Bit shifting of cross-component adaptive loop filtering for video coding

Abstract

An example method includes decoding a plurality of filter coefficients of a cross-component adaptive loop filter, wherein decoding a particular filter coefficient of the plurality of filter coefficients includes: decoding from an encoded video bitstream a syntax element that specifies an exponent value representing a base-2 logarithm of an absolute value (as a power of two) of the particular filter coefficient; and determining a value of the particular filter coefficient based on the exponent value; reconstructing samples of a block of video data; and cross-component adaptive loop filtering the block of video data based on the plurality of filter coefficients.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 17 / 028,209, filed on September 22, 2020, which claims the benefit of U.S. Provisional Application No. 62 / 904,508, filed on September 23, 2019, the entire contents of each of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to video coding, including video encoding and video decoding. Background Art

[0004] Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video game devices, video game consoles, cellular or satellite radio telephones, so-called "smart phones", video teleconferencing devices, video streaming devices, etc. Digital video devices implement video codec technologies, 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 Codec (AVC); ITU-T H.265 / High Efficiency Video Codec (HEVC), and extensions of such standards. By implementing such video codec technologies, video devices can more efficiently send, receive, encode, decode and / or store digital video information.

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

[0006] In general, the present disclosure describes techniques related to cross-component adaptive loop filtering (CC-ALF) of video data. To perform ALF, a video codec may filter corresponding luma and chroma blocks separately using different sets of coefficients (e.g., filtering a luma block using a luma set of coefficients and filtering a chroma block using one or more sets of chroma coefficients). However, in the codec loop, a luma block may include details that may be lost in a corresponding chroma block. As such, a video codec may perform CC-ALF in which information from a luma block is used to enhance a corresponding chroma block.

[0007] For example, a video codec may filter a luma block using a first set of chroma filter coefficients to generate an intermediate block for a first chroma component (e.g., Cb), and filter the luma block using a second set of chroma filter coefficients to generate an intermediate block for a second chroma component (e.g., Cr). The video encoder may signal the values ​​of the filter coefficients for CC-ALF (e.g., at least the first set and the second set of chroma filter coefficients used to filter the luma block) to a video decoder as one or more syntax elements in the encoded video bitstream. The video codec may then add the respective intermediate blocks to the ALF-filtered chroma blocks of the chroma components.

[0008] To filter the luma block to generate intermediate blocks for the chroma components, the video codec may perform multiple multiplication operations on each sample of the luma block. For example, the video codec may compute the filtered value for a particular sample of the luma block as the sum of the chroma filter coefficients multiplied by the samples of the luma block. Thus, performing CC-ALF may involve a large number of multiplication operations (e.g., seven for an 8×8 luma block). Performing such a large number of multiplication operations may be a resource-intensive endeavor for the video codec, which may undesirably increase encoding and decoding time and / or power consumption.

[0009] According to one or more techniques of the present disclosure, a video codec may encode and decode filter coefficients for CC-ALF (e.g., a video encoder may encode and a video decoder may decode) such that the absolute value of the filter coefficients is limited to zero or a power of two. When filtering a luminance block using the filter coefficients to generate an intermediate chrominance block, the video codec may utilize a bit shift operation (e.g., a left shift and a right shift operation) instead of a multiplication operation. Because the absolute value of the filter coefficients is limited to zero or a power of two, it may be mathematically equivalent to utilize a bit shift operation instead of a multiplication operation (i.e., produce the same intermediate chrominance block). However, although mathematically equivalent, the bit shift operation may be far less resource intensive than the multiplication operation. In addition, when implemented in dedicated hardware (e.g., an application specific integrated circuit (ASIC)), the hardware required to perform the bit shift operation may be simpler than the hardware required to perform the multiplication operation. In this way, the technology of the present disclosure reduces the resource requirements of CC-ALF.

[0010] As an example, a method includes decoding multiple filter coefficients of a cross-component adaptive loop filter, wherein decoding a specific filter coefficient among the multiple filter coefficients includes: decoding from an encoded video bitstream a syntax element that specifies an exponent value representing a base-2 logarithm of an absolute value (as a power of two) of the specific filter coefficient; and determining a value of the specific filter coefficient based on the exponent value; reconstructing samples of a block of video data; and performing cross-component adaptive loop filtering on the block of video data based on the multiple filter coefficients.

[0011] As another example, a method includes encoding values ​​of multiple filter coefficients for a cross-component adaptive loop filter, wherein encoding the value of a particular filter coefficient of the multiple filter coefficients includes: encoding in an encoded video bitstream a syntax element that specifies an exponent value representing a base-2 logarithm of an absolute value (as a power of two) of the particular filter coefficient; reconstructing samples of a block of video data; and cross-component adaptive loop filtering the block of video data based on the values ​​of the multiple filter coefficients.

[0012] As another example, a device includes a memory configured to store at least a portion of an encoded video bitstream; and one or more processors implemented in a circuit and configured to: decode multiple filter coefficients of a cross-component adaptive loop filter, wherein, to decode a specific filter coefficient among the multiple filter coefficients, the one or more processors are configured to: decode from the encoded video bitstream a syntax element that specifies an exponent value representing a base-2 logarithm of an absolute value (as a power of two) of the specific filter coefficient; and determine a value of the specific filter coefficient based on the exponent value; reconstruct samples of a block of video data; and perform cross-component adaptive loop filtering on the block of video data based on the multiple filter coefficients.

[0013] As another example, a device includes a memory configured to store at least a portion of an encoded video bitstream; and one or more processors implemented in a circuit and configured to: encode values ​​of multiple filter coefficients of a cross-component adaptive loop filter, wherein, to encode the value of a particular filter coefficient of the multiple filter coefficients, the one or more processors are configured to: encode in the encoded video bitstream a syntax element that specifies an exponent value representing a base-2 logarithm of an absolute value (as a power of two) of the particular filter coefficient; reconstruct samples of a block of video data; and perform cross-component adaptive loop filtering on the block of video data based on the values ​​of the multiple filter coefficients.

[0014] The details of one or more examples are set forth in the accompanying drawings and the description below.Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0016] Figure 2A and 2B is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure and a corresponding codec tree unit (CTU).

[0017] Figure 3 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0018] Figure 4 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0019] Figure 5 is a block diagram illustrating an example filter unit, in accordance with one or more techniques of this disclosure.

[0020] Figure 6 is a flowchart illustrating an example method for encoding a current block according to the techniques of this disclosure.

[0021] Figure 7 is a flow chart illustrating an example method for decoding a current block according to the techniques of this disclosure.

[0022] Figure 8 is a flow chart illustrating an example method for cross-component adaptive loop filtering (CC-ALF) on a current block, in accordance with one or more techniques of this disclosure. DETAILED DESCRIPTION

[0023] Figure 1 1 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 encoding and decoding (encoding and / or decoding) video data. Generally, video data includes any data used to process video. Thus, the data may include original unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling notification data.

[0024] like Figure 1 As shown, in this example, system 100 includes a source device 102 that provides encoded video data for decoding and display by a destination device 116. Specifically, source device 102 provides video data to destination device 116 via computer-readable medium 110. Source device 102 and destination device 116 may include any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such as smart phones, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, etc. In some cases, source device 102 and destination device 116 may be equipped for wireless communication, and thus may be referred to as wireless communication devices.

[0025] exist Figure 1In the example of , source device 102 includes video source 104, memory 106, video encoder 200, and output interface 108. Destination device 116 includes input interface 122, video decoder 300, memory 120 and display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply a technique for performing cross-component adaptive loop filtering. Therefore, source device 102 represents an example of a video encoding device, and destination device 116 represents an example of a video decoding device. In other examples, source device and destination device may include other components or arrangements. For example, source device 102 may receive video data from an external video source such as an external camera. Similarly, destination device 116 may interface with an external display device instead of including an integrated display device.

