Video decoding method and apparatus, and video encoding method

Abstract

In the method, coded information of a current block in a current picture is received from a coded video bitstream. The current block is partitioned into a plurality of sub-blocks. A first flag included in the coded information is obtained, the first flag indicating whether a cross-component linear model prediction (CCLM) is applied to the current block, in which chroma samples of the current block are predicted based on reconstructed luma samples of the current block. In response to the first flag indicating that CCLM is applied to the current block, a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks of the current block is determined based on the CCLM. The current block is further reconstructed based on the predicted sample value of each of the chroma samples in each of the plurality of sub-blocks of the current block.

Description

[Technical field]

[0001] [Incorporated by reference] This patent application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 252,395, filed October 5, 2021, and entitled "Subblock Cross Component Linear Model Prediction," which in turn claims the benefit of priority to U.S. Provisional Patent Application No. 17 / 946,299, filed September 16, 2022, and entitled "SUBBLOCK CROSS COMPONENT LINEAR MODEL PREDICTION." The disclosures of the prior applications are incorporated herein by reference in their entireties.

[0002] [Technical field] This disclosure describes embodiments generally relating to video coding. [Background technology]

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

[0004] Video encoding and decoding can be performed using inter-picture prediction with motion compensation. Uncompressed digital video can include a sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luminance samples and associated chrominance samples. The sequence of pictures can have a fixed or variable picture rate (commonly known as frame rate) of, for example, 60 pictures per second, i.e., 60 Hz. Uncompressed video has certain 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 more than 600 Gbytes of storage space.

[0005] One goal of video encoding and decoding can be the reduction of redundancy in the input video signal through compression. Compression can help reduce the above bandwidth and / or storage space requirements by more than two orders of magnitude in some cases. 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 and reconstructed signals 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 tolerable distortion depends on the application, e.g., a user of a particular consumer streaming application may tolerate higher distortion than a user of a television distribution application. The achievable compression ratio can reflect that a higher tolerable / acceptable distortion may result in a higher compression ratio.

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

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

[0008] Conventional intra-coding, for example as known from MPEG-2 generation coding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to do so from surrounding sample data and / or metadata obtained during the encoding and / or decoding of spatially adjacent and preceding blocks of data in the decoding order. Such techniques are hereinafter referred to as "intra-prediction" techniques. It should be noted that at least in some cases, intra-prediction uses only reference data from the current picture being reconstructed, and not from the reference picture.

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

[0010] 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 ​​belonging to already available samples. The sample values ​​of the neighboring samples are copied into the predictor block according to the direction. The reference of the direction in use may be coded into the bitstream or may itself be predicted.

[0011] Referring to FIG. 1, at the bottom right, a subset of 9 known predictor directions from the 33 possible predictor directions of H.265 (corresponding to the 33 angle modes of the 35 intra modes) is represented. The point where the arrows converge (101) corresponds to the sample being predicted. The arrows represent the direction in which the sample is predicted. For example, arrow (102) indicates that sample (101) is predicted from one or more samples to the upper right and at an angle of 45 degrees from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from one or more samples to the lower left of sample (101) and at an angle of 22.5 degrees from the horizontal.

[0012] Still referring to FIG. 1, at the top left is depicted a square block (104) of 4×4 samples (indicated by the 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" and 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, so negative values ​​do not need to be used.

[0013] Intra-picture prediction can work by copying reference sample values ​​from neighboring samples as necessary depending on 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.

[0014] In certain 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.

[0015] 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), and JEM / VVC / BMS can support up to 65 directions at the time of this disclosure. Experiments have been performed 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 some penalty for less likely directions. Furthermore, the direction itself can sometimes be predicted from neighboring directions used in neighboring, already decoded blocks.

[0016] FIG. 2 shows a schematic diagram (201) representing 65 intra prediction directions according to JEM to illustrate the growing number of prediction directions over time.

[0017] The mapping of intra-prediction direction bits in a coded video bitstream representing directions can vary from one video coding technique to another, and can range, for example, from a simple direct mapping of prediction directions to intra-prediction modes to codewords, to complex adaptation schemes including most-probable modes, and similar techniques. In all cases, however, 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. Summary of the Invention

[0018] Aspects of the disclosure provide a method and apparatus for video data encoding / decoding. In some examples, an apparatus for video decoding includes a receiving circuit and a processing circuit.

[0019] According to an aspect of the disclosure, a method of video decoding performed in a video decoder is provided. In the method, coded information of a current block in a current picture may be received from a coded video bitstream. The current block may be partitioned into a plurality of sub-blocks. A first flag included in the coded information may be obtained, and the first flag may indicate whether a Cross-Component Linear Model Prediction (CCLM) is applied to the current block, in which chroma samples of the current block are predicted based on reconstructed luma samples of the current block. In response to the first flag indicating that CCLM is applied to the current block, a predicted sample value of each of the chroma samples in each of a plurality of sub-blocks of the current block may be determined based on the CCLM. The current block may be further reconstructed based on the predicted sample value of each of the chroma samples in each of the plurality of sub-blocks of the current block.

[0020] In one example, the current block may be partitioned into multiple sub-blocks along the width direction based on the width of the current block being equal to or greater than the height of the current block.

[0021] In another example, the current block may be partitioned into multiple sub-blocks along the height direction based on the width of the current block being less than the height of the current block.

[0022] In yet another example, the current block may be partitioned into multiple sub-blocks of a minimum sub-block size along both the height and width directions.

[0023] In the method, a syntax element in the coded information may be determined. A minimum sub-block size may be determined based on the syntax element. The syntax element may be in one of a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice, and a tile.

