Derivation of Chroma Quantization Parameter (QP) for Video Codecs

Abstract

Techniques for decoding video data are described. A video decoder may determine chroma blocks in a chroma quantization group (QG) of the video data, determine a quantization parameter predictor that is the same for each chroma block of the chroma QG, determine an offset value that is the same for two or more chroma blocks of the chroma QG, determine a quantization parameter value for each of the two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value, inverse quantize coefficients of one or more residual blocks of the chroma blocks based on the determined quantization parameter values, generate one or more residual blocks based on the inverse quantized coefficients, and reconstruct the chroma blocks based on the one or more residual blocks.

Description

[0001] This application claims priority to U.S. Application No. 16 / 997,321, filed on August 19, 2020, which claims the benefit of U.S. Provisional Application No. 62 / 891,063, filed on August 23, 2019, and U.S. Provisional Application No. 62 / 911,870, filed on October 7, 2019, the entire contents of each of which are incorporated herein by reference. Technical Field

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

[0003] Digital video capabilities may be integrated 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 "smart phones", video teleconferencing devices, video streaming devices, etc. Digital video devices implement video codec technologies, 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 Codec (AVC), ITU-T H.265 / High Efficiency Video Codec (HEVC), and extensions of such standards. Video devices may more efficiently send, receive, encode, decode, and / or store digital video information by implementing such video codec technologies.

[0004] Video coding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or eliminate 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 partitioned into video blocks, which may also be referred to as coding tree units (CTUs), coding units (CUs), and / or coding nodes. For video blocks in an intra-coded (I) slice of a picture, spatial prediction relative to reference samples in neighboring blocks in the same picture is used for encoding. For video blocks in an inter-coded (P or B) slice of a picture, spatial prediction relative to reference samples in neighboring blocks in the same picture or temporal prediction relative to reference samples in other reference pictures may be used. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames. Summary of the invention

[0005] In general, this disclosure describes techniques for chroma quantization parameter (QP) derivation for video codecs. As described in this disclosure, in some techniques, a quantization group (QG) may have chroma blocks with different quantization parameter (QP) values, which may result in suboptimal visual quality. One technique to ensure uniform QP values ​​is to define a small QG, but this may negatively impact bandwidth efficiency because more bits are required to encode and decode a block.

[0006] This disclosure describes example techniques for improving QP value derivation for blocks such as chroma. In some examples, the result of the QP value derivation can be a uniform QP value for QG, but such a result is not necessarily required in all examples. By improving QP value derivation, the example techniques can improve visual quality while promoting efficient bandwidth usage, thereby improving the overall operation of the video encoding and decoding process.

[0007] In one example, the present disclosure describes a method for decoding video data, the method including determining a chroma block in a chroma quantization group (QG) of the video data, determining a quantization parameter predictor that is the same for each chroma block of the chroma QG, determining an offset value that is the same for two or more chroma blocks of the chroma QG, determining a quantization parameter value for each of the two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value, inverse quantizing coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter value, generating one or more residual blocks based on the inverse quantized coefficients, and reconstructing the chroma block based on the one or more residual blocks.

[0008] In one example, the present disclosure describes a method for encoding video data, the method including determining chroma blocks in a chroma quantization group (QG) of the video data, determining a quantization parameter predictor that is the same for each chroma block of the chroma QG, determining a quantization parameter value for two or more chroma blocks in the chroma QG, determining an offset value that is the same for the two or more chroma blocks of the chroma QG based on the quantization parameter value and the quantization parameter predictor, quantizing coefficients of one or more residual blocks of the chroma blocks based on the determined quantization parameter value, and signaling information indicating the quantization coefficients and the offset values.

[0009] In one example, the present disclosure describes a device for decoding video data, the device comprising a memory configured to store the video data and a processing circuit coupled to the memory, and the processing circuit is configured to determine a chroma block in a chroma quantization group (QG) of the video data, determine a quantization parameter predictor that is the same for each chroma block of the chroma QG, determine an offset value that is the same for two or more chroma blocks of the chroma QG, determine a quantization parameter value for each of the two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value, inverse quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter value, generate one or more residual blocks based on the inverse quantized coefficients, and reconstruct the chroma block based on the one or more residual blocks.

[0010] In one example, the present disclosure describes a computer-readable storage medium having instructions stored thereon that, when executed, cause one or more processors of a device for decoding video data to determine a chroma block in a chroma quantization group (QG) of the video data, determine a quantization parameter predictor that is the same for each chroma block of the chroma QG, determine an offset value that is the same for two or more chroma blocks of the chroma QG, determine a quantization parameter value for each of two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value, inverse quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter value, generate one or more residual blocks based on the inverse quantized coefficients, and reconstruct the chroma block based on the one or more residual blocks.

[0011] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0013] Figure 2A and 2B is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure and a corresponding coding tree unit (CTU).

[0014] Figure 3 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0015] Figure 4 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0016] Figure 5 is a conceptual diagram illustrating examples of chroma quantization parameters (QPs) derived for two cases of chroma quantization groups in a single-tree configuration.

[0017] Figure 6 is a conceptual diagram illustrating examples of chroma QPs derived for two cases of chroma quantization groups in a dual-tree configuration.

[0018] Figure 7 is a flow chart illustrating an example method of encoding video data.

[0019] Figure 8 is a flow chart illustrating an example method of decoding video data.

[0020] Fig. 9 is a flow chart illustrating another example method of encoding video data.

[0021] Fig.10 is a flow chart illustrating another example method of decoding video data. DETAILED DESCRIPTION

[0022] In video coding, a video encoder determines a prediction block for a current block and determines a residual block based on the difference between the prediction block and the current block. The video encoder may transform the residual block from a sample domain to a transform domain (also called a frequency domain), although the transform may be skipped, to generate coefficients of the residual block. The video encoder may then quantize the coefficients of the residual block according to a quantization parameter (QP) and signal information indicating the quantization coefficients.

[0023] The video decoder may receive information indicating a quantization parameter and information indicating a quantization coefficient. The video decoder may inverse quantize the quantization coefficient according to the quantization parameter and generate a residual block based on the inverse quantization coefficient (e.g., after inverse transformation of the inverse quantization coefficient). The video decoder may also determine a prediction block in the same manner as the video encoder and add the prediction block to the residual block to reconstruct the current block.

[0024] In some examples, the video encoder signals and the video decoder receives information indicating a quantization parameter. The information indicating the quantization parameter may be the quantization parameter itself, or may be an offset value to be added to a quantization parameter predictor, where the quantization parameter predictor is a predictor based on one or more quantization parameters of a previous codec block. As an example, the codec unit includes a luma codec block and two chroma codec blocks. The current block may be one of the two chroma codec blocks. In some examples, the quantization parameter of the luma codec block or a value based on the quantization parameter of the luma codec block may be a quantization parameter predictor of the chroma block corresponding to the luma codec block.

[0025] In these examples, the video encoder and the video decoder can each determine a quantization parameter predictor for a current block (e.g., a chroma codec block). The video encoder can determine an offset that is a difference between an actual quantization parameter and the quantization parameter predictor and signal the offset. The video decoder can receive the offset value and add the offset value to the quantization parameter predictor to determine the quantization parameter for the current block.

[0026] In one or more examples described in the present disclosure, instead of determining a quantization parameter on a chroma block-by-chroma basis, a quantization parameter for a chroma quantization group (QG) may be determined. For example, a chroma QG includes multiple chroma blocks. In such an example, a video encoder may signal information defining the chroma QG. The quantization parameter predictors for all chroma blocks in the QG may be the same, and the offset values ​​for two or more chroma blocks (including all chroma blocks) may be the same. In this way, a video encoder and a video decoder may determine a quantization parameter once for the chroma blocks in the QG and assign the quantization parameter to the chroma blocks in the QG. Therefore, the video encoder and the video decoder may not need to repeatedly check the quantization parameter predictor for each chroma block in the chroma QG or signal and receive the offset for each chroma block in the chroma QG.

[0027] Figure 1 1 is a block diagram illustrating an example video encoding and decoding system 100 that can perform the techniques of the present disclosure. The techniques of the present disclosure are generally directed to encoding and decoding (encoding and / or decoding) video data. Generally, video data includes any data used to process video. Therefore, video data may include original, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

[0028] 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 target device 116. Specifically, source device 102 provides video data to target device 116 via computer-readable medium 110. Source device 102 and target device 116 may include any of a variety of devices, including desktop computers, notebook (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 target device 116 may be equipped for wireless communication and, therefore, may be referred to as wireless communication devices.

[0029] exist Figure 1In the example of, source device 102 includes video source 104, memory 106, video encoder 200 and output interface 108. Target device 116 includes input interface 122, video decoder 300, memory 120 and display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of target device 116 can be configured to apply a technology for deriving a quantization parameter (QP) value (e.g., for a chroma codec block). Therefore, source device 102 represents an example of a video encoding device, and target device 116 represents an example of a video decoding device. In other examples, source device and target device may include other components or arrangements. For example, source device 102 may receive video data from an external video source (e.g., an external camera). Similarly, target device 116 may interface with an external display device, rather than including an integrated display device.

[0030] like Figure 1 The system 100 shown is merely an example. In general, any digital video encoding and / or decoding device can perform techniques for deriving QP values ​​(e.g., for chroma codec blocks). The source device 102 and the target device 116 are merely examples of such codec devices, where the source device 102 generates codec video data to send to the target device 116. The present disclosure refers to a "codec" device as a device that performs data encoding and decoding (encoding and / or decoding). Therefore, the video encoder 200 and the video decoder 300 represent examples of codec devices, particularly video encoders and video decoders, respectively. In some examples, the devices 102, 116 can operate in a substantially symmetrical manner, so that each of the devices 102, 116 includes video encoding and decoding components. Therefore, the system 100 can support one-way or two-way video transmission between video devices 102, 116, such as for video streaming, video playback, video broadcasting, or video telephony.

[0031] In general, video source 104 represents the source of video data (i.e., original, uncoded video data), and provides a continuous sequence of pictures (also referred to as "frames") of video data to video encoder 200, which encodes the data of the pictures. Video source 104 of source device 102 may include a video capture device, such as a camera, a video archive containing previously captured original video, and / or a video feed interface receiving video from a video content provider. As another alternative, video source 104 may generate computer graphics-based data as 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 pictures from the order received (sometimes referred to as "display order") into a codec order for encoding and decoding. Video encoder 200 may generate a bitstream including 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 target device 116 .

[0032] The memory 106 of the source device 102 and the memory 120 of the target device 116 represent general purpose memories. In some examples, the memories 106, 120 can store original video data, for example, original video from the video source 104 and original decoded video data from the video decoder 300. Additionally or alternatively, the memories 106, 120 can store software instructions that can be executed by, for example, the video encoder 200 and the video decoder 300, respectively. Although in this example, the video encoder 200 and the video decoder 300 are shown separately, it should be understood that the video encoder 200 and the video decoder 300 can also include internal memories for functionally similar or equivalent purposes. In addition, the memories 106, 120 can store encoded video data, for example, output from the video encoder 200 and input to the video decoder 300. In some examples, portions of the memories 106, 120 can be allocated as one or more video buffers, for example, for storing original, decoded and / or encoded video data.

[0033] The computer-readable medium 110 may represent any type of medium or device capable of transmitting encoded video data from the source device 102 to the target device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to transmit the encoded video data directly to the target device 116 in real time, for example, via a radio frequency network or a computer-based network. The output interface 108 may modulate a transmission signal including the encoded video data, and the input interface 122 may demodulate the received transmission signal according to a communication standard such as a wireless communication protocol. The communication medium may include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include a router, a switch, a base station, or any other device that can be used to facilitate communication from the source device 102 to the target device 116.

[0034] In some examples, source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, target 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, Blu-ray disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0035] In some examples, source device 102 may output the encoded video data to file server 114 or another intermediate storage device that may store the encoded video data generated by source device 102. Target device 116 may access the stored video data from file server 114 via streaming or downloading.

[0036] The file server 114 may be any type of server device capable of storing encoded video data and sending the encoded video data to the target device 116. The file server 114 may represent a web server (e.g., for a website), a server configured to provide a file transfer protocol service (e.g., a file transfer protocol (FTP) or a file delivery over one-way transport (FLUTE) protocol), a content delivery network (CDN) device, a hypertext transfer protocol (HTTP) server, a multimedia broadcast multicast service (MBMS) or an enhanced MBMS (eMBMS) server, and / or a network attached storage (NAS) device. The file server 114 may additionally or alternatively implement one or more HTTP streaming protocols, such as dynamic adaptive streaming over HTTP (DASH), HTTP real-time streaming (HLS), real-time streaming protocol (RTSP), HTTP dynamic streaming, etc.

[0037] The target device 116 may access the encoded video data from the file server 114 through 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 both, which is suitable for accessing the encoded video data stored on the file server 114. The input interface 122 may be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from the file server 114, or other such protocols for retrieving media data.

[0038] Output interface 108 and 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 output interface 108 and input interface 122 include wireless components, output interface 108 and input interface 122 may be configured to transmit data, such as 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 output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 may be configured to transmit data, such as encoded video data, according to other wireless standards (e.g., IEEE 802.11 specifications, IEEE 802.15 specifications (e.g., ZigBee TM ),Bluetooth TM Standards, etc.) to transmit data, such as encoded video data. In some examples, source device 102 and / or target device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include a SoC device for performing functions attributed to video encoder 200 and / or output interface 108, and target device 116 may include a SoC device for performing functions attributed to video decoder 300 and / or input interface 122.

[0039] The techniques disclosed herein may be applied to video encoding and 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.

[0040] The input interface 122 of the destination device 116 receives the encoded video bitstream from the computer-readable medium 110 (e.g., the storage device 112, the file server 114, etc.). The encoded video bitstream may include signaling information defined by the video encoder 200, which is also used by the video decoder 300, such as syntax elements with values ​​describing characteristics and / or processing of video blocks or other codec 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.

[0041] Despite Figure 1 200 and 300 may each be integrated with an audio encoder and / or an audio decoder and may include appropriate MUX-DEMUX units or other hardware and / or software to process a multiplexed stream including both audio and video in a common data stream. If applicable, the MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

[0042] 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, software, hardware, firmware, or any combination thereof. When these techniques are partially implemented in software, the device can store instructions for the software in an appropriate non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, any of which can be integrated into the corresponding device as part of a combined encoder / decoder (CODEC). 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.

[0043] The video encoder 200 and the video decoder 300 may operate in accordance with a video codec standard (e.g., ITU-T H.265, also known as High Efficiency Video Coding (HEVC)) or an extension thereof (e.g., a multi-view and / or scalable video codec extension). Alternatively, the video encoder 200 and the video decoder 300 may operate in accordance with other proprietary or industry standards (e.g., ITU-T H.266, also known as Versatile Video Coding (VVC)). Bross et al. describe a draft of the VVC standard. Tables 8-15 of "Versatile Video Coding (Draft 6)", ITU-T SG16WP3 and ISO / IEC JTC 1 / SC 29 / WG 11 Joint Video Experts Group (JVET), 15th Meeting: Gothenburg, SE, July 3-12, 2019, JVET-O2001-vE (hereinafter referred to as "VVC Draft 6"). Bross et al. describe the latest draft of the VVC standard. Table 8-15 of “Versatile Video Coding (Draft 10)”, ITU-T SG 16 WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11 Joint Video Experts Group (JVET), 18th Meeting: by teleconference, June 22-July 1, 2020, JVET-S2001-vA (hereinafter referred to as “VVC Draft 10”) However, the technology of the present disclosure is not limited to any particular codec standard.

