Advanced subblock transforms for video coding

Abstract

An example method of coding video data includes determining to apply a subblock transform mode to a current block of the video data. The method includes determining, based on determining to apply the subblock transform mode to the current block, a coordinate for the current block having a maximum gradient value. The method includes performing a search for a position and a direction using the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns. The method includes dividing the block into subblocks based on the position and direction, the plurality of subblocks including a single subblock to which to apply a subblock transform, and coding the subblocks based on the subblock transform mode.

Description

Qualcomm Ref. No. 2502091WO 1 / 58ADVANCED SUBBLOCK TRANSFORMS FOR VIDEO CODING

[0001] This application claims the benefit of U.S. Provisional Patent Application 63 / 745,649, filed January 15, 2025, and U.S. Provisional Patent Application 63 / 772,032, filed March 14, 2025, the entire content of each of which is incorporated by reference herein.TECHNICAL FIELD

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

[0003] Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio telephones, so-called “smart phones,” video teleconferencing devices, video streaming devices, and the like. 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), ITU-T H.266 / Versatile Video Coding (VVC), and extensions of such standards, as well as proprietary video codecs / formats such as AOMedia Video 1 (AVI) that was developed by the Alliance for Open Media. The video devices may transmit, receive, encode, decode, and / or store digital video information more efficiently by implementing such video coding techniques.

[0004] Video coding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be 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 intracoded (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 in1616-615WO01Qualcomm Ref. No. 2502091WO 2 / 58neighboring 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

[0005] In general, this disclosure describes techniques for an Advanced subblock transform (SBT) mode in video coding. In a representative design of Advanced SBT mode, a brute force search technique is used. The gradient value of the whole subblock is added up for each possible position and direction and a search step of one row / column is used for all subblock shapes. The subblock position and direction that provide the largest summation of gradient values are used as the subblock to which a transform is applied. This brute force search technique requires a relatively high level of complexity.

[0006] Also, the representative design of Advanced SBT does not support all subblock shapes. Only the subblock shapes of Width * Height / N and Width / N * Height are supported. However, for the subblock shape of Width / N * Height / N, the representative design of Advanced SBT does not apply Advanced SBT.

[0007] Finally, when deciding the best position and direction, only the gradient value from the predictor is being considered in the representative design of Advanced SBT. However, the position and direction can be decided after an inverse transform where the residual information is available.

[0008] The techniques of this disclosure may address such issues. For example, the techniques of this disclosure may reduce coder complexity and / or may improve coding performance and / or quality of decoded video data.

[0009] In one example, this disclosure is directed to a method of decoding video data, the method comprising determining to apply a subblock transform mode to a current block of the video data, determining, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value, performing a search for a position and a direction using the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns, dividing the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform, and decoding the plurality of subblocks based on the subblock transform mode.1616-615WO01Qualcomm Ref. No. 2502091WO 3 / 58

[0010] In another example, this disclosure is directed to a device for decoding video data, the device comprising one or more memories, and one or more processors in communication with the one or more memories, the one or more processors configured to determine to apply a subblock transform mode to a current block of the video data, determine, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value, perform a search for a position and a direction using the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns, divide the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform, and decode the plurality of subblocks based on the subblock transform mode.

[0011] In yet another example, this disclosure is directed to a device for encoding video data, the device comprising one or more memories, and one or more processors in communication with the one or more memories, the one or more processors configured to determine to apply a subblock transform mode to a current block of the video data, determine, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value, perform a search for a position and a direction using the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns, divide the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform, and encode the plurality of subblocks based on the subblock transform mode.

[0012] 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 DRAWINGS

[0013] FIG. 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0014] FIG. 2 is a conceptual diagram illustrating example subblock transform (SBT) modes including (a) the eight SBT modes in VVC and (b) additional SBT modes studied during VVC standardization.1616-615WO01Qualcomm Ref. No. 2502091WO 4 / 58

[0015] FIG. 3 is a conceptual diagram illustrating an example general principle of Advanced SBT at an encoder.

[0016] FIG. 4 is a conceptual diagram illustrating two example kernels used in a Sobel algorithm.

[0017] FIG. 5 is a conceptual diagram illustrating an example image continuity measure.

[0018] FIG. 6 is a conceptual diagram illustrating an example of an improved gradient search according to one or more aspects of this disclosure.

[0019] FIG. 7 is a conceptual diagram illustrating an example of two tap filters according to one or more aspects of this disclosure.

[0020] FIG. 8 is a conceptual diagram illustrating example, width / N * height / N subblocks according to one or more aspects of this disclosure.

[0021] FIG. 9 is a flowchart illustrating example Advanced subblock transform techniques according to one or more aspects of this disclosure.

[0022] FIG. 10 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0023] FIG. 11 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0024] FIG. 12 is a flowchart illustrating an example method for encoding a current block in accordance with the techniques of this disclosure.

[0025] FIG. 13 is a flowchart illustrating an example method for decoding a current block in accordance with the techniques of this disclosure.DETAILED DESCRIPTION

[0026] In general, this disclosure describes techniques for an Advanced subblock transform mode in video coding. In the current design of Advanced SBT mode, a brute force search technique is used which requires relatively high complexity of design to implement the search technique. It may be desirable to simplify such a design.

[0027] Also, the representative Advanced SBT mode does not support all subblock shapes. It may be desirable to support more subblock shapes. Supporting more subblock shapes may improve coding performance and / or the quality of decoded video data.

[0028] Additionally, when deciding the best position and direction, with the representative Advanced SBT mode, only the gradient value from the predictor is being considered. However, the position and direction can be decided after an inverse transform where the residual information is available. Determining the position and / or direction of 1616-615WO01Qualcomm Ref. No. 2502091WO 5 / 58a subblock for Advanced SBT mode after an inverse transform may improve coding performance and / or the quality of decoded video data.

[0029] As such, the techniques of this disclosure may reduce complexity and / or may improve coding performance and / or quality.

[0030] FIG. 1 is a block diagram illustrating an example video encoding and decoding system 100 that may perform the techniques of this disclosure. The techniques of this disclosure are generally directed to coding (encoding and / or decoding) video data. In general, video data includes any data for processing a video. Thus, video data may include raw, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

[0031] As shown in FIG. 1, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116, in this example. In particular, 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 be or include any of a wide range of devices, such as desktop computers, notebook (i.e., laptop) computers, mobile devices, tablet computers, set-top boxes, telephone handsets such as smartphones, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, broadcast receiver devices, or the like. In some cases, source device 102 and destination device 116 may be equipped for wireless communication, and thus may be referred to as wireless communication devices.

[0032] In the example of FIG. 1, 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. In accordance with this disclosure, video encoder 200 of source device 102 and video decoder 300 of destination device 116 may be configured to apply the techniques for Advanced SBT mode. 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, a source device and a destination device may include other components or arrangements. For example, source device 102 may receive video data from an external video source, such as an external camera. Likewise, destination device 116 may interface with an external display device, rather than include an integrated display device.

[0033] System 100 as shown in FIG. 1 is merely one example. In general, any digital video encoding and / or decoding device may perform techniques for Advanced SBT 1616-615WO01Qualcomm Ref. No. 2502091WO 6 / 58mode. Source device 102 and destination device 116 are merely examples of such coding devices in which source device 102 generates coded video data for transmission to destination device 116. This disclosure refers to a “coding” device as a device that performs coding (encoding and / or decoding) of data. Thus, video encoder 200 and video decoder 300 represent examples of coding devices, in particular, a video encoder and a video decoder, respectively. In some examples, source device 102 and destination device 116 may operate in a substantially symmetrical manner such that each of source device 102 and destination device 116 includes video encoding and decoding components. Hence, system 100 may support one-way or two-way video transmission between source device 102 and destination device 116, e.g., for video streaming, video playback, video broadcasting, or video telephony.

[0034] In general, 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 the video data to video encoder 200, which encodes data for the pictures. Video source 104 of source device 102 may include a video capture device, such as a video camera, a video archive containing previously captured raw video, and / or a video feed interface to receive video from a video content provider. As a further alternative, video source 104 may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. In each case, video encoder 200 encodes the captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange the pictures from the received order (sometimes referred to as “display order”) into a coding order for coding. Video encoder 200 may generate a bitstream including encoded video data. Source device 102 may then output the encoded video data via output interface 108 onto computer-readable medium 110 for reception and / or retrieval by, e.g., input interface 122 of destination device 116.

[0035] Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memories. In some examples, memories 106, 120 may store raw video data, e.g., raw video from video source 104 and raw, decoded video data from video decoder 300. Additionally or alternatively, memories 106, 120 may store software instructions executable by, e.g., video encoder 200 and video decoder 300, respectively. Although memory 106 and memory 120 are shown separately from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 may also include internal memories for functionally similar or equivalent purposes. Furthermore, memories 106, 120 may store encoded video data, 1616-615WO01Qualcomm Ref. No. 2502091WO 7 / 58e.g., output from video encoder 200 and input to video decoder 300. In some examples, portions of memories 106, 120 may be allocated as one or more video buffers, e.g., to store raw, decoded, and / or encoded video data.

[0036] Computer-readable medium 110 may represent any type of medium or device capable of transporting the encoded video data from source device 102 to destination device 116. In one example, computer-readable medium 110 represents a communication medium to enable source device 102 to transmit encoded video data directly to destination device 116 in real-time, e.g., via a radio frequency network or computer-based network. Output interface 108 may modulate a transmission signal including the encoded video data, and input interface 122 may demodulate the received transmission signal, according to a communication standard, such as a wireless communication protocol. The communication medium may include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device 102 to destination device 116.

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

[0038] In some examples, source device 102 may output encoded video data to file server 114 or another intermediate storage device that may store the encoded video data generated by source device 102. Destination device 116 may access stored video data from file server 114 via streaming or download.

[0039] File server 114 may be any type of server device capable of storing encoded video data and transmitting that encoded video data to the destination device 116. File server 114 may represent a web server (e.g., for a website), a server configured to provide a file transfer protocol service (such as File Transfer Protocol (FTP) or File Delivery over Unidirectional Transport (FLUTE) protocol), a content delivery network (CDN) device, a hypertext transfer protocol (HTTP) server, a Multimedia Broadcast Multicast Service 1616-615WO01Qualcomm Ref. No. 2502091WO 8 / 58(MBMS) or Enhanced MBMS (eMBMS) server, and / or a network attached storage (NAS) device. File server 114 may, additionally or alternatively, implement one or more HTTP streaming protocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP Dynamic Streaming, or the like.

[0040] Destination device 116 may access encoded video data from file server 114 through 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., digital subscriber line (DSL), cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on file server 114. Input interface 122 may be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from file server 114, or other such protocols for retrieving media data.

[0041] Output interface 108 and input interface 122 may represent wireless transmitters / receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of a variety of IEEE 802.11 standards, or other physical components. In examples where output interface 108 and input interface 122 include wireless components, output interface 108 and input interface 122 may be configured to transfer data, such as encoded video data, according to a cellular communication standard, such as 4G, 4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In some examples where output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 may be configured to transfer data, such as encoded video data, according to other wireless standards, such as an IEEE 802.11 specification, an IEEE 802.15 specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. In some examples, source device 102 and / or destination device 116 may include respective system-on-a-chip (SoC) devices. For example, source device 102 may include an SoC device to perform the functionality attributed to video encoder 200 and / or output interface 108, and destination device 116 may include an SoC device to perform the functionality attributed to video decoder 300 and / or input interface 122.

