Low-frequency non-separable transform (LFNST) simplification

Abstract

An example method of decoding video data includes receiving encoded data for a current block. The method further includes determining whether single tree partitioning is enabled for the current block, and decoding the encoded data to generate luma transform coefficients for the current block and chroma transform coefficients for the current block. The method further includes, in response to determining that single tree partitioning is enabled for the current block, applying an inverse low frequency non-separable transform (LFNST) only to the luma transform coefficients for the current block to generate a residual block for the current block. The method further includes reconstructing the current block of video data using the residual block and the prediction block for the current block.

Description

[0001] This application claims the benefit of priority to U.S. Application No. 17 / 029,416, filed on September 23, 2020, and U.S. Provisional Application No. 62 / 906,671, filed on September 26, 2019, both of which are incorporated by reference in their entirety. Technical Field

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

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

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

[0005] In general, the present disclosure describes techniques for transform coding using a low frequency non-separable transform (LFNST). A video encoder may represent a residual block for video data in a form suitable for signaling from a video encoder and for reception by a video decoder. For example, a video encoder may apply a separable transform that converts a residual block in a pixel domain to a coefficient block in a frequency domain, and then applies LFNST to low frequency coefficients while setting other coefficients to zero. In this way, LFNST may improve the energy concentration of the transform coefficient block. In this way, the data used to represent the residual block may be reduced, thereby reducing bandwidth and / or storage requirements for the video data, and potentially reducing energy usage of a video decoder and a video encoder.

[0006] Rather than always applying LFNST to both luma transform coefficients and chroma transform coefficients, the techniques described herein may selectively apply LFNST to chroma transform coefficients based on the partitioning of video data. For example, a video encoder may apply LFNST to chroma transform coefficients and avoid applying LFNST to chroma transform coefficients when a single tree partitioning is used. When a single tree partitioning is used, a video coder (e.g., a video encoder or a video decoder) may split a block of a luma component for a current block of video data according to a single tree, and split a corresponding block of a chroma component for the current block according to the same single tree. However, when separate tree partitioning is used, the video coder may split a block of a luma component for a current block of video data according to a dual tree luma, and split a corresponding block of a chroma component for the current block according to a dual tree chroma. By applying LFNST only when performing separate tree partitioning, a video coder (e.g., a video encoder or a video decoder) may potentially reduce the complexity of a video coder, and reduce signaling overhead with little or no loss in prediction accuracy.

[0007] In one example, the present disclosure describes a method of decoding video data, the method comprising: receiving encoded data for a current block; determining whether single tree partitioning is enabled for the current block; decoding the encoded data to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block; in response to determining that single tree partitioning is enabled for the current block, applying an inverse low frequency non-separable transform (LFNST) only to the luma transform coefficient for the current block to generate a residual block for the current block; and reconstructing the current block of video data using the residual block and a prediction block for the current block.

[0008] In another example, the present disclosure describes a method for encoding video data, the method comprising: determining whether single tree partitioning is enabled for a current block; generating a residual value for the current block based on a prediction block for the current block; applying a separable transform to the residual value to generate a separable luminance transform coefficient for the current block and a separable chrominance transform coefficient for the current block; in response to determining that single tree partitioning is enabled for the current block, applying a low frequency non-separable transform (LFNST) only to the separable luminance transform coefficient for the current block to generate a luminance transform coefficient for the current block and a chrominance transform coefficient for the current block; and encoding the luminance transform coefficient and the chrominance transform coefficient to generate encoded video data; and outputting the encoded video data.

[0009] In another example, the present disclosure describes a device for decoding video data, the device memory and processing circuitry configured to: receive encoded data for a current block; determine whether single tree partitioning is enabled for the current block; decode the encoded data to produce luma transform coefficients for the current block and chroma transform coefficients for the current block; in response to determining that single tree partitioning is enabled for the current block, apply an inverse low frequency non-separable transform (LFNST) only to the luma transform coefficients for the current block to generate a residual block for the current block; and reconstruct the current block of video data using the residual block and a prediction block for the current block.

[0010] In another example, the present disclosure describes a device for encoding video data, the device memory and processing circuitry configured to: determine whether single tree partitioning is enabled for a current block; generate a residual value for the current block based on a prediction block for the current block; apply a separable transform to the residual value to generate a separable luma transform coefficient for the current block and a separable chroma transform coefficient for the current block; in response to determining that single tree partitioning is enabled for the current block, apply a low frequency non-separable transform (LFNST) only to the separable luma transform coefficient for the current block to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block; encode the luma transform coefficient and the chroma transform coefficient to generate encoded video data; and output the encoded video data.

[0011] In another example, the present disclosure describes a computer-readable storage medium having instructions stored thereon that, when executed, configure the memory to: receive encoded data for a current block; determine whether single tree partitioning is enabled for the current block; decode the encoded data to produce luma transform coefficients for the current block and chroma transform coefficients for the current block; in response to determining that single tree partitioning is enabled for the current block, apply an inverse low frequency non-separable transform (LFNST) only to the luma transform coefficients for the current block to generate a residual block for the current block; and reconstruct the current block of video data using the residual block and a prediction block for the current block.

[0012] In another example, the present disclosure describes a computer-readable storage medium having instructions stored thereon that, when executed, configure a processor to: determine whether single tree partitioning is enabled for a current block; generate a residual value for the current block based on a prediction block for the current block; apply a separable transform to the residual value to generate a separable luma transform coefficient for the current block and a separable chroma transform coefficient for the current block; in response to determining that single tree partitioning is enabled for the current block, apply a low frequency non-separable transform (LFNST) only to the separable luma transform coefficient for the current block to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block; encode the luma transform coefficient and the chroma transform coefficient to generate encoded video data; and output the encoded video data.

[0013] In another example, the present disclosure describes an apparatus for decoding video data, the apparatus comprising: a unit for receiving encoded data for a current block; a unit for determining whether single tree partitioning is enabled for the current block; a unit for decoding the encoded data to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block; in response to determining that single tree partitioning is enabled for the current block, applying an inverse low frequency non-separable transform (LFNST) only to the luma transform coefficient for the current block to generate a residual block for the current block; and a unit for reconstructing the current block of video data using the residual block and a prediction block for the current block.

[0014] In another example, the present disclosure describes an apparatus for encoding video data, the apparatus comprising: a unit for determining whether single tree partitioning is enabled for a current block; a unit for generating a residual value for the current block based on a prediction block for the current block; a unit for applying a separable transform to the residual value to generate a separable luma transform coefficient for the current block and a separable chroma transform coefficient for the current block; in response to determining that single tree partitioning is enabled for the current block, applying a low frequency non-separable transform (LFNST) only to the separable luma transform coefficient for the current block to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block; and a unit for encoding the luma transform coefficient and the chroma transform coefficient to generate encoded video data; and a unit for outputting the encoded video data.

[0015] 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

[0016] Figure 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0017] Figure 2A and Figure 2B A conceptual diagram showing an example quadtree binary tree (QTBT) structure and corresponding coding tree units (CTUs).

[0018] Figure 3 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0019] Figure 4 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0020] Figure 5 is a conceptual diagram illustrating a low frequency non-separable transform (LFNST) at the encoder and decoder sides, where LFNST introduces a new stage between the separable transform and quantization in the codec.

[0021] Figure 6 is a conceptual diagram showing an inverse transform process when LFNST is used.

[0022] Figure 7 is a conceptual diagram illustrating a 4x4 inverse LFNST for reconstructing 16 intermediate coefficients from a list of 16 input coefficients.

[0023] Figure 8 is a conceptual diagram illustrating an 8x8 inverse LFNST for forming a list of 16 input coefficients to reconstruct 48 intermediate coefficients.

[0024] Fig. 9 is a flow chart illustrating an example method for encoding a current block of video data according to the techniques of this disclosure.

[0025] Fig.10 is a flow chart illustrating an example method for decoding a current block of video data according to the techniques of this disclosure.

[0026] Fig.11 is a flow chart illustrating an example method for encoding a current block of video data based on partitioning according to the techniques of this disclosure.

[0027] Fig.12 is a flow chart illustrating an example method for decoding a current block of video data based on partitioning according to the techniques of this disclosure. DETAILED DESCRIPTION

[0028] In general, the present disclosure describes techniques related to low frequency non-separable transforms (LFNST). A video encoder may represent a residual block for video data in a form suitable for signaling from a video encoder and for reception by a video decoder. It is desirable to reduce the amount of data used to represent the residual block so as to reduce the amount of data sent from the video encoder and received by the video decoder. In video decoding, separable transforms have been applied more than non-separable transforms because they can use fewer operations (e.g., addition, multiplication). A separable transform is a filter that can be written as the product of two or more filters. In contrast, a non-separable filter cannot be written as the product of two or more filters.

[0029] Rather than relying solely on a separable transform that converts a residual block in the pixel domain to a coefficient block in the frequency domain, a video encoder can also apply LFNST to increase the energy concentration of the transform coefficient block. For example, LFNST can concentrate the non-zero coefficients of the transform coefficient block to be closer to the DC coefficient of the transform coefficient block. As a result, there are fewer transform coefficients between the DC coefficient of the coefficient block and the last significant (i.e., non-zero) transform coefficient of the transform coefficient block, resulting in a reduced amount of data used to represent the residual block. Similarly, a video decoder can apply an inverse separable transform to transform the transform coefficient block into a residual block. In this way, the data used to represent the residual block can be reduced, thereby reducing the bandwidth and / or storage requirements for the video data, and potentially reducing the energy usage of the video decoder and video encoder.

[0030] In order to reduce the complexity of decoding with little or no loss in decoding accuracy, a video decoder (e.g., a video encoder or a video decoder) can be configured to use a luma component to represent the brightness of a block of video data and to use a chroma component to represent the color characteristics of a block of video data. The chroma component can include a blue minus a luma value ('Cb') and / or a red minus a luma value ('Cr'). For example, a video decoder (e.g., a video encoder or a video decoder) can be configured to represent an 8x8 block by an 8x8 luma block (e.g., 'Y') of a luma component, a first 4x4 chroma block (e.g., 'Cr') of a chroma component, and a second 4x4 chroma block (e.g., 'Cb') of a chroma component. That is, the chroma component of a block of video data can be subsampled to have fewer samples than the luma component of a block of video data. In this way, subsampling the chroma component can improve decoding efficiency with little or no loss in decoding accuracy.

[0031] A video encoder may be configured to partition video data into multiple blocks (e.g., separate tree partitioning) based on a dual tree including a luma tree (also referred to herein as "dual-tree luma") and a chroma tree (also referred to herein as "dual-tree chroma"). For example, instead of splitting blocks of luma components for a current block of video data according to a single tree (e.g., single-tree partitioning) and splitting corresponding blocks of chroma components for the current block according to the same single tree, the video encoder may split the luma components for the current block of video data according to the dual-tree luma, and split corresponding blocks of chroma components for the current block according to the dual-tree chroma. In this manner, the video encoder may split luma blocks and chroma blocks for the current block in different ways, which may potentially reduce the amount of data used to send the video data with little or no loss in prediction accuracy and / or complexity.

[0032] In some examples, a video encoder applying a single tree partitioning may partition the luma component for the current block into blocks of 8x8 luma transform coefficients. In this example, applying LFNST to the 8x8 luma transform coefficients may help significantly reduce the amount of data sent with a comparably small amount of additional processing burden. When a single tree partitioning is applied, the video encoder may partition the chroma components for the current block into blocks of 4x4 chroma transform coefficients because the chroma components may be subsampled relative to the luma components (e.g., 4:2:0 chroma subsampling). Applying LFNST to the 4x4 chroma transform coefficients may significantly increase the processing burden with a small or no comparable reduction in the amount of data sent.