[0026] like Figure 1 The system 100 shown is only an example. In general, any digital video encoding and / or decoding device can perform the technology for cross-component adaptive loop filtering. The source device 102 and the destination device 116 are only examples of such codec devices, wherein the source device 102 generates coded video data for transmission to the destination device 116. The present disclosure refers to a "codec" device as a device that performs the coding (coding and / or decoding) of data. Therefore, the video encoder 200 and the video decoder 300 represent examples of codec devices, specifically, examples of video encoders and video decoders, respectively. In some examples, the source device 102 and the destination device 116 can operate in a substantially symmetrical manner, so that each of the source device 102 and the destination 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 destination device 116, for example, for video streaming, video playback, video broadcasting or video telephony.

[0027] Typically, video source 104 represents the source of video data (i.e., original, unencoded video data) and provides a continuous series of pictures (also referred to as "frames") of video data to video encoder 200, which encodes the data for these pictures. Video source 104 of source device 102 may include a video capture device such as a video camera, a video archive containing previously captured original video, and / or a video feed interface for receiving video from a video content provider. As a further alternative, video source 104 may generate computer graphics-based data as source video, or a combination of live video, archived video, and computer-generated video. In each case, video encoder 200 encodes captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange pictures from a received order (sometimes referred to as "display order") into a codec order for encoding and decoding. Video encoder 200 may generate a bitstream comprising encoded video data. Source device 102 may then output the encoded video data onto computer-readable medium 110 via output interface 108 for receipt and / or retrieval by, for example, input interface 122 of destination device 116 .

[0028] The memory 106 of the source device 102 and the memory 120 of the destination device 116 represent general purpose memory. In some examples, the memories 106, 120 can store original video data, for example, original video from the video source 104 and original, decoded video data from the video decoder 300. Additionally or alternatively, the memories 106, 120 can store software instructions that can be executed by, for example, the video encoder 200 and the video decoder 300, respectively. Although 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 can also include internal memory for functionally similar or equivalent purposes. In addition, the memories 106, 120 can store, for example, encoded video data output from the video encoder 200 and input to the video decoder 300. In some examples, portions of the memories 106, 120 can be allocated as one or more video buffers, for example to store original, decoded and / or encoded video data.

[0029] The computer-readable medium 110 may represent any type of medium or device capable of transmitting encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium that enables the source device 102 to directly send the encoded video data to the destination device 116 in real time, for example, via a radio frequency network or a computer-based network. According to a communication standard such as a wireless communication protocol, the output interface 108 can modulate a transmission signal including the encoded video data, and the input interface 122 can 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 part of a packet-based network such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include a router, a switch, a base station, or any other equipment that may be useful to facilitate communication from the source device 102 to the destination device 116.

[0030] In some examples, source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access the encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0031] In some examples, the source device 102 may output the encoded video data to the file server 114 or another intermediate storage device that may store the encoded video generated by the source device 102. The destination device 116 may access the stored video data from the file server 114 via streaming or downloading. The file server 114 may be any type of server device capable of storing the encoded video data and sending the encoded video data to the destination device 116. The file server 114 may represent a web server (e.g., for a website), a file transfer protocol (FTP) server, a content delivery network device, or a network attached storage (NAS) device. The destination device 116 may access the encoded video data from the file server 114 via any standard data connection including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., 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 file server 114 and the input interface 122 may be configured to operate according to a streaming transmission protocol, a download transmission protocol, or a combination thereof.

[0032] 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 certain 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 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 attributed to video encoder 200 and / or output interface 108, while destination device 116 may include a SoC device for performing functionality attributed to video decoder 300 and / or input interface 122.

[0033] The techniques of the present disclosure may be applied to support video encoding and decoding for 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.

[0034] The input interface 122 of the destination device 116 receives an encoded video bitstream from the computer-readable medium 110 (e.g., the storage device 112, the 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 coded 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 cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0035] although Figure 12. Although not shown in the figure, in some examples, the video encoder 200 and the video decoder 300 may each 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 process multiplexed streams including both audio and video in a common data stream. If applicable, the MUX-DEMUX unit may conform to the ITU H.223 multiplexer protocol or other protocols, such as the User Datagram Protocol (UDP).

[0036] The video encoder 200 and the video decoder 300 can each be implemented as any of a variety of suitable encoder and / or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When the technology is partially implemented in software, the device can store instructions for the software in a suitable non-transitory computer-readable medium, and use one or more processors to execute these instructions in hardware to perform the technology of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, any of which can be integrated as part of a combined encoder / decoder (CODEC) in a corresponding device. The device including the video encoder 200 and / or the video decoder 300 can include an integrated circuit, a microprocessor, and / or a wireless communication device, such as a cellular phone.

[0037] The video encoder 200 and the video decoder 300 may operate according to a video codec standard, such as ITU-T H.265, also known as High Efficiency Video Codec (HEVC), or extensions thereof, such as multi-view and / or scalable video codec extensions. Alternatively, the video encoder 200 and the video decoder 300 may operate according to other private or industry standards, such as the Joint Exploration Test Model (JEM) or ITU-T H.266, also known as Versatile Video Codec (VVC). A recent draft of the VVC standard is described in Bross et al., "Versatile Video Coding (Draft 6)" - the 15th meeting of the Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11: JVET-O2001-vE, Gothenburg, Sweden, July 3-12, 2019 (hereinafter referred to as "VVC Draft 6"). However, the techniques of this disclosure are not limited to any particular codec standard.

[0038] Typically, the video encoder 200 and the video decoder 300 can perform block-based encoding and decoding of pictures. The term "block" generally refers to a structure that includes data to be processed (e.g., encoded, decoded, or otherwise used in the encoding and / or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. Generally speaking, the video encoder 200 and the video decoder 300 can encode and decode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, the video encoder 200 and the video decoder 300 can encode and decode luminance and chrominance components instead of encoding and decoding red, green, and blue (RGB) data for samples of a picture, where the chrominance components may include both red-toned and blue-toned chrominance components. In some examples, the video encoder 200 converts the received RGB formatted data into a YUV representation before encoding, and the video decoder 300 converts the YUV representation into an RGB format. Alternatively, a pre-processing unit and a post-processing unit (not shown) can perform these conversions.

[0039] The present disclosure may generally refer to the encoding and decoding of a picture (e.g., encoding and decoding), which is intended to include the process of encoding or decoding data for a picture. Similarly, the present disclosure may refer to the encoding and decoding of a block of a picture as including the process of encoding or decoding data for the block, for example, prediction and / or residual encoding and decoding. The encoded video bitstream typically includes a series of values ​​for syntax elements that represent encoding and decoding decisions (e.g., codec modes) and the partitioning of the picture into blocks. Therefore, references to encoding and decoding a picture or a block should generally be understood as encoding and decoding the values ​​of the syntax elements that form the picture or block.

[0040] HEVC defines various blocks, including codec units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video codec (such as video encoder 200) partitions a codec tree unit (CTU) into CUs according to a quadtree structure. That is, the video codec partitions the CTU and CU into four equal non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without a child node may be referred to as a "leaf node", and a CU of such a leaf node may include one or more PUs and / or one or more TUs. The video codec may further partition the PU and TU. For example, in HEVC, a residual quadtree (RQT) represents the partitioning of a TU. In HEVC, a PU represents inter-frame prediction data, and a TU represents residual data. An intra-predicted CU includes intra-frame prediction information, such as an intra-frame mode indication.

[0041] As another example, the video encoder 200 and the video decoder 300 may be configured to operate according to JEM or VVC. According to JEM or VVC, a video codec (such as the video encoder 200) partitions a picture into a plurality of codec tree units (CTUs). The video encoder may partition the CTU according to a tree structure such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure. The QTBT structure removes the concept of multiple partition types, such as the distinction between CU, PU, ​​and TU of HEVC. The QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to the codec units (CUs).

