Filtering in parallel with deblocking filtering in video coding

Abstract

An apparatus for decoding video data may be configured to apply a deblocking filter to a block of video data to determine a first filtered block; applying a second filter to the block of video data in parallel with the deblocking filter to determine a second filtered block, wherein the second filter comprises one of a guide filter, a bilateral filter, or an adaptive loop filter; combining the first filtered block and the second filtered block to determine a combined block; applying a third filter to the combined block to determine a third filtered block; processing the third filtered block to determine a decoded version of the block of video data; and outputting the decoded version of the block of video data.

Description

[0001] This application claims priority to U.S. Patent Application No. 18 / 346,613, filed on July 3, 2023, and U.S. Provisional Patent Application No. 63 / 358,496, filed on July 5, 2022. U.S. Patent Application No. 18 / 346,613 claims the benefit of U.S. Provisional Patent Application No. 63 / 358,496, and the entire contents of both applications are incorporated herein by reference. 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 gaming consoles, cellular or satellite wireless telephones (so-called "smart phones"), 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 Video 1 (AV1) developed by the Alliance for Open Media. By implementing such video coding techniques, a video device may 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 after 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 after 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] According to the techniques of the present disclosure, a video encoder and a video decoder may be configured to perform additional filtering in parallel with deblocking filtering and combine the results of the two parallel filters. Then, the video encoder or video decoder may only need to buffer the combined result, rather than buffering both the pre-deblocked samples and the post-deblocked samples. Therefore, by applying a deblocking filter to a block of video data to determine a first filter block, applying a second filter to the block of video data in parallel with the deblocking filter to determine a second filter block, and combining the first filter block and the second filter block to determine the combined block, the video encoder or video decoder can reduce the buffer (e.g., memory) requirements associated with the filtering stage of video decoding by eliminating the need to store pre-deblocked samples for use in a later stage (e.g., ALF) of the filtering pipeline.

[0006] According to an example of the present disclosure, a method for decoding video data includes applying a deblocking filter to a video data block to determine a first filter block; applying a second filter to the video data block in parallel with the deblocking filter to determine a second filter block, wherein the second filter includes one of a guided filter, a bilateral filter, or an adaptive loop filter; combining the first filter block and the second filter block to determine a combined block; applying a third filter to the combined block to determine a third filter block; processing the third filter block to determine a decoded version of the video data block; and outputting the decoded version of the video data block.

[0007] According to an example of the present disclosure, an apparatus for decoding video data includes a memory system configured to store video data; and a processing system coupled to the memory system, implemented in a circuit and configured to: apply a deblocking filter to a video data block to determine a first filter block; apply a second filter to the video data block in parallel with the deblocking filter to determine a second filter block, wherein the second filter includes one of a guided filter, a bilateral filter, or an adaptive loop filter; combine the first filter block and the second filter block to determine a combined block; apply a third filter to the combined block to determine a third filter block; process the third filter block to determine a decoded version of the video data block; and output a decoded version of the video data block.

[0008] A computer-readable storage medium stores instructions that, when executed by one or more processors, cause the one or more processors to apply a deblocking filter to a block of video data to determine a first filter block; apply a second filter to the block of video data in parallel with the deblocking filter to determine a second filter block, wherein the second filter comprises one of a guided filter, a bilateral filter, or an adaptive loop filter; combine the first filter block and the second filter block to determine a combined block; apply a third filter to the combined block to determine a third filter block; process the third filter block to determine a decoded version of the block of video data; and output the decoded version of the block of video data.

[0009] According to an example of the present disclosure, a folding plate for decoding video data includes: a component for applying a deblocking filter to a video data block to determine a first filter block; a component for applying a second filter in parallel with the deblocking filter to the video data block to determine a second filter block, wherein the second filter includes one of a guided filter, a bilateral filter, or an adaptive loop filter; a component for combining the first filter block and the second filter block to determine a combined block; a component for applying a third filter to the combined block to determine a third filter block; a component for processing the third filter block to determine a decoded version of the video data block; and a component for outputting a decoded version of the video data block.

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

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

[0012] Figure 2 Examples of adaptive loop filter (ALF) shapes are shown.

[0013] Figure 3 An example of sub-sampled Laplacian values ​​for sub-block ALF classification is shown.

[0014] Figure 4 The Laplacian values ​​for luma samples are shown.

[0015] Figure 5 An example of a merged class for ALF signaling is shown.

[0016] Figure 6 An example of a geometric transformation of a 7x7 diamond filter shape is shown.

[0017] Figures 7A to 7C An example of symmetric sample padding for luma ALF at the ALF virtual boundary is shown.

[0018] Figure 8 An example of ALF 4x4 sub-block classification at an ALF virtual boundary is shown.

[0019] Figures 9 to 12 An example implementation of an ALF is shown.

[0020] Fig.13 An example implementation of a new filter applied in parallel with deblocking filtering is shown.

[0021] Fig.14Examples of proposed 3x3 and 5x5 filter shapes are shown, which may be applied to samples prior to deblocking filtering.

[0022] Fig.15 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0023] Fig.16 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0024] Fig.17 is a flow chart illustrating an example process for encoding a current block according to techniques of this disclosure.

[0025] Fig.18 is a flow chart illustrating an example process for decoding a current block according to techniques of this disclosure.

[0026] Fig.19 is a flow chart illustrating an example process for decoding a current block according to techniques of this disclosure. DETAILED DESCRIPTION

[0027] Video decoding (e.g., video encoding and / or video decoding) typically involves predicting a block of video data based on already decoded video data blocks in the same picture (e.g., intra-frame prediction) or predicting a block of video data based on already decoded 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. Therefore, the residual data represents the difference between the predicted block and the original block. In order 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 may be lossy, which means that the transform and quantization process may introduce distortion in the decoded video data.

[0028] 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. The first reconstructed block may have distortion or artifacts due to losses introduced by the transformation and quantization of the residual data. One common type of artifact or distortion is known as blocking, where the boundaries of the blocks used to decode the video data are visible.

[0029] In order to further improve the quality of the decoded video, the video decoder can 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 video decoder can, for example, apply ALF to minimize the mean square error between the filtered samples and the original samples. The parameters of these filtering operations can be determined by the video encoder and explicitly signaled in the coded video bitstream, or can be implicitly determined by the video decoder without explicitly signaling in the coded video bitstream.

[0030] A common implementation of reconstruction block filtering is to perform deblocking filtering, followed by SAO, and then ALF in succession. Various implementations of ALF, described in more detail below, utilize pre-deblocking samples in the ALF stage. Since the ALF stage is performed after deblocking filtering and SAO in the filtering pipeline, these pre-deblocked samples must be buffered (e.g., stored in a buffer) while performing deblocking filtering and SAO. SAO and deblocking filtering may also each produce intermediate results that need to be buffered. These buffering requirements increase processing requirements and hardware complexity, especially for hardware-based video decoders.

[0031] According to the techniques of the present disclosure, a video encoder and a video decoder may be configured to perform additional filtering in parallel with deblocking filtering and combine the results of the two parallel filters. Then, the video encoder or video decoder may only need to buffer the combined result, rather than buffering both the pre-deblocked samples and the post-deblocked samples. Therefore, by applying a deblocking filter to a block of video data to determine a first filter block, applying a second filter to the block of video data in parallel with the deblocking filter to determine a second filter block, and combining the first filter block and the second filter block to determine the combined block, the video encoder or video decoder can reduce the buffer (e.g., memory) requirements associated with the filtering stage of video decoding by eliminating the need to store pre-deblocked samples for use in a later stage (e.g., ALF) of the filtering pipeline.

[0032] In this context, "parallel" means that the data for the two parallel filters can be processed independently. That is, in some implementations, the additional filter may not utilize or require data generated by the deblocking filter, so that the two filtering processes can be applied independently. Therefore, the two filtering processes can be performed completely or partially at the same time.

[0033] Figure 11 is a block diagram illustrating an example video encoding and decoding system 100 that can perform the techniques of the present disclosure. The techniques of the present disclosure generally relate to decoding (encoding and / or decoding) video data. Generally, video data includes any data used to process video. Therefore, video data may include unencoded raw video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

[0034] like Figure 1 As shown in , in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a target device 116. Specifically, source device 102 provides video data to target device 116 via computer-readable medium 110. Source device 102 and target device 116 may include any of a wide variety of devices, including desktop computers, notebook (i.e., laptop) computers, 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 target device 116 may be equipped for wireless communication and may therefore be referred to as wireless communication devices.

[0035] exist Figure 1 In the example of , source device 102 includes video source 104, memory 106, video encoder 200 and output interface 108. Target device 116 includes input interface 122, video decoder 300, memory 120 and display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply the technology of ALF with multiple classifiers. Therefore, source device 102 represents an example of video encoding device, and target device 116 represents an example of video decoding device. In other examples, source device and target device may include other components or arrangements. For example, source device 102 may receive video data from an external video source such as an external camera. Similarly, target device 116 may be docked with an external display device instead of including an integrated display device.

[0036] like Figure 1The system 100 shown is only an example. In general, any digital video encoding and / or decoding device can perform the technology of ALF with multiple classifiers. The source device 102 and the target device 116 are only examples of such decoding devices, wherein the source device 102 generates decoded video data for sending to the target device 116. The present disclosure refers to a "decoding" device as a device that performs decoding (e.g., encoding and / or decoding) of data. Therefore, the video encoder 200 and the video decoder 300 represent examples of decoding devices, specifically, video encoders and video decoders, respectively. In some examples, the source device 102 and the target device 116 can operate in a substantially symmetrical manner, so that each of the source device 102 and the target device 116 includes a video encoding and decoding component. Therefore, the system 100 can support one-way or two-way video transmission between the source device 102 and the target device 116, for example, for video streaming, video playback, video broadcasting or video telephony.

