Device and method for compiling an image

Abstract

According to one embodiment of this document, the in-loop filtering process during image / video compilation may include a cross-component adaptive in-loop filtering process. According to this embodiment, CCALF can improve the accuracy of in-loop filtering.

Description

Technical Field

[0001] The present disclosure relates to an apparatus and method for compiling an image. Background Art

[0002] Recently, there has been an increasing demand for high-resolution and high-quality images / videos such as 4K or 8K or higher ultra-high definition (UHD) images / videos in various fields. As image / video data has high resolution and high quality, the amount of information or bits to be transmitted increases compared to existing image / video data. Therefore, transmitting image data using a medium such as an existing wired / wireless broadband line or an existing storage medium or storing image / video data using an existing storage medium increases the transmission cost and storage cost.

[0003] In addition, there is an increasing interest in and demand for virtual reality (VR) and artificial reality (AR) content, as well as immersive media such as holograms, and there is also an increasing growth in the broadcasting of images / videos having characteristics different from real images (such as game images).

[0004] Therefore, highly efficient image / video compression techniques are required to effectively compress, transmit, store, or reproduce information of high-resolution and high-quality images / videos having various characteristics as described above.

[0005] During the compilation process for image / video compression, an in-loop filtering process may be performed. Recently, there has been a discussion about improving the accuracy of filtering. Summary of the Invention

[0006] Technical Solution

[0007] The present disclosure provides a method and apparatus for improving the efficiency of image / video compilation.

[0008] The present disclosure also provides an efficient filtering application method and apparatus.

[0009] The present disclosure also provides an efficient ALF application method and apparatus.

[0010] According to an embodiment of the present disclosure, a filtering process may be performed on a reconstructed chrominance sample based on a reconstructed luminance sample.

[0011] According to an embodiment of the present disclosure, a filtered reconstructed chrominance sample may be modified based on a reconstructed luminance sample.

[0012] According to an embodiment of the present disclosure, information about whether CCALF is available may be signaled in the SPS.

[0013] According to an embodiment of the present disclosure, information about values of cross-component filter coefficients may be derived from ALF data (normal ALF data or CCALF data).

[0014] According to an embodiment of the present disclosure, the identifier (ID) information of an APS including ALF data for deriving cross-component filter coefficients in a slice can be signaled.

[0015] According to an embodiment of the present disclosure, information on the filter set index of CCALF can be signaled in units of CTUs (blocks).

[0016] According to an embodiment of this document, a video / image decoding method performed by a decoding device is provided.

[0017] According to an embodiment of this document, a decoding device for performing video / image decoding is provided.

[0018] According to an embodiment of this document, a video / image encoding method performed by an encoding device is provided.

[0019] According to an embodiment of this document, an encoding device for performing video / image encoding is provided.

[0020] According to an embodiment of this document, a computer-readable digital storage medium is provided, in which encoded video / image information generated according to the video / image encoding method disclosed in at least one embodiment of this document is stored.

[0021] According to an embodiment of this document, a computer-readable digital storage medium is provided, in which encoded information or encoded video / image information that causes a decoding device to execute the video / image decoding method disclosed in at least one embodiment of this document is stored.

[0022] Beneficial effects

[0023] According to an embodiment of this document, the overall image / video compression efficiency can be improved.

[0024] According to an embodiment of this document, subjective / objective visual quality can be improved through efficient filtering.

[0025] According to an embodiment of the present disclosure, the ALF process can be efficiently performed and the filtering performance can be improved.

[0026] According to an embodiment of the present disclosure, the reconstructed chrominance samples filtered based on the reconstructed luminance samples can be modified to improve the picture quality and compilation accuracy of the chrominance component of the decoded picture.

[0027] According to an embodiment of the present disclosure, the CCALF process can be efficiently performed.

[0028] According to an embodiment of the present disclosure, ALF-related information can be efficiently signaled.

[0029] According to an embodiment of the present disclosure, CCALF-related information can be signaled efficiently.

[0030] According to an embodiment of the present disclosure, ALF and / or CCALF can be adaptively applied in units of pictures, slices, and / or coding blocks.

[0031] According to an embodiment of this document, when CCALF is used in a method and apparatus for encoding and decoding still images or videos, the filter coefficients for CCALF and the on / off transmission method in a block or CTU unit can be improved, thereby improving the encoding efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 An example of a video / image coding system to which embodiments of the present disclosure can be applied is schematically shown.

[0033] Figure 2 FIG. is a diagram schematically illustrating the configuration of a video / image encoding apparatus to which embodiments of the present disclosure can be applied.

[0034] Figure 3 FIG. is a diagram schematically illustrating the configuration of a video / image decoding apparatus to which embodiments of the present disclosure can be applied.

[0035] Figure 4 The hierarchical structure of coded images / videos is exemplarily shown.

[0036] Figure 5 FIG. is a flowchart illustrating a block reconstruction method based on intra prediction in a decoding apparatus.

[0037] Figure 6 FIG. is a flowchart illustrating a block reconstruction method based on inter prediction in an encoding apparatus.

[0038] Figure 7 FIG. is a flowchart illustrating a block reconstruction method based on inter prediction in a decoding apparatus.

[0039] Figure 8 An example of the shape of an ALF filter is shown.

[0040] Figure 9 FIG. is a diagram illustrating a virtual boundary applied to a filtering process according to an embodiment of the present disclosure.

[0041] Figure 10 An example of an ALF process using a virtual boundary according to an embodiment of the present disclosure is shown.

[0042] Figure 11 FIG. is a diagram illustrating a cross-component adaptive loop filtering (CC-ALF) process according to an embodiment of the present disclosure.

[0043] Figure 12 and Figure 13 Schematically shows examples of a video / image encoding method and related components according to an embodiment of the present disclosure.

[0044] Figure 14 and Figure 15 Schematically shows examples of an image / video decoding method and related components according to an embodiment of the present disclosure.

[0045] Figure 16 Shows an example of a content streaming system to which the embodiments disclosed in the present disclosure can be applied. Detailed Description

[0046] The present disclosure can be modified in various forms, and specific embodiments thereof will be described and shown in the drawings. However, the embodiments are not intended to limit the present disclosure. The terms used in the following description are only for describing specific embodiments and are not intended to limit the present disclosure. Singular expressions include plural expressions as long as they are not clearly understood differently. Terms such as "including" and "having" are intended to indicate the presence of the features, numbers, steps, operations, elements, components, or combinations thereof used in the following description, and thus it should be understood that the possibility of the presence or addition of one or more different features, numbers, steps, operations, elements, components, or combinations thereof is not excluded.

[0047] At the same time, each configuration in the drawings described in the present disclosure is independently shown for the convenience of describing different feature functions, and does not mean that each configuration is implemented as a separate hardware or a separate software. For example, two or more components among each component can be combined to form one component, or one component can be divided into multiple components. Embodiments in which each component is integrated and / or separated are also included within the scope of the document of the present disclosure.

[0048] The present disclosure relates to video / image compilation. For example, the methods / embodiments disclosed in the present disclosure can be applied to the methods disclosed in general video compilation (VVC). In addition, the methods / embodiments disclosed in the present disclosure can be applied to the methods disclosed in the basic video compilation (EVC) standard, the AOMedia Video 1 (AV1) standard, the second-generation audio-video compilation standard (AVS2), or the next-generation video / image compilation standard (e.g., H.267 or H.268, etc.).

[0049] The present disclosure presents various embodiments of video / image compilation, and unless otherwise mentioned, these embodiments can be executed in combination with each other.

[0050] In the present disclosure, a video may refer to a series of images over time. A picture generally refers to a unit representing an image in a specific time region, and a slice / tile is a unit that forms part of a picture in encoding. A slice / tile may include one or more coding tree units (CTUs). A picture may consist of one or more slices / tiles. A tile is a rectangular region of CTUs within a specific tile column and a specific tile row in a picture. A tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width specified by a syntax element in the picture parameter set. A tile row is a rectangular region of CTUs having a height specified by a syntax element in the picture parameter set and a width equal to the width of the picture. A tile scan is a specific sequential ordering of CTUs that partition a picture, where the CTUs are sequentially ordered in raster scan within a tile, and the tiles in a picture are sequentially ordered in raster scan of the tiles of the picture. A slice includes an integer number of complete tiles or an integer number of consecutive complete CTU rows that can be exclusively contained within a single NAL unit within the tiles of a picture.

[0051] Meanwhile, a picture can be divided into two or more sub-pictures. A sub-picture can be a rectangular region of one or more slices within a picture.

[0052] A pixel or pel may mean the smallest unit that constitutes a picture (or image). Additionally, the term "sample" can be used as a term corresponding to a pixel. A sample can generally represent a pixel or the value of a pixel, and can represent a pixel / pixel value of only a luminance component or a pixel / pixel value of only a chrominance component.

[0053] A unit can represent a basic unit of image processing. A unit can include at least one of a specific region of a picture and information related to that region. A unit can include one luminance block and two chrominance (e.g., cb, cr) blocks. In some cases, a unit can be used interchangeably with terms such as a block or a region. Generally, an M×N block can include samples (or an array of samples) or a set (or array) of transform coefficients in M columns and N rows.

[0054] In the present disclosure, "A or B (A or B)" may mean "only A", "only B", or "both A and B". In other words, "A or B (A or B)" in the present disclosure can be interpreted as "A and / or B (A and / or B)". For example, in the present disclosure, "A, B, or C (A, B, or C)" means "only A", "only B", "only C", or "any one and any combination of A, B, and C".

[0055] The slashes ( / ) or commas used in this disclosure may mean "and / or". For example, "A / B" may mean "A and / or B". Thus, "A / B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B, or C".

[0056] In this disclosure, "at least one of A and B" may mean "only A", "only B", or "both A and B". Additionally, in this disclosure, the expressions "at least one of A or B" or "at least one of A and / or B" may be equally interpreted as "at least one of A and B".

[0057] Furthermore, in this disclosure, "at least one of A, B, and C" means "only A", "only B", "only C", or "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".

[0058] Moreover, the parentheses used in this disclosure may mean "for example". Specifically, when "prediction (intra prediction)" is indicated, it may be referred to as this "intra prediction" being presented as an example of "prediction". In other words, "prediction" in this disclosure is not limited to "intra prediction", and "intra prediction" may be presented as an example of "prediction". Additionally, even when "prediction (i.e., intra prediction)" is indicated, it may be referred to as this "intra prediction" being presented as an example of "prediction".

[0059] The technical features separately described in one drawing in this disclosure may be implemented individually or simultaneously.

[0060] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Hereinafter, the same reference numerals in the drawings may be used for the same components, and repeated descriptions of the same components may be omitted.

[0061] Figure 1 An example of a video / image compilation system to which embodiments of this document can be applied is schematically illustrated.

[0062] Reference Figure 1 , the video / image compilation system may include a source device and a receiving device. The source device may deliver encoded video / image information or data to the receiving device in the form of a file or a stream via a digital storage medium or a network.

[0063] The source device may include a video source, an encoding device, and a transmitter. The receiving device may include a receiver, a decoding device, and a renderer. The encoding device may be referred to as a video / image encoding device, and the decoding device may be referred to as a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display, and the display may be configured as a separate device or an external component.

[0064] The video source may obtain video / images through processes such as capturing, synthesizing, or generating video / images. The video source may include a video / image capture device and / or a video / image generation device. For example, the video / image capture device may include one or more cameras, a video / image archive including previously captured video / images, etc. For example, the video / image generation device may include a computer, a tablet computer, and a smart phone, and may generate video / images (electronically). For example, virtual video / images may be generated by a computer or the like. In this case, the video / image capture process may be replaced by a process of generating relevant data.

[0065] The encoding device may encode the input video / images. For compression and compilation efficiency, the encoding device may perform a series of processes such as prediction, transformation, and quantization. The encoded data (encoded video / image information) may be output in the form of a bitstream.

[0066] The transmitter may send the encoded image / video information or data output in the form of a bitstream to the receiver of the receiving device in the form of a file or a stream via a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter may include elements for generating a media file in a predetermined file format and may include elements for transmitting via a broadcast / communication network. The receiver may receive / extract the bitstream and send the received bitstream to the decoding device.

[0067] The decoding device may decode the video / images by performing a series of processes such as dequantization, inverse transformation, and prediction corresponding to the operations of the encoding device.

[0068] The renderer may render the decoded video / images. The rendered video / images may be displayed via a display.

[0069] Figure 2 is a diagram schematically explaining the configuration of a video / image encoding device to which this document is applicable. Hereinafter, the video encoding device may include an image encoding device.

[0070] Reference Figure 2, the encoding device 200 includes an image splitter 210, a predictor 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The predictor 220 may include an inter-frame predictor 221 and an intra-frame predictor 222. The residual processor 230 may include a transformer 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235. The residual processor 230 may further include a subtractor 231. The adder 250 may be referred to as a reconstructor or a reconstruction block generator. According to an embodiment, the image splitter 210, the predictor 220, the residual processor 230, the entropy encoder 240, the adder 250, and the filter 260 may be configured by at least one hardware component (e.g., an encoder chipset or a processor). Additionally, the memory 270 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium. The hardware component may further include the memory 270 as an internal / external component.

[0071] The image splitter 210 may split an input image (or picture or frame) input to the encoding device 200 into one or more processing units. For example, the processing unit may be referred to as a coding unit (CU). In this case, the coding unit may be recursively split from a coding tree unit (CTU) or a largest coding unit (LCU) according to a quadtree binary tree ternary tree (QTBTTT) structure. For example, a coding unit may be split into multiple coding units with a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. In this case, for example, the quadtree structure may be applied first, and / or the binary tree structure and / or the ternary tree structure may be applied later. Alternatively, the binary tree structure may also be applied first. The coding process according to the present disclosure may be performed based on the final coding unit that is no longer splittable. In this case, based on the coding efficiency according to the image features, the largest coding unit may be used as the final coding unit, or if necessary, the coding unit may be recursively split into coding units with a deeper depth, and the coding unit with the optimal size may be used as the final coding unit. Here, the coding process may include the processes of prediction, transformation, and reconstruction described later. 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 partitioned or split from the aforementioned final coding unit. The prediction unit may be a unit for sample prediction, and the transformation unit may be a unit for deriving transformation coefficients and / or a unit for deriving a residual signal from the transformation coefficients.

