Method and apparatus for video coding in 4:4:4 chroma format

Abstract

To provide a system and method for improving encoding efficiency of video encoded in a particular chroma format.SOLUTION: The decoding method includes receiving video data corresponding to a coding unit that is coded in an inter prediction mode or an intra block copy mode, receiving a first syntax element from the video data, the first syntax element indicating whether the coding unit has a residue other than zero, receiving a second syntax element from the video data according to a determination that the first syntax element has a value other than zero, the second syntax element indicating whether the coding unit is coded using adaptive color space transform (ACT), receiving a second syntax element from the video data according to a determination that the first syntax element has a value of zero, and assigning a value of zero to the second syntax element.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 62 / 904,539, filed September 23, 2019, and entitled "METHODS AND APPARATUS OF VIDEO CODING IN 4:4:4 CHROMA FORMAT," which is incorporated by reference in its entirety.

[0002] This application relates generally to encoding and compressing video data, and more particularly to a method and system for improving the coding efficiency of video encoded in 4:4:4 chroma format. [Background technology]

[0003] Digital video is supported by a variety of electronic devices, such as digital televisions, laptop or desktop computers, tablet computers, digital cameras, digital recording devices, digital media players, video game consoles, smartphones, video teleconferencing devices, video streaming devices, etc. Electronic devices transmit, receive, encode, decode, and / or store digital video data by implementing video compression / decompression standards such as those defined by the MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4, Part 10, Advanced Video Coding (AVC), High Efficiency Video Coding (HEVC), and Versatile Video Coding (VVC) standards. Video compression typically involves performing spatial (intra-frame) prediction and / or temporal (inter-frame) prediction to reduce or remove redundancy inherent in the video data. In block-based video coding, a video frame is partitioned into one or more slices, each of which has multiple video blocks, sometimes referred to as coding tree units (CTUs). Each CTU may contain one coding unit (CU) or may be recursively divided into smaller CUs until a predetermined minimum CU size is reached. Each CU (also called a leaf CU) contains one or more transform units (TUs), and each CU also contains one or more prediction units (PUs). Each CU may be coded in either intra, inter, or IBC mode. Video blocks in an intra-coded (I) slice of a video frame are coded using spatial prediction with respect to reference samples in neighboring blocks within the same video frame. Video blocks in an inter-coded (P or B) slice of a video frame may use spatial prediction with respect to reference samples in neighboring blocks within the same video frame or temporal prediction with respect to reference samples in other earlier and / or later reference video frames.

[0004] Spatial or temporal prediction based on previously coded reference blocks, e.g., neighboring blocks, results in a predicted block for the current video block being coded. The process of finding the reference block may be accomplished by a block matching algorithm. Residual data representing pixel differences between the current block being coded and the predicted block is referred to as a residual block or prediction error. Inter-coded blocks are coded according to motion vectors that point to reference blocks in reference frames that form the predicted block, and the residual block. The process of determining the motion vector is typically referred to as motion estimation. Intra-coded blocks are coded according to an intra-prediction mode and the residual block. For further compression, the residual block may be transformed from the pixel domain to a transform domain, e.g., the frequency domain, resulting in residual transform coefficients, which may then be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, are scanned to produce a one-dimensional vector of transform coefficients, which may then be entropy coded into a video bitstream to achieve further compression.

[0005] The encoded video bitstream is then stored in a computer-readable storage medium (e.g., flash memory) for access by another electronic device having digital video capabilities or for transmission directly to the electronic device via wired or wireless connection. The electronic device then performs video decompression (the opposite process to video compression described above), for example, by parsing the encoded video bitstream to obtain syntax elements from the bitstream, reconstructing digital video data from the encoded video bitstream into its original form based at least in part on the syntax elements obtained from the bitstream, and rendering the reconstructed digital video data on a display of the electronic device.

[0006] As digital video quality increases from high definition to 4Kx2K or even 8Kx4K, the amount of video data to be encoded / decoded increases exponentially, which poses a constant challenge as to how the video data can be encoded / decoded more efficiently while maintaining the image quality of the decoded video data.

[0007] Certain video content, such as screen content video, is encoded in a 4:4:4 chroma format in which all three components (one luma component and two chroma components) have the same resolution. Although the 4:4:4 chroma format contains additional redundancy compared to the 4:2:0 chroma format and the 4:2:2 chroma format (which is unfavorable for achieving good compression efficiency), the 4:4:4 chroma format is still the preferred encoding format for many applications where high fidelity is required to maintain color information, such as sharp edges, in the decoded video. Given the redundancy present in 4:4:4 chroma format video, there is evidence that significant coding improvements can be achieved by exploiting the correlations between the three color components of 4:4:4 video (e.g., Y, Cb, and Cr in the YCbCr domain, or G, B, and R in the RGB domain). Due to these correlations, adaptive color space conversion (ACT) tools are used to exploit the correlations between the three color components during the development of the Screen Content Coding (SCC) extension to HEVC. Summary of the Invention [Problem to be solved by the invention]

[0008] This application describes implementations relating to systems and methods for improving the coding efficiency of video data encoding and decoding, and more particularly, video encoded in a particular chroma format. [Means for solving the problem]

[0009] According to a first aspect of the present application, a method for decoding video data includes receiving video data corresponding to a coding unit from a bitstream, the coding unit being coded in an inter prediction mode or an intra block copy mode; receiving a first syntax element from the video data, the first syntax element indicating whether the coding unit has a non-zero residual; receiving a second syntax element from the video data in accordance with a determination that the first syntax element has a non-zero value, the second syntax element indicating whether the coding unit is coded using adaptive color space transformation (ACT); assigning a value of 0 to the second syntax element in accordance with a determination that the first syntax element has a value of 0; and determining whether to perform inverse ACT on the video data of the coding unit in accordance with the value of the second syntax element.

[0010] According to a second aspect of the present application, an electronic device includes one or more processing units, a memory, and a plurality of programs stored in the memory, the programs, when executed by the one or more processing units, causing the electronic device to perform the method for decoding video data described above.

[0011] According to a third aspect of the present application, a non-transitory computer-readable storage medium stores a plurality of programs for execution by an electronic device having one or more processing units, the programs, when executed by the one or more processing units, causing the electronic device to perform the method for decoding video data described above.

[0012] The accompanying drawings, which are included to provide a further understanding of the implementations and which are incorporated in and constitute a part of this specification, illustrate the described implementations and, together with the description, serve to explain the underlying principles, and like reference numerals refer to corresponding parts. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 is a block diagram illustrating an example video encoding and decoding system according to some implementations of this disclosure. [Figure 2] FIG. 1 is a block diagram illustrating an example video encoder according to some implementations of this disclosure. [Figure 3] FIG. 2 is a block diagram illustrating an example video decoder according to some implementations of this disclosure. [Figure 4A] FIG. 10 is a block diagram illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes, according to some implementations of this disclosure. [Figure 4B] FIG. 10 is a block diagram illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes, according to some implementations of this disclosure. [Figure 4C] FIG. 10 is a block diagram illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes, according to some implementations of this disclosure. [Figure 4D] FIG. 10 is a block diagram illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes, according to some implementations of this disclosure. [Figure 4E] FIG. 10 is a block diagram illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes, according to some implementations of this disclosure. [Figure 5A] FIG. 1 is a block diagram illustrating an example of applying an adaptive color space conversion (ACT) technique to convert residuals between RGB and YCgCo color spaces, according to some implementations of the present disclosure. [Figure 5B] FIG. 1 is a block diagram illustrating an example of applying an adaptive color space conversion (ACT) technique to convert residuals between RGB and YCgCo color spaces, according to some implementations of the present disclosure. [Figure 6] FIG. 1 is a block diagram illustrating an example video data decoding process that applies a technique of Luminance Mapping with Chroma Scaling (LMCS), according to some implementations of the present disclosure. [Figure 7]FIG. 1 is a block diagram illustrating an example video decoding process in which a video decoder performs the technique of inverse adaptive color space conversion (ACT), according to some implementations of this disclosure. [Figure 8] 1 is a flowchart illustrating an example process by which a video decoder decodes video data by conditionally performing an inverse adaptive color space transformation, according to some implementations of this disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Reference will now be made in detail to specific implementations, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous non-limiting specific details are set forth to aid in understanding the subject matter presented herein. However, it will be apparent to those skilled in the art that various alternatives may be used and the subject matter may be practiced without these specific details without departing from the scope of the claims. For example, it will be apparent to those skilled in the art that the subject matter presented herein may be implemented on many types of electronic devices having digital video capabilities.

[0015] 1 is a block diagram illustrating an example system 10 for encoding and decoding video blocks in parallel, according to some implementations of the present disclosure. As shown in FIG. 1, system 10 includes a source device 12 that generates and encodes video data that is subsequently decoded by a destination device 14. Source device 12 and destination device 14 may include any of a wide variety of electronic devices, including desktop or laptop computers, tablet computers, smartphones, set-top boxes, digital televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, etc. In some implementations, source device 12 and destination device 14 are equipped with wireless communication capabilities.

