Decoding and encoding apparatus and apparatus for transmitting data for image

Abstract

A decoding and encoding apparatus and an apparatus for transmitting data for an image are disclosed. In an image decoding method according to the present disclosure, information indicating whether an adaptive loop filter (ALF) process to be applied to a current block is applied at a picture level or a slice level is proposed.

Description

[0001] This application is a divisional application of the original invention patent application with application number 202080095788.2 (international application number: PCT / KR2020 / 018071, application date: December 10, 2020, invention name: Video or image coding using adaptive loop filter). Technical Field

[0002] The present disclosure relates to video or image coding applying adaptive loop filters. Background Art

[0003] Recently, in various fields, the demand for high-resolution and high-quality images such as high-definition (HD) images and ultra-high-definition (UHD) images is growing. As the resolution and quality of image data become higher, the size of information or the bit size of transmission increases compared with existing image data. Therefore, when the image data is transmitted by using the same medium such as a conventional (or existing) wired / wireless broadband line, or when the image data is stored using a conventional (or existing) storage medium, the transmission cost and the storage cost increase.

[0004] Therefore, there is a need for efficient image compression technology for efficiently transmitting or storing and reproducing (or playing back) information about high-resolution and high-quality images. Summary of the invention

[0005] Technical Purpose

[0006] The technical purpose of the present disclosure is to provide a method and a device for increasing image encoding efficiency.

[0007] Another technical object of the present disclosure is to provide a method and apparatus for signaling information related to an adaptive loop filter applied at a picture level or a slice level.

[0008] Technical Solution

[0009] According to an embodiment of the present disclosure, an image decoding method performed by a decoding device is provided herein. The method may include the following steps: obtaining indication information including a first flag related to whether an adaptive loop filter (ALF) process to be applied to a current block is applied at a picture level or a slice level and residual information; parsing information related to the ALF process from a picture header or a slice header based on the first flag; generating a reconstructed sample of the current block based on the residual information; deriving a filter coefficient based on the information related to the ALF process; and generating a modified reconstructed sample of the current block based on the reconstructed sample and the filter coefficient.

[0010] According to another embodiment of the present disclosure, an image encoding method performed by an encoding device is provided herein. The method may include the following steps: deriving residual samples of a current block; generating reconstructed samples based on the residual samples; deriving filter coefficients for performing an adaptive loop filter (ALF) process on the reconstructed samples; generating information related to the ALF process based on the filter coefficients; and generating indication information including a first flag related to whether the ALF process is applied at a picture level or a slice level. Herein, the first flag indicates in which of the picture header and the slice header the information related to the ALF process exists.

[0011] According to another embodiment of the present disclosure, a computer-readable digital storage medium is provided herein in which encoded image information that allows the image decoding method to be executed by a decoding device is stored. The image decoding method according to the embodiment of the present disclosure may include the following steps: obtaining indication information including a first flag related to whether an adaptive loop filter (ALF) process to be applied to a current block is applied at a picture level or a slice level and residual information; parsing information related to the ALF process from a picture header or a slice header based on the first flag; generating a reconstructed sample of the current block based on the residual information; deriving a filter coefficient based on the information related to the ALF process; and generating a modified reconstructed sample of the current block based on the reconstructed sample and the filter coefficient.

[0012] Effects of the present disclosure

[0013] According to the present specification, the overall image / video compression efficiency can be improved.

[0014] According to the present specification, the efficiency of image decoding may be improved based on indication information indicating whether a tool applied to a current block is applied at a picture level or a slice level. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An example of a video / image encoding system to which the present disclosure is applicable is schematically illustrated.

[0016] Figure 2 is a diagram schematically illustrating a configuration of a video / image encoding device to which the present disclosure is applicable.

[0017] Figure 3 is a diagram schematically illustrating a configuration of a video / image decoding device to which the present disclosure is applicable.

[0018] Figure 4 An exemplary hierarchical structure of encoded data is illustrated.

[0019] Figure 5 is a diagram illustrating an example of candidate blocks that can be used in the case of performing inter-frame prediction on a current block.

[0020] Figure 6 is a flowchart illustrating a method for performing deblocking filtering.

[0021] Figure 7 is a flow chart schematically illustrating an example of an ALF process.

[0022] Figure 8 Examples of filter shapes used for ALF are illustrated.

[0023] Fig. 9 is a flowchart illustrating the operation of the image encoding device according to an embodiment.

[0024] Fig.10 is a block diagram illustrating a configuration of an image encoding apparatus according to an embodiment.

[0025] Fig.11 is a flowchart illustrating the operation of the image decoding device according to an embodiment.

[0026] Fig.12 is a block diagram illustrating a configuration of an image decoding apparatus according to an embodiment.

[0027] Fig.13 An exemplary structure of a content streaming system to which the present disclosure is applicable is illustrated. DETAILED DESCRIPTION

[0028] This document can be modified in various forms, and its specific embodiments will be described and illustrated in the accompanying drawings. However, these embodiments are not intended to limit this document. The terms used in the following description are only used to describe specific embodiments and are not intended to limit this document. Singular expressions include plural expressions as long as they are clearly interpreted differently. Terms such as "including" and "having" are intended to indicate the presence of features, quantities, steps, operations, elements, parts, or combinations thereof used in the following description, so it should be understood that the possibility of the presence or addition of one or more different features, quantities, steps, operations, elements, parts, or combinations thereof is not excluded.

[0029] In addition, the various configurations of the drawings described in this document are independent diagrams for the purpose of illustrating the functions of the features that are different from each other, and do not mean that the various configurations are implemented by different hardware or different software. For example, two or more configurations in the configuration can be combined to form one configuration, and one configuration can also be divided into multiple configurations. Without departing from the main purpose of this document, embodiments in which the configurations are combined and / or separated are included in the scope of the claims.

[0030] In the present disclosure, the term "A or B" may mean "only A", "only B", or "both A and B". In other words, in the present disclosure, the term "A or B" may be interpreted as indicating "A and / or B". For example, in the present disclosure, the term "A, B, or C" may mean "only A", "only B", "only C", or "any combination of A, B, C".

[0031] A slash ( / ) or a comma used in the present disclosure may mean "and / or". For example, "A / B" may mean "A and / or B". Thus, "A / B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B, or C".

[0032] In the present specification, "at least one of A and B" may mean "only A", "only B", or "both A and B". In addition, in the present specification, the expression "at least one of A or B" or "at least one of A and / or B" may be interpreted as being the same as "at least one of A and B".

[0033] In addition, in the present specification, "at least one of A, B, and C" may mean "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".

[0034] In addition, brackets used in the present specification may mean "for example". Specifically, in the case of expressing "prediction (intra-frame prediction)", it may indicate that "intra-frame prediction" is proposed as an example of "prediction". In other words, the term "prediction" in the present specification is not limited to "intra-frame prediction", and it may indicate that "intra-frame prediction" is proposed as an example of "prediction". In addition, even in the case of expressing "prediction (i.e., intra-frame prediction)", it may indicate that "intra-frame prediction" is proposed as an example of "prediction".

[0035] The technical features described separately in the drawings of this specification may be implemented separately or simultaneously.

[0036] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals will be used to indicate the same configuration elements within the accompanying drawings, and overlapping (or repeated) descriptions of the same configuration elements will be omitted for simplicity.

[0037] Figure 1 An example of a video / image encoding system to which the present disclosure is applicable is schematically illustrated.

[0038] refer to Figure 1The video / image coding system may include a first device (source device) and a second device (receiving device). The source device may send the coded video / image information or data to the receiving device in the form of a file or stream transmission via a digital storage medium or a network.

[0039] 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.

[0040] The video source may acquire the video / image by capturing, synthesizing or generating a video / image process. The video source may include a video / image capturing device, and / or a video / image generating device. For example, the video / image capturing device may include one or more cameras, a video / image archive including previously captured videos / images, etc. For example, the video / image generating 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 capturing process may be replaced by a process that generates relevant data.

[0041] The encoding device can encode the input video / image. For compression and encoding 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 bit stream.

[0042] The transmitter may transmit the encoded image / image information or data output in the form of a bit stream to a receiver of a receiving device in the form of a file or stream via a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter may include an element for generating a media file in a predetermined file format, and may include an element for transmission via a broadcast / communication network. The receiver may receive / extract a bit stream and transmit the received bit stream to a decoding device.

