RU2806728C2 - Equipment and method for image coding based on filtering - Google Patents

Abstract

FIELD: image encoding and decoding.

SUBSTANCE: residual samples for the current block, transform coefficients, and quantized transform coefficients are extracted. Residual information, reconstructed samples, information associated with adaptive loop filtering (ALF), and information associated with cross-component ALF (CCALF) are generated. The ALF filter coefficients for the ALF process of the reconstructed chroma samples are extracted. Filtered reconstructed samples of chrominance signals are generated based on the reconstructed samples of chrominance signals and the coefficients of the ALF filter. The coefficients of the cross-component filter are extracted. Modified filtered reconstructed samples of chrominance signals are generated based on the reconstructed samples of luminance signals, filtered reconstructed samples of chrominance signals and cross-component filter coefficients. The image information includes a sequence parameter set (SPS) including an ALF activation flag, and slice header information.

EFFECT: increased efficiency of encoding.

4 cl, 17 dwg, 30 tbl

Description

State of the art

Field of technology to which the invention relates

[1] The present disclosure relates to equipment and method for encoding images based on filtering.

Description of the Prior Art

[2] Recently, demand for high-quality, high-definition image/video, such as ultra-high-definition (UHD) image/video in 4K or 8K or higher, has been growing in various technology fields. Since the image/video data is of high resolution and high quality, the amount of information or bits that must be transmitted increases relative to the existing image/video data, and therefore, transmitting the image data using a medium such as an existing wired/wireless broadband line or existing storage media, or storing image/video data using an existing storage media increases transmission costs and storage costs.

[3] In addition, interest and demand for immersive multimedia such as virtual reality (VR) and artificial reality (AR) content or holograms has recently been increasing, and broadcasting for image/video having characteristics different from reality images , such as game images, increases.

[4] Accordingly, a high-performance image/video compression technology is required to efficiently compress, transmit, store and reproduce high-quality image/video information having various characteristics as described above.

The essence of the invention

[5] The present disclosure provides a method and equipment for improving the efficiency of image/video encoding.

[6] The present disclosure also provides a method and equipment for effectively applying filtering.

[7] The present disclosure also provides a method and equipment for efficient use of ALF.

[8] According to an embodiment of the present disclosure, a filtering process may be performed on the reconstructed chroma samples based on the reconstructed luma samples.

[9] According to an embodiment of the present disclosure, the filtered reconstructed chroma samples may be modified based on the reconstructed luma samples.

[10] According to an embodiment of the present disclosure, information regarding whether or not CCALF is available may be signaled to the SPS.

[11] According to an embodiment of the present disclosure, information regarding the values of the cross-component filter coefficients can be extracted from ALF data (normal ALF data or CCALF data).

[12] According to an embodiment of the present disclosure, APS identification information including ALF data for extracting cross-component filter coefficients in a slice may be signaled.

[13] According to an embodiment of the present disclosure, information regarding a filter bank index for a CCALF may be signaled in CTU units.

[14] According to an embodiment of the present document, a video/image decoding method performed by decoding equipment is provided.

[15] According to an embodiment of the present document, decoding equipment for performing video/image decoding is provided.

[16] According to an embodiment of the present document, a video/image encoding method carried out by encoding equipment is provided.

[17] According to an embodiment of the present document, encoding equipment for performing video/image encoding is provided.

[18] According to one embodiment of the present document, a computer-readable digital storage medium is provided on which encoded video/image information generated according to a video/image encoding method disclosed in at least one embodiment of the present document is stored.

[19] According to an embodiment of the present document, a computer-readable digital storage medium is provided on which encoded information or encoded video/image information instructing decoding equipment to perform a video/image decoding method disclosed in at least one embodiment is stored. implementation of this document.

Advantages of the invention

[20] According to an embodiment of the present document, overall image/video compression efficiency can be improved.

[21] According to an embodiment of the present document, subjective/objective visual quality can be improved through efficient filtering.

[22] According to an embodiment of the present disclosure, the ALF process can be efficiently performed, and filtering performance can be improved.

[23] According to an embodiment of the present disclosure, the reconstructed chrominance samples filtered based on the reconstructed luma samples can be modified to improve frame quality and encoding accuracy of the chroma component of the decoded frame.

[24] According to an embodiment of the present disclosure, the CCALF process can be efficiently executed.

[25] According to an embodiment of the present disclosure, ALF-related information can be efficiently transmitted in signaling signals.

[26] According to an embodiment of the present disclosure, CCALF-related information can be efficiently transmitted in overhead signals.

[27] According to an embodiment of the present disclosure, ALF and/or CCALF may be adaptively applied in units of frames, slices, and/or coding blocks.

[28] According to an embodiment of the present document, when CCALF is used in a still image or video encoding and decoding method and equipment, the filter coefficients for CCALF and the on-off transmission method in a block unit or CTU can be improved, thereby improving encoding efficiency.

Brief description of drawings

[29] FIG. 1 schematically shows an example of a video/image coding system that may be applied to embodiments of the present disclosure.

[30] FIG. 2 is a diagram schematically illustrating the configuration of video/image encoding equipment that may be applied to embodiments of the present document.

[31] FIG. 3 is a schematic diagram illustrating a configuration of video/image decoding equipment that may be applied to embodiments of the present document.

[32] FIG. 4 approximately shows the hierarchical structure for a coded image/video.

[33] FIG. 5 is a flowchart illustrating a method for recovering a block based on intra prediction in encoding equipment.

[34] FIG. 6 is a flowchart illustrating a method for recovering blocks based on intra prediction in decoding equipment.

[35] FIG. 7 is a flowchart illustrating a method for recovering blocks based on inter-prediction in encoding equipment.

[36] FIG. 8 is a flowchart illustrating a method for restoring blocks based on inter-prediction in decoding equipment.

[37] FIG. 9 shows an example of an ALF filter shape.

[38] FIG. 10 is a diagram illustrating a virtual boundary applied to a filtering process according to an embodiment of the present document.

[39] FIG. 11 illustrates an example of an ALF process using a virtual boundary according to an embodiment of the present disclosure.

[40] FIG. 12 is a diagram illustrating a cross-component adaptive loop filtering (CCALF) process according to an embodiment of the present disclosure.

[41] FIG. 13 and 14 schematically show an example of a method for encoding video/images and related components according to embodiment(s) of the present disclosure.

[42] FIG. 15 and 16 schematically show an example of a method for decoding images/videos and related components according to embodiment(s) of the present disclosure.

[43] FIG. 17 shows an example of a content streaming system to which the embodiments disclosed in the present disclosure may be applied.

Detailed Description of Embodiments

[44] The present document may be modified in various forms, and specific embodiments thereof are described and shown in the drawings. However, the embodiments are not intended to limit the present document. The terms used in the following description are used to simply describe specific embodiments, but are not intended to limit this document. The singular expression includes the plural expression as long as they are clearly interpreted differently. Terms such as “include” and “have” are intended to indicate that there are features, numbers, steps, operations, elements, components, or combinations thereof used in the following description, and as such are to be understood that the possibility of the presence or addition of one or more other features, numbers, steps, operations, elements, components or combinations of the above is not excluded.

[45] Meanwhile, each configuration in the drawings described herein is shown independently for convenience of description regarding various characteristic functions and does not mean that each configuration is implemented as separate hardware or separate software. For example, two or more components for each component may be combined to form one component, or one component may be divided into multiple components. Embodiments in which each component is integrated and/or separated are also included within the scope of this document.

[46] Hereinafter, examples of the present embodiment will be described in detail with reference to the accompanying drawings. In addition, like reference numerals are used to identify like elements throughout the drawings, and identical descriptions of like elements are omitted.

[47] This document deals with video/image coding. For example, the method/embodiment disclosed in the present disclosure is a Versatile Video Coding (VVC) standard (ITU-T Recommendation H.266), a next-generation video/image coding standard after VVC, or other video coding-related standards ( for example, it may refer to the High Efficiency Video Coding (HEVC) standard (ITU-T Recommendation H.265), the fundamental video coding (EVC) standard, the AVS2 standard, etc.).

[48] The present disclosure presents various embodiments associated with video/image encoding, and unless otherwise indicated, embodiments may be combined with each other.

[49] In the present disclosure, video may mean a collection of a sequence of images according to the passage of time. A frame generally means a unit representing one image at a particular time period, and a slice/tile is a unit that constitutes part of a frame when encoded. A slice/tile may include one or more coding tree units (CTUs). One frame can consist of one or more slices/tiles. One frame can include one or more groups of tiles. One tile group may include one or more tiles.

[50] Pixel or pel can mean the smallest unit that makes up one frame (or image). Additionally, "sample" can be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, and may represent only a pixel/pixel value of a luma component or only a pixel/pixel value of a chrominance component. Alternatively, a sample may refer to a pixel value in the spatial domain, and when such a pixel value is converted to the frequency domain, it may refer to a frequency domain conversion factor.

[51] The unit may represent a basic image processing unit. The unit may include at least one of a specific frame area and information associated with the area. One unit may include one block of luma signals and two blocks of chrominance signals (eg, Cb, Cr). Unit may be used interchangeably with terms such as block or zone in some cases. In general, an MxN block may include samples (or arrays of samples) or a set (or array) of transform coefficients of M columns and N rows. Alternatively, a sample may refer to a pixel value in the spatial domain, and when such a pixel value is converted to a frequency domain, it may refer to a frequency domain conversion factor.

[52] In the present disclosure, the terms “/” and “,” are to be interpreted to indicate “and/or.” For example, the expression "A/B" could mean "A and/or B". Additionally, "A, B" may mean "A and/or B". Additionally, "A/B/C" may mean "at least one of A, B and/or C". In addition, "A/B/C" may mean "at least one of A, B and/or C".

[53] Additionally, as used herein, the term “or” should be interpreted to indicate “and/or.” For example, the expression "A or B" may contain 1) only A, 2) only B, and/or 3) both A and B. In other words, the term "or" in this disclosure should be interpreted to indicate "in addition or alternatively ".

[54] As used herein, “at least one of A and B” may mean “A only,” “B only,” or “both A and B.” In addition, in this specification, the expression “at least one of A or B” or “at least one of A and/or B” means “at least one”. It may be interpreted identically to "at least one of A and B".

[55] Additionally, as used herein, "at least one of A, B and C" means "A only", "B only", "C only" or "A, B and C", " any combination of A, B and C." Additionally, “at least one of A, B, or C” or “at least one of A, B, and/or C” may mean “at least one of A, B, and C.”

[56] In addition, parentheses used herein may indicate "for example." In particular, when "forecasting (internal forecasting)" is specified, "internal forecasting" may be offered as an example of "forecasting". In other words, “prediction” in the present specification is not limited to “internal prediction,” and “internal prediction” may be offered as an example of “prediction.” Moreover, even when “forecasting (ie, internal forecasting)” is specified, “internal forecasting” may be offered as an example of “forecasting.”

[57] In this specification, technical features that are separately described within a single drawing may be implemented separately or simultaneously.

[58] FIG. 1 illustrates an example of a video/image coding system to which this document may be applied.

[59] Referring to FIG. 1, the video/image encoding system may include a source device and a receiving device. A source device may transmit encoded information or video/image data to a receiving device via a digital storage medium or network in the form of a file or stream.

[60] The source device may include a video source, encoding equipment, and a transmitter. The receiving device may include a receiver, decoding equipment, and a rendering module. The encoding equipment may be referred to as "video/image encoding equipment" and the decoding equipment may be referred to as "video/image decoding equipment". The transmitter may be included in the encoding equipment. The receiver may be included in the decoding equipment. The rendering module may include a display, and the display may be configured as a separate device or an external component.

[61] A video source may obtain video/image through a video/image capture, synthesis, or shaping process. The video source may include a video/image capture device and/or a video/image generation device. The video/image capturing device may include, for example, one or more cameras, video/image archives including previously captured video/images, and the like. The video/image generating apparatus may include, for example, computers, tablet computers and smartphones and may (electronically) generate video/images. For example, a virtual video/image may be generated via a computer or the like. In this case, the video/image capturing process can be replaced by the associated data generation process.

[62] Encoding equipment can encode the input video/image. Encoding hardware may perform a sequence of procedures such as prediction, transform, and quantization to achieve compression and encoding efficiency. Encoded data (encoded video/image information) may be output in the form of a bitstream.

[63] A transmitter may transmit information or encoded image/image data output in the form of a bit stream to a receiver of a receiving device via a digital storage medium or network in the form of a file or streaming. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-Ray, HDD, SSD, and the like. The transmitter may include an element for generating a multimedia file through a predefined file format and may include an element for transmission through a broadcast/communication network. The receiver may receive/extract the bit stream and transmit the received bit stream to decoding equipment.

[64] The decoding equipment may decode a video/image by performing a sequence of procedures such as dequantization, deconversion, and prediction corresponding to the operation of the encoding equipment.

[65] The rendering module may prepare a decoded video/image by rendering. The video/image prepared by rendering can be displayed through the display.

[66] FIG. 2 is a diagram schematically illustrating the configuration of video/image encoding equipment to which this document may be applied. Hereinafter in this document, what is referred to as “video encoding equipment” may include image encoding equipment.

[67] Referring to FIG. 2, the encoding equipment 200 includes an image segmentation module 210, a prediction module 220, a residual processor 230 and an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The prediction module 220 may include an inter-prediction module 221 and an internal prediction module 222. forecasting. Residual processor 230 may include a transformer 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235. Residual processor 230 may further include a subtractor 231. The adder 250 may be referred to as a “recovery module” or a “recovered block generator.” The image segmentation module 210, prediction module 220, residual processor 230, entropy encoder 240, adder 250, and filter 260 may be configured by at least one hardware component (eg, a chipset or encoder processor) according to an embodiment. In addition, storage device 270 may include a decoded frame buffer (DPB) or may be configured with a digital storage medium. The hardware component may further include a storage device 270 as an internal/external component.

[68] The image segmentation module 210 may segment an input image (either a frame or a movie frame) input to the encoding equipment 200 into one or more processing units. For example, a processing unit may be called a "coding unit (CU)". In this case, the coding unit may be recursively segmented according to a quadtree, binary tree, and ternary tree (QTBTTT) structure from a coding tree unit (CTU) or largest coding unit (LCU). For example, one coding unit may be segmented into multiple coding units of greater depth based on a quadtree structure, a binary tree structure, and/or a ternary structure. In this case, for example, a quadtree structure may be applied first, and a binary tree structure and a ternary structure may be subsequently applied. Alternatively, a binary tree structure may be used first. The encoding procedure of this document may be performed based on a final encoding unit that is no longer segmented. In this case, the largest coding unit can be used as the final coding unit based on the coding efficiency according to the characteristics of the images, or if necessary, the coding unit can be recursively segmented into coding units of greater depth, and the coding unit having the optimal size can be used as the final coding units. Here, the encoding procedure may include a prediction, transformation and reconstruction procedure, which is described below. As another example, the processing unit may further include a prediction unit (PU) or a transformation unit (TU). In this case, the prediction unit and the transformation unit may be split or segmented from the above final encoding unit. The prediction unit may be a sample prediction unit, and the transformation unit may be a unit for extracting a transformation coefficient and/or a unit for extracting a residual signal from the transformation coefficient.

[69] Unit may be used interchangeably with terms such as block or zone in some cases. In general, an MxN block can represent a set of samples or transform coefficients consisting of M columns and N rows. A sample may generally represent a pixel or a pixel value, may represent only a pixel/pixel value of a luma component, or may represent only a pixel/pixel value of a chrominance component. Sampling can be used as a term corresponding to one frame (or image) for a pixel or pel.

[70] The subtractor 231 subtracts the prediction signal (prediction block, prediction samples, or prediction sample array) output from the prediction unit 220 from the input image signal (source block, source samples, or source sample array) to obtain a remainder. A signal (a residual block, residual samples, or an array of residual samples) may be generated, and the generated residual signal is transmitted to transformer 232. Prediction module 220 may perform a prediction regarding a target processing block (hereinafter referred to as a "current block") and generate a predicted a block containing predictive samples for the current block. Prediction module 220 may determine whether intra-prediction or inter-prediction is applied based on the current block or CU. As described below in the description of each prediction mode, the prediction module may generate various prediction-related information, such as prediction mode information, and transmit the generated information to the entropy encoder 240. Information regarding the prediction may be encoded in the entropy encoder 240 and output in the form of a stream bits

[71] Intra prediction module 222 may predict the current block by reference to samples in the current frame. Samples for reference may be located in the surroundings of the current block or may be spaced according to the prediction mode. In intraprediction, prediction modes may include a plurality of non-directional modes and a plurality of directed modes. The omnidirectional mode may include, for example, DC mode and planar mode. The directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes according to the granularity of the prediction direction. However, this is merely an example; more or less directional prediction modes may be used depending on the setting. The intra prediction module 222 may determine the prediction mode applied to the current block by using the prediction mode applied to the adjacent block.

[72] The inter-prediction unit 221 can extract a predicted block for the current block based on a reference block (an array of reference samples) indicated by a motion vector for the reference frame. Here, in order to reduce the amount of motion information transmitted in the inter-prediction mode, motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between a neighboring block and the current block. The motion information may include a motion vector and a reference frame index. The motion information may further include inter-prediction direction information (L0-prediction, L1-prediction, bi-prediction, etc.). In the case of inter-prediction, the neighbor block may include a spatial neighbor block present in the current frame and a temporal neighbor block present in the reference frame. The reference frame including the reference block and the reference frame including the temporary adjacent block may be identical or different. A temporary neighbor block may be called a “co-located reference block”, a “col-located CU (colCU)”, etc., and a reference frame including a temporary neighboring block may be called a “col-located frame (colPic)”. For example, the inter-prediction module 221 may configure a list of motion information candidates based on neighboring blocks and generate information indicating which candidate is used to retrieve the motion vector and/or reference frame index of the current block. Mutual prediction can be performed based on different prediction modes. For example, in the case of the skip mode and the merge mode, the inter-prediction unit 221 may use the motion information of the adjacent block as the motion information of the current block. In the skip mode, unlike the combine mode, the residual signal may not be transmitted. In the case of the motion vector prediction (MVP) mode, the motion vector of an adjacent block may be used as a motion vector predictor, and the motion vector of the current block may be indicated by signaling a motion vector difference.

