Low frequency non-separable transform processing in video coding

Abstract

An example video codec includes a memory configured to store video data and one or more processors implemented in circuitry and communicatively coupled to the memory. The one or more processors are configured to determine that a current mode in which a current block of video data is coded is a single tree partitioning mode. Based on the current mode being the single tree partitioning mode, the one or more processors are configured to refrain from determining whether a non-DC coefficient exists for a chroma component of a transform unit (TU) for the current block and refrain from coding a low frequency non-separable transform (LFNST) index in response to refraining from determining whether the non-DC coefficient exists. The one or more processors are configured to code the current block in the single partitioning mode with LFNST disabled.

Description

[0001] This patent application claims priority to U.S. Application No. 17 / 210,918, filed March 24, 2021, and U.S. Provisional Patent Application No. 63 / 001,123, filed March 27, 2020, the entire contents of each of which are incorporated herein by reference. U.S. Application No. 17 / 210,918, filed March 24, 2021, claims the benefit of U.S. Provisional Patent Application No. 63 / 001,123, filed March 27, 2020. Technical Field

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

[0003] Digital video capabilities can be incorporated into a wide variety of devices, including digital televisions, digital live broadcast systems, wireless broadcasting systems, personal digital assistants (PDAs), laptops or desktop computers, tablets, e-book readers, digital cameras, digital recording devices, digital media players, video game devices, video game consoles, cellular or satellite radio phones (so-called "smartphones"), video conferencing equipment, video streaming devices, and more. Digital video devices implement video decoding technologies (such as those described in standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4 (Part 10, Advanced Video Decoding (AVC)), ITU-T H.265 / High Efficiency Video Decoding (HEVC), and extensions to such standards). By implementing such video decoding technologies, video devices can more efficiently send, receive, encode, decode, and / or store digital video information.

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

[0005] In summary, this disclosure describes techniques for Low Frequency Inseparable Transform (LFNST) decoding in video decoding. This disclosure describes techniques including removing unnecessary checks on non-DC coefficients used to determine the presence of chrominance components of a transform unit (TU) and removing unnecessary signaling that may be present in LFNST signaling. This removal of unnecessary checks and unnecessary signaling can improve (e.g., reduce) processing power and signaling overhead. The techniques of this disclosure can also be used in currently developing Multifunctional Video Decoding (VVC) standards or other advanced video codecs, including extensions to High Efficiency Video Decoding (HEVC). The techniques of this disclosure are applicable to next-generation video decoding standards and other video standards.

[0006] In one example, a method includes: determining that the current mode for decoding a current block of video data is a single-tree segmentation mode; based on the current mode being the single-tree segmentation mode, performing the following operations: avoiding determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; and in response to avoiding determining whether the non-DC coefficients exist, avoiding decoding the Low Frequency Inseparable Transform (LFNST) index; and decoding the current block in the single-tree segmentation mode with LFNST disabled.

[0007] In another example, a device includes: a memory configured to store video data; and one or more processors implemented in circuitry and communicatively coupled to the memory, the processors being configured to: determine that the current mode for decoding a current block of the video data is a single-tree segmentation mode; based on the current mode being the single-tree segmentation mode, to: avoid determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; and in response to avoiding determining whether the non-DC coefficients exist, avoid decoding the Low Frequency Inseparable Transform (LFNST) index; and decode the current block in the single-tree segmentation mode with LFNST disabled.

[0008] In another example, a computer-readable storage medium is encoded with instructions that, when executed, cause one or more processors to: determine that the current mode for decoding a current block of video data is a single-tree segmentation mode; based on the current mode being the single-tree segmentation mode, to: avoid determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; and in response to avoiding determining whether the non-DC coefficients exist, avoid decoding the Low Frequency Inseparable Transform (LFNST) index; and decode the current block in the single-tree segmentation mode with LFNST disabled.

[0009] In another example, an apparatus includes: a unit for determining that the current mode for decoding the current block of the video data is a single-tree segmentation mode; based on the current mode being the single-tree segmentation mode: a unit for avoiding determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; a unit for avoiding decoding the low-frequency non-separable transform (LFNST) index in response to avoiding determining whether the non-DC coefficients exist; and a unit for decoding the current block in the single-tree segmentation mode with LFNST disabled.

[0010] Details of one or more examples are set forth in the accompanying drawings and the following description. Other features, objects, and advantages will be apparent from the description, drawings, and claims. Attached Figure Description

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

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

[0013] Figure 3 This is a block diagram illustrating an example video encoder that can perform the techniques described in this disclosure.

[0014] Figure 4 This is a block diagram illustrating an example video decoder that can perform the techniques described in this disclosure.

[0015] Figure 5 This is a conceptual diagram illustrating the Low Frequency Inseparable Transform (LFNST) on a video encoder and video decoder.

[0016] Figure 6 This is a block diagram illustrating an example of the inverse transform technique when using LFNST.

[0017] Figure 7 It is a conceptual diagram of a 4x4 inverse LFNST used to reconstruct 16 intermediate coefficients from a list of 16 input coefficients.

[0018] Figure 8 It is a conceptual diagram of an 8x8 inverse LFNST used to reconstruct 48 intermediate coefficients from a list of 16 input coefficients.

[0019] Figure 9 This is a flowchart illustrating an example technique for LFNST decoding according to this disclosure.

[0020] Figure 10 This is a flowchart illustrating example technologies for video encoding.

[0021] Figure 11 This is a flowchart illustrating an example technology for video decoding. Detailed Implementation

[0022] In some techniques, a video encoder can check to determine whether the chroma components of a transform unit (TU) contain non-DC components, and when the chroma components of the transform unit contain non-DC coefficients in single-tree segmentation mode, signal the Low-Frequency Inseparable Transform (LFNST) index. However, in single-tree mode, LFNST can be disabled for the chroma components. According to the techniques of this disclosure, a video codec can avoid unnecessary checks and signaling by determining whether to use a single-tree segmentation mode. If a single-tree segmentation mode is used, the video codec can avoid checking whether the chroma components of the TU have non-DC coefficients, thus reducing processing power. Additionally, if a single-tree segmentation mode is used, and if no non-DC coefficients exist for the luminance components of the TU in single-tree segmentation mode, the video encoder can reduce signaling overhead by not signaling the LFNST index.

[0023] For example, a video encoder may not need to determine the presence of any non-DC coefficients for the chroma components of a block decoded using a single-tree segmentation mode, because LFNST is disabled for chroma in single-tree segmentation mode. Furthermore, even if non-DC coefficients for the chroma components exist, if no non-DC coefficients for the luma components of the block exist, it may not be necessary to signal the LFNST index, since LFNST can be disabled for chroma components in single-tree segmentation mode. Thus, this example technique reduces the signaling overhead and processing power required to check for the presence of non-DC coefficients in single-tree segmentation mode.

[0024] Figure 1This is a block diagram illustrating an example video encoding and decoding system 100 capable of performing the techniques of this disclosure. In summary, the techniques of this disclosure relate to decoding (encoding and / or decoding) video data. Typically, video data includes any data used for processing video. Therefore, video data can include raw, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata (e.g., signaling data).

[0025] like Figure 1 As shown, in this example, the encoding and decoding system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by the destination device 116. Specifically, the source device 102 provides the video data to the destination device 116 via a computer-readable medium 110. The source device 102 and the destination device 116 can include any of a wide variety of devices, including desktop computers, laptop computers, tablet computers, set-top boxes, mobile phones such as smartphones, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, etc. In some cases, the source device 102 and the destination device 116 may be equipped for wireless communication and may therefore be referred to as wireless communication devices.

[0026] exist Figure 1 In the example, source device 102 includes a video source 104, memory 106, video encoder 200, and output interface 108. Destination device 116 includes an input interface 122, video decoder 300, memory 120, and display device 118. According to this 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 LFNST inspection and signaling. 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 and destination devices 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 interface with an external display device, rather than including an integrated display device.

[0027] like Figure 1The encoding and decoding system 100 shown is merely an example. Typically, any digital video encoding and / or decoding device can perform techniques for LFNST checks and signaling. 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. In this disclosure, "decoding device" refers to a device that performs the decoding (e.g., encoding and / or decoding) of data. Therefore, video encoder 200 and video decoder 300 represent examples of decoding devices (specifically, video encoder and video decoder). In some examples, source device 102 and destination device 116 may operate in a substantially symmetrical manner, such that each of source device 102 and destination device 116 includes video encoding and decoding components. Therefore, encoding and decoding system 100 can support unidirectional or bidirectional video transmission between source device 102 and destination device 116, for example, for video streaming, video playback, video broadcasting, or video telephony.

[0028] Typically, video source 104 represents the source of video data (i.e., raw, unencoded video data) and provides a sequential series of pictures (also referred to as "frames") of the video data to video encoder 200, which encodes the data used for the pictures. Video source 104 of source device 102 may include video capture devices such as cameras, video archive units containing previously captured raw video, and / or video feed interfaces for receiving video from video content providers. Alternatively, video source 104 may generate computer graphics-based data as source video, or a combination of live video, archived video, and computer-generated video. In each case, video encoder 200 may encode the captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange the pictures from their received order (sometimes referred to as "display order") to a decoding order for decoding. Video encoder 200 may generate a bitstream comprising encoded video data. Then, the source device 102 can output the encoded video data to the computer-readable medium 110 via the output interface 108 so that it can be received and / or retrieved by, for example, the input interface 122 of the destination device 116.

[0029] The memory 106 of source device 102 and the memory 120 of destination device 116 represent general-purpose memory. In some examples, memories 106 and 120 may store raw video data, such as raw video from video source 104 and raw decoded video data from video decoder 300. Alternatively, memories 106 and 120 may store software instructions executable by, for example, video encoder 200 and video decoder 300 respectively. Although memories 106 and 120 are shown separately from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 may also include internal memory for functionally similar or equivalent purposes. Furthermore, memories 106 and 120 may 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 may be allocated as one or more video buffers, for example, to store raw, decoded, and / or encoded video data.

[0030] Computer-readable medium 110 can represent any type of medium or device capable of transmitting encoded video data from source device 102 to destination device 116. In one example, computer-readable medium 110 represents a communication medium that enables source device 102 to directly transmit encoded video data to destination device 116 in real time, for example, via a radio frequency network or a computer-based network. Output interface 108 can demodulate the transmitted signal including encoded video data according to a communication standard such as a wireless communication protocol, and input interface 122 can demodulate the received transmitted signal according to a communication standard such as a wireless communication protocol. The communication medium can include any wireless or wired communication medium, such as 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 a router, switch, base station, or any other device that may be useful for facilitating communication from source device 102 to destination device 116.

