Image compiling device and method based on cross-component adaptive loop filtering

Abstract

The present document relates to an image coding apparatus and method based on cross-component adaptive loop filtering. According to one embodiment of the document, an in-loop filtering process in a picture / video coding process may include a cross-component adaptive in-loop filtering process. According to the CCALF provided by the embodiment of the invention, the accuracy of filtering in a loop can be improved.

Description

[0001] This application is a divisional application of the patent application with application number 202080073409.X (PCT / KR2020 / 011601) filed on April 20, 2022, with an international application date of August 31, 2020, and the invention name is “Image coding device and method based on cross-component adaptive loop filtering”. Technical Field

[0002] The present disclosure relates to an image coding device and method based on cross-component adaptive loop filtering. Background Art

[0003] 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 relative 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 transmission costs and storage costs.

[0004] In addition, interest in and demand for immersive media such as virtual reality (VR) and artificial reality (AR) content and holograms are growing, and broadcasting of images / videos having characteristics different from real images (such as game images) is also increasing.

[0005] Therefore, highly efficient image / video compression technology is required to effectively compress, transmit, store or reproduce information of high-resolution, high-quality images / videos having various characteristics as described above.

[0006] A cross-component adaptive loop filtering process (CCALF) is a process performed to improve the accuracy of filtering within the loop filtering process, and discussions regarding transmission of information used in the CCALF process are ongoing. Summary of the Invention

[0007] Technical Solution

[0008] The present disclosure provides a method and apparatus for improving image / video coding efficiency.

[0009] The present disclosure also provides an efficient filtering application method and device.

[0010] The present disclosure also provides an efficient ALF application method and apparatus.

[0011] According to an embodiment of the present disclosure, a filtering process may be performed on the reconstructed chroma samples based on the reconstructed luma samples.

[0012] According to an embodiment of the present disclosure, filtered reconstructed chroma samples may be modified based on reconstructed luma samples.

[0013] According to an embodiment of the present disclosure, information on whether CCALF is available may be signaled in the SPS.

[0014] According to an embodiment of the present disclosure, information on the values of cross-component filter coefficients may be derived from ALF data (normal ALF data or CCALF data).

[0015] According to an embodiment of the present disclosure, identifier (ID) information of an APS including ALF data for deriving cross-component filter coefficients in a slice may be signaled.

[0016] According to an embodiment of the present disclosure, information about a filter set index of a CCALF can be signaled in units of CTU (block).

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

[0018] According to an embodiment of this document, a decoding apparatus for performing video / image decoding is provided.

[0019] According to an embodiment of this document, a video / image encoding method performed by an encoding device is provided.

[0020] According to an embodiment of this document, there is provided an encoding apparatus for performing video / image encoding.

[0021] According to one embodiment of this document, a computer-readable digital storage medium is provided, in which encoded video / image information generated according to the video / image encoding method disclosed in at least one embodiment of this document is stored.

[0022] According to an embodiment of this document, a computer-readable digital storage medium is provided, in which encoded information or encoded video / image information is stored for enabling a decoding device to perform the video / image decoding method disclosed in at least one embodiment of this document.

[0023] Beneficial effects

[0024] According to the embodiments of this document, the overall image / video compression efficiency can be improved.

[0025] According to the embodiments of this document, subjective / objective visual quality can be improved through efficient filtering.

[0026] According to an embodiment of the present disclosure, the ALF process may be efficiently performed and filtering performance may be improved.

[0027] According to an embodiment of the present disclosure, reconstructed chroma samples filtered based on reconstructed luma samples may be modified to improve picture quality and coding accuracy of chroma components of a decoded picture.

[0028] According to an embodiment of the present disclosure, the CCALF process may be efficiently performed.

[0029] According to the embodiments of the present disclosure, ALF-related information may be efficiently signaled.

[0030] According to an embodiment of the present disclosure, CCALF-related information may be efficiently signaled.

[0031] 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.

[0032] According to the embodiments of this document, when CCALF is used in encoding and decoding methods and devices for still images or videos, the filter coefficients used for CCALF and the on / off transmission method in blocks or CTU units can be improved, thereby improving encoding efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 An example of a video / image coding system that can be applied to an embodiment of the present disclosure is schematically shown.

[0034] Figure 2 is a diagram schematically illustrating a configuration of a video / image encoding device that can be applied to an embodiment of the present disclosure.

[0035] Figure 3 is a diagram schematically illustrating a configuration of a video / image decoding device that can be applied to an embodiment of the present disclosure.

[0036] Figure 4 The hierarchical structure of the compiled image / video is shown exemplarily.

[0037] Figure 5 3 is a flowchart illustrating a block reconstruction method based on intra prediction in a decoding apparatus.

[0038] Figure 6 3 is a flowchart illustrating a block reconstruction method based on inter-frame prediction in a decoding device.

[0039] Figure 7 An example of the shape of the ALF filter is shown.

[0040] Figure 8 is a diagram illustrating a virtual boundary applied to a filtering process according to an embodiment of the present disclosure.

[0041] Figure 9An example of an ALF process using a virtual boundary according to an embodiment of the present disclosure is illustrated.

[0042] Figure 10 is a diagram illustrating a cross-component adaptive loop filtering (CC-ALF (CCALF)) process according to an embodiment of the present disclosure.

[0043] Figure 11 and Figure 12 An example of a video / image encoding method and related components according to an embodiment of the present disclosure is schematically illustrated.

[0044] Figure 13 and Figure 14 An example of an image / video decoding method and related components according to an embodiment of the present disclosure is schematically illustrated.

[0045] Figure 15 An example of a content streaming system to which the embodiments disclosed in the present disclosure can be applied is shown. DETAILED DESCRIPTION

[0046] The present disclosure can be modified in various forms, and specific embodiments thereof will be described and shown in the accompanying drawings. However, the embodiments are not intended to limit the present disclosure. The terms used in the following description are used to describe specific embodiments only and are not intended to limit the present disclosure. A singular expression includes a plural expression as long as it is 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 it should be understood that the possibility of the presence or addition of one or more different features, numbers, steps, operations, elements, components, or combinations thereof is not excluded.

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

[0048] The present disclosure relates to video / image coding. For example, the methods / embodiments disclosed in the present disclosure may be applied to methods disclosed in Versatile Video Coding (VVC). In addition, the methods / embodiments disclosed in the present disclosure may be applied to methods disclosed in the Essential Video Coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the second-generation Audio Video Coding standard (AVS2), or next-generation video / image coding standards (e.g., H.267 or H.268, etc.).

[0049] The present disclosure presents various embodiments of video / image coding, and unless otherwise mentioned, these embodiments may be performed in conjunction with each other.

[0050] Figure 1 Schematically illustrates an example of a video / image coding system to which embodiments of this document can be applied.

[0051] refer to Figure 1 The video / image coding system may include a source device and a receiving device. The source device may deliver the encoded video / image information or data to the receiving device in the form of a file or stream via a digital storage medium or a network.

[0052] 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.

[0053] The video source can obtain the video / image by capturing, synthesizing, or generating a video / image. 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 videos / images, etc. For example, the video / image generation device may include a computer, a tablet computer, and a smart phone, and may generate the video / image (electronically). For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capture process may be replaced by a process that generates relevant data.

[0054] The encoding device can encode the input video / image. For compression and coding efficiency, the encoding device can perform a series of processes such as prediction, transformation, and quantization. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0055] The transmitter can transmit the encoded image / image information or data, output as a bitstream, in the form of a file or stream to a receiver in a receiving device via a digital storage medium or network. Digital storage media can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter can include components for generating media files in a predetermined file format and can also include components for transmission via a broadcast / communication network. The receiver can receive / extract the bitstream and transmit the received bitstream to a decoding device.

[0056] The decoding device may decode a video / image by performing a series of processes such as dequantization, inverse transform, and prediction corresponding to the operations of the encoding device.

[0057] The renderer can render the decoded video / image, and the rendered video / image can be displayed on a display.

[0058] In the present disclosure, 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 constitutes a part of a picture in encoding. A slice / tile may include one or more coding tree units (CTUs). A picture may be composed of one or more slices / tiles. A tile is a rectangular area of a CTU within a specific tile column and a specific tile row in a picture. A tile column is a rectangular area of a CTU with a height equal to the height of the picture and a width specified by a syntax element in a picture parameter set. A tile row is a rectangular area of a CTU with a height specified by a syntax element in a picture parameter set and a width equal to the width of the picture. Tile scan is a specific ordering of CTUs that partition a picture, where CTUs are continuously ordered in a CTU raster scan within a tile, and tiles in a picture are continuously ordered in a 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 in a single NAL unit within a tile of a picture.

[0059] At the same time, a picture can be divided into two or more sub-pictures. A sub-picture can be a rectangular area of one or more slices within a picture.

[0060] A pixel or picture element (pel) may refer to the smallest unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, and may represent a pixel / pixel value of only a luma component or a pixel / pixel value of only a chroma component.

[0061] A unit may represent a basic unit of image processing. A unit may include at least one of a specific area of a picture and information related to the area. A unit may include a luminance block and two chrominance (e.g., CB, CR) blocks. In some cases, a unit may be used interchangeably with terms such as block or area. In general, an M×N block may include a sample (or sample array) or a set (or array) of transform coefficients of M columns and N rows.

[0062] 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 may 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”.

[0063] As used herein, a slash ( / ) or a comma 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."

[0064] In the present disclosure, “at least one of A and B” may mean “only A”, “only B”, or “both A and B”. In addition, in the present disclosure, the expression “at least one of A or B” or “at least one of A and / or B” may be equally interpreted as “at least one of A and B”.

[0065] In addition, in the present disclosure, “at least one of A, B, and C” means “only A,” “only B,” “only C,” or “any combination of A, B, and C.” In addition, “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.”

[0066] In addition, the brackets used in this disclosure may mean "for example." Specifically, when "prediction (intra-frame prediction)" is indicated, it can be said that this "intra-frame prediction" is proposed as an example of "prediction." In other words, "prediction" in this disclosure is not limited to "intra-frame prediction," and "intra-frame prediction" can be proposed as an example of "prediction." In addition, even when "prediction (i.e., intra-frame prediction)" is indicated, it can be said that this "intra-frame prediction" is proposed as an example of "prediction."

[0067] Technical features described individually in one drawing in the present disclosure may be implemented individually or simultaneously.

[0068] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Hereinafter, the same reference numerals may be used for the same components in the accompanying drawings, and repeated description of the same components may be omitted.

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

[0070] refer to Figure 2, the encoding device 200 includes an image segmenter 210, a predictor 220, a residual processor 230 and 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 also 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 segmenter 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 processor). In addition, the memory 270 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware components may also include the memory 270 as an internal / external component.

