Image coding method and apparatus using deblocking filtering

Abstract

The present invention relates to an image coding method and apparatus using deblocking filtering. According to the present document, a method by which a decoding apparatus decodes an image includes the following steps: generating a reconstructed picture based on prediction samples of a coding block; deriving a boundary strength (BS) of a boundary of the coding block in the reconstructed picture; performing deblocking filtering on the boundary of the coding block based on the boundary strength; and deriving a modified reconstructed picture for the reconstructed picture based on the deblocking filtering, wherein the boundary strength is derived based on prediction modes of a first block and a second block adjacent to the boundary of the coding block, and the prediction mode of the first block or the second block is derived based on whether the prediction mode of the first block or the second block is a current picture reference (CPR) mode to be coded with reference to a current picture.

Description

[0001] This application is a divisional application of the patent application with the international application date of January 2, 2020, filed with the China Patent Office on July 20, 2021, application number 202080010032.3 (international application number PCT / KR2020 / 000025), and the invention name being “Image coding method and device using deblocking filtering”. Technical Field

[0002] This document relates to image coding technology, and more particularly, to an image coding method and apparatus using a deblocking filtering process. Background Art

[0003] Recently, the demand for high-resolution and high-quality images and videos such as ultra-high-definition (HUD) images and 4K or 8K or larger videos has been increasing in various fields. As image and video data becomes higher in resolution and higher in quality, the amount of information or the number of bits transmitted increases compared to existing image and video data. Therefore, if a medium such as an existing wired or wireless broadband line is used to transmit image data or an existing storage medium is used to store image and video data, the transmission cost and storage cost increase.

[0004] In addition, there has been a recent increase in interest and demand for immersive media such as virtual reality (VR), artificial reality (AR) content, or holograms, and the broadcasting of images and videos having image characteristics different from those of real images, such as game images, has increased.

[0005] Therefore, in order to efficiently compress and transmit or store and play back information of high-resolution and high-quality images and videos having such various characteristics, efficient image and video compression technology is required. Summary of the Invention

[0006] Technical issues

[0007] One object of this document is to provide a method and apparatus for improving image coding efficiency.

[0008] Another object of this document is to provide a method and apparatus for improving the image quality of an image.

[0009] Still another object of the present document is to provide a method and apparatus for designing boundary strength in consideration of characteristics of blocks in performing a deblocking filtering process.

[0010] Technical Solution

[0011] An exemplary embodiment of this document provides an image decoding method performed by a decoding device. The method includes: generating a reconstructed picture based on prediction samples of a coding block, deriving a boundary strength (bs) of a boundary of the coding block in the reconstructed picture, performing deblocking filtering on the boundary of the coding block based on the boundary strength, and deriving a modified reconstructed picture for the reconstructed picture based on the deblocking filtering, wherein the boundary strength is derived based on a prediction mode of a first block and a second block adjacent to the boundary of the coding block, and is derived based on whether the prediction mode of the first block or the prediction mode of the second block is a current picture reference (CPR) mode coded with reference to a current picture.

[0012] Another exemplary embodiment of the present document provides an image encoding method performed by an encoding device. The method includes: generating a reconstructed picture based on prediction samples of a coding block, deriving a boundary strength (bs) of a boundary of the coding block in the reconstructed picture, performing deblocking filtering on the boundary of the coding block based on the boundary strength, deriving a modified reconstructed picture for the reconstructed picture based on the deblocking filtering, and encoding image information including information about the coding block, wherein the boundary strength is derived based on prediction modes of a first block and a second block adjacent to the boundary of the coding block, and is derived based on whether the prediction mode of the first block or the prediction mode of the second block is a current picture reference (CPR) mode coded with reference to a current picture.

[0013] Yet another exemplary embodiment of the present disclosure provides a digital storage medium for storing encoded image information for enabling an image decoding method to be executed, as a computer-readable digital storage medium.

[0014] Beneficial effects

[0015] This file can improve overall image / video compression efficiency.

[0016] This file can improve the image quality of images / videos.

[0017] This document can design boundary strength by considering the characteristics of blocks during the deblocking filtering process to effectively remove artifacts at the boundaries between blocks, thereby improving subjective / objective image quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 An example of a video / image coding system suitable for use with the exemplary embodiments of this document is schematically illustrated.

[0019] Figure 2 is a diagram for schematically explaining the configuration of a video / image encoding device applicable to an exemplary embodiment of this document.

[0020] Figure 3is a diagram for schematically explaining a configuration of a video / image decoding device applicable to an exemplary embodiment of this document.

[0021] Figure 4 An example of an illustrative picture decoding process to which exemplary embodiments of this document are applicable is illustrated.

