Adaptive application of generalized sample offset

Abstract

The present disclosure relates to adaptive loop filtering (ALF) for cross-component sample offset (CCSO), local sample offset (LSO), and generalized sample offset (GSO). The ALF uses a reconstructed sample of a first color component as an input (e.g., Y or Cb or Cr). At least one of the GSO, LSO, or CCSO is determined to be enabled for a frame based on a syntax value in a coded video stream. The coded video stream is decoded by applying at least one of the GSO, LSO, or CCSO at a block level.

Description

[Technical field]

[0001] Incorporation by Reference This application is based on and claims the benefit of priority to U.S. Provisional Application No. 63 / 280,503, entitled "ADAPTIVE APPLICATION OF GENERALIZED SAMPLE OFFSET," filed on November 17, 2021, and U.S. Provisional Application No. 63 / 289,139, entitled "ADAPTIVE APPLICATION OF GENERALIZED SAMPLE OFFSET," filed on December 13, 2021, the contents of each of which are incorporated by reference in their entirety herein.

[0002] This disclosure describes a set of advanced video coding techniques. More specifically, the disclosed techniques include Cross-Component Sample Offset (CCSO), Local Sample Offset (LSO), and Generalized Sample Offset (GSO). [Background technology]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0022] AOMedia Video 1 (AV1) is an open video coding format designed for video transmission over the Internet. AV1 was developed as a successor to VP9 by building on the VP9 code base and incorporating additional techniques. The AV1 bitstream specification includes reference video codecs such as H.265, the High Efficiency Video Coding (HEVC) standard, and Versatile Video Coding (VVC). Summary of the Invention [Means for solving the problem]

[0023] The embodiments of the present disclosure provide methods and apparatus for cross-component sample offset (CCSO), local sample offset (LSO), and generalized sample offset (GSO). Adaptive loop filtering (ALF) uses a reconstructed sample of a first color component as an input (e.g., Y or Cb or Cr). In the case of CCSO, the output is applied to a second color component that is a different color component of the first color component. In the case of LSO, the output is applied to the first color component. In the case of GSO, the combined ALF may be generalized for CCSO and LSO by considering delta values ​​between adjacent samples of the co-located (or current) sample and also considering a level value of the co-located (or current) sample. At least one of CCSO, LSO, or GSO may be enabled for a frame based on a syntax value included in the coded video stream.

[0024] In one embodiment, a method includes receiving a coded video stream, the coded video stream including a syntax element indicating whether a sample offset filtering process is applied to a frame in the coded video stream at a block level; determining, based on the syntax element being a predefined value, that at least one of a generalized sample offset (GSO), a local sample offset (LSO), or a cross-component sample offset (CCSO) is enabled for the frame; and decoding the coded video stream by applying at least one of the GSO, the LSO, or the CCSO at the block level.

[0025] In another embodiment, an apparatus for decoding a video stream includes a memory that stores a plurality of instructions; and a processor configured to execute the plurality of instructions, wherein upon execution of the plurality of instructions, the processor is configured to receive a coded video stream, the coded video stream including a syntax element indicating whether a sample offset filtering process is applied to a frame in the coded video stream at a block level, determine based on the syntax element being a predefined value that at least one of a generalized sample offset (GSO), a local sample offset (LSO), or a cross-component sample offset (CCSO) is enabled for the frame at the block level, and decode the coded video stream by applying at least one of the GSO, the LSO, or the CCSO at the block level.

[0026] In another embodiment, a non-transitory computer-readable storage medium storing a plurality of instructions executable by a processor, the plurality of instructions being configured when executed by the processor to cause the processor to receive a coded video stream, the coded video stream including a syntax element indicating whether a sample offset filtering process is applied to a frame in the coded video stream at a block level, determine based on the syntax element being a predefined value that at least one of a generalized sample offset (GSO), a local sample offset (LSO), or a cross-component sample offset (CCSO) is enabled for the frame, and decode the coded video stream by applying at least one of the GSO, the LSO, or the CCSO at the block level.

[0027] In some other embodiments, a device for processing video information is disclosed. The device may include a circuit configured to perform any one of the implementations of the above methods.

[0028] Embodiments of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer, cause the computer to perform a method for video decoding and / or video encoding.

[0029] 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]

[0030] [Figure 1A] FIG. 13 is a schematic diagram of an example subset of intra-prediction directional modes. [Figure 1B] FIG. 2 illustrates an exemplary intra-prediction direction. [Diagram 2] FIG. 1 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) in accordance with an example embodiment. [Figure 4] FIG. 4 is a schematic diagram of a simplified block diagram of a communication system (400) in accordance with an example embodiment. [Diagram 5] FIG. 2 is a schematic diagram of a simplified block diagram of a video decoder according to an example embodiment. [Figure 6] FIG. 2 is a schematic diagram of a simplified block diagram of a video encoder according to an example embodiment; [Figure 7] FIG. 2 is a block diagram of a video encoder according to another example embodiment. [Figure 8] FIG. 4 is a block diagram of a video decoder according to another exemplary 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 division of a base block into coding blocks according to an exemplary division 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] 1 illustrates a scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure. [Figure 16] FIG. 2 illustrates 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. 2 illustrates another scheme for splitting a coding block into multiple transform blocks according to an exemplary embodiment of this disclosure. [Figure 18] FIG. 2 illustrates an example adaptive loop filter (ALF) shape. [Figure 19a] FIG. 13 illustrates subsampled positions in the Laplacian calculation for vertical gradients. [Figure 19b] FIG. 13 illustrates subsampled positions in the Laplacian calculation for horizontal gradients. [Figure 19c] FIG. 13 illustrates subsampled positions in the Laplacian calculation for diagonal gradients. [Figure 19d] FIG. 13 illustrates subsampled positions in the Laplacian calculation for another diagonal gradient. [Figure 20] FIG. 13 illustrates an example of modified block classification at a virtual boundary. [Figure 21] FIG. 13 illustrates an example of modified adaptive loop filtering for the luma component at the virtual boundary. [Figure 22]FIG. 2 is a diagram illustrating an example of maximum coding unit (LCU) aligned picture quadtree partitioning. [Diagram 23] FIG. 13 is a diagram showing an example of a quadtree split flag encoded at order z. [Figure 24] FIG. 1 illustrates an example of a cross-component adaptive loop filter (CC-ALF) arrangement. [Diagram 25] FIG. 1 illustrates an example of a diamond-shaped filter. [Figure 26] FIG. 2 illustrates an exemplary position of chroma samples relative to luma samples. [Figure 27] FIG. 13 is a diagram illustrating an example of a direction search. [Figure 28] FIG. 13 is a diagram illustrating an example of a subspace projection. [Figure 29] FIG. 13 is a diagram showing an example of a filter support area. [Diagram 30] FIG. 2 illustrates an example loop filter pipeline. [Diagram 31] FIG. 13 illustrates an exemplary input of a cross-component sample offset (CCSO). [Diagram 32] FIG. 13 illustrates an example filter shape for cross-component sample offset (CCSO). [Diagram 33] FIG. 2 illustrates an exemplary pixel pattern. [Diagram 34] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Diagram 35] FIG. 13 illustrates a flowchart of another method according to an exemplary embodiment of the present disclosure. [Diagram 36] FIG. 1 is a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] 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.

[0032] Generally, technical 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 as not necessarily intended to convey an exclusive set of factors, but instead may allow for the existence of additional factors not necessarily expressly recited, also depending at least in part on the context.

[0033] 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, for example, a plurality of terminal devices that can communicate with each other via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) may implement unidirectional transmission of data. For example, the terminal device (310) may code video data (e.g., of a stream of video pictures captured by the terminal device (310)) for transmission to the other terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to reconstruct the video pictures, and display the video pictures according to the reconstructed video data. Unidirectional data transmission may be implemented, such as for media serving applications.

[0034] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) implementing bidirectional transmission of coded video data, which may be implemented, for example, during video conferencing applications. For the bidirectional transmission of data, in one example, each of the terminal devices (330) and (340) may code video data (e.g., of a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may also receive coded video data transmitted by the other of the terminal devices (330) and (340), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device according to the recovered video data.

[0035] 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 connection) and / or wireless communication networks. The communication network (350) may exchange data over circuit-switched channels, packet-switched channels, and / or other types of channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this description, the architecture and topology of the network (350) may not be important to the operation of the present disclosure unless expressly described herein.

[0036] 4 shows an arrangement of video encoders and video decoders in a video streaming environment as one 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.

[0037] A video streaming system may include a video source (401) for creating a stream of uncompressed video pictures or images (402), a video capture subsystem (413) that may include, for example, a digital camera. In one example, the stream of video pictures (402) includes samples recorded by the digital camera of the video source 401. The stream of video pictures (402), shown as a thick line to emphasize the large amount of data when compared to the encoded video data (404) (or coded video bitstream), may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), shown with thin lines to emphasize its low amount of data compared to the stream of uncompressed video pictures (402), may be stored directly to the streaming server (405) or to a downstream video device (not shown) for future use. One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, may access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) may include, for example, a video decoder (410) within the electronic device (430). The video decoder (410) decodes the input copy of the encoded video data (407) and creates an output stream of video pictures (411) that is uncompressed and can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). The video decoder 410 may be configured to 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.

[0038] 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).

[0039] 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.

[0040] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In the same or another embodiment, one coded video sequence may be decoded at a time, with the decoding of each coded video sequence being independent of the other coded video sequences. Each video sequence may be associated with multiple video frames or video images. The coded video sequences may be received from a channel (501), which may be a hardware / software link to a storage device that stores the encoded video data, or a streaming source that transmits the encoded video data. The receiver (531) may receive the encoded video data along with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to respective processing circuits (not shown). The receiver (531) may separate the coded video sequences from other data. To combat network jitter, a buffer memory (515) may be disposed between the receiver (531) and the entropy decoder / parser (520) (hereinafter, "parser (520)"). In certain applications, the buffer memory (515) may be implemented as part of the video decoder (510). In other applications, the buffer memory (515) may be separate and external to the video decoder (510) (not shown). In still other applications, there may be a buffer memory (not shown) external to the video decoder (510), for example to combat network jitter, and there may be another additional buffer memory (515) internal to the video decoder (510), for example to handle playback timing. When the receiver (531) is receiving data from a storage / forwarding device with sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may be unnecessary or may be small. For use with best-effort packet networks such as the Internet, a sufficiently sized buffer memory (515) may be required, and its size may be relatively large.Such a buffer memory may be implemented with an adaptive size and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (510).

[0041] The video decoder (510) may include a parser (520) to reconstruct symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and potentially information for controlling a rendering device such as a display (512) (e.g., a display screen) that may or may not be an integral part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device may be in the form of a supplemental enhancement information (SEI message) or a parameter set fragment (not shown) of video usability information (VUI). The parser (520) may parse / entropy decode the coded video sequence received by the parser (520). The entropy coding of the coded video sequence may be according to a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (520) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the subgroup. The subgroups may include groups of pictures (GOPs), pictures, tiles, slices, macroblocks, coding units (CUs), blocks, transform units (TUs), prediction units (PUs), etc. The parser (520) may also extract information from the coded video sequence, such as transform coefficients (e.g., Fourier transform coefficients), quantization parameter values, motion vectors, etc.

[0042] The parser (520) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515) to produce symbols (521).

[0043] The reconstruction of the symbols (521) may involve a number of different processing or functional units, depending on the type of video picture or portion thereof being coded (inter-picture and intra-picture, inter-block and intra-block, etc.), as well as other factors. The units that are included and how they are included may be controlled by subgroup control information parsed from the coded video sequence by the parser (520). The flow of such subgroup control information between the parser (520) and the following processing or functional units is not shown for the sake of simplicity.