[0016] In some implementations, destination device 14 may receive encoded video data to be decoded via link 16. Link 16 may include any type of communication medium or device capable of moving encoded video data from source device 12 to destination device 14. In one example, link 16 may include a communication medium that allows source device 12 to transmit encoded video data directly to destination device 14 in real time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14. The communication medium may include any wireless or wired communication medium, such as the radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful in facilitating communication from source device 12 to destination device 14.

[0017] In some other implementations, the encoded video data may be transmitted from output interface 22 to storage device 32. The encoded video data in storage device 32 may then be accessed by destination device 14 via input interface 28. Storage device 32 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data. In a further example, storage device 32 may correspond to a file server or another intermediate storage device that may hold encoded video data generated by source device 12. Destination device 14 may access the stored video data from storage device 32 via streaming or download. The file server may be any type of computer capable of storing encoded video data and transmitting the encoded video data to destination device 14. Exemplary file servers include a web server (e.g., for a website), an FTP server, a network-attached storage (NAS) device, or a local disk drive. Destination device 14 may access the encoded video data through any standard data connection, including a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both, suitable for accessing encoded video data stored on a file server. The transmission of the encoded video data from storage device 32 may be a streaming transmission, a download transmission, or a combination of both.

[0018] 1 , source device 12 includes video source 18, video encoder 20, and output interface 22. Video source 18 may include sources such as a video capture device such as a video camera, a video archive containing previously captured video, a video feed interface for receiving video from a video content provider, and / or a computer graphics system for generating computer graphics data as source video, or a combination of such sources. As an example, if video source 18 is a video camera in a security surveillance system, source device 12 and destination device 14 may form a camera phone or video phone. However, implementations described in this application may be applicable to video encoding generally and may be applied to wireless and / or wired applications.

[0019] The captured, pre-captured, or computer-generated video may be encoded by video encoder 20. The encoded video data may be transmitted directly to destination device 14 via output interface 22 of source device 12. The encoded video data may also (or alternatively) be stored on storage device 32 for later access by destination device 14 or other devices for decoding and / or playback. Output interface 22 may further include a modem and / or a transmitter.

[0020] Destination device 14 includes an input interface 28, a video decoder 30, and a display device 34. Input interface 28 may include a receiver and / or a modem and receive encoded video data over link 16. The encoded video data communicated over link 16 or provided on storage device 32 may include various syntax elements generated by video encoder 20 for use by video decoder 30 in decoding the video data. Such syntax elements may be included within the encoded video data transmitted over a communication medium, stored on a storage medium, or stored on a file server.

[0021] In some implementations, destination device 14 may include a display device 34, which may be an integrated display device and an external display device configured to communicate with destination device 14. Display device 34 displays the decoded video data to a user and may include any of a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light-emitting diode (OLED) display, or another type of display device.

[0022] Video encoder 20 and video decoder 30 may operate in accordance with proprietary or industry standards, such as VVC, HEVC, MPEG-4, Part 10, Advanced Video Coding (AVC), or extensions of such standards. It should be understood that the present application is not limited to a particular video encoding / decoding standard and may be applicable to other video encoding / decoding standards. It is generally assumed that video encoder 20 of source device 12 may be configured to encode video data in accordance with any of these current or future standards. Similarly, it is also generally assumed that video decoder 30 of destination device 14 may be configured to decode video data in accordance with any of these current or future standards.

[0023] Video encoder 20 and video decoder 30 may each be implemented as any of a variety of suitable encoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. If implemented partially in software, an electronic device may store instructions for the software on a suitable non-transitory computer-readable medium and execute those instructions in hardware using one or more processors to perform the video encoding / decoding operations disclosed in this disclosure. Video encoder 20 and video decoder 30 may each be included in one or more encoders or decoders, any of which may be integrated as part of a combined encoder / decoder (CODEC) in the respective device.

[0024] 2 is a block diagram illustrating an example video encoder 20 according to some implementations described in this application. Video encoder 20 may perform intra- and inter-predictive coding of video blocks within a video frame. Intra-predictive coding relies on spatial prediction to reduce or remove spatial redundancy in video data within a given video frame or picture. Inter-predictive coding relies on temporal prediction to reduce or remove temporal redundancy in video data within adjacent video frames or pictures of a video sequence.

[0025] 2, video encoder 20 includes a video data memory 40, a prediction processing unit 41, a decoded picture buffer (DPB) 64, an adder 50, a transform processing unit 52, a quantization unit 54, and an entropy coding unit 56. Prediction processing unit 41 further includes a motion estimation unit 42, a motion compensation unit 44, a partitioning unit 45, an intra-prediction processing unit 46, and an intra-block copy (BC) unit 48. In some implementations, video encoder 20 also includes an inverse quantization unit 58 for video block reconstruction, an inverse transform processing unit 60, and an adder 62. A deblocking filter (not shown) may be disposed between adder 62 and DPB 64 to filter block boundaries to remove block distortion artifacts from the reconstructed video. In addition to the deblocking filter, an in-loop filter (not shown) may be used to filter the output of adder 62. Video encoder 20 may take the form of a fixed or programmable hardware unit, or may be divided among one or more of the illustrated fixed or programmable hardware units.

[0026] Video data memory 40 may store video data to be encoded by components of video encoder 20. The video data in video data memory 40 may be obtained, for example, from video source 18. DPB 64 is a buffer that stores reference video data for use in encoding video data by video encoder 20 (e.g., in intra- or inter-predictive coding modes). Video data memory 40 and DPB 64 may be formed by any of a variety of memory devices. In various examples, video data memory 40 may be on-chip with other components of video encoder 20 or off-chip with respect to those components.

[0027] As shown in FIG. 2, after receiving video data, partition unit 45 within prediction processing unit 41 partitions the video data into video blocks. This partitioning may include partitioning the video frame into slices, tiles, or other larger coding units (CUs) according to a predetermined partitioning structure, such as a quadtree structure, associated with the video data. The video frame may be divided into multiple video blocks (or sets of video blocks referred to as tiles). Prediction processing unit 41 may select one of multiple possible predictive coding modes, such as one of multiple intra-predictive coding modes or one of multiple inter-predictive coding modes, for the current video block based on error results (e.g., code rate and distortion level). Prediction processing unit 41 may provide the resulting intra- or inter-predictively coded block to adder 50 to generate a residual block, and to adder 62 to reconstruct the coded block for later use as part of a reference frame. Prediction processing unit 41 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy coding unit 56.

[0028] To select an appropriate intra-prediction coding mode for a current video block, intra-prediction processing unit 46 within prediction processing unit 41 may perform intra-prediction coding of the current video block relative to one or more neighboring blocks in the same frame as the current block to be coded to provide spatial prediction. Motion estimation unit 42 and motion compensation unit 44 within prediction processing unit 41 perform inter-prediction coding of the current video block relative to one or more predictive blocks in one or more reference frames to provide temporal prediction. Video encoder 20 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.

[0029] In some implementations, motion estimation unit 42 determines the inter-prediction mode for a current video frame by generating a motion vector that indicates the displacement of a prediction unit (PU) of a video block in a current video frame relative to a predictive block in a reference video frame according to a predetermined pattern in a sequence of video frames. Motion estimation performed by motion estimation unit 42 is the process of generating motion vectors that estimate motion for video blocks. The motion vector may indicate, for example, the displacement of a PU of a video block in a current video frame or picture relative to a predictive block in a reference frame (or other coding unit) relative to a current block being coded in the current frame (or other coding unit). The predetermined pattern may designate a video frame in the sequence as a P frame or a B frame. Intra BC unit 48 may determine vectors, such as block vectors, for intra BC coding in a manner similar to the determination of motion vectors by motion estimation unit 42 for inter prediction, or may utilize motion estimation unit 42 to determine block vectors.

[0030] A prediction block is a block of a reference frame that is deemed to closely match the PU of the video block to be encoded, with respect to pixel differences that may be determined by sum of absolute differences (SAD), sum of squared differences (SSD), or other difference metrics. In some implementations, video encoder 20 may calculate values ​​for sub-integer pixel positions of the reference frame stored in DPB 64. For example, video encoder 20 may interpolate values ​​for quarter-pixel positions, eighth-pixel positions, or other fractional-pixel positions of the reference frame. Thus, motion estimation unit 42 may perform motion searches for full-pixel and fractional-pixel positions and output motion vectors with fractional-pixel precision.

[0031] Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter-predictively coded frame by comparing the position of the PU with the position of a predictive block of a reference frame selected from a first reference frame list (List 0) or a second reference frame list (List 1), each of which identifies one or more reference frames stored in DPB 64. Motion estimation unit 42 sends the calculated motion vector to motion compensation unit 44 and then to entropy coding unit 56.

[0032] Motion compensation performed by motion compensation unit 44 may involve fetching or generating a predictive block based on the motion vector determined by motion estimation unit 42. Upon receiving the motion vector for the PU of the current video block, motion compensation unit 44 may locate the predictive block to which the motion vector points in one of the reference frame lists, obtain the predictive block from DPB 64, and forward the predictive block to summer 50. Summer 50 then subtracts pixel values ​​of the predictive block provided by motion compensation unit 44 from pixel values ​​of the current video block being coded to form a residual video block of pixel difference values. The pixel difference values ​​forming the residual video block may include luma or chroma difference components, or both. Motion compensation unit 44 may also generate syntax elements associated with the video blocks of the video frame for use by video decoder 30 in decoding the video blocks of the video frame. The syntax elements may include, for example, syntax elements defining the motion vector used to identify the predictive block, any flags indicating a prediction mode, or any other syntax information described herein. It should be noted that motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are shown separately for conceptual purposes.

