Secondary transform design for partitioned transform units in video coding

Abstract

An example device applies a main transform to a current block of video data to create main transform coefficients. The apparatus determines whether intra sub-segmentation is applied to a current block of video data. The apparatus applies the main transform to the current block. The apparatus also determines whether a main transform size of a current block of the video data is at least a predetermined size. Based on the application of the intra sub-partition and the main transform size being at least a predetermined size, the apparatus applies a secondary transform to the main transform coefficient, and codes a current block of the video data based on the secondary transform.

Description

[0001] This application is a divisional application of a patent application filed on January 31, 2020, entitled “Secondary transform design for partitioned transform units in video decoding” and application number 202080011500.9.

[0002] This application claims the benefit of U.S. Application No. 16 / 777,267, filed on January 30, 2020, and U.S. Provisional Patent Application No. 62 / 800,247, filed on February 1, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to video encoding and video decoding. Background Art

[0004] Digital video capabilities can be incorporated into a wide variety of devices, including digital televisions, digital live broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video game devices, video game consoles, cellular or satellite radio telephones (so-called "smartphones"), video teleconferencing devices, video streaming devices, etc. Digital video devices implement video coding techniques (such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4 (Part 10, Advanced Video Coding (AVC)), ITU-T H.265 / High Efficiency Video Coding (HEVC), and extensions of such standards). By implementing such video coding techniques, video devices can more efficiently send, receive, encode, decode, and / or store digital video information.

[0005] Video coding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as coding tree units (CTUs), coding units (CUs), and / or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames. Summary of the Invention

[0006] In summary, this disclosure describes techniques for transform coding in video coding. Transform coding is an element of modern video compression standards. In some examples, transform coding includes a secondary transform design that can be used with a transform coding scheme that applies partitioning to transform units (TUs). This disclosure describes a secondary transform design that can improve coding gain and can be used in the context of advanced video codecs, such as extensions of HEVC or next-generation video coding standards (e.g., H.266 / Versatile Video Coding (VVC)).

[0007] In one example, a method includes determining whether intra sub-partitioning is applied to a current block of video data; applying a primary transform to the current block of video data to generate primary transform coefficients; determining whether a size of the primary transform is at least a predetermined size based on applying intra sub-partitioning; applying a secondary transform to the primary transform coefficients based on applying intra sub-partitioning and the size of the primary transform being at least the predetermined size; and decoding the current block of video data based on the secondary transform.

[0008] In another example, a device includes: a memory configured to store video data; and one or more processors implemented in circuitry and in communication with the memory, the one or more processors configured to: determine whether intra-frame sub-partitioning is applied to a current block of video data; apply a primary transform to the current block of video data to generate primary transform coefficients; determine whether a size of the primary transform is at least a predetermined size based on applying intra-frame sub-partitioning; apply a secondary transform to the primary transform coefficients based on applying intra-frame sub-partitioning and the size of the primary transform being at least the predetermined size; and decode the current block of video data based on the secondary transform.

[0009] In yet another example, a computer-readable storage medium includes instructions stored thereon that, when executed, cause one or more processors to: determine whether intra-frame sub-partitioning is applied to a current block of video data; apply a primary transform to the current block of video data to generate primary transform coefficients; determine whether a size of the primary transform is at least a predetermined size based on applying intra-frame sub-partitioning; apply a secondary transform to the primary transform coefficients based on applying intra-frame sub-partitioning and the size of the primary transform being at least the predetermined size; and decode the current block of video data based on the secondary transform.

[0010] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0015] Figure 5 is a conceptual diagram illustrating a transformation scheme based on a residual quadtree partitioning structure.

[0016] Figure 6 is a block diagram illustrating an exemplary hybrid video coding system with adaptive transform selection.

[0017] Figure 7 is a block diagram illustrating the use of a quadratic transform at an encoder and a decoder.

[0018] Figure 8 is a conceptual diagram illustrating an example secondary transform for a 1x16 block.

[0019] Figure 9 is a conceptual diagram illustrating an example secondary transform for a 2x16 block.

[0020] Figure 10 is a conceptual diagram illustrating two example secondary transforms for a 2x16 block.

[0021] Figure 11 is a conceptual diagram illustrating different types of tree-based partitioning of square blocks.

[0022] Figure 12 is a flow chart illustrating the technique of the present disclosure.

[0023] Figure 13 is a flowchart illustrating an example video encoding method.

[0024] Figure 14 is a flow chart illustrating an example video decoding method. DETAILED DESCRIPTION

[0025] Figure 1is a block diagram illustrating an example video encoding and decoding system 100 that can perform the techniques of this disclosure. Generally speaking, the techniques of this disclosure relate to decoding (encoding and / or decoding) video data. Generally, video data includes any data used to process video. Thus, video data can include original, uncoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata (e.g., signaling data).

[0026] like Figure 1 As shown, in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, source device 102 provides the video data to destination device 116 via a computer-readable medium 110. Source device 102 and destination device 116 may include any of a variety of devices, including desktop computers, notebook computers (i.e., laptop computers), tablet computers, set-top boxes, telephone handsets such as smartphones, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, etc. In some cases, source device 102 and destination device 116 may be equipped for wireless communication and, therefore, may be referred to as wireless communication devices.

[0027] exist Figure 1 In the example of FIG, source device 102 includes video source 104, memory 106, video encoder 200, and output interface 108. Destination device 116 includes input interface 122, video decoder 300, memory 120, and display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply techniques for transform decoding. Thus, source device 102 represents an example of a video encoding device, while destination device 116 represents an example of a video decoding device. In other examples, the source device and destination device can include other components or arrangements. For example, source device 102 can receive video data from an external video source such as an external camera. Similarly, destination device 116 can interface with an external display device rather than including an integrated display device.

[0028] like Figure 1The illustrated system 100 is merely an example. In general, any digital video encoding and / or decoding device can implement techniques for transform coding. Source device 102 and destination device 116 are merely examples of such decoding devices, wherein source device 102 generates decoded video data for transmission to destination device 116. This disclosure refers to a "decoding" device as a device that performs decoding (e.g., encoding and / or decoding) of data. Thus, video encoder 200 and video decoder 300 represent examples of decoding devices (specifically, a video encoder and a video decoder, respectively). In some examples, source device 102 and destination device 116 can operate in a substantially symmetrical manner, such that each of source device 102 and destination device 116 includes video encoding and decoding components. Thus, system 100 can support one-way or two-way video transmission between source device 102 and destination device 116, for example, for video streaming, video playback, video broadcasting, or video telephony.

[0029] Typically, video source 104 represents a source of video data (i.e., raw, unencoded video data) and provides a sequential series of pictures (also referred to as "frames") of video data to video encoder 200, which encodes the data for the pictures. Video source 104 of source device 102 may include a video capture device, such as a camera, a video archive unit containing previously captured raw video, and / or a video feed interface for receiving video from a video content provider. As another alternative, video source 104 may generate computer graphics-based data as source video, or a combination of real-time video, archived video, and computer-generated video. In each case, video encoder 200 may encode captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange the pictures from the order in which they were received (sometimes referred to as "display order") into a decoding order for decoding. Video encoder 200 may generate a bitstream comprising the encoded video data. Source device 102 may then output the encoded video data onto computer-readable medium 110 via output interface 108 to be received and / or retrieved by, for example, input interface 122 of destination device 116 .

[0030] Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memory. In some examples, memory 106 and memory 120 can store raw video data, e.g., raw video from video source 104 and raw decoded video data from video decoder 300. Additionally or alternatively, memory 106 and memory 120 can store software instructions executable by, for example, video encoder 200 and video decoder 300, respectively. Although shown as separate from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 can also include internal memory for functionally similar or equivalent purposes. Furthermore, memory 106 and memory 120 can store, for example, encoded video data output from video encoder 200 and input to video decoder 300. In some examples, portions of memory 106 and memory 120 can be allocated as one or more video buffers, e.g., to store raw decoded and / or encoded video data.

[0031] The computer-readable medium 110 can represent any type of medium or device capable of transmitting encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to send the encoded video data directly to the destination device 116 in real time, for example, via a radio frequency network or a computer-based network. The output interface 108 can demodulate the transmission signal including the encoded video data according to a communication standard such as a wireless communication protocol, and the input interface 122 can modulate the received transmission signal according to a communication standard such as a wireless communication protocol. The communication medium can include any wireless or wired communication medium, for example, a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium can form part of a packet-based network such as a local area network, a wide area network, or a global network such as the Internet. The communication medium can include routers, switches, base stations, or any other device that can be useful for facilitating communication from the source device 102 to the destination device 116.

[0032] In some examples, source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access the encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0033] In some examples, source device 102 may output the encoded video data to a file server 114 or another intermediate storage device that may store the encoded video generated by source device 102. Destination device 116 may access the stored video data from file server 114 via streaming or downloading. File server 114 may be any type of server device capable of storing encoded video data and transmitting the encoded video data to destination device 116. File server 114 may represent a web server (e.g., for a website), a file transfer protocol (FTP) server, a content delivery network device, or a network attached storage (NAS) device. Destination device 116 may access the encoded video data from file server 114 via any standard data connection, including an internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of the two suitable for accessing the encoded video data stored on file server 114. File server 114 and input interface 122 may be configured to operate according to a streaming protocol, a download transfer protocol, or a combination thereof.

[0034] The output interface 108 and the input interface 122 may represent wireless transmitters / receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of the various IEEE 802.11 standards, or other physical components. In examples where the output interface 108 and the input interface 122 include wireless components, the output interface 108 and the input interface 122 may be configured to transmit data (such as encoded video data) according to a cellular communication standard (such as 4G, 4G-LTE (Long Term Evolution), Advanced LTE, 5G, etc.). In some examples where the output interface 108 includes a wireless transmitter, the output interface 108 and the input interface 122 may be configured to transmit data (such as encoded video data) according to other wireless standards (such as IEEE 802.11 specifications, IEEE 802.15 specifications (e.g., ZigBee 5G), etc.). TM ), Bluetooth TM Standards, etc.) to transmit data (such as encoded video data). In some examples, source device 102 and / or destination device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include a SoC device for performing the functions assigned to video encoder 200 and / or output interface 108, and destination device 116 may include a SoC device for performing the functions assigned to video decoder 300 and / or input interface 122.

