Image Compilation Device and Method Based on Cross-Component Adaptive Loop Filtering

Abstract

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

Description

Technical Field

[0001] The present disclosure relates to an image encoding apparatus and method based on cross-component adaptive loop filtering. Background Art

[0002] Recently, there has been an increasing demand for high-resolution, 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 has been an increasing interest in and demand for virtual reality (VR) and augmented reality (AR) content, as well as immersive media such as holograms, and there has also been an increasing growth in the broadcasting of images / videos having characteristics different from those of real-world images (such as game images).

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

[0005] The cross-component adaptive loop filtering process (CCALF) is a process performed to improve the accuracy of filtering within the loop filtering process, and discussions related to the transmission of information used in the CCALF process are underway. Summary of the Invention

[0006] Technical Solution

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

[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 reconstructed chrominance samples based on reconstructed luminance samples.

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

[0012] According to an embodiment of the present disclosure, information regarding 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 can 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 about a 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 executed 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 executed 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 at least one embodiment disclosed in the video / image encoding method in the embodiments 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 for causing a decoding device to execute the video / image decoding method disclosed in at least one embodiment in the embodiments 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, the 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 signaled efficiently.

[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. schematically illustrates the configuration of a video / image encoding apparatus to which embodiments of the present disclosure can be applied.

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

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

[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 a decoding apparatus.

[0038] Figure 7 An example of the shape of an ALF filter is shown.

[0039] Figure 8 FIG. is a diagram illustrating a virtual boundary applied to a filtering process according to an embodiment of the present disclosure.

[0040] Figure 9 FIG. illustrates an example of an ALF process using a virtual boundary according to an embodiment of the present disclosure.

[0041] Figure 10 FIG. is a diagram illustrating a cross-component adaptive loop filtering (CC-ALF (CCALF)) process according to an embodiment of the present disclosure.

[0042] Figure 11 and Figure 12 Schematically illustrate examples of a video / image encoding method and related components according to an embodiment of the present disclosure.

[0043] Figure 13 and Figure 14 Schematically illustrate examples of an image / video decoding method and related components according to an embodiment of the present disclosure.

[0044] Figure 15 Illustrate an example of a content streaming system capable of applying the embodiments disclosed in the present disclosure. Detailed Description

[0045] The present disclosure can be modified in various forms, and specific embodiments thereof will be described and illustrated in the accompanying 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 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.

[0046] Meanwhile, each configuration in the accompanying drawings described in the present disclosure is independently illustrated for the convenience of describing different feature functions, and does not mean that each configuration is implemented as a separate hardware or 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.

[0047] 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). Additionally, 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 standards (e.g., H.267 or H.268, etc.).

[0048] The present disclosure presents various embodiments of video / image compilation, and unless otherwise mentioned, these embodiments can be executed in combination with each other.

[0049] Figure 1 Schematically illustrate an example of a video / image compilation system to which the embodiments of this document can be applied.

[0050] Reference Figure 1 , a 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The renderer may render the decoded video / images. The rendered video / images may be displayed through a display.

[0057] 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.

[0058] 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.

[0059] 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 the luminance component or a pixel / pixel value of only the chrominance component.

[0060] 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.

[0061] 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".

[0062] 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".

[0063] 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 equivalently interpreted as "at least one of A and B".

[0064] 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".

[0065] 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".

[0066] The technical features separately described in one drawing in this disclosure may be implemented individually or simultaneously.

[0067] Hereinafter, embodiments of this 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.

[0068] Figure 2 is a diagram schematically explaining the configuration of a video / image encoding apparatus to which this document is applicable. Hereinafter, the video encoding apparatus may include an image encoding apparatus.

[0069] Refer to 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 reconstructed 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 also include the memory 270 as an internal / external component.

[0070] 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, one coding unit may be split into multiple coding units of 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 split. 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 of 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.

[0071] In some cases, the term "unit" can be used interchangeably with terms such as "block" or "region". Generally, an M×N block can represent a set of samples or transform coefficients consisting of M columns and N rows. Samples typically can 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).

[0072] 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 prediction or inter 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 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.

[0073] The intra 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 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 predictor 222 can determine the prediction mode applied to the current block by using the prediction mode applied to neighboring blocks.

[0074] 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 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 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.

[0075] 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. Intra-block copy may be used for content image / video compilation such as games, for example, screen content compilation (SCC). 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, IBC may use at least one of the inter-frame prediction techniques described in this document.

[0076] 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 a graph. CNT means a transform generated based on a prediction signal generated using all previously reconstructed pixels. Further, the transform process can be applied to a square pixel block having the same size, or can be applied to a block having a variable size rather than a square.

[0077] 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 encoding methods, for example, exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 240 can encode the information required for video / image reconstruction, in addition to the quantized transform coefficients (e.g., the values of syntax elements, etc.), together or separately. The encoded information (e.g., 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). Further, 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 over 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) for sending the signal output from the entropy encoder 240 and / or a storage unit (not shown) for storing 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.

[0078] 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.

[0079] Meanwhile, luminance mapping and chrominance scaling (LMCS) can be applied during picture encoding and / or reconstruction.

[0080] 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.

[0081] 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.

[0082] 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 adjacent blocks or temporally adjacent 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.

[0083] Figure 3 is a diagram schematically explaining the configuration of a video / image decoding device to which this document is applicable.

[0084] 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.

[0085] When the input is 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 the 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 according to a quadtree structure, a binary tree structure, and / or a ternary tree structure from a compilation tree unit or the largest compilation unit. 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.

[0086] The decoding device 300 may receive, in the form of a bitstream, from Figure 2The signal output by the encoding device, and the received signal 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 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 compilation methods such as exponential Golomb coding, CAVLC, or CABAC, as well as 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 occurrence according to the determined context model, and generate 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 signal 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.

[0087] 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 dequantize the quantized transform coefficients by using quantization parameters (e.g., quantization step information) and obtain the transform coefficients.

[0088] The inverse transformer 322 performs an inverse transformation on the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0089] 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.

[0090] 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, for example, 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.

[0091] 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 can be located 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.

[0092] The inter-frame predictor 332 may 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 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 spatially neighboring blocks present in the current picture and temporally neighboring blocks present in the reference picture. For example, the inter-frame predictor 332 may 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. The inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating the mode of inter-frame prediction for the current block.

[0093] The adder 340 may 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 there is no residual for the block to be processed, such as when the skip mode is applied, the prediction block may be used as the reconstructed block.

[0094] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra-frame prediction of the next block to be processed in the current picture, may be output through filtering as described below, or may be used for inter-frame prediction of the next picture.

[0095] Meanwhile, luminance mapping and chrominance scaling (LMCS) may be applied during picture decoding.

[0096] The filter 350 may improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 may 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 may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0097] 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.

[0098] In this specification, the embodiments explained in the predictor 330, dequantizer 321, inverse transform device 322, and filter 350 of the decoding device 300 can be applied to or correspond to the predictor 220, dequantizer 234, inverse transform device 235, and filter 260 of the encoding device 200 in the same way, respectively.

[0099] 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 in the same way in both the encoding device and the decoding device, and the encoding device decodes the 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.

[0100] The residual information can be generated through transform processing and quantization processing. For example, the encoding device can derive the residual block between the original block and the prediction block, perform transform processing on the residual samples (residual sample array) included in the residual block to derive transform coefficients, and then derive quantized transform coefficients by performing quantization processing on the transform coefficients to signal the residual-related information (via the bitstream) to the decoding device. Here, the residual information can include value information, position information, transform technology, transform core, and quantization parameters of the quantized transform coefficients, etc. The decoding device can perform dequantization / inverse transform 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 dequantize / inverse transform the quantized transform coefficients for inter-frame prediction reference of subsequent pictures to derive the residual block and generate a reconstructed picture based on this.

