Context modeling for low frequency inseparable transform signaling for video coding

Abstract

An example method includes determining a color component of a video data unit; determining, based at least on the color component, a context for context-adaptive binary arithmetic coding (CABAC) of a syntax element that specifies a value of a low-frequency non-separable transform (LFNST) index for the video data unit; CABAC decoding the syntax element that specifies the value of the LFNST index for the video data unit based on the determined context and via a syntax structure for the video data unit; and inversely transforming transform coefficients of the video data unit based on a transform indicated by the value of the LFNST index.

Description

[0001] This application claims priority to U.S. Application No. 16 / 905,663, filed on June 18, 2020, which claims the benefit of U.S. Provisional Application No. 62 / 864,939, filed on June 21, 2019, the entire contents of each of the above applications are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to video encoding (encode) and video decoding (decode). Background Art

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

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

[0005] In general, the present disclosure describes techniques for context modeling and coding of transform indices / flags for low frequency non-separable transforms (LFNST). The present disclosure introduces a new context model to reduce the signaling overhead of LFNST related indices / flags, thereby improving the coding efficiency of context adaptive binary arithmetic coding (CABAC) engines used in video compression standards. The techniques of the present disclosure can be used in advanced video codecs, including extensions of HEVC and next generation video coding standards, such as Versatile Video Coding (VVC / H.266) (Versatile Video Coding (Draft 5) found at http: / / phenix.it-sudparis.eu / jvet / doc_end_user / documents / 14_Geneva / wg11 / JVE T-N1001-v5.zip).

[0006] A video coder (e.g., a video encoder and / or a video decoder) may signal a syntax element that specifies a value of a low frequency non-separable transform (LFNST) index for a video data unit. In some examples, the video data unit may be a coding unit (CU) of video data (e.g., the LFNST index may be signaled at the CU level). In some examples, the video data unit may be a transform unit (TU) of video data (e.g., the LFNST index may be signaled at the TU level). In any case, the video coder may signal the LFNST index using CABAC. For example, the video coder may select a specific context for the LFNST index and decode the LFNST index using the selected specific context.

[0007] The video decoder can select contexts based on a variety of parameters. Some example parameters include, but are not limited to, block size, color component, partition depth, and the number of non-zero transform coefficients. As a specific example and in accordance with one or more techniques of the present disclosure, the video decoder can select a context for decoding the LFNST index for the video data unit based on the color component of the video data unit. For example, the video decoder can use a first context when the video data unit is a luminance component, and use a second context when the video data unit is a chrominance component. In some examples, the video decoder can select different contexts for chrominance red and chrominance blue. Selecting contexts based on color components can provide one or more advantages. For example, the bit rate of video data can be reduced by the selected context for CABAC decoding of LFNST indexes. This is because different color components (such as luminance and chrominance) have different uses of LFNST indexes and must be modeled separately using different contexts. In other words, the technology of the present disclosure can reduce the amount of data used to represent video data with similar perceptual quality.

[0008] As an example, a method for decoding video data includes: determining a color component of a video data unit; determining a context for CABAC of a syntax element specifying a value of an LFNST index for the video data unit based at least on the color component; CABAC decoding the syntax element specifying the value of the LFNST index for the video data unit based on the determined context and via a syntax structure for the video data unit; and inversely transforming transform coefficients of the video data unit based on a transform indicated by the value of the LFNST index.

[0009] As another example, a method for encoding video data includes: selecting an LFNST having an LFNST index from a plurality of LFNSTs; transforming transform coefficients of a video data unit using the LFNST; determining a color component of the video data unit; determining, based at least on the color component, a context for CABAC encoding a syntax element that specifies a value of the LFNST index for the video data unit; and CABAC encoding the syntax element that specifies the value of the LFNST index for the video data unit based on the determined context and via a syntax structure for the video data unit.

[0010] As another example, an apparatus for decoding video data includes: a memory; and one or more processors implemented in a circuit and configured to: determine a color component of a video data unit; determine, based at least on the color component, a context for CABAC of a syntax element that specifies a value of an LFNST index for the video data unit; perform CABAC decoding on the syntax element that specifies the value of the LFNST index for the video data unit based on the determined context and via a syntax structure for the video data unit; and transform transform coefficients of the video data unit based on a transform indicated by the value of the LFNST index.

[0011] As another example, a computer-readable storage medium stores instructions that, when executed, cause one or more processors of a video decoder to perform the following operations: determine a color component of a video data unit; determine, based at least on the color component, a context for CABAC-coding a syntax element that specifies a value of an LFNST index for the video data unit; based on the determined context and via a syntax structure for the video data unit, CABAC-code the syntax element that specifies the value of the LFNST index for the video data unit; and transform transform coefficients of the video data unit based on a transform indicated by the value of the LFNST index.

[0012] As another example, a video decoder includes: a unit for determining a color component of a video data unit; a unit for determining, based at least on the color component, a context for CABAC of a syntax element that specifies a value of an LFNST index for the video data unit; a unit for CABAC coding the syntax element that specifies the value of the LFNST index for the video data unit based on the determined context and via a syntax structure for the video data unit; and a unit for transforming a transform coefficient of the video data unit based on a transform indicated by the value of the LFNST index.

[0013] The details of one or more examples are set forth in the accompanying drawings and the description below.Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0015] Figure 2A and Figure 2B is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure and a corresponding coding tree unit (CTU).

[0016] Figure 3is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0017] Figure 4 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0018] Figure 5 is a block diagram illustrating a low frequency non-separable transform (LFNST) at an encoder and a decoder.

[0019] Figure 6 is a conceptual diagram showing coefficients obtained after applying LFNST to a block in the case of performing zeroing.

[0020] Figure 7 is a conceptual diagram showing coefficients obtained after applying LFNST to a block without zeroing.

[0021] Figure 8 is a conceptual diagram showing coefficients obtained after applying LFNST to a block according to the technology of the present disclosure in the case of performing zeroing.

[0022] Fig. 9 is a conceptual diagram showing coefficients obtained after applying LFNST to a block according to the technique of the present disclosure without performing zeroing.

[0023] Fig. 10A and 10B is a conceptual diagram illustrating a range update process in binary arithmetic decoding.

[0024] Fig.11 is a conceptual diagram showing an output process in binary arithmetic decoding.

[0025] Fig.12 is a block diagram illustrating a context-adaptive binary arithmetic decoder in a video encoder.

[0026] Fig.13 is a block diagram illustrating a context-adaptive binary arithmetic coder in a video decoder.

[0027] Fig.14 is a flow chart illustrating an example encoding method.

[0028] Fig.15 is a flow chart illustrating an example decoding method.

[0029] Fig.16 is a flow diagram illustrating an example method for context coding a syntax element that specifies a value of a low frequency non-separable transform (LFNST) index for a video data unit, in accordance with one or more techniques of this disclosure. DETAILED DESCRIPTION

[0030] Figure 1 1 is a block diagram illustrating an example video encoding and decoding system 100 that can perform the techniques of the present disclosure. The techniques of the present disclosure generally relate to encoding (encoding and / or decoding) video data. Generally, video data includes any data used to process video. Thus, video data may include original unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata (such as signaling data).

[0031] As in Figure 1 , in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. In particular, source device 102 provides the video data to destination device 116 via computer-readable medium 110. Source device 102 and destination device 116 may include any of a wide variety of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets (such as smart phones), televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, etc. In some cases, source device 102 and destination device 116 may be equipped for wireless communication and, therefore, may be referred to as wireless communication devices.

[0032] exist Figure 1 In the example of , source device 102 includes video source 104, memory 106, video encoder 200 and output interface 108. Destination device 116 includes input interface 122, video decoder 300, memory 120 and display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply techniques for transform decoding. Therefore, source device 102 represents an example of a video encoding device, and destination device 116 represents an example of a video decoding device. In other examples, source device and destination device may include other components or arrangements. For example, source device 102 may receive video data from an external video source (such as an external camera). Similarly, destination device 116 may be docked with an external display device instead of including an integrated display device.

[0033] As in Figure 1The system 100 shown in is only an example. In general, any digital video encoding and / or decoding device can perform techniques for transform decoding. The source device 102 and the destination device 116 are only examples of such decoding devices: wherein the source device 102 generates decoded video data for transmission to the destination device 116. The present disclosure refers to a "decoding" device as a device that performs decoding (e.g., encoding and / or decoding) of data. Therefore, the video encoder 200 and the video decoder 300 represent examples of decoding devices, in particular, respectively represent a video encoder and a video decoder. In some examples, the devices 102 and 116 can operate in a substantially symmetrical manner, so that each of the devices 102 and 116 includes a video encoding and decoding component. Therefore, the system 100 can support one-way or two-way video transmission between video devices 102 and 116, for example, for video streaming, video playback, video broadcasting, or video telephony.

[0034] Typically, video source 104 represents the source of video data (i.e., original, unencoded video data), and provides a series of pictures (also referred to as "frames") of the order of the video data to video encoder 200, which encodes the data for the pictures. The video source 104 of source device 102 may include a video capture device, such as a camera, a video archive unit containing previously captured original video, and / or a video feed interface for receiving video from a video content provider. As another alternative, video source 104 may generate computer graphics-based data as source video, or a combination of real-time video, archived video, and computer-generated video. In each case, video encoder 200 may encode captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange pictures from the received order (sometimes referred to as "display order") into a decoding order for decoding. Video encoder 200 may generate a bitstream comprising encoded video data. Source device 102 may then output the encoded video data onto computer-readable medium 110 via output interface 108 for receipt and / or retrieval by, for example, input interface 122 of destination device 116 .

[0035] The memory 106 of the source device 102 and the memory 120 of the destination device 116 represent general purpose memories. In some examples, the memories 106, 120 can store original video data, for example, original video from the video source 104 and original decoded video data from the video decoder 300. In addition or alternatively, the memories 106, 120 can store software instructions that can be executed by, for example, the video encoder 200 and the video decoder 300, respectively. Although shown as separate from the video encoder 200 and the video decoder 300 in this example, it should be understood that the video encoder 200 and the video decoder 300 may include internal memories for functionally similar or equivalent purposes. In addition, the memories 106, 120 can store, for example, encoded video data output from the video encoder 200 and input to the video decoder 300. In some examples, portions of the memories 106, 120 can be allocated as one or more video buffers, for example, to store original decoded and / or encoded video data.