[0031] In some examples, source device 102 can output encoded data from output interface 108 to storage device 112. Similarly, destination device 116 can access 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 hard disk drives, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0032] In some examples, source device 102 may output 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. File server 114 may be any type of server device capable of storing encoded video data and sending such encoded video data to destination device 116. File server 114 may represent a web server (e.g., for a website), a file transfer protocol (FTP) server, a content delivery network device, or a network attached storage (NAS) device. Destination device 116 may access the encoded video data from file server 114 via any standard data connection (including an Internet connection). This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., a digital subscriber line (DSL), a cable modem, etc.), or a combination of both, suitable for accessing the encoded video data stored on file server 114. File server 114 and input interface 122 may be configured to operate according to streaming protocols, download protocols, or combinations thereof.

[0033] Output interface 108 and input interface 122 can represent a wireless transmitter / receiver, a modem, a wired networking component (e.g., an Ethernet card), a wireless communication component 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 can be configured to transmit data (such as encoded video data) according to cellular communication standards (such as 4G, 4G-LTE (Long Term Evolution), improved LTE, 5G, etc.). In some examples where output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 can be configured to operate according to other wireless standards (such as the IEEE 802.11 specification, the IEEE 802.15 specification (e.g., ZigBee)). TM Bluetooth TM The source device 102 and / or destination device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include an SoC device for performing the functions assigned to video encoder 200 and / or output interface 108, and destination device 116 may include an SoC device for performing the functions assigned to video decoder 300 and / or input interface 122.

[0034] The technology disclosed herein can be applied to video decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, internet streaming video transmission (such as HTTP-based Dynamic Adaptive Streaming (DASH)), digital video encoded onto data storage media, decoding digital video stored on data storage media, or other applications.

[0035] The input interface 122 of the destination device 116 receives an encoded video bitstream from a computer-readable medium 110 (e.g., a communication medium, storage device 112, file server 114, etc.). The encoded video bitstream may include signaling information defined by the video encoder 200, such as syntax elements (also used by the video decoder 300), which have values ​​describing the characteristics and / or processing of video blocks or other decoding units (e.g., slices, pictures, picture groups, sequences, etc.). The display device 118 displays a decoded picture of the decoded video data to the user. The display device 118 may represent any of a variety of display devices, such as a cathode ray tube (CRT), liquid crystal display (LCD), plasma display, organic light-emitting diode (OLED) display, or another type of display device.

[0036] Despite Figure 1 Not shown, but in some examples, the video encoder 200 and video decoder 300 may each be integrated with the audio encoder and / or audio decoder, and may include appropriate MUX-DEMUX units or other hardware and / or software to process multiplexed streams including both audio and video in a common data stream. Where applicable, the MUX-DEMUX unit may comply with the ITU H.223 multiplexer protocol or other protocols (such as User Datagram Protocol (UDP)).

[0037] The video encoder 200 and 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 implemented in part in software, the device may store instructions for the software in a suitable non-transitory computer-readable medium and use one or more processors to execute the instructions in hardware to perform the technology of this disclosure. Each of the video encoder 200 and video decoder 300 may be included in one or more encoders or decoders, and either encoder or decoder may be integrated as part of a combined encoder / decoder (CODEC) in the respective device. Devices including the video encoder 200 and / or video decoder 300 may include integrated circuits, microprocessors, and / or wireless communication devices (such as cellular phones).

[0038] The video encoder 200 and video decoder 300 can operate according to video decoding standards such as ITU-T H.265 (also known as the High Efficiency Video Coding (HEVC) standard) or extensions thereof such as multi-view and / or scalable video decoding extensions. Alternatively, the video encoder 200 and video decoder 300 can operate according to other proprietary or industry standards such as ITU-T H.266 (also known as Universal Video Coding (VVC)). The latest draft of the VVC standard is described in the following document: Bross et al., “Versatile Video Coding (Draft 8)”, Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11, 17th meeting: Brussels, Belgium, January 7-17, 2020, JVET-Q2001-vE (hereinafter referred to as “VVC Draft 8”). However, the technology of this disclosure is not limited to any particular decoding standard.

[0039] As described above, this disclosure describes techniques related to low-frequency non-separable transforms; however, the example techniques can also be applied to other types of transforms. In one or more examples, this disclosure describes techniques that can remove unnecessary checks and signaling in VVC Draft 8. Thus, the example techniques can provide technical solutions to technical problems arising from practical applications rooted in video decoding technology.

[0040] Typically, video encoder 200 and video decoder 300 can perform block-based decoding of images. The term "block" generally refers to a structure that includes data to be processed (e.g., encoded, decoded, or otherwise used during encoding and / or decoding). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. Typically, video encoder 200 and video decoder 300 can decode video data represented in YUV (e.g., Y, Cb, Cr) format. That is, instead of decoding the red, green, and blue (RGB) data used for images, video encoder 200 and video decoder 300 can decode both luminance and chrominance components, where chrominance components may include both red hue and blue hue chrominance components. In some examples, video encoder 200 converts the received RGB-formatted data to a YUV representation before encoding, and video decoder 300 converts the YUV representation to RGB format. Alternatively, preprocessing and post-processing units (not shown) can perform these conversions.

[0041] In summary, this disclosure may relate to the decoding (e.g., encoding and decoding) of images to include the process of encoding or decoding the data of an image. Similarly, this disclosure may relate to the decoding of blocks of an image to include the process of encoding or decoding the data used for the blocks (e.g., prediction and / or residual decoding). Encoded video bitstreams typically include a series of values ​​for representing decoding decisions (e.g., decoding modes) and syntax elements that segment the image into blocks. Therefore, references to decoding images or blocks should generally be understood as decoding the values ​​of the syntax elements used to form images or blocks.

[0042] HEVC defines various blocks, including decoding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (such as a video encoder 200) partitions a decoding tree unit (CTU) into CUs based on a quadtree structure. That is, 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. Nodes without child nodes can be called "leaf nodes," and the CU of such leaf nodes can include one or more PUs and / or one or more TUs. The video decoder can further partition PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents a partition of a TU. In HEVC, PUs represent inter-frame prediction data, while TUs represent residual data. CUs with intra-frame prediction include intra-frame prediction information, such as intra-frame mode indication.

[0043] As another example, video encoder 200 and video decoder 300 can be configured to operate according to VVC. According to VVC, the video decoder (such as video encoder 200) segments the image into multiple decoding tree units (CTUs). Video encoder 200 can segment CTUs 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 segmentation types, such as the separation between CUs, PUs, and TUs in HEVC. The QTBT structure includes two levels: a first level segmented according to quadtree segmentation and a second level segmented according to binary tree segmentation. The root node of the QTBT structure corresponds to a CTU. The leaf nodes of the binary tree correspond to decoding units (CUs).

[0044] 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) partitioning (also known as triplet tree (TT)) partitioning. A ternary tree or triplet tree partitioning is a partition in which a block is divided into three sub-blocks. In some examples, a ternary tree or triplet tree partitioning divides a block into three sub-blocks without partitioning the original block through a center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0045] In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT or MTT structure to represent each of the luma and chroma components, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luma component and another QTBT / MTT structure for the two chroma components (or two QTBT / MTT structures for the respective chroma components).

[0046] The video encoder 200 and video decoder 300 can be configured to use quadtree segmentation, QTBT segmentation, MTT segmentation, or other segmentation structures based on HEVC. For illustrative purposes, a description of the techniques of this disclosure is given with respect to QTBT segmentation. However, it should be understood that the techniques of this disclosure can also be applied to video decoders configured to use quadtree segmentation or other types of segmentation.

[0047] In some examples, a CTU includes a decoded tree block (CTB) of luminance samples, two corresponding CTBs of chrominance samples of an image with three sample arrays, or a CTB of samples of a monochrome image or an image decoded using three separate color planes and a syntax structure for decoding the samples. A CTB can be an N×N block of samples (for some value of N) such that dividing a component into a CTB is a partition. A component is an array or a single sample of one of the three arrays (one luminance and two chrominance) that make up an image in a 4:2:0, 4:2:2, or 4:4:4 color format, or an array or a single sample of an array or array that makes up an image in monochrome format. In some examples, a decoded block is an M×N block of samples (for some values ​​of M and N) such that dividing a CTB into a decoded block is a partition.

[0048] Blocks (e.g., CTUs or CUs) can be grouped in various ways within an image. As an example, a brick can refer to a rectangular area of ​​a CTU row within a specific tile in an image. A tile can be a rectangular area of ​​a CTU within a specific tile column and a specific tile row in an image. A tile column refers to a rectangular area of ​​a CTU with a height equal to the height of the image and a width specified by syntax elements (e.g., as in an image parameter set). A tile row refers to a rectangular area of ​​a CTU with a height specified by syntax elements (e.g., as in an image parameter set) and a width equal to the width of the image.

[0049] In some examples, a tile can be divided into multiple bricks, each of which may include one or more CTU rows within the tile. A tile that is not divided into multiple bricks can also be referred to as a brick. However, bricks that are a true subset of a tile may not be referred to as tiles.

[0050] The bricks in an image can also be arranged as slices. A slice can be an integer number of bricks in the image, which can be uniquely contained within a single Network Abstraction Layer (NAL) unit. In some examples, a slice consists of multiple complete tiles or a continuous sequence of complete bricks that contain only one tile.

[0051] This disclosure uses "NxN" and "N by N" interchangeably to refer to the sample size of a block (such as a CU or other video block) in the 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). Similarly, an NxNCU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. Samples in a CU can be arranged in rows and columns. Furthermore, a CU does not necessarily need to have the same number of samples in the horizontal direction as it does in the vertical direction. For example, a CU can include NxM samples, where M is not necessarily equal to N.

[0052] The video encoder 200 encodes video data for use in predicting and / or residual information, as well as other information, for the CU. The prediction information indicates how the CU will be predicted to form a prediction block for the CU. The residual information typically represents the sample-by-sample difference between a sample of the CU before encoding and the prediction block.

[0053] To predict the Cubic Frame (CU), the video encoder 200 typically forms prediction blocks for the CU using either inter-frame prediction or intra-frame prediction. Inter-frame prediction generally refers to predicting the CU based on data from previously decoded images, while intra-frame prediction generally refers to predicting the CU based on data from previously decoded images of the same frame. To perform inter-frame prediction, the video encoder 200 can generate prediction blocks using one or more motion vectors. The video encoder 200 can typically perform a motion search to identify, for example, a reference block that closely matches the CU in terms of the difference between the CU and a reference block. The video encoder 200 can calculate a difference metric using the sum of absolute differences (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared difference (MSD), or other such difference calculations to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 can use unidirectional or bidirectional prediction to predict the current CU.

[0054] 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 types of motion).

[0055] To perform intra-frame prediction, the video encoder 200 can select an intra-frame prediction mode to generate prediction blocks. Some examples of VVC provide sixty-seven intra-frame prediction modes, including various directional modes, as well as planar and DC modes. Typically, the video encoder 200 selects an intra-frame prediction mode that describes the samples of the current block (e.g., a block of a CU) to be predicted based on, which are the neighboring samples of the current block. Assuming that the video encoder 200 decodes the CTU and CU in raster scan order (from left to right, from top to bottom), such samples can typically be located above, to the upper left, or to the left of the current block within the same image.