[0033] In some implementations, the intra BC unit 48 may generate vectors and fetch predictive blocks in a manner similar to that described above in connection with the motion estimation unit 42 and the motion compensation unit 44, except that the predictive block is in the same frame as the current block being coded, and the vectors are referred to as block vectors, as opposed to motion vectors. In particular, the intra BC unit 48 may determine an intra prediction mode to use to code the current block. In some examples, the intra BC unit 48 may code the current block using various intra prediction modes, e.g., during separate coding passes, and test their performance using rate-distortion analysis. The intra BC unit 48 may then select an appropriate intra prediction mode to use from the various tested intra prediction modes and generate an intra mode indicator accordingly. For example, the intra BC unit 48 may calculate rate-distortion values ​​for the various tested intra prediction modes using rate-distortion analysis, and select the intra prediction mode with the best rate-distortion characteristics from the tested modes as the appropriate intra prediction mode to use. Rate-distortion analysis generally determines the amount of distortion (or error) between the coded block and the original uncoded block that was coded to create the coded block, along with the bit rate (i.e., number of bits) used to create the coded block. Intra BC unit 48 may calculate ratios from the distortion and rate for various coded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block.

[0034] In other examples, intra BC unit 48 may use, in whole or in part, motion estimation unit 42 and motion compensation unit 44 to perform such functions for intra BC prediction, according to implementations described herein. In either case, for intra block copying, the predictive block may be a block that is deemed to closely match the block to be coded in terms of pixel differences, which may be determined by sum of absolute differences (SAD), sum of squared differences (SSD), or other difference metrics, and identifying the predictive block may include calculating values ​​for sub-integer pixel positions.

[0035] Regardless of whether the predictive block is from the same frame via intra prediction or a different frame via inter prediction, video encoder 20 may form a residual video block by subtracting pixel values ​​of the predictive block from pixel values ​​of the current video block being coded, thereby forming pixel difference values. The pixel difference values ​​that form the residual video block may include differences in both luma and chroma components.

[0036] Intra-prediction processing unit 46 may intra-predict the current video block as an alternative to the inter-prediction performed by motion estimation unit 42 and motion compensation unit 44 or the intra-block copy prediction performed by intra BC unit 48, as described above. In particular, intra-prediction processing unit 46 may determine an intra-prediction mode to use to encode the current block. To do so, intra-prediction processing unit 46 may encode the current block using various intra-prediction modes, e.g., during separate encoding passes, and intra-prediction processing unit 46 (or a mode selection unit in some examples) may select an appropriate intra-prediction mode to use from the tested intra-prediction modes. Intra-prediction processing unit 46 may provide information indicating the selected intra-prediction mode for the block to entropy coding unit 56. Entropy coding unit 56 may encode the information indicating the selected intra-prediction mode in the bitstream.

[0037] After prediction processing unit 41 determines a predictive block for the current video block via either inter-prediction or intra-prediction, adder 50 forms a residual video block by subtracting the predictive block from the current video block. The residual video data in the residual block may be included in one or more transform units (TUs) and provided to transform processing unit 52. Transform processing unit 52 converts the residual video data into residual transform coefficients using a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform.

[0038] Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54, which quantizes the transform coefficients to further reduce the bit rate. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, quantization unit 54 may then perform a scan of a matrix containing the quantized transform coefficients. Alternatively, entropy coding unit 56 may perform this scan.

[0039] Following quantization, entropy coding unit 56 entropy codes the quantized transform coefficients into a video bitstream, using, for example, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or another entropy coding method or technique. The coded bitstream may then be transmitted to video decoder 30 or archived in storage device 32 for later transmission to or retrieval by video decoder 30. Entropy coding unit 56 may entropy code motion vectors and other syntax elements for the current video frame being coded.

[0040] Inverse quantization unit 58 and inverse transform processing unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual video block into the pixel domain to generate reference blocks for predicting other video blocks. As described above, motion compensation unit 44 may generate motion-compensated prediction blocks from one or more reference blocks of frames stored in DPB 64. Motion compensation unit 44 may apply one or more interpolation filters to the prediction block to calculate sub-integer pixel values ​​for use in motion estimation.

[0041] Adder 62 adds the reconstructed residual block to the motion compensated prediction block produced by motion compensation unit 44 to create a reference block for storage in DPB 64. The reference block may then be used by intra BC unit 48, motion estimation unit 42, and motion compensation unit 44 as a prediction block to inter predict another video block in a subsequent video frame.

[0042] 3 is a block diagram illustrating an example video decoder 30 according to some implementations of the present application. Video decoder 30 includes a video data memory 79, an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, an adder 90, and a DPB 92. Prediction processing unit 81 further includes a motion compensation unit 82, an intra-prediction processing unit 84, and an intra-BC unit 85. Video decoder 30 may perform a decoding process that is generally opposite to the encoding process described above for video encoder 20 in connection with FIG. 2. For example, motion compensation unit 82 may generate prediction data based on a motion vector received from entropy decoding unit 80, while intra-prediction unit 84 may generate prediction data based on an intra-prediction mode indicator received from entropy decoding unit 80.

[0043] In some examples, a unit of video decoder 30 may be tasked with performing an implementation of the present application. Also, in some examples, an implementation of the present disclosure may be divided among one or more units of video decoder 30. For example, intra BC unit 85 may perform an implementation of the present application alone or in combination with other units of video decoder 30, such as motion compensation unit 82, intra prediction processing unit 84, and entropy decoding unit 80. In some examples, video decoder 30 may not include intra BC unit 85, and the functions of intra BC unit 85 may be performed by other components of prediction processing unit 81, such as motion compensation unit 82.

[0044] Video data memory 79 may store video data, such as an encoded video bitstream, to be decoded by other components of video decoder 30. The video data stored in video data memory 79 may be obtained, for example, from storage device 32, from a local video source such as a camera, via wired or wireless network communication of video data, or by accessing a physical data storage medium (e.g., a flash drive or hard disk). Video data memory 79 may include a coded picture buffer (CPB) that stores coded video data from the coded video bitstream. A decoded picture buffer (DPB) 92 of video decoder 30 stores reference video data for use in decoding video data by video decoder 30 (e.g., in intra- or inter-prediction coding modes). Video data memory 79 and DPB 92 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. For illustrative purposes, video data memory 79 and DPB 92 are shown in Figure 3 as two separate components of video decoder 30. However, it will be apparent to those skilled in the art that video data memory 79 and DPB 92 may be provided by the same memory device or separate memory devices. In some examples, video data memory 79 may be on the same chip as other components of video decoder 30 or off-chip relative to those components.

[0045] During the decoding process, video decoder 30 receives an encoded video bitstream representing video blocks and associated syntax elements of encoded video frames. Video decoder 30 may receive the syntax elements at the video frame level and / or the video block level. Entropy decoding unit 80 of video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements. Entropy decoding unit 80 then forwards the motion vectors and other syntax elements to prediction processing unit 81.

[0046] If a video frame is coded as an intra-prediction coded (I) frame or for intra-coded predictive blocks in other types of frames, intra-prediction processing unit 84 of prediction processing unit 81 may generate predictive data for video blocks of the current video frame based on a signaled intra-prediction mode and reference data from previously decoded blocks of the current frame.

[0047] If a video frame is coded as an inter-predictive coded (i.e., B or P) frame, motion compensation unit 82 of prediction processing unit 81 creates one or more predictive blocks for video blocks of the current video frame based on the motion vectors and other syntax elements received from entropy decoding unit 80. Each of the predictive blocks may be created from a reference frame in one of the reference frame lists. Video decoder 30 may construct the reference frame lists, List 0 and List 1, using a default construction technique based on the reference frames stored in DPB 92.

[0048] In some examples, when a video block is encoded according to the intra BC mode described herein, intra BC unit 85 of prediction processing unit 81 creates a predictive block for the current video block based on the block vectors and other syntax elements received from entropy decoding unit 80. The predictive block may be within the same reconstructed region of the picture as the current video block as determined by video encoder 20.

[0049] Motion compensation unit 82 and / or intra BC unit 85 determine prediction information for video blocks of the current video frame by parsing the motion vectors and other syntax elements, and then use the prediction information to create a predictive block for the current video block being decoded. For example, motion compensation unit 82 uses some of the received syntax elements to determine the prediction mode (e.g., intra- or inter-prediction) used to encode the video blocks of the video frame, the inter-prediction frame type (e.g., B or P), configuration information for one or more of the reference frame lists for the frame, the motion vector for each inter-predictively coded video block of the frame, the inter-prediction status for each inter-predictively coded video block of the frame, and other information for decoding the video blocks in the current video frame.

[0050] Similarly, intra BC unit 85 may use some of the received syntax elements, such as flags, to determine that the current video block was predicted using intra BC mode, configuration information about which video blocks of the frame are within the reconstructed region and should be stored in DPB 92, block vectors for each intra BC predicted video block of the frame, intra BC prediction status for each intra BC predicted video block of the frame, and other information for decoding the video blocks in the current video frame.