[0035] The techniques of the present disclosure can be applied to video decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission (such as Dynamic Adaptive Streaming over HTTP (DASH)), digital video encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0036] The input interface 122 of the destination device 116 receives an encoded video bitstream from the computer-readable medium 110 (e.g., storage device 112, file server 114, etc.). The encoded video bitstream computer-readable medium 110 may include signaling information such as syntax elements defined by the video encoder 200 (which are also used by the video decoder 300): the syntax elements have values ​​that describe the characteristics and / or processing of video blocks or other decoding units (e.g., slices, pictures, groups of pictures, sequences, etc.). The display device 118 displays the decoded pictures of the decoded video data to a user. The display device 118 may represent any of a variety of display devices, such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0037] Despite Figure 1 2. Although not shown, in some examples, the video encoder 200 and the video decoder 300 can each be integrated with an audio encoder and / or an audio decoder and can include appropriate MUX-DEMUX units or other hardware and / or software to process a multiplexed stream including both audio and video in a common data stream. If applicable, the MUX-DEMUX units can follow the ITU H.223 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

[0038] The video encoder 200 and the video decoder 300 can each be implemented as any of a variety of suitable encoder and / or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When the technology is partially implemented in software, the device can store instructions for the software in a suitable non-transitory computer-readable medium and, using one or more processors, execute the instructions in hardware to perform the technology of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, any of which can be integrated as part of a combined encoder / decoder (CODEC) in the corresponding device. The device including the video encoder 200 and / or the video decoder 300 can include an integrated circuit, a microprocessor, and / or a wireless communication device (such as a cellular phone).

[0039] The video encoder 200 and the video decoder 300 may operate in accordance with a video coding standard, such as the ITU-T H.265 standard (also known as the High Efficiency Video Coding (HEVC) standard) or an extension thereof, such as the multi-view and / or scalable video coding extension. Alternatively, the video encoder 200 and the video decoder 300 may operate in accordance with other proprietary or industry standards, such as the Joint Exploration Test Model (JEM) or the ITU-T H.266 standard, also known as Versatile Video Coding (VVC). A recent draft of the VVC standard is described in the following document: Bross et al., “Versatile Video Coding (Draft 3)”, Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11, 12th Meeting: Macau, China, October 3-12, 2018, JVET-L1001-v9 (hereinafter referred to as “VVC Draft 3”). However, the techniques of the present disclosure are not limited to any particular coding standard.

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

[0041] In general, the present disclosure may relate to the decoding (e.g., encoding and decoding) of a picture to include the process of encoding or decoding the data of the picture. Similarly, the present disclosure may relate to the decoding of a block of a picture to include the process of encoding or decoding the data for the block (e.g., prediction and / or residual decoding). A coded video bitstream typically includes a series of values ​​for syntax elements that represent decoding decisions (e.g., decoding modes) and the partitioning of a picture into blocks. Therefore, references to decoding a picture or block should generally be understood as decoding the values ​​of the syntax elements used to form the picture or block.

[0042] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (such as the video encoder 200) partitions a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video decoder partitions the CTU and CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without child nodes may be referred to as a "leaf node," and the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video decoder may further partition the PUs and TUs. For example, in HEVC, the residual quadtree (RQT) represents the partitioning of TUs. In HEVC, PU represents inter-frame prediction data, and TU represents residual data. An intra-predicted CU includes intra-frame prediction information, such as an intra-frame mode indication.

[0043] As another example, the video encoder 200 and the video decoder 300 can be configured to operate according to JEM or VVC. According to JEM or VVC, a video decoder (such as the video encoder 200) partitions a picture into multiple coding tree units (CTUs). The video encoder 200 can partition the CTU according to a tree structure (such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure). The QTBT structure removes the concept of multiple partitioning types, such as the separation between CU, PU, ​​and TU of HEVC. The QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to the coding units (CUs).

[0044] In the MTT partitioning structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more types of ternary tree (TT) partitioning. Ternary tree partitioning is a partitioning in which a block is divided into three sub-blocks. In some examples, ternary tree partitioning divides a block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

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

[0046] The video encoder 200 and the video decoder 300 can be configured to use quadtree segmentation per HEVC, QTBT segmentation, MTT segmentation, or other segmentation structures. For the purpose of explanation, the technology of the present disclosure is described with respect to QTBT segmentation. However, it should be understood that the technology of the present disclosure can also be applied to video decoders configured to use quadtree segmentation or other types of segmentation.

[0047] This disclosure may use "NxN" and "N by N" interchangeably to refer to the sample size of a block (such as a CU or other video block) in terms of the vertical and horizontal dimensions, for example, 16x16 samples or 16 by 16 samples. Typically, a 16x16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Likewise, an NxNCU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. Furthermore, a CU does not necessarily need to have the same number of samples in the horizontal direction as in the vertical direction. For example, a CU may include NxM samples, where M is not necessarily equal to N.

[0048] The video encoder 200 encodes video data representing prediction and / or residual information and other information for a CU. The prediction information indicates how the CU will be predicted in order to form a prediction block for the CU. The residual information typically represents the sample-by-sample difference between the samples of the CU before encoding and the prediction block.

[0049] To predict a CU, the video encoder 200 may typically form a prediction block for the CU through inter-frame prediction or intra-frame prediction. Inter-frame prediction typically refers to predicting a CU based on data of a previously decoded picture, while intra-frame prediction typically refers to predicting a CU based on previously decoded data of the same picture. To perform inter-frame prediction, the video encoder 200 may use one or more motion vectors to generate a prediction block. The video encoder 200 may typically perform a motion search to identify a reference block that closely matches the CU, for example, in terms of the difference between the CU and the reference block. The video encoder 200 may calculate a difference metric using the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), or other such difference calculations to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 may use unidirectional prediction or bidirectional prediction to predict the current CU.

[0050] Some examples of JEM and VVC also provide an affine motion compensation mode, which can be considered an inter-frame prediction mode. In the affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion (such as zooming in or out, rotation, perspective motion, or other irregular motion types).

[0051] To perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. Some examples of JEM and VVC provide sixty-seven intra prediction modes, including various directional modes, as well as planar mode and DC mode. Typically, the video encoder 200 selects an intra prediction mode that describes the neighboring samples of the current block (e.g., the block of the CU) based on which the samples of the current block are to be predicted. Assuming that the video encoder 200 decodes CTUs and CUs in raster scan order (from left to right, from top to bottom), such samples may typically be above, above left, or to the left of the current block in the same picture as the current block.

[0052] The video encoder 200 encodes data indicating a prediction mode for the current block. For example, for inter-frame prediction mode, the video encoder 200 may encode data indicating which of various available inter-frame prediction modes to use, as well as motion information for the corresponding mode. For unidirectional or bidirectional inter-frame prediction, for example, the video encoder 200 may encode motion vectors using Advanced Motion Vector Prediction (AMVP) or Merge Mode. The video encoder 200 may use a similar mode to encode motion vectors for affine motion compensation mode.

[0053] After a prediction, such as intra-frame prediction or inter-frame prediction, for a block, the video encoder 200 may calculate residual data for the block. The residual data, such as a residual block, represents the sample-by-sample difference between the block and a prediction block for the block, which is formed using a corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to produce transformed data in a transform domain rather than a sample domain. For example, the video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. In addition, the video encoder 200 may apply a secondary transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc., after the first transform. The video encoder 200 generates transform coefficients after applying the one or more transforms.

[0054] As described above, after any transform to produce transform coefficients, the video encoder 200 may perform quantization on the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to potentially reduce the amount of data used to represent the coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 may reduce the bit depth associated with some or all coefficients. For example, the video encoder 200 may round down an n-bit value to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, the video encoder 200 may perform a bitwise right shift of the value to be quantized.

[0055] After quantization, the video encoder 200 may scan the transform coefficients to produce a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place coefficients with higher energy (and therefore lower frequency) at the front of the vector and transform coefficients with lower energy (and therefore higher frequency) at the back of the vector. In some examples, the video encoder 200 may scan the quantized transform coefficients using a predefined scan order to produce a serialized vector and then entropy encode the quantized transform coefficients of the vector. In other examples, the video encoder 200 may perform adaptive scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, the video encoder 200 may entropy encode the one-dimensional vector, for example, according to context-adaptive binary arithmetic coding (CABAC). The video encoder 200 may also entropy encode the values ​​of syntax elements used to describe metadata associated with the encoded video data for use by the video decoder 300 when decoding the video data.

[0056] To perform CABAC, the video encoder 200 may assign context within a context model to a symbol to be transmitted. The context may relate to, for example, whether the neighboring values ​​of the symbol are zero values. The probability determination may be based on the context assigned to the symbol.

[0057] The video encoder 200 may also generate syntax data (such as block-based syntax data, picture-based syntax data, and sequence-based syntax data) or other syntax data (such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS)) for the video decoder 300, for example, in a picture header, a block header, or a slice header. Similarly, the video decoder 300 may decode such syntax data to determine how to decode the corresponding video data.

[0058] In this way, the video encoder 200 can generate a bitstream that includes coded video data, such as syntax elements describing the partitioning of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Ultimately, the video decoder 300 can receive the bitstream and decode the coded video data.

[0059] In general, the video decoder 300 performs a process that is inverse to the process performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 may use CABAC to decode the values ​​of syntax elements for the bitstream in a manner substantially similar to, but inverse to, the CABAC encoding process of the video encoder 200. The syntax elements may define partitioning information for partitioning a picture into CTUs and partitioning each CTU according to a corresponding partitioning structure (such as a QTBT structure) to define CUs of the CTU. The syntax elements may also define prediction and residual information for a block (e.g., a CU) of video data.

[0060] The residual information may be represented by, for example, quantized transform coefficients. The video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of the block to reproduce a residual block for the block. The video decoder 300 uses the signaled prediction mode (intra-frame prediction or inter-frame prediction) and related prediction information (e.g., motion information for inter-frame prediction) to form a prediction block for the block. The video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. The video decoder 300 may perform additional processing, such as a deblocking process to reduce visual artifacts along block boundaries.

[0061] In accordance with the techniques of this disclosure, video encoder 200 and video decoder 300 may be configured to code blocks of video data using one or more of a primary transform and a secondary transform in accordance with the techniques of this disclosure described below.

[0062] In general, the present disclosure may involve "signaling" certain information (such as syntax elements). The term "signaling" may generally refer to the transmission of values ​​for syntax elements and / or other data used to decode encoded video data. That is, video encoder 200 may signal values ​​for syntax elements in a bitstream. Generally, signaling refers to generating values ​​in a bitstream. As described above, source device 102 may transmit the bitstream to destination device 116 in substantially real time or in non-real time (such as may occur when storing syntax elements to storage device 112 for later retrieval by destination device 116).

[0063] Figure 2A and 2B1 is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure 124 and a corresponding coding tree unit (CTU) 126. Solid lines represent quadtree splits, while dashed lines indicate binary tree splits. In each split (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which split type (i.e., horizontal or vertical) is used, where, in this example, 0 indicates a horizontal split and 1 indicates a vertical split. For quadtree splits, since the quadtree node splits the block horizontally and vertically into 4 sub-blocks of equal size, there is no need to indicate the split type. Thus, the video encoder 200 can encode, and the video decoder 300 can decode, the following: syntax elements (such as split information) for the region tree level (i.e., solid lines) of the QTBT structure 124, and syntax elements (such as split information) for the prediction tree level (i.e., dashed lines) of the QTBT structure 124. The video encoder 200 may encode video data (such as prediction and transform data) for the CU represented by the terminal leaf node of the QTBT structure 124 , and the video decoder 300 may decode the video data.

