] ·PARTITION_VERT: Allocates a transformation size with a width half the block size and a height equal to the block size.

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

[0129] ·PARTITION_VERT4: Allocates a transformation size with a width of 1 / 4 of the block size and a height equal to the block size.

[0130] In the above example, the transform split types shown in Figure 17 include uniform transform sizes for all split transform blocks. This is not a limitation but merely an example. In some other implementations, mixed transform block sizes may be used for the split transform blocks in a particular split type (or pattern).

[0131] The PBs (or CBs, also called PBs when not further divided into predictive blocks) obtained from any of the above partitioning schemes can then become individual blocks for coding via either intra-prediction or inter-prediction. In the case of inter-prediction for the current PB, a residual between the current block and the predictive block may be generated, coded, and included in the coded bitstream.

[0132] Turning to some example implementations of specific types of signaling for coding blocks / units, for each intra-coding unit 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 2-4 and represented by the read_skip() function for retrieving these flags from the bitstream. This flag may indicate whether the transform coefficients are currently all zero in the coded 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 may 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 2-4, this flag may be signaled after a skip_mode flag indicating that the coding unit may be skipped for various reasons. When skip_mode is true, the coding unit should be skipped and there is no need to signal the skip_txfm flag and the skip_txfm 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 further signaled to indicate whether the coding unit is all zeros or not.

[0133] [Table 2]

[0134] [Table 3]

[0135] [Table 4]

[0136] 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. Y, U, and V are used below to denote the three color components. Furthermore, the terms "coding block" and "coding" block are used interchangeably to mean either a block to be coded or a block that has already been coded. They may be blocks of any of the three color components. Three corresponding color coding / coding blocks may be for a coding / coding unit.

[0137] Turning to the coding and decoding (entropy coding) of the residual transform coefficients in each color component, for each transform block, the transform coefficient coding can start with the signaling of a skip sign, followed by the transform kernel type and end of block (EOB) position when the skip sign is 0 (indicating the presence of non-zero coefficients). Then, each coefficient value is mapped to multiple level maps (amplitude maps) and signs.

[0138] After the EOB position is coded, the lower 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 lower 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 the signs of the coefficients as well as the residual values ​​of the coefficients greater than the higher level (e.g., 14) in forward scan order, for example by an Exp-Golomb code.

[0139] With regard to the use of context modeling, the lower level map coding can incorporate the size and direction of the transform as well as up to five neighboring coefficient information, while the mid-level map coding can follow a similar approach to the lower level amplitude coding, except that the number of neighboring coefficients is reduced to a smaller number (e.g., two). An exemplary Exp-Golomb code for the residual level as well as the signs of the AC coefficients are coded without a context model, and the signs of the DC coefficients are coded using the dc codes of their neighboring transform blocks.

[0140] 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 chroma coefficients of Cr and Cb 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 coded 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 coding / coding block flag (CBF).

[0141] Specifically, the flag tu_joint_cbcr_residual_flag may be present if either or both of the chroma CBFs for a TU (transform block) are equal to 1. In the PPS and slice header, chroma quantization parameter (QP) offset values ​​may be signaled for the joint chroma residual coding mode to distinguish them from the chroma QP offset values ​​signaled for the regular chroma residual coding mode. These chroma QP offset values ​​may be used to derive chroma QP values ​​for those blocks coded using the joint chroma residual coding mode. When the corresponding joint chroma coding mode (mode 2 in Table 5) is active in the TU, this chroma QP offset may be added to the luma-derived chroma QP applied during quantization and decoding of that TU. For other modes (modes 1 and 3 in Table 5), the chroma QP may be derived in the same manner as for a conventional Cb or Cr block. The reconstruction process of the chroma residuals (resCb and resCr) from the transmitted transform blocks is depicted in Table 5. When this mode is activated (mode 2), one single joint chroma residual block (resJointC[x][y] in Table 5) may be signaled, and the residual block for Cb (resCb) and the residual block for Cr (resCr) may be derived considering information such as tu_cbf_cb, tu_cbf_cr, and CSign, which is the sign value specified in the slice header, rather than at the transform block level. In some implementations, CSign may be −1 most of the time. In Table 5, the value CSign is the sign value (+1 or −1) that may be specified in the slice header, and resJointC[][] is the transmitted residual.

