Implicit conversion selection in video coding

Abstract

This provides techniques for implicit transformation selection in video coding. [Solution] The method includes inferring a transformation type for the current transformation block from a plurality of transformation types, each comprising one or more discrete cosine transforms (DCTs) and one or more discrete sine transforms (DSTs). Inferring the transformation type includes determining the size of the current transformation block, determining whether the current video block is partitioned using intra subblock partitions (ISPs), and, in response to determining that the size of the current transformation block is less than a threshold and that the current video block is partitioned using ISPs, selecting a specific DST from the one or more DSTs as the selected transformation type.

Description

[Technical Field]

[0001]

[0001] This application claims priority to U.S. Patent Application No. 16 / 815,920, filed on 11 March 2020, which claims the benefit of U.S. Provisional Patent Application No. 62 / 817,397, filed on 12 March 2019, the entirety of which is incorporated herein by reference.

[0002]

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

[0003]

[0003] Digital video capabilities can be incorporated into a wide range 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 gaming devices, video game consoles, cellular or satellite radiophones, so-called "smartphones," video teleconferencing devices, and video streaming devices. Digital video devices implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4, Part 10, Advanced Video Coding (AVC), ITU-T H.265 / High Efficiency Video Coding (HEVC), and extensions of such standards. By implementing such video coding techniques, video devices can transmit, receive, encode, decode, and / or store digital video information more efficiently.

[0004]

[0004] Video coding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or eliminate redundancy inherent in video sequences. In block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be divided into video blocks, which may also be called coding tree units (CTUs), coding units (CUs), and / or coding nodes. A video block in an intra-coded (I) slice of a picture is coded using spatial prediction for reference samples in adjacent blocks within the same picture. A video block in an inter-coded (P or B) slice of a picture may use spatial prediction for reference samples in adjacent blocks within the same picture, or temporal prediction for reference samples in other reference pictures. A picture may be called a frame, and a reference picture may be called a reference frame. [Overview of the project]

[0005]

[0005] In one example, the method comprises: inferring a transform type from a plurality of transform types, including one or more discrete cosine transforms (DCTs) and one or more discrete sine transforms (DSTs), where inferring the transform type is determined by determining the size of the current transform block, determining whether the current video block is partitioned using intra-subblock partitioning (ISP), determining that the size of the current transform block satisfies a size threshold and determining that the current video block is partitioned using ISP, and selecting a particular DST from one or more DSTs as the selected transform type; transforming the current transform block using the selected transform type to obtain a block of reconstructed residual data for the video block; and obtaining reconstructed residual data for the video block This includes reconstructing the video block based on the data.

[0006]

[0006] In another example, the device includes memory configured to store video blocks and one or more processors implemented in the circuit, wherein the one or more processors are configured to infer a transformation type for the current transformation block of the current video block from a plurality of transformation types including one or more DCTs and one or more DSTs, wherein in order to infer the transformation type, the one or more processors are configured to transform the current transformation block using the selected transformation type to obtain a block of reconstructed residual data for the video block, and to reconstruct the video block based on the reconstructed residual data for the video block.

[0007]

[0007] In another example, a computer-readable storage medium stores instructions that, when executed, cause one or more processors of a video coding device to infer a conversion type for the current conversion block of the current video block from a plurality of conversion types including one or more DCTs and one or more DSTs, wherein the instructions causing one or more processors to infer a conversion type include instructions causing one or more processors to determine the size of the current conversion block, determine whether the current video block is partitioned using an ISP, determine that the size of the current conversion block satisfies a size threshold and, in response to determining that the current video block is partitioned using an ISP, select a particular DST from one or more DSTs as the selected conversion type, convert the current conversion block using the selected conversion type to obtain a block of reconstructed residual data for the video block, and reconstruct the video block based on the reconstructed residual data for the video block.

[0008]

[0008] Details of one or more examples of the present disclosure are described in the accompanying drawings and the following description. Other features, purposes, and advantages of various aspects of the present technique will become apparent from the description and drawings, as well as the claims. [Brief explanation of the drawing]

[0009] [Figure 1]

[0009] A block diagram showing an exemplary video coding and decoding system capable of performing the techniques of the present disclosure. [Figure 2A]

[0010] A conceptual diagram illustrating an exemplary quadtree-binary tree (QTBT) structure. [Figure 2B] A conceptual diagram showing the corresponding coding tree unit (CTU). [Figure 2C]

[0011] Conceptual diagram showing another exemplary quadtree structure and corresponding tree units. [Figure 3]

[0012] Block diagram showing an exemplary video encoder capable of executing the techniques of the present disclosure. [Figure 4]

[0013] Block diagram showing an exemplary video decoder capable of executing the techniques of the present disclosure. [Figure 5]

[0014] Block diagram showing a system for hybrid video encoding using adaptive transform selection. [Figure 6]

[0015] Conceptual diagram showing a separable transform implementation in a state where horizontal and vertical lines are independently transformed. [Figure 7]

[0016] Conceptual diagram showing an exemplary block by which a video coder can implicitly derive a transform by one or more techniques of the present disclosure. [Figure 8]

[0017] Conceptual diagram showing an intra prediction direction. [Figure 9]

[0018] Flowchart showing an exemplary method for encoding a current block. [Figure 10]

[0019] Flowchart showing an exemplary method for decoding a current block. [Figure 11]

[0020] Flowchart showing an exemplary method for inferring a transform type for a transform block of a video block by one or more techniques of the present disclosure.

Mode for Carrying Out the Invention

[0010]

[0021] Generally, the present disclosure describes techniques for implicit transform selection in video coding. As will be described in more detail below, following prediction such as intra prediction or inter prediction of a block, a video encoder may calculate residual data for the block. Residual data, such as a residual block, represents the sample-by-sample difference between the block formed using the corresponding prediction mode and the predicted block for the block. The video encoder may apply one or more transforms to the residual block to generate transformed data in a transform domain rather than in a sample domain. For example, the video encoder may apply a discrete cosine transform (DCT). In some examples, the video encoder may utilize different types of transforms. For example, the video encoder may use various types of DCTs.

[0011]

[0022] A video decoder may apply an inverse transform when decoding video data. When the video encoder may utilize different types of transforms, the video decoder may need to determine which transform was used by the video encoder. In some examples, the video encoder may explicitly signal which type of transform was used when transforming the residual data (e.g., encode a syntax element having a value indicating it). However, in some examples, it may not be desirable to explicitly signal the type of transform used (e.g., due to signaling overhead).

[0012]

[0023] According to one or more techniques of this disclosure, a video decoder may implicitly determine what type of transformation was used when transforming residual data. For example, a video decoder may apply a set of rules to determine what type of transformation was used when transforming residual data based on side information available in the video decoder (either explicitly signaled or implicitly derived from signaled information). A video encoder may apply the same rules when determining what type of transformation should be used. Thus, both video encoders and video decoders may determine what type of transformation should be used without explicit signaling of the transformation type.

[0013]

[0024] Figure 1 is a block diagram illustrating an exemplary video coding and decoding system 100 capable of performing the techniques of the present disclosure. The techniques of the present disclosure generally concern coding (encoding and / or decoding) video data. Generally, video data includes any data for processing video. Thus, video data may include raw, uncoded video such as signaling data, coded video, decoded (e.g., reconstructed) video, and video metadata.

[0014]

[0025] As shown in Figure 1, system 100 includes, in this example, a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, the source device 102 provides the video data to the destination device 116 via a computer-readable medium 110. The source device 102 and destination device 116 may comprise any of a wide range 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, and so on. In some cases, the source device 102 and destination device 116 may be wireless communication devices, as they may be capable of wireless communication.

[0015]

[0026] In the example in Figure 1, the source device 102 includes a video source 104, a memory 106, a video encoder 200, and an output interface 108. The destination device 116 includes an input interface 122, a video decoder 300, a memory 120, and a display device 118. According to this disclosure, the video encoder 200 of the source device 102 and the video decoder 300 of the destination device 116 may be configured to apply techniques for implicit conversion selection. Thus, the source device 102 represents an example of a video encoding device, and the destination device 116 represents an example of a video decoding device. In other examples, the source and destination devices may include other components or configurations. For example, the source device 102 may receive video data from an external video source, such as an external camera. Similarly, the destination device 116 may interface with an external display device rather than including an integrated display device.

[0016]

[0027] The system 100 shown in Figure 1 is merely an example. In general, any digital video coding and / or decoding device may perform techniques for implicit conversion selection. Source device 102 and destination device 116 are merely examples of coding devices such that source device 102 generates coded video data for transmission to destination device 116. In this disclosure, a “coding” device is referred to as a device that performs coding (encoding and / or decoding) of data. Thus, video encoder 200 and video decoder 300 represent examples of coding devices, in particular, a video encoder and a video decoder, respectively. In some examples, devices 102 and 116 may operate substantially symmetrically such that each of devices 102 and 116 includes a video coding component and a video decoding component. Thus, system 100 may support one-way or two-way video transmission between video device 102 and video device 116 for, for example, video streaming, video playback, video broadcast, or video phone.

[0017]

[0028] Generally, the video source 104 represents a source of video data (i.e., raw, uncoded video data) and provides the video encoder 200 with a sequence of pictures (also called "frames") of video data to encode the data for the pictures. The video source 104 of the source device 102 may include a video capture device such as a video camera, a video archive containing previously captured raw video, and / or a video feed interface for receiving video from a video content provider. As a further alternative, the video source 104 may generate computer graphics-based data as source video, or a combination of live video, archived video, and computer-generated video. In each case, the video encoder 200 encodes the captured video data, pre-captured video data, or computer-generated video data. The video encoder 200 may rearrange the pictures from the reception order (sometimes called the "display order") to the coding order for encoding. The video encoder 200 may generate a bitstream() containing the encoded video data. The source device 102 may then output the encoded video data to a computer-readable medium 110 via the output interface 108 for reception and / or retrieval by the input interface 122 of the destination device 116, for example.

[0018]

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

[0019]

[0030] The computer-readable medium 110 may represent any type of medium or device capable of transferring encoded video data from the source device 102 to the destination device 116. For example, the computer-readable medium 110 may represent a communication medium that enables the source device 102 to directly transmit encoded video data to the destination device 116 in real time, for example, over a radio frequency network or a computer-based network. The output interface 108 may modulate the transmit signal containing the encoded video data, and the input interface 122 may modulate the received transmit signal according to a communication standard such as a wireless communication protocol. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful for enabling communication from the source device 102 to the destination device 116.

[0020]

[0031] In some examples, the source device 102 may output encoded data to the storage device 116 via the output interface 108. Similarly, the destination device 116 may access the encoded data from the storage device 116 via the input interface 122. The storage device 116 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.

[0021]

[0032] In some examples, source device 102 may output encoded video data to a file server 114 or another intermediate storage device capable of storing encoded video generated by source device 102. Destination device 116 may access the stored video data from file server 114 via streaming or download. File server 114 can be any type of server device capable of storing encoded video data and sending that encoded video data to destination device 116. File server 114 may represent a web server (for example, a website), a File Transfer Protocol (FTP) server, a Content Delivery Network device, or a Network Attached Storage (NAS) device. Destination device 116 may access the encoded video data from file server 114 through any standard data connection, including an Internet connection. This may include wireless channels (e.g., Wi-Fi® connection), wired connections (e.g., DSL, cable modem, etc.), or a combination of both suitable for accessing encoded video data stored on 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.

[0022]

[0033] The output interface 108 and input interface 122 may represent a wireless transmitter / receiver, a modem, a wired networking component (e.g., an Ethernet® card), a wireless communication component operating according to any of the various IEEE 802.11 standards, or other physical components. In examples where the output interface 108 and input interface 122 include wireless components, the output interface 108 and input interface 122 may be configured to transfer data such as encoded video data according to cellular communication standards such as 4G, 4G-LTE® (Long Term Evolution), LTE Advanced, or 5G. In some examples where the output interface 108 includes a wireless transmitter, the output interface 108 and input interface 122 may be configured to transfer data such as encoded video data according to other wireless standards such as the IEEE 802.11 specification, the IEEE 802.15 specification (e.g., ZigBee®), or the Bluetooth® standard. In some examples, the source device 102 and / or destination device 116 may include their respective system-on-chip (SoC) devices. For example, the source device 102 may include an SoC device for performing functions associated with the video encoder 200 and / or the output interface 108, and the destination device 116 may include an SoC device for performing functions associated with the video decoder 300 and / or the input interface 122.