[0024] In some embodiments, a predicted sample value of a chroma sample in a second sub-block of the plurality of sub-blocks may be determined based on a reconstructed sample of a first sub-block of the plurality of sub-blocks, the second sub-block being adjacent to the first sub-block.

[0025] In some embodiments, in response to the first flag indicating that CCLM is applied to the current block, a second flag included in the coded information may be obtained. The second flag may indicate whether CCLM is applied to each of the plurality of sub-blocks. In response to the second flag indicating that CCLM is applied to each of the plurality of sub-blocks, a predicted sample value for each of the chroma samples in each of the plurality of sub-blocks of the current block may be determined based on the CCLM.

[0026] In some embodiments, in response to the reconstructed neighboring sample being adjacent to a left side of a first subblock of the plurality of subblocks, a predicted sample value of a chroma sample in a first subblock of the plurality of subblocks may be determined based on a first mode of CCLM, the first mode of CCLM indicating that the predicted sample value of a chroma sample in the first subblock is determined based on a reconstructed neighboring sample adjacent to a left side of the first subblock. In response to the reconstructed neighboring sample being adjacent to a left side and an upper side of a second subblock of the plurality of subblocks, a predicted sample value of a chroma sample in a second subblock of the plurality of subblocks may be determined based on a second mode of CCLM, the second mode of CCLM indicating that the predicted sample value of a chroma sample in the second subblock is determined based on a reconstructed neighboring sample adjacent to a left side and an upper side of the second subblock.

[0027] In some embodiments, in response to the first flag indicating that CCLM is applied to the current block, a second flag included in the coded information may be obtained, the second flag indicating whether CCLM is applied to each of the plurality of sub-blocks. An index included in the coded information may be obtained, the index indicating a CCLM mode of the CCLM. The CCLM mode indicates which reconstructed neighboring samples are applied by the CCLM to generate a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks. In response to the second flag indicating that CCLM is applied to each of the plurality of sub-blocks and the index indicating a CCLM mode, a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks of the current block may be determined based on CCLM using the CCLM mode.

[0028] In some embodiments, in response to the index indicating a first CCLM mode, a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks may be determined based on reconstructed neighboring samples adjacent to the left and above of each one of the plurality of sub-blocks. In response to the index indicating a second CCLM mode, a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks may be determined based on reconstructed neighboring samples adjacent to the left and above of each one of the plurality of sub-blocks. In response to the index indicating a third CCLM mode, a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks may be determined based on reconstructed neighboring samples adjacent to the top of each one of the plurality of sub-blocks.

[0029] According to another aspect of the present disclosure, an apparatus is provided, the apparatus including a processing circuit, the processing circuit may be configured to perform any of the methods of video coding.

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

[0031] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0032] [Figure 1] FIG. 2 is a schematic diagram of an example subset of intra-prediction modes. [Diagram 2] FIG. 2 is an illustration of an exemplary intra-prediction direction. [Diagram 3] FIG. 1 is a schematic block diagram of a communication system (300) according to an embodiment. [Figure 4] FIG. 1 is a schematic block diagram of a communication system (400) according to an embodiment. [Diagram 5] FIG. 2 is a schematic block diagram of a decoder according to an embodiment; [Figure 6] FIG. 2 is a schematic block diagram of an encoder according to an embodiment. [Figure 7] 4 shows a block diagram of an encoder according to another embodiment; [Figure 8] 4 shows a block diagram of a decoder according to another embodiment; [Figure 9] 1 is an illustration of a cross-component linear model (CCLM) prediction according to some embodiments of the present disclosure. [Figure 10A] 1 is a first example block partition in CCLM prediction according to some embodiments of the present disclosure. [Figure 10B] 1 is a second example block partition in CCLM prediction according to some embodiments of the present disclosure. [Figure 10C] 11 is a third example block partition in CCLM prediction according to some embodiments of the present disclosure. [Figure 10D] 11 is a fourth example block partition in CCLM prediction according to some embodiments of the present disclosure. [Figure 11] 1 shows a flowchart illustrating an example decoding process according to some embodiments of the present disclosure. [Figure 12] 1 shows a flowchart illustrating an exemplary encoding process according to an embodiment of the present disclosure. [Figure 13] FIG. 1 is a schematic diagram of a computer system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] FIG. 3 illustrates a simplified block diagram of a communication system (300) according to an embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) 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.

[0034] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of coded video data that may occur, for example, 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.

[0035] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) may be represented as a server, a personal computer, and a smartphone, although the principles of the present disclosure may not be so limited. The embodiments of the present disclosure find use with laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. The network (350) represents any number of networks that convey coded video data between the terminal devices (310), (320), (330), and (340), including, for example, wireline and / or wireless communication networks. The 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 the network (350) may be irrelevant to the operation of the present disclosure, unless otherwise described hereinafter.

[0036] 4 illustrates the placement of a video encoder and a 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, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0037] 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 taken 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.

[0038] The electronics 420 and 430 may include other components (not shown). For example, the electronics 420 may include a video decoder (not shown), and the electronics 430 may also include a video encoder (not shown).

[0039] 5 shows a block diagram of a video decoder (510) according to an embodiment of the present disclosure. The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) of the example of FIG. 4.

[0040] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510), one coded video sequence at a time, in the same or other embodiments, with the decoding of each coded video sequence being independent 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 storing 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) (hereafter "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 can 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, advantageously of adaptive size, and at least partially implemented in an operating system or similar element (not shown) external to the video decoder (510).