[0044] Typically, the video encoder 200 and the video decoder 300 can perform block-based picture encoding and decoding. The term "block" generally refers to a structure that includes data to be processed (e.g., encoded, decoded, or otherwise used in the encoding and / or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. Typically, the video encoder 200 and the video decoder 300 can encode and decode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, the video encoder 200 and the video decoder 300 can encode and decode luminance and chrominance components instead of encoding and decoding red, green, and blue (RGB) data for samples of a picture, where the chrominance components may include red-toned and blue-toned chrominance components. In some examples, the video encoder 200 converts the received RGB format data into a YUV representation before encoding, and the video decoder 300 converts the YUV representation into an RGB format. Alternatively, a pre-processing unit and a post-processing unit (not shown) can perform these conversions.

[0045] The present disclosure may generally relate to encoding and decoding (e.g., encoding and decoding) a picture to include the process of encoding or decoding data of the picture. Similarly, the present disclosure may relate to encoding and decoding a block of a picture to include the process of encoding or decoding data of the block, such as prediction and / or residual encoding and decoding. The encoded video bitstream generally includes a series of values ​​of syntax elements that represent codec decisions (e.g., codec modes), and the partitioning of the picture into blocks. Therefore, references to encoding and decoding a picture or a block should generally be understood as the codec values ​​of the syntax elements that constitute the picture or block.

[0046] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video encoder (e.g., video encoder 200) partitions a codec tree unit (CTU) into CUs according to a quadtree structure. That is, the video codec partitions 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 a CU of such a leaf node may include one or more PUs and / or one or more TUs. The video codec may further partition the PU and TU. For example, in HEVC, the residual quadtree (RQT) represents the partitioning of a TU. In HEVC, PU represents inter-prediction data and TU represents residual data. An intra-predicted CU includes intra-prediction information, such as an intra-mode indication.

[0047] As another example, the video encoder 200 and the video decoder 300 may be configured to operate according to VVC. According to VVC, a video codec (e.g., the video encoder 200) partitions a picture into multiple codec tree units (CTUs). The video encoder 200 may partition the CTU according to a tree structure (e.g., 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 of CU, PU, ​​and TU of HEVC. The QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned 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 codec units (CUs).

[0048] In the MTT partitioning 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. A ternary tree or ternary tree partitioning is a partitioning in which a block is split into three sub-blocks. In some examples, a ternary tree or ternary tree partitioning divides a block into three sub-blocks without dividing the initial block through the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0049] 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, such as one QTBT / MTT structure for the luma component and another QTBT / MTT structure for the two chroma components (or two QTBT / MTT structures for the respective chroma components).

[0050] For example, the luma component includes a luma block, and the chroma component includes a chroma block. In dual-tree partitioning, partitioning the luma component into luma blocks and partitioning the chroma component into chroma blocks may be different. As an example, the video encoder 200 and the video decoder 300 may be configured to dual-tree partition the luma CTU and the chroma CTU, generating luma blocks of the luma CTU and chroma blocks of the CTU with different partitions.

[0051] The video encoder 200 and the video decoder 300 can be configured to use quadtree segmentation, QTBT segmentation, MTT segmentation or other segmentation structures per HEVC. For illustrative purposes, the description of the disclosed technology is presented for QTBT segmentation. However, it should be understood that the disclosed technology can also be applied to video codecs configured to use quadtree segmentation or other types of segmentation.

[0052] Blocks (e.g., CTUs or CUs) may be grouped in a picture in various ways. For example, a tile may refer to a rectangular region of a CTU row within a particular tile in a picture. A tile may be a rectangular region of a CTU within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular region of a CTU whose height is equal to the height of the picture and whose width is specified by a syntax element (e.g., in a picture parameter set). A tile row refers to a rectangular region of a CTU whose height is specified by a syntax element (e.g., in a picture parameter set) and whose width is equal to the width of the picture.

[0053] In some examples, a slice may be partitioned into multiple bricks, where each brick may include one or more CTU rows within the slice. A slice that is not partitioned into multiple bricks may also be referred to as a brick. However, a brick that is a proper subset of a slice may not be referred to as a slice.

[0054] The tiles in a picture can also be arranged in stripes. A stripe can be an integer multiple of the tiles of a picture, and these tiles can be contained exclusively in a single network abstraction layer (NAL) unit. In some examples, a stripe includes many complete tiles, or just a continuous sequence of complete tiles of a slice.

[0055] This disclosure may use "N×N" and "N by N" interchangeably to refer to the sample dimensions of a block (e.g., a CU or other video block) in the vertical and horizontal directions, for example, 16×16 samples or 16 by 16 samples. In general, a 16×16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Similarly, an N×N 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 the CU can be arranged in rows and columns. In addition, 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.

[0056] The video encoder 200 encodes the video data of the CU representing the prediction and / or residual information and other information. The prediction information indicates how to predict the CU, thereby forming a prediction block for the CU. The residual information generally represents the sample-by-sample difference between the samples of the CU before encoding and the prediction block.

[0057] In order to predict a CU, the video encoder 200 can generally form a prediction block for the CU by inter-frame prediction or intra-frame prediction. Inter-frame prediction generally refers to predicting a CU from data of a previously coded picture, while intra-frame prediction generally refers to predicting a CU from previously coded data of the same picture. In order to perform inter-frame prediction, the video encoder 200 can use one or more motion vectors to generate a prediction block. The video encoder 200 can generally perform motion search to identify a reference block that closely matches the CU, for example, in terms of the difference between the CU and the reference block. The video encoder 200 can use the sum of absolute differences (SAD), the sum of square differences (SSD), the mean absolute difference (MAD), the mean square difference (MSD) and other such difference calculations to calculate a difference metric to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 can use unidirectional prediction or bidirectional prediction to predict the current CU.

[0058] VVC can 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, such as enlargement or reduction, rotation, perspective motion, or other irregular motion types.

[0059] In order to perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. VVC can provide sixty-seven intra prediction modes, including various directional modes, as well as planar modes and DC modes. Generally, the video encoder 200 selects an intra prediction mode that describes neighboring samples to the current block (e.g., a block of a CU) to predict the samples of the current block from the neighboring samples. Assuming that the video encoder 200 encodes and decodes CTUs and CUs in a raster scan order (from left to right, from top to bottom), such samples can typically be above, to the left (upper left), or to the left of the current block in the same picture as the current block.

[0060] The video encoder 200 encodes data representing the prediction mode of the current block. For example, for inter-frame prediction mode, the video encoder 200 can encode data indicating which of the various available prediction modes is used and the motion information for the corresponding mode. For unidirectional or bidirectional inter-frame prediction, for example, the video encoder 200 can encode the motion vector using advanced motion vector prediction (AMVP) or merge mode. The video encoder 200 can use a similar mode to encode the motion vector for affine motion compensation mode.

[0061] After a prediction, such as intra prediction or inter prediction of a block, the video encoder 200 may calculate residual data for the block. The residual data, such as a residual block, represents the sample-by-sample difference between the block and a predicted block of the block formed using a corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to generate conversion 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. In addition, 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 karhun-Loeve transform (KLT), etc. The video encoder 200 generates transform coefficients after applying one or more transforms.

[0062] As described above, after any transforms used to generate transform coefficients, the video encoder 200 can perform quantization of the transform coefficients. Quantization generally refers to the process of quantizing transform coefficients to possibly reduce the amount of data used to represent the coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 can reduce the bit depth associated with some or all of the coefficients. For example, the video encoder 200 can round n-bit values ​​to m-bit values ​​during quantization, where n is greater than m. In some examples, to perform quantization, the video encoder 200 can perform a bit right shift on the values ​​to be quantized.

[0063] After quantization, the video encoder 200 can scan the transform coefficients to produce a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scan can be designed to place coefficients with higher energy (and therefore lower frequency) in front of the vector and coefficients with lower energy (and therefore higher frequency) in the back of the vector. In some examples, the video encoder 200 can 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 can perform adaptive scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, the video encoder 200 can entropy encode the one-dimensional vector, for example according to context-adaptive binary arithmetic coding and decoding (CABAC). The video encoder 200 can also entropy encode the values ​​of syntax elements, which describe metadata associated with the encoded video data for use by the video decoder 300 in decoding the video data.

[0064] 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.

[0065] The video encoder 200 may further generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, to the video decoder 300, such as in a picture header, a block header, a slice header, or other syntax data, such as 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.

[0066] In this way, the video encoder 200 can generate a bitstream including encoded video data, such as syntax elements describing the partitioning of a picture into blocks (eg, CUs) and prediction and / or residual information for the blocks. Finally, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0067] In general, the video decoder 300 performs the reverse process performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 can decode the values ​​of the syntax elements of the bitstream using CABAC in a manner substantially similar to (although reversed from) the CABAC encoding process of the video encoder 200. The syntax elements can define partitioning information for partitioning a picture into CTUs and partitioning each CTU according to a corresponding partitioning structure such as a QTBT structure to define CUs of the CTU. The syntax elements can further define prediction and residual information for a block (e.g., a CU) of video data.

[0068] 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-frame or inter-frame prediction) and related prediction information (e.g., motion information for inter-frame prediction) to form a prediction block for the block. The video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. The video decoder 300 may perform additional processing (such as performing a deblocking process) to reduce visual artifacts along block boundaries.

[0069] The present 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, the video encoder 200 may signal the values ​​of syntax elements in a bitstream. Generally, signaling refers to generating values ​​in a bitstream. As described above, the source device 102 may transport the bitstream to the target device 116 in substantially real time, or transport the bitstream to the target device 116 in non-real time, such as may occur when storing syntax elements to the storage device 112 for later retrieval by the target device 116.

[0070] As described above, the video encoder 200 may be configured to quantize coefficients based on a quantization parameter, and the video decoder 300 may be configured to inversely quantize coefficients based on a quantization parameter. In one or more examples, the video decoder 300 may determine a quantization parameter for a chroma block (e.g., a block of a chroma component) based on a quantization parameter for a corresponding luma block (e.g., a block of a luma component). For example, the quantization parameter for the luma block or a value determined from the quantization parameter for the luma block may be a quantization parameter predictor for the chroma block. The video encoder 200 may signal and the video decoder 300 may receive an offset value, which the video decoder 300 adds to the quantization parameter predictor to determine the quantization parameter for the chroma block.

[0071] The quantization parameter of the corresponding luma block is one example of a quantization parameter predictor. Another example of a quantization parameter predictor may be the quantization parameters of neighboring chroma QG or an average or weighted average of the quantization parameters of neighboring chroma QG. Other methods of determining a quantization parameter predictor are possible.

[0072] According to one or more examples described in the present disclosure, the video encoder 200 and the video decoder 300 may determine a quantization group (QG), wherein the QG includes a plurality of chroma blocks. In one or more examples, quantization parameters (e.g., parameter values) of chroma blocks in the chroma QG may be equal to each other. For example, the video encoder 200 and the video decoder 300 may determine a quantization parameter predictor for the chroma blocks in the chroma QG, and the offset value of each chroma block in the chroma QG may be the same. Therefore, the quantization parameter of each chroma block in the QG may be the same.

[0073] Because the quantization parameter predictor and offset value are the same for the chroma blocks in the chroma QG, the video decoder 300 can access the corresponding luma block once to determine the quantization parameter predictor for the chroma block in the chroma QG, rather than accessing the corresponding luma block each time for each chroma block in the chroma QG, which can reduce decoding time. In addition, the video encoder 200 may need to signal fewer offsets, which promotes bandwidth efficiency.

[0074] In the case where it is desired that the chroma blocks have different quantization parameters, the video encoder 200 and the video decoder 300 can determine a smaller size of the chroma QG to allow different quantization parameters for different chroma blocks. In this way, the example techniques facilitate flexibility to allow for situations where the chroma blocks will have different quantization parameters by having a smaller size of the chroma QG. However, in the case where the chroma blocks will have the same quantization parameter, the example techniques allow for a larger size of the chroma QG, which has the benefit of reduced signaling overhead and reduced decoding time.

[0075] In some examples, as described in more detail, the offset values ​​for chroma blocks in a chroma QG may be the same for all blocks that meet some criteria. For example, the offset values ​​may be the same for chroma blocks of a certain size in the chroma QG, or for chroma blocks for which there is at least one non-zero coefficient for the corresponding residual block. Thus, in some examples, the video encoder 200 and the video decoder 300 may determine the same offset value for two or more chroma blocks of the chroma QG (e.g., the same for all chroma blocks that meet the criteria). However, the offset value may be the same for all chroma blocks in the chroma QG (e.g., where there is no criterion to meet).

[0076] Figure 2A and Figure 2Bis a conceptual diagram showing an example quadtree binary tree (QTBT) structure 130 and a corresponding codec tree unit (CTU) 132. Solid lines represent quadtree partitioning, and dashed lines indicate binary tree partitioning. In each partition (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which partition type (i.e., horizontal or vertical) is used, where 0 indicates horizontal partitioning and 1 indicates vertical partitioning in this example. For quadtree partitioning, since the quadtree node partitions the block horizontally and vertically into 4 sub-blocks of equal size, there is no need to indicate the partition type. Accordingly, the video encoder 200 and the video decoder 300 can encode and decode syntax elements (e.g., split information) for the regional tree level (i.e., solid line) of the QTBT structure 130 and syntax elements (e.g., split information) for the prediction tree level (i.e., dashed line) of the QTBT structure 130, respectively. The video encoder 200 and the video decoder 300 may respectively encode and decode video data (such as prediction and transform data) for a CU represented by a terminal leaf node of the QTBT structure 130 .

[0077] Generally, Figure 2B The CTU 132 may be associated with parameters that define the size of blocks corresponding to nodes of the first and second level QTBT structures 130. These parameters may include a CTU size (indicating the size of the CTU 132 in a sample), a minimum quadtree size (MinQTSize, indicating the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, indicating the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, indicating the maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, indicating the minimum allowed binary tree leaf node size).

[0078] The root node of the QTBT structure corresponding to the CTU may have four child nodes at the first level of the QTBT structure, and each child node may be segmented according to the quadtree segmentation. That is, the node at the first level is a leaf node (without child nodes) or has four child nodes. The example of the QTBT structure 130 represents such a node, which includes a parent node and a child node with a solid line branch. If the node at the first level is not larger than the maximum allowed binary tree root node size (MaxBTSize), the node may be further segmented by the corresponding binary tree. The binary tree segmentation of a node may be iterated until the node generated by the segmentation 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 branch. The binary tree leaf node is called a coding unit (CU), which is used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further segmentation. As described above, a CU may also be referred to as a "video block" or "block".

