Cross-component adaptive loop filtering for video coding

Abstract

An example device for decoding video data includes: a memory configured to store the video data; and one or more processors implemented in a circuit and configured to: determine a number of bits k for representing a decimal value of a filter coefficient of a cross-component adaptive loop filter; determine that for a value c, a dynamic range of the filter coefficient includes (‑(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decode a block of the video data; and perform cross-component adaptive loop filtering on the decoded block using the filter coefficient, the filter coefficient being within the dynamic range.

Description

[0001] This application claims the benefit of U.S. Application No. 17 / 004,831, filed on August 27, 2020, and U.S. Provisional Application No. 62 / 892,908, filed on August 28, 2019, the entire contents of each of which are hereby incorporated by reference into this document. Technical Field

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

[0003] Digital video capabilities may be incorporated into a wide variety of devices, including digital televisions, digital live broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video 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 coding techniques (such as those described in standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4 (Part 10, Advanced Video Coding (AVC)), ITU-T H.265 / High Efficiency Video Coding (HEVC), and extensions of such standards). By implementing such video coding techniques, video devices can more efficiently send, receive, encode, decode and / or store digital video information.

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

[0005] In summary, the present disclosure describes techniques for cross-component adaptive loop filtering of video data. These techniques include, for example, encoding (encoding or decoding) filter coefficients for a cross-component adaptive loop filter (CCALF) and encoding data indicating which of the various CCALFs will be applied to a given set of video data, such as for slices, blocks, chroma components, etc. Typically, a video encoding device (video coder) applies CCALFs to chroma component blocks and refines samples of the chroma component blocks using samples of the corresponding luminance component. According to the techniques of the present disclosure, a video encoding device can encode data representing the filter coefficients of each CCALF.

[0006] For example, the filter coefficients may each have a rational value, including a decimal part and a fractional part. The video encoding device may determine the range of values ​​of the filter coefficients from the number of bits used to represent the decimal part of the filter coefficient value. Therefore, the video encoding device may use the range value to determine the value of the filter coefficient. After determining the value of each filter coefficient (using the range determined for the value of the filter coefficient), the video encoding device may use the CCALF with the determined filter coefficient value to perform cross-component adaptive loop filtering on a block of decoded video data.

[0007] In one example, a method for decoding video data includes: determining the number of bits k used to represent a decimal value of a filter coefficient of a cross-component adaptive loop filter; determining that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decoding a block of the video data; and performing cross-component adaptive loop filtering on the decoded block using the filter coefficient, the filter coefficient being within the dynamic range.

[0008] In another example, a device for decoding video data includes: a memory configured to store video data; and one or more processors implemented in a circuit and configured to: determine the number of bits k used to represent a decimal value of a filter coefficient of a cross-component adaptive loop filter; determine that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decode a block of the video data; and perform cross-component adaptive loop filtering on the decoded block using the filter coefficient, the filter coefficient being within the dynamic range.

[0009] In another example, a computer-readable storage medium has instructions stored thereon that, when executed, cause a processor to perform the following operations: determine the number of bits k used to represent a decimal value of a filter coefficient of a cross-component adaptive loop filter; determine that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decode a block of video data; and perform cross-component adaptive loop filtering on the decoded block using the filter coefficient, the filter coefficient being within the dynamic range.

[0010] In another example, an apparatus for decoding video data includes: a unit for determining a number of bits k of a decimal value for representing a filter coefficient of a cross-component adaptive loop filter; a unit for determining that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; a unit for decoding a block of video data; and a unit for performing cross-component adaptive loop filtering on the decoded block using the filter coefficient, wherein the filter coefficient is within the dynamic range.

[0011] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0013] Figure 2 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0014] Figure 3 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0015] Figure 4 is a block diagram illustrating an example adaptive loop filter including a cross-component adaptive loop filter that may be used in accordance with the techniques of this disclosure.

[0016] Figure 5 is a flowchart illustrating an example method for encoding a current block according to techniques of this disclosure.

[0017] Figure 6 is a flow chart illustrating an example method for decoding a current block according to techniques of this disclosure.

[0018] Figure 7 is a flow chart illustrating an example method of encoding a block of video data in accordance with the techniques of this disclosure.

[0019] Figure 8 is a flow chart illustrating an example method of encoding a block of video data in accordance with the techniques of this disclosure. DETAILED DESCRIPTION

[0020] A cross-component adaptive loop filter (CCALF) allows chrominance data to be filtered using corresponding luminance data. The CCALF can be incorporated into an adaptive loop filter (ALF) to refine the chrominance components of video data. The present disclosure describes various improvements to the CCALF. For example, the filter coefficients in the CCALF are represented as fixed-point decimal numbers encoded using ten bits. The present disclosure describes a fixed-length encoding that uses less than ten bits to encode the decimal portion of the filter coefficients. The CCALF filter coefficients are also encoded using a cost multiplier. The present disclosure describes a technique for reducing the cost multiplier by limiting the dynamic range of the filter coefficients. By reducing the number of bits and the cost multiplier used to represent the decimal portion of the coefficient, the size of the bitstream can be reduced, thereby improving the technical field of video encoding.

[0021] 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. In general, the techniques of the present disclosure relate to encoding (encoding and / or decoding) video data. In general, video data includes any data used to process video. Thus, video data can include original unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata (e.g., signaling data).

[0022] like Figure 1 As shown, in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, source device 102 provides the video data to destination device 116 via computer-readable medium 110. Source device 102 and destination device 116 may include any of a wide variety of devices, including desktop computers, notebook computers (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, therefore, may be referred to as wireless communication devices.

[0023] exist Figure 1 In the example of , the source device 102 includes a video source 104, a memory 106, a video encoder 200, and an output interface 108. The destination device 116 includes an input interface 122, a video decoder 300, a memory 120, and a display device 118. According to the present disclosure, the video encoder 200 of the source device 102 and the video decoder 300 of the destination device 116 can be configured to apply a technology for performing cross-component adaptive loop filtering. Therefore, the source device 102 represents an example of a video encoding device, and the destination device 116 represents an example of a video decoding device. In other examples, the source device and the destination device may include other components or arrangements. For example, the source device 102 may receive video data from an external video source such as an external camera. Similarly, the destination device 116 may be connected to an external display device in an interface manner, rather than including an integrated display device.

[0024] exist Figure 1 The system 100 shown in is only an example. In general, any digital video encoding and / or decoding device can perform techniques for cross-component adaptive loop filtering. The source device 102 and the destination device 116 are only examples of such encoding devices, wherein the source device 102 generates encoded video data for transmission to the destination device 116. The present disclosure refers to a "coding" device as a device that performs encoding (e.g., encoding and / or decoding) of data. Therefore, the video encoder 200 and the video decoder 300 represent examples of encoding devices (specifically, 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.

[0025] 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 the pictures. Video source 104 of source device 102 may include a video capture device, such as a camera, a video archive unit containing previously captured original video, and / or a video feed interface for receiving video from a video content provider. As another alternative, video source 104 may generate computer graphics-based data as source video, or a combination of real-time video, archived video, and computer-generated video. In each case, video encoder 200 may encode captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange images from the received order (sometimes referred to as "display order") to an encoding order for encoding. 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 to be received and / or retrieved by, for example, input interface 122 of destination device 116 .

[0026] 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 memory 106, 120 can store original video data, for example, the original video from the video source 104 and the original decoded video data from the video decoder 300. In addition or alternatively, the memory 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 as separate 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 memory 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 memory 106, 120 can be allocated as one or more video buffers, for example, to store original decoded and / or encoded video data.

[0027] The computer-readable medium 110 may represent any type of medium or device capable of moving the 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. The output interface 108 may modulate the transmission signal including the encoded video data according to a communication standard such as a wireless communication protocol, and the input interface 122 may demodulate the received transmission signal according to a communication standard such as a wireless communication protocol. The communication medium may include any wireless or wired communication medium, for example, a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form a portion of a packet-based network such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include a router, a switch, a base station, or any other device that may be useful for facilitating communication from the source device 102 to the destination device 116.

[0028] 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.

[0029] In some examples, source device 102 may output the encoded video data to file server 114 or another intermediate storage device that may store the encoded video data generated by source device 102. Destination device 116 may access the stored video data from file server 114 via streaming or downloading.

[0030] The file server 114 may be any type of server device capable of storing encoded video data and sending the encoded video data to the destination device 116. The file server 114 may represent a web server (e.g., for a website), a server configured to provide a file transfer protocol service (such as the File Transfer Protocol (FTP) or the File Delivery over Unidirectional Transport (FLUTE) protocol), a content delivery network (CDN) device, a hypertext transfer protocol (HTTP) server, a Multimedia Broadcast Multicast Service (MBMS) or an enhanced MBMS (eMBMS) server, and / or a network attached storage (NAS) device. The file server 114 may additionally or alternatively implement one or more HTTP streaming protocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Real-time Streaming (HLS), Real-time Streaming Protocol (RTSP), HTTP Dynamic Streaming, etc.

