Preprocessing of input data for adaptive loop filters in video coding

Abstract

An apparatus for decoding video data may be configured to: determine a prediction block for a current block of the video data; determining a residual block for the current block of the video data; processing residual data of the residual block to determine processed residual data; storing the processed residual data; adding the prediction block to the residual block to determine a reconstructed block; and performing adaptive loop filtering (ALF) on the reconstructed block based on the processed residual data.

Description

[0001] This application claims priority to U.S. Patent Application No. 18 / 589,777, filed February 28, 2024, and U.S. Provisional Patent Application No. 63 / 487,698, filed March 1, 2023, each of which is incorporated herein by reference in its entirety. U.S. Patent Application No. 18 / 589,777, filed February 28, 2024, claims the benefit of U.S. Provisional Patent Application No. 63 / 487,698, filed March 1, 2023. Technical Field

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

[0003] Digital video capabilities may be incorporated into a wide variety of devices, including digital televisions, digital live broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite wireless telephones (so-called "smartphones"), video teleconferencing devices, video streaming devices, etc. Digital video devices implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4 (Part 10, Advanced Video Coding (AVC)), ITU-T H.265 / High Efficiency Video Coding (HEVC), ITU-T H.266 / Versatile Video Coding (VVC), and extensions of such standards, as well as proprietary video codecs / formats such as AOMedia Video1 (AV1) developed by the Alliance for Open Media. By implementing such video coding techniques, video devices can more efficiently send, receive, encode, decode, and / or store digital video information.

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

[0005] Some implementations of adaptive loop filtering (ALF) utilize either or both residual samples or reconstructed samples to determine the filter used at the ALF stage. ALF is typically performed after deblocking and SAO filtering, whereas residual and reconstructed samples are determined before deblocking and SAO filtering. Therefore, in order to use residual or reconstructed samples for ALF, it is necessary to buffer the residual and reconstructed samples while deblocking and SAO are being performed. This buffering requires increased hardware complexity.

[0006] To reduce the amount of buffering required, this disclosure describes techniques for processing the residual data of a residual block to determine processed residual data and storing the processed residual data rather than the residual data itself. The processed residual data may have less data (e.g., fewer bits) than the residual data and therefore require less memory to buffer. In some examples, the processing may also modify the residual data so that it is more likely to result in a better filter selection during ALF.

[0007] According to an example of the present disclosure, a method for decoding video data includes: determining a prediction block for a current block of the video data; determining a residual block for the current block of the video data; processing residual data of the residual block to determine processed residual data; storing the processed residual data; adding the prediction block to the residual block to determine a reconstructed block; and performing adaptive loop filtering (ALF) on the reconstructed block based on the processed residual data.

[0008] According to an example of the present disclosure, a device for decoding video data includes: a memory configured to store video data; and one or more processors implemented in a circuit and configured to: determine a prediction block for a current block of the video data; determine a residual block for the current block of the video data; process residual data of the residual block to determine processed residual data; store the processed residual data; add the prediction block to the residual block to determine a reconstructed block; and perform adaptive loop filtering (ALF) on the reconstructed block based on the processed residual data.

[0009] According to an example of the present disclosure, a computer-readable storage medium stores instructions that, when executed, cause one or more processors to: determine a prediction block for a current block of video data; determine a residual block for the current block of video data; process residual data of the residual block to determine processed residual data; store the processed residual data; add the prediction block to the residual block to determine a reconstructed block; and perform adaptive loop filtering (ALF) on the reconstructed block based on the processed residual data.

[0010] According to an example of the present disclosure, an apparatus for decoding video data includes: a component for determining a prediction block for a current block of the video data; a component for determining a residual block for the current block of the video data; a component for processing residual data of the residual block to determine processed residual data; a component for storing the processed residual data; a component for adding the prediction block to the residual block to determine a reconstructed block; and a component for performing adaptive loop filtering (ALF) on the reconstructed block based on the processed residual data.

[0011] 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 and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0013] Figure 2A and Figure 2B is a conceptual diagram illustrating an example adaptive loop filter (ALF) shape that may be used according to techniques of this disclosure.

[0014] Figure 3 is a conceptual diagram illustrating example downsampled Laplacian values ​​for 4x4 sub-block ALF classification that may be used according to techniques of this disclosure.

[0015] Figure 4 is a conceptual diagram illustrating example Laplacian values ​​for luma samples that may be used in accordance with techniques of this disclosure.

[0016] Figure 5 is a conceptual diagram illustrating an example of ALF class merging that may be used according to the techniques of this disclosure.

[0017] Figure 6 is a conceptual diagram illustrating an example geometric transformation of a 7x7 diamond filter shape that may be used in accordance with the techniques of this disclosure.

[0018] 7A to 7C An example of symmetric sample padding in an ALF that may be used according to techniques of this disclosure is shown.

[0019] Figure 8 An example of ALF 4x4 sub-block classification that may be used according to the techniques of this disclosure is shown.

[0020] Figure 9 An example ALF framework using multiple classifiers is shown.

[0021] Figure 10 An example ALF framework with three classifiers is shown.

[0022] Figure 11 An example of LCU-level residual buffering is shown.

[0023] Figure 12 An example of residual pre-processing before storing for ALF is shown.

[0024] Figure 13 An example of residual preprocessing for classification is shown.

[0025] Figure 14 An example of pre-processing the reconstructed signal before being stored for ALF is shown.

[0026] Figure 15 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0027] Figure 16 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0028] Figure 17 is a block diagram illustrating an example filter unit for performing the techniques of this disclosure.

[0029] Figure 18 is a flowchart illustrating an example process for encoding a current block according to techniques of this disclosure.

[0030] Figure 19 is a flowchart illustrating an example process for decoding a current block according to techniques of this disclosure.

[0031] Figure 20 is a flowchart illustrating an example process for decoding a current block according to techniques of this disclosure. DETAILED DESCRIPTION

[0032] Video coding (e.g., video encoding and / or video decoding) typically involves predicting a block of video data based on already coded video data blocks in the same picture (e.g., intra-frame prediction) or predicting a block of video data based on already coded video data blocks in different pictures (e.g., inter-frame prediction). In some cases, the video encoder also calculates residual data by comparing the predicted block with the original block. Thus, the residual data represents the difference between the predicted block and the original block. To reduce the number of bits required to signal the residual data, the video encoder transforms and quantizes the residual data and signals the transformed and quantized residual data in the encoded bitstream. The compression achieved by the transform and quantization process can be lossy, meaning that the transform and quantization process can introduce distortion in the decoded video data.

[0033] The video decoder decodes the residual data and adds it to the prediction block to produce a reconstructed video block that more closely matches the original video block than the prediction block alone. Due to losses introduced by the transformation and quantization of the residual data, the first reconstructed block may have distortion or artifacts. A common type of artifact or distortion is called blocking, in which the boundaries of the blocks used to decode the video data are visible.

[0034] To further improve the quality of the decoded video, the video decoder may perform one or more filtering operations on the reconstructed video blocks. Examples of these filtering operations include deblocking filtering, sample adaptive offset (SAO) filtering, and adaptive loop filtering (ALF). The parameters of these filtering operations may be determined by the video encoder and explicitly signaled in the coded video bitstream, or may be implicitly determined by the video decoder without the need for explicit signaling in the coded video bitstream.

[0035] Some implementations of ALF utilize either or both residual samples or reconstructed samples to determine the filter used at the ALF level. ALF is typically performed after deblocking and SAO filtering, whereas residual and reconstructed samples are determined before deblocking and SAO filtering. Therefore, in order to use residual or reconstructed samples for ALF, it is necessary to buffer the residual and reconstructed samples while deblocking and SAO are being performed. This buffering requires increased hardware complexity.

[0036] To reduce the amount of buffering required, this disclosure describes techniques for processing the residual data of a residual block to determine processed residual data and storing the processed residual data rather than the residual data itself. The processed residual data may have less data (e.g., fewer bits) than the residual data and therefore require less memory to buffer. In some examples, the processing may also modify the residual data so that it is more likely to result in a better filter selection during ALF.

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

[0038] like Figure 1As shown, in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, source device 102 provides the video data to destination device 116 via a computer-readable medium 110. Source device 102 and destination device 116 can 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, handheld phones such as smartphones, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, broadcast receiver devices, etc. In some cases, source device 102 and destination device 116 can be equipped for wireless communication and, therefore, can be referred to as wireless communication devices.

[0039] exist Figure 1 In the example of , source device 102 includes a video source 104, a memory 106, a video encoder 200, and an output interface 108. Destination device 116 includes an input interface 122, a video decoder 300, the memory 120, and a display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply techniques for pre-processing input data for ALF. Thus, source device 102 represents an example of a video encoding device, while destination device 116 represents an example of a video decoding device. In other examples, the source device and destination device can include other components or arrangements. For example, source device 102 can receive video data from an external video source such as an external camera. Similarly, destination device 116 can interface with an external display device rather than including an integrated display device.

[0040] like Figure 1 The illustrated system 100 is merely an example. Generally speaking, any digital video encoding and / or decoding device can perform the techniques for preprocessing input data for ALF. Source device 102 and destination device 116 are merely examples of such decoding devices, where source device 102 generates decoded video data for transmission to destination device 116. This disclosure refers to a "decoding" device as a device that performs decoding (e.g., encoding and / or decoding) of data. Thus, video encoder 200 and video decoder 300 represent examples of decoding devices, specifically, a video encoder and a video decoder, respectively. In some examples, source device 102 and destination device 116 can operate in a substantially symmetrical manner, such that each of source device 102 and destination device 116 includes video encoding and decoding components. Thus, system 100 can support one-way or two-way video transmission between source device 102 and destination device 116, for example, for video streaming, video playback, video broadcasting, or video telephony.

[0041] Typically, video source 104 represents a source of video data (i.e., unencoded raw video data) and provides a sequential series of pictures (also referred to as "frames") of the video data to video encoder 200, which encodes the data for the pictures. Video source 104 of source device 102 may include a video capture device, such as a camera, a video archive containing previously captured raw video, and / or a video feed interface for receiving video from a video content provider. As another alternative, video source 104 may generate computer graphics-based data as the source video, or a combination of real-time 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 order in which they were received (sometimes referred to as "display order") into a decoding order for decoding. Video encoder 200 may generate a bitstream comprising the encoded video data. Source device 102 may then output the encoded video data onto computer-readable medium 110 via output interface 108 to be received and / or retrieved by, for example, input interface 122 of destination device 116 .

[0042] Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memory. In some examples, memories 106 and 120 may store raw video data, e.g., raw video from video source 104 and raw decoded video data from video decoder 300. Additionally or alternatively, memories 106 and 120 may store software instructions executable by, for example, 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 memory for functionally similar or equivalent purposes. Furthermore, memories 106 and 120 may store encoded video data, e.g., output from video encoder 200 and input to video decoder 300. In some examples, portions of memories 106 and 120 may be allocated as one or more video buffers, e.g., to store raw decoded and / or encoded video data.