[0079] In one example of a QTBT partitioning structure, the CTU size is set to 128×128 (luminance sample and two corresponding 64×64 chrominance samples), MinQTSize is set to 16×16, MaxBTSize is set to 64×64, MinBTSize (for both 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 be from 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If the leaf quadtree node is 128×128, it will not be further partitioned by the binary tree because its size exceeds MaxBTSize (i.e., 64x64 in this example). Otherwise, the binary tree will further partition the leaf quadtree node. Therefore, the quadtree leaf node is also the root node of the binary tree and has a binary tree depth of 0. When the binary tree depth reaches MaxBTDepth (4 in this example), further partitioning is not allowed. When the width of the binary tree node is equal to MinBTSize (4 in this case), 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 segmentation.

[0080] Figure 3 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 3The disclosure is provided for purposes of illustration and should not be considered limiting of the techniques extensively illustrated and described in the present disclosure. For purposes of illustration, the present disclosure describes the video encoder 200 in the context of video codec standards, such as the HEVC video codec standard and the H.266 video codec standard under development. However, the techniques of the present disclosure are not limited to these video codec standards and are generally applicable to video encoding and decoding.

[0081] exist Figure 3 In the example of , 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 may be implemented in one or more processors or processing circuits. In addition, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

[0082] 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 video data memory 230. DPB 218 can act as a reference picture memory, which stores reference video data for predicting subsequent video data by video encoder 200. Video data memory 230 and 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. Video data memory 230 and DPB 218 can be provided by the same memory device or a separate memory device. In various examples, as shown in the figure, video data memory 230 can be on chip with other components of video encoder 200, or off chip relative to those components.

[0083] In the present disclosure, references to the video data memory 230 should not be interpreted as limited to memory internal to the video encoder 200, unless specifically described as such, or to memory external to the video encoder 200, unless specifically described as such. Instead, references to the video data memory 230 should be understood as references to memory storing 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 of outputs from the various units of the video encoder 200 .

[0084] Show 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 preset on executable operations. Programmable circuits refer to circuits that are programmable to perform various tasks and provide flexible functions in executable operations. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally unchanged. In some examples, one or more units may be different circuit blocks (fixed function or programmable), and in some examples, one or more units may be integrated circuits.

[0085] 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 by a programmable circuit. In an example in which the operation of the video encoder 200 is performed using software executed by a programmable circuit, the memory 106 ( Figure 1 ) may store object code for software received and executed by the video encoder 200, or another memory within the video encoder 200 (not shown) may store such instructions.

[0086] The video data memory 230 is configured to store received video data. The video encoder 200 may retrieve pictures of 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 may be original video data to be encoded.

[0087] 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. As an 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, etc.

[0088] The mode selection unit 202 generally coordinates multiple encoding processes to test combinations of encoding parameters and rate-distortion values ​​for such combinations. The encoding parameters may include partitioning of the CTI into CUs, prediction modes of the CUs, transform types of residual data of the CUs, quantization parameters of residual data of the CUs, etc. The mode selection unit 202 may ultimately select a combination of encoding parameters that has a better rate-distortion value than other tested combinations.

[0089] The video encoder 200 may partition the picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs in a slice. The mode selection unit 202 may partition 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 from the partitioned CTUs according to the tree structure. Such CUs may also be generally referred to as "video blocks" or "blocks".

[0090] Typically, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the 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 the PU and TU). For inter prediction of the current block, the motion estimation unit 222 can 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 the DPB 218). Specifically, the motion estimation unit 222 can calculate a value representing the degree of similarity of the potential reference block to the current block, for example, based on the sum of absolute differences (SAD), the sum of square differences (SSD), the mean absolute difference (MAD), the mean square difference (MSD), etc. The motion estimation unit 222 can generally perform these calculations using the sample-by-sample difference between the current block and the reference block being considered. The motion estimation unit 222 can identify the reference block with the lowest value obtained from these calculations, which indicates the reference block that most closely matches the current block.

[0091] The 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 a current block in a current picture. The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, for unidirectional inter prediction, the motion estimation unit 222 may provide a single motion vector, and for bidirectional inter prediction, the motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, the motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, if the motion vectors have fractional sample precision, the motion compensation unit 224 may interpolate the prediction block according to one or more interpolation filters. In addition, for bidirectional inter prediction, the motion compensation unit 224 may retrieve data for two reference blocks identified by their respective motion vectors and combine the retrieved data, for example, by sample-by-sample averaging or weighted averaging.

[0092] As another example, for intra prediction or intra prediction codec, the intra prediction unit 226 can generate a prediction block from samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally mathematically combine the values ​​of the adjacent samples and pad these calculated values ​​in a defined direction across the current block to produce a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average value of the adjacent samples to the current block and generate a prediction block to include the resulting average value for each sample of the prediction block.

[0093] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives the original uncoded version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The generated sample-by-sample difference defines a residual block for the current block. In some examples, the residual generation unit 204 may also determine the difference between the sample values ​​in the residual block to generate the residual block using residual differential pulse code modulation (RDPCM). In some examples, the residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0094] In the example where the mode selection 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 the CU may refer to the size of the luma codec block of the CU, and the size of the PU may refer to the size of the luma prediction unit of the PU. Assuming that the size of a particular CU is 2N×2N, the video encoder 200 may support PU sizes of 2N×2N or N×N for intra-frame prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N or the like for inter-frame prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning of PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter-frame prediction.

[0095] In an example where the mode selection unit does not further partition the CU into PUs, each CU may be associated with a luma codec block and a corresponding chroma codec block. As described above, the size of the CU may refer to the size of the luma codec block of the CU. The video encoder 200 and the video decoder 300 may support a CU size of 2N×2N, 2N×N, or N×2N.

[0096] For other video codecs such as intra-block copy mode codecs, affine mode codecs, and linear model (LM) mode codecs, for example, the mode selection unit 202 generates a prediction block for the block currently being encoded via various units associated with the codec technology. In some examples, such as palette mode codecs, the mode selection unit 202 may not generate a prediction block, but instead generate syntax elements that indicate how to reconstruct the block based on the selected palette. In this mode, the mode selection unit 202 may provide these syntax elements to the entropy coding unit 220 to be encoded.

[0097] 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.

[0098] The transform processing unit 206 applies one or more transforms to the residual block to generate a transform coefficient block (referred to herein as a "transform coefficient block"). The transform processing unit 206 may apply various transforms to the residual block to form a transform coefficient block. For example, the transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a karhun-Loeve transform (KLT), or a transform conceptually similar to the residual block. In some examples, the 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, the transform processing unit 206 does not apply a transform to the residual block.

[0099] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to generate 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 introduce information loss, and therefore, the quantized transform coefficients may have lower precision than the original transform coefficients produced by the transform processing unit 206.

[0100] In one or more examples, the quantization unit 208 in conjunction with the mode selection unit 202 and the entropy coding unit 220 can be configured to perform example techniques described in this disclosure. For example, the mode selection unit 202 can cause the entropy coding unit 220 to signal an offset value representing the difference between the quantization parameter predictor and the quantization parameter of the chroma block, rather than signaling the actual quantization parameter of the chroma block.

[0101] In some examples, mode selection unit 202 may determine chroma blocks in a chroma quantization group (e.g., define a chroma QG that includes multiple chroma blocks). In some examples, quantization parameters for two or more (including all) chroma blocks within the chroma QG may be the same. For example, mode selection unit 202 may determine a quantization parameter predictor for the chroma QG, where the quantization parameter predictor may be the same for each chroma block in the chroma QG.

[0102] The mode selection unit 202 may determine the same offset value for two or more chroma blocks in the chroma QG (e.g., the offset value is based on a quantization parameter and a quantization parameter predictor). In some cases, there may be a criterion such as block size or whether there is a non-zero coefficient value in the residual block of the chroma block or whether the chroma block is not before the first chroma block with non-zero coefficients in the QG to meet, and the offset value may be the same for the chroma blocks in the chroma QG that meet the criterion. However, it is not necessary to have such a criterion that needs to be met in all cases, and in some examples, the offset value may be the same for each chroma block in the chroma QG. That is, in some examples, the mode selection unit 202 may determine the same offset value for all chroma blocks of the chroma QG. In some examples, the mode selection unit 202 may determine the same offset value for two or more chroma blocks having a size greater than a threshold size, or determine at least one non-zero coefficient for the corresponding residual block. In some examples, the mode selection unit 202 may determine that the offset value is the same for all blocks after the first block with non-zero coefficients in the QG, including the first block with non-zero coefficients in the QG.

[0103] In this way, the mode selection unit 202 may not need to repeatedly determine the quantization parameter for each chroma block or signal the offset value for each chroma block, which promotes bandwidth efficiency. For example, the mode selection unit 202 may determine the quantization parameter for only one chroma block in the chroma QG and assign the determined quantization parameter to two or more chroma blocks in the chroma QG.

[0104] There may be various ways in which the mode selection unit 202 may determine the quantization parameter predictor. As an example, the mode selection unit 202 may determine a chroma sample from one of the chroma blocks, determine a luma block corresponding to the chroma block based on the determined chroma sample, and determine the quantization parameter predictor based on the quantization parameter of the corresponding luma block. As another example, the mode selection unit 202 may determine the quantization parameter predictor based on the quantization parameter of the neighboring chroma QG.

[0105] In some examples, the example techniques described in this disclosure may be applicable where dual-tree partitioning exists. For example, in dual-tree partitioning, video encoder 200 and video decoder 300 may partition luma CTUs and chroma CTUs in a dual tree, generating luma blocks of luma CTUs with different partitions and chroma blocks of CTUs. In some examples, the example techniques described in this disclosure may be applicable when dual-tree partitioning is used.

[0106] The quantization unit 208 may quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter. The entropy encoding unit 220 may signal information representing the quantized coefficients and the offset value.

[0107] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform to the quantized transform coefficient block, respectively, 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 it may have a certain 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 from the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0108] 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 edge of the CU. In some examples, the operations of filter unit 216 may be skipped.

[0109] The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in an example where the operation of the filter unit 216 is not required, the reconstruction unit 214 can store the reconstructed blocks to the DPB 218. In an example where the operation of the filter unit 216 is required, the filter unit 216 can store the filtered reconstructed blocks to the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 can retrieve a reference picture formed by the reconstructed (and potentially filtered) blocks from the DPB 218 to perform inter-frame prediction on blocks of subsequently encoded pictures. In addition, the intra-frame prediction unit 226 can use the reconstructed blocks in the DPB 218 of the current picture to perform intra-frame prediction on other blocks in the current picture.

[0110] In general, the entropy coding unit 220 may entropy encode syntax elements received from other functional components of the video encoder 200. For example, the entropy coding unit 220 may entropy encode the quantized transform coefficient blocks from the quantization unit 208. As another example, the entropy coding unit 220 may entropy encode the prediction syntax elements (e.g., motion information for inter-frame prediction or intra-frame mode information for intra-frame prediction) from the mode selection unit 202. The entropy coding unit 220 may perform one or more entropy coding operations on syntax elements as another example of video data to generate entropy-encoded data. For example, the 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 type of entropy coding operation on the data. In some examples, the entropy coding unit 220 may operate in a bypass mode where the syntax elements are not entropy-encoded.

[0111] The video encoder 200 may output a bitstream including entropy-encoded syntax elements required to reconstruct a block of a slice or a picture. Specifically, the entropy encoding unit 220 may output a bitstream.

[0112] The above operations are described with respect to blocks. Such descriptions should be understood as operations for luma codec blocks and / or chroma codec blocks. As described above, in some examples, the luma codec block and the chroma codec block are the luma and chroma components of a CU. In some examples, the luma codec block and the chroma codec block are the luma and chroma components of a PU.

[0113] In some examples, the operations performed for the luma codec block do not need to be repeated for the chroma codec block. As an example, in order to identify the motion vector (MV) and reference picture of the chroma block, the operations for identifying the motion vector (MV) and reference picture of the luma codec block do not need to be repeated. Instead, the MV of the luma codec block can be scaled to determine the MV of the chroma block, and the reference picture can be the same. As another example, the intra prediction process can be the same for the luma codec block and the chroma codec block.

[0114] The video encoder 200 represents an example of a device configured to encode video data, the device including a memory configured to store the video data, and one or more processing units implemented in circuits and configured to perform one or more (including combinations) of the example techniques described in the present disclosure. For example, the video encoder 200 may be configured to encode a current block based on the chroma quantization parameter (QP) derivation techniques described in the present disclosure.

[0115] Figure 4 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Figure 4 It is provided for the purpose of illustration and does not limit the techniques widely illustrated and described in this disclosure. For the purpose of illustration, this disclosure describes a video decoder 300 according to the techniques of VVC and HEVC. However, the techniques of this disclosure can be performed by video codec devices configured to other video codec standards.

[0116] exist Figure 4In the example of , the video decoder 300 includes a codec 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 the CPB memory 320, the entropy decoding unit 302, the prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the DPB 314 may be implemented in one or more processors or processing circuits. In addition, the video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

[0117] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include an addition unit 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.

[0118] The CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of the video decoder 300. The video data stored in the CPB memory 320 may be, for example, received from the computer-readable medium 110 ( Figure 1 ). The CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. In addition, the CPB memory 320 may store video data other than syntax elements of a coded and decoded picture, such as temporary data representing outputs from various units of the video decoder 300. The DPB 314 typically stores decoded pictures, and the video decoder 300 may output the decoded pictures and / or use them as reference video data when decoding subsequent data or pictures of the encoded video bitstream. The CPB memory 320 and the DPB 314 may be formed by any of a variety of memory devices, such as DRAM, including SDRAM, MRAM, RRAM, or other types of memory devices. The CPB memory 320 and the DPB 314 may be provided by the same memory device or a separate memory device. In various examples, the CPB memory 320 may be on-chip with other components of the video decoder 300, or off-chip relative to those components.

[0119] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1) retrieves the encoded and decoded video data. That is, memory 120 may store data as discussed above with CPB memory 320. Likewise, when some or all of the functionality of video decoder 300 is implemented in software executed by processing circuitry of video decoder 300, memory 120 may store instructions to be executed by video decoder 300.

[0120] Show Figure 4 The various units shown in the figure are helpful for understanding 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, a fixed-function circuit refers to a circuit that provides a specific function and is preset on the executable operations. A programmable circuit refers to a circuit that can be programmed to perform various tasks and provide flexible functions in the executable operations. 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 (e.g., receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally unchanged. In some examples, one or more units can be different circuit blocks (fixed function or programmable), and in some examples, one or more units can be integrated circuits.

[0121] The video decoder 300 may include an ALU, an EFU, a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video decoder 300 is performed by software executed on the programmable circuit, an on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

[0122] The entropy decoding unit 302 may receive the encoded video data from the CPB and entropy decode the video data to reproduce the syntax elements. The prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, and the filter unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.

[0123] Typically, the video decoder 300 reconstructs a picture on a block-by-block basis. 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").

[0124] The entropy decoding unit 302 may entropy decode syntax elements defining quantized transform coefficients of the quantized transform coefficient block and 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 degree of quantization, and likewise, determine a degree of inverse quantization for the inverse quantization unit 306 to apply. 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 including the transform coefficients.