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

[0072] In some cases, the term "unit" can be used interchangeably with terms such as "block" or "region." In general, an M×N block can represent a set of samples or transform coefficients consisting of M columns and N rows. A sample can generally represent a pixel or pixel value, and can represent only the pixel / pixel value of the luma component or only the pixel / pixel value of the chroma component. A sample can be used as a term corresponding to a pixel or picture element of a picture (or image).

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

[0074] The intra-frame predictor 222 can predict the current block by referring to samples in the current picture. Depending on the prediction mode, the referenced samples can be located near the current block or can be spaced apart. In intra-frame prediction, the prediction mode can include multiple non-directional modes and multiple directional modes. For example, the non-directional mode can include a DC mode and a planar mode. For example, depending on the level of detail of the prediction direction, the directional mode 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 depending on the settings. The intra-frame predictor 222 can determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0075] The inter-frame predictor 221 can derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector in a reference picture. To reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of 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 information about the inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, neighboring blocks can include spatially neighboring blocks in the current picture and temporally neighboring blocks in the reference picture. The reference picture including the reference block and the reference picture including the temporally neighboring block can be the same or different. Temporally neighboring blocks can be referred to as collocated reference blocks, collocated CUs (colCUs), etc., and the reference picture including temporally neighboring blocks can be referred to as collocated pictures (colPics). For example, the inter-frame predictor 221 can configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index for the current block. Inter-frame prediction can be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame predictor 221 can use the motion information of the neighboring block as the motion information of the current block. In skip mode, unlike merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block can be used as a motion vector predictor, and the motion vector of the current block can be indicated by signaling the motion vector difference.

[0076] The predictor 220 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 at the same time. This can be called combined inter and intra prediction (CIIP). In addition, the predictor can perform intra block copying (IBC) for prediction of the block. Intra block copying can be used for content image / video coding of games, etc., for example, screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter prediction at the point of deriving a reference block in the current picture. That is, IBC can use at least one of the inter prediction techniques described in this document.

[0077] The prediction signal generated by the inter-frame predictor 221 and / or the intra-frame predictor 222 can be used to generate a reconstruction signal or to generate a residual signal. The transformer 232 can generate a transform coefficient by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a graph-based transform (GBT), or a conditional nonlinear 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. In addition, the transform process can be applied to square pixel blocks of the same size, or can be applied to blocks of variable size rather than square.

[0078] The quantizer 233 can quantize the transform coefficients and send them to the entropy encoder 240, and the entropy encoder 240 can encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients can be called residual information. The quantizer 233 can rearrange the block-type quantized transform coefficients into a one-dimensional vector form based on the coefficient scanning 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, such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), Context-Adaptive Binary Arithmetic Coding (CABAC), etc. The entropy encoder 240 can encode information required for video / image reconstruction in addition to the quantized transform coefficients (e.g., the values of syntax elements, etc.) together or separately. The encoded information (e.g., encoded video / image information) can be transmitted or stored in the form of a bitstream in units of NAL (Network Abstraction Layer). The video / image information may further include information about various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may further include general constraint information. In this document, the information and / or syntax elements to be signaled / transmitted described later in this document may be encoded by the above-mentioned encoding process and may be included in the bitstream. The bitstream may be transmitted over a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits the signal output from the entropy encoder 240 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the encoding device 200, and alternatively, the transmitter may be included in the entropy encoder 240.

[0079] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, the residual signal (residual block or residual sample) can be reconstructed by applying dequantization and inverse transform to the quantized transform coefficients by the dequantizer 234 and the inverse transformer 235. 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 when skip mode is applied, the prediction block can be used as the reconstructed block. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture through filtering as described below.

[0080] Meanwhile, luma mapping and chroma scaling (LMCS) may be applied during picture encoding and / or reconstruction.

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

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

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

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

[0085] refer to Figure 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 a hardware component (e.g., a decoder chipset or processor). In addition, the memory 360 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware component may also include the memory 360 as an internal / external component.

[0086] When a bit stream including video / image information is input, the decoding apparatus 300 can be used with Figure 2 The image is reconstructed accordingly to the processing of the video / image information in the encoding device. For example, the decoding device 300 can derive the unit / block based on the block partition related information obtained from the bit stream. The decoding device 300 can perform decoding using a processor applied in the encoding device. Therefore, the decoding processor can be, for example, a coding unit, and the coding unit can be partitioned from the coding tree unit or the largest coding unit according to a quadtree structure, a binary tree structure and / or a ternary tree structure. One or more transform units can be derived from the coding unit. The reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a reproduction device.

[0087] The decoding device 300 may receive the data in the form of a bit stream from Figure 2The received signal is output by the encoding device, and the entropy decoder 310 can decode the received signal. For example, the entropy decoder 310 can parse the bitstream to derive information required for image reconstruction (or picture reconstruction) (e.g., video / image information). The video / image information may further include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may 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 transmitted / received using the signal described later in this document can be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 310 can decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, as well as the output values of the syntax elements required for image reconstruction and the quantized values of the transform coefficients used for the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, determine a context model using information about the target syntax element to be decoded, information about decoded neighboring and target blocks, or information about a symbol / bin decoded in a previous stage, and perform arithmetic decoding on the bin by predicting the probability of the bin's occurrence based on the determined context model, thereby generating a symbol corresponding to the value of each syntax element. In this case, after determining the context model, the CABAC entropy decoding method can update the context model by applying the information about the decoded symbol / bin to the context model of the next symbol / bin. Information about prediction from the information decoded by the entropy decoder 310 can be provided to the predictor 330, and information about the residual for which entropy decoding has been performed in the entropy decoder 310, i.e., quantized transform coefficients and related parameter information, can be input to the dequantizer 321. In addition, information about filtering from the information decoded by the entropy decoder 310 can be provided to the filter 350. Meanwhile, a receiver (not shown) for receiving a signal output from 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 may be referred to as a video / image / picture decoding device, and the decoding device may be classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 310, and the sample decoder may include at least one of a dequantizer 321, an inverse transformer 322, a predictor 330, an adder 340, a filter 350, and a memory 360.

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

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

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

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

[0092] The intra-frame predictor 331 can predict the current block by referencing samples in the current picture. The referenced samples can be located near the current block or at a separate location depending on the prediction mode. In intra-frame prediction, the prediction mode can include multiple non-directional modes and multiple directional modes. The intra-frame predictor 331 can determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

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

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

[0095] 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.

[0096] At the same time, luminance mapping and chroma scaling (LMCS) can be applied during the picture decoding process.

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

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

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

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

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

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

[0103] In this document, quantized transform coefficients and transform coefficients may be referred to as transform coefficients and scaled transform coefficients, respectively. In this case, residual information may include information about the transform coefficients, and the information about the transform coefficients may be signaled via residual coding syntax. The transform coefficients may be derived based on the residual information (or information about the transform coefficients), and the scaled transform coefficients may be derived by inversely transforming (scaling) the transform coefficients. 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.

[0104] The predictor of the encoding / decoding device can derive prediction samples by performing inter-frame prediction on a block-by-block basis. Inter-frame 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 inter-frame prediction is applied to the current block, a prediction block (prediction sample array) for the current block can be derived based on a reference block (reference sample array) specified by a motion vector in a reference picture indicated by a reference picture index. Here, to reduce the amount of motion information transmitted in inter-frame prediction mode, the motion information of the current block can be predicted on a block, sub-block, or sample basis based on the correlation of 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 information on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, neighboring blocks can include spatially neighboring blocks in the current picture and temporally neighboring blocks in a reference picture. The reference picture comprising the reference block and the reference picture comprising the temporally neighboring blocks can be the same or different. Temporally neighboring blocks may be referred to as collocated reference blocks, collocated CUs (colCUs), etc., and a reference picture including temporally neighboring blocks may be referred to as collocated pictures (colPics). 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 skip mode and merge mode, the motion information of the current block may be the same as the motion information of the neighboring blocks. In skip mode, unlike merge mode, a residual signal may not be sent. In motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0105] Depending on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. A motion vector in the L0 direction may be referred to as an L0 motion vector or MVL0, and a motion vector in the L1 direction may be referred to as an L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as L0 prediction, prediction based on the L1 motion vector may be referred to as L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as bidirectional prediction. Here, the L0 motion vector may indicate a motion vector associated with reference picture list L0 (L0), and the L1 motion vector may indicate a motion vector associated with reference picture list L1 (L1). Reference picture list L0 may include pictures that are earlier in output order than the current picture as reference pictures, and reference picture list L1 may include pictures that are later in output order than the current picture. The preceding picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. Reference picture list L0 may also include pictures that are later in output order than the current picture as reference pictures. In this case, the previous picture may be indexed first in reference picture list L0, and the subsequent picture may be indexed later. Reference picture list L1 may also include pictures earlier in output order than the current picture as reference pictures. In this case, the subsequent picture may be indexed first in reference picture list 1, and the previous picture may be indexed later. The output order may correspond to the picture order count (POC) order.

[0106] Figure 4 The hierarchical structure of the compiled image / video is shown exemplarily.

[0107] refer to Figure 4 The coded image / video is divided into the video coding layer (VCL) that handles the image / video and its own decoding process, the subsystem that sends and stores the coding information, and the NAL (Network Abstraction Layer) that is responsible for the network adaptation function and exists between the VCL and the subsystem.

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

[0109] In 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, RBSP refers to slice data, parameter sets, SEI messages, etc. generated in the VCL. The NAL unit header can include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0110] As shown in the figure, NAL units can be divided into VCL NAL units and non-VCL NAL units according to RBSP generated in VCL. VCL NAL units can refer to NAL units that include information about images (slice data), and non-VCL NAL units can refer to NAL units that include information (parameter sets or SEI messages) required for decoding images.

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

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

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

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

[0115] -APS (Adaptation Parameter Set) NAL unit: type used for NAL units containing APS

[0116] -DPS (Decoding Parameter Set) NAL unit: type used for NAL units containing DPS

[0117] - VPS (Video Parameter Set) NAL unit: type used for NAL units containing VPS

[0118] - SPS (Sequence Parameter Set) NAL unit: type used for NAL units containing SPS

[0119] -PPS (Picture Parameter Set) NAL unit: type used for NAL units containing PPS

[0120] - PH (Picture Header) NAL unit: type used for NAL units including PH

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

[0122] At the same time, 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 mixed or replaced with tile groups. In addition, in this document, slice headers may be mixed or replaced with tile group headers.

