Quantization parameter signaling for joint chroma residual mode in video decoding

Abstract

An example method includes decoding a sequence parameter set (SPS) referenced by one or more video data pictures from an encoded video bitstream, wherein decoding the SPS includes parsing a syntax element at a first position in the SPS, the syntax element indicating whether joint decoding of chroma residual is enabled or disabled for the one or more video data pictures that reference the SPS; and parsing one or more syntax elements representing a quantization parameter (QP) mapping table at a second position in the SPS that is located after the first position.

Description

[0001] This application claims priority to U.S. Application No. 17 / 031,238, filed on September 24, 2020, which claims the benefit of U.S. Provisional Application No. 62 / 907,401, filed on September 27, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to video encoding and video decoding. Background Art

[0003] Digital video capabilities can be incorporated into a variety of devices, including digital televisions, digital live broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video game devices, video game consoles, cellular or satellite wireless telephones, so-called "smartphones," video teleconferencing devices, video streaming devices, and the like. Digital video devices may implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4 Part 10, Advanced Video Coding (AVC), ITU-T H.265 / High Efficiency Video Coding (HEVC), and extensions of these standards. By implementing such video coding techniques, video devices can more efficiently transmit, receive, encode, decode, and / or store digital video information.

[0004] Video coding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be divided into video blocks, which may also be referred to as coding tree units (CTUs), coding units (CUs), and / or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction relative to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction relative to reference samples in neighboring blocks in the same picture, or temporal prediction relative to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames. Summary of the Invention

[0005] In one example, a method for decoding video data includes: decoding a sequence parameter set (SPS) referenced by one or more video data pictures according to a coded video bitstream, wherein decoding the SPS includes: parsing a syntax element at a first position in the SPS, the syntax element indicating whether joint decoding of chroma residuals is enabled or disabled for the one or more video data pictures that reference the SPS; and parsing one or more syntax elements representing a quantization parameter (QP) mapping table at a second position in the SPS that is located after the first position; decoding a picture parameter set (PPS) referenced by a picture in the one or more video data pictures according to the coded video bitstream, wherein decoding the PPS includes: parsing syntax elements indicating whether a QP offset for a jointly decoded chroma residual is included in a chroma QP offset table, and specifying a QP offset for deriving QP′. CbCr The luminance quantization parameter Qp′ Y whether a syntax element of the offset is decoded; and decoding the picture based on the SPS and the PPS.

[0006] In another example, a device for decoding video data includes: a memory configured to: store at least a portion of an encoded video bitstream; and one or more processors implemented in circuits and configured to: decode an SPS referenced by one or more video data pictures according to the encoded video bitstream, wherein, to decode the SPS, the one or more processors are configured to: parse a syntax element at a first position in the SPS, the syntax element indicating whether joint decoding of chroma residuals is enabled or disabled for the one or more video data pictures that reference the SPS; and parse one or more syntax elements representing a QP mapping table at a second position in the SPS that is located after the first position; and decode a PPS referenced by a picture in the one or more video data pictures according to the encoded video bitstream, wherein, to decode the PPS, the one or more processors are configured to: parse syntax elements indicating whether a QP offset for a jointly decoded chroma residual is included in a chroma QP offset table, and specifying a QP offset for deriving QP′. CbCr The luminance quantization parameter Qp′ Y whether a syntax element of the offset is decoded; and decoding the picture based on the SPS and the PPS.

[0007] In another example, a method for encoding video data includes encoding an SPS referenced by one or more video data pictures in a coded video bitstream, wherein encoding the SPS includes encoding a syntax element at a first position in the SPS, the syntax element indicating whether joint decoding of chroma residuals is enabled or disabled for the one or more video data pictures that reference the SPS; and encoding one or more syntax elements representing a QP mapping table at a second position in the SPS that is located after the first position; and encoding a PPS referenced by pictures in the one or more video data pictures in the coded video bitstream, wherein encoding the PPS includes encoding syntax elements indicating whether a QP offset for a jointly decoded chroma residual is included in a chroma QP offset table and specifying a QP offset for a chroma QP offset used to derive Qp′. CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

[0008] In another example, an apparatus for encoding video data includes a memory configured to store at least a portion of an encoded video bitstream; and one or more processors implemented in circuitry and configured to encode an SPS referenced by one or more video data pictures in the encoded video bitstream, wherein to encode the SPS, the one or more processors are configured to encode a syntax element at a first position in the SPS, the syntax element indicating whether joint decoding of chroma residuals is enabled or disabled for the one or more video data pictures that reference the SPS; and encode one or more syntax elements representing a QP mapping table at a second position in the SPS that is located after the first position; and encode a PPS referenced by a picture of the one or more video data pictures in the encoded video bitstream, wherein to encode the PPS, the one or more processors are configured to parse syntax elements indicating whether a QP offset for a jointly decoded chroma residual is included in a chroma QP offset table and specifying a QP offset for deriving QP′. CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

[0009] The details of one or more examples are set forth in the accompanying drawings and the description below.Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0011] Figure 2A and Figure 2B is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure and corresponding coding tree units (CTUs).

[0012] Figure 3 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0013] Figure 4 is a block diagram illustrating an example video decoder that can perform the techniques of this disclosure.

[0014] Figure 5 is a flowchart illustrating an example method for encoding a current block.

[0015] Figure 6 is a flow chart illustrating an example method for decoding a current block.

[0016] Figure 7 is a flow chart illustrating an example method for coding a current block of video data. DETAILED DESCRIPTION

[0017] In summary, the techniques of this disclosure relate to techniques for signaling parameters for joint decoding of chroma residuals when decoding video data. Residual data for chroma blocks can be signaled separately as Cb residual blocks and Cr residual blocks. However, in some examples, the Cb residual blocks and Cr residual blocks can be signaled jointly in a so-called joint chroma decoding mode. In joint chroma decoding mode, a video encoder can encode a single joint chroma residual block, and a video decoder can derive the Cb residual block and the Cr residual block from the single joint chroma residual block.

[0018] The availability of the joint chroma coding mode may be controlled by one or more syntax elements. For example, a video coder may signal a syntax element in parameter set a that indicates whether joint coding of the chroma residual is enabled or disabled for one or more video data pictures that reference the parameter set (e.g., sps_joint_cbcr_enabled_flag).

[0019] A video decoder can signal a mapping table that provides parameters for deriving chroma quantization parameters (QPs) from a co-located / corresponding luma QP. A video decoder can signal multiple mapping tables that can be used in different scenarios. For example, a video decoder can signal a Cb mapping table, a Cr mapping table, and a joint Cb-Cr mapping table. However, always signaling all three mapping tables may not be an efficient arrangement. For example, if joint coding of chroma residual is not enabled, there may be no need to signal a joint Cb-Cr mapping table because such a table will not be used.

[0020] As discussed in further detail below, Chernyak et al., "AHG17 / AHG15: On quantization control parameters signaling," Joint Video Experts Group, JVET-P0426, Geneva, CH, October 2019 (hereinafter referred to as "JVET-P0426") proposes that signaling a mapping table is based on a syntax element indicating whether joint coding of chroma residual is enabled or disabled for one or more video data pictures. Specifically, JVET-P0426 allows a video coder to avoid signaling a joint Cb-Cr mapping table when joint coding of chroma residual is not enabled.

[0021] However, the arrangement in JVET-P0426 may have one or more disadvantages. Specifically, as specified in JVET-P0426, the mapping table is parsed from the bitstream before the syntax element indicating whether joint decoding of chroma residual is enabled or disabled for one or more video data pictures. As such, the claimed ability to avoid signaling a joint Cb-Cr mapping table may not be achieved.

[0022] According to one or more techniques of this disclosure, a video decoder can be configured to parse a syntax element that indicates whether joint decoding of chroma residuals is enabled or disabled for one or more video data pictures. Thus, if the syntax element indicates that joint decoding of chroma residuals is not enabled, the video decoder can avoid signaling / parsing a joint Cb-Cr mapping table. In this way, the techniques of this disclosure can improve the coding efficiency of video data (e.g., reduce the number of bits used to represent the video data).

[0023] As described above, a video coder may signal a syntax element in parameter set a that indicates whether joint coding of chroma residuals is enabled or disabled for one or more video data pictures that reference the parameter set. Additionally, the video coder may signal one or more other syntax elements that specify various parameters for a joint chroma coding mode (e.g., pps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i]). For example, the video coder may signal a syntax element that specifies an offset to be applied to the luma QP when deriving the chroma QP. In some examples, signaling a syntax element that specifies an offset to be applied to the luma QP when deriving the chroma QP may depend on the value of the syntax element that indicates whether joint coding of chroma residuals is enabled or disabled for one or more video data pictures.

[0024] A video coder may parse these syntax elements from a parameter set different from the parameter set from which the syntax element indicating whether joint coding of chroma residuals is enabled or disabled for one or more video data pictures may be parsed. For example, a video coder may signal a syntax element that specifies an offset to be applied to the luma QP when deriving the chroma QP in a picture parameter set (PPS), and may signal a syntax element in a sequence parameter set (SPS) that indicates whether joint coding of chroma residuals is enabled or disabled for one or more video data pictures. However, one design principle of video coding may be to avoid parsing dependencies. Encoding a syntax element that specifies an offset to be applied to the luma QP when deriving the chroma QP in the PPS based on the value of the syntax element indicating whether joint coding of chroma residuals is enabled or disabled for one or more video data pictures may violate this design principle.