[0023]

[0034] The techniques of this disclosure can be applied to video coding that supports any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, internet streaming video transmission such as Dynamic Adaptive Streaming over HTTP (DASH), digital video encoded on a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0024]

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

[0025]

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

[0026]

[0037] The video encoder 200 and video decoder 300 can each be implemented as one or more suitable encoder and / or decoder circuits, or any combination thereof, including one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, etc. When the technique is partially implemented in software, the device may store software instructions in a suitable non-temporary computer-readable medium and use one or more processors to execute those instructions in hardware to perform the technique of the Disclosure. Each of the video encoder 200 and video decoder 300 may consist of one or more encoders or decoders, any of which may be incorporated as part of a composite encoder / decoder (CODEC) in each device. A device including the video encoder 200 and / or video decoder 300 may include an integrated circuit, a microprocessor, and / or a wireless communication device such as a cellular telephone.

[0027]

[0038] The video encoder 200 and video decoder 300 may operate in accordance with video coding standards such as ITU-T H.265, also known as High Efficiency Video Coding (HEVC), or its extensions, such as the Multiview and / or Scalable Video Coding extension. Alternatively, the video encoder 200 and video decoder 300 may operate in accordance with other proprietary or industry standards, such as ITU-T H.266, also known as the Joint Exploration Test Model (JEM) or Versatile Video Coding (VVC). The latest draft of the VVC standard is described in Bross et al., "Versatile Video Coding (Draft 4)," Joint Video Experts Team (JVET) of ITU-T SG16 WP3 and ISO / IEC JTC1 / SC29 / WG11, 13th meeting: Marrakech, MA, January 9-18, 2019, JVET-M1001-v6 (hereinafter, "VVC Draft 4"). However, the techniques described herein are not limited to any specific coding standard.

[0028]

[0039] Generally, the video encoder 200 and video decoder 300 can perform block-based coding of pictures. The term "block" generally refers to a structure containing data to be processed (e.g., to be encoded, decoded, or otherwise used in other ways in the encoding and / or decoding process). For example, a block may contain a two-dimensional matrix of samples of luminance and / or chrominance data. Generally, the video encoder 200 and video decoder 300 can code video data represented in YUV (e.g., Y, Cb, Cr) format. That is, rather than coding red, green, and blue (RGB) data for the samples of a picture, the video encoder 200 and video decoder 300 can code luminance and chrominance components, where the chrominance component may include both red and blue chrominance components. In some examples, the video encoder 200 converts the received RGB format data to a YUV representation before encoding, and the video decoder 300 converts the YUV representation to RGB format. Alternatively, pre-processing and post-processing units (not shown) may perform these transformations.

[0029]

[0040] This disclosure may refer to coding a picture (e.g., encoding and decoding) to include, in general, the process of encoding or decoding the data of a picture. Similarly, this disclosure may refer to coding a block of a picture to include, for example, the process of encoding or decoding data for a block, such as predictive and / or residual coding. An encoded video bitstream generally contains a set of values ​​of syntax elements representing coding decisions (e.g., coding modes) and divisions of the picture into blocks. Thus, references to coding a picture or a block should generally be understood as coding the values ​​of the syntax elements that make up the picture or block.

[0030]

[0041] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video coder (such as video encoder 200) divides the coding tree units (CTUs) into CUs according to a quadtree structure. That is, the video coder divides the CTUs and CUs into four equal, non-overlapping squares, and each node in the quadtree has either zero or four child nodes. Nodes without child nodes are sometimes called "leaf nodes," and the CU of such a leaf node may contain one or more PUs and / or one or more TUs. The video coder may further divide the PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents a division of the TUs. In HEVC, PUs represent intra-predicted data, while TUs represent residual data. Intra-predicted CUs contain intra-predicted information, such as intra-mode indications.

[0031]

[0042] As another example, the video encoder 200 and video decoder 300 may be configured to operate according to JEM or VVC. According to JEM or VVC, the video coder (such as the video encoder 200) divides a picture into multiple coding tree units (CTUs). The video encoder 200 may divide the CTUs according to a tree structure, such as a quad-binary (QTBT) structure or a multi-type tree (MTT) structure. The QTBT structure eliminates the concept of multiple division types, such as the distinction between CUs, PUs, and TUs in HEVC. The QTBT structure has two levels: a first level divided according to quad-tree divisions and a second level divided according to binary tree divisions. The root node of the QTBT structure corresponds to a CTU. The leaf nodes of the binary tree correspond to coding units (CUs).

[0032]

[0043] In an MTT partitioning structure, blocks can be partitioned using quadtree (QT) partitions, binary (BT) partitions, and one or more types of ternary (TT) partitions. A ternary partition is a partition in which a block is divided into three subblocks. In some examples, a ternary partition divides a block into three subblocks without dividing the original block through a central point. The partition types in an MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0033]

[0044] In some examples, the video encoder 200 and video decoder 300 may use a single QTBT or MTT structure to represent the luminance component and the chrominance component, respectively, while in other examples, the video encoder 200 and video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luminance component and another QTBT / MTT structure for both chrominance components (or two QTBT / MTT structures for each chrominance component).

[0034]

[0045] The video encoder 200 and video decoder 300 may be configured to use a quadtree partition, QTBT partition, MTT partition, or other partitioning structure using HEVC. For illustrative purposes, the description of the techniques of this disclosure is presented in relation to the QTBT partition. However, it should be understood that the techniques of this disclosure may also be applicable to video coders configured to use a quadtree partition, or similarly other types of partitions.

[0035]

[0046] This disclosure may use "N×N" and "N by N" interchangeably to refer to the sample dimension of a block (such as a CU or other video block) with respect to vertical and horizontal dimensions, for example, 16×16 samples or 16 by 16 samples. Generally, a 16×16 CU has 16 samples vertically (y=16) and 16 samples horizontally (x=16). Similarly, an N×N CU generally has N samples vertically and N samples horizontally, where N represents a non-negative integer. The samples in a CU may be arranged in rows and columns. Furthermore, a CU does not necessarily have to have the same number of samples horizontally as it does vertically. For example, a CU may have N×M samples, where M is not necessarily equal to N.

[0036]

[0047] The video encoder 200 encodes video data for CUs, which represent prediction and / or residual information, as well as other information. The prediction information indicates how the CU should be predicted in order to form a prediction block for the CU. The residual information generally represents the sample-by-sample difference between the CU sample before encoding and the prediction block.

[0037]

[0048] To predict the CU, the video encoder 200 can generally form prediction blocks for the CU through inter-prediction or intra-prediction. Inter-prediction generally refers to predicting the CU from data of a previously coded picture, while intra-prediction generally refers to predicting the CU from previously coded data of the same picture. To perform inter-prediction, the video encoder 200 can generate prediction blocks using one or more motion vectors. The video encoder 200 can generally perform motion search to identify a reference block that exactly matches the CU, for example, with respect to the difference between the CU and the reference block. The video encoder 200 can compute a difference metric using absolute difference sum (SAD), squared difference sum (SSD), mean absolute difference (MAD), mean squared difference (MSD), or other such difference calculations to determine whether the reference block currently exactly matches the CU. In some examples, the video encoder 200 can predict the current CU using unidirectional or bidirectional prediction.

[0038]

[0049] Some examples of JEM and VVC also provide an affine motion compensation mode, which can be considered an inter-prediction mode. In affine motion compensation mode, the video encoder 200 may determine two or more motion vectors representing non-translational motion, such as zooming in or out, rotation, perspective motion, or other anomalous motion types.

[0039]

[0050] To perform intra-prediction, the video encoder 200 may select an intra-prediction mode to generate prediction blocks. Several examples with JEM and VVC provide 67 intra-prediction modes, including various directional modes, as well as planar and DC modes. Generally, the video encoder 200 selects an intra-prediction mode that describes adjacent samples to the current block (e.g., a block of CU) from which samples of the current block should be predicted. Such samples may generally be above, above and to the left of, or to the left of, the current block in the same picture as the current block, assuming that the video encoder 200 codes CTU and CU in raster scan order (left to right, top to bottom).

[0040]

[0051] The video encoder 200 encodes data representing the prediction mode for the current block. For example, in interprediction mode, the video encoder 200 may encode data representing which of the various available interprediction modes is used, as well as the motion information for the corresponding mode. For example, in unidirectional or bidirectional interprediction, the video encoder 200 may encode the motion vectors using advanced motion vector prediction (AMVP) or merge mode. The video encoder 200 may use a similar mode to encode the motion vectors in affine motion compensation mode.

[0041]

[0052] Following predictions such as intra-prediction or inter-prediction of a block, the video encoder 200 may compute residual data for the block. Residual data, such as residual blocks, represents the sample-by-sample difference between the block and the predicted block for the block, formed using the corresponding prediction mode. The video encoder 200 may apply one or more transformations to the residual blocks to generate transformation data in the transformation region rather than the sample region. For example, the video encoder 200 may apply a discrete cosine transform (DCT), integer transform, wavelet transform, or a conceptually similar transform to the residual video data. Furthermore, the video encoder 200 may apply a quadratic transform following a first transform, such as a mode-dependent non-separable secondary transform (MDNSST), signal-dependent transform, or Karhunen-Loeve transform (KLT). Following the application of one or more transformations, the video encoder 200 generates transform coefficients.

[0042]

[0053] As explained above, video encoders such as video encoder 200 can apply various types of transformations to transform residual data. Below is an overview of the discrete sine and cosine transforms (DCT and DST). A brief description of the transformation schemes used in the HEVC standard is also provided.

[0043]

[0054] Discrete sine and cosine transforms.

[0044]

[0055] The transformation shows the process of deriving an alternative representation of the input signal. N-point vector x = [x0, x1, ..., × N-1 ] T and given vector {Φ0,Φ1,...,Φ M-1 Assuming a set of}, x is approximated, or Φ0,Φ1,...,Φ M-1 It can be expressed precisely using a linear combination of , which can be formulated as follows:

[0045]

number

[0046]

[0056] Here,

[0047]

number

[0048] f can be an approximation or equivalent of x, and the vector f = [f i ,f2,...,f M-1 ] is called the transformation coefficient vector, and {Φ0,Φ1,...,Φ M-1} is a transformation basis vector.

[0049]

[0057] In video coding scenarios, the transformation coefficients are nearly non-correlated and sparse; that is, the energy of the input vector x is compressed into only a few transformation coefficients, with the vast majority of the remaining coefficients generally approaching zero.

[0050]

[0058] Given specific input data, the optimal transformation for energy compression is the so-called Carunenlobe transformation (KLT), which uses eigenvectors of the covariance matrix of the input data as transformation basis vectors. Therefore, the KLT is, in practice, a data-dependent transformation and does not have a general mathematical formula. However, under certain assumptions, for example, that the input data forms a first-order stationary Markov process, the literature has shown that the corresponding KLT is indeed a member of the sinusoidal family of unitary transformations. The sinusoidal family of unitary transformations exhibits transformations using transformation basis vectors that are formulated as follows:

[0051]

number

[0052]

[0059] Here, e is the base of the natural logarithm approximately equal to 2.71828, and A, B, and θ are generally complex numbers and depend on the value of m.

[0053]

[0060] Exemplary transforms including the discrete Fourier, cosine, sine, and KLT (for a first-order stationary Markov process) are members of this sine wave family of unitary transforms. According to S.A. Martucci, "Symmetric convolution and the discrete sine and cosine transforms", IEEE Trans. Sig. Processing SP-42, 1038-1051 (1994), the complete set of the discrete cosine transform (DCT) and discrete sine transform (DST) families includes a total of 16 transforms based on different types, i.e., different values of A, B, and θ, and the following gives the complete definitions of different types of DCT and DST.

[0054]

[0061] Assume that the input N-point vector is shown as x = [x0, x1,..., x N-1 T and it is transformed into another N-point transform coefficient vector shown as y = [y0, y1,..., y N-1 T by multiplying matrices. This process can be further shown according to one of the following transform formulations, where k ranges from 0 to N - 1 including both end values.