[0142] The three exemplary joint chroma coding modes described above may be supported only 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.

[0143] [Table 5]

[0144] The above joint chroma coding scheme assumes some correlation between transform coefficients between collocated Cr and Cb transform blocks. These assumptions are usually statistical and therefore may result in distortion in some situations. In particular, when one of the color coefficients in a transform block is non-zero but another color component has a zero coefficient, some of the assumptions made in the joint chroma coding scheme are indeed off, and such coding does not preserve any coding bits (because one of the chroma coefficients is zero anyway).

[0145] In the following various exemplary implementations, a coefficient-level (i.e., per transform coefficient) inter-component coding scheme is described that exploits some correlation between the collocated (collocated in the frequency domain) transform coefficients of color components. Such a scheme is particularly useful for transform blocks (or units) where the coefficient of one color component is zero, but the corresponding transform coefficient of another color component is non-zero. For those pairs of zero and non-zero color coefficients, either before or after inverse quantization, the non-zero color coefficient may be used to estimate the original small value of the zero coded coefficient of the other color component (which may be small before quantization in the coding process, but originally non-zero), thereby restoring some information that would otherwise be lost, for example, in the quantization process during encoding. Due to the statistically existing inter-color correlation, some lost information during quantization to zero may be restored. Such inter-component coding restores the lost information to some extent without significant coding cost (of the zero coefficients).

[0146] In particular, an inter-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 to code the sign of other Cr transform coefficients. Such inter-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 respect, the luma channel is considered to be one of the color components.

[0147] In some implementations, the inter-component coefficient sign coding method may include utilizing coefficient sign values ​​of a first color component to code coefficient signs of a second color component. In a non-limiting example, the sign values ​​of the Cb transform coefficients may be used as a context for coding the sign values ​​of the Cr transform coefficients.

[0148] In some implementations, the method may include deriving an offset value that is added to a transform coefficient level value of a second color component using the level value and / or the sign value of the transform coefficient of a first color component. This method is called cross-component level restoration (CCLR).

[0149] The following example implementations may be used separately or combined in any order. The term block size may refer to either 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.

[0150] There may be some issues / problems associated with some implementations. For example, in an inter-component coefficient sign coding method for more efficient coefficient sign coding, the inter-component coefficient coding method in some implementations may be limited to cases where there are pairs of non-zero coefficients for multiple color components located at the same frequency, since sign coding is not necessary for zero coefficients.

[0151] In some implementations where only one of the Cb transform coefficient and the Cr transform coefficient is nonzero, the method may use the level value and / or the sign value of the transform coefficient of the first color component to derive an offset value to be added to the transform coefficient level value of the second color component. Various implementations in this disclosure describe methods for deriving the offset value.

[0152] 18 shows a flowchart 1800 of an example method according to the principles underlying the above implementations for deriving offset values ​​in inter-component transform coefficient level reconstruction. The example decoding method flow starts at 1801 and may include some or all of the following steps: S1810: receiving a coded video bitstream; S1820: extracting from the coded video bitstream first transform coefficients of a first color component for a current video block; S1830: determining second transform coefficients of a second color component for the current video block; S1840: deriving an offset value based on at least one of the following quantization step sizes or the first transform coefficients; S1850: adding an offset value to the second transform coefficients to generate modified second transform coefficients for the second color component; and / or S1860: decoding the current video block based on the first transform coefficients of the first color component and the modified second transform coefficients of the second color component. The example method stops at S1899.

[0153] In some implementations, S1840 of Figure 18 may include deriving the offset value based on a quantization step size, where the magnitude of the offset value depends monotonically on the quantization step size. The offset value for the transform coefficient of the second color component may be derived based on the quantization step size.

[0154] In a non-limiting example, the quantization step size may be the same for the first and second color components (e.g., Cr and Cb). In another non-limiting example, the quantization step size may be different for the first and second color components (e.g., one chroma channel and one luma channel), and the quantization step size of the second color component may be selected to determine the offset value for the second color component.