[0025] According to one or more techniques of this disclosure, rather than signaling a syntax element in the PPS that specifies parameters for the joint chroma coding mode as dependent on a syntax element in the SPS that specifies whether the joint chroma coding mode is enabled, a video coder may signal a syntax element in the PPS that specifies the presence or absence of a syntax element that specifies parameters for the joint chroma coding mode (e.g., pps_joint_cbcr_qp_offset_present_flag) in the PPS. Although the value of the syntax element in the PPS that specifies the presence or absence of the syntax element that specifies parameters for the joint chroma coding mode in the PPS may be at least semi-redundant with respect to the syntax element in the SPS that specifies whether the joint chroma coding mode is enabled, signaling this additional syntax element may eliminate interdependencies of parameter sets, which may be desirable.

[0026] Figure 1is a block diagram illustrating an example video encoding and decoding system 100 that can perform the techniques of this disclosure. Generally speaking, the techniques of this disclosure relate to transcoding (encoding and / or decoding) video data. Generally speaking, video data includes any data used to process video. Thus, video data can include original, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

[0027] like Figure 1 As shown, in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, source device 102 provides the video data to destination device 116 via a computer-readable medium 110. Source device 102 and destination device 116 can include any of a variety of devices, including desktop computers, notebook computers (i.e., laptop computers), tablet computers, set-top boxes, telephone handsets such as smartphones, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, etc. In some cases, source device 102 and destination device 116 can be equipped for wireless communication and, therefore, can be referred to as wireless communication devices.

[0028] exist Figure 1 In the example of FIG, source device 102 includes a video source 104, a memory 106, a video encoder 200, and an output interface 108. Destination device 116 includes an input interface 122, a video decoder 300, the memory 120, and a display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply techniques for quantization parameter signaling for a joint chroma residual mode. Thus, source device 102 represents an example of a video encoding device, while destination device 116 represents an example of a video decoding device. In other examples, the source device and destination device can include other components or arrangements. For example, source device 102 can receive video data from an external video source such as an external camera. Similarly, destination device 116 can interface with an external display device rather than including an integrated display device.

[0029] Figure 1The illustrated system 100 is merely an example. Generally, any digital video encoding and / or decoding device can implement the techniques for quantization parameter signaling for the joint chroma residual mode. The source device 102 and the destination device 116 are merely examples of such decoding devices, where the source device 102 generates decoded video data for transmission to the destination device 116. This disclosure refers to a "decoding" device as a device that performs decoding (encoding and / or decoding) of data. Thus, the video encoder 200 and the video decoder 300 represent examples of decoding devices, specifically, a video encoder and a video decoder, respectively. In some examples, the source device 102 and the destination device 116 can operate in a substantially symmetrical manner, such that each of the source device 102 and the destination device 116 includes video encoding and decoding components. Thus, the system 100 can support one-way or two-way video transmission between the source device 102 and the destination device 116, for example, for video streaming, video playback, video broadcasting, or video telephony.

[0030] Typically, video source 104 represents the source of video data (i.e., raw, unencoded video data) and provides a series of sequential pictures (also referred to as "frames") of video data to video encoder 200, which encodes the picture data. Video source 104 of source device 102 may include a video capture device (e.g., a camera, a video archive containing previously captured raw video, and / or a video feed interface) to receive video from a video content provider. As another alternative, video source 104 may generate computer graphics-based data as the source video, or a combination of real-time video, archived video, and computer-generated video. In each case, video encoder 200 encodes captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange the images from the order in which they were received (sometimes referred to as "display order") into a decoding order for decoding. Video encoder 200 may generate a bitstream comprising the encoded video data. Source device 102 may then output the encoded video data onto computer-readable medium 110 via output interface 108 for receipt and / or retrieval by, for example, input interface 122 of destination device 116 .

[0031] Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memory. In some examples, memories 106 and 120 can store raw video data, e.g., raw video from video source 104 and raw, decoded video data from video decoder 300. Additionally or alternatively, memories 106 and 120 can store software instructions executable by, for example, video encoder 200 and video decoder 300, respectively. Although memory 106 and memory 120 are shown separately from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 may also include internal memory to achieve functionally similar or equivalent purposes. Furthermore, memories 106 and 120 can store encoded video data, e.g., encoded video data output from video encoder 200 and input to video decoder 300. In some examples, portions of memories 106 and 120 can be allocated as one or more video buffers, e.g., to store raw, decoded, and / or encoded video data.

[0032] The computer-readable medium 110 can represent any type of medium or device capable of transmitting encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium to enable the source device 102 to send the encoded video data directly to the destination device 116 in real time, for example, via a radio frequency network or a computer-based network. The output interface 108 can modulate a transmission signal including the encoded video data according to a communication standard (e.g., a wireless communication protocol), and the input interface 122 can demodulate the received transmission signal. The communication medium can include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium can 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 can include routers, switches, base stations, or any other device that facilitates communication from the source device 102 to the destination device 116.

[0033] In some examples, source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access the encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, a Blu-ray disc, a DVD, a CD-ROM, a flash memory, a volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0034] In some examples, source device 102 may output the encoded video data to a file server 114 or another intermediate storage device that may store the encoded video generated by source device 102. Destination device 116 may access the stored video data from file server 114 via streaming or downloading. File server 114 may be any type of server device capable of storing encoded video data and transmitting the encoded video data to destination device 116. File server 114 may represent a network server (e.g., for a website), a file transfer protocol (FTP) server, a content delivery network device, or a network attached storage (NAS) device. Destination device 116 may access the encoded video data from file server 114 via any standard data connection, including an internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., a digital subscriber line (DSL), a cable modem, etc.), or a combination of the two suitable for accessing the encoded video data stored on file server 114. File server 114 and input interface 122 may be configured to operate according to a streaming protocol, a download transfer protocol, or a combination thereof.

[0035] The output interface 108 and the input interface 122 may represent wireless transmitters / receivers, modems, wired network components (e.g., Ethernet cards), wireless communication components that operate according to any of the various IEEE 802.11 standards, or other physical components. In examples where the output interface 108 and the input interface 122 include wireless components, the output interface 108 and the input interface 122 may be configured to transmit data (e.g., encoded video data) according to a cellular communication standard (e.g., 4G, 4G-LTE (Long Term Evolution), LTE-Advanced, 5G, etc.). In some examples where the output interface 108 includes a wireless transmitter, the output interface 108 and the input interface 122 may be configured to transmit data (e.g., encoded video data) according to other wireless standards (e.g., IEEE 802.11 specifications, IEEE 802.15 specifications (e.g., ZigBee 5G), etc.). TM ), Bluetooth TM Standards, etc.) to transmit data (e.g., encoded video data). In some examples, source device 102 and / or destination device 116 may include respective system-on-chip (SoC) devices. For example, source device 102 may include an SoC device to perform functions contributed to video encoder 200 and / or output interface 108, and destination device 116 may include an SoC device to perform functions contributed to video decoder 300 and / or input interface 122.

[0036] The techniques of the present disclosure may be applied to video decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission, such as dynamic adaptive streaming over HTTP (DASH), digital video encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0037] The input interface 122 of the destination device 116 receives an encoded video bitstream from the computer-readable medium 110 (e.g., a communication medium, a storage device 112, a file server 114, etc.). The encoded video bitstream may include signaling information defined by the video encoder 200 and used by the video decoder 300, such as syntax elements with values ​​describing characteristics and / or processing of video blocks or other coding units (e.g., slices, pictures, groups of pictures, sequences, etc.). The display device 118 displays decoded pictures of the decoded video data to a user. The display device 118 may represent any of a variety of display devices, such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0038] Although not in Figure 1 , but in some examples, the video encoder 200 and the video decoder 300 may be integrated with an audio encoder and / or an audio decoder, respectively, and may include appropriate MUX-DEMUX units or other hardware and / or software for processing a multiplexed stream including both audio and video in a common data stream. If applicable, the MUX-DEMUX unit may conform to the ITU H.223 multiplexer protocol or other protocols, such as the User Datagram Protocol (UDP).

[0039] The video encoder 200 and the video decoder 300 can each be implemented as any of a variety of suitable encoder and / or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic units, software, hardware, firmware, or any combination thereof. When these techniques are partially implemented in software, the device may store instructions for the software in a suitable non-transitory computer-readable medium and use one or more processors to execute the instructions in hardware to perform the techniques of the present disclosure. Each of the video encoder 200 and the video decoder 300 may 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 corresponding device. A device including the video encoder 200 and / or the video decoder 300 may include an integrated circuit, a microprocessor, and / or a wireless communication device, such as a cellular phone.

[0040] Video coding standards include ITU-T H.261, ISO / IEC MPEG-1 Visual, ITU-T H.262 or ISO / IEC MPEG-2 Visual, ITU-T H.263, ISO / IEC MPEG-4 Visual (MPEG-4 Part 2), ITU-T H.264 (also known as ISO / IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multi-view Video Coding (MVC) extensions, and ITU-T H.265 (also known as ISO / IEC MPEG-4 HEVC) and its extensions. During the Joint Video Experts Group (JVET) meeting in April 2018, the Versatile Video Coding (VVC) standardization activity (also known as ITU-T H.266) began by evaluating video compression technologies submitted to the call for proposals.

[0041] The video encoder 200 and the video decoder 300 may operate in accordance with a video coding standard, such as ITU-T H.265, also known as High Efficiency Video Coding (HEVC), or extensions thereof, such as multi-view and / or scalable video coding extensions. Alternatively, the video encoder 200 and the video decoder 300 may operate in accordance with other proprietary or industry standards, such as the Joint Exploratory Test Model (JEM) or ITU-T H.266, also known as Versatile Video Coding (VVC). The latest draft of the VVC standard is described in Bross et al., “Versatile Video Coding (Draft 6)”, Joint Video Experts Team (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11, 15th Meeting, Gothenburg, SE, July 3-12, 2019, JVET-O2001-v14 (hereinafter referred to as “VVC Draft 6”). However, the techniques of the present disclosure are not limited to any particular coding standard.