[73] The prediction module 220 may generate a prediction signal based on various prediction methods described below. For example, the prediction module may not only apply intra-prediction or inter-prediction to predict one block, but also simultaneously apply both intra-prediction and inter-prediction. This may be referred to as "combined inter-intraprediction (CIIP)". In addition, the prediction module can perform intra-block copying (IBC) to predict a block. The IBC prediction mode can be used to encode game image/video content and the like, such as screen content encoding (SCC). IBC essentially performs prediction in the current frame, but can be performed similarly to inter-prediction in which the reference block is retrieved in the current frame. Thus, the IBC may use at least one of the inter-prediction technologies described herein.

[74] The prediction signal generated by the inter prediction module 221 and/or the intra prediction module 222 can be used to generate a reconstructed signal or generate a residual signal. Converter 232 may generate conversion coefficients by applying conversion technology to the residual signal. For example, the transform technology may include discrete cosine transform (DCT), discrete sine transform (DST), Karhunen-Loeve transform (KLT), graph-based transform (GBT), or conditionally nonlinear transform (CNT). Here, GBT means a graph-derived transformation when the relationship information between pixels is represented by the graph. CNT means a transform generated based on a prediction signal generated using all previously reconstructed pixels. In addition, the conversion process can be applied to square pixel blocks that are identical in size, or can be applied to blocks that are variable in size rather than square.

[75] Quantizer 233 may quantize the transform coefficients and transmit them to entropy encoder 240, and entropy encoder 240 may encode the quantized signal (information regarding the quantized transform coefficients) and output a bit stream. Information regarding the quantized transform coefficients may be referred to as "residual information". Quantizer 233 may re-arrange the block quantized transform coefficients into one-dimensional vector form based on the scanning order of the coefficients, and generate information regarding the quantized transform coefficients based on the quantized transform coefficients in one-dimensional vector form. Information regarding conversion factors can be generated. The entropy encoder 240 may implement various encoding techniques, such as, for example, exponential Golomb coding, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and the like. Entropy encoder 240 may encode information needed to reconstruct video/images other than quantized transform coefficients (eg, syntax element values, etc.), together or separately. Encoded information (eg, encoded video/image information) may be transmitted or stored in NAL (Network Abstraction Layer) units in the form of a bit stream. The video/image information may further include information regarding various parameter sets, such as an adaptation parameter set (APS), a frame parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video/image information may further include general restriction information. Herein, the signaling/transmitted information and/or syntax elements described later in the present disclosure may be encoded through the above encoding process and included in the bitstream. The bit stream may be transmitted over a network or may be stored on a digital storage medium. The network may include a broadcast network and/or a communications network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-Ray, HDD, SSD, and the like. A transmitter (not shown) transmitting the signal output from the entropy encoder 240 and/or a storage module (not shown) storing the signal may be included as an internal/external element of the encoding equipment 200, and alternatively, the transmitter may be included in the entropy encoder 240 .

[76] The quantized transform coefficients output from quantizer 233 can be used to generate a predictive signal. For example, a residual signal (residual block or residual samples) may be reconstructed by applying dequantization and inverse transform to the quantized transform coefficients through dequantizer 234 and inverter 235. Adder 250 adds the reconstructed residual signal with the predicted signal output from prediction module 220 to generate a reconstructed signal (reconstructed frame, reconstructed samples, or array of reconstructed samples). If there is no remainder for a block to be processed, for example in a case in which the skip mode is applied, the predicted block can be used as a reconstructed block. The generated reconstructed signal can be used to internally predict the next block to be processed in the current frame, and can be used to inter-predict the next frame through filtering, as described below.

[77] Meanwhile, luma conversion with chrominance scaling (LMCS) can be applied during encoding and/or reconstruction of frames.

[78] Filter 260 may enhance the subjective/objective quality of images by applying filtering to the reconstructed signal. For example, filter 260 may generate a modified reconstructed frame by applying various filtering techniques to the reconstructed frame and store the modified reconstructed frame in storage device 270, namely, a DPB of storage device 270. Various filtering techniques may include, for example, deblocking filtering. , sampled adaptive offset (SAO) filtering, adaptive loop filter, bilateral filter, etc. The filter 260 may generate various filtering-related information and transmit the generated information to the entropy encoder 240, as described below in the description of each filtering method. Information associated with filtering may be encoded by entropy encoder 240 and output in the form of a bitstream.

[79] The modified reconstructed frame transferred to the storage device 270 can be used as a reference frame in the inter-prediction unit 221. When inter prediction is applied by the encoding equipment, prediction mismatch between the encoding equipment 200 and the decoding equipment 300 can be eliminated, and the encoding efficiency can be improved.

[80] The DPB of the storage device 270 may store the modified reconstructed frame for use as a reference frame in the inter-prediction module 221. Memory 270 may store block motion information from which motion information in the current frame is retrieved (or encoded) and/or motion information of blocks in a frame that have already been reconstructed. The stored motion information may be transmitted to the inter-prediction unit 221 and used as spatial neighbor block motion information or temporal neighbor block motion information. Memory 270 may store reconstructed samples of reconstructed blocks in the current frame and may transmit reconstructed samples to intra prediction module 222.

[81] FIG. 3 is a circuit diagram illustrating the configuration of video/image decoding equipment to which this document can be applied.

[82] Referring to FIG. 3, the decoding equipment 300 may include an entropy decoder 310, a residual processor 320, a prediction module 330, an adder 340, a filter 350, a memory 360. The prediction module 330 may include an inter-prediction module 331 and an intra-prediction module 332. Residual processor 320 may include a dequantizer 321 and an inverse converter 321. Entropy decoder 310, residual processor 320, prediction module 330, adder 340, and filter 350 may be configured by a hardware component (eg, a chipset or decoder processor) according to an embodiment. In addition, storage device 360 may include a decoded frame buffer (DPB) or may be configured with a digital storage medium. The hardware component may further include storage device 360 as an internal/external component.

[83] When a bit stream including video/image information is input, the decoding equipment 300 can reconstruct an image corresponding to the process in which the video/image information is processed in the encoding equipment of FIG. 2. For example, decoding equipment 300 may extract units/blocks based on block segmentation-related information obtained from the bitstream. The decoding equipment 300 may perform decoding using a processing unit used in the encoding equipment. Thus, the decoding processing unit, for example, may be a coding unit, and the coding unit may be segmented according to a quadtree structure, a binary tree structure, and/or a ternary tree structure from a coding tree unit or a largest coding unit. One or more transformation units may be derived from a coding unit. The reconstructed image signal decoded and output by the decoding equipment 300 can be reproduced by the playback equipment.

[84] The decoding equipment 300 may receive a signal output from the encoding equipment of FIG. 2 in the form of a bit stream, and the received signal may be decoded through entropy decoder 310. For example, entropy decoder 310 may parse the bit stream to extract information (eg, video/image information) needed for image reconstruction (or frame reconstruction). The video/image information may further include information regarding various parameter sets, such as an adaptation parameter set (APS), a frame parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video/image information may further include general restriction information. The decoding equipment may further decode the frame based on information regarding the parameter set and/or general constraint information. The signaling/receiving information and/or syntax elements described later herein may be decoded, may be decoded by a decoding procedure, and obtained from the bitstream. For example, entropy decoder 310 decodes information in a bitstream based on an encoding method, such as exponential Golomb, CAVLC, or CABAC encoding, and the output syntax elements required for image reconstruction and the quantized values of the transform coefficients for the remainder. More specifically, the entropy CABAC decoding method may receive a resolution element corresponding to each syntax element in the bitstream, determine a context model using information of a target decoding syntax element, decoding information of a target decoding block, or information of a symbol/resolution element decoded in a previous stage, and perform arithmetic decoding for the permission element by predicting the probability of occurrence of the permission element according to the determined context model and generating a symbol corresponding to the meaning of each syntactic element. In this case, the entropy CABAC decoding method can update the context model by using the decoded symbol/grant element information for the context model of the next symbol/grant element after determining the context model. Prediction-related information from the information decoded by the entropy decoder 310 may be provided to the prediction module 330, and information regarding the remainder for which entropy decoding is performed in the entropy decoder 310, i.e. quantized conversion coefficients and related parameter information may be input to the dequantizer 321. In addition, information regarding filtering from information decoded by the entropy decoder 310 may be provided to the filter 350. Meanwhile, a receiver (not shown) for receiving a signal output from the equipment encoding may be further configured as an internal/external element of the decoding equipment 300, or the receiver may be a component of the entropy decoder 310. Meanwhile, the decoding equipment herein may be referred to as “video/image/frame decoding equipment”, and the decoding equipment may classified into information decoder (video/image/frame information decoder) and sample decoder (video/image/frame sample decoder). The information decoder may include an entropy decoder 310, and the sample decoder may include at least one of a dequantizer 321, an inverter 322, a predictor 330, an adder 340, a filter 350, and a memory 360.

[85] The dequantizer 321 may dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 321 may re-arrange the quantized transform coefficients into a two-dimensional block form. In this case, re-arrangement may be performed based on the order of coefficient scanning performed in the encoding equipment. The dequantizer 321 may perform dequantization on the quantized transform coefficients by using a quantization parameter (eg, quantization step size information) and obtain the transform coefficients.

[86] The inverse converter 322 inversely converts the transform coefficients to obtain a residual signal (residual block, residual sample array).

[87] Prediction module 230 may perform prediction for the current block and may generate a predicted block including prediction samples for the current block. The prediction module may determine whether intra prediction or inter prediction is applied to the current block based on the prediction information output from the entropy decoder 310, and may determine a particular intra/inter prediction mode.

[88] The prediction module may generate a prediction signal based on various prediction methods described below. For example, the prediction module may not only apply intra-prediction or inter-prediction to predict one block, but also simultaneously apply intra-prediction and inter-prediction. This may be referred to as "combined inter-intraprediction (CIIP)". In addition, the prediction engine can perform intra-block copying (IBC). In-block copying can be used to encode game image/video content and the like, such as screen content encoding (SCC). IBC essentially performs prediction in the current frame, but can be performed similarly to inter-prediction in which the reference block is retrieved in the current frame. Thus, the IBC may use at least one of the inter-prediction technologies described herein.

[89] The intra prediction module 331 may predict the current block by reference to the samples in the current frame. Samples for reference may be located in the surroundings of the current block or may be spaced according to the prediction mode. In intraprediction, prediction modes may include a plurality of non-directional modes and a plurality of directed modes. The intra prediction unit 331 may determine the prediction mode applied to the current block by using the prediction mode applied to the adjacent block.

[90] The inter-prediction unit 332 may extract a predicted block for the current block based on a reference block (an array of reference samples) indicated by a motion vector for the reference frame. In this case, in order to reduce the amount of motion information transmitted in the inter-prediction mode, the motion information may be predicted in units of blocks, sub-blocks or samples based on the correlation of the motion information between a neighboring block and the current block. The motion information may include a motion vector and a reference frame index. The motion information may further include inter-prediction direction information (L0-prediction, L1-prediction, bi-prediction, etc.). In the case of inter-prediction, the neighbor block may include a spatial neighbor block present in the current frame and a temporal neighbor block present in the reference frame. For example, the inter-prediction module 332 may configure a motion information candidate list based on neighboring blocks and extract the current block's motion vector and/or reference frame index based on the received candidate selection information. The inter-prediction may be performed based on various prediction modes, and the information regarding the prediction may include information indicating the inter-prediction mode for the current block.

[91] The adder 340 can generate a reconstructed signal (reconstructed frame, reconstructed block, reconstructed sample array) by adding the resulting residual signal with a predicted signal (predicted block, predicted sample array) output from prediction unit 330. If there is no remainder for a block to be processed, for example when a skip mode is applied, the predicted block can be used as the reconstructed block.

[92] The adder 340 may be referred to as a “recovery module” or a “recovered block generator.” The generated reconstructed signal may be used to internally predict the next block to be processed in the current frame, may be output by filtering as described below, or may be used to inter-predict the next frame.

[93] Meanwhile, luma conversion with chrominance scaling (LMCS) can be applied in the frame decoding process.

[94] Filter 350 may enhance the subjective/objective quality of images by applying filtering to the reconstructed signal. For example, filter 350 may generate a modified reconstructed frame by applying various filtering techniques to the reconstructed frame and store the modified reconstructed frame in storage device 360, namely, a DPB of storage device 360. Various filtering techniques may include, for example, deblocking filtering. , filtering based on sampled adaptive offset, adaptive loop filter, bilateral filter, etc.

[95] The (modified) reconstructed frame stored in the DPB of the storage device 360 can be used as a reference frame in the inter-prediction unit 332. Storage device 360 may store block motion information from which motion information in the current frame is retrieved (or decoded) and/or motion information of blocks in a frame that have already been reconstructed. The stored motion information may be transmitted to the inter-prediction unit 260 so that it is used as spatial neighbor block motion information or temporal neighbor block motion information. Storage device 360 may store reconstructed samples of reconstructed blocks in the current frame and transmit the reconstructed samples to intra prediction module 331.

[96] In this detailed description, the embodiments described in prediction module 330, dequantizer 321, inverse converter 322, and filter 350 of decoding equipment 300 are prediction module 220, dequantizer 234, inverse converter 235, and filter 260 and may be used identically or in an appropriate way.

[97] As described above, when encoding video, prediction is performed in order to improve compression efficiency. Through this, a predicted block can be generated including predictive samples for the current block, which is the block to be encoded. Here, the predicted block includes predictive samples in a spatial domain (or pixel domain). The predicted block is retrieved equally from the encoding apparatus and the decoding apparatus, and the encoding apparatus decodes information (residual information) regarding the remainder between the original block and the predicted block, rather than the original sample value of the original block itself. By transmitting overhead signals to the device, the efficiency of image encoding can be improved. The decoding equipment can extract a residual block including residual samples based on the residual information, and generate a reconstructed block including the reconstructed samples by adding the residual block with the predicted block, and generate a reconstructed frame including the reconstructed blocks.

[98] Residual information can be generated through transformation and quantization processes. For example, the encoding equipment may extract a residual block between an original block and a predicted block, and perform a transform process on the residual samples (an array of residual samples) included in the residual block to extract transform coefficients, and then, by performing a quantization process on the transform coefficients, extract quantized transform coefficients to signal the residual associated information to the decoding equipment (via the bit stream). Here, the residual information may include location information, transformation technology, transformation kernel and quantization parameter, quantized transformation coefficient value information, etc. The decoding equipment may perform a dequantization/deconversion process based on the residual information and extract the residual samples (or residual blocks). The decoding equipment may generate a reconstructed frame based on the predicted block and the residual block. The encoding equipment may also dequantize/de-quantize the quantized transform coefficients for the inter-prediction reference of a later frame to extract the residual block and generate a reconstructed frame based on it.

[99] Herein, at least one of quantize/dequantize and/or transform/de-transform may be omitted. When quantization/dequantization is omitted, the quantized conversion factor may be referred to as a "transformation factor". When the transform/inverse transform is omitted, the transform coefficients may be called "coefficients" or "residual coefficients" or may still be called "transform coefficients" for consistency of expression.

[100] Herein, the quantized transform coefficient and the transform coefficient may be referred to as the “transform coefficient” and the “scaled transform coefficient,” respectively. In this case, the residual information may include information regarding the transform coefficient(s), and the information regarding the transform coefficient(s) may be signaled through a residual encoding syntax. Transform coefficients can be extracted based on residual information (or information regarding the transform coefficient(s)), and scaled transform coefficients can be extracted via inverse transform (scaling) of the transform coefficients. Residual samples can be extracted based on the inverse transform (transform) of the scaled transform coefficients. This may also be applied/expressed elsewhere in this document.

[101] The encoding equipment/decoding equipment prediction module may extract the prediction sample by performing inter-prediction in units of blocks. The inter-prediction may be a prediction derived in a manner that depends on data elements (eg, sample values or motion information, etc.) of frame(s) other than the current frame. When inter-prediction is applied to the current block, a predicted block (prediction sample array) for the current block can be retrieved based on the reference block (reference sample array) indicated by the motion vector in the reference frame indicated by the reference frame index. Here, in order to reduce the amount of motion information transmitted in the inter-prediction mode, the motion information of the current block may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between a neighboring block and the current block. The motion information may include a motion vector and a reference frame index. The motion information may further include inter-prediction type information (L0 prediction, L1 prediction, bi-prediction, etc.). In the case of inter-prediction, the neighbor block may include a spatial neighbor block present in the current frame and a temporal neighbor block present in the reference frame. The reference frame including the reference block and the reference frame including the temporary adjacent block may be identical or different. A temporary neighbor block may be called a “co-located reference block”, a “col-located CU (colCU)”, etc., and a reference frame including a temporary neighboring block may be called a “col-located frame (colPic)”. For example, a list of motion information candidates may be configured based on neighboring blocks of the current block, and flag or index information indicating which candidate is selected (used) may be signaled to retrieve a motion vector and/or reference frame index current block. Mutual prediction can be performed based on different prediction modes. For example, in the case of the skip mode and the merge mode, the motion information of the current block may be identical to the motion information of the adjacent block. In the skip mode, unlike the combine mode, the residual signal may not be transmitted. In the case of a motion vector prediction (MVP) mode, the motion vector of a selected neighboring block can be used as a motion vector predictor, and the motion vector of the current block can be signaled. In this case, the motion vector of the current block can be extracted using the sum of the motion vector predictor and the motion vector difference.

[102] The motion information may include L0 motion information and/or L1 motion information according to a type of inter-prediction (L0 prediction, L1 prediction, bi-prediction, etc.). The motion vector in the L0 direction may be referred to as the "L0 motion vector" or "MVL0", and the motion vector in the L1 direction may be referred to as the "L1 motion vector" or "MVL1". Prediction based on L0 motion vector may be referred to as “L0 prediction,” prediction based on L1 motion vector may be referred to as “L1 prediction,” and prediction based on both L0 motion vector and L1 motion vector may be referred to as “biprediction.” ". Here, the L0 motion vector may indicate a motion vector associated with a reference frame list (L0) L0, and the L1 motion vector may indicate a motion vector associated with a reference frame list (L1) L1. The reference frame list L0 may include frames that are earlier in output order than the current frame as reference frames, and the reference frame list L1 may include frames that are later in output order than the current frame. Previous frames may be referred to as "forward (reference) frames" and subsequent frames may be referred to as "reverse (reference) frames". The reference frame list L0 may further include frames that are later in the output order than the current frame as reference frames. In this case, previous frames may be indexed first in the reference frame list L0, and subsequent frames may be indexed later. The reference frame list L1 may further include previous frames in output order relative to the current frame as reference frames. In this case, subsequent frames may be indexed first in reference frame list 1, and previous frames may be indexed later. The order of output may correspond to the order of numbers in the sequence of frames (POC).