[0072] In some cases, units can be used interchangeably with terms such as blocks or regions. In general, an M×N block can represent a set of samples or transform coefficients consisting of M columns and N rows. Samples can generally represent pixels or pixel values, which can be pixels / pixel values representing only the luminance component or pixels / pixel values representing only the chrominance component. Samples can be used as a term corresponding to the pixels or picture elements of a picture (or image).

[0073] The subtractor 231 can generate a residual signal (residual block, residual sample or residual sample array) by subtracting the prediction signal (prediction block, prediction sample or prediction sample array) output from the predictor 220 from the input image signal (original block, original sample or original sample array), and can send the generated residual signal to the transformer 232. The predictor 220 can perform prediction on the processing target block (hereinafter referred to as "current block") and can generate a prediction block including prediction samples for the current block. The predictor 220 can determine whether to apply intra-frame prediction or inter-frame prediction in units of the current block or CU. The predictor can generate and transmit various information about the prediction, such as prediction mode information which will be described later in the explanation of each prediction mode, to the entropy encoder 240. The information about the prediction can be encoded by the entropy encoder 240 and can be output in the form of a bitstream.

[0074] The intra-frame predictor 222 can predict the current block by referring to samples in the current picture. Depending on the prediction mode, the samples referred to can be located near the current block or can be separated. In intra-frame prediction, the prediction mode can include multiple non-directional modes and multiple directional modes. For example, the non-directional modes can include the DC mode and the planar mode. For example, depending on the level of detail of the prediction direction, the directional modes can include 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes can be used according to the settings. The intra-frame predictor 222 can determine the prediction mode applied to the current block by using the prediction mode applied to neighboring blocks.

[0075] The inter-frame predictor 221 may derive a prediction block of a current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. Here, in order to reduce the amount of motion information transmitted in the inter-frame 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 neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter-frame predictor 221 may configure a motion information candidate list based on neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or the reference picture index of the current block. The inter-frame prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter-frame predictor 221 may use the motion information of neighboring blocks as the motion information of the current block. In the skip mode, different from the merge mode, the residual signal may not be transmitted. In the case of the motion vector prediction (MVP) mode, the motion vector of a neighboring 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.

[0076] The predictor 220 may generate a prediction signal based on various prediction methods described below. For example, the predictor may not only apply intra-frame prediction or inter-frame prediction to predict a block, but also apply intra-frame prediction and inter-frame prediction simultaneously. This may be referred to as combined inter-frame and intra-frame prediction (CIIP). In addition, the predictor may perform intra-block copy (IBC) for prediction of a block. The intra-block copy may be used for content image / video compilation such as games, for example, screen content compilation (SCC). The IBC basically performs prediction in the current picture, but may be performed similarly to inter-frame prediction in terms of deriving a reference block in the current picture. That is, the IBC may use at least one of the inter-frame prediction techniques described in this document.

[0077] The prediction signal generated by the inter-frame predictor 221 and / or the intra-frame predictor 222 can be used to generate a reconstructed signal or to generate a residual signal. The transformer 232 can generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique can include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a graph-based transform (GBT), or a conditional non-linear transform (CNT). Here, GBT means a transform obtained from a graph 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 transform process can be applied to a square pixel block of the same size, or can be applied to a block having a variable size rather than a square.

[0078] The quantizer 233 can quantize the transform coefficients and send them to the entropy encoder 240 and the entropy encoder 240 can encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients can be referred to as residual information. The quantizer 233 can rearrange the block-based quantized transform coefficients into a one-dimensional vector form based on the coefficient scan order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoder 240 can perform various coding methods, for example, exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 240 can encode information required for video / image reconstruction, in addition to the quantized transform coefficients (for example, the values of syntax elements, etc.), together or separately. The encoded information (for example, encoded video / image information) can be sent or stored in the form of a bitstream in units of NAL (network abstraction layer). The video / image information can further include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information can further include general constraint information. In this document, the information and / or syntax elements signaled / sent later in this document can be encoded by the above encoding process and can be included in the bitstream. The bitstream can be sent through a network or can be stored in a digital storage medium. The network can include a broadcast network and / or a communication network, and the digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that sends the signal output from the entropy encoder 240 and / or a storage unit (not shown) that stores the signal can be included as an internal / external element of the encoding device 200, and alternatively, the transmitter can be included in the entropy encoder 240.

[0079] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, the quantized transform coefficients can be dequantized and inverse-transformed by the dequantizer 234 and the inverse-transformer 235 to reconstruct the residual signal (residual block or residual sample). The adder 250 adds the reconstructed residual signal to the prediction signal output from the predictor 220 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample, or reconstructed sample array). If the block to be processed has no residual, such as in the case of applying the skip mode, the predicted block can be used as the reconstructed block. The generated reconstructed signal can be used for intra prediction of the next block to be processed in the current picture and can be used for inter prediction of the next picture through filtering as described below.

[0080] Meanwhile, luminance mapping and chrominance scaling (LMCS) can be applied during picture encoding and / or reconstruction.

[0081] The filter 260 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 260 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture and store the modified reconstructed picture in the memory 270 (specifically, the DPB of the memory 270). The various filtering methods can include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filter 260 can generate various information related to the filtering and send the generated information to the entropy encoder 240, as described later in the description of each filtering method. The information related to the filtering can be encoded by the entropy encoder 240 and output in the form of a bitstream.

[0082] The modified reconstructed picture sent to the memory 270 can be used as a reference picture in the inter predictor 221. When inter prediction is applied by the encoding device, the prediction mismatch between the encoding device 200 and the decoding device 300 can be avoided, and the encoding efficiency can be improved.

[0083] The DPB of the memory 270 can store the modified reconstructed picture to be used as a reference picture in the inter predictor 221. The memory 270 can store the motion information of the blocks from which the motion information in the current picture is derived (or encoded) and / or the motion information of the blocks in the already reconstructed pictures. The stored motion information can be sent to the inter predictor 221 and used as the motion information of spatially neighboring blocks or temporally neighboring blocks. The memory 270 can store the reconstructed samples of the reconstructed blocks in the current picture and can pass the reconstructed samples to the intra predictor 222.

[0084] Figure 3 is a diagram schematically explaining the configuration of a video / image decoding device to which this document is applicable.

[0085] ReferenceFigure 3 , the decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter-frame predictor 331 and an intra-frame predictor 332. The residual processor 320 may include a dequantizer 321 and an inverse transformer 321. According to an embodiment, the entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 may be configured by hardware components (e.g., a decoder chipset or a processor). Additionally, the memory 360 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware components may also include the memory 360 as an internal / external component.

[0086] When receiving a bitstream including video / image information, the decoding device 300 may reconstruct an image corresponding to the processing of the video / image information in the Figure 2 encoding device. For example, the decoding device 300 may derive units / blocks based on block partitioning-related information obtained from the bitstream. The decoding device 300 may use the processor applied in the encoding device to perform decoding. Thus, the decoding processor may be, for example, a compilation unit, and the compilation unit may be partitioned from a compilation tree unit or the largest compilation unit according to a quadtree structure, a binary tree structure, and / or a ternary tree structure. One or more transform units may be derived from the compilation unit. The reconstructed image signal decoded and output by the decoding device 300 may be reproduced by a reproduction device.

[0087] The decoding device 300 may receive in the form of a bitstream from Figure 2The signals output by the encoding device, and the received signals can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive the information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information can further include information about various parameter sets, such as adaptive parameter set (APS), picture parameter set (PPS), sequence parameter set (SPS), or video parameter set (VPS). In addition, the video / image information can further include general constraint information. The decoding device can further decode the picture based on the information about the parameter set and / or the general constraint information. The information and / or syntax elements signaled / received later in this document can be decoded through the decoding process and obtained from the bitstream. For example, the entropy decoder 310 can decode the information in the bitstream based on encoding methods such as exponential Golomb coding, CAVLC, or CABAC, and the output values of the syntax elements required for image reconstruction and the quantization values of the transform coefficients for the residuals. More specifically, the CABAC entropy decoding method can receive the bins corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the neighborhood and the decoding information of the decoding target block, or the information of the symbols / bins decoded in the previous stage to determine the context model, and perform arithmetic decoding on the bins by predicting the probability of the bin appearance according to the determined context model, and generate the symbols corresponding to the values of each syntax element. In this case, the CABAC entropy decoding method can update the context model by using the information of the decoded symbols / bins for the context model of the next symbol / bin after determining the context model. The information about prediction among the information decoded by the entropy decoder 310 can be provided to the predictor 330, and the information about the residuals for which entropy decoding has been performed in the entropy decoder 310, that is, the quantized transform coefficients and the related parameter information can be input to the dequantizer 321. In addition, the information about filtering among the information decoded by the entropy decoder 310 can be provided to the filter 350. Meanwhile, the receiver (not shown) for receiving the signals output by the encoding device can be further configured as an internal / external element of the decoding device 300, or the receiver can be a component of the entropy decoder 310. Meanwhile, the decoding device according to this document can be referred to as a video / image / picture decoding device, and the decoding device can be classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder can include the entropy decoder 310, and the sample decoder can include at least one of the dequantizer 321, the inverse transformer 322, the predictor 330, the adder 340, the filter 350, and the memory 360.

[0088] The dequantizer 321 can dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 321 can rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement can be performed based on the coefficient scan order executed in the encoding device. The dequantizer 321 can perform dequantization on the quantized transform coefficients by using quantization parameters (e.g., quantization step information) and obtain the transform coefficients.

[0089] The inverse transformer 322 performs an inverse transformation on the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0090] The predictor can perform prediction on the current block and generate a prediction block including prediction samples for the current block. The predictor can determine whether to apply intra prediction or inter prediction to the current block based on the information about prediction output from the entropy decoder 310 and can determine a specific intra / inter prediction mode.

[0091] The predictor can generate a prediction signal based on various prediction methods described below. For example, the predictor can not only apply intra prediction or inter prediction to predict a block, but also apply intra prediction and inter prediction simultaneously. This can be referred to as combined inter and intra prediction (CIIP). In addition, the predictor can perform intra block copy (IBC) for prediction of a block. Intra block copy can be used for content image / video compilation such as games, e.g., screen content compilation (SCC). IBC basically performs prediction in the current picture, but can be performed similar to inter prediction because a reference block is derived in the current picture. That is, IBC can use at least one of the inter prediction techniques described in this document.

[0092] The intra predictor 331 can predict the current block by referring to samples in the current picture. The samples referred to can be located near the current block or at separate positions according to the prediction mode. In intra prediction, the prediction mode can include multiple non-directional modes and multiple directional modes. The intra predictor 331 can determine the prediction mode applied to the current block by using the prediction mode applied to neighboring blocks.

[0093] The inter - frame predictor 332 can derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter - frame prediction mode, the motion information can be predicted in units of blocks, sub - blocks, or samples based on the correlation of the motion information between neighboring blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can further include inter - frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter - frame prediction, neighboring blocks can include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter - frame predictor 332 can configure a motion information candidate list based on neighboring blocks and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter - frame prediction can be performed based on various prediction modes, and the information about the prediction can include information indicating the mode used for the inter - frame prediction of the current block.

[0094] The adder 340 can generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the predictor (330). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as the reconstructed block.

[0095] The adder 340 can be referred to as a reconstructor or a reconstructed - block generator. The generated reconstructed signal can be used for intra - frame prediction of the next block to be processed in the current picture, can be output through filtering as described below, or can be used for inter - frame prediction of the next picture.

[0096] Meanwhile, luminance mapping and chrominance scaling (LMCS) can be applied during picture decoding.

[0097] The filter 350 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture and store the modified reconstructed picture in the memory 360 (specifically, the DPB of the memory 360). The various filtering methods can include, for example, de - blocking filtering, sample - adaptive offset, adaptive loop filter, bilateral filter, etc.

[0098] The (modified) reconstructed picture stored in the DPB of the memory 360 can be used as a reference picture in the inter - frame predictor 332. The memory 360 can store the motion information of the blocks from which the motion information in the current picture is derived (or decoded) and / or the motion information of the blocks in the already - reconstructed pictures. The stored motion information can be sent to the inter - frame predictor 260 and used as the motion information of spatially - adjacent blocks or temporally - adjacent blocks. The memory 360 can store the reconstructed samples of the reconstructed blocks in the current picture and pass the reconstructed samples to the intra - frame predictor 331.

[0099] In this specification, the embodiments explained in the predictor 330, de - quantizer 321, inverse transformer 322, and filter 350 of the decoding device 300 can be applied to or correspond to the predictor 220, de - quantizer 234, inverse transformer 235, and filter 260 of the encoding device 200 in the same way, respectively.

[0100] As described above, in video coding, prediction is performed to improve the compression efficiency. Through this operation, a prediction block including prediction samples for the current block (i.e., the block to be coded) can be generated. Here, the prediction block includes prediction samples in the spatial domain (or pixel domain). The prediction block is derived identically in the encoding device and the decoding device, and the encoding device decodes information (residual information) regarding the residual between the original block and the prediction block (rather than the original sample values of the original block itself). Signaling to the device can improve the image coding efficiency. The decoding device can derive a residual block including residual samples based on the residual information, generate a reconstructed block including reconstructed samples by adding the residual block and the prediction block, and generate a reconstructed picture including the reconstructed block.

[0101] The residual information can be generated through transformation processing and quantization processing. For example, the encoding device can derive a residual block between the original block and the prediction block, perform transformation processing on the residual samples (residual sample array) included in the residual block to derive transformation coefficients, and then derive quantized transformation coefficients by performing quantization processing on the transformation coefficients to signal the residual - related information (via the bitstream) to the decoding device. Here, the residual information can include value information, position information, transformation technique, transformation core, and quantization parameters, etc., of the quantized transformation coefficients. The decoding device can perform de - quantization / inverse - transformation processing based on the residual information and derive the residual samples (or residual block). The decoding device can generate a reconstructed picture based on the prediction block and the residual block. The encoding device can also de - quantize / inverse - transform the quantized transformation coefficients for inter - frame prediction reference of subsequent pictures to derive a residual block and generate a reconstructed picture based on this.

[0102] In this document, at least one of quantization / dequantization and / or transform / inverse transform may be omitted. When quantization / dequantization is omitted, the quantized transform coefficients may be referred to as transform coefficients. When transform / inverse transform is omitted, the transform coefficients may be referred to as coefficients or residual coefficients, or, for the sake of consistency of expression, may still be referred to as transform coefficients.