[0041] The video decoder (510) may include a parser (520) 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) that 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 Supplemental 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 information from the coded video sequence, such as transform coefficients, quantizer parameter values, motion vectors, etc.

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

[0043] The reconstruction of the symbols (521) can have many different 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.

[0044] 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.

[0045] 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 which 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).

[0046] In some cases, the output samples of the scaler / inverse transformer (551) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) 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).

[0047] 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.

[0048] 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 contained in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to meta-information obtained during the decoding of previous portions (in decoding order) of the coded picture or coded video sequence, or even to previously constructed loop filtered sample values.

[0049] 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.

[0050] 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.

[0051] 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 a 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 must 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 levels may in some cases be further restricted through Hypothetical Reference Decoder (HRD) specifications and metadata for HRD buffer management signaled in the coded video sequence.

[0052] In an embodiment, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may 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.

[0053] 6 shows a block diagram of a video encoder (603) according to an embodiment of the present disclosure. The video encoder (603) is included in an electronic device (620). The electronic device (620) includes a transmitter (640) (e.g., a transmission circuit). The video encoder (603) may be used in place of the example video encoder (403) of FIG. 4.

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

[0055] The video source (601) may provide a source video sequence to be coded by the video encoder (603) in the form of a digital video sample stream that 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 pre-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.

[0056] 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 required by the application. 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. Couplings are 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.

[0057] 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 (given that any compression between the symbols and the coded video stream is lossless in the video compression techniques contemplated in the disclosed subject matter). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since the decoding of the symbol stream produces bit-perfect 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 prediction part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder will "see" when using the prediction during decoding. This basic principle of reference picture synchronicity (and the resulting drift when synchronicity cannot be maintained, e.g., due to channel errors) is also used in several related technologies.

[0058] 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, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (520) can be lossless, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633).

[0059] At this point, it can be observed that any decoder technique, other than parsing / entropy decoding, present in the decoder must necessarily be present in roughly the same functional form in the corresponding encoder. For this reason, the disclosed subject matter focuses on the operation of the decoder. Descriptions of the encoder techniques may be omitted, since they are the inverse of the decoder techniques described generically. Only to certain extents are more detailed descriptions required, which are given below.

[0060] 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 a video sequence designated as "reference pictures." In this manner, the coding engine (632) codes differences between pixel blocks of the reference pictures and pixel blocks of the input picture that may be selected as predictive references for the input picture.

[0061] The local video decoder (633) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols 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).

[0062] 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).

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

[0064] The output of all the 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 losslessly compressing the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0065] The transmitter (640) may buffer the coded video sequence 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).

[0066] 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:

[0067] 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.

[0068] A Predictive Picture (P-picture) may be a picture that can be encoded and decoded by intra- or inter-prediction using at most one motion vector and reference index to predict the sample values ​​of each block.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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, VUI parameter set fragments, etc.

[0073] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits correlation (temporal or other) between pictures. In an example, a particular picture being coded / decoded, called the current picture, is partitioned into blocks. If a block in the current picture is similar to a reference block in a reference picture that was coded earlier in the video and 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.

[0074] 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.

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

[0076] According to some embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed on a block-by-block basis. For example, 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 quad-tree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In an example, each CU is analyzed to determine a prediction type for that CU, such as an inter prediction type or an intra prediction type. A CU is divided into one or more Prediction Units (PUs) according to temporal and / or spatial predictability. In general, each PU includes 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.

[0077] 7 shows a diagram of a video encoder (703) according to another embodiment of the disclosure. 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.

[0078] 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.

[0079] In the example of FIG. 7, the video encoder (703) includes an inter-encoder (730), an intra-encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy encoder (725), coupled as shown in FIG.

[0080] The inter-encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in a previous picture and a subsequent picture), generate inter-prediction information (e.g., a description of redundant information according to an inter-coding technique, motion vectors, merge mode information), and calculate an inter-prediction result (e.g., a predicted block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the coded video information.

[0081] 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.

[0082] 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.

[0083] 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 and 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 and 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.

[0084] 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.

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

[0086] In the example of FIG. 8, the video decoder (810) includes an entropy decoder (871), an inter decoder (880), a residual decoder (873), a reconstruction module (874), and an intra decoder (872), coupled as shown in FIG.

[0087] 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, for example, prediction information (e.g., intra- or inter-prediction information) that may identify the mode in which the block is coded (e.g., intra- or bi-prediction mode in merge or other submodes), the specific samples or metadata used for prediction by the intra decoder (872) or the inter decoder (880), respectively, residual information in the form of, for example, quantized transform coefficients, etc. 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).

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

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

[0090] 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).

[0091] The reconstruction module (874) is configured to combine the residual 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. Note that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0092] It should be noted that the video encoders (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.

[0093] The present disclosure includes cross-component linear model prediction of sub-blocks.

[0094] ITU-T VCEG (Q6 / 16) and ISO / IEC MPEG (JTC 1 / SC 29 / WG 11) published the H.265 / HEVC (High Efficiency Video Coding) standard in 2013 (version 1), 2014 (version 2), 2015 (version 3), and 2016 (version 4). In 2015, the two standard organizations jointly organized the Joint Video Exploration Team (JVET) to explore the possibility of developing the next video coding standard beyond HEVC. In April 2018, JVET officially launched the standardization process for the next generation video coding beyond HEVC. The new standard was named Versatile Video Coding (VVC), and JVET was renamed Joint Video Expert Team. In July 2020, H.266 / VCC version 1 was finalized. In January 2021, an ad-hoc group was formed to study enhanced compression beyond VVC capabilities.