[0033] In contrast, when split tree partitioning (e.g., dual tree partitioning) is applied, the video encoder may partition the luma component for the current block into blocks of 8x8 luma transform coefficients and avoid further splitting the 8x8 chroma blocks. In this example, the video encoder may apply LFNST to the 8x8 luma transform coefficients and the 8x8 chroma transform coefficients, which may help significantly reduce the amount of data sent with a comparably small amount of additional processing burden. Similarly, the video decoder may apply inverse LFNST to the 8x8 luma transform coefficients and the 8x8 chroma transform coefficients, which may help significantly reduce the amount of data sent with a comparably small amount of additional processing burden.

[0034] According to the techniques of the present disclosure, a video coder (e.g., a video encoder or a video decoder) can selectively apply LFNST to chroma transform coefficients based on partitioning. For example, the video coder can apply LFNST to chroma transform coefficients when separate tree partitioning is used, and avoid applying LFNST to chroma transform coefficients when single tree partitioning is used. By applying LFNST only when separate tree partitioning is performed, the video coder (e.g., a video encoder or a video decoder) can potentially reduce the complexity of the video encoder and less signaling overhead with less or no loss in prediction accuracy.

[0035] One or more problems may exist in a system where a video encoder applies 4x4 LFNST (e.g., applies LFNST to a 4x4 block of transform coefficients) and a video decoder applies inverse 4x4 LFNST. For example, a video encoder applying 4x4 LFNST to a 4x4 block of chroma transform coefficients may introduce too much latency with a two-stage transform process. In some examples, encoding a 4x4 block (e.g., a transform unit (TU)) with LFNST may represent a worst-case latency. Similarly, a video decoder applying inverse 4x4 LFNST to a 4x4 block of chroma transform coefficients (e.g., applying inverse 4x4 LFNST to a 4x4 block of transform coefficients) may introduce too much latency with a two-stage transform process. In some examples, decoding a 4x4 block (e.g., a TU) with LFNST may represent a worst-case latency.

[0036] The techniques described herein may represent one or more solutions to the problems listed above and other problems, and thus improve the operation of a video decoder or video decoding process. For example, a video encoder may be configured to, in response to determining that a single tree partition is enabled for a current block, apply LFNST only to separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block. Similarly, a video decoder may be configured to, in response to determining that a single tree partition is enabled for the current block, apply inverse LFNST only to luma transform coefficients for the current block to generate a residual block for the current block.

[0037] Figure 1 1 is a block diagram illustrating an example video encoding and decoding system 100 that can perform the techniques of the present disclosure. The techniques of the present disclosure are generally directed to decoding (encoding and / or decoding) video data. Generally, video data includes any data used to process video. Thus, video data can include original, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

[0038] 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 target device 116. In particular, source device 102 provides video data to target device 116 via computer-readable medium 110. Source device 102 and target device 116 may include any of a wide variety of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets (such as smartphones), televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, etc. In some cases, source device 102 and target device 116 may be equipped for wireless communication, and thus may be referred to as wireless communication devices.

[0039] exist Figure 1In the example of , source device 102 includes video source 104, memory 106, video encoder 200 and output interface 108. Target device 116 includes input interface 122, video decoder 300 and display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of target device 116 can be configured to apply a technology for simplifying LFNST. Therefore, source device 102 represents an example of a video encoding device, and target device 116 represents an example of a video decoding device. In other examples, source device and target device may include other components or arrangements. For example, source device 102 may receive video data from an external video source (such as an external camera). Similarly, target device 116 may be connected to an external display device, rather than including an integrated display device.

[0040] As in Figure 1 The system 100 shown in is only an example. In general, any digital video encoding and / or decoding device can perform the technology for simplifying LFNST. The source device 102 and the target device 116 are only examples of such decoding devices, in which the source device 102 generates decoded video data for transmission to the target device 116. The present disclosure refers to a "decoding" device as a device that performs decoding (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 source device 102 and the target device 116 can work in a generally symmetrical manner, so that each of the source device 102 and the target device 116 includes an encoding and decoding component. Therefore, the system 100 can support one-way or two-way video transmission between the source device 102 and the target device 116, for example, for video streaming, video playback, video broadcasting or video telephony.

[0041] Typically, video source 104 represents the source of video data (i.e., original, uncoded data data) and provides a continuous series of images of video data to video encoder 200, which encodes the data for the image. The video source 104 of source device 102 can include a video capture device (such as a video camera), a video archive containing previously captured original video, and / or a video feed interface for receiving video from a video content provider. As a further option, video source 104 can generate computer graphics-based data as a combination of source video, or instant video, archived video, and computer-generated video. In each case, video encoder 200 encodes captured, pre-captured or computer-generated video data. Video encoder 200 can rearrange images from the received order (sometimes referred to as "display order") into a decoding order for decoding. Video encoder 200 can 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 by and / or retrieval by, for example, input interface 122 of target device 116 .

[0042] The memory 106 of the source device 102 and the memory 120 of the target device 116 represent general purpose memory. In some examples, the memory 106, the memory 120 can store original video data, such as the original video from the video source 104 and the original, decoded video data from the video decoder 300. Additionally or alternatively, the memory 106, the memory 120 can store software instructions executable by, for example, the video encoder 200 and the video decoder 300, respectively. Although the memory 106 and the memory 120 are shown in this example as being from the video encoder 200 and the video decoder 300, respectively, it should be understood that the video encoder 200 and the video decoder 300 can also include internal memory for functionally similar or equivalent purposes. In addition, the memory 106, the memory 120 can store encoded video data, such as the output from the video encoder 200 and the input to the video decoder 300. In some examples, a portion of the memory 106, the memory 120 can be allocated as one or more video buffers, for example to store original, decoded and / or encoded video data.

[0043] The computer-readable medium 110 may represent any type of medium or device capable of transmitting the encoded video data from the source device 102 to the target device 116. In one example, the computer-readable medium 110 represents a communication medium for enabling the source device 102 to directly send the encoded video data to the target 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 a transmission signal including the encoded video data, and the input interface 122 may demodulate 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 equipment that may be used to facilitate communication from the source device 102 to the target device 116.

[0044] In some examples, computer-readable medium 110 may include storage device 112. Source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, target device 116 may access the encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0045] In some examples, the computer-readable medium 110 may include a storage device 112. 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 target 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 target 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 target 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 digital subscriber line (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 a streaming transmission protocol, a download transmission protocol, or a combination thereof.

[0046] Output interface 108 and input interface 122 may represent wireless transmitters / receivers, modems, wired network components (e.g., Ethernet cards), wireless communication components that operate according to any of a variety of 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)). TM ), Bluetooth standard, etc.) to transmit data (such as encoded video data). In some examples, source device 102 and / or target device 116 may include respective system-on-chip (SoC) devices. For example, source device 102 may include an SoC device to perform functions attributed to video encoder 200 and / or output interface 108, and target device 116 may include an SoC device to perform functions attributed to video decoder 300 and / or input interface 122.

[0047] The techniques of the present disclosure may be applied to support video decoding for any of a variety of multimedia applications, such as wireless 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.

[0048] The input interface 122 of the target device 116 receives the encoded video bitstream from the computer-readable medium 110 (e.g., a communication medium, a storage device 112, a file server 114, etc.). The encoded video bitstream may include signaling information defined by the video encoder 200 and also used by the video decoder 300, such as syntax elements with values ​​describing characteristics and / or processing of video blocks or other encoded units (e.g., slices, images, groups of images, sequences, etc.). The display device 118 displays a decoded image of the decoded video data to a user. The display device 118 may represent any of a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0049] Although not in Figure 1 200 and 300, but in some examples, the video encoder 200 and the video decoder 300 may each be integrated with an audio encoder and / or an audio decoder, and may include appropriate MUX-DEMUX units or other hardware and / or software to process multiplexed streams of both audio and video included in a common data stream. If applicable, the MUX-DEMUX units may conform to the ITU H.233 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

[0050] The video encoder 200 and the video decoder 300 can each be implemented as any of a variety of suitable encoder and / or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When the technology is partially implemented in software, the device can store instructions for the software in an appropriate, non-transitory computer-readable medium, and use one or more processors to execute the instructions in hardware to perform the technology of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, any of which can be integrated as part of a combined encoder / decoder (codec) in the respective 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).

[0051] The video encoder 200 and the video decoder 300 may work 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 extension. Alternatively, the video encoder 200 and the video decoder 300 may work according to other proprietary standards or industry standards such as the Joint Exploration Test Model (JEM) or ITU-T H.266, also known as Versatile Video Coding (VVC). The most recent draft of the VVC standard is described in "Versatile Video Coding (Draft 6)" JVET-O2001-vE (hereinafter "VVC Draft 6") by Bross et al. at the 15th meeting of the Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11 held in Gothenburg, Sweden on July 3-12, 2019. However, the technology of the present disclosure is not limited to any particular coding standard.

[0052] Typically, the video encoder 200 and the video decoder 300 can perform block-based decoding of an image. The term "block" generally refers to a structure that includes data to be processed (e.g., encoded, decoded, or otherwise used in an 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 an image, the video encoder 200 and the video decoder 300 can decode luminance components 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 formatted data to a YUV representation before encoding, and the video decoder 300 may convert the YUV representation to an RGB format. Alternatively, a pre-processing and post-processing unit (not shown) may perform these conversions.

[0053] The present disclosure may generally relate to decoding (e.g., encoding and decoding) of an image to include the process of encoding and decoding data for an image. Similarly, the present disclosure may relate to decoding of blocks of an image to include the process of encoding and decoding data for the blocks, such as prediction and / or residual decoding. The encoded video bitstream generally includes a series of values ​​for syntax elements that represent decoding decisions (e.g., decoding modes) and partitioning of the image into blocks. Therefore, references to decoding an image or block should generally be understood as decoding the values ​​for the syntax elements that form the image or block.

[0054] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (such as the video encoder 200) divides a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video decoder divides the CTU and the CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without child nodes may be referred to as a "leaf node", and the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video decoder may further divide the PU and TU. For example, in HEVC, the residual quadtree (RQT) represents the division of the TU. In HEVC, PU represents inter-frame prediction data, and TU represents residual data. The CU that is intra-predicted includes intra-frame prediction information, such as an intra-mode indication.

[0055] As another example, the video encoder 200 and the video decoder 300 may be configured to work according to VVC. According to VVC, a video decoder (such as the video encoder 200) divides an image 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).

[0056] In the MTT partition structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more types of ternary tree (TT) (also known as ternary tree (TT)) partitioning. A ternary tree or ternary tree partitioning is a partitioning in which a block is split into three sub-blocks. In some examples, a ternary tree or ternary tree partitioning partitions a block into three sub-blocks without partitioning the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0057] 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 both chroma components (or two QTBT / MTT structures for respective chroma components).

[0058] The video encoder 200 and the video decoder 300 may be configured to use quadtree partitioning, QTBT partitioning, MTT partitioning, or other partitioning structures per HEVC. For purposes of explanation, the description of the techniques of the present disclosure is given with respect to QTBT partitioning. However, it should be understood that the techniques of the present disclosure may also be applied to video decoders that are configured to also use ternary tree partitioning or other types of partitioning.

[0059] Blocks (e.g., CTUs or CUs) may be grouped in various ways in an image. As an example, a brick may refer to a rectangular area of ​​a CTU row within a particular tile in an image. A tile may be a rectangular area of ​​a CTU within a particular tile column and a particular tile row in an image. A tile column refers to a rectangular area of ​​a CTU having a height equal to the height of the image and a width specified by a syntax element (e.g., such as in an image parameter set). A tile row refers to a rectangular area of ​​a CTU having a height specified by a syntax element (e.g., such as in an image parameter set) and a width equal to the width of the image.