[0103] In this document, the quantized transform coefficients and the transform coefficients may be referred to as transform coefficients and scaled transform coefficients, respectively. In this case, the residual information may include information about the transform coefficients, and the information about the transform coefficients may be signaled by the residual coding syntax. The transform coefficients may be derived based on the residual information (or the information about the transform coefficients), and the scaled transform coefficients may be derived by inverse-transforming (scaling) the transform coefficients. The residual samples may be derived based on the inverse-transform (transformation) of the scaled transform coefficients. This may also be applied / expressed in other parts of this document.

[0104] The predictor of an encoding device / decoding device may derive a prediction sample by performing inter-frame prediction in units of blocks. Inter-frame prediction may be prediction derived in a manner that depends on data elements (e.g., sample values or motion information) of pictures other than the current picture. When applying inter-frame prediction to a current block, a prediction block (prediction sample array) for the current block may be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. Here, in order to reduce the amount of motion information transmitted in the inter-frame 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 neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, a motion information candidate list may be configured based on neighboring blocks of the current block, and a flag or index information indicating which candidate is selected (used) may be signaled to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the motion information of the current block may be the same as the motion information of the neighboring block. In the skip mode, different from the merge mode, a residual signal may not be transmitted. In the case of the motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0105] Depending on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. 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. The prediction based on the L0 motion vector may be referred to as L0 prediction, the prediction based on the L1 motion vector may be referred to as L1 prediction, and the prediction based on both the L0 motion vector and the L1 motion vector may be referred to as bidirectional prediction. Here, the L0 motion vector may indicate the motion vector associated with the reference picture list L0 (L0), and the L1 motion vector may indicate the motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include pictures earlier than the current picture in the output order as reference pictures, and the reference picture list L1 may include pictures later than the current picture in the output order. The previous pictures may be referred to as forward (reference) pictures, and the subsequent pictures may be referred to as backward (reference) pictures. The reference picture list L0 may also include pictures later than the current picture in the output order as reference pictures. In this case, the previous pictures may be indexed first in the reference picture list L0, and the subsequent pictures may be indexed later. The reference picture list L1 may also include pictures earlier than the current picture in the output order as reference pictures. In this case, the subsequent pictures may be indexed first in the reference picture list 1, and the previous pictures may be indexed later. The output order may correspond to the picture order count (POC) order.

[0106] Figure 4 Exemplarily shows the hierarchical structure of the compiled image / video.

[0107] Reference Figure 4 , the compiled image / video is divided into a video coding layer (VCL) that processes the image / video and its own decoding process, a subsystem that transmits and stores the compiled information, and a NAL (network abstraction layer) that is responsible for the network adaptation function and exists between the VCL and the subsystem.

[0108] In the VCL, VCL data including compressed image data (slice data) may be generated, or parameter sets including picture parameter sets (PSP), sequence parameter sets (SPS), and video parameter sets (VPS), or supplementary enhancement information (SEI) messages additionally required for the image decoding process may be generated.

[0109] In the NAL, a NAL unit can be generated by adding header information (NAL unit header) to the raw byte sequence payload (RBSP) generated in the VCL. In this case, the RBSP refers to slice data, parameter sets, SEI messages, etc. generated in the VCL. The NAL unit header can include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0110] As shown in the figure, NAL units can be divided into VCL NAL units and non-VCL NAL units according to the RBSP generated in the VCL. A VCL NAL unit can mean a NAL unit including information about an image (slice data), and a non-VCL NAL unit can mean a NAL unit including information (parameter set or SEI message) required for decoding the image.

[0111] The aforementioned VCL NAL units and non-VCL NAL units can be sent over a network by attaching header information according to the data standards of the subsystem. For example, the NAL units can be transformed into a data format of a predetermined standard such as the H.266 / VVC file format, Real-Time Transport Protocol (RTP), Transport Stream (TS), etc., and sent over various networks.

[0112] As described above, the NAL unit can be specified using the NAL unit type according to the RBSP data structure included in the corresponding NAL unit, and information about the NAL unit type can be stored and signaled in the NAL unit header.

[0113] For example, NAL units can be classified into VCL NAL unit types and non-VCL NAL unit types according to whether the NAL unit includes information about an image (slice data). The VCL NAL unit types can be classified according to the nature and type of the pictures included in the VCL NAL units, and the non-VCL NAL unit types can be classified according to the type of the parameter sets.

[0114] The following are examples of NAL unit types specified according to the type of parameter sets included in the non-VCL NAL unit types.

[0115] - APS (Adaptive Parameter Set) NAL unit: The type for a NAL unit including APS

[0116] - DPS (Decoding Parameter Set) NAL unit: The type for a NAL unit including DPS

[0117] - VPS (Video Parameter Set) NAL unit: The type for a NAL unit including VPS

[0118] -SPS (Sequence Parameter Set) NAL unit: The type of NAL unit used to include SPS

[0119] -PPS (Picture Parameter Set) NAL unit: The type of NAL unit used to include PPS

[0120] -PH (Picture Header) NAL unit: The type of NAL unit used to include PH

[0121] The aforementioned NAL unit types may have syntax information for the NAL unit type and may store and signal the syntax information in the NAL unit header. For example, the syntax information may be nal_unit_type, and the NAL unit type may be specified by the nal_unit_type value.

[0122] Meanwhile, as described above, a picture may include multiple slices, and a slice may include a slice header and slice data. In this case, a picture header may be further added to the multiple slices (slice header and slice data set) in a picture. The picture header (picture header syntax) may include information / parameters that are commonly applicable to the picture. In this document, slices may be used interchangeably with or replaced by tile groups. Additionally, in this document, slice headers may be used interchangeably with or replaced by tile group headers.

[0123] The slice header (slice header syntax, slice header information) may include information / parameters that can be commonly applied to the slice. APS (APS syntax) or PPS (PPS syntax) may include information / parameters that can be commonly applied to one or more slices or pictures. SPS (SPS syntax) may include information / parameters that can be commonly applied to one or more sequences. VPS (VPS syntax) may include information / parameters that can be commonly applied to multiple layers. DPS (DPS syntax) may include information / parameters that can be commonly applied to the entire video. DPS may include information / parameters related to the concatenation of the compiled video sequence (CVS). The high-level syntax (HLS) in this document may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, and slice header syntax.

[0124] In this document, the image / image information encoded by the encoding device and signaled to the decoding device in the form of a bitstream includes not only information related to partitions in the picture, intra / inter prediction information, residual information, in-loop filter information, etc., but also information included in the slice header, information included in APS, information included in PPS, information included in SPS, and / or information included in VPS.

[0125] Meanwhile, in order to compensate for the difference between the original image and the reconstructed image caused by errors occurring during the compression encoding process such as quantization, the in-loop filtering process can be performed on the reconstructed samples or the reconstructed picture as described above. As described above, the in-loop filtering can be performed by the filter of the encoding device and the filter of the decoding device, and a deblocking filter, SAO, and / or an adaptive loop filter (ALF) can be applied. For example, the ALF process can be performed after the deblocking filtering process and / or the SAO process. However, even in this case, the deblocking filtering process and / or the SAO process can be omitted.

[0126] Hereinafter, a detailed description of picture reconstruction and filtering will be described. In image / video encoding, a reconstructed block can be generated based on intra prediction / inter prediction for each block, and a reconstructed picture including the reconstructed blocks can be generated. When the current picture / slice is an I picture / slice, the blocks included in the current picture / slice can be reconstructed only based on intra prediction. Meanwhile, when the current picture / slice is a P or B picture / slice, the blocks included in the current picture / slice can be reconstructed based on intra prediction or inter prediction. In this case, intra prediction can be applied to some of the blocks in the current picture / slice, and inter prediction can be applied to the remaining blocks.

[0127] Intra prediction can refer to a prediction that generates a prediction sample of a current block based on reference samples in the picture (hereinafter referred to as the current picture) to which the current block belongs. When applying intra prediction to the current block, the neighboring reference samples to be used for the intra prediction of the current block can be derived. The neighboring reference samples of the current block can include a total of 2xnH samples adjacent to the left boundary of the current block having a size of nWxnH and adjacent to the lower left, samples adjacent to the upper boundary of the current block and a total of 2xnW samples adjacent to the upper right, and one sample adjacent to the upper left of the current block. Alternatively, the neighboring reference samples of the current block can include a plurality of upper neighboring samples and a plurality of left neighboring samples. In addition, the neighboring reference samples of the current block can include a total of nH samples adjacent to the right boundary of the current block having a size of nWxnH, a total of nW samples adjacent to the lower boundary of the current block, and one sample adjacent to the lower right of the current block.

[0128] However, some of the neighboring reference samples of the current block may still not be decoded or available. In this case, the decoder can configure the neighboring reference samples to be used for prediction by replacing the unavailable samples with the available samples. Alternatively, the neighboring reference samples to be used for prediction can be configured by interpolation of the available samples.

[0129] When deriving neighboring reference samples, a predicted sample can be derived based on the average or interpolation of neighboring reference samples of the current block and (ii) a prediction among the neighboring reference samples of the current block. A predicted sample can be derived based on reference samples existing in a specific (prediction) direction relative to the sample. The case of (i) can be referred to as a non-directional mode or non-angle mode, and the case of (ii) can be referred to as a directional mode or angle mode. Additionally, based on the predicted sample of the current block among the neighboring reference samples, a first neighboring sample and a second neighboring sample located in a direction opposite to the prediction direction of the intra prediction mode of the current block are interpolated. A predicted sample can be generated. The above can be referred to as linear interpolation intra prediction (LIP). Additionally, a chrominance prediction sample can be generated based on a linear model using luminance samples. This case can be referred to as the LM mode. Additionally, a temporary prediction sample of the current block can be derived based on filtered neighboring reference samples, and a weighted sum of at least one reference sample (i.e., unfiltered neighboring reference samples) derived according to the intra prediction mode among the existing neighboring reference samples and the temporary prediction sample can be performed to derive the predicted sample of the current block. The above can be referred to as position-dependent intra prediction (PDPC). Additionally, a reference sample line with the highest prediction accuracy among the neighboring multi-reference sample lines of the current block can be selected to derive a predicted sample by using the reference samples located in the prediction direction on the corresponding line, and then the reference sample line indication (signaled) used herein can be given to the decoding device to perform intra prediction coding. The above can be referred to as multi-reference line (MRL) intra prediction or MRL-based intra prediction. Additionally, intra prediction can be performed based on the same intra prediction mode by dividing the current block into vertical or horizontal sub-partitions, and neighboring reference samples can be derived and used in the sub-partition unit. That is, in this case, the intra prediction mode for the current block is equally applied to the sub-partitions, and in some cases, the intra prediction performance can be improved by deriving and using neighboring reference samples in the sub-partition unit. Such a prediction method can be referred to as intra sub-partition (ISP) or ISP-based intra prediction. The foregoing intra prediction methods can be separately referred to as intra prediction types from the intra prediction mode. The intra prediction type can be called by various terms such as intra prediction techniques or additional intra prediction modes. For example, the intra prediction type (or additional intra prediction mode) can include at least one of the foregoing LIP, PDPC, MRL, and ISP. A general intra prediction method other than a specific intra prediction type such as LIP, PDPC, MRL, or ISP can be referred to as a normal intra prediction type. When a specific intra prediction type cannot be applied, the normal intra prediction type can generally be applied, and prediction can be performed based on the above intra prediction mode. Meanwhile, post-filtering can be performed on the derived predicted samples as needed.

[0130] Specifically, the intra prediction process may include an intra prediction mode / type determination step, a neighboring reference sample derivation step, and a predicted sample derivation step based on the intra prediction mode / type. Additionally, a post-filtering step may be performed on the derived predicted samples as needed.

[0131] Hereinafter, the intra prediction in the encoding device will be described. The encoding device may derive an intra prediction mode for a current block, derive neighboring reference samples of the current block, and generate predicted samples in the current block based on the intra prediction mode and the neighboring reference samples. Here, the intra prediction mode determination, the surrounding reference sample derivation, and the predicted sample generation processes may be performed simultaneously, or one process may be performed before another process. For example, the intra predictor 222 of the encoding device may include a prediction mode / type determiner, a reference sample deriver, and a predicted sample deriver, and the prediction mode / type determiner may determine the intra prediction mode / type for the current block, the reference sample deriver may derive the neighboring reference samples of the current block, and the predicted sample deriver may derive the motion samples of the current block. Meanwhile, although not shown, when performing the predicted sample filtering process to be described later, the intra predictor 222 may also include a predicted sample filter (not shown). The encoding device may determine a mode to be applied to the current block from among a plurality of intra prediction modes. The encoding device may compare the RD costs of the intra prediction modes and determine the best intra prediction mode for the current block.

[0132] Meanwhile, the encoding device may perform a predicted sample filtering process. The predicted sample filtering may be referred to as post-filtering. Some or all of the predicted samples may be filtered through the predicted sample filtering process. In some cases, the predicted sample filtering process may be omitted.

[0133] The encoding device derives residual samples for the current block based on the predicted samples (S510). The encoding device may compare the predicted samples in the original samples of the current block based on the phase and derive the residual samples.

[0134] The encoding device may perform transform / quantization on the residual samples to derive quantized transform coefficients (S520), and then perform dequantization / inverse transform on the quantized transform coefficients again to derive (modified) residual samples (S530). The reason for performing dequantization / inverse transform again after transform / quantization is to derive the same residual samples as the residual samples derived from the decoding device as described above.

[0135] The encoding device may generate a reconstructed block including reconstructed samples for the current block based on the predicted samples and the (modified) residual samples (S540). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0136] As described above, the encoding device may encode image information including prediction information regarding intra prediction (e.g., 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 bitstream. The residual information may include a residual compilation syntax. The encoding device may perform transform / quantization on the residual samples to derive quantized transform coefficients. The residual information may include information regarding the quantized transform coefficients.

[0137] Figure 5 is a flowchart illustrating a block reconstruction method based on intra prediction in a decoding device. Figure 5 The method may include steps S500, S510, S520, S530, and S540. The decoding device may perform operations corresponding to those performed in the encoding device.

[0138] S500 to S520 may be performed by the intra predictor 331 of the decoding device, and the prediction information of S500 and the residual information of S530 may be obtained by the entropy decoder 310 of the decoding device from the bitstream. The residual processor 320 of the decoding device may derive residual samples for the current block based on the residual information. Specifically, the dequantizer 321 of the residual processor 320 derives transform coefficients by performing dequantization based on the quantized transform coefficients derived based on the residual information, and the inverse transformer 322 of the residual processor may derive residual samples for the current block by performing an inverse transform on the transform coefficients. S540 may be performed by the adder 340 or the reconstructor of the decoding device.