[0056] The video encoder 200 encodes data representing the prediction mode used for the current block. For example, for inter-frame prediction modes, the video encoder 200 may encode data indicating which of the various available inter-frame prediction modes is used, as well as motion information for the corresponding mode. For unidirectional or bidirectional inter-frame prediction, for example, the video encoder 200 may use Advanced Motion Vector Prediction (AMVP) or merging modes to encode motion vectors. The video encoder 200 may use similar modes to encode motion vectors used for affine motion compensation modes.

[0057] Following a prediction, such as intra-frame or inter-frame prediction of a block, the video encoder 200 can compute residual data for that block. The residual data (such as a residual block) represents the sample-by-sample difference between the block and the prediction block used to form the block, which is 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 the transform domain rather than the 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. Additionally, the video encoder 200 can apply a secondary transform after the first transform, such as a Mode-dependent Inseparable Quadratic Transform (MDNSST), a Signal-dependent Transform, a Karhunen-Loeve Transform (KLT), etc. The video encoder 200 produces transform coefficients after applying one or more transforms.

[0058] As described above, after any transformation to produce transform coefficients, the video encoder 200 can perform quantization of the transform coefficients. Quantization generally refers to the process of quantizing the transform coefficients to reduce the amount of data used to represent them, 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 an n-bit value down 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 values ​​to be quantized.

[0059] After quantization, the video encoder 200 can scan the transform coefficients to generate a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scan can be designed to place higher-energy (and therefore lower-frequency) transform coefficients before the vector and lower-energy (and therefore higher-frequency) transform coefficients after the vector. In some examples, the video encoder 200 can utilize a predefined scan order to scan the quantized transform coefficients 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 an adaptive scan. 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 decoding (CABAC). The video encoder 200 can also entropy-encode the values ​​of syntax elements used to describe metadata associated with the encoded video data for use by the video decoder 300 when decoding the video data.

[0060] To perform CABAC, the video encoder 200 can assign context within a context model to the symbols to be transmitted. Context may involve, for example, whether the neighboring values ​​of a symbol are zero. Probability determination can be based on the context assigned to the symbols.

[0061] The video encoder 200 can also generate syntax data (such as block-based syntax data, image-based syntax data, and sequence-based syntax data) or other syntax data (such as sequence parameter sets (SPS), image parameter sets (PPS), or video parameter sets (VPS)) for the video decoder 300, for example, in image headers, block headers, or slice headers. Similarly, the video decoder 300 can decode such syntax data to determine how to decode the corresponding video data.

[0062] In this way, the video encoder 200 can generate a bitstream that includes encoded video data, such as syntax elements describing the segmentation of an image into blocks (e.g., CUs) and prediction and / or residual information for those blocks. Finally, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0063] Typically, the video decoder 300 performs the reverse process of the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 can use CABAC to decode the values ​​of syntax elements used for the bitstream in a manner substantially similar to, but reversed, the CABAC encoding process of the video encoder 200. Syntax elements can define segmentation information for segmenting images into CTUs, and for segmenting each CTU according to a corresponding segmentation structure (such as a QTBT structure) to define the CUs of the CTU. Syntax elements can also define prediction and residual information for blocks (e.g., CUs) of the video data.

[0064] The residual information can be represented, for example, by quantized transform coefficients. The video decoder 300 can inversely quantize and inverse transform the quantized transform coefficients of the block to reconstruct the residual block used for that block. The video decoder 300 uses a signal-informed prediction mode (intra-frame prediction or inter-frame prediction) and associated prediction information (e.g., motion information for inter-frame prediction) to form a prediction block for that block. The video decoder 300 can then combine the prediction block and the residual block (on a sample-by-sample basis) to reconstruct the original block. The video decoder 300 can perform additional processing, such as performing a deblocking process to reduce visual artifacts along the block boundaries.

[0065] As described above, according to some techniques, the video encoder 200 or video decoder 300 can check to determine whether the chroma component of the TU contains non-DC components, and when the chroma component of the transform unit contains non-DC coefficients in single-tree segmentation mode, it signals the LFNST index. However, in single-tree mode, LFNST can be disabled for the chroma component. According to the techniques of this disclosure, the video codec can avoid unnecessary checks and signaling by determining whether to use single-tree segmentation mode. If single-tree segmentation mode is used, the video encoder 200 or video decoder 300 can avoid checking whether the chroma component of the TU has non-DC coefficients to reduce processing power. In addition, if single-tree segmentation mode is used, if there are no non-DC coefficients for the luminance component of the TU in single-tree segmentation mode, the video encoder 200 can reduce signaling overhead by not signaling the LFNST index.

[0066] According to the technology of this disclosure, a method includes: determining that the current mode for decoding the current block of video data is a single-tree segmentation mode; based on the current mode being a single-tree segmentation mode, performing the following operations: avoiding determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) used for the current block; and in response to avoiding determining whether non-DC coefficients exist, avoiding decoding the low-frequency non-separable transform (LFNST) index; and decoding the current block in the single-tree segmentation mode with LFNST disabled.

[0067] According to the technology of this disclosure, an apparatus includes: a memory configured to store video data; and one or more processors implemented in a circuit and communicatively coupled to the memory, the one or more processors being configured to: determine that the current mode for decoding a current block of video data is a single-tree segmentation mode; based on the current mode being a single-tree segmentation mode, to: avoid determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; and in response to avoiding determining whether non-DC coefficients exist, avoid decoding the low-frequency non-separable transform (LFNST) index; and decode the current block in single-tree segmentation mode with LFNST disabled.

[0068] According to the technology of this disclosure, an apparatus includes: a unit for determining that the current mode for decoding the current block of video data is a single-tree segmentation mode; a unit for avoiding determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block based on the current mode being a single-tree segmentation mode; a unit for avoiding decoding the low-frequency non-separable transform (LFNST) index in response to avoiding determining whether non-DC coefficients exist; and a unit for decoding the current block in the single-tree segmentation mode with LFNST disabled.

[0069] According to the technology of this disclosure, a computer-readable storage medium is encoded with instructions that, when executed, cause one or more processors to: determine that the current mode for decoding the current block of video data is a single-tree segmentation mode; based on the current mode being a single-tree segmentation mode, perform the following operations: avoid determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; and in response to avoiding determining whether non-DC coefficients exist, avoid decoding the low-frequency non-separable transform (LFNST) index; and decode the current block in single-tree segmentation mode with LFNST disabled.

[0070] In summary, this disclosure may involve "signaling" certain information (such as syntax elements). The term "signaling" can generally refer to the transmission of values ​​for syntax elements and / or other data for decoding encoded video data. That is, video encoder 200 can signal values ​​for syntax elements in the bitstream. Generally, signaling refers to generating values ​​in the bitstream. As described above, source device 102 can transmit the bitstream to destination device 116 substantially in real time or not in real time (such as when syntax elements are stored in storage device 112 for later retrieval by destination device 116).

[0071] Figure 2A and Figure 2B This is a conceptual diagram illustrating an example Quadtree Binary Tree (QTBT) structure 130 and its corresponding Decoding 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 a horizontal split and 1 indicates a vertical split. For quadtree splits, since the quadtree node splits the block horizontally and vertically into four sub-blocks of equal size, there is no need to indicate the split type. Therefore, the video encoder 200 can encode the following, and the video decoder 300 can decode the following: syntax elements (such as split information) for the region tree level (i.e., solid lines) of the QTBT structure 130, and syntax elements (such as split information) for the prediction tree level (i.e., dashed lines) of the QTBT structure 130. The video encoder 200 can encode video data (such as prediction and transform data) for a CU represented by the terminal leaf nodes of the QTBT structure 130, while the video decoder 300 can decode the video data.

[0072] generally, Figure 2B The CTU 132 can be associated with parameters that define the size of the blocks corresponding to the nodes at the first and second levels of the QTBT structure 130. These parameters may include the CTU size (representing the size of the CTU 132 in units of samples), the minimum quadtree size (MinQTSize, which represents the minimum allowed size of the leaf nodes of the quadtree), the maximum binary tree size (MaxBTSize, which represents the maximum allowed size of the root node of the binary tree), the maximum binary tree depth (MaxBTDepth, which represents the maximum allowed depth of the binary tree), and the minimum binary tree size (MinBTSize, which represents the minimum allowed size of the leaf nodes of the binary tree).

[0073] The root node corresponding to the CTU in a QTBT structure can have four child nodes at the first level of the QTBT structure, each child node being partitioned according to a quadtree. That is, the nodes at the first level are either leaf nodes (without child nodes) or have four child nodes. An example of QTBT structure 130 represents such a node as including a parent node and child nodes with solid-line 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 partitioned by the corresponding binary tree. The binary tree partitioning of a node can be iterated until the nodes resulting from the partitioning reach the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). An example of QTBT structure 130 represents such a node as having dashed-line branches. The binary tree leaf nodes are called decoding units (CUs), which are used for prediction (e.g., intra-image or inter-image prediction) and transformation without any further partitioning. As discussed above, CUs can also be referred to as “video chunks” or “blocks”.

[0074] In one example of a QTBT segmentation structure, the CTU size is set to 128x128 (luminance sample and two corresponding 64x64 chrominance samples), MinQTSize is set to 16x16, MaxBTSize is set to 64x64, MinBTSize (for both width and height) is set to 4, and MaxBTDepth is set to 4. First, a quadtree segmentation is applied to the CTU to generate quadtree leaf nodes. Quadtree leaf nodes can have sizes ranging from 16x16 (i.e., MinQTSize) to 128x128 (i.e., the CTU size). If a quadtree leaf node is 128x128, it will not be further split by the binary tree because this size exceeds MaxBTSize (i.e., 64x64 in this example). Otherwise, the quadtree leaf node will be further split by the binary tree. Therefore, the quadtree leaf node is also used as the root node of the binary tree and has a binary tree depth of 0. When the depth of the binary tree reaches MaxBTDepth (4 in this example), further splitting is not allowed. When a binary tree node has a width equal to MinBTSize (4 in this example), it means that further vertical splitting is not allowed. Similarly, a binary tree node with a height equal to MinBTSize means that further horizontal splitting is not allowed for that binary tree node. As mentioned above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further splitting.

[0075] Figure 3 This is a block diagram illustrating an example video encoder 200 that can perform the techniques described in this disclosure. Figure 3This disclosure is provided for illustrative purposes and should not be construed as limiting the techniques illustrated and described in this disclosure in a general manner. For illustrative purposes, this disclosure describes a video encoder 200 based on VVC (ITU-T H.266 under development) and HEVC (ITU-T H.265) technologies. However, the techniques of this disclosure can be implemented by video encoding devices configured for other video decoding standards.