[0051] Motion compensation unit 82 may also perform interpolation using an interpolation filter to calculate interpolated values ​​for sub-integer pixels of the reference block, as used by video encoder 20 during encoding of the video block. In this case, motion compensation unit 82 may determine the interpolation filter used by video encoder 20 from the received syntax element and use the interpolation filter to create the predictive block.

[0052] Inverse quantization unit 86 inverse quantizes the quantized transform coefficients provided in the bitstream and entropy decoded by entropy decoding unit 80 using the same quantization parameter calculated by video encoder 20 for each video block in the video frame to determine the degree of quantization. Inverse transform processing unit 88 applies an inverse transform, such as an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process, to the transform coefficients in order to reconstruct the residual block in the pixel domain.

[0053] After motion compensation unit 82 or intra BC unit 85 generates a predictive block for the current video block based on the vectors and other syntax elements, summer 90 reconstructs a decoded video block for the current video block by adding the residual block from inverse transform processing unit 88 and the corresponding predictive block generated by motion compensation unit 82 and intra BC unit 85. To further process the decoded video block, an in-loop filter (not shown) may be disposed between summer 90 and DPB 92. The decoded video block for a given frame is then stored in DPB 92, which stores reference frames used for subsequent motion compensation of the next video block. DPB 92, or a memory device separate from DPB 92, may store the decoded video for later presentation on a display device, such as display device 34 of FIG. 1 .

[0054] In a typical video encoding process, a video sequence typically includes an ordered set of frames or pictures. Each frame may include three sample arrays, denoted SL, SCb, and SCr. SL is a two-dimensional array of luma samples. SCb is a two-dimensional array of Cb chroma samples. SCr is a two-dimensional array of Cr chroma samples. In other cases, a frame may be monochromatic and therefore include only one two-dimensional array of luma samples.

[0055] As shown in FIG. 4A, video encoder 20 (or more specifically, partitioning unit 45) generates a coded representation of a frame by first partitioning the frame into a set of coding tree units (CTUs). A video frame may include an integer number of CTUs, sequentially ordered in raster scan order from left to right and top to bottom. Each CTU is the largest logical coding unit, and the width and height of the CTU are signaled by video encoder 20 in the sequence parameter set so that all CTUs in a video sequence have the same size, either 128x128, 64x64, 32x32, or 16x16. However, it should be noted that the present application is not necessarily limited to a particular size. As shown in FIG. 4B, each CTU may include one coding tree block (CTB) for luma samples, two corresponding coding tree blocks for chroma samples, and syntax elements used to encode the samples in the coding tree blocks. The syntax elements describe the characteristics of different types of units of pixel blocks to be coded, including inter or intra prediction, intra prediction mode, motion vectors, and other parameters, and how the video sequence may be reconstructed at video decoder 30. In a monochrome picture or a picture with three distinct color planes, a CTU may include a single coding tree block and syntax elements used to code samples of the coding tree block. A coding tree block may be an N×N block of samples.

[0056] To achieve better performance, video encoder 20 may recursively perform quadtree partitioning, such as binary tree partitioning, ternary tree partitioning, quadtree partitioning, or a combination of both, on the coding tree blocks of the CTU to divide the CTU into smaller coding units (CUs). As shown in FIG. 4C , 64×64 CTU 400 is first partitioned into four smaller CUs, each with a block size of 32×32. Of the four smaller CUs, CU 410 and CU 420 are each partitioned into four CUs with a block size of 16×16. Two 16×16 CUs, 430 and 440, are further partitioned into four CUs with a block size of 8×8. FIG. 4D illustrates a quadtree data structure showing the final result of the partitioning process of CTU 400 as shown in FIG. 4C , where each leaf node of the quadtree corresponds to one CU, each ranging in size from 32×32 to 8×8. Similar to the CTU illustrated in FIG. 4B, each CU may include a coding block (CB) of luma samples and two corresponding coding blocks (CB) of chroma samples of the same size frame, as well as syntax elements used to encode the samples of the coding block. In a monochrome picture or a picture with three distinct color planes, a CU may include a single coding block and syntax structures used to encode the samples of the coding block. It should be noted that the quadtree partitioning illustrated in FIGS. 4C and 4D is for illustrative purposes only, and a CTU may be divided into CUs to suit various local characteristics based on quadtree / ternary tree / binary tree partitioning. In a multi-tree structure, a CTU is partitioned by a quadtree structure, and each leaf CU of the quadtree may be further partitioned by binary tree and ternary tree structures. As shown in FIG. 4E, there are five partition types: quadtree, horizontal bipartition, vertical bipartition, horizontal tripartition, and vertical tripartition.

[0057] In some implementations, video encoder 20 may further partition the coding blocks of a CU into one or more M×N prediction blocks (PBs). A prediction block is a rectangular (square or non-square) block of samples to which the same inter or intra prediction is applied. A prediction unit (PU) of a CU may include a prediction block of luma samples, two corresponding prediction blocks of chroma samples, and syntax elements used to predict the prediction block. In a monochrome picture or a picture with three separate color planes, a PU may include a single prediction block and syntax structures used to predict the prediction block. Video encoder 20 may generate predicted luma, Cb, and Cr blocks for the luma, Cb, and Cr prediction blocks of each PU of a CU.

[0058] Video encoder 20 may generate predictive blocks for a PU using intra prediction or inter prediction. If video encoder 20 generates predictive blocks for a PU using intra prediction, video encoder 20 may generate the predictive blocks for the PU based on decoded samples of a frame associated with the PU. If video encoder 20 generates predictive blocks for the PU using inter prediction, video encoder 20 may generate the predictive blocks for the PU based on decoded samples of one or more frames other than the frame associated with the PU.

[0059] After video encoder 20 generates predicted luma, Cb, and Cr blocks for one or more PUs of a CU, video encoder 20 may generate a luma residual block for the CU by subtracting the predicted luma block of the CU from its original luma coding block, such that each sample in the luma residual block of the CU indicates a difference between a luma sample in one of the predicted luma blocks of the CU and a corresponding sample in the original luma coding block of the CU. Similarly, video encoder 20 may generate Cb and Cr residual blocks for the CU, such that each sample in the Cb residual block of the CU indicates a difference between a Cb sample in one of the predicted Cb blocks of the CU and a corresponding sample in the original Cb coding block of the CU, and each sample in the Cr residual block of the CU indicates a difference between a Cr sample in one of the predicted Cr blocks of the CU and a corresponding sample in the original Cr coding block of the CU, respectively.

[0060] Further, as illustrated in FIG. 4C , video encoder 20 may use quadtree partitioning to decompose the luma, Cb, and Cr residual blocks of a CU into one or more luma, Cb, and Cr transform blocks. A transform block is a rectangular (square or non-square) block of samples to which the same transform is applied. A transform unit (TU) of a CU may include a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax elements used to transform the transform block samples. Thus, each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block. In some examples, the luma transform block associated with a TU may be a sub-block of the luma residual block of the CU. The Cb transform block may be a sub-block of the Cb residual block of the CU. The Cr transform block may be a sub-block of the Cr residual block of the CU. In a monochrome picture or a picture with three separate color planes, a TU may include a single transform block and syntax structures used to transform the samples of the transform block.

[0061] Video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU. The coefficient block may be a two-dimensional array of transform coefficients. The transform coefficients may be scalar quantities. Video encoder 20 may apply one or more transforms to a Cb transform block of the TU to generate a Cb coefficient block for the TU. Video encoder 20 may apply one or more transforms to a Cr transform block of the TU to generate a Cr coefficient block for the TU.

[0062] After generating a coefficient block (e.g., a luma coefficient block, a Cb coefficient block, or a Cr coefficient block), video encoder 20 may quantize the coefficient block. Quantization generally refers to a process by which transform coefficients are quantized to provide further compression by possibly reducing the amount of data used to represent the transform coefficients. After video encoder 20 quantizes the coefficient block, video encoder 20 may entropy encode syntax elements indicating the quantized transform coefficients. For example, video encoder 20 may perform context-adaptive binary arithmetic coding (CABAC) on the syntax elements indicating the quantized transform coefficients. Finally, video encoder 20 may output a bitstream including a sequence of bits forming a representation of the encoded frame and associated data to be stored in storage device 32 or transmitted to destination device 14.

[0063] After receiving the bitstream generated by video encoder 20, video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream. Video decoder 30 may reconstruct frames of video data based at least in part on the syntax elements obtained from the bitstream. The process of reconstructing video data is generally the opposite of the encoding process performed by video encoder 20. For example, video decoder 30 may inverse transform coefficient blocks associated with TUs of the current CU to reconstruct residual blocks associated with TUs of the current CU. Video decoder 30 also reconstructs coding blocks of the current CU by adding samples of predictive blocks for PUs of the current CU to corresponding samples of transform blocks of TUs of the current CU. After reconstructing the coding blocks for each CU of the frame, video decoder 30 may reconstruct the frame.

