Luma Mapping with Chroma Scaling (LMCS) in Video Coding

Abstract

A method for decoding video data includes: determining whether a chroma-related syntax element exists for luma map with chroma scaling (LMCS) video data for a coding unit (CU) of the video data, decoding a syntax element of the video data when a chroma-related syntax element exists for the LMCS for the CU, the syntax element indicating a value of a scaling parameter for determining chroma scaling in the LMCS, and decoding a chroma block of the CU based on the scaling parameter of the chroma scaling.

Description

[0001] This application claims priority to U.S. Application No. 17 / 218,898, filed on March 31, 2021, and U.S. Provisional Application No. 63 / 004,397, filed on April 2, 2020, each of which is incorporated herein by reference in its entirety. U.S. Application No. 17 / 218,898 claims the benefit of U.S. Provisional Application No. 63 / 004,397, filed on April 2, 2020. Technical Field

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

[0003] Digital video capabilities can be incorporated into a wide variety of devices, including digital televisions, digital direct 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 radio telephones, so-called "smart phones", video teleconferencing devices, video streaming devices, etc. Digital video devices implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4 (Part 10, Advanced Video Coding (AVC)), ITU-T H.265 / High Efficiency Video Coding (HEVC), and extensions of such standards. By implementing such video coding techniques, video devices can more efficiently send, receive, encode, decode, and / or store digital video information.

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

[0005] In general, this disclosure describes techniques for luma mapping with chroma scaling (LMCS). As described in more detail, this disclosure describes example techniques for minimizing the amount of information signaled by a video encoder and received by a video decoder to perform LMCS. This disclosure also describes examples of constraints that can be applied to minimize decoding errors at a video decoder. In this way, the example techniques improve the overall operation of video encoders and decoders and provide practical applications of video coding techniques.

[0006] In one example, the present disclosure describes a method for decoding video data, the method comprising: determining a luma map with chroma scaling (LMCS) for a decoding unit (CU) of the video data, a chroma-related syntax element of the video data being present, decoding the syntax element of the video data when the chroma-related syntax element is present for the LMCS for the CU, the syntax element indicating a value of a scaling parameter for determining chroma scaling in the LMCS, and decoding a chroma block of the CU based on the scaling parameter of the chroma scaling.

[0007] In one example, the present disclosure describes a device for decoding video data, the device including a memory and a processing circuit, the memory being configured to store the video data, the processing circuit being configured to determine a luma map with chroma scaling (LMCS) for a decoding unit (CU) for the video data, a chroma-related syntax element of the video data being present, decoding the syntax element of the video data when the chroma-related syntax element is present for the LMCS for the CU, the syntax element indicating a value of a scaling parameter for determining chroma scaling in the LMCS, and decoding a chroma block of the CU based on the scaling parameter of the chroma scaling.

[0008] In one example, the present disclosure describes a computer-readable storage medium having instructions stored thereon that, when executed, cause one or more processors to: determine a luma map with chroma scaling (LMCS) for a coding unit (CU) of video data, a chroma-related syntax element of the video data being present, decode the syntax element of the video data when the chroma-related syntax element is present for the LMCS for the CU, the syntax element indicating a value of a scaling parameter for determining chroma scaling in the LMCS, and decode the chroma blocks of the CU based on the scaling parameter of the chroma scaling.

[0009] In one example, the present disclosure describes an apparatus for decoding video data, the apparatus comprising: means for determining the presence of a chroma-related syntax element of the video data for a luma map with chroma scaling (LMCS) for a decoding unit (CU) of the video data, means for decoding the syntax element of the video data when the chroma-related syntax element is present for the LMCS for the CU, the syntax element indicating a value of a scaling parameter for determining chroma scaling in the LMCS, and means for decoding a chroma block of the CU based on the scaling parameter of the chroma scaling.

[0010] 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

[0011] Figure 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0012] Figure 2A and 2B is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure and a corresponding coding tree unit (CTU).

[0013] Figure 3 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0014] Figure 4 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0015] Figure 5 is a flowchart illustrating an example method for coding video data. DETAILED DESCRIPTION

[0016] In video coding techniques, a video encoder generates a prediction block for a current block (e.g., a coding unit (CU)). The prediction block can be based on samples in the same picture as the current block (e.g., for intra prediction or intra block copy (IBC) prediction), or can be based on samples in a different picture (e.g., for inter prediction). The video encoder determines a residual (e.g., a difference) between the current block and the prediction block and signals information indicating the residual (e.g., after transformation and quantization), which often requires fewer bits than signaling the values ​​of the samples of the current block.

[0017] The video decoder receives the information indicating the residual and generates a prediction block in the same manner as the video encoder. The video decoder then adds the residual to the prediction block to reconstruct the current block.

[0018] Luma mapping with chroma scaling (LMCS) is an example video coding tool that can be used with various prediction techniques. A current block (e.g., a coding unit (CU)) includes a luma block with luma samples and two chroma blocks (e.g., a Cb block and a Cr block) with chroma samples.

[0019] In LMCS, the video encoder maps luma samples of a luma block to generate mapped luma samples of a mapped luma block. The video encoder determines a residual (e.g., a difference) between the mapped luma block and a mapped luma prediction block (e.g., a luma prediction block mapped similarly to the luma block) to generate a mapped luma residual block. The video encoder performs transform and quantization on the mapped luma residual block and signals the resulting residual value.

[0020] For mapping luma samples, the video encoder can implement a mapping function. In the mapping function, there can be multiple separation points, and a separation point can be connected to another separation point by a segment. There can be 16 segments, and the slopes of the segments can be different. The video encoder can determine which segment the luma sample belongs to, and then map the luma sample to generate a mapped luma sample based on the slope of the segment to which the luma sample belongs.

[0021] For chroma, the video encoder determines the residual (e.g., difference) between samples of the chroma block and samples of the chroma prediction block. The video encoder then scales the result to generate a scaled chroma residual block. The video encoder performs transform and quantization on the scaled chroma residual block and signals the resulting residual value. In one or more examples, the video encoder may determine a scaling parameter (e.g., a coefficient indicating the amount of scaling the video encoder applies to the residual chroma block) based on the mapped luma reconstruction block. For convenience, the examples are described with respect to chroma blocks, which may be Cb chroma blocks or Cr chroma blocks, and the example techniques applied to one of the chroma blocks may also be applied to the other chroma block.

[0022] The video decoder may receive signaling notification of the residual block from the video encoder and may perform inverse quantization and inverse transform to generate a mapped luma residual block. The video decoder may also generate a mapped luma prediction block in the same manner as the video encoder generates the mapped luma prediction block. The video decoder may add the mapped luma prediction block to the mapped luma residual block to generate a mapped luma block. The video decoder may perform inverse mapping to reconstruct the luma block. For example, the video decoder may perform the inverse operation of the operation performed by the video encoder for mapping.

[0023] For chroma, the video decoder may receive signaling notification of the residual block from the video encoder and may perform inverse quantization and inverse transform to generate a scaled chroma residual block. The video decoder may determine a scaling parameter (e.g., a coefficient indicating the amount of scaling that the video decoder applies to the scaled chroma block) based on the mapped luma reconstruction block and the value signaled by the video encoder. The scaling parameter determined by the video decoder may be the inverse of the scaling parameter determined by the video encoder. The video decoder may perform inverse scaling on the scaled chroma residual block based on the scaling parameter to generate a chroma residual block. Similar to the video encoder, the video decoder may generate a chroma prediction block and add the chroma prediction block to the chroma residual block to reconstruct the chroma block.

[0024] The video decoder can repeat this operation for the two chroma blocks. In this way, using LMCS, the video decoder can reconstruct the luma block and the two chroma blocks. The luma block and the two chroma blocks can together form a CU.

[0025] LMCS techniques may present certain issues. As an example, certain video formats may not have chroma samples. For example, for a monochrome color format, there may be no chroma samples. However, in some LMCS techniques, the video encoder can still signal the values ​​used to determine scaling parameters even in the absence of chroma samples.

[0026] This disclosure describes example techniques for selectively signaling and parsing syntax elements for determining scaling parameters when chroma-related syntax elements (e.g., chroma samples) are present, while bypassing (e.g., avoiding) signaling and parsing syntax elements for determining scaling parameters when chroma-related syntax elements (e.g., chroma samples) are not present (e.g., such as in a monochrome color format). In other words, a bitstream may include chroma-related syntax elements (e.g., such as when chroma samples are present), and in such examples, the bitstream may also include syntax elements for determining scaling parameters. However, if the bitstream does not include chroma-related syntax elements (e.g., such as when chroma samples are not present), the bitstream may not include syntax elements for determining scaling parameters.

[0027] This disclosure also describes examples of constraints that can be applied when signaling syntax elements for LMCS. In some examples, certain constraints can also be included for other video coding tools, such as adaptive loop filtering (ALF). In this way, example techniques can improve bandwidth efficiency by selectively signaling and parsing syntax elements for LMCS based on the presence or absence of chroma-related syntax elements (e.g., chroma samples). Furthermore, example techniques can facilitate accurate reconstruction of blocks based on constraints that improve decoding operations.

[0028] Figure 1is a block diagram illustrating an example video encoding and decoding system 100 that can perform the techniques of this disclosure. The techniques of this disclosure generally relate to decoding (encoding and / or decoding) video data. Generally, video data includes any data used to process video. Thus, video data can include original unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata (such as signaling data).

[0029] like Figure 1 As shown, in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, source device 102 provides the video data to destination device 116 via a computer-readable medium 110. Source device 102 and destination device 116 may include any of a wide 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 destination device 116 may be equipped for wireless communication and, therefore, may be referred to as wireless communication devices.

[0030] exist Figure 1 In the example of , source device 102 includes a video source 104, a memory 106, a video encoder 200, and an output interface 108. Destination device 116 includes an input interface 122, a video decoder 300, a memory 120, and a display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply techniques for high-level syntax signaling notifications in video decoding. Therefore, source device 102 represents an example of a video encoding device, while destination device 116 represents an example of a video decoding device. In other examples, the source device and destination device may include other components or arrangements. For example, source device 102 may receive video data from an external video source (such as an external camera). Similarly, destination device 116 may be connected to an external display device interface rather than including an integrated display device.

[0031] like Figure 1The illustrated system 100 is merely an example. In general, any digital video encoding and / or decoding device can implement the techniques for high-level syntax signaling in video decoding. Source device 102 and destination device 116 are merely examples of such decoding devices, where source device 102 generates decoded video data for transmission to destination device 116. This disclosure refers to a "decoding" device as a device that performs decoding (encoding and / or decoding) of data. Thus, video encoder 200 and video decoder 300 represent examples of decoding devices, and more specifically, examples of a video encoder and a video decoder, respectively. In some examples, source device 102 and destination device 116 can operate in a substantially symmetrical manner, such that each of source device 102 and destination device 116 includes video encoding and decoding components. Thus, system 100 can support one-way or two-way video transmission between source device 102 and destination device 116, for example, for video streaming, video playback, video broadcasting, or video telephony.

[0032] Typically, video source 104 represents a source of video data (i.e., original, unencoded video data) and provides a continuous series of pictures (also referred to as "frames") of video data to video encoder 200, which encodes the picture data. Video source 104 of source device 102 may include a video capture device (such as a video camera), a video archive containing previously captured original video, and / or a video feed interface for receiving video from a video content provider. As a further 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 the pictures from the order in which they were received (sometimes referred to as "display order") into a decoded decoding order. Video encoder 200 may generate a bitstream comprising encoded video data. Source device 102 may then output the encoded video data onto computer-readable medium 110 via output interface 108 for receipt and / or retrieval by, for example, input interface 122 of destination device 116 .

[0033] Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memory. In some examples, memories 106 and 120 can store raw video data, e.g., raw video from video source 104 and raw, decoded video data from video decoder 300. Additionally or alternatively, memories 106 and 120 can store software instructions executable by, for example, video encoder 200 and video decoder 300, respectively. Although memory 106 and memory 120 are shown separately from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 can also include internal memory for functionally similar or equivalent purposes. Furthermore, memories 106 and 120 can store, for example, encoded video data output from video encoder 200 and input to video decoder 300. In some examples, portions of memories 106 and 120 can be allocated as one or more video buffers, e.g., for storing raw, decoded, and / or encoded video data.

[0034] The computer-readable medium 110 can represent any type of medium or device capable of transmitting encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to send the encoded video data directly to the destination device 116 in real time, for example, via a radio frequency network or a computer-based network. According to a communication standard (such as a wireless communication protocol), the output interface 108 can demodulate the transmission signal including the encoded video data, and the input interface 122 can demodulate the received transmission signal. The communication medium can include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium can form part of a packet-based network, such as a local area network, a wide area network, or a global network (such as the Internet). The communication medium can include routers, switches, base stations, or any other device that may be useful to facilitate communication from the source device 102 to the destination device 116.

[0035] In some examples, source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access the encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, 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.

[0036] 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. Destination device 116 may access the stored video data from file server 114 via streaming or downloading.

[0037] The file server 114 may be any type of server device capable of storing encoded video data and transmitting the encoded video data to the destination device 116. The file server 114 may represent a web server (e.g., for a website), a server configured to provide file transfer protocol services (e.g., File Transfer Protocol (FTP) or File Delivery over Unidirectional Transport (FLUTE)), a content delivery network (CDN) device, a hypertext transfer protocol (HTTP) server, a Multimedia Broadcast Multicast Service (MBMS) or 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 Live Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP Dynamic Streaming, etc.

[0038] The destination 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, 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.

[0039] Output interface 108 and input interface 122 may represent wireless transmitters / receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components operating 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 communicate data, such as encoded video data, according to a cellular communication standard such as 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 communicate data, such as encoded video data, according to other wireless standards such as the IEEE 802.11 specification, the IEEE 802.15 specification (e.g., ZigBee TM ),Bluetooth TM Standards, etc.) to transfer data, such as encoded video data. In some examples, source device 102 and / or destination device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include a SoC device for performing the functions attributed to video encoder 200 and / or output interface 108, and destination device 116 may include a SoC device for performing the functions attributed to video decoder 300 and / or input interface 122.