[103] FIG. 4 approximately shows the hierarchical structure for a coded image/video.

[104] Referring to FIG. 4, the encoded image/video is divided into a video coding layer (VCL) which handles the decoding process of the image/video and itself, a subsystem which transmits and stores the encoded information, and a NAL (network abstraction layer) responsible for the function and present between the VCL and subsystem.

[105] In VCL, VCL data including compressed image data (slice data) is generated, or a parameter set including a frame parameter set (PSP), a sequence parameter set (SPS) and a video parameter set (VPS) can be generated ), or an additional enhancement information (SEI) message additionally required for the image decoding process.

[106] In NAL, a NAL unit may be generated by adding header information (NAL unit header) to a primary byte sequence data (RBSP) generated in the VCL. In this case, RBSP means the slice data, parameter set, SEI message, etc. generated in the VCL. The NAL unit header may include NAL unit type information indicated according to the RBSP data included in the corresponding NAL unit.

[107] As shown in the drawing, a NAL unit can be classified into a VCL NAL unit and a non-VCL NAL unit according to the RBSP generated in the VCL. A VCL NAL unit can mean a NAL unit that includes information regarding an image (slice data) in the image, and a non-VCL NAL unit can mean a NAL unit that includes information (a set of parameters or an SEI message) required for image decoding.

[108] The above VCL NAL unit and non-VCL NAL unit can be transmitted through the network by attaching header information according to the subsystem data standard. For example, a NAL unit may be converted to a predefined standard data format, such as H.266/VVC file format, Real Time Transport Protocol (RTP), Transport Stream (TS), etc., and transmitted over various networks.

[109] As described above, a NAL unit may be indicated with a NAL unit type according to an RBSP data structure included in the corresponding NAL unit, and information regarding the NAL unit type may be stored and signaled in a NAL unit header.

[110] For example, a NAL unit can be classified into a VCL NAL unit type and a non-VCL NAL unit type according to whether or not the NAL unit includes information (slice data) regarding an image. The VCL type of a NAL unit can be classified according to the nature and type of frames included in the VCL NAL unit, and the type of a non-VCL NAL unit can be classified according to the types of parameter sets.

[111] The following is an example of a NAL unit type specified according to the type of a parameter set included in a non-VCL NAL unit type.

[112] - NAL unit APS (Adaptation Parameter Set): Type for NAL unit including APS

[113] - DPS (Decode Parameter Set) NAL unit: Type for a NAL unit including a DPS

[114] - VPS (Video Parameter Set) NAL unit: Type for the NAL unit including the VPS

[115] - SPS (Sequence Parameter Set) NAL unit: Type for a NAL unit including an SPS

[116] - NAL unit PPS (frame parameter set): Type for NAL unit including PPS

[117] - NAL unit PH (frame header): Type for NAL unit including PH

[118] The above NAL unit types may have syntax information for the NAL unit type, and the syntax information may be stored and signaled in a NAL unit header. For example, the syntax information may be nal_unit_type, and the NAL unit types may be indicated by the nal_unit_type value.

[119] Meanwhile, as described above, one frame may include a plurality of slices, and one slice may include a slice header and slice data. In this case, one frame header may further be added to multiple slices (slice header and slice data set) in one frame. The frame header (frame header syntax) may include information/parameters typically applicable to the frame. As used herein, a slice may be mixed or replaced by a group of tiles. Additionally, as used herein, the slice title may be mixed or replaced with the tile group title.

[120] The slice header (slice header syntax, slice header information) may include information/parameters that may be applied generically to the slice. APS (APS Syntax) or PPS (PPS Syntax) may include information/parameters that can be applied generically to one or more slices or frames. SPS (SPS syntax) may include information/parameters that may be applied generically to one or more sequences. VPS (VPS syntax) may include information/parameters that may be applied generically to multiple layers. DPS (DPS syntax) may include information/parameters that may be applied generally to the entire video. The DPS may include information/parameters associated with coded video sequence (CVS) concatenation. The high-level syntax (HLS) herein may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, and slice header syntax.

[121] Herein, the image/image information encoded from the encoding equipment and signaled to the decoding equipment in the form of a bitstream includes not only segmentation-related information in a frame, intra/inter-prediction information, residual information, in-loop filtering information and the like, but also information included in the slice header, information included in the APS, information included in the PPS, information included in the SPS, and/or information included in the VPS.

[122] Meanwhile, in order to compensate for the difference between the original image and the reconstructed image due to an error occurring in a compression encoding process such as quantization, an in-loop filtering process may be performed on the reconstructed samples or reconstructed frames as described above. As described above, in-loop filtering may be performed by an encoding equipment filter and a decoding equipment filter, and a deblocking filter, SAO, and/or an adaptive loop filter (ALF) may be applied. For example, the ALF process may be executed after the deblocking filtering process and/or the SAO process completes. However, even in this case, the deblocking filtering process and/or the SAO process may be omitted.

[123] Frame recovery and filtering are described in detail later in this document. When encoding images/videos, a reconstructed block may be generated based on intra prediction/inter prediction for each block, and a reconstructed frame including the reconstructed blocks may be generated. When the current frame/slice is an I-frame/slice, blocks included in the current frame/slice can only be reconstructed based on intra-prediction. Meanwhile, when the current frame/slice is a P- or B-frame/slice, blocks included in the current frame/slice can be reconstructed based on intra prediction or inter prediction. In this case, intra prediction can be applied to some blocks in the current frame/slice, and inter prediction can be applied to the remaining blocks.

[124] Intra prediction may refer to prediction that generates prediction samples for the current block based on reference samples in the frame to which the current block belongs (hereinafter referred to as the “current frame”). When intra prediction is applied to the current block, neighboring reference samples that should be used for intra prediction of the current block can be retrieved. The current block's adjacent reference samples may include samples adjacent to the left border of the current block having size nWxnH and a total of 2xnH samples bordering the bottom left, samples adjacent to the top border of the current block, and a total of 2xnW samples , bordering the top right part, and one selection bordering the top left part relative to the current block. Alternatively, the neighboring reference samples of the current block may include a plurality of top neighboring samples and a plurality of left neighboring samples. In addition, the adjacent reference samples of the current block may include a total of nH samples adjacent to the right border relative to the current block having size nWxnH, a total of nW samples adjacent to the lower border relative to the current block, and one sample adjacent to the lower right relative to current block.

[125] However, some adjacent reference samples of the current block may not yet be decoded or available. In this case, the decoder can configure adjacent reference samples to be used for prediction by substituting available samples for samples that are not available. Alternatively, neighboring reference samples to be used for prediction can be configured through interpolation of the available samples.

[126] When neighboring reference samples are retrieved, the prediction sample may be retrieved based on an average or interpolation of the current block's neighboring reference samples and (ii) a prediction from the current block's neighboring reference samples. The predictive sample may be retrieved based on a reference sample present in a particular direction (prediction) relative to the sample. Case (i) may be referred to as "non-directional mode" or "non-angular mode", and case (ii) may be referred to as "directional mode" or "angular mode". In addition, based on the prediction sample of the current block from the neighboring reference samples, the second neighboring sample located in the opposite direction to the prediction direction of the intra prediction mode of the current block and the first neighboring sample are interpolated. A predictive sample can be formed. The above case may be called "linear interpolation intraprediction (LIP)". In addition, chroma prediction samples can be generated from the luminance samples using a linear model. This case may be called "LM mode". In addition, the temporary prediction sample of the current block may be extracted based on the filtered neighboring reference samples and at least one reference sample extracted according to the intra prediction mode from the existing neighboring reference samples, i.e. the unfiltered neighboring reference samples and the temporary prediction sample can be summed with weighting to extract the current block's prediction sample. The above case may be called "position-dependent intraprediction (PDPC)". In addition, the reference sample line having the highest prediction accuracy from the adjacent multiple reference sample lines of the current block may be selected to extract the prediction sample by using the reference sample located in the prediction direction on the corresponding line, and then the reference sample line used herein , may be indicated (signalled) to the decoding equipment, thereby performing internal predictive coding. The above-described case may be called "multiple reference line (MRL) intra-prediction" or "MRL-based intra-prediction". In addition, intra-prediction can be performed based on the same intra-prediction mode by dividing the current block into vertical or horizontal sub-segments, and adjacent reference samples can be retrieved and used in a sub-segment unit. Thus, in this case, the intra-prediction mode for the current block is equally applied to the sub-segments, and the intra-prediction performance can be improved in some cases by retrieving and using adjacent reference samples in a unit of sub-segments. This forecasting method may be referred to as "internal subsegment-based (ISP) or ISP-based forecasting." The above intra prediction methods may be called "intra prediction type" separately from the intra prediction mode. The intra-prediction type may be referred to by various terms such as “intra-prediction technology” or “additional intra-prediction mode”. For example, the intra prediction type (or additional intra prediction mode) may include at least one of the above LIP, PDPC, MRL and ISP. The general intra-prediction method, excluding a specific intra-prediction type such as LIP, PDPC, MRL or ISP, may be referred to as a “normal intra-prediction type”. The normal intra prediction type can generally be applied when a specific intra prediction type is not applied, and prediction can be performed based on the intra prediction mode described above. Meanwhile, post-filtering can be performed on the predicted sample, retrieved as needed.

[127] In particular, the intra prediction procedure may include a step of determining an intra prediction mode/type, a step of retrieving neighboring reference samples, and a step of retrieving prediction samples based on the intra prediction mode/type. In addition, a post-filtering step can be performed on the predicted sample, extracted as needed.

[128] FIG. 5 is a flowchart illustrating a method for recovering a block based on intra prediction in encoding equipment. The method according to FIG. 5 may include steps S500, S510, S520, S530 and S540.

[129] S500 may be executed by the encoding equipment intra prediction unit 222, and S510 to S530 may be executed by the encoding equipment residual processor 230. Specifically, S510 may be performed by the encoding equipment subtractor 231, S520 may be performed by the encoding equipment converter 232 and quantizer 233, and S530 may be performed by the encoding equipment dequantizer 234 and inverse converter 235. At S500, prediction information may be retrieved by intra prediction unit 222 and encoded by entropy encoder 240. Residual information may be retrieved by S510 and S520 and encoded by entropy encoder 240. Residual information is information regarding residual samples. The residual information may include information regarding quantized transform coefficients for the residual samples. As described above, the residual samples can be extracted as transform coefficients through the encoding equipment transformer 232, and the transform coefficients can be extracted as quantized transform coefficients through the quantizer 2330. Information regarding the quantized transform coefficients can be encoded by the entropy encoder 240 through a residual encoding procedure.

[130] The encoding equipment performs intra prediction for the current block (S500). The encoding equipment may extract the intra prediction mode for the current block, extract adjacent reference samples of the current block, and generate prediction samples in the current block based on the intra prediction mode and the adjacent reference samples. Here, the procedures for determining the internal prediction mode, extracting peripheral reference samples, and generating prediction samples may be performed simultaneously, or one procedure may be performed before the other procedure. For example, the encoder intra prediction unit 222 may include a prediction mode/type determining unit, a reference sample extracting unit, and a prediction sample extracting unit, and the prediction mode/type determining unit may determine the intra prediction mode/type for the current block, the reference extracting unit. The samples can retrieve adjacent reference samples of the current block, and the predictive sample extractor can retrieve motion samples of the current block. Meanwhile, although not shown, when the above-described predictive sample filtering procedure is performed, the intra prediction unit 222 may further include a predictive sample filter (not shown). The encoding equipment may determine a mode applied to the current block from a plurality of intra prediction modes. The encoding hardware may compare the RD costs of the intra prediction modes and determine the optimal intra prediction mode for the current block.

[131] Meanwhile, the encoding equipment may perform a filtering procedure on the prediction samples. Filtering predictive samples can be called "post-filtering." Some or all of the predictive samples may be filtered through the predictive sample filtering procedure. In some cases, the procedure for filtering predictive samples may be omitted.

[132] The encoding equipment extracts residual samples for the current block based on the predictive samples (S510). The encoding hardware can compare the predicted samples in the original samples of the current block based on the phase and extract the residual samples.

[133] The encoding equipment may dequantize/quantize the residual samples to extract quantized transform coefficients (S520), and thereafter dequantize/dequantize the quantized transform coefficients again to extract (modified) residual samples (S530). The reason for performing dequantization/deconversion again after conversion/quantization is to extract residual samples identical to the residual samples extracted from the decoding equipment as described above.

[134] The encoding equipment may generate a reconstructed block including reconstructed samples for the current block based on the predictive samples and (modified) residual samples (S540). A reconstructed frame for the current frame may be generated based on the reconstructed block.

[135] The encoding equipment can encode image information including prediction information regarding intra prediction (eg, prediction mode information indicating a prediction mode) and residual information regarding intra and residual samples, and output the encoded image information in the form of a bit stream, as described higher. The residual information may include residual encoding syntax. The encoding hardware may transform/quantize the residual samples so as to extract the quantized transform coefficients. The residual information may include information regarding the quantized transform coefficients.

[136] FIG. 6 is a flowchart illustrating a method for recovering blocks based on intra prediction in decoding equipment. The method according to FIG. 6 may include steps S600, S610, S620, S630, and S640. The decoding equipment may perform an operation corresponding to an operation performed in the encoding equipment.

[137] S600 to S620 may be performed by the decoding equipment intra prediction unit 331, and the prediction information of S600 and residual information of S630 may be obtained from the bit stream by the entropy decoder 310 of the decoding equipment. Residual decoding equipment processor 320 may extract residual samples for the current block based on the residual information. Specifically, the dequantizer 321 of the residual processor 320 extracts transform coefficients by performing dequantization based on the quantized transform coefficients extracted based on the residual information, and the inverse transformer 322 of the residual processor may extract the residual samples for the current block by performing an inverse transform on the transform coefficients. S640 may be performed by an adder 340 or a decoding hardware recovery module.

[138] Specifically, the decoding equipment can extract the intra prediction mode for the current block based on the received prediction mode information (S600). The decoding equipment may extract peripheral reference samples of the current block (S610). The decoding equipment generates prediction samples in the current block based on the intra prediction mode and adjacent reference samples (S620). In this case, the image decoding equipment may perform a filtering procedure on the prediction samples. Filtering predictive samples can be called "post-filtering." Some or all of the predictive samples may be filtered through the predictive sample filtering procedure. In some cases, the procedure for filtering predictive samples may be omitted.

[139] The decoding equipment generates residual samples for the current block based on the received residual information (S630). The decoding equipment can generate reconstructed samples for the current block based on the predicted samples and residual samples, and extract the reconstructed block including the reconstructed samples (S640). A reconstructed frame for the current frame may be generated based on the reconstructed block.

[140] Here, the decoding equipment intra prediction unit 331 may include a prediction mode/type determining unit, a reference sample extracting unit, and a prediction sample extracting unit, and the prediction mode/type determining unit may determine the intra prediction mode for the current block based on the information prediction mode obtained by the entropy decoder 310 of the decoding equipment, the reference sample extractor may extract peripheral reference samples of the current block, and the prediction sample extractor may extract prediction samples of the current block. Meanwhile, although not shown, when the prediction sample filtering procedure described above is performed, the intra prediction unit 331 may further include a prediction sample filter (not shown).

[141] The prediction information may include intra prediction mode information and/or intra prediction type information. The intra prediction mode information may include, for example, flag information (eg, Intra_luma_mpm_flag) indicating whether the most probable mode (MPM) is applied to the current block or the remaining mode is applied, and when the MPM is applied to the current block, the mode information The prediction may further include index information (eg, intra_luma_mpm_idx) indicating one of the intra prediction mode options (MPM options). Possible options for internal prediction modes (possible MPM options) may include a list of possible MPM options or an MPM list. In addition, when MPM is not applied to the current block, the intra prediction mode information may further include remaining mode information (e.g., Intra_luma_mpm_remainder) indicating one of the remaining intra prediction modes excluding the intra prediction mode options (MPM options) . The decoding equipment may determine the intra prediction mode of the current block based on the intra prediction mode information. A separate MPM list can be configured for the above MIP.

[142] In addition, intraprediction type information may be implemented in various forms. For example, the intra-prediction type information may include intra-prediction type index information indicating one of the intra-prediction types. As another example, the intra prediction type information may include at least one of reference sample line information (e.g., Intra_luma_ref_idx) indicating whether or not the MRL is applied to the current block, and if applied, which reference sample line is used, ISP flag information (eg, Intra_subpartitions_mode_flag) indicating whether or not ISP is applied to the current block, ISP type information (eg, Intra_subpartitions_split_flag) indicating the type of subpartitioning when ISP is applied, flag information indicating whether or no PDCP, or flag information indicating whether or not LIP is applied. In addition, the intra prediction type information may include a MIP flag indicating whether or not a MIP is applied to the current block.

[143] The intra prediction mode information and/or intra prediction type information may be encoded/decoded through the encoding method described in the present disclosure. For example, intra prediction mode information and/or intra prediction type information may be encoded/decoded by entropy coding (eg, CABAC, CAVLC) based on a truncated binary code (Rice).

[144] The encoding equipment/decoding equipment prediction module can extract prediction samples by performing inter-prediction on a block-by-block basis. The inter-prediction may be a prediction derived in a manner that depends on data elements (eg, sample values or motion information) of frame(s) other than the current frame. When inter-prediction is applied to the current block, a predicted block (prediction sample array) for the current block can be retrieved based on the reference block (reference sample array) indicated by the motion vector in the reference frame indicated by the reference frame index. In this case, in order to reduce the amount of motion information transmitted in the inter-prediction mode, the motion information of the current block may be predicted in units of blocks, sub-blocks or samples based on the correlation of the motion information between a neighboring block and the current block. The motion information may include a motion vector and a reference frame index. The motion information may further include inter-prediction type information (L0 prediction, L1 prediction, bi-prediction, etc.). When mutual prediction is applied, the neighbor block may include a spatial neighbor block that is present in the current frame and a temporal neighbor block that is present in the reference frame. The reference frame including the reference block and the reference frame including the temporary adjacent block may be identical to each other or different from each other. A temporary neighbor block may be referred to by a name such as a "co-located reference block", a "co-located CU (colCU)", etc., and a reference frame including a temporary neighboring block may be called a "co-located frame ( colPic)". For example, a list of motion information candidates may be configured based on neighboring blocks of the current block, and flag or index information indicating which candidate is selected (used) to retrieve the motion vector and/or reference frame index of the current block may transmitted in service signals. Mutual prediction may be performed based on different prediction modes, and, for example, in the case of a skip mode and a merge mode, the motion information of the current block may be identical to the motion information of a neighboring block. In the case of the skip mode, the residual signal may not be transmitted, unlike the combine mode. In the case of the motion vector prediction (MVP) mode, the motion vector of the selected neighboring block is used as a motion vector predictor, and the motion vector difference may be signaled. In this case, the motion vector of the current block can be extracted using the sum of the motion vector predictor and the motion vector difference.