[0037] Typically, video source 104 represents the source of video data (i.e., uncoded raw video data), and a series of pictures (also referred to as "frames") of the order of the video data are provided 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 source video, or a combination of real-time video, archived video, and computer-generated video. In each case, video encoder 200 encodes captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange pictures from the received order (sometimes referred to as "display order") into a decoding order for decoding. Video encoder 200 may generate a bitstream including 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 target device 116 .

[0038] The memory 106 of the source device 102 and the memory 120 of the target device 116 represent general purpose memories. In some examples, the memories 106, 120 may store raw video data, for example, raw video from the video source 104 and raw decoded video data from the video decoder 300. Additionally or alternatively, the memories 106, 120 may store software instructions that can be executed by, for example, the video encoder 200 and the video decoder 300, respectively. Although the memory 106 and the memory 120 are shown separately from the video encoder 200 and the video decoder 300 in this example, it should be understood that the video encoder 200 and the video decoder 300 may also include internal memories for functionally similar or equivalent purposes. In addition, the memories 106, 120 may store encoded video data, for example, output from the video encoder 200 and input to the video decoder 300. In some examples, portions of the memories 106, 120 may be allocated as one or more video buffers, for example, to store raw decoded and / or encoded video data.

[0039] The computer-readable medium 110 may represent any type of medium or device capable of transmitting the encoded video data from the source device 102 to the target device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to directly transmit the encoded video data to the target device 116 in real time, for example, via a radio frequency network or a computer-based network. According to a communication standard such as a wireless communication protocol, the output interface 108 may modulate the transmission signal including the encoded video data, and the input interface 122 may demodulate the received transmission signal. The communication medium may include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form a portion of a packet-based network such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include a router, a switch, a base station, or any other equipment that may be useful for facilitating communication from the source device 102 to the destination device 116.

[0040] 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.

[0041] 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. Target device 116 may access the stored video data from file server 114 via streaming or downloading.

[0042] The file server 114 may be any type of server device capable of storing encoded video data and sending the encoded video data to the target device 116. The file server 114 may represent a web server (e.g., for a website), a server configured to provide a file delivery protocol service (such as a file delivery protocol (FTP) or a 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 an 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, etc.

[0043] The target 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.

[0044] Output interface 108 and input interface 122 may represent wireless transmitters / receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of the various IEEE 802.11 standards, or other physical components. In examples where output interface 108 and input interface 122 include wireless components, output interface 108 and input interface 122 may be configured to communicate data (such as encoded video data) according to a cellular communication standard (such as 4G, 4G-LTE (Long Term Evolution), Advanced LTE, 5G, etc.). In some examples where output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 may be configured to communicate data (such as encoded video data) according to other wireless standards (such as IEEE 802.11 specifications, IEEE 802.15 specifications (e.g., ZigBee 5G, etc.). TM),Bluetooth TM Standards, etc.) to transfer data (such as encoded video data). In some examples, source device 102 and / or destination device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include a SoC device for performing functionality belonging to video encoder 200 and / or output interface 108, and destination device 116 may include a SoC device for performing functionality belonging to video decoder 300 and / or input interface 122.

[0045] The techniques disclosed herein 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.

[0046] The input interface 122 of the target 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 decoding 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.

[0047] 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 an audio decoder and may include appropriate MUX-DEMUX units or other hardware and / or software to handle a multiplexed stream including both audio and video in a common data stream.

[0048] The video encoder 200 and the video decoder 300 may each be implemented as any of a variety of suitable encoder and / or decoder circuits including a processing system, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When the technology is partially implemented in software, the device may store instructions for the software in an appropriate non-transitory computer-readable medium, and a processing system using one or more processors executes the instructions in hardware to perform the technology of the present disclosure. Each of the video encoder 200 and the video decoder 300 may be included in one or more encoders or decoders, any of which may be integrated as part of a combined encoder / decoder (codec) in a corresponding device. A device including the video encoder 200 and / or the video decoder 300 may include an integrated circuit, a microprocessor, and / or a wireless communication device (such as a cellular phone).

[0049] 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 an extension thereof 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 the present 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 the present disclosure in combination with any video coding technique using a filter with multiple classifiers.

[0050] Typically, the video encoder 200 and the video decoder 300 may perform block-based decoding of a picture. The term "block" generally refers to a structure that includes data to be processed (e.g., to be encoded, decoded, or otherwise used in an encoding and / or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. Typically, the video encoder 200 and the video decoder 300 may decode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, instead of decoding red, green, and blue (RGB) data for samples of a picture, the video encoder 200 and the video decoder 300 may decode luminance components and chrominance components, wherein the chrominance components may include both red hue chrominance components and blue hue chrominance components. In some examples, the video encoder 200 converts the received RGB format data to a YUV representation before encoding, and the video decoder 300 converts the YUV representation to an RGB format. Alternatively, a pre-processing and post-processing unit (not shown) may perform these conversions.

[0051] The present disclosure may generally relate to the decoding (e.g., encoding and decoding) of a picture to include the process of encoding or decoding data of the picture. Similarly, the present disclosure may relate to the decoding of a block of a picture to include the process of encoding or decoding data for the block (e.g., prediction and / or residual decoding). The encoded video bitstream generally includes a series of values ​​of syntax elements used to represent decoding decisions (e.g., decoding modes) and the partitioning of the picture into blocks. Therefore, references to the decoding of a picture or a block should generally be understood as the decoding values ​​of the syntax elements that form the picture or block.

[0052] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video decoder (such as the video encoder 200) divides a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video decoder divides the CTU and the CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without child nodes may be referred to as a "leaf node", and the CU of such a leaf node may include one or more PUs and / or one or more TUs. The video decoder may further divide the PU and TU. For example, in HEVC, a residual quadtree (RQT) represents the division of a 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.

[0053] 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 a plurality of coding tree units (CTUs). The video encoder 200 may divide the CTU according to a tree structure (such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure). The QTBT structure removes the concept of multiple partition types, such as the separation between CU, PU, ​​and TU of HEVC. The QTBT structure includes two levels: a first level divided according to quadtree partitions, and a second level divided according to binary tree partitions. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to coding units (CUs).

[0054] 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 referred to 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. The partition types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0055] When operating according to the AV1 codec, the video encoder 200 and the video decoder 300 may be configured to decode the 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 coding 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 layer of the block quadtree. The video encoder 200 may further divide the super block into smaller decoding blocks. The video encoder 200 may divide the super block and other decoding blocks into smaller blocks using square or non-square partitions. 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.

[0056] AV1 also defines tiles of video data. A tile is a rectangular array of super blocks that can be decoded independently of other tiles. That is, the video encoder 200 and the video decoder 300 can encode and decode coded blocks within a tile, respectively, without using video data from other tiles. However, the video encoder 200 and the video decoder 300 can perform filtering across tile boundaries. The size of the tiles can be uniform or non-uniform. Tile-based decoding can enable parallel processing and / or multi-threading specifically implemented by the encoder and decoder.

[0057] In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT or MTT structure to represent each of the luma component and the chroma components, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luma component and another QTBT / MTT structure for the two chroma components (or two QTBT / MTT structures for the respective chroma components).

[0058] The video encoder 200 and the video decoder 300 may be configured to use quadtree partitioning, QTBT partitioning, MTT partitioning, super block partitioning, or other partitioning structures.

[0059] In some examples, a CTU includes a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples of a picture having three sample arrays, or a CTB of samples of 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 N value, such that one partition is to divide components into CTBs. A component is an array or a single sample from one of the three arrays (luminance 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 M and N values, such that one partition is to divide a CTB into coding blocks.

[0060] 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 area of ​​a CTU row within a particular tile in a picture. A tile may be a rectangular area of ​​a CTU within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular area 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 area 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.

[0061] In some examples, a tile may be divided into multiple bricks, each of which may include one or more CTU rows within the tile. Tiles that are not divided into multiple bricks may also be referred to as bricks. However, bricks that are true subsets of tiles may not be referred to as tiles. 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 continuous sequence of complete bricks that include only one tile.

[0062] This disclosure may use "N×N" 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, 16×16 samples or 16 by 16 samples. Typically, a 16×16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Similarly, an N×N CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. In addition, a CU does not necessarily need to have the same number of samples in the horizontal direction as in the vertical direction. For example, a CU may include N×M samples, where M is not necessarily equal to N.

[0063] 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 generally represents the sample-by-sample difference between the samples of the CU before encoding and the prediction block.

[0064] In order to predict a CU, the video encoder 200 may generally form a prediction block of the CU by 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. In order 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 generally perform a motion search to identify a reference block that closely matches the CU, for example, based on the difference between the CU and the reference block. The video encoder 200 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.

[0065] Some examples of VVC also provide an affine motion compensation mode, which can be considered an inter-prediction mode. In the affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion (such as zooming in or out, rotation, perspective motion, or other irregular motion types).

[0066] 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 modes and DC modes. 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, from top to bottom), such samples may typically be located above, above left, or to the left of the current block in the same picture as the current block.

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

[0068] AV1 includes two general techniques for encoding and decoding coded blocks of video data. The two general techniques are intra prediction (e.g., intra prediction or spatial prediction) and inter prediction (e.g., inter prediction or temporal prediction). In the context of AV1, when an intra 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 prediction modes, the video encoder 200 encodes a block of the current frame based on the difference between the sample values ​​in the current block and the prediction values ​​generated from the reference samples in the same frame. The video encoder 200 determines the prediction values ​​generated from the reference samples based on the intra prediction mode.

[0069] After prediction (such as intra-frame prediction or inter-frame prediction for a block), the video encoder 200 may calculate residual data for the block. The residual data (such as a residual block) represents the sample-by-sample difference between the block and a prediction block for the block, which is formed using a corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to produce transformed data in a transform domain rather than in a sample domain. For example, the video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. Additionally, 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 one or more transforms.

[0070] As noted above, after any transforms that produce transform coefficients, the video encoder 200 may perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly 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.

