Method of video processing performed by a decoder, device and computer program for video decoding, and method of video processing performed by an encoder - Patents.com

Abstract

Aspects of the present disclosure provide an apparatus and method that includes a processing circuit for decoding prediction information indicating that a cross-component linear model (CCLM) mode is to be applied to a chroma block in a current picture. For a first region in the chroma block, the processing circuit determines a first adjustment value used to modify an offset parameter in the CCLM mode based on a first subset of reconstructed samples in a luma block that is collocated with the chroma block, the first subset of reconstructed samples not including one or more samples in the luma block. The processing circuit updates the offset parameter based on the first adjustment value. The processing circuit determines a second adjustment value used to modify a gradient parameter in the CCLM mode based on a second subset of reconstructed samples in the luma block, and updates the gradient parameter based on the second adjustment value.

Description

[Technical field]

[0001] This disclosure describes embodiments generally relating to video coding. [Background technology]

[0002] The background description provided herein is intended to generally present the context of the present disclosure. The work of the presently named inventors is not expressly or impliedly admitted as prior art to the present disclosure to the extent that that work is described in this Background section, and any aspects of the description that may not otherwise qualify as prior art at the time of filing.

[0003] An uncompressed digital image and / or 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 (commonly known as frame rate) of, for example, 60 pictures per second, or 60 Hz. Uncompressed images and / or videos have specific bitrate requirements. For example, 1080p60 4:2:0 video (1920x1080 luminance sample resolution at a frame rate of 60 Hz) at 8 bits per sample requires a bandwidth approaching 1.5 Gbit / s. One hour of such video requires over 600 Gbytes of storage space.

[0004] One objective of image and / or video encoding and decoding can be the reduction of redundancy in the input image and / or video signal through compression. Compression can help reduce the above bandwidth and / or storage space requirements, in some cases by more than one order of magnitude. The description herein uses video encoding / decoding as an example, but the same techniques can be applied in a similar manner to image encoding / decoding without departing from the spirit of this disclosure. Both lossless and lossy compression, as well as combinations thereof, can 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 the same as the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely used. The amount of distortion that is tolerated 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 tolerable / acceptable distortion may result in a higher compression ratio.

[0005] Video encoders and decoders can utilize techniques from a number of broad categories, including, for example, motion compensation, transform processing, quantization, and entropy coding.

[0006] Video codec techniques can include a technique known as intra-coding. In intra-coding, sample values ​​are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, a picture is spatially subdivided into blocks of samples. If all blocks of samples are coded in intra mode, the picture can be an intra picture. Intra pictures and their derivatives, such as independent decoder refresh pictures, can be used to reset the decoder state and therefore can be used as the first picture of a coded video bitstream and video session or as a still image. Samples of an intra block can undergo a transform, and the transform coefficients can be quantized before entropy coding. Intra prediction can 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 needed for a given quantization step size to represent the block after entropy coding.

[0007] Conventional intra-coding, e.g., as used in MPEG-2 generation coding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to make predictions based on, e.g., surrounding sample data and / or metadata obtained during the encoding / decoding of a block of data. Such techniques are hereinafter referred to as "intra-prediction" techniques. It should be noted that, at least in some cases, intra-prediction uses reference data only from the current picture being reconstructed, and not from a reference picture.

[0008] There may be many different forms of intra prediction. If more than one such technique is available for a given video coding technique, the particular technique in use may be coded as a particular intra prediction mode that uses that particular technique. In some cases, an intra prediction mode may have sub-modes and / or parameters that may be coded independently or may be included in a mode codeword, which defines the prediction mode being used. Since which codeword to use for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency gains through intra prediction, entropy coding techniques may be used to convert the codewords into a bitstream.

[0009] A specific mode of intra prediction was introduced by H.264, refined in H.265, and further refined in newer coding techniques such as Joint Exploration Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). A predictor block may be formed using neighboring sample values ​​of already available samples. The sample values ​​of the neighboring samples are copied into the predictor block depending on the direction. The reference of the direction in use may be coded in the bitstream or may be predicted itself.

[0010] Referring to FIG. 1A, at the bottom right, a subset of 9 known predictor directions is represented from the 33 possible predictor directions defined in H.265 (corresponding to the 33 angle modes of the 35 intra modes). The point where the arrows converge (101) corresponds to the sample being predicted. The arrows correspond to the direction in which the sample is predicted. For example, the arrow (102) indicates that the sample (101) is predicted from one or more samples to the upper right and at an angle of 45 degrees from the horizontal. Similarly, the arrow (103) indicates that the sample (101) is predicted from one or more samples to the lower left of the sample (101) and at an angle of 22.5 degrees from the horizontal.

[0011] Still referring to FIG. 1A, at the top left is depicted a square block (104) of 4×4 samples (indicated by a thick dashed line). The square block (104) contains 16 samples, each labeled with "S", its position in the Y dimension (e.g., row index), and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample (from the top) in the Y dimension and the first sample (from the left) in the X dimension. Similarly, sample S44 is the fourth sample in the block (104) in both the Y and X dimensions. Since the block is 4×4 samples in size, S44 is at the bottom right. Also shown are reference samples that follow a similar numbering scheme. The reference samples are labeled with "R", their Y position (e.g., row index) and X position (column index) relative to the block (104). In both H.264 and H.265, the predicted samples are adjacent to the block being reconstructed, and therefore negative values ​​do not need to be used.

[0012] Intra-picture prediction can work by copying reference sample values ​​from neighboring samples indicated by the signaled prediction direction. For example, suppose the coded video bitstream includes signaling for this block indicating a prediction direction consistent with arrow (102), i.e., the sample is predicted from one or more prediction samples in the upper right corner at an angle of 45 degrees from the horizontal. 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.

[0013] In some cases, values ​​of multiple reference samples may be combined, for example through interpolation, to calculate a reference sample, particularly when the orientation is not equally divisible by 45 degrees.

[0014] The number of possible directions has increased as video coding techniques have developed. In H.264 (2003), nine different directions could be represented. That increased to 33 in H.265 (2013). Currently, JEM / VVC / BMS can support up to 65 directions. Experiments have been carried out to identify the most likely directions, and certain techniques in entropy coding are used to represent those likely directions with a small number of bits, while accepting a slight penalty for less likely directions. Furthermore, the direction itself can sometimes be predicted from neighboring directions used in neighboring, already decoded blocks.

[0015] FIG. 1B shows a schematic diagram (110) representing 65 intra prediction directions according to JEM to illustrate the growing number of prediction directions over time.

[0016] The mapping of intra-prediction direction bits representing directions in the coded video bitstream may vary from one video coding technique to another. Such mappings can vary, for example, from simple direction mappings, to codewords, to complex adaptation schemes including most-probable modes, and similar techniques. However, in most cases, there may be certain directions that are statistically less likely to occur in the video content than certain other directions. Since the goal of video compression is to reduce redundancy, these less likely directions will be represented by more bits than more likely directions in a video coding technique that works well.

[0017] Image and / or video encoding / decoding can be performed using inter-picture prediction with motion compensation. Motion compensation can be a lossy compression technique and can refer to a technique used for the prediction of 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 (hereafter MV). In some cases, the reference picture can be the same as the picture currently being reconstructed. The MV can have two dimensions X and Y, or three dimensions, the third dimension being an indication of the reference picture in use (the latter can indirectly be the temporal dimension).

[0018] In some video compression techniques, the MV applicable to a particular area of ​​sample data can be predicted from other MVs, e.g., from those that pertain to other areas of sample data that are spatially adjacent to the area being reconstructed and that precede it in decoding order. Doing so can significantly reduce the amount of data required to code the MV, thereby removing redundancy and increasing compression. For example, when coding an input video signal obtained from a camera (known as natural video), MV prediction can work because there is a statistical possibility that areas larger than the area to which a single MV is applicable move in a similar direction, and therefore, in some cases, can be predicted using similar motion vectors derived from MVs of neighboring areas. As a result, the MV determined for a given area is similar or the same as the MV predicted from the surrounding MVs, and after entropy coding, can be represented with fewer bits than would be used if coding the MV directly. In some cases, MV prediction can be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., a sample stream). In other cases, the MV prediction itself can be lossy, e.g., due to rounding errors when calculating a predictor from several surrounding MVs.

[0019] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Rec. H265, “High Efficiency Video Coding”, December 2016). Among the many MV prediction mechanisms proposed by H.265, a technique hereafter called “spatial merging” is described with reference to FIG.

[0020] Referring to Figure 2, a current block (201) has samples that are found by the encoder during the motion search process to be predictable from a previous block of the same size but spatially shifted. Instead of coding its MV directly, the MV can be derived from metadata associated with one or more reference pictures, for example, from the most recent reference picture (in decoding order), using the MV associated with any one of the five surrounding samples denoted as A0, A1 and B0, B1, B2 (202 to 206, respectively). In H.265, MV prediction can use predictors from the same reference picture that neighboring blocks use. Summary of the Invention

[0021] Aspects of the disclosure provide a method and apparatus for video encoding / decoding. In some examples, the apparatus for video decoding includes a receiving circuit and a processing circuit. The processing circuit decodes prediction information of a chroma block to be reconstructed in a current picture. The prediction information indicates that a Cross-Component Linear Model (CCLM) mode is applied to the chroma block. For a first region in the chroma block, a first adjustment parameter used to change an offset parameter in the CCLM mode may be determined based on a first subset of reconstructed samples in a co-located luma block in the current picture. The first subset of reconstructed samples does not include one or more samples in the co-located luma block. A first updated offset parameter for the first region in the chroma block may be determined based on the offset parameter and the first adjustment parameter. The first region in the chroma block may be reconstructed based at least on the first updated offset parameter using the CCLM mode.

[0022] In an example, the first region in the chroma block includes the entire chroma block, the first subset of reconstructed samples in the co-located luma block is one sample in the co-located luma block, and the first adjustment parameter may be determined to be a sample value of the one sample in the co-located luma block.

[0023] In an example, the first region includes an entire chroma block, the first subset of reconstructed samples includes a plurality of samples in the co-located luma block, and the first adjustment parameter may be determined to be an average of sample values ​​of the plurality of samples in the co-located luma block.

[0024] In an example, the first region includes an entire chroma block. The prediction information further indicates which samples in the co-located luma block are included in the first subset of reconstructed samples.

[0025] In an example, the chroma block further includes a second region. The first subset of reconstructed samples is a first sample in the co-located luma block. For the second region in the chroma block, a second adjustment parameter used to adjust the offset parameter in CCLM mode may be determined based on the second sample in the co-located luma block. In an example, the second sample is different from the first sample. A second updated offset parameter for the second region may be determined based at least on the offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed using CCLM mode based at least on the second updated offset parameter.