[0044] Besides the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into several functional units, as described below. In an actual implementation operating under commercial constraints, many of these functional units may closely interact with each other and may be, at least in part, integrated with each other. However, 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.

[0045] The first unit may include a scalar / inverse transform unit (551), which may receive quantized transform coefficients as well as control information from the parser (520) including information indicating which type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc. The scalar / inverse transform unit (551) may output blocks including sample values ​​that may be input to an aggregator (555).

[0046] In some cases, the output samples of the scaler / inverse transform (551) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may generate a block of the same size and shape as the block being reconstructed using information of surrounding blocks that have already been reconstructed and stored in the current picture buffer (558). The current picture buffer (558) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. In some implementations, the aggregator (555) may add, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551).

[0047] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded, potentially motion-compensated block. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for inter-picture prediction. After motion compensating the fetched samples according to the symbols (521) related to the block, these samples may be added to the output of the scalar / inverse transform unit (551) by the aggregator (555) to generate output sample information (the output of unit 551 may be referred to as a residual sample or residual signal). The address in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches the prediction sample may be controlled by a motion vector, available to the motion compensated prediction unit (553) in the form of a symbol (521), which may have, for example, an X component, a Y component (shift), and a reference picture component (time). Motion compensation may also include interpolation of sample values ​​fetched from a reference picture memory (557) when sub-sample accurate motion vectors are used, and may be associated with a motion vector prediction mechanism, etc.

[0048] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in the loop filter unit (556). Video compression techniques may include in-loop filter techniques that are controlled by parameters included in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to previously reconstructed and loop filtered sample values ​​as well as meta-information obtained during decoding of a previous portion (in decoding order) of the coded picture or coded video sequence. As described in more detail below, several types of loop filters may be included as part of the loop filter unit 556 in various orders.

[0049] The output of the loop filter unit (556) may be a sample stream that can be output to a rendering device (512) as well as stored in a reference picture memory (557) for use in future inter-picture prediction.

[0050] Once a particular coded picture is fully reconstructed, it may be used as a reference picture for future inter-picture prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified (e.g., by the parser (520)) as a reference picture, the current picture buffer (558) may become part of the reference picture memory (557), and any unused current picture buffer may be reallocated before beginning reconstruction of the next coded picture.

[0051] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard, such as ITU-T Recommendation H.265. The coded video sequence may conform to a syntax specified by the video compression technique or standard used in the sense that the coded video sequence adheres to both the syntax of the video compression technique or standard and to a profile documented in the video compression technique or standard. Specifically, a profile may select a particular tool from all tools available in the video compression technique or standard as the only tool that can be used under that profile. To conform to a standard, the complexity of the coded video sequence may be within a range defined by a level of the video compression technique or standard. In some cases, the level limits a maximum picture size, a maximum frame rate, a maximum reconstruction sample rate (e.g., measured in megasamples per second), a maximum reference picture size, etc. The limits set by the level may be further limited in some cases by a specification of a hypothetical reference decoder (HRD) and metadata for HRD buffer management signaled within the coded video sequence.

[0052] In some example embodiments, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0053] 6 shows a block diagram of a video encoder (603) according to an exemplary embodiment of the present disclosure. The video encoder (603) may be included in an electronic device (620). The electronic device (620) may further include a transmitter (640) (e.g., a transmission circuit). The video encoder (603) may be used in place of the video encoder (403) of the example of FIG.

[0054] The video encoder (603) may receive video samples from a video source (601) (which is not part of the electronic device (620) in the example of FIG. 6) that may capture video images to be coded by the video encoder (603). In another example, the video source (601) may be implemented as part of the electronic device (620).

[0055] The video source (601) may provide a source video sequence to be coded by the video encoder (603) in the form of a digital video sample stream that may be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, ...), any color space (e.g., BT.601 YCrCb, RGB, XYZ ...), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media serving system, the video source (601) may be a storage device capable of storing previously prepared video. In a video conferencing system, the video source (601) may be a camera that captures local image information as a video sequence. The video data may be provided as a number of individual pictures or images that give motion when viewed in sequence. The picture itself may be organized as a spatial array of pixels, each pixel may contain one or more samples depending on the sampling structure, color space, etc. being used. Those skilled in the art can easily understand the relationship between pixels and samples. The following description focuses on samples.

[0056] According to some example embodiments, the video encoder (603) may code and compress pictures of a source video sequence into a coded video sequence (643) in real time or under any other time constraint required by the application. Enforcing an appropriate coding rate constitutes one function of the controller (650). In some embodiments, the controller (650) may be operatively coupled to and control other functional units, as described below. For simplicity, couplings are not shown. Parameters set by the controller (650) may include rate control related parameters (picture skip, quantizer, lambda value for rate distortion optimization techniques, etc.), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured to have other appropriate functions associated with the video encoder (603) optimized for a particular system design.

[0057] In some example embodiments, the video encoder (603) may be configured to operate in a coding loop. As an oversimplified explanation, in one example, the coding loop may include a source coder (630) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to create sample data in a similar manner as a (remote) decoder would create them, even though the embedded decoder 633 processes the video stream coded by the source coder 630 without entropy coding (since in the video compression techniques contemplated in the disclosed subject matter, any compression between the symbols and the coded video bitstream may be lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since decoding of the symbol stream produces bit-exact results regardless of the location of the decoder (local or remote), the contents of the reference picture memory (634) are also bit-exact between the local and remote encoders. In other words, the predictive part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift when synchrony cannot be maintained, e.g., due to channel errors) is used to improve coding quality.

[0058] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. Referring also briefly to Figure 5, however, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (520) may be lossless, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633) within the encoder.

[0059] At this point, it can be said that any decoder technology, except for parsing / entropy decoding, which may only exist in the decoder, may necessarily also need to exist in the corresponding encoder in substantially the same functional form. For this reason, the disclosed subject matter may focus on the decoder operation, which is similar to the decoding part of the encoder. Thus, the description of the encoder technology may be omitted, since it is the reverse of the decoder technology described in general. Only in certain areas or aspects, a more detailed description of the encoder is provided below.

[0060] In operation, in some example implementations, the source coder (630) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from a video sequence designated as "reference pictures." In this manner, the coding engine (632) codes color channel differences (or residuals) between pixel blocks of the input picture and pixel blocks of reference pictures that may be selected as predictive references to the input picture. The terms "residual" and its adjective form "residual" may be used interchangeably.

[0061] The local video decoder (633) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols created by the source coder (630). The operation of the coding engine (632) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may typically be a replica of the source video sequence with some errors. The local video decoder (633) may replicate the decoding process that may be performed by the video decoder on the reference pictures, such that the reconstructed reference pictures are stored in the reference picture cache (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content with reconstructed reference pictures obtained by a far-end (remote) video decoder (without transmission errors).

[0062] The predictor (635) may perform a predictive search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or specific metadata such as reference picture motion vectors, block shapes, etc., that may serve as suitable predictive references for the new pixels. The predictor (635) may operate on sample blocks on a pixel block by pixel block basis to find suitable predictive references. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have predictive references drawn from multiple reference pictures stored in the reference picture memory (634).

[0063] The controller (650) may manage the coding operations of the source coder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0064] The output of all the aforementioned functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by lossless compression of the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0065] The transmitter (640) may buffer the coded video sequence created by the entropy coder (645) and prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0066] 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:

[0067] An intra picture (I-picture) may be one that can be coded and decoded without using other pictures in a sequence as a source of prediction. Some video codecs allow different types of intra pictures, including, for example, independent decoder refresh ("IDR") pictures. Those skilled in the art are aware of these variations of I-pictures, as well as their respective uses and characteristics.

[0068] 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.

[0069] A bidirectionally predicted picture (B-picture) may be a picture that can be coded and decoded using intra- or inter-prediction that uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, a multi-predicted picture may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0070] A source picture may generally be spatially subdivided into multiple sample coding blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and coded block by block. A block may be predictively coded with reference to other (already coded) blocks as determined by the coding assignment applied to the respective picture of the block. For example, a block of an I picture may be non-predictively coded or predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). A pixel block of a P picture may be predictively coded via spatial prediction or via temporal prediction with reference to one previously coded reference picture. A block of a B picture may be predictively coded via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures. A source picture or an intermediate processed picture may be subdivided into other types of blocks for other purposes. The division of coding blocks and other types of blocks may or may not follow the same method, as described in more detail below.

[0071] The video encoder (603) may perform coding operations in accordance with a given video coding technique or standard, such as ITU-T Recommendation H.265. In its operations, the video encoder (603) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0072] In some example embodiments, the transmitter (640) may transmit additional data along with the encoded video. The source coder (630) may include such data as part of the coded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0073] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits temporal or other correlation between pictures. For example, a particular picture being encoded / decoded, called the current picture, may be divided into blocks. If a block in the current picture is similar to a reference block in a previously coded yet buffered reference picture in the video, it may be coded by a vector, called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0074] In some exemplary embodiments, bi-prediction techniques may be used for inter-picture prediction. According to such bi-prediction techniques, two reference pictures, such as a first reference picture and a second reference picture, are used, both of which advance the current picture in the video in decoding order (but may be in the past or future, respectively, in display order). A block in the current picture may be coded by a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. A block may be jointly predicted by a combination of the first reference block and the second reference block.

[0075] Furthermore, merge mode techniques may be used to improve coding efficiency in inter-picture prediction.

[0076] According to some exemplary embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed on a block-by-block basis. For example, a picture in a sequence of video pictures is divided into coding tree units (CTUs) for compression, and the CTUs in a picture may have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may include three parallel coding tree blocks (CTBs), i.e., one luma CTB and two chroma CTBs. Each CTU may be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels. Each of one or more of the 32×32 blocks may be further partitioned into four CUs of 16×16 pixels. In some exemplary embodiments, each CU may be analyzed during encoding to determine a prediction type for that CU from among various prediction types, such as an inter prediction type and an intra prediction type. A CU may be divided into one or more prediction units (PUs) according to temporal and / or spatial predictability. In general, each PU includes one luma prediction block (PB) and two chroma PBs. In one embodiment, prediction operations in coding (encoding / decoding) are performed in units of prediction blocks. The division of a CU into PUs (or PBs of different color channels) may be performed in various spatial patterns. A luma PB or a chroma PB may include a matrix of sample values ​​(e.g., luma values), such as, for example, 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0077] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of the present disclosure. The video encoder (703) is configured to receive a processed block (e.g., a predictive block) of sample values ​​in a current video picture in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. The exemplary video encoder (703) can be used in place of the example video encoder (403) of FIG. 4.

[0078] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a predictive block of 8×8 samples. The video encoder (703) then determines, for example, using rate-distortion optimization (RDO), whether the processing block is best coded using intra-mode, inter-mode, or bi-predictive mode. If it is determined that the processing block is coded in intra-mode, the video encoder (703) may encode the processing block into a coded picture using intra-prediction techniques, and if it is determined that the processing block is coded in inter-mode or bi-predictive mode, the video encoder (703) may encode the processing block into a coded picture using inter-prediction techniques or bi-prediction techniques, respectively. In some exemplary embodiments, a merge mode may be used as a sub-mode of inter-picture prediction, in which a motion vector is derived from one or more motion vector predictors without the benefit of coded motion vector components outside the predictors. In some other exemplary embodiments, there may be motion vector components applicable to the current block. Thus, the video encoder (703) may include components not explicitly shown in FIG. 7, such as a mode decision module, to determine the prediction mode of a processing block.

[0079] 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.

[0080] The inter-encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures in display order), generate inter-prediction information (e.g., a description of redundancy information, motion vectors, merge mode information according to inter-encoding techniques), and calculate an inter-prediction result (e.g., a predicted block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the encoded video information using a decoding unit 633 incorporated in the example encoder 620 of FIG. 6 (shown as residual decoder 728 of FIG. 7, as described in more detail below).