[145] FIG. 7 is a flowchart illustrating a method for restoring blocks based on inter-prediction in encoding equipment. The method according to FIG. 7 may include steps S700, S710, S720, S730, and S740.

[146] S700 may be executed by the encoding equipment inter-prediction unit 221, and S710 to S730 may be executed by the encoding equipment residual processor 230. Specifically, S710 may be performed by the encoding equipment subtractor 231, S720 may be performed by the encoding equipment converter 232 and quantizer 233, and S730 may be performed by the encoding equipment dequantizer 234 and inverse converter 235. At S700, prediction information may be retrieved by the inter prediction unit 221 and encoded by the entropy encoder 240. Residual information may be retrieved by S710 and S720 and encoded by the entropy encoder 240. The residual information is information regarding the residual samples. The residual information may include information regarding quantized transform coefficients for the residual samples. As described above, the residual samples can be extracted as transform coefficients through the encoding equipment transformer 232, and the transform coefficients can be extracted as quantized transform coefficients through the quantizer 233. Information regarding the quantized transform coefficients can be encoded by the entropy encoder 240 through a residual encoding procedure.

[147] The encoding equipment performs inter-prediction for the current block (S700). The encoding equipment can extract the inter-prediction mode and motion information of the current block and generate predictive samples of the current block. Here, procedures for determining the mutual prediction mode, extracting motion information, and generating prediction samples may be performed simultaneously, or one procedure may be performed before another procedure. For example, the encoding equipment inter-prediction unit 221 may include a prediction mode determining unit, a motion information extracting unit, and a prediction sample extracting unit, and a prediction mode determining unit may determine a prediction mode for the current block, a motion information extracting unit may extract motion information of the current block. , and the prediction sample extractor may extract motion samples of the current block. For example, the encoding equipment inter-prediction module 221 can search for a block similar to the current block in a predetermined area (search area) of reference frames through motion estimation, and can extract a reference block in which the difference with respect to the current block is minimal or equal to a predetermined reference value or less. Based on this, a reference frame index indicating the reference frame in which the reference block is located can be retrieved, and a motion vector can be retrieved based on the position difference between the reference block and the current block. The encoding equipment may determine a mode applied to the current block from among various prediction modes. The encoding hardware can compare the distortion cost functions as a function of the bit rate (RD) for different prediction modes and determine the optimal prediction mode for the current block.

[148] For example, when a skip mode or a merge mode is applied to a current block, the encoding equipment may construct a list of possible merge options, which is described below, and extract a reference block in which the difference with respect to the current block is minimal or equal to or less than a predetermined reference value , from the reference blocks indicated by the join options included in the list of join options. In this case, a combine candidate associated with the extracted reference block can be selected, and combine index information indicating the selected combine candidate can be generated and signaled to the decoding equipment. The motion information of the current block may be extracted using the motion information of the selected combining candidate.

[149] As another example, when the (A)MVP mode is applied to the current block, the encoding equipment constructs a list of (A)MVP candidates, which is described below, and uses the motion vector of the selected MVP candidate from the candidate predictors motion vectors (MVPs) included in the list of possible (A)MVP options as the MVP of the current block. In this case, for example, a motion vector indicating a reference block extracted by the motion estimation described above can be used as a motion vector of the current block, and a possible MVP variant having a motion vector having the smallest difference with respect to the motion vector of the current block of possible MVP options may represent the selected possible MVP option. A motion vector difference (MVD), which is a difference obtained by subtracting the MVP from the motion vector of the current block, can be extracted. In this case, information regarding the MVD may be signaled to the decoding equipment. In addition, when the (A)MVP mode is applied, the reference frame index value can be configured as reference frame index information and separately signaled to the decoding equipment.

[150] The encoding equipment may extract residual samples based on the predictive samples (S710). The encoding hardware may extract residual samples by comparing the original samples of the current block with the predicted samples.

[151] The encoding equipment transforms/quantizes the residual samples to extract quantized transform coefficients (S720), and then dequantizes/de-quantizes the quantized transform coefficients again to extract (modified) residual samples (S730). The reason for performing dequantization/deconversion again after conversion/quantization is to extract residual samples identical to the residual samples extracted from the decoding equipment as described above.

[152] The encoding equipment may generate a reconstructed block including reconstructed samples for the current block based on the predictive samples and (modified) residual samples (S740). A reconstructed frame for the current frame may be generated based on the reconstructed block.

[153] Although not shown as described above, the encoding equipment 100 can encode video information including prediction information and residual information. The encoding equipment 100 may output encoded image information in the form of a bitstream. The prediction information may be information associated with a prediction procedure and may include prediction mode information (eg, a skip flag, a merge flag, or a mode index) and motion information. The motion information may include candidate selection information (eg, a pooling index, an MVP flag, or an MVP index), which is information for extracting a motion vector. In addition, information regarding the motion information may include the above-mentioned MVD information and/or reference frame index information. In addition, information regarding the motion information may include information indicating whether L0 prediction, L1 prediction, or bi-prediction is applied. Residual information is information regarding the residual samples. The residual information may include information regarding quantized transform coefficients for the residual samples.

[154] The output bitstream may be stored on a (digital) storage medium and transmitted to the decoding equipment, or may be transmitted to the decoding equipment via a network.

[155] FIG. 8 is a flowchart illustrating a method for restoring blocks based on inter-prediction in decoding equipment. The method according to FIG. 8 may include steps S800, S810, S820, S830, and S840. The decoding equipment may perform an operation corresponding to an operation performed by the encoding equipment.

[156] S800 to S820 may be performed by the decoding equipment inter-prediction unit 332, and the prediction information of S800 and residual information of S830 may be obtained from the bitstream by the entropy decoder 310 of the decoding equipment. Residual decoding equipment processor 320 may extract residual samples for the current block based on the residual information. In particular, the dequantizer 321 of the residual processor 320 may extract transform coefficients by performing dequantization based on the quantized transform coefficients extracted based on the residual information, and the inverse transformer 322 of the residual processor may extract the residual samples for the current block by performing an inverse transform on the transform coefficients. S840 may be performed by an adder 340 or a decoding hardware recovery module.

[157] Specifically, the decoding equipment may determine a prediction mode for the current block based on the received prediction information (S800). The decoding equipment may determine which inter-prediction mode should be applied to the current block based on the prediction mode information in the prediction information.

[158] For example, it may be determined whether or not an aggregation mode is applied to the current block, or whether or not an (A)MVP mode is determined based on the aggregation flag. Alternatively, one of the various possible inter-prediction mode options may be selected based on the mode index. Options for the inter-prediction mode may include a skip mode, an aggregation mode, and/or an (A)MVP mode, or may include various inter-prediction modes, which are described below.

[159] The decoding equipment extracts motion information of the current block based on a certain inter-prediction mode. For example, when a skip mode or a combine mode is applied to a current block, the decoding equipment may configure a list of combine candidates, which is described below, and select one combine candidate from among the combine candidates included in the list of combine candidates. The selection may be made based on the above selection information (merging index). The motion information of the current block may be extracted using the motion information of the selected combining candidate. The motion information of the selected combining candidate can be used as the motion information of the current block.

[160] As another example, when the (A)MVP mode is applied to the current block, the decoding equipment may construct a list of (A)MVP candidates, which is described below, and use the motion vector of the selected MVP candidate from among the candidates motion vector predictors (MVPs) included in the list of possible (A)MVP options as the MVP of the current block. The selection may be made based on the above-described selection information (MVP flag or MVP index) described above. In this case, the MVD of the current block can be extracted based on information regarding the MVD, and the motion vector of the current block can be extracted based on the MVP of the current block and the MVD. In addition, the reference frame index of the current block may be retrieved based on the reference frame index information. The frame indicated by the reference frame index in the list of reference frames for the current block may be retrieved as a reference frame referred to for inter-prediction of the current block.

[161] Meanwhile, as described below, motion information of the current block can be retrieved without configuring the candidate list. In this case, the movement information of the current block can be retrieved according to the procedure disclosed in the prediction mode, which is described below. In this case, configuring the list of possible options as described above may be omitted.

[162] The decoding equipment may generate predictive samples for the current block based on motion information of the current block (S820). In this case, the reference frame can be retrieved based on the reference frame index of the current block, and the prediction samples of the current block can be retrieved using the samples of the reference block indicated by the motion vector of the current block in the reference frame. In this case, as described below, the prediction sample filtering procedure may further be performed on all or some of the prediction samples of the current block in some cases.

[163] For example, the decoding equipment inter-prediction unit 332 may include a prediction mode determining unit, a motion information extracting unit, and a prediction sample extracting unit, and the prediction mode determining unit may determine the prediction mode for the current block based on the received prediction mode information, module The motion information extractor may extract motion information (motion vector and/or reference frame index, etc.) of the current block based on received information regarding the motion information, and the prediction sample extractor may extract prediction samples of the current block.

[164] The decoding equipment generates residual samples for the current block based on the received residual information (S830). The decoding equipment can generate reconstructed samples for the current block based on the predicted samples and residual samples, and can extract the reconstructed block including the reconstructed samples (S840). A reconstructed frame for the current frame may be generated based on the reconstructed block.

[165] Various inter-prediction modes can be used to predict the current block in a frame. For example, various modes may be used, such as a fusion mode, a skip mode, a motion vector prediction (MVP) mode, an affine mode, a sub-block fusion mode, and a MVD fusion mode (MMVD), and the like. Decoder Motion Vector Resolution (DMVR), Adaptive Motion Vector Resolution (AMVR), Bi-Prediction with CU Weights (BCW), Bidirectional Optical Flow (BDOF), etc. can also be used as additional modes in addition to or instead. The affine mode may be called "affine motion prediction mode". The MVP mode may be referred to as "Advanced Motion Vector Prediction (AMVP) mode". Herein, some modes and/or motion information options extracted by some modes may be included as one of the motion information options of other modes. For example, an HMVP candidate may be added as a merge candidate in merge/skip mode, or may be added as an MVP candidate in MVP mode.

[166] Prediction mode information indicating the inter-prediction mode of the current block may be signaled from the encoding equipment to the decoding equipment. Prediction mode information may be included in the bit stream and received by decoding equipment. The prediction mode information may include index information indicating one of a plurality of possible mode options. Alternatively, the inter-prediction mode may be indicated via hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, a skip flag may be signaled to indicate whether or not a skip mode is applied, and if a skip mode is not applied, a merge flag may be signaled to indicate whether or not a merge mode is applied, and if a merge mode is not applied. is applied, the need to use the MVP mode is indicated, or a flag for additional classification may additionally be transmitted in service signals. The affine mode may be signaled in an independent mode or may be signaled in a mode dependent on aggregation mode or MVP mode. For example, an affine mode may include an affine union mode and an affine MVP mode.

[167] Meanwhile, information indicating whether list 0 (L0) prediction, list 1 (L1) prediction or bi-prediction described above is used in the current block (current coding unit) may be transmitted in overhead signals in the current block. The information may be called "motion prediction direction information", "inter prediction direction information" or "inter prediction indicator information" and may be configured/encoded/transmitted in signaling, for example, in the form of an inter_pred_idc syntax element. Thus, the inter_pred_idc syntax element may indicate whether or not the above list-0 (L0) prediction, list-1 (L1) prediction, or bi-prediction is used for the current block (current encoding unit). In this document, for convenience of description, the inter-prediction type (L0-prediction, L1-prediction, or bi-prediction) indicated by the inter_pred_idc syntax element may be indicated as the motion prediction direction. L0 prediction can be represented as pred_L0, L1 prediction as pred_L1, and pairwise prediction as pred_BI. For example, the following prediction types may be determined according to the value of the inter_pred_idc syntax element.

[168] Tab. 1

Name of - Name

n.a. - N/A

[169] As described above, one frame may include one or more slices. A slice may have any of the slice types including an internal (I) slice, a predictive (P) slice, and a bipredictive (B) slice. The slice type may be specified based on the slice type information. For blocks in an I-slice, inter-prediction may not be used for prediction, and only intra-prediction may be used. Of course, even in this case, the original sample value may be encoded and signaled without prediction. Intra prediction or inter prediction can be used for blocks in a P-slice, and only uni prediction can be used when inter prediction is used. Meanwhile, intra prediction or inter prediction can be used for blocks in the B-slice, and up to bi prediction can be used when inter prediction is used.

[170] L0 and L1 may include reference frames that were previously encoded/decoded before the current frame. For example, L0 may include reference frames before and/or after the current frame in POC order, and L1 may include reference frames after and/or before the current frame in POC order. In this case, L0 may be assigned a smaller reference frame index relative to previous reference frames in POC order than relative to current reference frames, and L1 may be assigned a smaller reference frame index relative to previous reference frames in POC order than relative to the current frame. In the case of a B-slice, bi-prediction can be applied, in which case, unidirectional bi-prediction can be used, or bi-directional bi-prediction can be used. Bidirectional biforecasting may be referred to as "true biforecasting."

[171] As described above, the residual block (residual samples) can be retrieved based on the predicted block (prediction samples) extracted through prediction in the encoding stage, and the residual samples are transformed/quantized by the residual information can be generated. The residual information may include information regarding the quantized transform coefficients. The residual information may be included in the video/image information, and the video/image information may be encoded and transmitted to the decoding equipment in the form of a bit stream. The decoding equipment can obtain residual information from the bitstream and can extract residual samples based on the residual information. In particular, decoding equipment can extract quantized transform coefficients based on residual information and can extract residual blocks (residual samples) through a dequantization/inverse transform process.

[172] Meanwhile, at least one process of (inverse) transformation and/or (de)-quantization may be omitted.

[173] The in-loop filtering process performed on the reconstructed frame is described later in this document. The modified reconstructed sample, block, frame (or modified filtered sample, block, frame) may be generated through an in-loop filtering process, and the modified (modified and filtered) reconstructed frame may be output as a decoded frame in the decoding equipment and may also be stored in a decoded frame buffer or a memory of the encoding/decoding equipment and used as a reference frame in the inter-prediction process during encoding/decoding of the frame subsequently. The in-loop filtering process may include a deblocking filtering process, a sampled adaptive offset (SAO) filtering process, and/or an adaptive loop filtering (ALF) process as described above. In this case, one or some of the deblocking filtering process, the sampled adaptive offset (SAO) filtering process, the adaptive loop filtering (ALF) process, and the bilateral filtering process may be sequentially applied, or all may be sequentially applied. For example, the SAO process may be executed after the deblocking filtering process is applied to the reconstructed frame. Alternatively, for example, the ALF process may be performed after the deblocking filtering process is applied to the reconstructed frame. This can also be done in encoding hardware.

[174] Deblocking filtering is a filtering technique that removes distortion at the boundaries between blocks in a reconstructed frame. The deblocking filtering process, for example, may extract a target edge from the reconstructed frame, determine a boundary intensity (bS) for the target edge, and perform deblocking filtering for the target edge based on the bS; bS may be determined based on the prediction mode, the difference of motion vectors, whether or not the reference frame is identical, whether or not a non-zero significant coefficient exists, etc., for two blocks adjacent to the target boundary.

[175] SAO is a method for compensating the offset difference between a reconstructed frame and an original frame based on samples. For example, SAO can be applied on a type basis, such as band offset, edge offset, and the like. According to SAO, samples can be classified into different categories according to each SAO type, and the bias value can be summed with each sample based on the category. The filtering information for SAO may include information regarding whether or not SAO is applied, SAO type information, and SAO offset value information. SAO can be applied to the reconstructed frame after deblocking filtering is applied.

[176] An adaptive loop filter (ALF) is a technique for filtering a reconstructed frame based on samples based on filter coefficients according to the shape of the filter. The encoding equipment can determine whether or not to apply the ALF, the ALF shape and/or the ALF filter coefficient, etc., by comparing the reconstructed frame and the original frame, and can signal it to the decoding equipment. That is, the filtering information for ALF may include information regarding whether or not ALF is applied, ALF filter shape information, ALF filter coefficient information, and the like. ALF can be applied to the reconstructed frame after deblocking filtering is applied.

[177] FIG. 9 shows an example of an ALF filter shape.

[178] In FIG. 9, (a) shows the shape of a 7x7 diamond filter, (b) shows the shape of a 5x5 diamond filter. In fig. 9, Cn in filter form represents the filter coefficient. When n in Cn is identical, this indicates that identical filter coefficients can be assigned. In the present disclosure, the position and/or unit to which the filter coefficients are assigned according to the filter shape ALF may be referred to as a "filter tap". In this case, one filter coefficient may be assigned to each filter tap, and the arrangement of the filter taps may correspond to the shape of the filter. A filter tap located in the center of the filter mold may be referred to as a "center filter tap". Identical filter coefficients may be assigned to two filter taps having an identical n value existing at positions corresponding to each other relative to the central filter tap. For example, in the case of a 7x7 diamond shape filter, 25 filter taps are turned on, and since the filter coefficients C0-C11 are assigned in a centrally symmetrical manner, the filter coefficients can be assigned to the 25 filter taps using only 13 filter coefficients. Moreover, for example, in the case of a 5x5 diamond shape filter, 13 filter taps are turned on, and since filter coefficients C0-C5 are assigned in a centrally symmetrical manner, filter coefficients are assigned to 13 filter taps using only 7 filter coefficients. For example, to reduce the amount of information data regarding filter coefficients signaled, 12 of 13 filter coefficients for a 7x7 diamond shape filter may be signaled (explicitly) and 1 filter coefficient may be (implicitly) extracted. In addition, for example, 6 of 7 filter coefficients for a 5x5 diamond shape filter may be signaled (explicitly) and 1 filter coefficient may be extracted (implicitly).

[179] According to an embodiment of the present disclosure, an ALF parameter used for an ALF process may be signaled through an adaptation parameter set (APS). The ALF parameter may be derived from the filter information or the ALF data for the ALF.

[180] ALF is a type of in-loop filtering technology that can be used in video/image encoding as described above. ALF can be performed using an adaptive Wiener filter. This may serve to minimize the mean square error (MSE) between the original samples and the decoded samples (or reconstructed samples). High-level design for an ALF tool may include syntax elements available in the SPS and/or slice header (or tile group header).