[0031] Destination device 116 may access the encoded video data from file server 114 through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., a digital subscriber line (DSL), a cable modem, etc.), or a combination of both, suitable for accessing the encoded video data stored on file server 114. Input interface 122 may be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from file server 114, or other such protocols for retrieving media data.

[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 transmit data (such as encoded video data) according to a cellular communication standard (such as 4G, 4G-LTE (Long Term Evolution), Advanced LTE, 5G, etc.). In some examples where output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 may be configured to transmit data (such as encoded video data) according to other wireless standards (such as IEEE 802.11 specifications, IEEE 802.15 specifications (e.g., ZigBee TM ), Bluetooth TMStandards, etc.) to transmit data (such as encoded video data). In some examples, source device 102 and / or destination device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include a SoC device for performing the functions assigned to video encoder 200 and / or output interface 108, and destination device 116 may include a SoC device for performing the functions assigned to video decoder 300 and / or input interface 122.

[0033] The techniques of the present disclosure may be applied to video encoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission (such as Dynamic Adaptive Streaming over HTTP (DASH)), digital video encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0034] The input interface 122 of the destination device 116 receives the 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 such as the following syntax elements defined by the video encoder 200 (which are also used by the video decoder 300), the syntax elements having values ​​describing the characteristics and / or processing of video blocks or other coding units (e.g., slices, pictures, groups of pictures, sequences, etc.). The display device 118 displays the decoded pictures of the decoded video data to the 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] Despite Figure 1 200 and 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 units may follow 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 the instructions in hardware to perform the technology of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, and any of the encoders or decoders can be integrated as part of a combined encoder / decoder (CODEC) in the corresponding device. The device including the video encoder 200 and / or the video decoder 300 can include an integrated circuit, a microprocessor, and / or a wireless communication device (such as a cellular phone).

[0037] The video encoder 200 and the video decoder 300 may operate in accordance with a video coding standard, such as the ITU-T H.265 standard, also known as the High Efficiency Video Coding (HEVC) standard, or an extension thereof, such as the multi-view and / or scalable video coding extension. Alternatively, the video encoder 200 and the video decoder 300 may operate in accordance with other proprietary or industry standards, such as the ITU-T H.266 standard, also known as Versatile Video Coding (VVC). A recent draft of the VVC standard is described in Bross et al., “Versatile Video Coding (Draft 5)”, Joint Video Experts Group (JVET) of ITU-T SG 16 WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11, 14th Meeting, Geneva, Switzerland, March 19-27, 2019, JVET-N1001-v3 (hereinafter “VVC Draft 5”). However, the techniques of the present disclosure are not limited to any particular coding standard.

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

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

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

[0042] In the MTT segmentation structure, blocks can be segmented using quadtree (QT) segmentation, binary tree (BT) segmentation, and one or more types of ternary tree (TT) segmentation. A ternary tree segmentation is a segmentation in which a block is divided into three sub-blocks. In some examples, the ternary tree segmentation divides the block into three sub-blocks without dividing the original block through the center. The segmentation 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 or MTT structure to represent each of the luma and chroma components, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luma component and another QTBT / MTT structure for the two chroma components (or two QTBT / MTT structures for the respective chroma components).

[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 per HEVC. For purposes of explanation, a description of the techniques of the present disclosure is given with respect to QTBT segmentation. However, it should be understood that the techniques of the present disclosure may also be applied to video encoding devices configured to use quadtree segmentation or also use other types of segmentation.

[0045] Blocks (e.g., CTUs or CUs) may be grouped in a picture in various ways. As an example, a brick may refer to a rectangular area of ​​a CTU row within a particular tile in a picture. A tile may be a rectangular area of ​​a CTU within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular area of ​​a CTU having a height equal to the height of the picture and a width specified by a syntax element (e.g., such as in a picture parameter set). A tile row refers to a rectangular area of ​​a CTU having a height specified by a syntax element (e.g., such as in a picture parameter set) and a width equal to the width of the picture.

[0046] In some examples, a tile may be partitioned into multiple bricks, each of which may include one or more CTU rows within the tile. Tiles that are not partitioned into multiple bricks may also be referred to as bricks. However, bricks that are true subsets of tiles may not be referred to as tiles.

[0047] Tiles in a picture can also be arranged in slices. A slice can be an integer number of tiles of a picture that can be uniquely contained in a single network abstraction layer (NAL) unit. In some examples, a slice includes a continuous sequence of multiple complete tiles or only complete tiles of one tile.

[0048] This disclosure may use "NxN" and "N by N" interchangeably to refer to the sample size of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, for example, 16x16 samples or 16 by 16 samples. Typically, a 16x16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Similarly, an NxNCU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. 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 NxM 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 typically 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 encoded picture, while intra-frame prediction generally refers to predicting a CU based on previously encoded 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 motion search to identify a reference block that closely matches the CU, for example, in terms of the difference between the CU and the reference block. The video encoder 200 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 VVC also provide an affine motion compensation mode, which can be considered an inter-frame prediction mode. In the affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion (such as zooming in or out, rotation, perspective motion, or other irregular motion types).

[0052] In order to perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. Some examples of VVC provide sixty-seven intra prediction modes, including various directional modes, as well as planar modes and DC modes. Typically, the video encoder 200 selects an intra prediction mode that describes the neighboring samples of the current block according to which the samples of the current block (e.g., a block of a CU) are to be predicted. Assuming that the video encoder 200 encodes the CTU and CU in raster scan order (from left to right, from top to bottom), such samples can typically be above, above 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 a prediction mode for the current block. For example, for an inter-frame prediction mode, the video encoder 200 may encode data representing which of the various available inter-frame prediction modes is used and motion information for the corresponding mode. For unidirectional or bidirectional inter-frame prediction, for example, the video encoder 200 may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. The video encoder 200 may use a similar mode to encode motion vectors for affine motion compensation mode.

[0054] After a prediction such as intra prediction or inter prediction of a block, the video encoder 200 may calculate residual data for the block. The residual data (such as a residual block) represents the sample-by-sample difference between the block and a prediction block for the block, which is formed using a corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to produce transformed data in a transform domain rather than in a sample domain. For example, the video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. In addition, the video encoder 200 may apply a secondary transform after the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc. The video encoder 200 generates transform coefficients after applying one or more transforms.

[0055] As described above, after any transformation to produce transform coefficients, the video encoder 200 may perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to potentially reduce the amount of data used to represent the coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 may reduce the bit depth associated with some or all coefficients. For example, the video encoder 200 may round down an n-bit value to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, the video encoder 200 may perform a bitwise right shift of the value to be quantized.

[0056] After quantization, the video encoder 200 can scan the transform coefficients to generate a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scan can be designed to place coefficients of higher energy (and therefore higher frequency) in front of the vector and transform coefficients of lower energy (and therefore lower frequency) 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 generate 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 the values ​​of the syntax elements used to describe the 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 transmitted. 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 also generate syntax data (such as block-based syntax data, picture-based syntax data, and sequence-based syntax data) for the video decoder 300, for example, in a picture header, a block header, a slice header, or other syntax data (such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS). Likewise, the video decoder 300 may 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, which includes the encoded video data, for example, a syntax element 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 use CABAC to decode the values ​​of syntax elements for the bitstream in a manner substantially similar to, but reverse to, the CABAC encoding process of the video encoder 200. The syntax elements may define partitioning of 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 CTUs. The syntax elements may also 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 prediction or inter-frame prediction) and related prediction information (e.g., motion information for inter-frame prediction) to form a prediction block for the block. The video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. The video decoder 300 may perform additional processing, such as performing a deblocking process to reduce visual artifacts along the boundaries of the blocks.

[0062] The video encoder 200 and the video decoder 300 may also be configured to perform cross-component adaptive loop filtering. That is, after decoding the chroma block, the video encoder 200 and the video decoder 300 may use cross-component adaptive loop filtering to refine the samples of the decoded chroma block. Typically, the video encoder 200 and the video decoder 300 may apply a cross-component adaptive loop filter (CCALF) to the decoded chroma block, where CCALF refers to the corresponding luminance samples to be used to refine the samples of the decoded chroma block.

[0063] The CCALF contains a set of filter coefficients. The video encoder 200 and the video decoder 300 may encode (respectively encode or decode) the values ​​of the filter coefficients, for example, in an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), a slice header, a block header, or in other such structures. According to the technology of the present disclosure, the video encoder 200 and the video decoder 300 may use the number of bits representing the decimal portion of the filter coefficients and the offset value to calculate the dynamic range within which the values ​​of the filter coefficients will be. Therefore, using the dynamic range, the video encoder 200 and the video decoder 300 may reduce the number of bits required to encode the actual filter coefficient values ​​without determining the dynamic range.