[0064] generally, Figure 2B The CTU 126 may be associated with parameters defining the size of blocks corresponding to nodes at the first and second levels of the QTBT structure 124. These parameters may include a CTU size (indicating the size of the CTU 126 in samples), a minimum quadtree size (MinQTSize, indicating the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, indicating the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, indicating the maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, indicating the minimum allowed binary tree leaf node size).

[0065] The root node of the QTBT structure corresponding to the CTU can have four child nodes at the first level of the QTBT structure, each of which can be split according to a quadtree partitioning. That is, the nodes at the first level are leaf nodes (no child nodes) or have four child nodes. The example of the QTBT structure 124 represents such nodes as including parent nodes and child nodes with solid branches. If the nodes at the first level are not larger than the maximum allowed binary tree root node size (MaxBTSize), these nodes can be further partitioned by the corresponding binary tree. The binary tree splitting of a node can be iterated until the node resulting from the split reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of the QTBT structure 124 represents such nodes as having dotted branches. The binary tree leaf nodes are called decoding units (CUs), which are used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further partitioning. As discussed above, CUs can also be referred to as "video blocks" or "blocks."

[0066] In one example of a QTBT partitioning structure, the CTU size is set to 128x128 (luminance sample and two corresponding 64x64 chroma samples), MinQTSize is set to 16x16, MaxBTSize is set to 64x64, MinBTSize (for both width and height) is set to 4, and MaxBTDepth is set to 4. Quadtree partitioning is first applied to the CTU to generate quadtree leaf nodes. Quadtree leaf nodes can have sizes from 16x16 (i.e., MinQTSize) to 128x128 (i.e., CTU size). If the leaf quadtree node is 128x128, then since the size exceeds MaxBTSize (i.e., 64x64 in this example), the leaf quadtree node will not be further split by the binary tree. Otherwise, the leaf quadtree node will be further split by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and has a binary tree depth of 0. When the binary tree depth reaches MaxBTDepth (4 in this example), no further splitting is allowed. When a binary tree node has a width equal to MinBTSize (4 in this example), this means that no further horizontal splitting is allowed. Similarly, a binary tree node with a height equal to MinBTSize means that no further vertical splitting is allowed for the binary tree node. As described above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further segmentation.

[0067] Figure 3 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 3This is provided for purposes of explanation and should not be considered limiting of the techniques generally illustrated and described in this disclosure. For purposes of explanation, this disclosure describes video encoder 200 in the context of video coding standards such as the HEVC video coding standard and the developing H.266 video coding standard. However, the techniques of this disclosure are not limited to these video coding standards and are generally applicable to video encoding and decoding.

[0068] exist Figure 3 In the example of FIG, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218, and an entropy coding unit 220. Any one or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filter unit 216, the DPB 218, and the entropy coding unit 220 may be implemented in one or more processors or in processing circuitry. Furthermore, the video encoder 200 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0069] The video data memory 230 may store video data to be encoded by the components of the video encoder 200. The video encoder 200 may receive video data from, for example, the video source 104 ( Figure 1 ) receives video data stored in the video data memory 230. The DPB 218 can act as a reference picture memory that stores reference video data for use when the video encoder 200 predicts subsequent video data. The video data memory 230 and the DPB 218 can be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The video data memory 230 and the DPB 218 can be provided by the same memory device or a separate memory device. In various examples, the video data memory 230 can be on-chip with other components of the video encoder 200 (as shown), or off-chip relative to those components.

[0070] In this disclosure, references to video data memory 230 should not be construed as limited to memory internal to the video encoder 200 (unless specifically described as such), or to memory external to the video encoder 200 (unless specifically described as such). Rather, references to video data memory 230 should be understood as reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). Figure 1 The memory 106 may also provide temporary storage for outputs from the various units of the video encoder 200 .

[0071] Shown Figure 3 The various units of the video encoder 200 are described to help understand the operations performed by the video encoder 200. These units can be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide specific functions and are pre-set with respect to the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functionality with respect to the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive parameters or output parameters), but the types of operations performed by fixed-function circuits are generally immutable. In some examples, one or more of these units can be different circuit blocks (fixed-function or programmable), and in some examples, one or more units can be integrated circuits.

[0072] The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video encoder 200 is performed using software executed by a programmable circuit, the memory 106 ( Figure 1 ) may store object code for software that video encoder 200 receives and executes, or another memory (not shown) within video encoder 200 may store such instructions.

[0073] The video data memory 230 is configured to store the received video data. The video encoder 200 can retrieve the picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 can be the original video data to be encoded.

[0074] 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 that 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.

[0075] The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and the resulting rate-distortion values ​​for such combinations. The encoding parameters may include the partitioning of a CTU into CUs, the prediction mode used for a CU, the transform type used for the residual data of a CU, the quantization parameter used for the residual data of a CU, etc. The mode selection unit 202 may ultimately select a combination of encoding parameters that has a better rate-distortion value than other tested combinations.

[0076] The video encoder 200 may partition a picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs into a slice. The mode selection unit 202 may partition the CTUs of the picture according to a tree structure (such as the QTBT structure or quadtree structure of HEVC described above). As described above, the video encoder 200 may partition the CTUs according to the tree structure to form one or more CUs. Such CUs may also be generally referred to as "video blocks" or "blocks."

[0077] Typically, mode select unit 202 also controls its components (e.g., motion estimation unit 222, motion compensation unit 224, and intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU, or, in HEVC, the overlapping portions of a PU and TU). To inter-predict the current block, motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously decoded pictures stored in DPB 218). Specifically, motion estimation unit 222 may calculate values ​​representing how similar potential reference blocks are to the current block, such as based on sum of absolute differences (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared difference (MSD), and the like. Motion estimation unit 222 may typically perform these calculations using the sample-by-sample difference between the current block and the reference block under consideration. Motion estimation unit 222 may identify the reference block with the lowest value resulting from these calculations, indicating the reference block that most closely matches the current block.

[0078] Motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of a reference block in a reference picture relative to the position of a current block in the current picture. Motion estimation unit 222 may then provide the motion vectors to motion compensation unit 224. For example, for unidirectional inter prediction, motion estimation unit 222 may provide a single motion vector, while for bidirectional inter prediction, motion estimation unit 222 may provide two motion vectors. Motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, if the motion vectors have fractional sample precision, motion compensation unit 224 may interpolate values ​​for the prediction block based on one or more interpolation filters. Furthermore, for bidirectional inter prediction, motion compensation unit 224 may retrieve data for two reference blocks identified by the respective motion vectors and combine the retrieved data, for example, by sample-by-sample averaging or weighted averaging.

[0079] As another example, for intra prediction or intra prediction decoding, the intra prediction unit 226 can generate a prediction block based on samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally mathematically combine the values ​​of adjacent samples and pad these calculated values ​​across the current block in a defined direction to produce a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average of the adjacent samples of the current block and generate a prediction block to include the obtained average for each sample of the prediction block.

[0080] Mode selection unit 202 provides the prediction block to residual generation unit 204. Residual generation unit 204 receives the original, undecoded version of the current block from video data memory 230 and the prediction block from mode selection unit 202. Residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, residual generation unit 204 may also determine the difference between sample values ​​in the residual block to generate the residual block using residual differential pulse coded modulation (RDPCM). In some examples, residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0081] In the example where the mode select unit 202 partitions the CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs of various sizes. As noted above, the size of a CU may refer to the size of the luma coding block of the CU, while the size of a PU may refer to the size of the luma prediction unit of the PU. Assuming a particular CU size of 2Nx2N, the video encoder 200 may support PU sizes of 2Nx2N or NxN for intra prediction, and 2Nx2N, 2NxN, Nx2N, NxN, or similar symmetric PU sizes for inter prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.

[0082] In an example where mode select unit 202 does not further partition a CU into PUs, each CU may be associated with a luma coding block and a corresponding chroma coding block. As described above, the size of a CU may refer to the size of the luma coding block of the CU. Video encoder 200 and video decoder 300 may support CU sizes of 2Nx2N, 2NxN, or Nx2N.

[0083] For other video coding techniques (such as intra-block copy mode coding, affine mode coding, and linear model (LM) mode coding, to name a few), mode selection unit 202 generates a prediction block for the current block being encoded via the corresponding unit associated with the coding technique. In some examples (such as palette mode coding), mode selection unit 202 may not generate a prediction block, but instead generate syntax elements that indicate how to reconstruct the block based on the selected palette. In such a mode, mode selection unit 202 may provide these syntax elements to entropy coding unit 220 for encoding.

[0084] As described above, the residual generation unit 204 receives video data for a current block and a corresponding prediction block. The residual generation unit 204 then generates a residual block for the current block. To generate the residual block, the residual generation unit 204 calculates the sample-by-sample difference between the prediction block and the current block.

[0085] The transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a "transform coefficient block"). The transform processing unit 206 may apply various transforms to the residual block to form the transform coefficient block. For example, the transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 may apply multiple transforms to the residual block, such as a primary transform and a secondary transform (such as a rotation transform). In some examples, the transform processing unit 206 may apply the primary transform and the secondary transform according to examples of the present disclosure. For example, the video encoder 200 may determine whether intra sub-partitioning is applied to the current block of video data. The video encoder 200 may also determine whether the primary transform size of the current block of video data is at least a predetermined size, such as 4x4, 8x8, 16x16, or any other predetermined size. The transform processing unit 206 of the video encoder 200 may apply a secondary transform to the primary transform coefficients based on applying intra sub-partitioning and the primary transform size being at least a predetermined size. The video encoder 200 may encode the current block of video data based on at least one of the primary transform coefficients and the secondary transform. In some examples, the transform processing unit 206 does not apply a transform to the residual block.

[0086] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may result in a loss of information, and therefore, the quantized transform coefficients may have a lower precision than the original transform coefficients produced by the transform processing unit 206.

[0087] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct a residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0088] Filter unit 216 may perform one or more filter operations on the reconstructed block. For example, filter unit 216 may perform a deblocking operation to reduce blocking artifacts along the edges of the CU. In some examples, the operations of filter unit 216 may be skipped.

[0089] The video encoder 200 stores the reconstructed block in the DPB 218. For example, in an example where the operation of the filter unit 216 is not performed, the reconstruction unit 214 can store the reconstructed block in the DPB 218. In an example where the operation of the filter unit 216 is performed, the filter unit 216 can store the filtered reconstructed block in the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 can retrieve a reference picture formed by the reconstructed (and potentially filtered) block from the DPB 218 to perform inter-frame prediction on blocks of subsequently encoded pictures. In addition, the intra-frame prediction unit 226 can use the reconstructed block of the current picture in the DPB 218 to perform intra-frame prediction on other blocks in the current picture.