[0060] In some examples, a tile may be divided into a plurality of bricks, each of which may include one or more CTU rows within the tile. A tile that is not divided into a plurality of bricks may also be referred to as a brick. However, a brick that is a proper subset of a tile may not be a tile.

[0061] Tiles in an image may also be arranged in slices. A slice may be an integer number of tiles of an image that may be contained exclusively in a single network abstraction layer (NAL) unit. In some examples, a slice includes several complete tiles or only a continuous series of complete tiles of a tile.

[0062] 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 NxN CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. 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.

[0063] The video encoder 200 encodes video data for a CU representing prediction and / or residual information and other information. The prediction information indicates how the CU is predicted to form a prediction block for the CU. The residual information generally represents the sample-by-sample difference between the samples of the CU before encoding and the prediction block.

[0064] 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 image, while intra-frame prediction refers to predicting a CU based on previously decoded data of the same image. 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 a motion search to identify a reference block that closely matches the CU, for example, based on the difference between the CU and the reference block. The video encoder 200 can use the absolute difference sum (SAD), the square sum of the difference (SSD), the mean absolute difference (MAD), the mean square difference (MSD) or other such difference calculations to calculate the 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.

[0065] Some examples of 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).

[0066] In order to perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. Some examples of VVC provide sixty-seven intra prediction modes, including various directional modes as well as plane mode and DC mode. Typically, the video encoder 200 selects an intra prediction mode that describes samples adjacent to the current block (block of the CU), and predicts the samples of the current block based on the adjacent samples. Assuming that the video encoder 200 decodes the CTU and CU in raster scan order (left to right, top to bottom), such samples can usually be above, above left, or to the left of the current block in the same image as the current block.

[0067] 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 mode of a plurality of available inter-frame prediction modes is used and motion information for the corresponding mode. For example, for unidirectional or bidirectional inter-frame prediction, the video encoder 200 may encode motion vectors using improved motion vector prediction (AMVP) or merge mode. The video encoder 200 may use a similar mode to encode motion vectors for an affine motion compensation mode.

[0068] After prediction (such as intra-frame prediction or inter-frame prediction of a block), the video encoder 200 can calculate residual data for the block. The residual data (such as a residual block) represents the sample-by-sample difference between the block and the prediction block for the block formed using the corresponding prediction mode. The video encoder 200 can apply one or more transforms to the residual block to generate transformed data in the transform domain rather than the sample domain. For example, the video encoder 200 can apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. In addition, after the first transform, the video encoder 200 can apply a secondary transform (e.g., LFNST), such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc. After the application of one or more transforms, the video encoder 200 generates transform coefficients.

[0069] According to the techniques of the present disclosure, the video encoder 200 may determine whether single tree partitioning is enabled for the current block, and in response to determining that single tree partitioning is enabled for the current block, apply LFNST only to the luma transform coefficient for the current block to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block. Conversely, the video encoder 200 may apply LFNST to both the luma transform coefficient for the current block and the chroma transform coefficient for the current block in response to determining that separate tree partitioning is enabled for the current block to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block.

[0070] As noted above, after any transform used to generate 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 potentially reduce the amount of data used to represent the transform coefficients to provide further compression. By performing the quantization process, the video encoder 200 may reduce the bit depth associated with some or all of the transform 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.

[0071] After quantization, the video encoder 200 may scan the transform coefficients to generate a one-dimensional vector according to a two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place higher energy (and therefore lower frequency) transform coefficients in front of the vector and lower energy (and therefore higher frequency) transform coefficients in the back of the vector. In some examples, the video encoder 200 may 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 may perform adaptive scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, the video encoder 200 may entropy encode the one-dimensional vector, for example, according to context adaptive binary arithmetic coding (CABAC). The video encoder 200 may entropy encode the values ​​of the syntax elements for describing metadata associated with the encoded video data for use by the video decoder 300 when decoding the video data.

[0072] 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.

[0073] The video encoder 200 may further generate syntax data (such as block-based syntax data, image-based syntax data, and sequence-based syntax data) in, for example, a picture header, a block header, a slice header, or other syntax data (such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS)) to the video decoder 300. The video decoder 300 may likewise decode such syntax data to determine how to decode the corresponding video data.

[0074] In this way, the video encoder 200 can generate a bitstream including encoded video data, such as a syntax element describing the division of an image 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.

[0075] In general, the video decoder 300 performs a process that is inverse to the process performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 may use CABAC in a manner that is inverse but substantially similar to the CABAC encoding process of the video encoder 200 to decode the values ​​of the syntax elements for the bitstream. The syntax elements may define partitioning information for partitioning an image into CTUs and partitioning of each CTU according to a corresponding partitioning structure (such as a QTBT structure) to define CUs of the CTUs. The syntax elements may further define prediction and residual information for a block (e.g., CU) of video data.

[0076] The residual information may be represented by, for example, a quantized transform coefficient. The video decoder 300 may inverse quantize and inverse transform the quantized transform coefficient of the block to reproduce a residual block for the block.

[0077] According to the techniques of the present disclosure, the video decoder 300 may determine whether single tree partitioning is enabled for the current block, and in response to determining that single tree partitioning is enabled for the current block, apply inverse LFNST only to luma transform coefficients for the current block to generate a residual block for the current block. In contrast, the video decoder 300 may, in response to determining that separate tree partitioning is enabled for the current block, apply inverse LFNST to both luma transform coefficients for the current block and chroma transform coefficients for the current block to generate a residual block for the current block.

[0078] 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 blocks.

[0079] According to the technology of the present disclosure, the video encoder 200 may be configured to generate a residual value for a current block based on a prediction block for the current, and to apply a separable transform to the residual value to generate a separable luma transform coefficient for the current block and a separable chroma transform coefficient for the current block. The video encoder 200 may be configured to apply LFNST only to the separable luma transform coefficient for the current block to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block in response to determining that a single tree partition is enabled for the current block. The video encoder 200 may be configured to encode the luma transform coefficient and the chroma transform coefficient to generate encoded video data and output the encoded video data.

[0080] According to the technology of the present disclosure, the video decoder 300 may be configured to receive encoded video data for a current block, and decode the encoded video data to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block. The video decoder 300 may be configured to determine whether single tree partitioning is enabled for the current block. The video decoder 300 may be configured to, in response to determining that single tree partitioning is enabled for the current block, apply inverse LFNST only to the luma transform coefficient for the current block to generate a residual block for the current block, and reconstruct the current block of video data using the residual block for the current block and a prediction block.

[0081] The present disclosure may generally involve "signaling" certain information, such as syntax elements. The term "signaling" may generally refer to the transmission of values ​​for 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 a bitstream. Typically, signaling refers to values ​​generated in a bitstream. As noted above, the source device 102 may transmit the bitstream to the target device 116 in substantially real time, or in non-real time, such as when storing syntax elements to the storage device 112 for subsequent retrieval by the target device 116.

[0082] Figure 2A and Figure 2B 1 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 0 indicates horizontal splitting and 1 indicates vertical splitting in this example. For quadtree splitting, there is no need to indicate the split type because the quadtree node splits the block horizontally and vertically into 4 sub-blocks of the same size. Accordingly, the video encoder 200 can encode syntax elements (such as split information) at the regional tree level (i.e., first level) of the QTBT structure 130 (i.e., solid line) and syntax elements (such as split information) at the prediction tree level (i.e., second level) of the QTBT structure 130 (i.e., dashed line), and the video decoder 300 can decode it. 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 it.

[0083] generally, Figure 2BThe CTU 132 may be associated with parameters defining the size of blocks corresponding to nodes of the QTBT structure 130 at the first level and the second level. These parameters may include a CTU size (indicating the size of the CTU 132 in samples), a minimum quadtree size (MinQTSize, indicating the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, indicating the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, indicating the maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, indicating the minimum allowed binary tree leaf node size).

[0084] 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 at the first level may be a leaf node (without child nodes) or have four child nodes. The example of the QTBT structure 130 represents such a node as a child node including a parent node and a solid line for a branch. If the node at the first level is not larger than the maximum allowed binary tree root node size (MaxBTSize), the node may be further divided by a respective binary tree. The binary tree splitting of a node may be iterated until the node resulting from the split reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTSize). The example of the QTBT structure 130 represents such a node as having a dotted line for a branch. The binary tree leaf node is called a coding unit (CU), which is used for prediction (e.g., intra-image prediction and inter-image prediction) and transformation, and no further division is performed. As discussed above, a CU may also be referred to as a “video block” or a “block.”

[0085] 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 quadtree leaf node is 128x128, the quadtree leaf node will not be further split by the binary tree because the size exceeds MaxBTSize (i.e., 64x64, in this example). Otherwise, the quadtree leaf node will be further divided by the binary tree. Therefore, the quadtree leaf node is still the root node for the binary tree and has a binary tree depth of 0. When the binary tree depth reaches MaxBTSize (4, in this example), further splitting is not allowed. When a binary tree node has a depth equal to MinBTSize (4, in this example), it means that no further vertical splitting is allowed. Similarly, a binary tree node with a height equal to MinBTSize means that no further horizontal splitting is allowed for 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.

[0086] Figure 3 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 3 The above description is provided for the purpose of explanation and should not be considered as limiting the techniques as broadly illustrated and described in this disclosure. For the purpose 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 H.266 video coding standard under development). However, the techniques of this disclosure are not limited to these video coding standards and are generally applicable to video encoding and decoding.

[0087] exist Figure 3In 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. For example, the units of the video encoder 200 may be implemented as one or more circuits, or as a logic element as part of a hardware circuit, or as part of a processor, ASIC, FPGA. In addition, the video encoder 200 may include additional or alternative processors or processing circuits to perform these functions or other functions.

[0088] The video data memory 230 may store video data to be encoded by the components of the video encoder 200. The video encoder 200 may receive video data from, for example, the video source 104 ( Figure 1 ) receives video data stored in video data memory 230. DPB 218 can act as a reference picture memory, which stores reference video data for use by video encoder 200 in the prediction of subsequent video data. Video data memory 230 and DPB 218 can be formed by any storage device in a variety of storage devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM) or other types of storage devices. Video data memory 230 and DPB 218 can be provided by the same storage device or a separate storage device. In various examples, video data memory 230 can be on the chip with other components of video encoder 200, as shown, or off-chip relative to those components.

[0089] In the present disclosure, references to the video data memory 230 should not be interpreted as limited to memory inside the video encoder 200 (unless specifically described as such), or to memory outside the video encoder 200 (unless specifically described as such). Rather, references to the video data memory 230 should be understood as a reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data 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 .

[0090] Show Figure 3 Various units are provided to assist in understanding 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 pre-set 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 may execute software or firmware that causes the programmable circuit to operate in a manner defined by instructions of the software or firmware. Fixed-function circuits 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 distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits.

[0091] The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and / or a programmable core formed from programmable circuits. In an example where the operation of the video encoder 200 is performed using software executed by programmable circuits, the memory 106 ( Figure 1 ) may store instructions (eg, object code) for software that the video encoder 200 receives and executes, or another memory (not shown) within the video encoder 200 may store such instructions.

[0092] The video data memory 230 is configured to store received video data. The video encoder 200 may retrieve images of video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 may be original video data to be encoded.

[0093] 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 for performing video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

[0094] The mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and the resulting rate-distortion values ​​for such combinations. The encoding parameters may include the partitioning of CTUs into CUs, the prediction mode for a CU, the transform type for the residual data of a CU, the quantization parameter for the residual data of a CU, etc. The mode selection unit 202 may ultimately select a combination of encoding parameters that has a better rate-distortion value than other tested combinations.

[0095] The video encoder 200 may divide the image 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 image 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". Again, the tree structure may include a single tree (e.g., a single tree partition) and a dual tree (e.g., a separate tree partition) for both luminance blocks and chrominance blocks. Using a dual tree, the video encoder 200 may use a first tree to partition luminance blocks (e.g., dual tree luminance), and use a second tree to partition chrominance blocks (e.g., dual tree chrominance).