[0125] In one or more examples, the inverse quantization unit 306 in conjunction with the prediction processing unit 304 can be configured to perform example techniques described in the present disclosure. For example, the prediction processing unit 304 can determine the chroma blocks in the chroma quantization group (QG). As an example, the prediction processing unit 304 can receive information signaled by the video encoder 200 indicating which chroma blocks belong to the quantization group.

[0126] In some examples, the quantization parameter for two or more (including all) chroma blocks within a chroma QG may be the same. For example, the prediction processing unit 304 may determine a quantization parameter predictor for the chroma QG, where the quantization parameter predictor may be the same for each of the plurality of chroma blocks in the chroma QG.

[0127] The prediction processing unit 304 may determine an offset value that is the same for two or more chroma blocks in the chroma QG (e.g., the offset value is based on a quantization parameter and a quantization parameter predictor). In some cases, there may be a criterion such as block size or whether there are non-zero coefficient values ​​in the residual block of the chroma block to be met, and the offset value may be the same for the chroma blocks in the chroma QG that meet the criterion. However, it is not necessary to have such a criterion that needs to be met in all cases, and in some examples, the offset value may be the same for each chroma block in the chroma QG. That is, in some examples, the prediction processing unit 304 may determine the same offset value for all chroma blocks of the chroma QG. In some examples, the prediction processing unit 304 may determine the same offset value for two or more chroma blocks having a size greater than a threshold size, or determine at least one non-zero coefficient for the corresponding residual block.

[0128] In this way, the prediction processing unit 304 may not need to repeatedly determine the quantization parameter for each chroma block, which reduces the calculation time, or does not need to receive the offset value for each chroma block, which improves bandwidth efficiency. For example, the prediction processing unit 304 may determine the quantization parameter for only one chroma block in the chroma QG, and assign the determined quantization parameter to one or more other chroma blocks in the chroma QG, so that multiple chroma blocks in the chroma QG have the same quantization parameter.

[0129] There may be various ways in which prediction processing unit 304 may determine the quantization parameter predictor. As one example, prediction processing unit 304 may determine chroma samples from one of the chroma blocks, determine a luma block corresponding to the chroma block based on the determined chroma samples, and determine the quantization parameter predictor based on the quantization parameter of the corresponding luma block. As another example, prediction processing unit 304 may determine the quantization parameter predictor based on the quantization parameters of neighboring chroma QGs.

[0130] In some examples, the example techniques described in this disclosure may be applicable where dual-tree partitioning exists. For example, in dual-tree partitioning, the video encoder 200 and the video decoder 300 may partition the luma CTU and the chroma CTU in the dual tree, generating luma blocks of luma CTUs with different partitions and chroma blocks of CTUs. In some examples, the example techniques described in this disclosure may be applicable when dual-tree partitioning is used.

[0131] The inverse quantization unit 306 may inverse quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter. As described below, the inverse transform processing unit 308 may generate one or more residual blocks based on the inverse quantization coefficients, and the reconstruction unit 310 may reconstruct the chroma block based on the one or more residual blocks.

[0132] After the inverse quantization unit 306 forms the transform coefficient block, the 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, the 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 coefficient block.

[0133] 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, motion compensation unit 316 can generate a prediction block. In this case, the prediction information syntax element can indicate a reference picture in DPB 314 from which to retrieve the reference block, and a motion vector that identifies 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 can generally generate a prediction block in the same manner as described for motion compensation unit 224 ( Figure 3 ) is performed in a manner substantially similar to that described herein.

[0134] 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 perform intra-prediction processing in a manner substantially similar to that described with respect to the intra-prediction unit 226 ( Figure 3 ). The intra prediction unit 318 may retrieve data of neighboring samples of the current block from the DPB 314.

[0135] 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.

[0136] 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.

[0137] The video decoder 300 may store the reconstructed blocks in the DPB 314. As described 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 decoded pictures from the DPB 314 for subsequent use in, for example, Figure 1 is presented on the display device 118 .

[0138] 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 perform one or more (including combinations) of the example techniques described in this disclosure. For example, the video decoder 300 may be configured to decode a current block based on the chroma quantization parameter (QP) derivation techniques described in this disclosure.

[0139] As mentioned above, video codec standards include ITU-T H.261, ISO / IEC MPEG-1 Visual, ITU-TH.262 or ISO / IEC MPEG-2 Visual, ITU-T H.263, ISO / IEC MPEG-4 Visual, ITU-T H.264 (also known as ISO / IEC MPEG-4 AVC), including its Scalable Video Codec (SVC) and Multi-view Video Codec (MVC) extensions. Another video codec standard is High Efficiency Video Codec (HEVC), which was finalized in April 2013 by the Joint Collaboration Team on Video Codecs (JCT-VC) of the ITU-T Video Codec Experts Group (VCEG) and the ISO / IEC Motion Picture Experts Group (MPEG).

[0140] The Joint Video Experts Team (JVET), a collaborative group consisting of MPEG and VCEG of ITU-T Study Group 16, is currently working on a new video codec standard called Versatile Video Codec (VVC). VVC can provide improvements in compression performance over the existing HEVC standard, facilitating the deployment of higher quality video services and emerging applications such as 360° omnidirectional immersive multimedia and high dynamic range (HDR) video. The development of the VVC standard is expected to be completed in 2020.

[0141] As described above, one aspect of video coding is based on quantization parameters. The quantization parameter (QP) value is used to determine the step size for quantizing / inverse quantizing coefficients. The QP value is specified in the range of -QpBdOffset to 63 (including -QpBdOffset and 63), where 63 is the maximum QP value. QpBdOffset is specified as a fixed value for a specific bit depth, derived as 6*(bitDepth 8). The QP prime value calculated by adding QpBdOffset to the specified QP value is used to derive the actual step size. For ease of description, QP and QP prime values ​​may be used interchangeably in the present disclosure, and it is understood that the QP value may be used in most QP derivation processes (e.g., may only be used), and the QP prime value may be used before determining the step size (e.g., may only be used). A QP value change of 1 roughly represents a 12% change in step size. A QP value change of 6 corresponds to changing the step size by a factor of 2. In some examples, the higher the quantization parameter value, the larger the quantization step size becomes, and the representation of the quantized coefficients becomes coarser.

[0142] As described above, in some examples, quantization groups (QGs) may be used. Further description of QGs ​​is provided below. Quantization groups are regions of a picture for which QP offset parameters (e.g., the offset values ​​described above) may be signaled. That is, the video encoder 200 may signal and the video decoder 300 may receive QP offset parameters applicable to the regions defined by the QGs. When signaled, the QP offset parameters may be used to derive QP values ​​for one or more codec blocks in the quantization group. The QP offset parameters may be referred to as delta QP values.

[0143] The video encoder 200 may signal information indicating a quantization group based on a maximum depth from a CTB (codec tree block) level or using a variable indicating the number of samples in the group relative to the size of the CTB. As described above, a codec tree unit (CTU) may include three blocks, namely, luma (Y) and two chroma samples (CB and CR) and associated syntax elements. Each block (e.g., a luma and chroma block of a CTU) may be referred to as a codec tree block (CTB). In some examples, the QG may be based on a maximum depth from the CTB (e.g., the QG may be derived based on the maximum depth of the CTB). In some examples, the QG may be derived using a variable indicating the number of samples in the QG relative to the size of the CTB. For example, as described above, the video encoder 200 and the video decoder 300 may determine a chroma block in a chroma QG. In some examples, the video encoder 200 and the video decoder 300 may determine a chroma block in a chroma QG based on the size of the CTB.

[0144] In some techniques, for the first block with non-zero coefficients in a quantization group, a QP value may be signaled (e.g., only signaled) at the quantization group. For blocks before the first block with non-zero coefficients in the quantization group, the QP value is derived as a predicted QP value. Blocks with zero coefficients do not require any QP value because there are no coefficients to quantize / inverse quantize. However, the QP value is used in the deblocking process to determine some parameters of the deblocking filter to be applied. For example, instead of using the QP value to quantize the zero coefficients (since the values ​​are already zero, no quantization is required), the QP value may be used to determine the parameters of the deblocking filter applied to the reconstructed block.

[0145] Typically, QG refers to luma QG, where it is also specified as an area where the codec blocks have the same predicted QP value. For example, in luma QG, the codec blocks have the same predicted QP value. However, in some other technologies, chroma QG may have different QP values ​​(e.g., different quantization parameters). According to one or more examples described in the present disclosure, the quantization parameter may be the same for each chroma block in the chroma QG.

[0146] Some examples of signaling of quantization parameters are described below. In VVC draft 6, the following are the syntax elements used to derive QP values ​​for luma and chroma.

[0147] The following are the syntax elements in a sequence parameter set (SPS).

[0148] min_qp_prime_ts_minus4 ue(v)

[0149] The syntax element min_qp_prime_ts_minus4 is used to derive the minimum QP value for transform skip mode.

[0150]

[0151] The above syntax elements are used to specify a mapping table to derive chroma QP values ​​from luma QP values ​​of Cb, Cr, and joint Cb-Cr components.

[0152]

[0153]

[0154] The QP value related syntax elements in the above syntax table apply to the luma adaptive QP offset to be applied to luma deblocking.

[0155] The following are the syntax elements in a picture parameter set (PPS).

[0156]

[0157]

[0158] The video decoder 300 can use the syntax elements in the above table to derive the initial QP for the slice of the reference PPS and specify the quantization group for luma and chroma. The syntax elements can also specify an offset value table to indicate the CU chroma offset.

[0159] Following are the syntax elements in a stripe header.

[0160]

[0161] The syntax elements in the table above specify further increments of the initial QP of the slice for luma and chroma components.

[0162] The syntax elements of a transform unit are described below.

[0163]

[0164]

[0165] The syntax elements in the table above specify CU-level QP offsets for luma and chroma components that the video decoder 300 uses to derive QP values ​​for quantization groups.

[0166] The following describes the quantization parameter derivation for luma and chroma. In VVC draft 6, the video encoder 200 and / or the video decoder 300 may derive the QP values ​​for luma and chroma as follows. For luma, the video decoder 300 may derive the slice QP from the initial QP (signaled in the PPS) and the QP offset (signaled in the slice). A quantization group is specified, and for each QP, the video decoder 300 may derive the QP Y_PRED Based on the relative position of the quantization group in its brick and its CTB row, the QP Y_PRED The value of may vary. The video decoder 300 may be configured to receive the QP signaled for the quantization group. Y_PRED and deltaQP to derive QP Y value.

[0167] In some examples, QP is derived for all codec blocks in a quantization group Y_PRED However, deltaQP may only be signaled for a block under certain conditions. Therefore, video decoder 300 may derive QP values ​​only for certain situations. For example, if deltaQP is not signaled, video decoder 300 may set the QP value equal to QP Y_PRED If deltaQP is signaled, the video decoder 300 may Y_PRED and deltaQP to derive QP values.

[0168] The video decoder 300 may derive the chroma QP from the mapped value of the luma QP for the sample collocated with the center of the chroma block and any QP offset applicable to the codec block. Similar to luma, the chroma QP offset is signaled for the first chroma codec block in the chroma quantization group that has non-zero coefficients.

[0169] Some examples of quantization parameter derivation in VVC are described below.

[0170] The derivation process of the QP value in VVC is as follows.

[0171] The inputs to this process are:

[0172] – Luma position (xCb, yCb) specifies the top left luma sample of the current codec block relative to the top left luma sample of the current picture,

[0173] – The variable cbWidth specifies the width of the current coded deblock in luminance samples,

[0174] – The variable cbHeight specifies the height of the current codec block in luma samples,

[0175] – The variable treeType specifies whether a single tree (SINGLE_TREE) or a dual tree is used to split the CTU, and when using a dual tree, whether the luma (DUAL_TREE_LUMA) or chroma component (DUAL_TREE_CHROMA) is currently being processed.

[0176] In this process, the brightness quantization parameter Qp′ is derived Y and the chromaticity quantization parameter Qp′ Cb and Qp′ Cr .

[0177] The luma position (xQg, yQg) specifies the top left luma sample of the current quantization group relative to the top left luma sample of the current picture. The horizontal and vertical positions xQg and yQg are set equal to CuQgTopLeftX and CuQgTopLeftY, respectively.

[0178] Note: The current quantization group is sharing the same qP Y_PRED The rectangular area within the codec tree block of . Its width and height are equal to the width and height of the codec tree node, and the top left luma sample position of the node is assigned to the variables CuQgTopLeftX and CuQgTopLeftY.

[0179] When treeType is equal to SINGLE_TREE or DUAL_TREE_LUMA, the predicted luma quantization parameter qP Y_PRED Export in the following sequential steps:

[0180] 1. Variable qP Y_PREV The derivation is as follows:

[0181] —If one or more of the following conditions are true, qP Y_PREV Set equal to SliceQp Y :

[0182] - The current quantization group is the first quantization group in the slice.

[0183] —The current quantization group is the first quantization group in the brick.

[0184] - The current quantization group is the first quantization group in the CTB row of the brick, and entropy_coding_sync_enabled_flag is equal to 1.

[0185] Otherwise, qP Y_PREV Set equal to the luma quantization parameter Qp of the last luma codec unit in the previous quantization group in decoding order Y .

[0186] 2. The derivation process for the neighboring block availability specified in Section 6.4.4 is called with as input the position (xCurr, yCurr) set equal to (xCb, yCb), the neighboring position (xNbY, yNbY) set equal to (xQg-1, yQg), checkPredModeY set equal to FALSE, and cIdx set equal to 0, and the output is assigned to availableA. The variable qP Y_A The derivation is as follows:

[0187] —If one or more of the following conditions are true, qP Y_A Set equal to qP Y_PREV :

[0188] —availableA is equal to FALSE.

[0189] - the CTB containing the luma codec block covering luma position (xQg-1, yQg) is not equal to the CTB containing the current luma codec block at (xCb, yCb), i.e., all of the following conditions are true:

[0190] — (xQg-1)>>CtbLog2SizeY is not equal to (xCb)>>CtbLog2SizeY

[0191] — (yQg)>>CtbLog2SizeY is not equal to (yCb)>>CtbLog2SizeY

[0192] —Otherwise, qP Y_A is set equal to the luma quantization parameter Qp of the codec unit containing the luma codec block covering (xQg-1, yQg) Y .

[0193] 3. The derivation process for the neighboring block availability specified in Section 6.4.4 is called with as input the position (xCurr, yCurr) set equal to (xCb, yCb), the neighboring position (xNbY, yNbY) set equal to (xQg, yQg-1), checkPredModeY set equal to FALSE, and cIdx set equal to 0, and the output is assigned to availableB. The variable qP Y_B The derivation is as follows:

[0194] —If one or more of the following conditions are true, qP Y_B Set equal to qP Y_PREV :

[0195] —availableB is equal to FALSE.

[0196] - the CTB containing the luma codec block covering luma position (xQg, yQg-1) is not equal to the CTB containing the current luma codec block at (xCb, yCb), i.e., all of the following conditions are true:

[0197] — (xQg)>>CtbLog2SizeY is not equal to (xCb)>>CtbLog2SizeY

[0198] — (yQg-1)>>CtbLog2SizeY is not equal to (yCb)>>CtbLog2SizeY

[0199] —Otherwise, qP Y_B is set equal to the luma quantization parameter Qp of the codec unit containing the luma codec block covering (xQg, yQg-1) Y .