[0036] The computer-readable medium 110 may represent any type of medium or device capable of delivering the encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to directly send the encoded video data to the destination device 116 in real time, for example, via a radio frequency network or a computer-based network. According to a communication standard (such as a wireless communication protocol), the output interface 108 may modulate the transmission signal including the encoded video data, and the input interface 122 may modulate the received transmission signal. The communication medium may include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form a portion of a packet-based network such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include a router, a switch, a base station, or any other device that may be useful for facilitating communication from the source device 102 to the destination device 116.

[0037] In some examples, source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access the encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0038] In some examples, the source device 102 may output the encoded video data to a file server 114 or another intermediate storage device that may store the encoded video generated by the source device 102. The destination device 116 may access the stored video data from the file server 114 via streaming or downloading. The file server 114 may be any type of server device capable of storing the encoded video data and sending the encoded video data to the destination device 116. The 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. The destination device 116 may access the encoded video data from the 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 DSL, a cable modem, etc.), or a combination of both that is suitable for accessing the encoded video data stored on the file server 114. The file server 114 and the input interface 122 may be configured to operate according to the following: a streaming protocol, a download transmission protocol, or a combination thereof.

[0039] Output interface 108 and input interface 122 may represent wireless transmitters / receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of the various IEEE 802.11 standards, or other physical components. In examples where output interface 108 and input interface 122 include wireless components, output interface 108 and input interface 122 may be configured to transmit data (e.g., encoded video data) according to a cellular communication standard (e.g., 4G, 4G-LTE (Long Term Evolution), Advanced LTE, 5G, etc.). In some examples where output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 may be configured to transmit data (e.g., encoded video data) according to other wireless standards (e.g., IEEE 802.11 specifications, IEEE 802.15 specifications (e.g., ZigBee 5G, etc.). TM ),Bluetooth TM Standards, etc.) to transmit data (such as encoded video data). In some examples, source device 102 and / or destination device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include a SoC device for performing functions attributed to video encoder 200 and / or output interface 108, and destination device 116 may include a SoC device for performing functions attributed to video decoder 300 and / or input interface 122.

[0040] The techniques of the present disclosure may be applied to video decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission (such as Dynamic Adaptive Streaming over HTTP (DASH)), digital video encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0041] The input interface 122 of the destination device 116 receives the encoded video bitstream from the computer-readable medium 110 (e.g., the storage device 112, the file server 114, etc.). The encoded video bitstream computer-readable medium 110 may include signaling information defined by the video encoder 200 (which is also used by the video decoder 300), such as syntax elements with values ​​describing characteristics and / or processing of video blocks or other decoding units (e.g., slices, pictures, groups of pictures, sequences, etc.). The display device 118 displays the decoded pictures of the decoded video data to the user. The display device 118 can represent any of a variety of display devices, such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0042] Despite Figure 1 200 and 300 may be integrated with an audio encoder and / or an audio decoder and may include appropriate MUX-DEMUX units or other hardware and / or software to process multiplexed streams including both audio and video in a common data stream. If applicable, the MUX-DEMUX units may follow the ITU H.223 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

[0043] The video encoder 200 and the video decoder 300 can be implemented as any of a variety of suitable encoder and / or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When the technology is partially implemented in software, the device can store instructions for the software in a suitable non-temporary computer-readable medium, and use one or more processors to execute the instructions in the hardware to perform the technology of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, and any of the encoders or decoders can be integrated as part of a combined encoder / decoder (CODEC) in the corresponding device. The device including the video encoder 200 and / or the video decoder 300 may include an integrated circuit, a microprocessor, and / or a wireless communication device (such as a cellular phone).

[0044] The video encoder 200 and the video decoder 300 may operate according to a video coding standard such as ITU-T H.265, also known as high-efficiency video coding (HEVC), or an extension thereof such as multi-view and / or scalable video coding extensions. Alternatively, the video encoder 200 and the video decoder 300 may operate according to other proprietary or industry standards such as the Joint Exploration Test Model (JEM) or the ITU-T H.266 standard, also known as Versatile Video Coding (VVC). The latest draft of the VVC standard is described in the following document: Bross et al., "Versatile Video Coding (Draft 5)", Joint Video Experts Group (JVET) of ITU-TSG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11, 14th Meeting: Geneva, Switzerland, March 19-27, 2019, JVET-N1001-v5 (hereinafter referred to as "VVC Draft 5"). However, the technology of the present disclosure is not limited to any particular coding standard.

[0045] Typically, the video encoder 200 and the video decoder 300 can perform block-based decoding of the picture. The term "block" generally refers to a structure that includes data to be processed (e.g., to be encoded, decoded, or otherwise used in the encoding and / or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. Typically, the video encoder 200 and the video decoder 300 can decode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, instead of decoding red, green, and blue (RGB) data for samples of a picture, the video encoder 200 and the video decoder 300 can decode luminance and chrominance components, wherein the chrominance components may include both red hue and blue hue chrominance components. In some examples, the video encoder 200 converts the received RGB format data to a YUV representation before encoding, and the video decoder 300 converts the YUV representation to an RGB format. Alternatively, a pre-processing unit and a post-processing unit (not shown) may perform these conversions.

[0046] The present disclosure may generally relate to the decoding (e.g., encoding and decoding) of a picture to include the process of encoding or decoding data for the picture. Similarly, the present disclosure may relate to the decoding of a block of a picture to include the process of encoding or decoding data for the block (e.g., prediction and / or residual decoding). The encoded video bitstream generally includes a series of values ​​of syntax elements for representing decoding decisions (e.g., decoding modes) and partitioning of pictures into blocks. Therefore, references to decoding a picture or a block should generally be understood as decoding the values ​​of the syntax elements used to form the picture or the block.

[0047] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (such as video encoder 200) divides a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video decoder divides the CTU and CU into four equal non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without child nodes may be referred to as a "leaf node", and the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video decoder may further divide PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents the division of TUs. In HEVC, PU represents inter-frame prediction data, and TU represents residual data. An intra-predicted CU includes intra-frame prediction information, such as an intra-frame mode indication.

[0048] As another example, the video encoder 200 and the video decoder 300 may be configured to operate according to JEM or VVC. According to JEM or VVC, a video decoder (such as the video encoder 200) divides a picture into a plurality of coding tree units (CTUs). The video encoder 200 may divide the CTU according to a tree structure (such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure). The QTBT structure removes the concept of multiple partition types, such as the separation between CU, PU, ​​and TU in HEVC. The QTBT structure includes two levels: a first level divided according to quadtree partitioning, and a second level divided according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to the coding units (CUs).

[0049] In the MTT partition structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more types of ternary tree (TT) partitioning. Ternary tree partitioning is a partitioning in which a block is split into three sub-blocks. In some examples, ternary tree partitioning divides a block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

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

[0051] The video encoder 200 and the video decoder 300 may be configured to use quadtree partitioning, QTBT partitioning, MTT partitioning, or other partitioning structures according to HEVC. For the purpose of explanation, the description of the technology of the present disclosure is given with respect to QTBT partitioning. However, it should be understood that the technology of the present disclosure may also be applied to a video decoder configured to use quadtree partitioning or also use other types of partitioning.

[0052] This disclosure may use "NxN" and "N by N" interchangeably to refer to the sample size of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, for example, 16x16 samples or 16 by 16 samples. Typically, a 16x16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). 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. The samples in a CU may be arranged in rows and columns. In addition, a CU does not necessarily need to have the same number of samples in the horizontal direction as in the vertical direction. For example, a CU may include NxM samples, where M is not necessarily equal to N.

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

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

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

[0056] In order to perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. Some examples of JEM and VVC provide sixty-seven intra prediction modes, including various directional modes, as well as planar modes and DC modes. Typically, the video encoder 200 selects an intra prediction mode that describes the neighboring samples of the current block according to which the samples of the current block (e.g., the block of the CU) are to be predicted. 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 above, above left, or to the left of the current block in the same picture as the current block.

[0057] The video encoder 200 encodes data representing a prediction mode for the current block. For example, for an inter-frame prediction mode, the video encoder 200 may encode data representing which prediction mode of various available inter-frame prediction modes is used and motion information for the corresponding mode. For unidirectional or bidirectional inter-frame prediction, for example, the video encoder 200 may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. The video encoder 200 may use a similar mode to encode motion vectors for affine motion compensation mode.

[0058] After prediction of a block (such as intra-frame prediction or inter-frame prediction), the video encoder 200 can calculate residual data for the block. The residual data (such as a residual block) represents the sample-by-sample difference between the block and the prediction block for 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 generate transformed data in the transform domain rather than in 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. In addition, the video encoder 200 can apply a secondary transform after the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc. The video encoder 200 generates transform coefficients after applying one or more transforms.

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

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

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

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

[0063] In this way, the video encoder 200 can generate a bitstream that includes the encoded video data, for example, a syntax element describing the partition of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Finally, the video decoder 300 can receive the bitstream and decode the encoded video data.

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

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

[0066] According to the technology of the present disclosure, the video encoder 200 and the video decoder 300 may be configured to selectively context-code the value of a low-frequency inseparable transform (LFNST) index or flag based on one or more parameters. A video decoder (e.g., the video encoder 200 and / or the video decoder 300) may select a context based on a variety of parameters. Some example parameters include, but are not limited to, block size, color component, partition depth, and the number of non-zero transform coefficients. As a specific example and according to one or more technologies of the present disclosure, a video decoder may select a context for decoding an LFNST index for a video data unit based on a color component of a video data unit. For example, a video decoder may use a first context when the video data unit is a luminance component, and use a second context when the video data unit is a chrominance component. Selecting a context based on a color component may provide one or more advantages. For example, the bit rate of video data may be reduced by the selected context for CABAC decoding of an LFNST index, for example, because some LFNSTs are more likely to be used for certain color components. In other words, the technology of the present disclosure may reduce the amount of data used to represent video data with similar perceptual quality. Thus, these techniques may improve the field of video coding by reducing the bit rate of a bitstream comprising video data.

[0067] The present disclosure may generally involve "signaling" certain information (such as syntax elements). The term "signaling" may generally refer to the transmission of values ​​of syntax elements and / or other data used to decode the encoded video data. That is, the video encoder 200 may signal values ​​for syntax elements in the bitstream. Generally, signaling refers to generating values ​​in the bitstream. As noted above, the source device 102 may transmit the bitstream to the destination device 116 in substantially real time or in non-real time (such as may occur when storing syntax elements to the storage device 112 for later retrieval by the destination device 116).

