METHOD AND APPARATUS FOR VIDEO CODING - Patent application

Abstract

To provide a method and an apparatus for video coding.SOLUTION: An aspect of the present disclosure includes a method, an apparatus, and a non-transitory computer-readable storage medium for video encoding / decoding. The apparatus includes a processing circuit that decodes prediction information of a current block which indicates a plurality of combinations of processed reconstructed samples and corresponding output values of filter processing. The processing circuit executes the filter processing on processed reconstructed samples of a first color component of the current block. The processed reconstructed samples of the first color are not included in the plurality of combinations of the processed reconstructed samples. The processing circuit determines an output value of the filter processing based on one of a default value, a predicted output value, and one of the output values indicated in the prediction information. The processing circuit reconstructs the current block based on the output value being applied to a second color component of the current block that is different from the first color component.SELECTED DRAWING: Figure 20

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Application No. 63 / 113,120, entitled "IMPROVED CROSS-COMPONENT SAMPLE OFFSET," filed on November 12, 2020, which claims the benefit of priority to U.S. Patent Application No. 17 / 360,840, entitled "METHOD AND APPARATUS FOR VIDEO CODING," filed on June 28, 2021. The entire disclosures of the prior applications are hereby incorporated by reference in their entireties.

[0002] This disclosure describes embodiments generally related to video coding. [Background technology]

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

[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 luminance samples and associated chrominance samples. The sequence of pictures may have a fixed or variable picture rate (also informally known as frame rate), for example, 60 pictures per second or 60 Hz. Uncompressed video has significant bitrate requirements. For example, 1080p60 4:2:0 video (1920x1080 luminance sample resolution at a frame rate of 60 Hz) with 8 bits per sample 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 the input video signal through compression. Compression may help reduce the aforementioned bandwidth or storage space requirements, in some cases by more than two orders of magnitude. Both lossless and lossy compression, as well as combinations of these, may be used. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. 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 utilize the reconstructed signal for its intended application. For video, lossy compression is widely used. The amount of acceptable distortion depends on the application, for example, a user of a particular consumer streaming application may tolerate higher distortion than a user of a television distribution application. The achievable compression ratio may reflect that a higher acceptable / tolerable distortion may result in a higher compression ratio.

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

[0007] Video codec techniques may include a technique known as intra-coding, in which sample values ​​are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, pictures are spatially subdivided into blocks of samples. If all blocks of samples are coded in intra mode, the picture may be an intra picture. Intra pictures, and their derivatives, such as independent decoder refresh pictures, may be used to reset the decoder state and thus may be used as the first picture in the coded video bitstream and video session or as still images. Samples of intra blocks may undergo a transform, and the transform coefficients may be quantized before entropy coding. Intra prediction may be a technique that minimizes sample values ​​in the pre-transform domain. In some cases, the smaller the DC value after the transform and the smaller the AC coefficients, the fewer bits are required for 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 try from surrounding sample data and / or metadata obtained during encoding and / or decoding of spatially adjacent and preceding data blocks in decoding order. Such techniques are hereafter referred to as "intra-prediction" techniques. It should be noted that, at least in some cases, intra-prediction uses only reference data from the current picture being reconstructed, and not from reference pictures.

[0009] There may be many different forms of intra-prediction. If more than one of such techniques may be used in a given video coding technique, the technique in use may be coded in an intra-prediction mode. In some cases, the mode may have sub-modes and / or parameters, which may be coded separately or included in the mode codeword. Which codeword is used for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency / gain with intra-prediction, and therefore may also affect the entropy coding technique used to convert the codeword into a bitstream.

[0010] A specific mode of intra prediction was introduced in H.264, improved in H.265, and further refined in newer coding techniques such as the joint exploration model (JEM), versatile video coding (VVC), and benchmark sets (BMS). A predictor block may be formed using neighboring sample values ​​belonging to already available samples. The sample values ​​of the neighboring samples are copied to the predictor block according to the direction. The reference to the direction in use may be coded in the bitstream or may itself be predicted.

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

[0012] 1A, at the top left is shown a square block (104) of 4×4 samples (indicated by a thick dashed line). The square block (104) contains 16 samples, each of which is 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). S44 is at the bottom right because the size of the block is 4×4 samples. Also shown are reference samples that follow a similar numbering scheme. The reference sample is labeled with 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, the prediction samples are adjacent to the block being reconstructed, so negative values ​​do not need to be used.

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

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

[0015] The number of possible directions is increasing as video coding techniques develop. In H.264 (2003), nine different directions can be represented. This has increased to 33 in H.265 (2013), and at the time of this disclosure, JEM / VVC / BMS can support up to 65 directions. Experiments have been performed to identify the most likely directions, and certain techniques of entropy coding are used to represent those likely directions with a small number of bits, accepting a certain penalty for less likely directions. Furthermore, the direction itself may be predicted from neighboring directions used in neighboring already decoded blocks.

[0016] FIG. 1B shows a schematic diagram (105) showing 65 intra prediction directions with JEM to illustrate the increasing number of prediction directions over time.

[0017] The mapping of intra-prediction direction bits in a coded video bitstream that represent the direction may vary from one video coding technique to another, ranging from simple direct mappings from prediction directions to intra-prediction modes, to complex adaptation schemes involving codewords, most likely modes, and similar techniques. In all cases, however, there may be certain directions that are statistically less likely than certain other directions in the video content. Because the goal of video compression is to reduce redundancy, these less likely directions are represented by more bits than the more likely directions in a video coding technique that works well.

[0018] Motion compensation may be a lossy compression technique and may refer to a technique used to predict a newly reconstructed picture or picture portion after blocks of sample data from a previously reconstructed picture or portion thereof (reference picture) are 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 (the latter may indirectly be a temporal dimension).

[0019] In some video compression techniques, the MV applicable to a particular region of sample data may be predicted from other MVs, e.g., from an MV associated with another region of sample data that is spatially adjacent to the region being reconstructed and precedes that MV in decoding order. Doing so may significantly reduce the amount of data required to code the MV, resulting in the elimination of redundancy and increased compression. For example, when coding an input video signal derived from a camera (known as natural video), MV prediction may work effectively because there is a statistical likelihood that regions larger than the region to which a single MV is applicable move in similar directions and therefore, in some cases, may be predicted using similar MVs derived from MVs of neighboring regions. This results in the MV found for a given region being similar or the same as the MV predicted from the surrounding MVs, and as a result, after entropy coding, it may be represented with fewer bits than would be used if coding the MV directly. In some cases, MV prediction may be an example of lossless compression of a signal (i.e., MV) derived from the original signal (i.e., sample stream). In other cases, the MV prediction itself may be lossy, e.g., due to rounding errors when computing a predictor from some surrounding MVs.

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

[0021] Referring to FIG. 1C, the current block (111) may include samples found by the encoder during a motion search process that are predictable from a previous block of the same size but spatially shifted. 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 the five surrounding samples represented by A0, A1 and B0, B1, B2 (112 to 116, respectively). In H.265, MV prediction may use predictors from the same reference picture that neighboring blocks are using. Summary of the Invention [Means for solving the problem]

[0022] An aspect of the present disclosure provides an apparatus for video encoding / decoding. The apparatus includes a processing circuit for decoding prediction information of a current block in a current picture that is part of a coded video sequence. The prediction information indicates a plurality of combinations of processed reconstructed samples and corresponding output values ​​of a filter operation. The processing circuit performs a filter operation on the processed reconstructed samples of a first color component of the current block. The processed reconstructed samples of the first color are not included in the plurality of combinations of processed reconstructed samples. The processing circuit determines an output value of the filter operation based on one of a default value, a predicted output value, and one of the output values ​​indicated in the prediction information. The processing circuit reconstructs the current block based on an output value applied to the reconstructed samples of a second color component of the current block. The second color component is different from the first color component.

[0023] In one embodiment, the processing circuit determines one of a first value and a second value as an output value of the filtering process, the first value being one of the output values ​​indicated in the prediction information and the second value being the inverse of the first value.

[0024] In one embodiment, each of the processed reconstructed samples of the first color component is the inverse of a corresponding processed reconstructed sample in one of the multiple combinations of processed reconstructed samples indicated in the prediction information, and one of the output values ​​indicated in the prediction information corresponds to one of the multiple combinations of processed reconstructed samples indicated in the prediction information.

[0025] In one embodiment, the sum of the index of the processed reconstructed sample of the first color component in the filtering mapping table and the index of one of the output values ​​indicated in the prediction information in the filtering mapping table is equal to the maximum index of the mapping table.

[0026] In one embodiment, the processing circuit determines a default value as an output value of the filter process based on prediction information indicating that a plurality of combinations of processed reconstructed samples indicated in the prediction information is a subset of the total number of combinations of processed reconstructed samples in the filter process.

[0027] In one embodiment, the predicted output value is determined based on the output value of a filtering process applied to another coding block.

[0028] In one embodiment, the processed reconstructed sample of the first color component is determined based on the reconstructed sample of the first color component output from the first coding module, and the reconstructed sample of the second color component is output from the first coding module or a second coding module applied after the first coding module.

[0029] An aspect of the present disclosure provides a method for video encoding / decoding. In the method, prediction information of a current block in a current picture that is part of a coded video sequence is decoded. The prediction information indicates a plurality of combinations of processed reconstructed samples and corresponding output values ​​of a filter operation. The filter operation is performed on the processed reconstructed samples of a first color component of the current block. The processed reconstructed samples of the first color are not included in the plurality of combinations of processed reconstructed samples. The output value of the filter operation is determined based on one of a default value, a predicted output value, and one of the output values ​​indicated in the prediction information. The current block is reconstructed based on the output value applied to the reconstructed samples of a second color component of the current block. The second color component is different from the first color component.

[0030] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by at least one processor, cause the at least one processor to perform any one or combination of methods for video decoding.