[0081] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block with already coded blocks in the same picture, generate transformed quantized coefficients, and possibly also generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). The intra encoder (722) can calculate intra prediction results (e.g., prediction blocks) based on the intra prediction information and reference blocks in the same picture.

[0082] The generic controller (721) may be configured to determine generic control data and control other components of the video encoder (703) based on the generic control data. In one example, the generic controller (721) determines a prediction mode of the block and provides a control signal to the switch (726) based on the prediction mode. For example, if the prediction mode is an intra mode, the generic controller (721) controls the switch (726) to select an intra mode result for use by the residual calculator (723) and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream, and if the prediction mode of the block is an inter mode, the generic controller (721) controls the switch (726) to select an inter prediction result for use by the residual calculator (723) and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0083] The residual calculator (723) may be configured to calculate a difference (residual data) between a received block and a prediction result for a block selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) may be configured to encode the residual data to generate transform coefficients. For example, the residual encoder (724) may be configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various exemplary embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) may generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) may generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks may be appropriately processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures.

[0084] The entropy encoder (725) may be configured to format a bitstream to include the encoded block and to perform entropy coding. The entropy encoder (725) may be configured to include various information in the bitstream. For example, the entropy encoder (725) may be configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other suitable information in the bitstream. When coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode, the residual information may not be present.

[0085] 8 shows a diagram of an example video decoder (810) according to another embodiment of the present disclosure. The video decoder (810) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In one example, the video decoder (810) can be used in place of the example video decoder (410) of FIG. 4.

[0086] 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.

[0087] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols that represent syntax elements of which the coded picture is composed. Such symbols may include, for example, prediction information (e.g., intra- or inter-prediction information) that may identify the mode in which the block is coded (e.g., intra-mode, inter-mode, bi-prediction mode, merged submode, or another submode), certain samples or metadata used for prediction by the intra-decoder (872) or inter-decoder (880), residual information in the form of quantized transform coefficients, etc. In one example, if the prediction mode is an inter- or bi-prediction mode, the inter-prediction information is provided to the inter-decoder (880), and if the prediction type is an intra-prediction type, the intra-prediction information is provided to the intra-decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0088] The inter decoder (880) may be configured to receive the inter prediction information and generate inter prediction results based on the inter prediction information.

[0089] The intra decoder (872) may be configured to receive intra prediction information and to generate a prediction result based on the intra prediction information.

[0090] The residual decoder (873) may be configured to perform inverse quantization to extract inverse quantized transform coefficients, and process the inverse quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also utilize certain control information (to include quantizer parameters (QP)), which may be provided by the entropy decoder (871) (a data path is not shown, as this may be only a small amount of control information).

[0091] 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 visual quality.

[0092] 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.

[0093] 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).

[0094] 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.

[0095] In some implementations, the split tree scheme or structure used for the luma channel and the chroma channel may not need to be the same. In other words, the luma channel and the chroma channel may have separate coding tree structures or patterns. Furthermore, whether the luma channel and the chroma channel use the same coding partition tree structure or different coding partition tree structures, and the actual coding partition tree structure to be used may depend on whether the slice being coded is a P slice, a B slice, or an I slice. For example, for an I slice, the chroma channel and the luma channel may have separate coding partition tree structures or coding partition tree structure modes, while for a P slice or a B slice, the luma channel and the chroma channel may share the same coding partition tree scheme. When separate coding partition tree structures or modes are applied, the luma channel may be split into CBs by one coding partition tree structure, and the chroma channel may be split into chroma CBs by another coding partition tree structure.

[0096] 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 illustrated by 902, 904, 906, and 908, and the partition designated as R is capable of recursive partitioning in that the same partitioning option illustrated in FIG. 9 may be repeated at a lower scale down to the lowest level (e.g., 4×4 level). In some implementations, additional restrictions may be added to the partitioning scheme of FIG. 9. In the implementation of FIG. 9, rectangular partitions (e.g., 1:2 / 2:1 rectangular partitions) may be allowed but not recursive, while square partitions are allowed to be recursive. Subsequent partitioning of FIG. 9 by recursion, if necessary, generates a final set of coding blocks. 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 independently divided 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 independently). 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).

[0097] FIG. 10 illustrates another exemplary predefined partitioning pattern that allows the recursive partitioning to form a partitioning tree. As illustrated in FIG. 10, an exemplary 10-way partitioning structure or pattern may be predefined. The root block may start from a predefined level (e.g., from a base block at a 128×128 level or a 64×64 level). The exemplary partitioning structure in FIG. 10 includes various 2:1 / 1:2 and 4:1 / 1:4 rectangular partitions. A partition type with three subpartitions, shown at 1002, 1004, 1006, and 1008 in the second column of FIG. 10, may be referred to as a “T-shaped” partition. The “T-shaped” partitions 1002, 1004, 1006, and 1008 may be referred to as a left T-shaped, an upper T-shaped, a right T-shaped, and a lower T-shaped. In some exemplary implementations, none of the rectangular partitions in FIG. 10 may be further subdivided. A coding tree depth may be further defined to indicate the partitioning depth from the root node or root block. For example, the coding tree depth for a root node or root block of a 128×128 block may be set to 0, and after the root block is further divided 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 division to the next level of the division tree following the pattern of FIG. 10. In other words, recursive division may not be possible for the square partitions in the T-shaped patterns 1002, 1004, 1006, and 1008. The division 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 8×8 levels. For example, in some cases, 2×2 chroma inter prediction may be used.

[0098] 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 implemented at the picture boundary such that a block continues to be quadtree partitioned until its size fits into the picture boundary.

[0099] In some other example implementations, a hierarchical bisection from the base block may be used. For such a scheme, the base block or mid-level block may be divided into two partitions. The bisection may be either horizontal or vertical. For example, a horizontal bisection may divide the base block or mid-block into equal left and right partitions. Similarly, a vertical bisection may divide 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 division may stop at a predefined minimum partition size (in one or both dimensions). Alternatively, further division may stop once a predefined division 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.

[0100] 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 at 1302 in FIG. 13, or horizontally, as shown at 1304 in FIG. 13. The exemplary division ratio in 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 can capture objects located at block centers in one contiguous partition, whereas quadtrees and bipartitions always divide along block centers, thus dividing objects into separate partitions. In some implementations, the width and height of the partitions of the exemplary ternary tree are always powers of two to avoid further transformations.

[0101] The above partitioning schemes may be combined in any manner at different partitioning levels. As an example, the quadtree and bipartitioning schemes described above 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. Each of the resulting partitions is then 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 shown 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 shown in 1420, which matches the partitioning structure in 1410. In the case of quadtree partitioning, there is no need to indicate 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.

[0102] 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 (if exemplary chroma subsampling is considered and used), MinQTSize may be set as 16×16, MaxBTSize may be set as 64×64, MinBTSize (for both width and height) may be set as 4×4, and MaxBTDepth may be set as 4. Quad-tree partitioning may be applied to the CTU first to generate quad-tree leaf nodes. The quad-tree leaf nodes may have a size from its minimum allowed 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 first by the binary tree because the size exceeds MaxBTSize (i.e., 64×64). Otherwise, nodes that do not exceed MaxBTSize may be split by a binary tree. In the example of FIG. 14, the base block is 128×128. The base block can only be quadtree split according to a predefined set of rules. The base block has a split depth of 0. Each of the resulting four partitions is 64×64, not exceeding MaxBTSize, and may be further quadtree or binary tree split at level 1. The process continues. When the binary tree depth reaches MaxBTDepth (i.e., 4), no further splits may be considered. When the width of a binary tree node is equal to MinBTSize (i.e., 4), no further horizontal splits may be considered. Similarly, when the height of a binary tree node is equal to MinBTSize, no further vertical splits may be considered.

[0103] 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, for example, 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.

[0104] 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.

[0105] Two-level or multi-level tree designs, 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).

[0106] In some implementations, the CB may be further divided. For example, the CB may be further divided into multiple prediction blocks (PBs) for the purpose of intra-frame or inter-frame prediction during the coding and decoding processes. In other words, the CB may be further 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 implemented using a unique procedure based on, for example, various characteristics of the video data. The division schemes of the PBs and TBs may be independent in some exemplary implementations. The division schemes and boundaries of the PBs and TBs may be correlated in some other exemplary implementations. In some implementations, for example, the TBs may be divided after the PB division, and in particular, each PB may be determined following the division of the coding block, and then further divided into one or more TBs. For example, in some implementations, the PB may be divided into one, two, four, or other number of TBs.

[0107] In some implementations, the luma and chroma channels may be processed differently to split the base blocks into coding blocks and further into predictive and / or transform blocks. For example, in some implementations, splitting of coding blocks into predictive and / or transform blocks may be allowed for the luma channel, but such splitting of coding blocks into predictive and / or transform blocks may not be allowed for the chroma channels. In such implementations, the transform and / or prediction of luma blocks may thus be performed only at the coding block level. In another example, the minimum transform block size of the luma and chroma channels may be different, e.g., the coding blocks of the luma channel may be allowed to be split into smaller transform and / or predictive blocks than the chroma channels. In yet another example, the maximum depth of the splitting of coding blocks into transform and / or predictive blocks may be different between the luma and chroma channels, e.g., the coding blocks of the luma channel may be allowed to be split into deeper transform and / or predictive blocks than the chroma channels. As a specific example, a luma coding block may be divided into transform blocks of multiple sizes that can be represented by a recursive partitioning down by up to two levels, and transform block shapes such as square, 2:1 / 1:2, and 4:1 / 1:4, as well as transform block sizes from 4×4 to 64×64 may be allowed. However, for chroma blocks, only the largest possible transform block designated for the luma block may be allowed.

[0108] 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.

[0109] 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 in connection with Figures 15, 16, and 17.

[0110] 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 it 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.

[0111] The various CB division schemes described above, 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.

[0112] 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 to continue further quadtree division of a particular partition may be determined by local video data characteristics. The resulting CBs may be at various quadtree division levels 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 not be limited to a square. Furthermore, in this particular example, the PB may be square or rectangular in inter prediction, and only square in intra prediction. The coding block may be divided, for example, into four square TBs. Each TB may be further divided recursively (using quadtree partitioning) into smaller TBs called residual quadtrees (RQTs).

[0113] 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, the CBs can have either square or rectangular shapes. Specifically, the coding tree block (CTB) may first be split by a quadtree structure. The quadtree leaf nodes may then 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 Figure 11. Specifically, the example multi-type tree structure of Figure 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.

[0114] 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. Partition 1202 and partition 1208 each adopt another 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-split, and horizontal trisection 1108 of FIG. 11, respectively. Partition 1208 adopts another quadtree partitioning, and the second level quadtree partitioned top-left, top-right, bottom-left, and bottom-right partitions adopt the third level partitioning of vertical trisection 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 split according to horizontal bisection 1104 and horizontal trisection 1108 of FIG. 11, respectively. Partition 1206 adopts the second level partitioning pattern into two partitions following vertical bisection 1102 of FIG. 11, and the two partitions are further split at the third level according to horizontal trisection 1108 and vertical bisection 1102 of FIG. 11, respectively. A fourth level partitioning is further applied to one of them according to horizontal bisection 1104 of FIG. 11.

[0115] In the above specific example, the maximum luma transform size may be 64×64, and the maximum supported chroma transform size may be different from the luma, e.g., 32×32. Even if the above example CB of FIG. 12 is not generally further divided into smaller PBs and / or TBs, when the width or height of a luma coding block or a chroma coding block is larger than the maximum transform width or maximum transform height, the luma coding block or the chroma coding block may be automatically divided in the horizontal and / or vertical directions to satisfy the transform size constraints in that direction.