[0095] To reduce cross-component redundancy, a cross-component linear model (CCLM) prediction mode may be used, such as in VVC. In the CCLM prediction mode, the chroma samples of the current CU may be predicted based on the reconstructed luma samples of the current CU by using a linear model in equation (1) as follows: pred C (i,j)=α·rec L '(i,j)+β Equation (1) Here, pred C (i,j) may represent the predicted chroma sample in the current CU, and rec L(i,j) may represent the downsampled reconstructed luma samples of the current CU. The chroma CU may be smaller in size than the luma CU when the chroma subsampling is different from the luma subsampling, such as in YCbCr422 or YCbCr420 formats. Downsampling the reconstructed luma samples in the current CU may match the luma samples one-to-one.

[0096] The CCLM parameters (e.g., α and β) may be derived using at most four neighboring chroma samples and the corresponding downsampled luma samples of the neighboring chroma samples. If the current chroma block has a size of W×H, where W is the width of the current chroma block and H is the height of the current chroma block, the width W′ of the first reference region and the height H′ of the second reference region may be defined as follows: When LM mode is applied, W'=W, H'=H; When the LM-A mode is applied, W'=W+H; and When LM-L mode is applied, H'=H+W. The first reference region may be adjacent to the top side of the current chroma block. The height H'' of the second reference region may be adjacent to the left side of the current chroma block. In LM mode, the neighboring chroma samples may be located in both the first reference region and the second reference region. In LM-A mode, the neighboring chroma samples may be located in the first reference region. In LM-L mode, the neighboring chroma samples may be located in the second reference region.

[0097] Thus, the top neighbor position (or the position of the first reference region) can be expressed as S[0,-1] · · · S[W'-1,-1], and the left neighbor position (or the position of the second reference region) can be expressed as S[-1,0] · · · S[-1,H'-1]. Thus, the positions of the four neighboring chroma samples are: S[W' / 4,-1],S[3×W' / 4,-1],S[-1,H' / 4],S[-1,3×H' / 4] when LM mode is applied and both top and left adjacent samples are available; S[W' / 8,-1],S[3×W' / 8,-1],S[5×W' / 8,-1],S[7×W' / 8,-1] when LM-A mode is applied or only upper adjacent samples are available; S[-1,H' / 8], S[-1,3×H' / 8], S[-1,5×H' / 8], S[-1,7×H' / 8] when LM-L mode is applied or only left adjacent samples are available.

[0098] The four luma samples corresponding to the four neighboring chroma samples at the selected position are the larger of the two, x 0 A and x 1 A and the two smaller values ​​of x 0 B and x 1 B The chroma sample values ​​of the four neighboring chroma samples corresponding to the four luma samples are 0 A , y 1 A , y 0 B , and y 1 B The parameters Xa, Xb, Ya, and Yb can be derived from equations (2) to (5) as follows: Xa = (x 0 A +x 1 A +1)>>1 Formula (2) Xb = (x 0 B +x 1 B +1)>>1 Formula (3) Ya = (y 0 A +y1 A +1)>>1 Formula (4) Yb = (y 0 B +y 1 B +1)>>1 Formula (5)

[0099] Finally, the linear model parameters α and β can be obtained according to equations (6) and (7), respectively: α=(Ya-Yb) / (Xa-Xb) Equation (6) β=Yb-αXb Equation (7)

[0100] FIG. 9 illustrates an example location of the left and top neighboring samples of a current block, as well as the samples of the current block involved in the CCLM prediction mode. As illustrated in FIG. 9, a current chroma CU (902) may have a size of N×N (e.g., 8×8). A corresponding luma CU (904) of the current chroma CU (902) may have a size of 2N×2N (e.g., 16×16). Neighboring chroma samples of the current chroma CU (902) for deriving the linear model parameters α and β may be located in a first reference area (or top neighboring position) (906) and / or a second reference area (or left neighboring position) (908). Luma samples corresponding to the neighboring chroma samples (906) and (908) may be located in a first reference area (910) and a second reference area (912), respectively. As illustrated in FIG. 9, the luma samples (910) and (912) are downsampled to match the neighboring chroma samples one-to-one. The reconstructed values ​​Rec' of the luma samples (910) and (912) L and the reconstructed values ​​Rec of the neighboring chroma samples (906) and (908). Cmay be applied to derive the linear model parameters α and β based on equations (2)-(7). Once the linear model parameters α and β are obtained, chroma samples in the current chroma CU (902) may be predicted based on the downsampled reconstructed luma samples in the corresponding luma CU (904) using CCLM prediction.

[0101] Table 1 shows an example syntax of CCLM prediction. First, a CCLM mode flag (e.g., cclm_mode_flag) may be parsed (or coded) to determine whether a CCLM prediction mode is currently applied to the CU. When the CCLM mode flag (e.g., cclm_mode_flag) is 1 (or true), it indicates that a CCLM prediction mode is currently applied to the CU. A CCLM mode index (e.g., cclm_mode_idx) may be parsed to determine which CCLM mode is currently applied to the CU. The CCLM modes may include, but are not limited to, LM, LM-A, and LM-L. LM may use both left and top reference samples to derive linear model parameters α and β. LM-A may use top reference samples, and LM-L may use left reference samples to derive linear model parameters α and β. LM-A may use top reference samples, and LM-L may use left reference samples to derive linear model parameters α and β. [Table 1]

[0102] Chroma CUs to which CCLM has been applied (or intra-coded by CCLM) may have spatial correlation between spatial neighbors, so having (or deciding) a larger CU as a CCLM block containing sub-blocks therein can save signaling overhead and improve coding efficiency.