[0042] The techniques of this disclosure may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that 1616-615WO01Qualcomm Ref. No. 2502091WO 9 / 58is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0043] Input interface 122 of destination device 116 receives an encoded video bitstream from computer-readable medium 110 (e.g., a communication medium, storage device 112, file server 114, or the like). The encoded video bitstream may include signaling information defined by video encoder 200, which is also used by video decoder 300, such as syntax elements having values that describe characteristics and / or processing of video blocks or other coded units (e.g., slices, pictures, groups of pictures, sequences, or the like). Display device 118 displays decoded pictures of the decoded video data to a user. Display device 118 may represent any of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0044] Although not shown in FIG. 1, in some examples, video encoder 200 and video decoder 300 may each be integrated with an audio encoder and / or audio decoder (e.g., audio codec), and may include appropriate MUX-DEMUX units, or other hardware and / or software, to handle multiplexed streams including both audio and video in a common data stream. Example audio codecs may include AAC, AC-3, AC-4, ALAC, ALS, AMBE, AMR, AMR-WB (G.722.2), AMR-WB+, aptx (various versions), ATRAC, BroadVoice (BV16, BV32), CELT, Enhanced AC-3 (E-AC-3), EVS, FLAC, G.711, G.722, G.722.1, G.722.2 (AMR-WB). G.723.1, G.726, G.728, G.729, G.729.1, GSM-FR, HE-AAC, iLBC, iSAC, LA Lyra, Monkey's Audio, MP1, MP2 (MPEG-1, 2 Audio Layer II), MP3, Musepack, Nellymoser Asao, OptimFROG, Opus, Sac, Satin, SBC, SILK, Siren 7, Speex, SVOPC, True Audio (TTA), TwinVQ, USAC, Vorbis (Ogg), WavPack, and Windows Media Aud.

[0045] Video encoder 200 and video decoder 300 each may be implemented as any of a variety of suitable encoder and / or decoder circuitry that includes a processing system, 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 combinations thereof. When the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder 200 and video decoder 300 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder / decoder 1616-615WO01Qualcomm Ref. No. 2502091WO 10 / 58(CODEC) in a respective device. A device including video encoder 200 and / or video decoder 300 may implement video encoder 200 and / or video decoder 300 in processing circuitry such as an integrated circuit and / or a microprocessor. Such a device may be a wireless communication device, such as a cellular telephone, or any other type of device described herein.

[0046] Video encoder 200 and video decoder 300 may operate according to a video coding standard, such as ITU-T H.265, also referred to as High Efficiency Video Coding (HEVC) or extensions thereto, such as the multi-view and / or scalable video coding extensions. Alternatively, video encoder 200 and video decoder 300 may operate according to other proprietary or industry standards, such as ITU-T H.266, also referred to as Versatile Video Coding (VVC). In other examples, video encoder 200 and video decoder 300 may operate according to a proprietary video codec / format, such as AOMedia Video 1 (AVI), extensions of AVI, and / or successor versions of AVI (e.g., AV2). In other examples, video encoder 200 and video decoder 300 may operate according to other proprietary formats or industry standards. The techniques of this disclosure, however, are not limited to any particular coding standard or format. In general, video encoder 200 and video decoder 300 may be configured to perform the techniques of this disclosure in conjunction with any video coding techniques that use an Advanced SBT mode.

[0047] In general, video encoder 200 and video decoder 300 may perform block-based coding of pictures. The term “block” generally refers to a structure including data to be processed (e.g., encoded, decoded, or otherwise used in the encoding and / or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. In general, video encoder 200 and video decoder 300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, rather than coding red, green, and blue (RGB) data for samples of a picture, video encoder 200 and video decoder 300 may code luminance and chrominance components, where the chrominance components may include both red hue and blue hue chrominance components. In some examples, video encoder 200 converts received RGB formatted data to a YUV representation prior to encoding, and video decoder 300 converts the YUV representation to the RGB format. Alternatively, pre- and post-processing units (not shown) may perform these conversions.

[0048] This disclosure may generally refer to coding (e.g., encoding and decoding) of pictures to include the process of encoding or decoding data of the picture. Similarly, this 1616-615WO01Qualcomm Ref. No. 2502091WO 11 / 58disclosure may refer to coding of blocks of a picture to include the process of encoding or decoding data for the blocks, e.g., prediction and / or residual coding. An encoded video bitstream generally includes a series of values for syntax elements representative of coding decisions (e.g., coding modes) and partitioning of pictures into blocks. Thus, references to coding a picture or a block should generally be understood as coding values for syntax elements forming the picture or block.

[0049] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video coder (such as video encoder 200) partitions a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video coder partitions CTUs and CUs into four equal, nonoverlapping squares, and each node of the quadtree has either zero or four child nodes. Nodes without child nodes may be referred to as “leaf nodes,” and CUs of such leaf nodes may include one or more PUs and / or one or more TUs. The video coder may further partition PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents partitioning of TUs. In HEVC, PUs represent inter-prediction data, while TUs represent residual data. CUs that are intra-predicted include intra-prediction information, such as an intra-mode indication.

[0050] As another example, video encoder 200 and video decoder 300 may be configured to operate according to VVC. According to VVC, a video coder (such as video encoder 200) partitions a picture into a plurality of CTUs. Video encoder 200 may partition a CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure or Multi-Type Tree (MTT) structure. The QTBT structure removes the concepts of multiple partition types, such as the separation between CUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. A root node of the QTBT structure corresponds to a CTU. Leaf nodes of the binary trees correspond to CUs.

[0051] In an MTT partitioning structure, blocks may be partitioned using a quadtree (QT) partition, a binary tree (BT) partition, and one or more types of triple tree (TT) (also called ternary tree (TT)) partitions. A triple or ternary tree partition is a partition where a block is split into three subblocks. In some examples, a triple or ternary tree partition divides a block into three subblocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT), may be symmetrical or asymmetrical.

[0052] When operating according to the AVI codec, video encoder 200 and video decoder 300 may be configured to code video data in blocks. In AVI, the largest coding block 1616-615WO01Qualcomm Ref. No. 2502091WO 12 / 58that can be processed is called a superblock. In AVI, a superblock can be either 128x128 luma samples or 64x64 luma samples. However, in successor video coding formats (e.g., AV2), a superblock may be defined by different (e.g., larger) luma sample sizes. In some examples, a superblock is the top level of a block quadtree. Video encoder 200 may further partition a superblock into smaller coding blocks. Video encoder 200 may partition a superblock and other coding blocks into smaller blocks using square or nonsquare partitioning. Non-square blocks may include N / 2xN, NxN / 2, N / 4xN, and NxN / 4 blocks. Video encoder 200 and video decoder 300 may perform separate prediction and transform processes on each of the coding blocks.

[0053] AVI also defines a tile of video data. A tile is a rectangular array of superblocks that may be coded independently of other tiles. That is, video encoder 200 and video decoder 300 may encode and decode, respectively, coding blocks within a tile without using video data from other tiles. However, video encoder 200 and video decoder 300 may perform filtering across tile boundaries. Tiles may be uniform or non-uniform in size. Tile-based coding may enable parallel processing and / or multi-threading for encoder and decoder implementations.

[0054] In some examples, video encoder 200 and video decoder 300 may use a single QTBT or MTT structure to represent each of the luminance and chrominance components, while in other examples, video encoder 200 and video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luminance component and another QTBT / MTT structure for both chrominance components (or two QTBT / MTT structures for respective chrominance components).

[0055] Video encoder 200 and video decoder 300 may be configured to use quadtree partitioning, QTBT partitioning, MTT partitioning, superblock partitioning, or other partitioning structures.

[0056] In some examples, a CTU includes a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples of a picture that has three sample arrays, or a CTB of samples of a monochrome picture or a picture that is coded using three separate color planes and syntax structures used to code the samples. A CTB may be an NxN block of samples for some value of N such that the division of a component into CTBs is a partitioning. A component is an array or single sample from one of the three arrays (luma and two chroma) that compose a picture in 4:2:0, 4:2:2, or 4:4:4 color format or the array or a single sample of the array that compose a picture in monochrome format. In1616-615WO01Qualcomm Ref. No. 2502091WO 13 / 58some examples, a coding block is an MxN block of samples for some values of M and N such that a division of a CTB into coding blocks is a partitioning.

[0057] The blocks (e.g., CTUs or CUs) may be grouped in various ways in a picture. As one example, a brick may refer to a rectangular region of CTU rows within a particular tile in a picture. A tile may be a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements (e.g., such as in a picture parameter set). A tile row refers to a rectangular region of CTUs having a height specified by syntax elements (e.g., such as in a picture parameter set) and a width equal to the width of the picture.

[0058] In some examples, a tile may be partitioned into multiple bricks, each of which may include one or more CTU rows within the tile. A tile that is not partitioned into multiple bricks may also be referred to as a brick. However, a brick that is a true subset of a tile may not be referred to as a tile. The bricks in a picture may also be arranged in a slice. A slice may be an integer number of bricks of a picture that may be exclusively contained in a single network abstraction layer (NAL) unit. In some examples, a slice includes either a number of complete tiles or a consecutive sequence of complete bricks of one tile.

[0059] This disclosure may use “NxN” and “N by N” interchangeably to refer to the sample dimensions of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, e.g., 16x16 samples or 16 by 16 samples. In general, a 16x16 CU will have 16 samples in a vertical direction (y = 16) and 16 samples in a horizontal direction (x = 16). Likewise, an NxN CU generally has N samples in a vertical direction and N samples in a horizontal direction, where N represents a nonnegative integer value. The samples in a CU may be arranged in rows and columns. Moreover, CUs need not necessarily have the same number of samples in the horizontal direction as in the vertical direction. For example, CUs may include NxM samples, where M is not necessarily equal toN.

[0060] Video encoder 200 encodes video data for CUs representing prediction and / or residual information, and other information. The prediction information indicates how the CU is to be predicted in order to form a prediction block for the CU. The residual information generally represents sample-by-sample differences between samples of the CU prior to encoding and the prediction block.1616-615WO01Qualcomm Ref. No. 2502091WO 14 / 58

[0061] To predict a CU, video encoder 200 may generally form a prediction block for the CU through inter-prediction or intra-prediction. Inter-prediction generally refers to predicting the CU from data of a previously coded picture, whereas intra-prediction generally refers to predicting the CU from previously coded data of the same picture. To perform inter-prediction, video encoder 200 may generate the prediction block using one or more motion vectors. Video encoder 200 may generally perform a motion search to identify a reference block that closely matches the CU, e.g., in terms of differences between the CU and the reference block. Video encoder 200 may calculate a difference metric using a sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or other such difference calculations to determine whether a reference block closely matches the current CU. In some examples, video encoder 200 may predict the current CU using uni-directional prediction or bi-directional prediction.

[0062] Some examples of VVC also provide an affine motion compensation mode, which may be considered an inter-prediction mode. In affine motion compensation mode, video encoder 200 may determine two or more motion vectors that represent non-translational motion, such as zoom in or out, rotation, perspective motion, or other irregular motion types.

[0063] To perform intra-prediction, video encoder 200 may select an intra-prediction mode to generate the prediction block. Some examples of VVC provide sixty-seven intraprediction modes, including various directional modes, as well as planar mode and DC mode. In general, video encoder 200 selects an intra-prediction mode that describes neighboring samples to a current block (e.g., a block of a CU) from which to predict samples of the current block. Such samples may generally be above, above and to the left, or to the left of the current block in the same picture as the current block, assuming video encoder 200 codes CTUs and CUs in raster scan order (left to right, top to bottom).

[0064] Video encoder 200 encodes data representing the prediction mode for a current block. For example, for inter-prediction modes, video encoder 200 may encode data representing which of the various available inter-prediction modes is used, as well as motion information for the corresponding mode. For uni-directional or bi-directional inter-prediction, for example, video encoder 200 may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. Video encoder 200 may use similar modes to encode motion vectors for affine motion compensation mode.1616-615WO01Qualcomm Ref. No. 2502091WO 15 / 58

[0065] AVI includes two general techniques for encoding and decoding a coding block of video data. The two general techniques are intra prediction (e.g., intra frame prediction or spatial prediction) and inter prediction (e.g., inter frame prediction or temporal prediction). In the context of AVI, when predicting blocks of a current frame of video data using an intra prediction mode, video encoder 200 and video decoder 300 do not use video data from other frames of video data. For most intra prediction modes, video encoder 200 encodes blocks of a current frame based on the difference between sample values in the current block and predicted values generated from reference samples in the same frame. Video encoder 200 determines predicted values generated from the reference samples based on the intra prediction mode.

[0066] Following prediction, such as intra-prediction or inter-prediction of a block, video encoder 200 may calculate residual data for the block. The residual data, such as a residual block, represents sample by sample differences between the block and a prediction block for the block, formed using the corresponding prediction mode. Video encoder 200 may apply one or more transforms to the residual block, to produce transformed data in a transform domain instead of the sample domain. For example, video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to residual video data. Additionally, video encoder 200 may apply a secondary transform following the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal dependent transform, a Karhunen-Loeve transform (KLT), or the like. Video encoder 200 produces transform coefficients following application of the one or more transforms.