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

[0072] To perform CABAC, video encoder 200 may assign context within a context model to a symbol to be sent. The context may relate to, for example, whether neighboring values ​​of the symbol are zero values. The probability determination may be based on the context assigned to the symbol.

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

[0074] In this way, the video encoder 200 can generate a bitstream including encoded video data, for example, a syntax element describing the partition of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Finally, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0075] In general, the video decoder 300 performs a process that is the reverse of the process performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 may use CABAC to decode the values ​​of the syntax elements for the bitstream in a manner substantially similar to but reverse 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).

[0076] 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 performing a deblocking process to reduce visual artifacts along the boundaries of the blocks.

[0077] The present disclosure may generally involve "signaling" certain information (such as syntax elements). The term "signaling" may generally refer to the communication of values ​​of syntax elements and / or other data used to decode encoded video data. That is, video encoder 200 may signal values ​​of syntax elements in a bitstream. Generally speaking, 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).

[0078] As introduced above, the video encoder 200 and the video decoder 300 can be configured to perform various types of filtering on the reconstructed blocks, including ALF. In VVC, ALF can be applied to minimize the mean square error between the original samples and the filtered samples. Existing implementations of ALF use samples that have been filtered by SAO and / or deblocking filtering (DBF). In some examples, the input samples of the ALF are the output samples of the SAO filter. The output samples of the ALF are stored in the decoded picture buffer (DPB) or transmitted as an output picture. The filter shapes of the ALF used in the joint detection model (JEM) software are 5x5, 7x7 and 9x9 diamonds. The video encoder 200 can select and signal the filter shape at the picture level. In order to obtain a better compromise between decoding efficiency and filter complexity, in VVC, such as Figure 2 As shown, only 7x7 diamond 400 and 5x5 diamond 402 are supported for luma component and chroma component respectively. Figure 2 Example ALF filter shapes in VVC version 1 are shown.

[0079] In one example, for each filter, the integer coefficient 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 2 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 and number of multiplications associated with sending coefficients, Figure 2 The filter shape in is point symmetric. In addition, as shown in equation (1), the sum of all filter coefficients should be equal to 128, which is a fixed-point representation of 1.0 with 7-bit fractional precision.

[0080]

[0081] In equation (1), N is the number of coefficients and is equal to 13 and 7 for 7x7 and 5x5 filter shapes, respectively.

[0082] In VVC, nonlinearity is introduced into ALF. When the difference between the adjacent sample value and the current sample value to be filtered is too large, the video encoder 200 and the video decoder 300 may apply a simple clipping function to reduce the influence of the adjacent sample value. In order to filter the sample, the ALF process is performed as follows:

[0083]

[0084] Among them, R(x,y) is the sample value after SAO filtering.

[0085] The nonlinear function is defined with the clipping function as:

[0086] f i,j =min(b i ,max(-b i ,R(x+x i,j ,y+y i,j )-R(x,y))) (3)

[0087] 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 position is offset.

[0088] In VVC version 1, as in equation (4), the coefficient c i The clipping parameter b i By clipping index d i In equation (4), BD is the internal bit depth.

[0089]

[0090] In the filter, the number of coefficients signaled and the number of clipping indices signaled are both N-1. In one example, each coefficient is limited to the range of [-128, 127], which is equivalent to [-1.0, 1.0] with 7-bit fractional precision. In one example, each clipping index d i Can be 0, 1, 2 or 3 and is signaled 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 only be a power of 2. Therefore, a simple bitwise logical operation can be applied as a clipping operation.

[0091] The video encoder 200 and the video decoder 300 may be configured to perform sub-block level filter adaptation. In VVC version 1, ALF follows the same luma classification framework as ALF in JEM-7.0. In order to obtain a better trade-off between decoding efficiency and computational complexity, the block size used for classification may be increased from 2x2 samples to 4x4 samples. To determine the class index of a 4x4 block, a surrounding window with 8x8 luma samples is used to derive direction and activity information. In this 8x8 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 a 4×4 sub-block 404 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. For each sample with coordinates (k, l), Figure 4Four gradient values ​​are shown: horizontal gradient H 406, vertical gradient V 408, 135 degree gradient D1 410, and 45 degree gradient D2 412, which are derived as:

[0092]

[0093] The variables i and j refer to the coordinates of the top left sample in the 4x4 block. All calculated horizontal gradients g H , vertical gradient g V , 135 degree gradient g D1 and 45 degree gradient g D2 The sum is calculated as:

[0094]

[0095] 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 ) is calculated as shown in the following equation (7).

[0096]

[0097] Then, R H,V and R D1,D2 Using two thresholds (t 1 =2 and t 2 =4.5) are compared with each other to derive the directivity D as follows:

[0098] Step 1: If R H,V ≤t 1 And R D1,D2 ≤t 1 , then D is set to 0 (texture), otherwise continue with step 2.

[0099] Step 2: If R D1,D2 >R H,V , then continue with step 3, otherwise continue with step 4.

[0100] Step 3: If R D1,D2 ≤t 2 , then D is set to 1 (weak diagonal), otherwise, D is set to 2 (strong diagonal).

[0101] Step 4: If R H,V ≤t 2 , then D is set to 3 (weak horizontal / vertical), otherwise, D is set to 4 (strong horizontal / vertical).

[0102] The activity value A is calculated as:

[0103]

[0104] A is further mapped to a range of 0 to 4 (inclusive), and the quantized value is represented as Therefore, each 4x4 block is classified into one of 25 classes (C), such as:

[0105]

[0106] Therefore, 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. The merged classes use the same filters. The video encoder 200 can signal the merge table. In the merge table 414, as an example, Figure 5 As shown, the filter index of each class is signaled by using a fixed-length code. Figure 5 An example of merging 25 brightness classes into 7 merged classes is shown, where each square is based on the value of D and Represents a class (the index can be 0 to 24, inclusive). In this example filter bank, the video encoder 200 can be configured to signal 7 luma filters. For each class, the video encoder 200 can signal the filter index (0 to 6 in this example) in the ALF_APS (Adaptation Parameter Set).

[0107] Once the filter is obtained from the luma filter bank based on the class index C and the merge table for the 4x4 block, before obtaining the filter samples for the block, as Figure 6 As shown, a simple geometric transformation can be applied to the filter according to the gradient values ​​calculated for the 4x4 block as shown in Table 1.

[0108] Table 1: Geometric transformation based on gradient values

[0109] 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 ]]> Rotate Right

[0110] Figure 6 The geometric transformation of the 7x7 diamond filter shape is shown. The geometric transformation includes a diagonal flip 416, a vertical flip 418 and a right rotation 420.

[0111] The video encoder 200 and the video decoder 300 may be configured to perform coding tree block level adaptation. In JEM-7.0, only one luminance filter group is applied to all luminance CTBs of a slice and only one chrominance filter is applied to all chrominance CTBs of a slice. However, there are two disadvantages. First, when the statistical information between CTBs is substantially different, using the same filter / filter group for all CTBs of a color component may limit the coding efficiency of ALF, especially for large resolution sequences and mixed content video sequences (e.g., both natural content and screen content). Secondly, when deriving filters for slices, the filters can only be calculated until the statistical information of the entire slice is collected. This multi-channel coding technique may not be suitable for low-delay applications. To solve this problem, an example solution uses statistical information from previously decoded slices. However, this may result in some performance losses.

[0112] In addition to the luma 4x4 block-level filter adaptation, VVC supports CTB-level filter adaptation. In a slice, the video encoder 200 can be configured to use different luma filter groups for different luma CTBs, and can also use different chroma filters for different chroma CTBs. The video encoder 200 can use the same filter for CTBs with similar statistical information. This CTB-level filter adaptation improves decoding efficiency, especially for low-latency applications. In addition, VVC version 1 allows the video encoder 200 to use filters from previously decoded pictures for CTB. The temporal filter reuse mechanism can reduce the overhead of filter coefficients. In VVC version 1, up to seven signaled luma filter groups and eight signaled chroma filters can be applied to slices. When there is no signaled filter, one of the 16 fixed filter groups can be applied to the luma CTB.

[0113] When ALF is enabled, a fixed filter bank or a filter bank index of a signaled luma filter bank is signaled for a luma CTB. The filter index of the signaled chroma filter is signaled for a chroma CTB. By using the signaled filters and fixed filters from the previously decoded pictures, when encoding the current CTU in low-latency applications, the three CTU level on / off flags and filter / filter bank indexes can be decided 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.

[0114] The video encoder 200 and the video decoder 300 may be configured to implement line buffer reduction. Figure 2As shown, in the vertical direction, the filter shape has 7 taps for the luminance component and 5 taps for the chrominance component, respectively. Therefore, in VVC Test Model 2.0 (VTM-2.0), when a row of CTU is decoded, due to the delay of the deblocking filter and the SAO filter, the 7 luminance lines and 4 chrominance 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.

[0115] 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 location of VB is 4 luma samples and 2 chroma samples above the horizontal CTU boundary. When filtering one sample on one side of VB, the sample on the other side of VB cannot be utilized. Applying modified filtering with symmetric sample padding, such as 7A to 7C , where the center square of the filter 432 is the location of the current sample to be filtered and the thick line 430 (VB 430) is the location of VB. 7A to 7C , the filter tap positions with dashed lines are filled. Fig. 7A An example is shown where one filter tap position of filter 432 is above or below VB 430. In this example, one filter tap position is filled. Figure 7B An example is shown where four filter tap positions of filter 432 are above and below VB 430. In this example, four filter tap positions are filled.

[0116] However, when the sample is on the nearest row on each side of VB 430 (e.g., Figure 7C ), the 2D filter is equivalent to a horizontal filter. This may introduce visual artifacts. To address this problem, the filter strength is compensated when the current sample to be filtered is on the nearest row on each side of VB, as shown in equation (10). Comparing equation (10) with equation (2), an additional 3 bits are right-shifted.