[0042] In the MTT partitioning structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more types of ternary tree (TT) partitioning. A ternary tree partitioning is a partitioning in which a block is partitioned into three sub-blocks. In some examples, the ternary tree partitioning divides the block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0043] In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT structure or MTT structure to represent each of the luma component and the chroma component, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT structures 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 corresponding chroma components).

[0044] The video encoder 200 and the video decoder 300 may be configured to use quadtree segmentation, QTBT segmentation, MTT segmentation, or other segmentation structures in accordance with HEVC. For purposes of explanation, the description of the technology of the present disclosure is presented with respect to QTBT segmentation. However, it should be understood that the technology of the present disclosure may also be applied to a video codec configured to use quadtree segmentation or other types of segmentation.

[0045] Blocks (e.g., CTUs or CUs) can be grouped in various ways in a picture. 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.

[0046] In some examples, a tile may be partitioned into multiple blocks, where each block may include one or more CTU rows within the tile. A tile that is not partitioned into multiple blocks may also be referred to as a tile. However, a block that is a true subset of a tile may not be referred to as a tile.

[0047] The blocks in a picture may also be arranged in slices. A slice may be an integer number of blocks of a picture that may be contained exclusively in a single network abstraction layer (NAL) unit. In some examples, a slice includes a continuous sequence of multiple complete blocks or just complete blocks of one tile.

[0048] This disclosure may use "N×N" and "N by N" interchangeably to refer to the sample dimensions of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, 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.

[0049] The video encoder 200 encodes video data representing prediction and / or residual information and other information for a CU. The prediction information indicates how the CU will be predicted in order to form a prediction block for the CU. The residual information generally represents the sample-by-sample difference between the samples of the CU before encoding and the prediction block.

[0050] In order to predict a CU, the video encoder 200 can generally form a prediction block for the CU by inter-frame prediction or intra-frame prediction. Inter-frame prediction generally refers to predicting a CU based on data of a previously coded picture, while intra-frame prediction generally refers to predicting a CU based on previously coded data of the same picture. In order to perform inter-frame prediction, the video encoder 200 can use one or more motion vectors to generate a prediction block. The video encoder 200 can 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 can use the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean square difference (MSD), or other such difference calculations to calculate a difference metric to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 can use unidirectional prediction or bidirectional prediction to predict the current CU.

[0051] Some examples of JEM and 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: enlargement or reduction, rotation, perspective motion, or other irregular motion types.

[0052] To perform intra prediction, the video encoder 200 may select an intra prediction mode to generate a prediction block. Certain examples of JEM and VVC provide sixty-seven intra prediction modes, including various directional modes, as well as a plane mode and a DC mode. Typically, the video encoder 200 selects neighboring samples describing a current block (e.g., a block of a CU) to predict an intra prediction mode of the samples of the current block based thereon. Assuming that the video encoder 200 encodes and decodes CTUs and CUs in a raster scan order (from left to right, from top to bottom), such samples may typically be located above, to the upper left, or to the left of the current block in the same picture as the current block.

[0053] The video encoder 200 encodes data representing the prediction mode for the current block. For example, for inter-frame prediction mode, the video encoder 200 may encode data representing which of various available inter-frame prediction modes to use, and motion information for the corresponding mode. For example, for unidirectional or bidirectional inter-frame prediction, the video encoder 200 may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. For affine motion compensation mode, the video encoder 200 may use a similar mode to encode motion vectors.

[0054] After prediction of a block, such as intra prediction or inter prediction of a block, the video encoder 200 may calculate residual data for the block. Residual data, such as a residual block, represents the sample-by-sample difference between the block and a prediction block for the block formed using a corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to generate transformed data in a transform domain rather than a sample domain. For example, the video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. Additionally, the video encoder 200 may apply a secondary transform after the primary 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.

[0055] As described above, after any transform used to produce transform coefficients, the video encoder 200 can perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to potentially reduce the amount of data used to represent the coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 can reduce the bit depth associated with some or all of the coefficients. For example, the video encoder 200 can 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 can perform a bit-by-bit right shift of the value to be quantized.

[0056] After quantization, the video encoder 200 can scan the transform coefficients to produce a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scan can be designed to place higher energy (and therefore lower frequency) coefficients in front of the vector and lower energy (and therefore higher frequency) transform coefficients in the back of the vector. In some examples, the video encoder 200 can scan the quantized transform coefficients using a predefined scan order to produce a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, the video encoder 200 can perform adaptive scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, the video encoder 200 can entropy encode the one-dimensional vector, for example, according to context adaptive binary arithmetic coding (CABAC). The video encoder 200 can also entropy encode values ​​for syntax elements that describe metadata associated with the encoded video data for use by the video decoder 300 when decoding the video data.

[0057] To perform CABAC, the video encoder 200 may assign context within a context model to a symbol to be sent. The context may relate to, for example, whether neighboring values ​​of the symbol are zero values. The probability determination may be based on the context assigned to the symbol.

[0058] The video encoder 200 may further generate, for example, in a picture header, a block header, a slice header, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data or other syntax data such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS) to the video decoder 300. The video decoder 300 may also decode such syntax data to determine how to decode the corresponding video data.

[0059] In this way, the video encoder 200 can generate a bitstream that includes encoded video data, such as syntax elements describing the partitioning of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Finally, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0060] 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 decode values ​​for syntax elements in the bitstream using CABAC in a manner that is reversed but substantially similar to the CABAC encoding process of the video encoder 200. The syntax elements may define partitioning information of a picture into CTUs, and partitioning of each CTU according to a corresponding partitioning structure such as a QTBT structure to define CUs of the CTU. The syntax elements may further define prediction and residual information for a block (e.g., CU) of video data.

[0061] 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 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.

[0062] As discussed above and in accordance with one or more techniques of this disclosure, the video encoder 200 and / or the video decoder 300 may be configured to signal filter coefficients for CC-ALF whose absolute values ​​are restricted to zero or powers of two. In this way, the video encoder 200 and / or the video decoder 300 may replace multiplication operations in the execution of CC-ALF with less resource-intensive bit shift operations.

[0063] The present disclosure may generally involve "signaling" certain information, such as syntax elements. The term "signaling" may generally involve the communication of values ​​for syntax elements and / or other data used to decode encoded video data. That is, the video encoder 200 may signal values ​​for syntax elements in a bitstream. Typically, signaling involves generating values ​​in a bitstream. As described above, the source device 102 may transmit the bitstream to the destination device 116 substantially in real time or in non-real time, such as may occur when storing syntax elements to the storage device 112 for later retrieval by the destination device 116.

[0064] Figure 2A and 2B 1 is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure 130, and a corresponding codec tree unit (CTU) 132. Solid lines represent quadtree splits, while dashed lines indicate binary tree splits. In each split (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which split type (i.e., horizontal or vertical) is used, where in this example, 0 indicates horizontal splitting and 1 indicates vertical splitting. For quadtree splitting, there is no need to indicate the split type because the quadtree node splits the block horizontally and vertically into 4 equally sized sub-blocks. Accordingly, the video encoder 200 can encode and the video decoder 300 can decode syntax elements (such as split information) for the region tree level (i.e., solid lines) of the QTBT structure 130 and syntax elements (such as split information) for the prediction tree level (i.e., dashed lines) of the QTBT structure 130. The video encoder 200 may encode and the video decoder 300 may decode video data such as prediction and transform data for the CU represented by the terminal leaf node of the QTBT structure 130 .

[0065] generally, Figure 2BThe CTU 132 may be associated with parameters defining the size of blocks corresponding to nodes of the first and second levels in the QTBT structure 130. These parameters may include a CTU size (in terms of samples representing the size of the CTU 132), a minimum quadtree size (MinQTSize, representing the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, representing the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, representing the maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, representing the minimum allowed binary tree leaf node size).