[0042] Typically, the video encoder 200 and the video decoder 300 can perform block-based decoding of a picture. The term "block" generally refers to a structure that includes data to be processed (e.g., to be encoded and / or decoded, or to be used in other ways during the encoding and / or decoding process). For example, a block can include a two-dimensional matrix of luminance and / or chrominance data samples. Typically, the video encoder 200 and the video decoder 300 can decode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, instead of decoding the red, green, and blue (RGB) data of the picture samples, the video encoder 200 and the video decoder 300 can decode the luminance and chrominance components, where the chrominance components may include red and blue chrominance components. In some examples, the video encoder 200 converts the received RGB formatted data into a YUV representation before encoding, and the video decoder 300 converts the YUV representation into an RGB format. Alternatively, pre-processing and post-processing units (not shown) can perform these conversions.

[0043] This disclosure may generally refer to the decoding (e.g., encoding and decoding) of a picture to include the process of encoding or decoding the data of the picture. Similarly, this disclosure may refer to the decoding of a block of a picture to include the process of encoding or decoding the data of the block, such as prediction and / or residual decoding. A coded video bitstream typically includes a series of values ​​of syntax elements that represent decoding decisions (e.g., decoding mode) and the division of the picture into blocks. Therefore, references to decoding a picture or block should generally be understood to refer to decoding the values ​​of the syntax elements that form the picture or block.

[0044] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (e.g., video encoder 200) divides a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video decoder divides the CTU and CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without child nodes may be referred to as a "leaf node," and the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video decoder may further divide the PU and TU. For example, in HEVC, the residual quadtree (RQT) represents the division of the TU. In HEVC, PU represents inter-prediction data, and TU represents residual data. The intra-predicted CU includes intra-prediction information, such as intra-mode indication.

[0045] As another example, the video encoder 200 and the video decoder 300 can be configured to operate according to JEM or VVC. According to JEM or VVC, the video decoder (e.g., the video encoder 200) divides the picture into multiple coding tree units (CTUs). The video encoder 200 can divide the CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure. The QTBT structure eliminates the concept of multiple partition types, such as the separation between CU, PU, ​​and TU of HEVC. The QTBT structure includes two levels: a first level divided according to quadtree partitioning, and a second level divided according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to the coding units (CUs).

[0046] In the MTT partition structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more types of ternary tree (TT) (also known as ternary tree (TT)) partitioning. Ternary tree or ternary tree partitioning is a partitioning method that divides a block into three sub-blocks. In some examples, ternary tree or ternary tree partitioning divides a block into three sub-blocks instead of dividing the original block by the center. Partition types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0047] In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT or MTT structure to represent each of the luma and chroma components, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT or MTT structures, e.g., one QTBT / MTT structure for the luma component and another QTBT / MTT structure for the two chroma components (or two QTBT / MTT structures for corresponding chroma components).

[0048] The video encoder 200 and the video decoder 300 can be configured to use quadtree partitioning for each HEVC, QTBT partition, MTT partition, or other partitioning structure. For illustrative purposes, the technology of the present disclosure is described with respect to QTBT partitioning. However, it should be understood that the technology of the present disclosure can also be applied to video decoders configured to use quadtree partitioning or other types of partitioning.

[0049] Blocks (e.g., CTUs or CUs) can be grouped in a picture in various ways. As an example, a brick can refer to a rectangular area of ​​a CTU row within a particular tile in a picture. A tile can be a rectangular area of ​​a CTU within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular area of ​​a CTU with a height equal to the picture height and a width specified by a syntax element (e.g., as specified in a picture parameter set). A tile row refers to a rectangular area of ​​a CTU with a height specified by a syntax element (e.g., such as in a picture parameter set) and a width equal to the picture width.

[0050] In some examples, a tile can be divided into multiple bricks, each of which can include one or more CTU rows within the tile. Tiles that are not divided into multiple bricks can also be referred to as bricks. However, bricks that are true subsets of a tile cannot be referred to as tiles.

[0051] Tiles in a picture can also be arranged into slices. A slice can be an integer number of tiles of a picture that can be contained exclusively in a single Network Abstraction Layer (NAL) unit. In some examples, a slice includes a sequence of consecutive complete tiles of multiple complete tiles or just one tile.

[0052] This disclosure may use "NxN" and "N by N" interchangeably to refer to the sample dimensions of a block (e.g., a CU or other video block) in terms of vertical and horizontal dimensions, for example, 16x16 samples or 16 by 16 samples. Typically, a 16x16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Likewise, an NxN CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. Furthermore, a CU does not necessarily have the same number of samples in the horizontal direction as in the vertical direction. For example, a CU may include N×M samples, where M is not necessarily equal to N.

[0053] The video encoder 200 encodes the video data of the CU representing prediction and / or residual information and other information. The prediction information indicates how the CU will be predicted in order to form a prediction block for the CU. The residual information typically represents the sample-by-sample difference between the CU samples before encoding and the prediction block.

[0054] To predict a CU, the video encoder 200 may typically form a prediction block for the CU through inter-prediction or intra-prediction. Inter-prediction typically refers to predicting a CU based on data from a previously coded picture, while intra-prediction typically refers to predicting a CU based on previously coded data from the same picture. To perform inter-prediction, the video encoder 200 may use one or more motion vectors to generate a prediction block. The video encoder 200 may typically perform a motion search to identify a reference block that closely matches the CU, for example, in terms of the difference between the CU and a reference block. The video encoder 200 may calculate a difference metric using the sum of absolute differences (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared difference (MSD), or other such differences to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 may use unidirectional prediction or bidirectional prediction to predict the current CU.

[0055] Some examples of JEM and VVC also provide an affine motion compensation mode, which can be considered an inter-prediction mode. In the affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion (e.g., zooming in or out, rotation, perspective motion, or other irregular motion types).

[0056] To perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. Certain examples of JEM and VVC provide 67 intra prediction modes, including various directional modes as well as planar mode and DC mode. Typically, the video encoder 200 selects an intra prediction mode that describes samples adjacent to the current block (e.g., a block of a CU), from which the samples of the current block are predicted. Assuming that the video encoder 200 decodes CTUs and CUs in raster scan order (from left to right, from top to bottom), such samples may typically be above, above to the left, or to the left of the current block in the same picture as the current block.

[0057] The video encoder 200 encodes data indicating a prediction mode for the current block. For example, for inter-prediction mode, the video encoder 200 may encode data indicating which of various available inter-prediction modes to use, as well as motion information for the corresponding mode. For unidirectional or bidirectional inter-prediction, for example, the video encoder 200 may encode motion vectors using Advanced Motion Vector Prediction (AMVP) or merge mode. The video encoder 200 may use a similar mode to encode motion vectors for affine motion compensation mode.

[0058] After a prediction (e.g., intra-prediction or inter-prediction of a block), the video encoder 200 may calculate residual data for the block. The residual data (e.g., a residual block) represents the sample-by-sample difference between the block and a prediction block for the block formed using the corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to produce transformed data in a transform domain rather than a sample domain. For example, the video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. Additionally, the video encoder 200 may apply a secondary transform after the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), and the like. After applying the one or more transforms, the video encoder 200 generates transform coefficients.

[0059] As described above, after performing any transforms to produce transform coefficients, the video encoder 200 may perform quantization of the transform coefficients. Quantization generally refers to the process of quantizing transform coefficients to potentially reduce the amount of data used to represent the transform coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 may reduce the bit depth associated with some or all transform coefficients. For example, during quantization, the video encoder 200 may round down an n-bit value to an m-bit value, where n is greater than m. In some examples, to perform quantization, the video encoder 200 may perform a bitwise right shift of the value to be quantized.

[0060] After quantization, the video encoder 200 may scan the transform coefficients to produce a one-dimensional vector from the two-dimensional matrix comprising the quantized transform coefficients. The scan may be designed to place transform coefficients with higher energy (and therefore lower frequency) at the front of the vector and transform coefficients with lower energy (and therefore higher frequency) at the back of the vector. In some examples, the video encoder 200 may scan the quantized transform coefficients using a predefined scan order to produce a serialized vector and then entropy encode the quantized transform coefficients of the vector. In other examples, the video encoder 200 may perform adaptive scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, the video encoder 200 may entropy encode the one-dimensional vector, for example, according to context-adaptive binary arithmetic coding (CABAC). The video encoder 200 may also entropy encode the values ​​of syntax elements that describe metadata associated with the encoded video data for use by the video decoder 300 when decoding the video data.

[0061] To perform CABAC, the video encoder 200 may assign context within a context model to a symbol to be transmitted. The context may relate to, for example, whether the neighboring values ​​of the symbol are zero values. The probability determination may be based on the context assigned to the symbol.

[0062] The video encoder 200 may also generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, to the video decoder 300, for example, in a picture header, a block header, a slice header, or other syntax data (e.g., a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS). The video decoder 300 may similarly decode such syntax data to determine how to decode the corresponding video data.

[0063] In this way, the video encoder 200 can generate a bitstream including: coded video data, such as syntax elements describing the division of a picture into blocks (e.g., CUs), and prediction and / or residual information for the blocks. Ultimately, the video decoder 300 can receive the bitstream and decode the coded video data.

[0064] Generally, the video decoder 300 performs a process that is inverse to the process performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 can use CABAC to decode the values ​​of the syntax elements of the bitstream in a manner substantially similar to (although inverse to) the CABAC encoding process of the video encoder 200. The syntax elements can define partition information of a picture into CTUs and divide each CTU according to a corresponding partition structure (e.g., a QTBT structure) to define CUs of the CTU. The syntax elements can also define prediction and residual information for a block (e.g., a CU) of video data.