[0064] Let k represent the number of bits used to represent the decimal portion of the filter coefficient, and let c represent the offset value. The video encoder 200 and the video decoder 300 may calculate the dynamic range as (-(1<<(k–c))+1,(1<<(k–c))–1), where “<<” represents a bitwise left shift operator. The offset value c may be predetermined or encoded as part of a bitstream including the video data. The value k may be less than 10 and greater than 0. The video encoder 200 and the video decoder 300 may encode the values ​​of the filter coefficients using fixed-length codewords. As described above, the video encoder 200 and the video decoder 300 may encode the filter coefficients of the CCALF in, for example, an APS. The video encoder 200 and the video decoder 300 may encode an index value in a slice header or block that identifies one of the CCALFs to be used for the slice / block.

[0065] The present disclosure may generally involve "signaling" certain information (such as syntax elements). The term "signaling" may generally refer to the transmission of values ​​for syntax elements and / or other data used to decode the encoded video data. That is, the video encoder 200 may signal values ​​for syntax elements in the bitstream. Generally, signaling refers to generating values ​​in the bitstream. As described above, the source device 102 may transmit the bitstream to the destination device 116 in substantially real time or not in real time (such as may occur when storing syntax elements to the storage device 112 for later retrieval by the destination device 116).

[0066] Figure 2 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. Figure 2 The above description is provided for the purpose of explanation and should not be considered to limit the techniques generally exemplified and described in this disclosure. For the purpose of explanation, this disclosure describes the video encoder 200 in the context of video coding standards such as the HEVC video coding standard and the developing H.266 video coding standard. However, the techniques of this disclosure are not limited to these video coding standards and are generally applicable to video encoding and decoding.

[0067] exist Figure 2 In the example of , the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218, and an entropy coding unit 220. Any one or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filter unit 216, the DPB 218, and the entropy coding unit 220 may be implemented in one or more processors or in processing circuits. In addition, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

[0068] 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 the video data stored in the video data memory 230. DPB 218 can act as a reference picture memory, which stores reference video data for use when subsequent video data is predicted by the video encoder 200. Video data memory 230 and DPB 218 can be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Video data memory 230 and DPB 218 can be provided by the same memory device or a separate memory device. In various examples, video data memory 230 can be on chip with other components of the video encoder 200 (as shown), or off chip relative to those components.

[0069] In the present disclosure, references to the video data memory 230 should not be interpreted as limited to memory internal to the video encoder 200 (unless specifically described as such), or to memory external to the video encoder 200 (unless specifically described as such). Rather, references to the video data memory 230 should be understood as a reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). Figure 1 The memory 106 may also provide temporary storage for outputs from the various units of the video encoder 200 .

[0070] Shows Figure 2 The various units of the video encoder 200 are provided to help understand the operations performed by the video encoder 200. These units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide specific functions and are pre-set on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functions in the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive parameters or output parameters), but the types of operations performed by fixed-function circuits are generally immutable. In some examples, one or more of these units may be different circuit blocks (fixed-function or programmable), and in some examples, one or more units may be integrated circuits.

[0071] 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.

[0072] The video data memory 230 is configured to store the received video data. The video encoder 200 may retrieve the picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 may be the original video data to be encoded.

[0073] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. The mode selection unit 202 may include additional functional units that perform video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of the motion estimation unit 222 and / or the motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

[0074] The mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and the resulting rate-distortion values ​​for such combinations. The encoding parameters may include partitioning of a CTU into CUs, a prediction mode for a CU, a transform type for residual data of a CU, a quantization parameter for 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.

[0075] The video encoder 200 may partition the 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 the 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".

[0076] Typically, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU, or the overlapping portion of the PU and TU in HEVC). In order to inter-predict the current block, the motion estimation unit 222 can 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 encoded pictures stored in the DPB 218). Specifically, the motion estimation unit 222 can calculate a value representing the degree of similarity of the potential reference block 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 can generally perform these calculations using the sample-by-sample difference between the current block and the reference block under consideration. The motion estimation unit 222 can identify the reference block with the lowest value from these calculations, which indicates the reference block that most closely matches the current block.

[0077] The motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of the reference block in the reference picture relative to the position of the current block in the current picture. The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, for unidirectional inter prediction, the motion estimation unit 222 may provide a single motion vector, while for bidirectional inter prediction, the motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, the motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, if the motion vectors have fractional sample precision, the motion compensation unit 224 may interpolate the 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, for example, by sample-by-sample averaging or weighted averaging, and combine the retrieved data.

[0078] As another example, for intra prediction or intra prediction encoding, the intra prediction unit 226 can generate a prediction block based on samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally mathematically combine the values ​​of adjacent samples and fill these calculated values ​​along the defined direction on the current block to generate a prediction block. As another example, for DC mode, the intra prediction unit 226 can calculate the average value of adjacent samples to the current block and generate a prediction block to include the obtained average value for each sample of the prediction block.

[0079] 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 may 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 may be formed using one or more subtractor circuits that perform binary subtraction.

[0080] In the example where 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 noted above, the size of the CU may refer to the size of the luma coding 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 2Nx2N, the video encoder 200 may support PU sizes of 2Nx2N or NxN for intra-frame prediction, and 2Nx2N, 2NxN, Nx2N, NxN or similar symmetrical PU sizes for inter-frame prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter-frame prediction.

[0081] In an example where the mode selection unit 202 does not further split the CU into PUs, each CU may be associated with a luma coding block and a corresponding chroma coding block. As described above, the size of a CU may refer to the size of the luma coding block of the CU. The video encoder 200 and the video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

[0082] For other video coding techniques, such as intra-block copy mode coding, affine mode coding, and linear model (LM) mode coding, 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 coding technique. In some examples, such as palette mode coding, the mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating how to reconstruct the block based on the selected palette. In such a mode, the mode selection unit 202 may provide these syntax elements to the entropy coding unit 220 for encoding.

[0083] 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.

[0084] 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 can apply various transforms to the residual block to form a transform coefficient block. For example, the transform processing unit 206 can apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 can perform a variety of transforms on the residual block, for example, a primary transform and a secondary transform (such as a rotation transform). In some examples, the transform processing unit 206 does not apply a transform to the residual block.

[0085] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may result in a loss of information, and therefore, the quantized transform coefficients may have a lower precision than the original transform coefficients generated by the transform processing unit 206.

[0086] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct a residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (although potentially with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by the mode selection unit 202 to generate a reconstructed block.

[0087] 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 blocky artifacts along the edge of the CU. In some examples, the operation of the filter unit 216 may be skipped. The filter unit 216 may perform the cross-component adaptive loop filtering techniques of the present disclosure alone or in any combination. Similarly, the entropy coding unit 220 may be configured to entropy encode the cross-component adaptive loop filtering parameters according to the techniques of the present disclosure.

[0088] According to the techniques of the present disclosure, filter unit 216 retrieves CCALF filter coefficients from a cross-component adaptive loop filter (CCALF) coefficient memory 232. In other examples, CCALF coefficient memory 232 may form part of video data memory 230. Typically, CCALF coefficient memory 232 stores CCALF filter coefficients for one or more CCALFs. Mode selection unit 202 may perform multiple encoding passes to determine one of the appropriate CCALFs to be used for a chroma block of a current slice, and then send data representing one of the CCALFs to entropy encoding unit 220. Entropy encoding unit 220 may entropy encode an adaptive parameter set (APS) that includes a set of CCALF filter coefficients for one or more CCALFs for chroma components and a slice header that includes an index that identifies one of the CCALFs to be used for the chroma components in the slice.

[0089] In addition, in order to encode the data representing the CCALF filter coefficients, the entropy coding unit 220 may encode the data representing the number of bits used to represent the decimal part of the CCALF filter coefficients. For example, k may represent the number of bits used to represent the decimal part of the CCALF filter coefficients. In addition, c may represent an offset to be applied to k. In some examples, c may be predetermined, while in other examples, the entropy coding unit 220 may encode the data representing c, for example, in a sequence parameter set (SPS), a picture parameter set (SPS), an adaptive parameter set (APS), a slice header, a block header, or at a filter level (e.g., a value c specific to the corresponding CCALF, such as in an APS).

[0090] The filter unit 216 may use the value c and the value k to determine the dynamic range of the CCALF filter coefficients. The dynamic range may be within (-(1<<(k–c))+1,(1<<(k–c))–1), where “<<” represents a bitwise left shift operator. The filter unit 216 may use the dynamic range to determine appropriate values, such as an appropriate fixed-length codeword, to represent the CCALF filter coefficients. The filter unit 216 may pass the fixed-length codeword to the entropy coding unit 220. Alternatively, the entropy coding unit 220 may determine the values ​​of k, c, and the dynamic range, and use these values ​​to select an appropriate fixed-length codeword.