[0117]

[0118] When applying VB processing, the classification of the 4x4 block is also modified. When calculating the class index of the 4x4 block on one side of the VB, the gradients and samples on the other side of the VB are not used, as shown in Figure 8 However, when calculating the gradient value of the sample adjacent to VB, the samples on the other side of VB cannot be used. Therefore, Figure 8As 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 activity derivation in equation (8) is rescaled to:

[0119]

[0120] The video encoder 200 and the video decoder 300 may be configured to signal filter coefficients. In VVC version 1, the ALF coefficients are signaled in an ALF adaptation parameter set (APS). An APS may include a set of luminance filters having up to 25 filters, up to 8 chrominance filters, and up to 8 cross-component ALF (CC-ALF) filters. Each set of luminance filters supports applying ALF to 25 classes of luminance. In VVC version 1, up to 8 ALF_APS are supported.

[0121] Table 2 below shows the adaptive loop filter data syntax for VVC.

[0122] Table 2

[0123]

[0124]

[0125]

[0126] The video encoder 200 and the video decoder 300 can be configured to implement ALF with multiple classifiers. In VVC, only one classifier and one filter can be applied when filtering a sample. In order to improve the performance of ALF based on VVC, an ALF framework based on multiple classifiers is described in U.S. Provisional Patent Application No. 17 / 557,706 filed on December 21, 2021, which is incorporated herein by reference.

[0127] Fig. 9 An example of an ALF with multiple Laplacian classifiers is shown. Fig. 9 In the example of , the video encoder 200 and the video decoder 300 apply the first stage ALF 440 to the reconstructed samples R(x,y) of the reconstructed block. To apply the first stage ALF 440, the video encoder 200 and the video decoder 300 apply a classifier (C) to determine a first class index of the reconstructed sample and select a filter (f) from a first filter bank (F) based on the first class index. The video encoder 200 and the video decoder 300 apply the filters in the first filter bank to the reconstructed sample to determine a first intermediate sample value (R'). Fig. 9As shown in FIG. 4 , in the first stage 440 , the video encoder 200 and the video decoder 300 may use multiple classifiers and multiple filters to determine multiple intermediate sample values.

[0128] The video encoder 200 and the video decoder 300 apply the second stage ALF 442 to the reconstructed samples. The following equation (19) shows an example of how the video encoder 200 and the video decoder 300 may apply the second stage ALF.

[0129] N f represents the number of fixed (predefined) filter banks that can be applied to samples. Rs is the input to the ALF. F(f,i) (where i = 0...N f -1) represents the i-th fixed filter bank. C(f,i) (where i = 0...N f -1) denotes a classifier with the i-th fixed filter bank.

[0130] Through C(f,i), a filter index is calculated for each sample. Based on the filter index, a filter in the fixed filter bank F(f,i) is selected to filter the sample. In addition, C(f,i) determines how to apply the geometric transformation to the coefficients.

[0131] Fig.10 An example of ALF with three classifiers is shown, as proposed in JVET-U0100 (21st meeting held via teleconference on January 6-15, 2021). In JVET-U0100 adopted in ECM-1.0, an ALF framework with Nf=2 is proposed, as Fig.10 As shown. In ECM-1.0, in the classifier C(f,i) where i=0 or 1, the activity and direction values ​​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. The markers wi and hi can represent the width of the block and the height of the block, respectively, and (x, y) can represent the coordinates of the upper left sample of the block.

[0132] exist Fig.10 In the example of , the video encoder 200 and the video decoder 300 apply the first stage ALF 450 to the reconstructed samples R(x,y) of the reconstructed block. To apply the first stage ALF 450, the video encoder 200 and the video decoder 300 apply a classifier (C) to determine a first class index of the reconstructed sample and select a filter (f) from a first filter bank (F) based on the first class index. The video encoder 200 and the video decoder 300 apply the filters in the first filter bank to the reconstructed sample to determine a first intermediate sample value (R').

[0133] The video encoder 200 and the video decoder 300 apply the second stage ALF 452 to the reconstructed samples. The following equation (19) shows an example of how the video encoder 200 and the video decoder 300 may apply the second stage ALF.

[0134] Fig.10 The example of 450 utilizes three Laplace classifiers, two in the first stage 450 and one in the second stage 452. As will be explained in more detail below, different types of classifiers, not just Laplace classifiers, may be used according to the techniques of the present disclosure. For example, according to one specific implementation, different types of classifiers may be used at the second stage 452, such as a band-based classifier.

[0135] For a sample with coordinates (k, l), four Laplace (gradient) values: horizontal gradient H, vertical gradient V, 135 degree gradient D1 and 45 degree gradient D2 can be derived as:

[0136]

[0137] As with VVC, the video encoder 200 and the video decoder 300 may be configured to convert the activity value A into a pixel value by using a vertical gradient and a horizontal gradient. i Export as:

[0138]

[0139] Among them, a i and b i are the window sizes of the classifier C(f,i) in the horizontal and vertical directions respectively.

[0140] A i is further quantized to 0 to M A,i -1 (including the end value), and the quantized value is expressed as

[0141] In one example,

[0142]

[0143] Q

[193] ={0,1,2,3,4,4,5,5,6,6,6,6,7,7,7,7,8,8,8,8,8,8,8,8,9,9,9,9,9,9,9 ,9,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,11,11,11,11,11,11,1 1,11,11,11,11,11,11,11,11,11,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,13,13,13,13,13 ,13 ... 14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,14,15};

[0144] bitdepth is the bit depth of R(x,y), mult i Depends on the window size (a i , b i ), and mult i is equal to the following value:

[0145]

[0146] The video encoder 200 and the video decoder 300 may be configured to calculate a direction by using a horizontal gradient H, a vertical gradient V, a 135 degree gradient D1, and a 45 degree gradient D2.

[0147] The video encoder 200 and the video decoder 300 may be configured to first calculate the value g of the horizontal gradient i,H , the value of the vertical gradient g i,V and the values ​​of the two diagonal gradients g i,D1 and g i,D2 , as shown below:

[0148]

[0149] To assign the directionality D i , (maximum and minimum values ​​of horizontal gradient and vertical gradient), the video encoder 200 and the video decoder 300 may be configured to derive the maximum and minimum values ​​of the two diagonal gradients as follows:

[0150]

[0151] The video encoder 200 and the video decoder 300 may be configured to compare the ratio and threshold array (Th) to calculate the horizontal / vertical edge strength (ES i,HV ). The size of the threshold array can be expressed as S, and the thresholds are sorted in ascending order. The number of directions is M D,i =(S+1)*(S+2).

[0152] Step 1. Initialize m=0 and ES i，HV =0;

[0153] Step 2. If m is equal to S, stop; otherwise, go to step 3.

[0154] Step 3. If m=m+1 and ES i,HV =ES i,HV +1, go to step 2; otherwise, stop.

[0155] Diagonal direction (E i，D ) is similarly calculated as

[0156] Step 1. Initialize m=0 and E i，D =0;

[0157] Step 2. If m is equal to S, stop; otherwise, go to step 3.

[0158] Step 3. If m=m+1 and E i,D =E i,D +1, go to step 2; otherwise, stop.

[0159] An example of a threshold array is Th=[1.25, 1.5, 2, 3, 4.5, 8] and S=6.

[0160] The video encoder 200 and the video decoder 300 may be configured to determine the dominant edge strength (ES) as follows: M ) and secondary edge strength (ES S ):

[0161] if Then ES M Set to ES HV , and ESS Set to ES D ; Otherwise, ES M Set to ES D , and ES S Set to ES HV

[0162] If ES S Greater than ES M , then D i is set to 0. Otherwise, if ES M *(ES M +1) / 2+ES S Otherwise, D i =ES M *(ES M +1) / 2+ES S +M D,i / 2;

[0163] Class Index C i Can be exported as

[0164] C-based i , select the filter from C(f,i).

[0165] 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 its neighbors. C' can be used to determine which filter in F' to apply and how to transpose the coefficients.

[0166] C' may use R and / or R' to determine the filter indexes of filter bank F' by computing activity and direction as a first stage. A transpose may be applied when applying F'.

[0167] In one example, for a sample with coordinates (k, l), the video encoder 200 and the video decoder 300 may be configured to derive four Laplace (gradient) values, namely, a horizontal gradient H, a vertical gradient V, a 135 degree gradient D1, and a 45 degree gradient D2, such as:

[0168]

[0169] Like VVC, the video encoder 200 and the video decoder 300 may be configured to derive the activity value A by using the vertical gradient and the horizontal gradient as follows:

[0170]

[0171] where a and b are the window sizes of the classifier C' in the horizontal and vertical directions, respectively, and w and h are the width and height of a block in which all samples have the same classification index and the same transposed index.

[0172] The video encoder 200 and the video decoder 300 may be configured to quantize A to a value between 0 and M. A -1 (inclusive). Quantized values ​​can be expressed as For example,

[0173]

[0174] Q={0,1,2,2,2,2,2,3,3,3,3,3,3,3,3,4} (18)

[0176] bitdepth is the bit depth of R(x,y), mult may depend on the window size a*b and mult may be equal to the following values:

[0177]

[0178] After obtaining the class index of the sample from C', the video encoder 200 and the video decoder 300 may be configured to select a filter from the filter bank F' based on the class index. The video encoder 200 and the video decoder 300 may be configured to apply the filtering as:

[0179]

[0180] In the above equation, the filtering is divided into two parts:

[0181] ●Filtering part 1: By filtering using neighboring samples, a geometric transformation can be applied. 0 is the number of coefficients. It can be Fig. 9 5x5, 7x7, 9x9, 11x11, or 13x13 diamond filters as shown.

[0182] ●Filtering part 2: By filtering using the intermediate filtered samples, a geometric transformation can be applied. 1 is the number of coefficients.