[0068] Figure 2A and 2B1 is a conceptual diagram showing an example quadtree binary tree (QTBT) structure 130 and a corresponding coding tree unit (CTU) 132. Solid lines represent quadtree splits, and dashed lines indicate binary tree splits. In each split (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which split type (i.e., horizontal or vertical) is used, where, in this example, 0 indicates horizontal splitting and 1 indicates vertical splitting. For quadtree splitting, since the quadtree node splits the block horizontally and vertically into 4 equal-sized sub-blocks, 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 regional tree level (i.e., solid line) of the QTBT structure 130, and syntax elements (such as split information) for the prediction tree level (i.e., dashed line) of the QTBT structure 130. The video encoder 200 may encode video data (such as prediction and transform data) for a CU represented by a terminal leaf node of the QTBT structure 130 , and the video decoder 300 may decode the video data.

[0069] generally, Figure 2B The CTU 132 may be associated with parameters defining the size of blocks corresponding to nodes at the first and second levels of the QTBT structure 130. These parameters may include a CTU size (indicating the size of the CTU 132 in units of samples), a minimum quadtree size (MinQTSize, indicating the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, indicating the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, indicating the maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, indicating the minimum allowed binary tree leaf node size).

[0070] The root node of the QTBT structure corresponding to the CTU may have four child nodes at the first level of the QTBT structure, each of which may be divided according to a quadtree partition. That is, the node of the first level is a leaf node (without child nodes) or has four child nodes. The example of the QTBT structure 130 represents such a node as a parent node and a child node including a solid line for branching. If the nodes of the first level are not larger than the maximum allowed binary tree root node size (MaxBTSize), they may be further divided by the corresponding binary tree. The binary tree splitting of a node may be iterated until the node generated from the split reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of the QTBT structure 130 represents such a node as having a dotted line for branching. The binary tree leaf node is called a coding unit (CU), and the CU is used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further division. As discussed above, a CU may also be referred to as a "video block" or "block".

[0071] In one example of a QTBT partitioning 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. Quadtree partitioning is first applied to the CTU to generate a quadtree leaf node. The quadtree leaf node can have a size from 16x16 (i.e., MinQTSize) to 128x128 (i.e., CTU size). If the leaf quadtree node is 128x128, it will not be further split by the binary tree because the size exceeds MaxBTSize (i.e., 64x64 in this example). Otherwise, the leaf quadtree node will be further divided by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and has a binary tree depth of 0. When the binary tree depth 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), this means that no further horizontal splitting is allowed. Similarly, a binary tree node with a height equal to MinBTSize means that no further vertical splitting is allowed for the binary tree node. As noted above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further partitioning.

[0072] Figure 3 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 3 The present disclosure is provided for purposes of explanation and should not be considered limiting of the techniques as broadly illustrated and described in this disclosure. For purposes of explanation, this disclosure describes the video encoder 200 in the context of video coding standards such as the HEVC video coding standard and the developing H.266 video coding standard. However, the techniques of this disclosure are not limited to these video coding standards and are generally applicable to video encoding and decoding.

[0073] exist Figure 3 In the example of , the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filtering unit 216, a decoded picture buffer (DPB) 218, and an entropy coding unit 220. Any or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filtering unit 216, the DPB 218, and the entropy coding unit 220 may be implemented in one or more processors or in processing circuits. Furthermore, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

[0074] The video data memory 230 may store video data to be encoded by the components of the video encoder 200. The video encoder 200 may receive video data from, for example, the video source 104 ( Figure 1 ) receives the video data stored in the video data memory 230. DPB 218 can act as a reference picture memory, which stores reference video data for use when the video encoder 200 predicts subsequent video data. Video data memory 230 and DPB 218 can be formed by any memory device in a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Video data memory 230 and DPB 218 can be provided by the same memory device or a separate memory device. In various examples, video data memory 230 can be on the chip (shown in the figure) with other components of the video encoder 200, or off the chip relative to those components.

[0075] In the present disclosure, references to the video data memory 230 should not be interpreted as limited to memory internal to the video encoder 200 (unless explicitly described as such), or memory external to the video encoder 200 (unless explicitly described as such). Rather, references to the video data memory 230 should be understood as a reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). Figure 1 The memory 106 may also provide temporary storage for outputs from the various units of the video encoder 200 .

[0076] Show Figure 3 The various units of the video encoder 200 are provided to help understand the operations performed by the video encoder 200. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide specific functions and are pre-set with respect to the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functions on the operations that can be performed. For example, a programmable circuit may 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 may execute software instructions (e.g., to receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally immutable. In some examples, one or more of the units may be different circuit blocks (fixed-function or programmable), and in some examples, one or more units may be integrated circuits.

[0077] The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video encoder 200 is performed using software executed by a programmable circuit, the memory 106 ( Figure 1 ) may store object code for software received and executed by the video encoder 200, or another memory (not shown) within the video encoder 200 may store such instructions.

[0078] The video data memory 230 is configured to store the received video data. The video encoder 200 may retrieve the picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 may be the original video data to be encoded.

[0079] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. The mode selection unit 202 may include additional functional units to perform video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

[0080] The mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and rate-distortion values ​​obtained for such combinations. The encoding parameters may include the partitioning of CTUs into CUs, the prediction mode for the CUs, the transform type for the residual data of the CUs, the quantization parameter for the residual data of the CUs, etc. The mode selection unit 202 may ultimately select a coding parameter combination that has a better rate-distortion value than other tested combinations.

[0081] The video encoder 200 may divide the picture retrieved from the video data memory 230 into a series of CTUs, and encapsulate one or more CTUs in a slice. The mode selection unit 202 may divide the CTUs of the picture according to a tree structure (such as the QTBT structure or quadtree structure of HEVC described above). As described above, the video encoder 200 may form one or more CUs by dividing the CTUs according to the tree structure. Such CUs may also be generally referred to as "video blocks" or "blocks".

[0082] Typically, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the intra prediction unit 226) to generate a prediction block for a current block (e.g., a current CU, or the overlapping portion of a PU and a TU in HEVC). To inter-predict the current block, the 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 the DPB 218). In particular, the motion estimation unit 222 may calculate values ​​indicating how similar a potential reference block will be to the current block, for example, based on a sum of absolute differences (SAD), a sum of squared differences (SSD), a mean absolute difference (MAD), a mean squared difference (MSD), and the like. The motion estimation unit 222 may typically perform these calculations using sample-by-sample differences between the current block and the reference block under consideration. The motion estimation unit 222 may identify the reference block having the lowest value obtained from these calculations, indicating the reference block that most closely matches the current block.

[0083] The motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of the reference block in the reference picture relative to the position of the current block in the current picture. The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, for unidirectional inter prediction, the motion estimation unit 222 may provide a single motion vector, while for bidirectional inter prediction, the motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, the motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, if the motion vectors have fractional sample precision, the motion compensation unit 224 may interpolate the values ​​for the prediction block according to one or more interpolation filters. In addition, for bidirectional inter prediction, the motion compensation unit 224 may retrieve data for two reference blocks identified by the corresponding motion vectors and combine the retrieved data, for example, by sample-by-sample averaging or weighted averaging.

[0084] As another example, for intra prediction or intra prediction decoding, the intra prediction unit 226 can generate a prediction block based on samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally arithmetically combine the values ​​of adjacent samples and fill these calculated values ​​across the current block in a defined direction to produce a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average of adjacent samples of the current block and generate a prediction block to include the resulting average for each sample of the prediction block.

[0085] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives the original uncoded version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, the residual generation unit 204 may also determine the difference between the sample values ​​in the residual block to generate the residual block using residual differential pulse coding modulation (RDPCM). In some examples, the residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0086] In the example where the mode selection unit 202 divides the CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs of different sizes. As indicated above, the size of the CU may refer to the size of the luma coding block of the CU, and the size of the PU may refer to the size of the luma prediction unit of the PU. Assuming that the size of a particular CU is 2Nx2N, the video encoder 200 may support PU sizes of 2Nx2N or NxN for intra-frame prediction, and symmetrical PU sizes of 2Nx2N, 2NxN, Nx2N, NxN or similar sizes for inter-frame prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning of PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter-frame prediction.

[0087] In an example where the mode selection unit does not further divide the CU into PUs, each CU may be associated with a luma coding block and a corresponding chroma coding block. As above, the size of a CU may refer to the size of the luma coding block of the CU. The video encoder 200 and the video decoder 300 may support a CU size of 2Nx2N, 2NxN, or Nx2N.

[0088] For other video coding techniques (such as intra-block copy mode coding, affine mode coding, and linear model (LM) mode coding, to name a few examples), the mode selection unit 202 generates a prediction block for the current block being encoded via a corresponding unit associated with the coding technique. In some examples (such as palette mode coding), the mode selection unit 202 may not generate a prediction block, and instead generate syntax elements indicating the manner in which the block is reconstructed based on the selected palette. In such a mode, the mode selection unit 202 may provide these syntax elements to the entropy coding unit 220 for encoding.

[0089] As described above, the residual generation unit 204 receives video data for a current block and a 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.

[0090] The 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"). The transform processing unit 206 can apply various transforms to the residual block to form a transform coefficient block. For example, the transform processing unit 206 can apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 can perform multiple transforms on the residual block, for example, a primary transform and a secondary transform (such as a rotation transform). In some examples, the transform processing unit 206 does not apply a transform to the residual block.

[0091] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may cause a loss of information, and therefore, the quantized transform coefficients may have a lower precision than the original transform coefficients produced by the transform processing unit 206.

[0092] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct a residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (although potentially with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0093] Filtering unit 216 may perform one or more filtering operations on the reconstructed block. For example, filtering unit 216 may perform a deblocking operation to reduce blocking artifacts along the edges of the CU. In some examples, operations of filtering unit 216 may be skipped.

[0094] The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in an example where the operation of the filtering 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 filtering unit 216 is required, the filtering 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 the reference picture formed by the reconstructed (and potentially filtered) blocks from the DPB 218 to perform inter-frame prediction on the blocks of the subsequently encoded pictures. In addition, the intra-frame prediction unit 226 can use the reconstructed blocks of the current picture in the DPB 218 to perform intra-frame prediction on other blocks in the current picture.