[0043] The computer-readable medium 110 may represent any type of medium or device capable of transmitting encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to transmit the encoded video data directly to the destination device 116 in real time, for example, via a radio frequency network or a computer-based network. According to a communication standard such as a wireless communication protocol, the output interface 108 may modulate the transmit signal including the encoded video data, and the input interface 122 may demodulate the received transmit signal. The communication medium may include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful for facilitating communication from the source device 102 to the destination device 116.

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

[0045] In some examples, source device 102 may output the 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 the stored video data from file server 114 via streaming or downloading.

[0046] The file server 114 may be any type of server device capable of storing encoded video data and transmitting the encoded video data to the destination device 116. The file server 114 may represent a web server (e.g., for a website), a server configured to provide file delivery protocol services (such as the File Delivery Protocol (FTP) or the File Delivery over Unidirectional Transport (FLUTE) protocol), a content delivery network (CDN) device, a Hypertext Transfer Protocol (HTTP) server, a Multimedia Broadcast Multicast Service (MBMS) or enhanced MBMS (eMBMS) server, and / or a Network Attached Storage (NAS) device. The 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, and the like.

[0047] The destination device 116 may access the encoded video data from the 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., a digital subscriber line (DSL), a cable modem, etc.), or a combination of both, suitable for accessing the encoded video data stored on the file server 114. The 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 the file server 114, or other such protocols for retrieving media data.

[0048] The output interface 108 and the input interface 122 may represent wireless transmitters / receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of the various IEEE 802.11 standards, or other physical components. In examples where the output interface 108 and the input interface 122 include wireless components, the output interface 108 and the input interface 122 may be configured to communicate data, such as encoded video data, according to a cellular communication standard such as 4G, 4G-LTE (Long Term Evolution), LTE-Advanced, 5G, etc. In some examples where the output interface 108 includes a wireless transmitter, the output interface 108 and the input interface 122 may be configured to communicate data, such as encoded video data, according to other wireless standards such as the IEEE 802.11 specifications, the IEEE 802.15 specifications (e.g., ZigBee LTE), and the like. TM ), Bluetooth TMStandards, etc., for transferring data such as encoded video data. In some examples, source device 102 and / or destination device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include an SoC device for performing the functionality attributed to video encoder 200 and / or output interface 108, and destination device 116 may include an SoC device for performing the functionality attributed to video decoder 300 and / or input interface 122.

[0049] The techniques of the present disclosure may be applied to video decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission (such as Dynamic Adaptive Streaming over HTTP (DASH)), digital video encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0050] The input interface 122 of the destination device 116 receives an encoded video bitstream from the computer-readable medium 110 (e.g., a communication medium, a storage device 112, a file server 114, etc.). The encoded video bitstream may include signaling information defined by the video encoder 200 and also used by the video decoder 300, such as syntax elements with values ​​describing characteristics and / or processing of video blocks or other coding units (e.g., slices, pictures, groups of pictures, sequences, etc.). The display device 118 displays decoded pictures of the decoded video data to a user. The display device 118 may represent any of a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0051] Despite Figure 1 Not shown, but in some examples, the video encoder 200 and the video decoder 300 may be integrated with an audio encoder and / or audio decoder 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.

[0052] The video encoder 200 and the video decoder 300 can each be implemented as any of a variety of suitable encoder and / or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When the technology is partially implemented in software, the device can store instructions for the software in an appropriate non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the technology of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, either of which can be integrated as part of a combined encoder / decoder (codec) in the corresponding device. A device including the video encoder 200 and / or the video decoder 300 can implement the video encoder 200 and / or the video decoder 300 in a processing circuit such as an integrated circuit and / or a microprocessor. Such a device can be a wireless communication device (such as a cellular phone) or any other type of device described herein.

[0053] The video encoder 200 and the video decoder 300 may operate according to a video coding standard such as ITU-T H.265 (also known as High Efficiency Video Coding (HEVC)) or extensions thereto such as multi-view and / or scalable video coding extensions. Alternatively, the video encoder 200 and the video decoder 300 may operate according to other proprietary or industry standards such as ITU-T H.266, also known as Versatile Video Coding (VVC). In other examples, the video encoder 200 and the video decoder 300 may operate according to a proprietary video codec / format such as AOMedia Video 1 (AV1), an extension of AV1, and / or a subsequent version of AV1 (e.g., AV2). In other examples, the video encoder 200 and the video decoder 300 may operate according to other proprietary formats or industry standards. However, the techniques of this disclosure are not limited to any particular coding standard or format. In general, the video encoder 200 and the video decoder 300 may be configured to perform the techniques of this disclosure in conjunction with any video coding technique that uses ALF.

[0054] Typically, the video encoder 200 and video decoder 300 may perform block-based decoding of pictures. The term "block" generally refers to a structure that includes data to be processed (e.g., to be encoded, decoded, or otherwise used in the encoding and / or decoding process). For example, a block may include a two-dimensional matrix of samples of luma and / or chroma data. Typically, the video encoder 200 and video decoder 300 may decode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, rather than decoding red, green, and blue (RGB) data for samples of a picture, the video encoder 200 and video decoder 300 may decode luma and chroma components, where the chroma components may include both a red hue chroma component and a blue hue chroma component. In some examples, the video encoder 200 converts received RGB format data to a YUV representation before encoding, and the video decoder 300 converts the YUV representation to an RGB format. Alternatively, pre-processing and post-processing units (not shown) may perform these conversions.

[0055] The present disclosure may generally relate to the coding (e.g., encoding and decoding) of a picture, including the process of encoding or decoding data for the picture. Similarly, the present disclosure may relate to the coding of a block of a picture, including the process of encoding or decoding data for the block (e.g., prediction and / or residual coding). A coded video bitstream typically includes a series of values ​​for syntax elements that represent coding decisions (e.g., coding modes) and the partitioning of a picture into blocks. Therefore, references to the coding of a picture or block should generally be understood as referring to the coded values ​​of the syntax elements that form the picture or block.

[0056] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (such as the video encoder 200) divides a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video decoder divides the CTU and CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without child nodes may be referred to as a "leaf node," and the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video decoder may further divide the PUs and TUs. For example, in HEVC, the residual quadtree (RQT) represents the division of the TU. In HEVC, a PU represents inter-frame prediction data, and a TU represents residual data. The intra-predicted CU includes intra-frame prediction information, such as an intra-frame mode indication.

[0057] As another example, the video encoder 200 and the video decoder 300 may be configured to operate according to VVC. According to VVC, a video decoder (such as the video encoder 200) divides a picture into multiple CTUs. The video encoder 200 may divide the CTU according to a tree structure (such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure). The QTBT structure removes the concept of multiple partition types, such as the separation between CU, PU, ​​and TU of HEVC. The QTBT structure includes two levels: a first level divided according to quadtree partitioning, and a second level divided according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to the CU.

[0058] In the MTT partition structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more types of ternary tree (TT) (also known as ternary tree (TT)) partitioning. A ternary tree or ternary tree partition is a partition in which a block is divided into three sub-blocks. In some examples, the ternary tree or ternary tree partition divides the block into three sub-blocks without dividing the original block through the center. Partition types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0059] When operating according to the AV1 codec, the video encoder 200 and the video decoder 300 may be configured to decode video data in blocks. In AV1, the largest decoding block that can be processed is called a super block. In AV1, a super block can be 128×128 luma samples or 64×64 luma samples. However, in subsequent video decoding formats (e.g., AV2), super blocks may be defined by different (e.g., larger) luma sample sizes. In some examples, the super block is the top level of the block quadtree. The video encoder 200 may further divide the super block into smaller decoding blocks. The video encoder 200 may use square or non-square partitions to divide super blocks and other decoding blocks into smaller blocks. Non-square blocks may include N / 2×N blocks, N×N / 2 blocks, N / 4×N blocks, and N×N / 4 blocks. The video encoder 200 and the video decoder 300 may perform separate prediction and transform processing on each decoding block.

[0060] AV1 also defines tiles of video data. A tile is a rectangular array of superblocks that can be decoded independently of other tiles. That is, the video encoder 200 and video decoder 300 can encode and decode coded blocks within a tile independently without using video data from other tiles. However, the video encoder 200 and video decoder 300 can perform filtering across tile boundaries. Tiles can be uniform or non-uniform in size. Tile-based decoding enables parallel processing and / or multithreading, as implemented by the encoder and decoder.

[0061] In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT or MTT structure to represent each of the luma component and the chroma components, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luma component and another QTBT / MTT structure for the two chroma components (or two QTBT / MTT structures for the respective chroma components).

[0062] The video encoder 200 and the video decoder 300 may be configured to use quadtree partitioning, QTBT partitioning, MTT partitioning, superblock partitioning, or other partitioning structures.

[0063] In some examples, a CTU includes a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples for a picture with three sample arrays, or a CTB of samples for a monochrome picture or a picture coded using three separate color planes and syntax structures for coding the samples. A CTB can be an N×N block of samples for some value of N, such that one partition is to divide the components into CTBs. A component is an array or a single sample from one of the three arrays (luma and two chroma) that make up a 4:2:0, 4:2:2, or 4:4:4 color format picture, or an array or a single sample of an array that makes up a monochrome format picture. In some examples, a coding block is an M×N block of samples for some value of M and N, such that one partition is to divide the CTB into coding blocks.

[0064] Blocks (e.g., CTUs or CUs) may be grouped in a picture in various ways. As an example, a brick may refer to a rectangular region of a CTU row within a particular tile in a picture. A tile may be a rectangular region of a CTU within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular region of a CTU having a height equal to the height of the picture and a width specified by a syntax element (e.g., such as in a picture parameter set). A tile row refers to a rectangular region of a CTU having a height specified by a syntax element (e.g., such as in a picture parameter set) and a width equal to the width of the picture.

[0065] In some examples, a tile may be divided into multiple bricks, each of which may include one or more CTU rows within the tile. A tile that is not divided 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. Bricks in a picture may also be arranged in slices. A slice may be an integer number of bricks of a picture that may be uniquely contained in a single Network Abstraction Layer (NAL) unit. In some examples, a slice includes multiple complete tiles or a contiguous sequence of complete bricks of only one tile.

[0066] This disclosure may use "NxN" and "N by N" interchangeably to refer to the sample size of a block (such as a CU or other video block) in terms of the vertical and horizontal dimensions, for example, 16x16 samples or 16 by 16 samples. Typically, a 16x16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Likewise, an NxN CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. Furthermore, a CU does not necessarily need to have the same number of samples in the horizontal direction as in the vertical direction. For example, a CU may include NxM samples, where M is not necessarily equal to N.

[0067] The video encoder 200 encodes video data representing prediction and / or residual information and other information for a CU. The prediction information indicates how to predict the CU in order to form a prediction block for the CU. The residual information typically represents the sample-by-sample difference between the samples of the CU before encoding and the prediction block.

[0068] To predict a CU, the video encoder 200 may typically form a prediction block for the CU through inter-frame prediction or intra-frame prediction. Inter-frame prediction generally refers to predicting a CU from data of a previously decoded picture, while intra-frame prediction generally refers to predicting a CU from previously decoded data of the same picture. To perform inter-frame prediction, the video encoder 200 may use one or more motion vectors to generate a prediction block. The video encoder 200 may typically perform a motion search to identify a reference block that closely matches the CU, for example, based on the difference between the CU and the reference block. The video encoder 200 may calculate a difference metric using the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), or other such difference calculations to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 may use unidirectional prediction or bidirectional prediction to predict the current CU.