[0055]

[0062] DCT type I (DCT-1):

[0056]

Equation

[0057]

[0063] DCT type II (DCT-2):

[0058]

Equation

[0059] ​

[0064] DCT Type III (DCT-3):

[0060]

number

[0061]

[0065] DCT Type IV (DCT-4):

[0062]

number

[0063]

[0066] DCT Type V (DCT-5):

[0064]

number

[0065]

[0067] DCT Type VI (DCT-6):

[0066]

number

[0067]

[0068] DCT Type VII (DCT-7):

[0068]

number

[0069]

[0069] DCT Type VIII (DCT-8):

[0070]

number

[0071]

[0070] DST Type I (DST-1):

[0072]

number

[0073]

[0071] DST Type II (DST-2):

[0074]

number

[0075]

[0072] DST Type III (DST-3):

[0076]

number

[0077]

[0073] DST Type IV (DST-4):

[0078]

number

[0079]

[0074] DST Type V (DST-5):

[0080]

number

[0081]

[0075] DST Type VI (DST-6):

[0082]

number

[0083]

[0076] DCT Type VII (DST-7):

[0084]

number

[0085]

[0077] DST Type VIII (DST-8):

[0086]

number

[0087]

[0078] The transformation type is specified by the mathematical formula of the transformation basis function, for example, 4-point DST-VII and 8-point DST-VII have the same transformation type regardless of the value of N.

[0088]

[0079] Without loss of generality, all of the above transformation types can be expressed using the following generalized formulas.

[0089]

number

[0090]

[0080] Here, T is a transformation matrix specified by the definition of one transformation, for example, DCT type I to DCT type VIII or DST type I to DST type VIII, and a row vector of T, for example, [T i,0 ,T i,1 ,T i,2 ,…,T i,N-1 ] is the i-th transformation basis vector. A transformation applied to an N-point input vector is called an N-point transformation.

[0091]

[0081] It should also be noted that the above transformation formula applied to the one-dimensional input data x can be expressed in the following matrix multiplication form.

[0092]

number

[0093]

[0082] Here, T represents the transformation matrix, x represents the input data vector, and y represents the output transformation coefficient vector.

[0094]

[0083] Conversion of 2D input data.

[0095]

[0084] The transformations introduced in the previous section are applied to one-dimensional input data, and the transformations can also be extended to two-dimensional input data sources. Assume that X is an input M × N data array. Typical ways of applying transformations to 2D input data include separable and inseparable 2D transformations.

[0096]

[0085] The separable 2D transformation is formulated as follows, by applying the 1D transformation sequentially to the horizontal and vertical vectors of X.

[0097]

number

[0098]

[0086] Here, C and R represent given M×M and N×N transformation matrices, respectively. From the formula, it can be seen that C applies a 1D transformation to the column vectors of X, while R applies a 1D transformation to the row vectors of X. In later parts of this specification, for simplicity, C and R will be shown as left (vertical) and right (horizontal) transformations, and together they form a transformation pair. It is possible that C is equal to R and is an orthogonal matrix. In such a case, a separable 2D transformation is determined by only one transformation matrix.

[0099]

[0087] The inseparable 2D transformation first rearranges all elements of X into a single vector, i.e., X', by performing the following mathematical mapping as an example:

[0100]

number

[0101]

[0088] Next, the 1D transformation T' is applied to X' as follows.

[0102]

number

[0103]

[0089] Here, T' is the (M*N)×(M*N) transformation matrix.

[0104]

[0090] In video coding, separable 2D transformations may be applicable because they may use far fewer operations (addition, multiplication) counts compared to 1D transformations.

[0105]

[0091] In conventional video codecs such as H.264 / AVC, integer approximations of the 4-point and 8-point discrete cosine transform (DCT) type II are always applied to both intra-predictive residuals and inter-predictive residuals. More flexible types of transforms other than DCT type II are used in newer video codecs to better adapt to the various statistics of residual samples. For example, in HEVC, integer approximations of the 4-point type VII discrete sine transform (DST) are used for intra-predictive residuals, and it has been theoretically proven and experimentally verified that DST type VII is more efficient than DCT type II for residual vectors generated along the intra-predictive direction (for example, DST type VII is more efficient than DCT type II for row residual vectors generated by the horizontal intra-predictive direction). In HEVC, integer approximations of 4-point DST type VII are applied only to 4×4 lumane intra-predictive residual blocks. The 4-point DST-VII used in HEVC is shown below.

[0106]

[0092] 4×4DST-VII:

[0107]

number

[0108]

[0093] In HEVC, for residual blocks that are not 4x4 lumene intra-predictive residual blocks, integer approximations of 4-point, 8-point, 16-point and 32-point DCT type II are also applied, as shown below.

[0109]

[0094] 4-point DCT-II:

[0110]

number

[0111]

[0095] 8-point DCT-II:

[0112]

number

[0113]

[0096] 16-point DCT-II:

[0114]

number

[0115]

[0097] 32-point DCT-II:

[0116]

number

[0117]

[0098] A transformation method based on residual quadtrees in HEVC.

[0118]

[0099] To adapt to the various characteristics of residual blocks, HEVC employs a transform coding structure that uses a residual quadtree (RQT), which is briefly described at http: / / www.hhi.fraunhofer.de / fields-of-competence / image-processing / research-groups / image-video-coding / hevc-high-efficiency-video-coding / transform-coding-using-the-residual-quadtree-rqt.html. In RQT, each picture is divided into coding tree units (CTUs) which are coded in raster traversal order for a particular tile or slice. A CTU is a square block and represents the root of the quadtree, i.e., the coding tree. CTU sizes can range from 8x8 to 64x64 lumens, but 64x64 is commonly used. Each CTU can be further divided into smaller square blocks called coding units (CUs). After the CTU is recursively divided into CUs, each CU is further divided into a prediction unit (PU) and a transformation unit (TU).

[0119]

[0100] The division of CUs into TUs is performed recursively based on a quadtree method, and therefore the residual signal of each CU is coded by a tree structure, i.e., a residual quadtree (RQT). The RQT allows TU sizes from 4×4 to 32×32 lumens. Figure 2C shows an example where a CU contains 10 TUs labeled with letters a-j, and the corresponding block divisions. Each node in the RQT is actually a transform unit (TU). Individual TUs can be processed in a depth-first tree traversal order shown in the figure as alphabetical, following a recursive Z scan by depth-first traversal.

[0120]

[0101] The quadtree method allows for the adaptation of transformations to the fluctuating spatial frequency characteristics of residual signals. Generally, larger transformation block sizes with greater spatial support provide better frequency resolution. However, smaller transformation block sizes with less spatial support may also provide better spatial resolution. The trade-off between these two, namely spatial resolution and frequency resolution, can be selected by encoder mode determination, for example, based on rate-distortion optimization techniques. A video coder may calculate a weighted sum of coding bits and reconstruction distortion, i.e., rate-distortion cost, for each coding mode (e.g., a particular RQT partition structure), and perform rate-distortion optimization techniques to select the coding mode with the minimum rate-distortion cost as the best mode.

[0121]

[0102] Three parameters, namely the maximum tree depth, minimum allowable transformation size, and maximum allowable transformation size, may be defined in the RQT. The minimum and maximum transformation sizes may vary within a range of 4x4 to 32x32 samples, corresponding to the supported block transformations described in the previous paragraph. The maximum allowable depth of the RQT limits the number of TUs. A maximum depth equal to 0 means that if each contained TB reaches the maximum allowable transformation size, for example 32x32, the CB cannot be further subdivided.

[0122]

[0103] All these parameters interact and affect the RQT structure. Consider the case where the root CB size is 64×64, the maximum depth is equal to 0, and the maximum transformation size is equal to 32×32. In this case, the CB must be partitioned at least once, otherwise it would lead to an unacceptable 64×64TB. The RQT parameters, namely the maximum RQT depth, minimum and maximum transformation sizes, are transmitted in the bitstream at the sequence parameter set level. With respect to the RQT depth, different values ​​may be specified and signaled for intra-coded CUs and inter-coded CUs.

[0123]

[0104] The quadtree transform is applied to both intra residual blocks and inter residual blocks. Generally, the DCT-II transform of the same size as the current residual quadtree partition is applied to the residual block. However, if the current residual quadtree block is 4x4 and generated by intra prediction, the 4x4 DST-VII transform described above is applied.

[0124]

[0105] In HEVC, larger size conversions, such as 64x64 conversion, are not adopted, mainly due to considerations of their limited benefits and the relatively high complexity for videos with relatively lower resolutions.

[0125]

[0106] As described above, following any transformation to generate the transformation coefficients, the video encoder 200 may perform quantization of the transformation coefficients. Quantization generally refers to the process by which the transformation coefficients are quantized to reduce the amount of data used to represent the coefficients as much as possible, resulting in further compression. By performing the quantization process, the video encoder 200 may reduce the bit depth associated with some or all of the coefficients. For example, the video encoder 200 may round 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 of the value to be quantized.

[0126]

[0107] Following quantization, the video encoder 200 may scan the transformation coefficients to generate a one-dimensional vector from a two-dimensional matrix containing the quantized transformation coefficients. The scan may be designed to place higher energy (and therefore lower frequency) coefficients at the beginning of the vector and lower energy (and therefore higher frequency) transformation coefficients at the end of the vector. In some examples, the video encoder 200 may use a predefined scan order to scan the quantized transformation coefficients to generate a serialized vector, and then entropy encode the quantized transformation coefficients of the vector. In other examples, the video encoder 200 may perform adaptive scanning. After scanning the quantized transformation 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 also entropy encode values ​​for syntax elements that describe metadata associated with the encoded video data for use by the video decoder 300 when decoding the video data.

[0127]

[0108] In order to perform CABAC, the video encoder 200 may assign a context in the context model to the symbol to be transmitted. The context may relate, for example, to whether the adjacent value of the symbol is 0 or not. Probability decisions may be based on the context assigned to the symbol.

[0128]

[0109] The video encoder 200 may further generate syntax data for the video decoder 300, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, in other syntax data such as a picture header, block header, slice header, or sequence parameter set (SPS), picture parameter set (PPS), or video parameter set (VPS). The video decoder 300 may similarly decode such syntax data to determine how the corresponding video data should be decoded.

[0129]

[0110] In this way, the video encoder 200 can generate a bitstream containing encoded video data, for example, a bitstream containing syntax elements that describe the division of a picture into blocks (e.g., CUs) and block prediction and / or residual information. Finally, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0130]

[0111] Generally, the video decoder 300 performs the reverse process of what was done by the video encoder 200 in order to decode the encoded video data of the bitstream. For example, the video decoder 300 may decode the values ​​of the syntax elements of the bitstream using CABAC in a substantially similar manner to the CABAC encoding process of the video encoder 200, although this is the reverse of the CABAC encoding process. The syntax elements may define the partitioning information of the picture to the CTU and the partitions of each CTU, which follow a corresponding partitioning structure such as a QTBT structure, in order to define the CU of the CTU. The syntax elements may further define prediction and residual information for blocks of video data (e.g., CU).

[0131]

[0112] Residual information may be represented, for example, by quantized transformation coefficients. The video decoder 300 may dequantize and inverse transform the quantized transformation coefficients of a block in order to reconstruct the residual block of the block. The video decoder 300 uses a signaled prediction mode (intra or inter prediction) and associated prediction information (for example, motion information for inter prediction) to form a predicted block of the block. The video decoder 300 may then combine the predicted block and the residual block (sample by sample) to reconstruct the original block. The video decoder 300 may perform additional processing, such as performing a deblocking process to reduce visual artifacts along the boundaries of the block.

[0132]

[0113] According to the techniques of the present disclosure, a video coder (i.e., a video encoder 200 and / or a video decoder 300) may derive a transformation type from a plurality of transformation types for the current coefficient block of a video block. The video coder may transform the current transformation block (e.g., a coefficient block) using the selected transformation type to obtain a block of reconstructed residual data for the video block, and reconstruct the video block based on the reconstructed residual data for the video block.