[0040] The techniques of the present disclosure may be applied to support video decoding for 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.

[0041] The input interface 122 of the destination device 116 receives an encoded video bitstream from the computer-readable medium 110 (e.g., a communication medium, a storage device 112, a file server 114, etc.). The encoded video bitstream may include signaling information defined by the video encoder 200 and also used by the video decoder 300, such as syntax elements with values ​​describing characteristics and / or processing of video blocks or other coded 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.

[0042] although Figure 1Although not shown, in some examples, the video encoder 200 and the video decoder 300 can each be integrated with an audio encoder and / or an audio decoder and can include appropriate MUX-DEMUX units or other hardware and / or software to process the multiplexed stream including both audio and video in a common data stream. If applicable, the MUX-DEMUX unit can comply with the ITU H.223 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

[0043] 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 the technology is partially implemented in software, the device can store instructions for the software in an appropriate non-transitory computer-readable medium and use one or more processors to execute the instructions in hardware to perform the technology 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 as part of a combined encoder / decoder (CODEC) in the corresponding device. The device including the video encoder 200 and / or the video decoder 300 can include an integrated circuit, a microprocessor, and / or a wireless communication device (such as a cellular phone).

[0044] The video encoder 200 and the video decoder 300 may operate according to a video coding standard such as ITU-T H.265, also known as High Efficiency Video Coding (HEVC), or an extension thereof such as a multi-view and / or scalable video coding extension. Alternatively, the video encoder 200 and the video decoder 300 may operate according to other proprietary or industry standards such as ITU-T H.266, also known as Versatile Video Coding (VVC). The latest draft of the VVC standard is described in “(Versatile Video Coding (Draft 8))” by Bross et al., at the 17th meeting of the Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG11: JVET-Q2001-vE, Brussels, Belgium, January 7-17, 2020 (hereinafter referred to as “VVC Draft 8”). However, the technology of the present disclosure is not limited to any particular coding standard.

[0045] Generally, the video encoder 200 and video decoder 300 can perform block-based decoding of pictures. 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 can include a two-dimensional matrix of samples of luma and / or chroma data. Generally, the video encoder 200 and video decoder 300 can decode video data represented in a YUV (e.g., Y, Cb, Cr) format. In other words, rather than decoding red, green, and blue (RGB) data for samples of a picture, the video encoder 200 and video decoder 300 can decode luma and chroma components, where the chroma components can include both red-hue and blue-hue chroma components. In some examples, the video encoder 200 converts the received RGB-formatted data to a YUV representation before encoding, and the video decoder 300 converts the YUV representation to an RGB format. Alternatively, pre-processing and post-processing units (not shown) can perform these conversions.

[0046] The present disclosure may generally relate to the decoding (e.g., encoding and decoding) of a picture, including the process of encoding or decoding the data of the picture. Similarly, the present disclosure may relate to the decoding of a block of a picture, including the process of encoding or decoding the data for the block, such as prediction and / or residual decoding. A coded video bitstream typically includes a series of values ​​for syntax elements that represent decoding decisions (e.g., decoding mode) and the partitioning of the picture into blocks. Therefore, references to decoding a picture or block should generally be understood as decoding the values ​​of the syntax elements that form the picture or block.

[0047] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (such as the video encoder 200) partitions a coding tree unit (CTU) into CUs according to a quadtree structure. In other words, the video decoder 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 the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video decoder may further partition the PUs and TUs. For example, in HEVC, the residual quadtree (RQT) represents the partitioning of the TUs. In HEVC, a PU represents inter-prediction data, and a TU represents residual data. An intra-predicted CU includes intra-prediction information, such as an intra-mode indication.

[0048] As another example, the video encoder 200 and the video decoder 300 can be configured to operate according to VVC. According to VVC, a video decoder (such as the video encoder 200) partitions a picture into multiple coding tree units (CTUs). The video encoder 200 can partition the CTU according to a tree structure (such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure). The QTBT structure eliminates the concept of multiple partitioning types, such as the distinction between 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 the coding units (CUs).

[0049] 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 that splits a block into three sub-blocks. In some examples, a ternary tree or ternary tree partitioning divides a block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0050] In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT structure or MTT structure to represent each of the luma component and the chroma component, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT structures 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 corresponding chroma components).

[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 according to HEVC. For the purpose of explanation, the description of the technology of the present disclosure is presented with respect to QTBT segmentation. However, it should be understood that the technology of the present disclosure can also be applied to video decoders configured to use quadtree segmentation or other types of segmentation.

[0052] In some examples, a CTU includes: a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples for a picture with three sample arrays, or a CTB of samples for a monochrome picture or a picture coded using three separate color planes and syntax structures for coding the samples. A CTB can be an NxN block of samples for some value N that results in a partitioning of a component into a CTB. A component is an array or a single sample from one of the three arrays (luma and two chroma) that make up a picture in 4:2:0, 4:2:2, or 4:4:4 color format, or an array or a single sample of an array that makes up a picture in monochrome format. In some examples, a coding block is an MxN block of samples for some values ​​M and N that result in a partitioning of a CTB into a coding block.

[0053] Blocks (e.g., CTUs or CUs) can be grouped in various ways within a picture. As an example, a brick can refer to a rectangular area of ​​a CTU row within a particular tile in a picture. A tile can be a rectangular area of ​​a CTU within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular area of ​​a CTU having a height equal to the height of the picture and a width specified by a syntax element (e.g., such as in a picture parameter set). A tile row refers to a rectangular area of ​​a CTU having a height specified by a syntax element (e.g., such as in a picture parameter set) and a width equal to the width of the picture.

[0054] In some examples, a tile may be partitioned into multiple blocks, where each block may include one or more CTU rows within the tile. A tile that is not partitioned into multiple blocks may also be referred to as a tile. However, a block that is a proper subset of a tile may not be referred to as a tile.

[0055] The tiles in a picture can also be arranged in slices. A slice can be an integer number of tiles of a picture that can be contained exclusively in a single Network Abstraction Layer (NAL) unit. In some examples, a slice includes a contiguous sequence of multiple complete tiles or just complete tiles of a tile.

[0056] This disclosure may use "NxN" and "N by N" interchangeably to refer to the sample dimensions of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, for example, 16x16 samples or 16 by 16 samples. Typically, a 16x16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Likewise, an NxN CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. Furthermore, a CU does not necessarily have the same number of samples in the horizontal direction as in the vertical direction. For example, a CU may include NxM samples, where M is not necessarily equal to N.

[0057] The video encoder 200 encodes the video data of the CU representing prediction and / or residual information and other information. The prediction information indicates how the CU will be predicted to form the prediction block of the CU. The residual information generally represents the sample-by-sample difference between the samples of the CU and the prediction block before encoding.

[0058] To predict a CU, the video encoder 200 may typically form a prediction block for the CU through inter-frame prediction or intra-frame prediction. Inter-frame prediction typically refers to predicting a CU based on data of a previously decoded picture, while intra-frame prediction typically refers to predicting a CU based on previously decoded data of the same picture. To perform inter-frame prediction, the video encoder 200 may use one or more motion vectors to generate a prediction block. The video encoder 200 may typically perform a motion search to identify a reference block that closely matches the CU, for example, based on the difference between the CU and the reference block. The video encoder 200 may calculate a difference metric using the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), or other such difference calculations to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 may use unidirectional prediction or bidirectional prediction to predict the current CU.

[0059] Some examples of VVC also provide an affine motion compensation mode, which can be considered an inter-frame prediction mode. In affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion (such as zooming in or out, rotation, perspective motion, or other irregular motion types).

[0060] To perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. Some examples of VVC provide sixty-seven intra prediction modes, including various directional modes, as well as a planar mode and a DC mode. Typically, the video encoder 200 selects an intra prediction mode that describes neighboring samples of a current block (e.g., a block of a CU) from which the samples of the current block are predicted. Assuming that the video encoder 200 decodes CTUs and CUs in raster scan order (from left to right, from top to bottom), such samples may typically be located above, above and to the left of the current block in the same picture as the current block.

[0061] The video encoder 200 encodes data indicating the prediction mode for the current block. For example, for inter-frame prediction mode, the video encoder 200 may encode data indicating which of various available inter-frame prediction modes to use, as well as motion information for the corresponding mode. For example, for unidirectional or bidirectional inter-frame prediction, the video encoder 200 may encode motion vectors using Advanced Motion Vector Prediction (AMVP) or Merge Mode. The video encoder 200 may use a similar mode to encode motion vectors for affine motion compensation mode.

[0062] After predicting a block (such as after intra-frame prediction or inter-frame prediction of the block), the video encoder 200 can 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 prediction block for the block formed using the corresponding prediction mode. The video encoder 200 can apply one or more transforms to the residual block to produce transformed data in a transform domain rather than a sample domain. For example, the video encoder 200 can 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 can apply a second transform after the first transform, such as a mode-dependent non-separable quadratic transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc. The video encoder 200 generates transform coefficients after applying one or more transforms.

[0063] As described above, after any transform that produces transform coefficients, the video encoder 200 can perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to potentially reduce the amount of data used to represent the transform coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 can reduce the bit depth associated with some or all of the transform coefficients. For example, the video encoder 200 can round down an n-bit value to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, the video encoder 200 can perform a bitwise right shift of the value to be quantized.

[0064] 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 transform coefficients with higher energy (and therefore lower frequency) at the front of the vector and transform coefficients with lower energy (and therefore higher frequency) at the back of the vector. In some examples, the video encoder 200 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 (CABAC). The video encoder 200 can also entropy encode the values ​​of syntax elements that describe metadata associated with the encoded video data for use by the video decoder 300 when decoding the video data.

[0065] To perform CABAC, the video encoder 200 may assign context within a context model to a symbol to be sent. The context may relate to, for example, whether the neighboring values ​​of the symbol are zero. The probability determination may be based on the context assigned to the symbol.

[0066] The video encoder 200 may also generate syntax data (such as block-based syntax data, picture-based syntax data, and sequence-based syntax data) or other syntax data (such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS)) to the video decoder 300, for example, in a picture header, a block header, or a slice header. The video decoder 300 may also decode such syntax data to determine how to decode the corresponding video data.

[0067] In this way, the video encoder 200 can generate a bitstream that includes the encoded video data, such as syntax elements describing the partitioning of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Ultimately, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0068] In general, the video decoder 300 performs processing that is inverse to that performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 may use CABAC to decode the values ​​of syntax elements of the bitstream in a manner substantially similar to, but inverse to, the CABAC encoding process of the video encoder 200. The syntax elements may 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 may further define prediction and residual information for a block (e.g., a CU) of video data.

[0069] 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 deblocking, to reduce visual artifacts along block boundaries.

[0070] There may be some issues with signaling in VVC Draft 8. For example, with respect to APS types, in VVC Draft 8, some tools are used together with Adaptive Parameter Sets (APS), such as Adaptive Loop Filters (ALF). When these tools are disabled (e.g., in Sequence Parameter Sets (SPS)), the corresponding APS types may still be present in the bitstream. However, having the corresponding APS types in the bitstream is redundant.

[0071] As another example, for the CCALF filter in ALF_APS, in VVC draft 8, the cross-component adaptive loop filter (CCALF) coefficients are signaled in ALF_APS. However, when CCALF is disabled, the CCALF filter coefficients may still be present in the bitstream. Having the CCALF filter coefficients in the bitstream when CCALF is disabled may not be necessary and may affect bandwidth efficiency due to unnecessary signaling.

[0072] As another example, with respect to chroma deblocking filter parameters signaled for monochrome, chroma deblocking filter parameters are signaled for all chroma formats in VVC draft 8. However, these parameters are redundant (eg, unnecessary) for monochrome content.

[0073] As another example, for LMCS chroma scaling parameters signaled in LMCS_APS, LMCS chroma scaling parameters are signaled for all chroma formats in VVC draft 8. However, these parameters are redundant (eg, unnecessary) for monochrome content.

[0074] As another example, regarding the dependency between PPS (Picture Parameter Set), APS (Adaptation Parameter Set), and PPS, in VVC draft 8, there are constraints on syntax elements in APS and PPS that depend on SPS (Sequence Parameter Set), such as the chroma format and bit depth in SPS. However, when parsing APS and PPS, SPS may not be available, and therefore the chroma format and bit depth are not available. In such cases, there may be problems in ensuring that APS and PPS comply with the constraints on APS and PPS.

[0075] According to the techniques of this disclosure, the video encoder 200 and the video decoder 300 can be configured to solve one or more of the above-mentioned problems. The example techniques should not be construed as limited to solving the above-mentioned problems. The example techniques can be used alone or in any combination.

[0076] In some examples, the video decoder 300 can be configured to bypass parsing of information indicating an adaptive parameter set (APS) type for adaptive loop filtering (ALF) for one or more blocks based on ALF being disabled for the one or more blocks, and reconstruct the one or more blocks.

[0077] In some examples, the video decoder 300 may be configured to bypass parsing of information indicating a cross-component adaptive loop filter (CCALF) for one or more blocks based on the CCALF being disabled for the one or more blocks and reconstruct the one or more blocks.

[0078] In some examples, video decoder 300 may be configured to determine whether to parse syntax elements indicating whether chroma filters are signaled based on the chroma array type of the block, and reconstruct the block.

[0079] In some examples, the video decoder 300 may be configured to determine whether to parse information indicating luma mapping with chroma scaling (LMCS) based on the chroma array type, and perform LMCS based on whether the information indicating LMCS is parsed.

[0080] In some examples, video decoder 300 may be configured to receive one or more syntax elements indicating whether luma map with chroma scaling (LMCS) information is present in a syntax structure, and parse the LMCS information based on the one or more syntax elements.

[0081] In some examples, the video encoder 200 can be configured to determine that adaptive loop filtering (ALF) is disabled for one or more blocks, avoid setting an adaptation parameter set (APS) type to be equal to an APS type corresponding to the ALF based on the ALF being disabled for the one or more blocks, and signal information indicating that the ALF is disabled for the one or more blocks.