[0076] exist Figure 3 In the example, 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, mode selection unit 202, residual generation unit 204, transform processing unit 206, quantization unit 208, inverse quantization unit 210, inverse transform processing unit 212, reconstruction unit 214, filter unit 216, DPB 218, and entropy coding unit 220 can be implemented in one or more processors or in processing circuitry. For example, the units of the video encoder 200 can be implemented as one or more circuit or logic elements as part of hardware circuitry, or as part of a processor, ASIC, or FPGA. Furthermore, the video encoder 200 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0077] The video data storage device 230 can store video data to be encoded by the components of the video encoder 200. The video encoder 200 can obtain data from, for example, a video source 104 (…). Figure 1 The video data memory 230 receives video data stored in the video data memory 230. The DPB 218 can act as a reference picture memory, storing reference video data for use when the video encoder 200 predicts subsequent video data. The video data memory 230 and DPB 218 can be formed from 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 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 (as shown) with other components of the video encoder 200, or off-chip relative to those components.

[0078] In this disclosure, references to video data memory 230 should not be construed as limited to memory within video encoder 200 (unless so specifically described) or to memory outside video encoder 200 (unless so specifically described). Rather, references to video data memory 230 should be understood as reference memory storing video data received by video encoder 200 for encoding (e.g., video data for the current block to be encoded). Figure 1 The memory 106 can also provide temporary storage for the outputs from the various units of the video encoder 200.

[0079] It shows Figure 3 The various units help to understand the operations performed by the video encoder 200. These units can be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide a specific function and are pre-configured regarding the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functionality in terms of the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive or output parameters), but the type of operation performed by a fixed-function circuit is generally immutable. In some examples, one or more of these units can be different circuit blocks (fixed-function or programmable), and in some examples, one or more of these units can be integrated circuits.

[0080] The video encoder 200 may include an arithmetic logic unit (ALU), an essential function unit (EFU), digital circuitry, analog circuitry, and / or a programmable core, all formed by programmable circuitry. In an example where software executed by programmable circuitry is used to perform the operation of the video encoder 200, memory 106 ( Figure 1 The video encoder 200 may store instructions (e.g., object code) of the software received and executed by the video encoder 200, or another memory (not shown) within the video encoder 200 may store such instructions.

[0081] The video data storage unit 230 is configured to store the received video data. The video encoder 200 can retrieve images of the video data from the video data storage unit 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 storage unit 230 can be the raw video data to be encoded.

[0082] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra-frame prediction unit 226. The mode selection unit 202 may include additional functional units that perform video prediction based on other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

[0083] Mode selection unit 202 typically coordinates multiple coding paths to test combinations of coding parameters and the rate-distortion values ​​obtained for such combinations. Coding parameters may include segmenting the CTU into CUs, the prediction mode for the CUs, the transformation type of the residual data for the CUs, and the quantization parameters for the residual data for the CUs. Mode selection unit 202 can ultimately select a combination of coding parameters that yields a better rate-distortion value than other tested combinations.

[0084] The video encoder 200 can segment images retrieved from the video data storage 230 into a series of CTUs and encapsulate one or more CTUs within a slice. The mode selection unit 202 can segment the CTUs of the image according to a tree structure (such as the QTBT structure or quadtree structure of HEVC described above). As mentioned above, the video encoder 200 can form one or more CUs by segmenting CTUs according to a tree structure. Such CUs can also generally be referred to as "video blocks" or "blocks".

[0085] Typically, mode selection unit 202 also controls its components (e.g., motion estimation unit 222, motion compensation unit 224, and intra-prediction unit 226) to generate prediction blocks for the current block (e.g., the current CU, or the overlapping portion of PU and TU in HEVC). To perform inter-frame prediction for 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 ​​representing the similarity between a potential reference block and the current block, for example, based on sum of absolute differences (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared difference (MSD), etc. Motion estimation unit 222 may typically perform these calculations using sample-by-sample differences between the current block and the considered reference blocks. 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.

[0086] Motion estimation unit 222 can generate one or more motion vectors (MVs) that define the position of a reference block in a reference image relative to the position of the current block in the current image. Motion estimation unit 222 can then provide the motion vectors to motion compensation unit 224. For example, for unidirectional inter-frame prediction, motion estimation unit 222 can provide a single motion vector, while for bidirectional inter-frame prediction, motion estimation unit 222 can provide two motion vectors. Motion compensation unit 224 can then use the motion vectors to generate prediction blocks. For example, motion compensation unit 224 can use the motion vectors to retrieve data for the reference blocks. As another example, if the motion vectors have fractional-sample precision, motion compensation unit 224 can interpolate the values ​​used for the prediction blocks according to one or more interpolation filters. Furthermore, for bidirectional inter-frame prediction, motion compensation unit 224 can retrieve data for two reference blocks identified by corresponding motion vectors and combine the retrieved data, for example, by per-sample averaging or weighted averaging.

[0087] As another example, for intra-prediction or intra-prediction decoding, intra-prediction unit 226 can generate a prediction block based on samples adjacent to the current block. For example, in directional mode, intra-prediction unit 226 can typically mathematically combine the values ​​of adjacent samples and fill these calculated values ​​across the current block in a defined direction to generate a prediction block. As another example, in DC mode, intra-prediction unit 226 can calculate the average of the adjacent samples of the current block and generate a prediction block to include the obtained average for each sample of the prediction block.

[0088] Mode selection unit 202 provides a 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 and the prediction block from mode selection unit 202. Residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines the 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 decode-modulation (RDPCM). In some examples, one or more subtractor circuits performing binary subtraction may be used to form residual generation unit 204.

[0089] In the example where mode selection unit 202 divides a CU into PUs, each PU can be associated with a luma prediction unit and a corresponding chroma prediction unit. Video encoder 200 and video decoder 300 can support PUs of various sizes. As noted above, the size of a CU can refer to the size of the luma decoding block of the CU, while the size of a PU can refer to the size of the luma prediction unit of the PU. Assuming a particular CU size is 2Nx2N, video encoder 200 can support PU sizes of 2Nx2N or NxN for intra-frame prediction, and 2Nx2N, 2NxN, Nx2N, NxN, or similar symmetrical PU sizes for inter-frame prediction. Video encoder 200 and video decoder 300 can also support asymmetric segmentation for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter-frame prediction.

[0090] In an example where the mode selection unit 202 does not further divide the CU into PUs, each CU can be associated with a luminance decoding block and a corresponding chrominance decoding block. As mentioned above, the size of the CU can refer to the size of the luminance decoding block of the CU. The video encoder 200 and the video decoder 300 can support CU sizes of 2Nx2N, 2NxN, or Nx2N.

[0091] For other video decoding techniques (such as block-based copy mode decoding, affine mode decoding, and linear model (LM) mode decoding, mode selection unit 202 generates a prediction block for the current block being encoded via a corresponding unit associated with the decoding technique. In some examples (such as palette mode decoding), mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating how the block should be reconstructed based on the selected palette. In such a mode, mode selection unit 202 can provide these syntax elements to entropy coding unit 220 for encoding.

[0092] As described above, the residual generation unit 204 receives video data for the current block and the corresponding prediction block. Then, the residual generation unit 204 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.

[0093] 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 Discrete Cosine Transform (DCT), Direction Transform, Karhunen-Loeve Transform (KLT), or conceptually similar transforms to the residual block. In some examples, transform processing unit 206 may perform multiple transforms on the residual block, such as primary and secondary transforms (e.g., rotation transforms). In some examples, transform processing unit 206 may apply LFNST. In some examples, according to the techniques of this disclosure, when the current mode for decoding the current block of video data is a single-tree segmentation mode, transform processing unit 206 may avoid determining whether non-DC coefficients exist for the chrominance components of the TU used for the current block. In some examples, transform processing unit 206 does not apply any transforms to the residual block.

[0094] Quantization unit 208 can quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. Quantization unit 208 can quantize the transform coefficients of the transform coefficient block based on the quantization parameter (QP) value associated with the current block. Video encoder 200 (e.g., via mode selection unit 202) can 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 cause information loss, and therefore, the quantized transform coefficients may have lower accuracy compared to the original transform coefficients produced by transform processing unit 206.

[0095] The inverse quantization unit 210 and the inverse transform processing unit 212 can apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct the residual block from the transform coefficient block. The reconstruction unit 214 can generate a reconstructed block corresponding to the current block based on the reconstructed residual block and the prediction block generated by the mode selection unit 202 (although potentially with some degree of distortion). For example, the reconstruction unit 214 can add samples of the reconstructed residual block to corresponding samples of the prediction block generated by the mode selection unit 202 to generate the reconstructed block.

[0096] Filter unit 216 can perform one or more filtering operations on the reconstructed block. For example, filter unit 216 can perform deblocking to reduce block artifacts along the edges of the CU. In some examples, the operations of filter unit 216 can be skipped.

[0097] The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in an example where the operation of the filter unit 216 is not required, the reconstruction unit 214 can store the reconstructed blocks in the DPB 218. In an example where the operation of the filter unit 216 is required, the filter unit 216 can store the filtered reconstructed blocks 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 potentially filtered) blocks from the DPB 218 to perform inter-frame prediction of blocks in subsequently encoded pictures. Additionally, the intra-frame prediction unit 226 can use the reconstructed blocks of the current picture in the DPB 218 to perform intra-frame prediction of other blocks in the current picture.

[0098] Typically, entropy coding unit 220 can entropy-encode syntax elements received from other functional components of video encoder 200. For example, entropy coding unit 220 can entropy-encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy coding unit 220 can entropy-encode predictive 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 can perform one or more entropy coding operations on syntax elements, another example of video data, to generate entropy-encoded data. For example, entropy coding unit 220 can perform context-adaptive variable-length decoding (CAVLC), CABAC, variable-to-variable (V2V) length decoding, syntax-based context-adaptive binary arithmetic decoding (SBAC), probabilistic interval partitioned entropy (PIPE) decoding, exponential Golomb coding, or another type of entropy coding operation on the data. In some examples, entropy coding unit 220 can operate in a bypass mode where syntax elements are not entropy-encoded.

[0099] The video encoder 200 can output a bitstream that includes entropy-encoded syntax elements required for reconstructing slices or blocks of images. Specifically, the entropy coding unit 220 can output a bitstream.

[0100] The above operations are described in relation to the blocks. Such a description should be understood as referring to the operations used for the luma decoding block and / or the chroma decoding block. As mentioned above, in some examples, the luma decoding block and the chroma decoding block are the luma and chroma components of the CU. In some examples, the luma decoding block and the chroma decoding block are the luma and chroma components of the PU.

[0101] In some examples, it is not necessary to repeat the operations performed for the luma-coded block for the chroma-decoded block. As an example, it is not necessary to repeat the operations used to identify the motion vector (MV) and reference image for the luma-decoded block to identify the MV and reference image for the chroma-decoded block. Specifically, the MV for the luma-decoded block can be scaled to determine the MV for the chroma-decoded block, and the reference image can be the same. As another example, the intra-frame prediction process can be the same for both the luma-decoded block and the chroma-decoded block.