[0064] As mentioned above, video coding achieves video compression using two main modes: intra-frame prediction (or intra-prediction) and inter-frame prediction (or inter-prediction). Palette-based coding is another coding method adopted by many video coding standards. In palette-based coding, which may be particularly suitable for encoding screen-generated content, a video encoder (e.g., video encoder 20 or video decoder 30) forms a palette table of colors to represent a given block of video data. The palette table contains the most dominant (e.g., frequently used) pixel values ​​in the given block. Pixel values ​​that do not frequently appear in the video data of a given block are either not included in the palette table or are included in the palette table as escape colors.

[0065] Each entry in the palette table contains an index to a corresponding pixel value in the palette table. The palette index for a sample in a block may be coded to indicate which entry from the palette table should be used to predict or reconstruct which sample. This palette mode begins with the process of generating a palette predictor for the first block of a picture, slice, tile, or other such grouping of video blocks. As described below, palette predictors for subsequent video blocks are typically generated by updating a previously used palette predictor. For illustrative purposes, it is assumed that the palette predictor is defined at the picture level. In other words, a picture may contain multiple coding blocks, each with its own palette table, but there is one palette predictor for the entire picture.

[0066] To reduce the bits required to signal palette entries in a video bitstream, a video decoder may use a palette predictor to determine new palette entries in a palette table used to reconstruct a video block. For example, the palette predictor may include palette entries from a previously used palette table, or may be initialized with the most recently used palette table by including all entries from the most recently used palette table. In some implementations, the palette predictor may include fewer than all entries from the most recently used palette table, while incorporating some entries from other previously used palette tables. The palette predictor may have the same size as the palette table used to encode a different block, or may be larger or smaller than the palette table used to encode a different block. In one example, the palette predictor is implemented as a first-in-first-out (FIFO) table containing 64 palette entries.

[0067] To generate a palette table for a block of video data from the palette predictor, the video decoder may receive a one-bit flag for each entry of the palette predictor from the encoded video bitstream. The one-bit flag may have a first value (e.g., a binary 1) indicating that the associated entry of the palette predictor should be included in the palette table, or a second value (e.g., a binary 0) indicating that the associated entry of the palette predictor should not be included in the palette table. If the size of the palette predictor is larger than the palette table used for the block of video data, the video decoder may stop receiving more flags once a maximum size for the palette table has been reached.

[0068] In some implementations, some entries in the palette table may be directly signaled in the coded video bitstream instead of being determined using a palette predictor. For such entries, the video decoder may receive three separate m-bit values ​​from the coded video bitstream indicating the pixel value for the luma and two chroma components associated with the entry, where m represents the bit depth of the video data. Compared to the multiple m-bit values ​​required for directly signaled palette entries, palette entries derived from the palette predictor require only a one-bit flag. Thus, signaling some or all palette entries using a palette predictor can significantly reduce the number of bits required to signal new palette table entries, thereby improving the overall coding efficiency of palette mode coding.

[0069] In many cases, a palette predictor for a block is determined based on the palette table used to encode one or more previously encoded blocks. However, when encoding the first coding tree unit in a picture, slice, or tile, the palette table of the previously encoded block may not be available. Therefore, a palette predictor cannot be generated using entries in the previously used palette table. In such cases, a set of palette predictor initializers may be signaled in a sequence parameter set (SPS) and / or a picture parameter set (PPS), whose values ​​are used to generate a palette predictor when the previously used palette table is not available. An SPS generally refers to a syntactic structure of syntax elements that apply to a series of consecutive coded video pictures, referred to as a coded video sequence (CVS), determined by the content of syntax elements found in a PPS referenced by syntax elements found in each slice segment header. A PPS generally refers to a syntactic structure of syntax elements that apply to one or more individual pictures in a CVS, determined by the content of syntax elements found in each slice segment header. Thus, an SPS is generally considered a higher level syntactic structure than a PPS, which means that the syntax elements contained in an SPS generally change less frequently and apply to a larger portion of the video data compared to the syntax elements contained in a PPS.

[0070] 5A-5B are block diagrams illustrating examples of applying adaptive color space conversion (ACT) techniques to convert residuals between RGB and YCgCo color spaces, according to some implementations of the present disclosure.

[0071] In the HEVC screen content coding extension, ACT is applied to adaptively convert the residual from one color space (e.g., RGB) to another color space (e.g., YCgCo), so that the correlation (e.g., redundancy) between the three color components (e.g., R, G, and B) is significantly reduced in the YCgCo color space. Furthermore, in the existing ACT design, the adaptation of different color spaces is implemented at the transform unit (TU) level by signaling one flag, tu_act_enabled_flag, for each TU. When the flag tu_act_enabled_flag is equal to 1, it indicates that the residual of the current TU is coded in the YCgCo space; otherwise (i.e., the flag is equal to 0), it indicates that the residual of the current TU is coded in the original color space (i.e., without color space conversion). In addition, different color space conversion formulas are applied depending on whether the current TU is coded in a lossless mode or a lossy mode. Specifically, the forward and backward color space conversion formulas between the RGB color space and the YCgCo color space for the lossy mode are defined in FIG. 5A.

[0072] In lossless mode, a reversible RGB-to-YCgCo conversion (also known as YCgCo-LS) is used, which is implemented based on the lifting operation shown in Figure 5B and the related description.

[0073] As shown in Figure 5A, the forward and inverse color transform matrices used in the lossy mode are not normalized. Therefore, the magnitude of the YCgCo signal is smaller than the magnitude of the original signal after the color transform is applied. To compensate for the magnitude reduction caused by the forward color transform, an adjusted quantization parameter is applied to the residual in the YCgCo domain. Specifically, when the color space transform is applied, the QP value QP used to quantize the YCgCo domain residual is Y , Q.P. Cg , and QP Coare set to be QP-5, QP-5, and QP-3, respectively, where QP is the quantization parameter used in the original color space.

[0074] FIG. 6 is a block diagram illustrating an application of the technique of Luminance Mapping with Chroma Scaling (LMCS) in an exemplary video data decoding process, according to some implementations of the present disclosure.

[0075] In VVC, LMCS is used as a new coding tool applied before in-loop filters (e.g., deblocking filter, SAO, and ALF). Generally, LMCS has two main modules: 1) in-loop mapping of luma components based on an adaptive piecewise linear model, and 2) luma-dependent chroma residual scaling. FIG. 6 shows a modified decoding process in which LMCS is applied. In FIG. 6, the decoding modules performed in the mapped domain include an entropy decoding module, an inverse quantization module, an inverse transform module, a luma intra prediction module, and a luma sample reconstruction module (i.e., adding luma prediction samples and luma residual samples). The decoding modules performed in the original (i.e., unmapped) domain include a motion compensation prediction module, a chroma intra prediction module, a chroma sample reconstruction module (i.e., adding luma prediction samples and luma residual samples), and all in-loop filter modules, such as a deblocking module, an SAO module, and an ALF module. The new operation modules introduced by LMCS include a forward mapping of luma samples module 610 , a backward mapping of luma samples module 620 , and a chroma residual scaling module 630 .

[0076] The in-loop mapping of LMCS can adjust the dynamic range of the input signal to improve coding efficiency. The in-loop mapping of luma samples in existing LMCS designs is built based on two mapping functions: one forward mapping function FwdMap and one corresponding inverse mapping function InvMap. The forward mapping function is signaled from the encoder to the decoder using a piecewise linear model containing 16 equally sized pieces. The inverse mapping function can be derived directly from the forward mapping function and therefore does not need to be signaled.

[0077] The parameters of the luminance mapping model are signaled at the slice level. First, a presence flag is signaled to indicate whether a luminance mapping model should be signaled for the current slice. If a luminance mapping model is present in the current slice, the corresponding piecewise linear model parameters are further signaled. In addition, at the slice level, another LMCS control flag is signaled to enable / disable LMCS for the slice.

[0078] The chroma residual scaling module 630 is designed to compensate for quantization precision interactions between luma signals and their corresponding chroma signals when in-loop mapping is applied to the luma signal. Whether chroma residual scaling is enabled or disabled for the current slice is also signaled in the slice header. If luma mapping is enabled, an additional flag is signaled to indicate whether luma-dependent chroma residual scaling is applied. If luma mapping is not used, luma-dependent chroma residual scaling is always disabled, and no additional flag is required. Additionally, chroma residual scaling is always disabled for CUs that contain four or fewer chroma samples.

[0079] FIG. 7 is a block diagram illustrating an example video decoding process in which a video decoder performs the technique of inverse adaptive color space conversion (ACT), according to some implementations of this disclosure.

[0080] Similar to the ACT design in the SCC of HEVC, the ACT of VVC converts the intra / inter prediction residual of one CU in 4:4:4 chroma format from the original color space (e.g., RGB color space) to the YCgCo color space. As a result, redundancy among the three color components can be reduced for better coding efficiency. FIG. 7 shows a decoding flowchart in which inverse ACT is applied in the VVC framework by adding an inverse ACT module 710. When processing a CU coded with ACT enabled, entropy decoding, inverse quantization, and an inverse DCT / DST-based transform are first applied to the CU. Then, as shown in FIG. 7, the inverse ACT is invoked to convert the decoded residual from the YCgCo color space back to the original color space (e.g., RGB and YCbCr). In addition, because ACT is not normalized in lossy mode, a QP adjustment of (-5, -5, -3) is applied to the Y, Cg, and Co components to compensate for the magnitude change of the transformed residual.