[0091] The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in an example where the operation of the filter unit 216 is not required, the reconstruction unit 214 can store the reconstructed blocks in the DPB 218. In an example where the operation of the filter unit 216 is required, the filter unit 216 can store the filtered reconstructed blocks in the DPB 218. The filter unit 216 can apply CCALF to the decoded chroma blocks and store the filtered chroma blocks to the decoded picture buffer 218. The motion estimation unit 222 and the motion compensation unit 224 can retrieve the reference picture formed by the reconstructed (and potentially filtered) blocks from the DPB 218 to perform inter-frame prediction on the blocks of the 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. In another example, the reconstructed samples that do not run the filter in the filter unit 216 can be stored in the DPB and used for intra-frame prediction.

[0092] 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 the quantized transform coefficient blocks from the quantization unit 208. As another example, the entropy coding unit 220 may entropy encode the prediction syntax elements (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-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 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.

[0093] 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.

[0094] The above operations are described with respect to blocks. Such descriptions should be understood as operations for luma coding blocks and / or chroma coding blocks. As described above, in some examples, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a CU. In some examples, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a PU.

[0095] In some examples, operations performed with respect to luma coding blocks need not be repeated for chroma coding blocks. As an example, operations for identifying motion vectors (MVs) and reference pictures for luma coding blocks need not be repeated to identify MVs and reference pictures for chroma blocks. Specifically, the MVs for luma coding blocks may be scaled to determine MVs for chroma blocks, and the reference pictures may be the same. As another example, the intra prediction process may be the same for luma coding blocks and chroma coding blocks.

[0096] The video encoder 200 may represent an example of a device configured to encode video data, the device comprising: a memory configured to store the video data; and one or more processing units implemented in a circuit and configured to: determine a number of bits k for representing a decimal value of a filter coefficient of a cross-component adaptive loop filter; determine that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decode a block of the video data; and perform cross-component adaptive loop filtering on the decoded block using the filter coefficients, the filter coefficients being within the dynamic range.

[0097] Figure 3 is a block diagram illustrating an example video decoder 300 that may perform the techniques of this disclosure. Figure 3 It is provided for the purpose of explanation and does not limit the techniques generally illustrated and described in this disclosure. For the purpose of explanation, this disclosure describes the video decoder 300 according to the techniques of VVC and HEVC. However, the techniques of this disclosure can be performed by a video encoding device configured for other video encoding standards.

[0098] exist Figure 3 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 one or all of the CPB memory 320, the entropy decoding unit 302, the prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the DPB 314 may be implemented in one or more processors or in processing circuits. In addition, the video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

[0099] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include an addition unit to perform prediction according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0100] CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of video decoder 300. For example, the video bitstream may be obtained from computer readable medium 110 ( Figure 1 ) obtains video data stored in CPB memory 320. CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. In addition, CPB memory 320 may store video data other than syntax elements of encoded pictures, such as temporary data representing outputs from various units of video decoder 300. DPB 314 typically stores decoded pictures, and video decoder 300 may output decoded pictures, and / or use decoded pictures as reference video data when decoding subsequent data or pictures of the encoded video bitstream. CPB memory 320 and 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. CPB memory 320 and DPB 314 may be provided by the same memory device or a separate memory device. In various examples, CPB memory 320 may be on-chip with other components of video decoder 300, or off-chip relative to those components.

[0101] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1 ) to retrieve the encoded video data. That is, memory 120 may utilize CPB memory 320 to store data as discussed above. Likewise, when some or all of the functions of video decoder 300 are 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.

[0102] Shows Figure 3 The various units shown in FIG. 3 are used to help understand the operations performed by the video decoder 300. These units may be implemented as fixed function circuits, programmable circuits, or a combination thereof. Figure 2, fixed-function circuits refer to circuits that provide specific functions and are pre-set in the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functions in the operations that can be performed. For example, a programmable circuit can execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive parameters or output parameters), but the type of operations performed by the fixed-function circuits 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.

[0103] 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.

[0104] The entropy decoding unit 302 may receive the encoded video data from the CPB and entropy decode the video data to reproduce the syntax elements. The prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, and the filter unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.

[0105] 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 (wherein a block currently being reconstructed (ie, decoded) may be referred to as a "current block").

[0106] The entropy decoding unit 302 may entropy decode syntax elements defining the quantized transform coefficients of the quantized transform coefficient block and transform information such as a quantization parameter (QP) and / or a transform mode indication. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization, and likewise, 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.

[0107] After the inverse quantization unit 306 forms the transform coefficient block, the inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, the inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0108] In addition, prediction processing unit 304 generates a prediction block based on the prediction information syntax element entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax element indicates that the current block is inter-predicted, motion compensation unit 316 can generate a prediction block. In this case, the prediction information syntax element can indicate a reference picture in DPB 314 from which to retrieve the reference block, and a motion vector that identifies the position of the reference block in the reference picture relative to the position of the current block in the current picture. Motion compensation unit 316 can generally generate a prediction block in the same manner as described for motion compensation unit 224 ( Figure 2 )The inter-frame prediction process is performed in a manner substantially similar to that described in detail above.

[0109] As another example, if the prediction information syntax element indicates that the current block is intra-predicted, the intra-prediction unit 318 may generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Again, the intra-prediction unit 318 may generally generate a prediction block in the same manner as described with respect to the intra-prediction unit 226 ( Figure 2 ) is performed in a substantially similar manner as described in the foregoing. The intra prediction process is performed in a substantially similar manner as described in the foregoing. The intra prediction unit 318 can retrieve data of neighboring samples of the current block from the DPB 314. In one example, the unfiltered reconstructed samples without running the filter unit 312 can be stored in the DPB 314 and used for intra prediction.

[0110] The reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, the reconstruction unit 310 may reconstruct the current block by adding samples of the residual block to corresponding samples of the prediction block.

[0111] The entropy decoding unit 302 may also entropy decode cross-component adaptive loop filter (CCALF) parameters according to the techniques of the present disclosure. The entropy decoding unit 302 may provide the cross-component adaptive loop filter parameters to the filter unit 312. The filter unit 312 may perform one or more filter operations on the reconstructed block. For example, the filter unit 312 may perform a deblocking operation to reduce blocky artifacts along the edges of the reconstructed block. The operations of the filter unit 312 may not necessarily be performed in all examples. According to the techniques of the present disclosure, the filter unit 312 may use the cross-component adaptive loop filter parameters to perform cross-component adaptive loop filtering on the chroma components of the decoded blocks of the video data.

[0112] According to the techniques of the present disclosure, the entropy decoding unit 302 may entropy decode an adaptive parameter set (APS) that includes data for one or more cross-component adaptive loop filter (CCALF) filter coefficients (e.g., one or more CCALF filter coefficient sets). The entropy decoding unit 302 may also entropy decode a slice header for a slice that includes a current block, and the slice header may include one or more indexes that reference one or more CCALF filter coefficient sets that may be used to perform CCALF filtering on chroma block samples of the slice. Alternatively, the index may be included in a block header (e.g., a chroma block header, a CU header, a CTU header, or other such data structure).

[0113] Entropy decoding unit 302 may store CCALF filter coefficients to CCALF coefficient memory 322. In some examples, CCALF coefficient memory 322 may form part of the same memory including CPB memory 320. In general, CCALF coefficient memory 322 stores CCALF filter coefficients for one or more CCALFs.

[0114] In order to decode the data representing the CCALF filter coefficients, the entropy decoding unit 302 may decode the data representing the number of bits used to represent the decimal portion of the CCALF filter coefficients. For example, k may represent the number of bits used to represent the decimal portion of the CCALF filter coefficients. In addition, c may represent an offset to be applied to k. In some examples, c may be predetermined, while in other examples, the entropy decoding unit 302 may decode the data representing c, for example, in a sequence parameter set (SPS), a picture parameter set (SPS), an adaptive parameter set (APS), a slice header, a block header, or at a filter level (e.g., a value c specific to the corresponding CCALF, such as in an APS). The value k may be less than 10 and greater than 0.

[0115] The entropy decoding unit 302 and / or the filter unit 312 may use the value c and the value k to determine the dynamic range of the CCALF filter coefficient. The dynamic range may be within (-(1<<(k–c))+1,(1<<(k–c))–1), where “<<” represents a bitwise left shift operator. The entropy decoding unit 302 may entropy decode (or decode using bypass mode decoding) a fixed length codeword representing the CCALF filter coefficient. The filter unit 312 and / or the entropy decoding unit 302 may use the dynamic range to determine the value of the CCALF filter coefficient so that the value of the CCALF filter coefficient is within the dynamic range. For example, the entropy decoding unit 302 and / or the filter unit 312 may determine that the decoded value represents an offset to be added to the lower end of the range to reconstruct the actual value of the CCALF filter coefficient. The entropy decoding unit 302 may pass the decoded value or the CCALF filter coefficient to the filter unit 312, and the filter unit 312 may store the CCALF filter coefficient to the CCALF coefficient memory 322.