[0102] As described above, according to some techniques, the video encoder 200 can check to determine whether the chroma component of the TU contains non-DC components, and when the chroma component of the transform unit contains non-DC coefficients in single-tree segmentation mode, it signals the LFNST index. However, in single-tree mode, LFNST can be disabled for the chroma component. According to the techniques of this disclosure, the video codec can avoid unnecessary checks and signaling by determining whether to use single-tree segmentation mode. If single-tree segmentation mode is used, the video encoder 200 can avoid checking whether the chroma component of the TU has non-DC coefficients to reduce processing power. In addition, if single-tree segmentation mode is used, if there are no non-DC coefficients for the luminance component of the TU in single-tree segmentation mode, the video encoder 200 can reduce signaling overhead by not signaling the LFNST index.

[0103] According to the technology of this disclosure, video encoder 200 represents an example of a device configured to encode video data, the device including: a memory configured to store video data; and one or more processors implemented in circuitry and communicatively coupled to the memory, the one or more processors being configured to: determine that the current mode for decoding the current block of video data is a single-tree segmentation mode; avoid determining whether non-DC coefficients exist for the chroma components of the TU used for the current block based on the current mode being a single-tree segmentation mode; and encode the current block based on the current mode.

[0104] Figure 4 This is a block diagram illustrating an example video decoder 300 capable of performing the techniques described herein. Figure 4 This disclosure is provided for illustrative purposes and does not limit the techniques illustrated and described in this disclosure in a general manner. For illustrative purposes, this disclosure describes a video decoder 300 based on VVC (ITU-T H.266 under development) and HEVC (ITU-T H.265) technologies. However, the technologies of this disclosure can be implemented by video decoding devices configured for other video decoding standards.

[0105] exist Figure 4In the example, the video decoder 300 includes a decoded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 314. Any or all of the CPB memory 320, 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 can be implemented in one or more processors or in processing circuitry. For example, units of the video decoder 300 can be implemented as one or more circuit or logic elements as part of hardware circuitry, or as part of a processor, ASIC, or FPGA. Furthermore, the video decoder 300 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0106] The prediction processing unit 304 includes a motion compensation unit 316 and an intra-frame prediction unit 318. The prediction processing unit 304 may include an addition unit to perform predictions based on other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0107] CPB memory 320 can store video data to be decoded by components of video decoder 300, such as encoded video bitstreams. For example, it can be stored from computer-readable medium 110 ( Figure 1 The video data stored in the CPB memory 320 is obtained. The CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from the encoded video bitstream. Additionally, the CPB memory 320 may store video data other than the syntax elements of the decoded picture, such as temporary data representing the output from various units of the video decoder 300. The DPB 314 typically stores decoded pictures that the video decoder 300 may output and / or use as reference video data when decoding subsequent data or pictures of the encoded video bitstream. The CPB memory 320 and DPB 314 may be formed of any of a variety of memory devices, such as DRAM, including SDRAM, MRAM, RRAM, or other types of memory devices. The CPB memory 320 and DPB 314 may be provided by the same memory device or separate memory devices. In various examples, the CPB memory 320 may be on-chip with other components of the video decoder 300, or off-chip relative to those components.

[0108] Alternatively or concurrently, in some examples, the video decoder 300 can be derived from the memory 120 ( Figure 1 The decoded video data is retrieved. In other words, memory 120 can utilize CPB memory 320 to store data, as discussed above. Similarly, when some or all of the functions of video decoder 300 are implemented using software to be executed by the processing circuitry of video decoder 300, memory 120 can store instructions to be executed by video decoder 300.

[0109] It shows Figure 4 The various units shown help to understand the operations performed by the video decoder 300. These units can be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Similar to... Figure 3 Fixed-function circuits refer to circuits that provide a specific function and are pre-configured regarding the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functionality in terms of the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive or output parameters), but the type of operation performed by a fixed-function circuit is typically immutable. In some examples, one or more of these units may be different circuit blocks (fixed-function or programmable), and in some examples, one or more of these units may be integrated circuits.

[0110] The video decoder 300 may include an ALU, EFU, digital circuitry, analog circuitry, and / or a programmable core formed by programmable circuitry. In an example where the operation of the video decoder 300 is performed by software executing on the programmable circuitry, on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

[0111] Entropy decoding unit 302 can receive encoded video data from the CPB and perform entropy decoding on the video data to reconstruct the syntax elements. Prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, and filter unit 312 can generate decoded video data based on the syntax elements extracted from the bitstream.

[0112] Typically, the video decoder 300 reconstructs the image block by block. The video decoder 300 can perform the reconstruction operation on each block individually (where the block currently being reconstructed (i.e., decoded) can be referred to as the "current block").

[0113] Entropy decoding unit 302 can entropy decode the syntax elements of the quantized transform coefficients that define the quantized transform coefficient block, as well as transform information such as quantization parameters (QPs) and / or transform mode indications. Inverse quantization unit 306 can use the QPs associated with the quantized transform coefficient block to determine the degree of quantization, and similarly, determine the degree of inverse quantization to be applied by inverse quantization unit 306. Inverse quantization unit 306 can, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. Inverse quantization unit 306 can thus form a transform coefficient block including the transform coefficients. After inverse quantization unit 306 forms the transform coefficient block, inverse transform processing unit 308 can 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 can apply inverse DCT, inverse integer transform, inverse Karhunen-Loeve transform (KLT), inverse rotation transform, inverse direction transform, or another inverse transform to the transform coefficient block. In some examples, inverse transform processing unit 308 can apply inverse LFNST. In some examples, according to the techniques of this disclosure, when the current mode for decoding the current block of video data is a single-tree segmentation mode, the inverse transform processing unit 308 can avoid determining whether there are non-DC coefficients for the chrominance components of the TU used for the current block.

[0114] Furthermore, the prediction processing unit 304 generates a prediction block based on the prediction information syntax elements entropy-decoded by the entropy decoding unit 302. For example, if the prediction information syntax elements indicate that the current block is inter-frame predicted, the motion compensation unit 316 can generate the prediction block. In this case, the prediction information syntax elements may indicate the reference picture from which the reference block is to be retrieved in the DPB 314, and a motion vector identifying the position of the reference block in the reference picture relative to the position of the current block in the current picture. The motion compensation unit 316 can typically be configured with respect to the motion compensation unit 224 ( Figure 3 The method described is basically similar to the way the inter-frame prediction process is performed.

[0115] As another example, if the prediction information syntax element indicates that the current block is intra-predicted, then intra-prediction unit 318 can generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Again, intra-prediction unit 318 can typically be configured with respect to intra-prediction unit 226 ( Figure 3 The intra-prediction process is performed in a manner substantially similar to that described above. The intra-prediction unit 318 can retrieve data from neighboring samples of the current block from the DPB 314.

[0116] Reconstruction unit 310 can reconstruct the current block using the prediction block and the residual block. For example, reconstruction unit 310 can reconstruct the current block by adding the samples of the residual block to the corresponding samples of the prediction block.

[0117] Filter unit 312 can perform one or more filter operations on the reconstructed block. For example, filter unit 312 can perform a deblocking operation to reduce block artifacts along the edges of the reconstructed block. The operation of filter unit 312 is not necessarily performed in all examples.

[0118] The video decoder 300 can store the reconstructed blocks in the DPB 314. For example, in an example where the operation of the filter unit 312 is not performed, the reconstruction unit 310 can store the reconstructed blocks in the DPB 314. In an example where the operation of the filter unit 312 is performed, the filter unit 312 can store the filtered reconstructed blocks in the DPB 314. As discussed above, the DPB 314 can provide reference information (such as samples of the current image for intra-frame prediction and samples of previously decoded images for subsequent motion compensation) to the prediction processing unit 304. Furthermore, the video decoder 300 can output decoded images (e.g., decoded video) from the DPB 314 for use in applications such as... Figure 1 The subsequent presentation on display devices such as display device 118.

[0119] As described above, according to some techniques, the video decoder 300 can check to determine whether the chroma components of the TU contain non-DC components, and when the chroma components of the transform unit contain non-DC coefficients in single-tree segmentation mode, it signals the LFNST index. However, in single-tree mode, LFNST can be disabled for the chroma components. According to the techniques of this disclosure, the video codec can avoid unnecessary checks and signaling by determining whether to use single-tree segmentation mode. If single-tree segmentation mode is used, the video decoder 300 can avoid checking whether the chroma components of the TU have non-DC coefficients to reduce processing power.

[0120] In this manner, video decoder 300 represents an example of a video decoding device, which includes: a memory configured to store video data; and one or more processors implemented in circuitry and communicatively coupled to the memory, the one or more processors being configured to: determine that the current mode for decoding the current block of video data is a single-tree segmentation mode; avoid determining whether non-DC coefficients exist for the chroma components of the TU used for the current block based on the current mode being a single-tree segmentation mode; and decode the current block based on the current mode.

[0121] Prior to HEVC, video decoding standards applied fixed separable transforms (e.g., DCT-2) only vertically and horizontally to transform video data blocks. In HEVC, in addition to DCT-2, DST-7 is used as a fixed separable transform for 4x4 blocks.

[0122] The following U.S. patents and co-pending U.S. patent applications describe the Multi-Transform Selection (MTS) technology: U.S. Patent No. 10,306,229, published May 28, 2019, and U.S. Patent Application No. 16 / 426,749, filed May 30, 2019. MTS was previously referred to as Adaptive Multi-Transform (AMT). The MTS technology is generally the same as the previously described AMT technology. An example of the MTS described in U.S. Patent Application No. 16 / 426,749, filed May 30, 2019, has been adopted in the Joint Experimental Model (JEM-7.0) of the Joint Video Experts Group (JVET) (see ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC29 / WG 11, JEM Software), and a simplified version of MTS has subsequently been adopted in VVC.

[0123] Figure 5 This is a conceptual diagram illustrating an example of a low-frequency non-separable transform (LFNST) on a video encoder (e.g., video encoder 200) and a video decoder (e.g., video decoder 300). Figure 5 In the example, LFNST is introduced as a stage between the separable transform and quantization on the video encoder and between the inverse quantization and inverse transform (inverse LFNST) on the video decoder. For example, the video encoder 200 may include Figure 5 The example LFNST, and the video decoder 300 may include Figure 5 An example of the inverse LFNST. For example... Figure 5As shown, LFNST is used in JEM-7.0 to further improve the decoding efficiency of MTS. The implementation of LFNST is based on the example hypercube Givens transform (HWT) described in U.S. Patent No. 10,448,053, issued October 15, 2019. Other example designs and additional details are described in U.S. Patent No. 10,448,053, issued November 26, 2019; U.S. Patent No. 10,349,085, published July 9, 2019; and U.S. Patent Publication No. 2019 / 0297351-A1, published September 26, 2019. Furthermore, LFNST is adopted in the VVC standard. See the following document: Koo et al., “CE6: Reduced Secondary Transform (RST) (CE6-3.1)”, Joint Video Expert Group (JVT) of ITU-T SG 16WP 3 and ISO / IEC JTC1 / SC 29 / WG 11, 14th Meeting: Geneva, Switzerland, October 1-11, 2019, JVET-N0193. It should be noted that LFNST was previously referred to as the Inseparable Secondary Transform (NSST) or a secondary transform using the same abbreviation. LFNST can be used to compress redundancy in the low-frequency master transform coefficients. LFNST can be called inseparable because it involves matrix multiplication and is not suitable for implementation using more than one iteration.