[0026] In an example, the co-located luma block includes a first luma region and a second luma region that are respectively co-located with a first region and a second region in the chroma block. The first subset of reconstructed samples includes a plurality of samples in the first luma region. For the second region in the chroma block, a second adjustment parameter used to adjust the offset parameter in CCLM mode may be determined based on the plurality of samples in the second luma region. A second updated offset parameter for the second region may be determined based at least on the offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed based at least on the second updated offset parameter using CCLM mode.

[0027] In an example, the first subset of reconstructed samples includes a top left sample, a top right sample, a bottom left sample, and a bottom right sample in the first luma region. A first adjustment parameter may be determined to be an average of the top left sample, the top right sample, the bottom left sample, and the bottom right sample in the first luma region. A second adjustment parameter used to adjust the offset parameter in CCLM mode for a second region in the chroma block may be determined to be an average of the top left sample, the top right sample, the bottom left sample, and the bottom right sample in the second luma region. A second updated offset parameter for the second region may be determined based at least on the offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed based at least on the second updated offset parameter using CCLM mode.

[0028] In an example, for the first region, an updated scaling parameter may be determined to be the sum of the scaling parameter used in the CCLM mode and the adjustment parameter used to adjust the scaling parameter. The first updated offset parameter may be (bu×y r ), where b is an offset parameter, u is an adjustment parameter used to adjust the scaling parameter, and y r where is a first adjustment parameter. A first region in a chroma block may be reconstructed based on the first updated offset parameter and the updated scaling parameter using a CCLM mode.

[0029] In an example, for the first region, the adjustment parameters used to adjust the scaling parameter are determined based on (i) reconstructed luma samples in one or more neighboring luma blocks of the co-located luma block and (ii) samples within the co-located luma block.

[0030] In an example, for the first region, the adjustment parameter used to adjust the scaling parameter is determined based on a difference between an average of the reconstructed luma samples in one or more adjacent luma blocks and an average of the samples in the co-located luma block.

[0031] In an embodiment, for a first region in the chroma block, the processing circuit determines a first adjustment value used to modify an offset parameter in the CCLM mode based on a first subset of reconstructed samples in a luma block that is currently co-located with the chroma block in the picture. The first subset of reconstructed samples does not include one or more samples in the luma block. The processing circuit updates the offset parameter based on the first adjustment value. The processing circuit determines a second adjustment value used to modify a gradient parameter in the CCLM mode based on a second subset of reconstructed samples in the luma block and updates the gradient parameter based on the second adjustment value. The processing circuit can reconstruct the first region in the chroma block using the CCLM mode based at least on the updated offset parameter and the updated gradient parameter.

[0032] In an example, the second subset of reconstructed samples includes the first subset of reconstructed samples.

[0033] In an example, the processing circuit determines the second adjustment value based on reconstructed samples within the entire luma block.

[0034] Aspects of the present disclosure also provide a non-transitory computer-readable storage medium storing instructions that, when executed by a computer for video decoding, cause the computer to perform a method for video decoding.

[0035] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0036] [Figure 1A] FIG. 2 is a schematic diagram of an example subset of intra-prediction modes. [Figure 1B] FIG. 2 is an illustration of an exemplary intra-prediction direction. [Diagram 2] An example of a current block (201) and surrounding samples is shown. [Diagram 3] FIG. 3 is a schematic diagram of an example block diagram of a communication system (300). [Figure 4] FIG. 4 is a schematic diagram of an example block diagram of a communication system (400). [Diagram 5] FIG. 2 is a schematic diagram of an exemplary block diagram of a decoder. [Figure 6] FIG. 2 is a schematic diagram of an example block diagram of an encoder. [Figure 7] 1 shows a block diagram of an exemplary encoder. [Figure 8] 1 shows a block diagram of an exemplary decoder. [Figure 9] 4 shows an exemplary reference sample of the current block. [Figure 10] 13 shows examples of reconstructed adjacent luma samples and reconstructed adjacent chroma samples used in a cross-component linear model (CCLM) mode. [Figure 11] 13 shows an example of reconstructed adjacent luma samples and reconstructed adjacent chroma samples used in CCLM mode. [Figure 12] A and B show examples of parameter adjustments used in CCLM mode. [Figure 13] 13 illustrates an example of the same location of selected luma samples within a collocated luma block that is used to determine an adjustment parameter. [Figure 14] 1 illustrates an example chroma block and a co-located luma block. [Figure 15] 1 illustrates an example chroma block and a co-located luma block. [Figure 16] 1 shows a flowchart illustrating an encoding process according to some embodiments of the present disclosure. [Figure 17] 1 shows a flowchart illustrating a decoding process according to some embodiments of the present disclosure. [Figure 18] FIG. 1 is a schematic diagram of a computer system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] FIG. 3 illustrates an example block diagram of a communication system (300). The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) that are interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) perform a one-way transmission of data. For example, the terminal device (310) may code video data (e.g., a stream of video pictures captured by the terminal device (310)) for transmission to another terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to recover the video pictures, and display the video pictures according to the recovered video data. One-way data transmission may be common, such as in media serving applications.

[0038] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of coded video data, e.g., during a video conference. For the bidirectional transmission of data, in the example, each of the terminal devices (330) and (340) may code video data (e.g., a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may also receive coded video data transmitted by the other of the terminal devices (330) and (340), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device in accordance with the recovered video data.

[0039] In the example of FIG. 3, terminal devices (310), (320), (330), and (340) are depicted as a server, a personal computer, and a smartphone, respectively, although the principles of the present disclosure need not be so limited. Embodiments of the present disclosure find use with laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. Network (350) represents any number of networks that convey coded video data between terminal devices (310), (320), (330), and (340), including, for example, wireline and / or wireless communication networks. Communication network (350) may exchange data in circuit-switched and / or packet-switched channels. Exemplary networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this discussion, the architecture and topology of network (350) may be irrelevant to the operation of the present disclosure, unless otherwise described below.

[0040] 4 depicts a video encoder and video decoder in a streaming environment as an example application of the disclosed subject matter. The disclosed subject matter can be similarly applicable to other video-enabled applications including, for example, video conferencing, digital TV, streaming services, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0041] The streaming system may include a capture subsystem (413) that may include, for example, a video source (401), e.g., a digital camera, that generates a stream of uncompressed video pictures (402). In an example, the stream of video pictures (402) includes samples captured by the digital camera. The stream of video pictures (402) is represented by a bold line to emphasize its high data volume compared to the encoded video data (404) (or coded video bitstream), which may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or coded video bitstream (404)), is represented by a thin line to emphasize its lower data volume compared to the stream of video pictures (402), which may be stored in a streaming server (405) for future use. One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, can access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) can include a video decoder (410), for example in an electronic device (430). The video decoder (410) decodes an incoming copy (407) of the encoded video data and generates an outgoing stream (411) of video pictures that can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (404), (407), and (409) (e.g., a video bitstream) can be encoded according to a particular video coding / compression standard. An example of such a standard is ITU-T Recommendation H.265.In an example, the developing video coding standard is commonly known as Versatile Video Coding (VVC), and the disclosed subject matter may be used in conjunction with VVC.

[0042] It is noted that electronic devices 420 and 430 can include other components (not shown). For example, electronic device 420 can include a video decoder (not shown), and electronic device 430 can also include a video encoder (not shown).

[0043] 5 shows an example block diagram of a video decoder (510). The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) in the example of FIG. 4.

[0044] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In an embodiment, one coded video sequence is received at a time, and the decoding of each coded video sequence is independent of the decoding of the other coded video sequences. The coded video sequences may be received from a channel (501), which may be a hardware / software link to a storage device that stores the coded video data. The receiver (531) may receive the coded video data together with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to their respective use entities (not shown). The receiver (531) may separate the coded video sequences from the other data. To combat network jitter, a buffer memory (515) may be coupled between the receiver (531) and the entropy decoder / parser (520) (hereinafter "parser (520)"). In certain applications, the buffer memory (515) is part of the video decoder (510). In others, it can be external to the video decoder (510) (not shown). In still others, there can be a buffer memory (not shown) external to the video decoder (510), e.g., to combat network jitter, plus another buffer memory (515) within the video decoder (510), e.g., to manipulate playback timing. When the receiver (531) is receiving data from a storage / forwarding device of sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may not be needed or may be small. For use with best-effort packet networks such as the Internet, the buffer memory (515) may be needed, and can be relatively large and advantageously adaptively sized, and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (510).

[0045] The video decoder (510) may include a parser (520) for reconstructing symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and information for controlling a rendering device, such as a render device (512) (e.g., a display screen), which is not an essential part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device may take the form of a Supplementary Enhancement Information (SEI) message or a Video Usability Information (VUI) parameter set fragment (not shown). The parser (520) may parse / entropy decode the received coded video sequence. The coding of the coded video sequence may follow a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, context-dependent or non-context-dependent arithmetic coding, etc. The parser (520) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the group. The subgroups may include a group of pictures (GOP), a picture, a tile, a slice, a macroblock, a coding unit (CU), a block, a transform unit (TU), a prediction unit (PU), etc. The parser (520) may also extract quantization parameter values, motion vectors, etc. from the coded video sequence information, such as transform coefficients.

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

[0047] The reconstruction of symbols (521) can have a wide variety of units depending on the type of coded video picture or portion thereof (e.g., inter and intra pictures, inter and intra blocks) and other factors. Which units are included and how may be controlled by subgroup control information parsed by the parser (520) from the coded video sequence. The flow of such subgroup control information between the parser (520) and the following units is not shown for clarity.

[0048] Beyond the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into a number of functional units, which are 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 adequate.

[0049] The first unit is a scalar / inverse transform unit (551), which receives the quantized transform coefficients as symbols (521) from the parser (520), along with control information including what to transform to use, block size, quantization factor, quantization scaling matrix, etc. The scalar / inverse transform unit (551) can output blocks containing sample values ​​that can be input to an aggregator (555).

[0050] In some cases, the output samples of the scaler / inverse transformer (551) may relate to intra-coded blocks, which are blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) 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 (558). The current picture buffer (558) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. The aggregator (555) adds, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transformer unit (551).

[0051] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded and potentially motion-compensated block. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for prediction. After motion compensating the fetched samples according to the symbols (521) related to the block, the samples may be added by the aggregator (555) to the output of the scalar / inverse transform unit (551) (in this case referred to as residual samples or residual signals) to generate output sample information. The addresses in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches prediction samples may be controlled by motion vectors available to the motion compensated prediction unit (553), for example in the form of symbols (521), which may have X, Y, and reference picture components. Motion compensation can also include interpolation of sample values ​​fetched from the reference picture memory (557) when sub-sample accurate motion vectors are used, as well as motion vector prediction mechanisms.