[0133]

[0114] A video coder may infer the transformation type based on factors other than explicit signaling of the transformation type. Thus, a video coder may omit coding a syntax element that explicitly identifies the transformation type for the current block. Some examples of factors that a video coder may infer the transformation type from include the size of the current block (e.g., the height and / or width of the current block), whether the current block is partitioned using intra subblock partitions (ISPs), and the intra mode of the current block. A video coder may infer the transformation type based on any combination of factors. For example, a video coder may infer the transformation type for the current video block based on the size of the current transformation block and whether the current video block is partitioned using ISPs. In at least some of such examples, a video coder may infer the transformation type for the current transformation block regardless of the intra prediction mode used to predict the current video block.

[0134]

[0115] The video coder may select a transformation type from a plurality of transformation types, which include one or more discrete cosine transforms (DCTs) and one or more discrete sine transforms (DSTs). As will be described in more detail below, one or more DCTs may include one or more of DCT-1, DCT-2, DCT-3, DCT-4, DCT-5, DCT-6, DCT-7, and DCT-8, and / or one or more DSTs may include one or more of DST-1, DST-2, DST-3, DST-4, DST-5, DST-6, DST-7, and DST-8.

[0135]

[0116] As described above, the video coder may infer the transformation type for the current transformation block based on the size of the current transformation block. For example, the video coder may select a first transformation type for the current transformation block in response to determining that the size of the current transformation block meets a size threshold, and select a second transformation type for the current transformation block in response to determining that the size of the current transformation block does not meet a size threshold. In some examples, the video coder may determine whether the size of the current transformation block meets a size threshold by comparing the size of the current transformation block to a single threshold. In other examples, the video coder may determine whether the size of the current transformation block meets a size threshold by determining that the size of the current transformation block is greater than a lower bound (e.g., 2, 4, 6) and less than an upper bound (e.g., 8, 16, 32). If the size of the current transformation block is greater than the lower bound and less than the upper bound, the video coder may determine that the size of the current transformation block meets a size threshold. Similarly, if the size of the current transformation block is smaller than the lower limit or larger than the upper limit, the video coder may determine that the size of the current transformation block does not meet the size threshold.

[0136]

[0117] If the current video block is a coding unit (CU), the CU can be divided into multiple subdivisions using an ISP. Each subdivision may have associated transformation blocks. Thus, if a CU is divided using an ISP, multiple transformation blocks may be associated with the CU. For example, a 16x16 CU can be divided vertically into four 4x16 divisions, each of which may be associated with a 4x16 transformation block.

[0137]

[0118] As described above, the video coder may infer the transformation type for the current video block based on whether the current video block is segmented using an ISP and on the size of the current transformation block. For example, in response to determining that the size of the current transformation block meets a size threshold and that the current video block is segmented using an ISP, the video coder may select a particular DST (e.g., DST-7) from one or more DSTs as the transformation type for the current transformation block. In another example, in response to determining that the size of the current transformation block does not meet a size threshold and that the current video block is segmented using an ISP, the video coder may select a particular DCT (particular DCT) (e.g., DCT-2) from one or more DCTs as the transformation type for the current transformation block. In any of the above examples, the video coder may choose to select the transformation type regardless of the intra-prediction mode used to predict the current video block (e.g., regardless of the angular mode, DC mode, or planar mode used to intra-predict the current video).

[0138]

[0119] In some cases, the video coder may always perform transformation type inference. In other cases, the video coder may perform transformation type inference under certain conditions. For example, the video coder may infer the transformation type for the current transformation block in response to determining that multiple transform selection (MTS) is available for the current video block. In some cases, the video coder may determine whether MTS is available for the current video block based on the value of one or more syntax elements (e.g., sps_explicit_mts_intra_enabled_flag).

[0139]

[0120] In some cases, the video coder may infer the transformation type for performing a horizontal transformation (i.e., the transformation type for horizontal use) and the transformation type for performing a vertical transformation (i.e., the transformation type for vertical use). The video coder may use a common algorithm to infer the transformation types for horizontal and vertical use. For example, the video coder may infer the transformation type for horizontal use based on whether the width of the current transformation block satisfies a width size threshold and whether the current video block containing the current transformation block is partitioned using an ISP, and the transformation type for vertical use based on whether the height of the current transformation block satisfies a height size threshold and whether the current video block containing the current transformation block is partitioned using an ISP. In some cases, the video coder may use the same size threshold for inferring both horizontal and vertical transformation types. For example, if the size threshold includes an upper and lower limit, the upper and lower limits of the width size threshold may be equal to the upper and lower limits of the height size threshold. As one specific example, the lower limit for both the width and height thresholds could be 4, and the upper limit for both the width and height thresholds could be 16.

[0140]

[0121] In some examples, in order to derive (i.e., guess) the transformation type for the current coefficient block, the video coder may select the DST-7 transformation to transform any row or column with a number of samples (e.g., luma samples) less than or equal to a threshold number (e.g., 8, 16, 32), and select the DCT-2 transformation to transform any row or column with a number of samples greater than the threshold number.

[0141]

[0122] In relation to VVC Draft4 (for example, JVET-M1001), one example of the proposed changes can be achieved by replacing Table 8-15 with the following:

[0142]

number

[0143] Here, "0" and "1" represent DCT-2 and DST-7, respectively.

[0144]

[0123] Blocks partitioned using ISP may be prohibited from having rows / columns with only two samples. Accordingly, this disclosure proposes a two-point DST-7. Entries for a two-point DST-7 matrix (which brings in only 4 bytes of additional memory) may be as follows:

[0145]

number

[0146]

[0124] Alternatively, one example of the proposed changes can be achieved by modifying VVC Draft4 as follows:

[0147]

number

[0148] Here, "0" and "1" represent DCT-2 and DST-7, respectively, and changes (i.e., deleted parts) are underlined and italicized.

[0149]

[0125] In this disclosure, the term “signaling” may generally refer to “signaling” certain information, such as syntax elements. The term “signaling” may generally refer to the communication of value syntax elements and / or other data used to decode encoded video data. That is, the video encoder 200 may signal the values ​​of syntax elements in the bitstream. In general, signaling refers to generating values ​​in the bitstream. As described above, the source device 102 may transfer the bitstream to the destination device 116 in substantially real time, or it may transfer the bitstream to the destination device 116 in non-real time, as may occur when the syntax elements are stored in the storage device 112 for later retrieval by the destination device 116.

[0150]

[0126] Figures 2A and 2B are conceptual diagrams showing an exemplary quadtree-binary tree (QTBT) structure 130 and its corresponding coding tree unit (CTU) 132. Solid lines represent quadtree splitting, and dotted lines represent binary tree splitting. At each split (i.e., non-leaf) node of the binary tree, one flag is signaled to indicate which splitting type (i.e., horizontal or vertical) is used, where in this example, 0 indicates horizontal splitting and 1 indicates vertical splitting. In the case of quadtree splitting, the quadtree node divides the block horizontally and vertically into four subblocks of equal size, so it is not necessary to indicate the splitting type. Therefore, the video encoder 200 can encode and the video decoder 300 can decode syntax elements (such as splitting information) for the region tree level (i.e., solid lines) of the QTBT structure 130 and syntax elements (such as splitting information) for the prediction tree level (i.e., dashed lines) of the QTBT structure 130. The video encoder 200 can encode and the video decoder 300 can decode video data such as prediction and transformation data for CUs represented by terminal leaf nodes of the QTBT structure 130.

[0151]

[0127] Generally, the CTU132 in Figure 2B can be associated with parameters that define the size of the blocks corresponding to the nodes of the QTBT structure 130 at the first and second levels. These parameters may include the CTU size (representing the size of the CTU132 in samples), the minimum quadtree size (representing the minimum allowable quadtree leaf node size, MinQTSize), the maximum binary tree size (representing the maximum allowable binary tree root node size, MaxBTSize), the maximum binary tree depth (representing the maximum allowable binary tree depth, MaxBTDepth), and the minimum binary tree size (representing the minimum allowable binary tree leaf node size, MinBTSize).

[0152]

[0128] The root node of a QTBT structure corresponding to a CTU may have four child nodes at the first level of the QTBT structure, each of which may be divided according to a quadruple tree partition. That is, a node at the first level is either a leaf node (without child nodes) or has four child nodes. An example of QTBT structure 130 represents a node that includes a parent node and child nodes with solid lines for branching. A node at the first level may be further divided by its own binary tree, provided that it is not larger than the maximum allowable binary tree root node size (MaxBTSize). The binary tree partitioning of a node may be repeated until the node obtained from the partition reaches the minimum allowable binary tree leaf node size (MinBTSize) or the maximum allowable binary tree depth (MaxBTDepth). An example of QTBT structure 130 represents such a node as having dashed lines for branching. A binary tree leaf node is called a coding unit (CU), and a coding unit (CU) is used for prediction (e.g., intra-picture prediction or inter-picture prediction) and transformation without further subdivision. As described above, CUs are sometimes also called “video blocks” or “blocks.”

[0153]

[0129] In an example of a QTBT partition structure, the CTU size is set to 128×128 (a chroma sample and two corresponding 64×64 chroma samples), MinQTSize is set to 16×16, MaxBTSize is set to 64×64, MinBTSize (for both width and height) is set to 4, and MaxBTDepth is set to 4. To generate a quadtree leaf node, a quadtree partition is first applied to the CTU. A quadtree leaf node can have a size ranging from 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If a quadtree node is 128×128, it is not further partitioned by a binary tree because its size exceeds MaxBTSize (i.e., 64×64 in this example). Otherwise, the leaf quadtree node is further partitioned by a binary tree. Therefore, a quad tree leaf node is also the root node to a binary tree and has a binary tree depth of 0. When the binary tree depth reaches MaxBTDepth (4 in this example), no further partitioning is allowed. When a binary tree node has a width equal to MinBTSize (4 in this example), it implies that no further horizontal partitioning is allowed. Similarly, a binary tree node with a height equal to MinBTSize implies that no further vertical partitioning is allowed to that binary tree node. As mentioned above, a leaf node of a binary tree is called a CU and is further processed according to prediction and transformation without further partitioning.

[0154]

[0130] Figure 3 is a block diagram showing an exemplary video encoder 200 capable of performing the techniques of this disclosure. Figure 3 is provided for illustrative purposes and should not be considered to limit the techniques that are more broadly illustrated and described in this disclosure. For illustrative purposes, 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 coding and decoding.

[0155]

[0131] In the example shown in Figure 3, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a conversion processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse conversion processing unit 212, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218, and an entropy coding unit 220. Any or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the conversion processing unit 206, the quantization unit 208, the inverse quantization unit 210, an inverse conversion processing unit 212, a reconstruction unit 214, a filter unit 216, a DPB 218, and an entropy coding unit 220 may be implemented in one or more processors or processing circuits. Furthermore, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

[0156]

[0132] 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 stored in the video data memory 230 from, for example, the video source 104 (Figure 1). The DPB 218 may act as a reference picture memory that stores reference video data for use in predicting subsequent video data by the video encoder 200. The video data memory 230 and the DPB 218 may be formed by any of various memory devices, such as dynamic random access memory (DRAM) including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM®), or other types of memory devices. The video data memory 230 and the DPB 218 may be provided by the same memory device or by separate memory devices. In various examples, the video data memory 230 may be on-chip with the other components of the video encoder 200, as shown in the figure, or off-chip with respect to those components.

[0157]

[0133] In this disclosure, references to the video data memory 230 should not be interpreted as being limited to memory inside the video encoder 200 unless specifically described so, or as being limited to memory outside the video encoder 200 unless specifically described so. Rather, references to the video data memory 230 should be understood as reference memory that stores video data that the video encoder 200 receives for encoding (for example, video data of the current block to be encoded). Memory 106 in Figure 1 may also provide temporary storage of outputs from various units of the video encoder 200.

[0158]

[0134] The various units in Figure 3 are shown to help understand the operations performed by the video encoder 200. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide a specific function and are pre-configured with respect to the operations they may perform. Programmable circuits refer to circuits that can be programmed to perform various tasks and to provide flexible functionality in the operations they may perform. For example, a programmable circuit may run software or firmware that operates the programmable circuit in a manner defined by software or firmware instructions. Fixed-function circuits may run software instructions (for example, to receive or output parameters), but the type of operation that a fixed-function circuit performs is generally immutable. In some examples, one or more of the units may be separate circuit blocks (fixed-function or programmable), and in some examples, one or more units may be integrated circuits.