[0116] In addition, entropy decoding unit 302 can pass the value of one or more indices to filter unit 312, and filter unit 312 can use the indices to determine an appropriate set of CCALF filter coefficients to apply to the decoded chroma blocks of the video data. Filter unit 312 can retrieve samples of the luma block corresponding to the chroma block and apply the CCALF filter coefficients to modify the chroma block samples using the corresponding luma block samples.

[0117] The video decoder 300 may store the reconstructed and filtered blocks in the DPB 314. As discussed above, the DPB 314 may provide reference information (such as samples of the current picture for intra prediction and previously decoded pictures for subsequent motion compensation) to the prediction processing unit 304. In addition, the video decoder 300 may output decoded pictures from the DPB 314 for use in, for example, Figure 1 Subsequent presentation on a display device such as display device 118.

[0118] In this way, the video decoder 300 represents an example of a video decoding device, which includes: a memory configured to store video data; and one or more processing units implemented in a circuit and configured to: determine the number of bits k used to represent a decimal value of a filter coefficient of a cross-component adaptive loop filter; determine that for a value c, the dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decode a block of video data; and use the filter coefficients to perform cross-component adaptive loop filtering on the decoded block, the filter coefficients being within the dynamic range.

[0119] Figure 4 3 is a block diagram illustrating an example of a set of adaptive loop filters 330 including cross-component adaptive loop filters 332, 334 that can be used in accordance with the techniques of this disclosure. In particular, cross-component adaptive loop filter 332 is used for blue chrominance data, while cross-component adaptive loop filter 334 is used for red chrominance data. Figure 2 The filter unit 216 and / or Figure 3 The filter unit 312 may include Figure 4 An adaptive loop filter (ALF) set similar to or identical to the adaptive loop filter 330 of FIG.

[0120] In JVET-O0636, a tool called cross-component adaptive loop filter (CCALF) is proposed. CCALF operates as part of an adaptive loop filter (ALF) and uses luminance samples to refine each chrominance component. The tool is controlled by information in the bitstream, and the information includes filter coefficients for each chrominance component (signaled in an adaptive parameter set (APS)) and a mask that controls the block to which the filter is applied to the sample. In JVET-O0636, each filter coefficient is represented as a fixed-point decimal number. In particular, the filter coefficient uses the lower 10 bits to represent the decimal part. Exponential Golomb (EG) coding is used to signal each coefficient, and its order depends on the position of the coefficient in the filter template.

[0121] The present disclosure recognizes that the CCALF tool described in JVET-00636 may be improved and simplified, for example, in accordance with any or all of the techniques of the present disclosure. Thus, the CCALF tool may be configured in accordance with any or all of the techniques of the present disclosure (e.g., as described below, in any combination). Figure 4 Cross-component adaptive loop filters 332, 334.

[0122] According to the present disclosure, the coefficient codes may be simplified relative to the techniques of JVET-00636. In some examples, fixed length encoding may be used to signal the filter coefficients of the cross-component adaptive loop filters 332, 334. In some examples, all coefficients may be encoded as exponential Golombs (EG) with the same order value, where the order value may be fixed. Alternatively, the order value may be signaled at the sequence or APS level, and the same order value may be used to signal all filter coefficients of the cross-component adaptive loop filters 332, 334.

[0123] Alternatively, the order value may be signaled at the filter level, and the corresponding order value may be used to encode all coefficients across one of the component adaptive loop filters 332, 334. In this manner, the video encoder 200 may encode the filter coefficients across the component adaptive loop filters 332, 334 using the j-th order exponential Golomb codeword, and the video decoder 300 may decode the filter coefficients across the component adaptive loop filters 332, 334 using the j-th order exponential Golomb codeword, and the value of j may be encoded in the SPS, APS, PPS, slice header, block header, etc. Alternatively, the video encoder 200 and the video decoder 300 may be pre-configured with a value of j, or the filter coefficients across the component adaptive loop filters 332, 334 may be encoded using a fixed length encoding.

[0124] In some examples, the video encoder 200 and the video decoder 300 may encode the decimal portion of the filter coefficients of the cross-component adaptive loop filters 332 , 334 using fewer than 10 bits.

[0125] In some examples, the video encoder 200 and the video decoder 300 may be configured to constrain the dynamic range of the filter coefficients of the cross-component adaptive loop filters 332 and 334 to reduce the cost multiplier. Let k be the number of bits used to represent the decimal part of the coefficient. The dynamic range of the filter coefficients may be limited to an open interval (-(1<<(k–c))+1,(1<<(k–c))–1). In some examples, a fixed dynamic range may be applied to all coefficients, i.e., c is fixed for all coefficients of the cross-component adaptive loop filters 332 and 334. In some examples, the video encoder 200 and the video decoder 300 may encode c at the SPS, PPS, APS, or slice level, and the video encoder 200 and the video decoder 300 may apply the same value c when encoding all coefficients of the cross-component adaptive loop filters 332 and 334 in the same SPS, PPS, APS, or slice. In some examples, the video encoder 200 and the video decoder 300 may encode c at the filter level (i.e., for each of the cross-component adaptive loop filters 332, 334), and the video encoder 200 and the video decoder 300 may apply the same value c to all coefficients of a corresponding one of the cross-component adaptive loop filters 332, 334.

[0126] In some examples, the video encoder 200 and the video decoder 300 may encode an enable flag at each chroma coding tree block (CTB). If the flag of the CTB is true, the video encoder 200 and the video decoder 300 may encode a control mask for the CTB; otherwise, if the flag of the CTB is false, the video encoder 200 and the video decoder 300 do not encode a control mask for the CTB and do not apply CCALF to the CTB.

[0127] In some examples, the video encoder 200 and the video decoder 300 may use multiple CCALF filters for chroma components within a slice. The video encoder 200 and the video decoder 300 may encode the APS indices of all applied filters in a slice header of the slice. The video encoder 200 and the video decoder 300 may encode the APS index of each chroma component separately. Alternatively, all chroma components may share the same set of APS indices. Then, in the slice, for each chroma CTB in which a cross-component adaptive loop filter (CCALF) is applied, the video encoder 200 and the video decoder 300 may encode the index of the filter from those APSs (e.g., a set of filter coefficients defining the corresponding CCALF) representing the actual CCALF to be used.

[0128] In some examples, video encoder 200 and video decoder 300 may predict and encode filters of a CCALF in one APS based on another filter of a CCALF in the same APS. Video encoder 200 and video decoder 300 may encode a prediction flag to indicate whether prediction is applied.

[0129] In JVET-O636, the filter of CCALF can be signaled separately for each component, that is, a chroma component can only use the filter for the same component. According to the technology of the present disclosure, in order to remove this constraint so that the pixels of the chroma component can use any CCALF filter in the APS, the video encoder 200 and the video decoder 300 can encode the filter information (e.g., which filter / which filter coefficient set of the cross-component adaptive loop filter 332, 334) at the slice / CTB / sub-CTB level.

[0130] Figure 5 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 with respect to the video encoder 200 ( Figure 1 and 2 ), but it should be understood that other devices may be configured to perform the same Figure 5 A similar approach to the one used in this paper.

[0131] In this example, the video encoder 200 initially predicts the current block (350). For example, the video encoder 200 may form a prediction block for the current block. The video encoder 200 may then calculate a residual block for the current block (352). To calculate the residual block, the video encoder 200 may calculate the difference between the original 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).

[0132] 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 filters were 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).

[0133] In addition, video encoder 200 may encode and output (368) data representing cross-component adaptive loop filter (CCALF) filter coefficients in accordance with the techniques of this disclosure, as described above and below with respect to Figure 7 For example, the video encoder 200 may determine the dynamic range of the CCALF filter coefficients using a value k (representing the number of bits used to represent the decimal portion of the CCALF filter coefficient) and a value c (representing an offset to be applied to k), for example, using the formula (-(1<<(k–c))+1,(1<<(k–c))–1). In this example, “-(1<<(k–c))+1” represents the low end of the dynamic range, while “1<<(k–c))–1” represents the high end of the dynamic range.

[0134] In this way, Figure 5The method may represent an example of a method for decoding video data (after encoding), comprising: determining a number of bits k for representing a decimal value of a filter coefficient of a cross-component adaptive loop filter; determining that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decoding a block of video data; and performing cross-component adaptive loop filtering on the decoded block using the filter coefficients, the filter coefficients being within the dynamic range.

[0135] Figure 6 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 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] 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-frame or inter-frame prediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the reproduced coefficients (376) to create a block of quantized transform coefficients. The video decoder 300 may then inverse quantize and inverse transform the coefficients to produce a residual block (378). Finally, the video decoder 300 may decode the current block by combining the prediction block and the residual block (380).