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

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

[0054] Once a particular coded picture is fully reconstructed, it may be used as a reference picture for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (520)), the current picture buffer (558) may become part of the reference picture memory (557), and any unused current picture buffer may be reallocated before beginning reconstruction of a subsequent coded picture.

[0055] The video decoder (510) may perform decoding operations according to a given video compression technique in a standard such as ITU-T Recommendation H.265. The coded video sequence may conform to the syntax prescribed by the video compression technique or standard in use, in the sense that the coded video sequence conforms to both the syntax of the video compression technique or standard and a profile documented in the video compression technique or standard. In particular, a profile may select a particular tool from all tools available in the video compression technique or standard as the only tool available for use under that profile. Also, for compliance, the complexity of the coded video sequence is required to be within the bounds 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 / second), maximum reference picture size, etc. The limits set by the level may in some cases be further limited through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management signaled in the coded video sequence.

[0056] In an embodiment, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may also be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may take the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0057] 6 shows an example block diagram of a video encoder (603). The video encoder (603) is included in an electronic device (620). The electronic device (620) includes a transmitter (640) (e.g., a transmitting circuit). The video encoder (603) may be used in place of the video encoder (403) of the example of FIG.

[0058] The video encoder (603) may receive video samples from a video source (601) (which is not part of the electronic device (620) in the example of FIG. 6) that may capture video images to be coded by the video encoder (603). In other examples, the video source (601) is part of the electronic device (620).

[0059] The video source (601) may provide a source video sequence to be coded by the video encoder (603) in the form of a digital video sample stream that can be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, etc.), any color space (e.g., BT.601 YCrCB, RGB, etc.), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media serving system, the video source (601) may be a storage device that stores previously prepared video. In a video conferencing system, the video source (601) may be a camera that captures local image information as a video sequence. The video data may be provided as multiple individual pictures that, when viewed in sequence, impart motion. The picture itself may be organized as a spatial array of pixels, each of which may have one or more samples depending on the sampling structure, color space, etc., in use. Those skilled in the art can easily understand the relationship between pixels and samples. The remainder of this specification focuses on samples.

[0060] According to an embodiment, the video encoder (603) may code and compress pictures of a source video sequence into a coded video sequence (643) in real-time or under any other time constraints as required. Imposing an appropriate coding rate is one function of the controller (650). In some embodiments, the controller (650) controls and is operatively coupled to other functional units as described below. Coupling is not shown for clarity. Parameters set by the controller (650) may include parameters related to rate control (picture skip, quantizer, lambda value for rate-distortion optimization techniques, etc.), picture size, group-of-picture (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured with other appropriate functions related to the video encoder (603) optimized for a particular system design.

[0061] In some embodiments, the video encoder (603) is configured to operate in a coding loop. As an oversimplified description, in an example, the coding loop can include a source coder (630) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to generate sample data in a similar manner that a (remote) decoder would also generate. The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since the decoding of the symbol stream produces bit-exact results independent of the location of the decoder (local or remote), the content in the reference picture memory (634) is also bit-perfect between the local and remote encoders. That is, the predictive part of the encoder "sees" exactly the same sample values ​​as the decoder would "see" when using prediction during decoding. This basic principle of reference picture synchronicity (and the resulting drift when synchronicity cannot be maintained, for example due to channel errors) is also used in several related techniques.

[0062] The operation of the "local" decoder (633) can be the same as a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. Referring also momentarily to Figure 5, however, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and the parser (520), may not be fully implemented in the local decoder (633), given that symbols are available and the encoding / decoding of the symbols into a coded video sequence by the entropy coder (645) and parser (520) can be lossless.

[0063] In embodiments, the decoder techniques, except for parsing / entropy decoding, present in the decoder are present in the same or substantially the same functional form in the corresponding encoder. Thus, the disclosed subject matter focuses on the operation of the decoder. Descriptions of the encoder techniques may be omitted, in that they are the inverse of the decoder techniques described generically. To the extent that certain details are provided below.

[0064] In operation, in some examples, the source coder (630) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from the video sequence designated as "reference pictures." In this manner, the coding engine (632) codes differences between pixel blocks of the input picture and pixel blocks of the reference pictures that may be selected as predictive references for the input picture.

[0065] The local video decoder (633) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols generated by the source coder (630). The operation of the coding engine (632) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may usually be a copy of the source video sequence with some errors. The local video decoder (633) may reproduce the decoding process that may be performed by the video decoder on the reference pictures, causing the reconstructed reference pictures to be stored in the reference picture cache (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content with the reconstructed reference pictures that would be obtained by the far-end video decoder (without transmission errors).

[0066] The predictor (635) may perform a prediction search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may look for certain metadata, such as reference picture motion vectors, block shapes, or sample data (as candidate reference pixel blocks) from the reference picture memory (634) that may be suitable prediction references for the new picture. The predictor (635) 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 (635), the input picture may have prediction references derived from multiple reference pictures stored in the reference picture memory (634).

[0067] The controller (650) may manage the coding operations of the source coder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0068] The output of all the above functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by applying lossless compression to the symbols according to techniques such as Huffman coding, variable length coding, or arithmetic coding.

[0069] The transmitter (640) may buffer the coded video sequence produced by the entropy coder (645) to prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0070] A controller (650) may manage the operation of the video encoder (603). During coding, the controller (650) may assign a particular coded picture type to each coded picture, which may affect the coding technique that may be applied to each picture. For example, pictures may often be assigned as one of the following picture types:

[0071] An Intra Picture (I-picture) may be a picture that can be coded and decoded without using any other picture in a sequence as a source of prediction. Some video codecs allow various types of Intra pictures, including, for example, Independent Decoder Refresh (IDR) pictures. Those skilled in the art are aware of such variations of I-pictures and their respective applications and characteristics.

[0072] A Predictive Picture (P-picture) may be a picture that can be coded and decoded by intra- or inter-prediction using at most one motion vector and reference index to predict sample values ​​for each block.

[0073] A Bi-directionally Predictive Picture (B-picture) may be a picture that can be coded and decoded by intra- or inter-prediction using at most two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multiple-predictive picture(s) can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0074] A source picture may generally be spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples, respectively) and coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks as determined by the coding assignment applied to each picture of the block. For example, blocks of I pictures may be non-predictively coded or they may be predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of P pictures may be predictively coded by spatial prediction with reference to one previously coded reference picture or by temporal prediction. Blocks of B pictures may be predictively coded by spatial prediction with reference to one or two previously coded reference pictures or by temporal prediction.

[0075] The video encoder (603) may perform coding operations according to a given video coding technique or standard, such as ITU-T Recommendation H.265. During its operation, the video encoder (603) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax defined by the video coding technique or standard being used.

[0076] In an embodiment, the transmitter (640) may transmit additional data along with the encoded video. The source coder (630) may include such data as part of the coded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other types of redundant data such as redundant pictures and slices, SEI messages or VUI parameter set fragments, etc.

[0077] A 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 an example, a particular picture being coded / decoded, called a current picture, is partitioned into blocks. If a block in the current picture is similar to a reference block in a previously coded reference picture in the video that is still buffered, then that block in the current picture may be coded by a vector called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0078] In some embodiments, bi-prediction techniques may be used in inter-picture prediction. According to bi-prediction techniques, two reference pictures are used, e.g., a first reference picture and a second reference picture, both preceding in decoding order (but may be past and future, respectively, in display order) the current picture in the video. A block in the current picture may be coded with a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. The block is predictable by a combination of the first and second reference blocks.

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

[0080] According to some embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed in units of blocks. For example, according to the HEVC standard, pictures in a sequence of video pictures are partitioned 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), 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 can be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In an example, each CU is analyzed to determine a prediction type for the CU, such as an inter-prediction type or an intra-prediction type. The CU is partitioned into one or more prediction units (PUs) according to temporal and / or spatial predictability. In general, each PU includes one luma prediction block (PB) and two chroma PBs. In an 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, 16×8 pixels, etc.

[0081] 7 shows an example diagram of a video encoder (703). The video encoder (703) is configured to receive a processed block of sample values ​​(e.g., a predictive block) in a current video picture included 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 an example, the video encoder (703) is used in place of the video encoder (403) of the example of FIG. 4.

[0082] In an HEVC example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a prediction block of 8x8 samples. The video encoder (703) determines whether the processing block is best coded in intra mode, inter mode, or bi-prediction mode, for example using rate-distortion optimization. If the processing block is to be coded in intra mode, the video encoder (703) 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-prediction mode, the video encoder (703) 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 can be an inter-picture prediction sub-mode in which motion vectors are derived from one or more motion vector predictors without benefit of coded motion vector components outside the predictors. In certain other video coding techniques, there may be motion vector components applicable to the current block. In an example, the video encoder (703) includes other components, such as a mode decision module (not shown) that determines the mode of the processing block.

[0083] In the example of FIG. 7, the video encoder (703) includes an inter-encoder (730), an intra-encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy encoder (725), coupled as shown in FIG.

[0084] The inter-encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in a previous picture and a subsequent picture), generate inter-prediction information (e.g., a description of residual information according to an inter-coding technique, motion vectors, 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 has been decoded based on the coded video information.

[0085] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), in some cases compare the block to previously coded blocks in the same picture, and generate transformed quantized coefficients and, in some cases, intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). In an example, the intra encoder (722) also calculates an intra prediction result (e.g., a prediction block) based on the intra prediction information and a reference block in the same picture.

[0086] The generic controller (721) is configured to determine generic control data and control other components of the video encoder (703) based on the generic control data. In an example, the generic controller (721) determines the mode of the block and provides a control signal to the switch (726) based on the mode. For example, if the mode is an intra mode, the generic controller (721) controls the switch (726) to select the intra mode result for use by the residual calculator (723), and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream. If the mode is an inter mode, the generic controller (721) controls the switch (726) to select the inter prediction result for use by the residual calculator (723), and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0087] The residual calculator (723) is configured to calculate a difference (residual data) between the received block and a prediction result selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) is configured to operate on the residual data to encode the residual data to generate transform coefficients. In an example, the residual encoder (724) is configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are appropriately processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures in some examples.

[0088] The entropy encoder (725) is configured to format a bitstream to include the encoded block. The entropy encoder (725) is configured to include various information in accordance with an appropriate standard, such as the HEVC standard. In an example, the entropy encoder (725) 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 when coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode in accordance with the disclosed subject matter, the residual information is not present.

[0089] 8 shows an example diagram of a video decoder (810). The video decoder (810) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In an example, the video decoder (810) is used in place of the video decoder (410) of the example of FIG. 4.

[0090] In the example of FIG. 8, the video decoder (810) includes an entropy decoder (871), an inter decoder (880), a residual decoder (873), a reconstruction module (874), and an intra decoder (872), coupled as shown in FIG.