[0095] In general, the entropy coding unit 220 may entropy encode syntax elements received from other functional components of the video encoder 200. For example, the entropy coding unit 220 may entropy encode a quantized transform coefficient block from the quantization unit 208. As another example, the entropy coding unit 220 may entropy encode a prediction syntax element (e.g., motion information for inter-frame prediction or intra-frame mode information for intra-frame prediction) from the mode selection unit 202. The entropy coding unit 220 may perform one or more entropy coding operations on the syntax element (another example of video data) to generate entropy-encoded data. For example, the entropy coding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential Golomb coding operation, or another type of entropy coding operation on the data. In some examples, the entropy coding unit 220 may operate in a bypass mode, in which the syntax element is not entropy encoded. Referring to FIG. 2 , the entropy coding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential Golomb coding operation, or another type of entropy coding operation on the data. Fig.12 Further details of one example of the entropy encoding unit 220 are discussed.

[0096] The video encoder 200 may output a bitstream including entropy-encoded syntax elements required to reconstruct blocks of a slice or picture. In particular, the entropy encoding unit 220 may output a bitstream.

[0097] The operations described above are described with respect to blocks. Such descriptions should be understood as operations for luma coding blocks and / or chroma coding blocks. As described above, in some examples, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a CU. In some examples, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a PU.

[0098] In some examples, operations performed with respect to luma coding blocks need not be repeated for chroma coding blocks. As an example, operations for identifying motion vectors (MVs) and reference pictures for luma coding blocks need not be repeated in order to identify MVs and reference pictures for chroma blocks. Specifically, the MVs for luma coding blocks may be scaled to determine the MVs for chroma blocks, and the reference pictures may be the same. As another example, the intra prediction process may be the same for luma coding blocks and chroma coding blocks.

[0099] As will be explained in more detail below, the video encoder 200 represents an example of a device configured to encode video data, the device comprising: a memory configured to store the video data; and one or more processing units implemented in circuits and configured to: selectively context decode the value of a low-frequency inseparable transform index or flag; and transform blocks of the video data based on the low-frequency inseparable transform index or flag.

[0100] Figure 4 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Figure 4 The above description is provided for the purpose of explanation and is not a limitation of the techniques as broadly illustrated and described in this disclosure. For the purpose of explanation, this disclosure describes a video decoder 300 according to the techniques of JEM, VVC, and HEVC. However, the techniques of this disclosure may be performed by a video decoding device configured for other video decoding standards.

[0101] exist Figure 4 In the example of , the video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filtering unit 312, and a decoded picture buffer (DPB) 134. Any or all of the CPB memory 320, the entropy decoding unit 302, the prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filtering unit 312, and the DPB 134 may be implemented in one or more processors or in processing circuitry. Furthermore, the video decoder 300 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0102] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include an addition unit to perform prediction according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0103] CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of video decoder 300. For example, the video bitstream may be obtained from computer readable medium 110 ( Figure 1 ) obtains video data stored in CPB memory 320. CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. In addition, CPB memory 320 may store video data other than syntax elements of decoded pictures, such as temporary data representing outputs from various units of video decoder 300. DPB 314 typically stores decoded pictures, and video decoder 300 may output decoded pictures, and / or use decoded pictures as reference video data when decoding subsequent data or pictures of the encoded video bitstream. CPB memory 320 and DPB 314 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM) or other types of memory devices. CPB memory 320 and DPB 314 may be provided by the same memory device or a separate memory device. In various examples, CPB memory 320 can be on-chip with other components of video decoder 300 , or off-chip relative to those components.

[0104] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) to retrieve the decoded video data. That is, memory 120 may utilize CPB memory 320 to store data as discussed above. Likewise, when some or all of the functionality of video decoder 300 is implemented in software to be executed by processing circuitry of video decoder 300, memory 120 may store instructions to be executed by video decoder 300.

[0105] Shown in Figure 4 The various units shown in FIG. 3 are used to help understand the operations performed by the video decoder 300. The units may be implemented as fixed function circuits, programmable circuits, or a combination thereof. Figure 3, fixed-function circuits refer to circuits that provide specific functions and are pre-set with respect to the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functions in the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive parameters or output parameters), but the types of operations performed by fixed-function circuits are generally immutable. In some examples, one or more of the units may be different circuit blocks (fixed-function or programmable), and in some examples, one or more units may be integrated circuits.

[0106] The video decoder 300 may include an ALU, an EFU, a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video decoder 300 is performed by software executed on the programmable circuit, an on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

[0107] The entropy decoding unit 302 may receive the encoded video data from the CPB and entropy decode the video data to reproduce the syntax elements. The prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, and the filtering unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.

[0108] Generally, the video decoder 300 reconstructs a picture block by block. The video decoder 300 may perform a reconstruction operation on each block individually (wherein a block currently being reconstructed (ie, decoded) may be referred to as a "current block").

[0109] The entropy decoding unit 302 may entropy decode syntax elements defining the quantized transform coefficients of the quantized transform coefficient block and transform information, such as a quantization parameter (QP) and / or a transform mode indication. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, determine a degree of inverse quantization for the inverse quantization unit 306 to apply. The inverse quantization unit 306 may, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thereby form a transform coefficient block including the transform coefficients. Fig.13 Further details of one example of the entropy decoding unit 302 are discussed.

[0110] After the inverse quantization unit 306 forms the transform coefficient block, the inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, the inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0111] In addition, prediction processing unit 304 generates a prediction block based on the prediction information syntax elements entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax elements indicate that the current block is inter-predicted, motion compensation unit 316 can generate a prediction block. In this case, the prediction information syntax elements can indicate a reference picture in DPB 314 from which to retrieve the reference block, and a motion vector that identifies the position of the reference block in the reference picture relative to the position of the current block in the current picture. Motion compensation unit 316 can generally generate a prediction block in the same manner as described for motion compensation unit 224 ( Figure 3 )The inter-frame prediction process is performed in a manner substantially similar to that described in detail above.

[0112] As another example, if the prediction information syntax element indicates that the current block is intra-predicted, the intra-prediction unit 318 may generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Again, the intra-prediction unit 318 may generally generate a prediction block in the same manner as described with respect to the intra-prediction unit 226 ( Figure 3 The intra prediction process is performed in a substantially similar manner as described in the foregoing description. The intra prediction unit 318 may retrieve data of neighboring samples of the current block from the DPB 314.

[0113] The reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, the reconstruction unit 310 may reconstruct the current block by adding samples of the residual block to corresponding samples of the prediction block.

[0114] The filtering unit 312 may perform one or more filtering operations on the reconstructed block. For example, the filtering unit 312 may perform a deblocking operation to reduce blocking artifacts along the edges of the reconstructed block. The operations of the filtering unit 312 may not necessarily be performed in all examples.

[0115] The video decoder 300 may store the reconstructed blocks in the DPB 314. As discussed above, the DPB 314 may provide reference information (such as samples of the current picture for intra prediction and previously decoded pictures for subsequent motion compensation) to the prediction processing unit 304. In addition, the video decoder 300 may output decoded pictures from the DPB for display on a display device such as a Figure 1 for subsequent presentation on a display device 118).

[0116] In this way, as will be explained in more detail below, the video decoder 300 represents an example of a video decoding device, which includes: a memory configured to store video data; and one or more processing units implemented in circuits and configured to: selectively context decode the value of a low-frequency inseparable transform index or flag; and transform blocks of video data according to the low-frequency inseparable transform index or flag.

[0117] Overview of transform-related tools. In exemplary video coding standards prior to HEVC, only fixed separable transforms or fixed separable inverse transforms were used in video encoding and video decoding, where type 2 discrete cosine transform (DCT-2) was used vertically and horizontally. In HEVC, in addition to DCT-2, type 7 discrete sine transform (DST-7) is adopted as a fixed separable transform for 4x4 blocks.

[0118] The following co-pending U.S. patents and U.S. patent applications describe the Multi-Transform Selection (MTS) technique: U.S. Patent No. 10,306,229, issued on May 28, 2019, U.S. Patent Publication No. 2018 / 0020218, issued on January 18, 2018, and U.S. Patent Publication No. 2019 / 0373261, issued on December 5, 2019. Note that MTS was previously referred to as Adaptive Multi-Transform (AMT). The MTS technique is generally the same as the AMT technique described previously. An example of MTS described in U.S. Patent Publication No. 2019 / 0373261 was adopted in the Joint Experimental Model 7.0 (JEM-7.0) of the Joint Video Experts Team (JVET) (e.g., see hhi.fraunhofer.de / fields-of-competence / image-processing / research-groups / image-video-coding / hevc-high-efficiency-video-coding / transform-coding-using-the-residual-quadtree-rqt.html), and a simplified version of MTS was subsequently adopted in VVC.

[0119] In general, when using MTS to encode or decode a transform block of transform coefficients, the video encoder 200 and the video decoder 300 may determine one or more of a plurality of separable transforms to be used. By including more separable transform options, coding efficiency may be improved because the selected transform may be more suitable for the content being decoded.

[0120] Figure 5is an illustration of an example low frequency non-separable transform (LFNST) at the encoder and decoder side (eg, video encoder 200 and video decoder 300), where the use of LFNST introduces a new stage between the separable transform and quantization in the codec. Figure 5 As shown in , at the encoder side (e.g., video encoder 200), the transform processing unit 206 may first apply a separable transform 500 to the transform block to obtain transform coefficients. Then, the transform processing unit 206 may apply LFNST 502 to a portion (e.g., LFNST region) of the transform coefficients of the transform block. As described above, the transform processing unit 206 may apply a zeroing process in conjunction with LFNST. Then, the quantization unit 208 may quantize the resulting transform coefficients before entropy encoding.

[0121] At the decoder side (eg, video decoder 300), the inverse quantization unit 306 first quantizes the entropy decoded transform coefficients in the transform block (see Figure 4 ) is inverse quantized. Then, the inverse transform processing unit 308 of the video decoder 300 applies the inverse LFNST 504 to the LFSNT region of the transform block. Then, the inverse transform processing unit 308 applies the inverse separable transform 506 to the result of the inverse LFNST to generate a residual block.

[0122] Using the example LFNST in JEM-7.0 (e.g. Figure 5 ) to further improve the decoding efficiency of MTS, where the implementation of LFNST is based on the example hypercube Givens transform (HyGT) described in U.S. Patent Publication No. 10,448,053 filed on February 14, 2017. Other example designs and additional details are described in U.S. Patent No. 10,491,922 filed on September 20, 2016, U.S. Patent Publication No. 2017 / 0094314 issued on March 30, 2017, U.S. Patent No. 10,349,085 filed on February 14, 2017, and U.S. Patent Application No. 16 / 354,007 filed on March 25, 2019. Recently, LFNST has been adopted in the VVC standard (see JVET-N0193, Reduced Secondary Transform (RST) (CE6-3.1), available online at http: / / phenix.it-sudparis.eu / jvet / doc_end_user / documents / 14_Geneva / wg11 / JVE T-N0193-v5.zip). Note that LFNST was previously known as the Non-Separable Secondary Transform (NSST) or the Secondary Transform.