[0103] In this disclosure, a CU may include sub-blocks within the CU, and all sub-blocks may be CCLM coded.

[0104] In an embodiment, the partitions may be based on the size of the CU, such as the width and / or height of the CU. Thus, only one type of partition (e.g., horizontal or vertical) may be used for a CU. For example, if the width of the CU is equal to or greater than the height of the CU, the CU may be partitioned vertically as shown in FIG. 10A. As shown in FIG. 10A, the CU (1002) may be partitioned into multiple sub-blocks with indexes 0 to 3 along the width of the CU (1002). In another example, if the width of the CU is less than the height of the CU, the CU may be partitioned horizontally as shown in FIG. 10B. As shown in FIG. 10B, the CU (1004) may be partitioned into multiple sub-blocks with indexes 0 to 1 along the height of the CU (1004).

[0105] In other embodiments, the partitions may be based on a minimum subblock size, which may be defined as minSubblockCCLM for CCLM. The value of the minimum subblock size (e.g., minSubblockCCLM) may be predefined in the encoder and decoder without explicit signaling. Alternatively, the minimum subblock size (e.g., minSubblockCCLM) may be signaled. For example, the minimum subblock size may be signaled in a high-level syntax, such as in a sequence parameter set (SPS), picture parameter set (PPS), slice, or tile. Based on the value of the minimum subblock size (e.g., minSubblockCCLM), the CU may be partitioned both horizontally and / or vertically. For example, if a CU (1006) has a width of 4 and a height of 8, and the value of the minimum subblock size (e.g., minSubblockCCLM) is 2 (or 2×2), then the CU (1006) may be partitioned into 8 subblocks both horizontally and vertically. This may be shown in FIG. 10C.

[0106] In this disclosure, subblock prediction (or prediction for a subblock) may be based on reconstructed values ​​of previously decoded subblocks. Subblock prediction may be performed in a raster scan order, which may be shown in FIG. 10D. For each subblock, a reconstructed sample may be obtained by adding a redundancy signal to a prediction signal. The redundancy signal may be generated by a process that may include entropy decoding, inverse quantization, inverse transform, and / or the like. Thus, the reconstructed sample values ​​of a previous subblock may be available to generate a prediction sample value of a subsequent subblock.

[0107] In an embodiment, a sub-block of a current CU, such as a sub-block with index 0 in FIG. 10A, may use a reference sample (not shown) of the current CU to perform CCLM. Thus, the linear model parameters α and β may be derived from the reference sample of the current CU. Similarly, a subsequent sub-block, such as a sub-block with index 1 in FIG. 10A, may use a reconstructed sample of a previous sub-block, such as a sub-block with index 0, as a reference sample for performing CCLM. The linear model parameters α and β may be derived based on the reconstructed sample of the sub-block with index 0. Furthermore, a sub-block with index 2 may use a reconstructed sample of a sub-block with index 1 as a reference sample for performing CCLM. A sub-block with index 3 may use a reconstructed sample of a sub-block with index 2 as a reference sample for performing CCLM.

[0108] In this disclosure, the CCLM mode (e.g., LM, LM-A, or LM-L) of sub-blocks in a CU can be the same. In other words, when a CCLM mode is signaled using a CCLM mode index (e.g., cclm_mode_idx) as shown in Table 2, all sub-blocks in the CU can apply that CCLM mode. [Table 2]

[0109] As shown in Table 2, the CCLM mode flag (e.g., cclm_mode_flag) may be parsed (or coded) to determine whether CCLM applies to the current CU. If the CCLM mode flag (e.g., cclm_mode_flag) is 1 (or true), the CCLM subblock flag (e.g., cclm_subblock_flag) and the CCLM mode index (e.g., cclm_mode_idx) may be further parsed. The CCLM subblock flag may indicate whether CCLM applies to the subblock of the current CU. The CCLM mode index may indicate the CCLM mode (e.g., LM, LM-A, and LM-L) of the CCLM. When the CCLM subblock flag (e.g., cclm_subblock_flag) is equal to 1 (or true), CCLM applies to the subblock of the current CU. Otherwise, if the CCLM subblock flag is not 1, CCLM may not apply to the subblock of the current CU. The CCLM mode index (e.g., cclm_mode_idx) can be parsed to indicate which CCLM mode is currently applied to the CU (or sub-block). Thus, when the CCLM sub-block flag is not 1, the CCLM mode index can indicate which CCLM mode is currently applied to the CU. When the CCLM sub-block flag is 1, the CCLM mode index can indicate which CCLM mode is currently applied to all sub-blocks of the CU.

[0110] In this disclosure, the CCLM mode for a sub-block or each sub-block in a CU may depend on the availability of reference samples for the respective sub-block.

[0111] In an embodiment, as shown in FIG. 10D, the gray area (1010) adjacent to the left side of the current block (1008) may represent available reference samples of the current block (1008), and the blank area (1012) adjacent to the top side of the current block (1008) may represent unavailable reference samples of the current block (1008). Thus, the sub-block with index 0 may only have an available left reference sample. Thus, CCLM mode LM-L may be used to derive linear model parameters α and β for the sub-block with index 0. For the sub-block with index 4, both the left reference sample and the top reference sample are available. Thus, the sub-block with index 0 may use CCLM mode LM.