[0043] The decoding device may decode a video / image by performing a series of processes corresponding to the operations of the encoding device, such as inverse quantization, inverse transformation, and prediction.

[0044] The renderer may render the decoded video / image. The rendered video / image may be displayed through a display.

[0045] This specification relates to video / image coding. For example, the methods / examples disclosed in this specification can be applied to methods disclosed in the Versatile Video Coding (VVC) standard, the Essential Video Coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the second generation Audio Video Coding standard (AVS2), or other next generation video / image coding standards (e.g., H.267, H.268, etc.).

[0046] This document proposes various embodiments of video / image coding, and unless otherwise specified, the above embodiments may also be performed in combination with each other.

[0047] In this document, video may refer to a series of images over time. A picture generally refers to a unit representing an image in a specific time frame, and a slice / tile refers to a unit that constitutes a part of a picture from a coding perspective. A slice / tile may include one or more coding tree units (CTUs). A picture may consist of one or more slices / tiles.

[0048] 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 whose height is equal to the height of the picture and whose width is specified by a syntax element in a picture parameter set. A tile row is a rectangular area of ​​a CTU whose width is specified by a syntax element in a picture parameter set and whose height is equal to the height of the picture. Tile scanning is a specific order sorting of CTUs of the following partitioned pictures: CTUs are sorted continuously in tiles by CTU raster scanning, and tiles in pictures are sorted continuously by raster scanning of tiles of pictures. A slice may include multiple whole (complete) tiles or multiple continuous (or adjacent) CTU matrices within a tile of a picture that may be included in one NAL unit. In this specification, tile groups and slices may be used interchangeably. For example, in this specification, a tile group / tile group header may be referred to as a slice / slice header.

[0049] In addition, 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.

[0050] A pixel or a pel may refer to the smallest unit constituting a picture (or image). In addition, a "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a value of a pixel, and may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0051] 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 a block or an area. In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients. Alternatively, a sample may mean a pixel value in a spatial domain, and when such a pixel value is transformed into a frequency domain, it may mean a transform coefficient in a frequency domain.

[0052] Figure 2 2 is a diagram schematically illustrating a configuration of a video / image encoding device to which the present disclosure is applicable. Hereinafter, the so-called video encoding device may include an image encoding device.

[0053] Reference 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, an inverse quantizer 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 component may also include the memory 270 as an internal / external component.

[0054] The image divider 210 may divide the input image (or picture or frame) input to the encoding device 200 into one or more processors. For example, the processor may be referred to as a coding unit (CU). In this case, the coding unit may be recursively divided from a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QTBTTT) structure. For example, one coding unit may be divided into a plurality of coding units with a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary structure. In this case, for example, a quadtree structure may be applied first, and a binary tree structure and / or a ternary structure may be applied later. Alternatively, a binary tree structure may be applied first. The encoding process according to the present disclosure may be performed based on a final coding unit that is no longer divided. In this case, the maximum coding unit may be used as the final coding unit based on coding efficiency, etc. according to image characteristics, or if necessary, the coding unit may be recursively divided into coding units with a deeper depth and a coding unit with an optimal size may be used as the final coding unit. Here, the encoding process may include a process of prediction, transformation, and reconstruction (to be 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 split or divided from the above-mentioned 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.

[0055] In some cases, a unit may be used interchangeably with terms such as a block or region. In general, an M×N block may represent a set of samples or transform coefficients consisting of M columns and N rows. A sample may generally represent a pixel or a pixel value, and may represent only a pixel / pixel value of a luma component or only a pixel / pixel value of a chroma component. A sample may be used as a term corresponding to one picture (or image) of a pixel or a pixel element.

[0056] In the encoding device 200, a prediction signal (prediction block, prediction sample array) output from the inter predictor 221 or the intra predictor 222 is subtracted from the input image signal (original block, original sample array) to generate a residual signal (residual block, residual sample array), and the generated residual signal is sent to the transformer 232. In this case, as shown, the part of the encoding device 200 that subtracts the prediction signal (prediction block, prediction sample array) from the input image signal (original block, original sample array) can be referred to as a subtractor 231. The predictor may perform prediction on a block to be processed (hereinafter, referred to as a current block) and generate a prediction block including prediction samples of the current block. The predictor may determine whether intra prediction or inter prediction is applied on a current block or CU basis. As described later in the description of each prediction mode, the predictor may generate various information related to prediction such as prediction mode information, and send the generated information to the entropy encoder 240. Information about prediction may be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0057] The intra-frame predictor 222 may predict the current block with reference to samples in the current picture. Depending on the prediction mode, the referenced samples may be located near the current block or may be spaced apart. In intra-frame prediction, the prediction mode may include multiple non-directional modes and multiple directional modes. For example, the non-directional mode may include a DC mode and a plane mode. For example, depending on the level of detail of the prediction direction, the directional mode may include 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used depending on the settings. The intra-frame predictor 222 may use the prediction mode applied to the neighboring blocks to determine the prediction mode applied to the current block.

[0058] The inter-frame predictor 221 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. Here, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter-frame predictor 221 may configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame predictor 221 may use the motion information of the neighboring block as the motion information of the current block. In the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of the motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be indicated by signaling the motion vector difference.

[0059] The predictor 220 may generate a prediction signal based on various prediction methods described below. For example, the predictor may not only apply intra prediction or inter prediction to predict a block, but may also apply both intra prediction and inter prediction at the same time. This may be referred to as a combination of inter and intra prediction (CIIP). In addition, the predictor may predict a block based on an intra-block copy (IBC) prediction mode or a palette mode. The IBC prediction mode or the palette mode may be used for content image / video encoding of games, etc., such as screen content coding (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction in terms of deriving a reference block in the current picture. That is, IBC may use at least one of the inter prediction techniques described in the present disclosure. The palette mode may be considered as an example of intra coding or intra prediction. When the palette mode is applied, the sample values ​​within the picture may be signaled based on information about the palette table and the palette index.

[0060] The prediction signal generated by the predictor (including 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 Karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT means a transform obtained from a curve graph when the relationship information between pixels is represented by a curve graph. CNT refers to 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.

[0061] The quantizer 233 may quantize the transform coefficients and send them to the entropy encoder 240, and the entropy encoder 240 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 233 may rearrange the quantized transform coefficients of the block type 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. Information about the transform coefficients may be generated. The entropy encoder 240 may perform various encoding methods such as (for example) exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 240 may encode information necessary for video / image reconstruction (for example, values ​​of syntax elements, etc.) in addition to the quantized transform coefficients together or separately. The encoded information (for example, the encoded video / image information) may be transmitted or stored in units of NAL (Network Abstraction Layer) in the form of a bitstream. The video / image information may also 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 also include conventional constraint information. In the present disclosure, information and / or syntax elements sent / signaled to a decoding device from an encoding device may be included in the video / image information. The video / image information may be encoded and included in a bitstream by the above-mentioned encoding process. 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 a signal output from the entropy encoder 240 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.

[0062] 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 inverse quantization and inverse transformation to the quantized transform coefficients through the inverse quantizer 234 and the inverse transformer 235. The adder 250 adds the reconstructed residual signal to the prediction signal output from the inter-frame predictor 221 or the intra-frame predictor 222 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If the target block to be processed has no residual (such as, when the skip mode is applied), the prediction block can be used as a reconstructed block. The adder 250 can be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and as described below, can be used for inter-frame prediction of the next picture by filtering.

[0063] Furthermore, luma mapping with chroma scaling (LMCS) may be applied during the picture encoding and / or reconstruction process.

[0064] 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, in the DPB of the memory 270. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset (SAO), adaptive loop filter, bilateral filter, etc. The filter 260 can generate various types of information related to filtering, and transmit the generated information to the entropy encoder 290, as described in the subsequent description of each filtering method. The information related to filtering can be encoded by the entropy encoder 290 and output in the form of a bit stream.

[0065] The corrected 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 device, prediction mismatch between the encoding device 200 and the decoding device may be avoided, and encoding efficiency may be improved.