[0069] Some examples of VVC also provide an affine motion compensation mode, which can be considered an inter-frame prediction mode. In affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion (such as zooming in or out, rotation, perspective motion, or other irregular motion types).

[0070] To perform intra prediction, the video encoder 200 may select an intra prediction mode to generate a prediction block. Some examples of VVC provide sixty-seven intra prediction modes, including various directional modes, as well as planar mode and DC mode. Typically, the video encoder 200 selects an intra prediction mode that describes neighboring samples of a current block (e.g., a block of a CU) from which to predict the samples of the current block. Assuming that the video encoder 200 decodes CTUs and CUs in raster scan order (from left to right, top to bottom), such samples may typically be located above, above and to the left of the current block in the same picture as the current block.

[0071] The video encoder 200 encodes data indicating a prediction mode for the current block. For example, for inter-frame prediction mode, the video encoder 200 may encode data indicating which of various available inter-frame prediction modes to use, as well as motion information for the corresponding mode. For example, for unidirectional or bidirectional inter-frame prediction, the video encoder 200 may encode motion vectors using Advanced Motion Vector Prediction (AMVP) or merge mode. The video encoder 200 may use a similar mode to encode motion vectors for affine motion compensation mode.

[0072] AV1 includes two general techniques for encoding and decoding coded blocks of video data. These two general techniques are intra-frame prediction (e.g., intra-frame prediction or spatial prediction) and inter-frame prediction (e.g., inter-frame prediction or temporal prediction). In the context of AV1, when an intra-frame prediction mode is used to predict a block of a current frame of video data, the video encoder 200 and the video decoder 300 do not use video data from other frames of the video data. For most intra-frame prediction modes, the video encoder 200 encodes the block of the current frame based on the difference between sample values ​​in the current block and prediction values ​​generated from reference samples in the same frame. The video encoder 200 determines the prediction values ​​generated from the reference samples based on the intra-frame prediction mode.

[0073] After a prediction (such as intra-frame prediction or inter-frame prediction for a block), the video encoder 200 may calculate residual data for the block. The residual data (such as a residual block) represents the sample-by-sample difference between the block and a prediction block for the block, which was formed using the corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to produce transformed data in the transform domain rather than the sample domain. For example, the video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. In addition, the video encoder 200 may apply a secondary transform after the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc. The video encoder 200 generates transform coefficients after applying the one or more transforms.

[0074] As noted above, after any transforms that produce transform coefficients, the video encoder 200 may perform quantization on the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to potentially reduce the amount of data used to represent the transform coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 may reduce the bit depth associated with some or all transform coefficients. For example, the video encoder 200 may round down an n-bit value to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, the video encoder 200 may perform a bit-by-bit right shift of the value to be quantized.

[0075] After quantization, the video encoder 200 may scan the transform coefficients to produce a one-dimensional vector from the two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place transform coefficients with higher energy (and therefore lower frequency) at the front of the vector and transform coefficients with lower energy (and therefore higher frequency) at the back of the vector. In some examples, the video encoder 200 may scan the quantized transform coefficients using a predefined scan order to produce a serialized vector and then entropy encode the quantized transform coefficients of the vector. In other examples, the video encoder 200 may perform adaptive scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, the video encoder 200 may entropy encode the one-dimensional vector, for example, according to context-adaptive binary arithmetic coding (CABAC). The video encoder 200 may also entropy encode the values ​​of syntax elements that describe metadata associated with the encoded video data, which is used by the video decoder 300 when decoding the video data.

[0076] To perform CABAC, the video encoder 200 may assign context within a context model to a symbol to be sent. The context may relate to, for example, whether the neighboring values ​​of the symbol are zero values. The probability determination may be based on the context assigned to the symbol.

[0077] The video encoder 200 may further generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, in a picture header, a block header, or a slice header, to the video decoder 300, or generate other syntax data such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS). The video decoder 300 may also decode such syntax data to determine how to decode the corresponding video data.

[0078] In this way, the video encoder 200 can generate a bitstream including encoded video data, such as syntax elements describing the partitioning of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Ultimately, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0079] In general, the video decoder 300 performs a process that is inverse to that performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 may use CABAC to decode the values ​​of syntax elements for the bitstream in a manner substantially similar to, but inverse to, the CABAC encoding process of the video encoder 200. The syntax elements may define partition information for partitioning a picture into CTUs and partitioning each CTU according to a corresponding partition structure, such as a QTBT structure, to define CUs of the CTUs. The syntax elements may further define prediction and residual information for a block of video data (e.g., a CU).

[0080] The residual information may be represented by, for example, quantized transform coefficients. The video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of the block to reproduce a residual block for the block. The video decoder 300 uses the signaled prediction mode (intra-frame prediction or inter-frame prediction) and related prediction information (e.g., motion information for inter-frame prediction) to form a prediction block for the block. The video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. The video decoder 300 may perform additional processing, such as a deblocking process to reduce visual artifacts along block boundaries.

[0081] The present 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 the values ​​of syntax elements in a bitstream. Generally, signaling refers to generating values ​​in a bitstream. As noted above, source device 102 may transmit the bitstream to destination device 116 in substantially real time or in non-real time (such as may occur when storing syntax elements to storage device 112 for later retrieval by destination device 116).

[0082] In video decoding, such as in the H.266 / VVC standard, ALF is applied to minimize the mean square error between filtered samples and original samples. The ALF as implemented in H.266 / VVC only uses samples after SAO filtering. That is, the input samples of the ALF can be, for example, the output samples of the SAO. The output samples of the ALF can be stored in the decoded picture buffer (DPB) or output as a viewable picture. The filter shapes of the ALF used in the joint detection model (JEM) software are 5×5, 7×7 and 9×9 diamonds. The filter shape can be selected and signaled at the picture level in the JEM. In order to obtain a better trade-off between decoding efficiency and filter complexity, in VVC, only 7×7 diamonds and 5×5 diamonds are supported for the luminance component and chrominance components, respectively.

[0083] Figure 2A An example filter 140 is shown which is a 7x7 diamond filter. Figure 2B An example filter 142 is shown which is a 5×5 diamond filter. In each of the filters 140 and 142, the integer coefficients c i Expressed with 7-digit fractional precision. i The absolute value of is decoded by using the 0th order Exp-Golomb code followed by the sign bit of the non-zero coefficient. Figure 2A and Figure 2B In , each square corresponds to a luma sample or a chroma sample, and the center square corresponds to the current sample to be filtered. In order to reduce the overhead of transmitting coefficients and the number of multiplications, Figure 2A and Figure 2B The filter shape in is point symmetric. Additionally, as shown in equation (1), the sum of all filter coefficients is set equal to 128, which is a fixed-point representation of 1.0 with 7-bit fractional precision.

[0084]

[0085] In equation (1), N is the number of coefficients, where N is equal to 13 and 7 for 7×7 and 5×5 filter shapes, respectively.

[0086] In VVC, nonlinearity is introduced into the ALF. When the difference between the adjacent sample value and the current sample value to be filtered is too large, a simple clipping function is applied to reduce the influence of the adjacent sample value. In order to filter the sample, the ALF can be performed as follows:

[0087]

[0088] Where R(x,y) is the sample value after SAO.

[0089] The nonlinear function is defined using the clipping function:

[0090] f i,j =min(b i ,max(-b i ,R(x+x i,j ,y+y i,j )-R(x,y))) (3) Where j is equal to 0 or 1, and (x i,j ,y i,j ) is the i-th coefficient c i The filter tap positioning offset.

[0091] In VVC version 1, as shown in equation (4), the coefficient c i The clipping parameter b i By clipping index d i OK. BD is the internal bit depth.

[0092]

[0093] For the filter, the number of signaled coefficients and the number of signaled clipping indices are both N-1. Each coefficient is limited to the range [-128, 127], which is equivalent to [-1.0, 1.0] with 7-bit fractional precision. Each clipping index d i Can be 0, 1, 2 or 3 and is signaled by using a two-bit fixed length code. To simplify the clipping operation, as in equation (4), the clipping parameter b i The value of can be limited to powers of 2. Therefore, the bitwise logical operation can be applied as a clipping operation.

[0094] The video encoder 200 and the video decoder 300 can be configured to perform sub-block level filter adaptation. In VVC version 1, ALF follows the same luma classification framework as the ALF in JEM-7.0. In order to obtain a better trade-off between decoding efficiency and computational complexity, the block size for classification can be increased from 2×2 samples to 4×4 samples. In order to determine the class index of a 4×4 block, a surrounding window with 8×8 luma samples is used to derive direction and activity information. In this 8×8 luma sample window, four gradient values ​​are first calculated for every other sample, such as Figure 3 shown. Figure 3 The downsampled Laplacian values ​​of the 4×4 sub-block 150 for ALF classification are illustrated. The gradient values ​​of the samples marked with dots are calculated. The gradient values ​​of the other samples are set to 0.

[0095] Figure 4Four gradient values ​​are illustrated for each sample with coordinates (k, l). A dot represents the sample for which the gradient is being calculated. Block 160 illustrates the horizontal gradient (H), and block 162 illustrates the vertical gradient (V). Block 164 illustrates the 135 degree gradient (D1), and block 166 illustrates the 45 degree gradient (D2). H, V, D1, and D2 are derived as follows:

[0096]

[0097] The variables i and j can refer to the coordinates of the upper left sample in the 4×4 block. The horizontal gradient g is calculated H , vertical gradient g V , 135 degree gradient g D1 and 45 degree gradient g D2 The sum is calculated as follows:

[0098]

[0099] The ratio of the maximum and minimum values ​​of the horizontal and vertical gradients (denoted by R H,V ) and the ratio of the maximum and minimum values ​​of the two diagonal gradients (denoted by R D1,D2 denoted) is calculated as shown in equation (7).

[0100]

[0101] Then, R H,V and R D1,D2 Two thresholds (t1=2 and t2=4.5) are compared with each other to derive the directionality D:

[0102] Step 1: If R H,V ≤t1 and R D1,D2 ≤t1, then D is set to 0 (texture), otherwise continue with step 2.

[0103] Step 2: If R D1,D2 >R H,V , then continue with step 3, otherwise continue with step 4.

[0104] Step 3: If R D1,D2 ≤t2, D is set to 1 (weak diagonal), otherwise, D is set to 2 (strong diagonal).

[0105] Step 4: If R H,V ≤t2, D is set to 3 (weak horizontal / vertical), otherwise, D is set to 4 (strong horizontal / vertical).

[0106] The activity value A is calculated as follows:

[0107]

[0108] Figure 5 An example of merging 25 brightness classes into 7 merged classes (0 to 6) is shown, where each square represents a The 5×5 grid 170 represents 25 classes, and the numbers in each box of the 5×5 grid 170 represent the merged classes from 0 to 6. Each class (i.e., each square in the 5×5 grid 170) may have an index from 0 to 24 (inclusive). a is mapped to a range of 0 to 4 (inclusive), and the quantized value is represented as Therefore, each 4×4 block is classified into one of 25 classes as follows:

[0109]

[0110] The luminance filter bank contains 25 filters. However, in order to reduce the number of bits required to represent the filter coefficients while maintaining decoding efficiency, different classes can be merged, with the merged classes using the same filters. The merge table is signaled. In the merge table, for example, a fixed-length code is used to signal the filter index of each class. Figure 5 In the example filter bank of , 7 luma filters are signaled. For each class, the filter index is signaled in ALF_APS (in this example, from 0 to 6).