[0066] The root node of the QTBT structure corresponding to the CTU can have four child nodes at the first level of the QTBT structure, each of which can be segmented according to the quadtree segmentation. That is, the nodes of the first level are leaf nodes (no child nodes) or have four child nodes. The example of the QTBT structure 130 represents such nodes as a parent node and a child node including a solid line for branching. If the node of the first level is not larger than the maximum allowed binary tree root node size (MaxBTSize), it can be further segmented by the corresponding binary tree. The binary tree splitting of a node can be iterated until the node obtained by the split reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of the QTBT structure 130 represents such nodes as having a dotted line for branching. The binary tree leaf node is called a coding unit (CU), which is used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further segmentation. As described above, a CU may also be referred to as a "video block" or "block".

[0067] In one example of a QTBT partitioning structure, the CTU size is set to 128×128 (luminance sample and two corresponding 64×64 chrominance samples), MinQTSize is set to 16×16, MaxBTSize is set to 64×64, MinBTSize (for both width and height) is set to 4, and MaxBTDepth is set to 4. Quadtree partitioning is first applied to the CTU to generate a quadtree leaf node. The quadtree leaf node can have a size from 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If the leaf quadtree node is 128×128, it will not be further split by the binary tree because the size exceeds MaxBTSize (i.e., in this example, 64×64). Otherwise, the leaf quadtree node will be further split by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and has a binary tree depth of 0. When the binary tree depth reaches MaxBTDepth (4 in this example), no further splitting is allowed. When a binary tree node has a width equal to MinBTSize (4 in this example), this means that no further horizontal splitting is allowed. Similarly, a binary tree node with a height equal to MinBTSize means that no further vertical splitting is allowed for the binary tree node. As described above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further segmentation.

[0068] Figure 3 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 3 The present disclosure describes the video encoder 200 in the context of video codec standards such as the HEVC video codec standard and the developing H.266 video codec standard. However, the techniques of the present invention are not limited to these video codec standards and can be generally applied to video encoding and decoding.

[0069] exist Figure 3In 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 one or more processors or processing circuits. In addition, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

[0070] The video data memory 230 may store video data to be encoded by the components of the video encoder 200. The video encoder 200 may receive video data from, for example, the video source 104 ( Figure 1 ) receives video data stored in video data memory 230. DPB 218 can act as a reference picture memory for storing reference video data used to predict subsequent video data by video encoder 200. Video data memory 230 and DPB 218 can be formed by any of various memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Video data memory 230 and DPB 218 can be provided by the same memory device or separate memory devices. In various examples, video data memory 230 can be located on-chip with other components of video encoder 200, as shown, or off-chip relative to those components.

[0071] In the present disclosure, references to the video data memory 230 should not be construed as limited to memory internal to the video encoder 200, unless specifically described as such, or memory external to the video encoder 200, unless specifically described as such. Rather, references to the video data memory 230 should be understood as reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). Figure 1 The memory 106 may also provide temporary storage for outputs from the various units of the video encoder 200 .

[0072] Figure 3Various units are illustrated to help understand the operations performed by the video encoder 200. These units can be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide specific functionality and are preset on 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 so that the programmable circuit operates 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 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 units may be integrated circuits.

[0073] The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video encoder 200 is performed using software executed by a programmable circuit, the memory 106 ( Figure 1 ) may store object code for software received and executed by the video encoder 200, or another memory (not shown) within the video encoder 200 may store such instructions.

[0074] The video data memory 230 is configured to store received video data. The video encoder 200 may retrieve a picture of 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.

[0075] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. The mode selection unit 202 may include additional functional units for performing video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, and the like.

[0076] The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and the resulting rate-distortion values ​​for such combinations. The encoding parameters may include the partitioning of CTUs into CUs, the prediction mode for a CU, the transform type for the residual data of a CU, the quantization parameter for the residual data of a CU, etc. The mode selection unit 202 may ultimately select a combination of encoding parameters that has a better rate-distortion value than other tested combinations.

[0077] The video encoder 200 may partition a picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs in a slice. The mode selection unit 202 may partition the CTUs of the picture according to a tree structure such as the QTBT structure or quadtree structure of HEVC described above. As described above, the video encoder 200 may form one or more CUs by partitioning the CTUs according to the tree structure. Such CUs may also be generally referred to as "video blocks" or "blocks".

[0078] 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 overlapping portion of the current CU, or the PU and TU in HEVC). For inter prediction of 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 coded pictures stored in the DPB 218). Specifically, the motion estimation unit 222 may calculate a value indicating how similar the potential reference block is to the current block, for example, based on the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), etc. The motion estimation unit 222 may typically perform these calculations using the sample-by-sample difference between the current block and the reference block under consideration. The motion estimation unit 222 may identify the reference block having the lowest of these calculated values, which indicates the reference block that most closely matches the current block.

[0079] The motion estimation unit 222 may form one or more motion vectors (MVs) that define the positioning of a reference block in a reference picture relative to a current block in a 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, if the motion vectors have fractional sample precision, the motion compensation unit 224 may interpolate values ​​for 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.

[0080] As another example, for intra prediction or intra prediction codec, the intra prediction unit 226 can generate a prediction block based on samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally mathematically combine the values ​​of the adjacent samples and fill these calculated values ​​in a defined direction across the current block to generate a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average of the adjacent samples for the current block and generate a prediction block so that for each sample of the prediction block, this obtained average is included.

[0081] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives the original uncoded version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, the residual generation unit 204 can also determine the difference between the sample values ​​in the residual block to generate the residual block using residual differential pulse code modulation (RDPCM). In some examples, the residual generation unit 204 can be formed using one or more subtractor circuits that perform binary subtraction.

[0082] In an example in which the mode selection unit 202 partitions the CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs of various sizes. As described above, the size of the CU may refer to the size of the luma codec block of the CU, and the size of the 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 PUs of size 2N×2N or N×N for intra-frame prediction, and symmetric PUs of size 2N×2N, 2N×N, N×2N, N×N, or similar sizes for inter-frame prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning of PUs of size 2N×nU, 2N×nD, nL×2N, and nR×2N for inter-frame prediction.

[0083] In an example where the mode selection unit 202 does not further partition the CU into PUs, each CU may be associated with a luma codec block and a corresponding chroma codec block. As described above, the size of a CU may refer to the size of the luma codec block of the CU. The video encoder 200 and the video decoder 300 may support CUs of size 2N×2N, 2N×N, or N×2N.

[0084] For other video codec techniques such as intra-block copy mode codec, affine mode codec, and linear model (LM) mode codec, as some examples, the mode selection unit 202 generates a prediction block for the current block being encoded via a corresponding unit associated with the codec technique. In some examples, such as palette mode codec, the mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating a manner for reconstructing the block based on the selected palette. In such modes, the mode selection unit 202 may provide these syntax elements to the entropy coding unit 220 for encoding.

[0085] 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.

[0086] 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 Karnen-Loev transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 may perform multiple 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.

[0087] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce information loss, and therefore, the quantized transform coefficients may have lower precision than the original transform coefficients produced by the transform processing unit 206.

[0088] 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 of the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0089] The filter unit 216 may perform one or more filter operations on the reconstructed block. For example, the filter unit 216 may perform a deblocking operation to reduce blockiness artifacts along the edges of the CU. In some examples, the operations of the filter unit 216 may be skipped. The filter unit 216 may perform the cross-component adaptive loop filtering (CC-ALF) techniques of the present disclosure alone or in any combination. For example, as described below with reference to Figure 5 As discussed, filter unit 216 may perform CC-ALF. Filter unit 216 may generate one or more coefficients for CC-ALF. For example, filter unit 216 may generate a first set of filter coefficients to be used when generating a first intermediate chroma block from a luminance block and a second set of filter coefficients to be used when generating a second intermediate chroma block from a luminance block. As discussed above and in accordance with one or more techniques of the present disclosure, filter unit 216 may limit the absolute value of the generated filter coefficients to zero or a power of two (e.g., 1, 2, 4, 8, 16, 32, 64, 128, 256, etc.). Similarly, entropy coding unit 220 may be configured to entropy encode cross-component adaptive loop filtering parameters according to the techniques of the present disclosure. For example, in contrast to encoding the actual value of the filter coefficient, entropy coding unit 220 may encode the exponential value of the filter coefficient, and the video decoder may reconstruct the actual value of the filter coefficient based on the exponential value.