[0116] 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, for P slices and B slices, the luma CTB and chroma CTB in one CTU can share the same coding tree structure. For I slices, for example, luma and chroma may have separate coding block tree structures. When 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.

[0117] 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 methods. Exemplary implementations for dividing a coding block or a predictive 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, if the 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 multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32), respectively, of transform blocks.

[0118] In some example implementations of transform block partitioning, for both intra-coded and inter-coded blocks, a 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. [Table 1]

[0119] 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.

[0120] In some example implementations, further restrictions may be applied on transform block partitioning for the luma components of intra-coded blocks. For example, for each level of transform partitioning, all sub-transform blocks may be restricted to have equal size. For example, for a 32×16 coding block, level 1 transform partitioning creates two 16×16 sub-transform blocks, and 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 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.

[0121] In some example implementations, the above restrictions on intra-coding may not apply to the luma components of an inter-coded block. For example, after the first level of transform splitting, any one of the sub-transform blocks may be further split independently at another level. Thus, the resulting transform blocks may or may not be blocks of the same size. An example splitting of an inter-coded block into transform blocks according to their coding order is shown in FIG. 16. In the example of FIG. 16, an inter-coded block 1602 is split into transform blocks at two levels according to Table 1. At the first level, the inter-coded block is split into four transform blocks of equal size. Then, only one of the four transform blocks (but not all of them) is further split into four sub-transform blocks, resulting in a total of seven transform blocks with two different sizes, as shown by 1604. An example coding order of these seven transform blocks is shown by arrows at 1604 in FIG. 16.

[0122] In some example implementations, for chroma components, some further restrictions on the transform blocks may be applied: for example, for chroma components, the transform block size may be as large as the coding block size, but cannot be smaller than a predefined size, e.g., 8×8.

[0123] 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) transform units, respectively, where in this disclosure, “min(a,b)” can return the smaller value between a and b.

[0124] FIG. 17 further illustrates another alternative exemplary scheme for splitting a coding block or a predictive block into transform blocks. As illustrated in FIG. 17, instead of using recursive transform partitioning, a set of predefined partition types may be applied to a coding block according to the transform type of the coding block. In the particular example illustrated in FIG. 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.

[0125] 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 shown 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 transform partitioning types may be predefined. An example is shown below, where the capitalized labels indicate transform partitioning types that may be assigned to a coding block or predictive block based on a rate-distortion cost. ·PARTITION_NONE: Allocate the transformation size equal to the block size. ·PARTITION_SPLIT: Allocates a transformation size of 1 / 2 the block size in width and 1 / 2 the block size in height. ·PARTITION_HORZ: Allocates a transformation size with width equal to the block size and height equal to 1 / 2 the block size. ·PARTITION_VERT: Allocates a transformation size with a width half the block size and a height equal to the block size. ·PARTITION_HORZ4: Allocates a transformation size with width equal to the block size and height equal to 1 / 4 of the block size. ·PARTITION_VERT4: Allocates a transformation size with a width of 1 / 4 of the block size and a height equal to the block size.

[0126] 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).

[0127] The PBs (or CBs, also called PBs if not further divided into predictive blocks) obtained from any of the above partitioning schemes can become individual blocks for coding via either intra-prediction or inter-prediction. For inter-prediction on the current PB, a residual between the current block and the predictive block can be generated, coded, and included in the coded bitstream.

[0128] Inter prediction may be performed, for example, in single reference mode or mixed reference mode. In some implementations, a skip flag may be included in the bitstream of the current block first (or at a higher level) to indicate whether the current block is inter-coded and not skipped. If the current block is inter-coded, another flag may be further included in the bitstream as a signal indicating whether a single reference mode or a mixed reference mode is used for predicting the current block. In the case of a single reference mode, one reference block may be used to generate a prediction block of the current block. In the case of a mixed reference mode, two or more reference blocks may be used to generate a prediction block, for example, by weighted averaging. A mixed reference mode may be referred to as a multiple reference mode, a two-reference mode, or a multiple reference mode. One or more reference blocks may be identified using one or more reference frame indexes and further using a corresponding one or more motion vectors indicating a shift between the reference block and the current block, for example, in positions in horizontal and vertical pixels. For example, the inter-predicted block of the current block may be generated from a single reference block identified by one motion vector in a reference frame as the predictive block in a single reference mode, while in the case of a mixed reference mode, the predictive block may be generated by a weighted average of two reference blocks in two reference frames indicated by two reference frame indexes and two corresponding motion vectors. The motion vectors may be coded and included in the bitstream in various ways.

[0129] In some implementations, an encoding or decoding system may maintain a decoded picture buffer (DPB). Some images / pictures may be maintained in the DPB waiting to be displayed (in the decoding system), and some images / pictures in the DPB may be used as reference frames to enable inter prediction (in the decoding system or encoding system). In some implementations, reference frames in the DPB may be tagged as either short-term or long-term references for the current image being encoded or decoded. For example, short-term reference frames may include frames used for inter prediction of blocks in the current frame or a predefined number (e.g., two) of subsequent video frames closest to the current frame in decoding order. Long-term reference frames may include frames in the DPB that can be used to predict image blocks in frames beyond a predefined number of frames from the current frame in decoding order. Information regarding such tags for short-term and long-term reference frames may be referred to as a reference picture set (RPS) and may be added to the header of each frame in the encoded bitstream. Each frame in the encoded video stream can be identified by a Picture Order Counter (POC), which is numbered according to the playback sequence, either in an absolute manner or in relation to a group of pictures starting with, for example, an I-frame.

[0130] In some example implementations, one or more reference picture lists including identification of short-term and long-term reference frames for inter prediction may be formed based on information in the RPS. For example, a single picture reference list may be formed for unidirectional inter prediction, denoted as L0 reference (or reference list 0), and two picture reference lists may be formed for bidirectional inter prediction, denoted as L0 (or reference list 0) and L1 (or reference list 1) for each of the two prediction directions. The reference frames included in the L0 and L1 lists may be ordered in various predetermined manners. The lengths of the L0 and L1 lists may be signaled in the video bitstream. The unidirectional inter prediction may be either a single reference mode or a mixed reference mode, where multiple references for generating a prediction block by weighted averaging in the mixed prediction mode are on the same side of the block to be predicted. The bidirectional inter prediction may be only a mixed mode, in that the bidirectional inter prediction includes at least two reference blocks.

[0131] Adaptive Loop Filter In versatile video coding, an adaptive loop filter (ALF) with block-based filter adaptation is applied. For the luma component, one of many filters is selected for each 4x4 block based on local gradient direction and motion. In one example, 25 filters can be selected.

[0132] Figure 18 shows an example adaptive loop filter (ALF) shape. Specifically, Figure 18 shows two diamond filter shapes. A 7x7 diamond shape is applied to the luma component, and a 5x5 diamond shape is applied to the chroma component.

[0133] The block classification can be calculated for different examples as follows: For the luma component, each 4x4 block is classified into one of 25 classes. The classification index C is determined by its directionality D and the quantized value of the motion

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[0134] To reduce the complexity of block classification, a subsampled one-dimensional Laplacian calculation may be applied. As shown in Fig. 19a to Fig. 19d, the same subsampled positions can be used for gradient calculations in all directions. Fig. 19a shows the subsampled positions in the Laplacian calculation for a vertical gradient. Fig. 19b shows the subsampled positions in the Laplacian calculation for a horizontal gradient. Fig. 19c shows the subsampled positions in the Laplacian calculation for a diagonal gradient. Fig. 19d shows the subsampled positions in the Laplacian calculation for another diagonal gradient.

[0135] Next, set the maximum and minimum values ​​of D for the horizontal and vertical gradients as follows:

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number

number

[0136] There may be geometric transformations of the filter coefficients and clipping values. Before filtering each 4x4 luma block, a geometric transformation such as a rotation, or a diagonal and vertical flip, may be applied to the filter coefficients f(k,l) and the corresponding filter clipping values ​​c(k,l) depending on the gradient value calculated for that block. This may be equivalent to applying these transformations to samples within the filter support region. This may make the different blocks to which the ALF is applied more uniform by aligning their directionality. The three geometric transformations may include a diagonal, a vertical flip, and a rotation. Diagonal: f D (k, l) = f(l, k), c D (k, l) = c(l, k), (9) Vertical flip:f V (k, l) = f(k, Kl-1), c V (k, l) = c(k, Kl-1) (10) Rotation:f R (k, l) = f(Kl-1, k), c R (k, l) = c(Kl-1, k) (11) where K is the size of the filter, 0≦k, l≦K-1 are the coordinates of the coefficients, with position (0,0) being the top-left corner and position (K-1,K-1) being the bottom-right corner. The transformation is applied to the filter coefficients f(k,l) and clipping values ​​c(k,l) according to the gradient value calculated for that block. The relationship between the transformation and the four gradients in the four directions is summarized in Table 2 below. [Table 2] Table 2 - Mapping of gradients and transformations calculated for one block

[0137] In VVC, ALF filter parameters are signaled in an adaptive parameter set (APS). In one APS, several sets of luma filter coefficients and clipping value indexes can be used. For example, there may be 25 sets of luma filters. In addition, several sets of chroma filter coefficients and clipping value indexes can be signaled. In one example, there may be up to 8 sets of chroma filter coefficients and clipping value indexes that can be signaled. To reduce bit overhead, filter coefficients of different classifications of luma components can be merged. In the slice header, the index of the APS used for the current slice can be signaled. The signaling of the ALF may be coding tree unit (CTU) based.

[0138] The clipping value index decoded from the APS can determine the clipping values ​​using the luma and chroma clipping value tables. These clipping values ​​may depend on the internal bit depth. More precisely, the clipping value tables may be obtained by the following formula: AlfClip={round(2 B-α*n ), n∈[0..N-1]} (12) where B is equal to the internal bit depth, α is a predefined constant value equal to 2.35, and N is the number of clipping values ​​allowed in VVC in one embodiment, which is equal to 4. Table 3 shows the output of equation (12). [Table 3]

[0139] In one slice header example, up to seven APS indices may be signaled to specify the luma filter set used for the current slice. The filtering process may be further controlled at the coding tree block (CTB) level. A flag may be signaled to indicate whether the ALF is applied to the luma CTB. In one example, the luma CTB may select a filter set among 16 fixed filter sets and a filter set from the APS. A filter set index in the luma CTB is signaled to indicate which filter set to apply. The 16 fixed filter sets may be predefined and hard-coded in both the encoder and the decoder. For the chroma components, an APS index is signaled in the slice header to indicate the chroma filter set used in the current slice. At the CTB level, if an APS has multiple chroma filter sets, a filter index is signaled for each chroma CTB. The filter coefficients may be quantized with a norm equal to 128. To limit the multiplication complexity, bitstream compatibility is applied such that coefficient values ​​for non-center positions can range from -27 to 27-1 (inclusive). Center position coefficients are not signaled in the bitstream and are assumed to be equal to 128.

[0140] For the VVC example, the syntax and semantics of the clipping index or value are defined as follows: alf_luma_clip_idx[sfIdx][j] specifies the clipping index of the clipping value to use before multiplying the jth coefficient of the signaled luma filter indicated by sfIdx. The bitstream conformance requirement is that the value of alf_luma_clip_idx[sfIdx][j], for sfIdx=0..alf_luma_num_filters_signalled_minus1 and j=0..11, is in the range 0 to 3, inclusive. The luma filter clipping values ​​AlfClipL[adaptation_parameter_set_id] with element AlfClipL[adaptation_parameter_set_id][filtIdx][j], where filtIdx=0..NumAlfFilters-1 and j=0..11, are derived as specified in Table 3 according to the bit depth set equal to the bit depth Y and clipIdx set equal to alf_luma_clip_idx[alf_luma_coeff_delta_idx[filtIdx]][j]. alf_chroma_clip_idx[altIdx][j] specifies the clipping index of the clipping value to use, which is then multiplied by the jth coefficient of the alternative chroma filter with index altIdx. It is a bitstream conformance requirement that the value of alf_chroma_clip_idx[altIdx][j] for altIdx=0..alf_chroma_num_alt_filters_minus1, j=0..5 be in the range 0 to 3 (inclusive).The chroma filter clipping value AlfClipC[adaptation_parameter_set_id][altIdx] with element AlfClipC[adaptation_parameter_set_id][altIdx][j] is derived as specified in Table 3 in response to setting the bit depth set equal to bit depth C and setting clipIdx equal to alf_chroma_clip_idx[altIdx][j], with elements altIdx=0..alf_chroma_num_alt_filters_minus1, j=0..5.