[0065] The residual information may be represented by, for example, quantized transform coefficients. The video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of the block to reproduce a residual block for the block. The video decoder 300 uses the signaled prediction mode (intra-prediction or inter-prediction) and related prediction information (e.g., motion information for inter-prediction) to form a prediction block for the block. The video decoder 300 may then combine the prediction block and the residual block (sample by sample) to reproduce the original block. The video decoder 300 may perform additional processing, such as a deblocking process to reduce visual artifacts along block boundaries.

[0066] VVC draft 6 supports a mode for joint decoding of chroma residual. The use (activation) of the joint chroma decoding mode is indicated by the TU level flag tu_joint_cbcr_residual_flag, and the selected mode is implicitly indicated by the chroma CBF. The flag tu_joint_cbcr_residual_flag is present if one or both of the chroma CBFs of the TU are equal to 1. In the PPS and slice header, chroma QP offset values ​​are signaled for the joint chroma residual decoding mode to distinguish them from the regular chroma QP offset values ​​signaled for the regular chroma residual decoding mode. These chroma QP offset values ​​are used to derive the chroma QP values ​​for those blocks decoded using the joint chroma residual decoding mode. When the corresponding joint chroma decoding mode (mode 2 in Table 3-12) is active in a TU, the chroma QP offset will be added to the applied luma-derived chroma QP during quantization and decoding of that TU. For other modes (modes 1 and 3 in Table 3-12), the chroma QP can be derived in the same way as for regular Cb or Cr blocks. The process of reconstructing the chroma residuals (resCb and resCr) from the transmitted transform blocks is described in Table 3-12. When this mode is activated, a single joint chroma residual block (resJointC[x][y] in Table 3-12) can be signaled, and the residual block for Cb (resCb) and the residual block for Cr (resCr) are derived taking into account information such as tu_cbf_cb, tu_cbf_cr, and CSign (which are symbol values ​​specified in the slice header). Examples of this technique can be found in Helmrich et al., “Joint chroma residual coding with multiple modes (tests CE7-2.1, CE7-2.2)”, Joint Video Experts Group document, JVET-O0105, Gothenburg, SE, July 2019; and Helmrich et al., “Alternative configuration for joint chroma residual coding”, Joint Video Experts Group document, JVET-O0543, Gothenburg, SE, July 2019.

[0067] On the encoder side, the joint chroma components can be derived as follows. Depending on the mode (listed in the table above), the encoder can generate resJointC{1,2} as follows:

[0068] If mode equals 2 (single residual with reconstruction Cb=C, Cr=CSign*C), then according to

[0069] resJointC[x][y]=(resCb[x][y]+CSign*resCr[x][y]) / 2 to determine the joint residual.

[0070] Otherwise, if mode is equal to 1 (single residual with reconstruction Cb=C,Cr=(CSign*C) / 2), then according to

[0071] resJointC[x][y]=(4*resCb[x][y]+2*CSign*resCr[x][y]) / 5 to determine the joint residual.

[0072] Otherwise (mode equals 3, i.e., single residual, reconstruction Cr = C, Cb = (CSign*C) / 2), then according to

[0073] resJointC[x][y]=(4*resCr[x][y]+2*CSign*resCb[x][y]) / 5 to determine the joint residual.

[0074] Table 3-12 Reconstruction of chroma residual. The value CSign is the sign value (+1 or –1) specified in the slice header, and resJointC[][] is the residual sent.

[0075]

[0076] The three joint chroma coding modes described above are only supported in I slices. In P and B slices, only mode 2 can be supported. Therefore, in P and B slices, the syntax element tu_joint_cbcr_residual_flag is present only when both chroma cbfs are 1. Note that transform depth is removed from the context modeling of tu_cbf_luma and tu_cbf_cb.

[0077] In Yang et al., “Non-CE6: Refined LFNST restriction with MIP,” Joint Video Experts Group, JVET-P0376, Geneva, CH, October 2019 (see also Xu et al., “CE8-related: A SPS LevelFlag for BDPCM and JCCR,” Joint Video Experts Group document, JVET-O0376, Gothenburg, SE, July 2019), a sequence parameter set (SPS) level flag was added to control the enable / disable of joint Cb-Cr for each video sequence (see also Ramasubramonian et al., “AHG15: On signalling of chroma QP tables,” Joint Video Experts Group document, JVET-O0543, Gothenburg, SE, July 2019). VVC draft 6 includes these techniques, and the corresponding flag is called sps_joint_cbcr_enabled_flag.

[0078] In Ramasubramonian et al., "AHG15: On signalling of chroma QP tables," Joint Video Experts Group, JVET-O0650, Gothenburg, SE, July 2019 (hereinafter referred to as "JVET-O0650"), SPS-level signaling of chroma QP mapping tables for deriving chroma QP from co-located / corresponding luma block QPs is proposed. JVET-O0650 provides the flexibility to use different tables for Cb, Cr, and joint Cb-Cr, and to modify the tables based on the nature of the video content (SDR / HDR-PQ / HDR-HLG).

[0079] The aforementioned techniques may present one or more drawbacks. Specifically, in VVC draft 6, when sps_joint_cbcr_enabled_flag is 0, the following occurs:

[0080] 1. Chroma QP mapping tables (delta_qp_in_val_minus1[i][j] and delta_qp_out_val[i][j]) are still signaled for joint Cb-Cr.

[0081] 2. Likewise, pps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] are signaled at the picture parameter set (PPS) level.

[0082] This signaling may be redundant, which may unnecessarily reduce coding efficiency (e.g., increase the number of bits used to represent video data at a certain quality). The relevant part of VVC draft 6 is excerpted below:

[0083]

[0084]

[0085]

[0086] In Aspect 1 of Chernyak et al., “AHG17 / AHG15: On quantization control parameters signaling,” Joint Video Experts Group, JVET-P0426, Geneva, CH, October 2019 (hereinafter referred to as “JVET-P0426”), it is proposed to use the sps_joint_cbcr_enabled_flag to parse the chroma QP map and PPS level QP offset parameters, as shown in the modification in the normative text of JVET-P0426 shown below.

[0087]

[0088]

[0089]

[0090]

[0091] The solution proposed in aspect 1 of JVET-P0426 may have one or more shortcomings. Two specific shortcomings are discussed below. The first shortcoming is that, currently, at the SPS level, sps_joint_cbcr_enabled_flag is parsed after the chroma QP mapping table is parsed. Therefore, the desired result of the proposed aspect (removing the chroma QP mapping table for JCCR) may not be achieved unless the parsing order is modified. The second shortcoming is that, at the PPS level, the parsing of the PPS syntax elements pps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] depends on the SPS syntax element sps_joint_cbcr_enabled_flag. However, one of the design principles of VVC is to avoid parameter set parsing dependencies. In this case, the PPS parameters depend on the SPS parameters, which violates this design principle.

[0092] The present disclosure proposes several techniques that may address the shortcomings discussed above and / or provide other advantages. The techniques of the present disclosure may include two aspects, which may be used independently or in combination. According to a first aspect of the present disclosure, a video encoder (e.g., video encoder 200 and / or video decoder 300) may decode (e.g., encode or parse) a syntax element that indicates whether joint decoding of chroma residuals (e.g., sps_joint_cbcr_enabled_flag) is enabled or disabled before parsing the chroma QP mapping table. For example, the syntax table may be modified to adjust the parsing order of the sps_joint_cbcr_enabled_flag.

[0093] According to the second aspect of the present disclosure, the video encoder may code a syntax element (e.g., pps_joint_cbcr_qp_offset_present_flag) to control whether the chroma QP offset table includes a QP offset for the joint Cb-Cr residual and to specify a QP offset for deriving Qp′. CbCr The luminance quantization parameter Qp′ Y In contrast to the approach of JVET-P0426, this approach does not have any parsing dependencies.

[0094] Example changes compared to VVC draft 6 are italicized below:

[0095]

[0096]

[0097]

[0098] pps_joint_cbcr_qp_offset_present_flag equal to 1 indicates that pps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] are present in the PPS RBSP syntax structure. pps_joint_cbcr_qp_offset_present_flag equal to 0 indicates that pps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] are not present in the PPS RBSP syntax structure. When ChromaArrayType is equal to 0 or sps_joint_cbcr_enabled_flag is equal to 0, the value of pps_joint_cbcr_qp_offset_presnt_flag shall be equal to 0.

[0099] pps_joint_cbcr_qp_offset specifies the offset used to derive Qp′ CbCr The luminance quantization parameter Qp′ Y The value of pps_joint_cbcr_qp_offset shall be in the range of -12 to +12, inclusive. When pps_joint_cbcr_qp_offset_present_flag is equal to 0, pps_joint_cbcr_qp_offset is not present and is inferred to be equal to 0.

[0100] cb_qp_offset_list[i], cr_qp_offset_list[i] and joint_cbcr_qp_offset_list[i] specify Qp′ respectively Cb , Qp′ Cr and Qp′ CbC The offset used in the derivation of . The values ​​of cb_qp_offset_list[i], cr_qp_offset_list[i], and joint_cbcr_qp_offset_list[i] shall be in the range -12 to +12, inclusive. When pps_joint_cbcr_qp_offset_present_flag is equal to 0, joint_cbcr_qp_offset_list[i] is not present and is inferred to be equal to 0.

[0101] According to the techniques of the present disclosure, a video decoder may decode a sequence parameter set (SPS) referenced by one or more video data pictures, wherein, to decode the SPS, the video encoder may: decode a syntax element at a first position in the SPS, the syntax element indicating whether joint decoding of chroma residuals is enabled or disabled for the one or more video data pictures that reference the SPS; and decode one or more syntax elements representing a quantization parameter (QP) mapping table at a second position in the SPS that is located after the first position; and decode a picture parameter set (PPS) referenced by a picture in the one or more video data pictures, wherein, to decode the PPS, the video decoder may decode syntax elements indicating whether a QP offset for a joint chroma residual is included in a chroma QP offset table, and specifying a QP offset for deriving QP′. CbCr The luminance quantization parameter Qp′ Y whether the syntax element of the offset is decoded; and decoding the picture based on the SPS and PPS.