[0066] The DPB of the memory 270 may store the modified reconstructed picture for use as a reference picture in the inter-frame predictor 221. The memory 270 may 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 may be transmitted to the inter-frame predictor 221 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 270 may store the reconstructed samples of the reconstructed block in the current picture and may transmit the reconstructed samples to the intra-frame predictor 222.

[0067] Figure 3is a diagram schematically illustrating a configuration of a video / image decoding device to which the present disclosure is applicable.

[0068] Reference 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 332 and an intra-frame predictor 331. The residual processor 320 may include an inverse quantizer 321 and an inverse transformer 322. 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 a 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 a memory 360 as an internal / external component.

[0069] When a bit stream including video / image information is input, the decoding device 300 can reconstruct the bit stream corresponding to the bit stream in the video / image information. Figure 2 The image corresponding to the processing of the video / image information in the encoding device. For example, the decoding device 300 may derive the unit / block based on the block segmentation related information obtained from the bit stream. The decoding device 300 may use a processor applied in the encoding device to perform decoding. Therefore, for example, the decoding processor may be a coding unit, and the coding unit may be divided from a coding tree unit or a maximum coding unit according to a quadtree structure, a binary tree structure and / or a ternary tree structure. One or more transform units may be derived from the coding unit. The reconstructed image signal decoded and output by the decoding device 300 may be reproduced by a reproduction device.

[0070] The decoding device 300 may receive the Figure 2The received signal can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive information (e.g., video / image information) necessary for image reconstruction (or picture reconstruction). The video / image information may also 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 also include conventional constraint information. The decoding device may also decode the picture based on the information about the parameter set and / or the conventional constraint information. The signaled / received information and / or syntax elements described in the present disclosure may be decoded by a decoding process and obtained from the bitstream. For example, the entropy decoder 310 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CABAC, or CAVLC, and output syntax elements required for image reconstruction and quantized values ​​of transform coefficients for the residual. More specifically, the CABAC entropy decoding method can receive the bin element corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the decoding target block, or the information of the symbol / bin decoded in the previous stage to determine the context model, and perform arithmetic decoding on the bin by predicting the probability of the bin appearing according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model by using the decoded symbol / bin information for the context model of the next symbol / bin after determining the context model. The information related to prediction among the information decoded by the entropy decoder 310 can be provided to the predictor (inter-frame predictor 332 and intra-frame predictor 331), and the residual value (ie, the quantized transform coefficient and related parameter information) that has been entropy decoded in the entropy decoder 310 can be input to the residual processor 320. The residual processor 320 can derive a residual signal (residual block, residual sample, residual sample array). In addition, the information about filtering among the information decoded by the entropy decoder 310 can be provided to the filter 350. In addition, a receiver (not shown) for receiving a signal output from the encoding device may be additionally configured as an internal / external element of the decoding device 300, or the receiver may be a component of the entropy decoder 310. In addition, the decoding device according to the present disclosure 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 the entropy decoder 310, and the sample decoder may include at least one of the inverse quantizer 321, the inverse transformer 322, the adder 340, the filter 350, the memory 360, the inter-frame predictor 332, and the intra-frame predictor 331.

[0071] The dequantizer 321 may dequantize the quantized transform coefficient and output the transform coefficient. The dequantizer 321 may rearrange the quantized transform coefficient in a two-dimensional block form. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the encoding device. The dequantizer 321 may perform dequantization on the quantized transform coefficient using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficient.

[0072] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0073] The predictor may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The predictor may determine whether to apply intra prediction or inter prediction to the current block based on information on prediction output from the entropy decoder 310 and may determine a specific intra / inter prediction mode.

[0074] The predictor 330 may generate a prediction signal based on various prediction methods described below. For example, the predictor may not only apply intra prediction or inter prediction to predict a block, but may also apply intra prediction and inter prediction at the same time. This may be referred to as a combination of inter and intra prediction (CIIP). In addition, the predictor may predict a block based on an intra-block copy (IBC) prediction mode or a palette mode. The IBC prediction mode or the palette mode may be used for content image / video encoding of games, etc., such as screen content coding (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction in terms of deriving a reference block in the current picture. That is, IBC may use at least one of the inter prediction techniques described in the present disclosure. The palette mode may be considered as an example of intra coding or intra prediction. When the palette mode is applied, the sample values ​​within the picture may be signaled based on information about the palette table and the palette index.

[0075] The intra-frame predictor 331 can predict the current block by referencing samples in the current picture. Depending on the prediction mode, the referenced sample may be located in a neighbor of the current block, or its location may be separated from the current block. In intra-frame prediction, the prediction mode may include a plurality of non-directional modes and a plurality of directional modes. The intra-frame predictor 331 may determine the prediction mode to be applied to the current block by using the prediction mode applied to the neighboring blocks.

[0076] The inter-frame predictor 332 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the motion information correlation between the 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 about 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 present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter-frame predictor 332 may construct 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 may be performed based on various prediction modes, and information about the prediction may include information indicating a mode of inter-frame prediction for the current block.

[0077] The adder 340 may generate a reconstructed signal (reconstructed picture, reconstructed block, or reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block or prediction sample array) output from the predictor 330. If there is no residual of the processing target block (such as the case where the skip mode is applied), the prediction block may be used as the reconstructed block.

[0078] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next block to be processed in the current picture, and as described later, may also be output through filtering or may also be used for inter prediction of the next picture.

[0079] In addition, luminance mapping with chroma scaling (LMCS) can also be applied to the picture decoding process.

[0080] The filter 350 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 360, specifically, in the DPB of the memory 360. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0081] The (corrected) reconstructed picture stored in the DPB of the memory 360 may be used as a reference picture in the inter-frame predictor 332. The memory 360 may 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 may be transmitted to the inter-frame predictor 332 so as to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 360 may store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame predictor 331.

[0082] In this document, the embodiments described in the filter 260, the inter-frame predictor 221, and the intra-frame predictor 222 of the encoding device 200 may be the same as or respectively applied to the filter 350, the inter-frame predictor 332, and the intra-frame predictor 331 of the decoding device 300. The same may also be applied to the inter-frame predictor 332 and the intra-frame predictor 331.

[0083] In addition, as described above, when performing video encoding, prediction is performed to enhance compression efficiency. A prediction block including prediction samples of a current block (ie, a target coding block) may be generated by prediction. In this case, the prediction block includes prediction samples in a spatial domain (or a pixel domain). The prediction block is derived identically in the encoding device and the decoding device. The encoding device may enhance image coding efficiency by notifying the decoding device with a signal of information (residual information) about the residual between the original block (rather than the original sample value of the original block itself) and the prediction block. The decoding device may derive a residual block including residual samples based on the residual information, may generate a reconstructed block including reconstructed samples by adding the residual block to the prediction block, and may generate a reconstructed picture including the reconstructed block.

[0084] The residual information may be generated through a transform process and a quantization process. For example, the encoding device may derive a residual block between the original block and the prediction block, may derive a transform coefficient by performing a transform process on a residual sample (residual sample array) included in the residual block, may derive a quantized transform coefficient by performing a quantization process on the transform coefficient, and may signal the relevant residual information (through a bitstream) to the decoding device. In this case, the residual information may include value information, position information, transform technology, transform kernel, and quantization parameter of the quantized transform coefficient, etc. The decoding device may perform an inverse quantization / inverse transform process based on the residual information and may derive a residual sample (or residual block). The decoding device may generate a reconstructed picture based on the prediction block and the residual block. In addition, for the inter-frame prediction reference of subsequent pictures, the encoding device may derive a residual block by inverse quantizing / inverse transforming the quantized transform coefficient, and may generate a reconstructed picture based on this.

[0085] Figure 4 The hierarchical structure of the encoded data is exemplarily shown.

[0086] refer to Figure 4 , the coded data can be divided into a video coding layer (VCL) that manipulates the coding process of the video / image and the video / image itself, and a network abstraction layer (NAL) that exists between the VCL and the subsystem that stores and sends the coded video / image.

[0087] The VCL can generate parameter sets (picture parameter set (PPS), sequence parameter set (SPS), video parameter set (VPS), etc.) corresponding to the headers of the sequence and the picture, and the supplementary enhancement information (SEI) message required in the encoding process of the video / image. The SEI message is separated from the information about the video / image (slice data). The VCL including the information about the video / image consists of slice data and a slice header. In addition, the slice header can be called a tile group header, and the slice data can be called a tile group data.