[0101] 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.

[0102] 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 a 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 (transform) of the scaled transform coefficients. This may also be applied / expressed in other parts of this document.

[0103] 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 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 - 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 sum of the motion vector predictor and the motion vector difference may be used to derive the motion vector of the current block.

[0104] According to 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 called L0 prediction, the prediction based on the L1 motion vector may be called L1 prediction, and the prediction based on both the L0 motion vector and the L1 motion vector may be called 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 called forward (reference) pictures, and the subsequent pictures may be called 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

[0105] L0, and the subsequent pictures may be indexed later. The reference

[0106] 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.

[0107] Figure 4 Exemplarily shows the hierarchical structure of the compiled image / video.

[0108] 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 sends 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.

[0109] In the VCL, VCL data including compressed image data (slice data) is generated, or parameter sets including picture parameter set (PSP), sequence parameter set (SPS), and video parameter set (VPS), or supplementary enhancement information (SEI) messages additionally required for the image decoding process may be generated.

[0110] 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.

[0111] 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 required for decoding an image (parameter set or SEI message).

[0112] 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, 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.

[0113] As described above, NAL units 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.

[0114] For example, NAL units can be classified into a VCL NAL unit type and a non-VCL NAL unit type according to whether the NAL unit includes information about an image (slice data). The VCL NAL unit type can be classified according to the nature and type of the pictures included in the VCL NAL unit, and the non-VCL NAL unit type can be classified according to the type of the parameter set.

[0115] The following are examples of NAL unit types specified according to the type of parameter set included in the non-VCL NAL unit type.

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

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

[0118] - VPS (Video Parameter Set) NAL unit: The type for a NAL unit including VPS

[0119] - SPS (Sequence Parameter Set) NAL unit: The type of NAL unit for including SPS

[0120] - PPS (Picture Parameter Set) NAL unit: The type of NAL unit for including PPS

[0121] - PH (Picture Header) NAL unit: The type of NAL unit for including PH

[0122] The aforementioned NAL unit types may have syntax information for the NAL unit types 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.

[0123] 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 or replaced with tile groups. Additionally, in this document, slice headers may be used interchangeably or replaced with tile group headers.

[0124] 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.

[0125] 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 filtering 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.

[0126] Meanwhile, in order to compensate for the difference between the original image and the reconstructed image caused by errors occurring during compression encoding such as quantization, the in-loop filtering process may be performed on the reconstructed samples or the reconstructed picture as described above. As described above, the in-loop filtering may 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) may be applied. For example, the ALF process may 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 may be omitted.

[0127] Hereinafter, a detailed description of picture reconstruction and filtering will be described. In image / video encoding, a reconstructed block may be generated based on intra prediction / inter prediction for each block, and a reconstructed picture including the reconstructed blocks may be generated. When the current picture / slice is an I picture / slice, the blocks included in the current picture / slice may 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 may be reconstructed based on intra prediction or inter prediction. In this case, intra prediction may be applied to some of the blocks in the current picture / slice, and inter prediction may be applied to the remaining blocks.

[0128] Intra prediction may refer to a prediction for generating 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 intra prediction is applied to the current block, neighboring reference samples to be used for intra prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block having a size of nW x nH and a total of 2 x nH samples adjacent to the lower left, samples adjacent to the upper boundary of the current block and a total of 2 x nW 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 may include a plurality of upper neighboring samples and a plurality of left neighboring samples. In addition, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block having a size of nW x nH, 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.

[0129] However, some of the neighboring reference samples of the current block may still not be decoded or available. In this case, the decoder may configure the neighboring reference samples to be used for prediction by replacing the unavailable samples with available samples. Alternatively, the neighboring reference samples to be used for prediction may be configured by interpolation of available samples.

[0130] 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 case 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 a prediction sample of the current block. The above case can be referred to as position-dependent intra prediction (PDPC). Additionally, a reference sample line having 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 a reference sample located in the prediction direction on the corresponding line, and then the reference sample line used herein can be indicated (signaled) to the decoding device to perform intra prediction coding. The above case 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 technique or additional intra prediction mode. 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 be generally applied, and prediction can be performed based on the above intra prediction mode. Meanwhile, post-filtering can be performed on the derived predicted sample as needed.

[0131] 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.

[0132] Hereinafter, intra prediction in an encoding device will be described. The encoding device performs intra prediction on a current block. The encoding device may derive an intra prediction mode for the 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.

[0133] 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.

[0134] 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.

[0135] The encoding device may transform / quantize the residual samples to derive quantized transform coefficients (S520), and then dequantize / inverse-transform the quantized transform coefficients again to derive (modified) residual samples (S530). The reason for performing dequantization / inverse-transformation again after transformation / quantization is to derive the same residual samples as the residual samples derived from the decoding device as described above.

[0136] The encoding device may generate a reconstructed block including the 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.

[0137] 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 residual coding 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] Here, the intra predictor 331 of the decoding apparatus may include a prediction mode / type determiner, a reference sample derivator, and a predicted sample derivator, and 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 apparatus, 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).

[0143] 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) or the remaining mode to the current block, and when applying the 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 the MPM to the current block, the intra prediction mode information may further include remaining mode information (e.g., Intra_luma_mpm_remainder) indicating one of the remaining intra prediction modes other than the intra prediction mode candidates (MPM candidates). The decoding apparatus 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.

[0144] 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 the subpartition 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.

[0145] 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.

[0146] The predictor of the encoding device / decoding device 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 sum of the motion vector predictor and the motion vector difference can be used to derive the motion vector of the current block.

[0147] In the following, the inter-frame prediction process performed by the encoding device will be described. The encoding device performs inter-frame prediction on a current block. The encoding device can derive an inter-frame prediction mode and motion information of the current block, and generate 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 performed simultaneously, or one process can be performed 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, and the prediction mode determiner can determine a 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 a 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, a reference picture index indicating the reference picture in which the reference block is located can be derived, and a motion vector can be derived based on the positional difference between the reference block and the current block. The encoding device can determine a mode to be applied to the current block from 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.

[0148] For example, when applying the skip mode or the merge mode to the current block, the encoding device can construct a merge candidate list to be described later and derive a reference block whose difference from the current block is the smallest or a predetermined reference or less among the reference blocks indicated by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block can be selected, and merge index information indicating the selected merge candidate can be generated and signaled to the decoding device. The motion information of the selected merge candidate can be used to derive the motion information of the current block.

[0149] As another example, when applying the (A)MVP mode to a current block, the encoding device constructs an (A)MVP candidate list to be described later, and uses the motion vector of a selected mvp candidate among the motion vector predictor (mvp) candidates included in the (A)MVP candidate list as the mvp of the current block. In this case, for example, the motion vector indicating the reference block derived by the above-described motion estimation can be used as the motion vector of the current block, and the mvp candidate having the smallest difference from the motion vector of the current block among the mvp candidates can be the selected mvp candidate. A motion vector difference (MVD) can be derived as the difference obtained by subtracting the mvp from the motion vector of the current block. In this case, information about the MVD can be signaled to the decoding device. Additionally, when applying the (A)MVP mode, the value of the reference picture index can be configured as reference picture index information and signaled separately to the decoding device.

[0150] The encoding device may derive a residual sample based on a prediction sample (S710). The encoding device may derive the residual sample by comparing the original sample of the current block with the prediction sample.

[0151] The encoding device performs transform / quantization on the residual sample to derive quantized transform coefficients (S720), and then performs dequantization / inverse transform on the quantized transform coefficients again to derive a (modified) residual sample (S730). 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.