[0183] The function f,j (where j = 0 or 1) can be defined as a clipping function:

[0184] f i,j =f i,j (R(x+x i,j ,y+y i,j ),R(x,y))=min(b i ,max(-bi ,R(x+x i,j ,y+y i,j )-R(x,y))) (20)

[0186] Function g i The clipping function can be defined as

[0187] g i =g i (R′(x,y,iN 0 ),R(x,y))=min(b i ,max(-b i ,R′(c,y,iN 0 )-R(x,y))) (twenty one)

[0189] b i is the coefficient c i In ECM-1.0, N 1 =2.

[0190] The video encoder 200 and the video decoder 300 may be configured to utilize a signaled adaptive loop filter with multiple classifiers.

[0191] In ECM-1.0, C' is a Laplace-based classifier. In order to improve the performance of ALF, a multi-classifier-based ALF is proposed in U.S. patent application 17 / 853,274 filed on June 29, 2022, which is incorporated herein by reference. Fig.11 The band-based classifier shown.

[0192] exist Fig.11 In the example of , sample 460 is first filtered by DBF 462, then filtered by SAO 464, and then filtered by ALF 466 to produce filtered sample 468. ALF 466 illustrates the ALF as implemented in ECM-4.0. Fig.11 In ALF466 of , when filtering a sample using a signaled filter, a classifier is selected between C2 and C3 based on a signaled flag. The class index is used to select filter F2 from a set of signaled filters. C2 is a Laplacian-based classifier used in ECM-1.0. C3 is a band-based classifier. Similar to C2, C3 is applied to each non-overlapping 2×2 luma block, and the class index is determined as

[0193] (sum*num_classes)>>(2+bit_depth),

[0194] where sum is the sum of the luma sample values ​​of the 2x2 luma block, num_classes is equal to 25, and bit_depth is the bit depth of the luma samples.

[0195] Fig.12 An example of using samples before DBF for ALF is shown. To further improve performance, techniques for using samples before deblocking filtering (DBF) with ALF are described in U.S. Provisional Application 63 / 269,207 (filed March 11, 2022) and JVET-Z0146 (both of which are incorporated herein by reference). Fig.11 Same, in Fig.12 , sample 460 is first filtered by DBF 462, then by SAO 464, and then by ALF 466 to produce filtered sample 468. However, in Fig.12 In FIG. 4 , various aspects of filter selection and classification within ALF 466 rely on pre-DBF samples 470 , which requires that pre-DBF samples 470 be stored for use by ALF 466 .

[0196] When the samples before DBF and the samples before SAO are used for ALF filtering, equation (19) is rewritten as

[0197]

[0198] Function d i The clipping function can be defined as

[0199] d i =d i (R d (x+x i ,y+y i ),R(x,y))=min(b i ,max(-b i ,R d (x+x i ,y+y i )-R(x,y))) (twenty three)

[0201] Where R d (x+x i ,y+y i ) is the adjacent sample before DBF, and (x i ,y i ) is the coordinate offset relative to the current sample R(x,y), N d is the number of taps applied to the samples before DBF. In JVET-Z0146, two symmetrical diamond filter shapes are applied to the samples before DBF.

[0202] Existing implementations of ALF may have some disadvantages, and the present disclosure describes techniques that may improve those disadvantages. Using pre-DBF samples may improve coding efficiency. Since current implementations of ALF rely on samples between different hardware pipeline stages (e.g., pre-DBF and pre-ALF), ALF requires more line buffer storage.

[0203] This disclosure describes techniques that can reduce the hardware overhead for implementing ALF while maintaining or improving decoding efficiency. According to the techniques of this disclosure, it is proposed to apply a filter in parallel with DBF, such as Fig.13 shown.

[0204] Fig.13 An example of a new filter that can be applied to a block of video data in parallel with DBF is shown. Fig.13 472 to determine a deblocked sample, and in parallel with the DBF 472, a new filter 474 is applied to the sample 470 to determine a second filtered sample. The video decoder 300 then performs weighting 476 to combine the deblocked sample and the second filtered sample. The video decoder 300 applies a third filter SAO 478 to the combined sample. The video decoder 300 then applies an ALF 480 to the output of the SAO 478 to produce a filtered sample 482. The ALF 480 may, for example, have the same Fig.11 ALF 466 has a similar structure, with only post-SAO samples as input. Video decoder 300 outputs filtered samples 482, for example as part of a decoded version of a block of video data.

[0205] Fig.14 An example of a proposed filter 490 (which is a cross or diamond 3×3 filter) and a proposed filter 492 (which is a 5×5 diamond filter) is shown. Filters 490 and 492 are examples of filters that can be used Fig.13 An example of a filter of the new filter 474 in FIG.

[0206] To implement the techniques of the present disclosure, the video encoder 200 and the video decoder 300 may be configured to implement filtering as follows:

[0207] 1. The input samples of the new filter can be the same as the input samples of DBF.

[0208] 2. The new filter may filter only samples identified by the DBF (e.g., samples close to block boundaries). For example, only samples within a certain distance from a block edge may be filtered. In one example, a block edge may be identified by a DBF. In another example, the distance may be 1 sample from an intra 4×4 block and 3 samples from other edges. In another example, the edge strength may exceed a threshold or be within a threshold in order to filter a sample.

[0209] 3. When the new filter 474 is applied in parallel with the DBF 472, the filtered samples from the DBF 472 and the parallel new filter 474 may be weighted summed to generate the output of the stage. In one example, the weights may be fixed for all samples. In another example, the weights may be signaled at the sequence / APS / picture / slice / block / filter and other levels.

[0210] 4. The on / off flag of the parallel filter can be signaled at the sequence / parameter set / frame / slice / block level.

[0211] 5. The new filter 474 can be a fixed (pre-trained) filter or a signaled filter. Classification can be applied to determine which filter to apply to a sample.

[0212] 6. The new filter 474 can be an ALF, a bilateral filter, a guided filter, or any other type of filter.

[0213] 7. Information from this level can be applied to the ALF level ( Fig.13 For example, the decision to filter a sample in the new filter can be used by a classifier in the ALF stage. For example, the final class index in the ALF stage can be derived as

[0214] class_idx+num_classes*i,

[0215] where class_idx is derived from the classifier in the ALF level, num_classes is the number of classes in that classifier,

[0216] And i (=0 or 1) is the decision to filter the sample by a filter in parallel with the DBF.

[0217] Fig.15 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Fig.15It is provided for the purpose of explanation and should not be considered as limiting the techniques extensively illustrated and described in this disclosure. For the purpose of explanation, this disclosure describes a video encoder 200 according to VVC (ITU-T H.266, under development) and HEVC (ITU-T H.265) techniques. 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 subsequent formats of the AV1 video coding format.

[0218] exist Fig.15 In the example of , the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a 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 a processing system of one or more processors and / or processing circuits. 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. In addition, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

[0219] Video data memory 230 is an example of a memory system that can store video data to be encoded by components of video encoder 200. Video encoder 200 can store video data from, for example, video source 104 ( Figure 1 ) receives video data stored in video data memory 230. DPB218 is another example of a memory system that can act as a reference picture memory, which stores reference video data for use when subsequent video data is predicted by video encoder 200. Video data memory 230 and DPB 218 can each be formed by any of a variety of one or more memory devices or memory cells, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM) or other types of memory devices. Video data memory 230 and DPB218 can be provided by the same memory device or a separate memory device. In various examples, video data memory 230 can be on-chip with other components of video encoder 200 (as illustrated), or off-chip relative to those components.

[0220] In the present disclosure, references to the video data memory 230 should not be interpreted as limited to a memory inside the video encoder 200 (unless otherwise specified) or a memory outside the video encoder 200 (unless otherwise specified). Rather, references to the video data memory 230 should be understood as a reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). Figure 1 Memory 106 may also provide temporary storage for outputs from various units of video encoder 200 .

[0221] Illustrated Fig.15 The various units of the video encoder 200 are described to help understand the operations performed by the video encoder 200. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide 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 (e.g., to receive parameters or output parameters), but the types of operations performed by fixed-function circuits are generally immutable. In some examples, one or more of the units may be different circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits.

[0222] 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 the video encoder 200, or another memory (not shown) within the video encoder 200 may store such instructions.

[0223] The video data memory 230 is configured to store the received video data. The video encoder 200 may retrieve a picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 may be original video data to be encoded.

[0224] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. The mode selection unit 202 may include additional functional units to perform video prediction according to other prediction modes. 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.

[0225] The mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and resulting rate-distortion values ​​for such combinations. The encoding parameters may include the partitioning of CTUs into CUs, the prediction mode for a CU, the transform type for residual data of a CU, the quantization parameter for residual data of a CU, etc. The mode selection unit 202 may ultimately select an encoding parameter combination that has a better rate-distortion value than other tested combinations.

[0226] The video encoder 200 may divide the 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 a tree structure, such as an MTT structure, a QTBT structure, a super block structure, or the above-mentioned quadtree structure. 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".

[0227] Typically, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU, or in HEVC, the overlapping portion of the PU and TU). In order to inter-predict the current block, the motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously decoded pictures stored in the DPB 218). Specifically, the motion estimation unit 222 may calculate a value representing the degree of similarity of the potential reference block to the current block, for example, based on SAD, SSD, MAD, MSD, etc. The motion estimation unit 222 may typically perform these calculations using the sample-by-sample differences between the current block and the reference block under consideration. The motion estimation unit 222 may identify the reference block having the lowest value produced by these calculations to indicate the reference block that best matches the current block.

[0228] The motion estimation unit 222 may form one or more motion vectors (MVs) that define the positioning of the reference block in the reference picture relative to the positioning of the current block in the current picture. The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, for unidirectional inter prediction, the motion estimation unit 222 may provide a single motion vector, while for bidirectional inter prediction, the motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, the motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, in the case where the motion vectors have fractional sample precision, the motion compensation unit 224 may interpolate the values ​​of the prediction block according to one or more interpolation filters. In addition, for bidirectional inter prediction, the motion compensation unit 224 may retrieve data for two reference blocks identified by the corresponding motion vectors and combine the retrieved data, for example, by sample-by-sample averaging or weighted averaging.