[0088] In NAL, a NAL unit may be generated by adding header information (NAL unit header) to a raw byte sequence payload (RBSP) generated in a VCL. In this case, RBSP refers to slice data, parameter sets, SEI messages, etc. generated in a VCL. The NAL unit header may include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0089] The NAL unit plays a role of mapping a coded image to a bit sequence of a subsystem such as a file format, a real-time transport protocol (RTP), a transport stream (TS), and the like.

[0090] As shown in the figure, according to the RBSP generated in the VCL, the NAL unit can be classified into a VCL NAL unit and a non-VCL NAL unit. The VCL NAL unit may mean a NAL unit including information about an image (slice data), and the non-VCL NAL unit may mean a NAL unit including information required for decoding an image (parameter set or SEI message).

[0091] The above-mentioned VCL NAL unit and non-VCL NAL unit can be sent via the network by attaching header information according to the data standard of the subsystem. For example, the NAL unit can be converted into a predetermined standard data format such as H.266 / VVC file format, real-time transport protocol (RTP), transport stream (TS), etc., and sent through various networks.

[0092] As described above, a NAL unit may be specified with a NAL unit type according to an RBSP data structure included in a corresponding NAL unit, and information on the NAL unit type may be stored and signaled in a NAL unit header.

[0093] 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.

[0094] The following is an example of a NAL unit type specified according to a parameter set type included in a non-VCL NAL unit type. For example, the NAL unit type may be specified as an APS NAL unit as a NAL unit type including an adaptation parameter set (APS), a DPS NAL unit as a NAL unit type including a decoding parameter set (DPS), a VPS NAL unit as a NAL unit type including a video parameter set (VPS), an SPS NAL unit as a NAL unit type including a sequence parameter set (SPS), and a PPS NAL unit as a NAL unit type including a picture parameter set (PPS).

[0095] The above-mentioned NAL unit type may have syntax information for the NAL unit type, and the syntax information may be stored in the NAL unit header and signaled. For example, the syntax information may be nal_unit_type, and the NAL unit type may be specified by the nal_unit_type value.

[0096] In addition, 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 multiple slices (slice headers and slice data sets) in a picture. The picture header (picture header syntax) may include information / parameters that are generally applicable to pictures. The slice header (slice header syntax) may include information / parameters that are generally applicable to slices. APS (APS syntax) or PPS (PPS syntax) may include information / parameters that are generally applicable to one or more slices or pictures. SPS (SPS syntax) may include information / parameters that are generally applicable to one or more sequences. VPS (VPS syntax) may include information / parameters that are generally applicable to multiple layers. DPS (DPS syntax) may include information / parameters that are generally applicable to the entire video. DPS may include information / parameters related to the concatenation of a coded video sequence (CVS). The high-level syntax (HLS) in this document may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, and slice header syntax.

[0097] In this document, the image / image information encoded from the encoding device and signaled to the decoding device in the form of a bitstream includes not only the segmentation related information, intra / inter prediction information, residual information, loop filtering information, etc. in the picture, but also includes the information included in the slice header, the information included in the APS, the information included in the PPS, the information included in the SPS, the information included in the VPS and / or the information included in the DPS. In addition, the image / image information may also include NAL unit header information.

[0098] Figure 5 is a diagram illustrating an example of candidate blocks that can be used in the case of performing inter-frame prediction on a current block.

[0099] The predictors of the encoding device and the decoding device may use blocks at predetermined neighboring positions of the current block 500 as candidate blocks. Figure 5 In the example of , two blocks A0 510 and A1 520 located at the lower left side of the current block and three blocks B0 530, B1 540 and B2 550 located at the upper right and upper left sides of the current block can be selected as spatial candidate blocks. In addition, in addition to the spatially adjacent blocks, as a temporal candidate block, the above-mentioned collocated block 560 can be used as a candidate block.

[0100] In addition, regarding the reference picture used in inter-frame prediction, the reference picture used for the current block can be derived from the reference picture of the neighboring block, or can be indicated by information received from the encoding device. In the case of skip mode or merge mode, the predictor of the decoding device can use the reference picture of the neighboring block as the reference picture of the current block. In the case of applying MVP, the predictor of the decoding device can receive information indicating the reference picture of the current block.

[0101] A previously encoded / decoded picture before the current picture is stored in a memory (e.g., a decoded picture buffer (DPB)) and can be used for prediction of the current block (current picture). Pictures that can be used for inter prediction of the current block can be maintained in a reference picture list. At this time, among the reference pictures included in the reference picture list, a reference picture used for inter prediction of the current block can be indicated by a reference picture index. That is, the reference picture index can mean an index indicating a reference picture used for inter prediction of the current block among the reference pictures configuring (or constructing) the reference picture list.

[0102] An I slice is a slice decoded via intra prediction. A P slice is a slice decoded via intra prediction or inter prediction, which uses up to one motion vector and one reference picture. A B slice is a slice decoded via intra prediction or inter prediction, which uses up to two motion vectors and two reference pictures. At this time, the reference picture may include a short-term reference picture (STRP) (hereinafter referred to as "STRP") and a long-term reference picture (LTRP) (hereinafter referred to as "LTRP").

[0103] Here, STRP and LTRP may be reconstructed pictures stored in a decoded picture buffer (DPB). STRP may be marked as "for short-term reference" or "for reference". In addition, LTRP may be marked as "for long-term reference" or "for reference". For example, the POC difference between a decoding target picture and a long-term reference picture (LTRP) may be assigned a value corresponding to a range from "1" to "224-1". Here, a picture order count (POC) may indicate a picture display order.

[0104] Reference picture list 0 (hereinafter referred to as "L0" for simplicity of description) is a reference picture list for inter prediction of a P slice or a B slice. Reference picture list 1 (hereinafter referred to as "L1" for simplicity of description) can be used for inter prediction of a B slice. Therefore, when inter prediction is performed on a block of a P slice, unidirectional (or unidirectional) prediction based on L0 can be performed. And, when inter prediction is performed on a block of a B slice, bidirectional prediction can be performed based on L0 and l1.

[0105] When encoding and / or decoding is performed on a P slice and a B slice via inter-frame prediction, the encoding device and / or decoding device may construct a reference picture list. At this time, the reference picture used for inter-frame prediction may be specified by a reference picture index. As described above, the reference picture index may mean an index indicating a reference picture within a reference picture list used for inter-frame prediction.

[0106] The reference picture list may be constructed based on a reference picture set determined or generated by the encoding device and the decoding device. The reference pictures for constructing the reference picture list may be stored in a memory (e.g., a DPB). The pictures stored in the memory (previously encoded / decoded pictures before the current picture) may be managed by the encoding device and the decoding device.

[0107] In addition, as described above, in order to enhance the subjective / objective picture quality, the encoding device / decoding device may perform a loop filtering process for the reconstructed picture. The modified reconstructed picture may be generated by the loop filtering process, and the modified reconstructed picture may be output from the decoding device as a decoded picture, and may also be stored in a decoded picture buffer or memory of the encoding device / decoding device. In addition, in subsequent processing, the modified reconstructed picture may be used as a reference picture in the inter-frame prediction process when performing encoding / decoding. As described above, the loop filtering process may include a deblocking filtering process, a sampling adaptive offset (SAO) process, and / or an adaptive loop filter (ALF) process. In this case, one or a part of the deblocking filtering process, the sampling adaptive offset (SAO) process, and the adaptive loop filter (ALF) process may be applied sequentially, or all processes may be applied sequentially. For example, after applying the deblocking filtering process to the reconstructed picture, the SAO process may be performed. Alternatively, for example, after applying the deblocking filtering process to the reconstructed picture, the ALF process may be performed. This may be performed identically in the encoding device.

[0108] The deblocking filtering process is a process of removing any distortion generated at the boundaries between blocks in the reconstructed picture. For example, the deblocking filtering process can derive a target boundary from the reconstructed picture, determine the boundary strength (bS) of the target boundary, and perform deblocking filtering on the target boundary based on the determined bS. ​​The bS can be determined based on the prediction mode of two blocks adjacent to the target block, the motion vector difference, whether the reference picture is the same, whether there is a non-zero significant coefficient, etc.