[0159]

[0135] The video encoder 200 may include a logic unit (ALU), an elementary function unit (EFU), digital circuits, analog circuits, 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 the programmable circuits, memory 106 (Figure 1) may store object code of the software that the video encoder 200 receives and executes, or another memory (not shown) within the video encoder 200 may store such instructions.

[0160]

[0136] The video data memory 230 is configured to store the received video data. The video encoder 200 can take a picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 may be raw video data to be encoded.

[0161]

[0137] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra-prediction unit 226. The mode selection unit 202 may include additional functional units to perform video prediction according to other prediction modes. For example, the mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, and the like.

[0162]

[0138] The mode selection unit 202 generally coordinates multiple coding paths to test combinations of coding parameters and generates rate distortion values ​​for such combinations. The coding parameters may include the division of the CTU to the CU, the prediction mode for the CU, the transformation type for the residual data of the CU, the quantization parameters for the residual data of the CU, and so on. The mode selection unit 202 may ultimately select a combination of coding parameters that has a rate distortion value that is better than other tested combinations.

[0163]

[0139] The video encoder 200 may divide the picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs within a slice. The mode selection unit 210 may divide the CTUs of a picture according to a tree structure such as the HEVC QTBT structure or quadtree structure described above. As described above, the video encoder 200 may form one or more CUs from dividing the CTUs according to a tree structure. Such CUs are sometimes commonly referred to as “video blocks” or “blocks”.

[0164]

[0140] Generally, the mode selection unit 202 also controls its components (e.g., motion estimation unit 222, motion compensation unit 224, and intra-prediction unit 226) to generate a predictive block for the current block (e.g., the overlapping portion of PU and TU in the current CU or HEVC). For intra-prediction of the current block, the motion estimation unit 222 may perform a motion search to identify one or more exactly matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in the DPB 218). In particular, the motion estimation unit 222 may calculate a value representing how similar the potential reference blocks are to the current block, for example, according to the sum of absolute differences (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared difference (MSD), etc. The motion estimation unit 222 may generally perform these calculations using sample-by-sample differences between the current block and the reference blocks being considered. The motion estimation unit 222 can identify the reference block with the lowest value obtained from these calculations, which indicates the reference block that most closely matches the current block.

[0165]

[0141] The motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of a reference block in a reference picture relative to the position of the current block in the current picture. The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, in unidirectional interpretation, the motion estimation unit 222 may provide a single motion vector, but in bidirectional interpretation, the motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate predicted blocks. For example, the motion compensation unit 224 may use the motion vectors to extract data for a reference block. As another example, if the motion vectors have partial sample accuracy, the motion compensation unit 224 may interpolate the values ​​of the predicted blocks according to one or more interpolation filters. Furthermore, in the case of bidirectional interpretation, the motion compensation unit 224 may extract data for the two reference blocks identified by their respective motion vectors and combine the extracted data, for example, through sample-wise averaging or weighted averaging.

[0166]

[0142] As another example, for intra-prediction or intra-prediction coding, the intra-prediction unit 226 may generate a prediction block from samples adjacent to the current block. For example, in directional mode, the intra-prediction unit 226 may mathematically combine the values ​​of adjacent samples and populate these calculated values ​​in a specified direction across the current block to generate a prediction block. As another example, in DC mode, the intra-prediction unit 226 may calculate the average of adjacent samples for the current block and generate a prediction block so that each sample of the prediction block contains this obtained average.

[0167]

[0143] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives a raw, uncoded version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines the residual block for the current block. In some examples, the residual generation unit 204 may also determine the difference between sample values ​​in the residual block in order 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.

[0168]

[0144] In an example where the mode selection unit 202 divides the CU into PUs, each PU may be associated with a lumar prediction unit and a corresponding chroma prediction unit. The video encoder 200 and video decoder 300 may support PUs of various sizes. As described above, the size of the CU may refer to the size of the lumar coding block of the CU, and the size of the PU may refer to the size of the lumar prediction unit of the PU. Assuming that the size of a particular CU is 2N × 2N, the video encoder 200 may support PU sizes of 2N × 2N or N × N for intra prediction, and 2N × 2N, 2N × N, N × 2N, N × N, or similar symmetric PU sizes for inter prediction. The video encoder 200 and video decoder 300 may also support asymmetric divisions of PU sizes of 2N × nU, 2N × nD, nL × 2N, and nR × 2N for inter prediction.

[0169]

[0145] In cases where the mode selection unit does not further subdivide the CUs into PUs, each CU may be associated with a ruma coding block and a corresponding chroma coding block. As described above, the size of the CU may refer to the size of the ruma coding block of the CU. The video encoder 200 and video decoder 120 may support CU sizes of 2N×2N, 2N×N, or N×2N.

[0170]

[0146] In some examples, for other video coding techniques such as intra-block copy mode coding, affine mode coding, and linear model (LM) mode coding, the mode selection unit 202 generates a predicted block for the current block being coded 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 predicted block, but instead generate syntax elements indicating the pattern in which the block should be reconstructed based on the selected palette. In such modes, the mode selection unit 202 may provide these syntax elements to the entropy coding unit 220 for coding.

[0171]

[0147] As described above, the residual generation unit 204 receives video data for the current block and the corresponding predicted 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 predicted block and the current block.

[0172]

[0148] The transformation processing unit 206 applies one or more transformations to the residual block to generate blocks of transformation coefficients (referred to herein as “transform coefficient blocks”). The transformation processing unit 206 may apply various transformations to the residual block to form transformation coefficient blocks. For example, the transformation processing unit 206 may apply a discrete cosine transform (DCT), a direction transform, a Carunenlebe transform (KLT), or a conceptually similar transformation to the residual block. In some examples, the transformation processing unit 206 may perform multiple transformations on the residual block, such as linear and quadratic transformations, such as a rotation transform. In some examples, the transformation processing unit 206 does not apply any transformations to the residual block. As described herein, the transformation processing unit 206 may selectively apply different transformations to different coefficient blocks (i.e., blocks of transformation coefficients).

[0173]

[0149] The quantization unit 208 may quantize the transformation coefficients in the transformation coefficient block in order to generate a quantized transformation coefficient block. The quantization unit 208 may quantize the transformation coefficients in the transformation coefficient block according to the quantization parameter (QP) value associated with the current block. The video encoder 200 may adjust the degree of quantization applied to the current block and the associated coefficient block by adjusting the QP value associated with the CU (for example, via the mode selection unit 202). Quantization may result in a loss of information, and therefore the quantized transformation coefficients may have lower precision than the original transformation coefficients generated by the transformation processing unit 206.

[0174]

[0150] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantization transform coefficient block in order to reconstruct the residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block that corresponds to the current block (with some potential distortion) based on the reconstructed residual block and the predicted block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add the samples of the reconstructed residual block to the corresponding samples from the predicted block generated by the mode selection unit 202 in order to generate the reconstructed block.

[0175]

[0151] The filter unit 216 may perform one or more filtering operations on the reconfigured block. For example, the filter unit 216 may perform a deblocking operation to reduce blockiness artifacts along the edges of the CU. The operation of the filter unit 216 may be skipped in some examples.

[0176]

[0152] The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in cases where the operation of the filter unit 224 is not required, the reconstruction unit 214 may store the reconstructed blocks in the DPB 218. In cases where the operation of the filter unit 224 is required, the filter unit 216 may store the filtered reconstructed blocks in the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 may retrieve a reference picture formed from the reconstructed (and potentially filtered) blocks from the DPB 218 to interpret blocks of the picture to be encoded later. In addition, the intraprediction unit 226 may use the reconstructed blocks in the DPB 218 of the current picture to intrapret other blocks in the current picture.

[0177]

[0153] In general, the entropy coding unit 220 can entropy code syntax elements received from other functional components of the video encoder 200. For example, the entropy coding unit 220 can entropy code a quantized transformation coefficient block from the quantization unit 208. As another example, the entropy coding unit 220 can entropy code a prediction syntax element from the mode selection unit 202 (for example, motion information for inter-prediction or intra-mode information for intra-prediction). The entropy coding unit 220 can perform one or more entropy coding operations on syntax elements, which are another example of video data, to generate entropy coded data. For example, the entropy coding unit 220 may perform context-adaptive variable-length coding (CAVLC) operation, CABAC operation, variable-to-variable (V2V) length coding operation, syntax-based context-adaptive binary arithmetic coding (SBAC) operation, probability interval partitioned entropy (PIPE) coding operation, 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 syntax elements are not entropically coded.

[0178]

[0154] The video encoder 200 may output a bitstream containing entropy-encoded syntax elements necessary to reconstruct a slice or block of picture. In particular, the entropy encoding unit 220 may output a bitstream.

[0179]

[0155] The operation described above will now be described in relation to blocks. Such an explanation should be understood as the operation for ruma-coding blocks and / or chroma-coding blocks. As described above, in some examples the ruma-coding blocks and chroma-coding blocks are the ruma and chroma components of the CU. In some examples the ruma-coding blocks and chroma-coding blocks are the ruma and chroma components of the PU.

[0180]

[0156] In some cases, operations performed for a rumacoding block do not need to be repeated for a chromacoding block. For example, operations to identify the motion vector (MV) and reference picture for a rumacoding block do not need to be repeated to identify the MV and reference picture for a chromablock. Rather, the MV for the rumacoding block may be scaled to determine the MV for the chromablock, and the reference picture may be the same. In another example, an intra-prediction process may be the same for both the rumacoding block and the chromacoding block.

[0181]

[0157] The video encoder 200 represents an example of a device configured to encode video data, which includes a memory configured to store video data and one or more processing units implemented in the circuit and configured to derive a transformation type from a plurality of transformation types for the current coefficient block of the video block. The video coder may transform the current coefficient block using a selected transformation type to obtain a block of reconstructed residual data for the video block, and reconstruct the video block based on the reconstructed residual data for the video block.

[0182]

[0158] Figure 4 is a block diagram showing an exemplary video decoder 300 capable of performing the techniques of this disclosure. Figure 4 is provided for illustrative purposes and is not intended to limit the techniques that are more broadly illustrated and described in this disclosure. For illustrative purposes, this disclosure states that the video decoder 300 will be described in accordance with the JEM, VVC, and HEVC techniques. However, the techniques of this disclosure may be performed by video coding devices configured to other video coding standards.

[0183]

[0159] In the example of Figure 4, the video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transformation processing unit 308, a reconstruction unit 310, a filter unit 312, and a coded 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 transformation processing unit 308, the reconstruction unit 310, the filter unit 312, and the DPB 314 may be implemented in one or more processors or processing circuits. Furthermore, the video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

[0184]

[0160] 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 for performing predictions according to other prediction modes. For example, the prediction processing unit 304 may include a pallet unit, an intra-block copy unit (which may form part of the motion compensation unit 318), an affine unit, a linear model (LM) unit, and the like. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0185]

[0161] The CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by the components of the video decoder 300. The video data stored in the CPB memory 320 may be obtained, for example, from a computer-readable medium 110 (Figure 1). The CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from the encoded video bitstream. The CPB memory 320 may also store video data other than syntax elements of the coded picture, such as temporary data representing the output from various units of the video decoder 300. The DPB 314 generally stores the decoded picture, which can be output and / or used as reference video data when the video decoder 300 decodes subsequent data or pictures from the encoded video bitstream. The CPB memory 320 and DPB 314 may be formed by any of the following types of memory devices: dynamic random access memory (DRAM) including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The CPB memory 320 and DPB 314 may be provided by the same memory device or by separate memory devices. In various examples, the CPB memory 320 may be on-chip with the other components of the video decoder 300, or off-chip relative to those components.

[0186]

[0162] In addition or alternatively, in some examples, the video decoder 300 may retrieve coded video data from memory 120 (Figure 1). That is, memory 120 may store the data discussed above using CPB memory 320. Similarly, memory 120 may store instructions to be executed by the video decoder 300 when some or all of the functions of the video decoder 300 are implemented in software that can be executed by the processing circuit of the video decoder 300.