[0229] 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.

[0230] As another example, for intra prediction or intra prediction coding, the intra prediction unit 226 may generate a prediction block from samples neighboring the current block. For example, for directional mode, the intra prediction unit 226 may generally mathematically combine the values ​​of neighboring samples and pad these calculated values ​​across the current block in a defined direction to produce a prediction block. As another example, for DC mode, the intra prediction unit 226 may calculate an average of neighboring samples of the current block and generate a prediction block to include the resulting average for each sample of the prediction block.

[0231] When operating according to the AV1 video coding format, the intra prediction unit 226 may be configured to encode 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, 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.

[0232] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives the uncoded original version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, the residual generation unit 204 may also determine the difference between the sample values ​​in the residual block to generate the residual block using residual differential pulse coding modulation (RDPCM). In some examples, the residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0233] In an example where the mode selection unit 202 divides the CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs of various sizes. As noted above, the size of a CU may refer to the size of the luma coding block of the CU, and the size of a PU may refer to the size of the luma prediction unit of the PU. Assuming that the size of a particular CU is 2N×2N, the video encoder 200 may support PU sizes of 2N×2N or N×N for intra-prediction, and 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.

[0234] In examples where mode select unit 202 does not further divide a CU into PUs, each CU may be associated with a luma coding block and a corresponding chroma coding block. As above, the size of a CU may refer to the size of the luma coding block of the CU. Video encoder 200 and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

[0235] 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 a 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 the manner in which the block is reconstructed based on the selected palette. In such modes, mode selection unit 202 may provide these syntax elements to entropy encoding unit 220 for encoding.

[0236] 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.

[0237] 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 a 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, for example, 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.

[0238] When operating according to 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 a 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., an ADST in reverse order), and an identity transform (IDTX). When the identity transform is used, the transform is skipped in one of the vertical direction or the horizontal direction. In some examples, the transform process may be skipped.

[0239] Quantization unit 208 may quantize transform coefficients in a transform coefficient block to produce 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 selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may cause 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.

[0240] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct a residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (although potentially with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0241] 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. Filter unit 216 may also perform the ALF techniques described in this disclosure. In some examples, the operations of filter unit 216 may be skipped.

[0242] When operating according to AV1, 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 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 recovery filter applied after CDEF, and may include a separable symmetric normalized Wiener filter or a dual self-guided filter.

[0243] The filter unit 216 may, for example, perform the techniques described in the present disclosure. The filter unit 216 may, for example, determine a classifier for a current block of video data from a plurality of available classifiers, wherein each of the plurality of available classifiers defines a process for calculating a class index; determine a class index based on the determined classifier and one or more sample values ​​of the current block; select a filter from a filter bank based on the class index; and apply the filter to the current block. The filter unit 216 may use a plurality of classifiers to apply the two-stage ALF described above.

[0244] According to the techniques of the present disclosure, filter unit 216 may be configured to apply a first filter (such as a deblocking filter) to a block of video data to determine a first filter block, and apply a second filter to the block of video data in parallel with the first filter to determine a second filter block. Filter unit 216 may then combine the first filter block and the second filter block to determine a combined block and apply a third filter to the combined block to determine a third filter block. Filter unit 216 or other units of video encoder 200 may then process the third filter block to determine a decoded version of the block of video data and output a decoded version of the block of video data.

[0245] The video encoder 200 stores the reconstructed block in the DPB 218. For example, in an example where the operation of the filter unit 216 is not performed, the reconstruction unit 214 may store the reconstructed block in the DPB 218. In an example where the operation of the filter unit 216 is performed, the filter unit 216 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.

[0246] In general, the entropy coding unit 220 may entropy encode syntax elements received from other functional components of the video encoder 200. For example, the entropy coding unit 220 may entropy encode a quantized transform coefficient block from the quantization unit 208. As another example, the entropy coding unit 220 may entropy encode a prediction syntax element (e.g., motion information for inter prediction or intra mode information for intra prediction) from the mode selection unit 202. The entropy coding unit 220 may perform one or more entropy coding operations on the syntax element (the syntax element is another example of video data) to generate entropy encoded data. For example, the entropy coding unit 220 may perform a context adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context adaptive binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential Golomb coding operation, or another type of entropy coding operation on the data. In some examples, the entropy coding unit 220 may operate in a bypass mode where the syntax element is not entropy encoded.

[0247] The video encoder 200 may output a bitstream including syntax elements of entropy coding required to reconstruct a block of a slice or a picture. Specifically, the entropy coding unit 220 may output a bitstream.

[0248] According to AV1, the entropy coding unit 220 may be configured as a symbol-to-symbol adaptive multi-symbol arithmetic decoder. The 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 may store the probabilities as an n-bit (e.g., 15-bit) cumulative distribution function (CDF). The entropy coding unit 220 may perform recursive scaling using an update factor based on the size of the alphabet to update the context.

[0249] 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.

[0250] In some examples, operations performed with respect to luma coding blocks do not need to be repeated for chroma coding blocks. As an example, operations to identify motion vectors (MVs) and reference pictures for luma coding blocks do not need to be repeated for MVs and reference pictures used to identify chroma blocks. Instead, the MVs for luma coding blocks may be scaled to determine MVs for chroma blocks, and the reference pictures may be the same. As another example, the intra prediction process may be the same for luma coding blocks and chroma coding blocks.

[0251] Fig.16 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Fig.16 It is provided for the purpose of explanation and is not a limitation of the techniques extensively illustrated and described in this disclosure. For the purpose of explanation, this disclosure describes a video decoder 300 according to VVC (ITU-T H.266, under development) and HEVC (ITU-T H.265) techniques. However, the techniques of this disclosure may be performed by video decoding devices configured for other video decoding standards.

[0252] exist Fig.16 In the example of , the video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 314. Any or all of the CPB memory 320, the entropy decoding unit 302, the prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the DPB 314 may be implemented in a processing system of one or more processors and / or processing circuits. For example, the units of the video decoder 300 may be implemented as one or more circuits or logic elements as part of a hardware circuit, or as part of a processor, ASIC, or FPGA. In addition, the video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

[0253] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include additional units to perform predictions according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0254] When operating according to 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, intra-block copy (IBC), and / or palette mode, as described above.

[0255] CPB memory 320 is an example of a memory system that can store video data (such as an encoded video bitstream) to be decoded by components of video decoder 300. For example, the video bitstream can 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 coded video data (e.g., syntax elements) from a coded video bitstream. In addition, CPB memory 320 may store video data other than syntax elements of a decoded picture, such as temporary data representing outputs from various units of video decoder 300. DPB 314 is an example of a memory system that typically stores decoded pictures, which video decoder 300 may output, and / or use the decoded pictures as reference video data when decoding subsequent data or pictures of the coded video bitstream. CPB memory 320 and DPB 314 may each be formed by any of a variety of memory devices or memory units, such as DRAM (including SDRAM), MRAM, RRAM, or other types of memory devices. CPB memory 320 and DPB 314 may be provided by the same memory device or a separate memory device. In various examples, CPB memory 320 may be on-chip with other components of video decoder 300, or off-chip relative to those components.

[0256] 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.

[0257] Illustrated Fig.16 The various units shown in FIG. 3 are used to help understand the operations performed by the video decoder 300. The units may be implemented as fixed function circuits, programmable circuits, or a combination thereof. Fig.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 operation performed by the fixed-function circuit is generally immutable. In some examples, one or more of the units may be different circuit blocks (fixed function or programmable), and in some examples, one or more of the units may be integrated circuits.

[0258] The video decoder 300 may include an ALU, an EFU, a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video decoder 300 is performed by software executed on the programmable circuit, an on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

[0259] 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 syntax elements extracted from the bitstream.

[0260] Generally, 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").

[0261] The entropy decoding unit 302 may entropy decode syntax elements defining the quantized transform coefficients of the quantized transform coefficient block and transform information, such as a quantization parameter (QP) and / or a transform mode indication. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, a degree of inverse quantization 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 including the transform coefficients.

[0262] After inverse quantization unit 306 forms the transform coefficient block, inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0263] 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, in the case where the prediction information syntax elements indicate that the current block is inter-predicted, motion compensation unit 316 can generate a prediction block. In this case, the prediction information syntax elements can indicate a reference picture in DPB 314 from which to retrieve the reference block, and a motion vector that identifies the position of the reference block in the reference picture relative to the position of the current block in the current picture. Motion compensation unit 316 can generally generate ... Fig.15 )The inter-frame prediction process is performed in a manner substantially similar to that described in the accompanying drawings.

[0264] 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. Fig.15 ) The intra prediction process is performed in a substantially similar manner as described in . The intra prediction unit 318 may retrieve data of neighboring samples of the current block from the DPB 314.

[0265] 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.

[0266] 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 filter unit 312 may also perform the ALF techniques described in the present disclosure. The operations of the filter unit 312 may not necessarily be performed in all examples.

[0267] The filter unit 312 may, for example, perform the techniques described in the present disclosure. The filter unit 312 may, for example, determine a classifier for a current block of video data from a plurality of available classifiers, wherein each of the plurality of available classifiers defines a process for calculating a class index; determine a class index based on the determined classifier and one or more sample values ​​of the current block; select a filter from a filter bank based on the class index; and apply the filter to the current block. The filter unit 312 may use a plurality of classifiers to apply the two-stage ALF described above.

[0268] According to the techniques of the present disclosure, filter unit 312 may be configured to apply a first filter (such as a deblocking filter) to the video data block to determine a first filter block, and apply a second filter to the video data block in parallel with the first filter to determine a second filter block. Filter unit 312 may then combine the first filter block and the second filter block to determine a combined block and apply a third filter to the combined block to determine a third filter block. Filter unit 312 or other units of video decoder 300 may then process the third filter block to determine a decoded version of the video data block and output a decoded version of the video data block.