[0090] The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in examples where the operation of the filter unit 216 is not required, the reconstruction unit 214 can store the reconstructed blocks to the DPB 218. In examples where the operation of the filter unit 216 is required, the filter unit 216 can store the filtered reconstructed blocks to the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 can retrieve a reference picture formed by the reconstructed (and possibly filtered) blocks from the DPB 218 to perform inter-frame prediction on blocks of subsequent encoded pictures. In addition, the intra-frame prediction unit 226 can use the reconstructed blocks of the current picture in the DPB 218 to perform intra-frame prediction on other blocks in the current picture.

[0091] 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-frame prediction or intra-frame mode information for intra-frame prediction) from the mode selection unit 202. The entropy coding unit 220 may perform one or more entropy coding operations on syntax elements as 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 in which the syntax elements are not entropy encoded.

[0092] The video encoder 200 may output a bitstream including entropy-encoded syntax elements required for reconstructing blocks of a slice or picture. Specifically, the entropy encoding unit 220 may output a bitstream.

[0093] The operations described above are described with respect to blocks. Such descriptions should be understood as operations for luma codec blocks and / or chroma codec blocks. As described above, in some examples, the luma codec block and the chroma codec block are the luma and chroma components of a CU. In some instances, the luma codec block and the chroma codec block are the luma and chroma components of a PU.

[0094] In some examples, operations performed with respect to luma codec blocks need not be repeated for chroma codec blocks. As an example, operations for identifying motion vectors (MVs) and reference pictures for luma codec blocks need not be repeated for identifying MVs and reference pictures for chroma codec blocks. Specifically, the MVs for luma codec blocks may be scaled to determine MVs for chroma blocks, while the reference pictures may be the same. As another example, the intra prediction process may be the same for luma codec blocks and chroma codec blocks.

[0095] Video encoder 200 represents an example of a device configured to encode video data and includes a memory configured to store video data and one or more processing units implemented in circuits and configured to perform cross-component adaptive loop filtering techniques according to the present disclosure.

[0096] Figure 4is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Figure 4 The above description is provided for the purpose of explanation and is not intended to limit the techniques extensively illustrated and described in this disclosure. For the purpose of explanation, this disclosure describes a video decoder 300 based on techniques of JEM, VVC, and HEVC. However, the techniques of this disclosure may be performed by video codec devices configured for other video codec standards.

[0097] exist Figure 4 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 one or more processors or processing circuits. Moreover, the video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

[0098] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include additional units for performing predictions according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra block copy unit (which may be 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.

[0099] The CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of the video decoder 300. The video data stored in the CPB memory 320 may be, for example, received from the computer-readable medium 110 ( Figure 1) is obtained. The CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. Similarly, the CPB memory 320 may store video data other than syntax elements of encoded and decoded pictures, such as temporary data representing outputs from various units of the video decoder 300. The DPB 314 typically stores decoded pictures, which the video decoder 300 may output and / or use as reference video data when decoding subsequent data or pictures of the encoded video bitstream. The CPB memory 320 and the DPB 314 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The CPB memory 320 and the DPB 314 may be provided by the same memory device or separate memory devices. In various examples, the CPB memory 320 may be located on-chip with other components of the video decoder 300, or off-chip relative to those components.

[0100] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) to retrieve the encoded and decoded video data. That is, memory 120 may store data as discussed above in conjunction with CPB memory 320. 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.

[0101] Figure 4 The various units shown in FIG. 3 are illustrated to aid in understanding the operations performed by the video decoder 300. These units may be implemented as fixed function circuits, programmable circuits, or a combination thereof. Figure 3 Similarly, a fixed-function circuit refers to a circuit that provides a specific function and is preset on the operations that can be performed. A programmable circuit refers to a circuit that can be programmed to perform various tasks and provides flexible functionality in the operations that can be performed. For example, a programmable circuit can execute software or firmware so that the programmable circuit operates in a manner defined by the instructions of the software or firmware. A fixed-function circuit 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 units may be different circuit blocks (fixed-function or programmable), and in some examples, one or more units may be integrated circuits.

[0102] 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.

[0103] 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.

[0104] Typically, the video decoder 300 reconstructs a picture on a block-by-block basis. The video decoder 300 may perform a reconstruction operation on each block individually (where the block currently being reconstructed, ie, decoded, may be referred to as a "current block").

[0105] The entropy decoding unit 302 may entropy decode syntax elements defining quantized transform coefficients of the quantized transform coefficient block and transform information such as a quantization parameter (QP) and / or (one or more) transform mode indications. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, determine a degree of inverse quantization for the inverse quantization unit 306 to apply. The inverse quantization unit 306 may, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thereby form a transform coefficient block including the transform coefficients.

[0106] After the inverse quantization unit 306 forms the transform coefficient block, the inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, the inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karnof-Loev transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the coefficient block.

[0107] 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, if the prediction information syntax elements indicate that the current block is inter-predicted, motion compensation unit 316 can generate the 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 use the same syntax elements as those for motion compensation unit 224 ( Figure 3 ) describes the inter-frame prediction process in a manner substantially similar to that described herein.

[0108] As another example, if the prediction information syntax element indicates that the current block is intra-predicted, the intra-prediction unit 318 can generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Again, the intra-prediction unit 318 can generally be used with respect to the intra-prediction unit 226 ( Figure 3 The intra prediction process is performed in a manner substantially similar to that described in the foregoing description. The intra prediction unit 318 may retrieve data of neighboring samples for the current block from the DPB 314.

[0109] 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.

[0110] The entropy decoding unit 302 may further entropy decode the cross-component adaptive loop filter parameters according to the techniques of the present disclosure. For example, according to one or more techniques of the present disclosure, the entropy decoding unit 302 may decode, for each of the plurality of filter coefficients and from the encoded video bitstream, a syntax element specifying an exponential value representing the logarithm of the absolute value (as a power of the exponential value of two) of the particular filter coefficient with a base of 2. In the case where the exponential value for the particular filter coefficient is non-zero, the entropy decoding unit 302 may decode, from the encoded video bitstream and for the particular filter coefficient, a syntax element having a value specifying the sign (e.g., positive or negative) of the particular filter coefficient. The entropy decoding unit 302 may reconstruct the values ​​of the plurality of filter coefficients based on the exponential value. For example, the entropy decoding unit 302 may reconstruct the values ​​of the particular filter coefficient according to the following equation:

[0111] c(i)=sign(i)*2 c′(i)+1

[0112] Where c(i) is the value of the particular filter coefficient, sign(i) is negative one if the signaled sign is negative and positive one if the signaled sign is positive, and c′(i) is the signaled exponential value of the particular filter coefficient.

[0113] Entropy decoding unit 302 may provide reconstructed cross-component adaptive loop filter coefficients to filter unit 312. Filter unit 312 may perform one or more filter operations on the reconstructed block. For example, filter unit 312 may perform a deblocking operation to reduce blocking artifacts along the reconstructed block edges. The operations of filter unit 312 need not be performed in all examples. According to the techniques of the present disclosure, filter unit 312 may use the cross-component adaptive loop filter coefficients to perform cross-component adaptive loop filtering of the decoded blocks of video data.

[0114] The video decoder 300 may store the reconstructed blocks in the DPB 314. As described above, the DPB 314 may provide reference information to the prediction processing unit 304, such as samples of the current picture for intra prediction and previously decoded pictures for subsequent motion compensation. Furthermore, the video decoder 300 may output the decoded pictures from the DPB for display devices such as Figure 1 for subsequent presentation on a display device 118).