[0109] The SAO process is a method of compensating the offset difference between the reconstructed picture and the original picture in units of samples. For example, the SAO process can be applied according to the offset type such as band offset, edge offset, etc. According to SAO, samples can be divided into different categories according to the SAO type, and an offset value can be added to each sample according to the category. The filter information of SAO may include information on whether SAO is applied or not, SAO type information, and SAO offset value information. For example, SAO can be applied to the reconstructed picture after applying deblocking filtering.

[0110] The adaptive loop filter (ALF) process is a process of filtering a reconstructed picture in units of samples based on filter coefficients according to a filter shape. The encoding device may compare the reconstructed picture with the original picture to determine whether to apply ALF, ALF shape and / or ALF filter coefficients, etc., and may signal the reconstructed picture to the encoding device. That is, the filtering information about the ALF process may include information about whether to apply ALF, ALF shape information, ALF filter coefficient information, etc. The ALF process may be applied to the reconstructed picture after applying deblocking filtering.

[0111] Figure 6 is a flowchart illustrating a method for performing deblocking filtering.

[0112] As described above, the encoding device / decoding device can reconstruct the picture in units of blocks. When such image reconstruction is performed in units of blocks, block distortion may occur at the boundaries between blocks in the reconstructed picture. Therefore, in order to remove the block distortion that occurs at the boundaries between blocks in the reconstructed image, the encoding device and the decoding device may use a deblocking filter.

[0113] Therefore, the encoding device / decoding device can derive the boundary between the blocks to which deblocking filtering is performed within the reconstructed image. In addition, the boundary to which deblocking filtering is performed can be referred to as an edge. In addition, the boundary to which deblocking filtering is performed can include two different types, and these two different types of boundaries can be vertical boundaries and horizontal boundaries. The vertical boundary can also be referred to as a vertical edge, and the horizontal boundary can also be referred to as a horizontal edge. The encoding device / decoding device can perform deblocking filtering on the vertical edge, and can also perform deblocking filtering on the horizontal edge.

[0114] For example, the encoding device / decoding device may derive a target boundary to be processed using filtering from a reconstructed picture ( S610 ).

[0115] In addition, the encoding device / decoding device may determine the boundary strength (bS) of the boundary on which the deblocking filtering is performed (S620). bS may also be indicated as boundary filtering strength. For example, it may be assumed that the bS value of the boundary (block edge) between block P and block Q is obtained. In this case, the encoding device / decoding device may obtain the bS value of the boundary (block edge) between block P and block Q based on block P and block Q. For example, bS may be determined according to the table shown below.

[0116] [Table 1]

[0117]

[0118]

[0119] Herein, p may indicate a sample of a block P adjacent to a deblocking filtering target boundary, and q may indicate a sample of a block Q adjacent to a deblocking filtering target boundary.

[0120] In addition, for example, p0 may indicate a sample of a block adjacent to the left or top side of the deblocking filter target boundary, and q0 may indicate a sample of a block adjacent to the right or bottom side of the deblocking filter target boundary. For example, in the case where the direction of the target boundary is vertical (i.e., in the case where the target boundary is a vertical boundary), p0 may indicate a sample of a block adjacent to the left side of the deblocking filter target boundary, and q0 may indicate a sample of a block adjacent to the right side of the deblocking filter target boundary. Alternatively, for example, in the case where the direction of the target boundary is horizontal (i.e., in the case where the target boundary is a horizontal boundary), p0 may indicate a sample of a block adjacent to the top side of the deblocking filter target boundary, and q0 may indicate a sample of a block adjacent to the bottom side of the deblocking filter target boundary.

[0121] Return to reference Figure 6 , the encoding device / decoding device can perform deblocking filtering based on bS (S630). For example, when the bS value is equal to 0, deblocking filtering is not applied to the target boundary. In addition, based on the determined bS value, the filter applied to the boundary between blocks can be determined. The filter can be classified into a strong filter and a weak filter. By using different filters to filter each of the boundaries of the positions where the possibility of block distortion in the reconstructed picture is high and the boundaries of the positions where the possibility of block distortion is low, the encoding device / decoding device can improve the encoding efficiency.

[0122] Figure 7 is a flowchart schematically illustrating an example of ALF processing. Figure 7 The ALF processing disclosed in can be performed in an encoding device and a decoding device. In this document, an encoding device may include an encoding device and / or a decoding device.

[0123] Reference Figure 7 , the encoding device derives a filter for ALF (S710). The filter may include filter coefficients. The encoding device may determine whether ALF is applied, and when it is determined that ALF is applied, a filter including filter coefficients for ALF may be derived. Information for deriving a filter (coefficient) for ALF or a filter (coefficient) for ALF may be referred to as an ALF parameter. Information about whether ALF is applied (i.e., an ALF enable flag) and ALF data for deriving the filter may be signaled from the encoding device to the decoding device. ALF data may include information for deriving a filter for ALF. In addition, for example, for hierarchical control of ALF, an ALF enable flag may be signaled at the SPS, picture header, slice header, and / or CTB level, respectively.

[0124] In order to derive the filter for ALF, the activity and / or directionality of the current block (or ALF target block) is derived, and the filter can be derived based on the activity and / or directionality. For example, ALF processing can be applied in units of 4×4 blocks (based on the luminance component). The current block or ALF target block can be, for example, a CU, or can be a 4×4 block within a CU. Specifically, for example, a filter for ALF can be derived based on a first filter derived from information included in the ALF data and a predefined second filter, and the encoding device can select one of the filters based on the activity and / or directionality. The encoding device can use the filter coefficients included in the selected filter for ALF.

[0125] The encoding device performs filtering based on the filter (S720). The modified reconstructed samples can be derived based on the filtering. For example, the filter coefficients in the filter can be arranged or allocated according to the filter shape, and the filtering can be performed on the reconstructed samples in the current block. Here, the reconstructed samples in the current block can be reconstructed samples after the deblocking filtering process and the SAO process are completed. For example, one filter shape can be used, or one filter shape can be selected and used from a plurality of predetermined filter shapes. For example, the filter shape applied to the luminance component and the filter shape applied to the chrominance component can be different. For example, a 7×7 diamond filter shape can be applied to the luminance component, and a 5×5 diamond filter shape can be applied to the chrominance component.

[0126] Figure 8 Examples of filter shapes used for ALF are illustrated. C0 to C11 of (a) and C0 to C5 of (b) may be filter coefficients depending on the position within each filter shape.

[0127] Figure 8 (a) shows the shape of a 7×7 diamond filter, and Figure 8 (b) shows the shape of a 5×5 diamond filter. Figure 8In 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 this document, the position and / or unit to which the filter coefficient is assigned according to the filter shape of the ALF can be referred to as a filter tap. In this case, a 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 a center filter tap. The same filter coefficient can be assigned to two filter taps of the same n value at positions corresponding to each other relative to the center filter tap. For example, in the case of a 7×7 diamond filter shape, 25 filter taps are included, and since the filter coefficients C0 to C11 are assigned in a centrally symmetrical form, only 13 filter coefficients can be used to assign filter coefficients to the 25 filter taps. In addition, for example, in the case of a 5×5 diamond filter shape, 13 filter taps are included, and since the filter coefficients C0 to C5 are assigned in a centrally symmetrical form, only 7 filter coefficients can be used to assign filter coefficients to the 13 filter taps. For example, in order to reduce the amount of data of the information about the filter coefficients that is signaled, 12 filter coefficients out of the 13 filter coefficients of a 7×7 diamond filter shape may be (explicitly) signaled, and one filter coefficient may be (implicitly) derived. In addition, for example, 6 filter coefficients out of the 7 filter coefficients of a 5×5 diamond filter shape may be (explicitly) signaled, and one filter coefficient may be (implicitly) derived.

[0128] According to an embodiment of the present document, ALF parameters for ALF processing may be signaled through an adaptive parameter set (APS). The ALF parameters may be derived from filter information for ALF or ALF data.

[0129] ALF is a loop filtering technique that can be applied to 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). A high-level design for an ALF tool can include syntax elements accessible from the SPS and / or slice header (or tile group header).

[0130] In addition, the picture header includes syntax elements that apply to the picture header, and the syntax elements can apply to all slices of the picture related to the picture header. When a specific syntax element applies only to a specific slice, the specific syntax element should be signaled from the slice header instead of the picture header.