[0137] In addition, video decoder 300 can decode and reproduce CCALF filter coefficients (382), for example, as discussed above and below with respect to Figure 8explained in more detail. For example, the video decoder 300 can determine the dynamic range of the CCALF filter coefficients using a value k (representing the number of bits used to represent the decimal portion of the CCALF filter coefficient) and a value c (representing an offset to be applied to k), for example, using the formula (-(1<<(k–c))+1,(1<<(k–c))–1). In this example, “-(1<<(k–c))+1” represents the low end of the dynamic range, while “1<<(k–c))–1” represents the high end of the dynamic range. The video decoder 300 can also use the CCALF filter coefficients (e.g., using cross-component adaptive loop filtering according to any technique of the present disclosure) to filter the decoded blocks (384). The video decoder 300 can then store the filtered blocks (386), for example, for reference when predicting future blocks to be decoded.

[0138] In this way, Figure 6 The method may represent an example of a method for decoding video data, comprising: determining a number of bits k for representing a decimal value of a filter coefficient of a cross-component adaptive loop filter; determining that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decoding a block of video data; and performing cross-component adaptive loop filtering on the decoded block using the filter coefficient, the filter coefficient being within the dynamic range.

[0139] Figure 7 is a flowchart illustrating an example method of encoding a block of video data according to the techniques of this disclosure. Figure 1 and 2 The video encoder 200 describes Figure 7 However, it should be understood that other devices may be configured to perform this method or similar methods.

[0140] The video encoder 200 may initially encode chroma blocks of video data (400). The video encoder 200 may generally perform the above-discussed Figure 5 The method is used to encode the chrominance block, such as Figure 2 Then, again as above about Figure 5 and Figure 2 As discussed above, video encoder 200 may decode chrominance blocks (402). Figure 2 As shown, the video encoder 200 also includes video decoding components, such as an inverse quantization unit 210, an inverse transform unit 212, and a reproduction unit 214, which decode the encoded blocks.

[0141] The video encoder 200 may also determine a value k and a value c of the CCALF filter coefficient (404). As explained above, the video encoder 200 may determine the value k of each CCALF filter coefficient as the number of bits representing the decimal portion of the CCALF filter coefficient value. The value c represents an offset to be applied to the value k and may be fixed for all CCALF filter coefficients of the CCALF. The value k may be less than 10 and greater than 0. In some examples, c may be predetermined, while in other examples, the video encoder 200 may encode the value c, for example, in a sequence parameter set (SPS), a picture parameter set (PPS), an adaptive parameter set (APS), a slice header, a block header, or at a filter level (e.g., together with other filter data in the APS). Similarly, the video encoder 200 may dynamically determine the value k and encode the value k as part of the video bitstream.

[0142] The video encoder 200 may then use the value k and the value c to determine the dynamic range of the CCALF filter coefficients (406). For example, the video encoder 200 may use the value k and the value c of a given CCALF filter coefficient to determine the dynamic range of the CCALF filter coefficient using the formula (-(1<<(k-c))+1,(1<<(k-c))-1), where "-(1<<(k-c))+1" represents the low end of the dynamic range and "1<<(k-c))-1" represents the high end of the dynamic range.

[0143] In addition, the video encoder 200 may determine a fixed length codeword (408) representing the value of the CCALF filter coefficient. The fixed length codeword may represent the value of the CCALF filter coefficient as the difference between the CCALF filter coefficient and the low end of the dynamic range. In addition, the fixed length codeword may be constructed so as not to include a codeword representing a CCALF filter coefficient value that exceeds the high end of the dynamic range. In addition, the video encoder 200 may encode other data for the CCALF, such as an index to one or more appropriate CCALFs in a slice header that identifies a slice that includes a chroma block or a block header of a chroma block.

[0144] In other examples, instead of using fixed length codewords, the video encoder 200 can entropy encode the CCALF filter coefficients using the jth order exponential Golomb codeword, where j can be the same for each filter coefficient. The video encoder 200 can also entropy encode the value of j, for example, in an SPS, PPS, APS, slice header, block header, or at the filter level. Alternatively, the value of j can be preconfigured.

[0145] In addition, in some examples, the video encoder 200 can predict the CCALF filter coefficients of a CCALF based on the CCALF filter coefficients of another CCALF. For example, the video encoder 200 can predict the CCALF filter coefficients of a red chroma block CCALF based on the CCALF filter coefficients of a blue chroma block, and vice versa. Additionally or alternatively, the video encoder 200 can predict the first CCALF filter coefficient set based on the second CCALF filter coefficient set, both of which are for the same chroma component (e.g., both for the blue component or both for the red component). The video encoder 200 can encode a flag indicating whether the CCALF filter coefficients of a certain CCALF filter are predicted based on another CCALF filter.

[0146] Video encoder 200 may also encode and output codewords for CCALF filter coefficients (410). In some examples, the codewords themselves may be fully encoded representations of the CCALF filter coefficients, while in other examples, the codewords may represent binarized values ​​of the CCALF filter coefficients, which video encoder 200 may also entropy encode, for example, using CABAC. Video encoder 200 may then filter the decoded chroma blocks using the set of CCALF filter coefficients (412) and store the filtered chroma blocks (414).

[0147] In this way, Figure 7 The method may represent an example of a method for decoding video data (after encoding), comprising: determining a number of bits k for representing a decimal value of a filter coefficient of a cross-component adaptive loop filter; determining that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decoding a block of video data; and performing cross-component adaptive loop filtering on the decoded block using the filter coefficients, the filter coefficients being within the dynamic range.

[0148] Figure 8 is a flowchart illustrating an example method of encoding a block of video data according to the techniques of this disclosure. Figure 1 and 3 The video decoder 300 describes Figure 8 However, it should be understood that other devices may be configured to perform this method or similar methods.

[0149] Video decoder 300 may initially decode chrominance blocks of video data (420). Video decoder 300 may generally perform the above-discussed Figure 6 Method to decode the chrominance block, such as Figure 3 Explained.

[0150] The video decoder 300 may also determine a value k and a value c of the CCALF filter coefficient (422). As explained above, the video decoder 300 may determine the value k of each CCALF filter coefficient as the number of bits representing the decimal portion of the CCALF filter coefficient value. The value c represents an offset to be applied to the value k and may be fixed for all CCALF filter coefficients of the CCALF. The value k may be less than 10 and greater than 0. In some examples, c may be predetermined, while in other examples, the video decoder 300 may decode the value c, for example, in a sequence parameter set (SPS), a picture parameter set (PPS), an adaptive parameter set (APS), a slice header, a block header, or at a filter level (e.g., together with other filter data in the APS). Similarly, the video decoder 300 may decode the value k as part of the video bitstream.

[0151] The video decoder 300 may then use the value k and the value c to determine the dynamic range of the CCALF filter coefficients (424). For example, the video decoder 300 may use the value k and the value c of a given CCALF filter coefficient to determine the dynamic range of the CCALF filter coefficient using the formula (-(1<<(k-c))+1,(1<<(k-c))-1), where "-(1<<(k-c))+1" represents the low end of the dynamic range and "1<<(k-c))-1" represents the high end of the dynamic range.

[0152] In addition, the video decoder 300 may decode (426) a fixed length codeword representing the value of the CCALF filter coefficient. The fixed length codeword may represent the value of the CCALF filter coefficient as the difference between the CCALF filter coefficient and the low end of the dynamic range. In addition, the fixed length codeword may be constructed so as not to include a codeword representing a CCALF filter coefficient value that exceeds the high end of the dynamic range. In addition, the video decoder 300 may decode other data for the CCALF, such as an index to one or more appropriate CCALFs in a slice header that identifies a slice that includes a chroma block or a block header of a chroma block.

[0153] In other examples, instead of using fixed length codewords, the video decoder 300 can entropy decode the CCALF filter coefficients using the jth order Exponential Golomb codeword, where j can be the same for each filter coefficient. The video decoder 300 can also entropy decode the value of j, for example, in the SPS, PPS, APS, slice header, block header, or at the filter level. Alternatively, the value of j can be preconfigured.

[0154] In addition, in some examples, the video decoder 300 can predict the CCALF filter coefficients of a CCALF based on the CCALF filter coefficients of another CCALF. For example, the video decoder 300 can predict the CCALF filter coefficients of a red chroma block CCALF based on the CCALF filter coefficients of a blue chroma block, and vice versa. Additionally or alternatively, the video decoder 300 can predict the first CCALF filter coefficient set based on the second CCALF filter coefficient set, both of which are for the same chroma component (e.g., both for the blue component or both for the red component). The video decoder 300 can decode a flag indicating whether the CCALF filter coefficients of a certain CCALF filter are predicted based on another CCALF filter.

[0155] Video decoder 300 may then filter the decoded chroma block using the set of CCALF filter coefficients (430) and store the filtered chroma block (432).