[0124] The decoding process using LFNST will now be described. Figure 6 This is a block diagram illustrating an example of the inverse transform technique when using LFNST. For example, a video decoder 300 could employ... Figure 6 The inverse transform process. The inverse transform technique of LFNST involves, for example... Figure 6 The following steps are shown.

[0125] For example, video decoder 300 can use the decoded transform coefficients (sub-block 400) as input to inverse LFNST by converting two-dimensional blocks into a one-dimensional list (or vector) of coefficients via a predefined scan / sorting. Video decoder 300 can apply inverse LFNST to the one-dimensional list of input coefficients to decompress redundancy in the low-frequency master transform coefficients and reorganize the output coefficients into two-dimensional blocks (sub-block 410) via a predefined scan / sorting. Video decoder 300 can use the inverse-transformed LFNST coefficients as input to separable inverse DCT-2 to obtain the reconstructed residual 420.

[0126] In VVC Draft 8, LFNST can be applied to both 4x4 and 8x8 subblocks. For example, video encoder 200 can apply LFNST to both 4x4 and 8x8 subblocks, or video decoder 300 can apply inverse LFNST to both 4x4 and 8x8 subblocks. For video decoder 300, in the case of both 4x4 and 8x8 subblocks, the 16 decoded coefficients (some of which can be normalized to zero) of the 4x4 subblock are input to inverse LFNST.

[0127] Figure 7 This is a conceptual diagram of a 4x4 inverse LFNST used to reconstruct 16 intermediate coefficients from a list of 16 input coefficients. For the 4x4 case, 16x16 inverse LFNST is used to construct the 16 intermediate coefficients 430 before the separable inverse DCT-2, as shown below. Figure 7 As shown.

[0128] Figure 8 This is a conceptual diagram of an 8x8 inverse LFNST used to reconstruct 48 intermediate coefficients from a list of 16 input coefficients. For the 8x8 sub-block case, before applying separable inverse DCT-2, the video decoder 300 can use a 16x48 inverse LFNST to construct 48 intermediate coefficients 440, as shown below. Figure 8 As shown. Using 48 intermediate coefficients reduces the number of multiplications, thus reducing complexity. Note that the 48 intermediate coefficients are reorganized in an L-shaped pattern.

[0129] The inverse LFNST process can be fully defined based on (i) the transformation (e.g., LFNST) matrix and (ii) the recombination pattern / scan for intermediate coefficients. Details of the zeroing process in VVC Draft 8 are discussed in U.S. Patent Publication No. 2020-0366937 A1, published November 19, 2020.

[0130] For 4x4 LFNST, the following two modes / scans are used depending on the intra-frame mode:

[0131]

[0132]

[0133] The two modes / scans described above indicate a reordering of intermediate coefficients. For example, g_lfnstRGScan4x4 does not change the rows or perform a major reordering of the coefficients. However, lfnstRGTranScan4x4 reorders the coefficients by swapping their order (e.g., coefficients at positions 1, 2, 3, 6, 7, and 11 are swapped with coefficients at positions 4, 8, 12, 9, 13, and 14, respectively).

[0134] For 4x4 LFNST, according to VVC Draft 8, eight 16x16 matrices are used as candidate matrices, which are also listed in Section 8.7.4.3 of the following document: Bross et al., “Versatile Video Coding (Draft 6)”, 15th meeting of the Joint Video Experts Group (JVET) of ITU-TSG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11: Gothenburg, Sweden, July 3-12, 2019, JVET-O2001-vE (hereinafter referred to as “VVC Draft 6”).

[0135] For 8x8 LFNST, the following two modes / scans are used depending on the intra-frame mode:

[0136]

[0137]

[0138]

[0139] The two modes / scans mentioned above represent the reordering of intermediate coefficients. Specifically, g_lfnstRGScan8x8 reorganizes the 48 intermediate coefficients in an L-shaped pattern (e.g., the 48th coefficient is mapped to...). Figure 8 Position 59 in the middle). The scan lfnstRGTranScan4x4 reorders the L-shaped pattern by swapping coefficients (e.g., coefficient 48 is mapped to). Figure 8 (Position 31 in the middle).

[0140] For 8x8 LFNST, eight 16x48 matrices are used as candidates in VVC Draft 8, and these matrices are also listed in Section 8.7.4.3 of VVC Draft 6.

[0141] The following document discusses applying LFNST only to the luma component and disabling LFNST for the chroma component in single-tree segmentation mode: HEEgilmez, A. Nalci, M. Coban, V. Seregin, M. Karczewicz, “Chroma LFNST Simplification and Signaling,” JVET-Q0686, 17th meeting of the Joint Video Exploration Group (JVET) of ISO / IEC JTC 1 / SC 29 / WG 11, Brussels, Belgium, January 7-17, 2020 (reference software VTM-8.0). This disabling of LFNST for the chroma component in single-tree segmentation mode is also disclosed in U.S. Patent Application No. 17 / 029,416, filed September 23, 2020, which claims priority to U.S. Provisional Patent Application No. 62 / 906,671, filed September 26, 2019. In single-tree segmentation mode, there are situations where it may be unnecessary to signal the LFNST index, as described in more detail. This disclosure describes removing unnecessary signaling for the LFNST index. The LFNST index may be based on the position of the last non-zero coefficient of TU, ​​and when necessary and signaled by the video encoder 200, it can be used by the video decoder 300 to determine whether to apply the inverse LFNST and which inverse LFNST to apply. For example, an LFNST index value of 0 may indicate that the inverse LFNST will not be applied, an LFNST index value of 1 may indicate that a first candidate inverse LFNST will be applied, and an LFNST index value of 2 may indicate that a second candidate inverse LFNST will be applied.

[0142] According to VVC draft 8, the video encoder (such as video encoder 200) signals the LFNST index (lfnst_idx) after residual decoding of all color components based on the following set of conditions:

[0143]

[0144]

[0145] The LfnstDcOnly variable is used to check for the presence of non-DC coefficients in TU. If at least one non-DC coefficient exists (e.g., LfnstDcOnly equals 0), the LFNST index can be signaled.

[0146] However, according to VVC draft 8, the value of LfnstDcOnly depends on the chroma component, even if LFNST is disabled for chroma in single-tree split mode. This issue can lead to unnecessary checks and signaling for the LFNST index when there are no non-DC coefficients in the luminance component and when there are non-DC coefficients in the chroma component, thus signaling the LFNST index that will not be used. This unnecessary signaling negatively impacts signaling overhead. That is, if the chroma component includes non-DC coefficients and single-tree split mode is enabled, the video encoder 200 can signal the LFNST index because non-DC coefficients are present in the chroma component, even if LFNST is disabled (because LFSNT is disabled for chroma in single-tree split mode).

[0147] The following section of VVC Draft 8 shows the conditions for updating the LfnstDcOnly flag:

[0148]

[0149] This disclosure describes how to remove unnecessary signaling from the LFNST index by adding the following condition to VVC draft 8. The condition begins with... <add> The marker, and the end of the condition, is...< / add> This condition may cause a video codec (such as video encoder 200 or video decoder 300) to skip checking the DC coefficients for the chroma component in single-tree segmentation mode, allowing the DC coefficient check to be performed only for the luma component. For example, in single-tree segmentation mode, video encoder 200 or video decoder 300 may not check the DC coefficients for the chroma component.

[0150]

[0151]

[0152] Where the segmentation pattern is not a single tree ( <add> treeType! = SINGLE_TREE< / add> ) or the currently processed TB comes from the luminance component ( <add> cIdx==0< / add> If the condition is met, then updating the variable LfnstDcOnly is allowed. Adding this condition eliminates unnecessary signaling for the LFNST index in VVC Draft 8 and reduces signaling overhead by having the video encoder 200 signal the video decoder 300 to potentially unused LFNST indexes.

[0153] Figure 9This is a flowchart illustrating an example technique for LFNST decoding according to this disclosure. The video encoder 200 or video decoder 300 can determine that the current mode for decoding the current block of video data is a single-tree segmentation mode (450). For example, the video encoder 200 can test various decoding modes and perform a rate-distortion check to determine that the current mode for decoding the current block is a single-tree segmentation mode, and signal syntax elements indicating that the current mode is a single-tree segmentation mode. The video decoder 300 can parse the syntax elements to determine that the current mode is a single-tree segmentation mode.

[0154] Given that the current mode is a single-tree segmentation mode, video encoder 200 or video decoder 300 can avoid determining whether non-DC coefficients exist for the chroma components of the TU used for the current block (452). For example, video encoder 200 may not check whether non-DC coefficients exist for the chroma components of the TU, and may not update variables (such as LfnstDcOnly) based on whether non-DC coefficients exist for the chroma components of the TU. Video decoder 300 may not check whether non-DC coefficients exist for the chroma components of the TU, and may not update variables (such as LfnstDcOnly) even if one or more non-DC components exist for the chroma components of the TU.

[0155] Additionally, given that the current mode is a single-tree segmentation mode, the video encoder 200 or the video decoder 300 can avoid decoding the LFNST index (454) in order to avoid determining the existence of non-DC coefficients. For example, the video encoder 200 may not encode the LFNST index, and the video decoder 300 may not decode the LFNST index.

[0156] Video encoder 200 or video decoder 300 can decode the current block in single-segment mode with LFNST disabled (456). For example, video encoder 200 can encode the current block using single-tree segmentation mode without applying LFNST, or video decoder 300 can decode the current block using single-tree segmentation mode without applying LFNST. In some examples, the chroma components include non-DC coefficients.

[0157] In some examples, the current mode is the first mode and the current block is the first block. In such examples, the video encoder 200 or the video decoder 300 can determine that the second mode used to decode the second block of video data is not a single-tree segmentation mode. Based on the fact that the second mode is not a single-tree segmentation mode, the video encoder 200 or the video decoder 300 can determine whether there are non-DC coefficients for the chroma components of the TU used for the second block. Furthermore, based on the fact that the second mode is not a single-tree segmentation mode, the video encoder 200 or the video decoder 300 can decode the LFNST index for the second block in response to the presence of non-DC coefficients for the chroma components of the TU used for the second block. The video encoder 200 or the video decoder 300 can decode the second block based on the current mode and the determination regarding the presence of non-DC coefficients for the chroma components. For example, if non-DC coefficients exist for the chroma components, the video encoder 200 can update the variable indicating the presence of non-DC coefficients for the chroma components (such as LfnstDcOnly), signal the LFNST index, and use the LFNST to encode the second block. The video decoder 300 can parse the LFNST index and use the inverse LFNST based on the LFNST index to decode the second block.