[0139] Specifically, the decoding device may derive an intra prediction mode for the current block based on the received prediction mode information (S500). The decoding device may derive surrounding reference samples of the current block (S510). The decoding device generates prediction samples in the current block based on the intra prediction mode and neighboring reference samples (S520). In this case, the decoding device may perform a prediction sample filtering process. The prediction sample filtering may be referred to as post-filtering. Some or all of the prediction samples may be filtered through the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0140] The decoding device generates residual samples for the current block based on the received residual information (S530). The decoding device may generate reconstruction samples for the current block based on the prediction samples and the residual samples, and derive a reconstruction block including the reconstruction samples (S540). A reconstructed picture for the current picture may be generated based on the reconstruction block.

[0141] Here, the intra predictor 331 of the decoding device may include a prediction mode / type determiner, a reference sample derivator, and a predicted sample derivator. The prediction mode / type determiner may determine an intra prediction mode for a current block based on prediction mode information obtained by the entropy decoder 310 of the decoding device. The reference sample derivator may derive surrounding reference samples of the current block, and the predicted sample derivator may derive predicted samples of the current block. Also, although not shown, when performing the above-described predicted sample filtering process, the intra predictor 331 may further include a predicted sample filter (not shown).

[0142] 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 (e.g., Intra_luma_mpm_flag) indicating whether to apply the most probable mode (MPM) to the current block or to apply a residual mode. When applying MPM to the current block, the prediction mode information may further include index information (e.g., intra_luma_mpm_idx) indicating one of the intra prediction mode candidates (MPM candidates). The intra prediction mode candidates (MPM candidates) may include an MPM candidate list or an MPM list. Additionally, when not applying MPM to the current block, the intra prediction mode information may further include residual mode information (e.g., Intra_luma_mpm_remainder) indicating one of the remaining intra prediction modes other than the intra prediction mode candidates (MPM candidates). The decoding device may determine the intra prediction mode of the current block based on the intra prediction mode information. A separate MPM list may be configured for the foregoing MIP.

[0143] Additionally, the intra prediction type information can 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 the following: reference sample line information (e.g., Intra_luma_ref_idx) indicating whether to apply MRL to the current block and indicating which reference sample line is used in the case of application, ISP flag information (e.g., Intra_subpartitions_mode_flag) indicating whether to apply ISP to the current block, ISP type information (e.g., Intra_subpartitions_split_flag) indicating the split type of subpartitions when ISP is applied, flag information indicating whether PDCP is applied, or flag information indicating whether LIP is applied. Additionally, the intra prediction type information may include an MIP flag indicating whether to apply MIP to the current block.

[0144] The intra prediction mode information and / or intra prediction type information can be encoded / decoded by the encoding / decoding methods described in this disclosure. For example, the intra prediction mode information and / or intra prediction type information can be encoded / decoded by entropy encoding (e.g., CABAC, CAVLC) based on truncated (Rice) binary codes.

[0145] The predictor of the encoding / decoding apparatus can derive a predicted sample by performing inter prediction on a block-by-block basis. Inter prediction can be a prediction derived in a manner that depends on data elements (e.g., sample values or motion information) of pictures other than the current picture. When applying inter prediction to the current block, a predicted block (predicted sample array) for the current block can be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture 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 can be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between neighboring blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can also include inter prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When applying inter prediction, neighboring blocks can include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block can be the same as or different from each other. The temporal neighboring block can be referred to by names such as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block can be referred to as a collocated picture (colPic). For example, a motion information candidate list can be configured based on neighboring blocks of the current block, and a flag or index information indicating which candidate is selected (used) to derive the motion vector and / or reference picture index of the current block can be signaled. Inter prediction can be performed based on various prediction modes, and for example, in the case of the skip mode and the merge mode, the motion information of the current block can be the same as the motion information of the neighboring blocks. In the case of the skip mode, different from the merge mode, a residual signal may not be transmitted. 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 a motion vector difference can be signaled. In this case, the motion vector of the current block can be derived using the sum of the motion vector predictor and the motion vector difference.

[0146] Figure 6 is a flowchart illustrating a block reconstruction method based on inter prediction in an encoding apparatus. Figure 6 The method can include steps S600, S610, S620, S630, and S640.

[0147] S600 can be executed by the inter - frame predictor 221 of the encoding device, and S610 to S630 can be executed by the residual processor 230 of the encoding device. Specifically, S610 can be executed by the subtractor 231 of the encoding device, S620 can be executed by the transformer 232 and the quantizer 233 of the encoding device, and S630 can be executed by the de - quantizer 234 and the inverse transformer 235 of the encoding device. In S600, the prediction information can be derived by the inter - frame predictor 221 and encoded by the entropy encoder 240. The residual information can be derived through S610 and S620 and encoded by the entropy encoder 240. The residual information is information about the residual samples. The residual information can include information about the quantized transform coefficients for the residual samples. As described above, the residual samples can be derived as transform coefficients by the transformer 232 of the encoding device, and the transform coefficients can be derived as quantized transform coefficients by the quantizer 233. The information about the quantized transform coefficients can be encoded by the entropy encoder 240 through the residual encoding process.

[0148] The encoding device performs inter - frame prediction (S600) on the current block. The encoding device can derive the inter - frame prediction mode and motion information of the current block and generate the prediction samples of the current block. Here, the processes for determining the inter - frame prediction mode, deriving the motion information, and generating the prediction samples can be executed simultaneously, or one process can be executed before another process. For example, the inter - frame predictor 221 of the encoding device can include a prediction mode determiner, a motion information deriver, and a prediction sample deriver. The prediction mode determiner can determine the prediction mode for the current block, the motion information deriver can derive the motion information of the current block, and the prediction sample deriver can derive the motion samples of the current block. For example, the inter - frame predictor 221 of the encoding device can search for a block similar to the current block within a predetermined area (search area) of the reference picture through motion estimation and can derive a reference block whose difference from the current block is the smallest or a predetermined reference or less. Based on this, the reference picture index indicating the reference picture where the reference block is located can be derived, and the motion vector can be derived based on the position difference between the reference block and the current block. The encoding device can determine the mode applied to the current block from among various prediction modes. The encoding device can compare the rate - distortion (RD) costs for various prediction modes and determine the best prediction mode for the current block.

[0149] For example, when applying a skip mode or a merge mode to a current block, an encoding device may construct a merge candidate list to be described later and derive, among reference blocks indicated by merge candidates included in the merge candidate list, a reference block having the smallest difference from the current block or a reference block that is a predetermined reference or less. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information indicating the selected merge candidate may be generated and signaled to a decoding device. Motion information of the selected merge candidate may be used to derive motion information of the current block.

[0150] As another example, when applying an (A)MVP mode to a current block, an encoding device constructs an (A)MVP candidate list to be described later and uses a motion vector of a selected mvp candidate among motion vector predictors (mvps) included in the (A)MVP candidate list as the mvp of the current block. In this case, for example, a motion vector indicating a reference block derived by the above-described motion estimation may be used as the motion vector of the current block, and an mvp candidate having a motion vector with the smallest difference from the motion vector of the current block among the mvp candidates may be the selected mvp candidate. A motion vector difference (MVD) that is a difference obtained by subtracting the mvp from the motion vector of the current block may be derived. In this case, information about the MVD may be signaled to the decoding device. Additionally, when applying the (A)MVP mode, a value of a reference picture index may be configured as reference picture index information and signaled separately to the decoding device.

[0151] The encoding device may derive a residual sample based on a prediction sample (S610). The encoding device may derive the residual sample by comparing an original sample of the current block with the prediction sample.

[0152] The encoding device performs transform / quantization on the residual sample to derive quantized transform coefficients (S620), and then performs dequantization / inverse transform on the quantized transform coefficients again to derive a (modified) residual sample (S630). The reason for performing dequantization / inverse transform again after transform / quantization is to derive the same residual sample as the residual sample derived from the decoding device as described above.

[0153] The encoding device may generate a reconstructed block including reconstructed samples for the current block based on the prediction sample and the (modified) residual sample (S640). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0154] Although not shown, as described above, the encoding device 100 may encode video information including prediction information and residual information. The encoding device 100 can output the encoded picture information in the form of a bitstream. The prediction information may be information related to the prediction process and may include prediction mode information (e.g., skip flag, merge flag, or mode index) and motion information. The motion information may include candidate selection information (e.g., merge index, mvp flag, or mvp index) as information for deriving a motion vector. Additionally, information about the motion information may include the aforementioned MVD information and / or reference picture index information. Additionally, information about the motion information may include information indicating whether L0 prediction, L1 prediction, or bi prediction is applied. The residual information is information about residual samples. The residual information may include information about the quantization transform coefficients for the residual samples.

[0155] The output bitstream may be stored in a (digital) storage medium and sent to the decoding device, or may be sent to the decoding device via a network.

[0156] Figure 7 is a flowchart illustrating an inter-frame prediction-based block reconstruction method in a decoding device. Figure 7 The method may include steps S700, S710, S720, S730, and S740. The decoding device may perform operations corresponding to those performed by the encoding device.

[0157] S700 to S720 may be performed by the inter-frame predictor 332 of the decoding device, and the prediction information of S700 and the residual information of S730 may be obtained by the entropy decoder 310 of the decoding device from the bitstream. The residual processor 320 of the decoding device may derive residual samples for the current block based on the residual information. Specifically, the dequantizer 321 of the residual processor 320 may derive transform coefficients by performing dequantization based on the quantization transform coefficients derived based on the residual information, and the inverse transformer 322 of the residual processor may derive residual samples for the current block by performing an inverse transform on the transform coefficients. S740 may be performed by the adder 340 or the reconstructor of the decoding device.

[0158] Specifically, the decoding device may determine a prediction mode for the current block based on the received prediction information (S700). The decoding device may determine which inter-frame prediction mode to apply to the current block based on the prediction mode information in the prediction information.

[0159] For example, it is possible to determine whether to apply the merge mode to the current block or to determine the (A)MVP mode based on a merge flag. Alternatively, one of various inter prediction mode candidates can be selected based on a mode index. The inter prediction mode candidates can include a skip mode, a merge mode, and / or the (A)MVP mode, or can include various inter prediction modes to be described later.

[0160] The decoding apparatus derives motion information for the current block based on the determined inter prediction mode (S710). For example, when the skip mode or the merge mode is applied to the current block, the decoding apparatus can configure a merge candidate list to be described below and select one merge candidate from among the merge candidates included in the merge candidate list. The selection can be performed based on the aforementioned selection information (merge index). The motion information of the selected merge candidate can be used to derive the motion information of the current block. The motion information of the selected merge candidate can be used as the motion information of the current block.

[0161] As another example, when the (A)MVP mode is applied to the current block, the decoding apparatus can construct an (A)MVP candidate list to be described below and use the motion vector of the selected mvp candidate among the motion vector predictors (mvps) candidates included in the (A)MVP candidate list as the mvp of the current block. The selection can be performed based on the above selection information (mvp flag or mvp index). In this case, the MVD of the current block can be derived based on the information about the MVD, and the motion vector of the current block can be derived based on the mvp and the MVD of the current block. Additionally, the reference picture index of the current block can be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list for the current block can be derived as the reference picture referred to for the inter prediction of the current block.

[0162] Meanwhile, as will be described below, it is possible to derive the motion information of the current block without configuring a candidate list. In this case, the motion information of the current block can be derived according to the process disclosed in the prediction mode to be described later. In this case, the configuration of the candidate list as described above can be omitted.

[0163] The decoding apparatus can generate a prediction sample for the current block based on the motion information of the current block (S720). In this case, the reference picture can be derived based on the reference picture index of the current block, and the sample of the reference block indicated by the motion vector of the current block on the reference picture can be used to derive the prediction sample of the current block. In this case, as will be described later, a prediction sample filtering process for all or some of the prediction samples of the current block can be further performed depending on the situation.

[0164] For example, the inter - frame predictor 332 of the decoding device may include a prediction mode determiner, a motion information derivator, and a predicted sample derivator. The prediction mode determiner may determine a prediction mode for the current block based on the received prediction mode information. The motion information derivator may derive the motion information (motion vector and / or reference picture index, etc.) of the current block based on the received information about the motion information. And the predicted sample derivation unit may derive the predicted sample of the current block.

[0165] The decoding device generates residual samples for the current block based on the received residual information (S730). The decoding device may generate reconstructed samples for the current block based on the predicted samples and the residual samples, and may derive a reconstructed block including the reconstructed samples (S740). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0166] Various inter - frame prediction modes may be used for the prediction of the current block in a picture. For example, various modes such as the merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub - block merge mode, and merge with MVD (MMVD) mode, etc. may be used. Additionally or alternatively, decoder - side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, bi - prediction with CU - level weight (BCW), bidirectional optical flow (BDOF), etc. may be used as additional modes. The affine mode may be referred to as the affine motion prediction mode. The MVP mode may be called the advanced motion vector prediction (AMVP) mode. In this document, some modes and / or motion information candidates derived by some modes may be included as one of the motion information candidates of other modes. For example, HMVP candidates may be added as merge candidates in the merge / skip mode or may be added as mvp candidates in the MVP mode.

[0167] The prediction mode information indicating the inter - frame prediction mode of the current block may be signaled from the encoding device to the decoding device. The prediction mode information may be included in the bitstream and received by the decoding device. The prediction mode information may include index information indicating one of multiple candidate modes. Alternatively, the inter - frame prediction mode may be indicated by 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 the skip mode is applied. If the skip mode is not applied, a merge flag may be signaled to indicate whether the merge mode is applied. And if the merge mode is not applied, it indicates that the MVP mode is to be applied or flags for additional classification may be further signaled. The affine mode may be signaled in an independent mode or in a mode dependent on the merge mode or MVP mode. For example, the affine mode may include an affine merge mode and an affine MVP mode.

[0168] Meanwhile, information indicating whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used in the current block (current compilation unit) can be signaled in the current block. This information can be referred to as motion prediction direction information, inter-frame prediction direction information, or inter-frame prediction indication information, and can be configured / encoded / signaled in the form of, for example, an inter_pred_idc syntax element. That is, the inter_pred_idc syntax element can indicate whether the aforementioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used for the current block (current compilation unit). In this document, for the convenience of description, the inter-frame prediction type (L0 prediction, L1 prediction, or BI prediction) indicated by the inter_pred_idc syntax element can be referred to as the motion prediction direction. The L0 prediction can be represented as pred_L0, the L1 prediction can be represented as pred_L1, and the bi-prediction can be represented as pred_BI. For example, the following prediction types can be determined according to the value of the inter_pred_idc syntax element.