[0082] In some examples, the video encoder 200 can be configured to determine that a cross-component adaptive loop filter (CCALF) is disabled for one or more blocks, avoid signaling information indicating the CCALF for the one or more blocks based on the CCALF being disabled for the one or more blocks, and signal information indicating that the CCALF is disabled for the one or more blocks.

[0083] In some examples, video encoder 200 may be configured to determine whether to signal a syntax element indicating whether a chroma filter is signaled based on the chroma array type of the block.

[0084] In some examples, video encoder 200 may be configured to determine whether to signal information indicating luma mapping with chroma scaling (LMCS) based on the chroma array type, and to signal information indicating the LMCS based on the determination.

[0085] In some examples, video encoder 200 can be configured to signal one or more syntax elements indicating whether luma map with chroma scaling (LMCS) information is present in a syntax structure, and signal LMCS information based on the one or more syntax elements.

[0086] The present disclosure may generally relate to "signaling" certain information, such as syntax elements. The term "signaling" may generally relate to the communication of syntax element values ​​and / or other data used to decode encoded video data. In other words, video encoder 200 may signal the values ​​of syntax elements in a bitstream. Typically, signaling involves generating values ​​in the bitstream. As described above, source device 102 may transmit the bitstream to destination device 116 in substantially real time or in non-real time (such as may occur when storing syntax elements to storage device 112 for later retrieval by destination device 116).

[0087] As described above, in VVC Draft 8, LMCS chroma scaling parameters are signaled for all chroma formats. However, these parameters are redundant for monochrome content. For example, the video encoder 200 can encode a syntax element (referred to as lmcs_delta_abs_crs) that indicates the value of the scaling parameter used to determine the chroma scaling in LMCS (referred to as lmcsDeltaCrs). For example, lmcs_delta_abs_crs specifies the absolute codeword value of the variable lmcsDeltaCrs. The value of lmcs_delta_abs_crs should be in the range of 0 to 7 (inclusive). When not present, lmcs_delta_abs_crs is inferred to be equal to 0.

[0088] The video decoder 300 may decode the syntax element from the bitstream (e.g., parse lmcs_delta_abs_crs) to obtain a value (e.g., lmcsDeltaCrs). For example, lmcsDeltaCrs is equal to (1–2*lmcs_delta_sign_crs_flag)*lmcs_delta_abs_crs. In addition to lmcs_delta_abs_crs (e.g., when lmcs_delta_abs_crs is greater than 0), the video encoder 200 may signal lmcs_delta_sign_crs_flag. lmcs_delta_sign_crs_flag may indicate whether lmcsDeltaCrs is positive or negative. For example, if lmcs_delta_sign_crs_flag is 1, (1–2*lmcs_delta_sign_crs_flag) is equal to -1 and lmcsDeltaCrs is a negative number (e.g., -1*lmcs_delta_abs_crs). If lmcs_delta_sign_crs_flag is 0, (1–2*lmcs_delta_sign_crs_flag) is equal to 1 and lmcsDeltaCrs is a positive number (e.g., 1*lmcs_delta_abs_crs).

[0089] Using lmcsDeltaCrs, the video decoder 300 can determine the scaling parameters for chroma scaling in LMCS. For example, the video decoder 300 can perform the following pseudo code operations:

[0090]

[0091] In the above pseudo code, ChromaScaleCoeff can be considered as the scaling parameter of chroma scaling. In this way, the video decoder 300 can determine the scaling parameter of chroma scaling of LMCS.

[0092] However, there may be situations where LMCS is enabled but chroma scaling is not required. For example, for certain color formats, such as monochrome (also known as 4:0:0 format), LMCS can be enabled but chroma scaling may not be required because there are no chroma components. For monochrome, only the luma component may be required because there are no color components.

[0093] In some techniques (such as in VVC draft 8), the video encoder 200 may signal and the video decoder 300 may parse the lmcs_delta_abs_crs syntax element even if chroma-related syntax elements (e.g., chroma components) are not present (e.g., in a monochrome color format). Including the lmcs_delta_abs_crs syntax element even when chroma components (e.g., chroma-related syntax elements) are not present results in unnecessary signaling and inefficient bandwidth utilization.

[0094] This disclosure describes example techniques for selectively signaling lmcs_delta_abs_crs. The lmcs_delta_abs_crs syntax element indicates a value (e.g., lmcsDeltaCrs) of a scaling parameter (e.g., ChromaScaleCoeff) used to determine chroma scaling in LMCS. For example, the video encoder 200 may determine whether chroma-related syntax elements exist for LMCS. If chroma-related syntax elements exist, the video encoder 200 may encode the lmcs_delta_abs_crs syntax element (e.g., include signaling). However, if chroma-related syntax elements do not exist for LMCS, the video encoder 200 may not encode the lmcs_delta_abs_crs syntax element (e.g., bypass signaling).

[0095] In one or more examples, the video encoder 200 may also signal a flag indicating whether LMCS chroma components are present (e.g., whether LMCS chroma-related syntax elements are present). The video decoder 300 may receive the flag and determine whether LMCS chroma components are present (e.g., whether LMCS chroma-related syntax elements are present). In other words, the video decoder 300 may determine whether LMCS chroma components are present based on the flag.

[0096] If the video decoder 300 determines (e.g., based on a flag signaled by the video encoder 200) that a LMCS chroma component exists (e.g., a chroma-related syntax element exists), the video decoder 300 may decode (e.g., parse) the syntax element (e.g., lmcs_delta_abs_crs) if the LMCS chroma-related syntax element exists. However, if the video decoder 300 determines (e.g., based on a flag signaled by the video encoder 200) that a LMCS chroma-related syntax element does not exist, the video decoder 300 may bypass decoding (e.g., bypass parsing) lmcs_delta_abs_crs if the LMCS chroma-related syntax element does not exist.

[0097] Accordingly, a video decoder (e.g., the video encoder 200 or the video decoder 300) may determine that a chroma-related syntax element exists for a luma map with chroma scaling (LMCS) for a coding unit (CU). In an example where the video decoder is the video encoder 200, the video encoder 200 may signal a flag indicating the presence of the chroma-related syntax element based on the determination of the presence of the chroma-related syntax element. In an example where the video decoder is the video decoder 300, the video decoder 300 may receive a flag indicating the presence of the chroma-related syntax element and may determine the presence of the chroma-related syntax element based on the flag.

[0098] When a syntax element related to chroma in the LMCS for a CU is present, a video decoder may decode (e.g., encode or decode) the syntax element. The syntax element indicates a value of a scaling parameter for determining chroma scaling in the LMCS. For example, the syntax element may be lmcs_delta_abs_crs. The lmcs_delta_abs_crs syntax indicates a value of lmcsDeltaCrs (e.g., the value of lmcs_delta_abs_crs is equal to the absolute value of lmcsDeltaCrs). In other words, the syntax element (e.g., lmcs_delta_abs_crs) specifies an absolute codeword value of a variable (e.g., lmcsDeltaCrs) for determining a scaling parameter (e.g., ChromaScaleCoeff) for chroma scaling. Therefore, determining the scaling parameters is a multi-step process, comprising first determining lmcs_delta_abs_crs, determining lmcsDeltaCrs from lmcs_delta_abs_crs, and then determining ChromaScaleCoeff from lmcsDeltaCrs.

[0099] In an example where the video coder is the video encoder 200, the video encoder 200 may signal a syntax element (e.g., lmcs_delta_abs_crs) only when a chroma-related syntax element is present. In an example where the video coder is the video decoder 300, the video decoder 300 may parse the syntax element (e.g., lmcs_delta_abs_crs) based on a determination of the presence of the chroma-related syntax element (e.g., based on a flag indicating the presence of a chroma component).

[0100] The video decoder can decode syntax elements (e.g., lmcs_delta_abs_crs) in the LMCS syntax structure (e.g., lmcs_data()) in the adaptation parameter set (APS). Similarly, as described above, the video encoder 200 can signal and the video decoder 300 can parse a flag indicating whether chroma-related syntax elements are present. In one or more examples, this flag can be referred to as lmcs_cs_present_flag (also referred to as aps_chroma_present_flag). The lmcs_cs_present_flag can also be signaled and parsed in the APS.

[0101] The video decoder may decode the chroma block of the CU based on a scaling parameter (e.g., ChromaScaleCoeff) for chroma scaling. In an example where the video decoder is the video encoder 200, the video encoder 200 may determine a chroma prediction block and subtract the chroma prediction block from the chroma block to generate a residual block. The video encoder 200 may scale the residual block based on the scaling parameter (e.g., for LMCS) to generate a scaled residual block and signal information indicating the scaled residual block. In an example where the video decoder is the video decoder 300, the video decoder 300 may inversely scale the scaled residual chroma block based on the scaling parameter to generate a residual chroma block. The video decoder 300 may determine a chroma prediction block and add the residual chroma block to the chroma prediction block to reconstruct the chroma block.

[0102] In the above example of a CU (e.g., a first CU), chroma-related syntax elements may be present. However, for a second CU, chroma-related syntax elements may not be present. For example, the video decoder may determine that LMCS chroma-related syntax elements for the second CU do not exist. For example, for the second CU, the video encoder 200 may signal and the video decoder 300 may parse a flag (e.g., lmcs_cs_present_flag (also known as aps_chroma_present_flag)) indicating that LMCS chroma-related syntax elements for the second CU do not exist.

[0103] In such an example, when the LMCS chroma-related syntax element for the second CU is not present, the video decoder can bypass decoding the syntax element. For example, the video encoder 200 can avoid signaling (e.g., bypass signaling) the lmcs_delta_abs_crs syntax element. The video decoder 300 can avoid parsing (e.g., bypass parsing) the lmcs_delta_abs_crs syntax element. In other words, when the lmcs_cs_present_flag indicates that the chroma-related syntax element is not present, the video decoder 300 can determine that the bits normally used for the lmcs_delta_abs_crs syntax element belong to another syntax element.

[0104] As described above, the presence of a chroma-related syntax element may indicate the presence of a chroma component. Similarly, the absence of a chroma-related syntax element may indicate the absence of a chroma component.

[0105] This disclosure also describes examples of constraints for the video encoder 200 in forming a conforming bitstream. For example, the lmcs_delta_abs_crs syntax element can be considered a first syntax element. In some examples, the video encoder 200 can determine a value for a second syntax element that specifies the number of bits used to represent a third syntax element of the LMCS, which is signaled in the APS for the CU. In some examples, the value of the second syntax element is constrained to a range of 0 to a value based on the bit depth. An example of the second syntax element is lmcs_delta_cw_prec_minus1, and an example of the third syntax element is lmcs_delta_abs_cw[i].

[0106] This disclosure also describes examples of adaptive loop filtering (ALF), such as cross-component ALF (CCALF). For example, the video encoder 200 may determine that a sequence parameter set (SPS) indicates that CCALF is disabled. In such examples, when the SPS indicates that CCALF is disabled, the video encoder 200 may set at least one flag in the APS that specifies that cross-component filters for chroma components are not signaled. In other words, when CCALF is disabled in the SPS, the video encoder 200 may ensure that a flag in the APS that specifies whether cross-component filters are signaled indicates that cross-component filters are not signaled.

[0107] The following describes various example techniques, as well as changes to VVC Draft 8. In the following, additions to VVC Draft 8 are denoted as <add> ....< / add> The text between , and the deleted part is represented as <delete> ...< / delete> The text between.

[0108] For APS type constraints, when a tool is disabled (e.g., in an SPS), an APS with the corresponding tool type may not appear in the bitstream. Example techniques are described with the following semantics. As specified in Table 1, the syntax element aps_params_type specifies the type of APS parameters carried in the APS.

[0109] Table 1 — APS parameter type codes and APS parameter types

[0110] aps_params_type The name of aps_params_type Types of APS parameters 0 ALF_APS ALF parameters 1 LMCS_APS LMCS parameters 2 SCALING_APS Scaling List Parameters 3..7 reserve reserve

[0111] <add> When sps_alf_enabled_flag is equal to 0, aps_params_type shall not be equal to ALF_APS. When sps_lmcs_enabled_flag is equal to 0, aps_params_type shall not be equal to LMCS_APS. When sps_scaling_list_enabled_flag is equal to 0, aps_params_type shall not be equal to SCALING_APS.< / add> The above constraints can be expressed as bitstream consistency constraints.

[0112] For CCALF filter constraints in ALF_APS, when CCALF is disabled (e.g., in SPS), CCALF filter information should not be present in the bitstream (such as ALF_APS in VVC). Example techniques are described as the following semantics.

[0113]

[0114]

[0115]

[0116] For semantic constraints:

[0117] alf_cc_cb_filter_signal_flag equal to 1 specifies that the cross-component filter of the Cb color component is signaled. alf_cc_cb_filter_signal_flag equal to 0 specifies that the cross-component filter of the Cb color component is not signaled. <delete> ChromaArrayType< / delete> <add> sps_ccalf_enabled_flag< / add> When equal to 0, alf_cc_cb_filter_signal_flag should be equal to 0.

[0118] alf_cc_cr_filter_signal_flag equal to 1 specifies that cross-component filters for Cr color components are signaled. alf_cc_cr_filter_signal_flag equal to 0 specifies that cross-component filters for Cr color components are not signaled. <delete> ChromaArrayType< / delete> <add>sps_ccalf_enabled_flag< / AD D> When equal to 0, alf_cc_cr_filter_signal_flag should be equal to 0.

[0119] In some examples, there may be cases where conditional signaling is performed based on sps_ccalf_enabled_flag. The CCALF filter may be conditionally signaled based on sps_ccalf_enabled_flag. When sps_ccalf_enabled_flag is false, no signaling of the CCALF filter is required. In VVC draft 8, in this case, alf_cc_cb / cr_filter_signal_flag may not be present in the bitstream and is inferred to be 0 at the decoder.