[0022] Figure 5 An example of an illustrative picture encoding process to which exemplary embodiments of this document are applicable is illustrated.

[0023] Figure 6 Exemplary embodiments of a method for performing a deblocking filtering process are exemplarily illustrated.

[0024] Figure 7 is a flowchart schematically illustrating an encoding method that can be performed by an encoding device according to an exemplary embodiment of this document.

[0025] Figure 8 is a flowchart schematically illustrating a decoding method that can be performed by a decoding device according to an exemplary embodiment of this document.

[0026] Figure 9 An example of a content streaming system to which the exemplary embodiments disclosed in this document are applicable is illustrated. DETAILED DESCRIPTION

[0027] This document can be modified in various ways and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit this document to specific embodiments. The terms commonly used in this specification are used to describe specific embodiments rather than to limit the technical spirit of this document. Unless otherwise clearly indicated in the context, singular expressions include plural expressions. Terms such as "including" or "having" in this specification should be understood to indicate the presence of characteristics, numbers, steps, operations, elements, components, or combinations thereof described in this specification, without excluding the possibility of the presence or addition of one or more characteristics, numbers, steps, operations, elements, components, or combinations thereof.

[0028] In addition, to facilitate descriptions related to different feature functions, the elements in the drawings described in this document are illustrated independently. This does not mean that each element is implemented as separate hardware or separate software. For example, at least two elements can be combined to form a single element, or a single element can be divided into multiple elements. Embodiments in which elements are combined and / or separated are also included in the scope of the rights of this document unless it deviates from the essence of this document.

[0029] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Hereinafter, in the accompanying drawings, the same reference numerals are used for the same elements, and redundant descriptions of the same elements may be omitted.

[0030] Figure 1 An example of a video / image coding system to which embodiments of this document can be applied is schematically illustrated.

[0031] Reference Figure 1 The video / image coding system may include a first device (source device) and a second device (receiver device). The source device may transmit the encoded video / image information or data to the receive device in the form of a file or stream transmission via a digital storage medium or a network.

[0032] 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.

[0033] The video source can obtain the video / image by capturing, synthesizing, or generating a video / image. The video source may include a video / image capture device and / or a video / image generation device. The video / image capture device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generation device may include, for example, a computer, a tablet computer, and a smart phone, and may (electronically) generate the video / image. For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capture process may be replaced by a process that generates relevant data.

[0034] An encoding device can encode input video / images. It can perform a series of processes such as prediction, transformation, and quantization for compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0035] The transmitter can transmit the encoded video / image information or data, output as a bitstream, to a receiver in a receiving device via a digital storage medium or network in the form of a file or streaming. Digital storage media can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter can include components for generating a media file in a predetermined file format and can also include components for transmitting via a broadcast / communication network. The receiver can receive / extract the bitstream and transmit the received / extracted bitstream to a decoding device.

[0036] The decoding device may decode a video / image by performing a series of processes such as inverse quantization, inverse transformation, prediction, etc. corresponding to the operation of the encoding device.

[0037] The renderer can render the decoded video / image, and the rendered video / image can be displayed on a display.

[0038] This document relates to video / image coding. For example, the methods / implementations disclosed in this document 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 next-generation video / image coding standards (e.g., H.267 or H.268, etc.).

[0039] In this document, various embodiments related to video / image coding may be provided, and unless otherwise specified, these embodiments may be combined with each other and performed.

[0040] In this document, video may mean a collection of a series of images over time. Generally, a picture means a unit of an image representing a specific time region, and a slice / tile is a unit that constitutes a part of a picture in coding. A slice / tile may include one or more coding tree units (CTUs). A picture may be composed of one or more slices / tiles. A picture may be composed of one or more tile groups. A tile group may include one or more tiles. A brick may represent a rectangular area of ​​a CTU row within a tile in a picture. A tile may be divided into multiple bricks, each consisting of one or more CTU rows within a tile. A tile that is not divided into multiple bricks may also be referred to as a brick. Block scanning may be a specific order sorting of the CTUs of a partitioned picture as follows: continuously sorting the CTUs in the block by CTU raster scanning, continuously sorting the block within the tile by raster scanning of the block of the tile, and continuously sorting the tiles in the picture by raster scanning of the tile of the picture. 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 the picture parameter set. A tile row is a rectangular area of ​​a CTU whose height is specified by a syntax element in the picture parameter set and whose width is equal to the width of the picture. Tile scanning can be a specific sequential ordering of CTUs of a partitioned picture as follows: CTUs can be sorted continuously in tiles by CTU raster scanning, while tiles in a picture can be sorted continuously by raster scanning of tiles of a picture. A slice includes an integer number of block portions of a picture that can be exclusively contained in a single NAL unit. A slice can consist of multiple complete tiles or only of a continuous sequence of complete block portions of a tile. In this document, tile groups and slices can be used interchangeably. For example, in this document, tile groups / tile group headers can be referred to as slices / slice headers.