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

[0124] In this document, the image / image information encoded from the encoding device and notified to the decoding device by signal in the form of a bit stream includes not only partition-related information, intra-frame / inter-frame prediction information, residual information, in-loop filtering information, etc. in the picture, but also includes information included in the slice header, information included in the APS, information included in the PPS, information included in the SPS and / or information included in the VPS.

[0125] At the same time, in order to compensate for the difference between the original image and the reconstructed image due to errors occurring in the compression coding process such as quantization, an in-loop filtering process may be performed on the reconstructed sample or reconstructed picture as described above. As described above, 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 are completed. However, even in this case, the deblocking filtering process and / or the SAO process may be omitted.

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

[0127] Intra-frame prediction may refer to the generation of prediction samples for the current block based on reference samples in the picture to which the current block belongs (hereinafter referred to as the current picture). When intra-frame prediction is applied to the current block, neighboring reference samples to be used for intra-frame 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 (nWxnH) and a total of 2xnH samples adjacent to the lower left portion, samples adjacent to the upper boundary of the current block and a total of 2xnW samples adjacent to the upper right portion, and one sample adjacent to the upper left portion of the current block. Alternatively, the neighboring reference samples of the current block may include multiple upper neighboring samples and multiple 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 (nWxnH), a total of nW samples adjacent to the lower boundary of the current block, and one sample adjacent to the lower right portion of the current block.

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

[0129] When deriving neighboring reference samples, the prediction samples can be derived based on (i) an average or interpolation of neighboring reference samples of the current block and (ii) a prediction from neighboring reference samples of the current block. The prediction samples can be derived based on reference samples located in a specific (prediction) direction relative to the sample. Case (i) can be referred to as non-directional mode or non-angle mode, and case (ii) can be referred to as directional mode or angle mode. In addition, based on the prediction samples of the current block from neighboring reference samples, a first neighboring sample and a second neighboring sample located in a direction opposite to the prediction direction of the intra-frame prediction mode of the current block are interpolated. The prediction samples can be generated. This case is referred to as linear interpolation intra-frame prediction (LIP). In addition, chroma prediction samples can be generated based on luma samples using a linear model. This case is referred to as LM mode. In addition, temporary prediction samples for the current block can be derived based on filtered neighboring reference samples, and the prediction samples for the current block can be derived by weighted summing at least one reference sample derived according to the intra-frame prediction mode (i.e., an unfiltered neighboring reference sample) from the existing neighboring reference samples and the temporary prediction sample. The above situation can be referred to as position-dependent intra prediction (PDPC). In addition, a reference sample line with the highest prediction accuracy among multiple reference sample lines adjacent to the current block can be selected to derive prediction samples by using reference samples located in the prediction direction on the corresponding line, and then the reference sample line used in this article can be indicated (notified by signal) to the decoding device, thereby performing intra-frame prediction encoding. The above situation can be referred to as multiple reference line (MRL) intra prediction or MRL-based intra prediction. In addition, intra prediction can be performed based on the same intra prediction mode by dividing the current block into vertical or horizontal sub-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-partition, 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 aforementioned intra prediction method can be referred to as an intra prediction type separately from the intra prediction mode. The intra prediction type can be referred to by various terms such as intra prediction technology or additional intra prediction mode. For example, the intra prediction type (or additional intra prediction mode) may include at least one of the aforementioned LIP, PDPC, MRL, and ISP. A general intra prediction method other than a specific intra prediction type such as LIP, PDPC, MRL, or ISP may be referred to as a normal intra prediction type. When a specific intra prediction type cannot be applied, the normal intra prediction type may be generally applied, and prediction may be performed based on the aforementioned intra prediction mode. At the same time, post-filtering may be performed on the derived prediction samples as needed.

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

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

[0132] At the same time, the encoding device may perform a prediction sample filtering process. Prediction sample filtering may be referred to as post-filtering. Some or all prediction samples may be filtered by the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0133] The encoding apparatus derives residual samples for the current block based on the prediction samples (S510). The encoding apparatus may compare the prediction samples with the original samples of the current block based on a phase and derive the residual samples.

[0134] The encoding apparatus 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 transform again after transform / quantization is to derive residual samples identical to the residual samples derived from the decoding apparatus as described above.

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

[0136] As described above, the encoding device may encode image information including prediction information about intra prediction (e.g., prediction mode information indicating a prediction mode) and residual information about 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 transform / quantize the residual samples to derive quantized transform coefficients. The residual information may include information about the quantized transform coefficients.

[0137] Figure 5 3 is a flowchart illustrating a block reconstruction method based on intra prediction in a decoding apparatus. Figure 5 The method may include steps S500, S510, S520, S530, and S540. The decoding apparatus may perform operations corresponding to those performed in the encoding apparatus.

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

[0139] Specifically, the decoding device may derive an intra-frame 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-frame prediction mode and the neighboring reference samples (S520). In this case, the decoding device may perform a prediction sample filtering process. Prediction sample filtering may be referred to as post-filtering. Some or all prediction samples may be filtered through the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

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

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

[0142] The prediction information may include intra-frame prediction mode information and / or intra-frame prediction type information. The intra-frame prediction mode information may include, for example, flag information (e.g., intra_luma_mpm_flag) indicating whether the most probable mode (MPM) is applied to the current block or the residual mode is applied, and when MPM is applied to the current block, the prediction mode information may also include index information (e.g., intra_luma_mpm_idx) indicating one of the intra-frame prediction mode candidates (MPM candidates). The intra-frame prediction mode candidate (MPM candidate) may include an MPM candidate list or an MPM list. In addition, when MPM is not applied to the current block, the intra-frame prediction mode information may also include residual mode information (e.g., intra_luma_mpm_remainder) indicating one of the remaining intra-frame prediction modes other than the intra-frame prediction mode candidate (MPM candidate). The decoding device may determine the intra-frame prediction mode of the current block based on the intra-frame prediction mode information. A separate MPM list may be configured for the aforementioned MIP.

[0143] In addition, the intra-frame prediction type information can be implemented in various forms. For example, the intra-frame prediction type information may include intra-frame prediction type index information indicating one of the intra-frame prediction types. As another example, the intra-frame prediction type information may include at least one of the following: reference sample line information indicating whether MRL is applied to the current block and, if applied, which reference sample line is used (e.g., Intra_luma_ref_idx), ISP flag information indicating whether ISP is applied to the current block (e.g., Intra_subpartitions_mode_flag), ISP type information indicating the split type of the sub-partition when ISP is applied (e.g., Intra_subpartitions_split_flag), flag information indicating whether PDCP is applied, or flag information indicating whether LIP is applied. In addition, the intra-frame prediction type information may include a MIP flag indicating whether MIP is applied to the current block.

[0144] The intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by the coding method described in the present disclosure. For example, the intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by entropy coding (e.g., CABAC, CAVLC) based on truncated (Rice) binary code.

[0145] The predictor of the encoding / decoding device can derive prediction samples by performing inter-frame prediction on a block-by-block basis. Inter-frame 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 inter-frame prediction is applied to the current block, the prediction block (prediction sample array) for the current block can be derived based on a reference block (reference sample array) specified by a motion vector in a reference picture indicated by a reference picture index. In this case, to reduce the amount of motion information transmitted in inter-frame 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 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 information on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.). When inter-frame prediction is applied, neighboring blocks may include spatially neighboring blocks in the current picture and temporally neighboring blocks in a reference picture. The reference picture including the reference block and the reference picture including the temporally neighboring blocks may be the same as or different from each other. Temporally neighboring blocks may be referred to as collocated reference blocks, collocated CUs (colCUs), and the reference picture including the temporally neighboring blocks may be referred to as collocated pictures (colPics). 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) to derive the motion vector and / or reference picture index of the current block may be signaled. Inter-frame prediction may be performed based on various prediction modes, and for example, in skip mode and merge mode, the motion information of the current block may be the same as that of the neighboring blocks. In skip mode, unlike merge mode, a residual signal may not be transmitted. In motion vector prediction (MVP) mode, the motion vector of the selected neighboring block is used as a motion vector predictor, and the motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0146] The inter-frame prediction process performed by the encoding device will be described below. The encoding device performs inter-frame prediction on the current block. The encoding device may derive an inter-frame prediction mode and motion information for the current block, and generate prediction samples for the current block. Here, the processes for determining the inter-frame prediction mode, deriving motion information, and generating prediction samples may be performed simultaneously, or one process may be performed before the other. For example, the inter-frame predictor 221 of the encoding 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, the motion information deriver may derive motion information for the current block, and the prediction sample deriver may derive motion samples for the current block. For example, the inter-frame predictor 221 of the encoding device may search for a block similar to the current block within a predetermined area (search area) of a reference picture through motion estimation, and may derive a reference block whose difference from the current block is minimal or a predetermined reference or less. Based on this, a reference picture index indicating the reference picture in which the reference block is located may be derived, and a motion vector may be derived based on the position difference between the reference block and the current block. The encoding apparatus may determine a mode to be applied to the current block from among various prediction modes.The encoding apparatus may compare rate-distortion (RD) costs for various prediction modes and determine an optimal prediction mode for the current block.

[0147] For example, when skip mode or merge mode is applied to the current block, the encoding device may construct a merge candidate list (described later) and derive a reference block that has the smallest difference from the current block or is a predetermined reference or less from 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 may be selected, and merge index information indicating the selected merge candidate may be generated and signaled to the decoding device. The motion information of the selected merge candidate may be used to derive the motion information of the current block.

[0148] As another example, when applying the (A)MVP mode to the 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-mentioned motion estimation can be used as the motion vector of the current block, and the MVP candidate with the motion vector having the smallest difference with 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. In addition, when the (A)MVP mode is applied, the value of the reference picture index can be configured as reference picture index information and separately signaled to the decoding device.

[0149] The encoding apparatus may derive residual samples based on the prediction samples ( S710 ).The encoding apparatus may derive residual samples by comparing original samples of the current block with the prediction samples.

[0150] The encoding apparatus transforms / quantizes the residual samples to derive quantized transform coefficients (S720), and then dequantizes / inverse transforms the quantized transform coefficients again to derive (modified) residual samples (S730). The reason for performing dequantization / inverse transform again after transform / quantization is to derive the same residual samples as the residual samples derived from the decoding apparatus as described above.

[0151] The encoding apparatus may generate a reconstructed block including reconstructed samples of the current block based on the prediction samples and the (modified) residual samples (S740). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0152] Although not shown, as described above, the encoding device 100 can encode video information including prediction information and residual information. The encoding device 100 can output the encoded image information in the form of a bitstream. The prediction information can be information related to the prediction process and can include prediction mode information (e.g., a skip flag, a merge flag, or a mode index) and motion information. The motion information may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index) as information for deriving a motion vector. In addition, the information about the motion information may include the aforementioned MVD information and / or reference picture index information. In addition, the 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 used for the residual sample.