[0111] After determining a filter from the luma filter bank based on the class index C and the merge table of the 4×4 block, before filtering samples of the 4×4 block, a geometric transformation may be applied to the filter according to the gradient value calculated for the 4×4 block as illustrated in Table 1.

[0112] Table 2: Geometric transformation based on gradient values

[0113] Gradient value Transform <![CDATA[g D2 <g D1 And g H <g V ]]> No transformation <![CDATA[g D2 <g D1 And g V ≤g H ]]> Diagonal flip <![CDATA[g D1 ≤g D2 And g H <g V ]]> Flip vertically <![CDATA[g D1 ≤g D2 And g V ≤g H ]]> Right rotation

[0114] Figure 6 Shown Figure 2A An example of a geometric transformation of the filter 140 in FIG. Figure 6 As can be seen in , filter 180 corresponds to a diagonal flip of filter 140. Filter 182 corresponds to a vertical flip of filter 140, and filter 184 corresponds to a right rotation of filter 140.

[0115] The video encoder 200 and the video decoder 300 can be configured to perform coding tree block level adaptation. In JEM-7.0, only one luma filter group is applied to all luma CTBs of a slice, and only one chroma filter is applied to all chroma CTBs of a slice. However, there are two potential disadvantages. First, when there is a certain amount of difference in the statistical information between the CTBs, using the same filter or filter group for all CTBs of a color component can limit the decoding efficiency of the ALF, especially for large resolution sequences and mixed content video sequences. Second, when deriving the filter for a slice, the filter cannot be calculated until the statistical information of the entire slice is collected. This multi-channel decoding is not friendly to low-latency applications. To solve this problem, one solution is to use statistical information from previously decoded slices. However, this may result in some performance loss.

[0116] In addition to luma 4×4 block-level filter adaptation, VVC supports CTB-level filter adaptation. In a slice, different luma CTBs are allowed to use different luma filter groups, and different chroma CTBs can use different chroma filters. CTBs with similar statistical information can use the same filters. This CTB-level filter adaptation improves decoding efficiency, especially for low-latency applications. In addition, VVC version 1 allows filters from previously decoded pictures to be used for CTBs. This temporal filter reuse mechanism can reduce the overhead of signaling filter coefficients. In VVC version 1, up to seven signaled luma filter groups and eight signaled chroma filters can be applied to a slice. When no signaled filters are present, one of 16 fixed filter groups can be applied to the luma CTB. When ALF is enabled, the fixed filter group or the filter group index of the signaled luma filter group is signaled for the luma CTB. The filter index of the signaled chroma filter is signaled for the chroma CTB. By using the filters signaled from the previously decoded pictures and the fixed filters, when encoding the current CTU in low-latency applications, the three CTU-level on / off flags and filter / filter group indices can be determined by using only the statistics of the current CTU. Therefore, the coded bitstream of each CTU can be generated on the fly without waiting for the statistics of the entire picture to be available.

[0117] The video encoder 200 and the video decoder 300 may be configured to perform techniques for line buffer reduction. Figure 2A and Figure 2BAs shown, in the vertical direction, the filter shape has 7 taps for the luma component and 5 taps for the chroma component. Therefore, in VVC Test Model 2.0 (VTM-2.0), when decoding a row of CTUs, due to the delay of the deblocking filter and SAO filter, the 7 luma lines and 4 chroma lines of the upper CTU row must be stored in the line buffer for ALF. However, the additional line buffer requires a larger chip area, especially for high-definition (HD) and ultra-high-definition (UHD) video sequences.

[0118] To make ALF hardware-friendly (e.g., by reducing line buffer requirements), the concept of virtual boundary (VB) can be applied to remove all line buffer overhead of ALF. Considering the deblocking filter and SAO filter in VVC version 1, the positioning of VB is 4 luma samples and 2 chroma samples above the horizontal CTU boundary. When filtering one sample on one side of the VB, the samples on the other side of the VB cannot be utilized, and a modified filtering with symmetrical sample padding can be applied.

[0119] 7A to 7C An example of symmetrical sample padding for luma ALF filtering at ALF VB is shown. 7A to 7C In the example of , the center square of filter 190 is the location of the current sample to be filtered, and the bold line is the location of VB (VB192). 7A to 7C , the filter tap positions with dashed lines are filled. Figure 7A An example is shown of one filter tap position of filter 190 being above or below VB 192. In this example, one filter tap position is filled. Figure 7B An example is shown of four filter tap positions of filter 190 above and below VB 192. In this example, four filter tap positions are filled.

[0120] However, when the sample is on the nearest row on each side of VB 192 (e.g. Figure 7C (as shown in ), a 2D filter is equivalent to a horizontal filter. This may introduce visual artifacts. To address this issue, the filter strength can be compensated when the current sample to be filtered is located on the nearest row on each side of VB, as shown in equation (10). Comparing equation (10) with equation (2), it can be seen that an additional 3 bits are right-shifted.

[0121]

[0122] When applying VB processing, the classification of the 4×4 block can also be modified. When calculating the class index of the 4×4 block on one side of the VB, the gradients and samples on the other side of the VB may not be used, such as Figure 8 As shown in .

[0123] Figure 8 An example of ALF 4×4 sub-block classification at ALF VB is shown. When calculating the gradient value of samples adjacent to VB, the samples on the other side of VB cannot be used. Therefore, Figure 8 As shown, the boundary samples on the current side are repeatedly extended. That is, the boundary samples on the current side of VB are mirrored to the other side of VB. Since the number of available gradient values ​​is reduced, the active derivation in equation (8) is rescaled to:

[0124]

[0125] The video encoder 200 and the video decoder 300 may be configured to signal filter coefficients. In VVC version 1, ALF coefficients are signaled in an ALF adaptation parameter set (APS). An APS may include a set of luma filters with a maximum of 25 filters, a maximum of 8 chroma filters, and a maximum of 8 cross-component ALF (CC-ALF) filters. Each set of luma filters supports applying ALF to 25 luma classes. In VVC version 1, a maximum of 8 ALF_APSs are supported.

[0126] Table 2 below shows an example syntax signal table for signaling filter coefficients according to the techniques of this disclosure.

[0127] Table 2

[0128]

[0129] The video encoder 200 and the video decoder 300 can be configured to use multiple classifiers to perform ALF. In VVC, only one classifier and one filter can be applied when filtering a sample. In order to improve the ALF performance based on VVC, an ALF framework based on multiple classifiers has been proposed. An example of such a framework is specifically implemented in Figure 9 When filtering the samples, as shown in Figure 9 As shown, multiple classifiers are applied. Filters are applied to samples corresponding to the classifiers. Figure 9 There are two stages. First (first stage 540), the pre-filtering stage comprises a filter bank F(f,i) of the i-th fixed filter bank (i=0...N f -1) and classifier C(f,i)(i=0……N f -1). Next (second stage 542), the final filtering stage comprises a signaled filter or predefined filter bank F' and a corresponding classifier C'.

[0130] Figure 10An example ALF framework with three classifiers is shown. In this regard, Figure 10 The ALF framework represents relative to Figure 9 A specific implementation of the general ALF framework described in ECM-1.0. Figure 10 In the example, N f =2. Figure 10 There are two stages. First (first stage 544), the pre-filtering stage comprises a filter bank F(f,i) of the i-th fixed filter bank (i=0...N f -1) and classifier C(f,i)(i=0……N f -1). Next (second stage 546), the final filtering stage comprises a signaled filter or predefined filter bank F' and a corresponding classifier C'.

[0131] In ECM-1.0, in the classifier C(f,i) (i=0 or 1), the activity value and direction value can be determined based on the 2-D Laplacian value. The classifier can be applied to each sample or block. When the classifier is applied to a block, all samples in the block have the same class index and the same transposition type. Assume w i Indicates the width of the block, h i represents the height of the block, and (x,y) represents the coordinates of the top left sample of the block.

[0132] Similar to as in VVC, the video decoder 300 may be configured to derive the activity value A by using the vertical gradient and the horizontal gradient. i and the directivity value D i .

[0133] A i Can be further quantized to 0 to M A,i -1 (inclusive), where the quantized value is expressed as Value D i Can be from 0 to M D,i -1 (inclusive).

[0134] The video decoder 300 may use the class index C i Derived as C-based i , the video decoder 300 can select a filter from C(f,i).

[0135] In the second stage, F' is the signaled filter or predefined filter bank, and C' is the corresponding classifier. The intermediate filtered result can be further filtered using the current sample and / or neighbors. C' can be used to determine which filter in F' to apply and how to transpose the coefficients.

[0136] C' can use R and / or R' to determine the filter indices of filter bank F' by computing activity and direction as a first stage. A transpose can be applied when applying F'.

[0137] In ECM-7.0, classification based on two classifiers is applied to each 2x2 block to select filters from a signaled filter bank, as proposed in U.S. patent application Ser. No. 17 / 853,274, filed on June 29, 2022. For each 2x2 block, either a Laplacian-based classifier or a band-based classifier is applied to the CTB. This selection is signaled for each filter bank in the APS. The classifier is applied to the input of the ALF.

[0138] When applying a Laplace-based process, such as in VVC, the video decoder 300 can derive the activity value A by using the vertical gradient and the horizontal gradient. A is then further quantized to 0 to M. A -1 (inclusive), and the quantized value is expressed as The video decoder 300 can derive the range from 0 to M based on the use of vertical gradient and horizontal gradient. D A directionality value D of -1.

[0139] Class Index

[0140] When a band-based process is applied to N classes, the dynamic range of values ​​(e.g., the value of a sample or the sum of the sample values ​​of a block) can be evenly or unevenly divided into N non-overlapping intervals. When classifying a sample or block, the video decoder 300 can derive the value of the sample or the sum of the sample values ​​of the block. The interval index of the sample value or sum can then be used as a class index. For example, when the dynamic range of the sum of the block is evenly divided into N intervals, the class index can be derived as:

[0141] (sum*N) >> {bitdepth + [log2(number of samples in block)]}

[0142] where bitdepth is the bit depth of the sample values.

[0143] After determining the class index of the sample from C', the video decoder 300 can select a filter from the filter bank F' based on the class index. The video decoder 300 can apply the filter as:

[0144]

[0145] In the above equation, filtering is divided into 2 parts:

[0146] Filtering part 1: A geometric transform can be applied by filtering using neighboring samples. N0 is the number of coefficients. The filter shape and size can be, for example, a 5×5, 7×7, 9×9, 11×11, or 13×13 diamond filter or a filter with some other shape.

[0147] Filtering part 2: By filtering using the intermediate filtered samples, a geometric transform can be applied. N1 is the number of coefficients.