[0090] In general, entropy coding unit 220 may entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy coding unit 220 may entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy coding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-frame prediction or intra-frame mode information for intra-frame prediction) from mode selection unit 202. Entropy coding unit 220 may perform one or more entropy encoding operations on syntax elements, another example of video data, to generate entropy-encoded data. For example, entropy coding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential Golomb coding operation, or another type of entropy encoding operation on the data. In some examples, entropy coding unit 220 may operate in a bypass mode in which syntax elements are not entropy encoded.

[0091] The video encoder 200 may output a bitstream that includes entropy-encoded syntax elements required to reconstruct blocks of a slice or picture. For example, the entropy encoding unit 220 may output a bitstream.

[0092] The above operations are described with respect to blocks. Such descriptions should be understood as operations for luma coding blocks and / or chroma coding blocks. As described above, in some examples, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a CU. In some examples, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a PU.

[0093] In some examples, the operations performed for luma coding blocks do not need to be repeated for chroma coding blocks. As an example, the operations for identifying the motion vector (MV) and reference picture for the luma coding block do not need to be repeated to identify the MV and reference picture for the chroma blocks. Specifically, the MV for the luma coding block can be scaled to determine the MV for the chroma blocks, and the reference picture can be the same. As another example, the intra prediction process can be the same for luma coding blocks and chroma coding blocks.

[0094] Video encoder 200 represents an example of a device configured to encode video data, the device comprising: a memory configured to store the video data; and one or more processing units implemented in circuitry and in communication with the memory and configured to: determine whether intra-frame sub-partitioning is applied to a current block of video data; apply a primary transform to the current block of video data to generate primary transform coefficients; determine whether a size of the primary transform is at least a predetermined size based on applying the intra-frame sub-partitioning; apply a secondary transform to the primary transform coefficients based on applying the intra-frame sub-partitioning and the size of the primary transform being at least the predetermined size; and decode the current block of video data based on the secondary transform.

[0095] Figure 4 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Figure 4 This is provided for purposes of explanation and does not limit the techniques generally illustrated and described in this disclosure. For purposes of explanation, this disclosure describes the video decoder 300 based on the techniques of JEM, VVC, and HEVC. However, the techniques of this disclosure can be performed by video decoding devices configured for other video decoding standards.

[0096] exist Figure 4 In the example of FIG, the video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 314. Any or all of the CPB memory 320, the entropy decoding unit 302, the prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the DPB 314 may be implemented in one or more processors or in processing circuitry. Furthermore, the video decoder 300 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0097] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include an addition unit that performs prediction according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0098] CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of video decoder 300. For example, the video bitstream may be encoded from computer readable medium 110 ( Figure 1 ) obtains video data stored in CPB memory 320. CPB memory 320 may include a CPB that stores coded video data (e.g., syntax elements) from a coded video bitstream. In addition, CPB memory 320 may store video data other than syntax elements for decoded pictures, such as temporary data representing outputs from various units of video decoder 300. DPB 314 typically stores decoded pictures, which video decoder 300 may output and / or use as reference video data when decoding subsequent data or pictures of the coded video bitstream. CPB memory 320 and DPB 314 may be formed from any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. CPB memory 320 and DPB 314 may be provided by the same memory device or separate memory devices. In various examples, CPB memory 320 can be on-chip with other components of video decoder 300 , or off-chip relative to those components.

[0099] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) to retrieve the decoded video data. That is, memory 120 may utilize CPB memory 320 to store data as discussed above. Similarly, when some or all of the functions of video decoder 300 are implemented in software to be executed by the processing circuitry of video decoder 300, memory 120 may store instructions to be executed by video decoder 300.

[0100] Shown Figure 4 The various units shown in FIG. 300 help understand the operations performed by the video decoder 300. These units can be implemented as fixed function circuits, programmable circuits, or a combination thereof. Figure 3, fixed-function circuits refer to circuits that provide specific functions and are pre-set with respect to the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functionality in terms of the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive parameters or output parameters), but the types of operations performed by the fixed-function circuits are generally immutable. In some examples, one or more of these units may be different circuit blocks (fixed-function or programmable), and in some examples, one or more units may be integrated circuits.

[0101] The video decoder 300 may include an ALU, an EFU, digital circuits, analog circuits, and / or a programmable core formed by programmable circuits. In examples where the operation of the video decoder 300 is performed by software executed on the programmable circuits, on-chip or off-chip memory may store instructions (e.g., object code) of the software that the video decoder 300 receives and executes.

[0102] The entropy decoding unit 302 may receive the encoded video data from the CPB and perform entropy decoding on the video data to reproduce the syntax elements. The prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, and the filter unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.

[0103] Typically, the video decoder 300 reconstructs a picture block by block. The video decoder 300 may perform a reconstruction operation on each block individually (wherein a block currently being reconstructed (ie, decoded) may be referred to as a "current block").

[0104] The entropy decoding unit 302 may entropy decode syntax elements defining the quantized transform coefficients of the quantized transform coefficient block, as well as transform information such as a quantization parameter (QP) and / or a transform mode indication. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, similarly, determine a degree of inverse quantization for the inverse quantization unit 306 to apply. The inverse quantization unit 306 may, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thereby form a transform coefficient block comprising the transform coefficients.

[0105] After the inverse quantization unit 306 forms the transform coefficient block, the inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, the inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the coefficient block. In some examples, the inverse transform processing unit 308 may apply a secondary inverse transform and a primary inverse transform according to the techniques of this disclosure. For example, the video decoder 300 may determine whether intra sub-partitioning is applied to the current block of video data. The video decoder 300 may also determine whether the primary transform size of the current block of video data is at least a predetermined size, such as 4x4, 8x8, 16x16, or any other predetermined size. The inverse transform processing unit 308 may apply a secondary inverse transform to the inverse quantized data based on the application of intra sub-partitioning and the primary transform size being at least the predetermined size. The video decoder 300 may decode the current block of video data based on at least one of the primary transform coefficients or the secondary transform.

[0106] In addition, prediction processing unit 304 generates a prediction block based on the prediction information syntax elements (the prediction information syntax elements entropy decoded by entropy decoding unit 302). For example, if the prediction information syntax elements indicate that the current block is inter-predicted, motion compensation unit 316 may generate a prediction block. In this case, the prediction information syntax elements may indicate a reference picture in DPB 314 from which to retrieve the reference block, and a motion vector that identifies the position of the reference block in the reference picture relative to the position of the current block in the current picture. Motion compensation unit 316 may generally generate a prediction block in the same manner as described for motion compensation unit 224 ( Figure 3 ) is performed in a manner substantially similar to that described in the foregoing.

[0107] As another example, if the prediction information syntax element indicates that the current block is intra-predicted, the intra-prediction unit 318 may generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Again, the intra-prediction unit 318 may generally generate a prediction block in the same manner as described with respect to the intra-prediction unit 226 ( Figure 3 The intra prediction process is performed in a manner substantially similar to that described in the preceding claims. The intra prediction unit 318 may retrieve data of neighboring samples of the current block from the DPB 314.

[0108] The reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, the reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

[0109] The filter unit 312 may perform one or more filter operations on the reconstructed block. For example, the filter unit 312 may perform a deblocking operation to reduce blocking artifacts along the edges of the reconstructed block. The operations of the filter unit 312 may not necessarily be performed in all examples.

[0110] The video decoder 300 may store the reconstructed blocks in the DPB 314. As discussed above, the DPB 314 may provide reference information (such as samples of the current picture for intra prediction and previously decoded pictures for subsequent motion compensation) to the prediction processing unit 304. In addition, the video decoder 300 may output decoded pictures from the DPB 314 for use in other video processing operations such as Figure 1 Subsequent presentation on a display device such as display device 118.

[0111] In this manner, the video decoder 300 represents an example of a video decoding device comprising: a memory configured to store video data; and one or more processing units implemented in circuitry and configured to: determine whether intra-frame sub-partitioning is applied to a current block of video data; determine whether the size of a primary inverse transform is at least a predetermined size based on applying the intra-frame sub-partitioning; apply secondary inverse transform coefficients based on applying the intra-frame sub-partitioning and the size of the primary transform being at least the predetermined size; apply the primary inverse transform; and decode the current block of video data based on the primary inverse transform and the secondary inverse transform.

[0112] In the next section, this disclosure provides an overview of discrete sine transform and discrete cosine transform (DCT and DST). In addition, the transform scheme used in the HEVC standard is briefly discussed.

[0113] A specific transformation defines the process of deriving an alternative representation of the input signal. Given an N-point vector x = [x0, x1, ..., x N-1 ] T and a given vector {Φ0,Φ1,…,φ M-1}, you can use φ0, Φ1, ..., φ M-1 The linear combination of can be used to approximate or accurately represent x, and its formula can be as follows:

[0114]

[0115] in It can be an approximate value or equivalent value of x, and the vector f = [f i ,f2,..,f M-1 ] is the transform coefficient vector, and {Φ0,Φ1,…,Φ M-1} are the transformation basis vectors.

[0116] In video coding, transform coefficients are essentially uncorrelated and sparse. In other words, the energy of the input vector x is only compressed on a few transform coefficients, and the remaining majority of transform coefficients are usually close to zero.

[0117] Given a specific input data, the best transformation in terms of energy compression is the KLT, which uses the eigenvectors of the covariance matrix of the input data as the transformation basis vectors. Therefore, the KLT is actually a data-dependent transformation and there is no universal mathematical formula. However, under certain assumptions, for example, that the input data forms a first-order stationary Markov process, it has been shown that the corresponding KLT is actually a member of the sinusoidal unitary transformation family, which is introduced in the following document: Jain, AK, Sine Unitary Transformation Family, Pattern Analysis and Machine Intelligence IEEE Transactions, 1, 1356, (1979). The sinusoidal unitary transformation family refers to a transformation using a transformation basis vector, and its formula is as follows:

[0118] Φ m (k) = A·e ikθ +B·e -ikθ ,

[0119] where e is the base of the natural logarithm, approximately equal to 2.71828, A, B, and θ are typically complex numbers and depend on the value of m, and k represents the frequency component.

[0120] Several well-known transforms, including discrete Fourier, cosine, sine, and KLT (for first-order stationary Markov processes), are members of this family of sinusoidal unitary transforms. According to the literature (e.g., S.A. Martucci, "Symmetric convolution and the discrete sine and cosine transforms," ​​IEEE Transactions on Signal Processing SP-42, pp. 1038-1051 (1994)), the complete family of discrete cosine transforms (DCT) and discrete sine transforms (DST) includes a total of 16 transforms based on different types (i.e., different values ​​of A, B, and θ). The complete definitions of the different types of DCT and DST are given below.