[0141] The filtering process may be implemented in the following example: On the decoder side, when ALF is enabled for the CTB, each sample R(i,j) in a CU is filtered to become a sample value R'(i,j). R'(i, j) = R(i, j) + ((Σ k≠0 Σ l≠0 f(k, l)×K(R(i+k, j+l)-R(i, j), c(k, l))+64)≫7) (13) where f(k,l) represents the decoded filter coefficients, K(x,y) is the clipping function, and c(k,l) represents the decoded clipping parameters. The variables k and l are

number

number

[0142] There may be a virtual boundary filtering process for line buffer reduction. To reduce the line buffer requirement of the ALF, modified block classification and filtering may be applied to samples near the horizontal CTU boundary. Thus, as shown in FIG. 20, a virtual boundary may be defined as a line by shifting the horizontal CTU boundary by "N" samples. FIG. 20 shows an example of modified block classification at the virtual boundary. In this example, N is equal to 4 for the luma component and 2 for the chroma component.

[0143] A modified block classification is applied for the luma component as illustrated in Figure 20. The 1D Laplacian gradient computation for 4x4 blocks above the virtual boundary uses only samples above the virtual boundary. Similarly, the 1D Laplacian gradient computation for 4x4 blocks below the virtual boundary uses only samples below the virtual boundary. The quantization of the motion value A is scaled to account for the reduction in the number of samples used in the 1D Laplacian gradient computation.

[0144] Figure 21 shows an example of modified adaptive loop filtering for the luma component at the virtual boundary. For the filtering process, a symmetric padding operation at the virtual boundary may be used for both the luma component and the chroma component. As shown in Figure 21, if the sample being filtered is located below the virtual boundary, it pads the adjacent sample located above the virtual boundary. The other corresponding sample is also padded symmetrically.

[0145] FIG. 22 shows an example of largest coding unit (LCU) aligned picture quadtree partitioning. To improve coding efficiency, a coding unit synchronized picture quadtree based adaptive loop filter can be used. A luma picture may be divided into several multi-level quadtree partitions, and each partition boundary is aligned to the boundary of the largest coding unit (LCU). Each partition has its own filtering process and may be called a filter unit (FU). The two-pass encoding flow may include the following: In the first pass, a quadtree partitioning pattern and an optimal filter for each FU are determined. During the determination process, the filtering distortion is estimated by FFDE. According to the determined quadtree partitioning pattern and the selected filters of all FUs, the reconstructed picture is filtered. In the second pass, the on / off control of the CU synchronized ALF is implemented. According to the on / off result of the ALF, the first filtered picture is partially restored by the reconstructed picture.

[0146] A top-down partitioning strategy can be adopted to partition a picture into multi-level quadtree partitions by using a rate-distortion criterion. Each partition may be called a filter unit. The partitioning process aligns the quadtree partitions to the boundaries of the LCUs. The encoding order of the FUs follows the z-scanning order. For example, in FIG. 22, a picture is partitioned into 10 FUs, and the encoding order is FU0, FU1, FU2, FU3, FU4, FU5, FU6, FU7, FU8, and FU9.

[0147] FIG. 23 shows an example of a quadtree partition flag encoded at the z-th order. To indicate the picture quadtree partition pattern, a partition flag is encoded and transmitted at the z-th order. FIG. 23 shows the quadtree partition pattern corresponding to FIG. 22. The filter for each FU is selected from two filter sets based on the rate-distortion criteria. The first set has a 1 / 2 symmetric square and diamond filter newly derived for the current FU. The second set comes from the time-delay filter buffer. The time-delay filter buffer stores the filters previously derived for the FUs of the previous picture. The filter with the minimum rate-distortion cost of these two sets is selected for the current FU. Similarly, if the current FU is not the smallest FU and can be further partitioned into four child FUs, the rate-distortion cost of the four child FUs is calculated. By recursively comparing the rate-distortion cost for partitioning and no partitioning, the picture quadtree partition pattern can be determined. In one example, the maximum quadtree partition level may be 2, which means that the maximum number of FUs is 16. During the quadtree partitioning decision, the correlation values ​​for deriving the Wiener coefficients of the 16 FUs at the lowest quadtree level (smallest FU) can be reused. The remaining FUs can derive their Wiener filters from the correlations of the 16 FUs at the lowest quadtree level. Therefore, there may be only one frame buffer access to derive the filter coefficients of all FUs. After the quadtree partitioning pattern is determined, the CU-synchronous ALF on / off control is implemented to further reduce the filtering distortion. By comparing the filtering distortion and the non-filtering distortion, the leaf CU can explicitly switch the ALF on / off in its local region. The coding efficiency can be further improved by redesigning the filter coefficients according to the ALF on / off result. However, the redesign process may require additional frame buffer access. In the modified encoder design, there may be no redesign process after the CU-synchronous ALF on / off decision to minimize the number of frame buffer accesses.

[0148] Cross-component adaptive loop filter (CC-ALF) Figure 24 shows an example of a cross-component adaptive loop filter (CC-ALF) arrangement. The CC-ALF can refine each chroma component using luma sample values. Figure 24 shows the arrangement of the CC-ALF relative to the other loop filters.

[0149] Figure 25 shows an example of a diamond-shaped filter. CC-ALF can operate by applying the linear diamond-shaped filter of Figure 25 to the luma channel of each chroma component. The filter coefficients are sent in the APS and in one example are scaled by a factor of 210 and rounded for fixed-point representation. The application of the filters is controlled by variable block sizes and signaled by a context-coded flag received for each block of samples. The block sizes are received at the slice level for each chroma component along with the CC-ALF enable flag. In one example, the following block sizes (in chroma samples) were supported: 16x16, 32x32, 64x64.

[0150] An example syntax for CC-ALF may include the following: [Table 4]

[0151] The semantics of CC-ALF related syntax may include: alf_ctb_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] equal to 0 indicates that no cross-component Cb filter is applied to the block of Cb color component samples at luma position (xCtb, yCtb). alf_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] not equal to 0 indicates that the alf_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]th cross-component Cb filter is applied to the block of Cb color component samples at luma position (xCtb, yCtb). alf_ctb_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] equal to 0 indicates that no cross-component Cr filter is applied to the block of Cr color component samples at luma position (xCtb, yCtb). alf_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] not equal to 0 indicates that the alf_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]th cross-component Cr filter is applied to the block of Cr color component samples at luma position (xCtb, yCtb).

[0152] Chroma Sampling Format FIG. 26 illustrates an example location of chroma samples relative to luma samples. FIG. 26 illustrates the indicated relative location of the top-left chroma sample when chroma_format_idc is equal to 1 (4:2:0 chroma format) and chroma_sample_loc_type_top_field or chroma_sample_loc_type_bottom_field is equal to the value of the variable ChromaLocType. The area represented by the top-left 4:2:0 chroma sample (illustrated as a large square with a large dot in the center) is shown relative to the area represented by the top-left luma sample (illustrated as a small square with a small dot in the center). The area represented by the adjacent luma sample is shown as a small shaded gray square with a small shaded gray dot in the center.

[0153] Directional Emphasis Features One objective of the in-loop constrained directional emphasis filter (CDEF) is to remove coding artifacts while preserving image details. In HEVC, the sample adaptive offset (SAO) algorithm can achieve a similar objective by defining signal offsets for different classes of pixels. Unlike SAO, the CDEF is a nonlinear spatial filter. The design of the filter is constrained to be easily vectorizable (i.e., implementable with SIMD operations), which may not be true for other nonlinear filters such as median and bilateral filters. The CDEF design stems from the following observations: The amount of ringing artifacts in a coded image tends to be roughly proportional to the quantization step size. Although the level of detail is a property of the input image, the smallest details preserved in the quantized image also tend to be proportional to the quantization step size. For a given quantization step size, the amplitude of the ringing is generally smaller than the amplitude of the details.

[0154] CDEF works by identifying the orientation of each block, then adaptively filtering along the identified orientation and to a lesser extent along orientations rotated 45 degrees from the identified orientation. The filter strength is explicitly signaled, allowing a high degree of control over blurring. An efficient encoder search is designed for the filter strength. CDEF is based on two previously proposed in-loop filters, and the combined filter was adopted in the emerging AV1 codec.

[0155] FIG. 27 shows an example of a direction search. The direction search operates on the reconstructed pixels immediately after the deblocking filter. These pixels are available to the decoder, so the direction does not require signaling. The search operates on 8×8 blocks, which are small enough to properly handle non-linear edges and large enough to reliably estimate the direction when applied to a quantized image. Having a certain directionality in the 8×8 region makes it easier to vectorize the filter. For each block, we determine the direction that best matches the pattern in the block by minimizing the sum of squared differences (SSD) between the quantized block and the nearest fully directional block. A fully directional block is a block where all pixels along a line in a direction have the same value. FIG. 27 shows an example of a direction search for an 8×8 block.

[0156] There may be a non-linear low-pass directional filter. One reason to identify a direction is to align filter taps along that direction to reduce ringing while preserving the directional edge or pattern. However, directional filtering alone may not be enough to reduce ringing. It may also be desirable to use filter taps for pixels that are not along the main direction. These extra taps are treated more conservatively to reduce the risk of blurring. For this reason, CDEF defines a primary tap and a secondary tap. A complete two-dimensional CDEF filter can be expressed as follows:

number

[0157] Loop Recovery Besides the conventional deblocking operation, a set of in-loop restoration schemes have been proposed for use in post-deblocking video coding to generally remove noise and improve edge quality. These schemes are switchable within a frame for each tile of appropriate size. The particular schemes described are based on a separable symmetric Wiener filter and a dual self-guided filter with subspace projection. Since content statistics can change substantially within a frame, these tools are integrated within a switchable framework where different tools can be triggered in different regions of the frame.

[0158] There may be a separable symmetric Wiener filter used as the restoration tool. Every pixel of the degraded frame can be reconstructed as a non-causal filtered version of the pixels in a w × w window around it, where w = 2r + 1 is odd for the integer r. If the 2D filter taps are represented by a w2 × 1 element vector F in column-vectorized form, a straightforward LMMSE optimization leads to the filter parameters given by F = H-1M, where H = E[XXT] is the autocovariance of x, a column-wise vectorized version of the w2 samples in the w × w window around the pixel, and M = E[YXT] is the cross-correlation of x and the scalar source sample y to be estimated. The encoder could estimate H and M from the realization of the deblocked frame and the source and send the resulting filter F to the decoder. However, doing so would incur a significant bitrate cost in transmitting the w2 taps, as well as making the decoding prohibitively complicated due to the non-separable filtering. Therefore, some additional constraints are imposed on the nature of F. First, F is constrained to be separable, and the filtering can be implemented as a separable horizontal and vertical w-tap convolution. Second, each of the horizontal and vertical filters is constrained to be symmetric. Third, both the horizontal and vertical filter coefficients are assumed to sum to 1.