[0041] A pixel or pel may refer to the smallest unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, and may represent only a pixel / pixel value of a luminance component, or only a pixel / pixel value of a chrominance component.

[0042] A unit may represent a basic unit of image processing. A unit may include at least one of a specific region and information related to the region. A unit may include a luma block and two chroma (e.g., CB, CR) blocks. Depending on the situation, terms such as unit, block, and region may be used interchangeably. In general, an MxN block may include a set (or array) of samples (or sample arrays) or transform coefficients consisting of M columns and N rows.

[0043] In this document, the terms " / " and "," should be interpreted as indicating "and / or". For example, the expression "A / B" may mean "A and / or B". In addition, "A, B" may mean "A and / or B". In addition, "A / B / C" may mean "at least one of A, B, and / or C". In addition, "A / B / C" may mean "at least one of A, B, and / or C".

[0044] Additionally, in this document, the term "or" should be interpreted as meaning "and / or." For example, the expression "A or B" may include 1) "only A," 2) "only B," and / or 3) "both A and B." In other words, the term "or" in this document should be interpreted as meaning "additionally or alternatively."

[0045] Figure 2 The figure schematically illustrates the configuration of a video / image encoding device to which the present document can be applied. Hereinafter, the so-called video encoding device may include an image encoding device.

[0046] Reference Figure 2 , the encoding device 200 may include an image segmenter 210, a predictor 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The predictor 220 may include an inter-frame predictor 221 and an intra-frame predictor 222. The residual processor 230 may include a transformer 232, a quantizer 233, 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. Depending on the embodiment, the image segmenter 210, the predictor 220, the residual processor 230, the entropy encoder 240, the adder 250, and the filter 260 described above may be composed of one or more hardware components (e.g., an encoder chipset or processor). In addition, the memory 270 may include a decoded picture buffer (DPB) and may be composed of a digital storage medium. The hardware components may also include the memory 270 as an internal / external component.

[0047] The image splitter 210 splits the input image (or picture, or frame) input to the encoding device 200 into one or more processing units. As an example, a processing unit may be referred to as a coding unit (CU). In this case, starting from a coding tree unit (CTU) or a largest coding unit (LCU), the coding units may be recursively split according to a quadtree, binary tree, ternary tree (QTBTTT) structure. For example, a coding unit may be divided into multiple coding units of increasing depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. In this case, for example, the quadtree structure may be applied first, followed by the binary tree structure and / or the ternary tree structure. Alternatively, the binary tree structure may be applied first. The coding process according to this document may be performed based on the final coding unit that has not been further split. In this case, based on coding efficiency according to image characteristics, the largest coding unit may be directly used as the final coding unit. Alternatively, the coding unit may be recursively split into coding units of increasing depth as needed, so that the optimally sized coding unit can be used as the final coding unit. Here, the coding process may include processes such as prediction, transformation, and reconstruction, which will be described later. As another example, the processing unit may also include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be divided or partitioned from the final coding unit described above. 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 based on the transform coefficient.

[0048] Depending on the situation, the terms such as unit and block, region, etc. can be used interchangeably. In general, an MxN block can represent a set of samples or transform coefficients consisting of M columns and N rows. A sample can generally represent a pixel or a pixel value, and can represent only a pixel / pixel value of a luma component or only a pixel / pixel value of a chroma component. A sample can be used as a term corresponding to a pixel or pel of a picture (or image).

[0049] In the encoding device 200, the 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 unit in the encoder 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 can perform prediction on a processing target block (hereinafter referred to as a "current block") and can generate a prediction block including prediction samples for the current block. The predictor can determine whether to apply intra prediction or inter prediction based on the current block or CU. As discussed later in the description of each prediction mode, the predictor can generate various information related to prediction, such as prediction mode information, and send the generated information to the entropy encoder 240. The information about the prediction can be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0050] The intra-frame predictor 222 can predict the current block by referring to samples in the current picture. Depending on the prediction mode, the reference sample can be located near the current block or separated from the current block. In intra-frame prediction, the prediction mode can include multiple non-directional modes and multiple directional modes. The non-directional mode can include, for example, a DC mode and a planar mode. Depending on the level of detail of the prediction direction, the directional mode can include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is merely an example, and more or fewer directional prediction modes can be used depending on the settings. The intra-frame predictor 222 can determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