[0031] 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]

[0032] [Figure 1A] FIG. 2 is a schematic diagram of an example subset of intra-prediction modes. [Figure 1B] FIG. 2 is a diagram of an example intra-prediction direction. [Figure 1C] FIG. 2 is a schematic diagram of a current block and its surrounding spatial merge candidates in one example. [Diagram 2] FIG. 1 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Diagram 3] FIG. 1 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Figure 4]FIG. 2 is a schematic diagram of a simplified block diagram of a decoder according to one embodiment. [Diagram 5] FIG. 2 is a schematic diagram of a simplified block diagram of an encoder according to one embodiment. [Figure 6] 4 shows a block diagram of an encoder according to another embodiment; [Figure 7] 4 shows a block diagram of a decoder according to another embodiment; [Figure 8A] FIG. 2 illustrates an example diamond filter shape for an adaptive loop filter (ALF) according to some embodiments. [Figure 8B] FIG. 2 illustrates an example diamond filter shape for an adaptive loop filter (ALF) according to some embodiments. [Figure 9A] FIG. 13 illustrates exemplary sub-sample positions used for gradient calculations in the vertical, horizontal, and two diagonal directions, respectively, according to some embodiments. [Figure 9B] FIG. 13 illustrates exemplary sub-sample positions used for gradient calculations in the vertical, horizontal, and two diagonal directions, respectively, according to some embodiments. [Figure 9C] FIG. 13 illustrates exemplary sub-sample positions used for gradient calculations in the vertical, horizontal, and two diagonal directions, respectively, according to some embodiments. [Figure 9D] FIG. 13 illustrates exemplary sub-sample positions used for gradient calculations in the vertical, horizontal, and two diagonal directions, respectively, according to some embodiments. [Figure 10] FIG. 4 illustrates an exemplary modified block classification applied to a luma component according to one embodiment. [Figure 11] FIG. 1 illustrates an example modified ALF of a luma component at a virtual boundary in accordance with some embodiments. [Figure 12] FIG. 2 illustrates an exemplary maximum coding unit (LCU) aligned picture quadtree partitioning according to one embodiment. [Figure 13] FIG. 11 illustrates an exemplary quadtree split flag encoded in z-order according to one embodiment. [Figure 14A] FIG. 2 illustrates an exemplary arrangement of a cross-component adaptive loop filter (CC-ALF) according to one embodiment. [Figure 14B] FIG. 2 illustrates an exemplary linear diamond-shaped filter applied to the luma channel of each chroma component during CC-ALF operation according to one embodiment. [Figure 15] FIG. 2 illustrates an example position of a chroma sample relative to a luma sample according to some embodiments. [Figure 16] FIG. 2 illustrates an exemplary direction search for an 8×8 block according to one embodiment. [Figure 17] FIG. 2 illustrates an exemplary subspace projection according to one embodiment. [Figure 18] FIG. 2 illustrates an exemplary filter support region of a cross-component sample offset (CCSO) filter in accordance with one embodiment. [Figure 19A] FIG. 13 illustrates a table showing, in tabular form, 81 exemplary combinations of nonlinear mappings in a CCSO filter in accordance with one embodiment. [Figure 19B] FIG. 13 illustrates a table showing, in tabular form, 81 exemplary combinations of nonlinear mappings in a CCSO filter in accordance with one embodiment. [Figure 19C] FIG. 19B illustrates a table showing, in tabular form, 40 exemplary combinations of non-linear mappings that are not signaled according to one embodiment and that may be derived based on the table shown in FIG. 19A. [Figure 19D] FIG. 19B shows a table illustrating, in another tabular format, 40 exemplary combinations of non-linear mappings that are not signaled according to one embodiment and that may be derived based on the table shown in FIG. 19A. [Figure 19E] FIG. 13 illustrates a table showing, in tabular form, 17 signaled combinations of nonlinear mappings in a CCSO filter according to one embodiment. [Figure 19F] FIG. 13 illustrates a table showing, in tabular form, 16 signaled combinations of nonlinear mappings in a CCSO filter according to one embodiment. [Figure 19G]FIG. 13 illustrates a table showing, in tabular form, 33 signaled combinations of nonlinear mappings in a CCSO filter according to one embodiment. [Figure 19H] FIG. 13 illustrates a table showing, in tabular form, 32 signaled combinations of nonlinear mappings in a CCSO filter according to one embodiment. [Figure 20] FIG. 1 illustrates an exemplary flow chart according to one embodiment. [Figure 21] FIG. 1 is a schematic diagram of a computer system according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] I. Video Decoder and Encoder Systems FIG. 2 shows a simplified block diagram of a communication system (200) according to one embodiment of the present disclosure. The communication system (200) includes a plurality of terminal devices that may communicate with each other, for example, via a network (250). For example, the communication system (200) includes a first pair of terminal devices (210) and (220) interconnected via the network (250). In the example of FIG. 2, the first pair of terminal devices (210) and (220) perform unidirectional transmission of data. For example, the terminal device (210) may code video data (e.g., a stream of video pictures captured by the terminal device (210)) for transmission to another terminal device (220) via the network (250). The encoded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (220) may receive the coded video data from the network (250), 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 common, such as in media serving applications.

[0034] In another example, the communication system (200) includes a second pair of terminal devices (230) and (240) performing bidirectional transmission of coded video data, which may take place, for example, during a video conference. For the bidirectional transmission of data, in one example, each of the terminal devices (230) and (240) may code video data (e.g., a stream of video pictures captured by the terminal device) for transmission to the other of the terminal devices (230) and (240) over the network (250). Each of the terminal devices (230) and (240) may also receive coded video data transmitted by the other of the terminal devices (230) and (240), 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. 2, the terminal devices (210), (220), (230), and (240) may be depicted as a server, a personal computer, and a smartphone, although the principles of the present disclosure may not be so limited. The embodiments of the present disclosure apply to laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. The network (250) represents any number of networks that convey coded video data between the terminal devices (210), (220), (230), and (240), including, for example, wired and / or wireless communication networks. The communication network (250) may exchange data over circuit-switched and / or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this discussion, the architecture and topology of the network (250) may not be important to the operation of the present disclosure unless otherwise described herein below.

[0036] 3 shows an arrangement of a video encoder and a video decoder in a streaming environment as an example of an application of the disclosed subject matter. The disclosed subject matter may be equally applicable to other video-enabled applications including, for example, video conferencing, digital TV, storage of compressed video on digital media including CDs, DVDs, memory sticks, and the like.

[0037] The streaming system may include a video source (301) that creates a stream of uncompressed video pictures (302), a capture subsystem (313) that may include, for example, a digital camera. In one example, the stream of video pictures (302) includes samples taken by a digital camera. The stream of video pictures (302), shown as a thick line to emphasize the high amount of data compared to the encoded video data (304) (or coded video bitstream), may be processed by an electronic device (320) that includes a video encoder (303), coupled to the video source (301). The video encoder (303) 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 (304) (or encoded video bitstream (304)), shown as a thin line to emphasize the lower amount of data compared to the stream of video pictures (302), may be stored in a streaming server (305) for future use. One or more streaming client subsystems, such as the client subsystems (306) and (308) of FIG. 3, may access the streaming server (305) to retrieve copies (307) and (309) of the encoded video data (304). The client subsystem (306) may include a video decoder (310), for example within an electronic device (330). The video decoder (310) decodes an input copy (307) of the encoded video data and creates an output stream (311) of video pictures that may be rendered on a display (312) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (304), (307), and (309) (e.g., a video bitstream) may be coded according to a particular video coding / compression standard. Examples of such standards include ITU-T Recommendation H.265.In one example, a developing video coding standard is informally known as Versatile Video Coding (VVC), and the disclosed subject matter may be used in the context of VVC.

[0038] It should be noted that the electronic devices (320) and (330) may include other components (not shown). For example, the electronic device (320) may include a video decoder (not shown), and the electronic device (330) may also include a video encoder (not shown).

[0039] 4 shows a block diagram of a video decoder (410) according to one embodiment of the present disclosure. The video decoder (410) may be included in an electronic device (430). The electronic device (430) may include a receiver (431) (e.g., a receiving circuit). The video decoder (410) may be used in place of the video decoder (310) of the example of FIG. 3.

[0040] The receiver (431) may receive one or more coded video sequences to be decoded by the video decoder (410), in the same or another embodiment, one coded video sequence at a time, where the decoding of each coded video sequence is independent of the other coded video sequences. The coded video sequences may be received from a channel (401), which may be a hardware / software link to a storage device that stores the encoded video data. The receiver (431) may receive the encoded video data along with other data, such as a coded audio data stream and / or an auxiliary data stream, that may be forwarded to a respective using entity (not shown). The receiver (431) may separate the coded video sequences from the other data. To combat network jitter, a buffer memory (415) may be coupled between the receiver (431) and the entropy decoder / parser (420) (hereinafter "parser (420)"). In certain applications, the buffer memory (415) is part of the video decoder (410). In others, it may be external to the video decoder (410) (not shown). In still others, there may be a buffer memory (not shown) external to the video decoder (410), e.g., to combat network jitter, plus another buffer memory (415) internal to the video decoder (410), e.g., to handle playout timing. If the receiver (431) is receiving data from a storage / forwarding device with sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (415) may not be needed or may be small. For use with best-effort packet networks such as the Internet, the buffer memory (415) may be needed and may be relatively large, preferably adaptively sized, and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (410).

[0041] The video decoder (410) may include a parser (420) for reconstructing symbols (421) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (410) and, in some cases, information for controlling a rendering device (e.g., a display screen), such as a render device (412) that is not an integral part of the electronic device (430) but may be coupled to the electronic device (430) as shown in FIG. 4. The rendering device control information may be in the form of a Supplemental Enhancement Information (SEI) message or a Video Usability Information (VUI) parameter set fragment (not shown). The parser (420) may parse / entropy decode the received coded video sequence. The coding of the coded video sequence may conform to a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, and arithmetic coding with or without context dependency, etc. The parser (420) 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 group. 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 (420) may also extract from the coded video sequence information such as transform coefficients, quantizer parameter values, and MVs.

[0042] The parser (420) may perform an entropy decoding / parsing operation on the video sequence received from the buffer memory (415) to produce symbols (421).

[0043] The reconstruction of the symbols (421) may involve several different 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. Which units are involved and how may be controlled by subgroup control information parsed from the coded video sequence by the parser (420). The flow of such subgroup control information between the parser (420) and the following units is not shown for clarity.

[0044] In addition to the functional blocks already mentioned, the video decoder (410) may be conceptually subdivided into several functional units as described below. In an actual implementation operating under commercial constraints, many of these units may interact closely with each other and may be at least partially integrated with each other. However, for purposes of describing the disclosed subject matter, the following conceptual subdivision into functional units is appropriate.