[0153] The output bitstream may be stored in a (digital) storage medium and sent to the decoding device, or may be sent to the decoding device over a network.

[0154] Figure 6 3 is a flowchart illustrating a block reconstruction method based on inter-frame prediction in a decoding device. Figure 6 The method may include steps S600, S610, S620, S630, and S640. The decoding apparatus may perform operations corresponding to those performed by the encoding apparatus.

[0155] 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 from the bitstream by the entropy decoder 310 of the decoding device. The residual processor 320 of the decoding device may derive residual samples for the current block based on the residual information. Specifically, the dequantizer 321 of the residual processor 320 may derive transform coefficients by performing dequantization based on the 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. S640 may be performed by the adder 340 or the reconstructor of the decoding device.

[0156] Specifically, the decoding apparatus may determine a prediction mode for the current block based on the received prediction information (S600).The decoding apparatus may determine which inter prediction mode to apply to the current block based on prediction mode information in the prediction information.

[0157] For example, whether to apply merge mode to the current block or whether to determine (A)MVP mode can be determined based on the merge flag. Alternatively, one of various inter-frame prediction mode candidates can be selected based on the mode index. Inter-frame prediction mode candidates may include skip mode, merge mode and / or (A)MVP mode, or may include various inter-frame prediction modes to be described later.

[0158] The decoding device derives the motion information of the current block based on the determined inter-frame prediction mode (S610). For example, when skip mode or merge mode is applied to the current block, the decoding device may configure a merge candidate list to be described below and select a 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.

[0159] 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 motion vector predictor (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-mentioned 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. In addition, 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 referenced for inter-frame prediction of the current block.

[0160] At the same time, as will be described below, the motion information of the current block can be derived without configuring a candidate list. In this case, the motion information of the current block can be derived according to the process disclosed in the prediction mode to be described later. In this case, the configuration of the candidate list as described above can be omitted.

[0161] The decoding apparatus may generate prediction samples of the current block based on the motion information of the current block (S620). In this case, a reference picture may be derived based on a reference picture index of the current block, and the prediction samples of the current block may be derived using samples of the reference block indicated by the motion vector of the current block on the reference picture. In this case, as described later, a prediction sample filtering process may be further performed on all or some of the prediction samples of the current block depending on the situation.

[0162] For example, the inter-frame predictor 332 of the decoding device may include a prediction mode determiner, a motion information deriver and a prediction sample deriver, and 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.

[0163] The decoding apparatus generates residual samples for the current block based on the received residual information (S630). The decoding apparatus may generate reconstructed samples for the current block based on the predicted samples and the residual samples, and may derive a reconstructed block including the reconstructed samples (S640). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0164] Various inter prediction modes can be used for the prediction of the current block in the picture. For example, various modes such as merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub-block merge mode, and merge with MVD (MMVD) mode can be used. Decoder-side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, bi-prediction with CU-level weights (BCW), bidirectional optical flow (BDOF), etc. can also be used in addition or alternatively as additional modes. Affine mode can be referred to as affine motion prediction mode. MVP mode can be referred to as 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 of other modes. For example, an HMVP candidate can be added as a merge candidate in merge / skip mode or can be added as an MVP candidate in MVP mode.

[0165] Prediction mode information indicating the inter 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 may include index information indicating one of a plurality of candidate modes. Alternatively, the inter prediction mode may be indicated by hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, a skip flag may be signaled to indicate whether the skip mode is applied, and if the skip mode is not applied, a merge flag may be signaled to indicate whether the merge mode is applied, and if the merge mode is not applied, an MVP mode is to be applied, or a flag for additional classification may be further signaled. The affine mode may be signaled in an independent mode or may be signaled in a mode that depends on the merge mode or the MVP mode. For example, the affine mode may include an affine merge mode and an affine MVP mode.

[0166] At the same time, information indicating whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used in the current block (current coding unit) can be signaled in the current block. This information can be called motion prediction direction information, inter-frame prediction direction information, or inter-frame prediction indication information, and can be configured / encoded / signaled in the form of, for example, an inter_pred_idc syntax element. That is, the inter_pred_idc syntax element can indicate whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used for the current block (current coding 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 can be indicated as a motion prediction direction. L0 prediction can be expressed as pred_L0, L1 prediction can be expressed as pred_L1, and paired prediction can be expressed as pred_BI. For example, the following prediction types can be determined according to the value of the inter_pred_idc syntax element.

[0167] [Table 1]

[0168]

[0169] 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 predicted (P) slice, and a bidirectional predicted (B) slice. The slice type may be indicated based on slice type information. For blocks in an I slice, inter prediction may not be used for prediction, and only intra prediction may be used. Of course, even in this case, the original sample values may be encoded and signaled without prediction. Intra prediction or inter prediction may be used for blocks in a P slice, and only unidirectional prediction may be used when inter prediction is used. Meanwhile, intra prediction or inter prediction may be used for blocks in a B slice, and up to bidirectional prediction may be used when inter prediction is used.

[0170] L0 and L1 may include reference pictures that were previously encoded / decoded before the current picture. For example, L0 may include reference pictures that are before and / or after the current picture in POC order, and L1 may include reference pictures that are after and / or before the current picture in POC order. In this case, L0 may be assigned a reference picture index that is lower than the current picture relative to the previous reference picture in the POC order, and L1 may be assigned a reference picture index that is lower than the current picture relative to the subsequent reference picture in the POC order. In the case of B slices, bi-prediction may be applied, and in this case, unidirectional bi-prediction may be applied or bi-directional bi-prediction may be applied. Bi-directional bi-prediction may be referred to as true bi-prediction.

[0171] As described above, a residual block (residual sample) can be derived based on a prediction block (prediction sample) derived by prediction at the encoding stage, and a residual sample transformed / quantized by residual information can be generated. The residual information may include information about the quantized transform coefficients. The residual information may be included in the video / image information, and the video / image information may be encoded and sent to a decoding device in the form of a bitstream. The decoding device may obtain the residual information from the bitstream and may derive the residual sample based on the residual information. Specifically, the decoding device may derive the quantized transform coefficients based on the residual information and may derive the residual block (residual sample) through a dequantization / inverse transform process.

[0172] At the same time, at least one process of (inverse) transformation and / or (de)quantization may be omitted.

[0173] Hereinafter, the in-loop filtering process performed on the reconstructed picture will be described. Modified reconstructed samples, blocks, pictures (or modified filtered samples, blocks, pictures) can be generated by the in-loop filtering process, and the modified (modified and filtered) reconstructed pictures can be output as decoded pictures at the decoding device and can also be stored in the decoded image buffer or memory of the encoding device / decoding device and used as reference pictures in the inter-frame prediction process when the picture is later encoded / decoded. The in-loop filtering process may include the deblocking filtering process, sample adaptive offset (SAO) process and / or adaptive loop filter (ALF) process as described above. In this case, one or some of the deblocking filtering process, sample adaptive offset (SAO) process, adaptive loop filter (ALF) process and bilateral filter process can be applied sequentially or all can be applied sequentially. For example, the SAO process can be performed after the deblocking filtering process is applied to the reconstructed picture. Or, for example, the ALF process can be performed after the deblocking filtering process is applied to the reconstructed picture. This can also be performed in the encoding device.

[0174] Deblocking filtering is a filtering technique that removes distortion at the boundaries between blocks in a reconstructed image. For example, the deblocking filtering process can derive a target boundary from the reconstructed image, determine the boundary strength (bS) of the target boundary, and perform deblocking filtering on the target boundary based on the bS. The bS can be determined based on the prediction mode of the two blocks adjacent to the target boundary, the difference in motion vectors, whether the reference pictures are the same, the presence of non-zero significant coefficients, and other factors.

[0175] SAO is a method for compensating for the offset difference between the reconstructed image and the original image 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. Filter information for SAO may include information on whether SAO is applied, SAO type information, and SAO offset value information. SAO can be applied to the reconstructed image after deblocking filtering is applied.

[0176] An adaptive loop filter (ALF) is a technique for filtering a reconstructed picture on a sample-by-sample basis using filter coefficients according to a filter shape. The encoding device can determine whether to apply the ALF, the ALF shape, and / or ALF filter coefficients by comparing the reconstructed picture with the original picture, and can notify the decoding device of this information using a signal. That is, the filter information used for the ALF may include information on whether the ALF is applied, ALF filter shape information, ALF filter coefficient information, and the like. The ALF can be applied to the reconstructed picture after deblocking filtering has been applied.

[0177] Figure 7 An example of the shape of the ALF filter is shown.

[0178] exist Figure 7 In FIG, (a) shows the shape of a 7x7 diamond filter, and (b) shows the shape of a 5x5 diamond filter. Figure 7In the filter shape, Cn represents the filter coefficient. When n in Cn is the same, this indicates that the same filter coefficient can be assigned. In the present disclosure, the position and / or unit for assigning filter coefficients according to the filter shape of the ALF can 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 can correspond to the filter shape. The filter tap located at the center of the filter shape can be referred to as the central filter tap. The same filter coefficient can be assigned to two filter taps with the same n value that are located at positions corresponding to each other relative to the central filter tap. For example, in the case of a 7x7 diamond filter shape, 25 filter taps are included, and since the filter coefficients C0 to C11 are assigned in a centrally symmetrical manner, only 13 filter coefficients can be used to assign the filter coefficients to the 25 filter taps. Alternatively, in the case of a 5x5 diamond filter shape, 13 filter taps are included, and since the filter coefficients C0 to C5 are assigned in a centrally symmetrical manner, only 7 filter coefficients can be used to assign the filter coefficients to the 13 filter taps. For example, to reduce the amount of information about the signaled filter coefficients, 12 of the 13 filter coefficients for a 7x7 diamond filter shape may be (explicitly) signaled, and one filter coefficient may be (implicitly) derived. Alternatively, for example, 6 of the 7 filter coefficients for a 5x5 diamond filter shape may be (explicitly) signaled, and one filter coefficient may be (implicitly) derived.

[0179] According to an embodiment of the present disclosure, ALF parameters for the ALF process may be signaled through an adaptive parameter set (APS), and the ALF parameters may be derived based on filter information or ALF data for the ALF process.

[0180] ALF is an in-loop filtering technique that can be applied in video / image coding as described above. ALF can be performed using a Wiener-based adaptive filter. This can be to minimize the mean square error (MSE) between the original sample and the decoded sample (or reconstructed sample). Advanced designs for ALF tools can incorporate syntax elements accessible in the SPS and / or slice header (or tile group header).