[181] In the example, before filtering for each 4x4 block of luminance signals, geometric transformations such as rotation or diagonal and vertical flipping can be applied to the filter coefficients f(k, l) depending on the gradient values computed for the block, and the corresponding cutoff values c(k, l) in the filter. This is equivalent to applying these transformations to samples in the filter media region. Creating other blocks to which ALF applies can be similar to placing those blocks according to their directionality.

[182] For example, three transformations, diagonal, vertical flip and rotation, can be performed based on the following equations.

[183] equation 1

Diagonal: f_D(k, l)=f(l, k), c_D(k, l)=c(l, k)

[184] equation 2

Vertical flip: f_V(k, l)=f(k, K-l-1), c_V(k, l)=c(k, K-l-1)

[185] equation 3

Rotation: f_R(k, l)=f(K-l-1, k), c_R(k, l)=c(K-l-1, k)

[186] In Equations 1-3, K may represent the filter size. 0≤k and 1≤K-1 can represent the coordinates of the coefficients. For example, (0, 0) may represent the upper left corner coordinate, and/or (K-1, K-1) may represent the lower right corner coordinate. The relationship between the transformations and the four gradients in the four directions can be summarized in the following table.

[187] Tab. 2

Gradient values Conversion g _d2 <g _d1 and g _h <g _v No conversion g _d2 <g _d1 and g _v <g _h Diagonal g _d1 <g _d2 and g _h <g _v Vertical inversion g _d1 <g _d2 and g _v <g _h Rotation

[188] ALF filter parameters may be signaled in the APS and slice header. In one APS, up to 25 luminance signal filter coefficients and cutoff value indices can be signaled. In one APS, up to 8 chrominance filter coefficients and cutoff value indices can be signaled. To reduce the additional number of bits, the filter coefficients of the different classifications for the luminance signal component may be combined. In the slice header, APS indices (indicated by reference by the current slice) used for the current slice may be signaled.

[189] The cutoff value indices decoded from the APS may allow the cutoff values to be determined using the cutoff value luma signal table and the cutoff value chrominance signal table. These cutoff values may depend on the internal bit depth. More specifically, the luminance signal table of the cutoff values and the chrominance signal table of the cutoff values can be extracted based on the following equations.

[190] equation 4

AlfClipL={round(2^(B(N-n+1)/N)) for n∈[1…N]}

[191] equation 5

AlfClipC={round(2^((B-8)+8((N-n))/(N-1))) for n∈[1…N]}

[192] In the above equations, B may be the internal bit depth, and N may be the number of allowed cutoff values (a predetermined number). For example, N could be 4.

[193] In the slice header, up to 7 APS indices may be signaled to indicate the luminance filter sets used for the current slice. The filtering process can additionally be controlled at the CTB level. For example, a flag indicating whether or not ALF is applied to the CTB of luma signals may be signaled. The luminance CTB can select from 16 fixed filter sets and APS filter sets. A filter bank index may be signaled for CTB luminance signals to indicate which filter bank is being applied. 16 sets of fixed filters can be preset and hard-coded in the encoder and decoder.

[194] For the chrominance component, the APS index may be signaled in the slice header to indicate the chrominance filter sets used for the current slice. At the CTB layer, when there are two or more chrominance filter banks in the APS, the filter index may be signaled for each chrominance CTB.

[195] Filter coefficients can be quantized with 128 as the norm. To limit the complexity of the multiplication, bitstream matching may be applied such that the coefficient values of the off-center position may range from 0 to 28, and/or the coefficient values of the remaining positions may range from -27 to 27-1. The center position coefficient may not be signaled in the bit stream and may be predetermined (considered) to be 128.

[196] When ALF is available for the current block, each sample R(i, j) can be filtered, and the filtered result R'(i, j) can be expressed by the following equation.

[197] equation 6

[198] In the above equation, f(k, l) may represent decoded filter coefficients, K(x, y) may represent a cutoff function, and c(k, l) may represent decoded cutoff parameters. For example, the variables k and/or l can range from -L/2 to L/2. Here, L may represent the length of the filter. The clipping function K(x, y)=min (y, max(-y, x)) can correspond to the function Clip3(-y, y, x).

[199] In an example, to reduce the ALF linear buffer requirement, modified block classification and filtering may be applied to samples adjacent to horizontal CTU boundaries. For this purpose, virtual boundaries can be specified.

[200] FIG. 10 is a diagram illustrating a virtual boundary applied to a filtering process according to an embodiment of the present document. Fig. 11 illustrates an example of an ALF process using a virtual boundary according to an embodiment of the present disclosure. Next, FIG. 11 in combination with FIG. 10.

[201] Referring to FIG. 10, the virtual boundary may be a line defined by shifting the horizontal CTU boundary by N samples. In an example, N may be equal to 4 for the luma component, and/or N may be equal to 2 for the chrominance component.

[202] In FIG. 10, the modified block classification may be applied to the luminance signal component. For one-dimensional Laplacian gradient computation of a 4x4 block on a virtual boundary, only samples above the virtual boundary can be used. Similarly, to calculate the one-dimensional Laplacian gradient of a 4x4 block below the virtual boundary, only samples below the virtual boundary can be used. The quantization of the activity A value can be scaled accordingly to account for the reduced number of samples used in the one-dimensional Laplacian gradient calculation.

[203] For the filtering process, a symmetrical padding operation on virtual boundaries can be used for the luma and chrominance signal components. Referring to FIG. 10, when a filtered sample is located below the virtual boundary, neighboring samples located above the virtual boundary may be complemented. Meanwhile, the corresponding samples on the other side can also be symmetrically complemented.

[204] The process described in FIG. 11 can also be used for slice, brick and/or tile boundaries when a filter is not available at the boundaries. To classify ALF blocks, only samples contained in an identical slice, brick and/or tile can be used, and the activity value can be scaled accordingly. For ALF filtering, symmetric padding can be applied to each of the horizontal and/or vertical directions relative to the horizontal and/or vertical boundaries.

[205] FIG. 12 is a diagram illustrating a cross-component adaptive loop filtering (CCALF) process according to an embodiment of the present document. The CCALF process may be called a "cross-component filtering process".

[206] In an aspect, an ALF process may include a general ALF process and a CCALF process. Thus, a CCALF process can mean some processes of an ALF process. In another aspect, the filtering process may include a deblocking process, an SAO process, an ALF process, and/or a CCALF process.

[207] CCALF can detail each component of the chrominance signals using sampled values of the luminance signals. The CCALF is controlled by bitstream information (images) that includes (a) information regarding filter coefficients for each chroma component and (b) information regarding a mask that controls the application of filtering to blocks of samples. The filter coefficients may be signaled in the APS, and the block size and mask may be signaled at the slice level.

[208] Referring to FIG. 12, CCALF may operate by applying a linear diamond filter ((b) of FIG. 12) to the luma signal channel for each chrominance signal component. The filter coefficients are passed to APS, scaled by a factor of 210, and rounded up for fixed-point representation. The application of the filter may be controlled at a variable block size and signaled via a context encoding flag received for blocks of each sample. The block size along with the CCALF enable flag may be received at the slice level for each chroma component. The block size (for chroma samples) can be 16x16, 32x32, 64x64, or 128x128.

[209] In the following embodiments, a method is provided for refiltering or modifying reconstructed chroma samples filtered by ALF based on the reconstructed luminance samples.

[210] An embodiment of the present disclosure relates to transmitting filtering on/off and transmitting filter coefficients to CCALF. As described above, information (syntax element) in the syntax table disclosed in the present disclosure may be included in image/video information, configured/encoded in an encoding device, and transmitted to a decoding device in the form of a bit stream. The decoding equipment can parse/decode information (syntax element) in the corresponding syntax table. The decoding equipment may perform a frame/image/video decoding process (particularly, for example, a CCALF process) based on the decoded information. This applies to other embodiments later in this document.

[211] The following table shows some syntax of slice header information according to an embodiment of the present disclosure.

[212] Tab. 3

[213] The following table shows approximate semantics for the syntactic elements included in the table above.

[214] Tab. 4

slice_cross_component_alf_cb_enabled_flag equal to 0 indicates that the cross-component Cb filter is not applied to the Cb color component; slice_cross_component_alf_cb_enabled_flag equal to 1 indicates that the cross component Cb filter is applied to the Cb color component.

slice_cross_component_alf_cr_enabled_flag equal to 0 indicates that the cross component Cr filter is not applied to the color Cr component; slice_cross_component_alf_cb_enabled_flag equal to 1 indicates that the cross component Cr filter is applied to the color Cr component.

slice_cross_component_alf_cb_reuse_temporal_layer_filter equal to 1 indicates that the coefficients of the cross-component Cb filter, with j=0...13 inclusive, are set equal to AlfCCTemporalCoeffcb[TemporalId][j].

slice_cross_component_alf_cb_reuse_temporal_layer_filter equal to 0 and slice_cross_component_alf_cb_enabled_flag equal to 1 indicate that the slice_cross_component_alf_cb_aps_id syntax element is present in the slice header.

When slice_cross_component_alf_cb_enabled_flag is 1 and slice_cross_component_alf_cb_reuse_temporal_layer_filter is 0, the elements of AlfCCTemporalCoeffcb[TemporalId][j], with j=0...13, are extracted as follows:

AlfCCTemporalCoeffcb[TemporalId][j]=AlfCCCoeffcb[slice_cross_component_alf_cb_aps_id][j]

slice_cross_component_alf_cr_reuse_temporal_layer_filter equal to 1 indicates that the coefficients of the cross-component Cr filter, with j=0...13 inclusive, are set equal to AlfCCTemporalCoeffcr[TemporalId][j].

slice_cross_component_alf_cr_reuse_temporal_layer_filter equal to 0 and slice_cross_component_alf_cr_enabled_flag equal to 1 indicate that the slice_cross_component_alf_cr_aps_id syntax element is present in the slice header.

When slice_cross_component_alf_cr_enabled_flag is 1 and slice_cross_component_alf_cr_reuse_temporal_layer_filter is 0, the elements of AlfCCTemporalCoeffcr[TemporalId][j], with j=0...13, are extracted as follows:

AlfCCTemporalCoeffcr[TemporalId][j]=AlfCCCoeffcr[slice_cross_component_alf_cr_aps_id][j]

slice_cross_component_alf_cb_aps_id specifies the adaptation_parameter_set_id referenced by the slice color Cb component for the cross component Cb filter. When slice_cross_component_alf_cb_aps_id is not present, it is logically deduced to be slice_alf_aps_id_luma[0]. The TemporalId of an ALF APS NAL unit having an adaptation_parameter_set_id equal to slice_cross_component_alf_cb_aps_id shall be less than or equal to the TemporalId of the encoded slice NAL unit.

slice_cross_component_alf_cr_aps_id specifies the adaptation_parameter_set_id referenced by the slice color Cr component for the cross component Cr filter. When slice_cross_component_alf_cr_aps_id is not present, it is logically deduced to be slice_alf_aps_id_luma[0]. The TemporalId of an ALF APS NAL unit having an adaptation_parameter_set_id equal to slice_cross_component_alf_cr_aps_id shall be less than or equal to the TemporalId of the encoded slice NAL unit.

slice_cross_component_alf_cb_log2_control_size_minus4 specifies the value of the square block sizes in the number of samples as follows:

AlfCCSamplesCbW=AlfCCSamplesCbH=2(slice_cross_component_alf_cb_log2_control_size_minus4 | 4)

slice_cross_component_alf_cb_log2_control_size_minus4 must be in the range 0-3, inclusive.

slice_cross_component_alf_cr_log2_control_size_minus4 specifies the value of the square block sizes in the number of samples as follows:

AlfCCSamplesCrW=AlfCCSamplesCrH=2 (slice_cross_component_alf_cr_log2_control_size_minus4 | 4), slice_cross_component_alf_cr_log2_control_size_minus4 must be in the range 0-3, inclusive.

[215] Referring to the above two tables, when sps_cross_component_alf_enabled_flag is equal to 1 in the slice header, slice_cross_component_alf_cb_enabled_flag parsing can be performed to determine whether or not Cb CCALF is applied in the slice. When slice_cross_component_alf_cb_enabled_flag is 1, CCALF is applied to the corresponding Cb slice, and when slice_cross_component_alf_cb_reuse_temporal_layer_filter is 1, the filter of an identical existing temporal layer can be reused. When slice_cross_component_alf_cb_enabled_flag is 0, CCALF can be applied using a filter on the corresponding adaptation parameter set (APS) identifier via slice_cross_component_alf_cb_aps_id parsing. Slice_cross_component_alf_cb_log2_control_size_minus4 may mean that CCALF applies a block unit in the Cb slice.

[216] For example, when the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 0, then whether or not CCALF is applied is determined in units of 16×16. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 1, then whether or not CCALF is applied is determined in units of 32x32. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 2, then whether CCALF is applied or not is determined in 64x64 units. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 3, then whether or not CCALF is applied is determined in units of 128x128. In addition, a structure syntax identical to the structure described above is used for Cr CCALF.

[217] The following table shows example syntax for ALF data.

[218] Tab. 5

[219] The following table shows approximate semantics for the syntactic elements included in the table above.

[220] Tab. 6

alf_luma_filter_signal_flag equal to 1 indicates that the luminance signal filter set is signaled; alf_luma_filter_signal_flag equal to 0 indicates that the luminance signal filter set is not signaled. When alf_luma_filter_signal_flag is not present, it is logically output to 0.

alf_chroma_filter_signal_flag equal to 1 indicates that a chroma filter is signaled; alf_chroma_filter_signal_flag equal to 0 indicates that the chroma filter is not signaled. When alf_chroma_filter_signal_flag is not present, it is logically output to 0.

alf_cross_component_cb_filter_signal_flag equal to 1 indicates that a set of cross-component Cb filters is transmitted in the service signals; alf_cross_component_cb_filter_signal_flag equal to 0 indicates that the cross-component Cb filter set is not signaled. When alf_cross_component_cb_filter_signal_flag is not present, it is logically output to 0.

alf_cross_component_cr_filter_signal_flag equal to 1 indicates that a set of cross-component Cr filters is transmitted in the service signals; alf_cross_component_cb_filter_signal_flag equal to 0 indicates that the cross-component Cr filter set is not signaled. When alf_cross_component_cr_filter_signal_flag is not present, it is logically output to 0.

alf_cross_component_cb_min_eg_order_minusl plus 1 specifies the minimum exponential Golomb code order for signaling cross-component Cb filter coefficients. The value of alf_cross_component_cb_min_eg_order_minus1 must be in the range 0-9, inclusive.

alf_cross_component_cr_min_eg_order_minus1 plus 1 specifies the minimum exponential Golomb code order for signaling cross-component Cr filter coefficients. The value of alf_cross_component_cb_min_eg_order_minus1 must be in the range 0-9, inclusive.

alf_cross_component_cb_eg_order_increase_flag[i] equal to 1 indicates that the minimum exponential Golomb code order for transmitting cross-component Cb filter coefficients in service signals is gradually increased by 1; alf_cross_component_cb_eg_order_increase_flag[i] equal to 0 indicates that the minimum exponential Golomb code order for signaling cross-component Cb filter coefficients is not incrementally increased by 1.

The expGoOrderCb[i] order of the exponential Golomb code used to decode the alf_cross_component_cb_coeff_abs[j] values is extracted as follows:

expGoOrdcrCb[i]=(i==0?alf_cross_component_cb_min_eg_order_minus1+1:expGoOrderCb[i-1])+alf_cross_component_cb_eg_order_increase_flag[i]

alf_cross_component_cr_eg_order_increase_flag[i] equal to 1 indicates that the minimum exponential Golomb code order for transmitting cross-component Cr filter coefficients in service signals is gradually increased by 1; alf_cross_component_cr_eg_order_increase_flag[i] equal to 0 indicates that the minimum exponential Golomb code order for signaling cross-component Cr filter coefficients is not incrementally increased by 1.

The expGoOrderCr[i] order of the exponential Golomb code used to decode the alf_cross_component_cb_coeff_abs[j] values is extracted as follows:

expGoOrderCr[i]=(i==0?alf_cross_component_cr_min_eg_order_minus1+1:expGoOrderCr [i-1])+alf_cross_component_cr_eg_order_increase_flag[i]

alf_cross_component_cb_coeff_abs[j] indicates the absolute value of the j-th coefficient transmitted in the service signals of the cross-component Cb filter. When alf_cross_component_cb_coeff_abs[j] is not present, it is logically output to 0.

The order k of exponential conversion to binary Golomb form uek(v) is extracted as follows:

golombOrderIdxCb[]={0,2,2,2,1,2,2,2,2,2,2,1,2,1} [this could represent a classification of the coefficient into 3 categories, each category using an identical exponential code Golomb order k]

k=expGoOrderCb[golombOrderIdxCb[j]]

[221] alf_cross_component_cr_coeff_abs[j] indicates the absolute value of the j-th coefficient transmitted in the service signals of the cross-component Cr filter. When alf_cross_component_cr_coeff_abs[j] is not present, it is logically output to 0.

The order k of the exponential conversion to binary Golomb form uck(v) is extracted as follows:

golombOrderIdxCr []={0,1,2,1,0,1,2,2,2,2,2,1,2,1} [this could represent a classification of the coefficient into 3 categories, each category using an identical exponential code Golomb order k]

k=expGoOrderCr [golombOrderIdxCr[j]]

alf_cross_component_cb_coeff_sign[j] specifies the sign of the j-th cross-component Cb filter coefficient as follows:

If alf_cross_component_cb_coeff_sign[j] is 0, the corresponding cross-component Cb filter coefficient has a positive value.

Otherwise (alf_cross_component_cb_coeff_sign[j] is equal to 1), the corresponding cross-component Cb filter coefficient has a negative value.

When alf_cross_component_cb_coeff_sign[j] is not present, it is logically output to 0.

The coefficients AlfCCCoeffcb[adaptation_parameter_set_id] of the cross-component Cb filter with elements AlfCCCoeffcb[adaptation_parameter_set_id][j], with j=0...13, are extracted as follows:

AlfCCCoeffcb[adaptation_parameter_set_id][j]=alf_cross_component_cb_coeff_abs[j]*(l-2*alf_cross_component_cb_coeff_sign[j])

The bitstream compliance requirement is that the values of AlfCCCoeffcb[adaptation_parameter_set_id][j], with j=0...13, must be in the range -2 ¹⁰ -1 to 2 ¹⁰ -1, inclusive.

alf_cross_component_cr_coeff_sign[j] indicates the sign of the j-th cross-component Cr filter coefficient as follows:

If alf_cross_component_cr_coeff_sign[j] is 0, the corresponding cross component Cr filter coefficient has a positive value.