[0159] There may be a dual self-guided filtering with subspace projection for image filtering, where the local linear model is: y=Fx+G (15) The above formula is used to calculate the filtered output y from the unfiltered sample x, where F and G are determined based on the statistics of the degraded image and the guidance image in the neighborhood of the filtered pixel. If the guide image is the same as the degraded image, the resulting so-called self-guided filtering has the effect of edge-preserving smoothing. The specific form of self-guided filtering proposed by the inventors depends on two parameters, the radius r and the noise parameter e, and is listed as follows: 1. Calculate the pixel mean μ and variance σ in a (2r+1) × (2r+1) window around every pixel. 2 which can be efficiently implemented with box filtering based on integral imaging. 2. Calculate for every pixel: f = σ 2 / (σ 2 +e);g=(1-f)μ 3. Calculate F and G for every pixel as the average of the f and g values ​​in a 3x3 window around the pixel being used. Filtering can be controlled by r and e, where a larger r results in greater spatial variance and a larger e results in greater range variance.

[0160] An example of subspace projection is shown in Figure 28. The principle of subspace projection is shown diagrammatically in Figure 28. None of the inexpensive reconstructions X1, X2 are close to the source Y, but a suitable multiplier {α, β} can bring them much closer to the source, as long as they are somewhat moved in the right direction.

[0161] Cross Component Sample Offset (CCSO) The loop filtering technique may include cross-component sample offset (CCSO) to reduce distortion of the reconstructed samples. In CCSO, given the processed input reconstructed samples of a first color component, a nonlinear mapping is used to derive an output offset, which is added to the reconstructed samples of another color component in the proposed CCSO filtering process.

[0162] FIG. 29 shows an example of a filter support area. The input reconstructed samples are from the first color component located in the filter support area. As shown in FIG. 29, the filter support area includes four reconstructed samples: p0, p1, p2, p3. The four input reconstructed samples follow a cross shape in the vertical and horizontal directions. The center sample (represented by c) of the first color component and the filtered sample of the second color component are collocated. When processing the input reconstructed samples, the following steps are applied: · Step 1: The delta values ​​between p0~p3 and c are first calculated and denoted as m0, m1, m2, and m3. Step 2: The delta values ​​m0~m3 are further quantized, and the quantized values ​​are represented as d0, d1, d2, d3. The quantized values ​​can be -1, 0, 1 based on the following quantization process: If am<-N, then d=-1, (16) b.-If N<=m<=N, then d=0. (17) If cm>N, then d=1(18) N is called the quantization step size, and example values ​​for N are 4, 8, 12, and 16.

[0163] The variables d0-d3 can be used to identify one combination of the nonlinear mapping. In this example, the CCSO has four filter taps d0-d3, and each filter tap can have one of three quantization values, resulting in a total of 3^4=81 combinations. Table 4 (below) shows the 81 example combinations, with the last column representing the output offset value for each combination. The example offset values ​​are integers such as 0, 1, -1, 3, -3, 5, -5, -7, etc.

[0164] [Table 5]

[0165] The CCSO final filtering process is applied as follows: f'=clip(f+s), (19) where f is the reconstructed sample to be filtered, s is the output offset value obtained from Table 4, and the filtered sample value f' is further clipped to the range associated with the bit depth.

[0166] Local Sample Offset (LSO) is another exemplary offset embodiment, in which a similar filtering technique as in CCSO is applied, but the output offset is applied to the color components whose reconstructed samples are the same color components used as input to the filtering process.

[0167] In an alternative embodiment, a simplified CCSO design may be adopted in the reference software for AV2, i.e., AVM for CWG-B022.

[0168] Figure 30 shows an example loop filter pipeline. CCSO is a loop filter process that is implemented in parallel with CDEF in the loop filter pipeline, i.e., the input is the same as CDEF, and the output is applied to the CDEF filtered samples as shown in Figure 30. Note that CCSO may be applied only to chroma color components.

[0169] FIG. 31 shows an example input of cross-component sample offset (CCSO). The CCSO filter is applied to a chroma reconstructed sample represented as rc. The collocated luma reconstructed sample of rc is represented as rl. An example of a CCSO filter is shown in FIG. 31. In CCSO, a set of 3-tap filters is used. The input luma reconstructed samples located at the three filter taps include a central rl and two adjacent samples p0 and p1.

[0170] p iGiven i = 0, 1 and rl, the following steps are applied to process the input samples: -p i The delta value between and rl is first calculated, and m i It is expressed as: - delta value m i is calculated using the following quantization process: i is quantized as: -m is -Q CCSO If it is less than d i is set equal to -1. -m is -Q CCSO ~Q CCSO If it is between (inclusive), then d i is set equal to 0. -m is Q CCSO If it is greater than d i is set equal to 1. In the above steps, Q CCSO is called the quantization step size, and Q CCSO can be 8, 16, 32, or 64.

[0171] After d0 and d1 are calculated, the offset value (denoted as s) is derived using the CCSO look-up table (LUT). The CCSO LUT is shown in Table 5. Each combination of d0 and d1 is used to identify a row in the LUT from which to obtain the offset value. The offset values ​​are integers, including 0, 1, -1, 3, -3, 5, -5, and -7.

[0172] [Table 6]

[0173] Finally, the CCSO derived offsets are applied to the chroma color components as follows: rc'=clip(rc+s), (20) where rc is the reconstructed sample that is filtered by CCSO, s is the derived offset value obtained from the LUT, and the filtered sample value rc' is further clipped to the range specified by the bit depth.

[0174] FIG. 32 shows an example filter shape in cross-component sample offset (CCSO). CCSO includes f i , i=1...6. These six filter shapes are switchable at the frame level, and the selection is signaled by the syntax ext_filter_support, which uses a 3-bit fixed-length code.

[0175] Signaling of the cross-component sample offset (CCSO) may be performed at both the frame level and the block level. At the frame level, the signal may include: A one-bit flag indicating whether CCSO applies ext_filter_support - 3-bit syntax indicating CCSO filter shape selection A 2-bit index indicating the quantization step size selection 9 3-bit offset values ​​used in the LUT At the 128x128 chroma block level, a flag is signaled to indicate whether the CCSO filter is enabled.

[0176] Sample Adaptive Offset (SAO) In HEVC, Sample Adaptive Offset (SAO) is applied to the reconstructed signal after the deblocking filter using an offset value given in the slice header. For luma samples, the encoder decides whether SAO is applied to the current slice. If SAO is enabled, the current picture can be recursively divided into four sub-regions, and each region can choose one of six SAO types as shown in Table 6. SAO reduces distortion by classifying reconstructed pixels into categories and adding offsets to pixels of each category in the current region. Edge properties are used for pixel classification in SAO types 1-4, and pixel intensity is used for pixel classification in SAO types 5-6.

[0177] [Table 7]

[0178] Band Offset (BO) classifies all pixels of a region into multiple bands, where each band contains pixels of the same intensity interval. The intensity range is divided equally into 32 intervals from 0 to the maximum intensity value (e.g., 255 for 8-bit pixels), and each interval has an offset. The 32 bands are then divided into two groups: one group consists of the central 16 bands, and the other group consists of the remaining 16 bands. Only the offset of one group is transmitted. For pixel classification operations in BO, the most significant 5 bits of each pixel can be directly used as a band index.

[0179] Figure 33 shows an example pixel pattern. Edge Offset (EO) uses four one-dimensional three-pixel patterns for pixel classification considering edge direction information as shown in Figure 33. Each region of the picture can choose one pattern to classify pixels into multiple categories by comparing each pixel with its two neighboring pixels. The selection is sent in the bitstream as side information. Table 7 shows the pixel classification rules for EO.

[0180] [Table 8]

[0181] The decoder-side SAO can be operated independently for each LCU to save line buffers. To achieve this, the pixels in the top and bottom rows in each LCU may not be SAO processed when the 90-degree, 135-degree, and 45-degree classification patterns are selected. The pixels in the leftmost and rightmost columns in each LCU may not be SAO processed when the 0-degree, 135-degree, and 45-degree patterns are selected.

[0182] Table 8 below shows an example syntax that may need to be signaled to a CTU if parameters are not merged from neighboring CTUs.

[0183] [Table 9]

[0184] Cross-component sample offset (CCSO) and local sample offset (LSO) can utilize the value of the pixel being filtered to select an offset value on one color component. However, further extending these inputs for offset selection can significantly increase the signaling overhead of CCSO and LSO, which may limit / reduce coding performance, especially for smaller resolution sequences.

[0185] As mentioned above, CCSO is defined as a filtering process that uses reconstructed samples of a first color component as an input (e.g., Y or Cb or Cr), and the output is applied to a second color component that is a different color component of the first color component. An exemplary filter shape of CCSO is shown in FIG. 29. LSO is a filtering process that uses reconstructed samples of a first color component as an input (e.g., Y or Cb or Cr), and the output is applied to the same first color component. Therefore, the difference between LSO and CCSO is different inputs.

[0186] As described below and shown in FIG. 34, a generalized design of CCSO and LSO is presented by not only considering the delta values ​​between adjacent samples of the collocated (or current) sample, as considered in CCSO and LSO, but also considering the level value of the collocated (or current) sample itself.

[0187] FIG. 34 shows a flowchart of a method according to an exemplary embodiment of the present disclosure. In block 3402, coded information about a reconstructed sample of a current component in a current picture is decoded from a coded video bitstream. The coded information indicates a sample offset filter to be applied to the reconstructed sample. The sample offset filter may include two types of offset values, gradient offset (GO) and band offset (BO), in one example. In block 3404, an offset type is selected to be used with the sample offset filter. In block 3406, an output value of the sample offset filter is determined based on the first reconstructed sample and the selected offset type. In block 3408, a filtered sample value of the reconstructed sample of the current component is determined based on the reconstructed sample and the output value of the sample offset filter. Further embodiments are described below.

[0188] The Generalized Sample Offset (GSO) method can include two types of offset values, CCSO and LSO, including gradient offset (GO) and band offset (BO). The selection of the offset type can be signaled or implicitly derived.

[0189] In one embodiment, the gradient offset may be an offset derived using a delta value between an adjacent sample and a collocated sample of a different color component (in the case of CCSO), or a delta value between an adjacent sample and the current sample to be filtered (in the case of CCSO or LSO).

[0190] In one embodiment, the band offset may be an offset derived using values ​​of the co-located samples or the current sample to be filtered of the different color components. The band may be used to determine the offset value. In one example, the values ​​of the co-located samples or the current sample to be filtered of the different color components may be represented as a variable v, and the BO value is derived using v>>s, where >> indicates a right shift operation and s is a predefined value that specifies the interval of sample values ​​that use the same band offset. In one example, the value of s may vary for the different color components. In another example, the values ​​of the co-located samples or the current sample to be filtered of the different color components are represented as a variable v, and the band indexes bi are derived using a predefined lookup table, where the input of the lookup table is v and the output value is the band indexes bi, and the BO value is derived using the band indexes bi.

[0191] In one embodiment, when a combination of GO and BO is applied (e.g., used simultaneously), the offset is derived using both 1) a delta value between an adjacent sample and a co-located sample of a different color component (in the case of CCSO) or a delta value between an adjacent sample and the current sample to be filtered (in the case of CCSO or LSO) and 2) a value of the co-located sample of a different color component or the current sample to be filtered.

[0192] In one embodiment, the application of GO or BO is signaled. This signaling may be applied in a high-level syntax. As some examples, the signaling may include VPS, PPS, SPS, slice header, picture header, frame header, superblock header, CTU header, tile header.

[0193] In another embodiment, whether GO or BO is signaled at a block level, the block level includes but is not limited to a coding unit (block) level, a predicted block level, a transform block level, or a filtering unit level. This example includes a block level signaling to identify GO or BO.