[0200] 4. Predicted brightness quantization parameter qP Y_PRED The derivation is as follows:

[0201] – If all of the following conditions are true, then qP Y_PRED Set equal to the luma quantization parameter Qp of the codec unit containing the luma codec block covering (xQg, yQg-1) Y :

[0202] – availableB is equal to TRUE.

[0203] – The current quantization group is the first quantization group in the CTB row within the brick, and entropy_coding_sync_enabled_flag is equal to 0

[0204] – Otherwise, qP Y_PRED The derivation is as follows:

[0205] Q Y_PRED =(qP Y_A +qP Y_B +1)>>1 (8-932)

[0206] Variable Qp Y The derivation is as follows:

[0207] Q Y =((qP Y_PRED +CuQpDeltaVal+64+2*QpBdOffset Y )%(64+QpBdOffset Y ))-QpBdOffset Y (8-933)

[0208] Luma quantization parameter Qp′ Y The derivation is as follows:

[0209] Qp′ Y =Qp Y +QpBdOffset Y (8-934)

[0210] When ChromaArrayType is not equal to 0 and treeType is equal to SINGLE_TREE or DUAL_TREE_CHROMA, the following applies:

[0211] —When treeType is equal to DUAL_TREE_CHROMA, the variable Qp Y Set equal to the luma quantization parameter Qp of the luma codec unit covering the luma position (xCb+cbWidth / 2, yCb+cbHeight / 2) Y .

[0212] —Variable qP Cb ,qP Cr and qP CbCr The derivation is as follows:

[0213] Q Chroma =Clip3(-QpBdOffset C , 63, Qp Y ) (8-935)

[0214] Q Cb =ChromaQpTable[0][qPi Chroma ] (8-936)

[0215] Q Cr =ChromaQpTable[1][qPi Chroma ] (8-937)

[0216] Q CbCr =ChromaQpTable[2][qPi Chroma ] (8-938)

[0217] —Cb and Cr components, QP′ Cb and QP′ Cr And joint Cb-Cr codec QP′ CbCr The derivation of the chromaticity quantization parameters is as follows:

[0218] QP′ Cb =Clip3(-QpBdOffset C , 63,

[0219] Q Cb +pps_cb_qp_offset+slice_cb_qp_offset+CuQpOffset Cb )+QpBdOffset C (8-939)

[0220] QP′ Cr =Clip3(-QpBdOffset C , 63, qP Cr +pps_cr_qp_offset+slice_cr_qp_offset+CuQpOffset Cr )+QpBdOffset C (8-940)

[0221] Qp′ CbCr =Clip3(-QpBdOffset C , 63, qP CbCr +pps_cbcr_qp_offset+slice_cbcr_qp_offset+CuQpOffset CbCr )+QpBdOffset C (8-941)

[0222] There may be some issues with deriving QP or QG. In some cases, a chroma quantization group (indicated by a syntax element such as cu_chroma_qp_offset_subdiv) may correspond to multiple luma quantization groups (i.e., collocated luma samples of various chroma samples in a quantization group belong to multiple luma quantization groups). When LUMA delta QP is signaled at the QG level, the resulting codec blocks of the chroma QG may have different QP values.

[0223] In some examples, there may be a problem of codec blocks with chroma QGs having different QP values ​​under dual-tree codec conditions, where the partitioning structures of chroma and luminance can be very different. For example, a chroma codec block with non-zero coefficients in the chroma QG can have different QP values. This results in codec blocks with quantization groups having different QP values. Quantization groups of codec blocks with different QP values ​​may result in a situation where the texture in the area corresponding to the QG may have different quality, resulting in suboptimal visual quality of the video. Alternatively or additionally, the chroma quantization group is specified to be very small so that a uniform QP value can be maintained in the chroma quantization group. However, specifying such a small quantization group may result in sending more bits (e.g., negatively affecting bandwidth efficiency).

[0224] Figure 5 and Figure 6It shows how the QPs of blocks within the chroma QG differ when the luma QP varies among collocated blocks. Figure 5 is a conceptual diagram illustrating examples of chroma QPs derived for two cases of chroma quantization groups in a single-tree configuration. Figure 6 is a conceptual diagram illustrating examples of chroma QPs derived for two cases of chroma quantization groups in a dual-tree configuration. Figure 5 and Figure 6 Examples from the Virtual Test Model (VTM6.0) may be represented.

[0225] exist Figure 5 and Figure 6 In , the chroma QP derived for a codec block within a chroma QG may be different. Figure 5 and Figure 6 In the example, italics indicate blocks with zero coefficients. The first of the two numbers in each block indicates the predicted QP value, while the number "+n" indicates the offset value. Thus, 30+1 indicates that the QP value for the block is 31.

[0226] Additional techniques related to chroma delta quantization parameter (QP) in video codecs can be found in U.S. Provisional Application No. 62 / 871,028, filed on July 5, 2019, U.S. Non-Provisional Application No. 16 / 918,741, filed on July 1, 2020, U.S. Provisional Application No. 62 / 868,771, filed on June 28, 2019, and U.S. Non-Provisional Application No. 16 / 912,232, filed on June 25, 2020.

[0227] For example, Figure 5A luma codec block (e.g., luma CTU) 500 is shown that includes four luma quantization groups (QGs) 502A, 502B, 502C, and 502D. QG 502A has a QP value of 30 (e.g., an initial quantization parameter of 30 and an offset of 0) and may include one luma block. QG 502B has a QP value of 31 (e.g., an initial quantization parameter of 31 and an offset of 0) and may include one luma block. QG 502C has four QP values: 30 for the upper left luma block, 31 for the upper right luma block (e.g., 30+1), 31 for the lower left luma block (e.g., 30+1), and 31 for the lower right luma block (e.g., 30+1). In this example, the initial quantization parameter for each luma block in QG 502C is the same; however, since the top left luma block in QG 502C does not have any non-zero coefficients in its corresponding residual block (e.g., only zero coefficients after transformation), no offset is added to the top left luma block. QG 502D has two QP values: 31 for the left luma block and 34 for the right luma block (e.g., 31+3). In this example, the initial quantization parameter for each luma block in QG 502D is the same; however, since the left luma block in QG 502D does not have any non-zero coefficients in its corresponding residual block, no offset is added to the left luma block.

[0228] In a single-tree configuration, the chroma CTU corresponding to the luma CTU 500 may be partitioned in the same manner. For example, Figure 5 Shown are chroma CTU 504 and chroma CTU 508. Chroma CTU 504 is one example of a corresponding chroma CTU to luma CTU 500, and chroma CTU 508 is another example of a corresponding chroma CTU to luma CTU 500.

[0229] exist Figure 5 In the example shown, chroma CTU 504 includes four QGs 506A, 506B, 506C, and 506D. In some examples, to determine the QP value for each of QGs ​​506A-506D, video decoder 300 may access the corresponding luma block and add an offset. For example, for QG 506A, video decoder 300 may determine the QP value (e.g., quantization parameter predictor) of corresponding QG 502A and add an offset (e.g., signaled by video encoder 200). For example, the QP value of QG 502A is 30, which is the quantization parameter predictor of QG 506A, to which video decoder 300 adds an offset of 3 to determine the QP value of QG 506A is 33.

[0230] As another example, QG 506C includes four chroma blocks. As shown, for the bottom left chroma block in 506C, the quantization parameter predictor is 31 because the QP value of the bottom left luma block in QG 502C is 31. Video decoder 300 may add an offset of 2 (e.g., as signaled by video encoder 200) to determine that the QP value of the bottom left chroma block in QG 506C is 33. Similarly, italic numbers in QGs 506A-506D represent chroma blocks for which there are no non-zero coefficients in the corresponding residual block (i.e., the residual block has only zero-valued coefficients). If all previous blocks in the QG also have non-zero coefficients, then no offset may be added to the initial quantization parameter for chroma blocks that do not have non-zero coefficients.

[0231] In the example of chroma CTU 508, instead of chroma CTU 508 being divided into four QGs, chroma CTU 508 may be divided into only one QG 510. That is, the chroma blocks in chroma QG 510 include the chroma blocks of CTU 508, and chroma QG 510 includes all chroma blocks of CTU 510. In this example, for each chroma block of chroma CTU 508, video decoder 300 may access the corresponding luma block and add the same offset for each chroma block. Figure 5 In the example of , for chroma CTU 508, the offset is 2. Figure 5 As shown, for the upper left chroma block of CTU 508, the QP value is 30+2 because the QP value of the upper left luma block of CTU 500 is 30, which is the quantization parameter predictor, and 2 is the offset. Similarly, for the lower right block of chroma CTU 508, since the QP value of the lower right block of luma CTU 500 is 34 (quantization parameter predictor) and the offset is 2, the QP value is 34+2.

[0232] like Figure 5 As shown, for CTU 508, there is only one QG 510. However, there may be multiple different QP values ​​within QG 510. Determining QP values ​​in this manner may have drawbacks. For example, better visual quality may be achieved if the QP values ​​of chroma blocks (e.g., chroma blocks with non-zero coefficients) are the same across the QG, and Figure 5 In the example shown, the result of different QP values ​​in QG 510 may result in suboptimal visual quality. One way to solve this problem is to define smaller QGs (e.g., instead of having QG 510, QG 510 is divided into many smaller QGs). However, in this case, additional signaling will be required for each QG (e.g., an offset may need to be signaled for each QG), which has a negative impact on bandwidth.

[0233] Figure 6 Similar to Figure 5, but provides an example using a dual-tree partition instead of a single-tree partition. For example, Figure 6 Shown is luma CTU 600. Luma CTU 600 is similar to luma CTU 500 and includes QGs 602A, 602B, 602C, and 602D that are similar to QGs 502A-502D.

[0234] In dual-tree validation, the chroma CTU corresponding to the luma CTU 600 may be partitioned differently. For example, Figure 6 Shown are chroma CTU 604 and chroma CTU 608. Chroma CTU 604 is one example of a corresponding chroma CTU to luma CTU 600, and chroma CTU 608 is another example of a corresponding chroma CTU to luma CTU 600.

[0235] exist Figure 6 In the example shown, chroma CTU 604 includes three QGs 606A, 606B, and 606C. In some examples, to determine the QP value for each of QGs ​​606A-606C, video decoder 300 may access the corresponding luma block (e.g., which is an example of a quantization parameter predictor) and add an offset. Figure 6 In the example of FIG. 6 , QGs 606A-606C may each include a chroma block. Figure 6 In the example of , each chroma block in QG 606A-606C may correspond to multiple luma blocks in luma CTU 600. For example, QG 606A corresponds to the first N columns including the upper left and lower left luma blocks of luma CTU 600. In this example, video decoder 300 may select one of the two luma blocks (e.g., the block of QG 602B) to determine the QP value of QG 606A. For example, the QP value of QG 606A is 31 (e.g., quantization parameter predictor), which is the QP value of the luma block of QG 602B plus an offset of 0.

[0236] QG 606B corresponds to the upper left and lower left blocks of QG 602C and the left block of QG 602D. In this example, the video decoder 300 can select one of these luma blocks (e.g., the left block of QG 602D) to determine the QP value of QG 606B. In some examples, a block containing luma samples collocated with a chroma sample as the center of a chroma block is selected for the QP predictor. For example, the QP value of QG 606B is 31 (e.g., a quantization parameter predictor), which is the QP value of the left block of QG 602D plus an offset of 0. QG 606C corresponds to the upper right and lower right blocks of QG 602C and the right block of QG 602D. In this example, the video decoder 300 can select one of these luma blocks (e.g., the right block of QG 602D) to determine the QP value of QG 606C. For example, the QP value of QG 606C is 34 (eg, quantization parameter predictor), which is the QP value of the right block of QG 602D plus an offset of 0.

[0237] In the example of chroma CTU 608, instead of chroma CTU 608 being divided into three QGs, chroma CTU 608 may be divided into only one QG 610. That is, the chroma blocks in chroma QG 610 include the chroma blocks of CTU 608, and chroma QG 610 includes all chroma blocks of CTU 610. In this example, for each chroma block of chroma CTU 608, video decoder 300 may access the corresponding luma block and add the same offset for each chroma block. Figure 6 In the example of , for chroma CTU 608, the offset is 0. Figure 6 As shown, for the left chroma block of CTU 608, the QP value is 31+0 because the QP value of the lower left luma block of CTU 600 is 31 (e.g., quantization parameter predictor), and 0 is the offset. For the middle block of chroma CTU 608, the QP value is 31+0 because the QP value of the left block of QG 602D is 31 (e.g., quantization parameter predictor), and 0 is the offset. For the right block of chroma CTU 608, the QP value is 34+0 because the QP value of the right block of QG 602D is 34 (e.g., quantization parameter predictor), and 0 is the offset.

[0238] like Figure 6 As shown, for CTU 608, there is only one QG 610. However, there may be multiple different QP values ​​within QG 610. Determining QP values ​​in this manner may have drawbacks. For example, better visual quality may be achieved if the QP values ​​of chroma blocks (e.g., chroma blocks with non-zero coefficients) are the same across the QG, and Figure 6In the example shown, the result of different QP values ​​in QG 610 may result in suboptimal visual quality. One way to solve this problem is to define smaller QGs (e.g., instead of having QG 610, QG 610 is divided into many smaller QGs). However, in this case, additional signaling is required for each QG, which has a negative impact on bandwidth.

[0239] This disclosure describes example techniques for improving chroma QP derivation for hybrid transform-based video codecs, including signaling. The example techniques can be used independently or in combination with other techniques.

[0240] In some examples, the video encoder 200 and the video decoder 300 may specify a chroma quantization group based on one or more syntax elements. The one or more syntax elements may include a depth or related syntax element from the CTU block size. For example, when the number of samples in the CTB is N and the QP depth factor k is specified, a quantization group of size N>>k is specified. In this way, the video encoder 200 and the video decoder 300 can determine the chroma blocks in the chroma quantization group (QG) of the video data. However, there may be other methods for determining the chroma blocks in the chroma quantization group (QG) of the video data.

[0241] The video encoder 200 and the video decoder 300 may be configured to determine a quantization parameter predictor that is the same for each chroma block of the chroma QG. As an example, the video encoder 200 and the video decoder 300 may determine a chroma sample from one of the chroma blocks and determine a luma block corresponding to the chroma block based on the determined chroma sample. For example, the video encoder 200 and the video decoder 300 may identify a chroma sample value for identifying a collocated luma sample. For example, the video encoder 200 and the video decoder 300 may identify a chroma block chromaQpPredictorBlock that may be used to derive an initial QP value (e.g., a quantization parameter predictor) for the chroma QG. A block having certain properties in the chroma QG is selected as a chromaQpPredictorBlock.

[0242] In some examples, the first chroma CB (codec block) in the chroma QG is selected as the chromaQpPredictorBlock. In this case, one or more parameters (e.g., width, height) of the first chroma codec block can be specified and stored for use by other blocks in the QG. In some examples, the first chroma CB with non-zero coefficients in the chroma QG is selected as the chromaQpPredictorBlock. In some examples, the chroma QG itself can be selected as the chromaQpPredictorBlock.