[0112] In an embodiment, the CCLM mode index (e.g., cclm_mode_idx) may not be signaled in the case of a CCLM CU (or a CCLM-applied CU) that includes a sub-block CCLM (or a CCLM-applied sub-block). The CCLM mode applied to each sub-block in a CCLM CU may depend on the available reference samples of each sub-block. Exemplary pseudocode for skipping the CCLM mode index in the case of a CCLM CU that includes a sub-block CCLM may be shown in Table 3. [Table 3]

[0113] As shown in Table 3, the CCLM mode flag (e.g., cclm_mode_flag) may be parsed (or coded) to determine whether CCLM is applied to the current CU. If the CCLM mode flag (e.g., cclm_mode_flag) is 1 (or true), the CCLM subblock flag (e.g., cclm_subblock_flag) may be further parsed. When the CCLM subblock flag (e.g., cclm_subblock_flag) is equal to 1, it indicates that CCLM is applied to the subblock. In addition, the CCLM mode applied to each of the subblocks may depend on the available reference samples of each subblock. Otherwise, when the CCLM subblock flag is not equal to 1, it indicates that CCLM is not applied to the subblock.

[0114] In other embodiments, the CCLM sub-block flag (e.g., cclm_subblock_flag) may not be signaled and may always be assumed to be true. Thus, CCLM may also be applied to the sub-blocks of the current CU when the CCLM mode flag (e.g., cclm_mode_flag) is equal to 1. Furthermore, the CCLM mode applied to each of the sub-blocks may depend on the available reference samples of each sub-block.

[0115] FIG. 11 shows a flow chart illustrating an exemplary decoding process (1100) according to some embodiments of the present disclosure. FIG. 12 shows a flow chart illustrating an exemplary encoding process (1200) according to some embodiments of the present disclosure. The proposed processes may be used separately or combined in any order. Furthermore, each of the processes (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.

[0116] In embodiments, the operations of any of the processes (e.g., 1100 and 1200) may be combined or arranged in any amount or order as desired. In embodiments, two or more of the operations of the processes (e.g., 1100 and 1200) may be performed in parallel.

[0117] The processes (e.g., 1100 and 1200) may be used in the reconstruction and / or encoding of a block to generate a prediction block for the block being reconstructed. In various embodiments, the processes (e.g., 1100 and 1200) are performed by processing circuitry, such as the processing circuitry of terminal devices (310), (320), (330), and (340), processing circuitry performing the functions of a video encoder (403), processing circuitry performing the functions of a video decoder (410), processing circuitry performing the functions of a video decoder (510), processing circuitry performing the functions of a video encoder (603), etc. In some embodiments, the processes (e.g., 1100 and 1200) are implemented with software instructions, such that the processing circuitry performs the processes (e.g., 1100 and 1200) when the processing circuitry executes the software instructions.

[0118] As shown in Figure 11, the process (1100) may begin at (S1101) and proceed to (S1110), where coded information for a current block in a current picture may be received from a coded video bitstream.

[0119] At (S1120), the current block may be partitioned into multiple sub-blocks.

[0120] At (S1130), a first flag included in the coded information may be obtained, and the first flag may indicate whether cross-component linear model prediction (CCLM) is applied to the current block and chroma samples of the current block are predicted based on reconstructed luma samples of the current block.

[0121] At (S1140), in response to the first flag indicating that CCLM is applied to the current block, a predicted sample value for each of the chroma samples in each of a plurality of sub-blocks of the current block may be determined based on the CCLM.

[0122] At (S1150), the current block may be further reconstructed based on the predicted sample values ​​of each of the chroma samples in each of the multiple sub-blocks of the current block.

[0123] In one example, the current block may be partitioned into multiple sub-blocks along the width direction based on the width of the current block being equal to or greater than the height of the current block.

[0124] In another example, the current block may be partitioned into multiple sub-blocks along the height direction based on the width of the current block being less than the height of the current block.

[0125] In yet another example, the current block may be partitioned in both height and width into multiple sub-blocks of a minimum sub-block size.

[0126] In the process (1100), a syntax element in the coded information may be determined. A minimum sub-block size may be determined based on the syntax element. The syntax element may be one of a sequence parameter set (SPS), a picture parameter set (PPS), a slice, and a tile.

[0127] In some embodiments, a predicted sample value of a chroma sample in a second sub-block of the plurality of sub-blocks may be determined based on a reconstructed sample of a first sub-block of the plurality of sub-blocks, the second sub-block being adjacent to the first sub-block.

[0128] In some embodiments, in response to the first flag indicating that CCLM is applied to the current block, a second flag included in the coded information may be obtained. The second flag may indicate whether CCLM is applied to each of the plurality of sub-blocks. In response to the second flag indicating that CCLM is applied to each of the plurality of sub-blocks, a predicted sample value for each of the chroma samples in each of the plurality of sub-blocks of the current block may be determined based on the CCLM.

[0129] In some embodiments, in response to the reconstructed neighboring sample being adjacent to a left side of a first subblock of the plurality of subblocks, a predicted sample value of a chroma sample in a first subblock of the plurality of subblocks may be determined based on a first mode of CCLM, the first mode of CCLM may indicate that the predicted sample value of a chroma sample in the first subblock is determined based on a reconstructed neighboring sample adjacent to a left side of the first subblock. In response to the reconstructed neighboring sample being adjacent to a left side and an upper side of a second subblock of the plurality of subblocks, a predicted sample value of a chroma sample in a second subblock of the plurality of subblocks may be determined based on a second mode of CCLM, the second mode of CCLM may indicate that the predicted sample value of a chroma sample in the second subblock is determined based on a reconstructed neighboring sample adjacent to a left side and an upper side of the second subblock.