[0120]

[0121] alf_cc_cb_filter_signal_flag equal to 1 specifies that the cross-component filter of the Cb color component is signaled. alf_cc_cb_filter_signal_flag equal to 0 specifies that the cross-component filter of the Cb color component is not signaled. <add> When alf_cc_cb_filter_signal_flag is not present, it is inferred to be equal to 0.< / add>

[0122] alf_cc_cr_filter_signal_flag equal to 1 specifies that cross-component filters for Cr color components are signaled. alf_cc_cr_filter_signal_flag equal to 0 specifies that cross-component filters for Cr color components are not signaled. <add> When alf_cc_cr_filter_signal_flag is not present, it is inferred to be equal to 0.< / add>

[0123] In some examples, there may be conditional signaling based on sps_ccalf_enabled_flag. The CCALF filter may be conditionally signaled based on ChromaArrayType (e.g., chroma array type). When sps_ccalf_enabled_flag is false, no signaling of the CCALF filter may be required. In VVC draft 8, in this case, alf_cc_cb / cr_filter_signal_flag may not be present in the bitstream and inferred to be 0 at the decoder.

[0124]

[0125] alf_cc_cb_filter_signal_flag equal to 1 specifies that the cross-component filter of the Cb color component is signaled. alf_cc_cb_filter_signal_flag equal to 0 specifies that the cross-component filter of the Cb color component is not signaled. <add> When alf_cc_cb_filter_signal_flag is not present, it is inferred to be equal to 0.< / add>

[0126] alf_cc_cr_filter_signal_flag equal to 1 specifies that cross-component filters for Cr color components are signaled. alf_cc_cr_filter_signal_flag equal to 0 specifies that cross-component filters for Cr color components are not signaled. <add> When alf_cc_cr_filter_signal_flag is not present, it is inferred to be equal to 0.< / add>

[0127] In some examples, conditional signaling can be based on sps_ccalf_enabled_flag and ChromaArrayType. The CCALF filter can be conditionally signaled based on sps_ccalf_enabled_flag and ChromaArrayType. When sps_ccalf_enabled_flag is false or ChromaArrayType is false, no signaling of the CCALF filter may be required. In VVC draft 8, in this case, alf_cc_cb / cr_filter_signal_flag may not be present in the bitstream and inferred to be 0 at the decoder.

[0128]

[0129]

[0130] alf_cc_cb_filter_signal_flag equal to 1 specifies that the cross-component filter of the Cb color component is signaled. alf_cc_cb_filter_signal_flag equal to 0 specifies that the cross-component filter of the Cb color component is not signaled. <add> When alf_cc_cb_filter_signal_flag is not present, it is inferred to be equal to 0.< / add>

[0131] alf_cc_cr_filter_signal_flag equal to 1 specifies that cross-component filters for Cr color components are signaled. alf_cc_cr_filter_signal_flag equal to 0 specifies that cross-component filters for Cr color components are not signaled. <add> When alf_cc_cr_filter_signal_flag is not present, it is inferred to be equal to 0.< / add>

[0132] In some examples, alf_chroma_filter can be conditionally signaled based on ChromaArrayType. Additionally or alternatively, chroma ALF can be conditionally signaled based on ChromaArrayType. When ChromaArrayType is false, no chroma ALF filter signaling may be required. In VVC draft 8, in this case, alf_chroma_filter_signal_flag may not be present in the bitstream and is inferred to be 0 at the decoder.

[0133]

[0134] alf_chroma_filter_signal_flag equal to 1 specifies that the chroma filter is signaled. alf_chroma_filter_signal_flag equal to 0 specifies that the chroma filter is not signaled. <add> When not present, alf_chroma_filter_signal_flag is inferred to be equal to 0.< / add>

[0135] In some examples, there may be chroma deblocking filter parameter signaling for monochrome. Constraints on the deblocking tc and beta offsets for Cb and Cr for monochrome content may be added. One or more (including any) of the following techniques may be applied to the PPS (Picture Parameter Set), PH (Picture Header), and / or SH (Slice Header).

[0136] With respect to semantic constraints, in one example, for monochrome content, semantic constraints may be added to constrain the values ​​of deblocking tc and beta offsets for Cb and Cr to be 0.

[0137] pps_cb_beta_offset_div2 and pps_cb_tc_offset_div2 specify the default deblocking parameter offsets (divided by 2) for β and tC applied to the Cb component of the slice that references the PPS, unless the default deblocking parameter offsets are overridden by the deblocking parameter offsets present in the picture header or in the slice header of the slice that references the PPS. The values ​​of pps_cb_beta_offset_div2 and pps_cb_tc_offset_div2 should both be in the range of -12 to 12 (inclusive). When not present <add> Or ChromaArrayType is equal to 0< / add> When , the values ​​of pps_cb_beta_offset_div2 and pps_cb_tc_offset_div2 are both inferred to be equal to 0.

[0138] pps_cr_beta_offset_div2 and pps_cr_tc_offset_div2 specify the default deblocking parameter offsets (divided by 2) applied to the β and tC components of the Cr components of the slice that references the PPS, unless the default deblocking parameter offsets are overridden by the deblocking parameter offsets present in the picture header or in the slice header of the slice that references the PPS. The values ​​of pps_cr_beta_offset_div2 and pps_cr_tc_offset_div2 should both be in the range of -12 to 12 (inclusive). When not present <add> Or ChromaArrayType is equal to 0< / add> When , the values ​​of pps_cr_beta_offset_div2 and pps_cr_tc_offset_div2 are both inferred to be equal to 0.

[0139] The following describes some example conditional signaling where monochrome content is used.For monochrome content, the deblocking tc and beta offsets for the Cb and Cr components may not be present in the bitstream.

[0140] The present disclosure also describes conditional signaling based on chroma formats and flags. The deblocking tc and beta offsets for Cb and Cr can be conditionally signaled based on some signaling flags. For example, <add> pps_chroma_tool_offsets_present_flag< / add> Can be reused for the chroma deblocking filter. Alternatively, instead of reusing pps_chroma_tool_offsets_present_flag, a new flag indicating the presence of chroma deblocking offsets can be introduced. This flag can be signaled in the PPS and / or picture and / or slice header, for example.

[0141] Image parameter set:

[0142]

[0143]

[0144] Image header:

[0145]

[0146] Slice header:

[0147]

[0148] The semantics of pps_chroma_tool_offsets_present_flag may be updated to reflect usage in PH and SH as follows.

[0149] pps_chroma_tool_offsets_present_flag equal to 1 specifies that the chroma tool offset related syntax elements are present in the PPS RBSP syntax structure <add> , and the relevant syntax elements exist in the PH and SH that reference the PPS.< / add> pps_chroma_tool_offsets_present_flag equal to 0 specifies that the chroma tool offset related syntax elements are not present in the PPS RBSP, <add> PH and SH< / add> In the syntax structure, when ChromaArrayType is equal to 0, the value of pps_chroma_tool_offsets_present_flag shall be equal to 0.

[0150] There may be some changes to the luminance mapping with chroma scaling (LMCS) chroma scaling parameters signaled in LMCS_APS. The following describes modifications to the lmcs_delta_cw_prec_minus1 signaling. To decouple LMCS_APS signaling from the SPS and avoid infinite values ​​of lmcs_delta_cw_prec_minus1 at the video decoder 300, lmcs_delta_cw_prec_minus1 can be signaled with a fixed-length code, such as u(4).

[0151]

[0152] Conditional signaling of chroma scaling can be performed by adding some semantic constraints. For example, lmcs_delta_abs_crs specifies the absolute codeword value of the variable lmcsDeltaCrs. The value of lmcs_delta_abs_crs should be in the range of 0 to 7 (inclusive). When not present, lmcs_delta_abs_crs is inferred to be equal to 0. <add> When ChromaArrayType is equal to 0, lmcs_delta_abs_crs should be equal to 0.< / add>

[0153] Conditional signaling of chroma scaling by chroma format is described below.

[0154]

[0155] lmcs_delta_abs_crs specifies the absolute codeword value of the variable lmcsDeltaCrs. The value of lmcs_delta_abs_crs should be in the range of 0 to 7 (inclusive). When not present, lmcs_delta_abs_crs is inferred to be equal to 0.

[0156] 2.4.4 Conditional Signaling of Chroma Scaling via Another Signaling Flag

[0157]

[0158]

[0159] <add> lmcs_cs_present_flag equal to 1 specifies that lmcs_delta_abs_crs is present in LMCS_APS. lmcs_cs_present_flag equal to 0 specifies that lmcs_delta_abs_crs is not present in LMCS_APS. When ChromaArrayType is equal to 0, lmcs_cs_present_flag shall be equal to 0.< / add>

[0160] lmcs_delta_abs_crs specifies the absolute codeword value of the variable lmcsDeltaCrs. The value of lmcs_delta_abs_crs should be in the range of 0 to 7 (inclusive). When not present, lmcs_delta_abs_crs is inferred to be equal to 0.

[0161] Conditionally signaling the chroma scaling list based on the chroma format is described below. For monochrome content, the chroma scaling list parameters may not be signaled. In VVC, scaling_list_chroma_present_flag may not be present in the bitstream for monochrome content and is inferred to be 0 at the video decoder 300.

[0162]

[0163] scaling_list_chroma_present_flag equal to 1 specifies that the chroma scaling list is present in scaling_list_data(). scaling_list_chroma_present_flag equal to 0 specifies that the chroma scaling list is not present in scaling_list_data(). <add>When absent, it is inferred to be equal to 0.

[0164] < / add>

[0165] The dependency relationships among PPS, APS, and SPS are described below. Syntax constraints that depend on SPS can be moved from PPS and APS to locations that reference syntax elements, such as PH and SH.

[0166] For LMCS, constraints on the lmcs_delta_cw_prec_minus1 value may be checked when referencing the LMCS. In one example, lmcs_delta_cw_prec_minus1 may be signaled with a fixed length code such as u(4).

[0167]

[0168]

[0169] <add>It is required that when ph_lmcs_aps_id is present, the value of lmcs_delta_cw_prec_minus1 of the APS NAL unit with aps_params_type equal to LMCS_APS and adaptation_parameter_set_id equal to ph_lmcs_aps_id shall be in the range of 0 to BitDepth-2 (inclusive).

[0170] < / add>

[0171] In another example,

[0172]

[0173]

[0174] lmcs_delta_cw_prec_minus1 plus 1 specifies the number of bits used to represent the syntax lmcs_delta_abs_cw[i]. The value of lmcs_delta_cw_prec_minus1 shall be between 0 and <add> max_lmcs_delta_cw_prec_minus1< / add> (inclusive) range. <add>max_lmcs_delta_cw_prec_minus1< / add> It is a fixed value for all bitstreams. For example, max_lmcs_delta_cw_prec_minus1 can be 14.

[0175] <add>It is required that when ph_lmcs_aps_id is present, the value of lmcs_delta_cw_prec_minus1 of the APS NAL unit with aps_params_type equal to LMCS_APS and adaptation_parameter_set_id equal to ph_lmcs_aps_id shall be in the range of 0 to BitDepth-2 (inclusive).

[0176] < / add>

[0177] Conditional signaling of chroma scaling via another signaling flag is described below.

[0178]

[0179] <add> lmcs_cs_present_flag equal to 1 specifies that lmcs_delta_abs_crs is present in LMCS_APS. lmcs_cs_present_flag equal to 0 specifies that lmcs_delta_abs_crs is not present in LMCS_APS.< / add>

[0180] <add> It is required that when ph_lmcs_aps_id is present, the value of lmcs_cs_present_flag of the APS NAL unit with aps_params_type equal to LMCS_APS and adaptation_parameter_set_id equal to ph_lmcs_aps_id shall be equal to 0 if ChromaArrayType is equal to 0, otherwise it shall be 1.< / add>

[0181] The following describes techniques related to ALF: When ALF_APS is referenced in the bitstream (such as at PH, SH, block and sample), if sps_ccalf_enabled_flag is false, then ALF_APS shall not contain any CCALF filter.

[0182] slice_alf_aps_id_luma[i] specifies the adaptation_parameter_set_id of the i-th ALF APS referenced by the luma component of the slice. When slice_alf_enabled_flag is equal to 1 and slice_alf_aps_id_luma[i] is not present, the value of slice_alf_aps_id_luma[i] is inferred to be equal to the value of ph_alf_aps_id_luma[i].

[0183] <add> When slice_alf_aps_id_luma[i] is present, the following applies:< / add>

[0184] a. The TemporalId of the APS NAL unit with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to slice_alf_aps_id_luma[i] shall be less than or equal to the TemporalId of the coded slice NAL unit.

[0185] b. The value of alf_luma_filter_signal_flag shall be equal to 1 for APS NAL units with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to slice_alf_aps_id_luma[i].

[0186] c. <add> When sps_ccalf_enabled_flag is equal to 0, the values ​​of alf_cc_cb_filter_signal_flag and alf_cc_cr_filter_signal_flag shall both be equal to 0 for the APS NAL units with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to slice_alf_aps_id_luma[i].< / add>

[0187] slice_alf_aps_id_chroma specifies the adaptation_parameter_set_id of the ALF APS referenced by the chroma components of the slice. When slice_alf_enabled_flag is equal to 1 and slice_alf_aps_id_chroma is not present, the value of slice_alf_aps_id_chroma is inferred to be equal to the value of ph_alf_aps_id_chroma.

[0188] <add> When slice_alf_aps_id_chroma is present, the following applies:< / add>

[0189] a. The TemporalId of the APS NAL unit with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to slice_alf_aps_id_chroma shall be less than or equal to the TemporalId of the coded slice NAL unit.

[0190] b. The value of alf_chroma_filter_signal_flag shall be equal to 1 for APS NAL units with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to slice_alf_aps_id_chroma.

[0191] c. <add> When sps_ccalf_enabled_flag is equal to 0, the values ​​of alf_cc_cb_filter_signal_flag and alf_cc_cr_filter_signal_flag shall both be equal to 0 for the APS NAL units with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to slice_alf_aps_id_chroma.< / add>

[0192] ph_alf_aps_id_luma[i] specifies the adaptation_parameter_set_id of the i-th ALFAPS referenced by the luma component of the slice associated with the PH.