[0148] Function f i,j (where j = 0 or 1) the available clipping function is defined as

[0149] f i,j =f i,j (R(x+x i,j ,y+y i,j ),R(x,y))

[0150] = minimum value (b i ,max(-b i ,R(x+x i,j ,y+y i,j )-R(x,y))) (13)

[0151] Function g i The clipping function can be defined as

[0152] g i =g i (R′(x,y,i-N0),R(x,y))=minimum value(b i ,max(-b i ,R′(x,y,i-N0)-R(x,y))) (14)

[0153] b i is the coefficient c i In ECM-1.0, N1=2.

[0154] The video decoder 300 may be configured to use the reconstructed samples before the deblocking filter for ALF. In JVET-Z0146 and JVET-AA0095, it is proposed to use the reconstructed samples before the deblocking filter for ALF.

[0155] As discussed above, in video coding (such as H.266 / VVC), ALF is applied to minimize the mean square error between the filtered samples and the original samples. In VVC, ALF is applied after SAO, and the reconstructed signal before the deblocking filter is also fed into the ALF unit.

[0156] The video decoder 300 can be configured to use prediction data or residual data for ALF. JVET-AB0181 and JVET-AC0162 proposed using prediction samples or residual samples as additional input to ALF. JVET-AC0173 proposed adding a third classifier to ALF, which is applied to residual samples.

[0157] Using prediction samples or residual samples as additional input to the ALF requires an extra buffer to store these samples until they are used in the ALF stage.

[0158] In typical hardware designs, this typically requires LCU-level pipeline processing, meaning that the results for the next stage are buffered after processing from the current stage. In this case, the residual used for both classification and filtering in the ALF involves keeping the LCU's residual for two more stages (DB and SAO). Figure 11 The above LCU level residual buffer concept is shown in FIG.

[0159] Similarly, if reconstructed samples before deblocking filtering are used for ALF, the reconstructed samples need to be buffered and maintained at two additional stages (DB 1242 and SAO 1244).

[0160] exist Figure 11 In the example of , the adder 1110 adds the residual to the predictor to form a reconstructed picture or a portion of the reconstructed picture, such as one or more blocks. The portion of the reconstructed picture is filtered by the deblocking filter 1142 and the SAO 1144. When the deblocking filter 1142 and the SAO 1144 filter the portion of the reconstructed picture, the residual is stored in the buffer 1152 and the buffer 1154. The buffer 1152 and the buffer 1154 are Figure 11 1144 , but can actually be implemented as a single memory or portion of a memory. The ALF 1146 filters the output of the SAO 1144 and, as described above, can determine one or more filters based on the residual stored in the buffer 1154.

[0161] This disclosure describes techniques for preprocessing prediction samples or residual samples to reduce the amount of data that needs to be stored for ALF. Furthermore, preprocessing can increase the robustness of the data and, therefore, improve the performance of the ALF. In this process, prediction samples or residual samples are preprocessed before being stored for use in the ALF. This process can include filtering and / or downsampling the data (where "data" refers to either prediction samples or residual samples, depending on which is used). Figure 12In the example of , the residual data is pre-processed before being stored and used for ALF. Typically, filtering uses a smoothing filter or a low-pass filter or simply averaging over a predefined support region.

[0162] exist Figure 12 In the example of , the adder 1210 adds the residual to the predictor to form a reconstructed picture or a portion of the reconstructed picture, such as one or more blocks. The portion of the reconstructed picture is filtered by the deblocking filter 1242 and the SAO 1244. Figure 11 Different, in Figure 12 In the example of FIG, the pre-processing unit 1250 processes the residual data, and the processed residual data is stored in the buffer 1252 and the buffer 1234. The buffer 1252 and the buffer 1254 are Figure 12 1254, but may actually be implemented as a single memory or portion of a memory. The ALF 1246 filters the output of the SAO 1244 and, as described above, may determine one or more filters based on the residual stored in the buffer 1254.

[0163] If the residual is only used for classification, then there may be no need to store the residual for two additional stages, since no filters are actually applied to the residual. Therefore, the preprocessing described for classification derivation can be performed on the residual at the reconstruction (or DB) level, and then only the classification results need to be buffered, which may require a smaller buffer (lower complexity). This concept is discussed in Figure 13 Shown in.

[0164] exist Figure 13 In the example of , the adder 1310 adds the residual to the predictor to form a reconstructed picture or a portion of the reconstructed picture, such as one or more blocks. The portion of the reconstructed picture is filtered by the deblocking filter 1342 and the SAO 1344. Figure 11 Different, in Figure 13 In the example of , the pre-processing unit 1250 processes the residual data to determine a class, and the class is stored in the buffer 1354. The ALF 1346 filters the output of the SAO 1344 and, as described above, may determine one or more filters based on the class stored in the buffer 1354.

[0165] The video decoder 300 can be configured to use the residual data as additional input data for filtering in the ALF. In some examples, the residual data may be preprocessed before being stored and used in the ALF. The process can also be used for applications that use prediction data or both prediction data and residual data. Specifically, the process includes downsampling to reduce the amount of data to be stored. It should be noted that when the data is used in the ALF, upsampling may be required. However, in some specific implementations, upsampling can be performed implicitly. For example, the downsampling rate is M in the horizontal direction and N in the vertical direction, then the sample with coordinates (m,n) corresponds to the sample with coordinates (m / M,n / N) in the downsampled data.

[0166] When downsampling the residual samples for ALF, a representative sample value is derived for each subblock of samples. Assuming the width and height of the original data are W and H, and the subblock width and height are sW and sH, the downsampling ratio is W / sW in the horizontal direction and H / sH in the vertical direction. The subblock size can be adaptively selected and signaled in the bitstream (e.g., high-level syntax).

[0167] In one example, a representative sample in a sub-block is derived by selecting any sample among the samples in the sub-block (e.g., the top left sample, the sample with coordinates (sW / 2 -1, sH / 1) that is "centered" relative to the top left sample, etc.).

[0168] In another example, a representative sample in a sub-block is derived by averaging all or some of the sample values ​​in the sub-block or the sample values ​​in a surrounding window of the sub-block. All samples may share the same weight, or have different weights depending on the position (e.g., samples near the center of the sub-block have a greater weight).

[0169] In yet another example, a filtering process can be applied. For example, smoothing using a bilinear filter, a Gaussian filter, or another filter can be used. The filter can be a fixed filter trained offline, or selected from a set of filters trained offline. If the filter is selected from a set of filters, the index can be signaled in the bitstream as one of the ALF parameters. Filtering can be applied before downsampling, or without downsampling. In another example, the filter coefficients can be signaled.

[0170] The video decoder 300 can be configured to use the residual data for classification in the ALF. In some examples, such as Figure 13 As illustrated in , the residual data is preprocessed before being used for classification in ALF. Preprocessing includes a filtering process (usually a smoothing filter or a low-pass filter) to increase the robustness of the classification result.

[0171] The video decoder 300 may be configured to use the residual data as additional input data for both classification and filtering in the ALF.

[0172] In one example, the same pre-processed residual data is used for classification and filtering in the ALF.

[0173] In another example, the pre-processed residual data is stored and used for filtering in the ALF. However, the original residual data is used for classification in the ALF, so the classification result can be stored as additional data fed into the ALF stage.

[0174] In another example, a first preprocessing process is performed on the residual data that is stored and used for filtering in the ALF, and a second preprocessing process is performed on the residual data that is used for classification in the ALF. Typically, the first preprocessing process may include downsampling to reduce the amount of data that needs to be stored. The second preprocessing process may include only filtering without downsampling, storing the classification results instead of the preprocessed residual data.

[0175] In some examples, the video decoder 300 may be configured to perform pre-processing on the reconstructed data prior to the deblocking filter. Figure 14 In the example of , the adder 1410 adds the residual to the predictor to form a reconstructed picture or a portion of the reconstructed picture, such as one or more blocks. The portion of the reconstructed picture is filtered by the deblocking filter 1442 and the SAO 1444. Figure 11 Different, in Figure 14 In the example of FIG, the pre-processing unit 1450 processes the reconstructed picture or a portion thereof, and the processed reconstructed data is stored in the buffer 1452 and the buffer 1454. The buffer 1452 and the buffer 1454 are Figure 14 1444, but may actually be implemented as a single memory or portion of a memory. The ALF 1446 filters the output of the SAO 1444 and, as described above, may determine one or more filters based on the processed reconstructed data stored in the buffer 1454.

[0176] As described above, the video decoder 300 can feed the reconstructed signal before the deblocking filter as an additional input to the ALF module. Therefore, it is necessary to store the reconstructed signal before the deblocking filter. This disclosure describes a technique for preprocessing the reconstructed signal before storing it. Similar to the process described above, the preprocessing may include a filter and / or downsampling. However, the filter can be any of the following types: a low-pass filter, a high-pass filter, or a smoothing filter. Downsampling can be applied to reduce the amount of data that needs to be stored.

[0177] Figure 15is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 15 This is provided for purposes of explanation and should not be considered limiting of the techniques broadly illustrated and described in this disclosure. For purposes of explanation, this disclosure describes the video decoder 200 in terms of techniques for VVC and HEVC. However, the techniques of this disclosure may be performed by video encoding devices configured for other video coding standards and video coding formats, such as AV1 and successors to the AV1 video coding format.

[0178] exist Figure 15 In the example of FIG, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218, and an entropy coding unit 220. Any or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filter unit 216, the DPB 218, and the entropy coding unit 220 may be implemented in one or more processors or in processing circuitry. For example, the units of the video encoder 200 may be implemented as one or more circuits or logic elements as part of a hardware circuit, or as part of a processor, ASIC, or FPGA. Furthermore, the video encoder 200 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0179] The video data memory 230 may store video data to be encoded by the components of the video encoder 200. The video encoder 200 may receive video data from, for example, the video source 104 ( Figure 1 ) receives video data stored in the video data memory 230. The DPB 218 can act as a reference picture memory that stores reference video data for use when the video encoder 200 predicts subsequent video data. The video data memory 230 and the DPB 218 can be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The video data memory 230 and the DPB 218 can be provided by the same memory device or separate memory devices. In various examples, the video data memory 230 can be on-chip with other components of the video encoder 200 (as illustrated in the figure), or off-chip relative to those components.

[0180] In the present disclosure, references to the video data memory 230 should not be construed as limited to memory internal to the video encoder 200 (unless specifically described) or memory external to the video encoder 200 (unless specifically described). Rather, references to the video data memory 230 should be understood as reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). Figure 1 Memory 106 may also provide temporary storage for outputs from the various units of video encoder 200 .

[0181] Illustrated Figure 15 The various units of the video encoder 200 are described to help understand the operations performed by the video encoder 200. The units can be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide specific functionality and are pre-set for 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 example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (for example, to receive parameters or output parameters), but the type of operations performed by the fixed-function circuits are generally immutable. In some examples, one or more of the units can be different circuit blocks (fixed-function or programmable), and in some examples, one or more of the units can be integrated circuits.

[0182] The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example in which the operation of the video encoder 200 is performed using software executed by a programmable circuit, the memory 106 ( Figure 1 ) may store instructions (eg, object code) for software received and executed by video encoder 200, or another memory (not shown) within video encoder 200 may store such instructions.

[0183] The video data memory 230 is configured to store the received video data. The video encoder 200 can retrieve the picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 can be the original video data to be encoded.