[0152] The encoding device may generate a reconstructed block including the reconstructed sample of the current block based on the prediction sample and the (modified) residual sample (S740). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0153] Although not shown, as described above, the encoding device 100 may encode video information including prediction information and residual information. The encoding device 100 may 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 the residual sample. The residual information may include information about the quantized transform coefficients for the residual sample.

[0154] The output bitstream can be stored in a (digital) storage medium and sent to the decoding device, or can be sent to the decoding device via a network.

[0155] Figure 6 is a flowchart illustrating an inter - frame prediction - based block reconstruction method in a decoding device. Figure 6 The method may include steps S600, S610, S620, S630, and S640. The decoding device may perform operations corresponding to those performed by the encoding device.

[0156] S600 to S620 may be performed by the inter - frame predictor 332 of the decoding device, and the prediction information of S600 and the residual information of S630 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 the residual samples of the current block based on the residual information. Specifically, the de - quantizer 321 of the residual processor 320 may derive the transform coefficients by performing de - quantization based on the quantization transform coefficients derived based on the residual information, and the inverse transformer 322 of the residual processor may derive the residual samples for the current block by performing an inverse transform on the transform coefficients. S640 may be performed by the adder 340 or the reconstructor of the decoding device.

[0157] Specifically, the decoding device may determine a prediction mode for the current block based on the received prediction information (S600). 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.

[0158] For example, based on the merge flag, it may be determined whether to apply the merge mode to the current block or whether to determine the (A)MVP mode. Alternatively, one of various inter - frame prediction mode candidates may be selected based on the mode index. The inter - frame prediction mode candidates may include the skip mode, the merge mode, and / or the (A)MVP mode, or may include various inter - frame prediction modes to be described later.

[0159] The decoding device derives the motion information of the current block based on the determined inter - frame prediction mode (S610). For example, when applying the skip mode or the merge mode to the current block, the decoding device may configure a merge candidate list to be described below and select one merge candidate from the merge candidates included in the merge candidate list. The selection may be performed based on the aforementioned selection information (merge index). The motion information of the selected merge candidate may be used to derive the motion information of the current block. The motion information of the selected merge candidate may be used as the motion information of the current block.

[0160] As another example, when applying the (A)MVP mode to the current block, the decoding device may construct an (A)MVP candidate list to be described below and use the motion vector of a selected mvp candidate among the motion vector predictor (mvp) candidates included in the (A)MVP candidate list as the mvp of the current block. The selection may be performed based on the above selection information (mvp flag or mvp index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the mvp and MVD of the current block. Additionally, the reference picture index of the current block may 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 may be derived as the reference picture referred to for the inter prediction of the current block.

[0161] Meanwhile, as will be described below, the motion information of the current block may be derived without configuring a candidate list. In this case, the motion information of the current block may 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 may be omitted.

[0162] The decoding device may generate a prediction sample of the current block based on the motion information of the current block (S620). In this case, the reference picture may be derived based on the reference picture index of the current block, and the prediction sample of the current block may be derived using the samples of the reference block indicated by the motion vector of the current block on the reference picture. In this case, as will be described later, the prediction sample filtering process for all or some of the prediction samples of the current block may be further performed depending on the situation.

[0163] For example, the inter predictor 332 of the decoding device may include a prediction mode determiner, a motion information deriver, and a prediction sample deriver. The prediction mode determiner may determine the prediction mode for the current block based on the received prediction mode information. The motion information deriver 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 prediction sample derivation unit may derive the prediction sample of the current block.

[0164] The decoding device generates a residual sample for the current block based on the received residual information (S630). The decoding device may generate a reconstructed sample for the current block based on the prediction sample and the residual sample, and may derive a reconstructed block including the reconstructed sample (S640). The reconstructed picture for the current picture may be generated based on the reconstructed block.

[0165] Various inter - frame prediction modes can be used for the prediction of the current block in a picture. For example, various modes can be used, such as merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub - block merge mode, and merge with MVD (MMVD) mode, etc. 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. can be used as additional modes. The affine mode can be referred to as the affine motion prediction mode. The MVP mode can be called the advanced motion vector prediction (AMVP) mode. In this document, some modes and / or motion information candidates derived by some modes can be included as one of the motion information candidates for other modes. For example, HMVP candidates can be added as merge candidates in the merge / skip mode or can be added as mvp candidates in the MVP mode.

[0166] The prediction mode information indicating the inter - frame prediction mode of the current block can be signaled from the encoding device to the decoding device. The prediction mode information can be included in the bitstream and received by the decoding device. The prediction mode information can include index information indicating one of multiple candidate modes. Alternatively, the inter - frame prediction mode can be indicated by hierarchical signaling of flag information. In this case, the prediction mode information can include one or more flags. For example, a skip flag can be signaled to indicate whether the skip mode is applied, and if the skip mode is not applied, a merge flag can be signaled to indicate whether the merge mode is applied, and if the merge mode is not applied, it is indicated that the MVP mode is to be applied or flags for additional classification can be further signaled. The affine mode can be signaled in an independent mode or can be signaled in a mode dependent on the merge mode or the MVP mode. For example, the affine mode can include an affine merge mode and an affine MVP mode.

[0167] Meanwhile, it is possible to signal in the current block an indication of whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used in the current block (current compilation unit). This information may be referred to as motion prediction direction information, inter-frame prediction direction information, or inter-frame prediction indication information, and may be configured / encoded / signaled in the form of, for example, an inter_pred_idc syntax element. That is, the inter_pred_idc syntax element may 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 convenience of description, the inter-frame prediction type (L0 prediction, L1 prediction, or BI prediction) indicated by the inter_pred_idc syntax element may be referred to as the motion prediction direction. The L0 prediction may be represented as pred_L0, the L1 prediction may be represented as pred_L1, and the bi-prediction may be represented as pred_BI. For example, the following prediction types may be determined according to the value of the inter_pred_idc syntax element.

[0168] [Table 1]

[0169]

[0170] As described above, a picture may include one or more slices. A slice may have one of slice types including an intra (I) slice, a predictive (P) slice, and a bi-predictive (B) slice. The slice type may be indicated based on slice type information. For blocks in an I slice, inter-frame prediction may not be used for prediction, and only intra prediction may be used. Of course, even in this case, the original sample values may be compiled and signaled without prediction. Intra prediction or inter-frame prediction may be used for blocks in a P slice, and only uni-directional prediction may be used when inter-frame prediction is used. Meanwhile, intra prediction or inter-frame prediction may be used for blocks in a B slice, and up to bi-directional prediction may be used when inter-frame prediction is used.

[0171] L0 and L1 may include reference pictures 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 the previous reference picture in POC order, and L1 may be assigned a reference picture index lower than the current picture with respect to the subsequent reference picture in POC order. In the case of a B slice, bi-prediction may be applied, and in this case, uni-directional bi-prediction or bi-directional bi-prediction may be applied. The bi-directional bi-prediction may be referred to as true bi-prediction.

[0172] As described above, a residual block (residual sample) can 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 can be generated. The residual information can include information on quantized transform coefficients. The residual information can be included in video / image information, and the video / image information can be encoded and sent to a decoding device in the form of a bitstream. The decoding device can obtain the residual information from the bitstream and can derive a residual sample based on the residual information. Specifically, the decoding device can derive quantized transform coefficients based on the residual information and can derive a residual block (residual sample) through an inverse quantization / inverse transformation process.

[0173] Meanwhile, at least one of the (inverse) transformation and / or (de)quantization processes can be omitted.