[0243] The video encoder 200 and the video decoder 300 may specify a sample value in the chromaQpPredictorBlock that is used to identify a collocated (e.g., corresponding) luma sample. In some examples, the video encoder 200 and the video decoder 300 may use the center sample of the chroma codec block to identify the collocated luma sample. For example, if (x0, y0) represents the top left sample of the current codec block, and W and H represent the width and height of the codec block, the center sample of the chroma codec block may be selected as (x0+W / 2, y0+H / 2). In some examples, the video encoder 200 and the video decoder 300 may use the top left sample of the chroma codec block to identify the collocated (e.g., corresponding) luma sample. For example, if (x0, y0) represents the top left sample of the current codec block, and W and H represent the width and height of the codec block, the sample of the chroma codec block may be selected as (x0, y0).

[0244] In general, any sample in the chromaQpPredictorBlock may be used to identify the collocated luma sample. The location of the sample may also vary based on one or more syntax elements in the bitstream. For example, for a single tree, the center sample may be selected as the designated chroma sample, and for a dual tree, the top left luma sample may be selected. In some examples, the location may be selected based on whether one or more collocated luma samples of the chromaQpPredictorBlock have an associated deltaQP value.

[0245] The video encoder 200 and the video decoder 300 may determine a QP value QP for the collocated luma samples. L .QP L The value may be used to derive the chroma QP. That is, the video encoder 200 and the video decoder 300 may derive the chroma QP based on the corresponding luma block (eg, including a chroma block having a quantization parameter QP L quantization parameter (e.g., QP L ) to determine the quantization parameter predictor. For example, QP L The QP value selected for blocks containing collocated luma samples is Y As QP L In some examples, QP L Can be selected as QP with added offset Y The offset may be determined based on one or more factors, including but not limited to other syntax elements, content type (SDR / HDR / etc.), chroma format IDC (intra-frame displacement compensation), chroma sampling position, etc. In other words, in some examples, QP Y(e.g., the quantization parameter of the corresponding chroma block to the luma block in the chroma QG) can be used as a quantization parameter predictor (QP L ). In some examples, QP Y plus some offset can be used to determine the quantization parameter predictor (QP L ). Used to determine QP L The offset should not be the same as the signaled QP added to it L To generate an offset confusion of the QP value of the chroma QG. That is, in some examples, there may be a Y To generate QP L The first offset, and added to the QP L To determine a second offset for the QP value of chroma QG.

[0246] The video encoder 200 and the video decoder 300 can be obtained from the QP L An initial QP value (eg, quantization parameter predictor) for chroma QG is derived. In some examples, the initial QP value for chroma QG is set equal to QP L In some examples, video encoder 200 and video decoder 300 may apply a mapping function from QP L Determine the initial QP value for chroma QG. One or more parameters of the mapping function may be signaled or predetermined in the bitstream. For example, HEVC has a specified chroma QP mapping table, and in VVC draft 6, the chroma QP mapping table is signaled in the bitstream.

[0247] For one or more codec blocks in the chroma QG, video encoder 200 and video decoder 300 may identify an initial QP value (eg, a quantization parameter predictor). In some examples, the initial QP value of the chroma CB in the chroma QG is set equal to the initial QP value of the chroma QG.

[0248] The video encoder 200 and the video decoder 300 may use the initial QP value of the chroma codec block to derive the QP value to be used for the codec block. For two or more chroma CBs, the video encoder 200 and the video decoder 300 may use the initial QP value and the chroma QP offset to derive the chroma QP value to be used for the block. In other words, the video encoder 200 and the video decoder 300 may determine the same quantization parameter predictor for each chroma block of the chroma QG. The video encoder 200 may determine the quantization parameter values ​​for two or more chroma blocks in the chroma QG, and determine the same offset value for the two or more chroma blocks of the chroma QG based on the quantization parameter values ​​and the quantization parameter predictor. The video decoder 300 may determine the same offset value for the two or more chroma blocks of the chroma QG, and may determine the quantization parameter values ​​for the two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value.

[0249] The video encoder 200 and the video decoder 300 may encode or decode one or more samples in a block using a QP derived by one or more example techniques described in this disclosure. For example, the video encoder 200 and the video decoder 300 may encode or decode a current block of video data using a QP value determined using one or more (including a combination) of the techniques described in this disclosure.

[0250] As an example, the video decoder 300 may inverse quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter value, generate one or more residual blocks based on the inverse quantization coefficients, and reconstruct the chroma block based on the one or more residual blocks. The video encoder 200 may quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter value and signal information indicating the quantization coefficient and the offset value.

[0251] In some cases, the video encoder 200 and the video decoder 300 may derive a chroma QG for each chroma component separately. For example, the video encoder 200 and the video decoder 300 may derive a first QG for a first chroma component of a sample, and derive a second QG for a second chroma component of the same sample.

[0252] In some examples, the example techniques described in the present disclosure may be applied to a single tree codec mode and / or a dual tree codec mode. For example, the video encoder 200 and the video decoder 300 may be configured to dual-tree partition a luma codec tree unit (CTU) (e.g., luma CTU 600) and a chroma CTU (e.g., chroma CTU 604 or chroma CTU 608), generating a luma block of the luma CTU 600 and a chroma block of a CTU with a different partition (e.g., chroma CTU 604 or chroma CTU 608). The chroma blocks in the chroma QG 610 may include the chroma blocks of the CTU 608, and the chroma QG 610 includes all chroma blocks of the CTU 608.

[0253] Some example ways of determining a quantization parameter predictor such as based on the quantization parameter of the corresponding luma block are described above. However, the example techniques are not limited thereto. There may be other ways of determining a quantization parameter predictor.

[0254] In some examples, the initial QP (e.g., quantization parameter predictor) of the chroma QG can be predicted by the QP from the neighboring coded chroma QG. For example, to determine the quantization parameter predictor, the video encoder 200 and the video decoder 300 can determine the quantization parameter predictor based on the quantization parameter values ​​of the neighboring chroma QGs.

[0255] In one example, the video encoder 200 and the video decoder 300 may predict an initial QP (e.g., a quantization parameter predictor) by averaging the QP of the left adjacent chroma QG and the QP of the upper adjacent chroma QG. If the left or upper chroma QG is not available, the video encoder 200 and the video decoder 300 may replace the corresponding QP with a QP derived from the corresponding luma region. In some examples, the video encoder 200 and the video decoder 300 may also use the QP of the last chroma codec block in the previous chroma QG when deriving the QP of the current QG. Deriving the QP from the luma region may be one or a combination of the techniques described in the present disclosure. In some examples, the initial QP of the chroma QG may be updated by the chroma offset value signaled for the chroma QG.

[0256] In some examples, the video encoder 200 and the video decoder 300 may derive (e.g., determine) an initial QP (e.g., a quantization parameter predictor) for the chroma QG using one or more of the following QP values: the QP of the left QG, the QP of the top QG, the QP of the luma sample concatenated with one of the chroma samples in the chroma QG, and the QP of the last coded chroma block in the previous chroma QG. For example, the initial QP may be derived by a weighted average of the following three values: initial QP = (QP-left + QP-above + 2*f(QP-luma) + 2) >> 2, where f() may represent a chroma mapping table, or (QP-left + QP-above + *f(QP-luma) + QP-prev + 2) >> 2.

[0257] Under certain conditions (e.g., the first chroma QG in a CTU row in a brick), the video encoder 200 and video decoder 300 may derive the chroma QP only from the luma QP. In some cases, the video encoder 200 and video decoder 300 may derive from neighboring QGs and the luma QG. In general, the QP derivation of the chroma QG may depend on the location of the chroma QG, e.g., in a picture or brick or CTU row, etc.

[0258] As described above, the video encoder 200 and the video decoder 300 may determine the same offset value for two or more chroma blocks of the chroma QG. For example, in order to determine the same offset value for two or more chroma blocks of the chroma QG, the video encoder 200 and the video decoder 300 may determine the same offset value for all chroma blocks of the chroma QG. However, the techniques described in the present disclosure are not limited to this. In some examples, instead of the offset value being the same for all chroma blocks of the chroma QG, the offset values ​​for the chroma blocks of the chroma QG that meet certain criteria may be the same. For example, the video encoder 200 and the video decoder may determine the same offset value for two or more chroma blocks having a size greater than a threshold size, or determine at least one non-zero coefficient for the corresponding residual block. Examples of such criteria are described below.

[0259] In some examples, for the first block with non-zero coefficients, the QP offset of the chroma block can be signaled. One or more blocks in the QG with zero coefficients can adopt the initial QP of the chroma QG. In some examples, one or more blocks in the QG with zero coefficients and before the first block with non-zero coefficients can adopt the initial QP of the chroma QG.

[0260] The chroma QP offset may be signaled in the chroma QG of one or more blocks based on block characteristics (e.g., width, height, aspect ratio, number of samples, etc.). The determination to signal in the chroma QG of one or more blocks based on block characteristics may not be based on the presence of non-zero coefficients (e.g., excluding the presence of non-zero coefficients from the characteristics). For example, when the chroma block size is greater than 32×32, or when the width or height of the chroma block is greater than 32, the chroma QP offset may be signaled for the first block of the chroma QG. For other block sizes, the chroma QP offset may be signaled for the first block in the chroma QG with non-zero coefficients. In some examples, when the size of the chroma codec block is greater than 32 (width or height or both), the chroma offset may be signaled in the first block in the chroma codec block.

[0261] In some examples, when the sample size (width w, height h, or both) of the chroma coding block is greater than 32, the chroma offset may be applied only to blocks with non-zero coefficients and may not be applied to other blocks in the codec block that are located before the first block with non-zero coefficients. In some examples, when the size (w, h, or both) of the chroma coding block is greater than 32, the chroma offset may be signaled for all blocks with non-zero coefficients and may not be applied to blocks in the codec block that are located before the first block with non-zero coefficients. In some examples, when the size (w, h, or both) of the chroma coding block is greater than 32, the chroma offset may be signaled for all blocks with non-zero coefficients and may not be applied to blocks in the codec block that are located before the first block with non-zero coefficients.

[0262] In some examples, the chroma QP offset may be applied to the first block in the codec block having non-zero coefficients, and the chroma QP offset may also be applied to subsequent blocks in the codec block. In some examples, one or more example techniques described in the present disclosure may be applied only to blocks within a quantization group. In some examples, one or more example techniques described in the present disclosure may be applied to all codec blocks in a quantization group. In one example, the block size may be selected as a value N, where N is signaled in the bitstream (or derived from the bitstream), or may be determined based on other block characteristics such as virtual pipe data unit (VPDU) constraints, maximum TB size, etc.

[0263] In some examples, the size of the chroma QG may be limited to be less than or equal to the size of the corresponding luma QG. For example, the size of the chroma QG is limited to be no greater than the size of the luma QG. In some examples, only one offset may be signaled for both luma and chroma QG. In some examples, the size of the chroma QG is derived from the size of the luma QG with an offset or within a threshold. For example, if the luma QG size is indicated by a depth variable of 4, the chroma QG may be limited to two values ​​from the luma QG variable size (e.g., within the range [2, 6]). In this example, the chroma QG may be larger than the luma QG size but not greater than a threshold amount, and in some cases not less than a threshold amount. The signaling of the chroma QG size variable may be modified to perform incremental encoding and decoding based on the luma QG size variable.

[0264] One or more of the restrictions or properties described above may only apply to certain codec tree types (e.g., single-tree configurations). One or more of the restrictions described above may apply only when certain tools are enabled (e.g., when chroma-related tools such as CCLM, joint Cb-Cr codec, etc. are enabled).

[0265] In some examples, the size of the luma and chroma QGs may be signaled separately. For some tree types (e.g., a single tree), the same QG size is used for luma and chroma. For example, for a single tree, the luma QG size is taken and applied to luma and chroma.

[0266] One or more example techniques disclosed in this disclosure may be further constrained by one or more characteristics of the samples to which the chroma map is applied. Examples of characteristics include block shape, aspect ratio, prediction mode used, characteristics of neighboring blocks, and / or the location of the sample relative to the picture (close to or far from a boundary, including picture boundaries, slice boundaries, strip boundaries, brick boundaries, etc.).

[0267] Some of the example techniques described above may be applied to video encoder 200 or video decoder 300 or both. Although various example techniques are described with respect to chroma components, the example techniques may also be applicable to luma components and components in other color spaces that may be used to represent video.

[0268] Although one or more example techniques described in this disclosure may be described with respect to a particular type of block, the example techniques may be applied to different types of blocks, such as codec blocks, prediction blocks, transform blocks, or other types of blocks that specify certain spatial partitions of a picture.

[0269] Examples of how one or more example techniques may be implemented are described below. The following examples should not be considered limiting, but are merely some example ways to implement the example techniques.

[0270] In a first example, the QP of the chroma QG is derived from the collocated luma block of the top left sample of the first chroma codec block in the QG.

[0271] For this example, the syntax table changes as follows, <add> …< / add> Add the text between:

[0272]

[0273]

[0274]

[0275] In some examples, CuQpOffset Cb 、CuQpOffset Cr and CuQpOffset CbCr The value of is set to zero in the above two syntax tables where CuChromaQgTopLeftX / Y are initialized.

[0276] The following <add> ...< / add> Used to show additions relative to VVC draft 6, while <delete> ...< / delete> The text in is used to show deletions relative to VVC draft 6.

[0277] The inputs to this process are:

[0278] – Luma position (xCb, yCb) specifies the top left luma sample of the current codec block relative to the top left luma sample of the current picture,

[0279] – The variable cbWidth specifies the width of the current coded deblock in luminance samples,

[0280] – The variable cbHeight specifies the height of the current codec block in luma samples,

[0281] – The variable treeType specifies whether a single tree (SINGLE_TREE) or a dual tree is used to split the CTU, and when using a dual tree, whether the luma (DUAL_TREE_LUMA) or chroma component (DUAL_TREE_CHROMA) is currently being processed.

[0282] In this process, the brightness quantization parameter Qp′ is derived Y and the chromaticity quantization parameter Qp′ Cb and Qp′ Cr .

[0283] The luma position (xQg, yQg) specifies the current position relative to the top left luma sample of the current picture. <add> brightness< / add> The top left luma sample of the quantized group. The horizontal and vertical positions xQg and yQg are set equal to CuQgTopLeftX and CuQgTopLeftY respectively.

[0284] Note: The current quantization group is sharing the same qP Y_PRED The rectangular area within the codec tree block of . Its width and height are equal to the width and height of the codec tree node, and the top left luma sample position of the node is assigned to the variables CuQgTopLeftX and CuQgTopLeftY.

[0285] <add> Chroma position (xChromaQg, yChromaQg) specifies the top left luma sample of the current chroma quantization group relative to the top left luma sample of the current picture. The horizontal and vertical positions xChromaQg and yChromaQg are set equal to CuChromaQgTopLeftX and CuChromaQgTopLeftY, respectively.< / add>

[0286] When treeType is equal to SINGLE_TREE or DUAL_TREE_LUMA, the predicted luma quantization parameter qP Y_PRED Export in the following sequential steps:

[0287] 1. Variable qP Y_PREV The derivation is as follows:

[0288] —If one or more of the following conditions are true, qPY_PREV is set equal to SliceQp Y :

[0289] - The current quantization group is the first quantization group in the slice.