[0067] As noted above, following any transforms to produce transform coefficients, video encoder 200 may perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. By performing the quantization process, video encoder 200 may reduce the bit depth associated with some or all of the transform coefficients. For example, video encoder 200 may round an zz-bit value down to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, video encoder 200 may perform a bitwise right-shift of the value to be quantized.

[0068] Following quantization, video encoder 200 may scan the transform coefficients, producing a one-dimensional vector from the two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place higher energy (and 1616-615WO01Qualcomm Ref. No. 2502091WO 16 / 58therefore lower frequency) transform coefficients at the front of the vector and to place lower energy (and therefore higher frequency) transform coefficients at the back of the vector. In some examples, video encoder 200 may utilize a predefined scan order to scan the quantized transform coefficients to produce a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, video encoder 200 may perform an adaptive scan. After scanning the quantized transform coefficients to form the one-dimensional vector, video encoder 200 may entropy encode the one-dimensional vector, e.g., according to context-adaptive binary arithmetic coding (CABAC). Video encoder 200 may also entropy encode values for syntax elements describing metadata associated with the encoded video data for use by video decoder 300 in decoding the video data.

[0069] To perform CABAC, video encoder 200 may assign a context within a context model to a symbol to be transmitted. The context may relate to, for example, whether neighboring values of the symbol are zero-valued or not. The probability determination may be based on a context assigned to the symbol.

[0070] Video encoder 200 may further generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, to video decoder 300, e.g., in a picture header, a block header, a slice header, or other syntax data, such as a sequence parameter set (SPS), picture parameter set (PPS), or video parameter set (VPS). Video decoder 300 may likewise decode such syntax data to determine how to decode corresponding video data.

[0071] In this manner, video encoder 200 may generate a bitstream including encoded video data, e.g., syntax elements describing partitioning of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Ultimately, video decoder 300 may receive the bitstream and decode the encoded video data.

[0072] In general, video decoder 300 performs a reciprocal process to that performed by video encoder 200 to decode the encoded video data of the bitstream. For example, video decoder 300 may decode values for syntax elements of the bitstream using CABAC in a manner substantially similar to, albeit reciprocal to, the CABAC encoding process of video encoder 200. The syntax elements may define partitioning information for partitioning of a picture into CTUs, and partitioning of each CTU according to a corresponding partition structure, such as a QTBT structure, to define CUs of the CTU. The syntax elements may further define prediction and residual information for blocks (e.g., CUs) of video data.1616-615WO01Qualcomm Ref. No. 2502091WO 17 / 58

[0073] The residual information may be represented by, for example, quantized transform coefficients. Video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of a block to reproduce a residual block for the block. Video decoder 300 uses a signaled prediction mode (intra- or inter-prediction) and related prediction information (e.g., motion information for inter-prediction) to form a prediction block for the block. Video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. Video decoder 300 may perform additional processing, such as performing a deblocking process to reduce visual artifacts along boundaries of the block.

[0074] Any of the video encoding or video decoding processes described above may be performed using a neural network (NN). Additionally or alternatively, a neural network may be trained to efficiently compress video data without necessarily separately performing prediction and residual coding. Studies have shown that embedding neural networks into the hybrid video coding framework of video encoder 200 and video decoder 300 can improve compression efficiency. Neural networks may be used for intraprediction and inter-prediction to improve the prediction efficiency. NN-based in-loop filtering and / or post-filtering have also performed well in heuristic testing.

[0075] For example, video encoder 200 and video decoder may use one or more NN-based filters for existing filters, such as deblocking filters, sample adaptive offset (SAO), and / or adaptive loop filtering (ALF). NN-based filters can also be applied exclusively, where NN-based filters are designed to replace all of the existing filters. Additionally or alternatively, NN-based filters may be designed to supplement, enhance, or replace any or all of the other filters.

[0076] In some examples, an NN-based filter may be a convolutional neural network (CNN)-based filter with multiple layers. An NN-based filtering process may take reconstructed samples as inputs, and may add the intermediate outputs back to the inputs to refine the input samples. The NN-based filter may use all color components (e.g., Y, U, and V, or Y, Cb, and Cr) as inputs to exploit cross-component correlations. Different color components may share the same filters (including network structure and model parameters) or each component may have its own specific filters.

[0077] The filtering process can also be generalized as follows:7?'(i,j) = R(i,j) + NN_filter_residual_ouput R) Here, R(i, j) represents a reconstructed sample at position (i, j) in the picture, R’(i, j) represents the filtered version of the reconstructed sample, and 1616-615WO01Qualcomm Ref. No. 2502091WO 18 / 58NN filter residual output(R) represents the intermediate samples discussed above that are calculated by the NN filter. The model structure and model parameters of NN-based filter(s) can be pre-defined and be stored at video encoder 200 and video decoder 300. The filters can also be signalled in the bitstream.

[0078] In some examples, an NN-based filter may include a series of feature extraction layers, followed by an output convolution. The feature extraction layers may include a 3x3 convolution (conv) layer followed by a parametric rectified linear unit (PReLU) layer. The convolutional layer applies a convolution operation to the input data, which involves a filter or kernel processing the input data (e.g., the reconstruction samples) in a sliding window fashion and computing dot products at each position. The convolution operation essentially captures local patterns within the input data. For example, in the context of image processing, these patterns could be edges, textures, or other visual features. The filter or kernel is a small matrix of weights that gets updated during the training process. By sliding this filter across the input data (or feature map from a previous layer) and computing the dot product at each position, the convolutional layer creates a feature map that encodes spatial hierarchies and patterns detected in the input. The output of a convolutional layer is a set of feature maps, each corresponding to one filter, capturing different aspects of the input data. This layer helps the neural network to learn increasingly complex and abstract features as the data passes through deeper layers of the network.

[0079] The PReLU layer is an activation function used in neural networks, and is a variant of the ReLU (Rectified Linear Unit) activation function. As described above, the convolution layer outputs feature maps, each corresponding to one filter, representing detected features in the input. Following the convolution layer, the PReLU layer applies the PReLU activation function to each element of the feature maps produced by the convolution layer. For positive values, the PReLU layer acts like a standard ReLU, passing the value through. For negative values, instead of setting them to zero (e.g., as ReLU does), the PReLU layer allows a small, linear, negative output. This keeps neurons of the NN active and maintains the gradient flow, which can be beneficial for learning in deep networks.

[0080] When NN-based filtering is applied in video coding, the whole video signal (pixel data) may be split into multiple processing units (e.g., 2D blocks), and each processing unit can be processed separately or be combined with other information associated with this block of pixels. For example, a processing unit may be a frame, a slice / tile, a CTU, 1616-615WO01Qualcomm Ref. No. 2502091WO 19 / 58or any pre-defined or signaled shapes and sizes. Typically, NN-based filtering is performed on reconstructed blocks of video data. Here, reconstructed blocks and samples may refer to both decoded blocks produced by video decoder 300, as well as blocks reconstructed in a reconstruction loop of video encoder 200.

[0081] To further improve the performance of NN-based filtering, different types of input data can be processed jointly to produce the filtered output. Input data may include, but is not limited to, reconstruction pixels / samples, prediction pixels / samples, pixels / samples after the loop filter(s), partitioning structure information, deblocking parameters (e.g., boundary strength (BS)), quantization parameter (QP) values, slice or picture types, or a filters applicability or coding modes map. Input data can be provided at different granularities. Luma reconstruction and prediction samples may be provided at the original resolution, whereas chroma samples may be provided at lower resolution, e.g. for 4:2:0 representation, or can be up-sampled to the Luma resolution to achieve per-pixel representation. Similarly, QP, BS, partitioning, or coding mode information can be provided at lower resolution, including cases with a single value per frame, slice or processing block (e.g. QP). In other examples, QP, BS, partitioning, or coding mode information can be expanded (e.g., replicated) to achieve per-pixel / sample representation.

[0082] To further improve the performance of NN-based filtering, multi-mode solutions can be used. For example, for each processing unit, video encoder 200 may select a mode from a set of modes based on rate-distortion optimization and signal the selected mode in the bitstream. The different modes may include different NN models, different values that may be used as the input information of the NN models, etc. In one example, video encoder 200 and video decoder 300 may use an NN-based filtering solution with multiple modes based on a single NN model by using different QP values as input to the NN model for different modes.

[0083] This disclosure may generally refer to “signaling” certain information, such as syntax elements. The term “signaling” may generally refer to the communication 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 the bitstream. In general, signaling refers to generating a value in the bitstream. As noted above, source device 102 may transport the bitstream to destination device 116 substantially in real time, or not in real time, such as might occur when storing syntax elements to storage device 112 for later retrieval by destination device 116.1616-615WO01Qualcomm Ref. No. 2502091WO 20 / 58

[0084] In accordance with the techniques of this disclosure, a method includes applying a subblock transform mode to a current block of video data according to any of the techniques described herein.

[0085] In accordance with the techniques of this disclosure, a device includes one or more memories configured to store video data and one or more processors operatively coupled to the one or more memories, the one or more processors being configured to apply a subblock transform mode to a current block of video data according to any of the techniques described herein.

[0086] In accordance with the techniques of this disclosure, a device includes at least one means for applying a subblock transform mode to a current block of video data according to any of the techniques described herein.

[0087] In accordance with the techniques of this disclosure, computer-readable storage media is encoded with instructions that, when executed, cause one or more programmable processors to apply a subblock transform mode to a current block of video data according to any of the techniques described herein.

[0088] The techniques of this disclosure may be applied to residual coding of the blocks in video codecs, and may be applicable to any codecs in general, particularly for VVC, Enhanced Compression Model (ECM), AVI, AV2 and future codecs.

[0089] Subblock transform mode is now discussed. Video encoder 200 or video decoder 300 may apply subblock transform mode. In VVC, subblock transform mode is adopted, for example described in X. Zhao et al, “Transform Coding in the VVC Standard”, IEEE Trans. Circuits Syst. Video Technol., vol. 31, no. 10, pp. 3878-3890, Oct. 2021. Video encoder 200 or video decoder 300 may implement subblock transform mode and partition a transform block.

[0090] FIG. 2 is a conceptual diagram illustrating example subblock transform (SBT) modes including (a) the eight SBT modes in VVC and (b) additional SBT modes studied during VVC standardization. In the example subblock transform mode of VVC, the transform block can be partitioned into either horizontal binary splits or vertical binary splits, where the resulting subblocks have a size that is one-half or one-quarter of the height and / or width of the transform block.

[0091] As shown in FIG. 2, example vertical partitions include subblock partition 520, which is a left side vertical split with one-half the width of the transform block, subblock partition 522 which is a right side vertical split with one-half the width of the transform block, subblock partition 524, which is a left side vertical split with one-quarter the width 1616-615WO01Qualcomm Ref. No. 2502091WO 21 / 58of the transform block, and subblock partition 526 which is a right side vertical split with one-quarter the width of the transform block. Example horizontal partitions include subblock partition 530, which is a top side horizontal split with one-half the height of the transform block, subblock partition 532 which is a bottom side horizontal split with one-half the height of the transform block, subblock partition 534, which is a top side horizontal split with one-quarter the height of the transform block, and subblock partition 536 which is a bottom side horizontal split with one-quarter the height of the transform block.

[0092] In another example, a transform block may be partitioned into a quad tree, where the size of the resulting subblocks are width / 2 or height / 2, where width and height are the width and height of the transform blocks. As shown in FIG. 2, one example quadtree split results in subblock 540 in the upper left quadrant of the transform block. Another quadtree split results in subblock 542 in the upper right quadrant of the transform block. Another quadtree split results in subblock 544 in the lower left quadrant of the transform block. Another quadtree split results in subblock 546 in the lower right quadrant of the transform block.

[0093] In other examples, the transform block may be partitioned with a ternary split. As shown in FIG. 2, a transform block may be partitioned into three subblocks, with a center vertical subblock 550 having non-zero residual values. In another example, a transform block may be partitioned into three subblocks, with a center horizontal subblock 552 having non-zero residual values. In other examples, of ternary splits, the upper, lower, left or right subblocks may include the non-zero residual values.

[0094] In all of the examples of FIG. 2, the shaded and numbered subblock partitions are partitions that have non-zero residual values. The other subblock partitions (unshaded) may have zeroed out residual values.