[0193] <add> When ph_alf_aps_id_luma[i] is present, the following applies:< / add>

[0194] a. The value of alf_luma_filter_signal_flag shall be equal to 1 for APS NAL units with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to ph_alf_aps_id_luma[i].

[0195] b. The TemporalId of the APS NAL unit with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to ph_alf_aps_id_luma[i] shall be less than or equal to the TemporalId of the picture associated with the PH.

[0196] c. <add> When sps_ccalf_enabled_flag is equal to 0, the values ​​of alf_cc_cb_filter_signal_flag and alf_cc_cr_filter_signal_flag of the APS NAL units with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to ph_alf_aps_id_luma[i] shall both be equal to 0.< / add>

[0197] ph_alf_aps_id_chroma specifies the adaptation_parameter_set_id of the ALF APS referenced by the chroma components of the slice associated with the PH.

[0198] <add> When ph_alf_aps_id_chroma is present, the following applies:< / add>

[0199] a. The value of alf_chroma_filter_signal_flag of the APS NAL unit with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to ph_alf_aps_id_chroma shall be equal to 1.

[0200] b. The TemporalId of the APS NAL unit with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to ph_alf_aps_id_chroma shall be less than or equal to the TemporalId of the picture associated with the PH.

[0201] c. <add>When sps_ccalf_enabled_flag is equal to 0, the values ​​of alf_cc_cb_filter_signal_flag and alf_cc_cr_filter_signal_flag of the APS NAL unit with aps_params_type equal to ALF_APS and adaptation_parameter_set_id equal to ph_alf_aps_id_chroma shall both be equal to 0.< / add>

[0202] The following description is related to the chroma QP offset. In the slice header:

[0203]

[0204] In some examples, when pps_slice_chroma_qp_offsets_present_flag is used and the current content is monochrome, the value of pps_slice_chroma_qp_offsets_present_flag should be 0.

[0205] if(pps_cu_chroma_qp_offset_list_enabled_flag) cu_chroma_qp_offset_enabled_flag u(1)

[0206] In some examples, when pps_cu_chroma_qp_offset_list_enabled_flag is used and the current content is monochrome, the value of pps_cu_chroma_qp_offset_list_enabled_flag should be 0.

[0207] Alternatively or additionally, slice_qp_offsets of chroma components may be conditionally signaled only when pps_slice_chroma_qp_offsets_present_flag is true and the current content is not monochrome. If the current content is monochrome, sliceqp_offsets of chroma components shall not be signaled.

[0208]

[0209] cu_chroma_qp_offset_enabled_flag for chroma components may be conditionally signaled only when pps_cu_chroma_qp_offset_list_enabled_flag is true and the current content is not monochrome. cu_chroma_qp_offset_enabled_flag for chroma components shall not be signaled if the current content is monochrome.

[0210]

[0211] In PH,

[0212] if(pps_cu_chroma_qp_offset_list_enabled_flag) ph_cu_chroma_qp_offset_subdiv_intra_slice ue(v)

[0213] if(pps_cu_chroma_qp_offset_list_enabled_flag) ph_cu_chroma_qp_offset_subdiv_inter_slice ue(v)

[0214] In some examples, when pps_cu_chroma_qp_offset_list_enabled_flag is used and the current content is monochrome, the value of pps_cu_chroma_qp_offset_list_enabled_flag should be 0.

[0215] Alternatively or additionally, ph_cu_chroma_qp_offset_subdiv_intra_slice and ph_cu_chroma_qp_offset_subdiv_inter_slice for chroma components may be conditionally signaled only when pps_slice_chroma_qp_offsets_present_flag is true and the current content is not monochrome. If the current content is monochrome, ph_cu_chroma_qp_offset_subdiv_intra_slice and ph_cu_chroma_qp_offset_subdiv_inter_slice for chroma components shall not be signaled.

[0216]

[0217]

[0218] Figure 2A and Figure 2B is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure 130 and a corresponding coding tree unit (CTU) 132. Solid lines represent quadtree splits, while dashed lines indicate binary tree splits. In each split (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which split type (i.e., horizontal or vertical) is used, where in this example, 0 indicates horizontal splitting and 1 indicates vertical splitting. For quadtree splitting, there is no need to indicate the split type because the quadtree node splits the block horizontally and vertically into 4 equally sized sub-blocks. Accordingly, the video encoder 200 can encode syntax elements (such as split information) at the region tree level (i.e., solid lines) of the QTBT structure 130 and syntax elements (such as split information) at the prediction tree level (i.e., dashed lines) of the QTBT structure 130, and the video decoder 300 can decode them. The video encoder 200 may encode video data (such as prediction and transform data) of the CU represented by the terminal leaf node of the QTBT structure 130 , and the video decoder 300 may decode it.

[0219] 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 levels of the QTBT structure 130. These parameters may include a CTU size (indicating the size of the CTU 132 in samples), 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).

[0220] The root node of the QTBT structure corresponding to the CTU can have four child nodes at the first level of the QTBT structure, each of which can be split according to quadtree partitioning. In other words, the nodes at the first level are leaf nodes (no child nodes) or have four child nodes. The example of the QTBT structure 130 represents such nodes as parent nodes and child nodes including solid lines with branches. If the nodes at the first level are not larger than the maximum allowed binary tree root node size (MaxBTSize), these nodes can be further split by the corresponding binary tree. The binary tree splitting of a node can be iterated until the node resulting from the split reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of the QTBT structure 130 represents such nodes as dotted lines with branches. The binary tree leaf nodes are called decoding units (CUs), which are used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further partitioning. As described above, CUs can also be referred to as "video blocks" or "blocks."

[0221] In one example of a QTBT partitioning structure, the CTU size is set to 128×128 (luminance sample and two corresponding 64×64 chroma 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. Quadtree leaf nodes can have sizes from 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If the quadtree leaf node is 128×128, the quadtree leaf node will not be further split by the binary tree because the size exceeds MaxBTSize (i.e., 64×64 in this example). Otherwise, the quadtree leaf node will be further split by the binary tree. 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), no further splitting is allowed. When a binary tree node has a width equal to MinBTSize (4 in this example), this means that no further vertical splitting is allowed. Similarly, a binary tree node with a height equal to MinBTSize means that no further horizontal splitting is allowed for that binary tree node. As described above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further splitting.

[0222] Figure 3 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 3 This is provided for purposes of explanation and should not be construed as limiting the techniques broadly illustrated and described in this disclosure. For purposes of explanation, this disclosure describes a video encoder 200 based on techniques of VVC (ITU-T H.266, under development) and HEVC (ITU-T H.265). However, the techniques of this disclosure may be performed by video encoding devices configured to other video coding standards.

[0223] exist Figure 3 In the example of FIG, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218, and an entropy coding unit 220. Any or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filter unit 216, the DPB 218, and the entropy coding unit 220 may be implemented in one or more processors or processing circuits. For example, the units of the video encoder 200 may be implemented as one or more circuits or logic elements, as part of a hardware circuit or as part of a processor, ASIC, or FPGA. Furthermore, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

[0224] The video data memory 230 may store video data to be encoded by the components of the video encoder 200. The video encoder 200 may receive video data from, for example, the video source 104 ( Figure 1 ) receives video data stored in the video data memory 230. The DPB 218 can act as a reference picture memory for storing reference video data used to predict subsequent video data by the video encoder 200. The video data memory 230 and the DPB 218 can be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The video data memory 230 and the DPB 218 can be provided by the same memory device or separate memory devices. In various examples, the video data memory 230 can be on-chip with the other components of the video encoder 200 (as shown), or off-chip relative to those components.

[0225] In this disclosure, references to the video data memory 230 should not be construed 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). Rather, references to the video data memory 230 should be understood as a reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data of 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 .

[0226] Figure 3 The various units are illustrated to aid in understanding the operations performed by the video encoder 200. These units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. A fixed-function circuit refers to a circuit that provides a specific function and is preset for the operations that can be performed. A programmable circuit refers to a circuit that can be programmed to perform various tasks and provides flexible functionality in the operations that can be performed. For example, a programmable circuit can run software or firmware so that the programmable circuit operates in a manner defined by the instructions of the software or firmware. A fixed-function circuit can execute software instructions (e.g., to receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally immutable. In some examples, one or more of the units may be different circuit blocks (fixed-function or programmable), while in some examples, one or more of the units may be integrated circuits.

[0227] 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 where the operation of the video encoder 200 is performed using software executed by a programmable circuit, the memory 106 ( Figure 1 ) may store instructions (eg, object code) for software that video encoder 200 receives and executes, or another memory (not shown) within video encoder 200 may store such instructions.

[0228] The video data memory 230 is configured to store received video data. The video encoder 200 may retrieve a picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 may be the original video data to be encoded.

[0229] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, an intra prediction unit 226, and a luma mapping with chroma scaling (LMCS) unit 227. The mode selection unit 202 may include additional functional units for performing 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, and the like.

[0230] The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and the rate-distortion values ​​obtained for such combinations. The encoding parameters may include the partitioning of CTUs into CUs, the prediction mode of the CU, the transform type of the residual data of the CU, the quantization parameter of the residual data of the CU, 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.

[0231] The video encoder 200 may partition a picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs into a slice. The mode selection unit 202 may partition the CTUs of the picture according to a tree structure (such as the QTBT structure or quadtree structure of HEVC described above). As described above, the video encoder 200 may form one or more CUs by partitioning the CTUs according to the tree structure. Such CUs may also be generally referred to as "video blocks" or "blocks."

[0232] Typically, mode select unit 202 also controls its components (e.g., motion estimation unit 222, motion compensation unit 224, and intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU or, in HEVC, the overlapping portion of a PU and TU). For inter prediction of the current block, motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously decoded pictures stored in DPB 218). Specifically, motion estimation unit 222 may calculate values ​​indicating how similar potential reference blocks are to the current block, such as based on sum of absolute differences (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared difference (MSD), and the like. Motion estimation unit 222 may typically perform these calculations using the sample-by-sample difference between the current block and the reference block under consideration. Motion estimation unit 222 may identify the reference block with the lowest value obtained from these calculations, indicating the reference block that most closely matches the current block.

[0233] 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. Motion estimation unit 222 may then provide the motion vectors to motion compensation unit 224. For example, for unidirectional inter prediction, motion estimation unit 222 may provide a single motion vector, while for bidirectional inter prediction, motion estimation unit 222 may provide two motion vectors. Motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, if the motion vectors have fractional sample precision, motion compensation unit 224 may interpolate the values ​​of the prediction block based on one or more interpolation filters. Furthermore, for bidirectional inter prediction, motion compensation unit 224 may retrieve data for the two reference blocks identified by the corresponding motion vectors and combine the retrieved data, for example, by sample-by-sample averaging or weighted averaging.

[0234] As another example, for intra prediction or intra prediction decoding, the intra prediction unit 226 can generate a prediction block based on samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally mathematically combine the values ​​of adjacent samples and pad these calculated values ​​along a defined direction on the current block to generate a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average value of adjacent samples of the current block and generate a prediction block to include this calculated average value for each sample of the prediction block.

[0235] The LMCS unit 227 may be configured to perform operations of the LMCS video decoding tool. For example, the LMCS unit 227 may perform luma mapping on the luma block of the CU and chroma scaling on the chroma blocks of the CU. For luma mapping, the LMCS unit 227 may map the luma samples of the luma block of the CU to generate mapped luma samples of the mapped luma block. The LMCS unit 227 may also generate a mapped luma prediction block for a prediction block generated by the motion compensation unit 224 or the intra prediction unit 226.

[0236] Mode selection unit 202 provides the prediction block or the mapped luma prediction block to residual generation unit 204. Residual generation unit 204 receives the original, uncoded version of the current block from video data memory 230, or the mapped luma block and prediction block from mode selection unit 202. Residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, residual generation unit 204 may also determine the difference between sample values ​​in the residual block to generate the residual block using residual differential pulse coded modulation (RDPCM). In some examples, residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0237] For LMCS, the residual generation unit 204 may generate a mapped luma residual block based on the difference between the mapped luma block and the mapped prediction block of the CU. For chroma components, the residual generation unit 204 may generate a chroma residual block based on the difference between the chroma block and the chroma prediction block to generate a chroma residual block. The LMCS unit 227 may perform scaling on the chroma residual block to generate a scaled chroma residual block.

[0238] In the example where the mode select unit 202 partitions the CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs of various sizes. As described above, the size of a CU may refer to the size of the luma coding block of the CU, and the size of a PU may refer to the size of the luma prediction unit of the PU. Assuming that the size of a particular CU is 2N×2N, the video encoder 200 may support PU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N, or similar sizes for inter prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

[0239] In an example where mode select unit 202 does not further partition a CU into PUs, each CU may be associated with a luma coding block and a corresponding chroma coding block. As described above, the size of a CU may refer to the size of the luma coding block of the CU. Video encoder 200 and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

[0240] For other video coding techniques (such as intra block copy mode coding, affine mode coding, and linear model (LM) mode coding, to name a few), mode selection unit 202 generates a prediction block for the current block being encoded via the corresponding unit associated with the coding technique. In some examples, such as palette mode coding, mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating how to reconstruct the block based on the selected palette. In such modes, mode selection unit 202 may provide these syntax elements to entropy coding unit 220 for encoding.

[0241] 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.

[0242] Transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a "transform coefficient block"). Transform processing unit 206 may apply various transforms to the residual block to form the transform coefficient block. For example, transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, transform processing unit 206 may perform multiple transforms on the residual block, e.g., a primary transform and a secondary transform, such as a rotation transform. In some examples, transform processing unit 206 does not apply a transform to the residual block.

[0243] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce a loss of information, and therefore, the quantized transform coefficients may have lower precision than the original transform coefficients produced by the transform processing unit 206.

[0244] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct a residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0245] Filter unit 216 may perform one or more filter operations on the reconstructed block. For example, filter unit 216 may perform a deblocking operation to reduce blockiness artifacts along the edges of the CU. In some examples, the operations of filter unit 216 may be skipped.