[0102] This disclosure may generally refer to "signaling" certain information, such as syntax elements. The term "signaling" may generally refer to the communication of values ​​for syntax elements and / or other data used to decode encoded video data. That is, video encoder 200 may signal the values ​​of syntax elements in a bitstream. Generally, signaling refers to generating values ​​in the bitstream. As described above, source device 102 may transmit the bitstream to destination device 116 in substantially real time or in non-real time, such as may occur when storing syntax elements to storage device 112 for later retrieval by destination device 116.

[0103] Figure 2A and Figure 2Bis a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure 130 and a corresponding coding tree unit (CTU) 132. Solid lines represent quadtree splits and dashed lines represent binary tree splits. In each split (i.e., non-leaf) node of the binary tree, a flag bit is signaled to indicate which split type (i.e., horizontal or vertical) is used, in this example, 0 indicates horizontal split and 1 indicates vertical split. For quadtree splits, since the quadtree node splits a block horizontally and vertically into 4 sub-blocks of equal size, there is no need to indicate the split type. Therefore, the video encoder 200 can encode syntax elements (e.g., split information) at the region tree level (i.e., solid line) of the QTBT structure 130 and syntax elements (e.g., split information) at the prediction tree level (i.e., dashed line) of the QTBT structure 130, and the video decoder 300 can decode the above syntax elements. The video encoder 200 may encode video data (eg, prediction and transform data) of the CU represented by the terminal leaf node of the QTBT structure 130 , and the video decoder 300 may decode the video data.

[0104] generally, Figure 2B The CTU 132 may be associated with parameters that define the size of blocks corresponding to nodes of the QTBT structure 130 at first and second levels. These parameters may include a CTU size (representing the size of the CTU 132 in a sample), a minimum quadtree size (MinQTSize, representing the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, representing the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, representing the maximum allowed maximum binary tree depth), and a minimum binary tree size (MinBTSize, representing the minimum allowed binary tree leaf node size).

[0105] The root node of the QTBT structure corresponding to the CTU can have four child nodes at the first level of the QTBT structure, and each child node can be divided according to the quadtree partitioning. That is, the node at the first level is a leaf node (no child nodes) or has four child nodes. The example of the QTBT structure 130 represents such a node, including a parent node and child nodes with solid line branches. If the node at the first level is not larger than the maximum allowed binary tree root node size (MaxBTSize), the node can be further divided by the corresponding binary tree. The binary tree splitting of a node can be iterated until the node generated by the split reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of the QTBT structure 130 represents such a node as having a dotted line for branching. The binary tree leaf node is called a coding unit (CU), which is used for prediction (e.g., intra-picture prediction or inter-picture prediction) and transformation without any further partitioning. As discussed above, a CU may also be referred to as a "video block" or "block."

[0106] In one example of a QTBT partitioning structure, the CTU size is set to 128x128 (luminance sample and two corresponding 64x64 chroma samples), MinQTSize is set to 16x16, MaxBTSize is set to 64x64, MinBTSize (for width and height) is set to 4, and MaxBTDepth is set to 4. Quadtree partitioning is first applied to the CTU to generate quadtree leaf nodes. The size of the quadtree leaf node can range from 16x16 (i.e., MinQTSize) to 128x128 (i.e., the CTU size). If the leaf quadtree node is 128x128, the leaf quadtree node will not be further split by the binary tree because the size exceeds MaxBTSize (i.e., 64x64 in this example). Otherwise, the binary tree will further split the leaf quadtree node. Therefore, the quadtree leaf node is also the root node of the binary tree, and the depth of the binary tree is 0. When the binary tree depth reaches MaxBTDepth (4 in this example), further splitting is not allowed. When the width of the binary tree node is equal to MinBTSize (4 in this example), it means that no further horizontal splitting is allowed. Similarly, a binary tree node with a height equal to MinBTSize means that no further vertical splitting is allowed for the binary tree node. As mentioned above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further partitioning.

[0107] Figure 3 is a block diagram illustrating an example video encoder 200 that can perform the techniques of this disclosure. Figure 3This is for purposes of explanation and should not be considered limiting of the techniques broadly illustrated and described in this disclosure. For illustrative purposes, this disclosure describes video encoder 200 in the context of video coding standards, such as the developing HEVC video coding standard and the H.266 video coding standard. However, the techniques of this disclosure are not limited to these video coding standards and are generally applicable to video encoding and decoding.

[0108] exist Figure 3 In the example of FIG, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218, and an entropy coding unit 220. Any or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filter unit 216, the DPB 218, and the entropy coding unit 220 can be implemented in one or more processors or in processing circuitry. For example, the units of the video encoder 200 can be implemented as one or more circuits or logic elements as part of a hardware circuit, or as part of a processor, ASIC, or FPGA. Furthermore, the video encoder 200 can include additional or alternative processors or processing circuitry to perform these and other functions.

[0109] The video data memory 230 may store video data to be encoded by the components of the video encoder 200. The video encoder 200 may receive video data from, for example, the video source 104 ( Figure 1 ) receives video data stored in the video data memory 230. The DPB 218 can be used as a reference picture memory that stores reference video data for use by the video encoder 200 when predicting subsequent video data. The video data memory 230 and the DPB 218 can 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.

[0110] Video data memory 230 and DPB 218 may be provided by the same memory device or separate memory devices. In various examples, video data memory 230 may be on-chip with other components of video encoder 200, as shown, or off-chip relative to those components.

[0111] In this disclosure, unless specifically described as such, references to the video data memory 230 should not be construed as limited to memory internal to the video encoder 200, nor should references to the video data memory 230 be construed as limited to memory external to the video encoder 200, unless specifically described as such. Rather, references to the video data memory 230 should be understood as reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). Figure 1 The memory 106 may also provide temporary storage for the outputs of the various units of the video encoder 200 .

[0112] Shown Figure 3 The various units of the video encoder 200 are described to help understand the operations performed by the video encoder 200. These units can be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide specific functions and are pre-set in the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functions in the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (for example, to receive parameters or output parameters), but the type of operations performed by fixed-function circuits is generally immutable. In some examples, one or more of these units can be different circuit blocks (fixed-function or programmable), and in some examples, one or more of these units can be integrated circuits.

[0113] The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and / or a programmable core formed from programmable circuits. In an example where the operation of the video encoder 200 is performed using software executed by a programmable circuit, the memory 106 ( Figure 1 ) may store instructions (eg, object code) for software received and executed by the video encoder 200, or another memory (not shown) within the video encoder 200 may store these instructions.

[0114] The video data memory 230 is configured to store received video data. The video encoder 200 can retrieve a picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 can be the original video data to be encoded.

[0115] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. The mode selection unit 202 may include additional functional units to perform video prediction according to other prediction modes. For example, the mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, and the like.

[0116] The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and the resulting rate-distortion values ​​for these combinations. The encoding parameters may include the division of a CTU into CUs, the prediction mode used for a CU, the transform type used for the residual data of a CU, the quantization parameter used for the residual data of a CU, etc. The mode selection unit 202 may ultimately select a combination of encoding parameters that has a better rate-distortion value than the other tested combinations.

[0117] The video encoder 200 may divide a picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs into a slice. The mode selection unit 202 may divide the CTUs of the picture according to a tree structure (e.g., the QTBT structure or quadtree structure of HEVC described above). As described above, the video encoder 200 may form one or more CUs by dividing the CTUs according to the tree structure. Such CUs may also be generally referred to as "video blocks" or "blocks."

[0118] In general, mode select unit 202 also controls its components (e.g., motion estimation unit 222, motion compensation unit 224, and intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU, or, in HEVC, the overlapping portion of a PU and TU). For inter prediction of the current block, motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in DPB 218). Specifically, motion estimation unit 222 may calculate values ​​representing how similar potential reference blocks are to the current block, such as based on sum of absolute differences (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared difference (MSD), and the like. Motion estimation unit 222 may typically perform these calculations using the sample-by-sample differences between the current block and the reference block under consideration. Motion estimation unit 222 may identify the reference block with the lowest value resulting from these calculations, indicating the reference block that most closely matches the current block.

[0119] Motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of a reference block in a reference picture relative to the position of the current block in the current picture. Motion estimation unit 222 may then provide the motion vectors to motion compensation unit 224. For example, for unidirectional inter prediction, motion estimation unit 222 may provide a single motion vector, while for bidirectional inter prediction, motion estimation unit 222 may provide two motion vectors. Motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, motion compensation unit 224 may use the motion vectors to retrieve data for a reference block. As another example, if the motion vectors have fractional sample precision, motion compensation unit 224 may interpolate the values ​​of the prediction block based on one or more interpolation filters. Furthermore, for bidirectional inter prediction, motion compensation unit 224 may retrieve data for two reference blocks identified by the corresponding motion vectors and combine the retrieved data (e.g., by sample-by-sample averaging or weighted averaging).

[0120] As another example, for intra prediction or intra prediction decoding, the intra prediction unit 226 can generate a prediction block based on samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally mathematically combine the values ​​of adjacent samples and fill these calculated values ​​along a defined direction on the current block to generate a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average value of adjacent samples to the current block and generate a prediction block to include the obtained average value for each sample of the prediction block.