[0095] FIG. 2 also shows example transform kernel types for the various subblocks partitions, including discrete sine transform (DST) Type 7 (DST-7) and DCT Type 8 (DCT-8) transform kernels in the horizontal or vertical direction. In some examples, video encoder 200 and video decoder 300 may be configured to implicitly determine the transform kernels for horizontal and vertical transforms based on the split type. In one example of the subblock transform mode for VVC, only one subblock partition of a transform block may have a residual, while other subblock partitions of the transform block are assumed to have a zero residual. In this case, the transform is applied to the non-1616-615WO01Qualcomm Ref. No. 2502091WO 22 / 58zero subblock partition. The choice of the subblock which has a residual may be signaled to the video decoder.

[0096] Advanced subblock transform (SBT) mode is now described. Video encoder 200 or video decoder 300 may apply Advanced SBT mode. The principle of the Advanced SBT mode, described in Guillaume Laroche, Patrice Onno, "EE2: Tests 3.3 on Advanced SBT with direction and position inference", JVET- AK0131, January 2025, is to determine the position and the direction of a subblock partition based on the inter prediction block. The possible subblock partitions are the same as those of SBT in the VVC specifications. However, the proposed Advanced SBT infers the position and the direction of the subblock partitioning to save some signaling (e.g., reduce signaling from video encoder 200 to video decoder 300). For example, video decoder 300 implementing Advanced SBT may infer the position and direction of subblock partitioning rather than parse syntax element(s) in a bitstream to determine the position and direction of subblock partitioning.

[0097] FIG. 3 is a conceptual diagram illustrating an example general principle of Advanced SBT at an encoder. For each subblock size and direction, video encoder 200 may evaluate the best (e.g., preferred) position of the transform part (e.g., shaded area) of a block. Then, based on the best position, video encoder 200 may determine the direction for each subdivision. Eventually, video encoder 200 determines the best (e.g., preferred) subdivision.

[0098] For example, video encoder 200 may select the position of subblock 562 and the position of subblock 566 as the best positions and directions for the respective sizes of the subblocks 562 and 566. Video encoder 200 may perform rate distortion (RD) selection 560 to select subblock 566 as the best subdivision.

[0099] For example, the position selected by video encoder 200 is the position of the subblock which maximizes the sum of gradients obtained on the corresponding inter predictor block. Regarding the direction (vertical or horizontal), the selected direction is the one that maximizes the sum of gradients of each best position.

[0100] In this example, video encoder 200 or video decoder 300 may apply a subblock transform (which in the case of video decoder 300 may be an inverse transform) to subblock 566. Video encoder 200 or video decoder 300 may assume that any other subblocks of the block have zero coefficients and may not apply a subblock transform to such other subblocks.1616-615WO01Qualcomm Ref. No. 2502091WO 23 / 58

[0101] In essence, Advanced SBT mode provides video encoder 200 or video decoder 300 with the ability to “shift” a subblock location around within the block when selecting the single subblock to which to apply the subblock transform. This is in contrast to the SBT mode of VVC where the subblock to which to apply the subblock transform is limited to specific subblock locations, such as those shown in FIG. 2.

[0102] Compared to the SBT mode of VVC, the subblock subdivision is signaled if the enabled flag of the proposed Advanced SBT mode is true. The proposed Advanced SBT mode is signaled at TU level and is also allowed for SBT TUs with residuals in order to obtain a smaller subblock residual. The enabled flag and the subdivision flags are CAB AC-coded and the context probability increment value depends on the use of SBT.

[0103] The Advanced SBT mode may not be allowed for intra slices and for some inter modes, such as combined inter-intra prediction (CUP) and geometric partitioning mode (GPM). The Advanced SBT mode may also be disabled for low-frequency non-separable transform (LFNST) and multi -transform selection (MTS) and for Screen Content sequences, based on or due to an SPS flag. In some examples, the Advanced SBT mode is applied only for the luma component.

[0104] It should be noted that the implementation of this SBT mode (e.g., Advanced SBT mode) has no parsing issue even if the position and the direction is based on the inter predictor block. To reduce the encoding time, some early encoder terminations may also be used to limit the number of evaluations of this proposed Advanced SBT mode.

[0105] A Sobel gradient is now described. A Sobel operator uses kernels and a convolution operation to detect edges in an image. The algorithm works with two kernels:1. A kernel to approximate intensity change in the x-direction (horizontal) 2. A kernel to approximate intensity change at a pixel in the y-direction (vertical).

[0106] As used herein, “approximating the intensity change” may mean approximating the gradient of the intensity values at a pixel. The gradient is the multivariable generalization of the derivative or slope.

[0107] FIG. 4 is a conceptual diagram illustrating two example kernels used in a Sobel algorithm. For example, kernel 570 may be an example x-direction kernel and kernel 572 may be an example y-direction kernel. Kernel 570 and kernel 572 of FIG. 4 may be convolved with each pixel in the original image to identify the regions where the change (gradient) is maximized in magnitude in the x and y directions. For example, video encoder 200 may convolve kernels 570 and 572 with each pixel in the original image.1616-615WO01Qualcomm Ref. No. 2502091WO 24 / 58

[0108] An image continuity measure is now described. FIG. 5 is a conceptual diagram illustrating an example image continuity measure. FIG. 5 shows a reconstructed block 584 (which may be a reconstruction hypothesis) including a plurality of reconstructed pixels and previously reconstructed pixels 582 two columns of which are to the left of reconstructed block 584 and two rows of which are above reconstructed block 584. As shown in FIG. 5, for each reconstructed pixel po,yof reconstructed block 584 at the left hand side of reconstructed block 584, a simple linear prediction using the two pixels of previously reconstructed pixels 582 to the left is performed to obtain its prediction predo.y = (2p-i,y- p~2,y). The absolute difference between this prediction and the reconstructed pixel po,yis used as the measure of continuity. For example, for pixel po.3, video encoder 200 may determine predo.s = (2p-i,3 - p-2,3). Video encoder 200 may then determine a measure of continuity as \ predo.s -po,s\.

[0109] Similar processing occurs for pixels in the top row of reconstructed block 584, summing the absolute differences of each prediction predx,o = (2px,-i - px,-2) and reconstructed pixel px,o. For example, for pixel po.o, video encoder 200 may determine predo.o = (2po,-i - po,-2). Video encoder 200 may then determine a measure of continuity as \predo,o -po,o\.

[0110] In the current design of Advanced SBT, a brute force search technique is used. The gradient value of the whole subblock is added up for each position and direction and a search step of one row / column is used for all subblock shapes. For example, video encoder 200 may determine:costThe subblock position and direction that provide the largest summation of gradient values are used. This brute force search technique requires relatively high complexity. Also, the representative Advanced SBT does not support all subblock shapes. Only the subblock shapes of Width * Height / N and Width / N * Height are supported. However, for the subblock shape of Width / N * Height / N, the representative Advanced SBT is not applied.

[0111] Finally, when deciding the best position and direction, only the gradient value from the predictor is being considered. However, the position and direction can be decided after an inverse transform where the residual information is available. For example, under the representative Advanced SBT, video encoder 200 may only use the gradient value from the predictor when deciding a best position and direction for a subblock.1616-615WO01Qualcomm Ref. No. 2502091WO 25 / 58

[0112] The disclosed techniques addressing the above-mentioned problems may be used individually or in any combination.

[0113] An improved search technique is now described. Video encoder 200 or video decoder 300 may perform a search using the improved search technique described herein. When searching for the best position and direction, in one example, instead of global searching that searches among all the possible subblock positions, a localized search technique is used for a potential subblock. When deriving the gradient value for the transform block, the coordinate with the maximum gradient value is found. Afterwards, when searching for the best position and direction, the coordinate is used as the center position of the subblock and a localized search with a search range of M rows and / or N columns around the center position is performed. For example, video encoder 200 or video decoder 300 may find the coordinate with the maximum gradient value. Video encoder 200 or video decoder 300 may then use that coordinate as a center position of a potential subblock and perform a localized search with a search range of M rows and / or N columns around the center position to determine the best position and / or best direction. Video encoder 200 or video decoder 300 may use the best position and / or best direction to determine a subblock (e.g., a single subblock) of the block to which to apply a subblock transform. Video encoder 200 or video decoder 300 may split the current block into a plurality of subblocks. The plurality of subblocks may include the single subblock. When coding the plurality of subblocks, video encoder 200 or video decoder 300 may apply a transform (e.g., a transform or an inverse transform) to the single subblock.

[0114] In some examples, video encoder 200 or video decoder 300 may use the gradient values to derive only a subset of the transformation parameters. For instance, video encoder 200 or video decoder 300 may use the gradient derivation techniques described herein to determine only the direction (e.g., horizontal or vertical) of the subblock, while the position of the subblock is signaled in the bitstream or determined via another technique. In another example, video encoder 200 or video decoder 300 may use the gradient derivation techniques to determine only the position of the subblock, while the direction is signaled in the bitstream or determined via another technique. In yet other examples, video encoder 200 or video decoder 300 uses the gradient values to derive both the position and the direction of the subblock.

[0115] FIG. 6 is a conceptual diagram illustrating an example of an improved gradient search according to one or more aspects of this disclosure. Video encoder 200 or video decoder 300 may implement the gradient search of FIG. 6. For example, TU 590 is shown.1616-615WO01Qualcomm Ref. No. 2502091WO 26 / 58Video encoder 200 or video decoder 300 may determine the maximum gradient point 592 which video encoder 200 or video decoder 300 may use as a center position of residual subblock 594. Residual subblock 594 may be referred to herein as a potential subblock because residual subblock may or may not be a subblock to which a subblock transform is applied. Video encoder 200 may search in search area 596 which may be located above and below and / or left and right of subblock 594. For example, search area 596 may include M rows where M may be equal to or greater than 1. In some examples, where the search area is vertical, rather than horizontal, the search area may include N columns where N may be equal to or greater than 1.

[0116] In another example, when computing the gradient summation for the subblocks, for example as in the representative example of Advanced SBT, instead of adding up all the gradient values of the whole subblock, a sub-set of the gradient values are used. For example, video encoder 200 or video decoder 300 may add up a sub-set of the gradient values rather than all of the gradient values when determining a gradient summation for subblocks.

[0117] Improved position derivation is now described. Video encoder 200 or video decoder 300 may implement the improved position derivation techniques of this disclosure. The direction information of a subblock may be needed to correctly perform an inverse coefficient transform. However, the position of the residual can be derived after the inverse transform is applied so that the residual information can be used as additional information other than the gradient value of the prediction.

[0118] A continuity measure may be used to decide (e.g., determine) the best (e.g., preferred) position of the residual block. Each time, the residual subblock is added to one position of the coding block, and a continuity cost is used to determine the best residual subblock position. For example, video encoder 200 may use a continuity cost to determine a best residual subblock position.

[0119] In one example, regardless of the position of the residual subblock, the reconstructed samples from the above coding block and the left coding block are always used in the continuity cost computation, while the reconstructed samples within the current residual subblock used are based on the position of the residual subblock. In a second example, the reconstructed samples outside of the residual subblock to be used are also dependent on the location of the residual subblocks. Instead of always using the reconstructed samples from above the coding block and left of the coding block, the rows above the residual subblock or the columns to the left of the residual subblock are used, 1616-615WO01Qualcomm Ref. No. 2502091WO 27 / 58because in SBT mode the residuals outside of the residual subblock are all 0, and therefore the prediction result may be the same as a reconstruction result outside of the residual subblock.

[0120] In some examples, the techniques for deriving the position of the subblock based on residual information may be used in conjunction with transform coefficient sign prediction. For instance, if the signs of the transform coefficients are not explicitly signaled, video encoder 200 or video decoder 300 may assume a default sign (e.g., positive) to generate the residual block and the subsequent reconstructed block. This hypothesis reconstruction is then evaluated using the continuity measure to determine the optimal position of the subblock.

[0121] A simplified gradient is now described. Video encoder 200 or video decoder 300 may implement the simplified gradient described herein. In one example, to reduce the complexity of the Sobel gradient, instead of using 6 tap filters, video encoder 200 or video decoder 300 may use 2 tap filters. FIG. 7 is a conceptual diagram illustrating an example of two tap filters according to one or more aspects of this disclosure. For example, video encoder 200 or video decoder 300 may use the 2 tap filters 600 and / or 602 of FIG. 7.