[0156] In this way, Figure 8 The method may represent an example of a method for decoding video data, comprising: determining a number of bits k for representing a decimal value of a filter coefficient of a cross-component adaptive loop filter; determining that for a value c, a dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1), where c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator; decoding a block of video data; and performing cross-component adaptive loop filtering on the decoded block using the filter coefficient, the filter coefficient being within the dynamic range.

[0157] Certain techniques of this disclosure are summarized in the following examples.

[0158] Example 1: A method of decoding video data, the method comprising: encoding filter coefficients of a cross-component adaptive loop filter using fixed-length codewords; decoding a block of the video data; and performing cross-component adaptive loop filtering on the decoded block using the filter coefficients.

[0159] Example 2: A method for decoding video data, the method comprising: encoding all filter coefficients of a cross-component adaptive loop filter using corresponding k-th order exponential Golomb codewords, wherein k is the same for each of the filter coefficients; decoding a block of video data; and performing cross-component adaptive loop filtering on the decoded block using the filter coefficients.

[0160] Example 3: The method of Example 2, wherein the value k is preconfigured.

[0161] Example 4: The method according to Example 2 also includes: encoding the value k.

[0162] Example 5: A method according to Example 4, wherein encoding the value k includes encoding the value k in at least one of the following: a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a slice header, a block header, or at a filter level.

[0163] Example 6: A method for decoding video data, the method comprising: encoding filter coefficients of a cross-component adaptive loop filter using a number of bits less than 10 and greater than 0 to represent decimal values ​​of the filter coefficients; decoding a block of video data; and using the filter coefficients to perform cross-component adaptive loop filtering on the decoded block.

[0164] Example 7: A method comprising a combination of the method according to any one of Examples 1-5 and the method according to Example 6.

[0165] Example 8: A method for decoding video data, the method comprising: determining the number of bits k used to represent a decimal value of a filter coefficient of a cross-component adaptive loop filter; determining that for a value c, the dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1); decoding a block of the video data; and using the filter coefficients to perform cross-component adaptive loop filtering on the decoded block.

[0166] Example 9: The method of Example 8, wherein the value c is fixed for all filter coefficients of the cross-component adaptive loop filter.

[0167] Example 10: The method according to any one of Examples 8 and 9 also includes encoding the value c in at least one of the following: a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a slice header, a block header, or at a filter level.

[0168] Example 11: A method comprising a combination of the method according to any one of Examples 1-7 and the method according to any one of Examples 8-10.

[0169] Example 12: A method for decoding video data, the method comprising: encoding a value of a cross-component adaptive loop filter enable flag for a coding tree block (CTB) of video data, the value indicating whether cross-component adaptive loop filtering is enabled for the CTB; decoding the CTB; and performing cross-component adaptive loop filtering on the decoded CTB only when the value indicates that cross-component adaptive loop filtering is enabled for the CTB.

[0170] Example 13: A method comprising a combination of the method according to any one of Examples 1-11 and the method according to Example 12.

[0171] Example 14: A method for decoding video data, the method comprising: encoding multiple filter coefficient sets for multiple cross-component adaptive loop filters in an adaptive parameter set (APS); encoding one or more indexes referencing one or more of the multiple filter coefficient sets in a slice header of a slice of the video data; decoding a block of the slice; and performing cross-component adaptive loop filtering on the decoded block using the one or more filter coefficient sets in the multiple filter coefficient sets referenced by the one or more indexes.

[0172] Example 15: A method for decoding video data, the method comprising: encoding multiple filter coefficient sets of multiple cross-component adaptive loop filters in an adaptive parameter set (APS); encoding one or more indexes referencing one or more of the multiple filter coefficient sets in a coding tree block (CTB) of the video data; decoding the CTB; and performing cross-component adaptive loop filtering on the decoded CTB using the one or more filter coefficient sets in the multiple filter coefficient sets referenced by the one or more indexes.

[0173] Example 16: A method comprising a combination of the method according to any one of Examples 1-13 and the method according to any one of Examples 14 or 15.

[0174] Example 17: A method for decoding video data, the method comprising: encoding a first set of filter coefficients for a first cross-component adaptive loop filter; encoding a second set of filter coefficients for a second cross-component adaptive loop filter, wherein encoding the second set of filter coefficients comprises: predicting one or more filter coefficients in the second set of filter coefficients based on the first set of one or more filter coefficients; decoding a block of video data; and using the second set of filter coefficients to perform cross-component adaptive loop filtering on the decoded block.

[0175] Example 18: The method according to Example 17 further includes: encoding a value of a prediction flag, wherein the prediction flag indicates that the one or more filter coefficients in the second filter coefficient set are predicted based on the first filter coefficient set.

[0176] Example 19: A method comprising a combination of the method according to any one of Examples 1-16 and the method according to any one of Examples 17 or 18.

[0177] Example 20: A method for decoding video data, the method comprising: encoding a set of filter coefficients for a cross-component adaptive loop filter; decoding a first block of a first chroma component and a second block of a second chroma component, the first chroma component being different from the second chroma component; using the set of filter coefficients to perform cross-component adaptive loop filtering on the first decoded block; and using the set of filter coefficients to perform cross-component adaptive loop filtering on the second decoded block.

[0178] Example 21: A method according to Example 20, wherein the first chrominance component includes a blue chrominance component and the second chrominance component includes a red chrominance component.

[0179] Example 22: The method according to any one of Examples 20 and 21 also includes: encoding a filter index identifying the filter coefficient set of the first decoded block; and encoding the filter index identifying the filter coefficient set of the second decoded block.

[0180] Example 23: A method according to Example 22, wherein encoding the filter index includes: encoding the filter index in a slice header, a coding tree block (CTB) header, or a sub-CTB level.

[0181] Example 24: A method comprising a combination of the method according to any one of Examples 1-19 and the method according to any one of Examples 20-23.

[0182] Example 25: The method according to any one of Examples 1-24 also includes: encoding the block or CTB before decoding the block or CTB.

[0183] Example 26: A device for encoding or decoding video data, the device comprising: one or more units for performing the method according to any one of Examples 1-25.

[0184] Example 27: The apparatus of Example 26, further comprising: a display configured to display the decoded video data.

[0185] Example 28: The device of Example 26, wherein the device comprises one or more of: a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0186] Example 29: The device according to Example 26 also includes: a memory configured to store video data.

[0187] Example 30: The device of Example 26 further comprising: a camera configured to capture video data.

[0188] Example 31: A device according to Example 26, wherein the device includes at least one of the following: an integrated circuit; a microprocessor; or a wireless communication device.

[0189] Example 32: A computer-readable storage medium having instructions stored thereon, which when executed cause a processor to perform a method according to any one of Examples 1-25.

[0190] Example 33: A device for decoding video data, the device comprising: a unit for encoding filter coefficients of a cross-component adaptive loop filter using fixed-length codewords; a unit for decoding a block of video data; and a unit for performing cross-component adaptive loop filtering on the decoded block using the filter coefficients.

[0191] Example 34: A device for decoding video data, the device comprising: a unit for encoding all filter coefficients of a cross-component adaptive loop filter using corresponding k-th order exponential Golomb codewords, wherein k is the same for each of the filter coefficients; a unit for decoding a block of video data; and a unit for performing cross-component adaptive loop filtering on the decoded block using the filter coefficients.

[0192] Example 35: A device for decoding video data, the device comprising: a unit for encoding filter coefficients of a cross-component adaptive loop filter using a number of bits less than 10 and greater than 0 to represent decimal values ​​of the filter coefficients; a unit for decoding a block of video data; and a unit for performing cross-component adaptive loop filtering on the decoded block using the filter coefficients.

[0193] Example 36: A device for decoding video data, the device comprising: a unit for determining the number of bits k used to represent the decimal value of the filter coefficient of a cross-component adaptive loop filter; a unit for determining that for a value c, the dynamic range of the filter coefficient includes (-(1<<(k–c))+1,(1<<(k–c))–1); a unit for decoding a block of video data; and a unit for using the filter coefficients to perform cross-component adaptive loop filtering on the decoded block.

[0194] Example 37: A device for decoding video data, the device comprising: a unit for encoding a value of a cross-component adaptive loop filter enable flag for a coding tree block (CTB) for video data, the value indicating whether cross-component adaptive loop filtering is enabled for the CTB; a unit for decoding the CTB; and a unit for performing cross-component adaptive loop filtering on the decoded CTB only when the value indicates that cross-component adaptive loop filtering is enabled for the CTB.

[0195] Example 38: A device for decoding video data, the device comprising: a unit for encoding multiple filter coefficient sets for multiple cross-component adaptive loop filters in an adaptive parameter set (APS); a unit for encoding one or more indexes referencing one or more of the multiple filter coefficient sets in a slice header of a slice of the video data; a unit for decoding a block of the slice; and a unit for performing cross-component adaptive loop filtering on the decoded block using the one or more filter coefficient sets in the multiple filter coefficient sets.