[0121] Mode selection unit 202 provides the prediction block to residual generation unit 204. Residual generation unit 204 receives the original, unencoded version of the current block from video data memory 230 and the prediction block from mode selection unit 202. Residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, residual generation unit 204 may also determine the difference between sample values ​​in the residual block to generate the residual block using residual differential pulse code modulation (RDPCM). In some examples, residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0122] In the example where the mode select unit 202 partitions the CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs of various sizes. As described above, the size of a CU may refer to the size of the luma coding block of the CU, and the size of a PU may refer to the size of the luma prediction unit of the PU. Assuming that the size of a particular CU is 2Nx2N, the video encoder 200 may support PU sizes of 2Nx2N or NxN for intra prediction, and symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, NxN, or similar for inter prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.

[0123] In instances where mode select unit 202 does not further split a CU into PUs, each CU may be associated with a luma coding block and a corresponding chroma coding block. As described above, the size of a CU may refer to the size of the luma coding block of the CU. Video encoder 200 and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

[0124] For other video coding techniques (e.g., intra-block copy mode coding, affine mode coding, and linear model (LM) mode coding, to name a few), mode selection unit 202 generates a prediction block for the current block being encoded via various units associated with the coding technique. In some examples (e.g., palette mode coding), mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating how the block is to be reconstructed based on the selected palette. In such a mode, mode selection unit 202 may provide these syntax elements to entropy coding unit 220 for encoding.

[0125] As described above, the residual generation unit 204 receives video data of a current block and a corresponding prediction block. The residual generation unit 204 then generates a residual block for the current block. To generate the residual block, the residual generation unit 204 calculates the sample-by-sample difference between the prediction block and the current block.

[0126] Transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a "transform coefficient block"). Transform processing unit 206 may apply various transforms to the residual block to form the transform coefficient block. For example, transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, transform processing unit 206 may perform multiple transforms on the residual block, such as a primary transform and a secondary transform, such as a rotation transform. In some examples, transform processing unit 206 does not apply a transform to the residual block.

[0127] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may result in a loss of information, and thus, the precision of the quantized transform coefficients may be lower than the precision of the original transform coefficients generated by the transform processing unit 206.

[0128] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct a residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (although possibly with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples of the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0129] Filter unit 216 may perform one or more filtering operations on the reconstructed block. For example, filter unit 216 may perform a deblocking operation to reduce blocking artifacts along the edges of the CU. In some examples, the operations of filter unit 216 may be skipped.

[0130] The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in examples where the operation of the filter unit 216 is not required, the reconstruction unit 214 can store the reconstructed blocks in the DPB 218. In examples where the operation of the filter unit 216 is required, the filter unit 216 can store the filtered reconstructed blocks in the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 can retrieve a reference image formed by the reconstructed (and possibly filtered) blocks from the DPB 218 to perform inter-prediction on blocks of subsequently encoded images. In addition, the intra-prediction unit 226 can use the reconstructed blocks in the DPB 218 of the current picture to perform intra-prediction on other blocks in the current picture.

[0131] In general, entropy coding unit 220 may entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy coding unit 220 may entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy coding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-prediction or intra-mode information for intra-prediction) from mode selection unit 202. Entropy coding unit 220 may perform one or more entropy encoding operations on syntax elements, another example of video data, to generate entropy-encoded data. For example, entropy coding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential Golomb coding operation, or another entropy coding operation on the data. In some examples, entropy coding unit 220 may operate in a bypass mode in which syntax elements are not entropy encoded.

[0132] The video encoder 200 may output a bitstream including entropy coding syntax elements required to reconstruct blocks of a slice or picture. In particular, the entropy coding unit 220 may output a bitstream.

[0133] The above operations are described for blocks. Such descriptions should be understood as operations for luma coding blocks and / or chroma coding blocks. As described above, in some examples, the luma coding blocks and chroma coding blocks are the luma and chroma components of a CU. In some examples, the luma coding blocks and chroma coding blocks are the luma and chroma components of a PU.

[0134] In some examples, the operations performed for luma coding blocks do not need to be repeated for chroma coding blocks. As an example, the operations for identifying the motion vector (MV) and reference picture for the luma coding block do not need to be repeated to identify the MV and reference picture for the chroma blocks. Instead, the MV for the luma coding block can be adjusted to determine the MV for the chroma blocks, and the reference picture can be the same. As another example, the intra prediction process can be the same for luma coding blocks and chroma coding blocks.

[0135] The video encoder 200 represents an example of a device configured to encode video data, comprising: a memory configured to store video data; and one or more processing units implemented in circuitry and configured to: encode a sequence parameter set (SPS) referenced by one or more video data pictures, wherein to encode the SPS, the video encoder may: encode a syntax element at a first position in the SPS, the syntax element indicating whether joint decoding of chroma residuals is enabled or disabled for the one or more video data pictures that reference the SPS; and encode one or more syntax elements representing a quantization parameter (QP) mapping table at a second position in the SPS that is located after the first position; and encode a picture parameter set (PPS) referenced by a picture in the one or more video data pictures, wherein to encode the PPS, the video encoder may encode syntax elements indicating whether a QP offset for a joint chroma residual is included in a chroma QP offset table and specifying a QP offset for deriving QP′. CbCr The luminance quantization parameter Qp′ Y whether the syntax element of the offset is encoded; and encoding the picture based on the SPS and PPS.

[0136] Figure 4 is a block diagram illustrating an example video decoder 300 that can perform the techniques of this disclosure. Figure 4 This is for purposes of explanation and does not limit the techniques broadly illustrated and described in this disclosure. For illustrative purposes, this disclosure describes a video decoder 300 based on techniques from JEM, VVC, and HEVC. However, the techniques of this disclosure can be performed by video decoding devices configured for other video decoding standards.

[0137] exist Figure 4In the example of FIG, video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and DPB 314 may be implemented in one or more processors or processing circuits. For example, the units of video decoder 300 may be implemented as one or more circuits or logic elements as part of a hardware circuit, or as part of a processor, ASIC, or FPGA. Furthermore, video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

[0138] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include additional units to perform prediction according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0139] CPB memory 320 may store video data (e.g., an encoded video bitstream) to be decoded by components of video decoder 300. The video bitstream may be obtained, for example, from computer-readable medium 110 ( Figure 1 ) obtains video data stored in CPB memory 320. CPB memory 320 may include a CPB that stores coded video data (e.g., syntax elements) from the coded video bitstream. Furthermore, CPB memory 320 may store video data other than syntax elements for decoded pictures, such as temporary data representing outputs from various units of video decoder 300. DPB 314 typically stores decoded pictures, which video decoder 300 may output and / or use as reference video data when decoding subsequent data or pictures in the coded video bitstream. CPB memory 320 and DPB 314 may be formed from any of a variety of memory devices, such as DRAM (including SDRAM, MRAM, RRAM), or other types of memory devices. CPB memory 320 and DPB 314 may be provided by the same memory device or separate memory devices. In various examples, CPB memory 320 may be on-chip with other components of video decoder 300, or off-chip relative to those components.

[0140] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) retrieves the decoded video data. That is, memory 120 may store data as discussed above with respect to CPB memory 320. Similarly, when some or all of the functionality of video decoder 300 is implemented in software to be executed by processing circuitry of video decoder 300, memory 120 may store instructions to be executed by video decoder 300.

[0141] Shown Figure 4 The various units are described to help understand the operations performed by the video decoder 300. These units can be implemented as fixed function circuits, programmable circuits, or a combination thereof. Figure 3 Similarly, fixed-function circuits refer to circuits that provide specific functionality and are pre-set in the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform a variety of tasks and provide flexible functionality in the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the software or firmware's instructions. Fixed-function circuits can execute software instructions (e.g., to receive parameters or output parameters), but the types of operations performed by fixed-function circuits are generally immutable. In some examples, one or more of these units can be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of these units can be integrated circuits.

[0142] The video decoder 300 may include an ALU, an EFU, digital circuits, analog circuits, and / or a programmable core formed by programmable circuits. In examples where the operation of the video decoder 300 is performed by software executed on the programmable circuits, on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

[0143] Entropy decoding unit 302 may receive encoded video data from the CPB and perform entropy decoding on the video data to reproduce syntax elements. Prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, and filter unit 312 may generate decoded video data based on syntax elements extracted from the bitstream.

[0144] Typically, the video decoder 300 reconstructs a picture block by block. The video decoder 300 may perform a reconstruction operation on each block individually (where the block currently being reconstructed, ie, decoded, may be referred to as a "current block").

[0145] The entropy decoding unit 302 may entropy decode syntax elements that define the quantized transform coefficients of the quantized transform coefficient block, as well as transform information, such as a quantization parameter (QP) and / or a transform mode indication. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a quantization level, and similarly, determine an inverse quantization level for application by the inverse quantization unit 306. The inverse quantization unit 306 may, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thereby form a transform coefficient block comprising the transform coefficients.

[0146] After inverse quantization unit 306 forms a transform coefficient block, inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0147] In addition, prediction processing unit 304 generates a prediction block based on the prediction information syntax element entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax element indicates that the current block is inter-predicted, then motion compensation unit 316 may generate a prediction block. In this case, the prediction information syntax element may indicate: a reference picture in DPB 314 from which the reference block is retrieved, and a motion vector used to identify the position of the reference block in the reference picture relative to the position of the current block in the current picture. Motion compensation unit 316 may generally perform an inter-prediction process in a manner substantially similar to that described for motion compensation unit 224 ( Figure 3 ).

[0148] As another example, if the prediction information syntax element indicates that the current block is intra-predicted, the intra-prediction unit 318 may generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Again, the intra-prediction unit 318 may generally be used in conjunction with the intra-prediction unit 226 ( Figure 3 The intra prediction process is performed in a manner substantially similar to that described in the preceding claims. The intra prediction unit 318 may retrieve data of neighboring samples for the current block from the DPB 314.