[0045] The first unit is a scalar / inverse transform unit (451), which receives quantized transform coefficients and control information from the parser (420) as symbols (421), including the transform to use, block size, quantization coefficients, quantization scaling matrix, etc. The scalar / inverse transform unit (451) may output blocks containing sample values ​​that may be input to an aggregator (455).

[0046] In some cases, the output samples of the scaler / inverse transform (451) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but may use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (452). In some cases, the intra-picture prediction unit (452) generates a block of the same size and shape as the block being reconstructed using surrounding already reconstructed information fetched from a current picture buffer (458). The current picture buffer (458) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. The aggregator (455) adds, possibly on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (452) to the output sample information provided by the scaler / inverse transform unit (451).

[0047] In other cases, the output samples of the scaler / inverse transform unit (451) may relate to an inter-coded, possibly motion-compensated block. In such cases, the motion compensated prediction unit (453) may access a reference picture memory (457) to fetch samples used for prediction. After motion compensating the fetched samples according to the symbols (421) related to the block, these samples (in this case referred to as residual samples or residual signals) may be added to the output of the scaler / inverse transform unit (451) by an aggregator (455) to generate output sample information. The addresses in the reference picture memory (457) from which the motion compensated prediction unit (453) fetches the prediction samples may be controlled by the MVs available to the motion compensated prediction unit (453) in the form of symbols (421), which may have, for example, X, Y, and reference picture components. Motion compensation may also include interpolation of sample values ​​fetched from the reference picture memory (457) when sub-sample accurate MVs are used, MV prediction mechanisms, etc.

[0048] The output samples of the aggregator (455) may be subjected to various loop filtering techniques in a loop filter unit (456). Video compression techniques may include in-loop filter techniques controlled by parameters contained in the coded video sequence (also called a coded video bitstream) and made available to the loop filter unit (456) as symbols (421) from the parser (420), but may also be responsive to meta-information obtained during decoding of a previous portion (in decoding order) of the coded picture or coded video sequence, and to previously reconstructed loop filtered sample values.

[0049] The output of the loop filter unit (456) may be a sample stream that can be output to a render device (412) as well as stored in a reference picture memory (457) for use in future inter-picture prediction.

[0050] Once a particular coded picture has been fully reconstructed, it may be used as a reference picture for future prediction. For example, once a coded picture corresponding to a current picture has been fully reconstructed and the coded picture has been identified as a reference picture (e.g., by the parser (420)), the current picture buffer (458) may become part of the reference picture memory (457), and a new current picture buffer may be reallocated before beginning reconstruction of a subsequent coded picture.

[0051] The video decoder (410) may perform decoding operations according to a given video compression technique in a standard such as ITU-T Rec. H.265. The coded video sequence may comply with the syntax specified by the video compression technique or standard being used in the sense that the coded video sequence complies with both the syntax and the profile of the video compression technique or standard as documented in the video compression technique or standard. Specifically, the profile may select a particular tool as the only tool available for use under that profile, among all tools available in the video compression technique or standard. Also, what is required for compliance may be that the complexity of the coded video sequence is within a range defined by the level of the video compression technique or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. The limits set by the level may be further limited in some cases by the specification of a Hypothetical Reference Decoder (HRD) and metadata of HRD buffer management signaled in the coded video sequence.

[0052] In one embodiment, the receiver (431) 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 (410) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0053] 5 shows a block diagram of a video encoder (503) according to one embodiment of the present disclosure. The video encoder (503) is included in an electronic device (520). The electronic device (520) includes a transmitter (540) (e.g., a transmission circuit). The video encoder (503) may be used in place of the example video encoder (303) of FIG.

[0054] The video encoder (503) may receive video samples from a video source (501) (not part of the electronic device (520) in the example of FIG. 5) that may capture video images to be coded by the video encoder (503). In another example, the video source (501) is part of the electronic device (520).

[0055] The video source (501) may provide a source video sequence to be coded by the video encoder (503) 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 Y CrCB, RGB, ...), and any suitable sampling structure (e.g., Y CrCb 4:2:0, Y CrCb 4:4:4). In a media serving system, the video source (501) may be a storage device that stores previously prepared video. In a video conferencing system, the video source (501) 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 that convey motion when viewed in sequence. The pictures themselves may be organized as a spatial array of pixels, each of which may contain one or more samples depending on the sampling structure, color space, etc. in use. Those skilled in the art will readily appreciate the relationship between pixels and samples. The following discussion will focus on samples.

[0056] According to an embodiment, the video encoder (503) may code and compress pictures of a source video sequence into a coded video sequence (543) in real-time or under any other time constraints, depending on the requirements of the application. Enforcing an appropriate coding rate is one function of the controller (550). In some embodiments, the controller (550) controls and is functionally coupled to other functional units as described below. For clarity, coupling is not shown. Parameters set by the controller (550) may include rate control related parameters (picture skip, quantizer, lambda value for rate distortion optimization techniques, ...), picture size, group of pictures (GOP) layout, and maximum MV allowed reference region, etc. The controller (550) may be configured with other appropriate functions related to the video encoder (503) optimized for a particular system design.

[0057] In some embodiments, the video encoder (503) is configured to operate in a coding loop. As an oversimplified explanation, in one example, the coding loop may include a source coder (530) (e.g., responsible for creating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (533) embedded in the video encoder (503). The decoder (533) reconstructs the symbols to create sample data in a similar manner as the (remote) decoder does (when the compression between the symbols and the coded video bitstream is lossless in the video compression techniques considered in the disclosed subject matter). The reconstructed sample stream (sample data) is input to a reference picture memory (534). The decoding of the symbol stream produces bit-accurate results regardless of the location of the decoder (local or remote), so the contents of the reference picture memory (534) are also bit-accurate between the local and remote encoders. In other words, the prediction part of the encoder "sees" exactly the same sample values ​​as the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchrony (and the drift that occurs when synchrony cannot be maintained, e.g., due to channel errors) is also used in several related technologies.

[0058] The operation of the "local" decoder (533) may be the same as the operation of a "remote" decoder, such as the video decoder (410), already described in detail above in connection with Figure 4. However, with brief reference also to Figure 4, because symbols are available and the encoding / decoding of symbols into / from a coded video sequence by the entropy coder (545) and parser (420) may be lossless, the entropy decoding portion of the video decoder (410), including the buffer memory (415) and parser (420), may not be implemented entirely in the local decoder (533).

[0059] An observation that may be made in this regard is that decoder techniques other than analysis / entropy decoding present in a decoder must necessarily be present in the corresponding encoder in substantially the same functional form. For this reason, the disclosed subject matter focuses on the decoder operation. A description of the encoder techniques may be omitted, since they are the inverse of the decoder techniques described generically. Only in certain areas is a more detailed description necessary, which is provided below.

[0060] In operation, in some examples, the source coder (530) 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 (532) codes differences between pixel blocks of the input picture and pixel blocks of reference pictures that may be selected as predictive references for the input picture.

[0061] The local video decoder (533) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols created by the source coder (530). The operation of the coding engine (532) may preferably be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 5), the reconstructed video sequence may usually be a replica of the source video sequence with some errors. The local video decoder (533) may replicate the decoding process that may be performed by the video decoder on the reference pictures and store the reconstructed reference pictures in a reference picture cache (534). In this way, the video encoder (503) may locally store copies of reconstructed reference pictures that have common content with the reconstructed reference pictures obtained by the far-end video decoder (in the absence of transmission errors).

[0062] The predictor (535) may perform a prediction search for the coding engine (532). That is, for a new picture to be coded, the predictor (535) may search the reference picture memory (534) for sample data (as candidate reference pixel blocks) that may serve as suitable prediction references for the new picture, or for specific metadata such as reference picture MV and block shape. The predictor (535) may operate on a sample block-by-pixel block basis to find a suitable prediction reference. In some cases, as determined by the search results obtained by the predictor (535), the input picture may have a prediction reference drawn from among multiple reference pictures stored in the reference picture memory (534).

[0063] The controller (550) may manage the coding operations of the source coder (530), 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 (545), which converts the symbols produced by the various functional units into a coded video sequence by losslessly compressing the symbols according to techniques such as Huffman coding, variable length coding, and arithmetic coding.

[0065] The transmitter (540) may buffer the coded video sequence created by the entropy coder (545) to prepare it for transmission over a communication channel (560), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (540) may merge the coded video data from the video coder (503) with other data to be transmitted, such as a coded audio data stream and / or an auxiliary data stream (source not shown).

[0066] The controller (550) may manage the operation of the video encoder (503). During coding, the controller (550) may assign a particular coded picture type to each coded picture, which may affect the coding techniques that may be applied to the respective picture. For example, pictures may often be assigned as one of the following picture types:

[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 support various types of intra pictures, including, for example, Independent Decoder Refresh ("IDR") pictures. Those skilled in the art are aware of these variants of I-pictures and their respective uses and characteristics.

[0068] A predictive picture (P picture) may be one that can be coded and decoded using intra prediction or inter prediction, which uses at most one MV and a reference index to predict the sample values ​​of each block.

[0069] Bidirectionally predicted pictures (B-pictures) may be those that can be coded and decoded using intra- or inter-prediction that uses up to two MVs and reference indices to predict the sample values ​​of each block. Similarly, multiple predicted pictures 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 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 may be 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 with reference to one previously coded reference picture by spatial prediction or by temporal prediction. A block of a B picture may be predictively coded with reference to one or two previously coded reference pictures by spatial prediction or by temporal prediction.

[0071] The video encoder (503) may perform coding operations according to a given video coding technique or standard, such as ITU-T Rec. H.265. In its operations, the video encoder (503) 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 one embodiment, the transmitter (540) may transmit additional data along with the encoded video. The source coder (530) 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, and 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 correlation (temporal or other) between pictures. In one example, a particular picture being encoded / decoded, called the current picture, is divided into blocks. If a block in the current picture is similar to a reference block in a previously coded and still buffered reference picture in the video, the block in the current picture may be coded by a vector called a MV. The MV refers to a reference block in the reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

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

[0075] Furthermore, to improve coding efficiency, merge mode techniques can be used for inter-image prediction.