[0246] The video encoder 200 stores the reconstructed block in the DPB 218. For example, in examples where the operation of the filter unit 216 is not required, the reconstruction unit 214 can store the reconstructed block in the DPB 218. In examples where the operation of the filter unit 216 is required, the filter unit 216 can store the filtered reconstructed block in the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 can retrieve a reference picture formed by the reconstructed (and possibly filtered) block 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 block of the current picture in the DPB 218 to perform intra-frame prediction on other blocks in the current picture.

[0247] In general, entropy coding unit 220 may entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy coding unit 220 may entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy coding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-frame prediction or intra-frame mode information for intra-frame prediction) from mode selection unit 202. Entropy coding unit 220 may perform one or more entropy encoding operations on the syntax elements (which are another example of video data) to generate entropy-encoded data. For example, entropy coding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential-Golomb coding operation, or another type of entropy coding operation on the data. In some examples, entropy coding unit 220 may operate in a bypass mode in which syntax elements are not entropy encoded.

[0248] The video encoder 200 may output a bitstream including entropy-encoded syntax elements required to reconstruct a block of a slice or picture. In particular, the entropy encoding unit 220 may output the bitstream.

[0249] The above operations are described with respect to blocks. Such descriptions should be understood as operations for luma coding blocks and / or chroma coding blocks. As described above, in some examples, the luma coding blocks and chroma coding blocks are the luma and chroma components of a CU. In some examples, the luma coding blocks and chroma coding blocks are the luma and chroma components of a PU.

[0250] In some examples, operations performed with respect to luma coding blocks do not need to be repeated for chroma coding blocks. As an example, operations for identifying a motion vector (MV) and reference picture for a luma coding block do not need to be repeated to identify the MV and reference picture for a chroma block. Specifically, the MV for a luma coding block can be scaled to determine the MV for a chroma block, and the reference picture can be the same. As another example, the intra prediction process can be the same for luma and chroma coding blocks.

[0251] 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 circuitry and configured to perform the example techniques described in this disclosure.

[0252] For example, as described above, the video encoder 200 can be configured to implement LMCS. The video encoder 200 can be configured to signal syntax elements used by the video decoder 300 to implement LMCS. For example, the video encoder 200 can be configured to encode and signal syntax elements used to determine scaling parameters that the video decoder 300 will use for chroma scaling. However, there may be cases where a CU has no chroma components but LMCS is enabled for that CU. In such cases, unnecessary or erroneous signaling may occur, such as where the video encoder 200 signals syntax elements to determine scaling parameters for chroma scaling despite the absence of chroma components.

[0253] As an example, when ChromaArrayType is equal to zero, there may be no chroma components. ChromaArrayType being equal to zero may mean that the color format is monochrome (eg, black and white).

[0254] According to one or more examples, video encoder 200 may determine that chroma-related syntax elements are present for a luma map with chroma scaling (LMCS) for a coding unit (CU). In other words, video encoder 200 may determine that chroma components are present for the LMCS for the CU. In such examples, video encoder 200 may signal a flag (e.g., lmcs_cs_present_flag (also known as aps_chroma_present_flag)) indicating the presence of chroma-related syntax elements (e.g., chroma components) based on the determination that the chroma-related syntax elements (e.g., chroma components) are present.

[0255] When a syntax element related to chroma in the LMCS for a CU is present, the video encoder 200 may encode the syntax element (e.g., lmcs_delta_abs_crs). The syntax element may indicate a value of a scaling parameter for determining chroma scaling in the LMCS. For example, lmcs_delta_abs_crs may indicate a lmcsDeltaCrs value (e.g., lmcs_delta_abs_crs is the absolute value of lmcsDeltaCrs), and lmcsDeltaCrs may be used to determine a scaling parameter for chroma scaling in the LMCS (e.g., ChromaScaleCoeff). The video encoder 200 may encode the syntax element in the LMCS syntax structure in an adaptive parameter set (APS).

[0256] The video encoder 200 may encode the chroma blocks of the CU based on the scaling parameters of the chroma scaling. For example, the video encoder 200 may determine a chroma prediction block, subtract the chroma prediction block from the chroma block to generate a residual block, scale the residual block based on the scaling parameters to generate a scaled residual block, and signal information indicating the scaled residual block.

[0257] In some examples, the video encoder 200 may encode (e.g., signal) a syntax element (e.g., lmcs_delta_abs_crs) only when a chroma-related syntax element is present. For example, the above CU may be considered a first CU. For a second CU, the video encoder 200 may determine that no LMCS chroma-related syntax element for the second CU exists. In this example, when no LMCS chroma-related syntax element for the second CU exists, the video encoder 200 may bypass encoding (e.g., including signaling) the syntax element. In other words, if no chroma component is present, the video encoder 200 may not signal lmcs_delta_abs_crs.

[0258] There may also be certain constraints on the video encoder 200. For example, the video encoder 200 may determine a value for a second syntax element (e.g., lmcs_delta_cw_prec_minus1) for specifying the number of bits of a third syntax element (e.g., lmcs_delta_abs_cw[i]) for representing the LMCS, which is signaled in the adaptation parameter set (APS) for the CU. The value of the second syntax element may be constrained to a range of 0 to a value based on the bit depth (e.g., a range of 0 to BitDepth−2).

[0259] As another example, the video encoder 200 may determine that a sequence parameter set (SPS) indicates that a cross-component adaptive loop filter (CCALF) is disabled. In such an example, when the SPS indicates that CCALF is disabled, the video encoder 200 may be constrained (e.g., configured to operate according to the constraint) to set at least one flag in an adaptation parameter set (APS) that specifies that cross-component filters for chroma components are not signaled.

[0260] In some examples, the video encoder 200 can be configured to determine that adaptive loop filtering (ALF) is disabled for one or more blocks, avoid setting an adaptive parameter set (APS) type to be equal to an APS type corresponding to the ALF based on the ALF being disabled for the one or more blocks, and signal information indicating that the ALF is disabled for the one or more blocks.

[0261] In some examples, the video encoder 200 can be configured to determine that a cross-component adaptive loop filter (CCALF) is disabled for one or more blocks, avoid signaling information indicating the CCALF for the one or more blocks based on the CCALF being disabled for the one or more blocks, and signal information indicating that the CCALF is disabled for the one or more blocks.

[0262] In some examples, video encoder 200 may be configured to determine whether to signal a syntax element indicating whether a chroma filter is signaled based on the chroma array type of the block.

[0263] In some examples, video encoder 200 may be configured to determine whether to signal information indicating luma mapping with chroma scaling (LMCS) based on the chroma array type, and signal information indicating the LMCS based on the determination.

[0264] In some examples, video encoder 200 can be configured to signal one or more syntax elements indicating whether luma map with chroma scaling (LMCS) information is present in a syntax structure, and signal LMCS information based on the one or more syntax elements.

[0265] Figure 4 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Figure 4 This is provided for purposes of explanation and is not intended to limit the techniques broadly illustrated and described in this disclosure. For purposes of explanation, this disclosure describes a video decoder 300 based on techniques of VVC (ITU-T H.266, under development) and HEVC (ITU-T H.265). However, the techniques of this disclosure may be performed by video coding devices configured for other video coding standards.

[0266] exist Figure 4 In the example of FIG, video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and DPB 314 may be implemented in one or more processors or processing circuits. For example, the units of video decoder 300 may be implemented as one or more circuits or logic elements as part of a hardware circuit or as part of a processor, ASIC, or FPGA. Furthermore, video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

[0267] The prediction processing unit 304 includes a motion compensation unit 316, an intra prediction unit 318, and a luma mapping with chroma scaling (LMCS) unit 319. The prediction processing unit 304 may include additional units for performing 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, and the like. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0268] CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of video decoder 300. The video data may be obtained, for example, from computer readable medium 110 ( Figure 1 ) obtains video data stored in CPB memory 320. CPB memory 320 may include a CPB that stores coded video data (e.g., syntax elements) from a coded video bitstream. Furthermore, CPB memory 320 may store video data other than syntax elements for decoded pictures, such as temporary data representing outputs from various units of video decoder 300. DPB 314 typically stores decoded pictures, which video decoder 300 may output and / or use as reference video data when decoding subsequent data or pictures in the coded video bitstream. CPB memory 320 and DPB 314 may be formed from any of a variety of memory devices, such as DRAM (including SDRAM), MRAM, RRAM, or other types of memory devices. CPB memory 320 and DPB 314 may be provided by the same memory device or separate memory devices. In various examples, CPB memory 320 may be on-chip with other components of video decoder 300 or off-chip relative to those components.

[0269] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) to retrieve the decoded video data. In other words, memory 120 may use CPB memory 320 to store the data described above. Similarly, when some or all of the functions of video decoder 300 are implemented in software to be executed by the processing circuitry of video decoder 300, memory 120 may store instructions to be executed by video decoder 300.

[0270] Figure 4 The various units shown in FIG3 are illustrated to aid in understanding the operations performed by the video decoder 300. These units may be implemented as fixed function circuits, programmable circuits, or a combination thereof. Figure 3 Similarly, fixed-function circuits refer to circuits that provide specific functions and are preset for the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functionality in the operations that can be performed. For example, a programmable circuit can run software or firmware so that the programmable circuit operates in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive parameters or output parameters), but the type of operations performed by the fixed-function circuits is generally immutable. In some examples, one or more of the units can be different circuit blocks (fixed-function or programmable), and in some examples, one or more of the units can be integrated circuits.

[0271] The video decoder 300 may include an ALU, an EFU, digital circuits, analog circuits, and / or a programmable core formed by programmable circuits. In examples where the operation of the video decoder 300 is performed by software running on the programmable circuits, on-chip or off-chip memory may store instructions (e.g., object code) for the software received and executed by the video decoder 300.

[0272] 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.

[0273] 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 the "current block").

[0274] The entropy decoding unit 302 may entropy decode syntax elements defining the quantized transform coefficients of the quantized transform coefficient block and transform information, such as a quantization parameter (QP) and / or (one or more) transform mode indications. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, similarly, a degree of inverse quantization to be applied by the inverse quantization unit 306. The inverse quantization unit 306 may, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thereby form a transform coefficient block comprising the transform coefficients.

[0275] After inverse quantization unit 306 forms a transform coefficient block, inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0276] 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 may generate a prediction block. In this case, the prediction information syntax element may 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 may generally generate a prediction block in the same manner as described with respect to motion compensation unit 224 ( Figure 3 ) is performed in a manner substantially similar to that described in the foregoing.

[0277] 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 generate a prediction block in the same manner as 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.

[0278] The LMCS unit 319 can be configured to perform operations of the LMCS video decoding tool. For example, the LMCS unit 319 can receive a mapped luma residual block. The LMCS unit 319 can also generate a mapped prediction block. For example, the LMCS unit 319 can perform a mapping operation on the prediction block generated by the motion compensation unit 316 or the intra prediction unit 318 to generate a mapped prediction block. The reconstruction unit 310 can add the mapped prediction block to the mapped luma residual block to generate a mapped luma block. The LMCS unit 319 can perform inverse mapping to generate a luma block.

[0279] For chroma, the LMCS unit 319 may receive a scaled residual block (e.g., from the inverse transform processing unit 308). The LMCS unit 319 may scale (e.g., inversely scale) the scaled residual block with a scaling parameter to generate a chroma residual block. The reconstruction unit 310 may add the chroma residual block to the chroma prediction block to reconstruct the chroma block.

[0280] 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.

[0281] The filter unit 312 may perform one or more filter 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 need not be performed in all examples.

[0282] The video decoder 300 may store the reconstructed block in the DPB 314. For example, in an example where the operation of the filter unit 312 is not performed, the reconstruction unit 310 may store the reconstructed block to the DPB 314. In an example where the operation of the filter unit 312 is performed, the filter unit 312 may store the filtered reconstructed block to the DPB 314. As described above, the DPB 314 may provide reference information to the prediction processing unit 304, such as samples of the current picture for intra-frame prediction and previously decoded pictures for subsequent motion compensation. In addition, the video decoder 300 may output a decoded picture (e.g., a decoded video) from the DPB 314 for display on a display device such as a video processor. Figure 1 subsequent presentation on the display device 118).

[0283] In this manner, video decoder 300 represents an example of a video decoding device that includes memory configured to store video data and one or more processing units implemented in circuitry and configured to perform the example techniques described in this disclosure.

[0284] As described above, the video decoder 300 can be configured to perform LMCS. The video decoder 300 can be configured to parse syntax elements that the video encoder 200 signals to perform LMCS. For example, the video decoder 300 can be configured to parse and decode syntax elements that determine scaling parameters that the video decoder 300 will use for chroma scaling. However, there may be situations where a CU has no chroma components but LMCS is enabled for that CU. In such situations, unnecessary or erroneous signaling may occur, such as where the video encoder 200 signals syntax elements despite the absence of chroma components and the video decoder 300 parses the syntax elements to determine scaling parameters for chroma scaling.

[0285] As described above, when ChromaArrayType is equal to zero, there may be no chroma components. ChromaArrayType being equal to zero may mean that the color format is monochrome (eg, black and white).

[0286] According to one or more examples, the video decoder 300 may determine that chroma-related syntax elements (e.g., chroma components) are present for a luma map with chroma scaling (LMCS) for a coding unit (CU). For example, the video decoder 300 may parse a flag (e.g., lmcs_cs_present_flag (also known as aps_chroma_present_flag)) indicating that chroma-related syntax elements are present (e.g., chroma components are present). The video decoder 300 may determine that chroma-related syntax elements (e.g., chroma components) are present based on the flag.

[0287] When a LMCS chroma-related syntax element exists for a CU, the video decoder 300 may decode the syntax element (e.g., lmcs_delta_abs_crs). The syntax element may indicate a value for a scaling parameter used to determine chroma scaling in the LMCS. For example, lmcs_delta_abs_crs may indicate a lmcsDeltaCrs value (e.g., lmcs_delta_abs_crs is the absolute value of lmcsDeltaCrs), and lmcsDeltaCrs may be used to determine a scaling parameter (e.g., ChromaScaleCoeff) for chroma scaling in the LMCS. The video decoder 300 may decode the syntax element in the LMCS syntax structure in an adaptive parameter set (APS).