[0149] The reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, the reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

[0150] The filter unit 312 may perform one or more filtering operations on the reconstructed block. For example, the filter unit 312 may perform a deblocking operation to reduce blocking artifacts along the edges of the reconstructed block. The operations of the filter unit 312 may not necessarily be performed in all examples.

[0151] The video decoder 300 may store the reconstructed block in the DPB 314. For example, in examples where the operation of the filter unit 312 is not performed, the reconstruction unit 310 may store the reconstructed block to the DPB 314. In examples where the operation of the filter unit 312 is performed, the filter unit 312 may store the filtered reconstructed block to the DPB 314. As discussed above, the DPB 314 may provide reference information to the prediction processing unit 304, such as samples of the current picture for intra-prediction and previously decoded pictures for subsequent motion compensation. In addition, the video decoder 300 may output a decoded picture (e.g., a decoded video) from the DPB 314 for subsequent display on a display device (e.g., Figure 1 is presented on a display device 118).

[0152] In this manner, the video decoder 300 represents an example of a video decoding device that includes: a memory configured to store video data; and one or more processing units implemented in circuitry and configured to: decode a sequence parameter set (SPS) referenced by one or more video data pictures, wherein, to decode the SPS, the video decoder may: decode a syntax element at a first position in the SPS, the syntax element indicating whether joint coding of chroma residuals is enabled or disabled for the one or more video data pictures that reference the SPS; and decode one or more syntax elements representing a quantization parameter (QP) mapping table at a second position in the SPS that is located after the first position; and decode a picture parameter set (PPS) referenced by a picture in the one or more video data pictures, wherein, to decode the PPS, the video decoder may decode syntax elements indicating whether a QP offset for a joint chroma residual is included in a chroma QP offset table, and specifying a QP offset for a chroma QP offset used to derive QP′. CbCr The luminance quantization parameter Qp′ Y whether a syntax element indicating an offset of is signaled; and decoding a picture based on the SPS and PPS.

[0153] Figure 5 1 is a flowchart illustrating an example method for encoding a current block. The current block may include a current CU. Although for the video encoder 200 ( Figure 1 and Figure 3 ) is described, but it should be understood that other devices may be configured to perform the same Figure 5 Similar approach.

[0154] In this example, the video encoder 200 initially predicts a current block (350). For example, the video encoder 200 may form a prediction block for the current block. The video encoder 200 may then calculate a residual block for the current block (352). To calculate the residual block, the video encoder 200 may calculate the difference between the original unencoded block and the prediction block for the current block. The video encoder 200 may then transform and quantize the coefficients of the residual block (354). Next, the video encoder 200 may scan the quantized transform coefficients of the residual block (356). During or after the scan, the video encoder 200 may entropy encode the transform coefficients (358). For example, the video encoder 200 may encode the transform coefficients using CAVLC or CABAC. The video encoder 200 may then output entropy encoded data for the block (360).

[0155] Figure 6 is a flowchart illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although for the video decoder 300 ( Figure 1 and Figure 4 ) is described, but it should be understood that other devices may be configured to perform the same Figure 6 Similar approach.

[0156] The video decoder 300 may receive entropy coded data for a current block, e.g., entropy coded prediction information and entropy coded data of coefficients of a residual block corresponding to the current block (370). The video decoder 300 may entropy decode the entropy coded data to determine prediction information for the current block and reproduce coefficients of the residual block (372). The video decoder 300 may predict the current block (374), e.g., using an intra-prediction or inter-prediction mode indicated by the prediction information for the current block, to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the reproduced coefficients (376) to create a block of quantized transform coefficients. The video decoder 300 may then inverse quantize and inverse transform the transform coefficients to produce a residual block (378). The video decoder 300 may ultimately decode the current block by combining the prediction block and the residual block (380).

[0157] Figure 7 is a flowchart illustrating an example method for encoding a current block of video data. The current block may include a current CU. Although for the video decoder 300 ( Figure 1 and Figure 4 ) is described, but it should be understood that other devices may be configured to perform the same Figure 7 Similar approach.

[0158] The video decoder 300 may decode a sequence parameter set (SPS) referenced by one or more video data pictures according to an encoded video bitstream. For example, the entropy decoding unit 302 may parse a syntax element at a first position in the SPS, the syntax element indicating whether joint coding of chroma residuals is enabled or disabled for one or more video data pictures that reference the SPS (702); and parse one or more syntax elements representing a quantization parameter (QP) mapping table at a second position in the SPS that is located after the first position (704). In some examples, the syntax element indicating whether joint coding of chroma residuals is enabled or disabled for one or more video data pictures that reference the SPS may include an sps_joint_cbcr_enabled_flag syntax element. In some examples, the one or more syntax elements representing the quantization parameter (QP) mapping table may include one or more num_points_in_qp_table_minus1[i] syntax elements, one or more delta_qp_in_val_minus1[i][j] syntax elements, and one or more delta_qp_out_val[i][j] syntax elements. As discussed above, by parsing a syntax element indicating whether joint coding of chroma residuals is enabled or disabled for one or more video data pictures that reference an SPS preceding one or more syntax elements representing a quantization parameter (QP) mapping table, the video decoder 300 may avoid decoding the syntax element representing the quantization parameter (QP) mapping table for the joint Cb-Cr mapping table if joint coding of chroma residuals is disabled.

[0159] The video decoder 300 may decode a picture parameter set (PPS) referenced by a picture in one or more video data pictures according to an encoded video bitstream. For example, the entropy decoding unit 302 may parse a syntax element from the PPS, the syntax element indicating whether there is a syntax element related to joint decoding of chroma residuals in the PPS (706). The syntax element indicating whether there is a syntax element related to joint decoding of chroma residuals in the PPS may be a syntax element indicating whether a QP offset for the jointly decoded chroma residual is included in a chroma QP offset table, and specifying a QP offset for deriving Qp′. CbCr The luminance quantization parameter Qp′ Y In some examples, the syntax element indicating whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table, and the syntax element specifying the offset for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y The syntax element indicating whether the offset syntax element is decoded may be the pps_joint_cbcr_qp_offset_present_flag syntax element.

[0160] In some examples, to decode the PPS, entropy decoding unit 302 may parse syntax elements related to joint coding of the chroma residual based on the value of the parsed syntax element (e.g., based on the value of pps_joint_cbcr_qp_offset_present_flag). For example, if pps_joint_cbcr_qp_offset_present_flag indicates the presence of pps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i], entropy decoding unit 302 may parse the pps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] syntax elements from the PPS.

[0161] Video decoder 300 may decode the picture based on the SPS and PPS (708). For example, entropy decoding unit 302 may selectively perform joint chroma residual coding based on the values ​​of the syntax elements of the SPS and PPS. In some examples, to decode the picture based on the SPS and PPS, video decoder 300 may decode the picture based on a QP mapping table specified by the SPS.

[0162] The following numbered examples may illustrate one or more aspects of the present disclosure:

[0163] Example 1. A method for encoding video data, the method comprising: decoding a sequence parameter set (SPS) referenced by one or more video data pictures, wherein decoding the SPS comprises: decoding a syntax element at a first position in the SPS, the syntax element indicating whether joint decoding of chroma residuals is enabled or disabled for the one or more video data pictures that reference the SPS; and decoding one or more syntax elements representing a quantization parameter (QP) mapping table at a second position in the SPS that is located after the first position; decoding a picture parameter set (PPS) referenced by a picture in the one or more video data pictures, wherein decoding the PPS comprises: encoding syntax elements indicating whether a QP offset for a jointly decoded chroma residual is included in a chroma QP offset table, and specifying a QP offset for deriving QP′ CbCr The luminance quantization parameter Qp′ Y whether a syntax element of the offset is decoded; and decoding the picture based on the SPS and the PPS.

[0164] Example 2. The method of Example 1, wherein the syntax element indicating whether joint coding of chroma residual is enabled or disabled for one or more video data pictures referencing the SPS comprises a sps_joint_cbcr_enabled_flag syntax element.

[0165] Example 3. The method of Example 1 or Example 2, wherein the syntax element indicating whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the pps_joint_cbcr_qp_offset_present_flag syntax element indicates ... CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

[0166] Example 4. The method of any of Examples 1-3, wherein the method for deriving Qp′ is specified. CbCr The luminance quantization parameter Qp′ Y The syntax element for the offset comprises a pps_joint_cbcr_qp_offset syntax element.

[0167] Example 5. The method of any of Examples 1-4, wherein the decoding comprises decoding.

[0168] Example 6. The method of any of Examples 1-5, wherein decoding includes encoding.

[0169] Example 7. An apparatus for decoding video data, the apparatus comprising one or more means for performing the method according to any of Examples 1-6.

[0170] Example 8. The apparatus of Example 7, wherein the one or more units include one or more processors implemented in a circuit.

[0171] Example 9. The apparatus of Example 7 or 8, further comprising a memory for storing the video data.

[0172] Example 10. The apparatus of any of Examples 7-9, further comprising a display configured to display the decoded video data.

[0173] Example 11. The device of any of Examples 7-10, wherein the device comprises one or more of: a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0174] Example 12. The apparatus of any of Examples 7-11, wherein the apparatus comprises a video decoder.

[0175] Example 13. The apparatus of any of Examples 7-12, wherein the apparatus comprises a video encoder.

[0176] Example 14. A computer-readable storage medium having instructions stored thereon, which, when executed, cause one or more processors to perform the method of any one of Examples 1-6.

[0177] It should be appreciated that, depending on the examples, certain actions or events of any of the techniques described herein may be performed in a different order, may be added, combined, or omitted altogether (e.g., not all described actions may be necessary for implementation of the techniques). Furthermore, in some examples, actions or events may be performed concurrently (e.g., through multithreading, interrupt handling, or multiple processors) rather than sequentially.