[0091] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols representing syntax elements from which the coded picture is constructed. Such symbols may include prediction information (e.g., intra prediction information or inter prediction information) that may, for example, identify the mode in which the block is coded (e.g., intra mode, or inter mode or bi-prediction mode in merged or other submodes), the specific samples or metadata used for prediction by the intra decoder (872) or the inter decoder (880), respectively. The symbols may also include residual information, for example in the form of quantized transform coefficients. In an example, if the prediction mode is an inter or bi-prediction mode, the inter prediction information is provided to the inter decoder (880), and if the prediction type is an intra prediction type, the intra prediction information is provided to the intra decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

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

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

[0094] The residual decoder (873) is configured to perform inverse quantization to retrieve inverse quantized transform coefficients, and process the inverse quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also require certain control information (to include quantization parameters (QPs)), which may be provided by the entropy decoder (871) (datapath not shown since this is only low volume control information).

[0095] The reconstruction module (874) is configured to combine the residual information output by the residual decoder (873) and the prediction result (possibly output by an inter- or intra-prediction module) in the spatial domain to form a reconstructed block. The reconstructed block may be part of a reconstructed picture, which in turn may be part of a reconstructed video. It is noted that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0096] It is understood that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using any suitable technology. In some embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more integrated circuits. In other embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more processors executing software instructions.

[0097] In intra prediction or intra prediction modes, sample values ​​of a coding block can be predicted from neighboring samples that are already reconstructed or have been reconstructed (called reference samples).

[0098] An example of intra prediction is directional intra prediction. In directional intra prediction, a sample in a current block (e.g., a current sample) can be predicted using a reference sample (e.g., a predicted sample) or a stored reference sample. For example, the connected link between the current sample and the predicted sample forms a given angular direction as used in the angular mode.

[0099] Another example of intra prediction uses a planar mode based on sample interpolation. In the planar mode, one or more key positions in or around the current block can be predicted using neighboring reference samples. Other positions in the current block can be predicted as linear combinations of samples at one or more key positions and reference samples. Weights (combination weights) can be determined according to the position of the current sample in the current block.

[0100] An example of a planar mode, such as that found in VVC, is calculated as follows:

number

[0101] Referring to FIG. 9, the current block (900) includes samples located at positions (0,0) to (H-1,W-1) in the current block (900). W and H are the width and height of the current block (900), respectively. The predicted sample value pred[x][y] of the current sample located at position (x,y) (x=0,1,··· or W-1, and y=0,1,··· or H-1) in the current block (900) can be calculated as a weighted average of the reference sample values ​​(e.g., p[-1][y], p[x][-1], p[-1][H], and p[w][-1] of the reference samples located at positions (-1,y), (x,-1), (-1,H), and (W,-1), respectively) as shown in Equations 1 to 3. The reference samples may include a reference sample located at position (-1,y) in the same row as the current sample, a reference sample at position (x,-1) in the same column as the current sample, a reference sample at a bottom left position (-1,H) with respect to the current block, and a reference sample at a top right position (W,-1) with respect to the current block.

[0102] As described above, the reference sample values ​​of the reference samples may include p[-1][y] of the reference sample located at position (-1,y), p[x][-1] of the reference sample located at position (x,-1), p[-1][H] of the reference sample located at the lower left position (-1,H), and [W][-1] of the reference sample located at the upper right position (W,-1). In the example shown in Equation 1, the vertical predictor predV[x][y] is determined based on the reference samples located at positions (x,-1) and (-1,H). In the example shown in Equation 2, the horizontal predictor predH[x][y] is determined based on the reference samples located at positions (-1,y) and (W,1). In Equation 3, the predicted sample value pred[x][y] is determined based on the average (e.g., weighted average) of the horizontal predictor predH[x][y] and the vertical predictor predV[x][y].

[0103] The cross-component linear model prediction (CCLM) mode is a cross-component prediction method. In CCLM, chroma samples can be predicted based on reconstructed luma samples using a linear model. The linear model can be formed by adjacent already reconstructed samples of a current block (e.g., a chroma block to be coded). In some embodiments, the prediction performance is high when the linear correlation of the luma channel and the chroma channel is high.

[0104] In an embodiment, a chroma block (e.g., a current Cb block or a current Cr block) is predicted based on a co-located luma block. A prediction block pred_C of the chroma block can be derived as follows:

number

[0105] pred_C(x,y) represents a predicted chroma sample at sample location (x,y) of a chroma block (e.g., in a chroma channel or chroma picture of a current picture). Rec_L'(x,y) may be determined from reconstructed samples in a co-located luma block (e.g., in a luma channel or luma picture of a current picture) that have already been reconstructed. Rec_L'(x,y) may represent reconstructed luma samples in the co-located luma block or downsampled luma samples of the co-located luma block.

[0106] In an example, Rec_L' is the co-located luma block that has already been reconstructed, e.g., when the color format is 4:4:4 and the size of the chroma block is the same as the size of the co-located luma block. Thus, Rec_L'(x,y) may represent the reconstructed sample in the co-located luma block, where the reconstructed sample corresponds to sample position (x,y) of the chroma block.

[0107] In an example, Rec_L' is different from the co-located luma block already reconstructed. The current chroma block is co-located with the co-located luma block, and the luma and chroma channels have different resolutions. In an example, when the color format is 4:2:0, the resolution of the luma block is twice that of the chroma block in both the vertical and horizontal directions. Thus, when the color format is 4:2:0, Rec_L' can be a downsampled block of the corresponding luma block to match the chroma block size during derivation of the linear model. In some embodiments, the co-located luma block is downsampled when the color format is 4:4:4.

[0108] The parameters (e.g., model parameters) a and b in Equation 4 may represent a gradient and an offset in the linear model shown in Equation 4 and may be referred to as a gradient parameter and an offset parameter, respectively. The parameters a and b in Equation 4 may be derived from reconstructed neighboring samples (e.g., chroma samples and luma samples) around (i) the current chroma block in the chroma channel and (ii) the co-located luma block in the luma channel. The parameters a and b may be determined in any suitable manner.

[0109] In an example, the parameters a and b are determined by classical linear regression theory: a minimum linear least-squares solution between (i) the reconstructed adjacent luma samples or downsampled samples of the reconstructed adjacent luma samples and (ii) the reconstructed adjacent chroma samples may be applied to derive the parameters a and b below.

number

[0110] In Equation 5 and Equation 6, N reconstructed adjacent chroma samples Rec_C(i) and N corresponding luma samples Rec_L'(i) are used. In an example, for example, when the color format is 4:4:4, the N corresponding luma samples Rec_L'(i) include N reconstructed adjacent luma samples of a luma block. In an example, for example, when the color format is 4:2:0, the N corresponding luma samples Rec_L'(i) include N downsampled samples of reconstructed adjacent luma samples of a luma block. i can be an integer from 1 to N.

[0111] The N reconstructed neighboring chroma samples used to determine the parameters a and b may include any suitable, already reconstructed neighboring samples of a chroma block. The reconstructed neighboring luma samples used to determine the parameters a and b may include any suitable, already reconstructed neighboring samples of a co-located luma block.

[0112] The prediction process of the CCLM mode may include the steps of (1) downsampling the co-located luma block and the reconstructed neighboring luma samples of the co-located luma block to obtain Rec_L′ and downsampled neighboring luma samples, so as to fit the size of the corresponding chroma block, (2) deriving parameters a and b based on the downsampled neighboring luma samples and the reconstructed neighboring chroma samples, for example, using Equations 5 and 6, and (3) applying a CCLM model (e.g., Equation 4) to generate a chroma prediction block Pred_C. In some examples, step (1) is omitted when the spatial resolutions of the co-located luma block and the chroma block are the same, and step (2) is based on the reconstructed neighboring luma samples.

[0113] FIG. 10 illustrates an example of reconstructed adjacent luma samples and reconstructed adjacent chroma samples used in CCLM derivation. A chroma block (1000) is being reconstructed. The width and height of the chroma block (1000) are M (e.g., 8) and N (e.g., 4), respectively. N and M can be positive integers. A luma block (e.g., a colocated luma block) (1001) that is colocated with the chroma block (1000) is used to predict the chroma block (1000). The luma block (1001) includes luma samples (1040). The luma block (1001) can have any suitable width and any suitable height. In the example illustrated in FIG. 10, the width and height of the luma block (1001) are 2M (e.g., 16) and 2N (e.g., 8), respectively.

[0114] Neighboring chroma samples (1010) (e.g., shaded) of the chroma block (1000) have already been reconstructed. Neighboring luma samples (1020) of the luma block (1001) have already been reconstructed. The neighboring chroma samples (1010) may include an above neighboring chroma sample (1011) and a left neighboring chroma sample (1012). The neighboring luma samples (1020) of the luma block (1001) may include an above neighboring luma sample (1021) and a left neighboring luma sample (1022).

[0115] In the example of Figure 10, the neighboring luma samples (1020) are subsampled or downsampled to generate downsampled neighboring luma samples (1030) (e.g., shaded) to match the number of neighboring chroma samples (e.g., 12). In the example shown in Figure 10, the neighboring chroma samples (1010) and the downsampled neighboring luma samples (1030) may be used to determine parameters a and b, for example, as shown in Equations 5 and 6.

[0116] In the example, the neighboring chroma samples of the chroma block (1000) include only the above neighboring chroma sample (1011) and do not include the left neighboring chroma sample (1012). Accordingly, the neighboring luma samples of the luma block (1001) include only the above neighboring luma sample (1021) and do not include the left neighboring luma sample (1022). As described above, the above neighboring luma sample (1021) may be downsampled (e.g., the downsampled luma sample is shaded) to match the number of above neighboring chroma samples (1011) (e.g., 8).

[0117] In the example, the neighboring chroma samples of the chroma block (1000) include only the left neighboring chroma sample (1012) and do not include the above neighboring chroma sample (1011). Accordingly, the neighboring luma samples of the luma block (1001) include only the left neighboring luma sample (1022) and do not include the above neighboring luma sample (1021). As described above, the left neighboring luma sample (1022) may be downsampled (e.g., the downsampled luma sample is shaded) to match the number of left neighboring chroma samples (1012) (e.g., 4).

[0118] In some examples, chroma samples in neighboring reconstructed blocks of the chroma block (1000) and corresponding luma samples in neighboring reconstructed blocks of the luma block (1001) may be used to determine the parameters a and b.

[0119] The chroma block (1000) can be a Cb block in the Cb channel and a Cr block in the Cr channel. In an example, for each chroma channel (e.g., Cr or Cb), the parameters a and b can be determined separately. For example, the parameters a and b of the Cr block are determined based on the chroma reconstructed neighboring samples of the Cr block, and the parameters a and b of the Cb block are determined based on the chroma reconstructed neighboring samples of the Cb block.