[0121] Assume that the input N-point vector is represented as x=[x0,x1,…,x N-1 ] T , and transform it into y=[y0,y1,…,y N-1 ] T Another N-point transform coefficient vector, the process can be further described according to one of the following transform formulas, where k ranges from 0 to N-1 (inclusive): DCT Type-I (DCT-1):

[0122]

[0123] in

[0124]

[0125] DCT Type-II (DCT-2):

[0126]

[0127] in DCT Type-III (DCT-3):

[0128]

[0129] in DCT Type-IV (DCT-4):

[0130]

[0131] DCT Type-V (DCT-5):

[0132]

[0133] in DCT Type-VI (DCT-6):

[0134]

[0135] in DCT Type-VII (DCT-7):

[0136]

[0137] in DCT Type-VIII (DCT-8):

[0138]

[0139] DST Type-I (DST-1):

[0140]

[0141] DST Type-II (DST-2):

[0142]

[0143] in DST Type-III (DST-3):

[0144]

[0145] in DST Type-IV (DST-4):

[0146]

[0147] DST Type-V (DST-5):

[0148]

[0149] DST Type-VI (DST-6):

[0150]

[0151] DST Type-VII (DST-7):

[0152]

[0153] DST Type-VIII (DST-8):

[0154]

[0155] in

[0156] The transform type is specified by the mathematical formula of the transform basis function, for example, 4-point DST-VII and 8-point DST-VII have the same transform type regardless of the value of N.

[0157] All of the above transformation types can be expressed using the following general formula:

[0158]

[0159] where T is the transform matrix specified by the definition of a particular transform, such as DCT Type I, DCT Type VIII, DST Type I, or DST Type VIII, and the row vectors of T (e.g., [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.

[0160] It should also be noted that the above transformation formula applied to 1-D input data x can be expressed in matrix multiplication form as follows:

[0161] y=T·x,

[0162] Where T denotes the transform matrix, x denotes the input data vector, and y denotes the output transform coefficient vector.

[0163] Apply the transformations discussed above to 1-D input data. Transformations can also be extended to 2-D input data sources. For example, define X as the input MxN array of data. Example methods for applying transformations to 2-D input data include using separable and non-separable 2-D transforms.

[0164] The separable 2-D transform sequentially applies a 1-D transform to the horizontal and vertical vectors of X, as follows:

[0165] Y=C·X·R T ,

[0166] where C and R represent the given MxM and NxN transformation matrices respectively.

[0167] From the above formula, it can be seen that C applies a 1-D transform to the column vectors of X, while R applies a 1-D transform to the row vectors of X. In the following part of this disclosure, for simplicity, C and R are represented as a left (vertical) transform and a right (horizontal) transform. Together they form a transform pair. There is a case where C is equal to R and is an orthogonal matrix. In such a case, the separable 2-D transform is determined by only one transform matrix. For example, the video encoder 200 can apply a left (vertical) transform and a right (horizontal) transform to the video data, and in the case of C=R, the video encoder 200 can apply one transform matrix. The video decoder 300 can apply the relevant inverse transform to reconstruct the video data.

[0168] A non-separable 2-D transformation first reorganizes all elements of X into a single vector, X', for example, by performing the following mathematical mapping:

[0169] X′ (i·N+j) =X i,j

[0170] Then apply a 1-D transformation T' to X' as follows:

[0171] Y=T′·X,

[0172] Where T' is an (M*N)x(M*N) transform matrix. For example, the video encoder 200 may reorganize the elements of X into a single vector X' and apply the 1-D transform T' to X. In video decoding, separable 2-D transforms are often used because they require significantly fewer operations (e.g., additions, multiplications) than 1-D transforms. For example, the video encoder 200 may apply separable 2-D transforms because they require fewer operations.

[0173] In some example video codecs, such as those implementing H.264 / AVC, integer approximations of 4-point and 8-point discrete cosine transform (DCT) type II are applied to both intra- and inter-frame prediction residuals. For example, the video encoder 200 may apply integer approximations of 4-point and 8-point discrete cosine transform (DCT) type II to both intra- and inter-frame prediction residuals.

[0174] In order to better adapt to the various statistics of residual samples, more flexible transform types other than DCT type II are utilized in some new generation video codecs (e.g., HEVC and VVC). For example, in HEVC, an integer approximation of a 4-point type VII discrete sine transform (DST) is utilized for intra prediction residuals. DST type VII is more efficient than DCT type II for residual vectors generated along the intra prediction direction. For example, DST type VII is more efficient than DCT type II for row residual vectors generated by the horizontal intra prediction direction. In HEVC, the integer approximation of the 4-point DST type VII is applied only to 4x4 luma intra prediction residual blocks. For example, the video encoder 200 may apply the integer approximation of the 4-point DST type VII only to 4x4 luma intra prediction residual blocks. The 4-point DST-VII used in HEVC is shown below,

[0175] 4x4 DST-VII:

[0176] {29,55,74,84}

[0177] {74,74,0,-74}

[0178] {84,-29,-74,55}

[0179] {55,-84,74,-29}

[0180] In HEVC, for residual blocks that are not 4x4 luma intra predicted residual blocks, integer approximations of 4-point, 8-point, 16-point, and 32-point DCT type II are also applied. For example, the video encoder 200 may apply integer approximations of 4-point, 8-point, 16-point, and 32-point DCT type II to residual blocks that are not 4x4 luma intra predicted residual blocks. The integer approximations of 4-point, 8-point, 16-point, and 32-point DCT type II are shown below:

[0181] 4-point DCT-II:

[0182] {64,64,64,64}

[0183] {83,36,-36,-83}

[0184] {64,-64,-64,64}

[0185] {36,-83,83,-36}

[0186] 8-point DCT-II:

[0187] {64,64,64,64,64,64,64,64}

[0188] {89,75,50,18,-18,-50,-75,-89}

[0189] {83,36,-36,-83,-83,-36,36,83}

[0190] {75,-18,-89,-50,50,89,18,-75}

[0191] {64,-64,-64,64,64,-64,-64,64}

[0192] {50,-89,18,75,-75,-18,89,-50}

[0193] {36,-83,83,-36,-36,83,-83,36}

[0194] {18,-50,75,-89,89,-75,50,-18}

[0195] 16-point DCT-II:

[0196] {64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64}

[0197] {90,87,80,70,57,43,25,9,-9,-25,-43,-57,-70,-80,-87,-90}

[0198] {89,75,50,18,-18,-50,-75,-89,-89,-75,-50,-18,18,50,75,89}

[0199] {87,57,9,-43,-80,-90,-70,-25,25,70,90,80,43,-9,-57,-87}

[0200] {83,36,-36,-83,-83,-36,36,83,83,36,-36,-83,-83,-36,36,83}

[0201] {80,9,-70,-87,-25,57,90,43,-43,-90,-57,25,87,70,-9,-80}

[0202] {75,-18,-89,-50,50,89,18,-75,-75,18,89,50,-50,-89,-18,75}

[0203] {70,-43,-87,9,90,25,-80,-57,57,80,-25,-90,-9,87,43,-70}

[0204] {64,-64,-64,64,64,-64,-64,64,-64,-64,-64,64,-64,-64,64,-64,-64,64}

[0205] {57,-80,-25,90,-9,-87,43,70,-70,-43,87,9,-90,25,80,-57}

[0206] {50,-89,18,75,-75,-18,89,-50,-50,89,-18,-75,75,18,-89,50}

[0207] {43,-90,57,25,-87,70,9,-80,80,-9,-70,87,-25,-57,90,-43}

[0208] {36,-83,83,-36,-36,83,-83,36,36,-83,83,-36,-36,83,-83,36}

[0209] {25,-70,90,-80,43,9,-57,87,-87,57,-9,-43,80,-90,70,-25}

[0210] {18,-50,75,-89,89,-75,50,-18,-18,50,-75,89,-89,75,-50,18}

[0211] {9,-25,43,-57,70,-80,87,-90,90,-87,80,-70,57,-43,25,-9}

[0212] 32-point DCT-II:

[0213] {64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64}

[0214] {90,90,88,85,82,78,73,67,61,54,46,38,31,22,13,4,-4,-13,-22,-31,-38,-46,-54,-61,-67,-73,-78,-82,-85,-88,-90,-90}

[0215] {90,87,80,70,57,43,25,9,-9,-25,-43,-57,-70,-80,-87,-90,-90,-87,-80,-70,-57,-43,-25,-9,9,25,43,57,70,80,87,90}

[0216] {90,82,67,46,22,-4,-31,-54,-73,-85,-90,-88,-78,-61,-38,-13,13,38,61,78,88,90,85,73,54,31,4,-22,-46,-67,-82,-90}

[0217] {89,75,50,18,-18,-50,-75,-89,-89,-75,-50,-18,18,50,75,89,89,75,50,18,-18,

[0218] -50,-75,-89,-89,-75,-50,-18,18,50,75,89}

[0219] {88,67,31,-13,-54,-82,-90,-78,-46,-4,38,73,90,85,61,22,-22,-61,-85,-90,-73,-38,4,46,78,90,82,54,13,-31,-67,-88}

[0220] {87,57,9,-43,-80,-90,-70,-25,25,70,90,80,43,-9,-57,-87,-87,-57,-9,43,80,90,70,25,-25,-70,-90,-80,-43,9,57,87}

[0221] {85,46,-13,-67,-90,-73,-22,38,82,88,54,-4,-61,-90,-78,-31,31,78,90,61,4,-

[0222] 54,-88,-82,-38,22,73,90,67,13,-46,-85}

[0223] {83,36,-36,-83,-83,-36,36,83,83,36,-36,-83,-83,-36,36,83,83,36,-36,-83,-83,-36,36,83,83,36,-36,-83,-83,-36,36,83}

[0224] {82,22,-54,-90,-61,13,78,85,31,-46,-90,-67,4,73,88,38,-38,-88,-73,-4,67,90,46,-31,-85,-78,-13,61,90,54,-22,-82}

[0225] {80,9,-70,-87,-25,57,90,43,-43,-90,-57,25,87,70,-9,-80,-80,-9,70,87,25,-57,-90,-43,43,90,57,-25,-87,-70,9,80}

[0226] {78,-4,-82,-73,13,85,67,-22,-88,-61,31,90,54,-38,-90,-46,46,90,38,-54,-90,-31,61,88,22,-67,-85,-13,73,82,4,-78}

[0227] {75,-18,-89,-50,50,89,18,-75,-75,18,89,50,-50,-89,-18,75,75,-18,-89,-50,50,89,18,-75,-75,18,89,50,-50,-89,-18,75}

[0228] {73,-31,-90,-22,78,67,-38,-90,-13,82,61,-46,-88,-4,85,54,-54,-85,4,88,46,-61,-82,13,90,38,-67,-78,22,90,31,-73}

[0229] {70,-43,-87,9,90,25,-80,-57,57,80,-25,-90,-9,87,43,-70,-70,43,87,-9,-90,-25,80,57,-57,-80,25,90,9,-87,-43,70}

[0230] {67,-54,-78,38,85,-22,-90,4,90,13,-88,-31,82,46,-73,-61,61,73,-46,-82,31,88,-13,-90,-4,90,22,-85,-38,78,54,-67}

[0231] {64,-64,-64,64,64,-64,-64,64,64,-64,-64,64,64,-64,-64,64,64,-64,-64,64,64,-64,-64,64,64,-64,-64,64,64,-64,-64,64}