[0196] Example 39: A device for decoding video data, the device comprising: a unit for encoding multiple filter coefficient sets of multiple cross-component adaptive loop filters in an adaptive parameter set (APS); a unit for encoding one or more indexes referencing one or more filter coefficient sets in the multiple filter coefficient sets in a coding tree block (CTB) of the video data; a unit for decoding the CTB; and a unit for performing cross-component adaptive loop filtering on the decoded CTB using the one or more filter coefficient sets in the multiple filter coefficient sets.

[0197] Example 40: A device for decoding video data, the device comprising: a unit for encoding a first set of filter coefficients for a first cross-component adaptive loop filter; a unit for encoding a second set of filter coefficients for a second cross-component adaptive loop filter, wherein encoding the second set of filter coefficients comprises: predicting one or more filter coefficients in the second set of filter coefficients based on the first set of one or more filter coefficients; a unit for decoding a block of video data; and a unit for performing cross-component adaptive loop filtering on the decoded block using the second set of filter coefficients.

[0198] Example 41: A device for decoding video data, the device comprising: a unit for encoding a set of filter coefficients for a cross-component adaptive loop filter; a unit for decoding a first block of a first chroma component and a second block of a second chroma component, the first chroma component being different from the second chroma component; a unit for performing cross-component adaptive loop filtering on the first decoded block using the set of filter coefficients; and a unit for performing cross-component adaptive loop filtering on the second decoded block using the set of filter coefficients.

[0199] It is to be appreciated that, according to examples, certain actions or events of any of the techniques described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary to implement the techniques). In addition, in some examples, actions or events may be performed concurrently rather than sequentially, such as through multithreading, interrupt handling, or multiple processors.

[0200] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted through a computer-readable medium as one or more instructions or codes and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium corresponding to a tangible medium such as a data storage medium or a communication medium, the communication medium including, for example, any medium that facilitates the transfer of a computer program from one place to another according to a communication protocol. In this manner, a computer-readable medium may generally correspond to (1) a non-temporary tangible computer-readable storage medium, or (2) a communication medium such as a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and / or data structures for implementing the techniques described in the present disclosure. A computer program product may include a computer-readable medium.

[0201] By way of example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program codes in the form of instructions or data structures and can be accessed by a computer. In addition, any connection is appropriately referred to as a computer-readable medium. For example, if a coaxial cable, optical fiber cable, twisted pair, digital subscriber line (DSL) or wireless technology (e.g., infrared, radio and microwave) is used to transmit instructions from a website, server or other remote source, then the coaxial cable, optical fiber cable, twisted pair, DSL or wireless technology (e.g., infrared, radio and microwave) is included in the definition of the medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other temporary media, but are instead directed to non-temporary tangible storage media. As used herein, disks and optical disks include compact disks (CDs), laser optical disks, optical disks, digital versatile disks (DVDs), floppy disks and blue-ray disks, wherein disks usually copy data magnetically, while optical disks use lasers to optically copy data. Combinations of the above should also be included within the scope of computer-readable media.

[0202] 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. Therefore, 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. In addition, the techniques may be implemented entirely in one or more circuits or logic elements.

[0203] The techniques of the present disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC), or a set of ICs (e.g., a chipset). Various components, modules, or units are described in the present disclosure to emphasize the functional aspects of a device configured to perform the disclosed techniques, but do not necessarily need to be implemented by different hardware units. Specifically, as described above, the various units 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.

[0204] 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 chrominance blocks of video data; determining, for a value k and a value c, a dynamic range equal to (-(1<<(k–c))+1,(1<<(k–c))–1), where k is the number of bits used to represent a decimal value of a filter coefficient, c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator, wherein the value c is decoded from at least one of: a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a slice header, a block header, or at a filter level; decoding fixed length codewords representing filter coefficients of a cross-component adaptive loop filter to determine filter coefficients having a determined dynamic range; as well as Cross-component adaptive loop filtering is performed on the decoded chroma blocks using the filter coefficients, the filter coefficients being within the dynamic range.

2. The method according to claim 1, wherein: The value c is fixed for all filter coefficients of the cross-component adaptive loop filter.

3. The method according to claim 1, wherein: The value k is less than 10 and greater than 0.

4. The method according to claim 1, wherein: The chroma block includes a coded tree block (CTB), and the method further includes decoding a value of a cross-component adaptive loop filter enable flag for the CTB, the value indicating whether cross-component adaptive loop filtering is enabled for the CTB.

5. The method according to claim 1, further comprising: decoding a plurality of sets of filter coefficients for a plurality of cross-component adaptive loop filters in an adaptive parameter set (APS) for a slice including a current block; as well as One or more indices referencing one or more of the plurality of sets of filter coefficients are decoded in a slice header of the slice, the one or more of the plurality of sets of filter coefficients comprising the filter coefficients.

6. The method according to claim 1, further comprising: decoding a plurality of sets of filter coefficients for a plurality of cross-component adaptive loop filters in an adaptive parameter set (APS) for a slice including a current block; as well as One or more indices referencing one or more of the plurality of sets of filter coefficients are decoded in a block header of the current block, the one or more of the plurality of sets of filter coefficients comprising the filter coefficients.

7. The method according to claim 1, wherein: The cross-component adaptive loop filter includes a second cross-component adaptive loop filter, and the method further includes: decoding a first set of filter coefficients for a first cross-component adaptive loop filter; A second set of filter coefficients of the second cross-component adaptive loop filter including the filter coefficients is decoded, wherein decoding the second set of filter coefficients comprises predicting one or more filter coefficients in the second set of filter coefficients from the first set of filter coefficients.

8. The method according to claim 7, further comprising: A value of a prediction flag is encoded, the prediction flag indicating that the one or more filter coefficients in the second set of filter coefficients are predicted from the first set of filter coefficients.

9. The method according to claim 1, wherein: The chrominance block comprises a first block of a first chrominance component, the method further comprising: decoding a second block of a second chrominance component, the first chrominance component being different from the second chrominance component; and Cross-component adaptive loop filtering is performed on the second decoded block using the filter coefficients.

10. The method according to claim 9, wherein: The first chrominance component includes a blue chrominance component, and the second chrominance component includes a red chrominance component.

11. The method according to claim 1, further comprising: The chroma blocks are encoded before being decoded.

12. A device for decoding video data, the device comprising: a memory configured to store video data; as well as One or more processors implemented in circuitry and configured to: Decoding chrominance blocks of video data; determining, for a value k and a value c, a dynamic range equal to (-(1<<(k–c))+1,(1<<(k–c))–1), where k is the number of bits used to represent a decimal value of a filter coefficient, c represents an offset value relative to the value k, and “<<” represents a bitwise left shift operator, wherein the value c is decoded from at least one of: a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a slice header, a block header, or at a filter level; decoding fixed length codewords representing filter coefficients of a cross-component adaptive loop filter to determine filter coefficients having a determined dynamic range; as well as Cross-component adaptive loop filtering is performed on the decoded chroma blocks using the filter coefficients, the filter coefficients being within the dynamic range.

13. The device according to claim 12, wherein: The value k is less than 10 and greater than 0.

14. The apparatus according to claim 12, wherein: The one or more processors are further configured to: decoding a plurality of sets of filter coefficients for a plurality of cross-component adaptive loop filters in an adaptive parameter set (APS) for a slice including the current block; and One or more indices referencing one or more of the plurality of sets of filter coefficients are decoded in a slice header of the slice, the one or more of the plurality of sets of filter coefficients comprising the filter coefficients.

15. The apparatus according to claim 12, wherein: The one or more processors are further configured to encode the chroma blocks prior to decoding the chroma blocks.

16. The apparatus of claim 12, further comprising: A display configured to display the decoded video data.

17. The apparatus according to claim 12, wherein: The device also includes one or more of: a camera, a computer, or a broadcast receiver device.

18. The apparatus of claim 12, further comprising: A camera is configured to capture the video data.

19. The apparatus according to claim 12, wherein: The device further comprises at least one of the following: integrated circuit; microprocessor; or Wireless communication equipment.

20. A computer-readable storage medium having stored thereon instructions which, when executed, cause a processor to: Decoding chrominance blocks of video data; For a value k and a value c, a dynamic range equal to (-(1<<(k–c))+1,(1<<(k–c))–1) is determined, k is the number of bits used to represent the decimal value of the filter coefficient, c represents an offset value relative to the value k, and "<<" represents a bitwise left shift operator, where, The value c is decoded from at least one of: a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), a slice header, a block header, or at a filter level; decoding fixed length codewords representing filter coefficients of a cross-component adaptive loop filter to determine filter coefficients having a determined dynamic range; as well as Cross-component adaptive loop filtering is performed on the decoded chroma blocks using the filter coefficients, the filter coefficients being within the dynamic range.

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