[0120] FIG. 10 shows an example of reconstructed adjacent luma samples and reconstructed adjacent chroma samples used in CCLM derivation for a chroma block (1000) having a rectangular shape. The example of FIG. 10 is applicable to chroma blocks and co-located luma blocks having any shape, such as a square shape. FIG. 11 shows an example of reconstructed adjacent luma samples (1120) and reconstructed adjacent chroma samples (1110) used in CCLM derivation for a chroma block (1100). The width and height of the chroma block (1100) are W1 (e.g., 8) and H1 (e.g., 8), respectively, where W1 is equal to H1. A luma block (e.g., a co-located luma block) (1101) that is co-located with the chroma block (1100) is used to predict the chroma block (1100). The width and height of the luma block are 2W1 (e.g., 16) and 2H1 (e.g., 16), respectively.

[0121] In some embodiments, the reference samples used to generate the linear model parameters a and b are noisy and / or not very representative of the content in the actual predicted block, so the prediction may be suboptimal in terms of coding efficiency. Therefore, it may be advantageous to develop a more content-adaptive linear model for, for example, chroma sample prediction.

[0122] This disclosure describes adaptive parameter selection for cross-component prediction in image and video compression. In an embodiment, the gradient and / or offset parameters (e.g., parameter a and / or parameter b) used in CCLM prediction are adaptively adjusted so that the linear model can be more content-adaptive for chroma sample prediction. For example, the linear model (e.g., parameter a and / or parameter b) is more adaptive to the content of the co-located luma block. In an example, the CCLM prediction can adapt to the content of the chroma block since the content of the chroma block is related to the content of the co-located luma block.

[0123] Adjustments to the gradient parameters and / or offset parameters can modify the linear model (e.g., Equation 4) that maps luma sample values ​​to chroma sample values ​​such that the chroma sample values ​​can be mapped from the luma sample values ​​according to the characteristics of the luma sample values ​​in the co-located luma block.

[0124] As described above, in CCLM mode, a model with two parameters (e.g., parameters a and b in Equation 4) is used to map luma values ​​to chroma values. A gradient parameter a and an offset parameter b are used in Equation 4. Adjustment of parameters a and b (e.g., gradient parameter and offset parameter) can be used to update the linear model in Equation 4 to an updated linear model in Equation 7.

number

[0125] In Equation 7, the updated gradient parameter a' is a function of the gradient parameter a, e.g., a' = f1(a), and the updated offset parameter b' is a function of the offset parameter, e.g., b' = f2(b). The adjustments to parameters a and b can be based on local sample information, e.g., local luma reconstruction sample information of a collocated luma block.

[0126] 12A and 12B show examples of parameter adjustments used in CCLM. FIG. 12A shows CCLM according to Equation 4. A predicted chroma sample value (e.g., Cb of a Cb block or Cr of a Cr block) has a linear relationship (1201) with a corresponding luma value (e.g., Y) corresponding to Equation 4, where the gradient of the linear relationship (1201) is gradient parameter a, and the offset of the linear relationship (1201) is offset parameter b. FIG. 12B shows two linear relationships (1201) and (1202) corresponding to Equation 4 and Equation 7, respectively. In the linear relationship (1202) corresponding to Equation 7, a predicted chroma sample value (e.g., Cb of a Cb block or Cr of a Cr block) has a linear relationship 1202 with a corresponding luma value (e.g., Y), where the gradient is updated gradient parameter a′, and the offset is updated offset parameter b′.

[0127] In the example shown in FIG. 12B, the updated gradient parameter a' is a linear relationship of the gradient parameter a, where a' is (a+u). The adjustment parameter u used to adjust the gradient parameter a may be referred to as the gradient adjustment parameter "u". The updated offset parameter b' may be a linear function of the offset parameter b. In the example, b'=bu×y r The adjustment parameter y, which is used to adjust the offset parameter b, is r is the offset adjustment parameter “y r With reference to FIG. 12B, the adjustment (e.g., a'=a+u and b'=bu×y r ), the linear relationship (1201) (e.g., the mapping function used in Equation 4) is rotated or tilted around point (1203) to generate the linear relationship (1202). In the example, the tuning parameter y r is the luminance value (e.g., y r Y) where

[0128] In some examples, the gradient parameter and the offset parameter are adjusted. In some examples, one of the gradient parameter and the offset parameter is adjusted. In some examples, the adjustment parameters u and y r In some examples, the tuning parameters u and y r One of the two is determined.

[0129] a' (e.g., a'=a+u) and b' (e.g., b'=bu×y r In the adjustment equation, the adjustment parameter u can be signaled or derived. The value of the adjustment parameter u can be either positive or negative. r The adjustment parameter y is used to adjust the offset parameter b. r may be determined based on the co-located luma block. For example, the adjustment parameter y r is determined based on the selected values ​​of each reference luma sample in the co-located luma block.

[0130] In CCLM, Equation 7 can be used to predict a chroma block (e.g., chroma block (1000)) based on a co-located luma block (e.g., luma block (1001)). As mentioned above, the updated offset parameter b' can be a linear function of the offset parameter b, e.g., b' is (bu × y r ) The adjustment parameter y used to adjust the offset parameter b according to an embodiment of the present disclosure. r may be determined based on a subset of luma samples in a co-located luma block (e.g., luma block (1001)). In an embodiment, the subset of luma samples in a co-located luma block (e.g., luma block (1001)) does not include one or more samples in the co-located luma block.

[0131] Figure 13 shows the adjustment parameter y r7 shows an example of sample positions of selected luma samples in a co-located luma block (1300) that may be used to determine the adjustment parameter y . The co-located luma block (1300) is co-located with a chroma block to be coded (e.g., to be reconstructed). The co-located luma block (1300) includes luma samples that have already been reconstructed (e.g., reference luma samples). The co-located luma block (1300) or a downsampled luma block that is downsampled from the co-located luma block (1300) may be used as Rec_L′ in Equation 7 to predict the chroma block. Additionally, one or more of the selected luma samples in the co-located luma block (1300) may be used to predict the chroma block using the adjustment parameter y . r can be used to determine

[0132] The luma samples in the co-located luma block (1300) may include luma samples (e.g., selected luma samples) (1301)-(1309), which are located at the top left corner, top center, top right corner, left center, center, right center, bottom left corner, bottom center, and bottom right corner of the co-located luma block (1300), respectively.

[0133] Adjustment parameter y r may be selected as one of the luma samples (1301) to (1309). r may be selected as an average (eg, a weighted average) of sample values ​​of multiple samples among the luma samples (1301)-(1309).

[0134] In an embodiment, the adjustment parameter y r is selected as the sample value of the luma sample (1309) in the bottom-right corner of the co-located luma block (1300).

[0135] In an embodiment, the adjustment parameter y ris selected as the sample value of the luma sample (1305) in the center of the co-located luma block (1300).

[0136] In an embodiment, the adjustment parameter y r is selected as the sample value of the center-right luma sample (1306) of the co-located luma block (1300).

[0137] In an embodiment, the adjustment parameter y r is selected as the sample value of the luma sample (1308) that is located at the bottom center of the co-located luma block (1300).

[0138] In an embodiment, the adjustment parameter y r is selected as a sample value from a position such as the top left corner (e.g., corresponding to luma sample (1301)), the top right corner (e.g., corresponding to luma sample (1303)), or the bottom left corner (e.g., corresponding to luma sample (1307)) of the colocated luma block (1300).

[0139] In an embodiment, the adjustment parameter y r is determined as the average (e.g., weighted average) of sample values ​​of particular luma samples such as luma sample values ​​(1301), (1303), (1307), and (1309) located at the four corners (e.g., upper left corner, upper right corner, lower left corner, and lower right corner) of the co-located luma block (1300).

[0140] In an embodiment, the adjustment parameter y r is determined as the average (eg, weighted average) of sample values ​​of multiple samples among the luma samples (1301)-(1309) in the co-located luma block (1300).

[0141] Luma samples (1301) to (1309) are the adjustment parameters y ry , where another luma sample in the co-located luma block (1300) that is not in luma samples (1301)-(1309) or other luma samples in the co-located luma block (1300) can be used to determine the adjustment parameter y r may be used to determine

[0142] The selection of luma samples within a co-located luma block for adjusting the parameters a and b used in the CCLM model can be made more adaptive to different chroma blocks, or different regions (e.g., sub-blocks) within that chroma block with which the co-located luma block is co-located.

[0143] In an embodiment, different tuning parameters y r For example, luma samples located at different positions in each luma block may be used for different chroma blocks. r For a chroma block, such as a chroma block colocated with the colocated luma block (1300) of FIG. 13, one of the available choices, such as one of the luma samples (1301)-(1309), may be used for that chroma block. In an example, (i) the luma sample (1305) at the center position of the colocated luma block (1300) and (ii) one of the luma samples (1309) at the bottom right corner position of the colocated luma block (1300) may be used as the adjustment parameter y that is used to adjust the offset parameter b. r In the case of a chroma block, for example, which sample is the adjustment parameter y r A selection indicator may be signaled or derived that indicates which of the following is used to determine ?. The selection indicator may be a selection index or a selection flag.

[0144] Different chroma blocks are adjusted by the adjustment parameter yr In the example, the selection index for the first chroma block is the adjustment parameter y r is determined based on the luma sample at the center of the first luma block that is colocated with the first chroma block. Therefore, the adjustment parameter y r is determined based on the luma sample at the center position of the first luma block. The selection index for the second chroma block is determined based on the adjustment parameter y r is determined based on the center position of the right edge of the second luma block that is colocated with the second chroma block. Therefore, the adjustment parameter y r is determined based on the luma sample at the center-right position of the second luma block.

[0145] In an embodiment, the adjustment parameters y of different regions in a chroma block r may be determined using different sample values ​​in the co-located luma block. Figure 14 shows an example of a chroma block (1410) and a co-located luma block (1400) that is co-located with the chroma block (1410). The chroma block (1410) can be predicted based on the co-located luma block (1400), for example, if the spatial resolution of the chroma block (1410) is the same as the spatial resolution of the co-located luma block (1400) (e.g., the color format is 4:4:4). The chroma block (1410) can be predicted based on downsampled luma samples that are downsampled from the co-located luma block (1400), for example, if the spatial resolution of the chroma block (1410) is different from the spatial resolution of the co-located luma block (1400).

[0146] The chroma block (1410) includes multiple regions (also called multiple chroma regions), such as an upper left quarter region (1411), an upper right quarter region (1412), a lower left quarter region (1413), and a lower right quarter region (1414). r may be determined based on each sample in the co-located luma block (1400).