[0194] In another embodiment, GO or BO is signaled using a flag. A flag is signaled first to indicate whether LSO and / or CCSO are applied to one or more color components, and then another flag is signaled to indicate whether GO or BO is applied. For example, a flag is signaled first to indicate whether LSO and / or CCSO are applied to one or more color components, and then another flag is signaled to indicate whether GO is applied together with BO, and BO is always applied regardless of whether GO is applied. In another example, a flag is signaled first to indicate whether LSO and / or CCSO are applied to one or more color components, and then another flag is signaled to indicate whether BO is applied together with GO, and GO is always applied regardless of whether BO is applied.

[0195] In some embodiments, a signal may be derived to determine whether to use GO or BO or a combination thereof. The signal may be derived implicitly using coded information, including but not limited to, reconstructed samples of the current color component and / or different color components, whether the current block is intra- or inter-coded, whether the current picture is a key (or intra) picture, whether the current sample (or block) is coded with a particular prediction mode (a particular intra- or inter-prediction mode, a transform selection mode, a quantization parameter, etc.).

[0196] As mentioned above, LSO can be similar to CCSO, but the output offset is applied to the same color components whose reconstructed samples are used as input to the filtering process. GSO is a generalized design that considers two types of offset values, including gradient offset (GO), which considers the delta values ​​between collocated samples or adjacent samples of the current sample, and band offset (BO), which considers the level value of the current sample itself.

[0197] In addition, the signaling aspects CCSO, LSO, and GSO may be classified into frame level and block level. At the frame level, the enablement of CCSO, LSO, and / or GSO may be signaled (e.g., using a 1-bit flag) and / or the offset value of the LUT may be signaled (e.g., using 3 bits each). At the block level, for an M×N block, a flag is signaled to indicate the enablement of CCSO, LSO, and / or GSO of the current block. In various embodiments, the values ​​of M and N may each include, but are not limited to, 16, 32, 64, 128, or 256. As used herein, the term block refers to an area of ​​a frame.

[0198] In the following, the adaptive application of GSO is described.

[0199] As mentioned above, CCSO is defined as a filtering process that uses reconstructed samples of a first color component as input (e.g., Y or Cb or Cr), and the output is applied to a second color component, which is a different color component from the first color component. An exemplary filter shape of CCSO is shown in FIG. 29. In addition, LSO is a filtering process that uses reconstructed samples of a first color component as input (e.g., Y or Cb or Cr), and the output is applied to the same first color component. GSO can be considered as a generalized design of CCSO and LSO, and is a filtering process that utilizes delta values ​​between adjacent samples of a collocated (or current) sample like CCSO and LSO, and also considers the level value of the current sample. In GSO, two types of offset values ​​are used, namely, gradient offset (GO), which corresponds to the delta values ​​between adjacent samples of a collocated sample or current sample, and band offset (BO), which corresponds to the level value of the current sample itself.

[0200] 35 shows a flowchart of a method 3500 according to an exemplary embodiment of the present disclosure. The exemplary method 3500 may be performed by an apparatus configured to decode a video stream, such as the video decoder (510) or the video decoder (810) described above. At least some of the actions in the method of FIG. 35 may be performed by a loop filter, such as the loop filter (556) of FIG. 5.

[0201] At block 3502, a coded video stream (e.g., a bitstream) is received. The coded video stream includes a syntax element indicating whether a sample offset filtering process is applied to a frame in the coded video stream at a block level. At block 3504, at least one of GSO, LSO, or CCSO is determined to be enabled for the frame at a block level based on the syntax element being a predefined value. The predefined value may be one of a plurality of predefined values. Each of the plurality of predefined values ​​may indicate whether a particular sample offset process (GSO, LSO, or CCSO) or a particular combination of two or more sample offset processes (two or more of GSO, LSO, CCSO) is enabled. Thus, in some embodiments, at least GSO is determined to be enabled at block 3504. Additionally or alternatively, at least LSO is determined to be enabled. Additionally or alternatively, at least CCSO is determined to be enabled. At block 3506, the coded video stream may be decoded by applying at least one of GSO, LSO, or CCSO at a block level. For example, at least one of the GSO, LSO, or CCSO applied in block 3506 may correspond to or be based on the GSO, LSO, and / or CCSO determined to be enabled in block 3504. That is, if GSO is determined to be enabled in block 3504, GSO may be applied in block 3506, if LSO is determined to be enabled in block 3504, LSO may be applied in block 3506, and if CCSO is determined to be enabled in block 3504, CCSO may be applied in block 3506. In at least some embodiments of method 3500, block sizes of frames in the coded video stream are different for luma and chroma components in corresponding frames.

[0202] In some embodiments, applying at least one of the GSO, LSO, or CCSO in block 3506 includes applying a GSO, where a first block size of the luma component is the same as or smaller than a second block size of the chroma component. For example, the granularity of the application of the GSO is finer for the luma component compared to the chroma component. As an example, M×N used for the luma GSO is 128×128 or less when the chroma is 128×128. The values ​​of M and N may include, but are not limited to, 16, 32, 64, 128, or 256.

[0203] In some embodiments, the method 3500 may further include receiving a signal indicating a first block level flag for a luma component having a first block size equal to or smaller than the second block size of the chroma component when a second block level flag for the chroma component having a second block size is signaled. For example, the granularity of signaling the block level flag is finer for the luma component compared to the chroma component. As an example, the block level flag is signaled for a block size equal to or smaller than 128×128 when the chroma component is signaled for a block of 128×128 size.

[0204] In some embodiments, a block level flag indicating whether one of CCSO, LSO, or GSO is enabled or disabled, such as for application to a block, may also indicate whether another of CCSO, LSO, or GSO is enabled or disabled for the block. For example, a block level flag indicating CCSO is enabled for a chroma component of a block may also indicate LSO is enabled for a luma component of the block. Similarly, a block level flag indicating LSO is enabled for a luma component of a block may also indicate CCSO is enabled for a chroma component of the block. As an example, a block level flag indicating whether CCSO is enabled or applied for a block may depend on a block level flag indicating whether LSO is enabled or applied for the block, and / or a block level flag indicating whether LSO is applied for a block may depend on a block level flag indicating whether CCSO is applied for the block. Additionally or alternatively, a block level flag indicating whether CCSO or LSO is applied for a block may be used as a context for signaling a block level flag indicating whether LSO or CCSO is applied, respectively, for the block.

[0205] In some embodiments, the method 3500 may further include receiving a signal indicating a granularity of at least one of the chroma or luma components for applying the GSO in a high level syntax, the high level syntax including a video parameter set (VPS), a picture parameter set (PPS), a sequence parameter set (SPS), an adaptation parameter set (APS), a frame header, a slice header, a picture header, a tile header, a superblock header, or a coding tree unit (CTU) header. For example, the granularity of application of the GSO for the luma and / or chroma components may be signaled in a high level syntax including, but not limited to, a VPS, a PPS, an SPS, an APS, a frame header, a slice header, a picture header, a tile header, a superblock header, and / or a CTU header.

[0206] In some embodiments, the syntax element is or includes a high level syntax, GSO is enabled by the high level syntax, and the method 3500 may further include receiving a signal including additional high level syntax indicating a maximum number of bands to be used for the band offset. For example, if GSO is enabled by the high level syntax, additional high level syntax is signaled to indicate a maximum number of bands to be used for the BO. For some of these embodiments, the high level syntax includes, but is not limited to, a VPS, a PPS, an SPS, an APS, a frame header, a slice header, a picture header, a tile header, a superblock header, and / or a CTU header.

[0207] In some embodiments, a block level flag enables GSO for a block, and the method 3500 may further include receiving a signal including additional high level syntax indicating a number of bands used for a band offset (BO) in the block. For example, when a block level flag enables GSO for a block, additional block level syntax is signaled to indicate a number of bands used for a BO in that block. In some of these embodiments, the number of bands for a band offset in the block is less than the number of bands signaled at the frame level. For example, the number of bands used for a BO at the block level is always less than or equal to the maximum number of bands signaled at the frame level. Additionally or alternatively, the syntax element is or includes a high level syntax, and the method 3500 may further include receiving a signal including a flag indicating whether a single band or a maximum number of bands specified in the high level syntax applies to the current block. For example, a flag is signaled to indicate whether a single band or a maximum number of bands specified in the high level syntax applies to the current block.

[0208] The embodiments of the present disclosure may be used separately or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored in a non-transitory computer-readable medium. The term block may include a prediction block, a coding block, or a coding unit, i.e., a CU. The embodiments of the present disclosure may be applied to a luma block or a chroma block.

[0209] The techniques described above can be implemented as computer software using computer-readable instructions and physically stored on one or more computer-readable media. For example, Figure 36 illustrates a computer system (3600) suitable for implementing certain embodiments of the disclosed subject matter.

[0210] Computer software can be coded using any suitable machine code or computer language that is amenable to mechanisms such as assembly, compilation, linking, etc. to create code that includes 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.

[0211] The instructions may be executed on various types of computers or computer components including, for example, personal computers, tablet computers, servers, smart phones, gaming consoles, Internet of Things devices, and the like.

[0212] 36 with respect to the computer system (3600) 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 (3600).

[0213] The computer system (3600) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more human users via, for example, tactile input (e.g., keystrokes, swipes, data glove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), olfactory input (not shown). Human interface devices may also be used to capture certain media not necessarily directly associated with conscious human input, such as audio (voice, music, ambient sounds, etc.), images (scanned images, photographic images obtained from still image cameras, etc.), video (two-dimensional video, three-dimensional video including stereoscopic video, etc.).

[0214] The input human interface devices may include one or more (only one of each is depicted) of a keyboard (3601), a mouse (3602), a trackpad (3603), a touch screen (3610), a data glove (not shown), a joystick (3605), a microphone (3606), a scanner (3607), and a camera (3608).

[0215] The computer system (3600) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, for example, by tactile output, sound, light, and smell / taste. Such human interface output devices may include tactile output devices (e.g., tactile feedback via a touch screen (3610), data gloves (not shown), or joystick (3605), although there may also be tactile feedback devices that do not function as input devices), audio output devices (e.g., speakers (3609), headphones (not shown)), visual output devices (e.g., screens (3610), including CRT screens, LCD screens, plasma screens, OLED screens, etc., each with or without touch screen input capability, each with or without tactile feedback capability, some of which may be capable of outputting two-dimensional visual output or output in more than three dimensions via means such as stereo output, virtual reality glasses (not shown), holographic displays, and smoke generator tanks (not shown)), and printers (not shown).

[0216] The computer system (3600) may also include human accessible storage devices and their associated media, such as optical media, including a CD / DVD ROM / RW (3620) with media (3621) such as CDs / DVDs, thumb drives (3622), removable hard drives or solid state drives (3623), legacy magnetic media such as tapes and floppy disks (not shown), and dedicated ROM / ASIC / PLD based devices (not shown) such as security dongles.

[0217] Those skilled in the art should also understand that the term "computer-readable medium" as used in connection with the subject matter of this disclosure does not encompass transmission media, carrier waves, or other transitory signals.

[0218] The computer system (3600) may also include an interface (3654) to one or more communication networks (3655). The networks may be, for example, wireless, wired, optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LAN, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable television, satellite television, and terrestrial broadcast television, vehicular and industrial including CAN bus, etc. Certain networks typically require an external network interface adapter attached to a particular general-purpose data port (e.g., a USB port of the computer system (3600)) or peripheral bus (3649), while other networks are typically integrated into the core of the computer system (3600) by attachment to a system bus as described below (e.g., an Ethernet interface to a PC computer system, or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (3600) can communicate with other entities. Such communications may be unidirectional, receive only (e.g., broadcast television), unidirectional transmit only (e.g., CANbus to a particular CANbus device), or bidirectional, for example, to other computer systems using local or wide area digital networks. Specific protocols and protocol stacks may be used with each of these networks and network interfaces, as described above.