[0187]

[0163] The various units shown in Figure 4 are illustrated to help understand the operations performed by the video decoder 300. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Similar to Figure 3, fixed-function circuits refer to circuits that provide a specific function and are pre-configured to perform operations. Programmable circuits refer to circuits that can be programmed to perform various tasks and to provide flexible functionality in the operations they can perform. For example, a programmable circuit may run software or firmware that operates the programmable circuit in a manner defined by software or firmware instructions. A fixed-function circuit may run software instructions (e.g., to receive or output parameters), but the type of operation performed by a fixed-function circuit is generally immutable. In some examples, one or more of the units may be separate circuit blocks (fixed-function or programmable), and in some examples, one or more units may be integrated circuits.

[0188]

[0164] The video decoder 300 may include an ALU, EFU, digital circuitry, analog circuitry, and / or a programmable core formed from programmable circuitry. In an example where the operation of the video decoder 300 is performed by software running on the programmable circuitry, on-chip or off-chip memory may store software instructions (e.g., object code) that the video decoder 300 receives and executes.

[0189]

[0165] The entropy decoding unit 302 receives the video data encoded from the CPB and can entropy decode the video data to reconstruct the syntax elements. The prediction processing unit 304, the inverse quantization unit 306, the inverse transformation processing unit 308, the reconstruction unit 310, and the filter unit 312 can generate the decoded video data based on the syntax elements extracted from the bitstream.

[0190]

[0166] Generally, the video decoder 300 reconstructs the picture block by block. The video decoder 300 can perform the reconstruction operation individually for each block (wherein the block currently being reconstructed, i.e., the block currently being decoded, is sometimes called the "current block").

[0191]

[0167] The entropy decoding unit 302 can entropy decode conversion information such as syntax elements that define the quantization conversion coefficients of the quantization conversion coefficient block, as well as quantization parameters (QP) and / or conversion mode indications. The inverse quantization unit 306 may use the QP associated with the quantized conversion coefficient block to determine the degree of quantization, and similarly to determine the degree of inverse quantization that the inverse quantization unit 306 should apply. The inverse quantization unit 306 may, for example, perform a bitwise left shift operation to inverse quantize the quantized conversion coefficients. The inverse quantization unit 306 may thereby form a conversion coefficient block containing the conversion coefficients.

[0192]

[0168] After the inverse quantization unit 306 has formed a transformation coefficient block, the inverse transformation processing unit 308 may apply one or more inverse transformations to the transformation coefficient block to generate a residual block associated with the current block. For example, the inverse transformation processing unit 308 may apply an inverse DCT, an inverse integer transformation, an inverse Carunenlebe transformation (KLT), an inverse rotation transformation, an inverse direction transformation, or another inverse transformation to the coefficient block. As described herein, the transformation processing unit 206 may selectively apply different transformations to different coefficient blocks (i.e., blocks of transformation coefficients).

[0193]

[0169] Furthermore, the prediction processing unit 304 generates prediction blocks according to the prediction information syntax elements entropy-decoded by the entropy decoding unit 302. For example, if the prediction information syntax elements indicate that the current block is interpredicted, the motion compensation unit 316 may generate a prediction block. In this case, the prediction information syntax elements may indicate a reference picture in the DPB 314 from which the reference block is extracted, as well as a motion vector that identifies the location of the reference block in the reference picture relative to the location of the current block in the current picture. The motion compensation unit 316 may generally perform the interprediction process in a manner substantially similar to that described with respect to the motion compensation unit 224 (Figure 3).

[0194]

[0170] 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 predicted block according to the intra-prediction mode indicated by the prediction information syntax element. In this case as well, the intra-prediction unit 318 may perform the intra-prediction process in a manner that is generally substantially the same as that described with respect to the intra-prediction unit 226 (Figure 3). The intra-prediction unit 318 may retrieve adjacent sample data for the current block from the DPB 314.

[0195]

[0171] 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 the samples of the residual block to the corresponding samples of the prediction block in order to reconstruct the current block.

[0196]

[0172] The filter unit 312 may perform one or more filtering operations on the reconfigured block. For example, the filter unit 312 may perform a deblocking operation to reduce blocking artifacts along the edges of the reconfigured block. The operations of the filter unit 312 are not necessarily performed in all examples.

[0197]

[0173] The video decoder 300 may store the reconstructed blocks in the DPB 314. As discussed above, the DPB 314 may provide the prediction processing unit 304 with reference information, such as a sample of the current picture for intra-prediction and previously decoded pictures for subsequent motion compensation. Furthermore, the video decoder 300 may output the decoded pictures from the DPB onto a display device, such as the display device 118 in Figure 1, for later presentation.

[0198]

[0174] Thus, the video decoder 300 represents an example of a video decoding device, which includes a memory configured to store video data and one or more processing units implemented in the circuit and configured to derive a transformation type from a plurality of transformation types for the current coefficient block of a video block. The video coder may transform the current coefficient block using a selected transformation type to obtain a block of reconstructed residual data for the video block, and reconstruct the video block based on the reconstructed residual data for the video block.

[0199]

[0175] Figure 5 is a block diagram showing a system for hybrid video coding using adaptive transform selection. The video encoder 200' in Figure 5 can be considered to represent a video coding system similar to the video encoder 200 in Figures 1 and 3. For example, the block prediction 202', block transform 206', quantization 208', inverse quantization 210', inverse transform 212', frame buffer 218', and entropy coding 220' of the video encoder 200' in Figure 3 can be considered to perform similar operations to the mode selection unit 202, transform processing unit 206, quantization unit 208, inverse quantization unit 210, inverse transform processing unit 212, decoded picture buffer 218, and entropy coding unit 220 of the video encoder 200 in Figure 3. As shown in Figure 5, the video encoder 200' may include a transform bank 207', which may be configured to work in conjunction with the block transform 206' to transform residual data. For example, the transformation bank 207' and block transformation 206' may collectively select and perform various transformations (e.g., various DCTs or DSTs) for each block of the predicted residuals. As described above, in some examples, the transformation bank 207' and block transformation 206' may signal the selection of transformation-side information. For example, block transformation 206' may cause entropy coding 220' to encode a syntax element that explicitly indicates the transformation (i.e., t) to be used.

[0200]

[0176] In some examples, the transformation bank 207' and the block transformation 206' can compute the block transformation in a separable manner. For example, to reduce computational complexity, the transformation bank 207' and the block transformation 206' can transform the horizontal and vertical lines independently, as shown in Figure 6. In other words, the samples along the horizontal and vertical arrows in Figure 6 can be transformed independently.

[0201]

[0177] In video coding standards prior to HEVC, only fixed separable transforms were used, where DCT-2 was used for both vertical and horizontal. In HEVC, in addition to DCT-2, DST-7 is also adopted as a fixed separable transform for 4x4 blocks. US-2016-0219290-A1 and US-2018-0020218-A1 describe adaptive extensions of those fixed transforms, and an example of AMT in US-2016-0219290-A1 is the Joint Experimental Model (JEM) of the Joint Video Experts Team (JVET), ITU-T It is used in SG16 WP3 and the Joint Video Experts Team (JVET) of ISO / IEC JTC1 / SC29 / WG11, JEM Software, https: / / jvet.hhi.fraunhofer.de / svn / svn_HMJEMSoftware / tags / HM-16.6-JEM-7.0.

[0202]

[0178] According to one or more techniques of the present disclosure, a video coder (e.g., a video encoder and / or video decoder) may perform implicit transform selection. For example, a video coder may apply one or more sets of rules to implicitly select a transform for transforming residual data for a block. In this way, the video coder may improve coding efficiency. In particular, the techniques of the present disclosure enable a video decoder to take advantage of using adaptive transform selection without the overhead of actually signaling the selected transform.

[0203]

[0179] VVC Draft4 has two implicit transform derivations that are relatively complex and do not provide good coding performance. This disclosure proposes simpler alternative derivations that may provide similar or better compression / coding performance / efficiency.

[0180] The following describes the relevant techniques in VVC Draft4 and the reference software VTM-4.0.

[0204]

[0181] In VVC Draft4 / VTM-4.0, multiple transform selection (MTS) uses high-level flags to determine whether the transform is (i) explicitly signaled to be selected from multiple candidates, or (ii) implicitly derived based on the block shape. In the latter case, a combination of DST-7 and DCT-2 as horizontal or vertical transforms of a maximum size of 16. In particular, adhering to block shape-dependent conditions defines the implicit MTS in VTM-4.0. - If the width and height of a block are equal and both are 16 or less, DST-7 is used for both horizontal and vertical directions. - If the width of the block is less than its height, and it is 16 or less, DST-7 is used horizontally and DCT-2 is used vertically. - If the height of the block is less than its width and it is 16 or less, DST-7 is used vertically and DCT-2 is used horizontally. - Otherwise, DCT-2 is used in both directions.

[0205]

[0182] In VVC Draft4 / VTM-4.0, when an intra subblock (ISP) is used to code a rumor block, mode-dependent conversion selection is performed, where the horizontal and vertical conversions (trTypeHor and trTypeVer) are derived based on the following table in VVC Draft4.

[0206] [Table 1]

[0207]

[0183] As described above, according to one or more techniques of the present disclosure, a video coder may apply one or more sets of rules to implicitly derive a transform selection based on available side information.

[0208]

[0184] As a first example, a video coder may determine that a coding unit / conversion unit (CU / TU) will be coded using only DST-7 under certain conditions. For example, if the maximum allowed 1D conversion size is N in the codec, the video coder may determine that DST-7 can be used for all possible sizes. For example, given an N×M block (as shown in Figure 7, where N rows each have M samples and M columns of it have N samples), the video coder may determine that N points of DST-7 can be used vertically and M points of DST-7 can be used horizontally.

[0209]

[0185] As a second example, with respect to the dimensions of the selected set, the video coder may decide that different combinations of DST-7 and DCT-2 may be used. For example, the video coder may decide that DST-7 may be applied to any row or column having K or fewer samples, while DCT-2 may be used to transform any row or column having more than K samples. For example, in the example of Figure 7, if N is less than K and M is greater than K, the video coder may decide to use N-point DST-7 in the vertical direction and M-point DCT-2 in the horizontal direction. Also, in the example of Figure 7, if both N and M are less than K, the video coder may decide to use DST-7 in both the horizontal and vertical directions.

[0210]

[0186] As a third example, when CU / TU are partitioned, the video decoder may determine that all partitions can use the same implicit conversion selection scheme. In some examples, the video coder may use DST-7 for all partitioned subblocks (sub-TU or sub-CU). In some examples, the video coder may use a combination of DST-7 and DCT-2 depending on the dimensions of the partitioned block. In some examples, for coding blocks that use intra-subblock partitioning (ISP) in VVC (VTM-4.0), the video coder may use a combination of DST-7 and DCT-2 depending on the dimensions of the block, as described above in the second example. For example, for any row or column with 16 samples or less, the video coder may use DST-7. Otherwise, the video coder may use DCT-2 to convert any row or column with more than 16 samples. In some examples, since an ISP can have a row / column with 2 samples, the video coder may use 2-point DST-7. The previous standard did not use two-point DST-7. Therefore, a video coder may use a modified entry for the two-point DST-7 matrix as follows:

[0211]

number

[0212]

[0187] As a fourth example, the videocoder may derive transformations based on intra-predictive modes (modes are shown in Figure 8). In intra-planar and DC mode, the videocoder may use DST-7 for both horizontal and vertical directions. In intra-diagonal angular mode (mode index 34 in Figure 8), the videocoder may use DST-7 for both horizontal and vertical directions. In angular mode, indexed from 2 to 66, the videocoder may apply different combinations of DST / DCT to modes within a range of modes, such as predefined intervals between mode indices [2, 3, ..., 65, 66]. 1) The range of intervals consisting of all angular modes [2, 3, ..., 66] can be defined as follows for a given integer T between 2 and 30:

[0213]

number

[0214] 2) In angular mode with range R2, DST-7 can be applied to both the horizontal and vertical directions. 3) In angular mode with range R1, DST-7 may be applied horizontally and DST-2 may be applied vertically. 4) In angle mode with range R3, DST-2 may be applied horizontally and DST-7 may be applied vertically.