[0184] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. The mode selection unit 202 may include additional functional units for performing video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an intra block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

[0185] The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and the resulting rate-distortion values ​​for such combinations. The encoding parameters may include the partitioning of CTUs into CUs, the prediction mode for a CU, the transform type for the residual data of a CU, the quantization parameter for the residual data of a CU, etc. The mode selection unit 202 may ultimately select a coding parameter combination that has a better rate-distortion value than the other tested combinations.

[0186] The video encoder 200 may divide a picture retrieved from the video data memory 230 into a series of CTUs and pack one or more CTUs into a slice. The mode selection unit 202 may divide the CTUs of the picture according to the tree structure described above, such as the MTT structure, the QTBT structure, the super block structure, or the quadtree structure described above. As described above, the video encoder 200 may form one or more CUs by dividing the CTUs according to the tree structure. Such CUs may also be generally referred to as "video blocks" or "blocks."

[0187] Typically, mode select unit 202 also controls its components (e.g., motion estimation unit 222, motion compensation unit 224, and intra prediction unit 226) to generate a prediction block for a current block (e.g., the current CU, or, in HEVC, the overlapping portion of a PU and TU). To inter-predict the current block, motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in DPB 218). Specifically, motion estimation unit 222 may calculate values ​​representing how similar potential reference blocks are to the current block, such as based on sum of absolute differences (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared difference (MSD), and the like. Motion estimation unit 222 may typically perform these calculations using sample-by-sample differences between the current block and the reference block under consideration. Motion estimation unit 222 may identify the reference block with the lowest value resulting from these calculations, indicating the reference block that best matches the current block.

[0188] Motion estimation unit 222 may form one or more motion vectors (MVs) that define the positioning of a reference block in a reference picture relative to the positioning of a current block in the current picture. Motion estimation unit 222 may then provide the motion vectors to motion compensation unit 224. For example, for unidirectional inter prediction, motion estimation unit 222 may provide a single motion vector, while for bidirectional inter prediction, motion estimation unit 222 may provide two motion vectors. Motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, motion compensation unit 224 may use the motion vectors to retrieve data for a reference block. As another example, where the motion vectors have fractional sample precision, motion compensation unit 224 may interpolate the values ​​of the prediction block based on one or more interpolation filters. Furthermore, for bidirectional inter prediction, motion compensation unit 224 may retrieve data for two reference blocks identified by the respective motion vectors and combine the retrieved data, for example, by sample-by-sample averaging or weighted averaging.

[0189] When operating according to the AV1 video coding format, the motion estimation unit 222 and the motion compensation unit 224 may be configured to encode coding blocks of the video data (e.g., both luma coding blocks and chroma coding blocks) using translational motion compensation, affine motion compensation, overlapped block motion compensation (OBMC), and / or composite inter-intra prediction.

[0190] As another example, for intra prediction or intra prediction coding, the intra prediction unit 226 may generate a prediction block from samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 may generally mathematically combine the values ​​of the adjacent samples and pad these calculated values ​​across the current block in a defined direction to produce the prediction block. As another example, for DC mode, the intra prediction unit 226 may calculate the average of the adjacent samples of the current block and generate the prediction block to include the resulting average for each sample of the prediction block.

[0191] When operating according to the AV1 video coding format, the intra prediction unit 226 can 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, luma-chroma (CFL) prediction, intra-block copy (IBC), and / or palette mode. The mode selection unit 202 may include additional functional units for performing video prediction according to other prediction modes.

[0192] Mode selection unit 202 provides the prediction block to residual generation unit 204. Residual generation unit 204 receives the uncoded original version of the current block from video data memory 230 and the prediction block from mode selection unit 202. Residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, residual generation unit 204 may also determine the difference between sample values ​​in the residual block to generate the residual block using residual differential pulse coded modulation (RDPCM). In some examples, residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0193] In an example where the mode select unit 202 partitions the CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs of various sizes. As noted above, the size of a CU may refer to the size of the luma coding block of the CU, while the size of a PU may refer to the size of the luma prediction unit of the PU. Assuming the size of a particular CU is 2N×2N, the video encoder 200 may support PU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

[0194] In examples where mode select unit 202 does not further split a CU into PUs, each CU may be associated with a luma coding block and a corresponding chroma coding block. As described above, the size of a CU may refer to the size of the luma coding block of the CU. Video encoder 200 and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

[0195] For other video coding techniques, such as intra block copy mode coding, affine mode coding, and linear model (LM) mode coding, as some examples, mode selection unit 202 generates a prediction block for the current block being encoded via the corresponding unit associated with the coding technique. In some examples (such as palette mode coding), mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating how to reconstruct the block based on the selected palette. In such modes, mode selection unit 202 may provide these syntax elements to entropy coding unit 220 for encoding.

[0196] As described above, the residual generation unit 204 receives video data for a current block and a corresponding prediction block. The residual generation unit 204 then generates a residual block for the current block. To generate the residual block, the residual generation unit 204 calculates the sample-by-sample difference between the prediction block and the current block.

[0197] The transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a "transform coefficient block"). The transform processing unit 206 may apply various transforms to the residual block to form the transform coefficient block. For example, the transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 may perform a variety of transforms on the residual block, such as a primary transform and a secondary transform (such as a rotation transform). In some examples, the transform processing unit 206 does not apply a transform to the residual block.

[0198] When operating in accordance with AV1, the 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"). The transform processing unit 206 may apply various transforms to the residual block to form the transform coefficient block. For example, the transform processing unit 206 may apply a horizontal / vertical transform combination, which may include a discrete cosine transform (DCT), an asymmetric discrete sine transform (ADST), a flipped ADST (e.g., ADST in reverse order), and an identity transform (IDTX). When the identity transform is used, the transform is skipped in one of the vertical or horizontal directions. In some examples, the transform processing may be skipped.

[0199] Quantization unit 208 may quantize the transform coefficients in the transform coefficient block to generate a quantized transform coefficient block. Quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. Video encoder 200 (e.g., via mode select unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may result in a loss of information, and therefore, the quantized transform coefficients may have a lower precision than the original transform coefficients generated by transform processing unit 206.

[0200] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct a residual block based on the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by the mode selection unit 202 to generate the reconstructed block.

[0201] Filter unit 216 may perform one or more filtering operations on the reconstructed block. For example, filter unit 216 may perform a deblocking operation to reduce blocking artifacts along the edges of the CU. In some examples, the operations of filter unit 216 may be skipped.

[0202] When operating in accordance with AV1, filter unit 216 may perform one or more filtering operations on the reconstructed blocks. For example, filter unit 216 may perform a deblocking operation to reduce blocking artifacts along the edges of the CU. In 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 a non-separable, non-linear, low-pass directional filter based on the estimated edge direction. Filter unit 216 may also include a loop restoration filter applied after CDEF and may include a separable symmetric normalized Wiener filter or a dual self-guided filter.

[0203] The video encoder 200 stores the reconstructed block in the DPB 218. For example, in examples where the operation of the filter unit 216 is not performed, the reconstruction unit 214 may store the reconstructed block in the DPB 218. In examples where the operation of the filter unit 216 is performed, the filter unit 216 may store the filtered reconstructed block in the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 may retrieve a reference picture formed by the reconstructed (and potentially filtered) block from the DPB 218 to perform inter-frame prediction on blocks of subsequently encoded pictures. In addition, the intra-frame prediction unit 226 may use the reconstructed block of the current picture in the DPB 218 to perform intra-frame prediction on other blocks in the current picture.

[0204] In general, entropy coding unit 220 may entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy coding unit 220 may entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy coding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-frame prediction or intra-frame mode information for intra-frame prediction) from mode selection unit 202. Entropy coding unit 220 may perform one or more entropy encoding operations on the syntax elements (which are another example of video data) to generate entropy-encoded data. For example, entropy coding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential Golomb coding operation, or another type of entropy coding operation on the data. In some examples, entropy coding unit 220 may operate in a bypass mode in which syntax elements are not entropy encoded.

[0205] The video encoder 200 may output a bitstream including syntax elements for entropy coding required to reconstruct blocks of a slice or picture. Specifically, the entropy coding unit 220 may output a bitstream.

[0206] According to AV1, the entropy coding unit 220 can be configured as a symbol-to-symbol adaptive multi-symbol arithmetic decoder. Syntax elements in AV1 include an alphabet of N elements, and the context (e.g., a probability model) includes a set of N probabilities. The entropy coding unit 220 can store the probabilities as an n-bit (e.g., 15-bit) cumulative distribution function (CDF). The entropy coding unit 220 can perform recursive scaling using an update factor based on the alphabet size to update the context.

[0207] The operations described above are described with respect to blocks. Such descriptions should be understood as operations for luma coding blocks and / or chroma coding blocks. As described above, in some examples, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a CU. In some examples, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a PU.

[0208] In some examples, operations performed with respect to luma coding blocks do not need to be repeated for chroma coding blocks. As an example, the operations for identifying the motion vector (MV) and reference picture for a luma coding block do not need to be repeated for the operations used to identify the MV and reference picture for the chroma blocks. Instead, the MV for the luma coding block can be scaled to determine the MV for the chroma blocks, and the reference picture can be the same. As another example, the intra prediction process can be the same for luma and chroma coding blocks.

[0209] The video encoder 200 represents an example of a device configured to encode video data, the device including: a memory configured to store the video data; and one or more processing units implemented in circuitry and configured to determine a prediction block for a current block of the video data; determine a residual block for the current block of the video data; process reconstruction data for the current block to determine processed reconstruction data; store the processed reconstruction data; and perform adaptive ALF on the current block based on the processed reconstruction data. The reconstruction data may, for example, include one or both of the prediction data output by the motion compensation unit 224 or the decoded residual data output by the inverse transform processing unit 212.

[0210] Figure 16 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Figure 16 This is provided for the purpose of explanation and is not intended to limit the techniques broadly illustrated and described in this disclosure. For the purpose of explanation, this disclosure describes the video decoder 300 based on the techniques of VVC and HEVC. However, the techniques of this disclosure may be performed by video coding devices configured for other video coding standards.

[0211] exist Figure 16 In the example of FIG, video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a 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 processing circuitry. For example, the units of video decoder 300 may be implemented as one or more circuits or logic elements as part of a hardware circuit, or as part of a processor, ASIC, or FPGA. Furthermore, video decoder 300 may include additional or alternative processors or processing circuitry to perform these and other functions.

[0212] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include additional units that perform prediction according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0213] When operating in accordance with AV1, the motion compensation unit 316 may be configured to decode coding blocks of video data (e.g., both luma coding blocks and chroma coding blocks) using translational motion compensation, affine motion compensation, OBMC, and / or composite inter-intra prediction, as described above. The intra prediction unit 318 may be configured to decode coding blocks of video data (e.g., both luma coding blocks and chroma coding blocks) using directional intra prediction, non-directional intra prediction, recursive filter intra prediction, CFL, IBC, and / or palette mode, as described above.