[0169] [Table 1]

[0170]

[0171] As described above, a picture can include one or more slices. A slice can have one of the slice types including an intra (I) slice, a predictive (P) slice, and a bi-predictive (B) slice. The slice type can be indicated based on slice type information. For blocks in an I slice, inter-frame prediction can be not used for prediction, and only intra-frame prediction can be used. Of course, even in this case, the original sample values can be compiled and signaled without prediction. Intra-frame prediction or inter-frame prediction can be used for blocks in a P slice, and only uni-directional prediction can be used when inter-frame prediction is used. Meanwhile, intra-frame prediction or inter-frame prediction can be used for blocks in a B slice, and up to bi-prediction can be used when inter-frame prediction is used.

[0172] L0 and L1 may include reference pictures that were previously encoded / decoded before the current picture. For example, L0 may include reference pictures before and / or after the current picture in POC order, and L1 may include reference pictures after and / or before the current picture in POC order. In this case, L0 may be assigned a reference picture index lower than the current picture with respect to a previous reference picture in POC order, and L1 may be assigned a reference picture index lower than the current picture with respect to a subsequent reference picture in POC order. In the case of a B slice, bi-prediction may be applied, and in this case, unidirectional bi-prediction or bidirectional bi-prediction may be applied. Bidirectional bi-prediction may be referred to as true bi-prediction.

[0173] As described above, a residual block (residual sample) may be derived based on a predicted block (predicted sample) derived by prediction at the encoding stage, and a residual sample transformed / quantized by residual information may be generated. The residual information may include information about quantized transform coefficients. The residual information may be included in video / image information, and the video / image information may be encoded and sent to a decoding device in the form of a bitstream. The decoding device may obtain the residual information from the bitstream and may derive a residual sample based on the residual information. Specifically, the decoding device may derive quantized transform coefficients based on the residual information and may derive a residual block (residual sample) through an inverse quantization / inverse transform process.

[0174] Meanwhile, at least one of the (inverse) transform and / or (de)quantization processes may be omitted.

[0175] Hereinafter, the in-loop filtering process performed on a reconstructed picture will be described. A modified reconstructed sample, block, picture (or modified filtered sample, block, picture) may be generated through the in-loop filtering process, and the modified (modified and filtered) reconstructed picture may be output as a decoded picture at the decoding device and may also be stored in a decoded picture buffer or memory of the encoding device / decoding device and used as a reference picture in an inter prediction process when encoding / decoding a picture later. The in-loop filtering process may include the deblocking filtering process, sample adaptive offset (SAO) process, and / or adaptive loop filter (ALF) process as described above. In this case, one or some of the deblocking filtering process, sample adaptive offset (SAO) process, adaptive loop filter (ALF) process, and bilateral filter process may be applied sequentially or all may be applied sequentially. For example, the SAO process may be performed after applying the deblocking filtering process to the reconstructed picture. Or, for example, the ALF process may be performed after applying the deblocking filtering process to the reconstructed picture. This may also be performed in the encoding device.

[0176] Deblocking filtering is a filtering technique for removing distortions at the boundaries between blocks in a reconstructed picture. For example, in the deblocking filtering process, a target boundary can be derived from the reconstructed picture, a boundary strength (bS) of the target boundary can be determined, and deblocking filtering can be performed on the target boundary based on bS. bS can be determined based on, for example, the prediction modes of two blocks adjacent to the target boundary, the motion vector difference, whether the reference pictures are the same, and whether there are non-zero valid coefficients, etc.

[0177] SAO is a method for compensating for the offset difference between a reconstructed picture and an original picture on a sample basis. For example, SAO can be applied based on types such as band offset, edge offset, etc. According to SAO, samples can be classified into different categories according to each SAO type, and an offset value can be added to each sample based on the category. Filtering information for SAO can include information on whether SAO is applied, SAO type information, and SAO offset value information. SAO can be applied to the reconstructed picture after deblocking filtering is applied.

[0178] Adaptive loop filter (ALF) is a technique for filtering a reconstructed picture on a sample basis based on filter coefficients according to the filter shape. An encoding device can determine whether to apply ALF, the ALF shape, and / or the ALF filter coefficients, etc. by comparing the reconstructed picture and the original picture and can signal them to a decoding device. That is, filtering information for ALF can include information on whether ALF is applied, ALF filter shape information, ALF filter coefficient information, etc. ALF can be applied to the reconstructed picture after deblocking filtering is applied.

[0179] Figure 8 An example showing the shape of the ALF filter.

[0180] In Figure 8 ,(a) shows the shape of a 7x7 diamond filter, and (b) shows the shape of a 5x5 diamond filter. In Figure 8Among them, Cn in the filter shape represents a filter coefficient. When n in Cn is the same, this indicates that the same filter coefficient can be assigned. In the present disclosure, the position and / or unit for assigning filter coefficients according to the filter shape of the ALF may be referred to as a filter tab. In this case, one filter coefficient can be assigned to each filter tab, and the arrangement of the filter tabs may correspond to the filter shape. The filter tab located at the center of the filter shape may be referred to as the central filter tab. The same filter coefficient can be assigned to two filter tabs having the same n value at positions corresponding to each other with respect to the central filter tab. For example, in the case of a 7×7 rhombic filter shape, including 25 filter tabs, and since the filter coefficients C0 to C11 are assigned in a centrosymmetric form, only 13 filter coefficients can be used to assign filter coefficients to 25 filter tabs. Additionally, for example, in the case of a 5x5 rhombic filter shape, including 13 filter tabs, and since the filter coefficients C0 to C5 are assigned in a centrosymmetric form, only 7 filter coefficients are used to assign filter coefficients to 13 filter tabs. For example, in order to reduce the amount of data on the information of the signalized filter coefficients, 12 out of 13 filter coefficients for the 7x7 rhombic filter shape can be (explicitly) signaled, and 1 filter coefficient can be (implicitly) derived. Additionally, for example, 6 out of 7 filter coefficients for the 5x5 rhombic filter shape can be (explicitly) signaled, and 1 filter coefficient can be (implicitly) derived.

[0181] According to an embodiment of the present disclosure, the ALF parameters for the ALF process can be signaled through an Adaptive Parameter Set (APS). The ALF parameters can be derived based on the filter information or ALF data for the ALF.

[0182] ALF is an in-loop filtering technique that can be applied in video / image coding as described above. An Adaptive Wiener-based filter can be used to perform ALF. This can be to minimize the Mean Square Error (MSE) between the original samples and the decoded samples (or reconstructed samples). The advanced design for the ALF tool can incorporate syntax elements accessible in the SPS and / or slice header (or tile group header).

[0183] In an example, before filtering each 4x4 luminance block, geometric transformations such as rotation or diagonal and vertical flipping can be applied to the filter coefficients f(k,l) and the corresponding filter limit values c(k,l) depending on the gradient value calculated for the block. This is equivalent to applying these transformations to the samples in the filter support region. Creating other blocks to which ALF is applied can be similar to arranging these blocks according to their directivity.

[0184] For example, three kinds of transformations can be performed based on the following equations: diagonal, vertical flip, and rotation.

[0185] [Equation 1]

[0186] Diagonal: f_D(k, l) = f(l, k), c_D(k, l) = c(l, k)

[0187] [Equation 2]

[0188] Vertical flip: f_V(k, l) = f(k, K - l - 1), c_V(k, l) = c(k, K - l - 1)

[0189] [Equation 3]

[0190] Rotation: f_R(k, l) = f(K - l - 1, k), c_R(k, l) = c(K - l - 1, k)

[0191] In Equations 1 to 3, K can be the size of the filter. 0 ≤ k and 1 ≤ K - 1 can be the coefficient coordinates. For example, (0, 0) can be the upper left corner coordinate, and / or (K - 1, K - 1) can be the lower right corner coordinate. The relationship between the transformation and the four gradients in the four directions can be summarized in the following table.

[0192] [Table 2]

[0193] Gradient value Transformation <![CDATA[g d2 <g d1 and g h <g v > No transformation <![CDATA[g d2 <g d1 and g v <g h > Diagonal <![CDATA[g d1 <g d2 and g h <g v > Vertical flip <![CDATA[g d1 <g d2 and g v <g h > Rotation

[0194] The ALF filter parameters can be signaled in the APS and slice headers. In one APS, up to 25 luminance filter coefficients and the clipping value index can be signaled. In one APS, up to 8 chrominance filter coefficients and the clipping value index can be signaled. To reduce the bit overhead, the filter coefficients for different classifications of the luminance component can be combined. In the slice header, the index of the APS (referenced by the current slice) for the current slice can be signaled.

[0195] The clipping value index decoded from the APS can make it possible to determine the clipping value using the luminance table of the clipping value and the chrominance table of the clipping value. These clipping values may depend on the internal bit depth. More specifically, the luminance table of the clipping value and the chrominance table of the clipping value can be derived based on the following equations.

[0196] [Equation 4]

[0197] AlfClipL = {round(2^(B(N - n + 1) / N)) for n ∈ [1..N]}

[0198] [Equation 5]

[0199] R′(i, j) = R(i, j) + ((∑ k≠0 ∑ 1≠0 f(k, l) × K(R(i + k, j + l) - R(i, j), c(k, l)) + 64) >> 7)

[0200] In the above equation, B can be the internal bit depth, and N can be the number of allowable clipping values (predetermined number). For example, N can be 4.

[0201] In the slice header, up to 7 APS indices can be signaled to indicate the luma filter set for the current slice. The filtering process can be further controlled at the CTB level. For example, a flag indicating whether to apply ALF to the luma CTB can be signaled. The luma CTB can select one of 16 fixed filter sets and the filter set from the APS. A filter set index can be signaled for the luma CTB to indicate which filter set is applied. The 16 fixed filter sets can be predefined and hard-compiled in both the encoder and the decoder.

[0202] For the chroma component, an APS index can be signaled in the slice header to indicate the chroma filter set for the current slice. At the CTB level, when there are two or more chroma filter sets in the APS, a filter index can be signaled for each chroma CTB.

[0203] 128 can be used as the norm to quantize the filter coefficients. To limit the multiplication complexity, bitstream conformance can be applied such that the coefficient values at non-central positions can vary from 0 to 28 and / or the coefficient values at the remaining positions can be in the range from -27 to 27 - 1. The coefficient at the central position can be not signaled in the bitstream and can be pre-determined (considered) as 128.

[0204] 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 represented by the following equation.

[0205] [Equation 6]

[0206] Diagonal: f_D(k, l) = f(l, k), c_D(k, l) = c(l, k)

[0207] In the above equation, f(k, l) can be the decoding filter coefficients, K(x, y) can be the clipping function, and c(k, l) can be the decoding clipping parameter. For example, the variables k and / or l can vary from -L / 2 to L / 2. Here, L can represent the filter length. The clipping function K(x, y) = min(y, max(-y, x)) can correspond to the function Clip3(-y, y, x).

[0208] In an example, to reduce the row buffer requirements of the ALF, a modified block classification and filtering can be applied to samples adjacent to the horizontal CTU boundary. For this purpose, a virtual boundary can be defined.

[0209] Figure 9 is a diagram showing a virtual boundary applied to a filtering process according to an embodiment of this document. Figure 10 illustrates an example of an ALF process using a virtual boundary according to an embodiment of the present disclosure. It will be described in conjunction with Figure 9 description Figure 10 .

[0210] Referring to Figure 9 , the virtual boundary can be a line defined by shifting the horizontal CTU boundary by N samples. In an example, N can be 4 for the luminance component and / or N can be 2 for the chrominance component.

[0211] In Figure 9 , a modified block classification can be applied to the luminance component. For the 1D Laplacian gradient calculation of 4×4 blocks on the virtual boundary, only the samples above the virtual boundary can be used. Similarly, to calculate the 1D Laplacian gradient of 4×4 blocks below the virtual boundary, only the samples below the virtual boundary can be used. Considering the reduced number of samples used in the 1D Laplacian gradient calculation, the quantization of the activity value A can be scaled accordingly.

[0212] For the filtering process, a symmetric padding operation at the virtual boundary can be used for both the luminance and chrominance components. Referring to Figure 9 , when the sample to be filtered is below the virtual boundary, the neighboring samples above the virtual boundary can be filled. At the same time, the corresponding samples on the other side can also be filled symmetrically.

[0213] When no filter is available across the boundary, according to Figure 10The described process can also be used for the boundaries of slices, bricks, and / or tiles. For ALF block classification, only samples contained within the same slice, brick, and / or tile can be used and the activity values can be scaled accordingly. For ALF filtering, symmetric padding can be applied for each of the horizontal and / or vertical directions with respect to horizontal and / or vertical boundaries.

[0214] Figure 11 is a diagram illustrating a cross-component adaptive loop filtering (CC-ALF) process according to an embodiment of this document. The CCALF process can be referred to as a cross-component filtering process.

[0215] In one aspect, the ALF process can include a general ALF process and a CCALF process. That is, the CCALF process can refer to some processes of the ALF process. In another aspect, the filtering process can include a deblocking process, a SAO process, an ALF process, and / or a CCALF process.

[0216] CC-ALF can use the luma sample values to refine each chroma component. CC-ALF is controlled by the (picture) information of the bitstream, which includes (a) information about the filter coefficients for each chroma component and (b) information about the mask that controls the application of the filter to the sample blocks. The filter coefficients can be signaled at the APS, and the block size and mask can be signaled at the slice level.

[0217] Refer to Figure 11 , CC-ALF can operate by applying a linear diamond filter ( Figure 11 (b) of ) to the luma channel of each chroma component. The filter coefficients are sent to the APS, scaled by a factor of 210, and rounded up to obtain a fixed-point representation. The application of the filter can be controlled at variable block sizes and signaled by the context compilation flag received for each block of samples. The block size and the CC-ALF enable flag can be received at the slice level for each chroma component. The block size (for chroma samples) can be 16x16, 32x32, 64x64, or 128x128.

[0218] In the following embodiments, a method for re-filtering or modifying the reconstructed chroma samples filtered by ALF based on the reconstructed luma samples is proposed.