[0158] In some examples, video encoder 200 or video decoder 300 may determine whether non-DC coefficients exist for the luminance component of the TU used for the current block. In some examples, decoding includes encoding (e.g., by video encoder 200) and no non-DC coefficients exist for the luminance component. In such examples, video encoder 200 may avoid signaling the LFNST index used for the current block based on the absence of non-DC coefficients for the luminance component. For example, video encoder 200 may also avoid signaling the LFNST index used for the current block based on the absence of non-DC coefficients for the luminance component. In some examples, video encoder 200 may set the value of a variable (e.g., LfnstDcOnly) to indicate the presence of non-DC coefficients for the luminance component based on the determination of whether non-DC coefficients exist for the luminance component.

[0159] In some examples, the video encoder 200 can avoid updating variables to indicate the presence of non-DC coefficients for the chroma component based on the current mode being a single-tree segmentation mode. For example, the video encoder 200 can determine that there are no non-DC coefficients for the luminance component of the current TU and set the value of LfnstDcOnly to 1. The video encoder 200 can determine that the current mode is a single-tree segmentation mode. Based on the current mode being a single-tree segmentation mode, the video encoder 200 may not update the value of LfnstDcOnly to 0, even if non-DC coefficients exist for the chroma component of the current TU.

[0160] In some examples, decoding includes decoding (e.g., by video decoder 300), and determining whether non-DC coefficients exist for the luminance component of the TU for the current block includes determining the value of a variable indicating whether non-DC coefficients exist for the luminance component. For example, video decoder 300 may use the value of LfnstDcOnly to determine whether non-DC coefficients exist for the TU for the current block.

[0161] In some examples, source device 102 may include a camera configured to capture video data (e.g., video source 104). In some examples, destination device may include a display device 118 configured to display video data.

[0162] Figure 10 This is a flowchart illustrating an example method for encoding the current block. The current block may include the current CU. Although regarding video encoder 200 ( Figure 1 and Figure 3 The description is provided, but it should be understood that other devices can be configured to perform the same actions. Figure 10 Similar to the method.

[0163] In this example, the video encoder 200 initially predicts the current block (350). For example, the video encoder 200 may form a prediction block for the current block. Then, the video encoder 200 may compute a residual block for the current block (352). To compute the residual block, the video encoder 200 may compute the difference between the original unencoded block and the prediction block for the current block. The video encoder 200 may then transform the residual block and transform and quantize its coefficients (354). In some examples, the video encoder 200 may perform [the following steps] as part of transforming the residual block. Figure 9 The technology is described above. Next, the video encoder 200 can scan the quantized transform coefficients of the residual block (356). During or after scanning, the video encoder 200 can entropy encode the transform coefficients (358). For example, the video encoder 200 can use CAVLC or CABAC to encode the transform coefficients. Then, the video encoder 200 can output the entropy-encoded data of the block (360).

[0164] Figure 11 This is a flowchart illustrating an example method for decoding the current block of video data. The current block may include the current CU. Although regarding video decoder 300 ( Figure 1 and 4 The description is provided, but it should be understood that other devices can be configured to perform the same actions. Figure 11 Similar to the method.

[0165] The video decoder 300 can receive entropy-coded data for the current block (e.g., entropy-coded prediction information and entropy-coded data for the transform coefficients of the residual block corresponding to the current block) (370). The video decoder 300 can entropy decode the entropy-coded data to determine the prediction information for the current block and reproduce the transform coefficients of the residual block (372). The video decoder 300 can predict the current block, for example, using an intra-frame or inter-frame prediction mode indicated by the prediction information for the current block (374), to compute a prediction block for the current block. The video decoder 300 can then perform an inverse scan (376) on the reproduced transform coefficients to create a block of quantized transform coefficients. The video decoder 300 can then inverse quantize the transform coefficients and apply the inverse transform to the transform coefficients to produce the residual block (378). In some examples, as part of applying the inverse transform, the video decoder 300 can perform... Figure 9 The technology. Ultimately, the video decoder 300 can decode the current block by combining the predicted block and the residual block (380).

[0166] According to the technology disclosed herein, by avoiding checking whether the chroma components of the TU have non-DC coefficients when decoding blocks in single-tree segmentation mode, the video encoder can reduce processing power usage. Furthermore, if there are no non-DC coefficients for the luminance components of the TU in single-tree segmentation mode, the video encoder can reduce signaling overhead by notifying the LFNST index.

[0167] This disclosure includes the following examples.

[0168] Clause 1A. A method for decoding video data, the method comprising: determining whether a current mode is a single-tree segmentation mode; determining, based on the premise that the current mode is not the single-tree segmentation mode, whether non-DC coefficients exist for the chroma components; and decoding the video data based on the current mode and the determination regarding the existence of the non-DC coefficients for the chroma components.

[0169] Clause 2A. A method for decoding video data, the method comprising: determining whether a current mode is a single-tree segmentation mode; avoiding determining whether non-DC coefficients exist for the chroma components based on the current mode being the single-tree segmentation mode; and decoding the video data based on the current mode when it is uncertain whether the non-DC coefficients exist for the chroma components.

[0170] Clause 3A. The method described in Clause 2A further includes: based on the fact that the current mode is the single-tree segmentation mode, not updating LfnstDcOnly for the current block of video data.

[0171] Clause 4A. A method for decoding video data, the method comprising: for a first instance of the video data, performing the following operations: determining whether a current mode in the first instance is a single-tree segmentation mode; determining, based on the fact that the current mode in the first instance is not the single-tree segmentation mode, whether non-DC coefficients exist for the chroma components; and decoding the video data in the first instance based on the current mode and the determination regarding the existence of the non-DC coefficients for the chroma components; and for a second instance of the video data, performing the following operations: determining whether a current mode in the second instance is the single-tree segmentation mode; avoiding determining whether non-DC coefficients exist for the chroma components based on the fact that the current mode in the second instance is the single-tree segmentation mode; and decoding the video data in the second instance based on the current mode when it is uncertain whether non-DC coefficients exist for the chroma components.

[0172] Clause 5A. The method according to any one of Clauses 1A-4A, wherein decoding includes decoding.

[0173] Clause 6A. The method according to any one of Clauses 1A-5A, wherein decoding includes encoding.

[0174] Clause 7A. An apparatus for decoding video data, said apparatus comprising one or more units for performing the method according to any one of Clauses 1A-6A.

[0175] Clause 8A. The device according to Clause 7A, wherein the one or more units include one or more processors implemented in a circuit.

[0176] Clause 9A. The device according to any one of Clauses 7A and 8A further includes: a memory for storing the video data.

[0177] Clause 10A. The device according to any one of Clauses 7A-9A further includes: a display configured to display decoded video data.

[0178] Clause 11A. The device according to any one of Clauses 7A-10A, wherein the device includes one or more of a camera, computer, mobile device, broadcast receiver device or set-top box.

[0179] Clause 12A. The device according to any one of Clauses 7A-11A, wherein the device includes a video decoder.

[0180] Clause 13A. The device according to any one of Clauses 7A-12A, wherein the device includes a video encoder.

[0181] Clause 14A. A computer-readable storage medium having instructions stored thereon, which, when executed, cause one or more processors to perform the method according to any one of Clauses 1A-6A.

[0182] Clause 15A. An apparatus for encoding video data, the apparatus comprising: a unit for determining whether a current mode is a single-tree segmentation mode; a unit for determining, based on the premise that the current mode is not the single-tree segmentation mode, whether non-DC coefficients exist for the chroma components; and a unit for encoding the video data based on the current mode.

[0183] Clause 16A. An apparatus for encoding video data, the apparatus comprising: a unit for determining whether a current mode is a single-tree segmentation mode; a unit for avoiding determining whether non-DC coefficients exist for chroma components based on the current mode being the single-tree segmentation mode; and a unit for encoding the video data based on the current mode.

[0184] Clause 17A. The device comprises a combination of Clauses 15A and 16A, wherein the video data described under Clause 15A is a first instance of the video data, and the video data described under Clause 16A is a second instance of the video data.

[0185] Clause 1B. A method for decoding video data, the method comprising: determining that a current mode for decoding a current block of the video data is a single-tree segmentation mode; based on the current mode being the single-tree segmentation mode, performing the following operations: avoiding determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; and avoiding decoding of the low-frequency non-separable transform (LFNST) index in response to avoiding determining whether the non-DC coefficients exist; and decoding the current block in the single-tree segmentation mode with LFNST disabled.

[0186] Clause 2B. The method according to Clause 1B, wherein the chromaticity component includes non-DC coefficients.

[0187] Clause 3B. The method according to Clause 1B or 2B, wherein the current mode is a first mode and the current block is a first block, the method further comprising: determining that a second mode for decoding a second block of the video data is not a single-tree segmentation mode; based on the second mode not being the single-tree segmentation mode, performing the following operations: determining whether there are non-DC coefficients for the chroma components of the TU for the second block; and decoding the LFNST index for the second block in response to the presence of the non-DC coefficients for the chroma components of the TU for the second block; and decoding the second block based on the second mode and using the LFNST index.

[0188] Clause 4B. The method described under any combination of Clauses 1B-3B further comprises: determining whether a non-DC coefficient exists for the luminance component of the TU used for the current block.

[0189] Clause 5B. The method according to Clause 4B, wherein decoding includes encoding, and wherein there are no non-DC coefficients for the luminance component, and wherein signaling is avoided to notify the LFNST index for the current block that it is based on the absence of non-DC coefficients for the luminance component.

[0190] Clause 6B. The method according to Clause 4B or 5B, wherein decoding includes encoding, the method further comprising: setting the value of a variable to indicate the presence of the non-DC coefficient for the luminance component based on the determination regarding the presence of the non-DC coefficient for the luminance component.

[0191] Clause 7B. The method described in Clause 6B further includes: based on the fact that the current mode is the single-tree segmentation mode, avoiding updating the variable to indicate the presence of the non-DC coefficient for the chromaticity component.

[0192] Clause 8B. The method according to Clause 4B, wherein decoding includes decoding, and wherein determining whether a non-DC coefficient exists for the luminance component of the TU for the current block includes: determining the value of a variable indicating whether the non-DC coefficient exists for the luminance component.

[0193] Clause 9B. An apparatus for decoding video data, the apparatus comprising: a memory configured to store the video data; and one or more processors implemented in circuitry and communicatively coupled to the memory, the one or more processors being configured to: determine that a current mode for decoding a current block of the video data is a single-tree segmentation mode; based on the current mode being the single-tree segmentation mode, to: avoid determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; and in response to avoiding determining whether the non-DC coefficients exist, to avoid decoding the Low Frequency Inseparable Transform (LFNST) index; and to decode the current block in the single-tree segmentation mode with LFNST disabled.

[0194] Clause 10B. The apparatus as described in Clause 9B, wherein the chromaticity components include non-DC coefficients.