[0123] In the LFNST design in VVC draft 5, the encoder (e.g., the video encoder 200) can be configured to perform a zeroing operation that keeps the K-lowest frequency transform coefficients unchanged (e.g., the values ​​of the K-lowest frequency transform coefficients are not zeroed). The K-lowest frequency transform coefficients are transformed by an LFNST of size N (e.g., for an 8x8 LFNST region, N=64). The decoder (e.g., the video decoder 300) reconstructs the separable coefficients (e.g., MTS coefficients) by using only these K coefficients (also referred to as K LFNST coefficients). In VVC draft 5, normatively, such a zeroing process is performed only for LFNSTs of size 4x4 and 8x8, where the decoder implicitly infers (assumes or determines without receiving signaling) that the values ​​of the remaining NK high frequency transform coefficients are set to have zero values, and the K LFNST coefficients are used for reconstruction.

[0124] Figure 6 is a representative illustration of transform coefficients obtained after applying LFNST of size N to a transform block 602 of size HxW with zeroing, where Z of the N transform coefficients are zeroed and K coefficients are retained. Figure 6 As shown in , the video encoder 200 applies a separable transform (e.g., using an MTS technique) to a transform block 602 to obtain MTS coefficients. Then, the video encoder 200 applies LFNST to an LFNST region 600 (having a size of hxw) of the transform block 602. The dark region 601 of the LFNST region 600 is the K coefficients that are retained (e.g., LFNST coefficients). The white region of the LFNST region 600 is the Z (NK) coefficients that are zeroed (e.g., zeroed coefficients).

[0125] As described in U.S. Patent No. 10,491,922 filed on September 20, 2016, U.S. Patent Publication No. 2017 / 0094314 issued on March 30, 2017, and U.S. Provisional Application No. 62 / 799,410 filed on January 31, 2019, the LFNST regions (e.g., Figure 6 LFNST is performed by converting a 2-D sub-block of the transform coefficients (e.g., the LFNST region 600 in FIG. 4 ) into a 1-D list (or vector) of transform coefficients, and then applying the transform on a subset of the transform coefficients (e.g., the transform coefficients that are not zeroed).

[0126] Figure 7 An example of separable transform coefficients (MTS) and LFNST coefficients obtained without any zeroing is shown. Figure 7As shown in , the video encoder 200 applies a separable transform (e.g., using an MTS technique) to a transform block 702 (having a size of HxW) to obtain MTS coefficients. Then, the video encoder 200 applies LFNST to a LFNST region 700 (having a size of hxw) of the transform block 702. Figure 7 In the example of , all N coefficients (eg, LFNST coefficients) of the LFNST region 700 are retained. That is, in Figure 7 No zeroing is performed in the example.

[0127] Figure 8 and 9 An example of LFNST proposed in U.S. Provisional Application No. 62 / 799,410, filed on January 31, 2019, and U.S. Provisional Application No. 62 / 849,689, filed on May 17, 2019 (hereinafter referred to as the "'689 Application") is shown, which applies zeroing to coefficients outside the LFNST region. In particular, Figure 8 An example of obtaining LFNST coefficients by applying LFNST and zeroing both the Z highest frequency coefficients in the LFNST region (in block 800) and the MTS coefficients outside the LFNST region (outside block 800) is shown. In addition, Fig. 9 An example of obtaining LFNST coefficients by applying LFNST and zeroing only the MTS coefficients outside the LFNST region (outside the block 900 ) is shown.

[0128] The following sections describe Binary Arithmetic Coding (BAC) and Context-Adaptive Binary Arithmetic Coding (CABAC) techniques in more detail. In general, BAC is a recursive interval subdivision process. In the H.264 / AVC and H.265 / HEVC video coding standards, BAC is used to encode binary symbols in the CABAC process. The output of the BAC decoder is a binary stream that represents a value or pointer to the probability within the final decoded probability interval. The probability interval is specified by a range ("range") and a lower limit value ("low"). The range is an extension of the probability interval. The lower limit is the lower boundary of the decoding / probability interval.

[0129] The application of arithmetic coding to video coding is described in the following document: D. Marpe, H. Schwarz, and T. Wiegand, "Context-Based Adaptive Binary Arithmetic Coding in the H.264 / AVC Video Compression Standard," IEEE Transactions on Circuits and Systems for Video Technology, Vol. 13, No. 7, July 2003. CABAC involves three main functions, namely binarization, context modeling, and arithmetic coding. Binarization refers to the function of mapping syntax elements to binary symbols (or "bins"). Binary symbols may also be referred to as "binary symbol strings." Context modeling refers to the function of estimating the probability of individual binary symbols. Arithmetic coding refers to the subsequent function of compressing binary symbols into bits based on the estimated probabilities. Various devices and / or modules thereof (such as binary arithmetic decoders) may perform the function of arithmetic coding.

[0130] Several different binarization processes are used in HEVC, including unary (U), truncated unary (TU), k-th exponential Golomb (EGk), and fixed length (FL). The details of the various binarization processes are described in the following document: V. Sze and M. Budagavi, "High throughput CABAC entropy coding in HEVC", IEEE Transactions on Circuits and Systems for Video Technology (TCSVT), Vol. 22, No. 12, pp. 1778-1791, December 2012.

[0131] Each context (i.e., probability model) in CABAC is represented by a state. Each state (σ) implicitly represents the probability (p) that a particular symbol (e.g., a binary symbol) is the least likely symbol (LPS). σ ). The symbol can be an LPS or a most probable symbol (MPS). The symbol is binary, and therefore, the MPS and LPS can be either 0 or 1. The probability is estimated for the corresponding context and (implicitly) used to entropy code the symbol using an arithmetic coder.

[0132] The process of BAC is handled by a state machine that changes its internal value "range" and "floor" according to the context to be decoded and the value of the binary symbol being decoded. Depending on the state of the context (i.e., its probability), the range is divided into rangeMPS σ (state σThe range of most likely symbols in the σ (state σ Theoretically, the probability state σ rangeLPS σ The value is derived by multiplication:

[0133] rangeLPS σ =range×p σ ,

[0134] where p σ is the probability of choosing LPS. Of course, the probability of MPS is 1-p σ . Equivalently, rangeMPS σ Equal to range minus rangeLPS σ The BAC iteratively updates the range based on the state of the context binary symbol to be decoded, the current range, and the value of the binary symbol being decoded (ie, the binary symbol is equal to the LPS or MPS).

[0135] Fig. 10A and 10B An example of this process is shown at a binary symbol n. Fig. 10A In example 201, the range at the binary symbol n includes RangeMPS and RangeLPS, and RangeLPS is composed of the probability (p) of LPS given a specific context state (σ). σ ). Example 201 shows the updating of the range at binary symbol n+1 when the value of binary symbol n is equal to MPS. In this example, the lower limit remains unchanged, but the value of the range at binary symbol n+1 is reduced to the value of RangeMPS at binary symbol n. Fig. 10B Example 203 shows the updating of the range at binary symbol n+1 when the value of binary symbol n is not equal to MPS (i.e., equal to LPS). In this example, the lower limit is moved to the lower range value of RangeLPS at binary symbol n. In addition, the value of the range at binary symbol n+1 is reduced to the value of RangeLPS at binary symbol n.

[0136] In HEVC, the range is represented using 9 bits and the floor is represented using 10 bits. There is a renormalization process to maintain sufficient accuracy for the range and floor values. Renormalization occurs whenever the range is less than 256. Therefore, after renormalization, the range is always equal to or greater than 256. Depending on the values ​​of the range and floor, the BAC outputs "0" or "1" to the bitstream, or updates an internal variable (called BO: Unfinished Bit) for future output. Fig.11An example of a BAC output that depends on the range is shown. For example, when the range and lower limit are above a certain threshold (e.g., 512), a "1" is output to the bit stream. When the range and lower limit are below a certain threshold (e.g., 512), a "0" is output to the bit stream. When the range and lower limit are between certain thresholds, nothing is output to the bit stream. Instead, the BO value is incremented and the next binary symbol is encoded.

[0137] As described above, in video compression standards such as VVC, arithmetic coding methods are used to provide high compression efficiency. This is achieved by first converting non-binary syntax elements into binary representations (e.g., 0, 1) using a process called binarization. The resulting transformed entries are called binary symbols or binary symbol strings. These binary symbols or binary symbol strings are then fed into the arithmetic coding process. FIG. 10 shows an example context-adaptive binary arithmetic coding (CABAC) encoding stage. The example CABAC encoding stage can be implemented in a video encoder, for example, by Figure 3 The entropy encoding unit 220 of the video encoder 200.

[0138] In VVC draft 5, context-adaptive binary arithmetic coding (CABAC) is used to generate binary symbols through a binarization process. For each decoded binary symbol value, an appropriate context model is selected. These context models are used to encode each binary symbol value into an output bit based on the binary symbol probability value. When the binary symbol is equally likely to be 0 or 1, the CABAC engine bypasses context modeling and binary symbol encoding. This is the bypass decoding stage discussed below. Otherwise, based on the probability of the binary symbol value, an appropriate context model is specified to encode and model the binary symbol value. As the encoder encodes more binary symbols, the context is adapted. Finally, the context-coded binary symbol value or the original bit stream is sent or otherwise provided to the decoder.

[0139] Fig.121 is a block diagram of an example entropy coding unit 220 that can be configured to perform CABAC according to the techniques of the present disclosure. Syntax elements 1180 are input to the entropy coding unit 220. If the syntax element is already a binary valued syntax element (e.g., a flag or other syntax element that has only values ​​0 and 1), the binarization step can be skipped. If the syntax element is a non-binary valued syntax element (e.g., a syntax element that may have values ​​other than 1 or 0), the non-binary valued syntax element is binarized by a binarizer 1200. The binarizer 1200 performs a mapping of non-binary valued syntax elements to a sequence of binary decisions. These binary decisions are often referred to as "binary symbols". For example, for a transform coefficient level, the value of the level can be decomposed into consecutive binary symbols, each binary symbol indicating whether the absolute value of the coefficient level is greater than a certain value. For example, a binary symbol 0 (sometimes referred to as a significance flag) indicates whether the absolute value of the transform coefficient level is greater than 0. A binary symbol 1 indicates whether the absolute value of the transform coefficient level is greater than 1, and so on. A unique mapping can be developed for each non-binary valued syntax element.