[0232] {61,-73,-46,82,31,-88,-13,90,-4,-90,22,85,-38,-78,54,67,-67,-54,78,38,-85,-22,90,4,-90,13,88,-31,-82,46,73,-61}

[0233] {57,-80,-25,90,-9,-87,43,70,-70,-43,87,9,-90,25,80,-57,-57,80,25,-90,9,87,-43,-70,70,43,-87,-9,90,-25,-80,57}

[0234] {54,-85,-4,88,-46,-61,82,13,-90,38,67,-78,-22,90,-31,-73,73,31,-90,22,78,-67,-38,90,-13,-82,61,46,-88,4,85,-54}

[0235] {50,-89,18,75,-75,-18,89,-50,-50,89,-18,-75,75,18,-89,50,50,-89,18,75,-75,-18,89,-50,-50,89,-18,-75,75,18,-89,50}

[0236] {46,-90,38,54,-90,31,61,-88,22,67,-85,13,73,-82,4,78,-78,-4,82,-73,-13,85,

[0237] -67,-22,88,-61,-31,90,-54,-38,90,-46}

[0238] {43,-90,57,25,-87,70,9,-80,80,-9,-70,87,-25,-57,90,-43,-43,90,-57,-25,87,-

[0239] 70,-9,80,-80,9,70,-87,25,57,-90,43}

[0240] {38,-88,73,-4,-67,90,-46,-31,85,-78,13,61,-90,54,22,-82,82,-22,-54,90,-61,

[0241] -13,78,-85,31,46,-90,67,4,-73,88,-38}

[0242] {36,-83,83,-36,-36,83,-83,36,36,-83,83,-36,-36,83,-83,36,36,-83,83,-36,-36,83,-83,36,36,-83,83,-36,-36,83,-83,36}

[0243] {31,-78,90,-61,4,54,-88,82,-38,-22,73,-90,67,-13,-46,85,-85,46,13,-67,90,-

[0244] 73,22,38,-82,88,-54,-4,61,-90,78,-31}

[0245] {25,-70,90,-80,43,9,-57,87,-87,57,-9,-43,80,-90,70,-25,-25,70,-90,80,-43,-

[0246] 9,57,-87,87,-57,9,43,-80,90,-70,25}

[0247] {22,-61,85,-90,73,-38,-4,46,-78,90,-82,54,-13,-31,67,-88,88,-67,31,13,-

[0248] 54,82,-90,78,-46,4,38,-73,90,-85,61,-22}

[0249] {18,-50,75,-89,89,-75,50,-18,-18,50,-75,89,-89,75,-50,18,18,-50,75,-89,89,

[0250] -75,50,-18,-18,50,-75,89,-89,75,-50,18}

[0251] {13,-38,61,-78,88,-90,85,-73,54,-31,4,22,-46,67,-82,90,-90,82,-67,46,-22,-

[0252] 4,31,-54,73,-85,90,-88,78,-61,38,-13}

[0253] {9,-25,43,-57,70,-80,87,-90,90,-87,80,-70,57,-43,25,-9,-9,25,-43,57,-70,80,

[0254] -87,90,-90,87,-80,70,-57,43,-25,9}

[0255] {4,-13,22,-31,38,-46,54,-61,67,-73,78,-82,85,-88,90,-90,90,-90,88,-85,82,-

[0256] 78,73,-67,61,-54,46,-38,31,-22,13,-4}

[0257] In order to adapt to the various characteristics of the residual block, a transform decoding structure using RQT is applied in HEVC. In RQT, the video encoder 200 can divide each picture into CTUs, where the CTUs are decoded in raster scan order for a specific tile or slice. A CTU is a square block and represents the root of a quadtree (i.e., a coding tree). The CTU size can range from 8×8 to 64×64 luminance samples, but is typically 64×64. Each CTU can be further divided into smaller square blocks, referred to as CUs. After the CTU is recursively split into CUs, each CU is further divided into PUs and TUs. The partitioning of the CU into TUs is recursively performed based on a quadtree method. Therefore, the residual signal of each CU is decoded by a tree structure called RQT. RQT allows TU sizes from 4×4 to 32×32 luminance samples.

[0258] Figure 5 An example is shown in which a CU consists of 10 TUs (labeled with letters a to j) and the corresponding block partitioning. Each node of the RQT is actually a TU. Figure 5 The quadtree method can adapt the transform to the changing spatial frequency characteristics of the residual signal.

[0259] Typically, a larger transform block size (which has a larger spatial support) provides better frequency resolution. However, a smaller transform block size (which has a smaller spatial support) provides better spatial resolution. The trade-off between spatial resolution and frequency resolution is selected by an encoder mode decision, for example, based on a rate-distortion optimization technique. For example, by performing a rate-distortion optimization technique, the mode selection unit 202 of the video encoder 200 may determine to use a larger transform block size to provide better frequency resolution, or may determine to use a smaller transform block size to provide better spatial resolution. The mode selection unit 202 of the video encoder 200 may utilize a rate-distortion optimization technique, which may calculate a weighted sum of decoded bits and reconstruction distortion (i.e., a rate-distortion cost) for each decoding mode (e.g., a specific RQT split structure), and select the decoding mode with the smallest rate-distortion cost as the optimal mode.

[0260] Three parameters can be defined in the RQT: the maximum depth of the tree, the minimum allowed transform size, and the maximum allowed transform size. The minimum and maximum transform sizes can vary in the range of 4×4 to 32×32 samples, which corresponds to the supported block transforms mentioned in the previous paragraph. The maximum allowed depth of the RQT limits the number of TUs. A maximum depth equal to zero means that if each included transform block (TB) reaches the maximum allowed transform size (e.g., 32x32), the CB cannot be split further.

[0261] All of these parameters can interact and affect the RQT structure. Consider the following case: where the root CB size is 64×64, the maximum depth is equal to zero, and the maximum transform size is equal to 32×32. In this case, the CB must be split at least once, because otherwise it will result in a 64×64 TB, which is not allowed in HEVC. The RQT parameters (i.e., maximum RQT depth, minimum and maximum transform sizes) are sent in the bitstream at the SPS level. For example, the video encoder 200 can send the RQT parameters in the SPS, and the video decoder 300 can determine the RQT parameters by reading the RQT parameters in the SPS. Regarding the RQT depth, different values ​​can be specified for intra- and inter-coded CUs and notified by signals. For example, the video encoder 200 can signal different RQT depth values ​​for intra- and inter-coded CUs.

[0262] Quadtree transforms can be applied to both intra-frame and inter-frame residual blocks. Typically, a DCT-II transform of the same size as the current residual quadtree partition is applied to the residual block. For example, the video encoder 200 can apply a DCT-II transform of the same size as the current residual quadtree partition to the residual block. However, if the current residual quadtree block is 4x4 and is generated by intra-frame prediction, the above-mentioned 4x4 DST-VII transform can be applied.

[0263] In HEVC, larger transform sizes (e.g., 64x64 transforms) are not adopted, primarily because of their limited benefits and relatively high complexity for relatively small resolution videos.

[0264] The technology of this disclosure is applicable to Figure 6 A typical adaptive transform decoding scheme is shown. Figure 3 The video encoder 200 can be configured to use Figure 6 The adaptive transform decoding scheme shown operates. Figure 6 The video encoder includes a block separation unit 130, a residual generation unit 148, a block transform unit 132, a quantization unit 134, an entropy decoding unit 136, an inverse quantization unit 138, an inverse transform unit 140, a frame buffer 144, a block prediction unit 146, and a transform bank unit 142. For example, the block separation unit 130 may provide a block of video data to the residual generation unit 148. The residual generation unit 148 may accept the block of video data and the prediction information from the block prediction unit 146 and generate a residual r. The block transform unit 132 may select a transform t from the transform bank unit 142 and may signal the selected transform in the bitstream output from the entropy decoding unit 136. The block transform unit 132 may apply the transform selected from the transform bank unit 142 to create transform coefficients T(t) r. In some examples, block transform unit 132 may apply a secondary transform (which may also be in transform bank unit 142) after applying the primary transform. The transform coefficients may be provided to quantization unit 134. Quantization unit 134 may quantize the transform coefficients and provide the quantized transform coefficients to entropy decoding unit 136 and inverse quantization unit 138. Entropy decoding unit 136 may entropy encode the quantized transform coefficients and output the entropy decoded information to a bitstream. Inverse quantization unit 138 may inverse quantize the quantized transform coefficients to recreate the transform coefficients and provide the transform coefficients to inverse transform unit 140. Inverse transform unit 140 may inverse transform the transform coefficients and provide video data to frame buffer 144. Frame buffer 144 may provide the video data to block prediction unit 146, which may predict the current block of video data.

[0265] exist Figure 6 For each block of prediction residual, the video encoder 200 may select a different transform from the transform bank unit 142. The video encoder 200 may encode the transform selection as side information for signaling. For example, the video encoder 200 may signal the transform selection, and the video decoder 300 may determine the transform selection by reading the signal.

[0266] In video coding standards prior to HEVC, only fixed separable transforms were used when DCT-2 was used vertically and horizontally. In HEVC, in addition to DCT-2, DST-7 is also used as a fixed separable transform for 4x4 blocks. Adaptive extensions of these fixed transforms are described in U.S. Patent Publication No. 2016 / 0219290, published on July 28, 2016, U.S. Patent Publication No. 2018 / 0020218, published on January 18, 2018, and U.S. Provisional Patent Application No. 62 / 679,570, filed on June 1, 2018 (the entire contents of each of which are incorporated herein by reference), and examples of adaptive multiple transforms (AMTs) described in the following documents have been adopted in the Joint Video Experts Group (JVET) Joint Experimental Model (JEM-7.0) (e.g., see ITU-T SG 16 WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11 Joint Video Experts Group (JVET), JEM software). Residuals,” January 2015. A simplified version of AMT is also used in VVC, called Multiple Transform Selection (MTS). In addition, a quadratic transform is used in JEM-7.0 to further improve decoding efficiency, where the implementation is based on the hypercube Givens transform (HyGT) described in U.S. Patent Publication No. 2017 / 0238013, published on August 17, 2017 (see also U.S. Patent Publication No. 2017 / 0094313, published on March 30, 2017, U.S. Patent Publication No. 2017 / 0094314, published on March 30, 2017, U.S. Patent Publication No. 2017 / 0238014, published on August 17, 2017, U.S. Provisional Patent Application No. 62 / 668,105, filed on May 7, 2018, and U.S. Provisional Patent Application No. 62 / 648,321, filed on March 26, 2018, the entire contents of each of which are incorporated herein by reference, for alternative designs of the quadratic transform and additional details). For the VVC standard, the secondary transform is still under study and may be included in the VVC standard in subsequent JVET meeting cycles.