[0122] In one example, one of the directional gradients is determined using the above and below samples of the current sample.Gradient = a*nl - b*n2For example, video encoder 200 or video decoder 300 may determine one of the direction gradients using filter 602 and the above and below samples of the current sample.

[0123] In another example, one of the directional gradients is determined using the left and right samples of the current sample.Gradient = a*nl - b*n2For example, video encoder 200 or video decoder 300 may determine one of the direction gradients using filter 600 and the left and right samples of the current sample.

[0124] In one example, one of the directional gradients is determined using the current and below samples of the current sample.Gradient = a*c - b*n2For example, video encoder 200 or video decoder 300 may determine one of the direction gradients using filter 602 and the current sample and the below sample of the current sample.

[0125] In another example, one of the directional gradients is determined using the current and right samples of the current sample1616-615WO01Qualcomm Ref. No. 2502091WO 28 / 58Gradient = a*c - b*n2For example, video encoder 200 or video decoder 300 may determine one of the direction gradients using filter 600 and the current sample and the right sample of the current sample.

[0126] In one example, one of the directional gradients is determined using the current and above samples of the current sample.Gradient = a*nl - b*cFor example, video encoder 200 or video decoder 300 may determine one of the direction gradients using filter 602 and the current sample and the above sample of the current sample.

[0127] In another example, one of the directional gradients is determined using the current and left samples of the current sampleGradient = a*nl - b*cFor example, video encoder 200 or video decoder 300 may determine one of the direction gradients using filter 600 and the current sample and the left sample of the current sample.

[0128] In another example, one of the directional gradients is determined using two diagonal samples, with or without the current sample. For example, video encoder 200 or video decoder 300 may determine one of the direction gradients using two diagonal samples, which may or may not include the current sample.

[0129] In another example, one of the directional gradients is determined using two antidiagonal samples, with or without the current sample. For example, video encoder 200 or video decoder 300 may determine one of the direction gradients using two antidiagonal samples, which may or may not include the current sample.

[0130] In some examples, the final gradient is the magnitude of two gradients, which can be any two from the above-described gradients. For example, video encoder 200 or video decoder 300 may determine the final gradient based on the magnitude of two directional gradients. In some examples, video encoder 200 or video decoder 300 may determine the final gradient based on the following formula:Gradient magnitude = gradientl*gradientl + gradient2*gradient2

[0131] In the above examples, the a and b are two numbers that can be either positive or negative, nl is neighbor 1, n2 is neighbor 2, and c is the current sample in FIG. 7.

[0132] An Advanced SBT extension is now described. FIG. 8 is a conceptual diagram illustrating example, width / N * height / N subblocks according to one or more aspects of this disclosure. Advanced SBT may be extended to Width / N * Height / N sized subblocks.1616-615WO01Qualcomm Ref. No. 2502091WO 29 / 58For example, N may be 2 or 4 as shown in FIG. 8. For example, Advanced SBT may be extended to be able to be used for subblock 612 and subblock 614 of block 610. N is 2 for subblock 612 where the width and height of subblock 612 are both half of that of block 610. N is 4 for subblock 614 where the width and height of subblock 614 are both a quarter of that of block 610. Video encoder 200 or video decoder 300 may implement this Advanced SBT extension.

[0133] In one example, a flag may be signaled to indicate if both width and height size are changed. For example, video encoder 200 may signal a flag in a bitstream to indicate to video decoder 300 if both the width and height of a subblock are different than the width and height of the block. In yet another example, another technique may be used to indicate if both width and height size are changed. In yet another example, the Advanced SBT extension techniques of this disclosure may be applied to certain block sizes. For example, for some block sizes video encoder 200 or video decoder 300 may apply the Advanced SBT extension techniques described herein, while for other block sizes, video encoder 200 or video decoder 300 may not. In other words, application of the Advanced SBT extension techniques may be based on block size.

[0134] Gradient padding is now described. When computing the gradient value using either a Sobel gradient or a simplified gradient derivation technique, additional rows or columns outside of the current CU may, in some examples, be needed. However, these samples may not be available. Therefore, padding may be used to derive the gradient values for boundary positions in the CU. In one example, repetitive padding is used. For example, the samples in the first row are used to pad above, first column samples are used to pad left, last column samples are used to pad right, and bottom row samples are used to pad below, as needed. For example, video encoder 200 or video decoder 300 may use repetitive padding to pad the samples outside of the current CU.

[0135] In a second example, instead of padding the sample values, the gradient value is padded. In a first step, the gradient values are derived for all positions in the CU except for the first and last row and column. Afterwards, the gradient values are used to perform the repetitive padding on the first and last row and column. For example, video encoder 200 or video decoder 300 may pad the gradient values.

[0136] In another example, zero padding is performed after the derivation of the gradient value except for the first and last row and column. This is equivalent to not considering the first and last row and column when searching for the maximum gradient positions. For example, video encoder 200 or video decoder 300 may perform zero padding.1616-615WO01Qualcomm Ref. No. 2502091WO 30 / 58

[0137] FIG. 9 is a flowchart illustrating example Advanced subblock transform techniques according to one or more aspects of this disclosure. The techniques of FIG. 9 may be performed by video encoder 200 or video decoder 300. For purposes of this description, these techniques are described in the context of video decoder 300.

[0138] Video decoder 300 may determine to apply a subblock transform mode to a current block of the video data (700). For example, video encoder 200 may determine that subblock transform mode should be applied to a current block for efficiency purposes and may signal one or more syntax elements in a bitstream to video decoder 300. Video decoder 300 may determine to apply the subblock transform mode based on, for example, the one or more syntax elements signaled in the bitstream.

[0139] Video decoder 300 may determine, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value (702). For example, video decoder 300 may determine one or more gradient values for the transform block. In some examples, video decoder 300 determines the gradient value using a Sobel gradient, which may be a simplified Sobel gradient using two tap filters as described with reference to FIG. 7.

[0140] Video decoder 300 may perform a search for a position and a direction using the coordinate as a center position of a potential subblock (704). For example, video decoder 300 may use a localized search, as opposed to a global search that evaluates all possible subblock positions. The example localized search may include a search range of at least one of M rows or N columns around the potential subblock.

[0141] Video decoder 300 may divide the current block into a plurality of subblocks based on the position and direction (706). For example, video decoder 300 may divide the block into the plurality of subblocks based on the position and direction determined from the search. The plurality of subblocks may include a single subblock to which a subblock transform is to be applied. In some examples, the other subblocks of the plurality of subblocks are assumed to have zero residual.

[0142] Video decoder 300 may decode the plurality of subblocks based on the subblock transform mode (708). For example, video decoder 300 may apply an inverse subblock transform to the single subblock determined from the search.

[0143] In some examples, video decoder 300 may apply the subblock transform to the single subblock. In some examples, as part of performing the search, video decoder 300 may determine a gradient summation for the potential subblock, wherein the gradient summation includes the sum of gradient values of a subset of gradient values for the 1616-615WO01Qualcomm Ref. No. 2502091WO 31 / 58potential subblock, wherein the subset includes fewer gradient values than a total number of gradient values for the potential subblock.

[0144] In some examples, as part of performing the search, video decoder 300 may apply an inverse transform to the potential subblock and determine the position after applying the inverse transform to the potential subblock based on residual information.

[0145] In some examples, video decoder 300 may determine a continuity measure. As part of determining the continuity measure, video decoder 300 may use reconstructed samples from an above coding block and a left coding block. Video decoder 300 may use reconstructed samples within the potential subblock based on a position of the potential subblock.

[0146] In some examples, as part of performing the search, video decoder 300 may determine, based on the position of the potential subblock, whether to use reconstructed samples from an above coding block or a left coding block. Video decoder 300 may determine, based on a determination to use reconstructed samples from the above coding block, a continuity measure using the reconstructed samples from the above coding block.

[0147] In some examples, as part of determining the coordinate for the current block having the maximum gradient value, video decoder 300 may determine a Sobel gradient using two tap filters.

[0148] In some examples, the Sobel gradient includes at least one of: a directional gradient using an above sample and a below sample of a current sample according to Gradient = a*nl - b*n2; a directional gradient using a left sample and a right sample of the current sample according to Gradient = a*nl - b*n2; a directional gradient using the current sample and the below sample of the current sample according to Gradient = a*c - b*n2; a directional gradient using the current sample and the right sample of the current sample according to Gradient = a*c - b*n2; a directional gradient using the current sample and the above sample of the current sample according to Gradient = a*nl - b*c; or a directional gradient using the current sample and the left sample of the current sample according to Gradient = a*nl - b*c, wherein a and b are numbers, nl is neighbor 1, n2 is neighbor 2, and c is the current sample.

[0149] In some examples, the Sobel gradient includes a final gradient, wherein the final gradient includes a magnitude of two directional gradients. In some examples, as part of determining the Sobel gradient, video decoder 300 may apply padding. In some examples, as part of applying padding, video decoder 300 may apply repetitive padding, gradient value padding, or zero padding.1616-615WO01Qualcomm Ref. No. 2502091WO 32 / 58

[0150] In some examples, the single subblock includes a width equal to a width of the current block divided by N and having a height equal to a height of the current block divided by N.

[0151] FIG. 10 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. FIG. 10 is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video encoder 200 according to the techniques of VVC and HEVC. However, the techniques of this disclosure may be performed by video encoding devices that are configured to other video coding standards and video coding formats, such as AVI and successors to the AVI video coding format.

[0152] In the example of FIG. 10, video encoder 200 includes video data memory 230, mode selection unit 202, residual generation unit 204, transform processing unit 206, quantization unit 208, inverse quantization unit 210, inverse transform processing unit 212, reconstruction unit 214, filter unit 216, decoded picture buffer (DPB) 218, and entropy encoding unit 220. Any or all of video data memory 230, mode selection unit 202, residual generation unit 204, transform processing unit 206, quantization unit 208, inverse quantization unit 210, inverse transform processing unit 212, reconstruction unit 214, filter unit 216, DPB 218, and entropy encoding unit 220 may be implemented in one or more processors or in processing circuitry. For instance, the units of video encoder 200 may be implemented as one or more circuits or logic elements as part of hardware circuitry, or as part of a processor, ASIC, or FPGA. Moreover, video encoder 200 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0153] Video data memory 230 is an example of a memory system that may store video data to be encoded by the components of video encoder 200. Video encoder 200 may receive the video data stored in video data memory 230 from, for example, video source 104 (FIG. 1). DPB 218 is an example of a memory system that may act as a reference picture memory that stores reference video data for use in prediction of subsequent video data by video encoder 200. Video data memory 230 and DPB 218 may each be formed by any of a variety of one or more memory devices or memory units, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Video data memory 230 and DPB 218 may be provided by the same memory 1616-615WO01Qualcomm Ref. No. 2502091WO 33 / 58device or separate memory devices. In various examples, video data memory 230 may be on-chip with other components of video encoder 200, as illustrated, or off-chip relative to those components.

[0154] In this disclosure, reference to video data memory 230 should not be interpreted as being limited to memory internal to video encoder 200, unless specifically described as such, or memory external to video encoder 200, unless specifically described as such. Rather, reference to video data memory 230 should be understood as reference memory that stores video data that video encoder 200 receives for encoding (e.g., video data for a current block that is to be encoded). Memory 106 of FIG. 1 may also provide temporary storage of outputs from the various units of video encoder 200.

[0155] The various units of FIG. 10 are illustrated to assist with understanding the operations performed by video encoder 200. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. In some examples, one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits.

[0156] Video encoder 200 may include arithmetic logic units (ALUs), elementary function units (EFUs), digital circuits, analog circuits, and / or programmable cores, formed from programmable circuits. In examples where the operations of video encoder 200 are performed using software executed by the programmable circuits, memory 106 (FIG. 1) may store the instructions (e.g., object code) of the software that video encoder 200 receives and executes, or another memory within video encoder 200 (not shown) may store such instructions.

[0157] Video data memory 230 is configured to store received video data. Video encoder 200 may retrieve a picture of the video data from video data memory 230 and provide the video data to residual generation unit 204 and mode selection unit 202. Video data in video data memory 230 may be raw video data that is to be encoded.1616-615WO01Qualcomm Ref. No. 2502091WO 34 / 58

[0158] Mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra-prediction unit 226. Mode selection unit 202 may include additional functional units to perform video prediction in accordance with other prediction modes. As examples, mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of motion estimation unit 222 and / or motion compensation unit 224), an affine unit, a linear model (LM) unit, or the like.