[0051] The inter-frame predictor 221 can derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector in a reference picture. To reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation of motion information between neighboring blocks and the current block. Motion information can include a motion vector and a reference picture index. It can also include information about the inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, neighboring blocks can include spatially neighboring blocks in the current picture and temporally neighboring blocks in a reference picture. The reference picture including the reference block and the reference picture including the temporally neighboring block can be the same or different. Temporally neighboring blocks can be referred to as collocated reference blocks, collocated CUs (colCUs), etc., and the reference picture including temporally neighboring blocks can be referred to as collocated pictures (colPics). For example, the inter-frame predictor 221 can configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index for the current block. Inter-frame prediction can be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame predictor 221 can use the motion information of the neighboring block as the motion information of the current block. In skip mode, unlike merge mode, the residual signal cannot be sent. In the case of motion information prediction (motion vector prediction, MVP) mode, the motion vector of the neighboring block can be used as a motion vector prediction item, and the motion vector of the current block can be indicated by signaling the motion vector difference.

[0052] The predictor 220 can generate prediction signals based on various prediction methods. For example, the predictor can apply intra prediction or inter prediction to predict a block, and can also apply intra prediction and inter prediction simultaneously. This can be referred to as combined inter and intra prediction (CIIP). In addition, the predictor can perform prediction on the block based on an intra-block copy (IBC) prediction mode or a palette mode. The IBC prediction mode or palette mode can be used for content image / video coding such as games such as screen content coding (SCC). Although IBC essentially performs prediction in the current picture, its execution is similar to inter prediction in that it derives a reference block in the current picture. That is, IBC can use at least one of the inter prediction techniques described in this document. The palette mode can be considered an example of intra coding or intra prediction. When the palette mode is applied, the sample values ​​in the picture can be signaled based on information about the palette index and the palette table.

[0053] 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-LoSve 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 obtained 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 blocks.

[0054] The quantizer 233 can quantize the transform coefficients and send them to the entropy encoder 240. The entropy encoder 240 can encode the quantized signal (information about the quantized transform coefficients) and output the encoded signal in a bitstream. The information about the quantized transform coefficients can be called residual information. The quantizer 233 can 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. The entropy encoder 240 can perform various encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 240 can encode information required for video / image reconstruction in addition to the quantized transform coefficients (e.g., syntax element values, etc.) together or separately. The encoded information (e.g., encoded video / image information) can be transmitted or stored in the form of a bitstream on a unit basis of the network abstraction layer (NAL). The video / image information may also include information about various parameter sets such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), a video parameter set (VPS), and the like. In addition, the video / image information may also include general constraint information. In this document, information and / or syntax elements transmitted / signaled from an encoding device to a decoding device may be included in the video / image information. The video / image information may be encoded through the above-described encoding process and included in a bitstream. The bitstream may be transmitted over a network or stored in a digital storage medium. Here, the network may include a broadcast network, a communication network, and / or the like, and the digital storage medium may include various storage media such as a USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. A transmitter (not shown) that transmits the signal output from the entropy encoder 240 or a memory (not shown) that stores the signal may be configured as an internal / external component of the encoding device 200, or the transmitter may be included in the entropy encoder 240.

[0055] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, by applying inverse quantization and inverse transform to the quantized transform coefficients using the inverse quantizer 234 and the inverse transformer 235, a residual signal (residual block or residual sample) can be reconstructed. The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame predictor 221 or the intra-frame predictor 222, so that a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) can be generated. When there is no residual for the processing target block as in the case of applying the skip mode, 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 processing target block in the current picture, and as described later, can be used for inter-frame prediction of the next picture performed by filtering.

[0056] Furthermore, in the picture encoding and / or reconstruction process, luma mapping with chroma scaling (LMCS) may be applied.

[0057] The filter 260 can improve the subjective / objective video 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 the modified reconstructed picture can be stored in the memory 270, especially in the DPB of the memory 270. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive ring filtering, bilateral filtering, etc. As discussed later in the description of each filtering method, the filter 260 can generate various information related to filtering and send the generated information to the entropy encoder 240. The information about filtering can be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0058] The modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter-frame predictor 221. Accordingly, the encoding apparatus can avoid prediction mismatch in the encoding apparatus 100 and the decoding apparatus when applying inter-frame prediction, and can also improve encoding efficiency.

[0059] The memory 270DPB can store the modified reconstructed picture so that it can be used as a reference picture in the inter-frame predictor 221. The memory 270 can store the motion information of the blocks in the current picture from which the motion information has been derived (or encoded) and / or the motion information of the blocks in the reconstructed picture. The stored motion information can be sent to the inter-frame predictor 221 to be used as the motion information of the neighboring blocks or the motion information of the temporally neighboring blocks. The memory 270 can store the reconstructed samples of the reconstructed blocks in the current picture and send them to the intra-frame predictor 222.

[0060] Figure 3This is a diagram schematically illustrating the configuration of a video / image decoding device to which this document can be applied.