[0267] In the recent JVET meeting, a partitioning method for TU has been adopted in VVC (to be available in the VTM-4.0 reference software), in which the intra-coded TU block can be further partitioned horizontally or vertically (referred to as intra sub-partitioning in this article) according to the intra prediction mode and block size. In the adopted method, multiple horizontal / vertical partitions are allowed, and the size of TU can be 1x16 and 16x1. However, the existing secondary transform design (including the secondary transform design in JEM-7.0) implicitly assumes that the minimum TU size is 4x4, so for the current secondary transform design, the secondary transform may not be applicable to certain sizes of TU, ​​including 1x16, 16x1, 2x8 and 8x2.

[0268] The techniques of this disclosure may allow applying a secondary transform to TUs of sizes 1x16, 16x1, 2x8, and 8x2 in order to achieve better coding gain.

[0269] This disclosure describes a secondary transform design that can be applied to any encoder / decoder (e.g., video encoder 200 and video decoder 300) that supports various TU (block) sizes (e.g., 1x16, 16x1, 2x8, 8x2). The techniques described below can be used alone or in any combination with each other. Figure 7 is a block diagram illustrating the use of a secondary transform on the encoder and decoder sides. For example, the video encoder 200 may apply a primary transform (150), a secondary transform (152), and quantize (154) video data. The transform processing unit 206 of the video encoder 200 may apply the primary transform and the secondary transform to the video data, and the quantization unit 208 may quantize the transform coefficients. The video decoder 300 may inverse quantize (156), perform a secondary inverse transform (158), and perform a primary inverse transform (160) on the video data received in the bitstream. The inverse quantization unit 306 of the video decoder 300 may inverse quantize the video data in the bitstream, and the inverse transform processing unit 308 of the video decoder 300 may apply the secondary inverse transform and the primary inverse transform to the inverse quantized video data.

[0270] In one example of the present disclosure, when intra-frame sub-partitioning is applied to a block, a secondary transform is not applied. In this case, the secondary transform overhead may not be signaled. For example, when the video encoder 200 applies intra-frame sub-partitioning to a block, the video encoder 200 may not apply the secondary transform to the block. In this example, the video encoder 200 may not signal the secondary transform overhead, and the video decoder 300 may not read the secondary transform overhead signaling. In other words, intra-frame sub-partitioning and the secondary transform may not be used together.

[0271] In another example of the present disclosure, a secondary transform may be applied to the entirety of the primary transform coefficients, regardless of the intra-frame sub-division method. That is, the primary transform is applied to all sub-blocks, and the secondary transform is applied to the primary transform coefficients. In this case, the secondary transform may be applied across the primary transform blocks, or may be applied to only a portion of multiple primary transform blocks. For example, the video encoder 200 may apply the secondary transform across all primary transform blocks or to less than all primary transform blocks.

[0272] In another example of the present disclosure, the video encoder 200 may apply a secondary transform to a subset of coefficients obtained from a primary transform, such as the primary transform defined by AMT / MTS. In this example, the video decoder 300 first applies the secondary inverse transform and then applies the primary inverse transform. As described above, Figure 7 A secondary transform scheme for a video encoder and a video decoder, such as the video encoder 200 and the video decoder 300 , is shown.

[0273] In another example of the present disclosure, a secondary transform of size K may be implemented based on matrix multiplication, HyGT, or hierarchical decomposition, as described in U.S. Patent Publication No. 2017 / 0094313, published on March 30, 2017, U.S. Patent Publication No. 2017 / 0094314, published on March 30, 2017, U.S. Patent Publication No. 2017 / 0238014, published on August 17, 2017, U.S. Provisional Patent Application No. 62 / 668,105, filed on May 7, 2018, and U.S. Provisional Patent Application No. 62 / 648,321, filed on March 26, 2018. For example, the video encoder 200 may apply the secondary transform of size K to the primary transform coefficients.

[0274] In another example of the present disclosure, the secondary transform may be a separable transform or an inseparable transform. For example, the video encoder 200 may apply a separable secondary transform to the primary transform coefficients. In other examples, the video encoder 200 may apply an inseparable secondary transform to the primary transform coefficients.

[0275] In another example of the present disclosure, if TU partitioning is used or signaled, the secondary transform may not be applied. For example, if the TU size is the same as the CU size, the secondary transform may be used. For example, if the video encoder 200 uses TU partitioning on a given CU, the video encoder 200 may not use the secondary transform, and if the video encoder 200 does not use TU partitioning on a given CU, the video encoder 200 may use the secondary transform.

[0276] In other examples of the present disclosure, the secondary transform can be applied regardless of whether the TU is split. The following are specific examples where the video encoder 200 can apply the secondary transform regardless of whether the TU is split.

[0277] For example, if the TU is not split, the secondary transform can be applied to a subset of samples. For example, if a given TU is not split, the video encoder 200 can apply the secondary transform to a subset of samples. Examples include the designs described in U.S. Patent Application No. 16 / 020,511 filed on June 27, 2018. As another example, the secondary transform in JEM-7.0 can be applied when the TU size is the same as the CU size. For example, when the TU size is the same as the CU size, the video encoder 200 can apply the secondary transform described in JEM-7.0.

[0278] In another example, if the split results in a TU of size 1xN or Nx1, where N>1, the secondary transform can be applied to a subset of N samples / pixels, represented by K<N. Figure 8 An example where N = 16 and K = 8 is shown, where the subset of samples / pixels is represented by the shaded boxes. For example, if the split results in a TU of size 1xN or Nx1, the video encoder 200 can apply the secondary transform to a subset of N samples / pixels.

[0279] In another example, if the split results in a TU of size 2xN or 2xN, where N>2, the secondary transform can be applied to a subset of 2N samples / pixels, represented by K<2N. Figure 9 An example where 2N = 32 and K = 16 is shown, where the subset of samples / pixels is represented by the shaded boxes. Figure 10 Two examples where 2N = 32 and K = 8 are shown, where the subset of samples / pixels is represented by the shaded boxes. For example, if the split results in a TU of size 2xN or Nx2, the video encoder 200 can apply the secondary transform to a subset of 2N samples / pixels.

[0280] In another example of the present disclosure, the secondary transform can be applied to the K lowest-frequency coefficients obtained from the primary transform. For example, the video encoder 200 can apply the secondary transform to the K lowest-frequency coefficients obtained from the primary transform, where K is an integer.

[0281] In another example of the present disclosure, the secondary transform can be applied to any subset of samples obtained from the primary transform. For example, the video encoder 200 can apply the secondary transform to any subset of samples obtained from the primary transform.

[0282] In another example of the present disclosure, a secondary transform may be applied to a certain type of segmentation or certain types of segmentation. For example, if the segmentation is obtained based on a binary tree or a quadtree, a secondary transform may be applied. In some examples, if the segmentation is defined based on a ternary tree, a secondary transform may not be allowed (for examples of tree-based segmentation, see Figure 11 ). Figure 11 Different types of tree-based partitioning on a square block are shown. For example, quadtree partitioning 162 is depicted using its corresponding example CTU 170, binary tree partitioning 164 is depicted using corresponding example CTUs (CTU 172 and CTU 174), binary tree partitioning 166 is depicted using corresponding example CTUs (CTU 176 and CTU 178), and ternary tree partitioning 168 is depicted using corresponding example CTUs (CTU 180 and CTU 182). For example, if the partitioning is binary tree partitioning or quadtree partitioning, then the video encoder 200 may apply a secondary transform, but if the partitioning is ternary tree partitioning, then the video encoder 200 may not apply a secondary transform.

[0283] In some examples, one or a combination of the above techniques may be used only for intra-predicted CUs. For example, the video encoder 200 may apply any one of the above techniques only for intra-predicted CUs.

[0284] In some examples, one or a combination of the above techniques may be used only for inter-predicted CUs. For example, video encoder 200 may apply any one of the above techniques only for inter-predicted CUs.

[0285] In some examples, one or a combination of the above techniques can be used for both intra-predicted CUs and inter-predicted CUs. For example, the video encoder 200 can apply any one of the above techniques to both intra-predicted CUs and inter-predicted CUs.

[0286] In some examples, one or a combination of the above techniques may be used for the luma channel or the chroma channels or both. For example, video encoder 200 may apply any one of the above techniques to the luma channel or the chroma channels or both.

[0287] In another example of the present disclosure, for intra sub-partitioning mode, the primary transform size (width x height) can be a multiple of 16, so the transform blocks can be rearranged before applying the secondary transform. For example, 1x16 or 16x1 primary transform coefficients can be rearranged into 4x4 coefficient blocks before applying the secondary transform. For example, the video encoder 200 can limit the primary transform size to a multiple of 16. In the case of 1x16 or 16x1 primary transform coefficients, the video encoder 200 can rearrange the primary transform coefficients into 4x4 coefficient blocks and then apply the secondary transform. Various methods (such as various scan modes) can be used to rearrange the blocks. The rearrangement method can depend on the intra sub-partitioning block size and / or the intra mode.

[0288] In other alternatives, the secondary transform may be applied only when the primary transform size is at least a predetermined size (such as 4x4, 8x8, 16x16, or any other predetermined size) in the intra sub-division method. Otherwise, the secondary transform may not be applied and the secondary transform overhead may not be signaled. For example, the video encoder 200 may apply the secondary transform only when the primary transform size is at least 4x4, and if the primary transform size is not at least 4x4, the video encoder 200 may not apply the secondary transform or may not signal the secondary transform overhead.

[0289] Figure 12 is a flow chart illustrating an example method according to techniques of the present disclosure. Video encoder 200 may determine whether intra sub-partitioning is used for a current block of video data (184). Video encoder 200 may apply a primary transform to the current block of video data (186). The video encoder may also determine whether the primary transform size is at least a predetermined size (188). If video encoder 200 determines that intra sub-partitioning is not used (“NO” path from diamond 184), or if video encoder 200 determines that the primary transform size is not at least a predetermined size (e.g., 4x4, 8x8, 16x16, or any other predetermined size) (“NO” path from diamond 188), transform processing unit 206 of video encoder 200 may not apply a secondary transform (194). Because the secondary transform is not applied, video encoder 200 may decode the current block of video data based on the primary transform coefficients (192). If video encoder 200 determines that intra sub-partitioning is used ("yes" path from diamond 184) and the primary transform is at least the predetermined size ("yes" path from diamond 188), transform processing unit 206 of video encoder 200 may apply a secondary transform to the primary transform coefficients (190). If the secondary transform is applied, video encoder 200 may decode the current block of video data based on the secondary transform (192).

[0290] Figure 131 is a flowchart illustrating an example method for encoding a current block. The current block may include a current CU. Although with respect to the video encoder 200 ( Figure 1 and 2), but it should be understood that other devices may be configured to perform the same Figure 13 A similar approach to the one in the previous section.