[0174] Hereinafter, an in-loop filtering process performed on a reconstructed picture will be described. A modified reconstructed sample, block, picture (or modified filtered sample, block, picture) can be generated through the in-loop filtering process, and the modified (modified and filtered) reconstructed picture can be output as a decoded picture at the decoding device and can also be stored in a decoded image 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 can 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 can be applied sequentially or all can be applied sequentially. For example, the SAO process can be performed after applying the deblocking filtering process to the reconstructed picture. Or, for example, the ALF process can be performed after applying the deblocking filtering process to the reconstructed picture. This can also be performed in the encoding device.

[0175] Deblocking filtering is a filtering technique for removing distortions at the boundaries between blocks in a reconstructed picture. For example, the deblocking filtering process can derive a target boundary based on the reconstructed picture, determine the boundary strength (bS) of the target boundary, and perform deblocking filtering on the target boundary based on bS. The bS can be determined based on the prediction mode of two blocks adjacent to the target boundary, the motion vector difference, whether the reference pictures are the same, whether there are non-zero valid coefficients, etc.

[0176] 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 applying deblocking filtering.

[0177] Adaptive Loop Filter (ALF) is a technique for filtering a reconstructed picture on a sample basis based on filter coefficients according to a filter shape. An encoding device can determine whether to apply ALF, an ALF shape, and / or an ALF filtering coefficient, etc. by comparing the reconstructed picture and the original picture and can signal it to a decoding device. That is, filtering information for ALF can include information on whether ALF is applied, ALF filter shape information, ALF filtering coefficient information, etc. ALF can be applied to the reconstructed picture after applying deblocking filtering.

[0178] Figure 7 An example showing the shape of an ALF filter.

[0179] In Figure 7 (a) shows the shape of a 7x7 diamond filter, and (b) shows the shape of a 5x5 diamond filter. In Figure 7In this case, 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 to which the filter coefficient is assigned according to the filter shape of the ALF may be referred to as a filter tap. In this case, one filter coefficient can be assigned to each filter tap, and the arrangement of the filter taps may correspond to the filter shape. The filter tap located at the center of the filter shape may be referred to as the central filter tap. The same filter coefficient can be assigned to two filter taps having the same n value that are located at positions corresponding to each other with respect to the central filter tap. For example, in the case of a 7x7 diamond filter shape, it includes 25 filter taps, and since the filter coefficients C0 to C11 are assigned in a centrosymmetric form, only 13 filter coefficients can be used to assign the filter coefficients to 25 filter taps. Additionally, for example, in the case of a 5x5 diamond filter shape, it includes 13 filter taps, and since the filter coefficients C0 to C5 are assigned in a centrosymmetric form, only 7 filter coefficients are used to assign the filter coefficients to 13 filter taps. For example, in order to reduce the amount of data on the information of the filter coefficients signaled, 12 out of 13 filter coefficients for the 7x7 diamond filter shape can be signaled (explicitly), and 1 filter coefficient can be derived (implicitly). Additionally, for example, 6 out of 7 filter coefficients for the 5x5 diamond filter shape can be signaled (explicitly), and 1 filter coefficient can be derived (implicitly).

[0180] 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.

[0181] ALF is an in-loop filtering technique that can be applied in video / image compilation as described above. An Adaptive filter based on Wiener can be used to perform ALF. This can be to minimize the Mean Square Error (MSE) between the original sample and the decoded sample (or reconstructed sample). The advanced design for the ALF tool can incorporate syntax elements accessible in the SPS and / or slice header (or tile group header).

[0182] In an example, before filtering for each 4x4 luminance block, geometric transformations such as rotation or diagonal and vertical flipping can be applied to the filter coefficient f(k, l) and the corresponding filter limit value 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.

[0183] For example, three types of transformations can be performed based on the following equations: diagonal, vertical flip, and rotation.

[0184] [Equation 1]

[0185] Diagonal: f_D(k, l) = f(l, k), c_D(k, l) = c(l, k)

[0186] [Equation 2]

[0187] Vertical flip: f_V(k, l) = f(k, K - l - 1), c_V(k, l) = c(k, K - l - 1)

[0188] [Equation 3]

[0189] Rotation: f_R(k, l) = f(K - l - 1, k), c_R(k, l) = c(K - l - 1, k)

[0190] 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.

[0191] [Table 2]

[0192] 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

[0193] The ALF filter parameters can be signaled in the APS and slice headers. In one APS, up to 25 luminance filter coefficients and amplitude limit index can be signaled. In one APS, up to 8 chrominance filter coefficients and amplitude limit 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 (referred to by the current slice) for the current slice can be signaled.

[0194] The amplitude limit index decoded from the APS can make it possible to determine the amplitude limit using the luminance table of the amplitude limit and the chrominance table of the amplitude limit. These amplitude limits may depend on the internal bit depth. More specifically, the luminance table of the amplitude limit and the chrominance table of the amplitude limit can be derived based on the following equations.

[0195] [Equation 4]

[0196] AlfClipL = {round(2^(B(N - n + 1) / N)) for n ∈ [1..N]}

[0197] [Equation 5]

[0198] AlfClipC = {round(2^((B - 8)+8((N - n)) / (N - 1))) for n ∈ [1..N]}

[0199] In the above equation, B can be the internal bit depth, and N can be the number (predetermined number) of allowed clipping values. For example, N can be 4.

[0200] In the slice header, up to 7 APS indices can be signaled to indicate the luminance filter set for the current slice. The filtering process can be further controlled at the CTB level. For example, a flag indicating whether ALF is applied to the luminance CTB can be signaled. The luminance CTB can select one of 16 fixed filter sets and the filter set from APS. A filter set index can be signaled for the luminance 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.

[0201] For the chrominance component, an APS index can be signaled in the slice header to indicate the chrominance filter set for the current slice. At the CTB level, when there are two or more chrominance filter sets in APS, a filter index can be signaled for each chrominance CTB.

[0202] 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 central position coefficient can not be signaled in the bitstream and can be pre-determined (considered) as 128.

[0203] 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.

[0204] [Equation 6]

[0205] R′(i, j) = R(i, j)+((∑ k≠0 ∑ l≠0 f(k, l)×K(R(i + k, j + l)-R(i, j), c(k, l))+64) >> 7)

[0206] 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).

[0207] In an example, to reduce the row buffer requirements of the ALF, 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.

[0208] Figure 8 FIG. is a diagram showing a virtual boundary applied to a filtering process according to an embodiment of the present disclosure. Figure 9 FIG. 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 8 description Figure 9 .

[0209] reference 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.

[0210] In Figure 8 , modified block classification can be applied to the luminance component. For the 1D Laplacian gradient calculation of 4x4 blocks on the virtual boundary, only the samples above the virtual boundary can be used. Similarly, to calculate the 1D Laplacian gradient of 4x4 blocks below the virtual boundary, only the samples below the virtual boundary can be used. Considering the reduction in the number of samples used in the 1D Laplacian gradient calculation, the quantization of the activity value A can be scaled accordingly.

[0211] For the filtering process, a symmetric padding operation at the virtual boundary can be used for both the luminance component and the chrominance component. Referring to Figure 8 , when the filtered sample 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 symmetrically filled.

[0212] When no filter is available across the boundary, the process described in Figure 9 can also be used for the boundaries of slices, bricks, and / or tiles. For ALF block classification, only the samples included in the same slice, brick, and / or tile can be used and the activity value can be scaled accordingly. For ALF filtering, symmetric padding can be applied for each of the horizontal direction and / or the vertical direction with respect to the horizontal boundary and / or the vertical boundary.

[0213] Figure 10 FIG. is a diagram illustrating a cross-component adaptive loop filtering (CC-ALF) process according to an embodiment of the present disclosure. The CCALF process may be referred to as a cross-component filtering process.

[0214] In one aspect, the ALF process may include a general ALF process and a CCALF process. That is, the CCALF process may refer to some processes of the ALF process. In another aspect, the filtering process may include a deblocking process, a SAO process, an ALF process, and / or a CCALF process.