[0130] In some embodiments, in response to the first flag indicating that CCLM is applied to the current block, a second flag included in the coded information may be obtained, and the second flag may indicate whether CCLM is applied to each of the plurality of sub-blocks. An index included in the coded information may be obtained, and the index may indicate a CCLM mode of the CCLM. The CCLM mode may indicate which reconstructed neighboring samples are applied by the CCLM to generate a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks. In response to the second flag indicating that CCLM is applied to each of the plurality of sub-blocks and the index indicating a CCLM mode, the predicted sample value of the chroma sample in each of the plurality of sub-blocks of the current block may be determined based on CCLM using the CCLM mode.

[0131] In some embodiments, in response to the index indicating a first CCLM mode, a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks may be determined based on reconstructed neighboring samples adjacent to the left and above of each one of the plurality of sub-blocks. In response to the index indicating a second CCLM mode, a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks may be determined based on reconstructed neighboring samples adjacent to the left and above of each one of the plurality of sub-blocks. In response to the index indicating a third CCLM mode, a predicted sample value of each of the chroma samples in each of the plurality of sub-blocks may be determined based on reconstructed neighboring samples adjacent to the top of each one of the plurality of sub-blocks.

[0132] As shown in Figure 12, the process (1200) may start at (S1201) and proceed to (S1210), where a current block in a current picture may be partitioned into multiple sub-blocks.

[0133] At (S1220), a predicted sample value of each of the chroma samples in each of a plurality of sub-blocks of the current block may be determined based on a cross-component linear model prediction (CCLM) in which the chroma samples of the current block are predicted based on the reconstructed luma samples of the current block.

[0134] At (S1230), intra prediction may be performed on the current block based on predicted sample values ​​of each of the chroma samples in each of the multiple sub-blocks of the current block.

[0135] At (S1240), a first flag may be generated to indicate that CCLM applies to multiple sub-blocks of the current block.

[0136] The above techniques may be implemented as computer software using computer-readable instructions and physically stored on one or more computer-readable media. For example, Figure 13 illustrates a computer system (1300) suitable for implementing certain embodiments of the disclosed subject matter.

[0137] Computer software can be coded in any suitable machine code or computer language that can be subject to mechanisms such as assembly, compilation, linking, etc. to generate code including instructions that can be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., directly, or through interpretation, microcode execution, etc.

[0138] The instructions may be executable by various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smart phones, gaming consoles, Internet of Things devices, and the like.

[0139] 13 for computer system (1300) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of computer system (1300).

[0140] The computer system (1300) 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., keystrokes, 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).

[0141] The input human interface devices may include one or more of a keyboard (1301), a mouse (1302), a trackpad (1303), a touch screen (1310), a data glove (not shown), a joystick (1305), a microphone (1306), a scanner (1307), and a camera (1308) (only one of each is shown).

[0142] The computer system 1300 may also include certain human interface output devices, such as those that stimulate one or more of the user's senses through 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 (1310), data gloves (not shown), or joystick (1305), although there may also be haptic feedback devices that do not function as input devices), audio output devices (e.g., speakers (1309), headphones (not shown)), visual output devices (e.g., screens (1310) 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).

[0143] The computer system (1300) may also include human accessible storage devices and their associated media, such as CD / DVD ROM / RW (1320) with CD / DVD or similar media (1321), thumb drives (1322), removable hard disks or solid state drives (1323), 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.

[0144] 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.

[0145] The computer system (1300) may also include an interface (1354) to one or more communication networks (1355). 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 CANBus, etc. Certain networks generally require an external network interface adapter attached to a particular general-purpose data port or peripheral bus (1349) (e.g., a USB port of the computer system (1300)). Others are generally built into the core of the computer system (1300) 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 (1300) can communicate with other entities. Such communications can be one-way receive-only (e.g., broadcast TV) or one-way transmit-only (e.g., CANBus to a specific CANBus device), or can be bidirectional to other computer systems, for example, using local or wide area digital networks. Specific protocols or protocol stacks can be used with each of the networks and network interfaces as described above.

[0146] The above-mentioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (1340) of the computer system (1300).

[0147] The cores (1340) may include one or more central processing units (CPUs) (1341), graphics processing units (GPUs) (1342), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (1343), hardware accelerators for specific tasks (1344), graphics adapters (1350), etc. These devices may be connected through a system bus (1348), along with read only memory (ROM) (1345), random access memory (RAM) (1346), internal mass storage devices such as internal non-user accessible hard drives, SSDs, etc. (1347). In some computer systems, the system bus (1348) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be attached directly to the core's system bus (1348) or through a peripheral bus (1349). In one example, a screen 1310 may be connected to a graphics adapter 1350. Architectures for peripheral buses include PCI, USB, etc.

[0148] The CPU (1341), GPU (1342), FPGA (1343), and accelerator (1344) can execute certain instructions that, in combination, may constitute the above computer code. The computer code may be stored in a ROM (1345) or a RAM (1346). Temporary data may also be stored in the RAM (1346), while persistent data may be stored, for example, in an internal mass storage device (1347). Rapid storage and retrieval from any of the memory devices is made possible through the use of a cache memory. A cache memory may be closely associated with one or more of the CPU (1341), GPU (1342), mass storage device (1347), ROM (1345), RAM (1346), etc.

[0149] 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.

[0150] By way of example, and not by way of limitation, a computer system having the architecture (1300), and in particular the core (1340), 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 (1340) that is non-transitory in nature, such as the core's internal mass storage (1347) or ROM (1345). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (1340). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (1340), 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 (1346) 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 hardwired or otherwise embodied logic in circuitry (e.g., accelerators (1344)) 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 appropriate combination of hardware and software.