[0096] Typically, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU, or in HEVC, the overlapping portion of the PU and TU). For inter prediction of the current block, the motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference images (e.g., one or more previously decoded images stored in the DPB 218). Specifically, the motion estimation unit 222 may calculate values ​​representing how similar the potential reference blocks are to the current block, for example, based on the sum of absolute errors (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), etc. The motion estimation unit 222 may generally perform these calculations using the 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 minimum value resulting from these calculations, indicating the reference block that most closely matches the current block.

[0097] The motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of the reference block in the reference image relative to the position of the current block in the current image. 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 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 respective motion vectors, and combine the retrieved data, for example, by averaging or weighted averaging sample by sample.

[0098] 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 the adjacent samples and fill in these calculated values ​​in a defined direction across the current block to generate a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average of samples adjacent to the current block and generate a prediction block to include the resulting average for each sample of the prediction block.

[0099] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives the current block from the video data memory 230 and the original uncoded code version of 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 code modulation (RDPCM). In some examples, the residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0100] 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 various sizes. As noted above, the size of a CU may refer to the size of a luma coding block of the CU, and the size of a PU may refer to the size of a luma prediction unit of the PU. Assuming that the size of a particular CU is 2Nx2N, the video encoder 200 may support PU sizes of 2Nx2N or NxN for intra-prediction, and symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, NxN or similar sizes for inter-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-prediction.

[0101] In an example where the mode selection unit 202 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.

[0102] For other video coding techniques, such as intra-block copy mode coding, affine mode coding, and linear model (LM) mode coding, as a few examples, the mode selection unit 202 generates a prediction block for the current block being encoded via the respective units associated with the coding technique. In some examples, such as palette mode coding, the mode selection unit 202 may not generate a prediction block, but instead generate syntax elements for indicating the manner in which the block is reconstructed based on the selected palette. In such a mode, the mode selection unit 202 can provide these syntax elements to the entropy coding unit 220 for encoding.

[0103] As described above, the residual generation unit 204 receives video data for a current block and a corresponding prediction block. The residual generation unit 204 then generates a residual block for the current block. To generate the residual block, the residual generation unit 204 calculates the sample-by-sample difference between the prediction block and the current block.

[0104] Transform processing unit 206 applies one or more transforms to the residual block to produce a block of transform coefficients (referred to herein as a "transform coefficient block"). Transform processing unit 206 may apply various transforms to the residual block to produce a block of transform coefficients. For example, transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, transform processing unit 206 may perform multiple transforms on the residual block, such as a primary transform and a secondary transform, such as a rotation transform. In some examples, transform processing unit 206 does not apply a transform to the residual block.

[0105] According to the techniques of the present disclosure, the transform processing unit 206 may be configured to, in response to determining that single tree partitioning is enabled for the current block, apply LFNST only to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block. For example, in response to the mode selection unit 202 determining to apply single tree partitioning, the transform processing unit 206 may apply LFNST only to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block. In contrast, in response to the mode selection unit 202 determining to apply separate tree partitioning (e.g., dual tree partitioning), the transform processing unit 206 may apply LFNST to both the separable luma transform coefficients for the current block and the separable chroma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block.

[0106] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to generate a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce a loss of information, and thus the quantized transform coefficients may have a lower precision than the original transform coefficients generated by the transform processing unit 206.

[0107] 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. In some examples, the inverse transform processing unit 212 may apply the techniques described herein for simplified LFNST. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (although possibly with a certain degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0108] Filter unit 216 may perform one or more filtering operations on the reconstructed blocks. For example, filter unit 216 may perform a deblocking operation to reduce blocking artifacts along the edges of the CU. In some examples, the operations of filter unit 216 may be skipped.

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

[0110] In general, the entropy coding unit 220 may entropy encode syntax elements received from other functional components of the video encoder 200. For example, the entropy coding unit 220 may entropy encode quantized transform coefficient blocks from the quantization unit 208. As another example, the entropy coding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-frame prediction or intra-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 elements (which is 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 elements are not entropy encoded.

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

[0112] 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 and chroma components of a CU. In some examples, the luma coding blocks and chroma coding blocks are the luma and chroma components of a PU.

[0113] 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 a motion vector (MV) and a reference image for a luma coding block need not be repeated for identifying an MV and a reference image for a chroma block. Specifically, the MV for a luma coding block may be scaled to determine an MV for a chroma block, and the reference image may be the same. As another example, the intra prediction process may be the same for luma coding blocks and chroma coding blocks.

[0114] The video encoder 200 represents an example of a device configured to encode video data, the device including a memory configured to store video data and a processing circuit configured to determine whether a single tree partition is enabled for a current block and to generate a residual value for the current block based on a prediction block for the current block. The video encoder 200 may be further configured to apply a separable transform to the residual value to generate a separable luma transform coefficient for the current block and a separable chroma transform coefficient for the current block. The video encoder 200 may be configured to apply LFNST only to the separable luma transform coefficient for the current block in response to determining that a single tree partition is enabled for the current block to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block. The video encoder 200 may be configured to encode the luma transform coefficient and the chroma transform coefficient to generate encoded video data and output the encoded video data.

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

[0116] exist Figure 4 In the example of , the video decoder 300 includes a decoded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 314. Any or all of the CPB memory 320, the entropy decoding unit 302, the prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the DPB 314 may be implemented in one or more processors or in processing circuits. For example, the units of the video decoder 300 may be implemented as one or more circuits or logic elements as part of a hardware circuit, or as part of a processor, an ASIC, or an FPGA. In addition, the video decoder 300 may include additional or alternative processors or processing circuits to perform these or other functions.

[0117] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include additional units to perform predictions according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

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

[0119] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) 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 functions of video decoder 300 are 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.

[0120] Show Figure 4 The various units shown in the figure are used to assist in understanding 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 preset 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 work in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (for example, to receive parameters or output parameters), but the type of operations performed by the fixed-function circuits is generally immutable. In some examples, one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits.

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

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

[0123] Typically, the video decoder 300 reconstructs an image on a block-by-block basis. The video decoder 300 may perform a reconstruction operation on each block individually (where a block currently being reconstructed (ie, decoded) may be referred to as a "current block").

[0124] The entropy decoding unit 302 may entropy decode syntax elements defining 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, 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 thus form a transform coefficient block including the transform coefficients.

[0125] After inverse quantization unit 306 forms the transform coefficient block, inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to produce a residual block associated with the current block. For example, inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block. In some examples, inverse transform processing unit 308 may apply the techniques described herein for simplified LFNST.

[0126] According to the techniques of the present disclosure, the inverse transform processing unit 308 may be configured to, in response to determining that a single tree partition is enabled for the current block, apply inverse LFNST only to the separable luma transform coefficients for the current block to generate a residual block for the current block. For example, in response to the prediction processing unit 304 determining to apply a single tree partition, the inverse transform processing unit 308 may apply inverse LFNST only to the separable luma transform coefficients for the current block to generate a residual block for the current block. That is, the inverse transform processing unit 308 may avoid applying inverse LFNST to the separable chroma transform coefficients for the current block. In contrast, in response to the prediction processing unit 304 determining to apply a separate tree partition (e.g., dual tree partition), the inverse transform processing unit 308 may apply inverse LFNST to both the separable luma transform coefficients for the current block and the separable chroma transform coefficients for the current block to generate a residual block for the current block.

[0127] 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 a manner substantially similar to that of motion compensation unit 224 ( Figure 3 )The inter-frame prediction process is performed in a manner similar to that described in FIG.

[0128] 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 the intra-prediction unit 226 ( Figure 3 The intra prediction process is performed in a manner similar to that described in the preceding paragraph. The intra prediction unit 318 may retrieve data of samples neighboring the current block from the DPB 314.

[0129] The reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, the reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

[0130] The filter unit 312 may perform one or more filtering operations on the reconstructed block. For example, the filter unit 312 may perform a deblocking operation to reduce blocking artifacts along the edges of the reconstructed block. The operations of the filter unit 312 are not necessarily performed in all examples.

[0131] The video decoder 300 may store the reconstructed blocks in the DPB 314. For example, in an example where the operation of the filtering unit 312 is not performed, the reconstruction unit 310 may store the reconstructed blocks to the DPB 314. In an example where the operation of the filtering unit 312 is performed, the filtering unit 312 may store the filtered reconstructed blocks to the DPB 314. As discussed above, the DPB 314 may provide reference information to the prediction processing unit 304, such as samples of the current image for intra-frame prediction and samples of previously decoded images for subsequent motion compensation. In addition, the video decoder 300 may output the decoded images from the DPB 314 for subsequent presentation on a display device (such as a Figure 1 on a display device 118).

[0132] In this manner, the video decoder 300 represents an example of a video decoding device, the video decoding device including a memory configured to store video data and one or more processing units, the one or more processors being implemented in circuits and configured to: receive encoded data for a current block, and decode the encoded data to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block. The video decoder 300 may be configured to determine whether single tree partitioning is enabled for the current block. The video decoder 300 may be configured to, in response to determining that single tree partitioning is enabled for the current block, apply inverse LFNST only to the luma transform coefficient for the current block to generate a residual block for the current block, and reconstruct the current block of video data using the residual block for the current block and a prediction block.

[0133] The present disclosure is related to transform coding, which is typically an essential element of modern video compression standards. The present disclosure includes techniques for various low-frequency inseparable transform designs that can simplify some prior art techniques, including the design in VVC draft 6. The techniques described herein can be used in other improved video codecs including extensions of HEVC and next generation video coding standards.

[0134] In video coding standards prior to HEVC, only fixed separable transforms were used when DCT-2 was used both vertically and horizontally. In HEVC, in addition to DCT-2, DST-7 is also adopted as a fixed separable transform for 4x4 blocks. Examples of multi-transform selection (MTS) technology can be found in, for example, U.S. Patent No. 10,306,229, U.S. Publication No. 2018 / 0020218, and U.S. Patent Application No. 16 / 426,749, each of which is incorporated herein by reference. MTS was previously called adaptive multi-transform (AMT), which is only a name change and the technology is the same. The example of MTS in the U.S. Publication No. 2018 / 0020218 has been used in the Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC1 / SC 29 / WG 11, JEM Software,

[0135] The MTS was adopted in https: / / jvet.hhi.fraunhofer.de / svn / svn_HMJEMSoftware / tags / HM-16.6-JEM-7.0 (hereinafter “Joint Experimental Model-7.0” or simply “JEM-7.0”), and a simplified version of MTS was subsequently adopted in VVC Draft 6.

[0136] exist Figure 5 The low frequency non-separable transform (LFNST) shown in JEM-7.0 is used to further improve the decoding efficiency of MTS, wherein an example implementation of LFNST is described in U.S. Patent No. 10,448,053, which is incorporated herein by reference. Examples of alternative implementations of LFNST can also be found in, for example, U.S. Patent Publication No. 2017 / 009431, U.S. Patent Publication No. 2017 / 0094314, U.S. Patent No. 10,349,085, U.S. Patent Application No. 62 / 668,105, and U.S. Patent Application No. 16 / 364,007, each of which is incorporated herein by reference. Recently, LFNST has been adopted in JVET-N0193, Simplified Secondary Transform (RST) (CE6-3.1), available online: http: / / phenix.it-sudparis.eu / jvet / doc_end_user / documents / 14_Geneva / wg11 / JVET-N0193-v5.zip. LFNST was previously known as the Non-Separable Secondary Transform (NSST) or the Secondary Transform, where all these abbreviations are the same.