[0181] In this example, before filtering for each 4x4 luma block, geometric transformations such as rotations or diagonal and vertical flips can be applied to the filter coefficients f(k, l) and corresponding filter clipping values c(k, l) that depend on the gradient values calculated for the block. This is equivalent to applying these transformations to the samples in the filter support region. Creating other blocks to which the ALF is applied can be similar to arranging these blocks according to their directionality.

[0182] For example, three transformations can be performed based on the following equations: diagonal, vertical flip, and rotation.

[0183] [Equation 1]

[0184] Diagonal: f_D(k,l)=f(l,k), c_D(k,l)=c(l,k)

[0185] [Equation 2]

[0186] Vertical flip: f_V(k,l)=f(k,Kl-1), c_V(k,l)=c(k,Kl-1)

[0187] [Equation 3]

[0188] Rotation: f_R(k,l)=f(Kl-1,k), c_R(k,l)=c(Kl-1,k)

[0189] In equations 1 to 3, K may be the size of the filter. 0 ≤ k and 1 ≤ K-1 may be coefficient coordinates. For example, (0, 0) may be the upper left corner coordinate, and / or (K-1, K-1) may be the lower right corner coordinate. The relationship between the transform and the four gradients in the four directions can be summarized in the following table.

[0190] [Table 2]

[0191] Gradient value Transform <![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 ]]> Flip vertically <![CDATA[g d1 <g d2 And g v <g h ]]> Rotation

[0192] ALF filter parameters can be signaled in the APS and slice header. In one APS, up to 25 luma filter coefficients and clipping value indices can be signaled. In one APS, up to 8 chroma filter coefficients and clipping value indices can be signaled. To reduce bit overhead, filter coefficients of different classifications for luma components can be merged. In the slice header, the index of the APS for the current slice (referenced by the current slice) can be signaled.

[0193] The clip value index decoded from the APS can make it possible to determine the clip value using the clip value's luminance table and the clip value's chrominance table. These clip values may depend on the internal bit depth. More specifically, the clip value's luminance table and the clip value's chrominance table can be derived based on the following equations.

[0194] [Equation 4]

[0195] AlfClipL = {round(2^(B(N-n+1) / N)) for n∈[1..N]}

[0196] [Equation 5]

[0197] AlfClipC = {round(2^((B-8)+8((Nn)) / (N-1))) for n∈[1..N]}

[0198] In the above equation, B may be the internal bit depth, and N may be the number of allowable clipping values (a predetermined number). For example, N may be 4.

[0199] In the slice header, up to 7 APS indices can be signaled to indicate the luma filter set for the current slice. The filtering process can be further controlled at the CTB level. For example, a flag indicating whether the ALF is applied to the luma CTB can be signaled. The luma CTB can select one of 16 fixed filter sets and a filter set from the APS. A filter set index can be signaled for the luma CTB to indicate which filter set is applied. The 16 fixed filter sets can be predefined and hard-coded in both the encoder and decoder.

[0200] For chroma components, an APS index may be signaled in the slice header to indicate the chroma filter set used for the current slice. At the CTB level, when two or more chroma filter sets are present in the APS, a filter index may be signaled for each chroma CTB.

[0201] The filter coefficients may be quantized with a norm of 128. To limit the multiplication complexity, bitstream conformance may be applied such that the coefficient values at non-center positions may vary from 0 to 28 and / or the coefficient values at the remaining positions may range from -27 to 27-1. The center position coefficient may not be signaled in the bitstream and may be predetermined (considered) to be 128.

[0202] When ALF is available for the current block, each sample R(i, j) may be filtered, and the filtering result R'(i, j) may be expressed by the following equation.

[0203] [Equation 6]

[0204] 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)

[0205] 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).

[0206] In an example, to reduce the line buffer requirements of the ALF, modified block classification and filtering may be applied for samples adjacent to horizontal CTU boundaries. For this purpose, a virtual boundary may be defined.

[0207] Figure 8 is a diagram illustrating a virtual boundary applied to a filtering process according to an embodiment of the present disclosure. Figure 9 FIGURE 1 illustrates an example of an ALF process using a virtual boundary according to an embodiment of the present disclosure. Figure 8 describe Figure 9 .

[0208] refer to Figure 9 , a virtual boundary may be a line defined by shifting the horizontal CTU boundary by N samples. In an example, N may be 4 for the luma component and / or 2 for the chroma components.

[0209] exist Figure 8 In

[15] , a modified block classification can be applied to the luma component. For the 1D Laplacian gradient calculation of a 4x4 block on a virtual boundary, only samples above the virtual boundary can be used. Similarly, to calculate the 1D Laplacian gradient of a 4x4 block below the virtual boundary, only samples below the virtual boundary can be used. Given the reduced number of samples used in the 1D Laplacian gradient calculation, the quantization of the activity value A can be scaled accordingly.

[0210] For the filtering process, symmetric padding operations at the imaginary boundaries can be applied to both luma and chroma components. Figure 8 When a filtered sample is below a virtual boundary, the adjacent samples above the virtual boundary can be filled in. At the same time, the corresponding samples on the other side can also be filled in symmetrically.

[0211] When no filter is available across the boundary, Figure 9 The described process can also be applied to slice, brick, and / or tile boundaries. For ALF block classification, only samples contained in the same slice, brick, and / or tile can be used and the activity values can be scaled accordingly. For ALF filtering, symmetric padding can be applied in each of the horizontal and / or vertical directions relative to the horizontal and / or vertical boundaries.

[0212] Figure 10 2 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.

[0213] 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, an SAO process, an ALF process, and / or a CCALF process.

[0214] CC-ALF can use luma sample values to refine each chroma component. CC-ALF is controlled by (image) information in the bitstream, which includes (a) information about the filter coefficients for each chroma component and (b) information about a mask that controls the application of the filter to the sample block. The filter coefficients can be signaled at the APS, and the block size and mask can be signaled at the slice level.

[0215] refer to Figure 10 , can be obtained by applying a linear diamond filter ( Figure 10 (b)) to operate CC-ALF. The filter coefficients are sent to the APS, scaled by a factor of 210, and rounded up to obtain a fixed-point representation. The application of the filter can be controlled at a variable block size and signaled by a context coding flag received for each block of samples. The block size and CC-ALF enable flag can be received at the slice level for each chroma component. The block size (for chroma samples) can be 16x16, 32x32, 64x64, or 128x128.

[0216] In the following embodiment, a method is proposed to re-filter or modify the reconstructed chroma samples filtered by the ALF based on the reconstructed luma samples.

[0217] 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 table disclosed in the present disclosure can be included in the image / video information, can be configured / encoded in the encoding device and sent to the decoding device in the form of a bitstream. The decoding device can parse / decode the information (syntax elements) in the corresponding syntax table. The decoding device can perform a picture / image / video decoding process (specifically, for example, a CC-ALF process) based on the decoded information. Hereinafter, the same applies to other embodiments.

[0218] The following table shows some syntax of slice header information according to an embodiment of the present disclosure.

[0219] [Table 3]

[0220]

[0221] The following table shows exemplary semantics for the syntax elements included in the table above.

[0222] [Table 4]

[0223]

[0224]

[0225]

[0226] Referring to the above two tables, when sps_cross_component_alf_enabled_flag is 1 in the slice header, the slice_cross_component_alf_cb_enabled_flag can be parsed to determine whether Cb CC-ALF is applied 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 using the filter in the corresponding adaptation parameter set (APS) id through slice_cross_component_alf_cb_aps_id parsing. Slice_cross_component_alf_cb_log2_control_size_minus4 may mean a block unit to which CC-ALF is applied in a Cb slice.

[0227] For example, when the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 0, whether CC-ALF is applied is determined in 16x16 units. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 1, whether CC-ALF is applied is determined in 32x32 units. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 2, whether CC-ALF is applied is determined in 64x64 units. When the value of slice_cross_component_alf_cb_log2_control_size_minus4 is 3, whether CC-ALF is applied is determined in 128x128 units. In addition, the same syntax as above is used for Cr CC-ALF.

[0228] The following table shows an example syntax for ALF data.

[0229] [Table 5]

[0230]

[0231] The following table is example semantics for the syntax elements included in the above table.

[0232] [Table 6]

[0233]

[0234]

[0235]

[0236]

[0237] Referring to the two tables above, 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, CC-ALF can be applied even when the ALF tool on the SPS is disabled. A new hardware pipeline design is required because CC-ALF must be able to operate independently of the existing ALF structure. This results in increased hardware implementation costs and increased hardware latency.

[0238] In addition, in ALF, whether to apply both luma and chroma images is determined on a CTU basis, and the result of this determination is signaled to the decoder. However, whether to apply the variable CC-ALF is determined on a 16x16 to 128x128 basis, and this application can cause a conflict between the existing ALF structure and CC-ALF. This causes problems in hardware implementation and also increases the number of line buffers required for various variable CC-ALF applications.

[0239] In the present disclosure, the above-mentioned problems in the hardware implementation of CC-ALF are solved by applying the CC-ALF syntax structure as a whole to the ALF syntax structure.

[0240] According to an embodiment of the present disclosure, in order to determine whether CC-ALF is used (applied), a sequence parameter set (SPS) may include a CC-ALF enable flag (sps_ccalf_enable_flag). The CC-ALF enable flag may be transmitted independently of the ALF enable flag (sps_alf_enabled_flag) used to determine whether ALF is used (applied).

[0241] The following table shows some exemplary syntaxes of the SPS according to this embodiment.

[0242] [Table 7]

[0243]

[0244] Referring to the table above, CC-ALF can only be applied when ALF is always in operation. That is, the CC-ALF enable flag (sps_ccalf_enabled_flag) can only be parsed when the ALF enable flag (sps_alf_enabled_flag) is 1. CC-ALF and ALF can be combined according to the table above. The CC-ALF enable flag can indicate whether CC-ALF is available (and may be related to whether CC-ALF is available).

[0245] The following table shows some example syntax for a slice header.

[0246] [Table 8]

[0247]

[0248] Referring to the above table, 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 an example, image information encoded by an encoding device or obtained (received) by a 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 the Cb color component of the filtered reconstructed chroma sample and a second flag (slice_cross_component_alf_cr_enabeld_flag) related to whether CC-ALF can be used for the Cr color component of the filtered reconstructed chroma sample.

[0249] In an 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 ID information (slice_cross_component_alf_cb_aps_id) of the first APS for deriving the cross-component filter coefficient 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 ID information (slice_cross_component_alf_cr_aps_id) of the second APS for deriving the cross-component filter coefficient for the Cr color component.

[0250] The following table shows a portion of the SPS syntax according to another example of this embodiment.