[0155] In some implementations, the magnitude of the offset value has a monotonic relationship with the quantization step size, and the quantization step size may be represented by a monotonic function for deriving the offset value. In one example, the magnitude of the offset value has a linear relationship to the quantization step size (e.g., offset=k*quantization_step_size+offset_zero). In another example, the magnitude of the offset value has a polynomial relationship to the quantization step size. In some implementations, the relationship (or a function representing the relationship) may be selected based on the sign or magnitude of the first transform coefficient.

[0156] In some implementations, S1840 of FIG. 18 may include deriving the offset value based on the quantization step size and a sign or magnitude value of the first transform coefficient.

[0157] In some implementations, S1840 of FIG. 18 may include deriving an offset value based on a quantization step size corresponding to a direct current (DC) coefficient in response to an offset value corresponding to a DC coefficient, and / or deriving an offset value based on a quantization step size corresponding to an alternating current (AC) coefficient in response to an offset value corresponding to an AC coefficient. In a non-limiting example, the quantization step size may be different for the DC coefficient and the AC coefficient, and the offset values ​​for the DC coefficient and the AC coefficient may be derived based on the quantization step size for the DC coefficient and the AC coefficient, respectively. When a monotonic relationship is used, a larger quantization step size results in a larger offset value being derived.

[0158] In some implementations, S1840 of FIG. 18 may include a step of mapping an index in a look-up table (LUT) based on a quantization step size, and a step of obtaining an element in the LUT indicated by the index as the offset value.

[0159] In some implementations, the LUT includes one of the following: a fixed table, a dynamic table signaled in the coded video bitstream, and / or a dynamic table derived according to the coded video bitstream.

[0160] In a non-limiting example, the magnitude of the offset value is obtained from a look-up table (LUT), the quantization step size is mapped to an index in the look-up table, and the associated offset is used. In some circumstances, the LUT may be a hard-coded fixed table, in some other circumstances, the LUT may be a dynamic table that is explicitly signaled, and / or in some other circumstances, the LUT may be a dynamic table that is implicitly derived using coded information.

[0161] In some implementations, the LUT is selected based on the sign or magnitude of the first transform coefficient. Separate monotonic functions and / or LUTs are used depending on the sign value and / or magnitude of the transform coefficient of the first color component.

[0162] In some implementations, the LUT is obtained from a high-level syntax including at least one of the following: a video parameter set (VPS), a picture parameter set (PPS), a sequence parameter set (SPS), a picture header, a frame header, a slice header, a tile header, or a coding tree unit (CTU) header.

[0163] In some implementations, S1840 of Figure 18 may include deriving the offset value based on a bit depth of the coded video bitstream and a quantization step size, where the bit depth of the coded video bitstream includes one of 8 bits, 10 bits, or 12 bits, and the offset value is monotonically dependent on the bit depth of the coded video bitstream. For example, a larger offset value is devised for a larger bit depth of the coded video bitstream.

[0164] In the embodiments and implementations of the present disclosure, any steps and / or operations may be combined or arranged in any quantity or order, as desired. Two or more of the steps and / or operations may be performed in parallel. The embodiments and implementations of the present disclosure may be used separately or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored in a non-transitory computer-readable medium. The embodiments of the present disclosure may be applied to a luma block or a chroma block. The term block may be interpreted as a prediction block, a coding block, or a coding unit, i.e., a CU. The term block here may also be used to refer to a transform block. In the following items, when referring to a block size, it may refer to either the width or height of the block, or the maximum value of the width and height, or the minimum value of the width and height, or the size of the region (width*height), or the aspect ratio of the block (width:height or height:width).

[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, FIG. 19 illustrates a computer system (1900) suitable for implementing certain embodiments of the disclosed subject matter.

[0166] The computer software may be coded using any suitable machine or computer language that can be assembled, compiled, linked, or similar mechanisms to produce code including instructions that can be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., directly, or via interpretation, microcode execution, etc.

[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] 19 for the computer system (1900) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of the computer system (1900).