[0131] In the prior art, signaling of control flags and parameters for enabling or disabling multiple tools for picture encoding or decoding exists in the picture header and is overwritten in the slice header. This method provides flexibility to allow tool control to be performed at both the picture level and the slice level. However, when this method is used, it may burden the decoder because the slice header needs to be verified after the picture header is verified.

[0132] Therefore, an embodiment of the present disclosure proposes indication information indicating whether at least one tool is applied at a picture level or a slice level. At this time, the indication information may be included in any one of a sequence parameter set (SPS) and a picture parameter set (PPS). That is, when a specific tool is activated (or enabled) within a CLV, an indication or flag indicating whether the specific tool is applied at a picture level or a slice level may be signaled from a parameter set such as an SPS or a PPS. Although the indication or flag may correspond to one tool, the present disclosure will not be limited thereto. For example, an indication or flag indicating whether all tools, not just specific tools, are applied at a picture level or a slice level may be signaled from a parameter set such as an SPS or a PPS.

[0133] Although the control flags and parameters for enabling or disabling a tool may be signaled at a picture level or a slice level, signaling is not performed at both the picture level and the slice level. For example, in the case where indication information indicating whether a specific tool is applied at a picture level is obtained, the control flags and parameters for enabling or disabling a specific tool may be signaled only at a picture level. Similarly, in the case where indication information indicating whether a specific tool is applied at a slice level is obtained, the control flags and parameters for enabling or disabling a specific tool may be signaled only at a slice level.

[0134] Additionally, for example, a tool that is specified to be applied at the picture level from a particular parameter set may be specified to be applied at the slice level from another parameter set of the same type.

[0135] For example, the PPS syntax including the indication information may be as shown in the following table.

[0136] [Table 2]

[0137]

[0138] The semantics of the syntax elements included in the syntax of Table 2 may be indicated as follows, for example, as shown in Table 3.

[0139] [Table 3]

[0140]

[0141]

[0142] Referring to the table proposed above, the indication information may include a flag indicating whether the signaling of the reference picture list is applied at the picture level or the slice level. For example, the indication information may specify whether the information related to the signaling of the reference picture list appears (or exists) in the picture header or in the slice header. For example, the flag may be indicated as rpl_present_in_ph_flag. Based on the case where the value of the corresponding flag is equal to 1, the information related to the signaling of the reference picture list is present in the picture header. And, based on the case where the value of the corresponding flag is equal to 0, the information related to the signaling of the reference picture list is present in the slice header.

[0143] In addition, the indication information may include a flag indicating whether a sample adaptive offset (SAO) process is applied at a picture level or a slice level. For example, the indication information may specify whether the information related to the SAO process appears (or exists) in a picture header or in a slice header. For example, the flag may be indicated as sao_present_in_ph_flag. Based on the case where the value of the corresponding flag is equal to 1, the information related to the SAO process is present in the picture header. And, based on the case where the value of the corresponding flag is equal to 0, the information related to the SAO process is present in the slice header.

[0144] In addition, the indication information may include a flag indicating whether an adaptive loop filter (ALF) process is applied at a picture level or a slice level. For example, the indication information may specify whether information related to the ALF process appears (or exists) in a picture header or in a slice header. For example, the flag may be indicated as alf_present_in_ph_flag. Based on the case where the value of the corresponding flag is equal to 1, the information related to the ALF process is present in the picture header. And, based on the case where the value of the corresponding flag is equal to 0, the information related to the ALF process is present in the slice header.

[0145] In addition, the indication information may include at least one flag indicating whether the deblocking process is applied at the picture level or at the slice level. For example, based on the at least one flag, information related to the deblocking process may appear in (or may exist in) any one of the picture header and the slice header. For example, at least one flag may be indicated as deblocking_filter_ph_override_enabled_flag or deblocking_filter_sh_override_enabled_flag. For example, based on the case where the value of at least one flag is equal to 1, a flag indicating whether parameters related to the deblocking process are present in the picture header may be present in the picture header. And, based on the case where the value of at least one flag is equal to 0, a flag indicating whether parameters related to the deblocking process are present in the picture header may not be present in the picture header.

[0146] Alternatively, based on the case where the value of at least one flag is equal to 1, the flag indicating whether the parameter related to the deblocking process exists in the slice header may exist in the slice header. And, based on the case where the value of at least one flag is equal to 0, the flag indicating whether the parameter related to the deblocking process exists in the slice header may not exist in the slice header. At this time, the values ​​of deblocking_filter_ph_override_enabled_flag and deblocking_filter_sh_override_enabled_flag may not both be equal to 1.

[0147] In addition, the picture header syntax can be as shown in the following table.

[0148] [Table 4]

[0149]

[0150] The semantics of the syntax elements included in the syntax of Table 4 may be indicated as follows, for example, as shown in Table 5 below.

[0151] [Table 5]

[0152]

[0153] Referring to the table given above, when the value of deblocking_filter_ph_override_enabled_flag corresponding to the flag indicating whether the deblocking process is applied at the picture level is equal to 1, pic_deblocking_filter_override_present_flag may be signaled. When the value of pic_deblocking_filter_override_present_flag is equal to 1, pic_deblocking_filter_override_flag corresponding to the flag indicating whether the parameters related to the deblocking process are present in the picture header may be present in the picture header. Alternatively, when the value of pic_deblocking_filter_override_present_flag is equal to 0, pic_deblocking_filter_override_flag corresponding to the flag indicating whether the parameters related to the deblocking process are present in the picture header may not be present in the picture header.

[0154] In addition, when the value of pic_deblocking_filter_override_flag corresponding to the flag indicating whether the parameters related to the deblocking process are present in the picture header is equal to 1, the deblocking parameters may be present (or may be present) in the picture header. And, when the value of pic_deblocking_filter_override_flag corresponding to the flag indicating whether the parameters related to the deblocking process are present in the picture header is equal to 0, the deblocking parameters may not be present (or may not be present) in the picture header.

[0155] In addition, when the value of pic_deblocking_filter_disabled_flag is equal to 1, deblocking filtering may not be applied to the slice associated with the picture header. And, when the value of pic_deblocking_filter_disabled_flag is equal to 0, deblocking filtering may be applied to the slice associated with the picture header.

[0156] In addition, pic_beta_offset_div2 and pic_tc_offset_div2 may specify deblocking parameter offsets of β and tC (values ​​divided by 2) for slices associated with a picture header, respectively. The values ​​of pic_beta_offset_div2 and pic_tc_offset_div2 may all be in the range of -6 to 6.

[0157] Additionally, the slice header syntax can be as shown in the following table.

[0158] [Table 6]

[0159]

[0160]

[0161] The semantics of the syntax elements included in the syntax of Table 6 may be indicated as follows, for example, as shown in Table 7.

[0162] [Table 7]

[0163]

[0164]

[0165] Referring to the table given above, when the value of deblocking_filter_sh_override_enabled_flag corresponding to the flag indicating whether the deblocking process is applied at the slice level is equal to 1, slice_deblocking_filter_override_present_flag may be signaled. When the value of slice_deblocking_filter_override_present_flag is equal to 1, slice_deblocking_filter_override_flag corresponding to the flag indicating whether the parameters related to the deblocking process are present in the slice header may be present in the slice header. Alternatively, when the value of slice_deblocking_filter_override_present_flag is equal to 0, slice_deblocking_filter_override_flag corresponding to the flag indicating whether the parameters related to the deblocking process are present in the slice header may not be present in the slice header.

[0166] In addition, when the value of slice_deblocking_filter_override_flag corresponding to the flag indicating whether the parameters related to the deblocking process exist in the slice header is equal to 1, the deblocking parameters may be present (or may be present) in the slice header. And, when the value of slice_deblocking_filter_override_flag corresponding to the flag indicating whether the parameters related to the deblocking process exist in the slice header is equal to 0, the deblocking parameters may not be present (or may not be present) in the slice header.

[0167] In addition, when the value of slice_deblocking_filter_disabled_flag is equal to 1, the deblocking filter may not be applied to the slice associated with the slice header. And, when the value of slice_deblocking_filter_disabled_flag is equal to 0, the deblocking filter may be applied to the slice associated with the slice header.