[0251] [Table 9]

[0252]

[0253] The following table exemplarily shows a part of the slice header syntax.

[0254] [Table 10]

[0255]

[0256] Referring to Table 9, when ChromaArrayType is not 0 and the ALF enabled flag (sps_alf_enabled_flag) is 1, the SPS may include a CCALF enabled flag (sps_ccalf_enabled_flag). For example, if ChromaArrayType is not 0, the chroma format may not be monochrome, and the CCALF enabled flag may be transmitted through the SPS based on the fact that the chroma format is not monochrome.

[0257] Referring to Table 9, based on a 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.

[0258] In an example, image information encoded by an encoding device or obtained by a decoding device may include an SPS. The SPS may include a first ALF enable flag (sps_alf_enabled_flag) related to whether ALF is available. For example, based on a 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).

[0259] The following table shows a portion of the slice header syntax according to another example of this embodiment.

[0260] [Table 11]

[0261]

[0262] Referring to the above table, parsing of the CCALF enabled flag (sps_ccalf_enabled_flag) can be performed only when the ALF enabled flag (sps_alf_enabled_flag) is 1.

[0263] The following table shows exemplary semantics for the syntax elements included in the table above.

[0264] [Table 12]

[0265]

[0266]

[0267] The semantics of slice_ccalf_chroma_idc in the above table can be described by the following table.

[0268] [Table 13]

[0269]

[0270] The following table shows a portion of the slice header syntax according to another example of this embodiment.

[0271] [Table 14]

[0272]

[0273] The syntax elements included in the table may be described according to Table 12 or Table 13. In addition, when the chroma format is not monochrome, CCALF related information may be included in the slice header.

[0274] The following table shows a portion of the slice header syntax according to another example of this embodiment.

[0275] [Table 15]

[0276]

[0277] The following table shows exemplary semantics for the syntax elements included in the table above.

[0278] [Table 16]

[0279]

[0280]

[0281] The following table shows a portion 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.

[0282] [Table 17]

[0283]

[0284] Referring to the above table, whether to apply the slice unit ALF and CC-ALF can be determined 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.

[0285] Referring to the above table, whether sps_ccalf_enabeld_flag is 1 in the slice header information can be determined only when slice_alf_enabled_flag is 1. 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.

[0286] The following table exemplarily shows a part of the APS syntax: The syntax element adaptation_parameter_set_id may indicate identifier information (ID information) of the APS.

[0287] [Table 18]

[0288]

[0289] The following table shows an example syntax for ALF data.

[0290] [Table 19]

[0291]

[0292] Referring to the above two tables, the APS may include ALF data (alf_data()). The APS including the ALF data may be referred to as an ALF APS (ALF type APS). That is, the type of the APS including the ALF data may be an 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) regarding whether a cross component filter for a Cb color component is signaled. The ALF data may include a Cr filter signal flag (alf_cross_component_cr_filter_signal_flag or alf_cc_cr_filter_signal_flag) regarding whether a cross component filter for a Cr color component is signaled.

[0293] 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 coefficient for the Cr color component (alf_cross_component_cr_coeff_abs) and information about the sign of the cross-component filter coefficient for the Cr color component (alf_cross_component_cr_coeff_sign). Based on the information about the absolute value of the cross-component filter coefficient for the Cr color component and the information about the sign of the cross-component filter coefficient for the Cr color component, the cross-component filter coefficient for the Cr color component can be derived.

[0294] In an example, the ALF data may include information about the absolute value of the cross-component filter coefficient for the Cb color component (alf_cross_component_cb_coeff_abs) and information about the sign of the cross-component filter coefficient for the Cb color component (alf_cross_component_cb_coeff_sign). Based on the information about the absolute value of the cross-component filter coefficient for the Cb color component and the information about the sign of the cross-component filter coefficient for the Cb color component, the cross-component filter coefficient for the Cb color component can be derived.

[0295] The following table shows syntax related to ALF data according to another example.

[0296] [Table 20]

[0297]

[0298] Referring to the above table, after alf_cross_component_filter_signal_flag is first transmitted, the Cb / Cr filter signal flag may be transmitted when alf_cross_component_filter_signal_flag is 1. That is, alf_cross_component_filter_signal_flag integrates Cb / Cr to determine whether to transmit the CC-ALF filter coefficient.

[0299] The following table shows syntax related to ALF data according to another example.

[0300] [Table 21]

[0301]

[0302] The following table shows exemplary semantics for the syntax elements included in the table above.

[0303] [Table 22]

[0304]

[0305]

[0306]

[0307] The following table shows syntax related to ALF data according to another example.

[0308] [Table 23]

[0309]

[0310] The following table shows exemplary semantics for the syntax elements included in the table above.

[0311] [Table 24]

[0312]

[0313]

[0314]

[0315] In the above two tables, the order of exp-Golomb binarization used to parse the syntax of alf_cross_component_cb_coeff_abs[j] and alf_cross_component_cr_coeff_abs[j] can be defined by one of the values 0 to 9.

[0316] 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 a cross-component filter for the Cb color component is signaled. 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 coefficient for the Cb color component (alf_cross_component_cb_coeff_abs) and information about the sign of the cross-component filter coefficient for the Cb color component (alf_cross_component_cr_coeff_sign). Based on the information about the absolute value of the cross-component filter coefficient for the Cb color component and the information about the sign of the cross-component filter coefficient for the Cb color component, the cross-component filter coefficient for the Cb color component may be derived.

[0317] 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 a cross-component filter for a Cr color component is signaled. 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 coefficient for the Cr color component (alf_cross_component_cr_coeff_abs) and information about the sign of the cross-component filter coefficient for the Cr color component (alf_cross_component_cr_coeff_sign). Based on the information about the absolute value of the cross-component filter coefficient for the Cr color component and the information about the sign of the cross-component filter coefficient for the Cr color component, the cross-component filter coefficient for the Cr color component may be derived.

[0318] The following table shows the syntax of a coding tree unit according to an embodiment of the present disclosure.

[0319] [Table 25]

[0320]

[0321] The following table shows exemplary semantics for the syntax elements included in the table above.

[0322] [Table 26]

[0323]

[0324]

[0325] The following table shows another example compilation tree unit syntax according to this embodiment.

[0326] [Table 27]

[0327]

[0328] Referring to the above table, CCALF can be applied in units of CTUs. In an example, the image information may include information about a coding tree unit (coding_tree_unit()). The information about the coding tree unit may include information about whether a cross-component filter is applied to the current block of the Cb color component (ccalf_ctb_flag[0]) and / or information about whether a cross-component filter is applied to the current block of the Cr color component (ccalf_ctb_flag[1]). In addition, the information about the coding tree unit may include information about a filter set index of a cross-component filter applied to the current block of the Cb color component (ccalf_ctb_filter_alt_idx[0]) and / or information about a filter set index of a cross-component filter applied to the current block of the Cr color component (ccalf_ctb_filter_alt_idx[1]). The syntax may be adaptively transmitted according to the syntax slice_ccalf_enabled_flag and slice_ccalf_chroma_idc.

[0329] The following table shows another example of a coding tree unit syntax according to this embodiment.

[0330] [Table 28]

[0331]

[0332] The following table shows exemplary semantics for the syntax elements included in the table above.

[0333] [Table 29]

[0334]

[0335]

[0336] The following table shows another example coding tree unit syntax according to this embodiment. The syntax elements included in the following table can be described according to Table 29.

[0337] [Table 30]

[0338]

[0339] In an example, the image information may include information about a coding tree unit (coding_tree_unit()). The information about the coding tree unit may include information about whether a cross-component filter is applied to the current block of the Cb color component (ccalf_ctb_flag[0]) and / or information about whether a cross-component filter is applied to the current block of the Cr color component (ccalf_ctb_flag[1]). In addition, the information about the coding tree unit may include information about a filter set index of a cross-component filter applied to the current block of the Cb color component (ccalf_ctb_filter_alt_idx[0]) and / or information about a filter set index of a cross-component filter applied to the current block of the Cr color component (ccalf_ctb_filter_alt_idx[1]).

[0340] Figure 11 and Figure 12 An example of a video / image encoding method and related components according to an embodiment of the present disclosure is schematically illustrated. Figure 11 The method disclosed in Figure 2 Specifically, for example, Figure 11 S1100 may be performed by the adder 250 of the encoding apparatus, S1110 to S1140 may be performed by the filter 260 of the encoding apparatus, and S1570 may be performed by the entropy encoder 240 of the encoding apparatus. Figure 11 The disclosed method may include the embodiments described above in the present disclosure.

[0341] refer to Figure 11 , the encoding device may generate a reconstructed luma sample and a reconstructed chroma sample of the current block (S1100). The encoding device may generate a residual luma sample and / or a residual chroma sample. The encoding device may generate a reconstructed luma sample based on the residual luma sample and may generate a reconstructed chroma sample based on the residual chroma sample.

[0342] In this example, residual samples for the current block may be generated based on the original samples and predicted samples of the current block. Specifically, the encoding device may generate predicted samples for the current block based on a prediction mode. In this case, various prediction methods disclosed in this disclosure, such as inter-frame prediction or intra-frame prediction, may be applied. Residual samples may be generated based on the predicted samples and the original samples.

[0343] In an example, the encoding device may generate residual luma samples. The residual luma samples may be generated based on the original luma samples and the predicted luma samples. In an example, the encoding device may generate residual chroma samples. The residual chroma samples may be generated based on the original chroma samples and the predicted chroma samples.

[0344] The encoding device may derive transform coefficients. The encoding device may derive transform coefficients based on a transform process for the residual samples. The encoding device may derive transform coefficients for the residual luma samples (luminance transform coefficients) and / or transform coefficients for the residual chroma samples (chroma transform coefficients). For example, the transform process may include at least one of DCT, DST, GBT, or CNT.

[0345] The encoding device may derive quantized transform coefficients. The encoding device may derive the quantized transform coefficients based on a quantization process for the transform coefficients. The quantized transform coefficients may have a one-dimensional vector form based on a coefficient scan order. The quantized transform coefficients may include quantized luma transform coefficients and / or quantized chroma transform coefficients.

[0346] The encoding device may generate residual information. The encoding device may generate residual information indicating (including) quantized transform coefficients. The residual information may be generated by various encoding methods such as exponential Golomb, CAVLC, CABAC, etc.

[0347] The encoding device may generate prediction-related information. The encoding device may generate prediction-related information based on the prediction sample and / or the mode applied thereto. The prediction-related information may include information about various prediction modes (e.g., merge mode, MVP mode, etc.), MVD information, etc.