[0219] Embodiments of the present disclosure relate to filter on / off transmission and filter coefficient transmission in CC-ALF. As described above, the information (syntax elements) in the syntax tables disclosed in the present disclosure may be included in image / video information, may be configured / encoded in an encoding device, and sent to a decoding device in the form of a bitstream. The decoding device may parse / decode the information (syntax elements) in the corresponding syntax table. The decoding device may perform a picture / image / video decoding process (specifically, for example, the CC-ALF process) based on the decoded information. Hereinafter, the same applies to other embodiments.

[0220] The following table shows some syntax of slice header information according to an embodiment of the present disclosure.

[0221] [Table 3]

[0222]

[0223] The following table shows exemplary semantics for the syntax elements included in the above table.

[0224] [Table 4]

[0225]

[0226]

[0227]

[0228] Referring to the above two tables, when sps_cross_component_alf_enabled_flag is 1 in the slice header, the parsing of slice_cross_component_alf_cb_enabled_flag can be performed to determine whether to apply Cb CC-ALF in the slice. When slice_cross_component_alf_cb_enabled_flag is 1, CC-ALF is applied to the corresponding Cb slice, and when slice_cross_component_alf_cb_reuse_temporal_layer_filter is 1, the filter of the same existing temporal layer can be reused. When slice_cross_component_alf_cb_enabled_flag is 0, CC-ALF can be applied by parsing the filter in the corresponding Adaptive Parameter Set (APS) id through slice_cross_component_alf_cb_aps_id. Slice_cross_component_alf_cb_log2_control_size_minus4 can mean the block unit to which CC-ALF is applied in the Cb slice.

[0229] For example, when the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 0, it is determined whether to apply CC-ALF in units of 16x16. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 1, it is determined whether to apply CC-ALF in units of 32x32. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 2, it is determined whether to apply CC-ALF in units of 64x64. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 3, it is determined whether to apply CC-ALF in units of 128x128. Additionally, the same syntax as above is used for Cr CC-ALF.

[0230] The following table shows an example syntax for ALF data.

[0231] [Table 5]

[0232]

[0233] The following table shows the exemplary semantics of the syntax elements included in the above table.

[0234] [Table 6]

[0235]

[0236]

[0237]

[0238]

[0239]

[0240] Referring to the above two tables, the CC-ALF syntax elements do not follow the existing (general) ALF syntax structure, but are sent independently and configured to be applied independently. That is, even when the ALF tool on the SPS is turned off, the CC-ALF can still be applied. A new hardware pipeline design is required because the CC-ALF should be able to operate independently of the existing ALF structure. This leads to an increase in the cost of the hardware implementation method and an increase in the hardware latency.

[0241] In addition, in the ALF, it is determined whether to apply both the luminance image and the chrominance image in units of CTUs, and the determined result is signaled to the decoder. However, whether to apply the variable CC-ALF is determined in units of 16x16 to 128x128, and this application can cause a conflict between the existing ALF structure and the CC-ALF. This causes problems in terms of the hardware implementation method and at the same time causes an increase in the line buffer for various variable CC-ALF applications.

[0242] In the present disclosure, the problems in the hardware implementation method of the CC-ALF mentioned above are solved by applying the CC-ALF syntax structure as a whole to the ALF syntax structure.

[0243] According to an embodiment of the present disclosure, in order to determine whether to use (apply) the CC-ALF, the sequence parameter set (SPS) may include a CC-ALF enable flag (sps_ccalf_enable_flag). The CC-ALF enable flag can be sent independently of the ALF enable flag (sps_alf_enabled_flag) used to determine whether to use (apply) the ALF.

[0244] The following table shows some exemplary syntax of the SPS according to this embodiment.

[0245] [Table 7]

[0246]

[0247] Referring to the above table, CC-ALF can be applied only when ALF is always in operation. That is, the CC-ALF enable flag (sps_ccalf_enabled_flag) can be parsed only when the ALF enable flag (sps_alf_enabled_flag) is 1. CC-ALF and ALF can be combined according to the above table. The CC-ALF enable flag can indicate whether CC-ALF is available (and may be related to whether CC-ALF is available).

[0248] The following table shows some example syntax of the slice header.

[0249] [Table 8]

[0250]

[0251] Referring to the above table, the parsing of sps_ccalf_enabled_flag can be performed only when sps_alf_enabled_flag is 1. The syntax elements included in the table can be described based on Table 4. In the example, the image information encoded by the encoding device or obtained (received) by the decoding device can 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) related to whether CC-ALF is available for the Cb color component of the reconstructed chrominance samples to be filtered and a second flag (slice_cross_component_alf_cr_enabeld_flag) related to whether CC-ALF is available for the Cr color component of the reconstructed chrominance samples to be filtered.

[0252] In the example, based on the determination that the value of the first flag (slice_cross_component_alf_cb_enabeld_flag) is 1, the slice header information can include the ID information (slice_cross_component_alf_cb_aps_id) of the first APS for deriving the 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 can include the ID information (slice_cross_component_alf_cr_aps_id) of the second APS for deriving the cross-component filter coefficients for the Cr color component.

[0253] The following shows a part of the SPS syntax according to another example of this embodiment.

[0254] [Table 9]

[0255]

[0256] The following exemplarily shows a part of the slice header syntax.

[0257] [Table 10]

[0258]

[0259] Referring to Table 9, when ChromaArrayType is not 0 and the ALF enable flag (sps_alf_enabled_flag) is 1, the SPS may include the CCALF enable flag (sps_ccalf_enabled_flag). For example, if ChromaArrayType is not 0, the chroma format may not be monochrome, and the CCALF enable flag may be sent via the SPS based on the case where the chroma format is not monochrome.

[0260] Referring to Table 9, based on the case where ChromaArrayType is not 0, information about 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.

[0261] In an example, the image information encoded by the encoding device or obtained by the decoding device may include the SPS. The SPS may include a first ALF enable flag (sps_alf_enabled_flag) related to whether ALF is available. For example, based on the determination that the value of the first ALF enable flag is 1, the SPS may include a CCALF enable flag related to whether cross-component filtering is available. In another example, if sps_ccalf_enabled_flag is not used and sps_alf_enabled_flag is 1, CCALF may always be applied (sps_ccalf_enabled_flag == 1).

[0262] The following shows a part of the slice header syntax according to another example of this embodiment.

[0263] [Table 11]

[0264]

[0265] Referring to the above table, the parsing of the CCALF enable flag (sps_ccalf_enabled_flag) can be performed only when the ALF enable flag (sps_alf_enabled_flag) is 1.

[0266] The following table shows exemplary semantics for the syntax elements included in the above table.

[0267] [Table 12]

[0268]

[0269]

[0270] The slice_ccalf_chroma_idc in the above table can be described by the semantics in the following table.

[0271] [Table 13]

[0272]

[0273] The following table shows a part of the slice header syntax according to another example of this embodiment.

[0274] [Table 14]

[0275]

[0276] The syntax elements included in the table can be described according to Table 12 or Table 13. Additionally, when the chroma format is not monochrome, CCALF-related information can be included in the slice header.

[0277] The following table shows a part of the slice header syntax according to another example of this embodiment.

[0278] [Table 15]

[0279]

[0280] The following table shows exemplary semantics for the syntax elements included in the above table.

[0281] [Table 16]

[0282]

[0283]

[0284] The following table shows a part of the slice header syntax according to another example of this embodiment. The syntax elements included in the following table can be described according to Table 12 or Table 13.

[0285] [Table 17]

[0286]

[0287] Referring to the above table, it is possible to determine whether to apply the slice unit ALF and CC-ALF at once through the slice_alf_enabled_flag. After parsing the slice_alf_chroma_idc, when the first ALF enable flag (sps_alf_enabled_flag) is 1, the slice_ccalf_chroma_idc can be parsed.

[0288] Referring to the above table, it is possible to determine whether the sps_ccalf_enabeld_flag is 1 in the slice header information only when the slice_alf_enabled_flag is 1. The slice header information may include a second ALF enable flag (slice_alf_enabled_flag) related to whether the ALF is available. Based on the determination that the value of the second ALF enable flag (slice_alf_enabled_flag) is 1, CCALF may be available for the slice.

[0289] The following table exemplarily shows a part of the APS syntax. The syntax element adaptation_parameter_set_id may indicate the identifier information (ID information) of the APS.

[0290] [Table 18]

[0291]

[0292] The following table shows an example syntax for ALF data.

[0293] [Table 19]

[0294]

[0295] Referring to the above two tables, the APS may include ALF data (alf_data()). The APS including the ALF data may be referred to as an ALF APS (ALF type APS). That is, the type of the APS including the ALF data may be the ALF type. The type of the APS may be determined as information or a syntax element (aps_params_type) regarding the APS type. The ALF data may include a Cb filter signal flag (alf_cross_component_cb_filter_signal_flag or alf_cc_cb_filter_signal_flag) related to whether to signal a cross-component filter for the Cb color component. The ALF data may include a Cr filter signal flag (alf_cross_component_cr_filter_signal_flag or alf_cc_cr_filter_signal_flag) related to whether to signal a cross-component filter for the Cr color component.

[0296] In an example, based on the Cr filter signal flag, the ALF data may include information (alf_cross_component_cr_coeff_abs) regarding the absolute value of the cross-component filter coefficient for the Cr color component and information (alf_cross_component_cr_coeff_sign) regarding the sign of the cross-component filter coefficient for the Cr color component. Based on the information regarding the absolute value of the cross-component filter coefficient for the Cr color component and the information regarding the sign of the cross-component filter coefficient for the Cr color component, the cross-component filter coefficient for the Cr color component can be derived.

[0297] In an example, the ALF data may include information (alf_cross_component_cb_coeff_abs) regarding the absolute value of the cross-component filter coefficient for the Cb color component and information (alf_cross_component_cb_coeff_sign) regarding the sign of the cross-component filter coefficient for the Cb color component. Based on the information regarding the absolute value of the cross-component filter coefficient for the Cb color component and the information regarding the sign of the cross-component filter coefficient for the Cb color component, the cross-component filter coefficient for the Cb color component can be derived.

[0298] The following table shows the syntax related to the ALF data according to another example.

[0299] [Table 20]

[0300]

[0301] Referring to the above table, after first sending the alf_cross_component_filter_signal_flag, when the alf_cross_component_filter_signal_flag is 1, the Cb / Cr filter signal flag can be sent. That is, the alf_cross_component_filter_signal_flag integrates Cb / Cr to determine whether to send the CC-ALF filter coefficients.

[0302] The following table shows the syntax related to ALF data according to another example.

[0303] [Table 21]

[0304]

[0305] The following table shows the exemplary semantics for the syntax elements included in the above table.

[0306] [Table 22]

[0307]

[0308]

[0309]

[0310]

[0311] The following table shows the syntax related to ALF data according to another example.

[0312] [Table 23]

[0313]

[0314] The following table shows the exemplary semantics for the syntax elements included in the above table.

[0315] [Table 24]

[0316]

[0317]

[0318]

[0319]

[0320] In the above two tables, the order of the exp-Golomb binarization used to parse the syntax of alf_cross_component_cb_coeff_abs[j] and alf_cross_component_cr_coeff_abs[j] can be defined by one of the values from 0 to 9.

[0321] Referring to the above two tables, the ALF data may include a Cb filter signal flag (alf_cross_component_cb_filter_signal_flag or alf_cc_cb_filter_signal_flag) related to whether to signal the cross-component filter for the Cb color component. Based on the Cb filter signal flag (alf_cross_component_cb_filter_signal_flag), the ALF data may include information related to the number of cross-component filters for the Cb color component (ccalf_cb_num_alt_filters_minus1). Based on the information related to the number of cross-component filters for the Cb color component, the ALF data may include information about the absolute value of the cross-component filter coefficients for the Cb color component (alf_cross_component_cb_coeff_abs) and information about the signs of the cross-component filter coefficients for the Cb color component (alf_cross_component_cr_coeff_sign). Based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about 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 derived.

[0322] In an example, the ALF data may include a Cr filter signal flag (alf_cross_component_cr_filter_signal_flag or alf_cc_cr_filter_signal_flag) related to whether to signal a cross-component filter for the Cr color component. Based on the Cr filter signal flag (alf_cross_component_cr_filter_signal_flag), the ALF data may include information (ccalf_cr_num_alt_filters_minus1) related to the number of cross-component filters for the Cr color component. Based on the information related to the number of cross-component filters for the Cr color component, the ALF data may include information (alf_cross_component_cr_coeff_abs) about the absolute value of the cross-component filter coefficients for the Cr color component and information (alf_cross_component_cr_coeff_sign) about the signs of the cross-component filter coefficients for the Cr color component. Based on the information about the absolute value of the cross-component filter coefficients for the Cr color component and the information about 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 derived.

[0323] The following table shows the syntax related to the compilation tree unit according to an embodiment of the present disclosure.

[0324] [Table 25]

[0325]

[0326] The following table shows the exemplary semantics for the syntax elements included in the above table.

[0327] [Table 26]

[0328]

[0329]

[0330] The following table shows the compilation tree unit syntax according to another example of this embodiment.

[0331] [Table 27]

[0332]

[0333] Referring to the above table, CCALF can be applied on a CTU basis. In the example, the picture information may include information about a coding tree unit (coding_tree_unit()). The information about the coding tree unit may include information about whether to apply a cross-component filter to the current block of the Cb color component (ccalf_ctb_flag[0]) and / or information about whether to apply a cross-component filter to the current block of the Cr color component (ccalf_ctb_flag[1]). Additionally, the information about the coding tree unit may include information about the filter set index of the cross-component filter applied to the current block of the Cb color component (ccalf_ctb_filter_alt_idx[0]) and / or information about the filter set index of the cross-component filter applied to the current block of the Cr color component (ccalf_ctb_filter_alt_idx[1]). The syntax can be sent adaptively according to the syntax slice_ccalf_enabled_flag and slice_ccalf_chroma_idc.

[0334] The following table shows the coding tree unit syntax according to another example of this embodiment.

[0335] [Table 28]

[0336]

[0337] The following table shows the exemplary semantics for the syntax elements included in the above table.

[0338] [Table 29]

[0339]

[0340]

[0341] The following table shows the coding tree unit syntax according to another example of this embodiment. The syntax elements included in the following table can be described according to Table 29.