[0215] CC-ALF may use luminance sample values to refine each chrominance component. CC-ALF is controlled by information in the bitstream (image), which includes (a) information about filter coefficients for each chrominance component and (b) information about a mask that controls the application of the filter to sample blocks. The filter coefficients may be signaled at the APS, and the block size and mask may be signaled at the slice level.

[0216] Reference Figure 10 , CC-ALF may be operated by applying a linear diamond filter ( Figure 10 (b) of ) to the luminance channel of each chrominance 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 may be controlled at variable block sizes and signaled by a context compilation flag received for each sample block. The block size and the CC-ALF enable flag may be received at the slice level for each chrominance component. The block size (for chrominance samples) may be 16x16, 32x32, 64x64, or 128x128.

[0217] In the following embodiments, a method for re-filtering or modifying reconstructed chrominance samples filtered by ALF based on reconstructed luminance samples is proposed.

[0218] 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, 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.

[0219] The following table shows some syntax of slice header information according to an embodiment of the present disclosure.

[0220] [Table 3]

[0221]

[0222] The following table shows exemplary semantics for the syntax elements included in the above table.

[0223] [Table 4]

[0224]

[0225]

[0226]

[0227] 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 slice_cross_component_alf_cb_aps_id to use the filter in the corresponding adaptive parameter set (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.

[0228] 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.

[0229] The following table shows an example syntax for ALF data.

[0230] [Table 5]

[0231]

[0232] The following table is an example semantics of the syntax elements included in the above table.

[0233] [Table 6]

[0234]

[0235]

[0236]

[0237]

[0238]

[0239] 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, CC-ALF can be applied. A new hardware pipeline design is required because CC-ALF should be able to operate independently of the existing ALF structure. This causes an increase in the cost of the hardware implementation method and an increase in the hardware latency.

[0240] In addition, in ALF, it is determined whether to apply both the luminance picture and the chrominance picture in units of CTUs, and the determined result is signaled to the decoder. However, whether to apply variable CC-ALF is determined in units of 16x16 to 128x128, and this application can cause a conflict between the existing ALF structure and CC-ALF. This causes problems in terms of hardware implementation and also causes an increase in line buffers for various variable CC-ALF applications.

[0241] In the present disclosure, the problems in the hardware implementation of CC-ALF mentioned above are solved by applying the CC-ALF syntax structure as a whole to the ALF syntax structure.

[0242] According to an embodiment of the present disclosure, in order to determine whether to use (apply) CC-ALF, a sequence parameter set (SPS) may include a CC-ALF enable flag (sps_ccalf_enable_flag). The CC-ALF enable flag may be signaled independently of the ALF enable flag (sps_alf_enabled_flag) used to determine whether to use (apply) ALF.

[0243] The following table shows some exemplary syntax of the SPS according to this embodiment.

[0244] [Table 7]

[0245]

[0246] 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 may indicate whether CC-ALF is available (and may be related to whether CC-ALF is available).

[0247] The following table shows some example syntax of the slice header.

[0248] [Table 8]

[0249]

[0250] 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 may include slice header information (slice_header()). Based on the determination that the value of the CCALF enable flag (sps_ccalf_flag) is 1, the slice header information includes a first flag (slice_cross_component_alf_cb_enabeld_flag) related to whether CC-ALF can be used for filtering the Cb color component of the reconstructed chrominance samples and a second flag (slice_cross_component_alf_cr_enabeld_flag) related to whether CC-ALF can be used for filtering the Cr color component of the reconstructed chrominance samples.

[0251] 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 may 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 may 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.

[0252] The following table shows a part of the SPS syntax according to another example of this embodiment.

[0253] [Table 9]

[0254]

[0255] The following table exemplarily shows a part of the slice header syntax.

[0256] [Table 10]

[0257]

[0258] 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 signaled in the SPS based on the case where the chroma format is not monochrome.

[0259] 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.

[0260] In an example, the picture information encoded by an encoding device or obtained by a 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).

[0261] The following table shows a part of the slice header syntax according to another example of the present embodiment.

[0262] [Table 11]

[0263]

[0264] Referring to the above table, the parsing of the CCALF enable flag (sps_ccalf_enabled_flag) may be performed only when the ALF enable flag (sps_alf_enabled_flag) is 1.

[0265] The following table shows exemplary semantics for the syntax elements included in the above table.

[0266] [Table 12]

[0267]

[0268]

[0269] The slice_ccalf_chroma_idc in the above table can be described by the semantics in the following table.

[0270] [Table 13]

[0271]

[0272] The following table shows a part of the slice header syntax according to another example of this embodiment.

[0273] [Table 14]

[0274]

[0275] 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.

[0276] The following table shows a part of the slice header syntax according to another example of this embodiment.

[0277] [Table 15]

[0278]

[0279] The following table shows exemplary semantics for the syntax elements included in the above table.

[0280] [Table 16]

[0281]

[0282]

[0283] 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.

[0284] [Table 17]

[0285]

[0286] Referring to the above table, it is possible to determine whether to apply slice unit ALF and CC-ALF at once by slice_alf_enabled_flag. After parsing slice_alf_chroma_idc, when the first ALF enable flag (sps_alf_enabled_flag) is 1, slice_ccalf_chroma_idc can be parsed.

[0287] Referring to the above table, it is only when the slice_alf_enabled_flag is 1 that it can be determined whether the sps_ccalf_enabeld_flag is 1 in the slice header information. The slice header information may include a second ALF enable flag (slice_alf_enabled_flag) related to whether 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.

[0288] 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.

[0289] [Table 18]

[0290]

[0291] The following table shows an example syntax for ALF data.

[0292] [Table 19]

[0293]

[0294] Referring to the above two tables, the APS may include ALF data (alf_data()). The APS including ALF data may be referred to as an ALF APS (ALF type APS). That is, the type of the APS including 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.

[0295] In an example, based on the Cr filter signal flag, the ALF data may include information about the absolute value of the cross-component filter coefficients for the Cr color component (alf_cross_component_cr_coeff_abs) and information about the sign of the cross-component filter coefficients for the Cr color component (alf_cross_component_cr_coeff_sign). 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.

[0296] In an example, 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 sign of the cross-component filter coefficients for the Cb color component (alf_cross_component_cb_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 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.

[0297] The following table shows the syntax related to the ALF data according to another example.

[0298] [Table 20]

[0299] 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 may be sent. That is, the alf_cross_component_filter_signal_flag integrates Cb / Cr to determine whether to send the CC-ALF filter coefficients.

[0300] The following table shows the syntax related to the ALF data according to another example.

[0301] [Table 21]

[0302]

[0303] The following table shows the exemplary semantics for the syntax elements included in the above table.

[0304] [Table 22]

[0305]

[0306]

[0307]

[0308]

[0309] The following table shows the syntax related to the ALF data according to another example.

[0310] [Table 23]

[0311]

[0312] The following table shows the exemplary semantics for the syntax elements included in the above table.

[0313] [Table 24]

[0314]

[0315]

[0316]

[0317]

[0318] In the above two tables, the order of the exp-Golomb binarization for parsing 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.

[0319] 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 a 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 sign 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 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.

[0320] 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 related to the number of cross-component filters for the Cr color component (ccalf_cr_num_alt_filters_minus1). Based on the information related to the number of cross-component filters for the Cr color component, the ALF data may include information about the absolute value of the cross-component filter coefficients for the Cr color component (alf_cross_component_cr_coeff_abs) and information about the sign of the cross-component filter coefficients for the Cr color component (alf_cross_component_cr_coeff_sign). 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.