[0195] Clause 11B. The apparatus according to Clause 9B or 10B, wherein the current mode is a first mode and the current block is a first block, the one or more processors are further configured to: determine that a second mode for decoding a second block of the video data is not a single-tree segmentation mode; based on the second mode not being the single-tree segmentation mode, perform the following operations: determine whether non-DC coefficients exist for the chroma components of the TU for the second block; and based on the existence of the non-DC coefficients for the chroma components of the TU for the second block, decode the LFNST index for the second block; and decode the second block based on the second mode and using the LFNST index.

[0196] Clause 12B. The device described under any combination of Clauses 9B-11B, wherein the one or more processors are further configured to: determine whether a non-DC coefficient exists for the luminance component of the TU for the current block.

[0197] Clause 13B. The apparatus according to Clause 12B, wherein decoding includes encoding, and wherein there are no non-DC coefficients for the luminance component, and wherein the one or more processors further avoid signaling the LFNST index for the current block based on the absence of non-DC coefficients for the luminance component.

[0198] Clause 14B. The device according to Clause 12B or 13B, wherein decoding includes encoding, and the one or more processors are further configured to: set the value of a variable to indicate the presence of the non-DC coefficient for the luminance component based on the determination regarding the presence of the non-DC coefficient for the luminance component.

[0199] Clause 15B. The device according to Clause 14B, wherein the one or more processors are further configured to: avoid updating the variable to indicate the presence of the non-DC coefficient for the chromaticity component based on the fact that the current mode is the single-tree segmentation mode.

[0200] Clause 16B. The apparatus according to Clause 12B, wherein decoding includes decoding, and wherein, as part of determining whether a non-DC coefficient exists for the luminance component of the TU for the current block, the one or more processors are configured to: determine the value of a variable indicating whether the non-DC coefficient exists for the luminance component.

[0201] Clause 17B. The device according to any one of Clauses 9B-16B further includes: a camera configured to capture the video data.

[0202] Clause 18B. The device according to any one of Clauses 9B-17B further includes: a display device configured to display the video data.

[0203] Clause 19B. A non-transitory computer-readable storage medium storing instructions that, when executed, cause one or more processors to: determine that the current mode for decoding a current block of video data is a single-tree segmentation mode; based on the current mode being the single-tree segmentation mode, to: avoid determining whether non-DC coefficients exist for the chrominance components of the transform unit (TU) for the current block; and in response to avoiding determining whether the non-DC coefficients exist, avoid decoding the Low Frequency Inseparable Transform (LFNST) index; and decode the current block in the single-tree segmentation mode with LFNST disabled.

[0204] Clause 20B. An apparatus for decoding video data, the apparatus comprising: a unit for determining that a current mode for decoding a current block of the video data is a single-tree segmentation mode; a unit for avoiding determining whether non-DC coefficients exist for the chrominance components of a transform unit (TU) for the current block, based on the current mode being the single-tree segmentation mode; a unit for avoiding decoding a low-frequency non-separable transform (LFNST) index in response to avoiding determining whether the non-DC coefficients exist; and a unit for decoding the current block in the single-tree segmentation mode with LFNST disabled.

[0205] It should be recognized that, based on the examples, certain actions or events of any technique described herein may be performed in a different order, and may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary for implementing the technique). Furthermore, in some examples, actions or events may be performed concurrently rather than sequentially, for example, through multithreaded processing, interrupt handling, or multiple processors.

[0206] In one or more examples, the described functionality can be implemented using hardware, software, firmware, or any combination thereof. If implemented in software, the functionality can be stored or transmitted as one or more instructions or code on or through a computer-readable medium and executed by a hardware-based processing unit. A computer-readable medium can include a computer-readable storage medium, which corresponds to a tangible medium such as a data storage medium or a communication medium, including, for example, any medium that facilitates the transfer of a computer program from one place to another according to a communication protocol. In this way, a computer-readable medium can generally correspond to (1) a non-transitory tangible computer-readable storage medium or (2) a communication medium such as a signal or carrier wave. A data storage medium can be any available medium that can be accessed by one or more computers or one or more processors to obtain instructions, code, and / or data structures for implementing the techniques described in this disclosure. Computer program products can include computer-readable media.

[0207] For example, rather than limiting, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disc storage, disk storage or other magnetic storage devices, flash memory, or any other medium capable of storing desired program code in the form of instructions or data structures and accessible by a computer. Furthermore, any connection is appropriately referred to as a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology (e.g., infrared, radio, and microwave), then coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technology (e.g., infrared, radio, and microwave) is included in the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but rather refer instead to non-transient tangible storage media. As used herein, disks and optical discs include compact optical discs (CDs), laser optical discs, optical discs, digital versatile optical discs (DVDs), floppy disks, and Blu-ray discs, wherein disks typically magnetically copy data, while optical discs utilize lasers to optically copy data. Combinations of the above items should also be included within the scope of computer-readable media.

[0208] Instructions can be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Therefore, the terms "processor" and "processing circuitry" as used herein can refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described herein can be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into combined codecs. Furthermore, the techniques can be implemented entirely within one or more circuit or logic elements.

[0209] The technologies disclosed herein can be implemented in a wide variety of devices or apparatuses, including wireless mobile phones, integrated circuits (ICs), or a set of ICs (e.g., chipsets). Various components, modules, or units are described in this disclosure to emphasize functional aspects of a device configured to perform the disclosed technologies, but they do not necessarily need to be implemented through different hardware units. Specifically, as described above, the various units can be combined in a codec hardware unit, or provided by a collection of interoperable hardware units (including one or more processors as described above) combined with appropriate software and / or firmware.

[0210] Various examples have been described. These and other examples are within the scope of the appended claims.

Claims

1. A method for decoding video data, the method comprising: The current mode for decoding the current block of the video data is determined to be single-tree segmentation mode; Based solely on the premise that the current mode is the single-tree segmentation mode, the following operations are performed: Avoid determining whether there are non-DC coefficients for the chromaticity components of the transform unit (TU) used for the current block; as well as Avoid decoding the low-frequency non-separable transform (LFNST) index used for the chrominance components; as well as The chromaticity components are decoded with LFNST disabled.

2. The method according to claim 1, wherein, The chromaticity components include non-DC coefficients.

3. The method according to claim 1, wherein, The current mode is the first mode, and the current block is the first block. The method further includes: It is determined that the second mode used to decode the second block of the video data is not a single-tree segmentation mode; Since the second mode is not the single-tree segmentation mode, the following operations are performed: Determine whether there are non-DC coefficients for the chromaticity components of the TU used for the second block; and In response to the presence of the non-DC coefficient for the chromaticity component of the TU for the second block, the LFNST index for the second block is decoded; and The second block is decoded based on the second pattern and using the LFNST index.

4. The method according to claim 1, further comprising: Determine whether there are non-DC coefficients for the luminance component of the TU used for the current block.

5. The method according to claim 4, wherein, The decoding includes encoding, and wherein there are no non-DC coefficients for the luminance component, wherein the method further includes: avoiding signaling the LFNST index for the luminance component based on the absence of non-DC coefficients for the luminance component.

6. The method according to claim 4, wherein, Decoding includes encoding, and the method further includes: Based on the determination regarding the presence of the non-DC coefficient for the luminance component, the value of the variable is set to indicate whether the non-DC coefficient exists for the luminance component.

7. The method according to claim 6, further comprising: Since the current mode is the single-tree segmentation mode, the variable is avoided from being updated to indicate whether the non-DC coefficient exists for the chromaticity component.

8. The method according to claim 4, wherein, Decoding includes decoding, and wherein determining whether the non-DC coefficient exists for the luminance component of the TU for the current block includes: Determine the value of the variable that indicates whether the non-DC coefficient exists for the luminance component.

9. An apparatus for decoding video data, the apparatus comprising: A memory configured to store the video data; as well as One or more processors, implemented in a circuit and communicatively coupled to the memory, are configured to: The current mode for decoding the current block of the video data is determined to be single-tree segmentation mode; Based solely on the premise that the current mode is the single-tree segmentation mode, the following operations are performed: Avoid determining whether there are non-DC coefficients for the chromaticity components of the transform unit (TU) used for the current block; as well as Avoid decoding the low-frequency non-separable transform (LFNST) index used for the chrominance components; as well as The chromaticity components are decoded with LFNST disabled.

10. The device according to claim 9, wherein, The chromaticity components include non-DC coefficients.

11. The device according to claim 9, wherein, The current mode is the first mode, and the current block is the first block, and the one or more processors are further configured to: It is determined that the second mode used to decode the second block of the video data is not a single-tree segmentation mode; Since the second mode is not the single-tree segmentation mode, the following operations are performed: Determine whether there are non-DC coefficients for the chromaticity components of the TU used for the second block; as well as Based on the existence of the non-DC coefficients for the chromaticity components of the TU used for the second block, the LFNST index used for the second block is decoded; as well as The second block is decoded based on the second pattern and using the LFNST index.

12. The device according to claim 9, wherein, The one or more processors are further configured to: Determine whether there are non-DC coefficients for the luminance component of the TU used for the current block.

13. The device according to claim 12, wherein, The decoding includes encoding, and wherein there are no non-DC coefficients for the luminance component, and wherein the one or more processors are further configured to avoid signaling the LFNST index for the luminance component based on the absence of non-DC coefficients for the luminance component.

14. The device according to claim 12, wherein, Decoding includes encoding, and the one or more processors are further configured to: Based on the determination regarding the presence of the non-DC coefficient for the luminance component, the value of the variable is set to indicate the presence of the non-DC coefficient for the luminance component.

15. The device according to claim 14, wherein, The one or more processors are further configured to: Since the current mode is the single-tree segmentation mode, the variable is avoided from being updated to indicate whether the non-DC coefficient exists for the chromaticity component.

16. The device according to claim 12, wherein, Decoding includes decoding, and wherein, as part of determining whether the non-DC coefficient exists for the luminance component of the TU for the current block, the one or more processors are configured to: Determine the value of the variable that indicates whether the non-DC coefficient exists for the luminance component.

17. The device according to claim 9, further comprising: A camera configured to capture the video data.

18. The device according to claim 9, further comprising: A display device configured to display the video data.

19. A non-transitory computer-readable storage medium storing instructions, which, when executed, cause one or more processors to perform the following operations: The current mode for decoding the current block of video data is determined to be single-tree segmentation mode; Based solely on the premise that the current mode is the single-tree segmentation mode, the following operations are performed: Avoid determining whether there are non-DC coefficients for the chromaticity components of the transform unit (TU) used for the current block; as well as Avoid decoding the low-frequency non-separable transform (LFNST) index used for the chrominance components; as well as The chromaticity components are decoded with LFNST disabled.

20. An apparatus for decoding video data, the apparatus comprising: A unit used to determine whether the current mode for decoding the current block of the video data is a single-tree segmentation mode; Based solely on the fact that the current mode is the single-tree segmentation mode: A unit used to avoid determining whether non-DC coefficients exist for the chromaticity components of the transform unit (TU) used for the current block; as well as Units for avoiding decoding of the Low Frequency Inseparable Transform (LFNST) index used for the chrominance components; and units for decoding the chrominance components when LFNST is disabled.

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