[0269] The video decoder 300 may store the reconstructed block in the DPB 314. For example, in examples where the operation of the filter unit 312 is not performed, the reconstruction unit 310 may store the reconstructed block in the DPB 314. In examples where the operation of the filter unit 312 is 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-frame 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., a decoded video) from the DPB 314 for use in, for example, Figure 1 Subsequent presentation on a display device such as display device 118.

[0270] Fig.17 2 is a flowchart illustrating an example process for encoding a current block according to the techniques of the present disclosure. The current block may include a current CU. Although relative to the video encoder 200 ( Figure 1 and Fig.15 ), but it should be understood that other devices may be configured to perform the same Fig.17 The process is similar to the process.

[0271] In this example, the video encoder 200 initially predicts a current block (500). For example, the video encoder 200 may form a prediction block for the current block. Then, the video encoder 200 may calculate a residual block for the current block (502). In order 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. Then, the video encoder 200 may transform the residual block and quantize the transform coefficients of the residual block (504). Next, the video encoder 200 may scan the quantized transform coefficients of the residual block (506). During or after the scan, the video encoder 200 may entropy encode the transform coefficients (508). For example, the video encoder 200 may encode the transform coefficients using CAVLC or CABAC. Then, the video encoder 200 may output entropy encoded data for the block (510).

[0272] Fig.18 1 is a flowchart illustrating an example process for decoding a current block of video data according to the techniques of the present disclosure. The current block may include a current CU. Although with respect to the video decoder 300 ( Figure 1 and Fig.16 ), but it should be understood that other devices may be configured to perform the same Fig.18 The process is similar to the process.

[0273] 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 (520). 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 (522). The video decoder 300 may predict the current block (524), for example, using an intra prediction mode or an inter prediction mode as indicated by the prediction information of the current block, to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the reproduced transform coefficients (526) 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 (528). The video decoder 300 may ultimately decode the current block by combining the prediction block and the residual block to form a reconstructed block (530). The video decoder 300 may perform filtering techniques described in the present disclosure, including deblocking filtering, ALF, and other such filtering, on the reconstructed block.

[0274] Fig.19 is a flowchart illustrating an example process for decoding a current block of video data according to the techniques of the present disclosure. Although with respect to the video decoder 300 ( Figure 1 and Fig.16 ), but it should be understood that other devices may be configured to perform the same Fig.19 For example, the video decoding loop of video encoder 200 (including filter unit 216) may perform some of the techniques of FIG. 20 .

[0275] exist Fig.19 In the example of , video decoder 300 applies a first filter to a block of video data to determine a first filtered block (540). The first filter may be, for example, a deblocking filter that removes blocking artifacts from boundaries of blocks.

[0276] Video decoder 300 applies a second filter to the block of video data in parallel with the first filter to determine a second filtered block (542). The second filter may be, for example, a fixed, unsignaled filter, a signaled filter, or an implicitly determined filter determined without explicit signaling. The second filter may be, for example, an ALF, a bilateral filter, a guided filter, or some other such filter.

[0277] The video decoder 300 combines the first filter block and the second filter block to determine a combined block (544). To combine the first filter block and the second filter block to determine the combined block, the video decoder 300 may determine the combined block, for example, based on a weighted sum (e.g., a weighted average) of samples of the first filter block and samples of the second filter block. The video decoder 300 may receive, for example, in a bitstream including video data, a weighted value for determining a weighted sum of samples of the first filter block and samples of the second filter block. In some examples, the weighted value may be fixed or otherwise determined without explicit signaling.

[0278] Video decoder 300 applies a third filter to the combined block to determine a third filtered block (546). The third filter may be, for example, a sample adaptive offset filter, an ALF, or some other type of filter. The first filter, the second filter, and the third filter may be applied, for example, by filter unit 312.

[0279] Video decoder 300 processes the third filter block to determine a decoded version of the block of video data (548). In some examples, when the third filter is a SAO filter, then the processing of block 548 may include additional filtering, such as an ALF.

[0280] Video decoder 300 outputs a decoded version of the block of video data (550). Video decoder 300 may output a decoded version of the block of video data by outputting a decoded picture that includes the decoded version of the block. Video decoder 300 may, for example, store the picture in a decoded picture buffer for use in decoding subsequent pictures; store the decoded picture to a storage medium for subsequent display; or output the decoded picture to a display device for real-time or near real-time display. Fig.19 In an example of the techniques in, a video encoder may output a decoded picture, for example, by storing the picture in a decoded picture buffer for use in encoding subsequent pictures.

[0281] The following numbered clauses illustrate one or more aspects of the devices and techniques described in this disclosure.

[0282] Clause 1A: A method of coding, the method comprising: applying a deblocking filter in parallel with another filter to a block of video data; and outputting a filtered version of the block.

[0283] Clause 2A: The method of clause 1A, wherein decoding comprises decoding.

[0284] Clause 3A: The method of clause 1A, wherein decoding comprises encoding.

[0285] Clause 4A: An apparatus for decoding video data, the apparatus comprising one or more means for performing the method of any of clauses 1A to 3A.

[0286] Clause 5A: The apparatus of clause 4A, wherein the one or more components comprise one or more processors implemented in circuitry.

[0287] Clause 6A: The apparatus of any of clauses 4A and 5A, further comprising: a memory for storing the video data. Clause 7A: The apparatus of any of clauses 4A to 6A, further comprising: a display configured to display the decoded video data.

[0288] Clause 8A: The device of any of clauses 4A to 7A, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0289] Clause 9A: The apparatus of any of clauses 4A to 8A, wherein the apparatus comprises a video decoder.

[0290] Clause 10A: The apparatus of any of clauses 4A to 9A, wherein the apparatus comprises a video encoder.

[0291] Clause 11A: A computer-readable storage medium having stored thereon instructions which, when executed, cause one or more processors to perform the method of any of clauses 1A to 3A.

[0292] Clause 12A: An apparatus for encoding video data, the apparatus comprising: means for applying a deblocking filter in parallel with another filter to a block of video data; and means for outputting a filtered version of the block.

[0293] Item 1B: A method for decoding video data, the method comprising: applying a deblocking filter to a block of video data to determine a first filter block; applying a second filter to the block of video data in parallel with the deblocking filter to determine a second filter block, wherein the second filter comprises one of a guided filter, a bilateral filter, or an adaptive loop filter; combining the first filter block and the second filter block to determine a combined block; applying a third filter to the combined block to determine a third filter block; processing the third filter block to determine a decoded version of the block of video data; and outputting the decoded version of the block of video data.

[0294] Clause 2B: The method of clause 1B, wherein combining the first filter block and the second filter block to determine the combined block comprises determining the combined block based on a weighted sum of samples of the first filter block and samples of the second filter block.

[0295] Clause 3B: The method of clause 2B, further comprising: receiving, in a bitstream comprising the video data, a weight value for determining the weighted sum of the samples of the first filter block and the samples of the second filter block.

[0296] Clause 4B: The method of clause 1B, wherein the third filter comprises a sample adaptive offset filter.

[0297] Clause 5B: The method of clause 1B, wherein processing the third filter block to determine the decoded version of the block of video data comprises applying a second adaptive loop filter to the third filter block.

[0298] Clause 6B: The method of clause 1B, wherein the second filter comprises a fixed, unsignaled filter.

[0299] Clause 7B: The method of clause 1B, wherein the second filter comprises a signaled filter.

[0300] Clause 8B: A method according to clause 1B, wherein: the third filter includes a sample adaptive offset (SAO) filter and the third filter block includes a SAO filter block, and processing the third filter block to determine the decoded version of the video data block includes applying a second adaptive loop filter to the SAO filter block.

[0301] Clause 9B: The method of clause 1B, wherein outputting the decoded version of the block of video data comprises one or more of: outputting the decoded version of the block of video data for display or storing the decoded version of the block of video data.

[0302] Clause 10B: A method according to clause 1B, wherein the method of decoding the video data is performed as part of a video encoding process, and wherein outputting the decoded version of the block of video data includes storing the decoded version of the block of video data for use in encoding other blocks of the video data.

[0303] Item 11B: A device for decoding video data, the device comprising: a memory system, the memory system configured to store video data; and a processing system, the processing system coupled to the memory system, implemented in circuits and configured to: apply a deblocking filter to a block of video data to determine a first filter block; apply a second filter to the block of video data in parallel with the deblocking filter to determine a second filter block, wherein the second filter comprises one of a guided filter, a bilateral filter, or an adaptive loop filter; combine the first filter block and the second filter block to determine a combined block; apply a third filter to the combined block to determine a third filter block; process the third filter block to determine a decoded version of the block of video data; and output the decoded version of the block of video data.

[0304] Clause 12B: An apparatus according to clause 11B, wherein to combine the first filter block and the second filter block to determine the combined block, the processing system is further configured to determine the combined block based on a weighted sum of samples of the first filter block and samples of the second filter block.

[0305] Clause 13B: The apparatus of clause 12B, wherein the processing system is further configured to: receive in a bitstream comprising the video data a weight value for determining the weighted sum of the samples of the first filter block and the samples of the second filter block.

[0306] Clause 14B: The apparatus of clause 11B, wherein the third filter comprises a sample adaptive offset filter.

[0307] Clause 15B: The apparatus of clause 11B, wherein to process the third filter block to determine the decoded version of the block of video data, the processing system is further configured to apply a second adaptive loop filter to the third filter block.

[0308] Clause 16B: The apparatus of clause 11B, wherein the second filter comprises a fixed, unsignaled filter.

[0309] Clause 17B: The apparatus of clause 11B, wherein the second filter comprises a signaled filter.

[0310] Clause 18B: An apparatus according to clause 11B, wherein: the third filter includes a sample adaptive offset (SAO) filter and the third filter block includes a SAO filter block, and in order to process the third filter block to determine the decoded version of the video data block, the processing system is further configured to apply a second adaptive loop filter to the SAO filter block.