Otherwise (alf_cross_componcnt_cr_coeff_sign[j] is equal to 1), the corresponding cross-component Cr filter coefficient has a negative value.

When alf_cross_component_cr_coeff_sign[j] is not present, it is logically output to 0.

The coefficients AlfCCCoeffcr[adaptation_parameter_set_id] of the cross-component Cr filter with elements AlfCCCoeffcr[adaptation_parameter_set_id][j], with j=0...13, are extracted as follows:

AlfCCCoeffcr[adaptation_parameter_set_id][j]=alf_cross_component_cr_coeff_abs[j]*(l-2*alf_cross_component_cr_coeff_sign[j])

The bitstream compliance requirement is that the values of AlfCCCoeffcr[adaptation_parameter_set_id][j], with j=0...13, must be in the range -2 ¹⁰ -1 to 2 ¹⁰ -1, inclusive.

TemporalId is the temporary identifier of the current NAL unit.

[222] Referring to the above two tables, the CCALF syntax elements do not adhere to the existing (common) ALF syntax structure, but are transmitted independently and are designed to be independently applicable. Thus, CCALF can be applied even when the ALF tool in SPS is disabled. A new hardware pipeline design is required because CCALF must be able to operate independently of the existing ALF structure. This results in increased hardware implementation costs and increased hardware latency.

[223] In addition, in ALF, whether or not images based on luma signals and chrominance signals are applied is determined in units of CTU, and the determination result is transmitted to the decoder through signaling. However, whether or not a CCALF variable is applied is determined in units of 16x16-128x128, and this application may cause a collision between the existing ALF structure and the CCALF. This causes problems in the hardware implementation and at the same time causes the linear buffers to increase for various CCALF variable applications.

[224] In the present disclosure, the above problems in a hardware implementation of CCALF are resolved by integrally applying a CCALF syntax structure to an ALF syntax structure.

[225] According to an embodiment of the present disclosure, in order to determine whether CCALF is used or not, the sequence parameter set (SPS) may include a CCALF enable flag (sps_ccalf_enable_flag). The CCALF enable flag may be sent independently of the ALF enable flag (sps_alf_enabled_flag) to determine whether ALF is used (enabled) or not.

[226] The following table shows part of the exemplary SPS syntax according to the present embodiment.

[227] Tab. 7

[228] Referring to the table above, CCALF can only be used when ALF is always running. Thus, only when the ALF enable flag (sps_alf_enabled_flag) is 1 can the CCALF enable flag (sps_ccalf_enabled_flag) be parsed. CCALF and ALF can be combined according to the table above. The CCALF enable flag may indicate (and may be associated with) whether or not CCALF is available.

[229] The following table shows some of the example syntax for slice headers.

[230] Tab. 8

[231] Referring to the above table, parsing sps_ccalf_enabled_flag can be performed only when sps_alf_enabled_flag is 1. Syntax elements included in the table can be described based on Table 4. In an example, image information encoded by an encoder or received (received) via the decoding device, may include slice header information (slice_header()). Based on the determination that the value of the CCALF enable flag (sps_ccalf_flag) is 1, the slice header information includes a first flag (slice_cross_component_alf_cb_enabeld_flag) associated with whether or not CCALF is available for the Cb color component of the filtered reconstructed chroma samples, and a second flag (slice_cross_component_alf_cr_enabeld_flag) associated with whether or not CCALF is available for the Cr color component of the filtered reconstructed chroma samples.

[232] In an example, based on determining that the value of the first flag (slice_cross_component_alf_cb_enabeld_flag) is 1, the slice header information may include identification information (slice_cross_component_alf_cb_aps_id) of the first APS for extracting cross-component filter coefficients for the Cb color component. Based on the determination that the value of the second flag (slice_cross_component_alf_cr_enabeld_flag) is 1, the slice header information may include identification information (slice_cross_component_alf_cr_aps_id) of the second APS for extracting cross-component filter coefficients for the Cr color component.

[233] The following table shows part of the SPS syntax according to another example of the present embodiment.

[234] Tab. 9

[235] The following table roughly shows some of the slice header syntax.

[236] Tab. 10

[237] Referring to Table 9, when ChromaArrayType is not equal to 0 and the ALF enable flag (sps_alf_enabled_flag) is equal to 1, the SPS may include a CCALF enable flag (sps_ccalf_enabled_flag). For example, if ChromaArrayType is not 0, the format of the chroma signals may not be monochrome, and the CCALF enable flag may be transmitted through the SPS based on the case in which the format of the chroma signals is not monochrome.

[238] Referring to Table 9, based on the case in which ChromaArrayType is not 0, information regarding CCALF (slice_cross_component_alf_cb_enabled_flag, slice_cross_component_alf_cb_aps_id, slice_cross_component_alf_cr_enabled_flag, slice_cross_component_alf_cr) may be included in the slice header information.

[239] In an example, image information encoded by an encoding apparatus or obtained by a decoding apparatus may include an SPS. The SPS may include a first ALF enable flag (sps_alf_enabled_flag) associated with whether ALF is enabled or not. For example, based on determining that the value of the first ALF enable flag is 1, the SPS may include a CCALF enable flag associated with whether cross-component filtering is available or not. In another example, if sps_ccalf_enabled_flag is not used and sps_alf_enabled_flag is 1, CCALF can always be applied (sps_ccalf_enabled_flag==1).

[240] The following table shows part of the slice header syntax according to another example of this embodiment.

[241] Tab. eleven

[242] Referring to the table above, parsing of the CCALF enable flag (sps_ccalf_enabled_flag) can only be performed when the ALF enable flag (sps_alf_enabled_flag) is 1.

[243] The following table shows approximate semantics for the syntactic elements included in the table above.

[244] Tab. 12

slice_ccalf_enabled_flag equal to 1 indicates that the cross-component adaptive contour filter is enabled and can be applied to the Cb or Cr color component in the slice; slice_ccalf_enabled_flag equal to 0 indicates that the cross-component adaptive edge filter is disabled for all color components in the slice.

slice_ccalf_chroma_idc equal to 0 indicates that the cross-component adaptive contour filter is not applied to the Cb and Cr chroma components; slice_ccalf_chroma_idc equal to 1 indicates that a cross-component adaptive edge filter is applied to the Cb chroma component; slice_ccalf_chroma_idc equal to 2 indicates that a cross-component adaptive edge filter is applied to the Cr color component; slice_ccalf_chroma_idc equal to 3 indicates that a cross-component adaptive contour filter is applied to the Cb and Cr chroma components. When slice_ccalf_chroma_idc is not present, it is inferred to be 0.

slice_ccalf_aps_id_chroma indicates the adaptation_parameter_set_id CCALF APS referenced by the slice chroma signal component. The TemporalId of an APS NAL unit having an aps_params_type equal to CC_ALF_APS and an adaptation_parameter_set_id equal to slice_ccalf_aps_id_chroma shall be less than or equal to the TemporalId of the encoded slice NAL unit.

For internal slices and slices in an IRAP frame, slice_ccalf_aps_id_chroma shall not refer to a CCALF APS associated with frames other than the frame containing the internal slices or the IRAP frame.

[245] slice_ccalf_chroma_idc of the table above can be described by the semantics of the table below.

[246] Tab. 13

slice_ccalf_chroma_idc equal to 0 indicates that a cross-component adaptive edge filter is applied to the Cb chroma component; slice_ccalf_chroma_idc equal to 1 indicates that a cross-component adaptive edge filter is applied to the Cr color component; slice_ccalf_chroma_idc equal to 2 indicates that a cross-component adaptive edge filter is applied to the Cb and Cr chroma components. When slice_ccalf_chroma_idc is not present, it is inferred to be 0.

[247] The following table shows part of the slice header syntax according to another example of this embodiment.

[248] Tab. 14

[249] The syntax elements included in the table may be described according to Table 12 or Table 13. In addition, when the chrominance signal format is not monochrome, CCALF-related information may be included in the slice header.

[250] The following table shows part of the slice header syntax according to another example of this embodiment.

[251] Tab. 15

[252] The following table shows approximate semantics for the syntactic elements included in the table above.

[253] Tab. 16

slice_ccalf_chroma_idc equal to 0 indicates that the cross-component adaptive contour filter is not applied to the Cb and Cr chroma components; slice_ccalf_chroma_idc equal to 1 indicates that a cross-component adaptive edge filter is applied to the Cb chroma component; slice_ccalf_chroma_idc equal to 2 indicates that a cross-component adaptive edge filter is applied to the Cr color component; slice_ccalf_chroma_idc equal to 3 indicates that a cross-component adaptive contour filter is applied to the Cb and Cr chroma components. When slice_ccalf_chroma_idc is not present, it is inferred to be 0.

slice_ccalf_aps_id_chroma indicates the adaptation_paramctcr_sct_id CCALF APS referenced by the slice chroma signal component. The TemporalId of an APS NAL unit having an aps_params_type equal to CC_ALF_APS and an adaptation_parameter_set_id equal to slice_ccalf_aps_id_chroma shall be less than or equal to the TemporalId of the encoded slice NAL unit.

For internal slices and slices in an IRAP frame, slice_ccalf_aps_id_chroma shall not refer to a CCALF APS associated with frames other than the frame containing the internal slices or the IRAP frame.

[254] The following table shows part of the slice header syntax according to another example of this embodiment. The syntax elements included in the following table may be described according to Table 12 or Table 13.

[255] Tab. 17

[256] Referring to the above table, whether or not ALF and CCALF are applied based on slice units can be determined directly via slice_alf_enabled_flag. After slice_alf_chroma_idc is parsed, when the first ALF enable flag (sps_alf_enabled_flag) is 1, slice_ccalf_chroma_idc can be parsed.

[257] Referring to the above table, whether sps_ccalf_enabeld_flag is equal to 1 in the slice header information can only be determined when slice_alf_enabled_flag is equal to 1. The slice header information may include a second ALF enable flag (slice_alf_enabled_flag) associated with ALF is available or not. Based on the determination that the value of the second ALF enable flag (slice_alf_enabled_flag) is 1, CCALF can be sliced enabled.

[258] The following table roughly shows some of the APS syntax. The adaptation_parameter_set_id syntax element may indicate APS identifier information.

[259] Tab. 18

[260] The following table shows example syntax for ALF data.

[261] Tab. 19

[262] Referring to the above two tables, the APS may include ALF data (alf_data). An APS including ALF data may be referred to as "ALF APS" ("ALF-type APS"). Thus, an APS type including ALF data may be an ALF type. The APS type may be specified as information regarding an APS type or a syntax element (aps_params_type). The ALF data may include a Cb filter signal transmission flag (alf_cross_component_cb_filter_signal_flag or alf_cc_cb_filter_signal_flag) associated with whether or not cross component filters for the Cb color component are signaled. The ALF data may include a Cr filter signaling flag (alf_cross_component_cr_filter_signal_flag or alf_cc_cr_filter_signal_flag) associated with whether or not cross component filters for the Cr color component are signaled.

[263] In an example, based on the transmit flag in the Cr filter overhead signals, the ALF data may include information (alf_cross_component_cr_coeff_abs) regarding the absolute values of the cross component filter coefficients for the Cr color component and sign information (alf_cross_component_cr_coeff_sign) regarding the signs of the cross component coefficients filter for the Cr color component. Based on information regarding the absolute values of the cross-component filter coefficients for the Cr color component and information regarding the signs of the cross-component filter coefficients for the Cr color component, the cross-component filter coefficients for the Cr color component can be extracted.

[264] In an example, the ALF data may include information (alf_cross_component_cb_coeff_abs) regarding the absolute values of the cross-component filter coefficients for the Cb color component and information (alf_cross_component_cb_coeff_sign) regarding the signs of the cross-component filter coefficients for the Cb color component. Based on information regarding the absolute values of the cross-component filter coefficients for the Cb color component and information regarding the signs of the cross-component filter coefficients for the Cb color component, the cross-component filter coefficients for the Cb color component can be extracted.

[265] The following table shows the syntax associated with ALF data according to another example.

[266] Tab. 20

[267] Referring to the above table, after transmitting the alf_cross_component_filter_signal_flag first, when the alf_cross_component_filter_signal_flag is 1, the transmission flag in the Cb/Cr filter overhead signals can be transmitted. Thus, alf_cross_component_filter_signal_flag integrates Cb/Cr to determine whether or not the CCALF filter coefficients should be transmitted.

[268] The following table shows the syntax associated with ALF data according to another example.

[269] Tab. 21

[270] The following table shows approximate semantics for the syntactic elements included in the table above.

[271] Tab. 22

alf_cross_component_cb_filter_signal_flag equal to 1 indicates that a set of cross-component Cb filters is transmitted in the service signals; alf_cross_component_cb_filter_signal_flag equal to 0 indicates that the cross-component Cb filter set is not signaled. When alf_cross_component_cb_filter_signal_flag is not present, it is logically output to 0.

alf_cross_component_cr_filter_signal_flag equal to 1 indicates that a set of cross-component Cr filters is transmitted in the service signals; alf_cross_component_cr_filler_signal_nag equal to 0 indicates that the set of cross-component Cr filters is not transmitted in service signals. When alf_cross_component_cr_filter_signal_flag is not present, it is logically output to 0.

alf_cross_component_cb_coeff_abs[j] indicates the absolute value of the j-th coefficient transmitted in the service signals of the cross-component Cb filter. When alf_cross_component_cb_coeff_abs[j] is not present, it is logically output to 0.

The order k of the exponential transformation uek(v) into binary Golomb form is set to 3.

alf_cross_component_cb_coeff_sign[j] specifies the sign of the j-th cross-component Cb filter coefficient as follows:

If alf_cross_componcnt_cb_cocff_sign[j] is 0, the corresponding cross-component Cb filter coefficient has a positive value.

Otherwise (alf_cross_component_cb_coeff_sign[j] is equal to 1), the corresponding cross-component Cb filter coefficient has a negative value.

When alf_cross_component_cb_coeff_sign[j] is not present, it is logically output to 0.

The coefficients AlfCCCoeffCb[adaptation_paramctcr_set_id] of the cross-component Cb filter with elements AlfCCCoeffCb[adaptation_parameter_set_id][j], with j=0...13, are extracted as follows:

AlfCCCoeffCb[adaplation_parameter_set_id][j]=alf_cross_component_cb_coeff_abs[j]*(l-2*alf_cross_component_cb_coeff_sign[j])

The bitstream compliance requirement is that the values of AlfCCCoeffCb[adaptation_parameter_set_id][j], with j=0...13, must be in the range -2 ¹⁰ -1 to 2 ¹⁰ -1, inclusive.

alf_cross_component_cr_coeff_abs[j] indicates the absolute value of the j-th coefficient transmitted in the service signals of the cross-component Cr filter. When alf_cross_component_cr_coeff_abs[j] is not present, it is logically output to 0.

The order k of the exponential transformation uek(v) into binary Golomb form is set to 3.

[272] alf_cross_component_cr_coeff_sign[j] specifies the sign of the j-th cross-component Cr filter coefficient as follows:

If alf_cross_component_cr_coeff_sign[j] is 0, the corresponding cross component Cr filter coefficient has a positive value.

Otherwise (alf_cross_component_cr_coeff_sign[j] is equal to 1), the corresponding coefficient of the cross-component Cr filter has a negative value.

When alf_cross_component_cr_coeff_sign[j] is not present, it is logically output to 0.

The coefficients AlfCCCoeffCr[adaplalion_parameter_set_id] of the cross-component Cr filter with elements AlfCCCoeffcr[adaptation_parameter_set_id][j], with j=0...13, are extracted as follows:

AlfCCCoeffcr[adaptation_parameter_set_id][j]=alf_cross_component_cr_coeff_abs[j]*(l-2*alf_cross_component_cr_coeff_sign[j])

The bitstream compliance requirement is that the values of AlfCCCoeffCr[adaptation_parameter_set_id][j], with j=0...13, must be in the range -2 ¹⁰ -1 to 2 ¹⁰ -1, inclusive.

[273] The following table shows the syntax associated with ALF data according to another example.

[274] Tab. 23

[275] The following table shows approximate semantics for the syntactic elements included in the table above.

[276] Tab. 24

alf_cross_component_cb_filter_signal_flag equal to i indicates that a set of cross-component Cb filters is transmitted in service signals; alf_cross_componenl_cb_filter_signal_flag equal to 0 indicates that the cross-component Cb filter set is not transmitted in service signals. When alf_cross_component_cb_filter_signal_flag is not present, it is logically output to 0.

alf_cross_cotnponent_cr_filter_signal_flag equal to 1 indicates that a set of cross-component Cr filters is transmitted in service signals, alf_cross_component_cr_filter_signal_flag equal to 0 indicates that a set of cross-component Cr filters is not transmitted in service signals. When alf_cross_component_cr_filter_signal_flag is not present, it is logically output to 0.

alf_cb_num_alt_filters_minus1 plus 1 indicates the number of alternative cross-component adaptive loop filters for the Cb components.

alf_cross_component_cb_coeff_abs[j] indicates the absolute value of the j-th coefficient transmitted in the service signals of the cross-component Cb filter. When alf_cross_component_cb_coeff_abs[j] is not present, it is logically output to 0.

The order k of the exponential transformation uek(v) into binary Golomb form is set to 3.

alf_cross_component_cb_coeff_sign[j] specifies the sign of the j-th cross-component Cb filter coefficient as follows:

If alf_cross_componcnt_cb_cocff_sign[j] is 0, the corresponding cross-component Cb filter coefficient has a positive value.

Otherwise (alf_cross_component_cb_coeff_sign[j] is equal to 1), the corresponding cross-component Cb filter coefficient has a negative value.

When alf_cross_component_cb_coeff_sign[j] is not present, it is logically output to 0.

The coefficients AlfCCCoeffCb[adaptation_parameter_set_id] of the cross-component Cb filter with elements AlfCCCoeffCb[adaptation_parameter_set_id][j], with j=0...13, are extracted as follows:

AlfCCCoeffCb[adaptation_parameter_set_id][j]=alf_cross_component_cb_coeff_abs[j]*(l-2*alf_cross_component_cb_coeff_sign[j])

The bitstream compliance requirement is that the values of AlfCCCoeffCb[adaptation_parameter_sel_id][j], with j=0...13, must be in the range -2 ¹⁰ -1 to 2 ¹⁰ -1, inclusive.

alf_cr_num_alt_filters_minus1 plus 1 indicates the number of alternative cross-component adaptive loop filters for Cr components.

alf_cross_component_cr_coeff_abs[j] indicates the absolute value of the j-th coefficient transmitted in the service signals of the cross-component Cr filter. When alf_cross_component_cr_coeff_abs[j] is not present, it is logically output to 0.