[0147] For example, the center position (1401) of the colocated luma block (1400) is determined by the adjustment parameter y r The right-most center position (1402) of the co-located luma block (1400) is used to determine the adjustment parameter y r The lower center (1403) of the co-located luma block (1400) is used to determine the adjustment parameter y r The position (1404) of the bottom right corner of the colocated luma block (1400) is used to determine the adjustment parameter y r is used to determine

[0148] In an embodiment, the adjustment parameter y of one of the regions in the chroma block (1410) r is determined based on a corresponding region in the co-located luma block (1400). For example, the corresponding region in the co-located luma block (1400) is co-located with one of the regions in the chroma block (1410).

[0149] Referring to Figure 14, a co-located luma block (1400) includes multiple regions (also referred to as multiple luma regions) that are co-located with multiple chroma regions in a chroma block (1410). For example, the multiple luma regions in the co-located luma block (1400) include an upper left quarter region (1421), an upper right quarter region (1422), a lower left quarter region (1423), and a lower right quarter region (1424) that are co-located with an upper left quarter region (1411), an upper right quarter region (1412), a lower left quarter region (1413), and a lower right quarter region (1414) in the chroma block, respectively.

[0150] In the example, the average of the luma sample values ​​in the upper left quadrant (1421) of the colocated luma block (1400) is the average of the luma sample values ​​in the lower left quadrant (1411) of the chroma block (1410) with the adjustment parameter y r The average of the luma sample values ​​in the upper right quadrant (1422) of the colocated luma block (1400) is used to determine the adjustment parameter y r The average of the luma sample values ​​in the lower-left quadrant (1423) of the co-located luma block (1400) is used to determine the adjustment parameter y r The average of the luma sample values ​​in the lower right quadrant (1424) of the colocated luma block (1400) is used to determine the adjustment parameter y r is used to determine

[0151] In the example, a chroma region (e.g., 1411) is further divided into multiple chroma sub-regions, and a co-located luma region (e.g., 1421) is further divided into multiple luma sub-regions. r may be determined based on an average of the luma sample values ​​of each luma subregion within the region (1421).

[0152] 15 shows an example of a chroma block (1510) and a co-located luma block (1500) that is co-located with the chroma block (1510). The chroma block (1510) can be predicted based on the co-located luma block (1500) or downsampled luma samples that are downsampled from the co-located luma block (1500), as described in FIG.

[0153] The chroma block (1510) includes multiple chroma regions, such as an upper left quarter region (1511), an upper right quarter region (1512), a lower left quarter region (1513), and a lower right quarter region (1514). r may be determined based on an average of certain luma sample values, such as four luma samples located at the four corners of a corresponding luma region in a co-located luma block (1500).

[0154] The co-located luma block (1500) includes multiple luma regions that are co-located with multiple chroma regions in a chroma block (1510). For example, the multiple luma regions in the co-located luma block (1500) include an upper left quarter region (1521), an upper right quarter region (1522), a lower left quarter region (1523), and a lower right quarter region (1524) that are co-located with an upper left quarter region (1511), an upper right quarter region (1512), a lower left quarter region (1513), and a lower right quarter region (1514) in the chroma block, respectively.

[0155] In the example, the average of the luma sample values ​​at the four corners (1501) to (1504) of the upper left quarter region (1521) of the colocated luma block (1500) is the adjustment parameter y rThe average of the luma sample values ​​at the four corners of the upper right quadrant (1522) of the colocated luma block (1500) is used to determine the adjustment parameter y r The average of the luma sample values ​​at the four corners of the lower-left quadrant (1523) of the colocated luma block (1500) is used to determine the adjustment parameter y r The average of the luma sample values ​​at the four corners of the lower right quadrant (1524) of the colocated luma block (1500) is used to determine the adjustment parameter y r is used to determine

[0156] In the description with reference to Figures 14 and 15, a chroma block (e.g., 1410) includes four regions (e.g., (1411) to (1414)). The description of Figures 14 and 15 is applicable to a chroma block when it includes M regions, where M is an integer greater than 1.

[0157] Referring again to FIG. 14, the regions (1411)-(1414) may be sub-blocks within the chroma block (1410). An indicator associated with the chroma block (1410) may indicate a CCLM mode for the chroma block (1410). Each sub-block within the chroma block (1410) may be predicted differently using the embodiments described in FIG. 14. In one example, a forward or inverse transform is applied to the entire chroma block (1410) to transform the entire chroma block (1410). In an example, the chroma block (1410) is partitioned into multiple TBs that are different from the regions (1411)-(1414), and each of the multiple TBs is transformed using an appropriate transform.

[0158] As shown in FIG. 14 and FIG. 15, the adjustment parameters y r In an example, the same offset parameter b, as determined using Equation 6, is used for different regions, and the corresponding updated offset parameters b′ of the different regions are calculated by subtracting the offset parameter b from the adjustment parameters y of each of the different regions. r In an example, different offset parameters b may be used for different regions.

[0159] Adjustment formula (e.g., a'=a+u and b'=bu×y r The adjustment parameter of u may be derived based on (i) the reconstructed neighboring luma samples (e.g., (1020)) of the co-located luma block (e.g., luma block (1001)) and (ii) the co-located luma samples (e.g., (1040)) within the co-located luma block (e.g., luma block (1001)). In accordance with an embodiment of the present disclosure, the adjustment parameter u may be derived based on a difference between (i) the reconstructed neighboring luma samples and (ii) the co-located luma samples within the co-located luma block.

[0160] In an embodiment, the adjustment parameter u is determined based on the difference between (i) a first average (e.g., called Rec_L'(Nei)) based on reconstructed neighboring luma samples of the co-located luma block and (ii) a second average (called Rec_L'(Col)) based on co-located luma samples within the co-located luma block. In an example, the adjustment parameter u is a linear function of the difference, such as u=M(Rec_L'(Col)-Rec_L'(Nei))+K, where M and K are constants. In an example, the adjustment parameter u is a piecewise linear function of the difference, and a mapping table is designed to map the difference between the first average Rec_L'(Nei) and the second average Rec_L'(Col) to a value of the adjustment parameter u.

[0161] The first average Rec_L'(Nei) may be an average of multiple samples among reconstructed adjacent luma samples of the co-located luma block, and the second average Rec_L'(Col) may be an average of multiple samples among co-located luma samples within the co-located luma block.

[0162] In an example, the first average Rec_L'(Nei) is the average of all reconstructed neighboring luma samples (e.g., (1020)) of a co-located luma block (e.g., (1001)). In an example, the second average Rec_L'(Col) is the average of all co-located luma samples (e.g., (1040)) within a co-located luma block (e.g., (1001)).

[0163] In an embodiment, the reconstructed neighboring luma samples of the collocated luma block used to calculate the first average Rec_L'(Nei) are the selected neighboring samples Rec_L'(i) used to calculate the CCLM parameters a and b, as used in Equations 5 and 6. Referring to Figure 10, the selected neighboring samples Rec_L'(i) may include a subset of samples in the reconstructed neighboring luma samples (1020), such as the left neighboring luma samples (1022), the above neighboring luma samples (1021), etc.

[0164] In an embodiment, the second average Rec_L'(Col) may be determined based on a subset of collocated luma samples selected from the collocated luma block. Referring to Figure 13, one or more of samples (1301)-(1309) may be used in the selected subset.

[0165] In an embodiment, the number of samples used to calculate the second average Rec_L'(Col) is set based on the number of samples used to calculate the first average Rec_L'(Nei), e.g., the number of samples used to calculate the second average Rec_L'(Col) is set equal to the number of samples used to calculate the first average Rec_L'(Nei).

[0166] In some examples, the first average Rec_L'(Nei) is determined based on downsampled neighboring samples of reconstructed neighboring luma samples of the co-located luma block.

[0167] In an example, the same scaling parameter a, as determined using Equation 5, may be used for different regions within a chroma block, and corresponding updated scaling parameters a′ of the different regions may be obtained based on the scaling parameter a and the adjustment parameter u of each of the different regions. In an example, different scaling parameters a may be used for the different regions.

[0168] FIG. 16 shows a flow chart describing a process (e.g., encoding process) (1600) according to an embodiment of the present disclosure. The process (1600) may be performed by an apparatus for video coding, which may include processing circuitry. In various embodiments, the process (1600) is performed by processing circuitry within an apparatus, such as processing circuitry within terminal devices (310), (320), (330), and (340), processing circuitry performing the functions of a video encoder (e.g., (403), (603), (703)), etc. In some embodiments, the process (1600) is implemented with software instructions, such that the processing circuitry performs the process (1600) when the processing circuitry executes the software instructions. The process starts at (S1601) and proceeds to (S1610).

[0169] In (S1610), for a first region in a chroma block to be coded in a current picture using a cross-component linear model (CCLM) mode, a first adjustment parameter (e.g., y r ) may be determined based on a first subset of reconstructed samples in a co-located luma block in the current picture, where the first subset of reconstructed samples does not include one or more samples in the co-located luma block.

[0170] In an example, the first region in the chroma block includes the entire chroma block. The first subset of reconstructed samples in the co-located luma block is one sample in the co-located luma block. The first adjustment parameter may be determined to be a sample value of the one sample in the co-located luma block, as described in FIG. 13 .

[0171] In an example, the first region includes an entire chroma block. The first subset of reconstructed samples includes a plurality of samples in the co-located luma block. The first adjustment parameter may be determined to be an average of sample values ​​of the plurality of samples in the co-located luma block, as described in FIG.

[0172] At (S1620), a first updated offset parameter may be determined based on the offset parameter and the first adjustment parameter.

[0173] At (S1630), the first region may be encoded using a CCLM mode based at least on the first updated offset parameter. In an example, prediction information indicating that a CCLM mode is applied to the chroma block is encoded.

[0174] The encoded first region and the prediction region may be included in a coded video bitstream and then transmitted to a decoder.

[0175] In an example, the first region includes an entire chroma block. The prediction information further indicates which of the samples in the co-located luma block are included in the first subset of reconstructed samples. In an example, which of the samples in the co-located luma block are included in the first subset of reconstructed samples are signaled in the coded video bitstream.

[0176] The process then proceeds to (S1699) and ends.

[0177] The process (1600) can be adapted to various scenarios as appropriate, and the steps of the process (1600) can be adjusted accordingly. One or more of the steps of the process (1600) can be adapted, omitted, repeated, and / or combined. Any suitable order can be used to implement the process (1600). Additional steps can be added.

[0178] In an example, the chroma block further includes a second region. The first subset of reconstructed samples is a first sample in the co-located luma block. For the second region in the chroma block, a second adjustment parameter used to adjust the offset parameter in CCLM mode may be determined based on a second sample in the co-located luma block. The second sample may be different from the first sample. A second updated offset parameter may be determined based at least on the offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed based at least on the second updated offset parameter using CCLM mode.