[0061] Reference Figure 3 , the video decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter-frame predictor 331 and an intra-frame predictor 332. The residual processor 320 may include an inverse quantizer 321 and an inverse transformer 321. According to an embodiment, the entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 described above may be composed of one or more hardware components (e.g., a decoder chipset or processor). In addition, the memory 360 may include a decoded picture buffer (DPB) and may be composed of a digital storage medium. The hardware components may also include the memory 360 as an internal / external component.

[0062] When a bit stream including video / image information is input, the decoding device 300 can Figure 2 The image is reconstructed correspondingly to the processing of the video / image information in the encoding device. For example, the decoding device 300 can derive the unit / block based on the information related to the block segmentation obtained from the bit stream. The decoding device 300 can perform decoding by using the processing unit applied in the encoding device. Therefore, the decoding processing unit can be, for example, a coding unit, which can be divided into a quadtree structure, a binary tree structure and / or a ternary tree structure using a coding tree unit or a maximum coding unit. One or more transform units can be derived from the coding unit. In addition, the reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a reproducer.

[0063] The decoding device 300 may receive the data from the Figure 2The received signal is output by the encoding device, and the entropy decoder 310 can decode the received signal. For example, the entropy decoder 310 can parse the bitstream to derive information required for image reconstruction (or picture reconstruction) (e.g., video / image information). The video / image information may also include information about various parameter sets such as the Adaptive Parameter Set (APS), Picture Parameter Set (PPS), Sequence Parameter Set (SPS), and Video Parameter Set (VPS). In addition, the video / image information may also include general constraint information. The decoding device can further decode the picture based on the information about the parameter sets and / or general constraint information. In this document, the signaled / received information and / or syntax elements described later can be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 310 can decode the information in the bitstream based on a coding method such as Exponential Golomb coding, CAVLC, or CABAC, and can output the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive bins corresponding to each syntax element in the bitstream, use the decoded target syntax element information and the decoded information of the neighboring and decoded target blocks or the information of the symbol / bin decoded in the previous step to determine the context model, predict the bin generation probability based on the determined context model, and perform arithmetic decoding on the bin to generate the symbol corresponding to each syntax element value. Here, after determining the context model, the CABAC entropy decoding method can update the context model using the symbol / bin information decoded by the context model for the next symbol / bin. The information about prediction among the information decoded in the entropy decoder 310 can be provided to the predictor (inter-frame predictor 332 and intra-frame predictor 331), and the residual value (i.e., quantized transform coefficient) and associated parameter information for which entropy decoding has been performed 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 in the entropy decoder 310 can be provided to the filter 350. In addition, a receiver (not shown) that receives a signal output from the encoding device may also constitute the decoding device 300 as an internal / external element, and the receiver may be a component of the entropy decoder 310. In addition, the decoding device according to the present document may be referred to as a video / image / picture decoding device, and the decoding device may be divided 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.

[0064] The inverse quantizer 321 can output the transform coefficients by inverse quantizing the quantized transform coefficients. The inverse quantizer 321 can rearrange the quantized transform coefficients into a two-dimensional block form. In this case, the rearrangement can be performed based on the order of coefficient scanning performed in the encoding device. The inverse quantizer 321 can perform inverse quantization on the quantized transform coefficients using quantization parameters (e.g., quantization step size information) and obtain the transform coefficients.

[0065] The inverse transformer 322 obtains a residual signal (residual block, residual sample array) by performing inverse transformation on the transformation coefficients.

[0066] The predictor may perform prediction on the current block and generate a prediction block including prediction samples for the current block. The predictor may determine whether to apply intra prediction or inter prediction to the current block based on the information about prediction output from the entropy decoder 310, and specifically may determine the intra / inter prediction mode.

[0067] The predictor 320 can generate prediction signals based on various prediction methods. For example, the predictor can apply intra-frame prediction or inter-frame prediction to predict a block, and can also apply intra-frame prediction and inter-frame prediction simultaneously. This can be referred to as combined inter-frame and intra-frame prediction (CIIP). In addition, the predictor can perform prediction on the block based on an intra-block copy (IBC) prediction mode or a palette mode. The IBC prediction mode or palette mode can be used for content image / video coding such as games such as screen content coding (SCC). Although IBC essentially performs prediction in the current picture, its execution is similar to inter-frame prediction in that it derives a reference block in the current picture. That is, IBC can use at least one of the inter-frame prediction techniques described in this document. The palette mode can be considered an example of intra-frame coding or intra-frame prediction. When the palette mode is applied, information about the palette table and palette index can be included in the video / image information and signaled.