[0076] According to some embodiments of the present disclosure, predictions such as inter-image prediction and intra-image prediction are performed on a block-by-block basis. For example, according to the HEVC standard, pictures in a sequence of video pictures are divided into coding tree units (CTUs) for compression, and the CTUs in a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU includes three coding tree blocks (CTBs), which are 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, or 16 CUs of 16×16 pixels. In one example, each CU is analyzed to determine a prediction type of the CU, such as an inter prediction type or an intra prediction type. A CU is divided into one or more prediction units (PUs) according to temporal and / or spatial predictability. In general, each PU includes a luma prediction block (PB) and two chroma PBs. In one embodiment, prediction operations in coding (encoding / decoding) are performed in units of prediction blocks. Taking a luma prediction block as an example of a prediction block, the prediction block includes a matrix of pixel values ​​(e.g., luma values) such as 8×8 pixels, 16×16 pixels, 8×16 pixels, and 16×8 pixels.

[0077] 6 shows a diagram of a video encoder (603) according to another embodiment of the present disclosure. The video encoder (603) 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. In one example, the video encoder (603) is used in place of the video encoder (303) of the example of FIG. 3.

[0078] In an HEVC example, the video encoder (603) receives a matrix of sample values ​​for a processing block, such as a predictive block, such as 8×8 samples. The video encoder (603) determines whether the processing block is best coded using intra-mode, inter-mode, or bi-predictive mode, e.g., using rate-distortion optimization. If the processing block is to be coded in intra-mode, the video encoder (603) may use intra-prediction techniques to encode the processing block into a coded picture, and if the processing block is to be coded in inter-mode or bi-predictive mode, the video encoder (603) may use inter-prediction or bi-prediction techniques, respectively, to encode the processing block into a coded picture. In certain video coding techniques, the merge mode may be an inter-picture prediction sub-mode, and the MV is derived from one or more MV predictors without the benefit of coded MV components outside the predictors. In certain other video coding techniques, there may be MV components applicable to the current block. In one example, the video encoder (603) includes other components, such as a mode decision module (not shown) for determining the mode of the processing block.

[0079] In the example of FIG. 6, the video encoder (603) includes an inter-encoder (630), an intra-encoder (622), a residual calculator (623), a switch (626), a residual encoder (624), a general controller (621), and an entropy encoder (625), coupled to each other as shown in FIG. 6.

[0080] The inter-encoder (630) is configured to receive samples of a current block (e.g., a processing block), compare the block with one or more reference blocks in a reference picture (e.g., blocks in a previous picture and a subsequent picture), generate inter-prediction information (e.g., description of redundant information by inter-encoding technique, MV, merge mode information), and calculate an inter-prediction result (e.g., a prediction block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that is decoded based on the encoded video information.

[0081] The intra encoder (622) is configured to receive samples of a current block (e.g., a processing block), possibly compare the block with already coded blocks in the same picture, generate quantized coefficients after transformation, and possibly also generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). In one example, the intra encoder (622) also calculates intra prediction results (e.g., predicted blocks) based on the intra prediction information and reference blocks in the same picture.

[0082] The generic controller (621) is configured to determine generic control data and control other components of the video encoder (603) based on the generic control data. In one example, the generic controller (621) determines the mode of the block and provides a control signal to the switch (626) based on the mode. For example, if the mode is an intra mode, the generic controller (621) controls the switch (626) to select an intra mode result for use by the residual calculator (623), and controls the entropy encoder (625) to select intra prediction information and include the intra prediction information in the bitstream, and if the mode is an inter mode, the generic controller (621) controls the switch (626) to select an inter prediction result for use by the residual calculator (623), and controls the entropy encoder (625) to select inter prediction information and include the inter prediction information in the bitstream.

[0083] The residual calculator (623) calculates the difference (residual data) between the received block and a prediction result selected from the intra-encoder (622) or the inter-encoder (630). The residual encoder (624) is configured to operate on the residual data to encode the residual data to generate transform coefficients. In one example, the residual encoder (624) is configured to transform the residual data from the spatial domain to the frequency domain and generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various embodiments, the video encoder (603) also includes a residual decoder (628). The residual decoder (628) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (622) and the inter-encoder (630) as appropriate. For example, the inter-encoder (630) may generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (622) may generate decoded blocks based on the decoded residual data and the intra-prediction information. In some examples, the decoded blocks are 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 (625) is configured to format a bitstream to include the encoded block. The entropy encoder (625) is configured to include various information in accordance with an appropriate standard, such as HEVC. In one example, the entropy encoder (625) is configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other appropriate information in the bitstream. It should be noted that, according to the disclosed subject matter, when coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode, the residual information is not present.

[0085] 7 shows a diagram of a video decoder (710) according to another embodiment of the present disclosure. The video decoder (710) is configured to receive coded pictures that are part of a coded video sequence and to decode the coded pictures to generate reconstructed pictures. In one example, the video decoder (710) is used in place of the video decoder (310) of the example of FIG. 3.

[0086] In the example of FIG. 7, the video decoder (710) includes an entropy decoder (771), an inter-decoder (780), a residual decoder (773), a reconstruction module (774), and an intra-decoder (772), coupled to each other as shown in FIG. 7.

[0087] The entropy decoder (771) may be configured to reconstruct from the coded picture certain symbols that represent the syntax elements of which the coded picture is composed. Such symbols may include, for example, the mode in which the block is coded (e.g., intra mode, inter mode, bi-predictive mode, etc., the latter two being merged or separate submodes), prediction information (e.g., intra prediction information or inter prediction information, etc.) that may identify certain samples or metadata used for prediction by the intra decoder (772) or the inter decoder (780), respectively, and residual information, for example in the form of quantized transform coefficients. In one example, if the prediction mode is an inter prediction mode or a bi-predictive mode, the inter prediction information is provided to the inter decoder (780), and if the prediction type is an intra prediction type, the intra prediction information is provided to the intra decoder (772). The residual information may undergo inverse quantization and be provided to the residual decoder (773).

[0088] The inter decoder (780) is configured to receive the inter prediction information and to generate inter prediction results based on the inter prediction information.

[0089] The intra decoder (772) is configured to receive intra prediction information and to generate a prediction result based on the intra prediction information.

[0090] The residual decoder (773) is 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 (773) may also require certain control information (including Quantizer Parameters (QP)), which may be provided by the entropy decoder (771) (the data path not shown may be low volume control information only).

[0091] The reconstruction module (774) is configured to combine, in the spatial domain, the residual output by the residual decoder (773) and the prediction result (possibly output by the inter prediction module or the intra prediction module) to form a reconstructed block that may be part of a reconstructed picture that may be part of the resulting reconstructed video. It should be noted that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0092] It should be noted that the video encoders (303), (503), and (603) and the video decoders (310), (410), and (710) may be implemented using any suitable technology. In one embodiment, the video encoders (303), (503), and (603) and the video decoders (310), (410), and (710) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (303), (503), and (603) and the video decoders (310), (410), and (710) may be implemented using one or more processors executing software instructions.

[0093] II. Adaptive Loop Filter In some relevant examples, such as VVC Draft 8, an adaptive loop filter (ALF) with block-based filter adaptation may be applied. For the luma component, one of 25 filters may be selected for each 4×4 block based on the local gradient directionality and activity of the respective 4×4 block.

[0094] 8A-8B show example diamond filter shapes for ALF according to some embodiments of the present disclosure: Figure 8A shows a 5x5 diamond shape applicable to the chroma components, and Figure 8B shows a 7x7 diamond shape applicable to the luma component.

[0095] In some related examples, for the luma component, each 4×4 block may be classified into one of 25 classes. The classification index C of a 4×4 block depends on the orientation D and activity D of the 4×4 block.

number

number

[0096] D and

number

number

number

number

number

[0097] To reduce the complexity of block classification, a subsampled 1-D Laplacian computation can be applied. Figures 9A-9D show example subsample positions used for the vertical, horizontal, and two diagonal gradient computations, respectively.

[0098] Then, the maximum and minimum values ​​of the horizontal and vertical gradients may be set as follows:

number

number

[0099] The maximum and minimum values ​​of the two diagonal gradients may be set as follows:

number

number

[0100] These values ​​may be compared with each other and with two thresholds t1 and t2 to derive the value of the directionality D.

[0101] Step 1:

number

number

[0102] Step 2:

number

[0103] Step 3:

number

[0104] Step 4:

number

[0105] The motion value A is calculated as follows:

number

[0106] Furthermore, A is quantized to the range 0 to 4 (inclusive), and the quantized value is

number

[0107] For chroma components within a picture, no classification method is applied, e.g., a single set of ALF coefficients may be applied to each chroma component.

[0108] Before filtering each 4x4 luma block, geometric transformations such as rotation, diagonal flip, and vertical flip are applied to the filter coefficients f(k,l) and the corresponding filter clipping values ​​c(k,l) according to the gradient values ​​calculated for the respective block. This is equivalent to applying these transformations to samples within the filter support region in order to make different blocks to which ALF is applied more similar by aligning their orientations.

[0109] Three geometric transformations, including a diagonal flip, a vertical flip and a rotation, can be written as follows: Diagonal: f D (k,l) = f(l,k), c D (k,l)=c(l,k) Equation (11) Vertical flip:f V (k,l)=f(k,Kl-1), c V (k,l)=c(k,Kl-1) Equation (12) Rotation:f R (k,l)=f(Kl-1,k), c R (k,l)=c(Kl-1,k) Equation (13) where K is the size of the filter, 0≦k, l≦Kl are the coordinates of the transform coefficients, with position (0,0) being the top-left corner and position (K-1,K-1) being the bottom-right corner. The transform is applied to the filter coefficients f(k,l) and clipping values ​​c(k,l) according to the gradient values ​​calculated for the corresponding blocks. The relationship between the transform and the gradients in the four directions can be summarized in Table 1.

[0110] [Table 1]

[0111] In some relevant examples, such as VVC Draft 8, the filter parameters of ALF are signaled in an adaptive parameter set (APS). In one APS, up to 25 sets of luma filter coefficients and clipping value indexes and up to 8 sets of chroma filter coefficients and clipping value indexes may be signaled. To reduce bit overhead, filter coefficients of different classifications of luma components may be merged. In the slice header, the index of the APS used for the current slice is signaled. In VVC Draft 8, the signaling of ALF is CTU-based.