[0169] The computer system (1900) may include certain human interface input devices. Such human interface input devices may respond to input by one or more human users, for example, via tactile input (such as keystrokes, swipes, data glove movements), audio input (such as voice, clapping), visual input (such as gestures), or olfactory input (not depicted). Human interface devices may also be used to capture certain media not necessarily directly associated with conscious human input, such as audio (such as voice, music, ambient sounds), images (such as scanned images, photographic images obtained from a still camera), and video (such as two-dimensional video, three-dimensional video including stereoscopic video).

[0170] The input human interface devices may include one or more of a keyboard (1901), a mouse (1902), a trackpad (1903), a touch screen (1910), a data glove (not shown), a joystick (1905), a microphone (1906), a scanner (1907), and a camera (1908) (only one of each is depicted).

[0171] The computer system (1900) 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, via haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (1910), data gloves (not shown), or joystick (1905), although there may be haptic feedback devices that do not function as input devices), audio output devices (such as speakers (1909), headphones (not depicted)), visual output devices (such as screens (1910), 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 outputting two-dimensional visual output or three or more dimensional output via means such as stereographic output, virtual reality glasses (not depicted), holographic displays, and smoke tanks (not depicted)), and printers (not depicted).

[0172] The computer system (1900) may also include human accessible storage devices and their associated media, such as optical media, including CD / DVD ROM / RW (1920) with CD / DVD or similar media (1921), thumb drives (1922), removable hard drives or solid state drives (1923), legacy magnetic media such as tapes and floppy disks (not depicted), and specialized ROM / ASIC / PLD based devices (not depicted) such as security dongles.

[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 (1900) may also include an interface (1954) to one or more communication networks (1955). 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., TV wired or wireless wide area digital networks including cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial including CANbus, 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 (1900)) or peripheral bus (1949), while other networks are typically integrated into the core of the computer system (1900) 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 (1900) can communicate with other entities. Such communications may be one-way receive only (e.g., broadcast TV), one-way transmit only (e.g., CANbus to a specific CANbus device), or two-way with other computer systems, for example, using local or wide area digital networks. Specific protocols and protocol stacks may be used with each of these networks and network interfaces described above.

[0175] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (1940) of the computer system (1900).

[0176] The cores (1940) may include specialized programmable processing devices in the form of one or more central processing units (CPUs) (1941), graphics processing units (GPUs) (1942), field programmable gate areas (FPGAs) (1943), hardware accelerators for specific tasks (1944), graphics adapters (1950), and the like. These devices may be connected via a system bus (1948), along with read only memory (ROM) (1945), random access memory (1946), and internal mass storage (1947), such as an internal hard drive or SSD that is not user accessible. In some computer systems, the system bus (1948) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, and the like. Peripherals may be attached directly to the core's system bus (1948) or via a peripheral bus (1949). In one example, a screen (1910) may be connected to a graphics adapter (1950). Architectures for peripheral buses include PCI, USB, etc.

[0177] The CPU (1941), GPU (1942), FPGA (1943), and accelerator (1944) may combine to execute certain instructions that may constitute the aforementioned computer code. That computer code may be stored in ROM (1945) or RAM (1946). Persistent data may be stored, for example, in internal mass storage (1947), while transitory data may also be stored in RAM (1946). Rapid storage and retrieval from any of the memory devices may be enabled using cache memories that may be closely associated with one or more of the CPU (1941), GPU (1942), mass storage (1947), ROM (1945), RAM (1946), etc.