[0068] The intra-frame predictor 331 can predict the current block by referencing samples in the current picture. Depending on the prediction mode, the reference samples can be located near the current block or separated from the current block. In intra-frame prediction, the prediction mode can include multiple non-directional modes and multiple directional modes. The intra-frame predictor 331 can determine the prediction mode to be applied to the current block by using the prediction modes applied to neighboring blocks.

[0069] The inter-frame predictor 332 can derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector in a reference picture. To reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation of motion information between neighboring blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can also include information about the inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, neighboring blocks can include spatially neighboring blocks in the current picture and temporally neighboring blocks in the reference picture. For example, the inter-frame predictor 332 can configure a motion information candidate list based on the neighboring blocks and derive the motion vector and / or reference picture index for the current block based on received candidate selection information. Inter-frame prediction can be performed based on various prediction modes, and prediction information can include information indicating the inter-frame prediction mode for the current block.

[0070] The adder 340 adds the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the predictor (inter-frame predictor 332 or intra-frame predictor 331), so that a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) can be generated. When there is no residual for the processing target block as in the case of applying skip mode, the prediction block can be used as the reconstructed block.

[0071] 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, may be output through filtering as described below, or may be used for inter prediction of the next picture.

[0072] Furthermore, luma mapping with chroma scaling (LMCS) may be applied to the picture decoding process.

[0073] The filter 350 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 can generate a modified reconstructed image by applying various filtering methods to the reconstructed image, and store the modified reconstructed image in the memory 360, specifically, in the DPB of the memory 360. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc.

[0074] The (modified) reconstructed picture stored in the DPB of the memory 360 can be used as a reference picture in the inter-frame predictor 332. The memory 360 can store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the block in the reconstructed picture. The stored motion information can be sent to the inter-frame predictor 260 to be used as the motion information of the spatially adjacent block or the motion information of the temporally adjacent block. The memory 360 can store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame predictor 331.

[0075] In the present disclosure, 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 correspond to the filter 350, the inter-frame predictor 332, and the intra-frame predictor 331 of the decoding device 300. The same applies to the unit 332 and the intra-frame predictor 331.

[0076] As described above, when performing video coding, prediction is performed to improve compression efficiency. A prediction block including prediction samples of the current block, that is, a target coding block, can be generated by prediction. In this case, the prediction block includes prediction samples in the spatial domain (or pixel domain). The prediction block is derived similarly in the encoding device and the decoding device. The encoding device can improve image coding efficiency by signaling 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 to the decoding device. The decoding device can derive a residual block including residual samples based on the residual information, can generate a reconstructed block including reconstructed samples by adding the residual block to the prediction block, and can generate a reconstructed picture including the reconstructed block.

[0077] Residual information can be generated through a transformation and quantization process. For example, the encoding device can derive a residual block between the original block and the prediction block, can derive a transform coefficient by performing a transformation process on the residual samples (residual sample array) included in the residual block, can derive a quantized transform coefficient by performing a quantization process on the transform coefficient, and can signal the relevant residual information to the decoding device (through a bitstream). In this case, the residual information may include information such as value information, position information, a transformation scheme, a transform kernel, and a quantization parameter of the quantized transform coefficient. The decoding device can perform an inverse quantization / inverse transformation process based on the residual information and can derive residual samples (or residual blocks). The decoding device can generate a reconstructed picture based on the prediction block and the residual block. In addition, the encoding device can derive a residual block for inter-frame prediction reference of a subsequent picture by performing inverse quantization / inverse transformation on the quantized transform coefficient, and can generate a reconstructed picture.

[0078] In addition, to improve subjective / objective image quality, the encoding device / decoding device may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture. The modified reconstructed picture may be stored in a memory, specifically the DPB of the memory 270, 360 of the encoding device / decoding device. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, and bilateral filtering.

[0079] In addition, in image / video coding, the pictures constituting the image / video can be encoded / decoded in a series of decoding orders. The picture order corresponding to the output order of the decoded pictures can be set to be different from the decoding order, and based on the above, backward prediction as well as forward prediction can be performed during inter-frame prediction.

[0080] Figure 4 An example of an illustrative picture decoding process to which exemplary embodiments of this document are applicable is illustrated.

[0081] exist Figure 4 In the above, S400 can be referred to Figure 3 The entropy decoder 310 of the decoding device described in the present invention may be executed by the entropy decoder 310, S410 may be executed by the predictor 330 thereof, S420 may be executed by the residual processor 320 thereof, S430 may be executed by the adder 340 thereof, and S440 may be executed by the filter 350 thereof. S400 may include the information decoding process described in this document, S410 may include the inter / intra prediction process described in this document, S420 may include the residual processing process described in this document, S430 may include the block / picture reconstruction process described in this document, and S440 may include the loop filtering process described in this document.