[0288] The video decoder 300 may decode the chroma block of the CU based on the scaling parameters of the chroma scaling. For example, the video decoder 300 may inversely scale the scaled residual chroma block based on the scaling parameters to generate a residual chroma block, determine a chroma prediction block, and add the residual chroma block to the chroma prediction block to reconstruct the chroma block.

[0289] In some examples, the video decoder 300 may decode (e.g., parse) a syntax element (e.g., lmcs_delta_abs_crs) based on a determination that a chroma-related syntax element is present. For example, the CU described above may be considered a first CU. For a second CU, the video decoder 300 may determine that a chroma-related syntax element is not present for the LMCS for the second CU. In this example, when a chroma-related syntax element is not present for the LMCS for the second CU, the video decoder 300 may bypass decoding (e.g., including parsing) of the syntax element. In other words, if a chroma component is not present, the video decoder 300 may not parse lmcs_delta_abs_crs.

[0290] In some examples, the video decoder 300 can be configured to bypass parsing of information indicating an adaptation parameter set (APS) type for adaptive loop filtering (ALF) for one or more blocks based on ALF being disabled for the one or more blocks, and reconstruct the one or more blocks.

[0291] In some examples, the video decoder 300 may be configured to bypass parsing of information indicating a cross-component adaptive loop filter (CCALF) for one or more blocks based on the CCALF being disabled for the one or more blocks and reconstruct the one or more blocks.

[0292] In some examples, video decoder 300 may be configured to determine whether to parse syntax elements indicating whether chroma filters are signaled based on the chroma array type of the block, and reconstruct the block.

[0293] In some examples, the video decoder 300 may be configured to determine whether to parse information indicating luma mapping with chroma scaling (LMCS) based on the chroma array type, and perform LMCS based on whether the information indicating LMCS is parsed.

[0294] In some examples, video decoder 300 may be configured to receive one or more syntax elements indicating whether luma map with chroma scaling (LMCS) information is present in a syntax structure, and parse the LMCS information based on the one or more syntax elements.

[0295] Figure 5 is a flowchart illustrating an example method for coding video data. Figure 5 The examples are described with respect to a video decoder (e.g., video encoder 200 or video decoder 300). The video decoder can be part of a processing circuit (e.g., fixed-function or programmable). For example, a memory can be configured to store video data, and examples of memory include memory 106, memory 120, video data memory 230, DPB 218, CPB memory 320, DPB 314, or some other memory. Processing circuitry (e.g., processing circuitry of a video decoder) can be coupled to the memory and configured to perform the example techniques.

[0296] The video decoder may determine whether a chroma-related syntax element of the video data exists for a luma map with chroma scaling (LMCS) for a coding unit (CU) of the video data (350). For example, the video encoder 200 may signal a flag indicating the presence of the chroma-related syntax element (e.g., lmcs_cs_present_flag (also known as aps_chroma_present_flag)) based on the determination of the presence of the chroma-related syntax element. The video decoder 300 may parse the flag indicating the presence of the chroma-related syntax element (e.g., lmcs_cs_present_flag (also known as aps_chroma_present_flag)). In this example, the video decoder 300 may determine whether the chroma-related syntax element exists based on the flag. As described above, the presence or absence of the chroma-related syntax element may indicate the presence or absence of the chroma component.

[0297] The video coder may decode a syntax element for the video data when an LMCS chroma-related syntax element is present for the CU (352). The syntax element indicates a value (e.g., lmcsDeltaCrs) of a scaling parameter (e.g., ChromaScaleCoeff) used to determine chroma scaling in the LMCS. For example, the syntax element specifies an absolute codeword value of a value (e.g., lmcsDeltaCrs) of a scaling parameter (e.g., ChromaScaleCoeff) used to determine chroma scaling. In some examples, the video coder may decode the syntax element in an LMCS syntax structure in an adaptation parameter set (APS).

[0298] The video decoder may decode 354 a chroma block of the video data of the CU based on the scaling parameters of the chroma scaling. For example, the video encoder 200 may determine a chroma prediction block, subtract the chroma prediction block from the chroma block to generate a residual block, scale the residual block based on the scaling parameters to generate a scaled residual block, and signal information indicating the scaled residual block. As another example, the video decoder 300 may inversely scale the scaled residual chroma block based on the scaling parameters to generate a residual chroma block, determine a chroma prediction block, and add the residual chroma block to the chroma prediction block to reconstruct the chroma block.

[0299] In some examples, the video encoder 200 may signal a syntax element (e.g., lmcs_delta_abs_crs) only when a chroma-related syntax element is present, and the video decoder 300 may parse the syntax element (e.g., lmcs_delta_abs_crs) based on a determination that the chroma-related syntax element is present. For example, in the above example, the CU may be considered the first CU.

[0300] The video encoder 200 may determine that no LMCS chroma-related syntax elements are present for the second CU and, in this example, may signal lmcs_cs_present_flag to indicate that no chroma components are present for the second CU. The video decoder 300 may parse lmcs_cs_present_flag for the second CU and determine that no chroma components are present for the second CU.

[0301] When the LMCS chroma-related syntax element for the second CU does not exist, the video encoder 200 can bypass encoding the syntax element (e.g., lmcs_delta_abs_crs) and the video decoder 300 can bypass decoding the syntax element (e.g., lmcs_delta_abs_crs). For example, the above table provides:

[0302] if(lmcs_cs_present_flag){

[0303] lmcs_delta_abs_crs.

[0304] According to the above code, the video encoder 200 signals, and the video decoder 300 parses, the lmcs_delta_abs_crs syntax element only when lmcs_cs_present_flag is true (i.e., chroma components are present). However, if lmcs_cs_preseng_flag is false (i.e., chroma components are not present), the video encoder 200 bypasses signaling (e.g., does not signal), and the video decoder 300 bypasses parsing (e.g., does not parse) the lmcs_delta_abs_crs syntax element. Therefore, the video encoder 200 signals, and the video decoder 300 parses, the lmcs_delta_abs_crs syntax element only when chroma components are present.

[0305] The following describes example techniques according to the present disclosure. The example techniques can be utilized individually or in any combination.

[0306] Clause 1A. A method of decoding video data, the method comprising: bypassing parsing of information indicating an adaptation parameter set (APS) type for adaptive loop filtering (ALF) for one or more blocks based on the ALF being disabled for the one or more blocks, and reconstructing the one or more blocks.

[0307] Clause 2A. The method of Clause 1A, further comprising determining that ALF is disabled for the one or more blocks based on signaling received in a parameter set.

[0308] Clause 3A. A method of decoding video data, the method comprising: bypassing parsing of information indicating a cross-component adaptive loop filter (CCALF) for one or more blocks based on the CCALF being disabled for the one or more blocks, and reconstructing the one or more blocks.

[0309] Clause 4A. The method of Clause 3A, further comprising determining that CCALF is disabled for the one or more blocks based on signaling received in a parameter set.

[0310] Clause 5A. The method of any of clauses 3A and 4A, wherein bypassing parsing comprises bypassing parsing in an adaptive loop filter (ALF) adaptation parameter set (APS).

[0311] Clause 6A. The method of any of clauses 3A-5A, further comprising determining whether to parse a syntax element indicating whether cross-component filters for chroma components are signaled based on at least one of a syntax element indicating whether CCALF is enabled or a syntax element indicating a chroma array type.

[0312] Clause 7A. A method of decoding, the method comprising: determining whether to parse a syntax element indicating whether a chroma filter is signaled based on a chroma array type of a block, and reconstructing the block.

[0313] Clause 8A. A method of decoding video data, the method comprising: determining whether to parse information indicating a luma map with chroma scaling (LMCS) based on a chroma array type, and performing the LMCS based on whether the information indicating the LMCS is parsed.

[0314] Clause 9A. A method of decoding video data, the method comprising: receiving one or more syntax elements indicating whether luma map with chroma scaling (LMCS) information is present in a syntax structure, and parsing the LMCS information based on the one or more syntax elements.

[0315] Clause 10A. A method of encoding video data, the method comprising: determining that adaptive loop filtering (ALF) is disabled for one or more blocks, avoiding setting an adaptation parameter set (APS) type to be equal to an APS type corresponding to the ALF based on the ALF being disabled for the one or more blocks, and signaling information indicating that the ALF is disabled for the one or more blocks.

[0316] Clause 11A. A method of encoding video data, the method comprising: determining that a cross-component adaptive loop filter (CCALF) is disabled for one or more blocks, avoiding signaling information indicating the CCALF for the one or more blocks based on the CCALF being disabled for the one or more blocks, and signaling information indicating that the CCALF is disabled for the one or more blocks.

[0317] Clause 12A. The method of Clause 11A, wherein avoiding signaling comprises avoiding signaling in an adaptive loop filter (ALF) adaptation parameter set (APS).

[0318] Clause 13A. A method of encoding, the method comprising: determining whether to signal a syntax element indicating whether a chroma filter is signaled based on a chroma array type of a block.

[0319] Clause 14A. A method of encoding video data, the method comprising: determining whether to signal information indicating a luma map with chroma scaling (LMCS) based on a chroma array type, and signaling information indicating the LMCS based on the determination.

[0320] Clause 15A. A method of encoding video data, the method comprising: signaling one or more syntax elements indicating whether luma map with chroma scaling (LMCS) information is present in a syntax structure, and signaling LMCS information based on the one or more syntax elements.

[0321] Clause 16A. A method of decoding video data, the method comprising any one or any combination of clauses 1A-9A.

[0322] Clause 17A. A method of encoding video data, the method comprising any one or any combination of clauses 10A-15A.

[0323] Clause 18A. An apparatus for decoding video data, the apparatus comprising: a memory configured to store the video data, and processing circuitry configured to perform the method of Clause 16A.

[0324] Clause 19A. An apparatus for encoding video data, the apparatus comprising: a memory configured to store the video data, and processing circuitry configured to perform the method of Clause 17A.

[0325] Clause 20A. The apparatus of any of Clauses 18A and 19A, further comprising a display configured to display the decoded video data.

[0326] Clause 21A. The device of any of clauses 18A-20A, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0327] Clause 22A. The apparatus of any of clauses 18A-21A, wherein the apparatus comprises a video decoder.

[0328] Clause 23A. The apparatus of any of clauses 18A-22A, wherein the apparatus comprises a video encoder.

[0329] Clause 24A. A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to perform the method of any of clauses 16A or 17A.

[0330] Clause 25A. An apparatus for decoding video data, the apparatus comprising means for performing the method of either clause 16A or 17A.

[0331] Clause 1B. A method of decoding video data, the method comprising: determining the presence of a chroma-related syntax element of the video data for a luma map with chroma scaling (LMCS) for a decoding unit (CU) of the video data, decoding a syntax element of the video data when the chroma-related syntax element is present for the LMCS for the CU, the syntax element indicating a value of a scaling parameter used to determine the chroma scaling in the LMCS, and decoding a chroma block of the CU based on the scaling parameter of the chroma scaling.

[0332] Clause 2B. The method of Clause 1B, further comprising: parsing a flag indicating the presence of a chroma-related syntax element, wherein determining the presence of the chroma-related syntax element comprises determining the presence of the chroma-related syntax element based on the flag.

[0333] Clause 3B. The method of any of clauses 1B and 2B, further comprising: based on the determination that chroma-related syntax elements are present, signaling a flag indicating that chroma-related syntax elements are present.

[0334] Clause 4B. The method of any of clauses 1B-3B, wherein coding the syntax element comprises parsing the syntax element based on the determination that a chroma-related syntax element exists.

[0335] Clause 5B. The method of any of clauses 1B-4B, wherein coding the syntax element comprises signaling the syntax element only if the chroma-related syntax element is present.

[0336] Clause 6B. The method of any of clauses 1B-5B, wherein coding the syntax element comprises coding the syntax element in a LMCS syntax structure in an adaptation parameter set (APS).

[0337] Clause 7B. The method of any of clauses 1B-6B, wherein the syntax element specifies an absolute codeword value for determining the value of the scaling parameter for chroma scaling.

[0338] Clause 8B. A method as described in any of clauses 1B-7B, wherein the syntax elements include a first syntax element, and wherein the decoding method includes an encoding method, the method further comprising determining a value of a second syntax element for specifying a number of bits for a third syntax element representing an LMCS, the second syntax element being signaled in an adaptive parameter set (APS) for the CU, wherein the value of the second syntax element is constrained to a range of 0 to a value based on the bit depth.

[0339] Clause 9B. A method as described in any of clauses 1B-8B, wherein the decoding method includes the encoding method, the method further comprising: determining that a sequence parameter set (SPS) indicates that a cross-component adaptive loop filter (CCALF) is disabled, and setting at least one flag in an adaptive parameter set (APS) to specify that the cross-component filter for the chroma component is not signaled when the SPS indicates that the CCALF is disabled.

[0340] Clause 10B. A method as described in any of clauses 1B-9B, wherein the CU is a first CU, the method further comprising: determining that a chroma-related syntax element for the LMCS for a second CU does not exist, and bypassing decoding of the syntax element when the chroma-related syntax element for the LMCS for the second CU does not exist.

[0341] Clause 11B. The method of clauses 1B-10B, wherein coding the chroma block of the CU based on the scaling parameters of the chroma scaling comprises decoding the chroma block, and wherein decoding the chroma block comprises: inversely scaling the scaled residual chroma block based on the scaling parameters to generate a residual chroma block, determining a chroma prediction block, and adding the residual chroma block to the chroma prediction block to reconstruct the chroma block.

[0342] Clause 12B. A method as described in any of clauses 1B-11B, wherein decoding the chroma block based on the scaling parameter of the chroma scaling includes encoding the chroma block, and wherein encoding the chroma block includes: determining a chroma prediction block, subtracting the chroma prediction block from the chroma block to generate a residual block, scaling the residual block based on the scaling parameter to generate a scaled residual block, and signaling information indicating the scaled residual block.