[0214] CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of video decoder 300. For example, the video data may be obtained from computer readable medium 110 ( Figure 1 ) obtains video data stored in CPB memory 320. CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. Furthermore, CPB memory 320 may store video data other than syntax elements for coded pictures, such as temporary data representing outputs from various units of video decoder 300. DPB 314 typically stores decoded pictures, which video decoder 300 may output and / or use as reference video data when decoding subsequent data or pictures in the encoded video bitstream. CPB memory 320 and DPB 314 may be formed from any of a variety of memory devices, 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.

[0215] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) to retrieve the decoded video data. That is, memory 120 may utilize CPB memory 320 to store data as discussed above. Likewise, when some or all of the functionality of video decoder 300 is implemented in software to be executed by processing circuitry of video decoder 300, memory 120 may store instructions to be executed by video decoder 300.

[0216] Illustrated Figure 16 The various units are shown in FIG to aid in understanding the operations performed by the video decoder 300. The units may be implemented as fixed function circuits, programmable circuits, or a combination thereof. Figure 15, fixed-function circuits refer to circuits that provide specific functionality and are pre-set for 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 example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (for example, to receive parameters or output parameters), but the type of operations performed by the fixed-function circuits are generally immutable. In some examples, one or more of the units can be different circuit blocks (fixed-function or programmable), and in some examples, one or more of the units can be integrated circuits.

[0217] The video decoder 300 may include an ALU, an EFU, digital circuits, analog circuits, and / or a programmable core formed by programmable circuits. In examples where the operation of the video decoder 300 is performed by software executed on the programmable circuits, on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

[0218] 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.

[0219] Typically, the video decoder 300 reconstructs a picture block by block. The video decoder 300 may perform a reconstruction operation on each block individually (wherein a block currently being reconstructed (ie, decoded) may be referred to as a "current block").

[0220] The entropy decoding unit 302 may entropy decode syntax elements defining the quantized transform coefficients of the quantized transform coefficient block, as well as transform information, such as a quantization parameter (QP) and / or a transform mode indication. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, similarly, a degree of inverse quantization to be applied by the inverse quantization unit 306. The inverse quantization unit 306 may, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thereby form a transform coefficient block comprising the transform coefficients.

[0221] After inverse quantization unit 306 forms a 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 rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0222] In addition, prediction processing unit 304 generates a prediction block based on the prediction information syntax elements entropy decoded by entropy decoding unit 302. For example, where 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 the reference block, and a motion vector that identifies the position of the reference block in the reference picture relative to the position of the current block in the current picture. Motion compensation unit 316 is generally capable of generating a prediction block based on the same information as that obtained with respect to motion compensation unit 224 ( Figure 15 ) is performed in a manner substantially similar to that described in .

[0223] As another example, where the prediction information syntax element indicates that the current block is intra-predicted, the intra-prediction unit 318 may generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Similarly, the intra-prediction unit 318 is generally capable of generating a prediction block in accordance with the intra-prediction mode indicated by the prediction information syntax element. Figure 15 The intra prediction process is performed in a manner substantially similar to that described in the preceding claims. The intra prediction unit 318 may retrieve data of neighboring samples of the current block from the DPB 314.

[0224] The reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, the reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

[0225] The filter unit 312 may perform one or more filtering operations on the reconstructed block. For example, the filter unit 312 may perform a deblocking operation to reduce blocking artifacts along the edges of the reconstructed block. The operations of the filter unit 312 may not necessarily be performed in all examples.

[0226] The video decoder 300 may store the reconstructed block in the DPB 314. For example, in examples where the operations of the filter unit 312 are not performed, the reconstruction unit 310 may store the reconstructed block in the DPB 314. In examples where the operations of the filter unit 312 are performed, the filter unit 312 may store the filtered reconstructed block in the DPB 314. As discussed above, the DPB 314 may provide reference information (such as samples of the current picture for intra prediction and previously decoded pictures for subsequent motion compensation) to the prediction processing unit 304. In addition, the video decoder 300 may output a decoded picture (e.g., decoded video) from the DPB 314 for use in, for example, Figure 1 Subsequent presentation on a display device such as display device 118.

[0227] In this manner, video decoder 300 represents an example of a video decoding device that includes a memory configured to store video data, and one or more processing units implemented in circuitry and configured to: determine a prediction block for a current block of video data; determine a residual block for the current block of video data; process reconstruction data for the current block to determine processed reconstruction data; store the processed reconstruction data; and perform adaptive ALF on the current block based on the processed reconstruction data. The reconstruction data may, for example, include one or both of the prediction data output by the motion compensation unit 316 or the decoded residual data output by the inverse transform processing unit 308.

[0228] Figure 17 Shown Figure 16 An example implementation of the filter unit 312 in FIG. Figure 15 Filter unit 216 in FIG. 3 may be implemented in a substantially similar manner. Filter unit 216 and filter unit 312 may perform the techniques of this disclosure, possibly in conjunction with other components of video encoder 200 or video decoder 300. Figure 17 In the example of FIG, filter unit 312 includes a deblocking filter 342, an SAO filter 344, and an ALF unit 346. The SAO filter 344 can be configured, for example, to determine offset values ​​for samples of a block in the manner described in the present disclosure. The ALF unit 346 can also filter the block of video data in the manner described in the present disclosure.

[0229] Filter unit 312 may include fewer filters and / or may include additional filters. Figure 17 The specific filters shown in FIG3 may be implemented in a different order. Other loop filters may also be used (either in the decoding loop or after the decoding loop) to smooth pixel transitions or otherwise improve video quality. The filtered reconstructed video blocks output by filter unit 312 may be stored in DPB 314, which stores reference pictures for subsequent motion compensation. DPB 314 may be a storage device that stores decoded video for subsequent presentation to a display device (such as a Figure 1 part of or separate from the additional memory on the display device 118).

[0230] The filter unit 312 or some other unit of the video decoder 300 may store the processed reconstructed data prior to the operation of the deblocking filter 342 and the SAO filter 344. The processed reconstructed data may then be input to the ALF unit 346.

[0231] Figure 181 is a flowchart illustrating an example process for encoding a current block according to the techniques of this disclosure. The current block may be or may include a current CU. Although relative to the video encoder 200 ( Figure 1 and Figure 15 ) is described, but it should be understood that other devices may be configured to perform the same Figure 18 The process is similar to the process.

[0232] In this example, the video encoder 200 initially predicts a current block (350). For example, the video encoder 200 may form a prediction block for the current block. The video encoder 200 may then calculate a residual block for the current block (352). To calculate the residual block, the video encoder 200 may calculate the difference between the unencoded original block and the prediction block for the current block. The video encoder 200 may then transform the residual block and quantize the transform coefficients of the residual block (354). Next, the video encoder 200 may scan the quantized transform coefficients of the residual block (356). During or after the scan, the video encoder 200 may entropy encode the transform coefficients (358). For example, the video encoder 200 may encode the transform coefficients using CAVLC or CABAC. The video encoder 200 may then output entropy encoded data for the block (360).

[0233] Figure 19 1 is a flowchart illustrating an example process for decoding a current block of video data according to the techniques of this disclosure. The current block may be or may include a current CU. Although with respect to the video decoder 300 ( Figure 1 and Figure 16 ) is described, but it should be understood that other devices may be configured to perform the same Figure 19 The process is similar to the process.

[0234] The video decoder 300 may receive entropy coded data for a current block, such as entropy coded prediction information and entropy coded data for transform coefficients of a residual block corresponding to the current block (370). The video decoder 300 may entropy decode the entropy coded data to determine prediction information for the current block and reproduce transform coefficients of the residual block (372). The video decoder 300 may predict the current block (374), for example, using an intra-prediction mode or an inter-prediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the reproduced transform coefficients (376) to create a block of quantized transform coefficients. The video decoder 300 may then inverse quantize the transform coefficients and apply an inverse transform to the transform coefficients to produce a residual block (378). The video decoder 300 may finally decode the current block by combining the prediction block and the residual block (380).

[0235] Figure 201 is a flowchart illustrating an example process for decoding a current block of video data according to the techniques of this disclosure. The current block may be or may include a current CU. Although with respect to the video decoder 300 ( Figure 1 and Figure 16 ) is described, but it should be understood that other devices may be configured to perform the same Figure 19 The video encoder 200 may perform, for example, Figure 20 technology as part of the video encoding process.

[0236] The video decoder 300 determines a prediction block for a current block of video data (400). The video decoder 300 may determine the prediction block, for example, using intra-frame prediction, inter-frame prediction, or any other such prediction process. The video decoder 300 determines a residual block for the current block of video data (402). The video decoder 300 may determine the residual value, for example, by inverse quantizing transform coefficients received in a bitstream and inverse transforming the dequantized transform coefficients. In other examples, one or both of the inverse transform process and the inverse quantization process may be skipped.

[0237] The video decoder 300 processes the residual data of the residual block to determine processed residual data (404). In some examples, to process the residual data to determine the processed residual data, the video decoder 300 may downsample the sample values ​​of the residual block. In such examples, the processed residual data may include the downsampled sample values ​​of the residual block. In some examples, to process the residual data to determine the processed residual data, the video decoder 300 may determine a classification of ALF based on the residual data. In such examples, the processed residual data may include a classification, and to perform ALF on the reconstructed block, the video decoder 300 may be configured to select a filter based on the classification as described above. In some examples, to process the residual data to determine the processed residual data, the video decoder 300 may filter the sample values ​​of the residual block. In such examples, the processed residual data may include the filtered sample values ​​of the residual block.

[0238] Video decoder 300 stores the processed residual data (406).Video decoder 300 may store the processed residual data, for example, before performing one or both of deblocking filtering and sample adaptive offset filtering on the reconstructed block.

[0239] The video decoder 300 adds the prediction block to the residual block to determine a reconstructed block (408). The video decoder 300 performs ALF on the reconstructed block based on the processed residual data (410). The video decoder 300 may perform ALF on the reconstructed block, for example, after performing one or both of deblocking filtering and sample adaptive offset filtering on the reconstructed block.

[0240] The video decoder 300 may then output the picture of the decoded video data for display, for storage, or for use in decoding other frames of the video data. Figure 20 In examples where the process of decoding is performed by a video decoding loop of a video encoder, the video encoder may, for example, output a decoded picture for use in encoding other pictures of the video data.

[0241] The following numbered clauses exemplify one or more aspects of the devices and techniques described in this disclosure.

[0242] Item 1A: A method of decoding video data, the method comprising: determining a prediction block for a current block of the video data; determining a residual block for the current block of the video data; processing reconstruction data for the current block to determine processed reconstruction data, wherein the reconstruction data includes one or more of the prediction block or the residual block; storing the processed reconstruction data; and performing adaptive loop filtering (ALF) on the current block based on the processed reconstruction data.

[0243] Clause 2A: The method of clause 1A, wherein processing the reconstructed data of the current block to determine the processed reconstructed data comprises filtering the reconstructed data.

[0244] Clause 3A: The method of clause 1A or 2A, wherein processing the reconstructed data of the current block to determine the processed reconstructed data comprises downsampling the reconstructed data.

[0245] Clause 4A: The method of any of clauses 1A to 3A, wherein processing the reconstruction data of the current block to determine the processed reconstruction data comprises determining a classification of the ALF based on the reconstruction data.

[0246] Clause 5A: The method of any of clauses 1A to 4A, wherein performing the ALF on the current block based on the processed reconstruction data comprises performing the ALF on a filtered version of a reconstructed block.