[0140] Each binary symbol generated by the binarizer 1200 is fed to the binary arithmetic decoding side of the entropy coding unit 220. That is, for a predetermined set of non-binary valued syntax elements, each binary symbol type (e.g., binary symbol 0) is decoded before the next binary symbol type (e.g., binary symbol 1). Decoding can be performed in normal mode or bypass mode. In bypass mode, the bypass coding engine 1260 performs arithmetic decoding using a fixed probability model (e.g., using Golomb-Rice or exponential Golomb decoding). Bypass mode is typically used for more predictable syntax elements.

[0141] Decoding in normal mode involves performing CABAC. Normal mode CABAC is used to decode binary symbol values, where the probability of the value of the binary symbol is predictable given the value of the previously decoded binary symbol. The probability that the binary symbol is LPS is determined by the context modeler 1220. The context modeler 1220 outputs the binary symbol value and the probability state for the context (e.g., the probability state σ, including the value of the LPS and the probability of the LPS occurring). The context can be the initial context of a series of binary symbols, or can be determined based on the decoded values ​​of the previously decoded binary symbols. The identification of the context can be represented and / or determined based on the value of the variable ctxInc (context increment, such as the value of ctxInc representing the increment applied to the previous context). As described above, the context modeler 1220 can update the state based on whether the received binary symbol is MPS or LPS. After the context and probability state σ are determined by the context modeler 1220, the conventional coding engine 1240 performs BAC on the binary symbol value.

[0142] Fig.13 is a block diagram of an example entropy decoding unit 302 that may be configured to perform CABAC according to the techniques of this disclosure. Fig.13 The entropy decoding unit 302 is used in Fig.12 CABAC is performed in the reverse manner of the entropy coding unit 220 described in . The decoded bits from the bitstream 2180 are input to the entropy decoding unit 302. The decoded bits are fed to the context modeler 2200 or the bypass decoding engine 2220 based on whether the decoded bits were entropy coded using the normal mode or the bypass mode. If the decoded bits were decoded in the bypass mode, the bypass decoding engine will use Golomb-Rice or exponential Golomb decoding, for example, to retrieve binary valued syntax elements or binary symbols for non-binary syntax elements.

[0143] If the decoded bits are decoded in the conventional mode, the context modeler 2200 may determine a probability model for the decoded bits, and the conventional decoding engine 2240 may decode the decoded bits to produce a non-binary valued syntax element (or the syntax element itself, if a binary value) binary symbol. After the context and probability state σ are determined by the context modeler 2200, the conventional decoding engine 2240 performs BAC to decode the binary symbol value. In other words, the conventional decoding engine 2240 may determine the probability state of the context and decode the binary symbol value based on the previously decoded binary symbol and the current range. After decoding the binary symbol, the context modeler 2200 may update the probability state of the context based on the window size and the value of the decoded binary symbol.

[0144] The techniques proposed in the '689 application can reduce the signaling overhead of LFNST index / flag based on side information obtained from coefficient decoding. In particular, the techniques of the '689 application can use a return-to-zero coefficient pattern to infer the LFNST index. In addition, U.S. Provisional Application No. 62 / 861,828, filed on June 14, 2019 (hereinafter referred to as the "'828 application"), proposes alternative signaling of LFNST index / flag, and further proposes to signal LFNST index / flag at the transform unit (TU) level instead of the decoding unit (CU) level.

[0145] This disclosure describes various new context models for a CABAC engine to code LFNST indexes / flags.In this way, the techniques of this disclosure may enable a video coder to reduce the signaling overhead caused by LFNST.

[0146] According to one or more techniques of the present disclosure, a video decoder (e.g., a video encoder, such as the video encoder 200 , or a video decoder such as the video decoder 300 )) may perform context modeling / decoding of LFNST indexes at a transform unit (TU) level. In VVC Draft 5, LFNST signaling is performed at a coding unit (CU) level. The '828 application and U.S. Provisional Application No. 62 / 830,125 filed on April 5, 2019 (hereinafter referred to as the "'125 application") describe specific methods for signaling LFNST indexes at a transform unit (TU) level. The methods proposed by the '828 application and the '125 application implement signaling of both MTS and LFNST-related indexes / flags at the same level (i.e., TU level). The present disclosure proposes techniques for context-based signaling covering LFNST indexes / flags.

[0147] The following signaling techniques may be used alone or in any combination:

[0148] As a first example signaling technique, a video decoder may contextually decode LFNST indices / flags based on the value of the MTS index / flag at the TU level. As an example, if the MTS index (mtsIdx) for a TU is MTS_DCT-2_DCT-2 (mtsIdx = 0), the video decoder may contextually decode the LFNST indices / flags at the TU level. As another example, if the MTS index for a TU is greater than 2 (mtsIdx > 1, larger transform), the video decoder may contextually decode the LFNST indices / flags at the TU level. As another example, if the MTS index for a first TU is MTS_DCT-2_DCT-2 (mtsIdx = 0) (or any other MTS index combination), the video decoder may contextually decode the LFNST indices / flags that can be contextually decoded for the first TU, and the LFNST indices / flags for the remaining TUs may be inferred based on the first TU.

[0149] As a second example signaling technique, a video decoder may contextually decode the LFNST indices / flags that can be contextually decoded based on the block size of each TU (e.g., the width and height of the TU block). For example, if the TU block size is 4x4 (e.g., width x height) or the TU block size is less than / greater than a block size threshold (e.g., width x height < 16x16), the video decoder may contextually decode the LFNST indices / flags.

[0150] As a third example signaling technique, a video decoder may contextually decode the LFNST indices / flags that can be contextually decoded based on whether the TU is a luminance or chrominance component. For example, if the TU block is a chrominance block, the video decoder may contextually decode the LFNST indices / flags separately. Similarly, if the TU block is a luminance block, the video decoder may contextually decode the LFNST indices / flags separately.

[0151] As a fourth example signaling technique, a video decoder may contextually decode the LFNST indices / flags based on the TU depth. For example, if the TU depth is less than a threshold depth (e.g., TU.depth < threshold_depth), the video decoder may contextually decode the LFNST index. Example values of the threshold depth include, but are not limited to, 1, 2, 3, 4, and 5.

[0152] As a fifth example signaling technique, the video encoder may context-code the LFNST index / flag based on the number of non-zero transform coefficients at the TU level. For example, if the number of non-zero coefficients after MTS decoding is less than a threshold number, the video decoder may context-code the LFNST index. As a specific example, in a 32x32 TU on the upper left 8x8 sub-block of the TU, if the number of non-zero coefficients after MTS decoding is less than 8, the video decoder may context-code the LFNST index.

[0153] Note that a single CU may include multiple TUs. In the example signaling techniques discussed above, the video coder may (i) perform context coding for each TU separately, and (ii) perform context coding for a subset of TUs in a given CU (e.g., only the first TU in a given CU). In VVC draft 5, a CU of size 128x128 contains multiple TUs, so the methods covered in this disclosure can be applied to such TUs.

[0154] In another example, the context coding detailed in the example signaling technique discussed above may be performed only for the first TU in a given CU, and the signaling of the LFNST index may be skipped for other TUs. In this case, the skipped TU may infer (or reuse) the context-coded LFNST index / flag from the first TU.

[0155] According to one or more techniques of the present disclosure, a video decoder (e.g., a video encoder (such as video encoder 200) or a video decoder (such as video decoder 300)) may perform context modeling / decoding of LFNST indexes at a coding unit (CU) level and other partitions. As discussed above, the video decoder may perform context-based signaling of LFNST indexes / flags at the TU level. In addition to or in lieu of TU-level signaling, the video decoder may perform context decoding of LFNST indexes at other partitions and sub-blocks / units (e.g., context decoding at the CU level). For example, similar to the design in VVC Draft 5, the video decoder may contextually decode the LFNST indexes / flags based on certain CU-level parameters and information. In this case, LFNST context decoding may use the following signaling techniques alone or in any combination:

[0156] As a first example signaling technique, the video coder may contextually code the LFNST index based on whether the CU (i.e., or similar / arbitrary partition type) is a luma component or a chroma component. As an example, if the CU block is a chroma channel, the video coder may contextually code the LFNST index / flag based on this information. As another example, if the CU block is a luma channel, the video coder may contextually code the LFNST index / flag based on this information.

[0157] As a second example signaling technique, the video decoder may context-code the LFNST index that may be context-coded based on the number of non-zero transform coefficients at the CU level (or any partition type). For example, if the total number of non-zero coefficients after MTS decoding is less than a threshold, the video decoder may context-code the LFNST index based on this information. As a specific example, if the total number of non-zero coefficients after MTS decoding in a 128x128 CU is less than 32, the video decoder may context-code the LFNST index that may be context-coded.

[0158] As a third example signaling technique, the video coder may context code the LFNST index based on the block size of each CU or any other partition (e.g., the width and height of the CU or other partition block). For example, if the CU block size is 4x4 (e.g., width x height) or the CU block size is less than / greater than the block size threshold (e.g., width x height <16x16), the video coder may context code the LFNST index.

[0159] According to one or more techniques of the present disclosure, a video decoder (e.g., a video encoder (such as video encoder 200) or a video decoder (such as video decoder 300)) can perform context modeling / coding for unified LFNST index / flag with MTS index / flag signaling. In VVC draft 5, LFNST signaling is performed at the coding unit (CU) level. The '828 application proposes an alternative design that combines the signaling of LFNST index / flag with existing transform signaling (e.g., MTS index / flag signaling) so that the signaling of MTS and LFNST can be unified / coordinated. In this case, the context modeling and coding of LFNST index and MTS index can also be unified and coordinated to use the same context and context modeling.

[0160] The techniques described above for context modeling / coding of LFNST indexes at the transform unit (TU) level, context modeling / coding of LFNST indexes at the coding unit (CU) level and other partitions, and context modeling / coding of unified LFNST indexes / flags with MTS index / flag signaling may be used alone or in any combination.

[0161] Fig.14 2 is a flowchart illustrating an example method for encoding a current block. The current block may include a current CU. Although relative to the video encoder 200 ( Figure 1 and 3 ), but it should be understood that other devices may be configured to perform the same Fig.14 A similar approach to the one used in this paper.