[0343] Item 13B. A device for decoding video data, the device comprising a memory configured to store the video data and a processing circuit, the processing circuit being configured to determine the presence of a chroma-related syntax element of the video data for a luma map with chroma scaling (LMCS) for a decoding unit (CU) of the video data, decode a syntax element of the video data when the chroma-related syntax element is present for the LMCS for the CU, the syntax element indicating a value of a scaling parameter for determining chroma scaling in the LMCS, and decode a chroma block of the CU based on the scaling parameter of the chroma scaling.

[0344] Clause 14B. The apparatus of clause 13B, wherein the processing circuitry is configured to parse a flag indicating the presence of a chroma-related syntax element, wherein to determine the presence of the chroma-related syntax element, the processing circuitry is configured to determine the presence of the chroma-related syntax element based on the flag.

[0345] Clause 15B. The apparatus of any of clauses 13B and 14B, wherein the processing circuitry is configured to signal a flag indicating the presence of chroma-related syntax elements based on the determination that chroma-related syntax elements are present.

[0346] Clause 16B. The apparatus of any of clauses 13B-15B, wherein to decode the syntax element, the processing circuitry is configured to parse the syntax element based on the determination that a chroma-related syntax element exists.

[0347] Clause 17B. The apparatus of any of clauses 13B-16B, wherein to decode the syntax element, the processing circuitry is configured to signal the syntax element only if the chroma-related syntax element is present.

[0348] Clause 18B. The apparatus of any of clauses 13B-17B, wherein to code the syntax element, the processing circuitry is configured to code the syntax element in a LMCS syntax structure in an adaptive parameter set (APS).

[0349] Clause 19B. The apparatus of any of clauses 13B-18B, wherein the syntax element specifies an absolute codeword value for determining the value of the scaling parameter for chroma scaling.

[0350] Clause 20B. An apparatus as described in any of clauses 13B-19B, wherein the syntax elements include a first syntax element, and wherein the processing circuit is configured to determine a value of a second syntax element for specifying a number of bits of a third syntax element for representing an LMCS, the second syntax element being signaled in an adaptation parameter set (APS) for the CU, wherein the value of the second syntax element is constrained to a range of 0 to a value based on the bit depth.

[0351] Clause 21B. An apparatus as described in any of clauses 13B-20B, wherein the processing circuit is configured to determine that a sequence parameter set (SPS) indicates that a cross-component adaptive loop filter (CCALF) is disabled, and to set at least one flag in an adaptive parameter set (APS) that specifies that a cross-component filter for a chroma component is not signaled when the SPS indicates that the CCALF is disabled.

[0352] Clause 22B. An apparatus as described in any of clauses 13B-21B, wherein the CU is a first CU, and wherein the processing circuit is configured to determine that a chroma-related syntax element for the LMCS for a second CU is not present, and to bypass decoding of the syntax element when the chroma-related syntax element for the LMCS for the second CU is not present.

[0353] Clause 23B. An apparatus as described in any of clauses 13B-22B, wherein to decode the chroma block of the CU based on the scaling parameters of the chroma scaling, the processing circuit is configured to decode the chroma block, and wherein to decode the chroma block, the processing circuit is configured to inverse scale the scaled residual chroma block based on the scaling parameters to generate a residual chroma block, determine a chroma prediction block, and add the residual chroma block to the chroma prediction block to reconstruct the chroma block.

[0354] Clause 24B. An apparatus as described in any of clauses 13B-23B, wherein to decode the chroma block based on the scaling parameter of the chroma scaling, the processing circuit is configured to encode the chroma block, and wherein to encode the chroma block, the processing circuit is configured to determine a chroma prediction block, subtract the chroma prediction block from the chroma block to generate a residual block, scale the residual block based on the scaling parameter to generate a scaled residual block, and signal information indicating the scaled residual block.

[0355] Clause 25B. The device of any of clauses 13B-24B, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0356] Clause 26B. A computer-readable storage medium having instructions stored thereon that, when executed, cause one or more processors to: determine a luma map with chroma scaling (LMCS) for a coding unit (CU) for video data, a chroma-related syntax element of the video data being present, decode a syntax element of the video data when the chroma-related syntax element is present for the LMCS for the CU, the syntax element indicating a value of a scaling parameter used to determine chroma scaling in the LMCS, and decode a chroma block of the CU based on the scaling parameter of the chroma scaling.

[0357] Clause 27B. The computer-readable storage medium as described in Clause 26B further includes instructions that cause the one or more processors to perform at least one of the following operations: parsing a flag indicating the presence of a chroma-related syntax element or based on the determination of the presence of a chroma-related syntax element, signaling a flag indicating the presence of a chroma-related syntax element, wherein the instructions that cause the one or more processors to determine the presence of the chroma-related syntax element include instructions that cause the one or more processors to determine the presence of the chroma-related syntax element based on the flag.

[0358] Clause 28B. A computer-readable storage medium as described in any of clauses 26B and 27B, wherein the instructions that cause the one or more processors to decode the syntax element include instructions that cause the one or more processors to perform at least one of the following operations: parse the syntax element based on the determination that a chroma-related syntax element exists, or signal the syntax element only when the chroma-related syntax element exists.

[0359] Clause 29B. A computer-readable storage medium as described in any of clauses 26B-28B, wherein the instructions to cause one or more processors to decode the syntax element include instructions to cause the one or more processors to decode the syntax element in an LMCS syntax structure in an adaptive parameter set (APS), and wherein the syntax element specifies an absolute codeword value for determining the value of the scaling parameter for chroma scaling.

[0360] Item 30B. An apparatus for decoding video data, the apparatus comprising: means for determining the presence of a chroma-related syntax element of the video data for a luma map with chroma scaling (LMCS) for a decoding unit (CU) of the video data, means for decoding a syntax element of the video data when the chroma-related syntax element exists for the LMCS for the CU, the syntax element indicating a value of a scaling parameter used to determine the chroma scaling in the LMCS, and means for decoding a chroma block of the CU based on the scaling parameter of the chroma scaling.

[0361] It should be appreciated that, depending on the example, certain actions or events of any of the techniques described herein may be performed in a different sequence, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary for practice of the techniques). Furthermore, in some examples, actions or events may be performed in parallel, such as through multithreading, interrupt handling, or multiple processors, rather than sequentially.

[0362] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over a computer-readable medium as one or more instructions or code and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media corresponding to tangible media (such as data storage media); or communication media, including any media that facilitates the transfer of a computer program from one place to another, for example, according to a communication protocol. In this manner, computer-readable media may generally correspond to (1) a non-transitory tangible computer-readable storage medium or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code, and / or data structures for implementing the techniques described in this disclosure. A computer program product may include computer-readable media.

[0363] As an 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 that 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, 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 transient media, but are directed to non-transient, tangible storage media. Disks and optical disks used herein include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks and blue-ray discs, wherein disks typically reproduce data magnetically, while optical discs reproduce data optically with lasers. The above combination should also be included in the scope of computer-readable media.

[0364] 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. Accordingly, the terms "processor" and "processing circuitry" as used herein may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a combined codec. Furthermore, these techniques may be fully implemented in one or more circuits or logic elements.

[0365] The techniques of the present disclosure may be implemented in a variety of devices or apparatuses, including wireless handheld devices, integrated circuits (ICs), or IC sets (e.g., chipsets). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily need to be implemented by different hardware units. More specifically, 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) in combination with appropriate software and / or firmware.

[0366] Various examples have been described. These and other examples are within the scope of the following claims.< / add>

Claims

1. A method for decoding video data, the method comprising: a parsing flag indicating whether, for a luma map with chroma scaling LMCS for a coding unit CU of the video data, a chroma-related syntax element of the video data exists; Parsing syntax elements of the video data based on the flag indicating that there are chroma-related syntax elements for the LMCS of the CU, the syntax elements indicating values ​​of scaling parameters for determining chroma scaling in the LMCS, and decoding chroma blocks of the CU based on the scaling parameters of the chroma scaling; as well as Based on the flag indicating that no chroma-related syntax elements exist for the LMCS of the CU, parsing syntax elements of the video data is avoided. 2 . The method of claim 1 , wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS comprises a syntax element in an LMCS syntax structure in an adaptation parameter set (APS). 3 . The method of claim 1 , wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS specifies an absolute codeword value for determining the value of the scaling parameter for chroma scaling.

4. The method of claim 1 , wherein decoding the chroma block of the CU based on the scaling parameter of chroma scaling comprises: inversely scaling the scaled residual chroma block based on the scaling parameter to generate a residual chroma block; determining a chroma prediction block; as well as The residual chroma block is added to the chroma prediction block to reconstruct the chroma block.

5. A method for encoding video data, the method comprising: Determining whether a chroma sample exists for a coding unit CU of the video data; signaling a flag configured to indicate whether a chroma-related syntax element of the video data exists for a luma map LMCS with chroma scaling for a coding unit CU of the video data; Based on determining that chroma samples exist for the CU, signaling a syntax element of the video data, wherein the syntax element indicates a value of a scaling parameter for determining chroma scaling in an LMCS, and encoding a chroma block of the CU based on the scaling parameter for chroma scaling; as well as Based on determining that no chroma samples exist for the CU, signaling a syntax element indicating a value of a scaling parameter for determining chroma scaling in the LMCS is avoided. 6 . The method of claim 5 , wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS comprises a syntax element in an LMCS syntax structure in an adaptation parameter set (APS).

7. The method of claim 5, wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS specifies an absolute codeword value for determining the value of the scaling parameter for chroma scaling.

8. The method of claim 5 , wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS comprises a first syntax element, the method further comprising: Determine a value of a second syntax element for specifying a number of bits for representing a third syntax element of an LMCS, the second syntax element being signaled in an adaptation parameter set (APS) for the CU, wherein the value of the second syntax element is constrained to a range of 0 to a value based on the bit depth.

9. The method of claim 5, further comprising: Determining that a sequence parameter set SPS indicates that a cross-component adaptive loop filter CCALF is disabled; as well as When the SPS indicates that CCALF is disabled, at least one flag is set in the adaptation parameter set APS that specifies that cross-component filters for chroma components are not signaled.

10. The method of claim 5, wherein encoding the chroma blocks of the CU based on the scaling parameters of chroma scaling comprises: determining a chroma prediction block; subtracting the chroma prediction block from the chroma block to generate a residual block; scaling the residual block based on the scaling parameter to generate a scaled residual block; as well as Information indicating the scaled residual block is signaled.

11. A device for decoding video data, the device comprising: a memory configured to store the video data; as well as The processing circuit is configured to: a parsing flag indicating whether, for a luma map with chroma scaling LMCS for a coding unit CU of the video data, a chroma-related syntax element of the video data exists; Parsing syntax elements of the video data based on the flag indicating that there are chroma-related syntax elements for the LMCS of the CU, the syntax elements indicating values ​​of scaling parameters for determining chroma scaling in the LMCS, and decoding chroma blocks of the CU based on the scaling parameters of the chroma scaling; as well as Based on the flag indicating that no chroma-related syntax elements exist for the LMCS of the CU, parsing syntax elements of the video data is avoided. 12 . The apparatus of claim 11 , wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS comprises a syntax element in an LMCS syntax structure in an adaptation parameter set (APS).

13. The apparatus of claim 11, wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS specifies an absolute codeword value for determining the value of the scaling parameter for chroma scaling.

14. The apparatus of claim 11 , wherein to decode the chroma blocks of the CU based on the scaling parameters of chroma scaling, the processing circuit is configured to: inversely scaling the scaled residual chroma block based on the scaling parameter to generate a residual chroma block; determining a chroma prediction block; and The residual chroma block is added to the chroma prediction block to reconstruct the chroma block.

15. The device of claim 11, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

16. A device for encoding video data, the device comprising: a memory configured to store the video data; as well as The processing circuit is configured to: Determining whether a chroma sample exists for a coding unit CU of the video data; signaling a flag configured to indicate whether a chroma-related syntax element of the video data exists for a luma map LMCS with chroma scaling for a coding unit CU of the video data; Based on determining that chroma samples exist for the CU, signaling a syntax element of the video data, wherein the syntax element indicates a value of a scaling parameter for determining chroma scaling in an LMCS, and encoding a chroma block of the CU based on the scaling parameter for chroma scaling; as well as Based on determining that no chroma samples exist for the CU, signaling a syntax element indicating a value of a scaling parameter for determining chroma scaling in the LMCS is avoided. 17 . The apparatus of claim 16 , wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS comprises a syntax element in an LMCS syntax structure in an adaptation parameter set (APS).

18. The apparatus of claim 16, wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS specifies an absolute codeword value for determining the value of the scaling parameter for chroma scaling.

19. The apparatus of claim 16 , wherein the syntax element indicating a value of a scaling parameter for determining chroma scaling in LMCS comprises a first syntax element, and wherein the processing circuitry is configured to: Determine a value of a second syntax element for specifying a number of bits for representing a third syntax element of an LMCS, the second syntax element being signaled in an adaptation parameter set (APS) for the CU, wherein the value of the second syntax element is constrained to a range of 0 to a value based on the bit depth.

20. The apparatus of claim 16, wherein the processing circuit is configured to: determining that a sequence parameter set SPS indicates that a cross-component adaptive loop filter CCALF is disabled; and When the SPS indicates that CCALF is disabled, at least one flag is set in the adaptation parameter set APS that specifies that cross-component filters for chroma components are not signaled.

21. The apparatus of claim 16, wherein to encode the chroma blocks of the CU based on the scaling parameters of chroma scaling, the processing circuit is configured to: determining a chroma prediction block; subtracting the chroma prediction block from the chroma block to generate a residual block; scaling the residual block based on the scaling parameter to generate a scaled residual block; and Information indicating the scaled residual block is signaled.

22. The device of claim 16, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

23. A computer-readable storage medium having stored thereon instructions which, when executed, cause one or more processors to perform the method of any one of claims 1 to 10.

24. An apparatus for decoding video data, the apparatus comprising means for performing the steps of the method according to any one of claims 1 to 10.

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