[0348] The encoding device may derive ALF filter coefficients for the ALF process (S1110). The ALF filter coefficients may include ALF luma filter coefficients for reconstructing luma samples and ALF chroma filter coefficients for reconstructing chroma samples. Filtered reconstructed luma samples and / or filtered reconstructed chroma samples may be generated based on the ALF filter coefficients.

[0349] The encoding device may generate ALF-related information (S1120). The encoding device may generate ALF-related information based on the ALF filter coefficients. The encoding device derives ALF-related parameters that can be applied to filter the reconstructed samples and generates ALF-related information. For example, the ALF-related information may include the ALF-related information described above in this disclosure.

[0350] 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 chroma samples may be generated based on the cross-component filter and / or cross-component filter coefficients.

[0351] 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 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.

[0352] In an example, CCALF-related information may include a CCALF enable flag, a flag related to whether CCALF can be used for the Cb (or Cr) color component, a Cb (or Cr) filter signal flag related to whether a cross-component filter for the Cb (or Cr) color component is signaled, 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 the cross-component filter is applied to the current block of the Cb (or Cr) color component in the information about the coding tree unit (coding tree unit syntax).

[0353] The image / video information may include various types of information according to an embodiment of the present disclosure. For example, the image / video information may include information disclosed in at least one of Tables 1 to 30 above.

[0354] In an embodiment, the image information may include a sequence parameter set (SPS). The SPS may include a CCALF enable flag related to whether cross-component filtering is available. Based on the 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 image information may include slice header information.

[0355] According to an example of an embodiment, the slice header information may include ID information of the 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 the APS including ALF data for deriving cross-component filter coefficients.

[0356] In an embodiment, the SPS may include an ALF enable flag (sps_ccalf_enabled_flag) regarding 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 regarding whether cross-component filtering is available.

[0357] In an embodiment, the image information may include slice header information and an adaptive parameter set (APS). The header information may include information related to an identifier of the APS including the ALF data. For example, cross-component filter coefficients may be derived based on the ALF data.

[0358] In an embodiment, the slice header information may include an ALF enable flag (slice_alf_enabled_flag) related to whether ALF is available. 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 a 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 a determination that the value of the ALF enable flag is 1, CCALF may be available for the slice.

[0359] In an embodiment, the header information (slice header information) may include a first flag related to whether CCALF is applicable to the Cb color component of the filtered reconstructed chroma sample and a second flag related to whether CCALF is applicable to the Cr color component of the filtered reconstructed chroma sample. In another example, based on the determination that the value of the ALF enable flag (slice_alf_enabled_flag) is 1, the header information (slice header information) may include a first flag related to whether CCALF is applicable to the Cb color component of the filtered reconstructed chroma sample and a second flag related to whether CCALF is applicable to the Cr color component of the filtered reconstructed chroma sample.

[0360] 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 the first APS for deriving the cross-component filter coefficient for the Cb color component (information related to the identifier of the second APS). Based on the determination that the value of the second flag is 1, the slice header information may include ID information of the second APS for deriving the cross-component filter coefficient for the Cr color component (information related to the identifier of the second APS).

[0361] In an embodiment, the first ALF data included in the first APS may include a Cb filter signal flag related to whether a cross-component filter for a Cb color component is signaled. 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 coefficient for the Cb color component and information about the sign of the cross-component filter coefficient for the Cb color component. Based on the information about the absolute value of the cross-component filter coefficient for the Cb color component and the information about the sign of the cross-component filter coefficient for the Cb color component, the cross-component filter coefficient for the Cb color component may be derived.

[0362] In an embodiment, the information about the number of cross-component filters for the Cb color component may be zero-order exponential-Golomb (0th EG) coded.

[0363] In an embodiment, the second ALF data included in the second APS may include a Cr filter signal flag related to whether a cross-component filter for a Cr color component is signaled. 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 coefficient for the Cr color component and information about the sign of the cross-component filter coefficient for the Cr color component. Based on the information about the absolute value of the cross-component filter coefficient for the Cr color component and the information about the sign of the cross-component filter coefficient for the Cr color component, the cross-component filter coefficient for the Cr color component can be derived.

[0364] In an embodiment, the information about the number of cross-component filters for the Cr color component may be Zeroth Order Exponential Golomb (0th EG) coded.

[0365] 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 a cross-component filter is applied to the current block of the Cb color component and / or information about whether a cross-component filter is applied to the current block of the Cr color component.

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

[0367] Figure 13 and Figure 14 An example of a video / image decoding method and related components according to an embodiment of the present disclosure is schematically illustrated. Figure 13 The method disclosed in Figure 3 or Figure 14 Specifically, for example, Figure 13 S1300 may be performed by the entropy decoder 310 of the decoding apparatus, S1310 may be performed by the adder 340 of the decoding apparatus, and S1320 to S1330 may be performed by the filter 350 of the decoding apparatus.

[0368] refer to 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 image / video information through a bitstream. The residual information may be generated through various coding methods such as Exponential Golomb, CAVLC, CABAC, etc. In an example, the video / image information may also 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 can be used for a Cb (or Cr) color component, a Cb (or Cr) filter signal flag related to whether a cross-component filter for a Cb (or Cr) color component is signaled, information related to the number of cross-component filters for a Cb (or Cr) color component, information about the absolute value of the cross-component filter coefficient for a Cb (or Cr) color component, information about the sign of the cross-component filter coefficient for a Cb (or Cr) color component, and / or information about whether a cross-component filter is applied to a current block of a Cb (or Cr) color component in information about a coding tree unit (coding tree unit syntax).

[0369] The image / video information may include various types of information according to an embodiment of the present disclosure. For example, the image / video information may include information disclosed in at least one of Tables 1 to 30 above.

[0370] The decoding device may derive transform coefficients. Specifically, the decoding device may derive quantized transform coefficients based on residual information. The transform coefficients may include luma transform coefficients and chroma transform coefficients. The quantized transform coefficients may have a one-dimensional vector form based on a coefficient scan order. The decoding device may derive the transform coefficients based on a dequantization process for the quantized transform coefficients.

[0371] The decoding device may derive residual samples. The decoding device may derive residual samples based on transform coefficients. The residual samples may include residual luma samples and residual chroma samples. For example, residual luma samples may be derived based on luma transform coefficients, and residual chroma samples may be derived based on chroma transform coefficients. In addition, residual samples for the current block may be derived based on original samples and predicted samples of the current block.

[0372] The decoding device may perform prediction based on the image / video information and derive prediction samples for the current block. The decoding device may derive prediction samples for the current block based on prediction-related information. The prediction-related information may include prediction mode information. The decoding device may determine whether to apply inter-frame prediction or intra-frame prediction to the current block based on the prediction mode information and may perform prediction based on this. The prediction samples may include predicted luma samples and / or predicted chroma samples.

[0373] The decoding apparatus may generate / derive reconstructed luma samples and / or reconstructed chroma samples (S1310). The reconstructed samples may include reconstructed luma samples and / or reconstructed chroma samples. The decoding apparatus may generate reconstructed luma samples based on the residual luma samples. The decoding apparatus may generate reconstructed chroma samples based on the residual chroma samples. The luma component of the reconstructed samples may correspond to the reconstructed luma samples, and the chroma component of the reconstructed samples may correspond to the reconstructed chroma samples.

[0374] The decoding apparatus may perform an adaptive loop filter (ALF) process on the reconstructed chroma samples to generate filtered reconstructed chroma samples (S1320). In the ALF process, the decoding apparatus may derive ALF filter coefficients for the ALF process used to reconstruct the chroma samples. In addition, the decoding apparatus may derive ALF filter coefficients for the ALF process used to reconstruct the luma samples. The ALF filter coefficients may be derived based on ALF parameters included in the ALF data in the APS.

[0375] The decoding apparatus may generate filtered reconstructed chroma samples.The decoding apparatus may generate filtered reconstructed samples based on the reconstructed chroma samples and ALF filter coefficients.

[0376] In order to generate the modified filtered reconstructed chroma samples, the decoding device may perform a cross-component filtering process on the filtered reconstructed chroma samples (S1330). In the cross-component filtering process, the decoding device may derive cross-component filter coefficients for cross-component filtering. The cross-component filter coefficients may be derived based on 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 (which may be signaled).

[0377] The decoding device may generate modified filtered reconstructed chroma samples. The decoding device may generate the modified and filtered reconstructed chroma samples based on the reconstructed luma samples, the filtered reconstructed chroma samples, and the cross-component filter coefficients. In an example, the decoding device may derive a difference between two samples in the reconstructed luma samples and multiply the difference by one of the cross-component filter coefficients. Based on the multiplication result and the filtered reconstructed chroma samples, the decoding device may generate the modified filtered reconstructed chroma samples. For example, the decoding device may generate the modified filtered reconstructed chroma samples based on the sum of the multiplication product and one of the filtered reconstructed chroma samples.

[0378] In an embodiment, the image information may include a sequence parameter set (SPS). The SPS may include a CCALF enable flag related to whether cross-component filtering is available. Based on the 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 image information may include slice header information.

[0379] According to an example of an embodiment, the slice header information may include ID information of the 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 the APS including ALF data for deriving cross-component filter coefficients.

[0380] In an embodiment, the SPS may include an ALF enable flag (sps_ccalf_enabled_flag) regarding 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 regarding whether cross-component filtering is available.

[0381] In an embodiment, the image information may include slice header information and an adaptive parameter set (APS). The header information may include information related to an identifier of the APS including the ALF data. For example, cross-component filter coefficients may be derived based on the ALF data.

[0382] In an embodiment, the slice header information may include an ALF enable flag (slice_alf_enabled_flag) related to whether ALF is available. 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 a 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 a determination that the value of the ALF enable flag is 1, CCALF may be available.

[0383] In an embodiment, the header information (slice header information) may include a first flag related to whether CCALF is applicable to the Cb color component of the filtered reconstructed chroma sample and a second flag related to whether CCALF is applicable to the Cr color component of the filtered reconstructed chroma sample. In another example, based on the determination that the value of the ALF enable flag (slice_alf_enabled_flag) is 1, the header information (slice header information) may include a first flag related to whether CCALF is applicable to the Cb color component of the filtered reconstructed chroma sample and a second flag related to whether CCALF is applicable to the Cr color component of the filtered reconstructed chroma sample.

[0384] 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 the first APS for deriving the cross-component filter coefficient for the Cb color component (information related to the identifier of the second APS). Based on the determination that the value of the second flag is 1, the slice header information may include ID information of the second APS for deriving the cross-component filter coefficient for the Cr color component (information related to the identifier of the second APS).