[0178] In one or more examples, the functions described can be implemented using hardware, software, firmware, or any combination thereof. If implemented using software, the functions can be stored as one or more instructions or codes on a computer-readable medium, or sent via a computer-readable medium, and executed by a hardware-based processing unit. A computer-readable medium can include a computer-readable storage medium that corresponds to a tangible medium such as a data storage medium, or a communication medium (which includes, for example, any medium that facilitates the transfer of a computer program from one location to another according to a communication protocol). In this manner, a computer-readable medium can generally correspond to (1) a non-transitory tangible computer-readable storage medium or (2) a communication medium (such as a signal or carrier wave). A data storage medium can be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and / or data structures for the implementation of the technology described in this disclosure. A computer program product can include a computer-readable medium.

[0179] By way of example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. In addition, any connection can be appropriately referred to as a computer-readable medium. For example, if instructions are sent from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwaves, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwaves are included in the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other temporary media, but rather refer to non-temporary, tangible storage media. As used herein, disks and discs include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically, while optical discs use lasers to reproduce data optically. Combinations of the above should also be included within the scope of computer-readable media.

[0180] Instructions may be processed by one or more processors such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Thus, as used herein, the terms "processor" and "processing circuitry" may refer to any of the aforementioned structures or any other structures suitable for the implementation of the techniques described herein. Furthermore, in some aspects, the functionality described herein may be provided in dedicated hardware and / or software modules configured for encoding and decoding or incorporated into a combined codec. Furthermore, these techniques may be fully implemented in one or more circuits or logic units.

[0181] The techniques of the present disclosure can be implemented in a variety of devices or apparatuses, including wireless handheld devices, integrated circuits (ICs), or a set of ICs (e.g., chipsets). Various components, modules, or units are described in this disclosure to emphasize the functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require implementation by different hardware units. Rather, as described above, the various units can be combined in a codec hardware unit, or provided by a collection of interoperable hardware units, including one or more processors as described above in combination with appropriate software and / or firmware.

[0182] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

1. A method for decoding video data, the method comprising: Decoding a sequence parameter set (SPS) referenced by one or more pictures of video data from a coded video bitstream, wherein decoding the SPS comprises: parsing a syntax element at a first position in the SPS, the syntax element indicating whether joint coding of chroma residual is enabled or disabled for the one or more pictures of the video data referencing the SPS; and parsing, at a second position in the SPS that is located after the first position and based on a value of the syntax element indicating whether joint coding of chroma residual is enabled or disabled, one or more syntax elements representing a quantization parameter (QP) mapping table; Decoding a picture parameter set (PPS) referenced by a picture of the one or more pictures of video data according to the coded video bitstream, wherein decoding the PPS comprises: Parse the syntax elements indicating whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and specifying the QP offset for deriving the chroma quantization parameter Qp′. CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded; and The picture is decoded based on the SPS and the PPS.

2. The method according to claim 1, wherein The syntax element indicating whether joint coding of chroma residual is enabled or disabled for the one or more pictures of video data referencing the SPS comprises a syntax element sps_joint_cbcr_enabled_flag.

3. The method according to claim 1, wherein The syntax elements indicating whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the pps_joint_cbcr_qp_offset_present_flag specifying the QP offset for deriving Qp′ include: CbCr The brightness quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

4. The method according to claim 1, wherein Parsing the PPS also includes: Based on whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the QP offset for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded is determined by the value of the syntax element indicating whether it is decoded: a syntax element indicating whether the QP offset for the jointly coded chroma residual is included in a chroma QP offset table; and Specify the target for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y Whether the offset is decoded for the syntax element.

5. The method according to claim 1, further comprising: Based on whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the QP offset specified for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y The syntax element indicating whether the offset is decoded is used to parse the syntax element specified for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y The offset syntax element is specified for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y The syntax element for the offset comprises a syntax element pps_joint_cbcr_qp_offset.

6. A device for decoding video data, the device comprising: a memory configured to: store at least a portion of the encoded video bitstream; as well as One or more processors implemented as circuitry and configured to: decoding, from the coded video bitstream, a sequence parameter set (SPS) referenced by one or more pictures of video data, wherein, to decode the SPS, the one or more processors are configured to: parsing a syntax element at a first position in the SPS, the syntax element indicating whether joint coding of chroma residual is enabled or disabled for the one or more pictures of video data referencing the SPS; and parsing, at a second position in the SPS that is located after the first position and based on a value of the syntax element indicating whether joint coding of chroma residual is enabled or disabled, one or more syntax elements representing a quantization parameter (QP) mapping table; decoding a picture parameter set (PPS) referenced by a picture of the one or more pictures of video data according to the coded video bitstream, wherein, to decode the PPS, the one or more processors are configured to: Parse the syntax elements indicating whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and specifying the QP offset for deriving the chroma quantization parameter Qp′. CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded; and The picture is decoded based on the SPS and the PPS.

7. The apparatus according to claim 6, wherein The syntax element indicating whether joint coding of chroma residual is enabled or disabled for the one or more pictures of the video data referencing the SPS comprises a syntax element sps_joint_cbcr_enabled_flag.

8. The apparatus according to claim 6, wherein The syntax elements indicating whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and specifying the QP offset for deriving Qp′ include the syntax element pps_joint_cbcr_qp_offset_present_flag. CbCr The brightness quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

9. The apparatus according to claim 6, wherein To decode the PPS, the one or more processors are configured to: Based on whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the QP offset for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded is determined by the value of the syntax element indicating whether it is decoded: a syntax element indicating whether the QP offset for the jointly coded chroma residual is included in a chroma QP offset table; as well as Specify the target for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y The offset of the syntax element is decoded.

10. The apparatus according to claim 6, wherein Specify the target for deriving Qp′ CbCr The brightness quantization parameter Qp′ Y The syntax element for the offset comprises a syntax element pps_joint_cbcr_qp_offset.

11. A method for encoding video data, the method comprising: Encoding a sequence parameter set (SPS) referenced by one or more pictures of video data in a coded video bitstream, wherein encoding the SPS comprises: encoding, at a first position in the SPS, a syntax element indicating whether joint coding of chroma residuals is enabled or disabled for the one or more pictures of video data referencing the SPS; and encoding, at a second position in the SPS that is subsequent to the first position and based on whether joint coding of chroma residual is enabled or disabled, one or more syntax elements representing a quantization parameter (QP) mapping table; and encoding, in the coded video bitstream, a picture parameter set (PPS) referenced by a picture of the one or more pictures of video data, wherein encoding the PPS comprises: Encodes syntax elements indicating whether a QP offset for the jointly coded chroma residual is included in the chroma QP offset table and specifying the QP offset for deriving the chroma quantization parameter Qp′. CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

12. The method according to claim 11, wherein The syntax element indicating whether joint coding of chroma residual is enabled or disabled for the one or more pictures of the video data referencing the SPS comprises a syntax element sps_joint_cbcr_enabled_flag.

13. The method according to claim 11, wherein The syntax elements indicating whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the pps_joint_cbcr_qp_offset_present_flag specifying the QP offset for deriving Qp′ include: CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

14. The method according to claim 11, wherein Encoding the PPS further includes: Based on whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the QP offset for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y Whether the offset syntax element is decoded is indicated by the value of the syntax element, encoded as: a syntax element indicating whether the QP offset for the jointly coded chroma residual is included in a chroma QP offset table; and Specify the target for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y The offset of the syntax element being decoded.

15. The method according to claim 11, wherein Specify the target for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y The syntax element for the offset comprises a syntax element pps_joint_cbcr_qp_offset.

16. A device for encoding video data, the device comprising: a memory configured to: store at least a portion of the encoded video bitstream; as well as One or more processors implemented as circuitry and configured to: encoding, in the coded video bitstream, a sequence parameter set (SPS) referenced by one or more pictures of video data, wherein, to encode the SPS, the one or more processors are configured to: encoding, at a first position in the SPS, a syntax element indicating whether joint coding of chroma residuals is enabled or disabled for the one or more pictures of video data referencing the SPS; and encoding, at a second position in the SPS that is subsequent to the first position and based on whether joint coding of chroma residual is enabled or disabled, one or more syntax elements representing a quantization parameter (QP) mapping table; and encoding, in the coded video bitstream, a picture parameter set (PPS) referenced by a picture of the one or more pictures of video data, wherein, to encode the PPS, the one or more processors are configured to: Encodes syntax elements indicating whether a QP offset for the jointly coded chroma residual is included in the chroma QP offset table and specifying the QP offset for deriving the chroma quantization parameter Qp′. CbCr The luminance quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

17. The apparatus according to claim 16, wherein The syntax element indicating whether joint coding of chroma residual is enabled or disabled for the one or more pictures of the video data referencing the SPS comprises a syntax element sps_joint_cbcr_enabled_flag.

18. The apparatus according to claim 16, wherein The syntax elements indicating whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the pps_joint_cbcr_qp_offset_present_flag specifying the QP offset for deriving Qp′ include: CbCr The brightness quantization parameter Qp′ Y Whether the syntax element of the offset is decoded.

19. The apparatus according to claim 16, wherein To encode the PPS, the one or more processors are configured to: Based on whether the QP offset for the jointly coded chroma residual is included in the chroma QP offset table and the QP offset for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y Whether the offset syntax element is decoded is indicated by the value of the syntax element, to be encoded: a syntax element indicating whether the QP offset for the jointly coded chroma residual is included in a chroma QP offset table; as well as Specify the target for deriving Qp′ CbCr The luminance quantization parameter Qp′ Y The offset of the syntax element being decoded.

20. The apparatus of claim 16, wherein: Specify the target for deriving Qp′ CbCr The brightness quantization parameter Qp′ Y The syntax element for the offset comprises a syntax element pps_joint_cbcr_qp_offset.

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