[0159] Mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and resulting rate-distortion values for such combinations. The encoding parameters may include partitioning of CTUs into CUs, prediction modes for the CUs, transform types for residual data of the CUs, quantization parameters for residual data of the CUs, and so on. Mode selection unit 202 may ultimately select the combination of encoding parameters having rate-distortion values that are better than the other tested combinations.

[0160] Video encoder 200 may partition a picture retrieved from video data memory 230 into a series of CTUs, and encapsulate one or more CTUs within a slice. Mode selection unit 202 may partition a CTU of the picture in accordance with a tree structure, such as the MTT structure, QTBT structure, superblock structure, or the quad-tree structure described above. As described above, video encoder 200 may form one or more CUs from partitioning a CTU according to the tree structure. Such a CU may also be referred to generally as a “video block” or “block.”

[0161] In general, mode selection unit 202 also controls the components thereof (e.g., motion estimation unit 222, motion compensation unit 224, and intra-prediction unit 226) to generate a prediction block for a current block (e.g., a current CU, or in HEVC, the overlapping portion of a PU and a TU). For inter-prediction of a 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 coded pictures stored in DPB 218). In particular, motion estimation unit 222 may calculate a value representative of how similar a potential reference block is to the current block, e.g., according to sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or the like. Motion estimation unit 222 may generally perform these calculations using sample-by-sample differences between the current block and the reference block being considered. Motion estimation unit 222 may identify a reference block having a lowest value resulting from1616-615WO01Qualcomm Ref. No. 2502091WO 35 / 58these calculations, indicating a reference block that most closely matches the current block.

[0162] Motion estimation unit 222 may form one or more motion vectors (MVs) that defines the positions of the reference blocks in the reference pictures relative to the position of the current block in a 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, whereas for bi-directional inter-prediction, motion estimation unit 222 may provide two motion vectors. Motion compensation unit 224 may then generate a prediction block using the motion vectors. For example, motion compensation unit 224 may retrieve data of the reference block using the motion vector. As another example, if the motion vector has fractional sample precision, motion compensation unit 224 may interpolate values for the prediction block according to one or more interpolation filters. Moreover, for bi-directional inter-prediction, motion compensation unit 224 may retrieve data for two reference blocks identified by respective motion vectors and combine the retrieved data, e.g., through sample-by-sample averaging or weighted averaging.

[0163] When operating according to the AVI video coding format, motion estimation unit 222 and motion compensation unit 224 may be configured to encode coding blocks of video data (e.g., both luma and chroma coding blocks) using translational motion compensation, affine motion compensation, overlapped block motion compensation (OBMC), and / or compound inter-intra prediction.

[0164] As another example, for intra-prediction, or intra-prediction coding, intraprediction unit 226 may generate the prediction block from samples neighboring the current block. For example, for directional modes, intra-prediction unit 226 may generally mathematically combine values of neighboring samples and populate these calculated values in the defined direction across the current block to produce the prediction block. As another example, for DC mode, intra-prediction unit 226 may calculate an average of the neighboring samples to the current block and generate the prediction block to include this resulting average for each sample of the prediction block.

[0165] When operating according to the AVI video coding format, intra-prediction unit 226 may be configured to encode coding blocks of video data (e.g., both luma and chroma coding blocks) using directional intra prediction, non-directional intra prediction, recursive filter intra prediction, chroma-from-luma (CFL) prediction, intra block copy1616-615WO01Qualcomm Ref. No. 2502091WO 36 / 58(IBC), and / or color palette mode. Mode selection unit 202 may include additional functional units to perform video prediction in accordance with other prediction modes.

[0166] Mode selection unit 202 provides the prediction block to residual generation unit 204. Residual generation unit 204 receives a raw, unencoded version of the current block from video data memory 230 and the prediction block from mode selection unit 202. Residual generation unit 204 calculates sample-by-sample differences between the current block and the prediction block. The resulting sample-by-sample differences define a residual block for the current block. In some examples, residual generation unit 204 may also determine differences between sample values in the residual block to generate a residual block using residual differential pulse code modulation (RDPCM). In some examples, residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0167] In examples where mode selection unit 202 partitions CUs into PUs, each PU may be associated with a luma prediction unit and corresponding chroma prediction units. Video encoder 200 and video decoder 300 may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size of a luma prediction unit of the PU. Assuming that the size of a particular CU is 2Nx2N, video encoder 200 may support PU sizes of 2Nx2N or NxN for intra prediction, and symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, NxN, or similar for inter prediction. Video encoder 200 and video decoder 300 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.

[0168] In examples where mode selection unit 202 does not further partition a CU into PUs, each CU may be associated with a luma coding block and corresponding chroma coding blocks. As above, the size of a CU may refer to the size of the luma coding block of the CU. The video encoder 200 and video decoder 300 may support CU sizes of 2Nx2N, 2NxN, orNx2N.

[0169] For other video coding techniques such as an intra-block copy mode coding, an affine-mode coding, and linear model (LM) mode coding, as some examples, mode selection unit 202, via respective units associated with the coding techniques, generates a prediction block for the current block being encoded. In some examples, such as palette mode coding, mode selection unit 202 may not generate a prediction block, and instead generate syntax elements that indicate the manner in which to reconstruct the block based1616-615WO01Qualcomm Ref. No. 2502091WO 37 / 58on a selected palette. In such modes, mode selection unit 202 may provide these syntax elements to entropy encoding unit 220 to be encoded.

[0170] As described above, residual generation unit 204 receives the video data for the current block and the corresponding prediction block. Residual generation unit 204 then generates a residual block for the current block. To generate the residual block, residual generation unit 204 calculates sample-by-sample differences between the prediction block and the current block.

[0171] Transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a “transform coefficient block”). Transform processing unit 206 may apply various transforms to a residual block to form the transform coefficient block. For example, transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to a residual block. In some examples, transform processing unit 206 may perform multiple transforms to a residual block, e.g., a primary transform and a secondary transform, such as a rotational transform. In some examples, transform processing unit 206 does not apply transforms to a residual block.

[0172] When operating according to AVI, transform processing unit 206 may apply one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a “transform coefficient block”). Transform processing unit 206 may apply various transforms to a residual block to form the transform coefficient block. For example, transform processing unit 206 may apply a horizontal / vertical transform combination that may include a discrete cosine transform (DCT), an asymmetric discrete sine transform (ADST), a flipped ADST (e.g., an ADST in reverse order), and an identity transform (IDTX). When using an identity transform, the transform is skipped in one of the vertical or horizontal directions. In some examples, transform processing may be skipped.

[0173] Quantization unit 208 may quantize the transform coefficients in a transform coefficient block, to produce a quantized transform coefficient block. Quantization unit 208 may quantize transform coefficients of a transform coefficient block according to a quantization parameter (QP) value associated with the current block. Video encoder 200 (e.g., via mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient blocks associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce loss of information, and thus, 1616-615WO01Qualcomm Ref. No. 2502091WO 38 / 58quantized transform coefficients may have lower precision than the original transform coefficients produced by transform processing unit 206.

[0174] Inverse quantization unit 210 and inverse transform processing unit 212 may apply inverse quantization and inverse transforms to a quantized transform coefficient block, respectively, to reconstruct a residual block from the transform coefficient block. Reconstruction unit 214 may produce a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and a prediction block generated by mode selection unit 202. For example, reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by mode selection unit 202 to produce the reconstructed block.

[0175] Filter unit 216 may perform one or more filter operations on reconstructed blocks. For example, filter unit 216 may perform deblocking operations to reduce blockiness artifacts along edges of CUs. Operations of filter unit 216 may be skipped, in some examples.

[0176] When operating according to AVI, filter unit 216 may perform one or more filter operations on reconstructed blocks. For example, filter unit 216 may perform deblocking operations to reduce blockiness artifacts along edges of CUs. In other examples, filter unit 216 may apply a constrained directional enhancement filter (CDEF), which may be applied after deblocking, and may include the application of non-separable, non-linear, low-pass directional filters based on estimated edge directions. Filter unit 216 may also include a loop restoration filter, which is applied after CDEF, and may include a separable symmetric normalized Wiener filter or a dual self-guided filter.

[0177] Video encoder 200 stores reconstructed blocks in DPB 218. For instance, in examples where operations of filter unit 216 are not performed, reconstruction unit 214 may store reconstructed blocks to DPB 218. In examples where operations of filter unit 216 are performed, filter unit 216 may store the filtered reconstructed blocks to DPB 218. Motion estimation unit 222 and motion compensation unit 224 may retrieve a reference picture from DPB 218, formed from the reconstructed (and potentially filtered) blocks, to inter-predict blocks of subsequently encoded pictures. In addition, intra-prediction unit 226 may use reconstructed blocks in DPB 218 of a current picture to intra-predict other blocks in the current picture.

[0178] In general, entropy encoding unit 220 may entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy 1616-615WO01Qualcomm Ref. No. 2502091WO 39 / 58encoding unit 220 may entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy encoding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-prediction or intramode information for intra-prediction) from mode selection unit 202. Entropy encoding unit 220 may perform one or more entropy encoding operations on the syntax elements, which are another example of video data, to generate entropy-encoded data. For example, entropy encoding 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 (SB AC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, an Exponential-Golomb encoding operation, or another type of entropy encoding operation on the data. In some examples, entropy encoding unit 220 may operate in bypass mode where syntax elements are not entropy encoded.

[0179] Video encoder 200 may output a bitstream that includes the entropy encoded syntax elements needed to reconstruct blocks of a slice or picture. In particular, entropy encoding unit 220 may output the bitstream.

[0180] In accordance with AVI, entropy encoding unit 220 may be configured as a symbol -to- symbol adaptive multi-symbol arithmetic coder. A syntax element in AVI includes an alphabet of N elements, and a context (e.g., probability model) includes a set of N probabilities. Entropy encoding unit 220 may store the probabilities as n-bit (e.g., 15-bit) cumulative distribution functions (CDFs). Entropy encoding unit 220 may perform recursive scaling, with an update factor based on the alphabet size, to update the contexts.

[0181] The operations described above are described with respect to a block. Such description should be understood as being operations for a luma coding block and / or chroma coding blocks. As described above, in some examples, the luma coding block and chroma coding blocks are luma and chroma components of a CU. In some examples, the luma coding block and the chroma coding blocks are luma and chroma components ofaPU.

[0182] In some examples, operations performed with respect to a luma coding block need not be repeated for the chroma coding blocks. As one example, operations to identify a motion vector (MV) and reference picture for a luma coding block need not be repeated for identifying a MV and reference picture for the chroma blocks. Rather, the MV for the luma coding block may be scaled to determine the MV for the chroma blocks, and the 1616-615WO01Qualcomm Ref. No. 2502091WO 40 / 58reference picture may be the same. As another example, the intra-prediction process may be the same for the luma coding block and the chroma coding blocks.

[0183] Video encoder 200 represents an example of a device configured to encode video data including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to apply a subblock transform mode to a current block of the video data according to any of the techniques of this disclosure.

[0184] FIG. 11 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. FIG. 11 is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video decoder 300 according to the techniques of VVC and HEVC. However, the techniques of this disclosure may be performed by video coding devices that are configured to other video coding standards.

[0185] In the example of FIG. 11, video decoder 300 includes coded picture buffer (CPB) memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and DPB 314. Any or all of CPB memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and DPB 314 may be implemented in one or more processors or in processing circuitry. For instance, the units of video decoder 300 may be implemented as one or more circuits or logic elements as part of hardware circuitry, or as part of a processor, ASIC, or FPGA. Moreover, video decoder 300 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0186] Prediction processing unit 304 includes motion compensation unit 316 and intraprediction unit 318. Prediction processing unit 304 may include additional units to perform prediction in accordance with other prediction modes. As examples, prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of motion compensation unit 316), an affine unit, a linear model (LM) unit, or the like. In other examples, video decoder 300 may include more, fewer, or different functional components.

[0187] When operating according to AVI, motion compensation unit 316 may be configured to decode coding blocks of video data (e.g., both luma and chroma coding blocks) using translational motion compensation, affine motion compensation, OBMC, 1616-615WO01Qualcomm Ref. No. 2502091WO 41 / 58and / or compound inter-intra prediction, as described above. Intra-prediction unit 318 may be configured to decode coding blocks of video data (e.g., both luma and chroma coding blocks) using directional intra prediction, non-directional intra prediction, recursive filter intra prediction, CFL, IBC, and / or color palette mode, as described above.