[0385] In an embodiment, the first ALF data included in the first APS may include a Cb filter signal flag related to whether a cross-component filter for a Cb color component is signaled. 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 coefficient for the Cb color component and information about the sign of the cross-component filter coefficient for the Cb color component. Based on the information about the absolute value of the cross-component filter coefficient for the Cb color component and the information about the sign of the cross-component filter coefficient for the Cb color component, the cross-component filter coefficient for the Cb color component may be derived.

[0386] In an embodiment, the information about the number of cross-component filters for the Cb color component may be zero-order exponential-Golomb (0th EG) coded.

[0387] In an embodiment, the second ALF data included in the second APS may include a Cr filter signal flag related to whether a cross-component filter for a Cr color component is signaled. 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 coefficient for the Cr color component and information about the sign of the cross-component filter coefficient for the Cr color component. Based on the information about the absolute value of the cross-component filter coefficient for the Cr color component and the information about the sign of the cross-component filter coefficient for the Cr color component, the cross-component filter coefficient for the Cr color component can be derived.

[0388] In an embodiment, the information about the number of cross-component filters for the Cr color component may be Zeroth Order Exponential Golomb (0th EG) coded.

[0389] 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 a cross-component filter is applied to the current block of the Cb color component and / or information about whether a cross-component filter is applied to the current block of the Cr color component.

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

[0391] In the event that residual samples for the current block exist, 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 residual samples (or residual sample arrays) 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 a coefficient scanning order. The decoding device may derive the transform coefficients based on a dequantization process for the quantized transform coefficients. The decoding device may derive the residual samples based on the transform coefficients.

[0392] The decoding device may generate reconstructed samples based on the (intra-frame) prediction samples and the residual samples, and may derive a reconstructed block or a reconstructed picture based on the reconstructed samples. Specifically, the decoding device may generate reconstructed samples based on the sum of the (intra-frame) prediction samples and the residual samples. Thereafter, as described above, if necessary, the decoding device may apply loop filtering processing (e.g., deblocking filtering and / or SAO processing) to the reconstructed picture to improve subjective / objective picture quality.

[0393] 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 encoded information. In addition, the bitstream or encoded information can be stored in a computer-readable storage medium, or the above decoding method can be executed.

[0394] In the above embodiments, the methods are described based on a flow chart having a series of steps or boxes. The present disclosure is not limited to the order of the above steps or boxes. Some steps or boxes may occur simultaneously with other steps or boxes as described above or in an order different from that of other steps or boxes as described above. In addition, it will be understood by those skilled in the art that the steps shown in the above flow chart are not exclusive and may include additional steps or may delete one or more steps in the flow chart without affecting the scope of this document.

[0395] The method according to the above-mentioned embodiment of this document can be implemented in the form of software, and the encoding device and / or decoding device according to this document can be included in a device that performs image processing such as a TV, a computer, a smart phone, a set-top box, and a display device.

[0396] When the embodiments in this document are implemented in software, the above methods can be implemented as modules (processing, functions, etc.) that perform the above functions. The modules can be stored in a memory and executed by a processor. The memory can be inside or outside the processor and can be connected to the processor by various well-known means. The processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and / or data processing equipment. The memory may include a read-only memory (ROM), a random access memory (RAM), flash memory, a memory card, a storage medium, and / or other storage devices. In other words, 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 of the accompanying drawings can be implemented and executed on a computer, a processor, a microprocessor, a controller, or a chip. In this case, information about instructions or algorithms for the implementation can be stored in a digital storage medium.

[0397] In addition, the decoding device and encoding device to which this document is applied may be included in a multimedia broadcast transmission / reception device, a mobile communication terminal, a home theater video device, a digital theater video device, a surveillance camera, a video chat device, a real-time communication device such as a video communication device, a mobile streaming device, a storage medium, a camera, a VoD service provider, an over-the-top (OTT) video device, an Internet streaming service provider, a three-dimensional (3D) video device, a teleconferencing video device, a transportation user equipment (i.e., a vehicle-mounted user equipment, an aircraft user equipment, a ship user equipment, etc.), and a medical video device, and may be used to process video signals and data signals. For example, an over-the-top (OTT) video device may include a game console, a Blu-ray player, an Internet-connected television, a home theater system, a smart phone, a tablet computer, a digital video recorder (DVR), etc.

[0398] In addition, the processing method of applying this document can be generated in the form of a program executed by a computer and can be stored in a computer-readable recording medium. Multimedia data with a data structure according to the present disclosure can also be stored in a computer-readable recording medium. Computer-readable recording media include all kinds of storage devices that store data readable by a computer system. For example, computer-readable recording media may include BD, universal serial bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk and optical data storage device. In addition, computer-readable recording media include media implemented in the form of carrier waves (i.e., transmission over the Internet). In addition, the bit stream generated by the encoding method can be stored in a computer-readable recording medium or can be sent through a wired or wireless communication network.

[0399] In addition, the embodiments of this document can be implemented using a computer program product according to the program code, and the program code can be executed in a computer according to the embodiments of this document. The program code can be stored on a computer-readable carrier.

[0400] Figure 15 An example of a content streaming system to which the embodiments disclosed in this document can be applied is shown.

[0401] refer to Figure 15 The content streaming system to which the embodiments of this document are applied may mainly include an encoding server, a streaming server, a network (web) server, a media storage, a user device, and a multimedia input device.

[0402] The encoding server compresses the content input from the multimedia input device (e.g., a smartphone, a camera, a camcorder, etc.) into digital data to generate a bitstream, and sends the bitstream to the streaming server. As another example, when the multimedia input device such as a smartphone, a camera, a camcorder, etc. directly generates the bitstream, the encoding server can be omitted.

[0403] A bitstream may be generated by applying the encoding method or the bitstream generating method of the embodiment of the present disclosure, and the streaming server may temporarily store the bitstream in a process of transmitting or receiving the bitstream.

[0404] The streaming server sends multimedia data to the user device via a web server based on the user's request. The web server serves as a medium for notifying the user of the service. When the user requests the 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 may 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.

[0405] The streaming server can receive content from a media storage and / or encoding server. For example, when receiving content from the encoding server, the content can be received in real time. In this case, in order to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined time.

[0406] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation, tablet PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital TVs, desktop computers, digital signage, etc. Each server in the content streaming system may be operated as a distributed server, and in this case, data received from each server may be distributed.

[0407] Each server in the content streaming system may be operated as a distributed server, and in this case, data received from each server may be processed in a distributed manner.

[0408] The claims described herein may be combined in various ways. For example, the technical features of the method claims of this document may be combined and implemented as a device, and the technical features of the device claims of this document may be combined and implemented as a method. Furthermore, the technical features of the method claims of this document and the technical features of the device claims of this document may be combined to implement a device, and the technical features of the method claims of this document and the technical features of the device claims of this document may be combined and implemented as a method.

Claims

1. A decoding device for image decoding, the decoding device comprising: Memory; at least one processor connected to the memory, the at least one processor being configured to: Receiving image information via a bit stream; Based on the image information, generating reconstructed luminance samples and reconstructed chrominance samples; performing an adaptive loop filtering (ALF) process on the reconstructed chroma samples to generate filtered reconstructed chroma samples; as well as performing a cross-component filtering process on the filtered reconstructed chroma samples to generate modified filtered reconstructed chroma samples, Wherein, the image information includes information about cross-component filtering, and Wherein, for the execution of the cross-component filtering process, the at least one processor is configured to: deriving the number of cross-component filters used 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 said modified filtered reconstructed chroma samples based on said filtered reconstructed chroma samples and said cross-component filter coefficients, The image information includes sequence parameter set SPS and slice header information. 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 a determination that a 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 a value of the ALF enable flag included in the slice header information is 1 and a value of the CCALF enable flag included in the SPS is 1, the slice header information includes information on whether the CCALF is enabled for the filtered reconstructed chroma samples, and wherein, based on the value of the information on whether the CCALF is enabled for the filtered reconstructed chroma sample being 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; The image information includes information about the coding tree unit, and The information about the coding tree unit includes: information about whether a cross-component filter is applied to the Cb color component of the current block and information about whether a cross-component filter is applied to the Cr color component of the current block, as well as 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.

2. A coding apparatus for image coding, the coding apparatus comprising: Memory; as well as at least one processor connected to the memory, the at least one processor being configured to: Generate reconstructed luma samples and reconstructed chroma samples of a current block in a current picture; Deriving ALF filter coefficients for the ALF process; generating ALF related information based on the ALF filter coefficients; deriving a cross-component filter and cross-component filter coefficients for a cross-component filtering process; generating cross-component filtering related information based on the cross-component filter and the cross-component filter coefficients; as well as encoding image information including information for generating reconstructed luminance samples and reconstructed chrominance samples of the current block, the ALF related information, and the cross-component filtering related information, The cross-component filtering related information includes information about the number of cross-component filters and information about the cross-component filter coefficients. 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 a determination that a 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 a value of the ALF enable flag included in the slice header information is 1 and a value of the CCALF enable flag included in the SPS is 1, the slice header information includes information on whether the CCALF is enabled for the filtered reconstructed chroma samples, and wherein, based on the value of the information on whether the CCALF is enabled for the filtered reconstructed chroma sample being 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; The image information includes information about the coding tree unit, and The information about the coding tree unit includes: information about whether a cross-component filter is applied to the Cb color component of the current block and information about whether a cross-component filter is applied to the Cr color component of the current block, as well as 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.

3. A device for transmitting image data, the device comprising: at least one processor configured to: obtain a bitstream for the image, wherein the bitstream is generated based on: generating reconstructed luma samples and reconstructed chroma samples of a current block in a current picture, deriving ALF filter coefficients for an adaptive loop filtering (ALF) process, generating ALF-related information based on the ALF filter coefficients, deriving a cross-component filter and cross-component filter coefficients for a cross-component filtering process, generating cross-component filtering-related information based on the cross-component filter and the cross-component filter coefficients, and encoding image information including information used to generate the reconstructed luma samples and the reconstructed chroma samples of the current block, the ALF-related information, and the cross-component filtering-related information; and a transmitter configured to transmit the data comprising the bit stream, The cross-component filtering related information includes information about the number of cross-component filters and information about the cross-component filter coefficients. The image information includes sequence parameter set SPS and slice header information. 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 a determination that a 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 a value of the ALF enable flag included in the slice header information is 1 and a 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 chroma samples, wherein, based on the value of the information on whether the CCALF is enabled for the filtered reconstructed chroma sample being 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; The image information includes information about the coding tree unit, and The information about the coding tree unit includes: information about whether a cross-component filter is applied to the Cb color component of the current block and information about whether a cross-component filter is applied to the Cr color component of the current block, as well as 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