[0137] exist Figure 5In the example of , the video encoder 200 may apply a separable transform 301 to the residual values ​​of the current block to generate separable transform coefficients, apply LFNST 303 to the separable transform coefficients to generate transform coefficients, and apply quantization 305 to the transform coefficients to produce quantized transform coefficients. Similarly, the video decoder 300 may apply inverse quantization 307 to the quantized transform coefficients to generate transform coefficients, apply inverse LFNST 309 to the transform coefficients to generate separable transform coefficients, and apply an inverse separable transform 311 to the transform coefficients to generate residual values.

[0138] The decoding process using LFNST is described below. The inverse transform using LFNST involves Figure 6 The following steps are shown in:

[0139] 1) Decoded transform coefficients (see Figure 6 The shaded sub-blocks 315 in FIG. 3 are used as input to the inverse LFNST by first converting the 2-D blocks into 1-D lists (or vectors) of coefficients via a predefined scan / arrangement;

[0140] 2) Inverse LFNST is applied to the 1-D list of input coefficients, and the output coefficients are reorganized into 2-D blocks via a predefined scan / permutation (see Figure 6 The shaded sub-block 317 in FIG.

[0141] 3) The inverse transformed LFNST coefficients are used as input to a separable inverse DCT-2 to obtain the reconstructed residual.

[0142] In VVC draft 6, LFNST can be applied to 4x4 and 8x8 sub-blocks. In both cases, the 16 decoded coefficients in the 4x4 sub-block (some of which may be normalized to zero) are the input to the inverse LFNST:

[0143] For the 4x4 case, a 16x16 inverse LFNST is used as in Figure 7 The separable inverse DCT-2 shown in FIG. 1 is preceded by the construction of 16 intermediate coefficients.

[0144] For the 8x8 case, a 16x48 inverse LFNST is used as in Figure 7 48 intermediate coefficients are constructed before the separable inverse DCT-2 shown in . Note that the 48 intermediate coefficients are reorganized in an L-shaped pattern.

[0145] • The inverse LFNST process may be based on (i) the transformation (ie, LFNST) matrix and (ii) a reorganization pattern / scan for the intermediate coefficients.

[0146] • Example details of the zeroing process in VVC Draft 6 are described in US Patent Application No. 62 / 849,689, which is incorporated herein by reference.

[0147] Figure 7 is a conceptual diagram illustrating a 4x4 inverse LFNST for reconstructing 16 intermediate coefficients from a list of 16 input coefficients. For 4x4 LFNST, a video coder (eg, video encoder 200 or video decoder 300) may use the following two modes / scans depending on the intra mode:

[0148] const int g_lfnstRGScan4x4

[16] ={ / / 0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415

[0149] 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};

[0150] const int g_lfnstRGTranScan4x4

[16] ={ / / 0 1 2 3 4 5 6 7 8 9 10 11 1213 14 15

[0151] 0,4,8,12,1,5,9,13,2,6,10,14,3,7,11,15};

[0152] Among them, the above two modes / scans indicate the reordering of intermediate coefficients. For example, g_lfnstRGScan4x4 does not change the row-based reordering of coefficients. However, lfnstRGTranScan4x4 reorders by permuting the order of coefficients (e.g., coefficients at 1, 2, 3, 6, 7, and 11 are swapped with coefficients at 4, 8, 12, 9, 13, and 14, respectively).

[0153] Figure 8 is a conceptual diagram showing an 8x8 inverse LFNST for reconstructing 48 intermediate coefficients from a list of 16 input coefficients. The intermediate coefficients are reorganized in an L-shaped pattern as shown by the dotted line. For 4x4 LFNST, in VVC draft 6, the video coder can use eight 16x16 matrices as candidates, which are listed in section 8.7.4.3 of JVET-O2001. The intermediate coefficients are reorganized in an L-shaped pattern.

[0154] For 8x8 LFNST, the video decoder can use the following two modes / scans depending on the intra mode:

[0155] const int g_lfnstRGScan8x8

[48] ={ / / 0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415 16 17 1819 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 394041 42 43 44 45 46 47

[0156] 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,40,41,42,43,48,49,50,51,56,57,58,59};

[0157] const int g_lfnstRGTranScan8x8

[48] ={ / / 0 1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 17 1819 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 3839 4041 42 43 44 45 46 47

[0158] 0,8,16,24,32,40,48,56,1,9,17,25,33,41,49,57,2,10,18,26,34,42,50,58,3,11,19,27,35,43,51,59,4,12,20,28,5,13,21,29,6,14,22,30,7,15,23,31};

[0159] Among them, the above two modes / scans indicate the reordering of the intermediate coefficients. In particular, g_lfnstRGScan8x8 reorganizes the 48 intermediate coefficients in an L-shaped pattern (for example, the 48th coefficient is mapped to Figure 8 ScanlfnstRGTranScan4x4 reorders the L-shaped pattern by permuting the coefficients (e.g., the 48th coefficient maps to Figure 8 position 31).

[0160] For 8x8 LFNST, eight 16x48 matrices are used as candidates in VVC-Draft 6, which are listed in Section 8.7.4.3 of JVET-O2001.

[0161] In VVC draft 6, LFNST is applied to the 4x4 or 8x8 upper left sub-block (e.g., LFNST sub-block) in the TU. For example, for both 4x4 LFNST and 8x8 LFNST, there are 4 transform sets, each of which includes 2 LFNST matrices. The set is selected depending on the intra mode, and the LFNST index is signaled to select among the 2 LFNST matrices used for the transform. The problem with 4x4 LFNST is that 4x4 LFNST may introduce unwanted delays with the two-stage transform process. Decoding 4x4 TUs with LFNST may increase latency, and the decoding benefits of 4x4 LFNST are very limited for HD and UHD sequences. In addition, in VVC draft 6, LFNST is enabled for decoding luminance blocks, which may also be complex and provide limited benefits. This document proposes to remove 4x4 LFNST (e.g., applied to 4x4, Nx4, and 4xN blocks) to reduce the worst-case latency in the transform step. In addition, removing 4x4 LFNST can reduce the 8KB memory requirement for storing the LFNST matrix to 6KB.

[0162] In addition, the present disclosure proposes disabling LFNST and reducing latency for 4x4, 4xN, and Nx4 blocks, which can be helpful for small blocks and can reduce 2KB of memory. Experimental results show that the proposed simplification can cause 0.16% AI and 0.10% RA luminance BD-rate loss on VTM-6.0, and for AI decoding, the video decoder runtime can be reduced by about 10%.

[0163] This disclosure describes the following techniques for LFNST, which can be used individually or in any combination.

[0164] In a first example, LFNST may be used only for blocks whose width and height are greater than 4. For example, a video decoder (e.g., video encoder 200 or video decoder 300) may use LFNST only for blocks whose width and height are greater than 4. That is, the video decoder may determine whether the current block includes a height greater than 4 and determine whether the current block includes a width greater than 4. In this example, in response to determining that the height is greater than 4 and the width is greater than 4, the video encoder 200 may apply LFNST. Similarly, in response to determining that the height is greater than 4 and the width is greater than 4, the video decoder 300 may apply an inverse LFNST.

[0165] In the second example, only 8x8 LFNST can be used for blocks whose width and height are greater than 4 and the zeroing area can be outside the 8x8 LFNST sub-block (i.e., in Figure 6The shaded sub-block 317 in the figure may only be 8x8 in size. As used herein, a zeroed region may refer to a region where sample values ​​of a block are set to a value of zero. A video coder (e.g., video encoder 200 or video decoder 300) may use 8x8 LFNST only for blocks whose width and height are greater than 4 and whose zeroed regions are outside of an 8x8 LFNST sub-block (e.g., Figure 6 The size of the shaded sub-block 315 in is only 8x8).

[0166] That is, the video decoder may determine whether the current block includes a height greater than 4, determine whether the current block includes a width greater than 4, and determine whether the zeroing region of the luma transform coefficient is outside the 8x8 LFNST sub-block. In this example, in response to determining that the height is greater than 4 and the width is greater than 4 and the zeroing region of the luma transform coefficient is outside the 8x8 LFNST sub-block, the video encoder 200 may apply LFNST (e.g., apply 8x8 LFNST to the 8x8 LFNST sub-block of the separable luma transform coefficient). Similarly, in response to determining that the height is greater than 4 and the width is greater than 4 and the zeroing region of the luma transform coefficient is outside the 8x8 LFNST sub-block, the video decoder 300 may apply inverse LFNST (e.g., apply inverse 8x8 LFNST to the 8x8 LFNST sub-block of the luma transform coefficient).

[0167] In a third example, the LFNST index may not be signaled for a block whose width and height are greater than 4. For example, in response to determining that a block includes a width greater than 4 and a height greater than 4, the video encoder 200 may avoid signaling a LFNST index.

[0168] In a fourth example, if separate tree (e.g., dual tree) partitioning is used, LFNST index / flags may be signaled separately for luma and chroma channels, and LFNST is used and signaled only if the luma / chroma block width and height are greater than 4. For example, in response to determining to use separate tree partitioning, the video coder may use LFNST only if the luma / chroma block width and height are greater than 4. In some examples, in response to determining to use separate tree partitioning, if the luma / chroma block width and height are greater than 4, the video encoder 200 may signal LFNST index / flags separately for luma and chroma channels.

[0169] In a fifth example, if a single tree partition is used (e.g., if the chroma block split is inferred from the luma block split), the LFNST index / flag may be signaled only for luma. For example, in response to determining that a single tree partition is used, the video encoder 200 may signal only LFNST index / flag for luma (and avoid signaling LFNST index / flag for chroma).

[0170] For example, if the width and height of the luma or chroma coded block is greater than 4, then LFNST is applied and the LFNST index / flag is signaled. For example, in response to determining that the luma or chroma coded block width and height is greater than 4, the video coder may apply LFNST. In some examples, in response to determining that the luma or chroma coded block width and height is greater than 4, the video encoder 200 may signal the LFNST index / flag.

[0171] In some examples, if the size of the luma block is 8x8, 8xN, or Nx8 (where N>8), the size of the corresponding chroma block is 4x4, 4x(N / 2), and (N / 2)x4, in which case LFNST is signaled and LFNST is applied only for the luma block and LFNST is not applied for the chroma blocks. For example, in response to determining that the luma block size is 8x8, 8xN, or Nx8 (where N>8) and the corresponding chroma block size is 4x4, 4x(N / 2), and (N / 2)x4, the video coder can apply LFNST only for the luma block and avoid applying LFNST for the chroma blocks. In some examples, in response to determining that the luma block size is 8x8, 8xN, or Nx8 (where N>8) and the corresponding chroma block sizes are 4x4, 4x(N / 2), and (N / 2)x4, the video encoder 200 may signal an LFNST index / flag for the luma block and avoid signaling LFNST for the chroma blocks.

[0172] In a sixth example, a video coder (e.g., video encoder 200 or video decoder 300) may apply LFNST only to luma blocks, and / or video encoder 200 may signal LFNST only for luma blocks. For example, in a split tree (dual tree) partition, chroma block LFNST may be disabled and not signaled. For example, in response to a split tree (e.g., dual tree) partition, the video coder may disable chroma block LFNST. In some examples, in response to a split tree (e.g., dual tree) partition, the video encoder 200 may avoid signaling chroma block LFNST.

[0173] In a seventh example, if split tree (dual tree) partitioning is enabled, LFNST may be used for both luma blocks and chroma blocks, and LFNST indices / flags may be signaled separately. For example, in response to determining that split tree (e.g., dual tree) partitioning is enabled, a video decoder (e.g., video encoder 200 or video decoder 300) may use LFNST for both luma blocks and chroma blocks. That is, the video encoder 200 may apply LFNST to separable luma transform coefficients for the current block to generate luma transform coefficients for the current block, and apply LFNST to separable chroma transform coefficients for the current block to generate chroma transform coefficients for the current block, in response to determining that split tree partitioning is enabled for the current block. Similarly, the video decoder 300 may apply inverse LFNST to both luma transform coefficients and chroma transform coefficients to generate a residual block for the current block, in response to determining that split tree partitioning is enabled for the current block. In some examples, in response to determining that split-tree (eg, dual-tree) partitioning is enabled, video encoder 200 may separately signal a LFNST index / flag.