[0215]

[0188] As a fifth example, in addition to DST-7 and DCT-2, the video coder may apply different types of DCT / DST combinations (e.g., DST-4 and DCT-8) and 1D discriminant transformations.

[0216]

[0189] As a sixth example, the video coder may apply one or more combinations of the above examples only to intra-predicted CU / TU.

[0217]

[0190] As a seventh example, the video coder may apply one or more combinations of the above examples only to the inter-predicted CU / TU.

[0218]

[0191] As a eighth example, the video coder may apply one or more combinations of the above examples to be used for both intra-predicted CU / TU and inter-predicted CU / TU.

[0219]

[0192] As a ninth example, a video coder may apply one or more of the above examples to be used for a lumen channel or a chroma channel or both a lumen channel and a chroma channel.

[0220]

[0193] Figure 9 is a flowchart illustrating an exemplary method for encoding the current block. The current block may comprise the current CU. While the video encoder 200 (Figures 1 and 3) is described in reference, it should be understood that other devices may be configured to perform a similar method to that in Figure 9. For example, the video encoder 200' in Figure 5 may perform a similar method to that in Figure 9.

[0221]

[0194] In this example, the video encoder 200 first predicts the current block (350). For example, the video encoder 200 may form a predicted block for the current block. The video encoder 200 may then compute the residual block for the current block (352). To compute the residual block, the video encoder 200 may compute the difference between the original uncoded block and the predicted block for the current block. The video encoder 200 may then transform and quantize the coefficients of the residual block (354). As described above, the video encoder 200 may implicitly derive the type of transformation to be used when transforming the coefficients of the residual block. For example, the video encoder 200 may derive the type of transformation using the technique described below with respect to Figure 11.

[0222]

[0195] Next, the video encoder 200 scans the quantized transformation coefficients of the residual block (356). During or following the scan, the video encoder 200 may entropy encode the coefficients (358). For example, the video encoder 200 may encode the coefficients using CAVLC or CABAC. The video encoder 200 may then output the entropy encoded data of the block (360).

[0223]

[0196] Figure 10 is a flowchart illustrating an exemplary method for decoding the current block of video data. The current block may contain the current CU. While the video decoder 300 (Figures 1 and 4) is described, it should be understood that other devices may be configured to perform a similar method to that in Figure 10.

[0224]

[0197] The video decoder 300 may receive entropy-coded data for the current block, such as entropy-coded prediction information and entropy-coded data for the coefficients of the residual block corresponding to the current block (370). The video decoder 300 may entropy-decode the entropy-coded data to determine the prediction information for the current block and to reconstruct the coefficients of the residual block (372). The video decoder 300 may predict the current block, for example, using an intra-prediction or inter-prediction mode indicated by the prediction information for the current block, in order to compute a prediction block for the current block (374). The video decoder 300 may then back-scan the reconstructed coefficients to create a block of quantized transformed coefficients (376). The video decoder 300 may then inverse-quantize and inverse-transform the coefficients to generate a residual block (378). As described above, the video decoder 300 may implicitly derive the type of transformation to be used when transforming the coefficients of the residual block. For example, the video decoder 300 may derive the transformation type using the technique described below with respect to Figure 11. The video decoder 300 may then decode the current block by combining the prediction block and the residual block (380).

[0225]

[0198] Figure 11 is a flowchart illustrating an exemplary method for inferring the transformation type for a transformation block of a video block using one or more techniques of the present disclosure. The techniques of Figure 11 may be performed by a video coder (e.g., a video encoder 200 and / or a video decoder 300).

[0226]

[0199] The video coder may obtain the current transform block of the current video block (1102). The transform block may be a matrix of transform coefficients composed of one or more syntax elements decoded from the video bitstream (for example, a matrix of syntax elements contained in the residual coding syntax table of VVC Draft4). The current video block may be a coding unit (CU).

[0227]

[0200] The video coder may infer the transformation type from a plurality of transformation types for the current transformation block. The plurality of transformation types may include one or more discrete cosine transforms (DCTs) and one or more discrete sine transforms (DSTs).

[0228]

[0201] As described above, the video coder may infer the transformation type based on one or more factors, such as whether the current video block is partitioned using the ISP and / or the size of the transformation block. As shown in Figure 11, the video coder may determine that the current video block is partitioned using the ISP (1104). The video coder may determine that the current video block is partitioned using the ISP based on the values ​​of one or more syntax elements (e.g., sps_isp_enabled_flag, intra_subpartitions_mode_flag, and / or intra_subpartitions_split_flag). For example, based on the intra_subpartitions_split_flag syntax element, the video coder may determine whether the current video block is not partitioned (e.g., not split), is partitioned horizontally, or is partitioned vertically.

[0229]

[0202] In response to determining that the current video block will be segmented using an ISP (1104), the video coder may determine the size of the current transform block (1106). For example, the video coder may determine the width and / or height of the transform block. In some examples, the video coder may determine the transform block size separately for each sub-segment. In other examples, the video coder may determine the transform block size for a single segment and utilize the sizes determined for each segment of the coding unit.

[0230]

[0203] The video coder may determine whether the size of the current transformation block meets a size threshold. For example, as shown in Figure 11, the video coder may determine whether the size of the current transformation block is greater than the lower limit and less than the upper limit (i.e., whether both (size > lower limit) and (size < upper limit) are true) (1108). As described above, in some examples the lower limit may be 4 samples and the upper limit may be 16 samples).

[0231]

[0204] In response to determining that the size of the current transformation block meets the size threshold and that the current video block will be segmented using an ISP, the video coder may select a specific DST from one or more DSTs as the selected transformation type. For example, as shown in Figure 11, in response to determining that the size of the current transformation block meets the size threshold and that the current video block will be segmented using an ISP, the video coder may select DST-7 as the inferred transformation type for the current transformation block (yes branch of 1108, 1110). Alternatively, in response to determining that the size of the current transformation block does not meet the size threshold and that the current video block will be segmented using an ISP, the video coder may select DCT-2 as the inferred transformation type for the current transformation block (no branch of 1108, 1112).

[0232]

[0205] The video coder may transform the current transform block for a video block using a selected transform type (1114) to obtain a block of reconstructed residual data. For example, if the selected transform type is DST-7, the video coder (e.g., the inverse transform processing unit 212 / 212' of the video encoder 200 / 200' and / or the inverse transform processing unit 308 of the video decoder 300) may transform the coefficients of the transform block into reconstructed residual data by applying an inverse DST-7 transform.

[0233]

[0206] The video coder may reconstruct a video block based on the reconstructed residual data for the video block (1116). For example, the video encoder may add the residual data to a block of intra-predicted samples for the current block. If the video block is partitioned using ISP, the video encoder may add each block of the reconstructed residual data to each block of the intra-predicted samples for each sub-partition of the current video block.

[0234]

[0207] One or more aspects of the present disclosure may be shown in the following numbered examples.

[0235]

[0208] Example 1. A method of coding video data, the method comprising deriving a transform type from a plurality of transform types for a current coefficient block of a video block; transforming the current coefficient block using the selected transform type to obtain a block of reconstructed residual data for the video block; and reconstructing the video block based on the reconstructed residual data for the video block.

[0236]

[0209] Example 2. The method of Example 1, wherein the plurality of transform types includes one or more discrete cosine transforms (DCTs) and / or one or more discrete sine transforms (DSTs).

[0237]

[0210] Example 3. The method according to Example 2, wherein one or more DCTs include one or more of DCT-1, DCT-2, DCT-3, DCT-4, DCT-5, DCT-6, DCT-7, and DCT-8.

[0238]

[0211] Example 4. The method according to Example 2 or 3, wherein one or more DSTs include one or more of DST-1, DST-2, DST-3, DST-4, DST-5, DST-6, DST-7, and DST-8.

[0239]

[0212] Example 5. The method according to any one of Examples 1 to 4, wherein the derivation of the transformation type comprises deriving the transformation type based on the size of the current coefficient block.

[0240]

[0213] Example 6. Deriving a transformation type based on the size of the current coefficient block comprises selecting a DST-7 transformation type, where the maximum allowed 1D transformation size is N, as in Example 5.

[0241]

[0214] Example 7. The method according to Example 6, wherein the current coefficient block has dimensions N × M, and the selection of DST-7 transformation types is to select an N-point DST-7 transformation for vertical use and an M-point DST-7 transformation for horizontal use.

[0242]

[0215] Example 8. The method of any combination of Examples 1 to 7, wherein the derivation of the conversion type is comprised of selecting different combinations of DST-7 conversion and DCT-2 conversion.

[0243]

[0216] Example 9. The method of Example 8, wherein selecting different combinations of DST-7 and DCT-2 transformations comprises selecting DST-7 transformations for any row or column having K or fewer samples and selecting DCT-2 transformations for any row or column having more than K samples.

[0244]

[0217] Example 10. The method of any combination of Examples 1-9, further comprising, in response to determining that a video block is divided into multiple sections, using a common set of rules to select the respective transformation type for each coefficient block of the multiple sections.

[0245]

[0218] Example 11. The method of Example 10, wherein selecting a different transformation type for each of the multiple divisions is the same as selecting DST-7 for all coefficient blocks of the multiple divisions.

[0246]

[0219] Example 12. The method of Example 10, wherein selecting a different conversion type for each of the multiple divisions comprises selecting different combinations of DST-7 conversion and DCT-2 conversion based on the dimensions of the division.

[0247]

[0220] Example 13. The method of Example 12, wherein selecting different combinations of DST-7 and DCT-2 transformations based on the dimension of the division comprises selecting DST-7 transformation for any row or column having a number of samples less than or equal to a threshold number, and selecting DCT-2 transformation for any row or column having a number of samples greater than a threshold number.

[0248]

[0221] Example 14. The method of Example 13, wherein the threshold is 16.

[0249]

[0222] Example 15. The method of any combination of Examples 10-14, wherein dividing a video block into multiple sections comprises dividing the video block using intra-subblock divisions (ISPs).

[0250]

[0223] Example 16. The method of Example 15, wherein the transformation using the DST-7 transformation is the same as the method of Example 15, comprising transforming the current coefficient block using the following two-point DST-7 matrix.

[0251]

number

[0252]

[0224] Example 17. Determining an intra prediction mode used to predict a video block, where deriving a transform type for a current coefficient block of the video block comprises deriving a transform type for the current coefficient block of the video block based on the intra prediction mode, further comprising the method according to any combination of Examples 1 to 16.

[0253]

[0225] Example 18. Deriving a transform type for a current coefficient block of a video block based on an intra prediction mode comprises selecting a DST-7 transform for the current coefficient block in both the horizontal and vertical directions in response to determining that the intra prediction mode is a planar or DC mode, the method according to Example 17.

[0254]

[0226] Example 19. Deriving a transform type for a current coefficient block of a video block based on an intra prediction mode comprises selecting a DST-7 transform for the current coefficient block in both the horizontal and vertical directions in response to determining that the intra prediction mode is a diagonal angle mode, the method according to either Example 17 or 18.

[0255]

[0227] Example 20. The diagonal angle mode is mode index 34, the method according to Example 19.

[0256]

[0228] Example 21. Deriving a transform type for a current coefficient block of a video block based on an intra prediction mode comprises selecting a transform type for the current coefficient block based on the mode index of the intra prediction mode in response to determining that the intra prediction mode is an angle mode, the method according to any of Examples 17 to 20.

[0257]

[0229] Example 22. The method according to Example 21, wherein selecting a transformation type for the current coefficient block based on the mode index of the intra-prediction mode comprises identifying a range among a plurality of ranges including the mode index of the intra-prediction mode, and selecting a transformation type for the current coefficient block based on the identified range.

[0258]

[0230] Example 23. The method according to Example 22, wherein identifying a range comprises identifying a first range in response to determining that the mode index is between a first threshold and a second threshold, identifying a second range in response to determining that the mode index is between a second threshold and a third threshold, and identifying a third range in response to determining that the mode index is between a third threshold and a fourth threshold.