[0321] The following table shows the syntax of the compilation tree unit according to an embodiment of the present disclosure.

[0322] [Table 25]

[0323]

[0324] The following table shows the exemplary semantics for the syntax elements included in the above table.

[0325] [Table 26]

[0326]

[0327]

[0328] The following table shows the compilation tree unit syntax according to another example of this embodiment.

[0329] [Table 27]

[0330]

[0331] Referring to the above table, CCALF can be applied in units of CTU. In the example, the image information may include information about the compilation tree unit (coding_tree_unit()). The information about the compilation tree unit may include information about whether to apply the cross-component filter to the current block of the Cb color component (ccalf_ctb_flag[0]) and / or information about whether to apply the cross-component filter to the current block of the Cr color component (ccalf_ctb_flag[1]). Additionally, the information about the compilation 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 adaptively sent according to the syntax slice_ccalf_enabled_flag and slice_ccalf_chroma_idc.

[0332] The following table shows the compilation tree unit syntax according to another example of this embodiment.

[0333] [Table 28]

[0334]

[0335] The following table shows the exemplary semantics for the syntax elements included in the above table.

[0336] [Table 29]

[0337]

[0338]

[0339] The following table shows the syntax of the coding tree unit according to another example of the present embodiment. The syntax elements included in the following table can be described according to Table 29.

[0340] [Table 30]

[0341]

[0342] In the example, the picture information may include information about the 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]).

[0343] Figure 11 and Figure 12 Schematically shows an example of a video / image coding method and related components according to an embodiment of the present disclosure. Figure 11 The method disclosed in Figure 2 can be executed by the coding device disclosed in Figure 11 Specifically, for example, S1100 of Figure 11 can be executed by the adder 250 of the coding device, S1110 to S1140 can be executed by the filter 260 of the coding device, and S1570 can be executed by the entropy encoder 240 of the coding device.

[0344] Referring to Figure 11 , the coding device can generate the reconstructed luma samples and reconstructed chroma samples of the current block (S1100). The coding device can generate residual luma samples and / or residual chroma samples. The coding device can generate the reconstructed luma samples based on the residual luma samples and can generate the reconstructed chroma samples based on the residual chroma samples.

[0345] In an example, a residual sample for a current block can be generated based on an original sample and a predicted sample of the current block. Specifically, an encoding device can generate a predicted sample 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, can be applied. A residual sample can be generated based on the predicted sample and the original sample.

[0346] In an example, the encoding device can generate a residual luminance sample. The residual luminance sample can be generated based on an original luminance sample and a predicted luminance sample. In an example, the encoding device can generate a residual chrominance sample. The residual chrominance sample can be generated based on an original chrominance sample and a predicted chrominance sample.

[0347] The encoding device can derive transform coefficients. The encoding device can derive transform coefficients based on a transform process for the residual sample. The encoding device can derive transform coefficients for the residual luminance sample (luminance transform coefficients) and / or transform coefficients for the residual chrominance sample (chrominance transform coefficients). For example, the transform process can include at least one of DCT, DST, GBT, or CNT.

[0348] The encoding device can derive quantized transform coefficients. The encoding device can derive quantized transform coefficients based on a quantization process for the transform coefficients. The quantized transform coefficients can have a one-dimensional vector form based on a coefficient scan order. The quantized transform coefficients can include quantized luminance transform coefficients and / or quantized chrominance transform coefficients.

[0349] The encoding device can generate residual information. The encoding device can generate residual information indicating (including) the quantized transform coefficients. The residual information can be generated by various encoding methods such as exponential Golomb, CAVLC, CABAC, etc.

[0350] The encoding device can generate prediction-related information. The encoding device can generate prediction-related information based on the predicted sample and / or the mode applied thereto. The prediction-related information can include information about various prediction modes (e.g., merge mode, MVP mode, etc.), MVD information, etc.

[0351] The encoding device can derive ALF filter coefficients (S1110) for an ALF process. The ALF filter coefficients can include ALF luminance filter coefficients for reconstructing luminance samples and ALF chrominance filter coefficients for reconstructing chrominance samples. Filtered reconstructed luminance samples and / or filtered reconstructed chrominance samples can be generated based on the ALF filter coefficients.

[0352] The encoding device may generate ALF-related information (S1120). The encoding apparatus may generate ALF-related information based on the ALF filter coefficients. The encoding apparatus may derive ALF-related parameters that can be applied to filter reconstructed samples, and generate ALF-related information. For example, the ALF-related information may include the ALF-related information described above in the present disclosure.

[0353] The encoding apparatus may derive a cross-component filter (CCALF filter) and / or cross-component filter coefficients (CCALF filter coefficients) (S1130). The cross-component filter and / or cross-component filter coefficients may be used in the CCALF process. Modified filtered reconstructed chrominance samples may be generated based on the cross-component filter and / or cross-component filter coefficients.

[0354] The encoding device may generate cross-component filtering-related information (or CCALF-related information) (S1140). In an example, the cross-component filtering-related information may include information about the number of cross-component filters and information about the cross-component filter coefficients. The cross-component filters may include a cross-component filter for the Cb color component and a cross-component filter for the Cr color component.

[0355] 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 the cross-component filter for the Cb (or Cr) color component, information about the number of cross-component filters for the Cb (or Cr) color component, information about the values of the cross-component filter coefficients for the Cb (or Cr) color component, information about the absolute values of the cross-component filter coefficients for the Cb (or Cr) color component, information about the signs of the cross-component filter coefficients for the Cb (or Cr) color component, and / or information about whether to apply the 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.

[0356] The image / video information may include various types of information according to embodiments of the present disclosure. For example, the image / video information may include the information disclosed in at least one of Tables 1 to 30 above.

[0357] 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 determination that the CCALF enable flag is 1, ID information (identifier information) of an Adaptive Parameter Set (APS) including ALF data for deriving cross-component filter coefficients for CCALF may be derived. The picture information may include slice header information.

[0358] According to an example of an embodiment, the slice header information may include ID information of an APS including ALF data for deriving cross-component filter coefficients. In another example, based on the determination that the CCALF enable flag is 1, the slice header information may include ID information of an APS including ALF data for deriving cross-component filter coefficients.

[0359] In an embodiment, the SPS may include an ALF enable flag (sps_ccalf_enabled_flag) related to whether ALF is available. 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.

[0360] 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.

[0361] 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 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 ALF enable flag is 1, CCALF may be available for the slice.

[0362] In an embodiment, the header information (slice header information) may include a first flag related to the Cb color component of the reconstructed chrominance samples for which CCALF can be used for filtering and a second flag related to the Cr color component of the reconstructed chrominance samples for which CCALF can be used 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 the Cb color component of the reconstructed chrominance samples for which CCALF can be used for filtering and a second flag related to the Cr color component of the reconstructed chrominance samples for which CCALF can be used for filtering.

[0363] 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.

[0364] 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.

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

[0366] 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 can be derived.

[0367] 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).

[0368] 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 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.

[0369] 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.

[0370] Figure 13 and Figure 14 FIG. schematically illustrates an example of a video / image decoding method and related components according to an embodiment of the present disclosure. Figure 13 The method disclosed in Figure 3 or Figure 14 may be performed by the decoding device illustrated in Figure 13 Specifically, for example, S1300 of

[0371] may be performed by the entropy decoder 310 of the decoding device, S1310 may be performed by the adder 340 of the decoding device, and S1320 to S1330 may be performed by the filter 350 of the decoding device. Figure 13, the decoding device may receive / acquire video / image information (S1300). The video / image information may include prediction-related information and / or residual information. The decoding device may receive / acquire the image / video information through a bitstream. The residual information may be generated by various coding methods such as Exponential Golomb, CAVLC, CABAC, etc. 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 about the coding tree unit (coding tree unit syntax).