[0290] —The current quantization group is the first quantization group in the brick.

[0291] - The current quantization group is the first quantization group in the CTB row of the block, and entropy_coding_sync_enabled_flag is equal to 1.

[0292] Otherwise, qP Y_PREV Set equal to the luma quantization parameter Qp of the last luma codec unit in the previous quantization group in decoding orderY .

[0293] 2. The derivation process for the neighboring block availability specified in Section 6.4.4 is called with as input the position (xCurr, yCurr) set equal to (xCb, yCb), the neighboring position (xNbY, yNbY) set equal to (xQg-1, yQg), checkPredModeY set equal to FALSE, and cIdx set equal to 0, and the output is assigned to availableA. The variable qP Y_A The derivation is as follows:

[0294] —If one or more of the following conditions are true, qP Y_A Set equal to qP Y_PREV :

[0295] —availableA is equal to FALSE.

[0296] - the CTB containing the luma codec block covering luma position (xQg-1, yQg) is not equal to the CTB containing the current luma codec block at (xCb, yCb), i.e., all of the following conditions are true:

[0297] — (xQg-1)>>CtbLog2SizeY is not equal to (xCb)>>CtbLog2SizeY

[0298] — (yQg)>>CtbLog2SizeY is not equal to (yCb)>>CtbLog2SizeY

[0299] —Otherwise, qP Y_A is set equal to the luma quantization parameter Qp of the codec unit containing the luma codec block covering (xQg-1, yQg) Y .

[0300] 3. The derivation process for the neighboring block availability specified in Section 6.4.4 is called with as input the position (xCurr, yCurr) set equal to (xCb, yCb), the neighboring position (xNbY, yNbY) set equal to (xQg, yQg-1), checkPredModeY set equal to FALSE, and cIdx set equal to 0, and the output is assigned to availableB. The variable qP Y_B The derivation is as follows:

[0301] —If one or more of the following conditions are true, qP Y_B Set equal to qP Y_PREV :

[0302] —availableB is equal to FALSE.

[0303] — the CTB containing the luma codec block covering luma position (xQg, yQg-1) is not equal to the CTB containing the current luma codec block at (xCb, yCb), i.e., all of the following conditions are true:

[0304] —(xQg)>>CtbLog2SizeY is not equal to (xCb)>>CtbLog2SizeY

[0305] —(yQg-1)>>CtbLog2SizeY is not equal to (yCb)>>CtbLog2SizeY

[0306] —Otherwise, qP Y_B is set equal to the luma quantization parameter Qp of the codec unit containing the luma codec block covering (xQg, yQg-1) Y .

[0307] 4. Predicted brightness quantization parameter qP Y_PRED The derivation is as follows:

[0308] – If all of the following conditions are true, then qP Y_PRED Set equal to the luma quantization parameter Qp of the codec unit containing the luma codec block covering (xQg, yQg-1) Y :

[0309] – availableB is equal to TRUE.

[0310] – The current quantization group is the first quantization group in the CTB row within the brick, and entropy_coding_sync_enabled_flag is equal to 0

[0311] – Otherwise, qP Y_PRED The derivation is as follows:

[0312] Q Y_PRED =(qP Y_A +qP Y_B +1)>>1 (8-932)

[0313] Variable Qp Y The derivation is as follows:

[0314] Q Y =((qP Y_PRED +CuQpDeltaVal+64+2*QpBdOffset Y )%(64+QpBdOffset Y ))-QpBdOffset Y (8-933)

[0315] Luma quantization parameter Qp′ Y The derivation is as follows:

[0316] Qp′Y=Qp Y +QpBdOffset Y (8-934)

[0317] When ChromaArrayType is not equal to 0 and treeType is equal to SINGLE_TREE or DUAL_TREE_CHROMA, the following applies:

[0318] <delete>—When treeType is equal to DUAL_TREE_CHROMA, the variable Qp Y Set equal to the luma quantization parameter Qp of the luma codec unit covering the luma position (xCb+cbWidth / 2, yCb+cbHeight / 2) Y .< / delete>

[0319] <add>—qPYForChroma is set equal to the luma quantization parameter Qp of the luma codec covering the luma position (xChromaQg, yChromaQg) Y .< / add>

[0320] —Variable qP Cb ,qP Cr and qP CbCr The derivation is as follows:

[0321] Q Chroma =Clip3(-QpBdOffset C , 63, <add> qPYForChroma< / add> <delete>Qp Y < / delete> ) (8-935)

[0322] Q Cb =ChromaQpTable[0][qPi Chroma ] (8-936)

[0323] Q Cr =ChromaQpTable[1][qPi Chroma ] (8-937)

[0324] Q CbCr =ChromaQpTable[2][qPi Chroma ] (8-938)

[0325] —Cb and Cr components, QP′ Cb and QP′ Cr And joint Cb-Cr codec QP′ CbCr The derivation of the chromaticity quantization parameters is as follows:

[0326] QP′ Cb =Clip3(-QpBdOffset C , 63, qP Cb +pps_cb_qp_offset+slice_cb_qp_offset+CuQpOffset Cb)+QpBdOffset C (8-939)

[0327] QP′ Cr =Clip3(-QpBdOffset C , 63, qP Cr +pps_cr_qp_offset+slice_cr_qp_offset+CuQpOffset Cr )+QpBdOffset C (8-940)

[0328] Qp′ CbCr =Clip3(-QpBdOffset C , 63, qP CbCr +pps_cbcr_qp_offset+slice_cbcr_qp_offset+CuQpOffset CbCr )+QpBdOffset C (8-941)

[0329] In some examples, chroma QP derivation is only applied to the case of dual-tree coding. The changes associated with this case are as follows:

[0330] When ChromaArrayType is not equal to 0 and treeType is equal to SINGLE_TREE or DUAL_TREE_CHROMA, the following applies:

[0331] —When treeType is equal to DUAL_TREE_CHROMA, the variable Qp Y is set equal to the override brightness position ( <delete> xCb+cbWidth / 2,yCb+cbHeight / 2< / delete> <add> xChromaQg,yChromaQg< / add> ) of the luminance codec unit Y .

[0332] —Variable qP Cb ,qP Cr and qP CbCr The derivation is as follows:

[0333] Q Chroma =Clip3(-QpBdOffset C , 63, Qp Y ) (8-935)

[0334] Figure 7 2 is a flowchart illustrating an example method for encoding a current block. The current block may include a current CU. Although with respect to the video encoder 200 ( Figure 1 and Figure 3 ), but it should be understood that other devices may be configured to perform the same Figure 7 A similar approach to the one used in this paper.

[0335] In this example, the video encoder 200 initially predicts the 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, uncoded block and the prediction block of the current block. The video encoder 200 may then transform and quantize the coefficients of the residual block (354). In one or more examples, the video encoder 200 may be configured to quantize the coefficients using the example techniques described in the present disclosure to determine a quantization parameter (QP) value. 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 coefficients (358). For example, the video encoder 200 may encode the coefficients using CAVLC or CABAC. The video encoder 200 may then output entropy encoded data for the block (360).

[0336] Figure 8 is a flowchart illustrating an example method for decoding a current video data block. The current block may include a current CU. Although with respect to the video decoder 300 ( Figure 1 and Figure 4 ), but it should be understood that other devices may be configured to perform the same Figure 8 A similar approach to the one used in this paper.

[0337] The video decoder 300 may receive entropy-encoded data of a current block, such as entropy-encoded prediction information and entropy-encoded data corresponding to coefficients of a residual block of the current block (370). The video decoder 300 may entropy decode the entropy-encoded data to determine prediction information of the current block and reproduce coefficients of the residual block (372). The video decoder 300 may predict the current block, for example, using an intra-frame or inter-frame prediction mode indicated by the prediction information of the current block to calculate a prediction block of the current block (374). The video decoder 300 may then reverse scan the reproduced coefficients to create a quantized transform coefficient block (376). The video decoder 300 may then inverse quantize and inverse transform the coefficients to generate a residual block (378). In one or more examples, the video decoder 300 may be configured to quantize the coefficients using example techniques described in the present disclosure to determine a quantization parameter (QP) value. The video decoder 300 may ultimately decode the current block by combining the prediction block and the residual block (380).

[0338] Fig. 9is a flowchart illustrating an example method of encoding video data. Fig. 9 Example technology.

[0339] The processing circuitry of the video encoder 200 may determine chroma blocks in a chroma quantization group (QG) of the video data (900). For example, the processing circuitry may determine the chroma blocks in the chroma QG based on the size of the chroma CTU, the size of the luma QG, etc. As an example, the size of the chroma QG is limited to be less than or equal to the size of the corresponding luma QG. In some examples, the processing circuitry may dual-tree partition a luma coding tree unit (CTU) (e.g., luma CTU 600) and a chroma CTU (e.g., chroma CTU 608), generating luma blocks of the luma CTU 600 and chroma blocks of the CTU 608 with different partitioning. As an example, the chroma blocks in the chroma QG 610 include the chroma blocks of the CTU 608, and the chroma QG 610 includes all chroma blocks of the CTU 608.

[0340] The processing circuitry of the video encoder 200 may determine the same quantization parameter predictor for each chroma block of chroma QG (902). As an example, as described above, Figure 6 The three chroma blocks in QG 610 of chroma CTU 608 have quantization parameter predictors 31, 31, and 34, respectively. In one or more examples, instead of the chroma blocks in QG 610 of chroma CTU 608 having different quantization parameter predictors, the chroma blocks in QG 610 can each have the same quantization parameter predictor.

[0341] There may be various ways to determine the quantization parameter predictor. As one example, the processing circuitry of the video encoder 200 may determine chroma samples from one of the chroma blocks, determine a luma block corresponding to the chroma block based on the determined chroma samples, and determine the quantization parameter predictor based on the quantization parameter of the corresponding luma block. As another example, the processing circuitry of the video encoder 200 may determine the quantization parameter predictor based on the quantization parameter values ​​of the neighboring chroma QGs.

[0342] Processing circuitry of video encoder 200 may determine quantization parameter values ​​for one or more chroma blocks in the chroma QG (904). For example, the processing circuitry may determine the quantization parameter value based on rate-distortion checking and deblocking filtering needs. In some examples, the processing circuitry may determine the quantization parameter value for only one chroma block in the chroma QG and assign the determined quantization parameter value to one or more blocks in the chroma QG.

[0343] The processing circuitry may determine, based on the quantization parameter value and the quantization parameter predictor, an offset value that is the same for two or more chroma blocks of the chroma QG (906). In some examples, the processing circuitry may determine the offset value that is the same for all chroma blocks of the chroma QG. In some examples, the processing circuitry may determine the offset value that is the same for two or more chroma blocks having a size greater than a threshold size, or determine at least one non-zero coefficient for corresponding residual blocks.

[0344] The processing circuitry may quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter value (908). The processing circuitry may signal information representing the quantized coefficients and offset values ​​(910).

[0345] Fig.10 is a flowchart illustrating an example method of decoding video data. Fig.10 Example technology.

[0346] The processing circuitry of the video decoder 300 may determine chroma blocks in a chroma quantization group (QG) of the video data (1000). For example, the processing circuitry may determine the chroma blocks in the chroma QG based on the size of the chroma CTU, the size of the luma QG, etc. As an example, the size of the chroma QG is limited to be less than or equal to the size of the corresponding luma QG. In some examples, the processing circuitry may dual-tree partition a luma coding tree unit (CTU) (e.g., luma CTU 600) and a chroma CTU (e.g., chroma CTU 608), generating luma blocks of the luma CTU 600 and chroma blocks of the CTU 608 with different partitioning. As an example, the chroma blocks in the chroma QG 610 include the chroma blocks of the CTU 608, and the chroma QG 610 includes all chroma blocks of the CTU 608.

[0347] The processing circuitry of the video decoder 300 may determine the same quantization parameter predictor for each chroma block of chroma QG (1002). As an example, as described above, Figure 6 The three chroma blocks in QG 610 of chroma CTU 608 have quantization parameter predictors 31, 31, and 34, respectively. In one or more examples, instead of the chroma blocks in QG 610 of chroma CTU 608 having different quantization parameter predictors, the chroma blocks in QG 610 can each have the same quantization parameter predictor.

[0348] There may be various ways to determine the quantization parameter predictor. As one example, the processing circuitry of the video decoder 300 may determine chroma samples from one of the chroma blocks, determine a luma block corresponding to the chroma block based on the determined chroma samples, and determine the quantization parameter predictor based on the quantization parameter of the corresponding luma block. As another example, the processing circuitry of the video decoder 300 may determine the quantization parameter predictor based on the quantization parameter values ​​of the neighboring chroma QGs.

[0349] Processing circuitry of video decoder 300 may determine an offset value that is the same for two or more chroma blocks of chroma QG (1004). In some examples, the processing circuitry may determine an offset value that is the same for all chroma blocks of chroma QG. In some examples, the processing circuitry may determine an offset value that is the same for two or more chroma blocks having a size greater than a threshold size, or determine at least one non-zero coefficient for a corresponding residual block.

[0350] The processing circuitry of the video decoder 300 may determine quantization parameter values ​​for each of the two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value (1006). The quantization parameter value may be the sum of the quantization parameter predictor and the offset value. However, there may be other ways to determine the quantization parameter value based on the quantization parameter predictor and the offset value (e.g., such as mapping).

[0351] The processing circuitry of the video decoder 300 may inverse quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter value (1008). For example, the inverse quantization unit 306 may inverse quantize coefficients of one or more residual blocks of the chroma block based on the determined quantization parameter value. The processing circuitry of the video decoder 300 may generate one or more residual blocks based on the inverse quantization coefficients (1010). For example, the inverse transform processing unit 308 may generate one or more residual blocks based on the inverse quantization coefficients. The processing circuitry of the video decoder 300 may reconstruct the chroma block based on the one or more residual blocks (1012). For example, the reconstruction unit 310 may add the one or more residual blocks to the one or more prediction blocks generated by the prediction processing unit 304 to reconstruct the chroma block.

[0352] Some example techniques that can be used together or in combination are described below.

[0353] Example 1. A method of encoding and decoding video data, the method comprising determining a chroma quantization group (QG) based on one or more syntax elements, and encoding and decoding a current block of the video data based on the determined chroma QG.

[0354] Example 2. The method of Example 1, wherein determining the chroma QG comprises inferring the chroma QG based on one or more syntax elements without receiving or signaling syntax elements that explicitly define the chroma QG.

[0355] Example 3. The method of any of Examples 1 and 2, wherein the one or more syntax elements from which the chroma QG is determined include one or more of a depth from a codec tree unit (CTU) block size.

[0356] Example 4. A method for encoding and decoding video data, the method comprising determining a chroma predictor block, determining an initial quantization parameter (QP) value of a chroma quantization group (QG) based on the chroma predictor block, and encoding and decoding a current block of video data based on the determined QP value of the chroma QG.

[0357] Example 5. A method for encoding and decoding video data, the method comprising determining a chroma predictor block, determining sample values ​​in the chroma predictor block, identifying collocated luminance samples based on the sample values ​​in the chroma predictor block, and encoding and decoding a current block of video data based on the identified collocated luminance samples.