[0115] In this manner, video decoder 300 represents an example of a video decoding device that includes a memory configured to store video data and one or more processing units implemented in circuitry and configured to perform the cross-component adaptive loop filtering techniques of the present disclosure alone or in any combination.

[0116] Figure 5 is a block diagram illustrating an example filter unit, in accordance with one or more techniques of this disclosure. Figure 5 The filter unit 500 may be considered as an example of the filter unit 216 of the video encoder 200 or the filter unit 312 of the video decoder 300 .

[0117] The filter unit 500 may include components configured to perform various types of filtering. Figure 5 As shown, the filter unit 500 may include components configured to perform sample adaptive offset (SAO) filtering, such as a SAO luminance filter 502, a SAO Cb filter 504, and a SAO Cr filter 506. Figure 5 As shown, the filter unit 500 may include components configured to perform cross-component adaptive loop filtering (CC-ALF), such as an ALF luminance filter 508, a CC ALF Cb filter 510, a CC ALF Cr filter 512, an ALF chrominance filter 514, an adder 516, and an adder 518.

[0118] In operation, the SAO luma filter 502 may receive an input luma block of video data, perform SAO filtering on the input luma block to generate an output luma block of video data, and provide the output luma block of video data to one or more other filter components, such as the ALF luma filter 508, the CC ALF Cb filter 510, and the CC ALF Cr filter 512. The SAO Cb filter 504 may receive an input Cb chroma block of video data, perform SAO filtering on the input Cb chroma block to generate an output Cb chroma block of video data, and provide the output Cb chroma block of video data to one or more other filter components, such as the ALF chroma filter 514. Similarly, the SAO Cr filter 506 may receive an input Cr chroma block of video data, perform SAO filtering on the input Cr chroma block to generate an output Cr chroma block of video data, and provide the output Cr chroma block of video data to one or more other filter components, such as the ALF chroma filter 514.

[0119] The ALF component may perform ALF on blocks of video data provided by the SAO filtering component. For example, the ALF luma filter 508 may perform adaptive loop filtering on luma blocks provided by the SAO luma filter 502 to generate an output luma block, which is labeled Y. Additionally, the ALF chroma filter 514 may perform adaptive loop filtering on chroma blocks provided by the SAO Cb filter 504 and the SAO Cr filter 506 to generate output chroma blocks, which are labeled Cb' and Cr'.

[0120] Misra et al., "Cross-Component Adaptive Loop Filter for chroma" - 15th Meeting of the Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11: JVET-O0636, Gothenburg, July 3-12, 2019 (hereinafter referred to as "JVET-O0636") - proposed a tool called Cross-Component Adaptive Loop Filter (CC-ALF). CC-ALF operates as part of the adaptive loop filter (ALF) and uses luma samples to refine each chroma component. For example, the CC ALF Cb filter 510 and the CC ALF Cr filter 512 may each generate an enhanced / refined chroma block based on the luma block provided by the SAO luma filter 502 (e.g., the CC ALF Cb filter 510 may generate an enhanced chroma block Cb+ and the CC ALF Cr filter 512 may generate an enhanced chroma block Cr+). Each of the CC ALF Cb filter 510 and the CC ALF Cr filter 512 may generate its respective enhanced chroma block based on a respective set of filter coefficients (e.g., the CC ALF Cb filter 510 may use a first set of filter coefficients and the CC ALF Cr filter 512 may use a second set of filter coefficients). For example, the CC ALF Cb filter 510 may generate the chroma block Cb+ according to the following equation:

[0121]

[0122] Among them I i is filtered block, I o is the unfiltered block, (x C ,y C ) is the brightness position (x, y), S i is the filter support in the brightness of the color component Cb, c i (x0, y0) are the filter coefficients.

[0123] As shown in the above equations, each of CC ALF Cb filter 510 and CC ALF Cr filter 512 can perform a number of multiplication operations. As discussed above and in accordance with one or more techniques of the present disclosure, these multiplication operations can be replaced by bit shift operations, which are much less resource intensive and / or easier to implement in hardware than multiplication operations. For example, to perform filtering using bit shift operations, each of CC ALF Cb filter 510 and CC ALF Cr filter 512 can utilize the following equations:

[0124]

[0125] CC-ALF can be controlled by information in the bitstream, which includes the filter coefficients for each chrominance component described above (which can be signaled in the adaptive parameter set (APS)) and a mask that controls the application of the filter to the sample block. In JVET-00636, each of the filter coefficients is represented as a fixed-point fraction. In particular, the filter coefficients use the lower 10 bits to represent the fractional part. Each coefficient is signaled using the Exponential Golomb (EG) codec, and its order depends on the coefficient positioning in the filter template.

[0126] As described above, the present disclosure recognizes that the multiplication of the CC-ALF tool described in JVET-00636 can be improved and simplified, for example, according to any or all of the techniques of the present disclosure. Accordingly, the video encoder 200 and / or the video decoder 300 can be configured according to any or all of the techniques of the present disclosure (e.g., as described below, in any combination).

[0127] According to the first technique of the present disclosure, a video codec (e.g., video encoder 200 and / or video decoder 300) may constrain the values ​​of some or all coefficients for cross-component adaptive loop filters 510, 512. For example, the video codec may constrain the values ​​of some or all coefficients (e.g., limit their possible choices) to zero or a number that is a power of 2 (e.g., so that these coefficients do not require multiplication). In some examples, the video codec (i.e., video encoder 200 or video decoder 300) may apply a bit shift to the samples instead of having to perform multiplication. In one example, the video codec may constrain the absolute values ​​of all coefficients to only 0 or a number that is a power of 2. In another example, the video codec may constrain the absolute values ​​of certain coefficients to only 0 or a number that is a power of 2. In the absence of signaling, the information about which coefficients of the filter are constrained may be the same for all filters. Alternatively or additionally, in the absence of signaling, the information may be the same for all filters of a color component. Alternatively or additionally, the information may be signaled in the bitstream for a sequence, picture, sub-picture, block or color component (eg, as one or more syntax elements).

[0128] In some examples where the video codec signals information in the bitstream (e.g., signals the values ​​of those constrained coefficients), the video codec may signal only the mapping values ​​(which are the signed exponent values ​​of the non-zero coefficients). The constrained coefficients c(i) may be mapped to c'(i) as follows,

[0129] If c(i) is equal to 0, then c'(i) is 0;

[0130] Otherwise, c'(i)=sign(c(i))*(log2(abs(c(i))+1), where sign(c(i)) is -1 if c(i) is negative, and 1 otherwise.

[0131] In some examples, the video codec may utilize any combination of fixed-order Golomb codes, fixed-length codes, or unary codes to signal c'(i).

[0132] In some examples, the video codec may first signal (or resolve) the absolute value of c'(i) by utilizing any combination of fixed-order Golomb codes, fixed-length codes, or unary codes. If c'(i) is not 0, then thereafter (e.g., after signaling the absolute value of c'(i)), the video codec may then signal (or resolve) the symbol information.

[0133] In some examples, the video codec can be configured as follows: c”(i)=c'(i)-c' min (i) Convert c'(i) to a non-zero value and signal the converted value, where c' min (i) is the minimum mapping value for the i-th coefficient. The video decoder can parse c" (i), which is a non-negative value. Based on c" (i), the video decoder can calculate c' (i) = c" (i) + c' min (i).