[0082] Reference Figure 4 The picture decoding process may schematically include an image / video information acquisition process (S400) from a bit stream (by decoding), a picture reconstruction process (S410 to S430) and a loop filtering process (S440) for the reconstructed picture, as shown in FIG. Figure 3 described.

[0083] The picture reconstruction process (S430) can be performed based on the prediction samples and residual samples obtained through the inter-frame / intra-frame prediction (S410) and residual processing (S420) (dequantization and inverse transformation of quantized transform coefficients) processes described in this document. A modified reconstructed picture can be generated by a loop filtering process on the reconstructed picture generated by the picture reconstruction process. The modified reconstructed picture can be output as a decoded picture and can also be stored in a decoded picture buffer of the decoding device or its memory 360, and used as a reference picture in the inter-frame prediction process when the picture is later decoded. In some cases, the loop filtering process can be omitted, and in this case, the reconstructed picture can be output as a decoded picture and can also be stored in a decoded picture buffer of the decoding device or its memory 360, and can be used as a reference picture in the inter-frame prediction process when the picture is later decoded.

[0084] As described above, the loop filtering process (S440) may include a deblocking filtering process, a sample adaptive offset (SAO) process, an adaptive loop filtering (ALF) process, and / or a bilateral filtering process, and some or all of them may be omitted. In addition, one or some of the deblocking filtering process, the sample adaptive offset (SAO) process, the adaptive loop filtering (ALF) process, and the bilateral filtering process may be applied sequentially, or all of them may be applied sequentially. For example, the deblocking filtering process may be applied to the reconstructed picture, and then the SAO process may be performed. Alternatively, for example, the deblocking filtering process may be applied to the reconstructed picture, and then the ALF process may be performed. Similarly, this may also be performed in the encoding device.

[0085] Figure 5 An example of an illustrative picture encoding process to which exemplary embodiments of this document are applicable is illustrated.

[0086] exist Figure 5 In the above, S500 can be referred to Figure 2 The predictor 220 of the encoding device described in this document may be executed, S510 may be executed by its residual processor 230, and S520 may be executed by its entropy encoder 240. S500 may include the inter / intra prediction process described in this document, S510 may include the residual processing process described in this document, and S520 may include the information encoding process described in this document.

[0087] Reference Figure 5 , the picture encoding process may illustratively include a process of generating a reconstructed picture for the current picture and a process of applying loop filtering to the reconstructed picture (optional) and encoding information (eg, prediction information, residual information, or segmentation information) so as to Figure 2 The process of reconstructing a picture as described to output coded information in the form of a bitstream.

[0088] The encoding device can derive (modified) residual samples from the quantized transform coefficients through the inverse quantizer 234 and the inverse transformer 235, and generate a reconstructed picture based on the prediction samples and the (modified) residual samples as the output in S500. The reconstructed picture generated in this way can be the same as the aforementioned reconstructed picture generated by the decoding device. The modified reconstructed picture can be generated by a loop filtering process for the reconstructed picture, and can be stored in the decoded picture buffer or memory 270, and as in the case of the decoding device, used as a reference picture in the inter-frame prediction process when encoding the picture later. As described above, in some cases, some or all of the loop filtering process can be omitted. If the loop filtering process is performed, the (loop) filtering related information (parameters) is encoded by the entropy encoder 240 and output in the form of a bitstream, and the decoding device can perform the loop filtering process based on the filtering related information in the same way as the encoding device.

[0089] The loop filtering process can reduce noise generated when encoding images / videos, such as blocking artifacts and oscillation artifacts, and improve subjective / objective visual quality. In addition, by performing the loop filtering process in both the encoding device and the decoding device, the encoding device and the decoding device can derive the same prediction results, increase the reliability of picture coding, and reduce the amount of data to be transmitted for picture coding.

[0090] As described above, the picture reconstruction process can be performed in the encoding device and in the decoding device. Reconstructed blocks can be generated based on intra prediction / inter prediction in units of each block, and a reconstructed picture including the reconstructed blocks can be generated. If the current picture / slice / tile group is an I picture / slice / tile group, the blocks included in the current picture / slice / tile group can be reconstructed based on only intra prediction. In addition, if the current picture / slice / tile group is a P or B picture / slice / tile group, the blocks included in the current picture / slice / tile group can be reconstructed based on intra prediction or inter prediction. In this case, inter prediction can be applied to some blocks in the current picture / slice / tile group, and intra prediction can also be applied to other blocks. The color components of the picture may include luminance components and chrominance components, and unless explicitly limited in this document, the methods and exemplary embodiments proposed in this document may be applied to luminance components and chrominance components.