[0174] In an eighth example, if single tree partitioning is enabled, LFNST may be applied only for luma blocks, and LFNST may be disabled for chroma blocks. That is, the video encoder 200 may disable LFNST for separable chroma transform coefficients for the current block in response to determining that single tree partitioning is enabled for the current block. Similarly, the video encoder 200 may disable inverse LFNST for chroma transform coefficients for the current block in response to determining that single tree partitioning is enabled for the current block.

[0175] For example, in response to determining that single tree partitioning is enabled, the video decoder may use LFNST only for luma blocks and disable LFNST for chroma blocks. That is, the video encoder 200 may, in response to determining that single tree partitioning is enabled for the current block, apply LFNST only to separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block. Similarly, the video decoder 300 may, in response to determining that single tree partitioning is enabled for the current block, apply LFNST only to luma transform coefficients for the current block to generate a residual block for the current block.

[0176] In some examples, in response to determining that single tree partitioning is enabled, the video encoder 200 may signal LFNST indices / flags for luma blocks and avoid signaling indices / flags for chroma blocks. In this case, the LFNST indices / flags are signaled only for luma blocks. That is, the video encoder 200 may signal LFNST indices for luma transform coefficients for the current block in the encoded data in response to determining that single tree partitioning is enabled for the current block, and avoid signaling LFNST indices for chroma transform coefficients in the encoded data. Similarly, the video decoder 300 may determine LFNST indices for luma transform coefficients for the current block from the encoded data in response to determining that single tree partitioning is enabled for the current block, and avoid determining LFNST indices for chroma transform coefficients from the encoded data.

[0177] In the ninth aspect, only 4x4 LFNST can be used for blocks whose width and height are greater than 4 and whose zeroing area can be outside the 4x4 LFNST sub-block (i.e., within Figure 6 For example, in response to determining that a block includes a width greater than 4 and a height greater than 4 and the zeroing region may be outside the 4x4 LFNST sub-block (i.e., in Figure 6 The size of the shaded sub-block in can be only 4x4), the video decoder can use 4x4 LFNST.

[0178] That is, the video decoder may determine whether the current block includes a height greater than 4, whether the current block includes a width greater than 4, and whether the zeroing region of the luma transform coefficient is outside the 4x4 LFNST sub-block. In this example, in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficient is outside the 4x4 LFNST sub-block, the video encoder 200 may apply LFNST (e.g., apply 4x4 LFNST to the 4x4 LFNST sub-block of the separable luma transform coefficient). Similarly, in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficient is outside the 4x4 LFNST sub-block, the video decoder 300 may apply inverse LFNST (e.g., apply 4x4 inverse LFNST to the 4x4 LFNST sub-block of the luma transform coefficient).

[0179] In some examples, combining examples one to five above may be implemented with the following changes with respect to the VVC Draft 6 text (JVET-O2001-v14) (additions are indicated by +++ and deletions are indicated by ***):

[0180]

[0181] …

[0182] …

[0183] The inputs to this process are:

[0184] –Specifies the luminance position (xTbY, yTbY) of the upper left sample of the current luminance transform block relative to the upper left luminance sample of the current image

[0185] – Variable nTbW that specifies the width of the current transform block

[0186] – Variable nTbH that specifies the height of the current transform block

[0187] – Variable cIdx that specifies the color component of the current transform block

[0188] – (nTbW) x (nTbH) array d[x][y] of scaled transform coefficients, where x = 0..nTbW-1, y = 0..nTbH-1.

[0189] The output of this process is a (nTbW)x(nTbH) array r[x][y] of residual samples, where x=0..nTbW-1, y=0..nTbH-1.

[0190] When lfnst_idx[xTbY][yTbY] is not equal to 0 and both nTbW and nTbH are greater than *** or equal to ***4, the following operations apply:

[0191] – The variables predModeIntra, nLfnstOutSize, log2LfnstSize, nLfnstSize, and nonZeroSize are derived as follows:

[0192] predModeIntra=(cIdx==0)? IntraPredModeY[xTbY][yTbY]:IntraPredModeC[xTbY][yTbY] (8-965)

[0193] nLfnstOutSize=***(nTbW>=8&&nTbH>=8)? ***48***:16*** (8-966)

[0194] log2LfnstSize=***(nTbW>=8&&nTbH>=8)? ***3***:2*** (8-967)

[0195] nLfnstSize=1< <log2LfnstSize (8-968)

[0196] nonZeroSize=(***(nTbW==4&&nTbH==4)||***(nTbW==8&&nTbH==8))? 8:16 (8-969)

[0197] – When intra_mip_flag[xTbComp][yTbComp] is equal to 1 and cIdx is equal to 0, set predModeIntra equal to INTRA_PLANAR.

[0198] …

[0199] …

[0200] The variables nonZeroW and nonZeroH are derived as follows:

[0201] – If lfnst_idx[xTbY][yTbY] is not equal to 0 and nTbW is greater than *** or equal to ***4 and nTbH is greater than *** or equal to

[0202] ***4. Apply the following operations:

[0203] nonZeroW=***(nTbW==4||nTbH==4)? 4:***8 (8-977)

[0204] nonZeroH=***(nTbW==4||nTbH==4)? 4:***8 (8-978)

[0205] – Otherwise, apply the following actions:

[0206] nonZeroW=Min(nTbW,(trTypeHor>0)?16:32) (8-979)

[0207] nonZeroH=Min(nTbH,(trTypeVer>0)?16:32) (8-980)

[0208] …

[0209] Fig. 9 2 is a flowchart illustrating an example method for encoding a current block. The current block may include a current CU. Figure 1 and Figure 3 ), it should be understood that other devices may be configured to perform the same Fig. 9 A similar approach to the one used in this paper.

[0210] In this example, video encoder 200 first predicts a current block (350). For example, video encoder 200 may form a prediction block for the current block. Video encoder 200 may then calculate a residual block for the current block (352). To calculate the residual block, video encoder 200 may calculate the difference between the original, unencoded block and the prediction block for the current block.

[0211] The video encoder 200 may then transform and quantize the coefficients of the residual block (354). For example, the video encoder 200 may, in response to determining that single tree partitioning is enabled for the current block, apply LFNST only to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block. However, in response to determining that split tree partitioning is enabled for the current block, the video encoder 200 may apply LFNST to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block, and apply LFNST to the separable chroma transform coefficients for the current block to generate second chroma transform coefficients for the current block.

[0212] The video encoder 200 may scan the quantized transform coefficients of the residual block (356). During the scan, or after the scan, the video encoder 200 may entropy encode the transform coefficients (358). For example, the video encoder 200 may encode the transform coefficients using CAVLC or CABAC. The video encoder 200 may encode the transform coefficients using LFNST based on the partitioning. The video encoder 200 may then output the entropy encoded data of the block (360).

[0213] Fig.10 is a flowchart illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although with respect to the video decoder 300 ( Figure 1 and Figure 4 ), it should be understood that other devices may be configured to perform the same Fig.10 A similar approach to the one used in this paper.

[0214] 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). For example, the video decoder 300 may decode the transform coefficients using LFNST based on the partitioning. The video decoder 300 may predict the current block (374), such as using an intra-prediction mode or an inter-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.

[0215] The video decoder 300 may then inverse quantize and inverse transform the transform coefficients to generate a residual block (378). For example, the video decoder 300 may, in response to determining that single tree partitioning is enabled for the current block, apply inverse LFNST only to luma transform coefficients for the current block to generate a residual block for the current block. However, in response to determining that separate tree partitioning is enabled for the current block, the video decoder 300 may apply inverse LFNST to luma transform coefficients for the current block and chroma transform coefficients for the current block to generate a residual block for the current block. The video decoder 300 may finally decode the current block by combining the prediction block and the residual block (380).

[0216] The proposed simplification is implemented on top of VTM-6.0 and evaluated under Common Test Conditions (CTC). Note that low latency B results are omitted because LFSNT is disabled for low latency B in CTC. Table 1 gives the results of removing 4x4 LFNST on VTM-6.0.

[0217] Table 1. Results of the proposed simplifications under CTC on top of VTM-6.0.

[0218]

[0219] According to the techniques of the present disclosure, a video decoder (eg, video encoder 200 or video decoder 300) can remove 4x4 LFNST to reduce the worst-case latency during the transformation process. Experimental results show that the decoding benefit of 4x4 LFNST is very limited, especially for UHD sequences under AI and RA configurations.

[0220] Fig.114 is a flowchart illustrating an example method for encoding a current block of video data based on partitioning according to the techniques of the present disclosure. Video encoder 200 (e.g., mode selection unit 202) may determine whether single tree partitioning is enabled for the current block (400). Video encoder 200 (e.g., residual generation unit 204) may generate residual values ​​for the current block based on a prediction block for the current block (402). For example, video encoder 200 (e.g., residual generation unit 204) may generate a chroma residual block for the current block and a luma residual block for the current block.

[0221] The video encoder 200 (e.g., the transform processing unit 206) may apply a separable transform to the residual values ​​to generate a separable luma transform coefficient for the current block and a separable chroma transform coefficient for the current block (404). For example, the video encoder 200 (e.g., the residual generation unit 204) may apply a separable transform to the residual values ​​of the chroma residual block for the current block to generate a separable chroma transform coefficient for the current block, and apply a separable transform to the residual values ​​of the luma residual block for the current block to generate a separable luma transform coefficient for the current block.

[0222] The video encoder 200 (e.g., the transform processing unit 206) may, in response to determining that single tree partitioning is enabled for the current block, apply LFNST only to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block (406). For example, the video encoder 200 (e.g., the residual generation unit 204) may apply LFNST to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block. In this example, the video encoder 200 (e.g., the residual generation unit 204) may avoid applying LFNST to the separable chroma transform coefficients for the current block in order to generate chroma transform coefficients for the current block (e.g., bypass LFNST).

[0223] However, in response to determining that a single tree partition is enabled for the current block, the video encoder 200 may apply LFNST to both the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and to the separable chroma transform coefficients for the current block to generate chroma transform coefficients for the current block. For example, the video encoder 200 (e.g., the residual generation unit 204) may apply LFNST to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block. In this example, the video encoder 200 (e.g., the residual generation unit 204) may apply LFNST to the separable chroma transform coefficients for the current block to generate chroma transform coefficients for the current block.

[0224] In some examples, video encoder 200 may determine whether the current block includes a height greater than 4 and determine whether the current block includes a width greater than 4. In this example, video encoder 200 may further apply LFNST only to luma transform coefficients in response to determining that the height is greater than 4 and the width is greater than 4.

[0225] In some examples, video encoder 200 may determine whether the current block includes a height greater than 4 and determine whether the current block includes a width greater than 4. In this example, video encoder 200 may further apply LFNST only to luma transform coefficients in response to determining that the height is greater than 4 and the width is greater than 4.

[0226] In some examples, the video encoder 200 may determine whether the current block includes a height greater than 4, determine whether the current block includes a width greater than 4, and determine whether the zeroing region for the luma transform coefficient is outside the 8x8 LFNST sub-block for LFNST. In this example, the video encoder 200 may further apply LFNST only to the luma transform coefficient in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region for the luma transform coefficient is outside the 8x8 LFNST sub-block for LFNST.