[0311] Clause 19B: The apparatus of clause 11B, wherein the apparatus comprises a wireless communication device further comprising a receiver configured to receive a bitstream comprising an encoded version of the block of video data.

[0312] Clause 20B: The device of clause 19B, wherein the wireless communication device comprises a handset, and wherein the receiver is configured to demodulate a signal comprising the bit stream in accordance with a wireless communication standard.

[0313] Clause 21B: The apparatus of clause 11B, further comprising: a display, wherein to output the decoded version of the block of video data, the processing system is further configured to cause the display to display a picture including the decoded version of the block of video data.

[0314] Clause 22B: The device of clause 11B, wherein the device comprises one or more of a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0315] Clause 23B: The apparatus of clause 11B, further comprising: a camera configured to capture the video data, wherein the processing system is further configured to decode the video data block as part of a video encoding process used to encode the video data.

[0316] Item 24B: A computer-readable storage medium storing instructions that, when executed by one or more processors, cause the one or more processors to: apply a deblocking filter to a block of video data to determine a first filter block; apply a second filter to the block of video data in parallel with the deblocking filter to determine a second filter block, wherein the second filter comprises one of a guided filter, a bilateral filter, or an adaptive loop filter; combine the first filter block and the second filter block to determine a combined block; apply a third filter to the combined block to determine a third filter block; process the third filter block to determine a decoded version of the block of video data; and output the decoded version of the block of video data.

[0317] Clause 25B: A computer-readable storage medium according to clause 24B, wherein in order to combine the first filter block and the second filter block to determine the combined block, the instructions cause the one or more processors to determine the combined block based on a weighted sum of samples of the first filter block and samples of the second filter block.

[0318] Clause 26B: A computer-readable storage medium according to clause 25B, storing further instructions that, when executed, cause the one or more processors to: receive in a bitstream including the video data a weighted value for determining the weighted sum of the samples of the first filter block and the samples of the second filter block.

[0319] Clause 27B: The computer-readable storage medium of clause 24B, wherein the third filter comprises a sample adaptive offset filter.

[0320] Clause 28B: The computer-readable storage medium of clause 24B, wherein to process the third filter block to determine the decoded version of the block of video data, the instructions cause the one or more processors to apply a second adaptive loop filter to the third filter block.

[0321] Clause 29B: The computer-readable storage medium of clause 24B, wherein the second filter comprises a fixed, unsignaled filter.

[0322] Clause 30B: A computer-readable storage medium as described in clause 24B, wherein: the third filter comprises a sample adaptive offset (SAO) filter and the third filter block comprises a SAO filter block, and in order to process the third filter block to determine the decoded version of the video data block, the instructions cause the one or more processors to apply a second adaptive loop filter to the SAO filter block.

[0323] 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). In addition, in some examples, actions or events may be performed concurrently (e.g., by multithreading, interrupt handling, or multiple processors) rather than sequentially.

[0324] In one or more examples, the described functions can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the function 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 way, a computer-readable medium can generally correspond to (1) a non-transient 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 the present disclosure. A computer program product may include a computer-readable medium.

[0325] By way of example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store the desired program code in the form of instructions or data structures and can be accessed by a computer. In addition, any connection is appropriately referred to as a computer-readable medium. For example, if the instruction is sent from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technology (such as infrared, radio and microwave), the coaxial cable, fiber optic cable, twisted pair, DSL or wireless technology (such as infrared, radio and microwave) is included in the definition of the medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other transient media, but instead relate to non-transient tangible storage media. As used herein, disks and optical disks include compact disks (CDs), laser optical disks, optical optical disks, digital versatile disks (DVDs), floppy disks and blue-ray disks, wherein disks usually reproduce data magnetically, while optical disks reproduce data optically using lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0326] 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. Therefore, the terms "processor" and "processing circuit" as used herein may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a combined codec. In addition, these techniques may be fully implemented in one or more circuits or logic elements.

[0327] The techniques of the present disclosure may be implemented in a variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC), or a set of ICs (e.g., a chipset). Various components, modules, or units are described in the present 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 may be combined in a codec hardware unit, or the various units may 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.

[0328] 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: applying a deblocking filter to the block of video data to determine a first filtered block; applying a second filter to the block of video data in parallel with the deblocking filter to determine a second filtered block, wherein the second filter comprises one of a guided filter, a bilateral filter, or an adaptive loop filter; combining the first filter block and the second filter block to determine a combined block; applying a third filter to the combined block to determine a third filtered block; processing the third filter block to determine a decoded version of the block of video data; as well as The decoded version of the block of video data is output. 2 . The method of claim 1 , wherein combining the first filter block and the second filter block to determine the combined block comprises determining the combined block based on a weighted sum of samples of the first filter block and samples of the second filter block.

3. The method according to claim 2, further comprising: A weight value for determining the weighted sum of the samples of the first filter block and the samples of the second filter block is received in a bitstream including the video data. The method of claim 1 , wherein the third filter comprises a sample adaptive offset filter. 5 . The method of claim 1 , wherein processing the third filter block to determine the decoded version of the block of video data comprises applying a second adaptive loop filter to the third filter block. The method of claim 1 , wherein the second filter comprises a fixed, unsignaled filter. The method of claim 1 , wherein the second filter comprises a signaled filter.

8. The method according to claim 1, wherein: The third filter comprises a sample adaptive offset (SAO) filter and the third filter block comprises a SAO filter block, Processing the third filter block to determine the decoded version of the block of video data includes applying a second adaptive loop filter to the SAO filter block.

9. The method of claim 1, wherein outputting the decoded version of the block of video data comprises one or more of: outputting the decoded version of the block of video data for display or storing the decoded version of the block of video data.

10. The method of claim 1, wherein the method of decoding the video data is performed as part of a video encoding process, and wherein outputting the decoded version of the block of video data comprises storing the decoded version of the block of video data for use in encoding other blocks of the video data.

11. A device for decoding video data, the device comprising: a memory system configured to store video data; and a processing system coupled to the memory system, implemented in circuitry and configured to: applying a deblocking filter to the block of video data to determine a first filtered block; applying a second filter to the block of video data in parallel with the deblocking filter to determine a second filtered block, wherein the second filter comprises one of a guided filter, a bilateral filter, or an adaptive loop filter; combining the first filter block and the second filter block to determine a combined block; applying a third filter to the combined block to determine a third filtered block; processing the third filter block to determine a decoded version of the block of video data; as well as The decoded version of the block of video data is output.

12. The apparatus of claim 11, wherein in order to combine the first filter block and the second filter block to determine the combined block, the processing system is further configured to determine the combined block based on a weighted sum of samples of the first filter block and samples of the second filter block.

13. The apparatus of claim 12, wherein the processing system is further configured to: A weight value for determining the weighted sum of the samples of the first filter block and the samples of the second filter block is received in a bitstream including the video data.

14. The apparatus of claim 11, wherein the third filter comprises a sample adaptive offset filter.

15. The apparatus of claim 11, wherein to process the third filter block to determine the decoded version of the block of video data, the processing system is further configured to apply a second adaptive loop filter to the third filter block.

16. The apparatus of claim 11, wherein the second filter comprises a fixed, unsignaled filter.

17. The apparatus of claim 11, wherein the second filter comprises a signaled filter.

18. The apparatus of claim 11, wherein: The third filter comprises a sample adaptive offset (SAO) filter and the third filter block comprises a SAO filter block, and To process the third filter block to determine the decoded version of the block of video data, the processing system is further configured to apply a second adaptive loop filter to the SAO filter block.

19. The apparatus of claim 11, wherein the apparatus comprises a wireless communication device, the wireless communication device further comprising a receiver configured to receive a bitstream comprising an encoded version of the block of video data.

20. The device of claim 19, wherein the wireless communication device comprises a handset, and wherein the receiver is configured to demodulate a signal comprising the bit stream in accordance with a wireless communication standard.

21. The device according to claim 11, further comprising: A display, wherein to output the decoded version of the block of video data, the processing system is further configured to cause the display to display a picture including the decoded version of the block of video data.

22. The device of claim 11, wherein the device comprises one or more of a computer, a mobile device, a broadcast receiver device, or a set-top box.

23. The device according to claim 11, further comprising: A camera is configured to capture the video data, wherein the processing system is further configured to decode the blocks of video data as part of a video encoding process used to encode the video data.

24. A computer-readable storage medium storing instructions that, when executed by one or more processors, cause the one or more processors to: applying a deblocking filter to the block of video data to determine a first filtered block; applying a second filter to the block of video data in parallel with the deblocking filter to determine a second filtered block, wherein the second filter comprises one of a guided filter, a bilateral filter, or an adaptive loop filter; combining the first filter block and the second filter block to determine a combined block; applying a third filter to the combined block to determine a third filtered block; processing the third filter block to determine a decoded version of the block of video data; as well as The decoded version of the block of video data is output.

25. A computer-readable storage medium according to claim 24, wherein in order to combine the first filter block and the second filter block to determine the combined block, the instructions cause the one or more processors to determine the combined block based on a weighted sum of samples of the first filter block and samples of the second filter block.

26. The computer-readable storage medium of claim 25, the computer-readable storage medium storing further instructions that when executed cause the one or more processors to: A weight value for determining the weighted sum of the samples of the first filter block and the samples of the second filter block is received in a bitstream including the video data.

27. The computer-readable storage medium of claim 24, wherein the third filter comprises a sample adaptive offset filter.

28. The computer-readable storage medium of claim 24, wherein to process the third filter block to determine the decoded version of the block of video data, the instructions cause the one or more processors to apply a second adaptive loop filter to the third filter block.

29. The computer-readable storage medium of claim 24, wherein the second filter comprises a fixed, unsignaled filter.

30. The computer-readable storage medium of claim 24, wherein: The third filter comprises a sample adaptive offset (SAO) filter and the third filter block comprises a SAO filter block, and To process the third filter block to determine the decoded version of the block of video data, the instructions cause the one or more processors to apply a second adaptive loop filter to the SAO filter block.

Images