[0162] In this example, the video encoder 200 initially predicts a current block (350). For example, the video encoder 200 can form a prediction block for the current block. The video encoder 200 can then calculate a residual block for the current block (532). To calculate the residual block, the video encoder 200 can calculate the difference between the original, unencoded block and the prediction block for the current block. The video encoder 200 can then transform and quantize the coefficients of the residual block (354). As discussed above, in some examples, the video encoder 200 can use LFNST to transform the coefficients and encode a syntax element (e.g., LFNST index) that specifies which LFNST (if any) is used. Also as discussed above, the video encoder 200 can select a context for encoding the syntax element based on one or more parameters. As an example, the video encoder 200 can use the following reference to Fig.16 Discuss the techniques to choose the context.

[0163] Next, video encoder 200 may scan the quantized transform coefficients of the residual block (356). During or after the scan, video encoder 200 may entropy encode the coefficients (358). For example, video encoder 200 may encode the coefficients using CAVLC or CABAC. Video encoder 200 may then output entropy coded data for the block (360).

[0164] Fig.15 is a flowchart illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although relative to the video decoder 300 ( Figure 1 and 4 ), but it should be understood that other devices may be configured to perform the same Fig.15 A similar approach to the one used in this paper.

[0165] The video decoder 300 may receive entropy coded data for a current block, such as entropy coded prediction information and entropy coded data for coefficients of a residual block corresponding to the current block (370). The video decoder 300 may entropy decode the entropy coded data to determine prediction information for the current block and reproduce coefficients of the residual block (372). The video decoder 300 may predict the current block (374), for example, using an intra-frame or inter-frame prediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the reproduced coefficients (376) to create a block of quantized transform coefficients. The video decoder 300 may then inverse quantize and inverse transform the coefficients to produce a residual block (378). As discussed above, the video decoder 300 may decode a syntax element (e.g., an LFNST index) that specifies which LFNST (if any) was used to transform the coefficients, and inversely transform the coefficients using the indicated LFNST. Also as discussed above, the video decoder 300 may select a context for decoding the syntax element based on one or more parameters. As an example, the video decoder 300 may use the following reference to Fig.16 Finally, the video decoder 300 can decode the current block by combining the prediction block and the residual block (380).

[0166] Fig.16 1 is a flowchart illustrating an example method for context coding a syntax element that specifies a value of a low frequency non-separable transform (LFNST) index for a video data unit in accordance with one or more techniques of the present disclosure. The video data unit may include a current TU or a current CU. Although relative to the video decoder 300 ( Figure 1 and 4 ), but it should be understood that other devices may be configured to perform the same Fig.16 A method similar to the method of, for example, video encoder 200.

[0167] The video decoder 300 may determine a color component of a video data unit (1602). For example, the video decoder 300 may determine whether a transform unit (TU) of the video data is a luma TU or a chroma TU. As a specific example, the entropy decoding unit 302 may determine a value of cIdx for the video data unit.

[0168] The video decoder 300 may determine, based at least on the color component, a context for context-adaptive binary arithmetic coding (CABAC) of a syntax element specifying a value of a low-frequency non-separable transform (LFNST) index for a video data unit (1604). For example, the entropy decoding unit 302 may determine a value of a context increment (ctxInc) for a binary symbol of a lfnst_idx syntax element or a tu_lfnst_idx syntax element. As discussed above and in accordance with one or more techniques of the present disclosure, the entropy decoding unit 302 may determine a context (e.g., a value of ctxInc) based at least on the color component (e.g., a value of cIdx). In this manner, the entropy decoding unit 302 may use different contexts when coding LFNST indexes for different color components. For example, the entropy decoding unit 302 may use a first context when coding an LFNST index for a luma component and a second different context when coding an LFNST index for a chroma component.

[0169] The entropy decoding unit 302 may determine the context based on factors in addition to or instead of color components. Example factors include a multiple transform select (MTS) index, block size, number of non-zero transform coefficients, partition depth of the unit, and any other factors.

[0170] As an example, the entropy decoding unit 302 may determine the context based on a value of a multiple transform selection (MTS) index for the video data unit. For example, for the video data unit, the entropy decoding unit 302 may obtain a value of the MTS index (e.g., a value of tu_mts_idx for the video data unit) and determine the context based at least in part on the value of the MTS index. As a specific example, the entropy decoding unit 302 may determine the context for the LFNST index as follows:

[0171]

[0172] As another example, the entropy decoding unit 302 may determine the context based on the block size of the video data unit. For example, the entropy decoding unit 302 may determine the length and / or width of the video data unit, and determine the context based at least in part on the length and / or width (e.g., whether the length is less than a length threshold and / or whether the width is less than a width threshold).

[0173] As another example, the entropy decoding unit 302 may determine the context based on the number of non-zero transform coefficients at the level of the video data unit. For example, where the video data unit is a TU, the entropy decoding unit 302 may determine the number of non-zero transform coefficients at the TU level and determine the context based at least in part on the determined number of non-zero transform coefficients at the TU level.

[0174] As another example, the entropy decoding unit 302 may determine the context based on the depth of the video data unit in the partition structure. For example, where the video data unit is a TU, the entropy decoding unit 302 may determine the depth of the TU in the partition structure and determine the context based at least in part on the determined depth.

[0175] The video decoder 300 may CABAC decode 1606 a syntax element that specifies a value of a LFNST index for the video data unit based on the determined context and via a syntax structure for the video data unit. For example, the entropy decoding unit 302 may decode one or more binary symbols of a lfnst_idx syntax element or a tu_lfnst_idx syntax element using the determined context. The entropy decoding unit 302 may provide the decoded binary symbols to one or more components of the video decoder 300, such as the inverse transform processing unit 308.

[0176] In some examples, when the video data unit is a TU among multiple TUs included in a CU, the video decoder 300 may decode a separate syntax element for each TU that specifies an LFNST index for the TU. For example, when the CU includes four TUs, the video decoder 300 may decode four syntax elements, each syntax element specifying an LFNST index for a corresponding TU. However, in some examples, the video decoder 300 may decode a syntax element that specifies an LFNST index for the first TU of the CU and infer LFNST indexes for other TUs in the CU. In this way, the video decoder 300 may enable the video encoder 200 to avoid encoding LFNST index syntax elements for each and every TU.

[0177] The video decoder 300 may transform the transform coefficients of the video data unit based on the transform indicated by the value of the LFNST index (1608). For example, the inverse transform processing unit 308 may inversely transform the dequantized transform coefficients received from the inverse quantization unit 30. The inverse transform used by the inverse transform processing unit 308 may be selected based on the value of the LFNST index. For example, when the syntax element specifying the value of the LFNST index for the video data unit specifies a value of zero, the inverse transform processing unit 308 may apply a first inverse transform, when the syntax element specifying the value of the LFNST index for the video data unit specifies a value of one, the inverse transform processing unit 308 may apply a second inverse transform, and when the syntax element specifying the value of the LFNST index for the video data unit specifies a value of two, the inverse transform processing unit 308 may apply a third inverse transform.

[0178] The techniques of the present disclosure may provide one or more advantages. For example, selecting context based on color component and MTS index may improve decoding efficiency (e.g., reducing the number of bits used to represent video data with the same perceptual quality). The techniques of the present disclosure were tested on VTM-5.0 based on CTC configuration. These results for AI and RA cases are given in Tables 1 and 2. Note that in VTM-5.0, LFNST is disabled for the cases of Low Delay B (LDB) and Low Delay P (LDP) in CTC configuration.

[0179]

[0180] Table 1. AI results based on CTC on VTM5.0

[0181]

[0182]

[0183] Table 2. RA results based on CTC on VTM5.0

[0184] The following numbered examples may illustrate one or more aspects of the present disclosure:

[0185] Example 1A. A method of decoding video data, the method comprising: obtaining a value of a low frequency non-separable transform (LFNST) index or flag for a transform unit (TU) of the video data; and selectively context-coding the obtained value of the LFNST index or flag in a syntax structure for the TU.

[0186] Example 2A. The method of Example 1A, wherein selectively context coding the obtained value comprises context coding a tu_lfnst_idx syntax element.

[0187] Example 3A. The method of Example 1A or 2A further comprising: obtaining a value of a multiple transform selection (MTS) index for the TU; and context coding the obtained value of the MTS index in a syntax structure for the TU.

[0188] Example 4A. The method of Example 3A, wherein context coding the obtained value of the MTS index comprises context coding a tu_mts_idx syntax element.

[0189] Example 5A. The method of Example 3A or 4A, wherein selectively context coding the obtained value of the LFNST index or flag comprises selectively context coding the obtained value of the LFNST index or flag based on the obtained value of the MTS index.

[0190] Example 6A. The method of any of Examples 1A-5A, wherein selectively context coding the obtained value of the LFNST index or flag comprises: wherein selectively context coding the obtained value of the LFNST index or flag is based on a size of the TU.

[0191] Example 7A. The method of any of Examples 1A-6A, wherein selectively context coding the obtained value of the LFNST index or flag comprises: wherein the obtained value of the LFNST index or flag is selectively context coded based on whether the TU is a luma TU or a chroma TU.

[0192] Example 8A. The method of any of Examples 1A-7A, wherein selectively context coding the obtained value of the LFNST index or flag comprises: wherein the obtained value of the LFNST index or flag is selectively context coded based on a depth of the TU.

[0193] Example 9A. The method of any of Examples 1A-8A, wherein selectively context coding the obtained value of the LFNST index or flag comprises: wherein the obtained value of the LFNST index or flag is selectively context coded based on a number of non-zero transform coefficients at a TU level.

[0194] Example 10A. The method of any of Examples 1A-9A, wherein the TU is a first TU in a coding unit (CU), the method further comprising inferring values ​​of LFNST indices or flags for other TUs in the CU based on the value of the LFNST index or flag for the first TU.

[0195] Example 11A The method of any of Examples 1A-10A, wherein selectively context-coding the obtained value of the LFNST index or flag comprises inferring the value of the LFNST index or flag.

[0196] Example 12A. The method of any of Examples 1A-10A, wherein selectively context coding the obtained value of the LFNST index or flag comprises selectively coding the obtained value of the LFNST index or flag using context adaptive binary arithmetic coding (CABAC).

[0197] Example 1B. A method of decoding video data, the method comprising: obtaining a value of a low frequency non-separable transform (LFNST) index or flag for a coding unit (CU) of the video data; and selectively context-coding the obtained value of the LFNST index or flag in a syntax structure for the CU.

[0198] Example 2B. The method of Example 1B, wherein selectively context coding the obtained value comprises context coding a lfnst_idx syntax element.

[0199] Example 3B. The method of any of Examples 1B or 2B, wherein selectively context coding the obtained value of the LFNST index or flag comprises: wherein the obtained value of the LFNST index or flag is selectively context coded based on whether the CU is a luma CU or a chroma CU.