[0188] CPB memory 320 is an example of a memory system that may store video data, such as an encoded video bitstream, to be decoded by the components of video decoder 300. The video data stored in CPB memory 320 may be obtained, for example, from computer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. Also, CPB memory 320 may store video data other than syntax elements of a coded picture, such as temporary data representing outputs from the various units of video decoder 300. DPB 314 is an example of a memory system that generally stores decoded pictures, which video decoder 300 may output and / or use as reference video data when decoding subsequent data or pictures of the encoded video bitstream. CPB memory 320 and DPB 314 may each be formed by any of a variety of memory devices or memory units, such as DRAM, including SDRAM, MRAM, 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 may be on-chip with other components of video decoder 300, or off-chip relative to those components.

[0189] Additionally or alternatively, in some examples, video decoder 300 may retrieve coded video data from memory 120 (FIG. 1). That is, memory 120 may store data as discussed above with CPB memory 320. Likewise, memory 120 may store instructions to be executed by video decoder 300, when some or all of the functionality of video decoder 300 is implemented in software to be executed by processing circuitry of video decoder 300.

[0190] The various units shown in FIG. 11 are illustrated to assist with understanding the operations performed by video decoder 300. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Similar to FIG. 10, fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may execute 1616-615WO01Qualcomm Ref. No. 2502091WO 42 / 58software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. In some examples, one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits.

[0191] Video decoder 300 may include ALUs, EFUs, digital circuits, analog circuits, and / or programmable cores formed from programmable circuits. In examples where the operations of video decoder 300 are performed by software executing on the programmable circuits, on-chip or off-chip memory may store instructions (e.g., object code) of the software that video decoder 300 receives and executes.

[0192] Entropy decoding unit 302 may receive encoded video data from the CPB and entropy decode the video data to reproduce syntax elements. Prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, and filter unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.

[0193] In general, video decoder 300 reconstructs a picture on a block-by-block basis. Video decoder 300 may perform a reconstruction operation on each block individually (where the block currently being reconstructed, i.e., decoded, may be referred to as a “current block”).

[0194] Entropy decoding unit 302 may entropy decode syntax elements defining quantized transform coefficients of a quantized transform coefficient block, as well as transform information, such as a quantization parameter (QP) and / or transform mode indication(s). Inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 306 to apply. Inverse quantization unit 306 may, for example, perform a bitwise left-shift operation to inverse quantize the quantized transform coefficients. Inverse quantization unit 306 may thereby form a transform coefficient block including transform coefficients.

[0195] After inverse quantization unit 306 forms the transform coefficient block, inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational1616-615WO01Qualcomm Ref. No. 2502091WO 43 / 58transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0196] Furthermore, prediction processing unit 304 generates a prediction block according to prediction information syntax elements that were 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 the prediction block. In this case, the prediction information syntax elements may indicate a reference picture in DPB 314 from which to retrieve a reference block, as well as a motion vector identifying a location of the reference block in the reference picture relative to the location of the current block in the current picture. Motion compensation unit 316 may generally perform the inter-prediction process in a manner that is substantially similar to that described with respect to motion compensation unit 224 (FIG. 10).

[0197] As another example, if the prediction information syntax elements indicate that the current block is intra-predicted, intra-prediction unit 318 may generate the prediction block according to an intra-prediction mode indicated by the prediction information syntax elements. Again, intra-prediction unit 318 may generally perform the intraprediction process in a manner that is substantially similar to that described with respect to intra-prediction unit 226 (FIG. 10). Intra-prediction unit 318 may retrieve data of neighboring samples to the current block from DPB 314.

[0198] Reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

[0199] Filter unit 312 may perform one or more filter operations on reconstructed blocks. For example, filter unit 312 may perform deblocking operations to reduce blockiness artifacts along edges of the reconstructed blocks. Operations of filter unit 312 are not necessarily performed in all examples.

[0200] Video decoder 300 may store the reconstructed blocks in DPB 314. For instance, in examples where operations of filter unit 312 are not performed, reconstruction unit 310 may store reconstructed blocks to DPB 314. In examples where operations of filter unit 312 are performed, filter unit 312 may store the filtered reconstructed blocks to DPB 314. As discussed above, DPB 314 may provide reference information, such as samples of a current picture for intra-prediction and previously decoded pictures for subsequent 1616-615WO01Qualcomm Ref. No. 2502091WO 44 / 58motion compensation, to prediction processing unit 304. Moreover, video decoder 300 may output decoded pictures (e.g., decoded video) from DPB 314 for subsequent presentation on a display device, such as display device 118 of FIG. 1.

[0201] In this manner, video decoder 300 represents an example of a video decoding device including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to apply a subblock transform mode to a current block of the video data according to any of the techniques of this disclosure.

[0202] FIG. 12 is a flowchart illustrating an example method for encoding a current block in accordance with the techniques of this disclosure. The current block may be or include a current CU. Although described with respect to video encoder 200 (FIGS. 1 and 10), it should be understood that other devices may be configured to perform a method similar to that of FIG. 12.

[0203] In this example, video encoder 200 initially predicts the current block (400). For example, video encoder 200 may form a prediction block for the current block. Video encoder 200 may then calculate a residual block for the current block (402). To calculate the residual block, video encoder 200 may calculate a difference between the original, unencoded block and the prediction block for the current block. Video encoder 200 may then transform the residual block and quantize transform coefficients of the residual block (404). Next, video encoder 200 may scan the quantized transform coefficients of the residual block (406). During the scan, or following the scan, video encoder 200 may entropy encode the transform coefficients (408). For example, video encoder 200 may encode the transform coefficients using CAVLC or CAB AC. Video encoder 200 may then output the entropy encoded data of the block (410).

[0204] FIG. 13 is a flowchart illustrating an example method for decoding a current block of video data in accordance with the techniques of this disclosure. The current block may be or include a current CU. Although described with respect to video decoder 300 (FIGS.1 and 11), it should be understood that other devices may be configured to perform a method similar to that of FIG. 13.

[0205] Video decoder 300 may receive entropy encoded data for the current block, such as entropy encoded prediction information and entropy encoded data for transform coefficients of a residual block corresponding to the current block (500). Video decoder 300 may entropy decode the entropy encoded data to determine prediction information for the current block and to reproduce transform coefficients of the residual block (502). Video decoder 300 may predict the current block (504), e.g., using an intra- or inter- 1616-615WO01Qualcomm Ref. No. 2502091WO 45 / 58prediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. Video decoder 300 may then inverse scan the reproduced transform coefficients (506), to create a block of quantized transform coefficients. Video decoder 300 may then inverse quantize the transform coefficients and apply an inverse transform to the transform coefficients to produce a residual block (508). Video decoder 300 may ultimately decode the current block by combining the prediction block and the residual block (510).

[0206] The following numbered clauses illustrate one or more aspects of the devices and techniques described in this disclosure.

[0207] Aspect 1A. A method of coding video data, the method comprising: determining to apply a subblock transform mode to a current block of the video data; determining, based on determining to apply the subblock transform mode to the current block, a coordinate for the current block having a maximum gradient value; performing a search for a position and a direction using the coordinate as a center position of a subblock, wherein the search has a search range of M rows and N columns; dividing the block into subblocks based on the position and direction; and coding the subblocks based on the subblock transform mode.

[0208] Aspect 2A. A method of coding video data, the method comprising: determining to apply a subblock transform mode to a current block of the video data; determining, based on determining to apply the subblock transform mode to the current block, determining a gradient summation for a subblock, wherein the gradient summation comprises the sum of gradient values of a subset of gradient values for the subblock, wherein the subset comprises fewer gradient values than a total number of gradient values for the subblock; and coding the subblock based on the subblock transform mode.

[0209] Aspect 3 A. A method of coding video data, the method comprising: determining to apply a subblock transform mode to a current block of the video data; determining, based on determining to apply the subblock transform mode to the current block, direction information of a subblock of the current block; determining, the position of a residual of the subblock after applying an inverse transform to the subblock; and coding the subblock based on the subblock transform mode.

[0210] Aspect 4A. The method of aspect 3 A, further comprising: determining a continuity measure, wherein determining the continuity measure comprises using reconstructed samples from an above coding block and a left coding block; and using reconstructed samples within the subblock based on a position of the subblock.1616-615WO01Qualcomm Ref. No. 2502091WO 46 / 58

[0211] Aspect 5 A. The method of aspect 3A, further comprising: determining a position of the subblock; determining, based on the position of the subblock, whether to use reconstructed samples from an above coding block or a left coding block; and determining, based on a determination to use reconstructed samples from the above coding block, a continuity measure using the reconstructed samples from the above coding block.

[0212] Aspect 6A. A method of coding video data, the method comprising: determining to apply a subblock transform mode to a current block of the video data; determining, based on determining to apply the subblock transform mode to the current block, a Sobel gradient using two tap filters; determining, based on the Sobel gradient, a subblock of the current block, and coding the subblock based on the subblock transform mode.

[0213] Aspect 7A. The method of aspect 6A, wherein the Sobel gradient comprises at least one of: a directional gradient using an above sample and a below sample of a current sample according to Gradient = a*nl - b*n2; a directional gradient using a left sample and a right sample of the current sample according to Gradient = a*nl - b*n2; a directional gradient using the current sample and the below sample of the current sample according to Gradient = a*nl - b*n2; a directional gradient using the current sample and the right sample of the current sample according to Gradient = a*c - b*n2; a directional gradient using the current sample and the above sample of the current sample according to Gradient = a*nl - b*c; or a directional gradient using the current sample and the left sample of the current sample according to Gradient = a*nl - b*c, wherein a and b are numbers, nl is neighbor 1, n2 is neighbor 2, and c is the current sample.

[0214] Aspect 8A. The method of aspect 7A, wherein the Sobel gradient comprises a final gradient, wherein the final gradient comprises a magnitude of two directional gradients.

[0215] Aspect 9 A. The method of aspect 8 A, wherein the magnitude of the two directional gradients comprises a square of a magnitude of a first gradient plus a square of a magnitude of a second gradient.

[0216] Aspect 10A. The method of any of aspects 6A-9A, wherein determining the Sobel gradient comprises applying padding.

[0217] Aspect 11 A. The method of aspect 10A, wherein applying padding comprises applying repetitive padding, gradient value padding, or zero padding.1616-615WO01Qualcomm Ref. No. 2502091WO 47 / 58

[0218] Aspect 12A. A method of coding video data, the method comprising: determining to apply a subblock transform mode to a current block of the video data; determining a subblock of the current block, the subblock having a width equal to a width of the current block divided by N and having a height equal to a height of the current block divided by N; and coding the subblocks based on the subblock transform mode.

[0219] Aspect 13A. The method of any of aspects 1A-12A, wherein the subblock transform mode comprises an Advanced subblock transform mode.

[0220] Aspect 14 A. The method of any of aspects 1A-13A, wherein coding comprises decoding.

[0221] Aspect 15 A. The method of any of aspects 1 A-14A, wherein coding comprises encoding.

[0222] Aspect 16 A. A device for coding video data, the device comprising one or more means for performing the method of any of aspects 1A-15A.

[0223] Aspect 17 A. The device of aspect 16A, wherein the one or more means comprise one or more processors implemented in circuitry.

[0224] Aspect 18 A. The device of any of aspects 16A or 17A, further comprising a memory to store the video data.

[0225] Aspect 19A. The device of any of aspects 16A-18A, further comprising a display configured to display decoded video data.

[0226] Aspect 20A. The device of any of aspects 16A-19A, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0227] Aspect 21 A. The device of any of aspects 16A-20A, wherein the device comprises a video decoder.

[0228] Aspect 22 A. The device of any of aspects 16A-21A, wherein the device comprises a video encoder.

[0229] Aspect 23 A. A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to perform the method of any of aspects 1A-15A.

[0230] Aspect IB. Amethod of decoding video data, the method comprising: determining to apply a subblock transform mode to a current block of the video data; determining, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value; performing a search for a position and a direction using the coordinate as a center position of a potential 1616-615WO01Qualcomm Ref. No. 2502091WO 48 / 58subblock, wherein the search has a search range of at least one of M rows or N columns; dividing the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform; and decoding the plurality of subblocks based on the subblock transform mode.