[0151] 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

[0152] 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.

Claims

1. 1. A method of video decoding performed by a video decoder, comprising: receiving coded information for a current block in a current picture from a coded video bitstream; partitioning the current block into a plurality of sub-blocks; obtaining a first flag included in the coded information, the first flag indicating whether a cross-component linear model prediction (CCLM) is applied to the current block, in which chroma samples of the current block are predicted based on reconstructed luma samples of the current block; determining a predicted sample value for each of the chroma samples in each of the plurality of sub-blocks of the current block based on the CCLM in response to the first flag indicating that the CCLM is applied to the current block; reconstructing the current block based on the respective predicted sample values ​​of the chroma samples in each of the plurality of sub-blocks of the current block; The method according to claim 1,

2. The step of partitioning the current block comprises: partitioning the current block into the sub-blocks along a width direction based on a width of the current block being equal to or greater than a height of the current block; The method of claim 1.

3. The step of partitioning the current block comprises: partitioning the current block into the sub-blocks along a height direction based on a width of the current block being smaller than a height of the current block; The method of claim 1.

4. The step of partitioning the current block comprises: partitioning the current block along both a height direction and a width direction into the plurality of sub-blocks of a minimum sub-block size; The method of claim 1.

5. obtaining a syntax element in the coded information; determining the minimum sub-block size based on the syntax elements; Further comprising: The syntax element is in one of a sequence parameter set (SPS), a picture parameter set (PPS), a slice, and a tile. The method according to claim 4.

6. The determining step includes: determining the predicted sample values ​​of the chroma samples in a second sub-block of the plurality of sub-blocks based on reconstructed samples of a first sub-block of the plurality of sub-blocks; The second sub-block is adjacent to the first sub-block. The method of claim 1.

7. The determining step includes: in response to the first flag indicating that the CCLM applies to the current block, obtaining a second flag included in the coded information, the second flag indicating whether the CCLM is applied to each of the plurality of sub-blocks; determining the respective predicted sample values ​​of the chroma samples in each of the plurality of sub-blocks of the current block based on the CCLM in response to the second flag indicating that the CCLM is applied to each of the plurality of sub-blocks; Further comprising The method of claim 1.

8. The step of determining each predicted sample value comprises: determining a predicted sample value of the chroma sample in the first sub-block of the plurality of sub-blocks based on a first mode of the CCLM in response to a reconstructed neighboring sample being adjacent to a left side of a first sub-block of the plurality of sub-blocks, the first mode of the CCLM indicating that the predicted sample value of the chroma sample in the first sub-block is determined based on the reconstructed neighboring sample being adjacent to a left side of the first sub-block; determining a predicted sample value of the chroma sample in the second sub-block of the plurality of sub-blocks based on a second mode of the CCLM in response to the reconstructed neighboring samples being adjacent to a left side and an upper side of a second sub-block of the plurality of sub-blocks, the second mode of the CCLM indicating that the predicted sample value of the chroma sample in the second sub-block is determined based on the reconstructed neighboring samples being adjacent to a left side and an upper side of the second sub-block; Further comprising The method according to claim 7.

9. The determining step includes: in response to the first flag indicating that the CCLM applies to the current block, obtaining a second flag included in the coded information, the second flag indicating whether the CCLM is applied to each of the plurality of sub-blocks; obtaining an index included in the coded information, the index indicating a CCLM mode of the CCLM, the CCLM mode indicating which reconstructed neighboring samples are applied by the CCLM to generate the respective predicted sample values ​​of the chroma samples in each of the plurality of sub-blocks; determining the respective predicted sample values ​​of the chroma samples in each of the sub-blocks of the current block based on the CCLM using the CCLM mode in response to the second flag indicating that the CCLM is applied to each of the sub-blocks and the index indicating the CCLM mode; Further comprising The method of claim 1.

10. The determining step includes: determining, in response to the index indicating a first CCLM mode, the predicted sample value of each of the chroma samples in each of the plurality of sub-blocks based on reconstructed neighboring samples adjacent to the left and above a respective one of the plurality of sub-blocks; determining, in response to the index indicating a second CCLM mode, the predicted sample value of each of the chroma samples in each of the plurality of sub-blocks based on a reconstructed left neighboring sample of a respective one of the plurality of sub-blocks; determining, in response to the index indicating a third CCLM mode, the predicted sample value of each of the chroma samples in each of the plurality of sub-blocks based on a reconstructed neighboring sample adjacent to an upper side of a respective one of the plurality of sub-blocks; Further comprising 10. The method of claim 9.

11. at least one memory configured to store program code; processing circuitry configured to read the program code and to operate as directed by the program code; having Apparatus, wherein the program code, when executed by the processing circuitry, causes the processing circuitry to perform a method according to any one of claims 1 to 10.

12. 1. A method of video encoding performed by a video encoder, comprising: partitioning a current block in a current picture of a video into a plurality of sub-blocks; determining predicted sample values ​​for each of the chroma samples in each of the plurality of sub-blocks of the current block based on a cross-component linear model prediction (CCLM) in which the chroma samples of the current block are predicted based on reconstructed luma samples of the current block; performing intra prediction on the current block based on the predicted sample values ​​of the chroma samples in each of the plurality of sub-blocks of the current block; generating a first flag indicating that the CCLM applies to the plurality of sub-blocks of the current block, and encoding information including the first flag into a coded video bitstream; The method according to claim 1,

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