[0178] The computer-readable medium can have computer code thereon 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 (1900) having an architecture, and specifically a core (1940), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be the user-accessible mass storage introduced above, as well as media associated with a particular storage of the core (1940) of a non-transitory nature, such as the core internal mass storage (1947) or ROM (1945). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (1940). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (1940) and specifically the processor therein (including a CPU, GPU, FPGA, etc.) to perform a particular process or a particular portion of a particular process described herein, including defining data structures stored in RAM (1946) and modifying such data structures according to a process defined by the software. Additionally, or alternatively, a computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., an accelerator (1944)) that may operate in place of or together 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] While this disclosure describes several exemplary embodiments, there are alterations, permutations, and various alternative equivalents that fall within the scope of this disclosure. It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and are therefore within its spirit and scope. Appendix A: Acronyms JEM: Joint Exploration Model VVC: Versatile Video Coding BMS: Benchmark Set MV: Motion Vector HEVC: High Efficiency Video Coding SEI: Supplemental Extended Information VUI: Video Usability Information GOP: Group of Pictures TU: conversion unit PU: Prediction unit CTU: Coding Tree Unit CTB: coding tree block PB: Predicted block HRD: Hypothetical Reference Decoder SNR: Signal to Noise Ratio CPU: Central Processing Unit GPU: Graphics Processing Unit CRT: cathode ray tube LCD: Liquid crystal display OLED: Organic Light Emitting Diode CD:Compact Disc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random Access Memory ASIC: Application Specific Integrated Circuit PLD: Programmable Logic Device LAN: Local Area Network GSM: Global System for Mobile Communications LTE: Long Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: Field Programmable Gate Area SSD: Solid State Drive IC: Integrated Circuit HDR: High Dynamic Range SDR: Standard Dynamic Range JVET: Joint Video Exploration Team MPM: Most Probable Mode WAIP: Wide-angle Intra Prediction CU: coding unit PU: Prediction unit TU: conversion unit CTU: Coding Tree Unit PDPC: Position-dependent predictive coupling 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: Inter-component adaptive loop filter CDEF: Constrained Directivity Enhancement Filter CCSO: Inter-component sample offset LSO: Local Sample Offset LR: Loop recovery filter AV1:AOMedia Video 1 AV2:AOMedia Video 2 MVD: Motion Vector Difference CfL: Saturation from Luminance SDT: Semi-disjoint tree SDP: Semi-separate split SST: Semi-separated tree SB: Super Block IBC (or IntraBC): Intrablock copy CDF: Cumulative density function SCC: Screen Content Coding GBI: Generalized Biprediction BCW: Bi-prediction with CU-level weights CIIP: Combined Intra-Inter Prediction POC: Picture Order Count RPS: Reference Picture Set DPB: Decoded Picture Buffer CBF: Coded Block Flags CCLR: Inter-component level restoration [Explanation of symbols]

[0181] 101 Samples 102 Arrow 103 Arrow 104 Square Block 180 Schematic diagram 201 Current 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 Network 400 Communication Systems 401 Video Source 402 Video Picture Stream 403 Video Encoder 404 Video Data 405 Streaming Server 406 Client Subsystem 407 Copy video data 408 Client Subsystem 409 Copy of video data 410 Video Decoder 411 Video Picture Output Stream 412 Display 413 Capture Subsystem 420 Electronic Devices 430 Electronic Devices 501 Channel 510 Video Decoder 512 Rendering Device 515 Buffer Memory 520 Parser 521 Symbols 530 Electronic Devices 531 Receiver 551 Scaler / Descaler Unit 552 Intra-picture prediction unit 553 Motion Compensation Prediction Unit 555 Aggregator 556 Loop Filter Unit 557 Reference Picture Memory 558 Current Picture Buffer 601 Video Sources 603 Video Encoder 620 Electronic Devices 630 Source Coder 632 Coding Engine 633 Local Decoder 634 Reference Picture Memory 635 Predictor 640 Transmitter 643 coded video sequence 645 Entropy Coder 650 Controller 660 Communication Channels 703 Video Encoder 721 General-purpose controller 722 Intra Encoder 723 Residual Calculator 724 Residual Encoder 725 Entropy Encoder 726 Switch 728 Residual Decoder 730 InterEncoder 810 Video Decoder 871 Entropy Decoder 872 Intra Decoder 873 Residual Decoder 874 Recovery Module 880 Interdecoder 902 Splitting options or patterns 904 Splitting options or patterns 906 Splitting Options or Patterns 908 Splitting options or patterns 1002 Left T-shaped partition 1004 Upper T-shaped partition 1006 Right T-shaped partition 1008 Lower T-shaped partition 1010 All Square Partitions 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 Base Block 1202 Square Partition 1204 Square Partition 1206 Square Partition 1208 Square Partition 1302 Ternary Pattern 1304 Ternary Pattern 1402 Partition 1404 Partition 1406 Partition 1408 Partition 1410 Division Pattern 1420 Tree Structure / Representation 1502 Square coding block 1504 First Level Split 1506 Second Level Split 1602 Inter-coded Blocks 1604 Conversion Block 1800 Flowchart 1900 Computer Systems 1901 Keyboard 1902 Mouse 1903 Trackpad 1905 Joystick 1906 Microphone 1907 Scanner 1908 Camera 1909 Speaker 1910 Touch Screen 1920 CD / DVD ROM / RW 1921 CD / DVD or similar media 1922 Thumb Drive 1923 Removable Hard Drive or Solid State Drive 1940 Core 1941 Central Processing Unit (CPU) 1942 Graphics Processing Unit (GPU) 1943 Field Programmable Gate Area (FPGA) 1944 Hardware Accelerator 1945 Read-Only Memory (ROM) 1946 Random Access Memory (RAM) 1947 Internal Mass Storage 1948 System Bus 1949 Peripheral Bus 1950 Graphics Adapter 1954 Network Interface 1955 Network