[0291] In this example, the video encoder 200 initially predicts a current block (350). For example, the video encoder 200 may form a prediction block for the current block. The video encoder 200 may then calculate a residual block for the current block (352). To calculate the residual block, the video encoder 200 may calculate the difference between the original, uncoded block and the prediction block for the current block. The video encoder 200 may then transform and quantize the coefficients of the residual block (354). For example, the video encoder 200 may determine whether intra sub-partitioning is applied to the current block of video data. The transform processing unit 206 of the video encoder 200 may apply a primary transform. The video encoder 200 may also determine whether the primary transform size of the current block of video data is at least a predetermined size. The transform processing unit 206 of the video encoder 200 may apply a secondary transform to the primary transform coefficients based on applying the intra sub-partitioning and the primary transform size being at least the predetermined size, and the video encoder 200 may encode the current block of video data based on the secondary transform. Next, video encoder 200 may scan the quantized transform coefficients of the residual block (356). During or after the scan, video encoder 200 may entropy encode the coefficients (358). For example, video encoder 200 may encode the coefficients using CAVLC or CABAC. Video encoder 200 may then output entropy coded data for the block (360).

[0292] Figure 14 is a flowchart illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although with respect to the video decoder 300 ( Figure 1 and 3 ) is described, but it should be understood that other devices may be configured to perform the same Figure 14 A similar approach to the one in the previous section.

[0293] The video decoder 300 may receive entropy-coded data for a current block (such as entropy-coded prediction information and entropy-coded data for coefficients of a residual block corresponding to the current block) (370). The video decoder 300 may entropy decode the entropy-coded data to determine prediction information for the current block and reproduce coefficients of the residual block (372). The video decoder 300 may predict the current block (374), for example, using an intra-frame or inter-frame prediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the reproduced coefficients (376) to create a block of quantized transform coefficients. The video decoder 300 may then inverse quantize and inverse transform the coefficients to produce a residual block (378). For example, the video decoder 300 may determine whether intra sub-partitioning is applied to the current block of video data. The video decoder 300 may also determine whether the primary transform size of the current block of video data is at least a predetermined size. The inverse transform processing unit 308 may apply a secondary inverse transform to the inverse quantized data based on applying the intra-frame sub-partitioning and the primary transform size being at least a predetermined size. The inverse transform processing unit may also perform a primary inverse transform on the secondary inverse transformed data. The video decoder 300 may decode the current block of video data based on the secondary transform. Finally, the video decoder 300 may decode the current block by combining the prediction block and the residual block (380).

[0294] Examples according to the present disclosure include the following:

[0295] Example 1. A method of coding video data, the method comprising coding a block of the video data using one or more of a primary transform and a secondary transform according to the techniques of this disclosure.

[0296] Example 2. The method of example 1, wherein intra sub-partitioning is applied to the block of video data, the method further comprising decoding the block of video data using only the primary transform.

[0297] Example 3. The method of Example 1, wherein decoding the block of the video data using one or more of the primary transform and the secondary transform comprises: applying the primary transform to the block of the video data, including sub-blocks; and applying the secondary transform to primary transform coefficients.

[0298] Example 4. The method of Example 1, wherein decoding the block of video data using one or more of the primary transform and the secondary transform comprises: applying the primary transform to the block of video data; and applying the secondary transform to a subset of coefficients obtained from the primary transform.

[0299] Example 5. The method of Example 1, wherein decoding the block of video data using one or more of the primary transform and the secondary transform comprises decoding the block of video data using a secondary transform having a size K, wherein the secondary transform is based on matrix multiplication, HyGT, or hierarchical decomposition.

[0300] Example 6. The method of example 1, wherein the secondary transform is a separable transform.

[0301] Example 7. The method of example 1, wherein the secondary transform is a non-separable transform.

[0302] Example 8. The method of Example 1, wherein decoding the block of video data using one or more of the primary transform and the secondary transform comprises decoding the block of video data using the secondary transform if the block of video data is a transform unit having the same size as a decoding unit.

[0303] Example 9. The method of Example 1, wherein decoding the block of video data using one or more of the primary transform and the secondary transform comprises decoding the block of video data using the secondary transform on a subset of samples if the block of video data is a transform unit that does not have the same size as a coding unit.

[0304] Example 10. The method of example 1, further comprising: applying the primary transform to a block of the video data; and applying the secondary transform to the K lowest frequency coefficients obtained from the primary transform.

[0305] Example 11. The method of example 1, further comprising: applying the primary transform to a block of the video data; and applying the secondary transform to all frequency coefficients or samples obtained from the primary transform.

[0306] Example 12. Any combination of the techniques of Examples 1-11.

[0307] Example 13. An apparatus for decoding video data, the apparatus comprising one or more means for performing the method according to any of Examples 1-12.

[0308] Example 14. The apparatus of Example 13, wherein the one or more units include one or more processors implemented in circuitry.

[0309] Example 15. The apparatus of any one of Examples 13 and 14, further comprising a memory for storing the video data.

[0310] Example 16. The apparatus of any of Examples 13-15, further comprising a display configured to display the decoded video data.

[0311] Example 17. The device of any of Examples 13-16, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0312] Example 18. The apparatus of any of Examples 13-17, wherein the apparatus comprises a video decoder.

[0313] Example 19. The apparatus of any of Examples 13-18, wherein the apparatus comprises a video encoder.

[0314] Example 20. A computer-readable storage medium having instructions stored thereon that, when executed, cause one or more processors to perform the method of any of Examples 1-12.

[0315] It will be appreciated that, depending on the examples, certain actions or events of any of the techniques described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary to implement the techniques). Furthermore, in some examples, actions or events may be performed concurrently rather than sequentially, for example, through multithreading, interrupt handling, or multiple processors.

[0316] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted through a computer-readable medium as one or more instructions or codes and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to tangible media such as data storage media or communication media, including any media that facilitates the transfer of a computer program from one place to another, for example, according to a communication protocol. In this manner, computer-readable media may generally correspond to (1) non-transitory tangible computer-readable storage media, or (2) communication media such as signals or carrier waves. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to obtain instructions, codes, and / or data structures for implementing the techniques described in this disclosure. A computer program product may include computer-readable media.

[0317] By way of example and not 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 that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. In addition, any connection is appropriately referred to as a computer-readable medium. For example, if instructions are transmitted from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technology (e.g., infrared, radio and microwave), the coaxial cable, fiber optic cable, twisted pair, DSL or wireless technology (e.g., infrared, radio and microwave) is included in the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other temporary media, but are instead directed to non-temporary tangible storage media. As used herein, disks and optical disks include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks and Blu-ray discs, wherein disks typically copy data magnetically, while optical discs use lasers to copy data optically. Combinations of the above should also be included within the scope of computer-readable media.

[0318] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Thus, the terms "processor" and "processing circuitry" as used herein may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a combined codec. Furthermore, the techniques may be implemented entirely in one or more circuits or logic elements.

[0319] The techniques of the present disclosure can be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC), or a set of ICs (e.g., a chipset). Various components, modules, or units are described in this disclosure to emphasize functional aspects of a device configured to perform the disclosed techniques, but do not necessarily need to be implemented by different hardware units. Specifically, as described above, the various units can be combined in a codec hardware unit, or provided by a collection of interoperable hardware units (including one or more processors as described above) in combination with appropriate software and / or firmware.

[0320] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

1. A method for decoding video data, the method comprising: determining whether intra-frame sub-partitioning is applied to a current block of video data; determining whether a size of the primary inverse transform is at least a predetermined size based on applying the intra-frame sub-partitioning; applying a secondary inverse transform and the main inverse transform to the inverse quantized video data in sequence and reading or parsing a secondary inverse transform overhead based on a determination that intra sub-partitioning is applied and the size of the main inverse transform is at least the predetermined size, and decoding the current block of the video data based on at least one of the main inverse transform and the secondary inverse transform; as well as Based on determining that intra-frame sub-partitioning is not applied or the size of the main inverse transform is not at least the predetermined size, the main inverse transform is applied to the inverse quantized video data without applying any secondary inverse transform, and secondary inverse transform overhead is not read or parsed, and the current block of the video data is decoded based on the main inverse transform.

2. The method according to claim 1, wherein The predetermined size is 4x4.

3. The method according to claim 1, wherein The quadratic inverse transform is a non-separable transform.

4. The method according to claim 1, wherein The quadratic inverse transform is a separable transform.

5. The method according to claim 1, wherein Determining whether to apply intra sub-partitioning further includes determining a partitioning type for the current block of video data, and applying the second inverse transform is also based on the partitioning type for the current block of video data.

6. The method according to claim 5, wherein: The partitioning type used is either binary tree partitioning or quadtree partitioning.

7. A device for decoding video data, the device comprising: a memory configured to store video data; as well as one or more processors implemented in circuitry and in communication with the memory, the one or more processors being configured to: determining whether intra-frame sub-partitioning is applied to a current block of video data; determining whether a size of the primary inverse transform is at least a predetermined size based on applying the intra-frame sub-partitioning; applying a secondary inverse transform and the main inverse transform to the inverse quantized video data in sequence and reading or parsing a secondary inverse transform overhead based on a determination that intra sub-partitioning is applied and the size of the main inverse transform is at least the predetermined size, and decoding the current block of the video data based on at least one of the main inverse transform and the secondary inverse transform; as well as Based on determining that intra-frame sub-partitioning is not applied or the size of the main inverse transform is not at least the predetermined size, the main inverse transform is applied to the inverse quantized video data without applying any secondary inverse transform, and secondary inverse transform overhead is not read or parsed, and the current block of the video data is decoded based on the main inverse transform.

8. The apparatus according to claim 7, wherein The predetermined size is 4x4.

9. The apparatus according to claim 7, wherein The quadratic inverse transform is a non-separable transform.

10. The apparatus according to claim 7, wherein The quadratic inverse transform is a separable transform.

11. The apparatus according to claim 7, wherein The one or more processors are further configured to: determining a partitioning type for the current block of video data; and Wherein the one or more processors further apply the secondary inverse transform based on the partition type for the current block of video data.

12. The apparatus according to claim 11, wherein The partitioning type used is either binary tree partitioning or quadtree partitioning.

13. A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to: determining whether intra-frame sub-partitioning is applied to a current block of video data; determining whether a size of the primary inverse transform is at least a predetermined size based on applying the intra-frame sub-partitioning; applying a secondary inverse transform and the main inverse transform to the inverse quantized video data in sequence and reading or parsing a secondary inverse transform overhead based on a determination that intra sub-partitioning is applied and the size of the main inverse transform is at least the predetermined size, and decoding the current block of the video data based on at least one of the main inverse transform and the secondary inverse transform; as well as Based on determining that intra-frame sub-partitioning is not applied or the size of the main inverse transform is not at least the predetermined size, the main inverse transform is applied to the inverse quantized video data without applying any secondary inverse transform, and secondary inverse transform overhead is not read or parsed, and the current block of the video data is decoded based on the main inverse transform.

14. The computer-readable storage medium of claim 13, wherein: The predetermined size is 4x4.

15. The computer-readable storage medium of claim 13, wherein: The quadratic inverse transform is a non-separable transform.

Images