[0179] In an example, the chroma block further includes a second region. The co-located luma block includes a first luma region and a second luma region that are co-located with the first region and the second region, respectively. The first subset of reconstructed samples includes a plurality of samples in the first luma region. A second adjustment parameter used to adjust the offset parameter in CCLM mode for the second region in the chroma block may be determined based on a plurality of samples in the second luma region. A second updated offset parameter may be determined based at least on the offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed using CCLM mode based at least on the second updated offset parameter.

[0180] In an example, the chroma block further includes a second region. The co-located luma block includes a first luma region and a second luma region that are co-located with the first region and the second region, respectively. The first subset of reconstructed samples includes a top left sample, a top right sample, a bottom left sample, and a bottom right sample in the first luma region. The first adjustment parameter may be determined to be an average of the top left sample, the top right sample, the bottom left sample, and the bottom right sample in the first luma region. For the second region in the chroma block, a second adjustment parameter used to adjust the offset parameter in CCLM mode may be determined to be an average of the top left sample, the top right sample, the bottom left sample, and the bottom right sample in the second luma region. A second updated offset parameter may be determined based at least on the offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed based at least on the second updated offset parameter using CCLM mode.

[0181] In an example, for the first region, an updated scaling parameter (e.g., a') may be determined to be the sum of a scaling parameter (e.g., parameter a) used in the CCLM mode and an adjustment parameter (e.g., adjustment parameter u) used to adjust the scaling parameter. The first updated offset parameter (e.g., b') may be determined to be (bu × y r ), where b is an offset parameter, u is an adjustment parameter used to adjust the scaling parameter, and y r where is a first adjustment parameter. A first region in a chroma block may be reconstructed based on the first updated offset parameter and the updated scaling parameter using a CCLM mode.

[0182] In an example, for the first region, an adjustment parameter (e.g., u) used to adjust a scaling parameter (e.g., a) is determined based on (i) reconstructed luma samples in one or more neighboring luma blocks of the co-located luma block and (ii) samples in the co-located luma block. In an example, for the first region, an adjustment parameter used to adjust the scaling parameter may be determined based on a difference between an average of the reconstructed luma samples in the one or more neighboring luma blocks and an average of the samples in the co-located luma block.

[0183] FIG. 17 shows a flow chart describing a process (e.g., a decoding process) (1700) according to an embodiment of the present disclosure. The process (1700) may be used in a video decoder. The process (1700) may be performed by an apparatus for video coding, which may include receiving circuitry and processing circuitry. Processing circuitry in an apparatus, such as processing circuitry in terminal devices (310), (320), (330), and (340), processing circuitry performing the functions of a video decoder (410), processing circuitry performing the functions of a video decoder (510), etc., may be configured to perform the process (1700). In some examples, the process (1700) is used in a video encoder (e.g., video encoder (403), video encoder (603)). In an example, the process (1700) is performed by processing circuitry performing the functions of a video encoder (e.g., video encoder (403), video encoder (603)). In some embodiments, the process 1700 is implemented by software instructions, such that when the processing circuit executes the software instructions, the processing circuit performs the process 1700. The process starts at S1701 and proceeds to S1710.

[0184] At (S1710), prediction information for a chroma block to be reconstructed in a current picture may be decoded. The prediction information may indicate that a cross-component linear model (CCLM) mode is applied to the chroma block.

[0185] In (S1720), a first adjustment parameter (also called a first adjustment value) (e.g., y r) may be determined based on a first subset of reconstructed samples in a co-located luma block in the current picture. A co-located luma block is a luma block that is co-located with a chroma block. The first subset of reconstructed samples does not include one or more samples in the co-located luma block. In an example, the samples in the co-located luma block have already been reconstructed.

[0186] In an example, the first region in the chroma block includes the entire chroma block. The first subset of samples in the co-located luma block is one sample in the co-located luma block. The first adjustment parameter may be determined to be a sample value of the one sample in the co-located luma block, as described in FIG. 13.

[0187] In an example, the first region includes an entire chroma block. The first subset of samples includes a plurality of reconstructed samples in the co-located luma block. The first adjustment parameter may be determined to be an average of sample values ​​of the plurality of samples in the co-located luma block, as described in FIG.

[0188] In an example, the first region includes an entire chroma block. The prediction information further indicates which of the samples in the co-located luma block are included in the first subset of samples. In an example, which of the samples in the co-located luma block are included in the first subset of samples are signaled in the coded video bitstream. In an example, which of the samples in the co-located luma block are included in the first subset of samples are derived.

[0189] At (S1730), for a first region in the chroma block, a first updated offset parameter (e.g., b') is calculated by multiplying the offset parameter (e.g., b) and the first adjustment parameter (e.g., y r), for example, as described above, b'=bu×y r It is.

[0190] At (S1740), the first region within the chroma block may be reconstructed based at least on the first updated offset parameter using the CCLM mode. The process then proceeds to (S1799) and ends.

[0191] The process 1700 can be adapted to various scenarios as appropriate, and the steps of the process 1700 can be adjusted accordingly. One or more of the steps of the process 1700 can be adapted, omitted, repeated, and / or combined. Any suitable order can be used to implement the process 1700. Additional steps can be added.

[0192] In an example, the chroma block further includes a second region. The first subset of samples is a first sample in the co-located luma block. For the second region in the chroma block, a second adjustment parameter used to adjust the offset parameter in CCLM mode may be determined based on a second sample in the co-located luma block. The second sample may be different from the first sample. A second updated offset parameter may be determined based at least on the offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed using CCLM mode based at least on the second updated offset parameter.

[0193] In an example, the chroma block further includes a second region. The co-located luma block includes a first luma region and a second luma region that are co-located with the first region and the second region, respectively. The first subset of samples includes a plurality of samples in the first luma region. A second adjustment parameter used to adjust the offset parameter in CCLM mode for the second region in the chroma block may be determined based on the plurality of samples in the second luma region. A second updated offset parameter may be determined based at least on the offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed based at least on the second updated offset parameter using CCLM mode.

[0194] In an example, the chroma block further includes a second region. The co-located luma block includes a first luma region and a second luma region that are co-located with the first region and the second region, respectively. The first subset of samples includes a top left sample, a top right sample, a bottom left sample, and a bottom right sample in the first luma region. The first adjustment parameter may be determined to be an average of the top left sample, the top right sample, the bottom left sample, and the bottom right sample in the first luma region. A second adjustment parameter used to adjust the offset parameter in CCLM mode for the second region in the chroma block may be determined to be an average of the top left sample, the top right sample, the bottom left sample, and the bottom right sample in the second luma region. A second updated offset parameter may be determined based at least on the second offset parameter and the second adjustment parameter. The second region in the chroma block may be reconstructed based at least on the second updated offset parameter using CCLM mode.

[0195] In an example, for the first region, an updated scaling parameter (e.g., a') may be determined to be the sum of a scaling parameter (also called a gradient parameter) used in the CCLM mode (e.g., parameter a) and an adjustment parameter (also called an adjustment value) (e.g., adjustment parameter u) used to adjust the scaling parameter. A first updated offset parameter (e.g., b') may be determined to be (bu × y r ), b is an offset parameter, u is an adjustment parameter used to adjust the scaling parameter, and y r where is a first adjustment parameter. A first region in a chroma block may be reconstructed based on the first updated offset parameter and the updated scaling parameter using a CCLM mode.

[0196] In an embodiment, an adjustment parameter (e.g., u) used to adjust a scaling parameter (e.g., a) for the first region is determined based on (i) reconstructed luma samples in one or more neighboring luma blocks of the co-located luma block and (ii) samples in the co-located luma block. In an example, the adjustment parameter u used to adjust the scaling parameter for the first region may be determined based on a difference between an average of the reconstructed luma samples in the one or more neighboring luma blocks and an average of the samples in the co-located luma block.

[0197] In an embodiment, a first adjustment value used to change an offset parameter in CCLM mode for a first region in a chroma block is determined based on a first subset of reconstructed samples in a luma block that is currently colocated with the chroma block in the picture. The first subset of reconstructed samples does not include one or more samples in the luma block. The offset parameter may be updated based at least on the first adjustment value. A second adjustment value used to change a gradient parameter in CCLM mode may be determined based on a second subset of reconstructed samples in the luma block, and the gradient parameter may be updated based at least on the second adjustment value. The first region in the chroma block may be reconstructed using CCLM mode based at least on the updated offset parameter and the updated gradient parameter.

[0198] In an example, the second subset of reconstructed samples includes the first subset of reconstructed samples.

[0199] In an example, the second adjustment value is determined based on the reconstructed samples within the entire luma block.

[0200] The embodiments of the present disclosure may be used separately or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium.

[0201] It can be implemented as computer software using computer readable instructions and physically stored on one or more computer readable media. For example, Figure 18 illustrates a computer system (1800) suitable for implementing certain embodiments of the disclosed subject matter.

[0202] The computer software may be coded in any suitable machine code or computer language that may be subject to mechanisms such as assembly, compilation, linking, etc. to generate code including instructions that may be executed by one or more central processing units (CPUs), graphics processing units (GPUs), etc., directly or through interpretation, microcode execution, etc.

[0203] The instructions may be executable by various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming consoles, devices for the Internet of Things, and the like.

[0204] 18 for computer system (1800) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components described in the exemplary embodiment of computer system (1800).

[0205] The computer system (1800) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more users through, for example, tactile input (e.g., keyboard, swipes, dataglove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), and olfactory input (not shown). The human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (e.g., speech, music, ambient sounds), images (e.g., scanned images, photographic images obtained from a still camera), and video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

[0206] The input human interface devices may include one or more of a keyboard (1801), a mouse (1802), a trackpad (1803), a touch screen (1810), a data glove (not shown), a joystick (1805), a microphone (1806), a scanner (1807), and a camera (1808) (only one of each is shown).

[0207] The computer system 1800 may also include certain human interface output devices that may stimulate one or more of the user's senses through, for example, tactile output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (1810), data gloves (not shown), or joystick (1805), although there may also be haptic feedback devices that do not function as input devices), audio output devices (e.g., speakers (1809), headphones (not shown)), visual output devices (e.g., screens (1810) including CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch screen input capability, each with or without haptic feedback capability, some of which are capable of outputting two-dimensional visual output or output in more than three dimensions by means of stereoscopic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0208] The computer system (1800) may also include human accessible storage devices and their associated media, such as CD / DVD ROM / RW (1820) along with CD / DVD or similar media (1821), thumb drives (1822), removable hard disks or solid state drives (1823), legacy magnetic media such as tapes and floppy disks (not shown), dedicated ROM / ASIC / PLD based devices such as security dongles (not shown), and the like.

[0209] Those skilled in the art will also understand that the term "computer-readable medium" as used in connection with the presently disclosed subject matter does not include transmission media, carrier waves, or other transitory signals.