Claims

1. 1. A method for decoding a current video block of a video bitstream, comprising: receiving, by a device having a memory storing instructions and a processor in communication with the memory, a coded video bitstream; extracting, by the device, first transform coefficients of a first color component for a current video block from the coded video bitstream; determining, by the device, second transform coefficients of a second color component for the current video block; deriving, by the device, an offset value based on at least one of a quantization step size or the first transform coefficient; adding, by the device, the offset value to the second transform coefficients to generate modified second transform coefficients for the second color component; decoding, by the device, the current video block based on the first transform coefficients of the first color component and the modified second transform coefficients of the second color component; A method comprising:

2. deriving the offset value, deriving the offset value based on the quantization step size, the magnitude of the offset value being monotonically dependent on the quantization step size.

2. The method of claim 1, comprising:

3. the magnitude of the offset value depends on the quantization step size by a monotonic function; the monotonic function is selected based on a sign or a magnitude of the first transform coefficient. The method of claim 2.

4. deriving the offset value, deriving the offset value based on the quantization step size and a sign or magnitude value of the first transform coefficient.

2. The method of claim 1, comprising:

5. deriving the offset value, in response to the offset value corresponding to a direct current (DC) coefficient, deriving the offset value based on the quantization step size corresponding to the DC coefficient; in response to the offset value corresponding to an alternating current (AC) coefficient, deriving the offset value based on the quantization step size corresponding to the AC coefficient; 2. The method of claim 1, comprising:

6. deriving the offset value, mapping an index in a look-up table (LUT) based on the quantization step size; obtaining an element in the LUT indicated by the index as the offset value; 2. The method of claim 1, comprising:

7. The LUT is Fixed table, a dynamic table signaled within the coded video bitstream; or A dynamic table derived according to the coded video bitstream. Contains one of the following: The method of claim 6.

8. the LUT is selected based on a sign or a magnitude of the first transform coefficient; The method of claim 6.

9. the LUT is obtained from a high level syntax including at least one of the following: a video parameter set (VPS), a picture parameter set (PPS), a sequence parameter set (SPS), a picture header, a frame header, a slice header, a tile header, or a coding tree unit (CTU) header; The method of claim 6.

10. deriving the offset value, deriving the offset value based on a bit depth of the coded video bitstream and the quantization step size.

2. The method of claim 1, comprising:

11. the bit depth of the coded video bitstream comprises one of 8 bits, 10 bits, or 12 bits; the offset value depends monotonically on the bit depth of the coded video bitstream; The method of claim 10.

12. 1. An apparatus for decoding a current video block of a video bitstream, comprising: A memory for storing instructions; a processor in communication with the memory, the processor being configured, when the processor executes the instructions, to cause the apparatus to perform the method of any one of claims 1 to 11; An apparatus comprising:

13. A computer program product causing a processor to carry out any one of claims 1 to 11.

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