The order k of the exponential transformation uek(v) into binary Golomb form is set to 3.

[277] alf_cross_component_cr_coeff_sign[j] specifies the sign of the j-th cross-component Cr filter coefficient as follows:

If alf_cross_component_cr_coeff_sign[j] is 0, the corresponding cross component Cr filter coefficient has a positive value.

Otherwise (alf_cross_component_cr_coeff_sign[j] is equal to 1), the corresponding coefficient of the cross-component Cr filter has a negative value.

When alf_cross_component_cr_coeff_sign[j] is not present, it is logically output to 0.

The coefficients AlfCCCocffCr[adaptation_parameter_set_id] of the cross-component Cr filter with elements AlfCCCoeffCr[adaptation_parameter_set_id][j], with j=0...13, are extracted as follows:

AffCCCoeffCr[adaptation_parameter_set_id][j]=alf_cross_component_cr_coeff_abs[j]*(l-2*alf_cross_component_cr_coeff_sign[j])

The bitstream compliance requirement is that the values of AlfCCCoeffCr[adaptation_parameter_set_id][j], with j=0...13, must be in the range -2 ¹⁰ -1 to 2 ¹⁰ -1, inclusive.

[278] In the above two tables, the order of exponential Golomb code binarization for parsing syntax alf_cross_component_cb_coeff_abs[j] and alf_cross_component_cr_coeff_abs[j] can be specified by one of the values 0-9.

[279] Referring to the above two tables, the ALF data may include a Cb filter signaling flag (alf_cross_component_cb_filter_signal_flag or alf_cc_cb_filter_signal_flag) associated with whether or not cross-component filters for the Cb color component are signaled. Based on the transmit flag in the Cb filter signal (alf_cross_component_cb_filter_signal_flag), the ALF data may include information (ccalf_cb_num_alt_filters_minus1) associated with the number of cross component filters for the Cb color component. Based on the information associated with the number of cross-component filters for the Cb color component, the ALF data may include information (alf_cross_component_cb_coeff_abs) regarding the absolute values of the cross-component filter coefficients for the Cb color component and information (alf_cross_component_cr_coeff_sign) regarding the signs of the cross-component filter coefficients for the Cb color component -component. Based on information regarding the absolute values of the cross-component filter coefficients for the Cb color component and information regarding the signs of the cross-component filter coefficients for the Cb color component, the cross-component filter coefficients for the Cb color component can be extracted.

[280] In an example, the ALF data may include a Cr filter signaling flag (alf_cross_component_cr_filter_signal_flag or alf_cc_cr_filter_signal_flag) associated with whether or not cross component filters for the Cr color component are signaled. Based on the transmit flag in the Cr filter signal (alf_cross_component_cr_filter_signal_flag), the ALF data may include information (ccalf_cr_num_alt_filters_minus1) associated with the number of cross component filters for the Cr color component. Based on the information associated with the number of cross-component filters for the Cr color component, the ALF data may include information (alf_cross_component_cr_coeff_abs) regarding the absolute values of the cross-component filter coefficients for the Cr color component and information (alf_cross_component_cr_coeff_sign) regarding the signs of the cross-component filter coefficients for the Cr color component -component. Based on information regarding the absolute values of the cross-component filter coefficients for the Cr color component and information regarding the signs of the cross-component filter coefficients for the Cr color component, the cross-component filter coefficients for the Cr color component can be extracted.

[281] The following table shows the syntax regarding a coding tree unit according to an embodiment of the present disclosure.

[282] Tab. 25

[283] The following table shows approximate semantics for the syntactic elements included in the table above.

[284] Tab. 26

ccalf_ctb_flag[chromaIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] equal to 1 indicates that the cross-component adaptive loop filter is applied to the chroma component coding tree block indicated by chromaIdx, equal to 0 for Cb and equal to 1 for Cr , for a coding tree unit at location (xCtb, yCtb) of the luminance signal; ccalf_ctb_flag[chromaIdx][xCtb>>CtbLog2SizeY][yCtb>>, CtbLog2SizeY] equal to 0 indicates that the adaptive loop filter is not applied to the chroma component coding tree block indicated by the chromaIdx of the coding tree unit at location (xCtb, yCtb ) brightness signal.

When ccalf_ctb_flag[cIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is not present, it is logically output to 0.

[285] The following table shows the syntax of coding tree units according to another example of this embodiment.

[286] Tab. 27

[287] Referring to the above table, CCALF can be applied in CTU units. In an example, the image information may include information (coding_tree_unit()) regarding a coding tree unit. The information regarding the encoding tree unit may include information (ccalf_ctb_flag[0] regarding whether or not a cross-component filter is applied to the current Cb color component block, and/or information (ccalf_ctb_flag[1]) regarding whether or not a cross-component filter is applied to the current Cr color component block. In addition, the information regarding the encoding tree unit may include information (ccalf_ctb_filter_alt_idx[0]) regarding the filter bank index for the cross-component filter applied to the current Cb color component block, and/or information (ccalf_ctb_filter_alt_idx[1]) regarding the filter bank index for cross-component filter applied to the current block of Cr color component. The syntax may be adaptively transmitted according to the slice_ccalf_enabled_flag and slice_ccalf_chroma_idc syntax.

[288] The following table shows the syntax of coding tree units according to another example of this embodiment.

[289] Tab. 28

[290] The following table shows approximate semantics for the syntactic elements included in the above table.

[291] Tab. 29

ccalf_ctb_flag[chromaIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] equal to 1 indicates that the cross-component adaptive loop filter is applied to the chroma component coding tree block indicated by chromaIdx, equal to 0 for Cb and equal to 1 for Cr , for a coding tree unit at location (xCtb, yCtb) of the luminance signal; ccalf_ctb_flag[cIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] equal to 0 indicates that the adaptive contour filter is not applied to the chroma component coding tree block indicated by the chromaIdx of the coding tree unit at location (xCtb, yCtb) brightness signal.

When ccalf_ctb_flag[cIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is not present, it is logically output to 0.

ccalf_ctb_filter_alt_idx[chromaIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] specifies the index of an alternative cross-component adaptive loop filter applied to a chroma component coding tree block, with chromaIdx equal to 0 for Cb and chromaIdx equal to 1 for Cr, for one coding tree at the location (xCtb, yCtb) of the luminance signal. When ccalf_ctb_filter_alt_idx[chromaIdx][xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] is not present, it is logically output to zero.

[292] The following table shows the syntax of coding tree units according to another example of this embodiment. The syntactic elements included in the table below may be described according to Table 29.

[293] Tab. thirty

[294] In an example, the image information may include information regarding a coding tree unit (coding_tree_unit()). Information regarding a coding tree unit may include information regarding whether or not a cross-component filter is applied to the current Cb color component block (ccalf_ctb_flag[0), and/or information (ccalf_ctb_flag[1]) regarding whether or not a cross-component filter is applied to the current Cr color component block. In addition, the information regarding the encoding tree unit may include information (ccalf_ctb_filter_alt_idx[0]) regarding the filter bank index for the cross-component filter applied to the current Cb color component block, and/or information (ccalf_ctb_filter_alt_idx[1]) regarding the filter bank index for cross-component filter applied to the current block of Cr color component.

[295] FIG. 13 and 14 schematically show an example of a method for encoding video/images and related components according to embodiment(s) of the present disclosure.

[296] The method disclosed in FIG. 13 may be performed by the encoding equipment disclosed in FIG. 2 or fig. 14. In particular, for example, S1300-S1330 of FIG. 13 may be performed by the residual encoding equipment processor 230 of FIG. 14, S1340 according to FIG. 13 may be performed by the encoding equipment adder 250 of FIG. 14, S1350 according to FIG. 13 may be performed by the encoding equipment filter 260 of FIG. 14, and S1360 of FIG. 13 may be performed by the entropy encoder 240 of the encoding equipment of FIG. 14. In addition, although not shown in FIG. 13, prediction samples or prediction-related information may be retrieved by the prediction unit 220 of the encoding equipment in FIG. 13, and the bitstream may be generated from the residual information or prediction-related information by the entropy encoder 240 of the encoding equipment. The method disclosed in FIG. 13 may include the embodiments described above in the present disclosure.

[297] Referring to FIG. 13, the encoding equipment can extract residual samples (S1300). The encoding equipment may extract residual samples for the current block, and residual samples for the current block may be extracted based on the original samples and predicted samples of the current block. In particular, the encoding equipment may extract prediction samples of the current block based on the prediction mode. In this case, various forecasting methods disclosed in the present disclosure, such as inter-forecasting or intra-forecasting, can be applied. Residual samples can be extracted based on the prediction samples and the original samples.

[298] The encoding equipment may extract the transformation coefficients (S1310). The encoding hardware can extract transform coefficients based on the transform process for the residual samples. For example, the conversion process may include at least one of DCT, DST, GBT or CNT.

[299] The encoding equipment may extract the quantized transform coefficients (S1320). The encoding equipment may extract quantized transform coefficients based on a quantization process for the transform coefficients. The quantized transform coefficients can be in one-dimensional vector form based on the scanning order of the coefficients.

[300] The encoding equipment may generate residual information (S1330). The encoding equipment may generate residual information indicating the quantized transform coefficients. The residual information can be generated through various encoding methods, such as exponential Golomb code, CAVLC, CABAC, etc.

[301] The encoding equipment may generate reconstructed samples (S1340). The encoding equipment can generate reconstructed samples based on the residual information. Reconstructed samples can be formed by summing the residual samples based on the residual information with the predictive sample. In particular, the encoding equipment may perform prediction (intra or inter prediction) for the current block and may generate reconstructed samples based on the original samples and prediction samples generated from the prediction.

[302] The reconstructed samples may include reconstructed luma samples and reconstructed chrominance samples. In particular, the residual samples may include luma residual samples and chrominance residual samples. Residual luminance samples may be generated based on the original luminance samples and the predicted luminance samples. Residual chrominance samples may be generated based on the original chrominance samples and the predicted chrominance samples. The encoding equipment may extract transform coefficients (luminance transform coefficients) for the residual luminance signal samples and/or transform coefficients (chrominance transform coefficients) for the residual chrominance signal samples. The quantized transform coefficients may include quantized luma transform coefficients and/or quantized chrominance transform coefficients.

[303] The encoding equipment may generate ALF-related information and/or CCALF-related (CC-ALF) information for the reconstructed samples (S1350). The encoding equipment may generate ALF-related information for the reconstructed samples. The encoding hardware extracts the ALF-related parameter, which can be used to filter the reconstructed samples, and generates ALF-related information. For example, ALF-related information may include ALF-related information described above in the present disclosure.

[304] The encoding device can encode video/image information (S1360). The image information may include residual information, ALF-related information and/or CCALF-related information. The encoded video/image information may be output in the form of a bitstream. The bit stream may be transmitted to the decoding device via a network or storage medium.

[305] In an example, the CCALF-related information may include a CCALF enable flag, a flag associated with whether or not CCALF is available for the Cb-(or Cr-) color component, a transmit flag in the Cb-(or Cr-) signaling -) filters related to whether or not cross-component filters for the Cb-(or Cr-) color component are transmitted in the service signals, information related to the number of cross-component filters for the Cb-(or Cr-) color component, information regarding the values of the cross-component coefficients filter for the Cb-(or Cr-) color component, information regarding the absolute values of the cross-component filter coefficients for the Cb-(or Cr-) color component, information regarding the signs of the cross-component filter coefficients for the Cb-(or Cr-) color component and/or information as to whether or not a cross-component filter is applied to the current block of Cb-(or Cr-) color component in the information (coding tree unit syntax) regarding the coding tree unit.

[306] The image/video information may include various types of information according to an embodiment of the present document. For example, the image/video information may include information disclosed in at least one of the tables 1-30 described above.

[307] In an embodiment, the image information may include header information and an adaptation parameter set (APS). The header information may include information associated with the APS identifier, including ALF data. For example, cross-component filter coefficients can be extracted based on ALF data.

[308] In an embodiment, the image information may include a sequence parameter set (SPS). The SPS may include a CCALF enable flag associated with whether cross-component filtering is available or not.

[309] In an embodiment, the SPS may include an ALF enable flag (sps_alf_enabled_flag) associated with whether ALF is available or not. Based on the determination that the value of the ALF enable flag is 1, the SPS may include a CCALF enable flag associated with whether or not cross-component filtering is available.

[310] In an embodiment, the image information may include slice header information. The slice header information may include an ALF enable flag (slice_alf_enabled_flag) associated with whether or not ALF is enabled. Based on the determination that the value of the ALF enable flag is 1, it may be determined whether the value of the enable flag associated with whether or not CCALF is available is 1. In an example, CCALF may be available for the slice based on the determination that that the value of the ALF activation flag is 1.

[311] In an embodiment, the header information (slice header information) may include a first flag associated with whether or not CCALF is available for the Cb color component of the filtered reconstructed chrominance signal samples, and a second flag associated with whether or not CCALF is available. no CCLF for the Cr color component of the filtered reconstructed chrominance samples. In another example, based on determining that the value of the ALF enable flag (slice_alf_enabled_flag) is 1, the header information (slice header information) may include a first flag associated with whether or not CCALF is enabled for the Cb color component of the filtered reconstructed chrominance samples, and a second flag associated with whether or not CCLF is available for the Cr color component of the filtered reconstructed chrominance samples.

[312] In an embodiment, the image information may include adaptation parameter sets (APS). In an example, the slice header information may include first APS identification information (information associated with the second APS identifier) for extracting cross-component filter coefficients for the Cb chroma component of the filtered reconstructed chrominance signal samples. The slice header information may include identification information (information associated with a second APS identifier) of the second APS for extracting cross-component filter coefficients for the Cr color component of the filtered reconstructed chrominance signal samples. In another example, based on determining that the value of the first flag is 1, the slice header information may include identification information of the first APS (information regarding the identification of the second APS) for extracting cross-component filter coefficients for the Cb color component. Based on the determination that the value of the second flag is 1, the slice header information may include second APS identification information (information associated with the second APS ID) for extracting cross-component filter coefficients for the Cr color component.

[313] In an embodiment, the first ALF data included in the first APS may include a Cb filter signaling flag associated with whether or not cross-component filters for the Cb color component are signaled. Based on the transmit flag in the Cb filter overhead, the first ALF data may include information associated with the number of cross-component filters for the Cb color component. Based on the information associated with the number of cross-component filters for the Cb color component, the first ALF data may include information regarding the absolute values of the cross-component filter coefficients for the Cb color component and information regarding the signs of the cross-component filter coefficients for the Cb color component. Based on the information regarding the information regarding the absolute values of the cross-component filter coefficients for the Cb color component and the information regarding the signs of the cross-component filter coefficients for the Cb color component, the cross-component filter coefficients for the Cb color component can be extracted.

[314] In an embodiment, information associated with the number of cross-component filters for the Cb color component may be encoded with a zero-order exponential Golomb code (zero EG).

[315] In an embodiment, the second ALF data included in the second APS may include a Cr filter signaling flag associated with whether or not cross-component filters for the Cr color component are signaled. Based on the transmit flag in the Cr filter overhead, the second ALF data may include information associated with the number of cross-component filters for the Cr color component. Based on the information associated with the number of cross-component filters for the Cr color component, the second ALF data may include information regarding the absolute values of the cross-component filter coefficients for the Cr color component and information regarding the signs of the cross-component filter coefficients for the Cr color component. Based on the absolute values of the cross-component filter coefficients for the Cr color component and information regarding the signs of the cross-component filter coefficients for the Cr color component, the cross-component filter coefficients for the Cr color component can be extracted.

[316] In an embodiment, information associated with the number of cross-component filters for the Cr color component may be encoded with a zero-order exponential Golomb code (zero EG).

[317] In an embodiment, the image information may include information regarding a coding tree unit. The information regarding the coding tree unit may include information regarding whether or not a cross-component filter is applied to the current Cb color component block, and/or information regarding whether or not a cross-component filter is applied to the current Cr color component block.

[318] In an embodiment, information regarding a coding tree unit may include information regarding a filterbank index for a cross-component filter applied to the current block of a Cb color component and/or information regarding a filterbank index for a cross-component filter applied to the current block color Cr component.

[319] FIG. 15 and 16 schematically show an example of a method for decoding videos/images and related components according to embodiment(s) of the present disclosure.

[320] The method disclosed in FIG. 15 may be performed by the decoding equipment illustrated in FIG. 3 or 16. In particular, for example, S1500 according to FIG. 15 may be performed by the entropy decoder 310 of the decoding equipment, S1510 may be performed by the adder 340 of the decoding equipment, and S1520-S1550 may be performed by the filter 350 of the decoding equipment. The method disclosed in FIG. 15 may include the embodiments described above in the present disclosure.

[321] Referring to FIG. 15, the decoding equipment can receive/receive video/image information (S1500). The video/image information may include residual information. The decoding equipment can receive/receive image/video information through a bitstream. In an example, the video/image information may further include CCAL-related information. For example, in an example, the CCALF-related information may include a CCALF enable flag, a flag associated with whether or not CCALF is available for the Cb-(or Cr-) color component, a transmit flag in the Cb-(or Cr-) signaling )filters related to whether or not cross-component filters for the Cb-(or Cr-) color component are transmitted in the service signals, information related to the number of cross-component filters for the Cb-(or Cr-) color component, information regarding the absolute values of the cross-component coefficients filter for a Cb-(or Cr-) color component, information regarding the signs of the cross-component filter coefficients for the Cb-(or Cr-) color component, and/or information regarding whether or not a cross-component filter is applied to the current block of Cb-(or Cr-) color )component in the information (syntax of coding tree units) regarding a coding tree unit.

[322] The image/video information may include various types of information according to an embodiment of the present document. For example, the image/video information may include information disclosed in at least one of the tables 1-30 described above.

[323] The decoding equipment may extract the quantized transform coefficients. The decoding hardware can extract the quantized transform coefficients based on the residual information. The quantized transform coefficients can be in one-dimensional vector form based on the scanning order of the coefficients. The quantized transform coefficients may include quantized luma transform coefficients and/or quantized chrominance transform coefficients.

[324] The decoding equipment may extract the transform coefficients. Decoding equipment can extract transform coefficients based on a dequantization process for the quantized transform coefficients. Decoding equipment may extract luminance signal conversion coefficients through dequantization based on the quantized luminance signal conversion coefficients. Decoding equipment may extract chrominance transform coefficients through dequantization based on the quantized chrominance transform coefficients.