[0358] Example 6. A method for encoding and decoding video data, the method comprising determining a quantization parameter (QP) of a luma sample, the QP of the luma sample being QP L , based on QP L A chroma QP is determined for chroma samples collocated with luma samples, and a current block of video data is encoded and decoded based on the determined chroma QP.

[0359] Example 7. A method for encoding and decoding video data, the method comprising determining a quantization parameter (QP) of a luma sample, the QP of the luma sample being QP L , based on QP L An initial QP value for a chroma quantization group (QG) is determined, and a current block of video data is encoded and decoded based on the determined initial QP for the chroma QG.

[0360] Example 8. A method for encoding and decoding video data, the method comprising determining an initial quantization parameter (QP) value of a chroma codec block; determining a QP value of a codec block including a chroma codec block and a luma codec block based on the initial QP value of the chroma codec block; and encoding and decoding the codec block based on the determined QP value.

[0361] Example 9. A method for encoding and decoding video data, the method comprising determining a first quantization group (QG) for a first chroma component of a sample, determining a second quantization group (QG) for a second chroma component of the same sample position, and encoding and decoding a current block of video data based on the first QG and the second QG.

[0362] Example 10. A method including any one or a combination of Examples 1-9.

[0363] Example 11. The method according to Example 10, wherein the method of Example 10 is applied to a single-tree coding mode or a dual-tree coding mode.

[0364] Example 12. A method for encoding and decoding video data, the method comprising determining a chroma quantization parameter (QP) offset for a chroma quantization group (QG) of one or more blocks based on block characteristics, wherein the block characteristics exclude the presence of non-zero coefficients; and encoding and decoding a current block of the video data based on the determined chroma QP offset.

[0365] Example 13. A method including any one or a combination of Examples 1-12.

[0366] Example 14. The method of Example 13, wherein encoding and decoding comprises decoding the current block.

[0367] Example 15. The method of Example 13, wherein encoding and decoding comprises encoding the current block.

[0368] Example 16. An apparatus for encoding and decoding video data, the apparatus comprising a memory configured to store the video data and a processing circuit configured to perform the method of any one or a combination of Examples 1-13.

[0369] Example 17. The apparatus of Example 16, wherein the processing circuit comprises a video decoder configured to decode the current block.

[0370] Example 18. The apparatus of Example 16, wherein the processing circuit comprises a video encoder configured to encode the current block.

[0371] Example 19. The apparatus of any of Examples 16-18, further comprising a display configured to display the decoded video data.

[0372] Example 20. The device of any of Examples 16-19, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0373] Example 21. A computer-readable storage medium having instructions stored thereon, which, when executed, cause one or more processors to perform the method of any of Examples 1-15.

[0374] Example 22. An apparatus for encoding and decoding video data, the apparatus comprising means for performing the method of any of Examples 1-15.

[0375] It should be appreciated that, depending on the examples, certain actions or events of any technique described herein may be performed in a different order, may be added, combined, or excluded entirely (e.g., not all described actions or events are necessary for the practice of the technique). In addition, in some examples, actions or events may be performed in parallel, such as through multithreading, interrupt handling, or multiple processors, rather than sequentially.

[0376] In one or more examples, the functions may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored or transmitted on a computer-readable medium as one or more instructions or codes and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media corresponding to tangible media (e.g., data storage media), or communication media including any media that facilitates the transfer of a computer program from one place to another (e.g., according to a communication protocol). In this manner, computer-readable media may generally correspond to (1) non-temporary tangible computer-readable storage media or (2) communication media such as signals or carrier waves. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and / or data structures for implementing the techniques described in the present disclosure. A computer program product may include a computer-readable medium.

[0377] By way of example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage devices, flash memory or any other medium that can be used to store the required program code in the form of instructions or data structures and can be accessed by a computer. In addition, any connection is appropriately referred to as a computer-readable medium. For example, if a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technology (such as infrared, radio and microwave) is used to send instructions from a website, server or other remote source, then the coaxial cable, fiber optic cable, twisted pair, DSL or wireless technology (such as infrared, radio and microwave) is included in the definition of the 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 point to non-temporary tangible storage media. The disks and optical disks used herein include compact disks (CDs), laser optical disks, optical disks, digital versatile disks (DVDs), floppy disks and blue-ray disks, wherein the disks usually reproduce data magnetically, while the optical disks reproduce data in a laser optical manner. The above combination should also be included in the scope of computer-readable media.

[0378] Instructions may be executed 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. Therefore, the terms "processor" and "processing circuitry" used herein may refer to any of the above structures or any other structure suitable for implementing the techniques described herein. In addition, in some aspects, the functions described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a combined codec. In addition, these techniques may be fully implemented in one or more circuits or logic elements.

[0379] The techniques of the present disclosure may be implemented in a variety of devices or apparatuses, including wireless handsets, integrated circuits (ICs) or IC collections, such as chip collections. 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 need to be implemented by different hardware units. Instead, as described above, the various units may be combined in a codec hardware unit, or provided by a collection of interoperable hardware units (including one or more processors as described above) together with appropriate software and / or firmware.

[0380] 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: Determining chroma blocks in a chroma quantization group QG of the video data, wherein the chroma QG corresponds to a plurality of luma QGs, and each luma QG includes one or more luma blocks; determining a same quantization parameter predictor for each of said chroma blocks of said chroma QG; determining an offset value that is the same for two or more of the chroma blocks of the chroma QG, wherein the offset value indicates an adjustment of a degree of quantization; Determining a quantization parameter value for each of the two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value, wherein the quantization parameter value is equal to a degree of quantization of coefficients of one or more transform coefficient blocks applied to the chroma block, wherein determining the quantization parameter value for each of the two or more chroma blocks comprises: Determining the quantization parameter value for only one chroma block among the two or more chroma blocks in the chroma QG; and assigning the determined quantization parameter values ​​to other chroma blocks of the two or more chroma blocks in the chroma QG, wherein at least two of the plurality of luminances QG have different quantization parameter values, and wherein the quantization parameter values ​​of all chroma blocks in the two or more chroma blocks in the chroma QG are the same; inverse quantizing the coefficients of the one or more transform coefficient blocks of the chrominance block based on the determined quantization parameter value; generating one or more residual blocks based on the inverse quantized coefficients; and The chrominance block is reconstructed based on the one or more residual blocks.

2. The method of claim 1 , wherein determining the quantization parameter predictor comprises: determining a chroma sample from one of the chroma blocks; Determine a luma block corresponding to the chroma block in one of the plurality of luma blocks QG based on the determined chroma sample points; as well as The quantization parameter predictor is determined based on a quantization parameter value of the corresponding luma block. 3 . The method of claim 1 , wherein determining the quantization parameter predictor comprises determining the quantization parameter predictor based on quantization parameter values ​​of neighboring chrominance (QG).

4. The method of claim 1 , wherein determining the offset value that is the same for two or more chroma blocks of the chroma QG comprises: The offset value that is the same for all the chroma blocks of the chroma QG is determined.

5. The method of claim 1 , wherein determining the offset value that is the same for the two or more chroma blocks comprises: Determine the offset value to be the same for the two or more chroma blocks having a size greater than a threshold size or for a corresponding residual block having at least one non-zero coefficient, or a block not preceding a first block having a non-zero coefficient in the QG.

6. The method according to claim 1, further comprising: The dual-tree partitioning comprises a luma codec tree unit CTU and a chroma CTU, generating a luma block of the luma CTU and a chroma block of the CTU with different partitions, wherein the chroma block in the chroma QG comprises the chroma block of the CTU, and the chroma QG comprises all the chroma blocks of the CTU, so that the chroma QG has the same size as the CTU.

7. The method according to claim 1, wherein: The size of the chrominance QG is limited to be smaller than or equal to the size of one luminance QG corresponding to the chrominance QG among the plurality of luminance QGs.

8. A method for encoding video data, the method comprising: Determining chroma blocks in a chroma quantization group QG of the video data, wherein the chroma QG corresponds to a plurality of luma QGs, and each luma QG includes one or more luma blocks; determining a same quantization parameter predictor for each of said chroma blocks of said chroma QG; Determining quantization parameter values ​​for two or more chroma blocks in the chroma QG, wherein the quantization parameter values ​​are equal to a degree of quantization of coefficients of one or more residual blocks applied to the chroma blocks, wherein determining the quantization parameter values ​​for the two or more chroma blocks comprises: Determining the quantization parameter value for only one chroma block among the two or more chroma blocks in the chroma QG; and assigning the determined quantization parameter values ​​to other chroma blocks of the two or more chroma blocks in the chroma QG, wherein at least two of the plurality of luminances QG have different quantization parameter values, and wherein the quantization parameter values ​​of all chroma blocks in the two or more chroma blocks in the chroma QG are the same; determining, based on the quantization parameter value and the quantization parameter predictor, an offset value that is the same for the two or more chroma blocks of the chroma QG, wherein the offset value indicates an adjustment of a degree of quantization; quantizing the coefficients of the one or more residual blocks of the chroma block based on the determined quantization parameter value; and Information indicating the quantized coefficients and the offset value is signaled.

9. The method of claim 8, wherein determining the quantization parameter predictor comprises: determining a chroma sample from one of the chroma blocks; as well as The quantization parameter predictor is determined based on a quantization parameter value of a luma block corresponding to the chroma block in one of the plurality of luma blocks QG. 10 . The method of claim 8 , wherein determining the quantization parameter predictor comprises determining the quantization parameter predictor based on quantization parameter values ​​of neighboring chrominance (QG).

11. The method of claim 8, wherein determining the offset value that is the same for two or more chroma blocks of the chroma QG comprises: The offset value that is the same for all the chroma blocks of the chroma QG is determined.

12. The method of claim 8, wherein determining the offset value that is the same for the two or more chroma blocks comprises: The offset value that is the same for the two or more chroma blocks having a size greater than a threshold size or having at least one non-zero coefficient for a corresponding residual block is determined.

13. The method according to claim 8, further comprising: The dual-tree partitioning comprises a luma codec tree unit CTU and a chroma CTU, generating a luma block of the luma CTU and a chroma block of the CTU with different partitions, wherein the chroma block in the chroma QG comprises the chroma block of the CTU, and the chroma QG comprises all chroma blocks of the CTU, so that the chroma QG has the same size as the CTU.

14. The method according to claim 8, wherein: The size of the chrominance QG is limited to be smaller than or equal to the size of one luminance QG corresponding to the chrominance QG among the plurality of luminance QGs.

15. A device for decoding video data, the device comprising: a memory configured to store video data; as well as a processing circuit coupled to the memory and configured to: Determining chroma blocks in a chroma quantization group QG of the video data, wherein the chroma QG corresponds to a plurality of luma QGs, and each luma QG includes one or more luma blocks; determining a same quantization parameter predictor for each of said chroma blocks of said chroma QG; determining two or more identical offset values ​​in the chroma blocks for the chroma QG, wherein the offset values ​​indicate an adjustment of a degree of quantization; determining a quantization parameter value for each of the two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value, wherein the quantization parameter value is equal to a degree of quantization of coefficients of one or more transform coefficient blocks applied to the chroma block, wherein to determine the quantization parameter value for each of the two or more chroma blocks, the processing circuit is configured to: determining the quantization parameter value for only one chroma block among the two or more chroma blocks in the chroma QG; as well as assigning the determined quantization parameter values ​​to other chroma blocks of the two or more chroma blocks in the chroma QG, wherein at least two of the plurality of luminances QG have different quantization parameter values, and wherein the quantization parameter values ​​of all chroma blocks in the two or more chroma blocks in the chroma QG are the same, inverse quantizing the coefficients of the one or more transform coefficient blocks of the chrominance block based on the determined quantization parameter value; generating one or more residual blocks based on the inverse quantized coefficients; as well as The chrominance block is reconstructed based on the one or more residual blocks.

16. The apparatus of claim 15, wherein to determine the quantization parameter predictor, the processing circuit is configured to: determining a chroma sample from one of the chroma blocks; Determine a luma block corresponding to the chroma block in one of the plurality of luma blocks QG based on the determined chroma samples; and The quantization parameter predictor is determined based on a quantization parameter value of the corresponding luma block. 17 . The apparatus of claim 15 , wherein to determine the quantization parameter predictor, the processing circuit is configured to determine the quantization parameter predictor based on quantization parameter values ​​of neighboring chrominance (QG).

18. The apparatus of claim 15, wherein to determine the offset value that is the same for two or more chroma blocks of a chroma QG, the processing circuit is configured to determine the offset value that is the same for all of the chroma blocks of the chroma QG.

19. An apparatus according to claim 15, wherein in order to determine the offset value that is the same for the two or more chroma blocks, the processing circuit is configured to determine the offset value that is the same for the two or more chroma blocks having a size greater than a threshold size or having at least one non-zero coefficient for the corresponding residual block, or a block that is not before the first block having a non-zero coefficient in the QG.

20. The apparatus of claim 15, wherein the processing circuit is configured to: The dual-tree partitioning comprises a luma codec tree unit CTU and a chroma CTU, generating a luma block of the luma CTU and a chroma block of the CTU with different partitions, wherein the chroma block in the chroma QG comprises the chroma block of the CTU, and the chroma QG comprises all chroma blocks of the CTU, so that the chroma QG has the same size as the CTU.

21. The apparatus of claim 15, wherein: The size of the chrominance QG is limited to be smaller than or equal to the size of one luminance QG corresponding to the chrominance QG among the plurality of luminance QGs.

22. The device of claim 15, further comprising a display configured to display the decoded video data.

23. The device of claim 15, wherein the device comprises one of a camera, a computer, a wireless communication device, a broadcast receiver device, or a set-top box.

24. A non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors of a device for decoding video data to: Determining chroma blocks in a chroma quantization group QG of the video data, wherein the chroma QG corresponds to a plurality of luma QGs, and each luma QG includes one or more luma blocks; determining a same quantization parameter predictor for each of said chroma blocks of said chroma QG; determining two or more identical offset values ​​in the chroma blocks for the chroma QG, wherein the offset values ​​indicate an adjustment of a degree of quantization; determining quantization parameter values ​​for the two or more chroma blocks in the chroma QG based on the quantization parameter predictor and the offset value, wherein the quantization parameter values ​​are equal to a degree of quantization of coefficients of one or more transform coefficient blocks applied to the chroma blocks, wherein the instructions causing the one or more processors to determine the quantization parameter values ​​for each of the two or more chroma blocks include instructions causing the one or more processors to: Determining the quantization parameter value for only one chroma block among the two or more chroma blocks in the chroma QG; and assigning the determined quantization parameter values ​​to other chroma blocks of the two or more chroma blocks in the chroma QG, wherein at least two of the plurality of luminances QG have different quantization parameter values, and wherein the quantization parameter values ​​of all chroma blocks in the two or more chroma blocks in the chroma QG are the same, inverse quantizing the coefficients of the one or more transform coefficient blocks of the chrominance block based on the determined quantization parameter value; generating one or more residual blocks based on the inverse quantized coefficients; as well as The chrominance block is reconstructed based on the one or more residual blocks.

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