[0112] The clipping value index decoded from the APS allows the clipping values ​​to be determined using a table of clipping values ​​for the luma and chroma components. These clipping values ​​depend on the internal bit depth. For example, the table of clipping values ​​may be obtained by the following formula:

number

[0113] [Table 2]

[0114] In the slice header, up to seven APS indices can be signaled to specify the luma filter set to be used for the current slice. The filtering process can be further controlled at the CTB level. A flag can be signaled to indicate whether an ALF is applied to the luma CTB. The luma CTB can select a filter set among 16 fixed filter sets and a filter set from an APS. A filter set index in the luma CTB is signaled to indicate which filter set to apply. The 16 fixed filter sets can be predefined and hard-coded in both the encoder and the decoder.

[0115] For chroma components, the APS index can be signaled in the slice header to indicate the chroma filter set used for the current slice. At the CTB level, if an APS has more than one chroma filter set, a filter set index can be signaled for each chroma CTB.

[0116] The filter coefficients can be quantized with a norm equal to 128. To limit the multiplication complexity, bitstream conformance can be applied so that the coefficient values ​​of non-center positions are in the range of -27 to 27-1. The center position coefficients are not signaled in the bitstream and are assumed to be equal to 128.

[0117] In some relevant examples, such as VVC Draft 8, the syntax and semantics of clipping indexes and corresponding values ​​may be defined as follows:

[0118] alf_luma_clip_idx[sfIdx][j] specifies the clipping index of the clipping value used before multiplying the j-th 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.

[0119] The luma filter clipping value AlfClipL[adaptation_parameter_set_id][filtIdx] with element AlfClipL[adaptation_parameter_set_id][filtIdx][j], where filtIdx=0..NumAlfFilters-1 and j=0..11, is derived in Table 2 based on the bit depth set equal to bit depth Y and clipIdx set equal to alf_luma_clip_idx[alf_luma_coeff_delta_idx[filtIdx]][j].

[0120] alf_chroma_clip_idx[altIdx][j] specifies the clipping index of the clipping value to be used, 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).

[0121] The chroma filter clipping value AlfClipC[adaptation_parameter_set_id][altIdx] with element AlfClipC[adaptation_parameter_set_id][altIdx][j] is derived in Table 2 by setting the bit depth set equal to bit depth C and setting clipIdx set equal to alf_chroma_clip_idx[altIdx][j], with elements altIdx=0..alf_chroma_num_alt_filters_minus1,j=0..5.

[0122] On the decoder side, when ALF is enabled for the CTB, each sample R(i,j) in the CU is filtered to a sample value R'(i,j) as shown below.

number

number

number

[0123] 10 is a diagram illustrating an example modified block classification applied to the luma component according to an embodiment of the present disclosure. The modified block classification and filtering employed for samples near the horizontal CTU boundary can reduce the line buffer requirement of the ALF. As shown in FIG. 10, a virtual boundary can be defined as a line by shifting the horizontal CTU boundary by "N" samples, where N is equal to 4 for the luma component and 2 for the chroma component, respectively.

[0124] 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. Thus, the quantization of the activity value A is scaled by taking into account the reduction in the number of samples used in the 1D Laplacian gradient computation.

[0125] FIG. 11 is a diagram illustrating an exemplary modified ALF of the luma component at the virtual boundary according to some embodiments. For filtering processing, a symmetric padding operation at the virtual boundary may be used for both the luma component and the chroma component. As shown in FIG. 11, if the sample being filtered is located below the virtual boundary, the adjacent sample located above the virtual boundary is padded. Meanwhile, the other corresponding sample is also padded symmetrically.

[0126] In order to improve coding efficiency, some related examples use a coding unit synchronized picture quadtree-based ALP. A luma image may be divided into multiple multi-level quadtree partitions, and the boundaries of each partition are aligned with the boundaries of the largest coding unit (LCU). Each partition has its own filtering process and may therefore be referred to as a filter unit (FU).

[0127] The two-pass encoding flow is described below. In the first pass, determine the quadtree division pattern and the optimal filter for each FU. The filtering distortion is estimated by fast filtering distortion estimation (FFDE) during the decision process. According to the determined quadtree division pattern and the selected filters of all FUs, the reconstructed picture is filtered. In the second pass, perform CU synchronous ALF on / off control. According to the ALF on / off result, the filtered picture from the first pass is partially restored by the reconstructed picture.

[0128] FIG. 12 illustrates an exemplary LCU-aligned picture quadtree partitioning according to one embodiment. A top-down partitioning method is adopted to divide an image into multi-level quadtree partitions using a rate-distortion criterion. Each partition is 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, as shown in FIG. 12, a picture is partitioned into 10 FUs, and the encoding order is FU0, FU1, FU2, FU3, FU4, FU5, FU6, FU7, FU8, and FU9.

[0129] Figure 13 shows an exemplary quadtree division pattern corresponding to Figure 12. To indicate the picture quadtree division pattern, the division flags may be encoded and transmitted in z-order.

[0130] The filter for each FU can be selected from two filter sets based on the rate-distortion criterion. The first set has 1 / 2 symmetric square and diamond filters newly derived for the current FU. The second set comes from a time-delay filter buffer that stores previously derived filters for the FUs of the previous picture. The filter with the smallest rate-distortion cost of these two sets can be selected for the current FU. Similarly, if the current FU is not the smallest FU and can be further divided into four child FUs, the rate-distortion costs of the four child FUs are calculated. By recursively comparing the rate-distortion costs for the division and no division cases, a picture quadtree division pattern can be determined.

[0131] In some relevant examples, the maximum quadtree split level is 2, which means the maximum number of FUs is 16. During the quadtree split decision, the correlation values ​​for deriving 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. Thus, there is only one frame buffer access to derive the filter coefficients of all FUs.

[0132] After the quadtree division pattern is determined, a CU-synchronous ALF on / off control may be performed to further reduce the filtering distortion. By comparing the filtering distortion with 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 requires an additional frame buffer access. In some related examples, there is no redesign process after the CU-synchronous ALF on / off decision to minimize the number of frame buffer accesses.

[0133] III. Cross-component adaptive loop filter In some related examples, a cross-component adaptive loop filter (CC-ALF) is employed, which utilizes luma sample values ​​to refine each chroma component.

[0134] FIG. 14A illustrates an exemplary arrangement of CC-ALF according to one embodiment of the present disclosure. FIG. 14B illustrates an exemplary linear diamond-shaped filter applied to the luma channel of each chroma component during CC-ALF operation. The filter coefficients are transmitted in the APS and may be, for example, 2 10 The input signal may be scaled by a factor of 16x16 and rounded for fixed-point representation. Application of the filters is controlled by variable block sizes and signaled by a context-coded flag received for each block of samples. 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) are supported: 16x16, 32x32, 64x64.

[0135] Table 3 shows the syntax elements related to CC-ALF.

[0136] [Table 3]

[0137] In Table 3, the syntax element 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 samples of the Cb color component at the luma position (xCtb, yCtb). The syntax element alf_ctb_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] not equal to 0 indicates that the alf_ctb_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]th cross-component Cb filter is applied to the block of samples of the Cb color component at the luma position (xCtb, yCtb).

[0138] The syntax element 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 samples of the Cr color component at luma position (xCtb, yCtb). The syntax element alf_ctb_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] not equal to 0 indicates that the alf_ctb_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]th cross-component Cr filter is applied to the block of samples of the Cr color component at luma position (xCtb, yCtb).

[0139] IV. Chroma Sampling Format 15 shows an example relative position 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 is shown relative to the area represented by the top-left luma sample.

[0140] V. Constrained Directional Extension Filter One objective of the in-loop constrained directional enhancement filter (CDEF) is to remove coding artifacts while preserving image details. In some related examples, such as HEVC, the sample adaptive offset (SAO) algorithm can achieve a similar objective by defining signaling 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, such as being implementable in single instruction multiple data (SIMD) operations, which is not the case for other nonlinear filters such as median filters and bilateral filters.

[0141] The design of CDEF is based on 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 minimum level of detail retained in the quantized image also tends to be proportional to the quantization step size. For a given quantization step size, the amplitude of the ringing will generally be smaller than the amplitude of the detail.

[0142] CDEF identifies the orientation of each block and adaptively filters along the identified orientation and along orientations rotated 45 degrees from the identified orientation at a smaller angle. 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 a combined filter has been adopted in the new AOMedia Video 1 (AV1) codec.

[0143] FIG. 16 illustrates an exemplary direction search for an 8×8 block according to one embodiment of the present disclosure. The direction search is performed on the reconstructed pixels immediately after the deblocking filter. The direction does not require signaling since these pixels are available to the decoder. 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 the quantized image. Enforcing a certain directionality in the 8×8 region makes it easier to vectorize the filter. For each block, the direction that best matches the pattern in the respective block is determined by minimizing the sum of squared differences (SSD) between the quantized block and the nearest fully directional block. A fully directional block is one in which all pixels along a line in a direction have the same value.

[0144] One reason to identify a direction is to align filter taps along that direction to reduce ringing while preserving directional edges or patterns. However, directional filtering alone may not be enough to reduce ringing. It is also 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 primary and secondary taps. A complete 2-dimensional CDEF filter is expressed as follows:

number

number

number

[0145] Loop recovery in VI.AV1 Besides the conventional deblocking operation, a set of in-loop restoration schemes can be used in the post-deblocking video coding, generally to 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 into a switchable framework that allows different tools to be activated in different regions of the frame.

[0146] In the case of the Wiener filter, every pixel in the degraded frame can be reconstructed as a non-causal filtered version of each pixel in a w × w window around each pixel, where w = 2r + 1 is odd for the integer r. The 2-D filter taps are expressed as w in column vector form. 2 For a vector F of 1 × 1 elements, straightforward linear minimum mean square error (LMMSE) optimization gives F = H -1 The filter parameters are derived given by M, where H=E[XX T] is the autocovariance of x and w in a w × w window around the pixel. 2 is a column-wise vectorized version of the samples of T ] is the cross-correlation between 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. But then w 2 Not only does transmitting the taps incur a significant bit rate cost, but non-separable filtering makes decoding very complicated. 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 unity.

[0147] For the guided filtering process, the local linear model can be expressed as: y=F x+G Equation (17)

[0148] A local linear model is used to calculate the filtered output y from the unfiltered sample x, and 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 depends on two parameters, the radius r and the noise parameter e, and is enumerated as follows:

[0149] (1) The mean μ and variance σ of pixels in a (2r+1) × (2r+1) window around each pixel 2 This can be efficiently implemented with box filtering based on integral imaging.

[0150] (2) Calculate for all pixels, i.e., f=σ 2 / (σ 2 +e);g=(1-f)μ.