[0372] The image / video information may include various types of information according to embodiments of the present disclosure. For example, the image / video information may include the information disclosed in at least one of Tables 1 to 30 above.

[0373] The decoding device may derive transform coefficients. Specifically, the decoding device may 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 may derive the transform coefficients based on the dequantization process for the quantized transform coefficients.

[0374] The decoding device may derive residual samples. The decoding device may 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 may be derived based on the luminance transform coefficients, and the residual chrominance samples may be derived based on the chrominance transform coefficients. Additionally, the residual samples for the current block may be derived based on the original samples and the prediction samples of the current block.

[0375] The decoding device may perform prediction based on the image / video information and derive the prediction samples of the current block. The decoding device may derive the prediction samples of the current block based on the prediction-related information. The prediction-related information may include prediction mode information. The decoding device may determine whether to apply inter prediction or intra prediction to the current block based on the prediction mode information and may perform prediction based on this. The prediction samples may include prediction luminance samples and / or prediction chrominance samples.

[0376] The decoding device may generate / derive reconstructed luminance samples and / or reconstructed chrominance samples (S1310). The reconstructed samples may include reconstructed luminance samples and / or reconstructed chrominance samples. The decoding device may generate reconstructed luminance samples based on residual luminance samples. The decoding device may generate reconstructed chrominance samples based on residual chrominance samples. The luminance component of the reconstructed samples may correspond to the reconstructed luminance samples, and the chrominance component of the reconstructed samples may correspond to the reconstructed chrominance samples.

[0377] The decoding device may perform an Adaptive Loop Filter (ALF) process on the reconstructed chrominance samples to generate filtered reconstructed chrominance samples (S1320). During the ALF process, the decoding device may derive the ALF filter coefficients for the ALF process of the reconstructed chrominance samples. Additionally, the decoding device may derive the ALF filter coefficients for the ALF process of the reconstructed luminance samples. The ALF filter coefficients may be derived based on the ALF parameters included in the ALF data in the APS.

[0378] The decoding device may generate filtered reconstructed chrominance samples. The decoding device may generate the filtered reconstructed samples based on the reconstructed chrominance samples and the ALF filter coefficients.

[0379] To generate modified filtered reconstructed chrominance samples, the decoding device may perform a cross-component filtering process on the filtered reconstructed chrominance samples (S1330). During the cross-component filtering process, the decoding device may derive the cross-component filter coefficients for the cross-component filtering. The cross-component filter coefficients may 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 may be included in the slice header (by which it may be signaled).

[0380] The decoding device may generate modified filtered reconstructed chrominance samples. The decoding device may 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 may 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 may generate the modified filtered reconstructed chrominance samples. For example, the decoding device may generate the modified filtered reconstructed chrominance samples based on the sum of the product and one of the filtered reconstructed chrominance samples.

[0381] 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 determination that the CCALF enable flag is 1, the ID information (identifier information) of an Adaptive Parameter Set (APS) including ALF data for deriving cross-component filter coefficients for CCALF may be derived. The picture information may include slice header information.

[0382] According to an example of an embodiment, the slice header information may include the ID information of an APS including ALF data for deriving cross-component filter coefficients. In another example, based on the determination that the CCALF enable flag is 1, the slice header information may include the ID information of an APS including ALF data for deriving cross-component filter coefficients.

[0383] In an embodiment, the SPS may include an ALF enable flag (sps_ccalf_enabled_flag) related to whether ALF is available. Based on the determination that the value of the ALF enable flag (sps_ccalf_enabled_flag) is 1, the SPS may include a CCALF enable flag related to whether cross-component filtering is available.

[0384] 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.

[0385] 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 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 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 ALF enable flag is 1, CCALF may be available.

[0386] In an embodiment, the header information (slice header information) may include a first flag related to the Cb color component of the reconstructed chrominance samples for which CCALF can be used for filtering and a second flag related to the Cr color component of the reconstructed chrominance samples for which CCALF can be used 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 the Cb color component of the reconstructed chrominance samples for which CCALF can be used for filtering and a second flag related to the Cr color component of the reconstructed chrominance samples for which CCALF can be used for filtering.

[0387] 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.

[0388] 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.

[0389] 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).

[0390] 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 can be derived.

[0391] In an embodiment, the information related to the number of cross-component filters for the Cr color component may be coded in zero-order exponential Golomb (0EG).

[0392] 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.

[0393] 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.

[0394] In the presence of residual samples for the 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 the transform coefficients based on an inverse quantization process for the quantized transform coefficients. The decoding device may derive the residual samples based on the transform coefficients.

[0395] The decoding device can generate reconstructed samples based on (intra) prediction samples and residual samples, and can derive a reconstructed block or a reconstructed picture based on the reconstructed samples. Specifically, the decoding device can generate reconstructed samples based on the sum of (intra) prediction samples and residual samples. Thereafter, as described above, if necessary, the decoding device can apply loop filter processing (e.g., deblocking filter and / or SAO processing) to the reconstructed picture to improve the subjective / objective picture quality.

[0396] For example, the decoding device can obtain image information including all or some of the above information (or syntax elements) by decoding the bitstream or the encoded information. In addition, the bitstream or the encoded information can be stored in a computer-readable storage medium, or the above decoding method can be executed.

[0397] In the above embodiments, the 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 can occur simultaneously with other steps or blocks as described above or in an order different from other steps or blocks as described above. In addition, those skilled in the art will understand that the steps shown in the above flowchart are not exclusive and can include additional steps, or one or more steps in the flowchart can be deleted without affecting the scope of this document.

[0398] The method according to the above embodiments of this document can be implemented in software form, and the encoding device and / or the 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.

[0399] When the embodiments in this document are implemented in software, the above method can be implemented as a module (processing, function, etc.) that performs the above functions. The module 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.

[0400] In addition, the decoding apparatus and encoding apparatus applying this document may be included in a multimedia broadcast transmission / reception apparatus, a mobile communication terminal, a home theater video apparatus, a digital cinema video apparatus, a surveillance camera, a video chat apparatus, a real-time communication apparatus such as video communication, a mobile streaming apparatus, a storage medium, a camera, a VoD service providing apparatus, an over-the-top (OTT) video apparatus, an Internet streaming service providing apparatus, a three-dimensional (3D) video apparatus, a videoconference video apparatus, a transportation user equipment (i.e., in-vehicle user equipment, aircraft user equipment, ship user equipment, etc.), and a medical video apparatus, and may be used to process video signals and data signals. For example, an over-the-top (OTT) video apparatus may 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.

[0401] Furthermore, the processing method applying this document may be generated in the form of a program executable by a computer and may be stored in a computer-readable recording medium. Multimedia data having a data structure according to the present disclosure may also be stored in the computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices storing data readable by a computer system. For example, the computer-readable recording medium may include a BD, a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. In addition, the computer-readable recording medium includes a medium implemented in the form of a carrier wave (i.e., transmission through the Internet). Additionally, the bitstream generated by the encoding method may be stored in the computer-readable recording medium or may be transmitted through a wired or wireless communication network.

[0402] In addition, embodiments of this document may be implemented using a computer program product according to program code, and the program code may be executed in a computer according to embodiments of this document. The program code may be stored on a computer-readable carrier.

[0403] Figure 15 An example of a content streaming system to which embodiments disclosed in this document may be applied is shown.

[0404] Reference Figure 15 , a content streaming system applying embodiments of this document may mainly include an encoding server, a streaming server, a web server, a media storage, a user equipment, and a multimedia input device.

[0405] 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 bitstream, and sends the bitstream 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 bitstream, the encoding server can be omitted.