[325] Decoding equipment may generate/extract residual samples. The decoding equipment may extract residual samples based on an inverse transform process for the transform coefficients. The decoding equipment may extract the residual luminance signal samples through an inverse transform process based on the luminance signal transform coefficients. Decoding equipment may extract residual chrominance samples through an inverse transform process based on chrominance transform coefficients.

[326] The decoding equipment may generate/extract reconstructed luma samples and/or reconstructed chrominance samples (S1510). The decoding equipment may generate reconstructed luma samples and/or reconstructed chrominance samples based on the residual information. The decoding equipment can generate reconstructed samples based on the residual information. The reconstructed samples may include reconstructed luma samples and/or reconstructed chrominance samples. The luma component of the reconstructed samples may correspond to the reconstructed luma samples, and the chrominance component of the reconstructed samples may correspond to the reconstructed chrominance samples. The decoding equipment may generate predicted luma samples and/or predicted chrominance samples through a prediction process. The decoding equipment may generate reconstructed luminance samples based on the predicted luminance samples and residual luminance samples. The decoding equipment may generate reconstructed chrominance samples based on the predicted chrominance samples and residual chrominance samples.

[327] The decoding equipment may extract ALF filter coefficients for the ALF process of reconstructed chroma samples (S1520). In addition, the decoding equipment may extract ALF filter coefficients for the ALF process of the reconstructed luminance signal samples. The ALF filter coefficients can be extracted based on the ALF parameters included in the ALF data in the APS.

[328] The decoding equipment may generate filtered reconstructed chrominance samples (S1530). The decoding equipment may generate filtered reconstructed samples based on the reconstructed chroma samples and the ALF filter coefficients.

[329] The decoding equipment may extract cross-component filter coefficients for cross-component filtering (S1540). The cross-component filter coefficients may be extracted based on the CCALF-related information in the ALF data included in the above APS, and the identification information of the corresponding APS may be included in (may be signaled through) a slice header.

[330] The decoding equipment may generate modified filtered reconstructed chroma samples (S1550). The decoding equipment may generate modified and filtered reconstructed chrominance samples based on the reconstructed luma samples, the filtered reconstructed chrominance samples, and the cross-component filter coefficients. In an example, the decoding equipment may extract the difference between two samples from the reconstructed luminance samples and multiply the difference by one filter coefficient from the cross-component filter coefficients. Based on the result of the multiplication and the filtered reconstructed chrominance samples, the decoding equipment can generate modified filtered reconstructed chrominance samples. For example, the decoding equipment may generate modified filtered reconstructed chrominance samples based on the sum of the product and one of the filtered reconstructed chrominance samples.

[331] In an embodiment, the image information may include header information and an adaptation parameter set (APS). The header information may include information associated with the APS identifier, including ALF data. For example, cross-component filter coefficients can be extracted based on ALF data.

[332] In an embodiment, the image information may include a sequence parameter set (SPS). The SPS may include a CCALF enable flag associated with whether cross-component filtering is available or not.

[333] In an embodiment, the SPS may include an ALF enable flag (sps_alf_enabled_flag) associated with whether or not ALF is available. Based on the determination that the value of the ALF enable flag is 1, the SPS may include a CCALF enable flag associated with whether or not cross-component filtering is available.

[334] In an embodiment, the image information may include slice header information. The slice header information may include an ALF enable flag (slice_alf_enabled_flag) associated with whether or not ALF is enabled. Based on the determination that the value of the ALF enable flag is 1, it may be determined whether the value of the CCALF enable flag is 1. In an example, CCALF may be available for slicing based on the determination that the value of the ALF enable flag is 1 .

[335] In an embodiment, the header information (slice header information) may include a first flag associated with whether or not CCALF is available for the Cb color component of the filtered reconstructed chrominance signal samples, and a second flag associated with whether or not CCALF is available. no CCLF for the Cr color component of the filtered reconstructed chrominance samples. In another example, based on determining that the value of the ALF enable flag (slice_alf_enabled_flag) is 1, the header information (slice header information) may include a first flag associated with whether or not CCALF is enabled for the Cb color component of the filtered reconstructed chrominance samples, and a second flag associated with whether or not CCLF is available for the Cr color component of the filtered reconstructed chrominance samples.

[336] In an embodiment, the image information may include adaptation parameter sets (APS). In an example, the slice header information may include first APS identification information (information associated with the second APS identifier) for extracting cross-component filter coefficients for the Cb chroma component of the filtered reconstructed chrominance signal samples. The slice header information may include identification information (information associated with a second APS identifier) of the second APS for extracting cross-component filter coefficients for the Cr color component of the filtered reconstructed chrominance signal samples. In another example, based on determining that the value of the first flag is 1, the slice header information may include identification information of the first APS (information regarding the identification of the second APS) for extracting cross-component filter coefficients for the Cb color component. Based on the determination that the value of the second flag is 1, the slice header information may include second APS identification information (information associated with the second APS ID) for extracting cross-component filter coefficients for the Cr color component.

[337] In an embodiment, the first ALF data included in the first APS may include a Cb filter signaling flag associated with whether or not cross-component filters for the Cb color component are signaled. Based on the transmit flag in the Cb filter overhead, the first ALF data may include information associated with the number of cross-component filters for the Cb color component. Based on the information associated with the number of cross-component filters for the Cb color component, the first ALF data may include information regarding the absolute values of the cross-component filter coefficients for the Cb color component and information regarding the signs of the cross-component filter coefficients for the Cb color component. Based on the information regarding the information regarding the absolute values of the cross-component filter coefficients for the Cb color component and the information regarding the signs of the cross-component filter coefficients for the Cb color component, the cross-component filter coefficients for the Cb color component can be extracted.

[338] In an embodiment, information associated with the number of cross-component filters for the Cb color component may be encoded with a zero-order exponential Golomb code (zero EG).

[339] In an embodiment, the second ALF data included in the second APS may include a Cr filter signaling flag associated with whether or not cross-component filters for the Cr color component are signaled. Based on the transmit flag in the Cr filter overhead, the second ALF data may include information associated with the number of cross-component filters for the Cr color component. Based on the information associated with the number of cross-component filters for the Cr color component, the second ALF data may include information regarding the absolute values of the cross-component filter coefficients for the Cr color component and information regarding the signs of the cross-component filter coefficients for the Cr color component. Based on the absolute values of the cross-component filter coefficients for the Cr color component and information regarding the signs of the cross-component filter coefficients for the Cr color component, the cross-component filter coefficients for the Cr color component can be extracted.

[340] In an embodiment, information associated with the number of cross-component filters for the Cr color component may be encoded with a zero-order exponential Golomb code (zero EG).

[341] In an embodiment, the image information may include information regarding a coding tree unit. The information regarding the coding tree unit may include information regarding whether or not a cross-component filter is applied to the current Cb color component block, and/or information regarding whether or not a cross-component filter is applied to the current Cr color component block.

[342] In an embodiment, information regarding a coding tree unit may include information regarding a filterbank index for a cross-component filter applied to the current block of a Cb color component and/or information regarding a filterbank index for a cross-component filter applied to the current block color Cr component.

[343] When there is a residual sample for the current block, the decoding equipment may receive information regarding the residual for the current block. The residual information may include conversion factors for residual samples. The decoding equipment may extract residual samples (or an array of residual samples) for the current block based on the residual information. In particular, the decoding equipment can extract quantized transform coefficients based on the residual information. The quantized transform coefficients can be in one-dimensional vector form based on the scanning order of the coefficients. Decoding equipment can extract transform coefficients based on a dequantization process for the quantized transform coefficients. Decoding hardware can extract residual samples based on transform coefficients.

[344] The decoding equipment may generate reconstructed samples based on the (mutual) predictive samples and residual samples, and may extract a reconstructed block or reconstructed frame based on the reconstructed samples. In more detail, the decoding hardware may generate reconstructed samples based on the sum of the (internal) prediction samples and residual samples. Thereafter, as described above, the decoding equipment may apply an in-loop filtering process, eg, a deblocking filtering process and/or an SAO process, to the reconstructed frame so as to improve the subjective/objective quality of the frames, if necessary.

[345] For example, decoding equipment may obtain image information including all or part of the above information (or syntax elements) by decoding a bit stream or encoded information. In addition, the bitstream information or encoded information may be stored on a computer-readable storage medium and may cause the above decoding method to be performed.

[346] In the above embodiment, the methods are described based on a flowchart having a sequence of steps or blocks. The present disclosure is not limited to the order of the above steps or blocks. Some stages or blocks may occur simultaneously or in a different order from other stages or blocks as described above. Additionally, those skilled in the art will understand that the steps shown in the above flowchart are not exhaustive and other steps may be included or one or more steps in the flowchart may be deleted without affecting scope of this disclosure.

[347] The method according to the above embodiments of the present document may be implemented in software form, and the encoding equipment and/or decoding equipment according to the present document, for example, may be included in equipment that performs image processing for a television, computer, smartphone, set-top box, display devices, etc.

[348] When the embodiments herein are implemented in software, the above method may be implemented as a module (process, function, etc.) that performs the above function. The module may be stored in a storage device and executed by a processor. The storage device may be internal or external to the processor and may be coupled to the processor through various known means. The processor may include an application specific integrated circuit (ASIC), other chipsets, logic circuits, and/or data processing devices. The storage device may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and/or other storage devices. Thus, the embodiments described herein may be performed through implementation on a processor, microprocessor, controller, or chip. For example, the functional modules shown in each drawing may be implemented and executed on a computer, processor, microprocessor, controller, or chip. In this case, information regarding instructions or an algorithm to be implemented may be stored in a digital storage medium.

[349] In addition, the decoding equipment and encoding equipment to which the present disclosure applies may be included in multimedia broadcasting equipment, mobile communication terminal, home theater system video equipment, digital cinema system video equipment, surveillance camera, video chatting equipment, real-time communication equipment such as video communication, mobile streaming equipment, storage media, video recording camera, VoD service equipment, over-the-top (OTT) video equipment, Internet streaming service equipment, 3D video equipment, video teleconferencing equipment communications, transport user equipment (ie, vehicle user equipment, aircraft user equipment, marine user equipment, etc.) and medical video equipment, and can be used to process video and data signals. For example, over-the-top (OTT) video equipment may include a game console, Blu-ray player, Internet-enabled television, home theater system, smartphone, tablet PC, digital video recorder (DVR), etc.

[350] Additionally, the processing method to which the present document applies may be formed in the form of a program to be executed by a computer, and may be stored on a computer-readable recording medium. Multimedia data having a data structure according to the present disclosure may also be stored on computer-readable recording media. Computer-readable recording media include all types of storage devices on which data readable by a computer system is stored. Computer readable recording media, for example, may include BD, universal serial bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical storage device. In addition, computer-readable recording media include media implemented in the form of carrier waves (ie, as transmission over the Internet). In addition, the bit stream generated by the encoding method may be stored on a computer-readable recording medium or may be transmitted over wired/wireless communication networks.

[351] In addition, embodiments of the present document may be implemented with a computer program product according to program codes, and the program codes may be executed on a computer by the embodiments of this document. The program codes may be stored on a medium that can be read by a computer.

[352] FIG. 17 shows an example of a content streaming system to which the embodiments disclosed herein may be applied.

[353] Referring to FIG. 17, the content streaming system to which the embodiment(s) of this document applies may mainly include an encoding server, a streaming server, a web server, a media storage, a user device, and a media input device.

[354] The encoding server compresses content input from media input devices such as a smartphone, camera, video recorder, etc. into digital data to form a bitstream and transmit the bitstream to the streaming server. As another example, when media input devices such as smartphones, cameras, video recorders, etc. To directly generate the bit stream, the encoding server can be omitted.

[355] The bitstream may be generated by an encoding method or a bitstream generation method to which the embodiment(s) of the present disclosure applies, and the streaming server may temporarily store the bitstream while transmitting or receiving the bitstream.

[356] The streaming server transmits multimedia data to the user device based on the user's request through the web server, and the web server serves as a medium for informing the user regarding the service. When a user requests a required service from a web server, the web server delivers it to the streaming server and the streaming server transmits the media data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server serves to manage the command/response between devices in the content streaming system.

[357] The streaming server may receive content from a media storage and/or encoding server. For example, when content is received from an encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may maintain the bit stream for a predetermined time.

[358] Examples of a user device may include a mobile phone, a smartphone, a laptop computer, a digital broadcast terminal, a personal digital assistant (PDA), a portable media player (PMP), a navigation device, a tablet PC, tablet PCs, ultrabooks, wearable devices (such as smart watches, smart glasses, head-mounted displays), digital TVs, desktop computers, digital signage system, etc. Each server in a content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[359] Each server in a content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[360] The claims described herein may be combined in various ways. For example, the technical features of the method claims of this document can be combined and implemented as equipment, and the technical features of the equipment claims of this document can be combined and implemented as a method. In addition, the technical features of the method claim of this document and the technical features of the equipment claim can be combined to be implemented as equipment, and the technical features of the method claim of this document and the technical features of the equipment claim can be combined and implemented as a way.

Claims (47)

1. Decoding equipment for decoding images, wherein the decoding equipment comprises: Memory device; And at least one processor coupled to the storage device, wherein the at least one processor is configured to: - obtain image information including residual information through a bit stream; - generate reconstructed samples of brightness signals and reconstructed samples of chrominance signals based on residual information; - extract adaptive loop filtering (ALF) coefficients for the ALF process of reconstructed chroma samples; - generate filtered reconstructed samples of chrominance signals based on reconstructed samples of chrominance signals and ALF filter coefficients; - extract cross-component filter coefficients for cross-component filtering; And - generate modified filtered reconstructed samples of chrominance signals based on reconstructed samples of luminance signals, filtered reconstructed samples of chrominance signals and cross-component filter coefficients, wherein the image information includes a sequence parameter set (SPS) and slice header information, wherein the SPS includes an ALF activation flag associated with whether or not the ALF process is activated, wherein, based on determining that the value of the ALF enable flag is 1, the SPS includes a cross component adaptive loop filtering (CCALF) enable flag associated with whether cross component filtering is activated or not, wherein, based on determining that the value of the ALF activation flag in the SPS is 1, the slice header information includes an ALF activation flag associated with whether ALF is activated or not, wherein, based on determining that the value of the ALF activation flag included in the slice header information is 1 and the value of the CCALF activation flag included in the SPS is 1, the slice header information includes information regarding whether or not CCALF for filtered reconstructed chrominance samples, and wherein based on the value of the information regarding whether or not CCALF is enabled for filtered reconstructed chrominance samples equal to 1, the slice header information includes identification information (ID) of an adaptation parameter set (APS) associated with CCALF for filtered reconstructed chrominance samples . 2. Encoding equipment for encoding images, wherein the encoding equipment comprises: Memory device; And at least one processor coupled to the storage device, wherein the at least one processor is configured to: - extract residual samples for the current block; - extract conversion coefficients based on the conversion process for residual samples; - extract quantized transform coefficients based on the quantization process for the transform coefficients; - generate residual information indicating quantized conversion coefficients; - generate reconstructed samples based on residual information; - generate information associated with adaptive loop filtering (ALF) and information associated with cross-component ALF (CCALF) for the reconstructed samples; And - encode image information including residual information, ALF-related information and CCALF-related information, wherein the reconstructed samples include reconstructed luma samples and reconstructed chrominance samples, wherein at least one processor is additionally configured to: - extract ALF filter coefficients for the ALF process of reconstructed chroma samples; - generate filtered reconstructed samples of chrominance signals based on reconstructed samples of chrominance signals and ALF filter coefficients; - extract cross-component filter coefficients for cross-component filtering; And - generate modified filtered reconstructed samples of chrominance signals based on reconstructed samples of luminance signals, filtered reconstructed samples of chrominance signals and cross-component filter coefficients, wherein the image information includes a sequence parameter set (SPS) and slice header information, wherein the SPS includes an ALF activation flag associated with whether or not the ALF process is activated, wherein, based on determining that the value of the ALF enable flag is 1, the SPS includes a cross component adaptive loop filtering (CCALF) enable flag associated with whether cross component filtering is activated or not, wherein, based on determining that the value of the ALF activation flag in the SPS is 1, the slice header information includes an ALF activation flag associated with whether ALF is activated or not, wherein, based on determining that the value of the ALF activation flag included in the slice header information is 1 and the value of the CCALF activation flag included in the SPS is 1, the slice header information includes information regarding whether or not CCALF for filtered reconstructed chrominance samples, and wherein based on the value of the information regarding whether or not CCALF is enabled for filtered reconstructed chrominance samples equal to 1, the slice header information includes identification information (ID) of an adaptation parameter set (APS) associated with CCALF for filtered reconstructed chrominance samples . 3. A computer-readable storage medium storing instructions that, when executed, cause the image encoding method to be carried out by the image encoding equipment of claim 2. 4. Equipment for transmitting image data, the equipment comprising: at least one processor configured to obtain a bit stream for the image, wherein the bit stream is generated based on extracting residual samples for the current block, extracting transform coefficients based on a transform process for the residual samples, extracting quantized transform coefficients based on a quantization process for the coefficients transform, generating residual information indicating quantized transform coefficients, generating reconstructed samples based on the residual information, generating adaptive loop filtering (ALF) related information and cross component ALF (CCALF) related information for the reconstructed samples, and encoding image information to generate a bitstream, wherein the image information includes residual information, ALF-related information and CCALF-related information; And a transmitter configured to transmit data comprising a stream of bits, wherein the image information includes a sequence parameter set (SPS) and slice header information, wherein the SPS includes an ALF activation flag associated with whether or not the ALF process is activated, wherein, based on determining that the value of the ALF enable flag is 1, the SPS includes a cross component adaptive loop filtering (CCALF) enable flag associated with whether or not cross component filtering is available, wherein, based on determining that the value of the ALF activation flag in the SPS is 1, the slice header information includes an ALF activation flag associated with whether ALF is activated or not, wherein, based on determining that the value of the ALF activation flag included in the slice header information is 1 and the value of the CCALF activation flag included in the SPS is 1, the slice header information includes information regarding whether or not CCALF for filtered reconstructed chrominance samples, and wherein based on the value of the information regarding whether or not CCALF is enabled for filtered reconstructed chrominance samples equal to 1, the slice header information includes identification information (ID) of an adaptation parameter set (APS) associated with CCALF for filtered reconstructed chrominance samples .