[0342] [Table 30]

[0343]

[0344] In an example, the picture information may include information about a coding tree unit (coding_tree_unit()). The information about the coding tree unit may include information about whether to apply a cross-component filter to the current block of the Cb color component (ccalf_ctb_flag[0]) and / or information about whether to apply a cross-component filter to the current block of the Cr color component (ccalf_ctb_flag[1]). Additionally, the information about the coding tree unit may include information about the filter set index of the cross-component filter applied to the current block of the Cb color component (ccalf_ctb_filter_alt_idx[0]) and / or information about the filter set index of the cross-component filter applied to the current block of the Cr color component (ccalf_ctb_filter_alt_idx[1]).

[0345] Figure 12 and Figure 13 schematically shows an example of a video / image coding method and related components according to an embodiment of the present disclosure. Figure 12 The method disclosed in Figure 2 or Figure 13 may be executed by the coding device disclosed in Figure 12 Specifically, for example, Figure 12 S1200 and S1210 of Figure 12 may be executed by the predictor 220 of the coding device, and

[0346] S1220 to S1240 of Figure 12 may be executed by the residual processor 230 of the coding device. S1250 may be executed by the adder 250 of the coding device, S1260 may be executed by the filter 260 of the coding device, and S1270 may be executed by the entropy encoder 240 of the coding device.

[0347] The coding device may derive prediction samples (S1200). The prediction samples may include predicted luminance samples and predicted chrominance samples. The coding device may derive the prediction samples of the current block based on a prediction mode. In this case, various prediction methods disclosed in the present disclosure, such as inter prediction or intra prediction, may be applied.

[0348] The encoding device may generate residual samples (S1220). The residual samples may include residual luminance samples and residual chrominance samples. The encoding device may derive the residual samples for the current block, and may derive the residual samples for the current block based on the original samples and the predicted samples of the current block.

[0349] The encoding device may derive (quantize) transform coefficients (S1230). The encoding device may derive the transform coefficients based on the transform process for the residual samples. The transform coefficients may include luminance transform coefficients and chrominance transform coefficients. For example, the luminance transform coefficients may be derived based on the residual luminance samples, and the chrominance transform coefficients may be derived based on the residual chrominance samples. For example, the transform process may include at least one of DCT, DST, GBT, or CNT. The encoding device may derive the quantized transform coefficients. The encoding device may derive the quantized transform coefficients based on the quantization process for the transform coefficients. The quantized transform coefficients may have a one-dimensional vector form based on the coefficient scan order.

[0350] The encoding device may generate residual information (S1240). The encoding device may generate the residual information indicating the quantized transform coefficients. The residual information may be generated by various encoding methods such as exponential Golomb, CAVLC, CABAC, etc.

[0351] The encoding device may generate reconstructed samples (S1250). The reconstructed samples may include reconstructed luminance samples (luminance components of the reconstructed samples) and / or reconstructed chrominance samples (chrominance components of the reconstructed samples). The encoding device may generate the reconstructed samples based on the residual information. The reconstructed samples may be generated by adding the residual samples to the predicted samples based on the residual information.

[0352] The encoding device may generate ALF-related information and / or CCALF-related information (S1260). The encoding device may generate the ALF-related information and / or CCALF-related information for the reconstructed samples. The encoding device may derive the ALF-related parameters that can be used to filter the reconstructed samples, and generate the ALF-related information. For example, the ALF-related information may include the ALF-related information described above in this disclosure. The encoding device may generate the CCALF-related information for the reconstructed chrominance samples among the reconstructed samples.

[0353] The encoding device may encode video / image information (S1270). The image information may include the residual information and / or the ALF-related information. The encoded video / image information can be output in the form of a bitstream. The bitstream can be sent to the decoding device via a network or a storage medium.

[0354] In an example, the CCALF-related information may include a CCALF enable flag, a flag related to whether CCALF is available for the Cb (or Cr) color component, a Cb (or Cr) filter signal flag related to whether to signal a cross-component filter for the Cb (or Cr) color component, information related to the number of cross-component filters for the Cb (or Cr) color component, information about the values of the coefficients of the cross-component filter for the Cb (or Cr) color component, information about the absolute values of the coefficients of the cross-component filter for the Cb (or Cr) color component, information about the signs of the coefficients of the cross-component filter for the Cb (or Cr) color component, and / or information about whether to apply a cross-component filter to the current block of the Cb (or Cr) color component in the information (compilation tree unit syntax) about the compilation tree unit.

[0355] The image / video information may include various types of information according to the embodiments of this document. For example, the image / video information may include the information disclosed in at least one of Tables 1 to 30 above.

[0356] In an embodiment, the image information may include a sequence parameter set (SPS). The SPS may include a CCALF enable flag related to whether cross-component filtering is available. Based on the CCALF availability flag, ID information (identifier information) of an adaptive parameter set (APS) including ALF data for deriving cross-component filter coefficients for CCALF may be derived.

[0357] In an embodiment, the SPS may include an ALF enable flag (sps_alf_enabled_flag) related to whether ALF is available. Based on the determination that the value of the ALF enable flag (sps_alf_enabled_flag) is 1, the SPS may include a CCALF enable flag related to whether cross-component filtering is available.

[0358] In an embodiment, the image information may include slice header information and an adaptive parameter set (APS). The header information may include information related to the identifier of the APS including ALF data. For example, the cross-component filter coefficients may be derived based on the ALF data.

[0359] In an embodiment, the slice header information may include an ALF enable flag (slice_alf_enabled_flag) related to whether ALF is available. The sps_alf_enabled_flag and the slice_alf_enabled_flag may be referred to as the first ALF enable flag and the second ALF enable flag, respectively. Based on the determination that the value of the second ALF enable flag (slice_alf_enabled_flag) is 1, it can be determined whether the value of the CCALF enable flag is 1. In an example, based on the determination that the value of the second ALF availability flag is 1, CCALF may be available for the slice.

[0360] In an embodiment, the header information (slice header information) may include a first flag related to whether CCALF is available for the Cb color component of the reconstructed chrominance samples for filtering and a second flag related to whether CCALF is available for the Cr color component of the reconstructed chrominance samples for filtering. In another example, based on the determination 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 related to whether CCALF is available for the Cb color component of the reconstructed chrominance samples for filtering and a second flag related to whether CCALF is available for the Cr color component of the reconstructed chrominance samples for filtering.

[0361] In an embodiment, based on the determination that the value of the first flag is 1, the slice header information may include ID information of a first APS (information related to the identifier of a second APS) for deriving 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 ID information of a second APS (information related to the identifier of a second APS) for deriving cross-component filter coefficients for the Cr color component.

[0362] In an embodiment, the first ALF data included in the first APS may include a Cb filter signal flag related to whether to signal a cross-component filter for the Cb color component. Based on the Cb filter signal flag, the first ALF data may include information related to the number of cross-component filters for the Cb color component. Based on the information related to the number of cross-component filters for the Cb color component, the first ALF data may include information about the absolute value of the cross-component filter coefficients for the Cb color component and information about the sign of the cross-component filter coefficients for the Cb color component. Based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about the sign of the cross-component filter coefficients for the Cb color component, the cross-component filter coefficients for the Cb color component can be derived.

[0363] In an embodiment, information related to the number of cross-component filters for the Cb color component may be coded in zero-order exponential Golomb (0EG).

[0364] In an embodiment, the second ALF data included in the second APS may include a Cr filter signal flag related to whether to signal a cross-component filter for the Cr color component. Based on the Cr filter signal flag, the second ALF data may include information related to the number of cross-component filters for the Cr color component. Based on the information related to the number of cross-component filters for the Cr color component, the second ALF data may include information about the absolute value of the cross-component filter coefficients for the Cr color component and information about the signs of the cross-component filter coefficients for the Cr color component. Based on the information about the absolute value of the cross-component filter coefficients for the Cr color component and the information about the signs of the cross-component filter coefficients for the Cr color component, the cross-component filter coefficients for the Cr color component may be derived.

[0365] In an embodiment, information related to the number of cross-component filters for the Cr color component may be coded in zero-order exponential Golomb (0EG).

[0366] In an embodiment, the image information may include information about a coding tree unit. The information about the coding tree unit may include information about whether to apply a cross-component filter to a current block of the Cb color component and / or information about whether to apply a cross-component filter to a current block of the Cr color component.

[0367] In an embodiment, the information about the coding tree unit may include information about a filter set index of the cross-component filter applied to the current block of the Cb color component and / or information about a filter set index of the cross-component filter applied to the current block of the Cr color component.

[0368] Figure 14 and Figure 15 FIG. schematically illustrates an example of a video / image decoding method and related components according to an embodiment of the present disclosure.

[0369] Figure 14 The method disclosed in Figure 3 or Figure 15 may be performed by the decoding device illustrated in Figure 14S1400 can be executed by the entropy decoder 310 of the decoding device, S1410 and S1420 can be executed by the residual processor 320 of the decoding device, S1430 can be executed by the predictor 330 of the decoding device, S1440 can be executed by the adder 340 of the decoding device, and S1450 to S1480 can be executed by the filter 350 of the decoding device. Figure 14 The method disclosed in

[0370] Reference Figure 14 , the decoding device can receive / acquire video / image information (S1400). The video / image information may include prediction-related information and / or residual information. The decoding device can receive / acquire the 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 related to whether CCALF is available for the Cb (or Cr) color component, a Cb (or Cr) filter signal flag related to whether to signal a cross-component filter for the Cb (or Cr) color component, information related to the number of cross-component filters for the Cb (or Cr) color component, information about the absolute value of the cross-component filter coefficients for the Cb (or Cr) color component, information about the sign of the cross-component filter coefficients for the Cb (or Cr) color component, and / or information about whether to apply a cross-component filter to the current block of the Cb (or Cr) color component in the information (compilation tree unit syntax) about the compilation tree unit.

[0371] The image / video information may include various types of information according to the embodiments of this document. For example, the image / video information may include the information disclosed in at least one of Tables 1 to 30 above.

[0372] The decoding device can derive transform coefficients (S1410). Specifically, the decoding device can derive quantized transform coefficients based on the residual information. The transform coefficients may include luminance transform coefficients and chrominance transform coefficients. The quantized transform coefficients may have a one-dimensional vector form based on the coefficient scan order. The decoding device can derive the transform coefficients based on the dequantization process for the quantized transform coefficients.

[0373] The decoding device can derive residual samples (S1420). The decoding device can derive the residual samples based on the transform coefficients. The residual samples may include residual luminance samples and residual chrominance samples. For example, the residual luminance samples can be derived based on the luminance transform coefficients, and the residual chrominance samples can be derived based on the chrominance transform coefficients. Additionally, the residual samples for the current block can be derived based on the original samples and the predicted samples of the current block.

[0374] The decoding device can perform prediction based on image / video information and derive the prediction samples of the current block (S1430). The decoding device can derive the prediction samples of the current block based on prediction-related information. The prediction-related information can include prediction mode information. The decoding device can determine whether to apply inter prediction or intra prediction to the current block based on the prediction mode information, and can perform prediction based on this. The prediction samples can include prediction luminance samples and / or prediction chrominance samples.

[0375] The decoding device can generate / derive reconstructed samples (S1440). The reconstructed samples can include reconstructed luminance samples and / or reconstructed chrominance samples. The decoding device can generate the reconstructed luminance (or chrominance) samples based on the residual samples. The luminance component of the reconstructed samples can correspond to the reconstructed luminance samples, and the chrominance component of the reconstructed samples can correspond to the reconstructed chrominance samples.

[0376] The decoding device can derive the ALF filter coefficients for the ALF process for reconstructing chrominance samples (S1450). Additionally, the decoding device can derive the ALF filter coefficients for the ALF process for reconstructing luminance samples. The ALF filter coefficients can be derived based on the ALF parameters in the ALF data included in the APS.

[0377] The decoding device can generate filtered reconstructed chrominance samples (S1460). The decoding device can generate the filtered reconstructed samples based on the reconstructed chrominance samples and the ALF filter coefficients.

[0378] The decoding device can derive the cross-component filter coefficients for cross-component filtering (S1470). The cross-component filter coefficients can be derived based on the CCALF-related information in the ALF data included in the aforementioned APS, and the identifier (ID) information of the corresponding APS can be included in the slice header (and can be signaled thereby).

[0379] The decoding device can generate modified filtered reconstructed chrominance samples (S1480). The decoding device can generate the modified and filtered reconstructed chrominance samples based on the reconstructed luminance samples, the filtered reconstructed chrominance samples, and the cross-component filter coefficients. In an example, the decoding device can derive the difference between two samples among the reconstructed luminance samples and multiply the difference by one of the cross-component filter coefficients. Based on the multiplication result and the filtered reconstructed chrominance samples, the decoding device can generate the modified filtered reconstructed chrominance samples. For example, the decoding device can generate the modified filtered reconstructed chrominance samples based on the sum of the product and one of the filtered reconstructed chrominance samples.

[0380] In an embodiment, the picture information may include a Sequence Parameter Set (SPS). The SPS may include a CCALF enable flag related to whether cross-component filtering is available. Based on the CCALF availability flag, ID information (identifier information) of an Adaptive Parameter Set (APS) including ALF data for deriving cross-component filter coefficients for CCALF may be derived.

[0381] In an embodiment, the SPS may include an ALF enable flag (sps_alf_enabled_flag) related to whether ALF is available. Based on the determination that the value of the ALF enable flag (sps_alf_enabled_flag) is 1, the SPS may include a CCALF enable flag related to whether cross-component filtering is available.

[0382] In an embodiment, the picture information may include slice header information and an Adaptive Parameter Set (APS). The header information may include information related to the identifier of the APS including ALF data. For example, cross-component filter coefficients may be derived based on the ALF data.

[0383] In an embodiment, the slice header information may include an ALF enable flag (slice_alf_enabled_flag) related to whether ALF is available. The sps_alf_enabled_flag and the slice_alf_enabled_flag may be referred to as a first ALF enable flag and a second ALF enable flag, respectively. Based on the determination that the value of the second ALF enable flag (slice_alf_enabled_flag) is 1, it may be determined whether the value of the CCALF enable flag is 1. In an example, based on the determination that the value of the second ALF availability flag is 1, CCALF may be available for the slice.

[0384] In an embodiment, the header information (slice header information) may include a first flag related to whether CCALF is available for filtering the Cb color component of the reconstructed chrominance samples and a second flag related to whether CCALF is available for filtering the Cr color component of the reconstructed chrominance samples. In another example, based on the determination 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 related to whether CCALF is available for filtering the Cb color component of the reconstructed chrominance samples and a second flag related to whether CCALF is available for filtering the Cr color component of the reconstructed chrominance samples.