[0259]

[0231] Example 24. The method according to Example 23, wherein identifying a first range in response to determining that the mode index is between a first threshold and a second threshold is defined as identifying a first range in response to determining that the mode index is within [2,...,(33-T)], identifying a second range in response to determining that the mode index is between a second threshold and a third threshold is defined as identifying a second range in response to determining that the mode index is within [(34-T),...,(34+T)], and identifying a third range in response to determining that the mode index is between a third threshold and a fourth threshold is defined as identifying a third range in response to determining that the mode index is within [(35+T),...,66], where T is an integer between 2 and 30.

[0260]

[0232] Example 25. The method of Example 23 or Example 24, wherein selecting a transformation type for the current coefficient block based on an identified range comprises selecting DST-7 for horizontal use and DCT-2 for vertical use in response to identifying a first range, selecting DCT-7 for horizontal and vertical use in response to identifying a second range, and selecting DST-2 for horizontal use and DCT-7 for vertical use in response to identifying a third range.

[0261]

[0233] Example 26. The method according to any of Examples 1 to 25, wherein coding is performed, and decoding is performed.

[0262]

[0234] Example 27. The method of any one of Examples 1 to 26, wherein coding comprises encoding.

[0263]

[0235] Example 28. A device for coding video data, comprising one or more means for performing the method described in any of Examples 1 to 27.

[0264]

[0236] Example 29. The device according to Example 28, wherein one or more means comprises one or more processors implemented in the circuit.

[0265]

[0237] Example 30. The device according to either Example 28 or 29, further comprising memory for storing video data.

[0266]

[0238] Example 31. The device according to any of Examples 28-30, further comprising a display configured to display decoded video data.

[0267]

[0239] Example 32. A device as described in any of Examples 28-31, wherein the device comprises one or more of the following: a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0268]

[0240] Example 33. A device according to any of Examples 28-32, wherein the device is equipped with a video decoder.

[0269]

[0241] Example 34. A device according to any of Examples 28-33, wherein the device includes a video encoder.

[0270]

[0242] Example 35. A computer-readable storage medium storing instructions that, when executed, cause one or more processors to perform the method described in any of Examples 1 to 25.

[0271]

[0243] It should be noted that, depending on the example, some of the actions or events of any of the techniques described herein may be performed in different sequences, added, merged, or completely excluded (for example, not all of the actions or events described may be necessary for the practice of this technique). Furthermore, in some examples, the actions or events may not be performed sequentially, but rather simultaneously, for example, through multithreading, interrupt handling, or across multiple processors.

[0272]

[0244] In one or more examples, the functions described above may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or codes on a computer-readable medium, or transmitted through a computer-readable medium and executed by a hardware-based processing unit. The computer-readable medium may include computer-readable storage media corresponding to tangible media such as data storage media, or it may include communication media including any medium that facilitates the transfer of computer programs from one place to another in accordance with a communication protocol, for example. Thus, the computer-readable medium may generally correspond to (1) non-temporary tangible computer-readable storage media, or (2) communication media such as signals or carrier waves. The data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, codes and / or data structures for implementing the techniques described herein. A computer program product may include computer-readable media.

[0273]

[0245] As an example, and not an limitation, such computer-readable storage media may include RAM, ROM, EEPROM®, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium used to store desired program code in the form of instructions or data structures and accessible by a computer. Any connection is also appropriately called a computer-readable medium. For example, if instructions are transmitted from a website, server or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of a medium. However, it should be understood that computer-readable storage media and data storage media refer to non-temporary tangible storage media instead of connections, carriers, signals, or other temporary media. As used herein, the terms "disk" and "disc" include Compact Disc (CD), LaserDisc® (disc), Optical Disc (disc), Digital Multipurpose Disc (disc) (DVD), Floppy Disk (disk), and Blu-ray Disc (disc), where a disk typically reproduces data magnetically and a disc reproduces data optically using a laser. Any combination of the above should also be included within the scope of computer-readable media.

[0274]

[0246] 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 logic circuits or individual logic circuits. Accordingly, the terms “processor” and “processing circuit” as used herein may refer to the aforementioned structures or any other structures suitable for implementing the techniques described herein. In addition, in some embodiments, the functions described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a composite codec. Furthermore, the techniques may be adequately implemented in one or more circuits or logic elements.

[0275]

[0247] The techniques of the Disclosure may be implemented in a wide variety of devices or apparatus, including wireless handsets, integrated circuits (ICs) or sets of ICs (e.g., chipsets). While various components, modules, or units have been described in this Disclosure to highlight the functional aspects of devices configured to implement the techniques disclosed, these components, modules, or units do not necessarily need to be implemented by different hardware units. Rather, as described above, the various units may be combined in a codec hardware unit, including one or more processors described above, along with suitable software and / or firmware, or may be provided by a set of interoperable hardware units.

[0276]

[0248] Various examples have been described. These and other examples fall within the scope of the following claims.

Claims

1. A method for decoding video data, For the current transformation block of the current video block, the transformation type is inferred from a plurality of transformation types, including one or more discrete cosine transforms (DCTs) and one or more discrete sine transforms (DSTs), wherein the inference of the transformation type is Determining the size of the current transformation block, To determine whether the current video block is divided using an intra-subblock division (ISP), In response to determining that the size of the current conversion block satisfies the size threshold and that the current video block is partitioned using an ISP, a specific DST from the one or more DSTs is selected as the selected conversion type. Equipped with, To obtain a block of reconstructed residual data for the aforementioned video block, the current transformed block is transformed using the selected transform type, Reconstructing the video block based on the reconstructed residual data for the video block. A method for providing this.

2. The method according to claim 1, wherein the one-term DCT includes one or more of DCT-1, DCT-2, DCT-3, DCT-4, DCT-5, DCT-6, DCT-7, and DCT-8.

3. The method according to claim 2, wherein the one or more DSTs include one or more of DST-1, DST-2, DST-3, DST-4, DST-5, DST-6, DST-7, and DST-8.

4. The method according to claim 3, wherein determining that the size of the current conversion block satisfies the size threshold is determined to be greater than the lower limit and less than the upper limit.

5. The method of claim 4, wherein the selection of the particular DST is selected in response to the determination that the size of the current conversion block satisfies the size threshold and that the current video block is partitioned using the ISP.

6. In response to determining that the size of the current conversion block does not meet the size threshold and that the current video block is partitioned using an ISP, a specific DCT from the one or more DCTs is selected as the selected conversion type. The method according to claim 5, further comprising:

7. The method according to claim 6, wherein selecting the particular DCT is further comprising selecting the DCT-2 in response to determining that the size of the current transform block does not meet the size threshold and that the current video block is partitioned using an ISP.

8. The method according to claim 5, wherein the selection of the conversion type is performed regardless of the intra-prediction mode used to predict the current video block.

9. Determining the size of the current transformation block is: Determining the width of the current transformation block, The current height of the transformation block is determined as described above. The method according to claim 8, comprising:

10. The selection of the conversion type comprises selecting a conversion type for horizontal use and selecting a conversion type for vertical use, and the method is In response to determining that the width of the current conversion block satisfies the width size threshold and that the current video block is segmented using ISP, the DST-7 is selected as the selected conversion type for horizontal use. In response to determining that the height of the current conversion block satisfies the height size threshold and that the current video block is partitioned using ISP, the DST-7 is selected as the selected conversion type for vertical use. The method according to claim 9, further comprising:

11. The method according to claim 10, wherein the width threshold is equal to the height threshold.

12. The method according to claim 11, wherein both the width threshold and the height threshold are 16 samples.

13. The method of claim 12, wherein inferring the conversion type for the current conversion block is performed in response to determining that a Multiple Conversion Selection (MTS) is available for the current video block.

14. Whether the aforementioned current video block is partitioned using the ISP is, To determine whether the current video block is partitioned using the ISP based on the values ​​of one or more syntax elements decoded from the video bitstream. The method according to claim 8, comprising:

15. A device for coding video data, Memory configured to store video blocks, The circuit comprises one or more processors implemented in the circuit, and the one or more processors are For the current transformation block of the current video block, the transformation type is inferred from a plurality of transformation types, including one or more discrete cosine transforms (DCTs) and one or more discrete sine transforms (DSTs), wherein, in order to infer the transformation type, the one or more processors Determining the size of the current transformation block, To determine whether the current video block is divided using an intra-subblock division (ISP), In response to determining that the size of the current conversion block satisfies the size threshold and that the current video block is partitioned using an ISP, a specific DST from the one or more DSTs is selected as the selected conversion type. Configured to perform, To obtain a block of reconstructed residual data for the aforementioned video block, the current transformed block is transformed using the selected transform type, Reconstructing the video block based on the reconstructed residual data for the video block. A device configured to perform the following actions.

16. The device according to claim 15, wherein the one-or-more-DCT comprises one or more of DCT-1, DCT-2, DCT-3, DCT-4, DCT-5, DCT-6, DCT-7, and DCT-8.

17. The device according to claim 16, wherein the one or more DSTs include one or more of DST-1, DST-2, DST-3, DST-4, DST-5, DST-6, DST-7, and DST-8.

18. The device according to claim 17, wherein, in order to determine that the size of the current translation block satisfies the size threshold, one or more processors are configured to determine that the size of the current translation block is greater than a lower limit and less than an upper limit.

19. The device according to claim 18, wherein, in order to select the particular DST, one or more processors are configured to select the DST-7 in response to determining that the size of the current translation block satisfies the size threshold and that the current video block is partitioned using an ISP.

20. The one or more processors described above are In response to determining that the size of the current conversion block does not meet the size threshold and that the current video block is partitioned using an ISP, a specific DCT from the one or more DCTs is selected as the selected conversion type. The device according to claim 19, further configured to perform the following:

21. The device according to claim 20, wherein, in order to select the particular DCT, one or more processors are configured to select the DCT-2 in response to determining that the size of the current translation block does not meet the size threshold and that the current video block is segmented using an ISP.

22. The device according to claim 19, wherein, in order to select the conversion type, one or more processors are configured to select the conversion type regardless of the intra-prediction mode used to predict the current video block.

23. To determine the size of the current conversion block, one or more processors Determining the width of the current transformation block, The current height of the transformation block is determined as described above. The device according to claim 22, configured to perform the following:

24. To select the conversion type, one or more processors are configured to select a conversion type for horizontal use and a conversion type for vertical use, and the one or more processors In response to determining that the width of the current conversion block satisfies the width size threshold and that the current video block is segmented using ISP, the DST-7 is selected as the selected conversion type for horizontal use. In response to determining that the height of the current conversion block satisfies the height size threshold and that the current video block is partitioned using ISP, the DST-7 is selected as the selected conversion type for vertical use. The device according to claim 23, further configured to perform the following:

25. The device according to claim 24, wherein the width threshold is equal to the height threshold.

26. The device according to claim 25, wherein both the width threshold and the height threshold are 16 samples.

27. The device according to claim 26, wherein, in order to infer the conversion type for the current conversion block, one or more processors are configured to infer the conversion type for the current conversion block in response to determining that a multiple conversion selection (MTS) is available for the current video block.

28. A computer-readable storage medium that stores instructions, When executed, one or more processors of the video coding device, For the current transformation block of the current video block, the instruction to infer a transformation type from a plurality of transformation types including one or more discrete cosine transforms (DCTs) and one or more discrete sine transforms (DSTs), wherein the instruction to cause one or more processors to infer the transformation type is to cause one or more processors to: Determining the size of the current transformation block, To determine whether the current video block is divided using an intra-subblock division (ISP), In response to determining that the size of the current conversion block satisfies the size threshold and that the current video block is partitioned using an ISP, a specific DST from the one or more DSTs is selected as the selected conversion type. It is equipped with a command to cause it to do so. To obtain a block of reconstructed residual data for the aforementioned video block, the current transformed block is transformed using the selected transform type, Reconstructing the video block based on the reconstructed residual data for the video block. A computer-readable storage medium that stores commands to perform an action.

29. The computer-readable storage medium according to claim 28, wherein the one or more DSTs comprises at least a DST-7, and wherein the instruction causing the one or more processors to select a particular DST comprises an instruction causing the one or more processors to select the DST-7 regardless of the intra-prediction mode used to predict the current video block, in response to determining that the size of the current transformation satisfies the size threshold and that the current video block is partitioned using an ISP.

Images