[0151] (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.

[0152] Filtering is controlled by r and e, with larger r resulting in larger spatial variance and larger e resulting in larger range variance.

[0153] 17 shows an example subspace projection according to one embodiment. Even if neither of the inexpensive reconstructions X1 and X2 are close to the source Y, a suitable multiplier {α,β} can bring them quite close to the source as long as they are somewhat moved in the right direction. The inexpensive reconstruction can represent a reconstruction using relatively low-complexity computations.

[0154] VII. Cross-Component Sample Offset Filter A cross-component sample offset (CCSO) filter is a loop filtering technique for reducing distortion of reconstructed samples. In some embodiments, the reconstructed samples may be samples output from an aggregator (455). The reconstructed samples may be input to a loop filter (456). In a CCSO filter, given the processed input reconstructed samples of a first color component, a nonlinear mapping may be used to derive an output offset, which may be added to the reconstructed samples of a second color component in the filtering process of the CCSO filter. The input reconstructed samples of the first color component are placed in the filter support region.

[0155] FIG. 18 illustrates an exemplary filter support region according to one embodiment of the present disclosure. The filter support region includes four reconstructed samples, namely p0, p1, p2, and p3. The four input reconstructed samples follow a cross shape in the vertical and horizontal directions. The center sample (denoted as c) of the first color component and the filtered sample of the second color component are co-located. When processing the input reconstructed samples, the following steps are applied:

[0156] Step 1: The delta values ​​between p0-p3 and c are first calculated and denoted as m0, m1, m2, and m3.

[0157] Step 2: The delta values ​​m0-m3 are further quantized. The quantized values ​​are denoted as d0, d1, d2, and d3. The quantized values ​​can be -1, 0, and 1 based on the following quantization process: (a) d=-1 if m<-N, (b) d=0 if -N<=m<=N, and (c) d=1 if m>N, where N is called the quantization step size, and example values ​​of N include 4, 8, 12, and 16.

[0158] The quantized values ​​d0-d3 can be used to identify one combination of nonlinear mappings. For example, the CCSO filter of FIG. 8 has four filter taps d0-d3, each of which can have one of three quantized values ​​(e.g., −1, 0, and 1), for a total of three quantized values. 4 =81 possible combinations.

[0159] 19A-19B show a table illustrating 81 exemplary combinations of nonlinear mappings in a CCSO filter in tabular form according to one embodiment. The last column of the table represents the output offset value for each combination. The exemplary offset values ​​are integers such as 0, 1, -1, 3, -3, 5, -5, and -7.

[0160] The final filtering process of the CCSO filter may be applied as follows: f'=clip(f+s) Equation (18) where f is the reconstructed sample to be filtered and s is the output offset value looked up from the table of Figures 19A-19B. The filtered sample value f' is further clipped to the range associated with the bit depth.

[0161] VIII. Improved Cross-Component Sample Offset Filter The present disclosure includes methods for improving the performance of CCSO filters, such as improved cross-component sample offset methods.

[0162] According to an aspect of the present disclosure, the nonlinear mapping of the CCSO filter may include certain properties that allow the signaling overhead indicating the mapping relationship to be compressed. Reducing the size of the mapping relationship may reduce the signaling overhead. In this manner, improved coding efficiency may be achieved.

[0163] In this disclosure, a CCSO filter may be defined as a filtering process that uses a reconstructed sample of a first color component (e.g., Y, Cb, or Cr) as an input and applies an output to a second color component that is different from the first color component.

[0164] In the CCSO filter, a nonlinear mapping can be derived on the encoder side. The nonlinear mapping describes the relationship between the input reconstructed samples of one color component and the offset that is added to the other color component. The region of the nonlinear mapping can be determined by different combinations of processed input reconstructed samples, such as input reconstructed samples that have undergone linear processing.

[0165] According to aspects of the present disclosure, the nonlinear mapping of the CCSO filter may be compressed to reduce signaling overhead without significantly affecting the performance of the CCSO filter in terms of distortion reduction, and as a result, the overall coding efficiency may be improved.

[0166] In some embodiments, the nonlinear mapping can be used to derive the output offset given the processed input reconstructed samples when the CCSO filter is applied. The overhead bits for signaling the nonlinear mapping can be reduced. For example, instead of explicitly signaling each entry of the nonlinear mapping, only a subset of the nonlinear mapping can be signaled.

[0167] According to an aspect of the present disclosure, the output offset value of input combination A may be excluded from being signaled. Instead, the output offset value of input combination A may be derived from another input combination B. This derivation process may be referred to as mirroring derivation. One input combination refers to a combination of processed input reconstructed samples as described above (e.g., d0 to d3).

[0168] In one embodiment, the output offset value of input combination A can be derived as the inverse (e.g., a number having the same absolute value and different sign) of the output offset value of input combination B, where A and B have opposite sign values ​​for input combinations d0-d3. For example, if the output offset value of input combination B (d0=a, d1=b, d2=c, d3=d) is s, then the output offset value of input combination A (d0=-a, d1=-b, d2=-c, d3=-d) is -s.

[0169] In one embodiment, the output offset value of input combination A can be derived as the same number as the output offset value of input combination B, where A and B1 have opposite sign values ​​for the processed input reconstructed samples d0-d3. For example, if the output offset value of input combination B (d0=a, d1=b, d2=c, d3=d) is s, then the output offset value of input combination A (d0=-a, d1=-b, d2=-c, d3=-d) is s.

[0170] In one embodiment, the output offset value of input combination B may be signaled. The signaling may be provided in a high level syntax element such as APS, slice header, frame header, PPS, SPS, video parameter set (VPS), etc.

[0171] According to aspects of the present disclosure, a lookup table may be used to describe a compressed nonlinear mapping. Each row of the lookup table corresponds to an input combination d0-d3 and an associated output offset value. In some embodiments, a portion of the table shown in FIG. 19A-FIG. 19B may be used to describe the compressed nonlinear mapping. In one embodiment, the output offset values ​​of the first 41 rows of the table shown in FIG. 19A may be signaled, and the output offset values ​​of the remaining 40 rows may be derived based on the signaled output offset values ​​of the first 41 rows. FIG. 19C illustrates an example in which the output offset value of the Nth row of the remaining 40 rows may be derived as the same number as the output offset value of the (80-N)th row signaled in the first 41 rows. For example, as shown in FIG. 19C, the output offset value of the 41st row is s39, which is the output offset value of the 39th row of FIG. 19A. Figure 19D shows another example where the output offset value for line N of the remaining 40 lines may be derived as the inverse of the output offset value for line (80-N) signaled in the first 41 lines. For example, as shown in Figure 19D, the output offset value for line 41 is -s39, which is the inverse of the output offset value for line 39 in Figure 19A.

[0172] In one embodiment, a parameter indicating the enablement of mirroring derivation may be signaled. The signaling may be provided in a high level syntax element such as APS, slice header, frame header, PPS, SPS, VPS, etc.

[0173] According to an aspect of the present disclosure, only a subset of the non-linear mappings are signaled. For input combinations that are not signaled, the output offset values ​​can be derived as default values. Examples of default values ​​are integers such as 0, 1, -1, 3, -3, 5, -5, -7, etc.

[0174] In some embodiments, different subsets may be used and the signaled subset may be switched between different subsets. The selection of the signaled subset of the non-linear mapping may be signaled at a block level or a high level syntax element, e.g., APS, slice header, frame header, PPS, SPS, VPS, etc. In one example, two subsets with 16 and 81 combinations of the non-linear mappings of the tables shown in Figures 19A-19B are supported and the selection is signaled as a flag. In another example, two subsets with 17 and 81 combinations of the non-linear mappings of the tables shown in Figures 19A-19B are supported and the selection is signaled as a flag. In another example, two subsets with 33 and 81 combinations of the non-linear mappings of the tables shown in Figures 19A-19B are supported and the selection is signaled as a flag. In another example, three subsets with 16, 32, and 81 combinations of the non-linear mappings of the tables shown in Figures 19A-19B are supported, and the selection is signaled by an index. In another example, three subsets with 17, 33, and 81 combinations of the non-linear mappings of the tables shown in Figures 19A-19B are supported, and the selection is signaled by an index. In another example, five subsets with 16, 17, 32, 33, and 81 combinations of the non-linear mappings of the tables shown in Figures 19A-19B are supported, and the selection is signaled by an index.

[0175] FIG. 19E shows an example in which only 17 combinations of the non-linear mappings of the tables shown in FIGS. 19A-19B are signaled, and the output offset values ​​of the remaining combinations can be derived as default values ​​(e.g., 0).

[0176] FIG. 19F shows an example in which only 16 combinations of the non-linear mappings of the tables shown in FIGS. 19A-19B are signaled, and the output offset values ​​of the remaining combinations can be derived as default values ​​(e.g., 0).

[0177] FIG. 19G shows an example in which only 33 combinations of the non-linear mappings of the tables shown in FIGS. 19A-19B are signaled, and the output offset values ​​of the remaining combinations can be derived as default values ​​(e.g., 0).

[0178] FIG. 19H shows an example in which only 32 combinations of the non-linear mappings of the tables shown in FIGS. 19A-19B are signaled, and the output offset values ​​of the remaining combinations can be derived as default values ​​(e.g., 0).

[0179] According to aspects of the present disclosure, the nonlinear mapping may be divided into multiple subsets, such as three subsets A, B, and C, and only subset B is signaled. The output offset values ​​of the input combinations in subset A may be derived from subset B. The output offset values ​​of the input combinations in subset C may be derived as default values. Examples of default values ​​are integers such as 0, 1, -1, 3, -3, 5, -5, -7, etc.

[0180] In one embodiment, the output offset value of input combination A1 in subset A can be derived as the inverse of the output offset value of input combination B1 in subset B, where A1 and B1 have opposite sign values ​​for input combinations d0-d3. The output offset value for input combinations in subset C can be derived as a default value (e.g., 0). For example, if the output offset value of input combination B1 (d0=a, d1=b, d2=c, d3=d) in subset B is s, then the output offset value of input combination A1 (d0=-a, d1=-b, d2=-c, d3=-d) in subset A is -s.