[0134] According to the second technology of the present disclosure, the video codec can be configured to constrain the dynamic range of the filter coefficients for the cross-component adaptive loop filters 510, 512 to reduce the cost multiplier. Let k be the number of bits used to represent the fractional part of the coefficient. The dynamic range of the filter coefficient c(i) can be constrained in an open interval (-(1<<(kj)), (1<<(kj))-1). The video codec can use any combination of fixed-order Golomb codes, fixed-length codes and / or unary codes to signal c(i). The video codec can first signal (or parse) the absolute value of c(i). If c(i) is not zero, the video codec can then signal (parse) the sign information for c(i). Additionally or alternatively, the video codec can be signaled by c'(i)=c(i)-c min (i) Convert c(i) to a non-zero value. The video codec can then signal the converted value, where c min (i) is the minimum value for the i-th coefficient. The video decoder can parse c'(i), which is a non-negative value. The video decoder can calculate the value of c(i) as c'(i)+c min (i).

[0135] Figure 6 2 is a flowchart illustrating an example method 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 Figure 3 ), but it should be understood that other devices may be configured to perform the same Figure 6 A similar approach to the one used in this paper.

[0136] In this example, initially, the video encoder 200 predicts a current block (350). For example, the video encoder 200 may form a prediction block for the current block. The video encoder 200 may then calculate a residual block for the current block (352). In order to calculate the residual block, the video encoder 200 may calculate the difference between the original unencoded block and the prediction block for the current block. The video encoder 200 may then transform and quantize the coefficients of the residual block (354). Next, the video encoder 200 may scan the quantized transform coefficients of the residual block (356). During or after the scan, the video encoder 200 may entropy encode the coefficients (358). For example, the video encoder 200 may encode the coefficients using CAVLC or CABAC. The video encoder 200 may then output the entropy encoded data of the block (360).

[0137] The video encoder 200 may then decode the current block (362). For example, the video encoder 200 may inverse quantize and inverse transform the quantized transform coefficients to reproduce a residual block and combine the reproduced residual block with the prediction block. The video encoder 200 may then filter the decoded block (364), for example, using a cross-component adaptive loop filtering technique according to the present disclosure. The entropy encoded data for the block may also include, for example, a filter index indicating which cross-component adaptive loop filter is selected for the block. The video encoder 200 may then store the filtered block (366), for example, for reference when predicting future blocks to be encoded (and decoded).

[0138] Figure 7 is a flowchart illustrating an example method for decoding a current block 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 Figure 4 ), but it should be understood that other devices may be configured to perform the same Figure 7 A similar approach to the one used in this paper.

[0139] The video decoder 300 may receive entropy encoded data for a current block, such as entropy encoded prediction information, entropy encoded data for coefficients of a residual block corresponding to the current block, and entropy encoded cross-component adaptive loop filter information for the current block (370). The video decoder 300 may entropy decode the entropy encoded data to determine prediction information for the current block and reproduce coefficients of the residual block (372). The video decoder 300 may predict the current block (374), for example, using an intra-prediction or inter-prediction mode as indicated by the prediction information for the current block to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the reproduced coefficients (376) to create a quantized transform coefficient block. The video decoder 300 may then inverse quantize and inverse transform the coefficients to produce a residual block (378). The video decoder 300 may finally decode the current block by combining the prediction block and the residual block (380).

[0140] Furthermore, video decoder 300 may filter the decoded block (382), for example, using cross-component adaptive loop filtering according to any of the techniques of this disclosure. Video decoder 300 may then store the filtered block (384), for example, for reference when predicting future blocks to be decoded.

[0141] Figure 8 1 is a flowchart illustrating an example method for cross-component adaptive loop filtering (CC-ALF) of a current block according to one or more techniques of the present disclosure. The current block may include a current CU. Although with respect to the video decoder 300 ( Figure 1 and Figure 4 ), but it should be understood that other devices may be configured to perform the same Figure 8 A similar approach to the one used in this paper.

[0142] The video decoder 300 may decode (802) a plurality of filter coefficients of a cross-component adaptive loop filter. For example, to decode a particular filter coefficient from the plurality of filter coefficients, the entropy decoding unit 302 may decode from the encoded video bitstream a syntax element specifying an exponent value representing the base-2 logarithm of the absolute value (as a power of the exponent value of two) of the particular filter coefficient. In the event that the exponent value is non-zero (i.e., has a value other than zero), the entropy decoding unit 302 may decode from the encoded video bitstream a syntax element specifying the sign of the particular filter coefficient. The entropy decoding unit 302 may determine the value of the particular filter coefficient based on the exponent value (and, if present, the sign value). For example, the entropy decoding unit 302 may determine the value of the particular filter coefficient according to the following equation:

[0143] c(i)=sign(i)*2 c′(i)+1

[0144] Wherein c(i) is the value of the particular filter coefficient, sign(i) is negative one if the sign is negative and positive one if the sign is positive, and c′(i) is the exponential value of the particular filter coefficient.

[0145] Video decoder 300 may reconstruct samples of a block of video data (804). For example, video decoder 300 may reconstruct samples of a block of video data as described above with reference to Figure 7 As an example, the video decoder 300 may add the samples of the prediction block to the residual data to reconstruct the samples of the block.

[0146] The video decoder 300 may perform cross-component adaptive loop filtering (806) on a block of video data based on a plurality of filter coefficients. For example, as described above, the CC ALF Cb filter and the CC ALF Cr filter (e.g., CC ALF Cb filter 510 and CC ALF Cr filter 512) of the filter unit 312 may generate an enhanced chroma block by bit-shifting samples of a block of video data based on the values ​​of the plurality of filter coefficients without performing multiplication. In this way, the techniques of the present disclosure may reduce system resources required to perform CC-ALF.

[0147] The following numbered examples may illustrate one or more aspects of the present disclosure:

[0148] Example 1. A method for decoding video data, the method comprising: encoding and decoding multiple filter coefficients of a cross-component adaptive loop filter, wherein the value of one or more of the multiple filter coefficients is constrained to be zero or a power of two; bit shifting the value of one or more of the multiple filter coefficients constrained to be zero or a power of two; encoding and decoding a block of video data; and performing cross-component adaptive loop filtering of the decoded block using the filter coefficients.

[0149] Example 2. The method of Example 1, wherein the values ​​of all of the plurality of filter coefficients are constrained to be zero or a power of two.

[0150] Example 3. The method of Example 1, wherein at least one value of the plurality of filter coefficients is not constrained to be zero or a power of two.

[0151] Example 4. The method of any of Examples 1-3, wherein performing cross-component adaptive loop filtering comprises not multiplying filter coefficients having values ​​of zero or a power of two by samples of the decoded block.

[0152] Example 5. The method of any of Examples 1-4, further comprising encoding and decoding one or more syntax elements indicating values ​​of constrained filter coefficients in the plurality of filter coefficients.

[0153] Example 6. A method for decoding video data, the method comprising: determining the number of bits k used to represent a fractional value of a filter coefficient of a cross-component adaptive loop filter; determining that a dynamic range of the filter coefficient includes (-(1<<(k–j)), (1<<(k–j))–1); encoding and decoding a block of the video data; and performing cross-component adaptive loop filtering of the decoded block using the filter coefficients.

[0154] Example 7. The method of any of Examples 1-6, wherein encoding and decoding includes decoding.

[0155] Example 8. The method of any of Examples 1-7, wherein encoding and decoding includes encoding.

[0156] Example 9. A device for encoding and decoding video data, the device comprising one or more components for performing the method of any of Examples 1-8.

[0157] Example 10. The apparatus of Example 9, wherein the one or more components include one or more processors implemented in a circuit.

[0158] Example 11. The apparatus of any of Examples 9 and 10, further comprising a memory for storing video data.

[0159] Example 12. The apparatus of any of Examples 9-11, further comprising a display configured to display the decoded video data.

[0160] Example 13. The device of any of Examples 9-12, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0161] Example 14. The device of any of Examples 9-13, wherein the device comprises a video decoder.

[0162] Example 15. The device of any of Examples 9-14, wherein the device comprises a video encoder.

[0163] Example 16. A computer-readable storage medium having instructions stored thereon, which, when executed, cause one or more processors to perform the method of any of Examples 1-8.