[0081] In some embodiments, the ACT method reuses the same HEVC ACT core transform to perform color conversion between different color spaces. Specifically, two different color transforms are applied depending on whether the current CU is lossy or losslessly encoded. In the lossy case, the forward and inverse color transforms use the lossy YCgCo transform matrix shown in FIG. 5A. In the lossless case, the lossless color transform YCgCo-LS shown in FIG. 5B is applied. Furthermore, unlike existing ACT designs, the following changes are introduced in the proposed ACT scheme to address interactions with other coding tools in the VVC standard:

[0082] For example, the residual of one CU in HEVC may be partitioned into multiple TUs, so an ACT control flag is signaled separately for each TU to indicate whether color space conversion needs to be applied. However, as described above in connection with FIG. 4E, to replace the multi-partition concept and thus eliminate the separate CU, PU, ​​and TU partitions of HEVC, a quadtree nested by bipartitional and tripartitional structures is applied in VVC. This means that in most cases, as long as the supported maximum transform size is smaller than the width or height of one component of the CU, the leaf node of one CU is also used as the unit of prediction and transform processing without further partitioning. Based on such a partition structure, this disclosure proposes adaptively enabling and disabling ACT at the CU level. Specifically, a flag, cu_act_enabled_flag, is signaled for each CU to select between the original color space and the YCgCo color space for encoding the residual of the CU. When the flag is equal to 1, it indicates that the residuals of all TUs in the CU are encoded in the YCgCo color space. Otherwise, if the flag cu_act_enabled_flag is equal to 0, all residuals of the CU are coded in the original color space.

[0083] FIG. 8 is a flowchart 800 illustrating an example process by which a video decoder decodes video data by conditionally performing an inverse adaptive color space conversion (ACT) technique, according to some implementations of this disclosure.

[0084] As shown in Figures 5A and 5B, ACT can affect the decoded residual only when the current CU contains at least one non-zero coefficient. If all coefficients resulting from entropy decoding are zero, the reconstructed residual also remains zero, regardless of whether inverse ACT is applied. For inter and intra block copy (IBC) modes, information on whether a CU contains non-zero coefficients is indicated by the CU root coded block flag (CBF), i.e., cu_cbf. When the flag is equal to 1, this means that a residual syntax element exists in the video bitstream for the current CU. Otherwise (i.e., the flag is equal to 0), this means that the residual syntax element of the current CU is not signaled in the video bitstream, or in other words, all residuals of the CU are inferred to be zero. Therefore, in some embodiments, it is proposed that the flag cu_act_enabled_flag is signaled only when the root CBF flag cu_cbf of the current CU is equal to 1 for inter and IBC modes. Otherwise (i.e., the flag cu_cbf is equal to 0), the flag cu_act_enabled_flag is not signaled, and ACT is disabled for decoding the residual of the current CU. On the other hand, unlike Inter and IBC modes, the root CBF flag is not signaled for Intra mode, i.e., the flag cu_cbf is not used to condition the presence of the flag cu_act_enabled_flag for an intra CU. Conversely, when ACT is applied to an intra CU, the ACT flag is proposed to conditionally enable / disable the signaling of the CBF of the luma component. For example, if an intra CU uses ACT, the decoder assumes that at least one component contains a non-zero coefficient. Therefore, when ACT is enabled for an intra CU and there are no non-zero residuals in the transform blocks except for the last transform block, the CBF for that last transform block is inferred to be 1 without signaling.For an intra CU containing exactly one TU, if the CBFs for its two chroma components (indicated by tu_cbf_cb and tu_cbf_cr) are 0, then without signaling, the CBF flag of the last component (i.e., tu_cbf_luma) is always inferred to be 1. In one embodiment, such inference rule for luma CBF is only enabled for intra CUs containing only one single TU for residual coding.

[0085] To conditionally perform inverse ACT on a coding unit, the video decoder first receives video data corresponding to the coding unit (e.g., encoded in 4:4:4 format) from a bitstream, where the coding unit is encoded in inter prediction mode or intra block copy mode (810).

[0086] Next, the video decoder receives a first syntax element (e.g., a CU root coded block flag cu_cbf) from the video data, where the first syntax element indicates whether the coding unit has a non-zero residual (820).

[0087] If the first syntax element has a value other than 0 (e.g., 1 indicating the presence of a residual syntax element in the bitstream for the coding unit) (830), the video decoder then receives a second syntax element (e.g., cu_act_enabled_flag) from the video data, which indicates whether the coding unit is coded using adaptive color space conversion (ACT) (830-1).

[0088] On the other hand, if the first syntax element has a value of 0 (e.g., 0 indicating that no residual syntax elements are present in the bitstream for the coding unit) (840), the video decoder assigns a value of 0 to the second syntax element (e.g., sets cu_act_enabled_flag to 0) (840-1).

[0089] The video decoder then determines whether to perform reverse ACT on the video data of the coding unit according to the value of the second syntax element (e.g., if the second syntax element has a value of 0, refrain from performing reverse ACT, and if the second syntax element has a value other than 0, perform reverse ACT. The value of the second syntax element may be received from the video data or assigned based on the logic described above) (850).

[0090] In some embodiments, the coding unit is coded in a 4:4:4 chroma format, where each of the components (eg, one luma and two chroma) has the same sample rate.

[0091] In some embodiments, the first syntax element having a value of 0 indicates that no residual syntax elements are present in the bitstream for the coding unit, and the first syntax element having a value other than 0 indicates that a residual syntax element is present in the bitstream for the coding unit.

[0092] In some embodiments, the first syntax element includes a cu_cbf flag and the second syntax element includes a cu_act_enabled flag.

[0093] In some embodiments, when a coding unit is coded in an intra-prediction mode, the video decoder conditionally receives a syntax element (eg, tu_cbf_y) for decoding the luma component of the coding unit.

[0094] To conditionally receive syntax elements for decoding the luma component, the video decoder first receives video data corresponding to a coding unit from a bitstream. The coding unit is coded in an intra-prediction mode, and the coding unit includes a first chroma component, a second chroma component, and a luma component. In some embodiments, the coding unit includes only one transform unit.

[0095] Next, the video decoder receives a first syntax element (e.g., cu_act_enabled_flag) from the video data that indicates whether the coding unit is coded using ACT. For example, cu_act_enabled_flag equal to "1" indicates that the coding unit is coded using ACT, and cu_act_enabled_flag equal to "0" indicates that the coding unit is not coded using ACT (e.g., and therefore, inverse ACT does not need to be performed).

[0096] After receiving a first syntax element from the video data, the video decoder receives a second syntax element (e.g., tu_cbf_cb) and a third syntax element (e.g., tu_cbf_cr) from the video data, where the second syntax element indicates whether the first chroma component has a non-zero residual, and the third syntax element indicates whether the second chroma component has a non-zero residual. For example, tu_cbf_cb or tu_cbf_cr equal to “1” indicates that the first chroma component or the second chroma component, respectively, has at least one non-zero residual, and tu_cbf_cb or tu_cbf_cr equal to “0” indicates that the first chroma component or the second chroma component, respectively, does not have a non-zero residual.

[0097] If the first syntax element has a non-zero value (e.g., 1 indicating that inverse ACT should be performed) and at least one of the two chroma components contains a non-zero residual (e.g., tu_cbf_cb==1 or tu_cbf_cr==1), the video decoder receives a fourth syntax element (e.g., tu_cbf_y) from the video data, where the fourth syntax element indicates whether the luma component has a non-zero residual.

[0098] On the other hand, if the first syntax element has a non-zero value and both chroma components have only zero residuals (e.g., tu_cbf_cb==0 and tu_cbf_cr==0), the video decoder assigns the fourth syntax element a default value (e.g., a non-zero value) indicating that the luma component has a non-zero residual. As a result, the video decoder will not receive a value for the fourth syntax element from the video data.

[0099] After determining a value for the fourth syntax element (e.g., by receiving a value from the video data or by assigning a default value other than 0 to the fourth syntax element), the video decoder determines whether to reconstruct a coding unit from the video data according to the fourth syntax element.

[0100] In some embodiments, a coding unit includes only one transform unit (TU).

[0101] In some embodiments, determining whether to reconstruct the coding unit from the video data in accordance with the fourth syntax element includes reconstructing a residual of a luma component in accordance with a determination that the fourth syntax element has a value other than 0, and refraining from reconstructing the residual of the luma component in accordance with a determination that the fourth syntax element has a value of 0.