[0181] In one embodiment, the output offset value of input combination A1 in subset A can be derived as the same number as the output offset value of input combination B1 in subset B, where A1 and B1 have opposite sign values ​​for input combinations d0-d3. The output offset value for input combinations in subset C can be derived as a default value (e.g., 0). For example, if the output offset value of input combination B1 (d0=a, d1=b, d2=c, d3=d) in subset B is s, then the output offset value of input combination A1 (d0=-a, d1=-b, d2=-c, d3=-d) in subset A is s.

[0182] In one embodiment, a parameter indicating enablement of the mirroring derivation of a subset of the non-linear mapping may be signaled. The signaling may be provided in a high level syntax element such as APS, slice header, frame header, PPS, SPS, VPS, etc.

[0183] According to aspects of the present disclosure, only a limited set of selected output offset values ​​are supported in the non-linear mapping.

[0184] In one embodiment, the ranges of output offset values ​​supported are [-4,+3], [-8,+7], [-16,+15], [-2 K ,2K ], [K,L], which can cover predefined integers, 0 and odd integers, and 0 and even integers, where K and L are integers.

[0185] In one example, the set of supported output offset values ​​may include 0 and a set of odd integers with different sign values, such as 0, 1, -1, 3, -3, 5, -5, and -7. In another example, the set of supported output offset values ​​may include 0 and a set of even integers with different sign values, such as 0, 2, -2, 4, -4, 6, -6, and -8.

[0186] In one embodiment, the set of supported output offset values ​​can be signaled. The signaling can be provided in high level syntax elements such as APS, slice header, frame header, PPS, SPS, VPS, etc.

[0187] In one embodiment, an array of offset values ​​can be supported with a non-linear mapping and an index can be signaled. The signaling can be provided in a high level syntax element such as APS, slice header, frame header, PPS, SPS, VPS, etc. to indicate the output offset value within the array selected for the input combination.

[0188] In one embodiment, different input combinations may have different sets of supported output offset values.

[0189] In one embodiment, the set of supported offset values ​​may depend on the quantization parameter.

[0190] In one embodiment, the output offset value or an index of the output offset value may be signaled using fixed length coding.

[0191] According to aspects of the present disclosure, an output offset value for an input combination applied to a current coding block in a current slice of a current picture may be predicted from output offset values ​​applied to a different picture, a different slice, or a different coding block.

[0192] In one embodiment, instead of signaling the output offset value, a delta value between the output offset value and the predicted output offset value may be signaled.

[0193] In one embodiment, the output offset value of at least one input combination is not signaled and can be derived from the expected output offset value.

[0194] In one embodiment, whether an output offset value is predicted can be signaled through a flag, which can be provided in a high level syntax element such as APS, slice header, frame header, PPS, SPS, VPS, etc.

[0195] The prediction of the output offset value may depend on coding information including, but not limited to, frame type, temporal layer, and quantization parameter.

[0196] In some related examples, one or more filtering processes may be applied to the reconstructed samples of the coded blocks. For example, a deblocking module may be applied to the reconstructed samples of the coded blocks. A CDEF module may then be applied to the filtered reconstructed samples output from the deblocking module, and a loop reconstruction filter module may be applied to the filtered reconstructed samples output from the CDEF module.

[0197] According to aspects of the present disclosure, when a CCSO filter is applied to reconstructed samples of a coded block, the input and output positions of the CCSO filter are flexible. The input position of the CCSO filter is where the input reconstructed samples of the CCSO filter are selected. The output position of the CCSO filter is where the output offset value of the CCSO filter is applied (e.g., CCSO filtering is applied).

[0198] In some embodiments, the input and output can share the same location. That is, there are no other coding modules disposed between the input and output locations of the CCSO filter. In one example, both the input and output locations can be immediately before the deblocking module. In another example, both the input and output locations can be after the deblocking module and before the CDEF module. In another example, both the input and output locations can be after the CDEF module and before the Loop Recovery Filter (LR) module. In another example, both the input and output locations can be after the LR module.

[0199] In some embodiments, the input position and the output position may be different, and the input position is before the output position. That is, there is at least one coding module disposed between the input position and the output position of the CCSO filter. In one example, the input position may be immediately before the deblocking module, and the output position may be after the deblocking module and before the CDEF module. In another example, the input position may be after the deblocking module and before the CDEF module, and the output position may be after the CDEF module and before the LR module. In another example, the input position may be after the CDEF module and before the LR module, and the output position may be after the LR module.

[0200] In one embodiment, the CDEF and LR modules in the above embodiment can be replaced with a SAO module and an ALF module, respectively. The same method as in the above embodiment can be applied to this embodiment.

[0201] IX. Flowchart FIG. 20 shows a flow chart outlining an example process (2000) according to one embodiment of the disclosure. In various embodiments, the process (2000) is performed by processing circuitry such as processing circuitry in the terminal devices (210), (220), (230), and (240), processing circuitry performing the functions of the video encoder (303), processing circuitry performing the functions of the video decoder (310), processing circuitry performing the functions of the video decoder (410), processing circuitry performing the functions of the intra prediction module (452), processing circuitry performing the functions of the video encoder (503), processing circuitry performing the functions of the predictor (535), processing circuitry performing the functions of the intra encoder (622), and processing circuitry performing the functions of the intra decoder (772). In some embodiments, the process (2000) is implemented in software instructions, such that the processing circuitry performs the process (2000) when the processing circuitry executes the software instructions.

[0202] The process (2000) may generally begin at step (S2010), where the process (2000) decodes prediction information for a current block in a current picture that is part of a coded video sequence. The prediction information indicates a plurality of combinations of processed reconstructed samples and corresponding output values ​​of a filtering process. The filtering process may be used to reduce compression artifacts and distortions of the reconstructed samples. The filtering process may use the processed reconstructed samples of a first color component as an input (e.g., Y, Cb, or Cr) and apply an output to a second color component different from the first color component. In some embodiments, the filtering process may be performed in a loop filter unit (456). Examples of filtering processes include, but are not limited to, CCSO and CC-ALF. The process (2000) then proceeds to step (S2020).

[0203] In step (S2020), the process (2000) performs a filter operation on the processed reconstructed samples of the first color component of the current block. The processed reconstructed samples of the first color are not included in the multiple combinations of the processed reconstructed samples. Then, the process (2000) proceeds to step (S2030).

[0204] In step (S2030), the process (2000) determines an output value of the filtering process based on one of the default value, the predicted output value, and one of the output values ​​indicated in the prediction information. The process (2000) then proceeds to step (S2040).

[0205] In step S2040, the process 2000 reconstructs the current block based on the output values ​​applied to the reconstructed samples of a second color component of the current block, the second color component being different from the first color component, and the process 2000 ends.

[0206] In one embodiment, the process (2000) determines one of a first value and a second value as an output value of the filtering process, the first value being one of the output values ​​indicated in the prediction information, and the second value being the inverse of the first value.

[0207] In one embodiment, each of the processed reconstructed samples of the first color component is the inverse of a corresponding processed reconstructed sample in one of the multiple combinations of processed reconstructed samples indicated in the prediction information, and one of the output values ​​indicated in the prediction information corresponds to one of the multiple combinations of processed reconstructed samples indicated in the prediction information.

[0208] In one embodiment, the sum of the index of the processed reconstructed sample of the first color component in the filtering mapping table and the index of one of the output values ​​indicated in the prediction information in the filtering mapping table is equal to the maximum index of the mapping table.

[0209] In one embodiment, the process (2000) determines a default value as an output value of the filtering process based on prediction information indicating that a plurality of combinations of processed reconstructed samples indicated in the prediction information is a subset of the total number of combinations of processed reconstructed samples in the filtering process.

[0210] In one embodiment, the predicted output value is determined based on the output value of a filtering process applied to another coding block.

[0211] In one embodiment, the processed reconstructed sample of the first color component is determined based on the reconstructed sample of the first color component output from the first coding module, and the reconstructed sample of the second color component is output from the first coding module or a second coding module applied after the first coding module.

[0212] X. Computer Systems The techniques described above may be implemented as computer software using computer-readable instructions physically stored on one or more computer-readable media. For example, Figure 21 illustrates a computer system (2100) suitable for implementing certain embodiments of the disclosed subject matter.

[0213] Computer software may be coded using any suitable machine code or computer language that may undergo assembly, compilation, linking, or similar mechanisms to create code containing instructions that may be executed, such as by one or more computer central processing units (CPUs) and graphics processing units (GPUs), directly, or through interpretation and execution of microcode.

[0214] The instructions may be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, Internet of Things devices, and the like.

[0215] 21 with respect to the computer system (2100) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure, nor should the arrangement of components be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary embodiment of the computer system (2100).

[0216] The computer system (2100) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more human users, for example, via tactile input (keystrokes, swipes, data glove movements, etc.), audio input (voice, clapping, etc.), visual input (gestures, etc.), 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 (speech, 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.).

[0217] The input human interface devices may include one or more (only one of each shown) of a keyboard (2101), a mouse (2102), a trackpad (2103), a touch screen (2110), a data glove (not shown), a joystick (2105), a microphone (2106), a scanner (2107), and a camera (2108).

[0218] The computer system (2100) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, for example, through haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback may be included through a touch screen (2110), data gloves (not shown), or joystick (2105), although there may also be haptic feedback devices that do not function as input devices), audio output devices (such as speakers (2109), headphones (not shown)), visual output devices (such as screens (2110), including CRT screens, LCD screens, plasma screens, OLED screens, each of which may or may not have touch screen input capabilities, each of which may or may not have haptic feedback capabilities, some of which may be capable of two-dimensional visual output or three or more dimensional output through means such as stereographic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown). These visual output devices, such as a screen (2110), may be connected to the system bus (2148) via a graphics adapter (2150).

[0219] The computer system (2100) may also include human accessible storage devices and their associated media, such as optical media, including CD / DVD ROM / RW (2120) with media (2121) such as CDs / DVDs, thumb drives (2122), removable hard drives or solid state drives (2123), legacy magnetic media such as tapes and floppy disks (not shown), and dedicated ROM / ASIC / PLD based devices (not shown) such as security dongles.

[0220] 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.