[0231] Aspect 2B. The method of Aspect IB, wherein decoding the plurality of subblocks comprises applying a subblock transform to the single subblock.

[0232] Aspect 3B. The method of any of Aspects 1B-2B, wherein performing the search comprises determining a gradient summation for the potential subblock, wherein the gradient summation comprises a sum of gradient values of a subset of gradient values for the potential subblock, wherein the subset comprises fewer gradient values than a total number of gradient values for the potential subblock.

[0233] Aspect 4B. The method of any of Aspects 1B-2B, wherein performing the search comprises: applying an inverse transform to the potential subblock; and determining the position after applying the inverse transform to the potential subblock based on residual information.

[0234] Aspect 5B. The method of Aspect 4B, further comprising: determining a continuity measure, wherein determining the continuity measure comprises using reconstructed samples from an above coding block and a left coding block; and using reconstructed samples within the potential subblock based on a position of the potential subblock.

[0235] Aspect 6B. The method of Aspect 4B, further comprising: determining, based on the position of the potential subblock, whether to use reconstructed samples from an above coding block or a left coding block; and determining, based on a determination to use reconstructed samples from the above coding block, a continuity measure using the reconstructed samples from the above coding block.

[0236] Aspect 7B. The method of any of Aspects 1B-6B, wherein determining the coordinate for the current block having the maximum gradient value comprises determining a Sobel gradient using two tap filters.

[0237] Aspect 8B. The method of Aspect 7B, wherein the Sobel gradient comprises at least one of: a directional gradient using an above sample and a below sample of a current sample according to Gradient = a*nl - b*n2; a directional gradient using a left sample and a right sample of the current sample according to Gradient = a*nl - b*n2; a directional gradient using the current sample and the below sample of the current sample according to Gradient = a*c - b*n2; a directional gradient using the current sample and 1616-615WO01Qualcomm Ref. No. 2502091WO 49 / 58the right sample of the current sample according to Gradient = a*c - b*n2; a directional gradient using the current sample and the above sample of the current sample according to Gradient = a*nl - b*c; or a directional gradient using the current sample and the left sample of the current sample according to Gradient = a*nl - b*c, wherein a and b are numbers, nl is neighbor 1, n2 is neighbor 2, and c is the current sample.

[0238] Aspect 9B. The method of Aspect 8B, wherein the Sobel gradient comprises a final gradient, wherein the final gradient comprises a magnitude of two directional gradients.

[0239] Aspect 10B. The method of any of Aspects 7B-9B, wherein determining the Sobel gradient comprises applying padding.

[0240] Aspect 11B. The method of Aspect 10B, wherein applying padding comprises applying repetitive padding, gradient value padding, or zero padding.

[0241] Aspect 12B. The method of any of Aspects 1B-11B, wherein the subblock comprises a width equal to a width of the current block divided by N and having a height equal to a height of the current block divided by N.

[0242] Aspect 13B. Adevice for decoding video data, the device comprising: one or more memories; and one or more processors in communication with the one or more memories, the one or more processors configured to: determine to apply a subblock transform mode to a current block of the video data; determine, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value; perform a search for a position and a direction using the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns; divide the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform; and decode the plurality of subblocks based on the subblock transform mode.

[0243] Aspect 14B. The device of Aspect 13B, wherein to perform the search, the one or more processors are further configured to determine a gradient summation for the potential subblock, wherein the gradient summation comprises a sum of gradient values of a subset of gradient values for the potential subblock, wherein the subset comprises fewer gradient values than a total number of gradient values for the potential subblock.

[0244] Aspect 15B. The device of Aspect 13B, wherein to perform the search, the one or more processors are further configured to: apply an inverse transform to the potential1616-615WO01Qualcomm Ref. No. 2502091WO 50 / 58subblock; and determine the position after applying the inverse transform to the potential subblock based on residual information.

[0245] Aspect 16B. The device of Aspect 15B, wherein the one or more processors are further configured to: determine a continuity measure, wherein determining the continuity measure comprises using reconstructed samples from an above coding block and a left coding block; and use reconstructed samples within the potential subblock based on a position of the potential subblock.

[0246] Aspect 17B. The device of Aspect 15B, wherein the one or more processors are further configured to: determine, based on the position of the potential subblock, whether to use reconstructed samples from an above coding block or a left coding block; and determine, based on a determination to use reconstructed samples from the above coding block, a continuity measure using the reconstructed samples from the above coding block.

[0247] Aspect 18B. The device of any of Aspects 13B-17B, wherein as part of determining the coordinate for the current block having the maximum gradient value, the one or more processors are configured to determine a Sobel gradient using two tap filters, and wherein the Sobel gradient comprises at least one of: a directional gradient using an above sample and a below sample of a current sample according to Gradient = a*nl -b*n2; a directional gradient using a left sample and a right sample of the current sample according to Gradient = a*nl - b*n2; a directional gradient using the current sample and the below sample of the current sample according to Gradient = a*c - b*n2; a directional gradient using the current sample and the right sample of the current sample according to Gradient = a*c - b*n2; a directional gradient using the current sample and the above sample of the current sample according to Gradient = a*nl - b*c; or a directional gradient using the current sample and the left sample of the current sample according to Gradient = a*nl - b*c, wherein a and b are numbers, nl is neighbor 1, n2 is neighbor 2, and c is the current sample.

[0248] Aspect 19B. The device of any of Aspects 13B-18B, wherein the device further comprises a display for displaying decoded video data.

[0249] Aspect 20B. A device for encoding video data, the device comprising: one or more memories; and one or more processors in communication with the one or more memories, the one or more processors configured to: determine to apply a subblock transform mode to a current block of the video data; determine, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value; perform a search for a position and a direction using 1616-615WO01Qualcomm Ref. No. 2502091WO 51 / 58the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns; divide the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform; and encode the plurality of subblocks based on the subblock transform mode.

[0250] It is to be recognized that depending on the example, certain acts or events of any of the techniques described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the techniques). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.

[0251] 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 over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and / or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0252] By way of example, and not limitation, such computer-readable storage media may include one or more of 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. Also, any connection is properly termed 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 technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, 1616-615WO01Qualcomm Ref. No. 2502091WO 52 / 58DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0253] Instructions may be executed by one or more processors, such as one or more DSPs, general purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry. Accordingly, the terms “processor” and “processing circuitry,” as used herein may refer to any of the foregoing structures or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0254] The techniques of this disclosure may be implemented in a wide variety of devices, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and / or firmware.

[0255] Various examples have been described. These and other examples are within the scope of the following claims.1616-615WO01

Claims

Qualcomm Ref. No. 2502091WO 53 / 58WHAT IS CLAIMED IS:

1. A method of decoding video data, the method comprising:determining to apply a subblock transform mode to a current block of the video data;determining, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value;performing a search for a position and a direction using the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns;dividing the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform; anddecoding the plurality of subblocks based on the subblock transform mode.

2. The method of claim 1, wherein decoding the plurality of subblocks comprises applying a subblock transform to the single subblock.

3. The method of claim 1, wherein performing the search comprises determining a gradient summation for the potential subblock, wherein the gradient summation comprises a sum of gradient values of a subset of gradient values for the potential subblock, wherein the subset comprises fewer gradient values than a total number of gradient values for the potential subblock.

4. The method of claim 1, wherein performing the search comprises:applying an inverse transform to the potential subblock; anddetermining the position after applying the inverse transform to the potential subblock based on residual information.

5. The method of claim 4, further comprising:determining a continuity measure, wherein determining the continuity measure comprises using reconstructed samples from an above coding block and a left coding block; and1616-615WO01Qualcomm Ref. No. 2502091WO 54 / 58using reconstructed samples within the potential subblock based on a position of the potential subblock.

6. The method of claim 4, further comprising:determining, based on the position of the potential subblock, whether to use reconstructed samples from an above coding block or a left coding block; and determining, based on a determination to use reconstructed samples from the above coding block, a continuity measure using the reconstructed samples from the above coding block.

7. The method of claim 1, wherein determining the coordinate for the current block having the maximum gradient value comprises determining a Sobel gradient using two tap filters.

8. The method of claim 7, wherein the Sobel gradient comprises at least one of: a directional gradient using an above sample and a below sample of a current sample according to Gradient = a*nl - b*n2;a directional gradient using a left sample and a right sample of the current sample according to Gradient = a*nl - b*n2;a directional gradient using the current sample and the below sample of the current sample according to Gradient = a*c - b*n2;a directional gradient using the current sample and the right sample of the current sample according to Gradient = a*c - b*n2;a directional gradient using the current sample and the above sample of the current sample according to Gradient = a*nl - b*c; ora directional gradient using the current sample and the left sample of the current sample according to Gradient = a*nl - b*c,wherein a and b are numbers, nl is neighbor 1, n2 is neighbor 2, and c is the current sample.

9. The method of claim 8, wherein the Sobel gradient comprises a final gradient, wherein the final gradient comprises a magnitude of two directional gradients.1616-615WO01Qualcomm Ref. No. 2502091WO 55 / 5810. The method of claim 7, wherein determining the Sobel gradient comprises applying padding.

11. The method of claim 10, wherein applying padding comprises applying repetitive padding, gradient value padding, or zero padding.

12. The method of claim 1, wherein the single subblock comprises a width equal to a width of the current block divided by N and having a height equal to a height of the current block divided by N.

13. A device for decoding video data, the device comprising:one or more memories; andone or more processors in communication with the one or more memories, the one or more processors configured to:determine to apply a subblock transform mode to a current block of the video data;determine, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value;perform a search for a position and a direction using the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns;divide the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform; anddecode the plurality of subblocks based on the subblock transform mode.

14. The device of claim 13, wherein to perform the search, the one or more processors are further configured to determine a gradient summation for the potential subblock, wherein the gradient summation comprises a sum of gradient values of a subset of gradient values for the potential subblock, wherein the subset comprises fewer gradient values than a total number of gradient values for the potential subblock.1616-615WO01Qualcomm Ref. No. 2502091WO 56 / 5815. The device of claim 13, wherein to perform the search, the one or more processors are further configured to:apply an inverse transform to the potential subblock; anddetermine the position after applying the inverse transform to the potential subblock based on residual information.

16. The device of claim 15, wherein the one or more processors are further configured to:determine a continuity measure, wherein determining the continuity measure comprises using reconstructed samples from an above coding block and a left coding block; anduse reconstructed samples within the potential subblock based on a position of the potential subblock.

17. The device of claim 15, wherein the one or more processors are further configured to:determine, based on the position of the potential subblock, whether to use reconstructed samples from an above coding block or a left coding block; and determine, based on a determination to use reconstructed samples from the above coding block, a continuity measure using the reconstructed samples from the above coding block.

18. The device of claim 17, wherein as part of determining the coordinate for the current block having the maximum gradient value, the one or more processors are configured to determine a Sobel gradient using two tap filters, and wherein the Sobel gradient comprises at least one of:a directional gradient using an above sample and a below sample of a current sample according to Gradient = a*nl - b*n2;a directional gradient using a left sample and a right sample of the current sample according to Gradient = a*nl - b*n2;a directional gradient using the current sample and the below sample of the current sample according to Gradient = a*c - b*n2;a directional gradient using the current sample and the right sample of the current sample according to Gradient = a*c - b*n2;1616-615WO01Qualcomm Ref. No. 2502091WO 57 / 58a directional gradient using the current sample and the above sample of the current sample according to Gradient = a*nl - b*c; ora directional gradient using the current sample and the left sample of the current sample according to Gradient = a*nl - b*c,wherein a and b are numbers, nl is neighbor 1, n2 is neighbor 2, and c is the current sample.

19. The device of claim 13, wherein the device further comprises a display for displaying decoded video data.

20. A device for encoding video data, the device comprising:one or more memories; andone or more processors in communication with the one or more memories, the one or more processors configured to:determine to apply a subblock transform mode to a current block of the video data;determine, based on determining to apply the subblock transform mode to the current block, a coordinate within the current block having a maximum gradient value;perform a search for a position and a direction using the coordinate as a center position of a potential subblock, wherein the search has a search range of at least one of M rows or N columns;divide the current block into a plurality of subblocks based on the position and direction, the plurality of subblocks comprising a single subblock to which to apply a subblock transform; andencode the plurality of subblocks based on the subblock transform mode.1616-615WO01

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