[0164] It should be appreciated that, depending on the example, certain actions or events of any of the techniques described herein may be performed in a different sequence, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary for the practice of the techniques). Moreover, in some examples, actions or events may be performed concurrently, such as through multithreading, interrupt handling, or multiple processors, rather than sequentially.

[0165] In one or more examples, the described functions may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored or sent as one or more instructions or codes on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to tangible media such as data storage media; or communication media, including any media that facilitates the transfer of a computer program from one place to another, for example, according to a communication protocol. In this manner, computer-readable media may generally correspond to (1) non-transitory tangible computer-readable storage media or (2) communication media such as signals or carrier waves. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to 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.

[0166] As an 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 required program code in the form of instructions or data structures and can be accessed by a computer. Similarly, any connection is appropriately referred to as a computer-readable medium. For example, if a coaxial cable, optical fiber cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, microwaves are used to send instructions from a website, server or other remote source, then coaxial cable, optical fiber cable, twisted pair, DSL, or wireless technologies such as infrared, radio and microwaves are 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 are directed to non-transient, tangible storage media. Disks and optical disks used herein include compact disks (CDs), laser disks, optical disks, digital versatile disks (DVDs), floppy disks and blue optical disks, wherein disks usually reproduce data magnetically, while optical disks reproduce data optically with lasers. The combination of the above items should also be included in the scope of computer-readable media.

[0167] Instructions may be executed by one or more processors such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Accordingly, the terms "processor" and "processing circuitry" as used herein may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. 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. Similarly, the technology may be fully implemented in one or more circuits or logic elements.

[0168] The techniques of the present disclosure may be implemented in a variety of devices or apparatuses, including wireless handheld devices, integrated circuits (ICs) or IC sets (e.g., chipsets). 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 need to be implemented by different hardware units. More specifically, as described above, the various units may be combined in a codec hardware unit or provided by a collection of interoperable hardware units including one or more processors as described above in combination with appropriate software and / or firmware.

[0169] 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: Decoding a plurality of filter coefficients of a cross-component adaptive loop filter, wherein decoding a specific filter coefficient among the plurality of filter coefficients comprises: decoding from an encoded video bitstream using a fixed length code a syntax element that specifies an exponential value representing the base-2 logarithm of an absolute value of the particular filter coefficient, the absolute value being raised to the power of two; and determining a value of the particular filter coefficient based on the index value; reconstructing samples of a block of video data; and The block of the video data is cross-component adaptive loop filtered based on the plurality of filter coefficients.

2. The method of claim 1, wherein: Absolute values ​​of all of the plurality of filter coefficients are constrained to be zero or a power of two.

3. The method of claim 1, wherein: Decoding the specific filter coefficients further comprises: In response to the index value being a value other than zero, decoding from the encoded video bitstream a syntax element that specifies a sign for the particular filter coefficient, Wherein, determining the value of the specific filter coefficient further comprises determining the value of the specific filter coefficient based on the sign.

4. The method of claim 3, wherein: Determining the value of the specific filter coefficient includes determining the value of the specific filter coefficient according to the following equation: c(t)=sign(i))*2 c′(i)+1 wherein c(i) is the value of the particular filter coefficient, sign(i) is negative one if the sign is negative and positive one if the sign is positive, and c′(i) is the exponential value of the particular filter coefficient.

5. The method of claim 1, wherein: The cross-component adaptive loop filtering includes bit-shifting samples of the block of video data based on values ​​of the plurality of filter coefficients without performing multiplication.

6. A method for encoding video data, the method comprising: Encoding a plurality of filter coefficients of a cross-component adaptive loop filter, wherein encoding a value of a specific filter coefficient among the plurality of filter coefficients comprises: encoding in a coded video bitstream using a fixed length code a syntax element specifying an exponent value representing a base-2 logarithm of an absolute value of the particular filter coefficient, the absolute value being raised to a power of two; reconstructing samples of a block of video data; and The block of video data is cross-component adaptive loop filtered based on the values ​​of the plurality of filter coefficients.

7. The method of claim 6, wherein: Absolute values ​​of all of the plurality of filter coefficients are constrained to be zero or a power of two.

8. The method of claim 6, wherein: Encoding the specific filter coefficients further comprises: In response to the particular filter coefficient having a value other than zero, encoding a syntax element specifying a sign of the particular filter coefficient in the encoded video bitstream.

9. The method of claim 6, wherein: Cross-component adaptive loop filtering includes bit-shifting samples of the block of video data based on values ​​of the plurality of filter coefficients without performing multiplications.

10. A device for decoding video data, the device comprising: a memory configured to store at least a portion of an encoded video bitstream; as well as One or more processors implemented in circuitry and configured to: Decoding a plurality of filter coefficients of a cross-component adaptive loop filter, wherein, in order to decode a particular filter coefficient of the plurality of filter coefficients, the one or more processors are configured to: decoding from the encoded video bitstream using a fixed length code a syntax element that specifies an exponential value representing the base-2 logarithm of an absolute value of the particular filter coefficient, the absolute value being raised to the power of two; and determining a value of the particular filter coefficient based on the index value; reconstructing samples of a block of video data; and The block of the video data is cross-component adaptive loop filtered based on the plurality of filter coefficients.

11. The device of claim 10, wherein: Absolute values ​​of all of the plurality of filter coefficients are constrained to be zero or a power of two.

12. The device of claim 10, wherein: To decode the specific filter coefficients, the one or more processors are further configured to: In response to the index value being a value other than zero, decoding from the encoded video bitstream a syntax element that specifies a sign for the particular filter coefficient, In order to determine the value of the specific filter coefficient, the one or more processors are further configured to determine the value of the specific filter coefficient based on the sign.

13. The apparatus of claim 12, wherein: To determine the value of the specific filter coefficient, the one or more processors are configured to determine the value of the specific filter coefficient according to the following equation: c(i)=sign(i))*2 c′(i) +1 wherein c(i) is the value of the particular filter coefficient, sign(i) is negative one if the sign is negative and positive one if the sign is positive, and c′(i) is the exponential value of the particular filter coefficient.

14. The apparatus of claim 10, wherein: To perform cross-component adaptive loop filtering, the one or more processors are configured to bit-shift samples of the block of video data based on values ​​of the plurality of filter coefficients without performing multiplications.

15. A device for encoding video data, the device comprising: a memory configured to store at least a portion of an encoded video bitstream; as well as One or more processors implemented in circuitry and configured to: encoding a plurality of filter coefficients of a cross-component adaptive loop filter, wherein, to encode a particular filter coefficient of the plurality of filter coefficients, the one or more processors are configured to: encoding in the coded video bitstream using a fixed length code a syntax element specifying an exponent value representing the base-2 logarithm of an absolute value of the particular filter coefficient, the absolute value being raised to the power of two; reconstructing samples of a block of video data; and The block of video data is cross-component adaptive loop filtered based on the values ​​of the plurality of filter coefficients.

16. The device of claim 15, wherein: Absolute values ​​of all of the plurality of filter coefficients are constrained to be zero or a power of two.

17. The apparatus of claim 15, wherein: To further encode the specific filter coefficients, the one or more processors are further configured to: In response to the particular filter coefficient having a value other than zero, a syntax element specifying a sign of the particular filter coefficient is encoded from the encoded video bitstream.

18. The apparatus of claim 15, wherein to perform cross-component adaptive loop filtering, the one or more processors are configured to bit-shift samples of the block of video data based on the values ​​of the plurality of filter coefficients without performing multiplication.

19. A non-volatile computer-readable medium having one or more computer-executable instructions stored thereon, which, when executed by one or more processors of a device for decoding video data, cause the one or more processors to perform the method according to any one of claims 1-5.

20. A non-transitory computer-readable medium having one or more computer-executable instructions stored thereon, which, when executed by one or more processors of a device for encoding video data, cause the one or more processors to perform the method according to any one of claims 6 to 9.

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