[0210] The computer system (1800) may also include interfaces to one or more communication networks. The networks may be, for example, wireless, wireline, optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LANs, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., TV wireline or wireless wide area digital networks including cable TV, satellite TV, and terrestrial broadcast TV, vehicular and factory networks including CAN bus, etc. Certain networks generally require an external network interface adapter attached to a particular general purpose digital port or peripheral bus (1849) (e.g., a USB port of the computer system (1800)). Others are generally built into the core of the computer system (1800) by attachment to a system bus as described below (e.g., an Ethernet network to a PC computer system, or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (1800) may communicate with other entities. Such communications may be one-way receive-only (e.g., broadcast TV) or one-way transmit-only (e.g., a CAN bus to a specific CAN bus device), or may be two-way, for example, to other computer systems using local or wide area digital networks. Specific protocols or protocol stacks may be used with each of the networks and network interfaces as described above.

[0211] The above-mentioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (1840) of the computer system (1800).

[0212] The cores (1840) may include one or more central processing units (CPUs) (1841), graphics processing units (GPUs) (1842), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (1843), hardware accelerators (1844) for specific tasks, etc. These devices may be connected through a system bus (1848), along with read only memory (ROM) (1845), random access memory (RAM) (1846), internal mass storage devices such as internal non-user accessible hard drives, SSDs, etc. (1847). In some computer systems, the system bus (1848) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripherals may be attached to the core's system bus (1848) directly or through a peripheral bus (1849). In an example, a screen (1810) may be connected to a graphics adapter (1850). Architectures for peripheral buses include PCI and USB.

[0213] The CPU (1841), GPU (1842), FPGA (1843), and accelerator (1844) can execute certain instructions that, in combination, can constitute the above computer code. The computer code can be stored in ROM (1845) or RAM (1846). Temporary data can also be stored in RAM (1846), while persistent data can be stored, for example, in an internal mass storage device (1847). Rapid storage and retrieval from any of the memory devices can be made possible by the use of a cache memory. A cache memory can be closely associated with one or more of the CPU (1841), GPU (1842), mass storage device (1847), ROM (1845), RAM (1846), etc.

[0214] The computer-readable medium can bear computer code for performing various computer-implemented operations. The medium and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the kind well known and available to those of ordinary skill in the computer software arts.

[0215] By way of example, and not by way of limitation, a computer system having the architecture (1800), and in particular the core (1840), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be media associated with the user-accessible mass storage devices introduced above, in addition to specific storage of the core (1840) that is non-transitory in nature, such as the core's internal mass storage (1847) or ROM (1845). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (1840). The computer-readable media can include one or more memory devices or chips, depending on particular needs. The software can cause the core (1840), and in particular the processors therein (including CPUs, GPUs, FPGAs, etc.), to perform certain processes or certain portions of certain processes described herein, including defining data structures stored in RAM (1846) and modifying such data structures according to processes defined by the software. Additionally or alternatively, the computer system can provide functionality as a result of logic (e.g., accelerators (1844)) implemented by hardware or otherwise embodied in circuitry that can operate in place of or in conjunction with software to perform certain processes or certain portions of certain processes described herein. References to software can encompass logic, where appropriate, and vice versa. References to computer-readable media can encompass circuitry (e.g., integrated circuits (ICs)) storing software for execution, circuitry embodying logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0216] Appendix A: Acronyms JEM: Joint Exploration Model VVC:Versatile Video Coding BMS:benchmark set MV:Motion Vector HEVC:High Efficiency Video Coding SEI:Supplementary Enhancement Information VUI:Video Usability Information GOP:Group of Picture(s) TU:Transform Unit(s) PU:Prediction Unit(s) CTU:Coding Tree Unit(s) CTB:Coding Tree Block(s) PB:Prediction Block(s) HRD:Hypothetical Reference Decoder SNR:Signal Noise Ratio CPU:Central Processing Unit(s) GPU:Graphics Processing Unit(s) CRT:Cathode Ray Tube LCD:Liquid-Crystal Display OLED:Organic Light-Emitting Diode CD:Compact Disc DVD:Digital Video Disc ROM:Read-Only Memory RAM:Random Access Memory ASIC:Application-Specific Integrated Circuit PLD:Programmable Logic Device LAN: Local Area Network GSM: Global System for Mobile communications LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI:Peripheral Component Interconnect FPGA:Field Programmable Gate Area(s) SSD: Solid-State Drive IC: Integrated Circuit CU: Coding Unit CCLM:Cross-Component Linear model

[0217] While this disclosure has described several exemplary embodiments, there are alterations, permutations, and various substitute equivalents that are within the scope of this disclosure. Thus, it will be apparent to those skilled in the art that numerous systems and methods will be contemplated that embody the principles of the present disclosure and are therefore within its spirit and scope, even if not explicitly shown or described herein.

[0218] [Incorporated by reference] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 305,159, entitled "ADAPTIVE PARAMETER SELECTION FOR CROSS-COMPONENT PREDICTION IN IMAGE AND VIDEO COMPRESSION," filed on January 31, 2022, which claims the benefit of priority to U.S. Provisional Patent Application No. 17 / 976,556, entitled "ADAPTIVE PARAMETER SELECTION FOR CROSS-COMPONENT PREDICTION IN IMAGE AND VIDEO COMPRESSION," filed on October 28, 2022. The entire disclosures of these prior applications are incorporated herein by reference in their entirety.

Claims

1. 1. A method of video processing performed by a decoder, comprising: decoding prediction information for a chroma block to be reconstructed in a current picture, the prediction information indicating that a cross-component linear model (CCLM) mode is to be applied to the chroma block; For a first region within the chroma block, determining a first adjustment value used to modify an offset parameter in the CCLM mode based on a first subset of reconstructed samples in a luma block that is co-located with the chroma block in the current picture, the first subset of reconstructed samples not including one or more samples in the luma block; updating the offset parameter based at least on the first adjustment value; determining a second adjustment value used to modify a gradient parameter in the CCLM mode based on a second subset of the reconstructed samples in the luma block; updating the gradient parameter based at least on the second adjustment value; reconstructing the first region within the chroma block based at least on the updated offset parameter and the updated gradient parameter using the CCLM mode; having Determining the updated offset parameter includes determining the updated offset parameter to be (b−u×y r ), where b is the offset parameter, u is the second adjustment value used to change the gradient parameter, and y r is the first adjustment value; reconstructing the first region includes reconstructing the first region within the chroma block based on the updated offset parameters and the updated gradient parameters using the CCLM mode.

2. the first region within the chroma block includes the entire chroma block; the first subset of the reconstructed samples in the luma block is one reconstructed sample in the luma block; determining the first adjustment value includes determining the first adjustment value to be a sample value of the one reconstructed sample in the luma block. The method of claim 1.

3. the first region includes the entire chroma block; the first subset of reconstructed samples includes a plurality of reconstructed samples in the luma block; determining the first adjustment value includes determining the first adjustment value to be an average of sample values ​​of the reconstructed samples in the luma block. The method of claim 1.

4. the first region includes the entire chroma block; the prediction information further indicates which of the reconstructed samples in the luma block are included in the first subset of reconstructed samples. The method of claim 1.

5. The chroma block further includes a second region; the first subset of reconstructed samples is a first reconstructed sample in the luma block; The method further comprises, for the second region within the chroma block: determining a second adjustment parameter used to adjust the offset parameter in the CCLM mode based on a second reconstructed sample in the luma block that is different from the first reconstructed sample; determining a second updated offset parameter based at least on the offset parameter and the second adjustment parameter; reconstructing the second region within the chroma block based at least on the second updated offset parameter using the CCLM mode; Further comprising The method of claim 1.

6. The chroma block further includes a second region; the luma block includes a first luma region and a second luma region that are co-located with the first region and the second region, respectively; the first subset of the reconstructed samples includes a plurality of samples in the first luma region; The method further comprises, for the second region within the chroma block: determining a second adjustment parameter used to adjust the offset parameter in the CCLM mode based on a plurality of samples in the second luma region; determining a second updated offset parameter based at least on the offset parameter and the second adjustment parameter; reconstructing the second region within the chroma block based at least on the second updated offset parameter using the CCLM mode; Further comprising The method of claim 1.

7. The chroma block further includes a second region; the luma block includes a first luma region and a second luma region that are co-located with the first region and the second region, respectively; the first subset of reconstructed samples includes a top left sample, a top right sample, a bottom left sample, and a bottom right sample in the first luma region; determining the first adjustment value includes determining the first adjustment value to be an average of the top left sample, the top right sample, the bottom left sample, and the bottom right sample in the first luma region; The method further comprises, for the second region within the chroma block: determining a second adjustment parameter used to adjust the offset parameter in the CCLM mode to be an average of a top left sample, a top right sample, a bottom left sample, and a bottom right sample in the second luma region; determining a second updated offset parameter based at least on the offset parameter and the second adjustment parameter; reconstructing the second region within the chroma block based at least on the second updated offset parameter using the CCLM mode; Further comprising The method of claim 1.

8. determining, for the first region, the second adjustment value used to modify the gradient parameter based on (i) reconstructed luma samples in one or more neighboring luma blocks of the luma block and (ii) the second subset of the reconstructed samples in the luma block. The method of claim 7.

9. The step of determining the second adjustment value used to modify the gradient parameter comprises: and determining, for the first region, the second adjustment value used to modify the gradient parameter based on a difference between an average of the reconstructed luma samples in the one or more neighboring luma blocks and an average of the second subset of the reconstructed samples in the luma block. The method according to claim 8.

10. the second subset of the reconstructed samples comprises the first subset of the reconstructed samples. The method of claim 1.

11. The step of determining the second adjustment value includes: determining the second adjustment value based on the reconstructed samples within the entire luma block. The method of claim 1.

12. 1. An apparatus for video decoding, comprising: Apparatus comprising a processing circuit configured to perform the method of any one of claims 1 to 11 when executing a computer program stored in a memory.

13. 1. A computer program having instructions, comprising: A computer program product comprising instructions, when executed by at least one processor, causing the at least one processor to perform the method of any one of claims 1 to 11.

14. 1. A method of video processing performed by an encoder, comprising: determining a first adjustment value used to change an offset parameter in a cross-component linear model (CCLM) mode for a first region in a chroma block to be coded in a current picture using a CCLM mode based on a first subset of reconstructed samples in a luma block that is co-located with the chroma block in the current picture, the first subset of reconstructed samples not including one or more samples in the luma block; determining a first updated offset parameter based on the offset parameter and the first adjustment value; encoding the first region based at least on the first updated offset parameter using the CCLM mode; having Determining the first updated offset parameter includes determining the first updated offset parameter to be (b-u×y r ), where b is the offset parameter, u is a second adjustment value used to change a gradient parameter in the CCLM mode, and y r is the first adjustment value; the step of encoding the first region includes encoding the first region within the chroma block based on the first updated offset parameter and a gradient parameter updated based on the second adjustment value using the CCLM mode.

Images