[0219] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to the core (3640) of the computer system (3600).

[0220] The cores (3640) may include one or more central processing units (CPUs) (3641), graphics processing units (GPUs) (3642), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (3643), hardware accelerators for specific tasks (3644), graphics adapters (3650), etc. These devices may be connected via a system bus (3648), along with read-only memory (ROM) (3645), random access memory (3646), internal mass storage (3647) such as an internal hard drive or SSD that is not user accessible. In some computer systems, the system bus (3648) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be attached directly to the core's system bus (3648) or via a peripheral bus (3649). In one example, a screen (3610) may be connected to the graphics adapter (3650). Architectures for peripheral buses include PCI, USB, etc.

[0221] The CPU (3641), GPU (3642), FPGA (3643), and accelerator (3644) can execute certain instructions that, in combination, may constitute the computer code described above. That computer code may be stored in a ROM (3645) or a RAM (3646). Persistent data may be stored, for example, in an internal mass storage (3647), while transitory data may also be stored in a RAM (3646). Rapid storage and retrieval in any of the memory devices may be made possible by the use of cache memories that may be closely associated with one or more of the CPU (3641), GPU (3642), mass storage (3647), ROM (3645), RAM (3646), etc.

[0222] The computer-readable medium can bear computer code for performing various computer-implemented operations. The medium and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the available kind well known to those skilled in the computer software arts.

[0223] As a non-limiting example, a computer system (3600) having an architecture, and specifically a core (3640), 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 user-accessible mass storage as described above, as well as media associated with specific storage of the core (3640) of a non-transitory nature, such as a core internal mass storage (3647) or ROM (3645). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (3640). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (3640), and specifically the processor therein (including a CPU, GPU, FPGA, etc.) to perform certain processes or certain parts of certain processes described herein, including defining data structures stored in RAM (3646) and modifying such data structures according to the processes defined by the software. Additionally or alternatively, the computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator (3644)), which may operate in place of or in conjunction with software to perform particular processes or particular portions of particular processes described herein. References to software may encompass logic, and vice versa, where appropriate. References to computer-readable media may encompass circuitry (such as integrated circuits (ICs)) that stores software for execution, circuitry that embodies logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0224] While this disclosure describes several exemplary embodiments, there are alterations, permutations, and various substitute 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 the spirit and scope of the present disclosure. Appendix A: Acronyms ALF: Adaptive Loop Filter AMVP: Advanced Motion Vector Prediction APS: Adaptive Parameter Set ASIC: Application Specific Integrated Circuit AV1:AOMedia Video 1 AV2:AOMedia Video 2 BCW: Bi-prediction with CU-level weights BM: Bilateral matching BMS: Benchmark Set CANBus: Controller Area Network Bus CC-ALF: Cross-component adaptive loop filter CCSO: Cross component sample offset CD:Compact Disc CDEF: Constrained Directional Enhancement Filter CDF: Cumulative density function CfL: Chroma from Luma CIIP: Combined Intra-Inter Prediction CPU: Central Processing Unit CRT: cathode ray tube CTB: coding tree block CTB: coding tree block CTU: Coding Tree Unit CTU: Coding Tree Unit CU: coding unit DMVR: Decoder-side motion vector refinement DPB: Decoded Picture Buffer DPS: Decoding Parameter Set DVD: Digital Video Disc FPGA: Field Programmable Gate Area GBI: Generalized Biprediction GOP: Group of Pictures GPU: Graphics Processing Unit GSM: Global System for Mobile Communications HDR: High Dynamic Range HEVC: High Efficiency Video Coding HRD: Hypothetical Reference Decoder IBC (or IntraBC): Intrablock copy IC: Integrated Circuit ISP: Intra Subpartition JEM: Joint Exploration Model JVET: Joint Video Exploration Team LAN: Local Area Network LCD: Liquid crystal display LCU: Maximum coding unit LR: Loop recovery filter LSO: Local Sample Offset LTE: Long Term Evolution MMVD: Merge mode with motion vector difference MPM: Most Probable Mode MV: Motion Vector MV: Motion Vector MVD: Motion Vector Difference MVD: Motion Vector Difference MVP: Motion Vector Predictor OLED: Organic Light Emitting Diode PB: Predicted block PCI: Peripheral Component Interconnect PDPC: Position-dependent prediction combination PLD: Programmable Logic Device POC: Picture Order Count PPS: Picture Parameter Set PU: Prediction unit PU: Prediction unit RAM: Random Access Memory ROM: Read-Only Memory RPS: Reference Picture Set SAD: Sum of absolute differences SAO: Sample Adaptive Offset SB: Super Block SCC: Screen Content Coding SDP: Semi-separate split SDR: Standard Dynamic Range SDT: Semi-disjoint tree SEI: Supplemental Extended Information SNR: Signal to Noise Ratio SPS: Sequence Parameter Set SSD: Solid State Drive SST: Semi-separated tree TM: Template Matching TU: conversion unit TU: conversion unit USB: Universal Serial Bus VPS: Video Parameter Set VUI: Video Usability Information VVC: Versatile Video Coding WAIP: Wide-angle Intra Prediction End [Explanation of symbols]

[0225] 101 Samples 102 Arrow 103 Arrow 104 Square Block 180 Schematic diagram showing intra prediction direction 201 Current Block 202 Sample 203 Sample 204 Sample 205 Samples 206 Samples 300 Communication Systems 310 Terminal Devices 320 Terminal Devices 330 Terminal Devices 340 Terminal Devices 350 Communication Network 400 Communication Systems 401 Video Source 402 Stream of uncompressed video pictures 403 Video Encoder 404 Encoded video data 405 Streaming Server 406 Client Subsystem 407 Input copy of encoded video data / Encoded video data 408 Client Subsystem 409 Copy encoded video data / Encoded video data 410 Video Decoder 411 Video Picture Output Stream 412 Display 413 Video Capture Subsystem 420 Electronic Devices 430 Electronic Devices 501 Channel 510 Video Decoder 512 Display / Rendering Device 515 Buffer Memory 520 Entropy Decoder / Parser 521 Symbols 530 Electronic Devices 531 Receiver 551 Scaler / Descaler Unit 552 Intra-picture prediction unit 553 Motion Compensation Prediction Unit 555 Aggregator 556 Loop Filter Unit 557 Reference Picture Memory 558 Current Picture Buffer 601 Video Sources 603 Video Encoder 620 Electronic Devices / Encoders 630 Source Coder 632 Coding Engine 633 Local Video Decoder / Decoding Unit 634 Reference Picture Memory / Reference Picture Cache 635 Predictors 640 Transmitter 643 coded video sequence 645 Entropy Coder 650 Controller 660 Communication Channels 703 Video Encoder 721 General-purpose controller 722 Intra Encoder 723 Residual Calculator 724 Residual Encoder 725 Entropy Encoder 726 Switch 728 Residual Decoder 730 InterEncoder 810 Video Decoder 871 Entropy Decoder 872 Intra Decoder 873 Residual Decoder 874 Reconstruction Module 880 Interdecoder 902 Predefined split options or patterns 904 Predefined split options or patterns 906 Predefined split options or patterns 908 Predefined split options or patterns 1002 "T-shaped" partition / T-shaped pattern 1004 "T-shaped" partition / T-shaped pattern 1006 "T-shaped" partition / T-shaped pattern 1008 "T-shaped" partition / T-shaped pattern 1010 Square Partition 1102 Vertical bisection 1104 Horizontal bisection 1106 Vertical third division 1108 Horizontal third division 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 Split pattern / split structure 1420 Tree Structure / Representation 1502 Square coding block 1504 First Level Split 1506 Second Level Split 1602 Inter-coded Blocks 1604 Conversion Block 3500 methods 3600 Computer System 3601 Keyboard 3602 Mouse 3603 Trackpad 3605 Joystick 3606 Mike 3607 Scanner 3608 Camera 3609 Speaker 3610 Touch Screen 3620 CD / DVD ROM / RW 3621 Medium 3622 Thumb Drive 3623 Removable Hard Drive or Solid State Drive 3640 cores 3641 Central Processing Unit (CPU) 3642 Graphics Processing Unit (GPU) 3643 Field Programmable Gate Area (FPGA) 3644 Hardware Accelerator 3645 Read-Only Memory (ROM) 3646 Random Access Memory (RAM) 3647 core internal mass storage 3648 System Bus 3649 Surrounding bus 3650 Graphics Adapter 3654 Interface 3655 Communication Networks

Claims

1. receiving a coded video stream, the coded video stream including a syntax element indicating whether a sample offset filtering process is applied to frames in the coded video stream at a block level; determining, based on the syntax element being a predefined value, that at least one of a generalized sample offset (GSO), which is a design using two types of offset values ​​including a gradient offset (GO) corresponding to a delta value between collocated samples or adjacent samples of a current sample, and a band offset (BO) corresponding to a level value of the current sample itself, a local sample offset (LSO), which is a filtering process using a reconstructed sample of a first color component as an input, or a cross-component sample offset (CCSO) is enabled for the frame at the block level; decoding the coded video stream by applying the at least one of the GSO, the LSO, or the CCSO at the block level; A method comprising:

2. 2. The method of claim 1, wherein determining that the at least one of the GSO, the LSO, or the CCSO is enabled comprises determining that the GSO is enabled based on the syntax element being the predefined value.

3. 2. The method of claim 1, wherein determining that the at least one of the GSO, the LSO, or the CCSO is enabled comprises determining that the LSO is enabled based on the syntax element being the predefined value.

4. 2. The method of claim 1, wherein determining that the at least one of the GSO, the LSO, or the CCSO is enabled comprises determining that the CCSO is enabled based on the syntax element being the predefined value.

5. receiving a signal indicating a first block level flag for a luma component having a first block size that is the same as or smaller than the second block size of the chroma component when a second block level flag for the chroma component having a second block size is signaled; The method of claim 1 further comprising:

6. receiving a block level flag indicating that one of the GSO, the LSO, or the CCSO is enabled for a block, the block level flag also indicating that another of the GSO, the LSO, or the CCSO is also enabled for the block. The method of claim 1 further comprising:

7. receiving a signal indicating a granularity of at least one of the chroma or luma components for applying the GSO in a high level syntax, the high level syntax including a video parameter set (VPS), a picture parameter set (PPS), a sequence parameter set (SPS), an adaptation parameter set (APS), a frame header, a slice header, a picture header, a tile header, a superblock header, or a coding tree unit (CTU) header; The method of claim 1 further comprising:

8. The syntax elements include a high level syntax, the GSO is enabled by the high level syntax, and the method further comprises: receiving a signal including additional high level syntax indicating a maximum number of bands to be used for the band offset; The method of claim 1 further comprising:

9. 9. The method of claim 8, wherein the high level syntax comprises a video parameter set (VPS), a picture parameter set (PPS), a sequence parameter set (SPS), an adaptation parameter set (APS), a frame header, a slice header, a picture header, a tile header, a superblock header, or a coding tree unit (CTU) header.

10. a block level flag enables the GSO for a block, the method comprising: receiving a signal including additional high level syntax indicating a number of bands to be used for band offsets within the block; The method of claim 1 further comprising:

11. The method of claim 10 , wherein the number of bands for the band offset within the block is less than the number of bands signaled at a frame level.

12. The syntax elements include a high level syntax, and the method further comprises: receiving a signal including a flag indicating whether a single band or a maximum number of bands specified in said high level syntax applies to the current block. The method of claim 10 further comprising:

13. The method of claim 1 , wherein block sizes of the frames in the coded video stream are different for luma and chroma components corresponding to the frames.

14. Apparatus arranged to perform the method according to any one of claims 1 to 13.

15. A computer program product for causing a processor to carry out the method according to any one of claims 1 to 13.

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