[0102] Given the strong correlation among the three components of 4:4:4 video, the intra modes used to predict the luma and chroma components are often the same for a given coding block. Therefore, to reduce ACT signaling overhead, it is proposed to enable ACT for an intra CU only when its chroma component uses the same intra prediction mode (i.e., DM mode) as the luma component. In some embodiments, there are two methods for conditionally signaling the ACT enable / disable flag and the chroma intra prediction mode. In one embodiment of the present disclosure, it is proposed to signal the ACT enable / disable flag before signaling the intra prediction mode of an intra CU. In other words, when the ACT flag (i.e., cu_act_enabled_flag) is equal to 1, the intra prediction mode of the chroma component is not signaled but is inferred to be DM mode (i.e., reuse the same intra prediction mode as the luma component). Otherwise (i.e., cu_act_enabled_flag is 0), the intra prediction mode of the chroma component is still signaled. In another embodiment of the present disclosure, it is proposed to signal an ACT enable / disable flag after signaling the intra prediction mode. In this case, the ACT flag cu_act_enabled_flag needs to be signaled only when the value of the parsed chroma intra prediction mode is DM mode. Otherwise (i.e., the chroma intra prediction mode is not equal to DM), the flag cu_act_enabled_flag does not need to be signaled and is inferred to be 0. In yet another embodiment, it is proposed to enable ACT for all possible chroma intra modes. When such a method is applied, the flag cu_act_enabled_flag is always signaled regardless of the chroma intra prediction mode.

[0103] To conditionally signal the ACT enable / disable flag and the chroma intra-prediction mode, the video decoder first receives video data corresponding to a coding unit from a bitstream, where the coding unit is coded in an intra-prediction mode and the coding unit includes two chroma components and one luma component.

[0104] The video decoder then receives a first syntax element (eg, cu_act_enabled_flag) from the video data that indicates that the coding unit is coded using ACT.

[0105] The video decoder then receives a second syntax element from the video data, where the second syntax element represents intra-prediction parameters (e.g., representing one of 67 intra-prediction directions) for the luma component of the coding unit.

[0106] If the second syntax element has a non-zero value indicating that the coding unit is coded using ACT, the video decoder reconstructs the two chroma components of the coding unit by applying the same intra prediction parameters to the two chroma components of the coding unit as to the luma component of the coding unit.

[0107] In some embodiments, the intra prediction parameters indicate the intra prediction direction applied to generate the intra prediction samples of the coding unit.

[0108] When ACT is enabled for a CU, the ACT needs to access the residuals of all three components to perform color space conversion. However, as mentioned above, the VVC design cannot guarantee that each CU always contains information of all three components. In some embodiments of the present disclosure, when a CU does not contain information of all three components, ACT should be disabled.

[0109] First, when a separate tree (also known as a "dual tree") partitioning structure is applied, luma samples and chroma samples in one CTU are partitioned into CUs based on separate partitioning structures. As a result, CUs in the luma partitioning tree contain only the coding information of the luma component, and CUs in the chroma partitioning tree contain only the coding information of the two chroma components. Switching between the single tree partitioning structure and the separate tree partitioning structure can be performed at various levels, such as the sequence level, picture level, slice level, and coding unit group level. Therefore, when a separate tree is found to be applied to a region, ACT infers that all CUs (both luma CUs and chroma CUs) in the region are disabled and does not signal the ACT flag; instead, the ACT flag is inferred to be 0.

[0110] Second, when ISP mode is enabled, TU partitioning is applied only to luma samples, and chroma samples are coded but not further divided into multiple TUs. Assuming N is the number of ISP subpartitions (i.e., TUs) for one intra CU, according to the current ISP design, only the last TU contains both luma and chroma components, and the first N1 ISP TUs consist of only luma components. According to one embodiment of the present disclosure, ACT is disabled under ISP mode. There are two methods for disabling ACT for ISP mode. The first method proposes signaling an ACT enable / disable flag (i.e., cu_act_enabled_flag) before signaling the ISP mode syntax. In such a case, when the flag cu_act_enabled_flag is equal to 1, ISP mode is not signaled in the bitstream but is always inferred to be 0 (i.e., switched off). The second method proposes using ISP mode signaling to bypass signaling the ACT flag. Specifically, in this method, the ISP mode is signaled before the flag cu_act_enabled_flag. When the ISP mode is selected, the flag cu_act_enabled_flag is not signaled and is inferred to be 0. Otherwise (the ISP mode is not selected), the flag cu_act_enabled_flag is signaled to adaptively select a color space for residual coding of the CU.

[0111] In addition to disabling ACT for CUs whose luma and chroma partition structures are inconsistent, this disclosure also proposes disabling LMCS for CUs to which ACT is applied. In one embodiment, when a CU selects the YCgCo color space to encode its residual (i.e., ACT is 1), it is proposed to disable both luma mapping and chroma residual scaling. In another embodiment, when ACT is enabled for a CU, it is proposed to disable only chroma residual scaling, and luma mapping may still be applied to adjust the dynamic range of output luma samples. In a final embodiment, it is proposed to enable both luma mapping and chroma residual scaling for CUs that apply ACT to encode their residuals.

[0112] To disable ACT signaling with a dual tree partitioning structure, the video decoder obtains information from the bitstream indicating whether a coding unit in the video data is coded using a single tree partitioning or a dual tree partitioning.

[0113] If the coding units are coded using a single tree partition and each coding unit includes both luma and chroma components, the video decoder receives a second syntax element (e.g., cu_act_enabled_flag) from the video data, and the value of the first syntax element indicates whether to perform inverse adaptive color space conversion (ACT) for each coding unit.

[0114] On the other hand, if the coding unit is coded using a dual tree partition, and the coding units in the luminance partition tree of the dual tree partition contain only coding information related to the luminance component of the coding unit, and the coding units in the chroma partition tree of the dual tree partition contain only coding information related to the chroma component of the coding unit, the video decoder assigns a value of 0 to the second syntax element.

[0115] The video decoder then determines whether to perform reverse ACT for each coding unit in the coding tree unit according to the second syntax element.

[0116] In some embodiments, determining whether to perform inverse ACT for each coding unit in the coding tree unit in accordance with the second syntax element includes performing inverse ACT for each coding unit in accordance with a determination that the second syntax element has a value other than 0, and refraining from performing inverse ACT for each coding unit in accordance with a determination that the second syntax element has a value of 0.

[0117] In some embodiments, to disable ISP mode through ACT signaling, a video decoder first receives video data corresponding to a coding unit from a bitstream. Then, the video decoder receives a first syntax element (e.g., cu_act_enabled_flag) from the video data, where the first syntax element indicates whether the coding unit is coded using ACT. If the first syntax element has a value of 0, the video decoder receives a second syntax element from the video data, where the second syntax element indicates whether the coding unit is coded using ISP mode. If the first syntax element has a value other than 0, the video decoder assigns a value of 0 to the second syntax element to indicate that the coding unit is not coded using ISP mode. The video decoder then determines whether to reconstruct the coding unit from the video data using ISP mode according to the second syntax element. In current VVC, when ISP mode is enabled, TU partitioning is applied only to luma samples; chroma samples are coded but not further divided into multiple TUs. According to one embodiment of the present disclosure, it is also proposed to enable an ISP mode for chroma coding in 4:4:4 video because texture information is abundant in the chroma plane. Based on this embodiment, different methods may be used. In one method, one additional ISP index is signaled and shared by the two chroma components. In another method, it is proposed to signal two additional ISP indexes separately, one for Cb / B and the other for Cr / R. In a third method, it is proposed to reuse the ISP index used for the luma component for the ISP prediction of the two chroma components.

[0118] The matrix-weighted intra prediction (MIP) method is an intra prediction technique. To predict samples of a rectangular block of width W and height H, MIP takes as input one line of H reconstructed neighboring boundary samples to the left of the block and one line of W reconstructed neighboring boundary samples above the block. If reconstructed samples are not available, they are generated similarly to conventional intra prediction. The generation of the prediction signal is based on three steps: averaging, matrix-vector multiplication, and linear interpolation, as shown in Figure 10.

[0119] In the current VVC, MIP mode is only enabled for the luma component. For the same reason as enabling ISP mode for the chroma component, in one embodiment, it is proposed to enable MIP for the chroma component of .444 video. Two signaling methods can be applied. The first method proposes to signal two MIP modes separately, one for the luma component and the other for the two chroma components. The second method proposes to signal only one single MIP mode shared by the luma and chroma components.

[0120] To enable MIP for chroma components in a 4:4:4 chroma format, a video decoder receives video data corresponding to a coding unit from a bitstream, the coding unit being coded in an intra-prediction mode, the coding unit including two chroma components and one luma component, and the chroma and luma components having the same resolution. Next, the video decoder receives a first syntax element (e.g., intra_mip_flag) from the video data indicating that the luma component of the coding unit is coded using a MIP tool. If the first syntax element has a non-zero value indicating that the luma component of the coding unit is coded using a MIP tool, the video decoder receives a second syntax element (e.g., intra_mip_mode) from the video data indicating a MIP mode applied to the luma component of the coding unit, and reconstructs the two chroma components of the coding unit by applying the MIP mode of the luma component of the coding unit to the two chroma components of the coding unit. The following table shows syntax design specifications for decoding video data using ACT in VVC.