[0406] A bitstream can be generated by applying the encoding method or the bitstream generation method of the embodiments of the present disclosure, and the streaming server can temporarily store the bitstream in the process of sending or receiving the bitstream.

[0407] The streaming server sends multimedia data to the user device via a 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.

[0408] The streaming server can receive content from a media storage and / or an 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.

[0409] Examples of the user device can include a mobile phone, a smart phone, a laptop computer, a digital broadcast terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation device, a slate PC, a tablet PC, an ultrabook, a wearable device (e.g., a smart watch, smart glasses, a head-mounted display), a digital TV, a desktop computer, a digital sign, 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.

[0410] 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.

[0411] 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. In addition, the technical features of the method claims 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 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: receiving image information through a bitstream; generating reconstructed luminance samples and reconstructed chrominance samples based on the image information; performing an Adaptive Loop Filter (ALF) process on the reconstructed chrominance samples to generate filtered reconstructed chrominance samples; and performing a cross-component filtering process on the filtered reconstructed chrominance samples to generate modified filtered reconstructed chrominance samples, wherein the image information includes information about cross-component filtering, and the execution of the cross-component filtering process includes: deriving the number of cross-component filters for the cross-component filtering based on the information about the cross-component filtering; deriving cross-component filter coefficients for the cross-component filtering process based on the number of cross-component filters; and generating the modified filtered reconstructed chrominance samples based on 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, wherein the SPS includes an ALF enable flag related to whether the ALF process is enabled, wherein based on the determination that the value of the ALF enable flag is 1, the SPS includes a Cross-Component Adaptive Loop Filter (CCALF) enable flag related to whether the cross-component filtering is enabled, wherein based on the determination that the value of the ALF enable flag included in the SPS is 1, the slice header information includes an ALF enable flag related to whether the ALF is enabled, wherein 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 about whether the CCALF is enabled for the filtered reconstructed chrominance samples, and wherein based on the determination that the value of the information about whether the CCALF is enabled for the filtered reconstructed chrominance samples is 1, the slice header information includes identification (ID) information of an Adaptive Parameter Set (APS), and the APS includes ALF data for deriving the cross-component filter coefficients, wherein the image information includes information about a coding tree unit, and wherein the information about the coding tree unit includes: information about whether to apply a cross-component filter to the Cb color component of the current block and information about whether to apply a cross-component filter to the Cr color component of the current block, and information about the filter set index of the cross-component filter applied to the Cb color component of the current block and information about the filter set index of the cross-component filter applied to the Cr color component of the current block.

2. The method according to claim 1, wherein the ALF data includes information about the number of cross-component filters for the Cb color component and information about the number of cross-component filters for the Cr color component.

3. The method according to claim 2, wherein Based on information about the number of cross-component filters for the Cb color component, the ALF data includes information about the absolute values of the cross-component filter coefficients for the Cb color component and information about the signs of the cross-component filter coefficients for the Cb color component, and Derive the cross-component filter coefficients for the Cb color component based on the information about the absolute values 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.

4. The method according to claim 2, wherein, Based on information about the number of cross-component filters for the Cr color component, the ALF data includes information about the absolute values 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, and Derive the cross-component filter coefficients for the Cr color component based on the information about the absolute values 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.

5. A method for image coding to be performed by an encoding device, the method comprising: Generate reconstructed luminance samples and reconstructed chrominance samples of a current block in a current picture; Derive ALF filter coefficients for an Adaptive Loop Filter (ALF) process; Generate ALF-related information based on the ALF filter coefficients; Derive cross-component filters and cross-component filter coefficients for a cross-component filtering process; Generate cross-component filtering-related information based on the cross-component filters and the cross-component filter coefficients; and Encode image information including information for generating the reconstructed luminance samples and the reconstructed chrominance samples of the current block, the ALF-related information, and the cross-component filtering-related information, wherein the cross-component filtering-related information includes information about the number of the cross-component filters and information about the cross-component filter coefficients, wherein the image information includes a Sequence Parameter Set (SPS) and slice header information, wherein the SPS includes an ALF enable flag related to whether the ALF process is enabled, wherein based on the determination that the value of the ALF enable flag is 1, the SPS includes a Cross-Component Adaptive Loop Filter (CCALF) enable flag related to whether the cross-component filtering is enabled, wherein based on the determination that the value of the ALF enable flag included in the SPS is 1, the slice header information includes an ALF enable flag related to whether the ALF is enabled, wherein 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 about whether the CCALF is enabled for the reconstructed chrominance samples for the filtering, and Wherein, based on the value of the information on whether to enable the CCALF for the reconstructed chrominance samples of the filtering being 1, the slice header information includes the identification ID information of the Adaptive Parameter Set (APS), and the APS includes the ALF data for deriving the cross-component filter coefficients. Wherein, the image information includes information about the coding tree unit, and Wherein, the information about the coding tree unit includes: information on whether to apply a cross-component filter to the Cb color component of the current block and information on whether to apply a cross-component filter to the Cr color component of the current block, and information on the filter set index of the cross-component filter applied to the Cb color component of the current block and information on the filter set index of the cross-component filter applied to the Cr color component of the current block.

6. The method according to claim 5, Wherein, the ALF data includes information on the number of cross-component filters for the Cb color component and information on the number of cross-component filters for the Cr color component.

7. The method according to claim 6, Wherein, based on the information on 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 derive the cross-component filter coefficients for the Cb color component based on the information on the absolute value of the cross-component filter coefficients for the Cb color component and the information on the sign of the cross-component filter coefficients for the Cb color component.

8. The method according to claim 6, Wherein, based on the information on 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, and derive the cross-component filter coefficients for the Cr color component based on the information on the absolute value of the cross-component filter coefficients for the Cr color component and the information on the sign of the cross-component filter coefficients for the Cr color component.

9. A method for transmitting data of an image, the method comprises: Obtain a bitstream for the image, wherein the bitstream is generated based on the following: generate reconstructed luminance samples and reconstructed chrominance samples of a current block in a current picture, derive ALF filter coefficients for an adaptive loop filtering (ALF) process, generate ALF-related information based on the ALF filter coefficients, derive a cross-component filter and cross-component filter coefficients for a cross-component filtering process, generate cross-component filtering-related information based on the cross-component filter and the cross-component filter coefficients, and encode image information including information for generating the reconstructed luminance samples and the reconstructed chrominance samples of the current block, the ALF-related information, and the cross-component filtering-related information; And Transmit the data including the bitstream, wherein the cross-component filtering-related information includes information about the number of the cross-component filters and information about the cross-component filter coefficients, wherein the image information includes a sequence parameter set (SPS) and slice header information, wherein the SPS includes an ALF enable flag related to whether the ALF process is enabled, wherein based on a determination that the value of the ALF enable flag is 1, the SPS includes a cross-component adaptive loop filter (CCALF) enable flag related to whether the cross-component filtering is enabled, wherein based on a determination that the value of the ALF enable flag included in the SPS is 1, the slice header information includes an ALF enable flag related to whether the ALF is enabled, wherein 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 about whether the CCALF is enabled for the reconstructed chrominance samples of the filtering, and wherein based on a determination that the value of the information about whether the CCALF is enabled for the reconstructed chrominance samples of the filtering is 1, the slice header information includes identification (ID) information of an adaptive parameter set (APS), and the APS includes ALF data for deriving the cross-component filter coefficients, wherein the image information includes information about a coding tree unit, and wherein the information about the coding tree unit includes: information about whether to apply a cross-component filter to the Cb color component of the current block and information about whether to apply a cross-component filter to the Cr color component of the current block, and information about a filter set index of the cross-component filter applied to the Cb color component of the current block and information about a filter set index of the cross-component filter applied to the Cr color component of the current block.

Images