[0227] In some examples, the video encoder 200 may determine whether the current block includes a height greater than 4, determine whether the current block includes a width greater than 4, and determine whether the zeroing region for the luma transform coefficient is outside the 4x4 LFNST sub-block for LFNST. In this example, the video encoder 200 may further apply LFNST only to the luma transform coefficient in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region for the luma transform coefficient is outside the 4x4 LFNST sub-block for LFNST.

[0228] The video encoder 200 (e.g., the quantization unit 208 and the entropy encoding unit 220) may encode the luma transform coefficients and the chroma transform coefficients to generate encoded video data (408). For example, the quantization unit 208 may quantize the luma transform coefficients to produce quantized luma transform coefficients, and quantize the chroma transform coefficients to produce quantized chroma transform coefficients. In this example, the entropy encoding unit 220 may encode (e.g., entropy encode) the quantized luma transform coefficients and the quantized chroma transform coefficients to generate encoded video data. The video encoder 200 (e.g., the entropy encoding unit 220) may output the encoded video data (410).

[0229] In some examples, the video encoder 200 may signal an LFNST index (e.g., an LFNST flag). For example, in response to determining that single tree partitioning is enabled for the current block, the video encoder 200 may signal in the encoded data an LFNST index for luma transform coefficients for the current block, and avoid signaling in the encoded data an LFNST index for chroma transform coefficients. However, in response to determining that separate tree partitioning is enabled for the current block, the video encoder 200 may signal in the encoded data an LFNST index for luma transform coefficients for the current block, and signal in the encoded data an LFNST index for chroma transform coefficients.

[0230] Fig.12 4 is a flowchart illustrating an example method for decoding a current block of video data based on partitioning according to techniques of the present disclosure. Video decoder 300 (e.g., entropy decoding unit 302) may receive encoded data for the current block (452). Video decoder 300 (e.g., prediction processing unit 302) may determine whether single tree partitioning is enabled for the current block (454). For example, video decoder 300 may receive an indication signaled by video encoder 200 as to whether video data for the current block is partitioned using single tree partitioning or separate tree partitioning. In some examples, video decoder 300 may determine whether video data for the current block is partitioned using single tree partitioning or separate tree partitioning based on implicit signaling or in the absence of signaling by video encoder 200.

[0231] The video decoder 300 (e.g., entropy decoding unit 302) may decode the encoded data to generate luma transform coefficients for the current block and chroma transform coefficients for the current block (456). For example, the video decoder 300 (e.g., entropy decoding unit 302) may decode (e.g., entropy decode) quantized luma transform coefficients for the current block and quantized chroma transform coefficients for the current block. In this example, the video decoder 300 (e.g., inverse quantization unit 306) may inverse quantize the quantized luma transform coefficients to generate luma transform coefficients, and inverse quantize the quantized chroma transform coefficients to generate chroma transform coefficients. In some examples, inverse quantization of the luma transform coefficients and / or the chroma transform coefficients may be bypassed.

[0232] The video decoder 300 (e.g., the inverse transform processing unit 308) may, in response to determining that single tree partitioning is enabled for the current block, apply inverse LFNST only to luma transform coefficients for the current block to generate a residual block for the current block (458). For example, the video decoder 300 (e.g., the inverse transform processing unit 308) may apply inverse LFNST to luma transform coefficients for the current block to generate a luma residual block for the current block. In this example, the video decoder 300 (e.g., the inverse transform processing unit 308) may avoid applying inverse LFNST to chroma transform coefficients in order to generate a chroma residual block for the current block (e.g., bypass inverse LFNST). After performing the inverse LFNST, the video decoder 300 (e.g., the inverse transform processing unit 308) may apply an inverse separable transform to the luma transform coefficients (e.g., separable luma transform coefficients) generated by the inverse LFNST to generate a luma residual block, and apply an inverse separable transform to the inverse quantized chroma transform coefficients to generate chroma residual blocks (e.g., a Cr residual block or a Cb residual block).

[0233] However, in response to determining that split tree partitioning is enabled for the current block, the video decoder 300 (e.g., the inverse transform processing unit 308) may apply inverse LFNST to both the luma transform coefficient and the chroma transform coefficient to generate a residual block. For example, the video decoder 300 (e.g., the inverse transform processing unit 308) may apply inverse LFNST to the luma transform coefficient for the current block to generate a luma residual block for the current block. In this example, the video decoder 300 (e.g., the inverse transform processing unit 308) may apply inverse LFNST to the luma transform coefficient to generate a chroma residual block for the current block. Again, after performing the inverse LFNST, the video decoder 300 (e.g., the inverse transform processing unit 308) may apply an inverse separable transform to the separable luma transform coefficient to generate a luma residual block. Similarly, the video decoder 300 (e.g., the inverse transform processing unit 308) may apply an inverse separable transform to the separable chroma transform coefficient to generate a chroma residual block.

[0234] In some examples, the video decoder 300 may determine whether the current block includes a height greater than 4 and determine whether the current block includes a width greater than 4. In this example, the video decoder 300 may further apply inverse LFNST only to luma transform coefficients in response to determining that the height is greater than 4 and the width is greater than 4.

[0235] In some examples, the video decoder 300 may determine whether the current block includes a height greater than 4, determine whether the current block includes a width greater than 4, and determine whether the zeroing region of the luma transform coefficient is outside the 8x8 LFNST sub-block for inverse LFNST. In this example, the video decoder 300 may further apply inverse LFNST only to the luma transform coefficient in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficient is outside the 8x8 LFNST sub-block.

[0236] In some examples, the video decoder 300 may determine whether the current block includes a height greater than 4, determine whether the current block includes a width greater than 4, and determine whether the zeroing region of the luma transform coefficient is outside the 4x4 LFNST sub-block for inverse LFNST. In this example, the video decoder 300 may further apply inverse LFNST only to the luma transform coefficient in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficient is outside the 4x4 LFNST sub-block.

[0237] The video decoder 300 (e.g., reconstruction unit 310) may reconstruct a current block of video data using the residual block and the prediction block for the current block (460). For example, the video decoder 300 (e.g., reconstruction unit 310) may reconstruct the current block by combining a luma residual block for the current block with a luma prediction block for the current block and combining a chroma residual block for the current block with a chroma prediction block for the current block. The video decoder 300 (e.g., DPB 314) may output the encoded video data.

[0238] In some examples, the video decoder 300 may determine an LFNST index (e.g., an LFNST flag). For example, in response to determining that single tree partitioning is enabled for the current block, the video decoder 300 may determine an LFNST index for luma transform coefficients of the current block from the encoded data, and avoid determining an LFNST index for chroma transform coefficients from the encoded data. However, in response to determining that separate tree partitioning is enabled for the current block, the video decoder 300 may determine an LFNST index for luma transform coefficients for the current block from the encoded data, and determine an LFNST index for chroma transform coefficients from the encoded data. The LFNST index may indicate the type of inverse LFNST and / or whether LFNST is enabled.

[0239] A non-limiting, illustrative list of examples of techniques of the present disclosure is provided below.

[0240] Example 1. A method of decoding video data, the method comprising: determining whether a block includes a height greater than 4; determining whether the block includes a width greater than 4; in response to determining that the block includes a height greater than 4 and a width greater than 4, applying a low frequency non-separable transform (LFNST) to the block; and in response to determining that the block includes a height equal to or less than 4 or a width equal to or less than 4, avoiding applying the LFNST to the block.

[0241] Example 2. A method of decoding video data, the method comprising: determining whether a block includes a height greater than 4; determining whether the block includes a width greater than 4; determining whether a zeroing region is outside an 8x8 LFNST block; and in response to determining that the block includes a height greater than 4, the block includes a width greater than 4, and the zeroing region is outside an 8x8 LFNST sub-block, using 8x8 LFNST.

[0242] Example 3. A method of decoding video data, the method comprising: determining whether a block includes a height greater than 4; determining whether the block includes a width greater than 4; in response to determining that the block includes a height greater than 4 and a width greater than 4, signaling a low frequency non-separable transform (LFNST) index; and in response to determining that the block includes a height equal to or less than 4 or a width equal to or less than 4, refraining from signaling the LFNST index.

[0243] Example 4. A method of decoding video data, the method comprising: determining whether a block includes a height greater than 4; determining whether the block includes a width greater than 4; determining whether to use a single tree partition; in response to determining to use a single tree partition, using LFNST in response to determining that the block includes a height greater than 4 and a width greater than 4.

[0244] Example 5. A method of coding video data, the method comprising: determining whether to use a single tree partition; and in response to determining to use a single tree partition, signaling only a LFNST index / flag for luma.

[0245] Example 6. A method of decoding video data, the method comprising: applying LFNST only to luma blocks.

[0246] Example 7. A method of coding video data, the method comprising: determining whether split tree partitioning is enabled; and in response to determining that split tree partitioning is enabled, using LFNST for both luma and chroma blocks.

[0247] Example 8. A method of decoding video data, the method comprising: determining whether single tree partitioning is enabled; and in response to determining that single tree partitioning is enabled, using LFNST only for luma blocks and disabling LFNST for chroma blocks.

[0248] Example 9. A method of decoding video data, the method comprising: determining whether a block includes a height greater than 4; determining whether the block includes a width greater than 4; determining whether a zeroing region is outside an 8x8 LFNST sub-block; in response to determining that the block includes a height greater than 4, a width greater than 4, and the zeroing region is outside a 4x4 LFNST sub-block, using a 4x4 LFNST.

[0249] Example 10. The method of any of Examples 1-9, wherein the deciphering comprises decoding.

[0250] Example 11. The method of any of Examples 1-9, wherein decoding comprises encoding.

[0251] Example 12. An apparatus for decoding video data, the apparatus comprising one or more units for performing the blocks of any of Examples 1-11.

[0252] Example 13. The device of Example 12, wherein the one or more units include one or more processors implemented in circuitry.

[0253] Example 14. The apparatus of any of Examples 12 and 13, further comprising a memory to store video data.

[0254] Example 15. The device of any of Examples 12-14, further comprising a display configured to display the decoded video data.

[0255] Example 16. The device of any of Examples 12-15, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0256] Example 17. The device of any of Examples 12-16, wherein the device comprises a video decoder.

[0257] Example 18. The device of any of Examples 12-17, wherein the device comprises a video encoder.

[0258] Example 19. 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 1-9.

[0259] It is to be appreciated that, depending on the example, 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 in parallel (e.g., through multithreading, interrupt handling, or multiple processors) rather than sequentially.

[0260] 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 or transmitted as one or more instructions or codes on a computer-readable medium, and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium or a communication medium, the computer-readable storage medium corresponding to a tangible medium such as a data storage medium, the communication medium including, for example, any medium that facilitates the transfer of a computer program from one place to another according to a communication protocol. In this manner, a computer-readable medium may generally correspond to (1) a tangible computer-readable storage medium that is non-temporary, 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 the implementation of the techniques described in the present disclosure. A computer program product may include a computer-readable medium.

[0261] 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 sent from a website, server or other remote source using a coaxial cable, optical fiber cable, twisted pair, digital subscriber line (DSL) or wireless technology (such as infrared, radio and microwave), then the coaxial cable, optical fiber cable, twisted pair, DSL or wireless technology (such as infrared, radio and microwave) is included in the definition of the medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other temporary media, but are instead directed to non-temporary, tangible storage media. As used herein, disks and optical disks include compact disks (CDs), laser optical disks, optical optical disks, digital versatile disks (DVDs), floppy disks and blue-ray disks, wherein disks usually reproduce data magnetically, and optical disks reproduce data optically using lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0262] 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. Thus, the terms "processor" and "processing circuitry" as used herein may refer to any of the foregoing structures or any other structures suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software configured for encoding and decoding, or incorporated in a combined codec. Furthermore, the techniques may be fully implemented in one or more circuits or logic elements.