[0385] In an embodiment, based on the determination that the value of the first flag is 1, the slice header information may include ID information of a first APS for deriving cross-component filter coefficients for the Cb color component (information related to the identifier of the second APS). Based on the determination that the value of the second flag is 1, the slice header information may include ID information of a second APS for deriving cross-component filter coefficients for the Cr color component (information related to the identifier of the second APS).

[0386] In an embodiment, the first ALF data included in the first APS may include a Cb filter signal flag related to whether to signal a cross-component filter for the Cb color component. Based on the Cb filter signal flag, the first ALF data may include information related to the number of cross-component filters for the Cb color component. Based on the information related to the number of cross-component filters for the Cb color component, the first ALF data may include information about the absolute value of the cross-component filter coefficients for the Cb color component and information about the sign of the cross-component filter coefficients for the Cb color component. Based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about the sign of the cross-component filter coefficients for the Cb color component, the cross-component filter coefficients for the Cb color component can be derived.

[0387] In an embodiment, the information related to the number of cross-component filters for the Cb color component may be compiled in zero-order exponential Golomb (0EG).

[0388] In an embodiment, the second ALF data included in the second APS may include a Cr filter signal flag related to whether to signal a cross-component filter for the Cr color component. Based on the Cr filter signal flag, the second ALF data may include information related to the number of cross-component filters for the Cr color component. Based on the information related to the number of cross-component filters for the Cr color component, the second ALF data may include information about the absolute value of the cross-component filter coefficients for the Cr color component and information about the sign of the cross-component filter coefficients for the Cr color component. Based on the information about the absolute value of the cross-component filter coefficients for the Cr color component and the information about the sign of the cross-component filter coefficients for the Cr color component, the cross-component filter coefficients for the Cr color component can be derived.

[0389] In an embodiment, the information related to the number of cross-component filters for the Cr color component may be compiled in zero-order exponential Golomb (0EG).

[0390] In an embodiment, the picture information may include information about a coding tree unit. The information about the coding tree unit may include information about whether to apply a cross-component filter to the current block of the Cb color component and / or information about whether to apply a cross-component filter to the current block of the Cr color component.

[0391] In an embodiment, the information about the coding tree unit may include information about the filter set index of the cross-component filter applied to the current block of the Cb color component and / or information about the filter set index of the cross-component filter applied to the current block of the Cr color component.

[0392] In the presence of residual samples for a current block, the decoding device may receive information about the residual for the current block. The information about the residual may include transform coefficients for the residual samples. The decoding device may derive the residual samples (or an array of residual samples) for the current block based on the residual information. Specifically, the decoding device may derive quantized transform coefficients based on the residual information. The quantized transform coefficients may have a one-dimensional vector form based on the coefficient scan order. The decoding device may derive transform coefficients based on an inverse quantization process for the quantized transform coefficients. The decoding device may derive residual samples based on the transform coefficients.

[0393] The decoding device may generate reconstructed samples based on (intra) prediction samples and residual samples, and may derive a reconstructed block or a reconstructed picture based on the reconstructed samples. Specifically, the decoding device may generate reconstructed samples based on the sum of the (intra) prediction samples and the residual samples. Thereafter, as described above, if necessary, the decoding device may apply loop filter processing (e.g., deblocking filtering and / or SAO processing) to the reconstructed picture to improve the subjective / objective picture quality.

[0394] For example, the decoding device may obtain picture information including all or some of the above information (or syntax elements) by decoding a bitstream or encoded information. Further, the bitstream or encoded information may be stored in a computer-readable storage medium, or the above decoding method may be caused to be executed.

[0395] In the above embodiments, a method is described based on a flowchart having a series of steps or blocks. The present disclosure is not limited to the order of the above steps or blocks. Some steps or blocks may occur simultaneously with other steps or blocks as described above or in an order different from other steps or blocks as described above. Further, those skilled in the art will understand that the steps shown in the above flowchart are not exclusive and may include additional steps, or one or more steps in the flowchart may be deleted without affecting the scope of this document.

[0396] The method according to the above embodiments of this document can be implemented in software form, and the encoding device and / or decoding device according to this document can be included, for example, in devices that perform image processing such as TVs, computers, smart phones, set-top boxes, and display devices.

[0397] When the embodiments in this document are implemented in software, the above method can be implemented as modules (processing, functions, etc.) that perform the above functions. The modules can be stored in a memory and executed by a processor. The memory can be inside or outside the processor and can be connected to the processor by various well-known means. The processor can include an application-specific integrated circuit (ASIC), other chip sets, logic circuits, and / or data processing devices. The memory can include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium, and / or other storage devices. That is, the embodiments described in this document can be implemented and executed on a processor, a microprocessor, a controller, or a chip. For example, the functional units shown in each drawing can be implemented and executed on a computer, a processor, a microprocessor, a controller, or a chip. In this case, information about the instructions or algorithms for the implementation can be stored in a digital storage medium.

[0398] In addition, the decoding device and encoding device applying this document can be included in a multimedia broadcast transmission / reception device, a mobile communication terminal, a home theater video device, a digital cinema video device, a surveillance camera, a video chat device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camera, a VoD service providing device, an over-the-top (OTT) video device, an Internet streaming service providing device, a three-dimensional (3D) video device, a video conferencing device, a transportation user device (i.e., an in-vehicle user device, an aircraft user device, a ship user device, etc.), and a medical video device, and can be used to process video signals and data signals. For example, an over-the-top (OTT) video device can include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smart phone, a tablet computer, a digital video recorder (DVR), etc.

[0399] In addition, the processing method described in this document can be generated in the form of a program executable by a computer and can be stored in a computer-readable recording medium. Multimedia data having a data structure according to the present disclosure can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices that store data readable by a computer system. For example, the computer-readable recording medium can include BD, Universal Serial Bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical data storage devices. In addition, the computer-readable recording medium includes a medium implemented in the form of a carrier wave (i.e., transmission via the Internet). Additionally, the bit stream generated by an encoding method can be stored in a computer-readable recording medium or can be transmitted via a wired or wireless communication network.

[0400] In addition, embodiments of this document can be implemented using a computer program product according to program code, and the program code can be executed in a computer according to the embodiments of this document. The program code can be stored on a computer-readable carrier.

[0401] Figure 16 An example of a content streaming system to which the embodiments disclosed in this document can be applied is shown.

[0402] Reference Figure 16 , a content streaming system applying the embodiments of this document can mainly include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0403] The encoding server compresses the content input from a multimedia input device (e.g., a smart phone, a camera, a video camera, etc.) into digital data to generate a bit stream and sends the bit stream to the streaming server. As another example, when a multimedia input device such as a smart phone, a camera, a video camera, etc. directly generates a bit stream, the encoding server can be omitted.

[0404] A bit stream can be generated by applying the encoding method or the bit stream generation method of the present disclosure, and the streaming server can temporarily store the bit stream in the process of sending or receiving the bit stream.

[0405] The streaming server sends multimedia data to the user device via the web server based on the user's request, and the web server serves as a medium for notifying the user of the service. When the user requests a desired service from the web server, the web server passes the request to the streaming server, and the streaming server sends the multimedia data to the user. In this case, the content streaming system can include a separate control server. In this case, the control server is used to control the commands / responses between the devices in the content streaming system.

[0406] The streaming server can receive content from a media storage and / or encoding server. For example, when receiving content from the encoding server, the content can be received in real time. In this case, in order to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined time.

[0407] Examples of user equipment can include mobile phones, smartphones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, head-mounted displays), digital TVs, desktop computers, digital signage, etc. Each server in the content streaming system can be operated as a distributed server, and in this case, the data received from each server can be distributed.

[0408] Each server in the content streaming system can be operated as a distributed server, and in this case, the data received from each server can be processed in a distributed manner.

[0409] The claims described herein can be combined in various ways. For example, the technical features of the method claims in this document can be combined and implemented as a device, and the technical features of the device claims in this document can also be combined and implemented as a method. Additionally, the technical features of the method claims in this document and the technical features of the device claims in this document can be combined to be implemented as a device, and the technical features of the method claims in this document and the technical features of the device claims in this document can be combined and implemented as a method.

Claims

1. A method for image decoding performed by a decoding device, the method comprising: obtaining image information including prediction-related information and residual information through a bitstream; deriving transform coefficients based on the residual information; generating residual samples based on the transform coefficients; generating prediction samples based on the prediction-related information; and generating reconstructed samples based on the prediction samples and the residual samples, the reconstructed samples including reconstructed luminance samples and reconstructed chrominance samples; deriving ALF coefficients for an Adaptive Loop Filter (ALF) process for the reconstructed chrominance samples; generating filtered reconstructed chrominance samples based on the reconstructed chrominance samples and the ALF filter coefficients; deriving cross-component filter coefficients for cross-component filtering; and generating modified filtered reconstructed chrominance samples based on the reconstructed luminance samples, the filtered reconstructed chrominance samples, and the cross-component filter coefficients, wherein the image information includes a Sequence Parameter Set (SPS) and slice header information, the SPS includes an ALF enable flag related to whether the ALF process is enabled, based on the value of the ALF enable flag being 1, the SPS includes a Cross-Component Adaptive Loop Filter (CCALF) enable flag related to whether cross-component filtering is available, based on the determination that the value of the ALF enable flag in the SPS is 1, the slice header information includes an ALF enable flag related to whether the ALF is enabled, based on the determination that the value of the ALF enable flag included in the slice header information is 1 and the value of the CCALF enable flag included in the SPS is 1, the slice header information includes information on whether the CCALF is enabled for the filtered reconstructed chrominance samples, and based on the value of the information on whether the CCALF is enabled for the filtered reconstructed chrominance samples being 1, the slice header information includes identification (ID) information of an Adaptive Parameter Set (APS) associated with the CCALF for the filtered reconstructed chrominance samples, the ALF data included in the APS includes information related to the number of cross-component filters for the Cb color component and information related to the number of cross-component filters for the Cr color component, based on the information related to the number of cross-component filters for the Cb color component, the ALF data includes information on the absolute values of the cross-component filter coefficients for the Cb color component and information on the signs of the cross-component filter coefficients for the Cb color component, and based on the information related to the number of cross-component filters for the Cr color component, the ALF data includes information on the absolute values of the cross-component filter coefficients for the Cr color component and information on the signs of the cross-component filter coefficients for the Cr color component.

2. A method for image encoding performed by an encoding device, the method comprising: deriving prediction samples for a current block; generating prediction-related information based on the prediction samples; Generate a residual sample for the current block; Derive transform coefficients based on a transform process for the residual sample; Generate residual information based on the transform coefficients; Generate a reconstructed sample based on the residual sample and the prediction sample, the reconstructed sample including a reconstructed luminance sample and a reconstructed chrominance sample; Generate information related to an adaptive loop filter (ALF) and information related to a cross-component adaptive loop filter (CCALF) for the reconstructed sample; and Encode image information including the residual information, the prediction-related information, the ALF-related information, and the CCALF-related information, wherein the image information includes a sequence parameter set (SPS) and slice header information, the SPS includes an ALF enable flag related to whether the ALF process is enabled, based on the value of the ALF enable flag in the SPS being 1, the SPS includes a CCALF enable flag related to whether the CCALF is available, based on a determination that the value of the ALF enable flag in the SPS is 1, the slice header information includes an ALF enable flag related to whether the ALF is enabled, based on a determination that the value of the ALF enable flag included in the slice header information is 1 and the value of the CCALF enable flag included in the SPS is 1, the slice header information includes information on whether the CCALF is enabled for the filtered reconstructed chrominance sample, and based on the value of the information on whether the CCALF is enabled for the filtered reconstructed chrominance sample being 1, the slice header information includes identification (ID) information of an adaptive parameter set (APS) associated with the CCALF for the filtered reconstructed chrominance sample, the ALF data included in the APS includes information related to the number of cross-component filters for the Cb color component and information related to the number of cross-component filters for the Cr component, based on the information related to the number of cross-component filters for the Cb color component, the ALF data includes information on the absolute value of the cross-component filter coefficients for the Cb color component and information on the sign of the cross-component filter coefficients for the Cb color component, and based on the information related to the number of cross-component filters for the Cr color component, the ALF data includes information on the absolute value of the cross-component filter coefficients for the Cr color component and information on the sign of the cross-component filter coefficients for the Cr color component.

3. A method for transmitting data of an image, the method comprising: Obtain a bitstream of the image, wherein the bitstream is generated based on the following steps: Derive a prediction sample for a current block; Generate prediction-related information based on the prediction sample; Generate a residual sample for the current block; Derive transform coefficients based on a transform process for the residual sample; Generate residual information based on the transform coefficients; Generate a reconstructed sample based on the residual sample and the prediction sample, where the reconstructed sample includes a reconstructed luminance sample and a reconstructed chrominance sample; generate information related to an adaptive loop filter (ALF) and information related to a cross-component adaptive loop filter (CCALF) for the reconstructed sample; and encode image information including the residual information, the prediction-related information, the ALF-related information, and the CCALF-related information; and Transmit the data including the bitstream, wherein the image information includes a sequence parameter set (SPS) and slice header information, the SPS includes an ALF enable flag related to whether the ALF process is enabled, based on the value of the ALF enable flag being 1, the SPS includes a CCALF enable flag related to whether the CCALF is available, based on the determination that the value of the ALF enable flag in the SPS is 1, the slice header information includes an ALF enable flag related to whether the ALF is enabled, based on the determination that the value of the ALF enable flag included in the slice header information is 1 and the value of the CCALF enable flag included in the SPS is 1, the slice header information includes information on whether the CCALF is enabled for the filtered reconstructed chrominance sample, and based on the value of the information on whether the CCALF is enabled for the filtered reconstructed chrominance sample being 1, the slice header information includes identification (ID) information of an adaptive parameter set (APS) associated with the CCALF for the filtered reconstructed chrominance sample, the ALF data included in the APS includes information related to the number of cross-component filters for the Cb color component and information related to the number of cross-component filters for the Cr component, based on the information related to the number of cross-component filters for the Cb color component, the ALF data includes information on the absolute value of the cross-component filter coefficients for the Cb color component and information on the sign of the cross-component filter coefficients for the Cb color component, and based on the information related to the number of cross-component filters for the Cr color component, the ALF data includes information on the absolute value of the cross-component filter coefficients for the Cr color component and information on the sign of the cross-component filter coefficients for the Cr color component.

Images