[0168] In addition, slice_beta_offset_div2 and slice_tc_offset_div2 may specify deblocking parameter offsets of β and tC (values ​​divided by 2) for a slice, respectively. The values ​​of slice_beta_offset_div2 and slice_tc_offset_div2 may all be in the range of -6 to 6.

[0169] Fig. 9is a flowchart illustrating the operation of the image encoding device according to the embodiment, and Fig.10 is a block diagram illustrating a configuration of an image encoding apparatus according to an embodiment.

[0170] Fig. 9 The method disclosed in can be Figure 2 or Fig.10 The encoding device disclosed in is executed. Fig. 9 The S910 in Figure 2 The residual processor 230 shown in FIG. 1 is executed, and S920 may be performed by Figure 2 The adder 250 shown in FIG. Fig. 9 The S930 in Figure 2 The filter 260 shown in FIG. 1 is executed, and S940 and S950 can be performed by Figure 2 The entropy encoder 240 shown in FIG.

[0171] In addition, the operations according to S910 to S950 are based on the above Figures 1 to 8 Therefore, for the sake of simplicity, the description of Figures 1 to 8 A detailed description of the overlap.

[0172] Reference Fig. 9 , the encoding device according to the embodiment may derive the residual sample of the current block (S910). For example, the encoding device may derive the residual sample based on the predicted sample and the original sample. For example, the encoding device may derive the residual sample based on the comparison between the original sample and the modified reconstructed sample. In addition, the encoding device may derive the predicted sample of the current block based on the prediction mode. In this case, various prediction methods disclosed in this specification such as inter-frame prediction or intra-frame prediction may be applied.

[0173] The encoding apparatus according to the embodiment may generate a reconstructed sample based on the residual sample (S920). For example, the adder 250 of the encoding apparatus may add the reconstructed residual sample to the prediction sample output from the predictor 220 to generate the reconstructed sample.

[0174] The encoding device according to the embodiment may derive filter coefficients (S930) for performing an adaptive loop filter (ALF) process on the reconstructed sample. For example, the encoding device may derive parameters related to the ALF that can be applied to the filtering of the reconstructed sample. The filter 260 of the encoding device may generate a modified reconstructed sample by performing an SAO process on the reconstructed sample.

[0175] The encoding apparatus according to the embodiment may generate information related to the ALF process based on the filter coefficient ( S940 ).

[0176] The encoding device according to the embodiment may generate indication information (S950) including a first flag related to whether the ALF process is applied at the picture level or the slice level. For example, the indication information may be included in one of a sequence parameter set (SPS) and a picture parameter set (PPS). The first flag may indicate in which of the picture header and the slice header the information related to the ALF process exists. Based on the case where the value of the first flag is equal to 1, the information related to the ALF process may exist (or may appear) in the picture header. And, based on the case where the value of the first flag is equal to 0, the information related to the ALF process may exist (or may appear) in the slice header.

[0177] For example, the indication information may further include a second flag related to whether the signaling of the reference picture list is applied at the picture level or the slice level. Based on the case where the value of the second flag is equal to 1, the information related to the signaling of the reference picture list may be present in the picture header. And, based on the case where the value of the second flag is equal to 0, the information related to the signaling of the reference picture list may be present in the slice header.

[0178] For example, the indication information may further include a third flag related to whether a sample adaptive offset (SAO) process is applied at a picture level or a slice level. Based on the case where the value of the third flag is equal to 1, information related to the SAO process may be present in the picture header. And, based on the case where the value of the third flag is equal to 0, information related to the SAO process may be present in the slice header.

[0179] For example, the indication information may further include a fourth flag related to whether the deblocking parameter of the deblocking filtering process exists (or appears) in the picture header or the slice header. Based on the case where the value of the fourth flag is equal to 1, the deblocking parameter may exist in the picture header. And, based on the case where the value of the fourth flag is equal to 0, the deblocking parameter may not exist in the picture header.

[0180] For example, the encoding device may encode image information including indication information and information related to the SAO process (S950). For example, the filter 260 of the encoding device may generate information related to the ALF process, information related to the SAO process, or information related to the deblocking filtering process. Alternatively, for example, the predictor 220 of the encoding device may generate information related to the signaling of the reference picture list. The entropy encoder 240 of the encoding device may encode indication information including the first flag, the second flag, the third flag, or the fourth flag. In addition, the entropy encoder 240 of the encoding device may encode information related to the ALF process, information related to the SAO process, information related to the deblocking process, or information related to the reference picture list.

[0181] In addition, the image information may include prediction information of the current block. The prediction information may include information about an inter prediction mode or an intra prediction mode performed on the current block. In addition, the image information may include residual information generated from the original sample by the residual processor 230 of the encoding device.

[0182] In addition, the bit stream in which the image information is encoded can be sent to the decoding device via a network or a (digital) storage medium. Herein, the network may include a broadcast network and / or a communication network, etc., and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc.

[0183] Fig.11 is a flowchart illustrating the operation of an image decoding device according to an embodiment, and Fig.12 is a block diagram illustrating a configuration of an image decoding apparatus according to an embodiment.

[0184] Fig.11 The method disclosed in can be Figure 3 or Fig.12 More specifically, Fig.11 The S1110 and S1120 in Figure 3 The entropy decoder 310 shown in FIG. 1 is executed, and S1130 may be performed by Figure 3 The adder 340 shown in FIG. Fig.11 S1140 to S1150 in Figure 3 In addition, the operations according to S1110 to S1150 are based on the above Figures 1 to 8 Therefore, for the sake of simplicity, the description of Figures 1 to 8 A detailed description of the overlap.

[0185] The decoding device according to the embodiment may obtain indication information including a first flag related to whether an adaptive loop filter (ALF) process to be applied to the current block is applied at a picture level or a slice level and residual information (S1110). For example, the decoding device may also include information related to prediction.

[0186] For example, the indication information may be included in one of a sequence parameter set (SPS) and a picture parameter set (PPS). Alternatively, for example, the indication information may include a second flag related to whether the signaling of the reference picture list is applied at a picture level or a slice level. For example, the indication information may include a third flag related to whether a sample adaptive offset (SAO) process is applied at a picture level or a slice level. Alternatively, for example, the indication information may include a fourth flag related to whether a deblocking parameter of a deblocking filtering process is present (or appears) in a picture header or a slice header.

[0187] The decoding device according to the embodiment may parse information related to the ALF process from the picture header or the slice header based on the first flag (S1120). For example, based on the case where the value of the first flag is equal to 1, the decoding device may parse information related to the ALF process from the picture header. And, based on the case where the value of the first flag is equal to 0, the decoding device may parse information related to the ALF process from the slice header.

[0188] Alternatively, the decoding device according to the embodiment may parse information related to the signaling of the reference picture list from the picture header or the slice header based on the second flag. For example, based on the case where the value of the second flag is equal to 1, the decoding device may parse information related to the signaling of the reference picture list from the picture header. And, based on the case where the value of the second flag is equal to 0, the decoding device may parse information related to the signaling of the reference picture list from the slice header.

[0189] Alternatively, the decoding device according to the embodiment may parse information related to the SAO process from the picture header or the slice header based on the third flag. For example, based on the case where the value of the third flag is equal to 1, the decoding device may parse information related to the SAO process from the picture header. And, based on the case where the value of the third flag is equal to 0, the decoding device may parse information related to the SAO process from the slice header.

[0190] Alternatively, the decoding device according to the embodiment may parse the deblocking parameter from the picture header or the slice header based on the fourth flag. For example, based on the case where the value of the fourth flag is equal to 1, the decoding device may parse the deblocking parameter from the picture header. And, based on the case where the value of the fourth flag is equal to 0, the decoding device may not parse the deblocking parameter from the picture header.

[0191] The decoding device according to the embodiment may generate a reconstructed sample of the current block based on the residual information (S1130). The decoding device may derive the predicted sample of the current block based on the information related to the prediction included in the image information. The decoding device may derive the residual sample based on the residual information included in the image information. The decoding device may generate a reconstructed sample based on the predicted sample and the residual sample. A reconstructed block and a reconstructed picture may be derived based on the reconstructed sample.