[0263] The techniques of the present disclosure may be implemented in a variety of devices or apparatuses, including wireless handsets, integrated circuits (ICs), or IC sets (e.g., chip sets). Various components, modules, or units are described in the present disclosure to emphasize the functional aspects of devices configured to perform the disclosed techniques, but are not necessarily required to be implemented by different hardware units. Specifically, as described above, the various units may be combined in a codec hardware unit, or provided by some interoperable hardware units together with appropriate software and / or firmware, the hardware unit including one or more processors as described above.

[0264] 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: Receiving encoded data for a current block; determining whether single tree partitioning is enabled for the current block; Decoding the encoded data to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block; In response to determining that the single tree partitioning is enabled for the current block, applying an inverse low frequency non-separable transform (LFNST) only to the luma transform coefficients for the current block to generate a residual block for the current block, and disabling the inverse LFNST for the chroma transform coefficients for the current block; and The current block of the video data is reconstructed using the residual block and a prediction block for the current block.

2. The method according to claim 1, further comprising: receiving second encoded data for a second block; determining whether split tree partitioning is enabled for the second block; decoding the second encoded data to generate a second luma transform coefficient for the second block and a second chroma transform coefficient for the second block; responsive to determining that split tree partitioning is enabled for the second block, applying the inverse LFNST to both the second luma transform coefficient and the second chroma transform coefficient to generate a second residual block for the second block; as well as The second block of the video data is reconstructed using the second residual block and the second prediction block for the second block.

3. The method according to claim 1, further comprising: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; as well as Wherein applying the inverse LFNST only to the luma transform coefficients is further responsive to determining that the height is greater than 4 and the width is greater than 4.

4. The method according to claim 1, wherein: Applying the inverse LFNST comprises: applying an inverse 8x8 LFNST to the 8x8 LFNST sub-block of the luma transform coefficients, the method further comprising: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; determining whether a zeroing region of the luma transform coefficients is outside the 8x8 LFNST sub-block for the inverse LFNST; and Wherein applying the inverse LFNST only to the luma transform coefficients is further in response to determining that the height is greater than 4, the width is greater than 4, and the zeroed region of the luma transform coefficients is outside the 8x8 LFNST sub-block.

5. The method according to claim 1, wherein: Applying the inverse LFNST comprises: applying an inverse 4x4 LFNST to a 4x4 LFNST sub-block of the luma transform coefficients, the method further comprising: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; determining whether a zeroing region of the luma transform coefficients is outside the 4x4 LFNST sub-block for the inverse LFNST; and Wherein applying the inverse LFNST only to the luma transform coefficients is further in response to determining that the height is greater than 4, the width is greater than 4, and the zeroed region of the luma transform coefficients is outside the 4x4 LFNST sub-block.

6. The method according to claim 1, further comprising: In response to determining that the single tree partitioning is enabled for the current block, determining LFNST indices for the luma transform coefficients for the current block based on the coded data, and refraining from determining LFNST indices for the chroma transform coefficients based on the coded data; as well as Wherein applying the inverse LFNST only to the luma transform coefficient is based on a LFNST index for the luma transform coefficient.

7. A method for encoding video data, the method comprising: determining whether single tree partitioning is enabled for the current block; generating a residual value for the current block based on a prediction block for the current block; Applying a separable transform to the residual value to generate a separable luma transform coefficient for the current block and a separable chroma transform coefficient for the current block; In response to determining that the single tree partition is enabled for the current block, applying a low frequency non-separable transform (LFNST) only to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block; encoding the luma transform coefficient and the chroma transform coefficient to generate encoded video data; as well as The encoded video data is output.

8. The method according to claim 7, further comprising: In response to determining that the single tree partition is enabled for the current block, disabling the LFNST for the separable chroma transform coefficients for the current block.

9. The method according to claim 7, further comprising: determining that split tree partitioning is enabled for the second block; generating a second residual value for the second block based on a second prediction block for the second block; applying the separable transform to the second residual value to generate second separable luma transform coefficients for the second block and second separable chroma transform coefficients for the second block; responsive to determining that the split tree partitioning is enabled for the second block, applying the LFNST to the second separable luma transform coefficients for the second block to generate second luma transform coefficients for the second block, and applying the LFNST to the second separable chroma transform coefficients for the second block to generate second chroma transform coefficients for the second block; encoding the second luma transform coefficient and the second chroma transform coefficient to generate encoded video data; as well as The encoded video data is output.

10. The method according to claim 7, further comprising: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; as well as Wherein applying the LFNST only to the luma transform coefficients is further responsive to determining that the height is greater than 4 and the width is greater than 4.

11. The method according to claim 7, wherein: Applying the LFNST comprises: applying 8x8 LFNST to the 8x8 LFNST sub-block of the separable luma transform coefficients, the method further comprising: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; determining whether a zeroing region of the luma transform coefficients is outside the 8x8 LFNST sub-block for the LFNST; and Wherein applying the LFNST only to the luma transform coefficients is further in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficients is outside the 8x8 LFNST sub-block.

12. The method according to claim 7, wherein: Applying the LFNST comprises: applying a 4x4 LFNST to a 4x4 LFNST sub-block of the separable luma transform coefficients, the method further comprising: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; determining whether a zeroing region of the luma transform coefficients is outside the 4x4 LFNST sub-block for the LFNST; and Wherein applying the LFNST only to the luma transform coefficients is further in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficients is outside the 4x4 LFNST sub-block.

13. The method according to claim 7, further comprising: In response to determining that the single tree partitioning is enabled for the current block, signaling in the coded data LFNST indices for the luma transform coefficients for the current block, and avoiding signaling in the coded data LFNST indices for the chroma transform coefficients.

14. A device for decoding video data, the device comprising: a memory configured to store the video data; as well as A processing circuit configured to: Receiving encoded data for a current block; determining whether single tree partitioning is enabled for the current block; Decoding the encoded data to generate a luma transform coefficient for the current block and a chroma transform coefficient for the current block; In response to determining that the single tree partitioning is enabled for the current block, applying an inverse low frequency non-separable transform (LFNST) only to the luma transform coefficients for the current block to generate a residual block for the current block, and disabling the inverse LFNST for the chroma transform coefficients for the current block; and The current block of the video data is reconstructed using the residual block and a prediction block for the current block.

15. The device according to claim 14, wherein: The processing circuit is further configured to: receiving second encoded data for a second block; determining whether split tree partitioning is enabled for the second block; decoding the second encoded data to generate a second luma transform coefficient for the second block and a second chroma transform coefficient for the second block; responsive to determining that split tree partitioning is enabled for the second block, applying the inverse LFNST to both the second luma transform coefficient and the second chroma transform coefficient to generate a second residual block for the second block; as well as The second block of the video data is reconstructed using the second residual block and the second prediction block for the second block.

16. The apparatus according to claim 14, wherein: The processing circuit is further configured to: Determining whether the current block includes a height greater than 4; determining whether the current block includes a width greater than 4; and Wherein applying the inverse LFNST only to the luma transform coefficients is further responsive to determining that the height is greater than 4 and the width is greater than 4.

17. The apparatus according to claim 14, wherein: To apply the inverse LFNST, the processing circuit is configured to: apply the inverse 8x8 LFNST to the 8x8 LFNST sub-block of luma transform coefficients, wherein the processing circuit is further configured to: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; determining whether a zeroing region of the luma transform coefficients is outside the 8x8 LFNST sub-block for the inverse LFNST; and The processing circuit is configured to: further in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficient is outside the 8x8 LFNST sub-block, apply the inverse LFNST only to the luma transform coefficient.

18. The apparatus of claim 14, wherein: To apply the inverse LFNST, the processing circuit is configured to: apply the inverse 4x4 LFNST to the 4x4 LFNST sub-block of the luma transform coefficients, wherein the processing circuit is further configured to: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; determining whether a zeroing region of the luma transform coefficients is outside the 4x4 LFNST sub-block for the inverse LFNST; and The processing circuit is configured to: further in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficient is outside the 4x4 LFNST sub-block, apply the inverse LFNST only to the luma transform coefficient.

19. The apparatus of claim 14, wherein: The processing circuit is further configured to: In response to determining that the single tree partitioning is enabled for the current block, determining LFNST indices for the luma transform coefficients for the current block based on the coded data, and refraining from determining LFNST indices for the chroma transform coefficients based on the coded data; and Wherein, the processing circuit is configured to: apply the inverse LFNST only to the luma transform coefficient based on the LFNST index for the luma transform coefficient.

20. The device of claim 14, further comprising a display configured to display an image.

21. The apparatus of claim 14, wherein: The device includes one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

22. A device for encoding video data, the device comprising: a memory configured to store the video data; as well as A processing circuit configured to: determining whether single tree partitioning is enabled for the current block; generating a residual value for the current block based on a prediction block for the current block; Applying a separable transform to the residual value to generate a separable luma transform coefficient for the current block and a separable chroma transform coefficient for the current block; In response to determining that the single tree partition is enabled for the current block, applying a low frequency non-separable transform (LFNST) only to the separable luma transform coefficients for the current block to generate luma transform coefficients for the current block and chroma transform coefficients for the current block; encoding the luma transform coefficient and the chroma transform coefficient to generate encoded video data; as well as The encoded video data is output.

23. The apparatus of claim 22, wherein: The processing circuitry is further configured to, in response to determining that the single tree partition is enabled for the current block, disable the LFNST for the separable chroma transform coefficients for the current block.

24. The apparatus of claim 22, wherein: The processing circuit is further configured to: determining that split tree partitioning is enabled for the second block; generating a second residual value for the second block based on a second prediction block for the second block; applying the separable transform to the second residual value to generate second separable luma transform coefficients for the second block and second separable chroma transform coefficients for the second block; responsive to determining that the split tree partitioning is enabled for the second block, applying the LFNST to the second separable luma transform coefficients for the second block to generate second luma transform coefficients for the second block, and applying the LFNST to the second separable chroma transform coefficients for the second block to generate second chroma transform coefficients for the second block; encoding the second luma transform coefficient and the second chroma transform coefficient to generate encoded video data; as well as The encoded video data is output.

25. The apparatus of claim 22, wherein: The processing circuit is further configured to: Determining whether the current block includes a height greater than 4; determining whether the current block includes a width greater than 4; and Wherein the processing circuit is configured to: further in response to determining that the height is greater than 4 and the width is greater than 4, apply the LFNST only to the luma transform coefficients.

26. The apparatus of claim 22, wherein: To apply the LFNST, the processing circuit is configured to: apply 8x8 LFNST to the 8x8 LFNST sub-block of the separable luma transform coefficients, wherein the processing circuit is further configured to: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; determining whether a zeroing region of the luma transform coefficients is outside the 8x8 LFNST sub-block for the LFNST; and The processing circuit is configured to: further in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficient is outside the 8x8 LFNST sub-block, apply the LFNST only to the luma transform coefficient.

27. The apparatus of claim 22, wherein: To apply the LFNST, the processing circuit is configured to: apply 4x4 LFNST to 4x4 LFNST sub-blocks of separable luma transform coefficients, wherein the processing circuit is further configured to: Determining whether the current block includes a height greater than 4; Determining whether the current block includes a width greater than 4; determining whether a zeroing region of the luma transform coefficients is outside the 4x4 LFNST sub-block for the LFNST; and The processing circuit is configured to: further in response to determining that the height is greater than 4, the width is greater than 4, and the zeroing region of the luma transform coefficient is outside the 4x4 LFNST sub-block, apply the LFNST only to the luma transform coefficient.

28. The apparatus of claim 22, wherein: The processing circuit is further configured to, in response to determining that the single tree partitioning is enabled for the current block, signal LFNST indices for the luma transform coefficients for the current block in the encoded data, and avoid signaling LFNST indices for the chroma transform coefficients in the encoded data.

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