[0221] The computer system (2100) may also include a network interface (2154) to one or more communication networks (2155). The one or more communication networks (2155) may be, for example, wireless, wired, optical. Additionally, the one or more communication networks (2155) may be local, wide area, urban, vehicular and industrial, real-time, delay tolerant, etc. Examples of the one or more communication networks (2155) include local area networks such as Ethernet, wireless LAN, etc., cellular networks including GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable TV, satellite TV, terrestrial TV, etc., vehicular or industrial networks including CANBus, etc. Certain networks typically require an external network interface adapter (such as a USB port on the computer system (2100)) attached to a particular general-purpose data port or peripheral bus (2149), while others are typically integrated into the core of the computer system (2100) by attachment to a system bus as described below (such as 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 (2100) can communicate with other entities. Such communications may be unidirectional and receive only (e.g., broadcast TV), unidirectional and 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 those networks and network interfaces, as described above.

[0222] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to the core (2140) of the computer system (2100).

[0223] The cores (2140) may include one or more central processing units (CPUs) (2141), graphics processing units (GPUs) (2142), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (2143), hardware accelerators for specific tasks (2144), graphics adapters (2150), and the like. These devices may be connected via a system bus (2148), along with read-only memory (ROM) (2145), random access memory (2146), and internal mass storage (2147), such as internal, non-user accessible hard drives, SSDs, and the like. In some computer systems, the system bus (2148) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, and the like. Peripheral devices may be attached directly to the core's system bus (2148) or via a peripheral bus (2149). In one example, a screen (2110) may be connected to the graphics adapter (2150). Peripheral bus architectures include PCI and USB, among others.

[0224] The CPU (2141), GPU (2142), FPGA (2143), and accelerator (2144) can execute certain instructions that, in combination, can constitute the aforementioned computer code. That computer code can be stored in ROM (2145) or RAM (2146). Transient data can also be stored in RAM (2146), while persistent data can be stored, for example, in internal mass storage (2147). Rapid storage and retrieval in any of the memory devices can be made possible by the use of cache memory, which can be closely associated with one or more of the CPU (2141), GPU (2142), mass storage (2147), ROM (2145), RAM (2146), etc.

[0225] The computer-readable medium may bear computer code for performing various computer-implemented operations. The medium and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the type well known and available to those skilled in the computer software arts.

[0226] As an example, but not by way of limitation, a computer system having the architecture (2100), and in particular the core (2140), can provide functionality as a result of a processor(s) (including 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 (2140) of a non-transitory nature, such as the core internal mass storage (2147) or ROM (2145). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (2140). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (2140), and in particular the processor therein (including CPU, GPU, FPGA, etc.) to perform a particular process or a particular portion of a particular process as described herein, including defining data structures stored in RAM (2146) and modifying such data structures according to the process defined by the software. Additionally, or alternatively, the computer system may provide functionality as a result of logic embodied in hardwired or otherwise circuitry (e.g., accelerator (2144)), operating in place of or in conjunction with software to perform particular processes or portions of particular processes described herein. References to software may encompass logic, and vice versa, where appropriate. Where appropriate, references to computer-readable media may encompass circuitry (such as an integrated circuit (IC)) that stores software for execution, circuitry that embodies logic for execution, or both. The present disclosure encompasses any appropriate combination of hardware and software.

[0227] While this disclosure has described several exemplary embodiments, there are modifications, substitutions, and various substitute equivalents that are within the scope of this disclosure. It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and are therefore within its spirit and scope. Appendix A: Acronyms ALF: Adaptive Loop Filter AMVP: Advanced Motion Vector Prediction APS: Adaptation Parameter Set ASIC: Application-Specific Integrated Circuit ATMVP: Alternative / Advanced Temporal Motion Vector Prediction AV1:AOMedia Video 1 AV2:AOMedia Video 2 BMS: Benchmark Set BV: Block Vector CANBus: Controller Area Network Bus CB: Coding Block CC-ALF: Cross-Component Adaptive Loop Filter CD: Compact Disc CDEF: Constrained Directional Enhancement Filter CPR: Current Picture Referencing CPU: Central Processing Unit CRT: Cathode Ray Tube CTB: Coding Tree Block CTU: Coding Tree Unit CU: Coding Unit DPB: Decoder Picture Buffer DPCM: Differential Pulse-Code Modulation DPS: Decoding Parameter Set DVD: Digital Video Disc FPGA: Field Programmable Gate Area JCCR: Joint CbCr Residual Coding JVET: Joint Video Exploration Team GOP: Group of Pictures GPU: Graphics Processing Unit GSM: Global System for Mobile communication HDR: High Dynamic Range HEVC: High Efficiency Video Coding HRD: Hypothetical Reference Decoder IBC: Intra Block Copy IC: Integrated Circuit ISP: Intra Sub-Partition JEM: Joint Exploration Model LAN: Local Area Network LCD: Liquid Crystal Display LR: Loop Restoration Filter LRU: Loop Restoration Unit LTE: Long-Term Evolution MPM: Most Probable Mode MV: Motion Vector OLED: Organic Light-Emitting Diode PB: Prediction Block PCI: Peripheral Component Interconnect PDPC: Position Dependent Prediction Combination PLD: Programmable Logic Device PPS: Picture Parameter Set PU: Prediction Unit RAM: Random Access Memory ROM: Read-Only Memory SAO: Sample Adaptive Offset SCC: Screen Content Coding SDR: Standard Dynamic Range SEI: Supplementary Enhancement Information SNR: Signal Noise Ratio SPS: Sequence Parameter Set SSD: Solid-state drive TU: Transform Unit USB: Universal Serial Bus VPS: Video Parameter Set VUI: Video Usability Information VVC: Versatile Video Coding WAIP: Wide-Angle Intra Prediction [Explanation of symbols]

[0228] 101 points 102, 103 Arrows 104 Square Block 105 Schematic diagram 111 Current Block 112, 113, 114, 115, 116 Ambient samples 200 Communication Systems 210, 220, 230, 240 Terminal Devices 250 Network 301 Video Source 302 Stream of uncompressed video pictures 303, 503, 603 Video Encoder 304 encoded video data 305 Streaming Server 306, 308 Client Subsystem 307, 309 Copying encoded video data 310, 410, 710 Video Decoder 311 Output Stream 312 Display 313 Capture Subsystem 320, 330, 430, 520 Electronic Devices 401 Channel 412 Render Device 415 Buffer Memory 420 Parser 421 Symbols 431 Receiver 451 Scaler / Descaler Unit 452 Intra-picture Prediction Unit 453 Motion Compensation Prediction Unit 455 Aggregator 456 Loop Filter Unit 457 Reference Picture Memory 458 Current Picture Buffer 501 Video Sources 530 Source Coder 532 Coding Engine 533 Decoder 534 Reference Picture Memory 535 Predictor 540 Transmitter 543 coded video sequence 545 Entropy Coder 550 Controller 560 Communication Channels 621 General-purpose controller 622 Intra Encoder 623 Residual Calculator 624 Residual Encoder 625 Entropy Encoder 626 Switch 628 Residual Decoder 630 InterEncoder 771 Entropy Decoder 772 Intra Decoder 773 Residual Decoder 774 Reconstruction Module 780 Inter Decoder 2100 Computer Systems 2101 Keyboard 2102 Mouse 2103 Trackpad 2105 Joystick 2106 Microphone 2107 Scanner 2108 Camera 2109 Speaker 2110 Touch Screen 2120 Optical media 2121 Medium 2122 Thumb Drive 2123 Removable Hard Drive or Solid State Drive 2140 Core 2141 Processing Unit (CPU) 2142 Graphics Processing Unit (GPU) 2143 Field Programmable Gate Area (FPGA) 2144 Accelerator 2145 Read-Only Memory (ROM) 2146 Random Access Memory (RAM) 2147 Mass Storage 2148 System Bus 2149 Surrounding bus 2150 Graphics Adapter 2154 Network Interface 2155 Communication Network

Claims

1. 1. A method of video decoding performed by a decoder, comprising: - decoding prediction information for a current block in a current picture of a coded video sequence, the prediction information indicating a subset of combinations of processed reconstructed samples of a first color component of the coding block and corresponding offset values ​​of a filtering operation to be applied to a second color component of the coding block; determining a filtering offset value to apply to reconstructed samples of the second color component of the current block based on a combination of processed reconstructed samples of the first color component of the current block; reconstructing the current block based on the determined offset value being applied to the reconstructed samples of the second color component of the current block, the second color component being different from the first color component; based on the combination of the processed reconstructed samples of the first color component of the current block corresponding to a first combination of the subset of the combinations of the processed reconstructed samples, the determined offset value being the offset value corresponding to the first combination of the processed reconstructed samples indicated by the prediction information; based on the combination of the processed reconstructed samples of the first color component of the current block being different from each of the subset of the combinations of the processed reconstructed samples, the determined offset value is based on one of a default value, a predicted offset value, and the offset value of the filtering corresponding to a second combination of the subset of the combinations of the processed reconstructed samples; The method includes: the combination of processed reconstructed samples of the first color component of the current block is different from each of the subsets of the combinations of processed reconstructed samples; the determined offset value is based on a predetermined default value; The method of claim 1.

3. The combination of the processed reconstructed samples of the first color component of the current block is different from each of the subsets of the combinations of the processed reconstructed samples; the determined offset value is based on the predicted offset value of the filtering process applied to another coding block. The method of claim 1.

4. The combination of the processed reconstructed samples of the first color component of the current block is different from each of the subsets of the combinations of the processed reconstructed samples; the determined offset value is based on the offset value of the filtering process corresponding to the second combination of the processed reconstructed samples indicated in the prediction information. The method of claim 1.

5. The method of claim 1, wherein the determined offset value of the filtering process is equal to the offset value of the filtering process corresponding to the second combination of the processed reconstructed samples. The method of claim 4.

6. The method of claim 1, wherein the determined offset value of the filtering process and the offset value of the filtering process corresponding to the second combination of the processed reconstructed samples have different sign values. The method of claim 4.

7. The combination of the processed reconstructed samples of the first color component of the current block is different from each of the subsets of the combinations of the processed reconstructed samples; the determined offset value of the filtering process is based on (i) the offset value of the filtering process corresponding to the second combination of the processed reconstructed samples indicated in the prediction information, and (ii) a syntax element indicating whether the determined offset value of the filtering process and the offset value of the filtering process corresponding to the second combination of the processed reconstructed samples have the same sign. The method of claim 4.

8. The prediction information includes a syntax element indicating which of a plurality of subsets of the processed reconstructed samples is indicated by the prediction information. The method of claim 1.

9. An apparatus configured to perform a method according to any one of claims 1 to 8.

10. A computer program for causing a computer to carry out the method according to any one of claims 1 to 8.

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