[0192] The decoding device according to the embodiment may derive filter coefficients based on information related to the ALF process (S1140). For example, the decoding device may derive filter coefficients for ALF. A filter may include a set of filter coefficients. The filter or filter coefficients may be derived based on ALF information.

[0193] The decoding device according to the embodiment may generate a modified reconstructed sample of the current block based on the reconstructed sample and the filter coefficient (S1150). For example, the filter 350 of the decoding device may generate a modified reconstructed sample by performing an ALF process on the reconstructed sample.

[0194] Although the method has been described based on a flowchart that lists steps or blocks in sequence in the above-mentioned embodiments, the steps of this document are not limited to a specific order, and specific steps can be performed in different steps or in a different order or simultaneously relative to the above-mentioned steps. In addition, it will be understood by a person of ordinary skill in the art that the steps in the flowchart are not exclusive, and another step may be included therein, or one or more steps in the flowchart may be deleted without affecting the scope of the present disclosure.

[0195] The above-mentioned method according to the present disclosure can be implemented in the form of software, and the encoding device and / or decoding device according to the present disclosure can be included in a device for performing image processing (e.g., TV, computer, smart phone, set-top box, display device, etc.).

[0196] When the embodiments of the present disclosure are implemented by software, the above-mentioned methods can be implemented by modules (processing or functions) that perform the above-mentioned functions. The module can be stored in a memory and executed by a processor. The memory can be installed inside or outside the processor and can be connected to the processor via various well-known devices. The processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits and / or data processing devices. The memory may include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium and / or other storage devices. In other words, according to the embodiments of the present disclosure, it can be implemented and executed on a processor, a microprocessor, a controller or a chip. For example, the functional units illustrated in the corresponding figures can be implemented and executed on a computer, a processor, a microprocessor, a controller or a chip. In this case, information about the implementation (e.g., information about instructions) or an algorithm can be stored in a digital storage medium.

[0197] In addition, the decoding device and the encoding device of the embodiment of the present document can be included in a multimedia broadcast transceiver, 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 video communication, a mobile streaming device, a storage medium, a portable camera, a video on demand (VoD) service provider, an over-the-top (OTT) video device, an Internet streaming service provider, a 3D video device, a virtual reality (VR) device, an augmented reality (AR) device, an image phone video device, a vehicle terminal (e.g., a vehicle (including an autonomous vehicle) terminal, an aircraft terminal or a ship terminal) and a medical video device; and can be used to process image signals or data. For example, an OTT video device can include a game console, a Blueray player, a networked TV, a home theater system, a smart phone, a tablet PC, and a digital video recorder (DVR).

[0198] In addition, the processing method of the embodiment of the application of 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. The multimedia data with a data structure according to the embodiment of this document can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices and distributed storage devices storing computer-readable data. The computer-readable recording medium may include, for example, a Blu-ray disc (BD), a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. The computer-readable recording medium also includes a medium implemented in the form of a carrier wave (e.g., transmission on the Internet). In addition, the bit stream generated by the encoding method can be stored in a computer-readable recording medium, or can be transmitted through a wired or wireless communication network.

[0199] In addition, the embodiments of the present document can be implemented as a computer program product based on a program code, and the program code can be executed on a computer according to the embodiments of the present document. The program code can be stored on a computer readable carrier.

[0200] Fig.13 An example of a content streaming system to which the embodiments disclosed in this document can be applied is shown.

[0201] Reference Fig.13 The content streaming system applying the implementation mode of this document may mainly include an encoding server, a streaming server, a network server, a media storage, a user device and a multimedia input device.

[0202] The encoding server is used to compress the content input from the multimedia input device such as a smart phone, a camera, a camcorder, etc. into digital data, generate a bit stream, and transmit it to the streaming server. As another example, in the case where the multimedia input device such as a smart phone, a camera, a camcorder, etc. directly generates a bit stream, the encoding server can be omitted.

[0203] The bitstream may be generated by the encoding method or the bitstream generating method to which the embodiments of this document are applied, and the streaming server may temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0204] The streaming server transmits multimedia data to the user device based on the user's request through the network server, which acts as a tool to inform the user of what services exist. When the user requests the service the user wants, the network server transfers the request to the streaming server, and the streaming server transmits the multimedia data to the user. In this regard, the content streaming system may include a separate control server, and in this case, the control server is used to control the commands / responses between the various devices in the content streaming system.

[0205] The streaming server may receive content from a media storage device and / or an encoding server. For example, in the case where the content is received from the encoding server, the content may be received in real time. In this case, the streaming server may store the bitstream for a predetermined period of time to smoothly provide a streaming service.

[0206] For example, 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., watch-type terminals (smart watches), glasses-type terminals (smart glasses), head-mounted displays (HMDs)), digital TVs, desktop computers, digital signage, etc.

[0207] Each server in the content streaming system may be operated as a distributed server, and in this case, data received by each server may be processed in a distributed manner.

[0208] The claims in this specification can be combined in various ways. For example, the technical features in the method claims of this specification can be combined to be implemented or performed in a device, and the technical features in the device claims can be combined to be implemented or performed in a method. In addition, the technical features in the method claims and the device claims can be combined to be implemented or performed in a device. In addition, the technical features in the method claims and the device claims can be combined to be implemented or performed in a method.

Claims

1. A decoding device for image decoding, the decoding device comprising: Memory; as well as at least one processor, the at least one processor connected to the memory, the at least one processor configured to: Obtaining image information including residual information and a picture parameter set (PPS), wherein the PPS includes ALF-related flag information related to whether an adaptive loop filter (ALF) process is applied at a picture level or a slice level; Parsing information related to the ALF process from a picture header or a slice header based on the ALF related flag information; Generating a reconstructed sample for the current block based on the residual information; deriving filter coefficients based on the information related to the ALF process; and generating modified reconstructed samples for the current block based on the reconstructed samples and the filter coefficients, wherein the information related to the ALF process is parsed from only one of the picture header or the slice header, The picture header includes information commonly applied to all slices in the picture. wherein the PPS includes information commonly applied to one or more pictures, wherein, based on the value of the ALF-related flag information being equal to 1, parsing the information related to the ALF process from the picture header, and Wherein, based on the value of the ALF-related flag information being equal to 0, the information related to the ALF process is parsed from the slice header.

2. A coding device for image coding, the coding device comprising: Memory; as well as at least one processor, the at least one processor connected to the memory, the at least one processor configured to: Derive residual samples for the current block; generating a reconstructed sample based on the residual sample; deriving filter coefficients for performing an adaptive loop filter (ALF) process on the reconstructed samples; generating information related to the ALF process based on the filter coefficients; Generating ALF related flag information related to whether the ALF process is applied at the picture level or the slice level; as well as Encoding image information including residual information and a picture parameter set PPS, wherein the PPS includes the ALF related flag information, The ALF related flag information indicates in which header of the picture header and the slice header the information related to the ALF process exists, wherein the information related to the ALF process is present in only one of the picture header or the slice header, The picture header includes information commonly applied to all slices in the picture. wherein the PPS includes information commonly applied to one or more pictures, wherein, based on the value of the ALF-related flag information being equal to 1, the information related to the ALF process is included in the picture header, and Wherein, based on the value of the ALF-related flag information being equal to 0, the information related to the ALF process is included in the slice header.

3. A device for transmitting data for an image, the device comprising: at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on the following operations: deriving residual samples for a current block, generating reconstructed samples based on the residual samples, deriving filter coefficients for performing an adaptive loop filter ALF process on the reconstructed samples, generating information related to the ALF process based on the filter coefficients, generating ALF-related flag information related to whether the ALF process is applied at a picture level or a slice level, and generating the bitstream by encoding image information including residual information and a picture parameter set PPS, wherein the PPS includes the ALF-related flag information; and a transmitter configured to transmit the data including the bit stream, The ALF related flag information indicates in which of the picture header and the slice header the information related to the ALF process exists, wherein the information related to the ALF process is present in only one of the picture header or the slice header, The picture header includes information commonly applied to all slices in the picture. wherein the PPS includes information commonly applied to one or more pictures, wherein, based on the value of the ALF-related flag information being equal to 1, the information related to the ALF process is included in the picture header, and Wherein, based on the value of the ALF-related flag information being equal to 0, the information related to the ALF process is included in the slice header.

Images