[0200] Example 4B. The method of any of Examples 1B-3B, wherein selectively context coding the obtained value of the LFNST index or flag comprises: wherein the obtained value of the LFNST index or flag is selectively context coded based on a number of non-zero transform coefficients at a CU level.

[0201] Example 5B. The method of any of Examples 1B-4B, wherein selectively context coding the obtained value of the LFNST index or flag comprises: wherein the obtained value of the LFNST index or flag is selectively context coded based on a size of the CU.

[0202] Example 6B. The method of any of Examples 1B-5B, wherein selectively context-coding the obtained value of the LFNST index or flag comprises inferring the value of the LFNST index or flag.

[0203] Example 7B. The method of any of Examples 1B-6B, wherein selectively context coding the obtained value of the LFNST index or flag comprises selectively coding the obtained value of the LFNST index or flag using context adaptive binary arithmetic coding (CABAC).

[0204] Example 1C. A method of decoding video data, the method comprising: obtaining a value of a low frequency non-separable transform (LFNST) index or flag for a block of video data; obtaining a value of a multiple transform select (MTS) index for the block of video data; and context decoding a syntax element representing both the obtained value of the LFNST index or flag and the obtained value of the MTS index in a decoded video bitstream.

[0205] Example 2C. The method of Example 1C, wherein context coding the syntax element comprises coding the syntax element using context adaptive binary arithmetic coding (CABAC).

[0206] Example 1D. The method of any of Examples 1A-2C, wherein the decoding comprises decoding.

[0207] Example 2D. The method of any of Examples 1A-2C, wherein decoding includes encoding.

[0208] Example 3D. An apparatus for decoding video data, the apparatus comprising one or more units for performing the method according to any of Examples 1-2D.

[0209] Example 4D. The device of Example 3D, wherein the one or more units include one or more processors implemented in the circuit.

[0210] Example 5D. The apparatus of any of Examples 3D and 4D, further comprising: a memory for storing video data.

[0211] Example 6D. The apparatus of any of Examples 3D-5D, further comprising: a display configured to display the decoded video data.

[0212] Example 7D. The device of any of Examples 3D-6D, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0213] Example 8D. The apparatus of any of Examples 3D-7D, wherein the apparatus comprises a video decoder.

[0214] Example 9D. The device of any of Examples 3D-8D, wherein the device comprises a video encoder.

[0215] Example 10D. A computer-readable storage medium having instructions stored thereon that, when executed, cause one or more processors to perform the method of any of Examples 1A-2D.

[0216] Example 1E. Any combination of Examples 1A-10D.

[0217] It is to be appreciated that, according to examples, certain actions or events of any of the techniques described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary for the practice of the techniques). In addition, in some examples, actions or events may be performed concurrently rather than sequentially, such as through multithreading, interrupt handling, or multiple processors.

[0218] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or codes on a computer-readable medium or transmitted via a computer-readable medium and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium (which corresponds to a tangible medium such as a data storage medium) or a communication medium (which includes, for example, any medium that facilitates the transfer of a computer program from one place to another according to a communication protocol). In this manner, a computer-readable medium may generally correspond to (1) a non-temporary tangible computer-readable storage medium, or (2) a communication medium such as a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and / or data structures for implementing the techniques described in the present disclosure. A computer program product may include a computer-readable medium.

[0219] By way of example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage device, flash memory, or any other medium that can be used to store the desired program code in the form of instructions or data structures and can be accessed by a computer. In addition, any connection is appropriately referred to as a computer-readable medium. For example, if the instruction is transmitted from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technology (e.g., infrared, radio and microwave), the coaxial cable, fiber optic cable, twisted pair, DSL or wireless technology (e.g., infrared, radio and microwave) is included in the definition of the medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other temporary media, but are instead directed to non-temporary tangible storage media. As used herein, disks and optical disks include compact disks (CDs), laser optical disks, optical disks, digital versatile disks (DVDs), floppy disks and blue-ray disks, wherein disks usually copy data magnetically, while optical disks use lasers to optically copy data. Combinations of the above should also be included within the scope of computer-readable media.

[0220] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Therefore, the terms "processor" and "processing circuit" as used herein may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. In addition, in some aspects, the functions described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a combined codec. In addition, the techniques may be fully implemented in one or more circuits or logic elements.

[0221] The techniques of the present disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC), or a set of ICs (e.g., a chipset). Various components, modules, or units are described in the present disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require implementation by different hardware units. Specifically, as described above, the various units may be combined in a codec hardware unit, or provided by a collection of interoperable hardware units (including one or more processors as described above) in combination with appropriate software and / or firmware.

[0222] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

1. A method for decoding video data, the method comprising: determining a color component of a video data unit; For the video data unit, obtaining a value of a multiple transform select (MTS) index; determining, based at least on the color component and the value of the MTS index, a value of a context increment (ctxInc) for context adaptive binary arithmetic coding (CABAC) of a syntax element that specifies a value of a low frequency non-separable transform (LFNST) index for the video data unit; CABAC-decoding the syntax element specifying the value of the LFNST index for the video data unit based on the determined value of the context delta and via a syntax structure for the video data unit; as well as Transform coefficients of the video data unit are inversely transformed based on the transform indicated by the value of the LFNST index.

2. The method according to claim 1, further comprising: determining a block size of the video data unit, Wherein, determining the value of the context increment includes: determining the value of the context increment based on the color component, the value of the MTS index and the block size of the video data unit.

3. The method according to claim 1, further comprising: determining, at a level of said video data unit, a number of non-zero transform coefficients, Wherein, determining the value of the context increment includes: determining the value of the context increment based on the color component, the value of the MTS index and the number of the non-zero transform coefficients.

4. The method according to claim 1, wherein: The video data unit is a coding unit (CU) of video data.

5. The method according to claim 1, wherein: The video data unit is a transform unit (TU) of video data.

6. The method according to claim 5, further comprising: determining the depth of the TU in the partition structure, Wherein, determining the value of the context increment includes: determining the value of the context increment based on the color component, the value of the MTS index and the depth of the TU.

7. The method according to claim 5, wherein: The TU is a first TU in a coding unit (CU) of video data, and the method further includes: Values ​​of LFNST indexes for other TUs in the CU are inferred based on the value of the LFNST index for the first TU.

8. The method according to claim 1, wherein: The syntax element that specifies the value of the LFNST index for the video data unit comprises a lfnst_idx syntax element or a tu_lfnst_idx syntax element.

9. The method according to claim 1, wherein: The value of the ctxInc represents the increment to be applied to the previous context.

10. A method for encoding video data, the method comprising: selecting a low frequency non-separable transform (LFNST) having a LFNST index from among a plurality of LFNSTs; transforming transform coefficients of a video data unit using the LFNST; determining a color component of the video data unit; For the video data unit, obtaining a value of a multiple transform select (MTS) index; determining, based at least on the color component and the value of the MTS index, a value of a context increment (ctxInc) for context adaptive binary arithmetic coding (CABAC) of a syntax element that specifies a value of the LFNST index for the video data unit; as well as The syntax element that specifies the value of the LFNST index for the video data unit is CABAC encoded based on the determined value of the context delta and via a syntax structure for the video data unit.

11. The method according to claim 10, further comprising: determining a block size of the video data unit, Wherein, determining the value of the context increment includes: determining the value of the context increment based on the color component, the value of the MTS index and the block size of the video data unit.

12. The method according to claim 10, further comprising: determining, at a level of said video data unit, a number of non-zero transform coefficients, Wherein, determining the value of the context increment includes: determining the value of the context increment based on the color component, the value of the MTS index and the number of the non-zero transform coefficients.

13. The method according to claim 10, wherein: The video data unit is a coding unit (CU) of video data.

14. The method according to claim 10, wherein: The video data unit is a transform unit (TU) of video data.

15. The method according to claim 14, further comprising: determining the depth of the TU in the partition structure, Wherein, determining the value of the context increment includes: determining the value of the context increment based on the color component, the value of the MTS index and the depth of the TU.

16. The method according to claim 14, wherein: The TU is a first TU in a coding unit (CU) of video data, and the method further includes: Avoid encoding syntax elements that specify values ​​of LFNST indices for other TUs in the CU.

17. The method according to claim 10, wherein: The syntax element that specifies the value of the LFNST index for the video data unit comprises a lfnst_idx syntax element or a tu_lfnst_idx syntax element.

18. A device for decoding video data, the device comprising: Memory; as well as One or more processors implemented in circuitry and configured to: determining a color component of a video data unit; For the video data unit, obtaining a value of a multiple transform select (MTS) index; determining, based at least on the color component and the value of the MTS index, a value of a context increment (ctxInc) for context adaptive binary arithmetic coding (CABAC) of a syntax element that specifies a value of a low frequency non-separable transform (LFNST) index for the video data unit; CABAC coding the syntax element that specifies the value of the LFNST index for the video data unit based on the determined value of the context delta and via a syntax structure for the video data unit; as well as Transform coefficients of the video data unit are transformed based on a transform indicated by the value of the LFNST index.

19. The apparatus according to claim 18, wherein: The one or more processors are further configured to: determining a block size of the video data unit, Wherein, in order to determine the value of the context increment, the one or more processors are configured to: determine the value of the context increment based on the color component, the value of the MTS index and the block size of the video data unit.

20. The apparatus of claim 18, wherein: The one or more processors are further configured to: determining, at a level of said video data unit, a number of non-zero transform coefficients, Wherein, in order to determine the value of the context increment, the one or more processors are configured to: determine the value of the context increment based on the color component, the value of the MTS index and the number of non-zero transform coefficients.

21. The apparatus of claim 18, wherein: The video data unit is a coding unit (CU) of video data.

22. The apparatus of claim 18, wherein: The video data unit is a transform unit (TU) of video data.

23. The apparatus of claim 22, wherein: The one or more processors are further configured to: determining the depth of the TU in the partition structure, In order to determine the value of the context increment, the one or more processors are configured to: determine the value of the context increment based on the color component, the value of the MTS index and the depth of the TU.

24. The apparatus of claim 22, wherein: The TU is a first TU in a coding unit (CU) of video data, and wherein the one or more processors are configured to: Values ​​of LFNST indexes for other TUs in the CU are inferred based on the value of the LFNST index for the first TU.

25. The apparatus of claim 18, wherein: The syntax element that specifies the value of the LFNST index for the video data unit comprises a lfnst_idx syntax element or a tu_lfnst_idx syntax element.

Images