[0121] First, one additional syntax element, e.g., sps_act_enabled_flag, is added to the Sequence Parameter Set (SPS) to indicate whether ACT is enabled or not at the sequence level. In some embodiments, when color space conversion is applied to video content where the luma and chroma components have the same resolution, one bitstream compliance requirement needs to be added so that ACT can only be enabled for 4:4:4 chroma formats. Table 1 shows the modified SPS syntax table, with the above syntax added. [Table 1]

[0122] Flag sps_act_enabled_flag equal to 1 indicates that adaptive color space conversion is enabled. Flag sps_act_enabled_flag equal to 0 indicates that adaptive color space conversion is disabled, and flag cu_act_enabled_flag is not signaled and is inferred to be 0 for CUs that reference this SPS. It is a bitstream compliance requirement that the value of sps_act_enabled_flag be equal to 0 when ChromaArrayType is not equal to 3. [Table 2] JPEG2026035873000004.jpg251155JPEG2026035873000005.jpg249155JPEG20260358730 00006.jpg219159JPEG2026035873000007.jpg191158JPEG2026035873000008.jpg250152

[0123] The flag cu_act_enabled_flag equal to 1 indicates that the residual of the coding unit is coded in the YCgCo color space. The flag cu_act_enabled_flag equal to 0 indicates that the residual of the coding unit is coded in the original color space. If the flag cu_act_enabled_flag is not present, it is inferred to be equal to 0. [Table 3]

[0124] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over a computer-readable medium as one or more instructions or code and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which correspond to tangible media such as data storage media or communication media, including any medium that facilitates transfer of a computer program from one place to another, for example according to a communication protocol. As such, computer-readable media may generally correspond to (1) non-transitory tangible computer-readable storage media or (2) communication media such as a signal or carrier wave. Data storage media may be any available medium that can be accessed by one or more computers or one or more processors to obtain instructions, code, and / or data structures for implementing the implementations described herein. A computer program product may include computer-readable media.

[0125] The terms used in the description of implementations herein are for the purpose of describing particular implementations only and are not intended to limit the scope of the claims. When used in the description of implementations and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will also be understood that the term "and / or," as used herein, refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will also be understood that the terms "comprise" and / or "comprising," as used herein, specify the presence of stated features, elements, and / or components, but do not exclude the presence or addition of one or more other features, elements, components, and / or groups thereof.

[0126] Furthermore, although terms such as "first," "second," etc. may be used herein to describe various elements, it should be understood that these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first electrode may be referred to as a second electrode, and a second electrode may be referred to as a first electrode, without departing from the scope of implementation. The first electrode and the second electrode are both electrodes, but they are not the same electrode.

[0127] The description in this application has been presented for purposes of illustration and description and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, and alternative implementations will be apparent to those skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. The embodiments have been chosen and described to best explain the principles and practical applications of the invention and to enable others skilled in the art to understand the invention in various implementations and to best utilize the underlying principles and various implementations, with various modifications as suitable for the particular use contemplated. Therefore, it is to be understood that the scope of the claims should not be limited to the specific implementations disclosed, and that modifications and other implementations are intended to be included within the scope of the appended claims.

Claims

1. 1. A method for decoding video data, comprising: receiving video data corresponding to a coding unit from a bitstream, the coding unit being coded in an inter prediction mode or intra block copying; receiving a first syntax element from the video data, the first syntax element indicating whether the coding unit has a non-zero residual; upon determining that the first syntax element has a value other than zero, receiving a second syntax element from the video data, the second syntax element indicating whether the coding unit is coded using adaptive color space transformation (ACT); upon determining that the first syntax element has a value of 0, assigning a value of 0 to the second syntax element; determining whether to perform an inverse ACT on the video data of the coding unit according to a value of the second syntax element; A method comprising:

2. The method of claim 1 , wherein the coding unit is lossily coded with the ACT.

3. The method of claim 1 , wherein the coding unit is losslessly coded with the ACT.

4. The method of claim 1 , wherein the inverse ACT is from a YCgCo color space to an RGB color space.

5. The method of claim 1 , wherein the inverse ACT is from a YCgCo color space to a YCbCr color space.

6. The method of claim 1 , wherein the coding unit is coded in 4:4:4 chroma format.

7. 2. The method of claim 1 , wherein the first syntax element having the value of 0 indicates the absence of a residual syntax element in the bitstream for the coding unit, and the first syntax element having the value other than 0 indicates the presence of the residual syntax element in the bitstream for the coding unit.

8. The method of claim 1 , wherein the first syntax element is a cu_cbf flag and the second syntax element is a cu_act_enabled flag, both of which are CU-level flags.

9. 1. A method for decoding video data, comprising: receiving video data corresponding to a coding unit from a bitstream, the coding unit being coded in an intra prediction mode, the coding unit including a first chroma component, a second chroma component, and a luma component; receiving a first syntax element from the video data; receiving a second syntax element and a third syntax element from the video data, the second syntax element indicating whether the first chroma component has a non-zero residual, and the third syntax element indicating whether the second chroma component has a non-zero residual; In response to determining that the first syntax element has a non-zero value and that at least one of the two chroma components includes a non-zero residual, receiving a fourth syntax element from the video data, the fourth syntax element indicating whether the luma component has a non-zero residual; In response to determining that the first syntax element has a non-zero value and both of the saturation components have only zero residuals, assigning the fourth syntax element a non-zero value indicating that the luma component has a non-zero residual; determining whether to reconstruct the coding unit from the video data according to the fourth syntax element; A method comprising:

10. The method of claim 9 , wherein the first syntax element indicates whether the coding unit is coded using adaptive color space transformation (ACT).

11. The method of claim 9 , wherein the coding unit includes only one transform unit (TU).

12. determining whether to reconstruct the coding unit from the video data according to the fourth syntax element; reconstructing the residual of the luma component according to determining that the fourth syntax element has a value other than zero; and and abandoning reconstruction of the residual of the luma component in accordance with determining that the fourth syntax element has a value of 0.

13. 1. A method for decoding video data, comprising: receiving video data corresponding to a coding unit from a bitstream, the coding unit being coded in an intra prediction mode, the coding unit including two chroma components and one luma component; receiving a first syntax element from the video data, the first syntax element indicating whether the coding unit is coded using adaptive color space transformation (ACT); receiving a second syntax element from the video data, the second syntax element representing intra prediction parameters for the luma component of the coding unit; Upon determining that the second syntax element has a value other than zero indicating that the coding unit is coded using ACT, reconstructing the two chroma components of the coding unit by applying the same intra prediction parameters to the two chroma components of the coding unit as to the luma component of the coding unit; A method comprising:

14. The method of claim 13 , wherein the intra-prediction parameters indicate an intra-prediction direction to be applied to generate intra-predicted samples for the coding unit.

15. 1. A method for decoding video data, comprising: obtaining information from a bitstream indicating whether a coding unit in the video data is coded by a single tree partition or a dual tree partition; In response to determining that the coding units are coded using a single tree partition and that each coding unit includes both luma and chroma components, receiving a second syntax element for each coding unit from the video data, the value of the first syntax element indicating whether to perform an inverse adaptive color space transformation (ACT) for each coding unit; in response to determining that the coding unit is coded using a dual tree partition, and that coding units in a luma partition tree of the dual tree partition include only coding information related to luma components of the coding unit, and coding units in a saturation partition tree of the dual tree partition include only coding information related to chroma components of the coding unit; assigning a value of 0 to the second syntax element; determining whether to perform an inverse ACT for each coding unit in the coding tree unit according to the second syntax element; A method comprising:

16. determining whether to perform an inverse ACT on each coding unit in the coding tree unit according to the second syntax element; performing the inverse ACT for each coding unit in accordance with determining that the second syntax element has a value other than zero; and ceasing to perform the inverse ACT for each coding unit in accordance with determining that the second syntax element has a value of 0.

17. 1. A method for decoding video data, comprising: receiving video data corresponding to a coding unit from a bitstream; receiving a first syntax element from the video data, the first syntax element indicating whether the coding unit is coded using adaptive color space transformation (ACT); In accordance with determining that the first syntax element has a value of 0, receiving a second syntax element from the video data, the second syntax element indicating whether the coding unit is coded using an intra-subpartition prediction (ISP) mode; upon determining that the first syntax element has a value other than zero, assigning the second syntax element a value of 0, indicating that the coding unit is not coded using the ISP mode; and determining whether to reconstruct the coding unit from the video data using the ISP mode according to the second syntax element; A method comprising:

18. 1. A method for decoding video data, comprising: receiving video data corresponding to a coding unit from a bitstream, the coding unit being coded in an intra prediction mode, the coding unit including two chroma components and one luma component, the chroma components and the luma components having the same resolution; receiving a first syntax element from the video data indicating that the luma component of the coding unit is coded using a matrix weighted intra prediction (MIP) tool; upon determining that the first syntax element has a value other than zero indicating that the luma component of the coding unit is coded using the MIP tool, receiving a second syntax element from the video data indicating a MIP mode applied to the luminance component of the coding unit; reconstructing the two chroma components of the coding unit by applying the MIP mode of the luma component of the coding unit to the two chroma components of the coding unit; A method comprising:

19. one or more processing units; a memory coupled to the one or more processing units; a plurality of programs stored in said memory which, when executed by said one or more processing units, cause the electronic device to perform the method of claims 1 to 18; An electronic device comprising:

20. 20. A non-transitory computer-readable storage medium storing a plurality of programs for execution by an electronic device having one or more processing units, the plurality of programs, when executed by the one or more processing units, causing the electronic device to perform the method of claims 1 to 18.

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