[0247] Clause 6A: The method of Clause 5A, further comprising storing the processed reconstruction data before performing filtering to determine the filtered version of the reconstructed block.

[0248] Clause 7A: The method of any of clauses 1A to 6A, wherein the method of decoding the video data is performed as part of a video encoding process.

[0249] Clause 8A: An apparatus for coding video data, the apparatus comprising one or more means for performing the method of any of clauses 1A to 7A.

[0250] Clause 9A: The apparatus of clause 8A, wherein the one or more components comprise one or more processors implemented in circuitry.

[0251] Clause 10A: The apparatus of any of clauses 8A and 9A, further comprising a memory for storing the video data.

[0252] Clause 11A: The apparatus of any of clauses 8A to 10A, further comprising a display configured to display the decoded video data.

[0253] Clause 12A: The apparatus of any of clauses 8A to 11A, wherein the apparatus comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0254] Clause 13A: The apparatus of any of clauses 8A to 12A, wherein the apparatus comprises a video decoder.

[0255] Clause 14A: The apparatus of any of clauses 8A to 13A, wherein the apparatus comprises a video encoder.

[0256] Clause 15A: A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to perform the method of any of clauses 1A to 7A.

[0257] Clause 1B: A method of decoding video data, the method comprising: determining a prediction block for a current block of the video data; determining a residual block for the current block of the video data; processing residual data of the residual block to determine processed residual data; storing the processed residual data; adding the prediction block to the residual block to determine a reconstructed block; and performing adaptive loop filtering (ALF) on the reconstructed block based on the processed residual data.

[0258] Clause 2B: The method of clause 1B, wherein processing the residual data to determine the processed residual data comprises downsampling sample values ​​of the residual block, wherein the processed residual data comprises the downsampled sample values ​​of the residual block.

[0259] Clause 3B: The method of clause 1B, wherein processing the residual data to determine the processed residual data comprises determining a classification of the ALF based on the residual data, wherein the processed residual data comprises the classification, and wherein performing the ALF on the reconstructed block comprises selecting a filter based on the classification.

[0260] Clause 4B: The method of clause 1B, wherein processing the residual data to determine the processed residual data comprises filtering sample values ​​of the residual block, wherein the processed residual data comprises the filtered sample values ​​of the residual block.

[0261] Clause 5B: The method of any of clauses 1B to 4B, wherein the processed residual data comprises less data than the residual data.

[0262] Clause 6B: The method of any of clauses 1B to 5B, wherein performing the ALF on the reconstructed block comprises performing the ALF on the reconstructed block after performing one or both of deblocking filtering and sample adaptive offset filtering on the reconstructed block.

[0263] Clause 7B: The method of clause 6B, further comprising storing the processed residual data before performing said one or both of the deblocking filtering and the sample adaptive offset filtering on the reconstructed block.

[0264] Clause 8B: The method of any of clauses 1B to 7B, wherein the method of decoding the video data is performed as part of a video encoding process.

[0265] Item 9B: A device for decoding video data, the device comprising: a memory configured to store video data; one or more processors implemented in circuitry and configured to: determine a prediction block for a current block of the video data; determine a residual block for the current block of the video data; process residual data of the residual block to determine processed residual data; store the processed residual data; add the prediction block to the residual block to determine a reconstructed block; and perform adaptive loop filtering (ALF) on the reconstructed block based on the processed residual data.

[0266] Clause 10B: An apparatus according to clause 9B, wherein to process the residual data to determine the processed residual data, the one or more processors are further configured to downsample the sample values ​​of the residual block, wherein the processed residual data includes the downsampled sample values ​​of the residual block.

[0267] Clause 11B: An apparatus according to clause 9B, wherein to process the residual data to determine the processed residual data, the one or more processors are further configured to determine a classification of the ALF based on the residual data, wherein the processed residual data includes the classification, and wherein to perform the ALF on the reconstructed block, the one or more processors are further configured to select a filter based on the classification.

[0268] Clause 12B: An apparatus according to clause 9B, wherein to process the residual data to determine the processed residual data, the one or more processors are further configured to filter the sample values ​​of the residual block, wherein the processed residual data includes the filtered sample values ​​of the residual block.

[0269] Clause 13B: Apparatus as recited in any of clauses 9B to 12B, wherein the processed residual data comprises less data than the residual data.

[0270] Clause 14B: An apparatus according to any of clauses 9B to 13B, wherein to perform the ALF on the reconstructed block, the one or more processors are further configured to perform the ALF on the reconstructed block after performing one or both of deblocking filtering and sample adaptive offset filtering on the reconstructed block.

[0271] Clause 15B: The apparatus of clause 14B, wherein the one or more processors are further configured to store the processed residual data before performing said one or both of the deblocking filtering and the sample adaptive offset filtering on the reconstructed block.

[0272] Clause 16B: The apparatus of any of clauses 9B to 15B, further comprising a display configured to display the decoded video data.

[0273] Clause 17B: The device of any of clauses 9B to 16B, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0274] Clause 18B: The apparatus of any of clauses 9B to 16B, wherein the apparatus comprises a video decoder.

[0275] Clause 19B: The apparatus of any of clauses 9B to 16B, wherein the apparatus comprises a video encoder.

[0276] Item 20B: A computer-readable storage medium having instructions stored thereon that, when executed, cause one or more processors to: determine a prediction block for a current block of video data; determine a residual block for the current block of video data; process residual data of the residual block to determine processed residual data; store the processed residual data; add the prediction block to the residual block to determine a reconstructed block; and perform adaptive loop filtering (ALF) on the reconstructed block based on the processed residual data.

[0277] It should be appreciated that, according to examples, certain actions or events of any of the techniques described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all actions or events described are necessary to implement the technique). Furthermore, in some examples, actions or events may be performed concurrently (e.g., through multithreading, interrupt handling, or multiple processors) rather than sequentially.

[0278] In one or more examples, the functionality described can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality can be stored as one or more instructions or codes on a computer-readable medium or sent via a computer-readable medium and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium (which corresponds to a tangible medium such as a data storage medium) or a communication medium, which includes, for example, any medium that facilitates the transfer of a computer program from one place to another according to a communication protocol. In this manner, a computer-readable medium can generally correspond to (1) a non-transitory tangible computer-readable storage medium, or (2) a communication medium such as a signal or carrier wave. A data storage medium can be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and / or data structures for implementing the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0279] By way of example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage devices, magnetic disk storage devices or other magnetic storage devices, flash memory, or one or more of any other media that can be used to store desired program code in the form of instructions or data structures and can be accessed by a computer. Moreover, any connection is appropriately referred to as a computer-readable medium. For example, if an instruction is sent from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technology (such as infrared, radio and microwave), then the coaxial cable, fiber optic cable, twisted pair, DSL or wireless technology (such as infrared, radio and microwave) is included in the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other transient media, but are instead directed to non-transient tangible storage media. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc. 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.

[0280] The 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 circuits. Thus, as used herein, the terms "processor" and "processing circuitry" may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a combined codec. Furthermore, these techniques may be fully implemented in one or more circuits or logic elements.

[0281] The techniques of this disclosure can be implemented in a variety of devices or apparatuses, including wireless handsets, integrated circuits (ICs), or a set of ICs (e.g., a chipset). 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 implementation by different hardware units. Specifically, as described above, the various units can be combined in a codec hardware unit, or the various units can be provided by a collection of interoperable hardware units (including one or more processors as described above) in combination with appropriate software and / or firmware.

[0282] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

1. A method for decoding video data, the method comprising: determining a prediction block for a current block of the video data; determining a residual block for the current block of the video data; processing the residual data of the residual block to determine processed residual data; storing the processed residual data; adding the prediction block to the residual block to determine a reconstructed block; as well as Adaptive loop filtering (ALF) is performed on the reconstructed block based on the processed residual data.

2. The method of claim 1 , wherein processing the residual data to determine the processed residual data comprises downsampling sample values ​​of the residual block, wherein the processed residual data comprises the downsampled sample values ​​of the residual block.

3. The method of claim 1 , wherein processing the residual data to determine the processed residual data comprises determining a classification of the ALF based on the residual data, wherein the processed residual data comprises the classification, and wherein performing the ALF on the reconstructed block comprises selecting a filter based on the classification. 4 . The method of claim 1 , wherein processing the residual data to determine the processed residual data comprises filtering sample values ​​of the residual block, wherein the processed residual data comprises the filtered sample values ​​of the residual block. The method of claim 1 , wherein the processed residual data comprises less data than the residual data. 6 . The method of claim 1 , wherein performing the ALF on the reconstructed block comprises performing the ALF on the reconstructed block after performing one or both of deblocking filtering and sample adaptive offset filtering on the reconstructed block.

7. The method according to claim 6, further comprising: The processed residual data is stored before performing one or both of the deblocking filtering and the sample adaptive offset filtering on the reconstructed block.

8. The method of claim 1, wherein the method of decoding the video data is performed as part of a video encoding process.

9. A device for decoding video data, the device comprising: a memory configured to store video data; One or more processors implemented in circuitry and configured to: determining a prediction block for a current block of the video data; determining a residual block for the current block of the video data; processing the residual data of the residual block to determine processed residual data; storing the processed residual data; adding the prediction block to the residual block to determine a reconstructed block; as well as Adaptive loop filtering (ALF) is performed on the reconstructed block based on the processed residual data.

10. The apparatus of claim 9, wherein to process the residual data to determine the processed residual data, the one or more processors are further configured to downsample sample values ​​of the residual block, wherein the processed residual data comprises the downsampled sample values ​​of the residual block.

11. The apparatus of claim 9 , wherein to process the residual data to determine the processed residual data, the one or more processors are further configured to determine a classification of the ALF based on the residual data, wherein the processed residual data includes the classification, and wherein to perform the ALF on the reconstructed block, the one or more processors are further configured to select a filter based on the classification.

12. The apparatus of claim 9, wherein to process the residual data to determine the processed residual data, the one or more processors are further configured to filter sample values ​​of the residual block, wherein the processed residual data comprises the filtered sample values ​​of the residual block.

13. The apparatus of claim 9, wherein the processed residual data comprises less data than the residual data.

14. The apparatus of claim 9, wherein to perform the ALF on the reconstructed block, the one or more processors are further configured to perform the ALF on the reconstructed block after performing one or both of deblocking filtering and sample adaptive offset filtering on the reconstructed block.

15. The apparatus of claim 14, wherein the one or more processors are further configured to: The processed residual data is stored before performing one or both of the deblocking filtering and the sample adaptive offset filtering on the reconstructed block.

16. The device of claim 9, further comprising a display configured to display the decoded video data.

17. The device of claim 9, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

18. The apparatus of claim 9, wherein the apparatus comprises a video decoder.

19. The apparatus of claim 9, wherein the apparatus comprises a video encoder.

20. A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to: determining a prediction block for a current block of video data; determining a residual block for the current block of the video data; processing the residual data of the residual block to determine processed residual data; storing the processed residual data; adding the prediction block to the residual block to determine a reconstructed block; as well as Adaptive loop filtering (ALF) is performed on the reconstructed block based on the processed residual data.

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