[0091] In addition, as described above, the encoding device / decoding device can reconstruct the picture in units of blocks. If the image is reconstructed in units of blocks, block distortion may occur in the boundaries between blocks in the reconstructed picture. Therefore, the encoding device and the decoding device can use a deblocking filter to remove the block distortion that occurs in the boundaries between blocks in the reconstructed picture. For example, the deblocking filtering process can derive the target boundary in the reconstructed picture, determine the boundary strength (bs) of the target boundary, and perform deblocking filtering on the target boundary based on bs. bs can be determined based on the prediction mode of the two blocks adjacent to the target boundary, the difference between their motion vectors, whether their reference pictures are the same, and whether there are non-zero significant coefficients therein.

[0092] Figure 6 Exemplary embodiments of a method for performing a deblocking filtering process are exemplarily illustrated. Figure 6 The method exemplified in can be Figure 2 The aforementioned filter 260 and Figure 3 The aforementioned filter 350 in the decoding device illustrated in FIG.

[0093] Reference Figure 6 , the encoding device / decoding device can derive the boundaries between the blocks on which deblocking filtering is performed in the reconstructed picture. In addition, the boundaries on which deblocking filtering is performed can be referred to as edges. In addition, the boundaries on which deblocking filtering is performed can include two types, and the two types can be vertical boundaries and horizontal boundaries. The vertical boundaries can be referred to as vertical edges, and the horizontal boundaries can be referred to as horizontal edges. The encoding device / decoding device can perform deblocking filtering on vertical edges and perform deblocking filtering on horizontal edges.

[0094] When deblocking filtering is performed on one direction (ie, deblocking filtering is performed on a vertical boundary or deblocking filtering is performed on a horizontal boundary), the encoding device / decoding device may derive a transform block boundary (S600) or a coding subblock boundary (S610).

[0095] The encoding device / decoding device may derive block boundaries on which deblocking filtering is performed based on an NxN-sized grid.

[0096] For example, the encoding device / decoding device may derive the block boundaries on which deblocking filtering is performed based on whether the boundaries of the block (transform block or coding subblock) correspond to an NxN grid. In other words, for example, the encoding device / decoding device may derive the block boundaries on which deblocking filtering is performed based on whether the boundaries of the block (transform block or coding subblock) are block boundaries located on an NxN grid. The encoding device / decoding device may derive the boundaries of the blocks corresponding to the NxN grid as the block boundaries on which deblocking filtering is performed. Here, the NxN grid may mean a boundary derived by dividing the reconstructed picture into NxN squares. The NxN grid may be, for example, a 4x4 or 8x8 grid.

[0097] The encoding device / decoding device may determine a boundary strength (bs) of a boundary on which deblocking filtering is performed (S620). bs may also be referred to as boundary filtering strength.

[0098] The encoding device / decoding device may determine bs based on blocks adjacent to the boundary on which deblocking filtering is performed. For example, it is 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 determine the bs value of the boundary based on information about the positions of block P and block Q and / or whether block P and block Q are encoded in intra-frame mode.

[0099] Here, the block P may represent a block including p0 samples adjacent to a boundary on which deblocking filtering is performed, and the block Q may represent a block including q0 samples adjacent to a boundary on which deblocking filtering is performed.

[0100] For example, p0 may represent a sample of a block adjacent to the left or top of the boundary on which deblocking filtering is performed, and q0 may represent a sample of a block adjacent to the right or bottom of the boundary on which deblocking filtering is performed. As an example, if the direction of the filter boundary is a vertical direction (i.e., if the filter boundary is a vertical boundary), p0 may represent a sample of a block adjacent to the left of the boundary on which deblocking filtering is performed, and q0 may represent a sample of a block adjacent to the right of the boundary on which deblocking filtering is performed. Alternatively, as another example, if the direction of the filter boundary is a horizontal direction (i.e., if the filter boundary is a horizontal boundary), p0 may represent a sample of a block adjacent to the top of the boundary on which deblocking filtering is performed, and q0 may represent a sample of a block adjacent to the bottom of the boundary on which deblocking filtering is performed.

[0101] The encoding device / decoding device may perform deblocking filtering based on bs. For example, the encoding device / decoding device may determine whether a filtering process has been performed for all block boundaries in the reconstructed picture (S630), and if a filtering process has not been performed for all block boundaries, the encoding device / decoding device may determine whether the position of the sub-block boundary corresponds to an NxN grid (e.g., an 8x8 grid) (S640). For example, it may be determined whether the remainder derived by dividing the x-component and y-component of the sub-block boundary position by N is 0. If the remainder derived by dividing the x-component and y-component of the sub-block boundary position by N is 0, the position of the sub-block boundary may correspond to an NxN grid.

[0102] If the position of the boundary of the subblock corresponds to an NxN-sized grid, the encoding apparatus / decoding apparatus may perform deblocking filtering on the boundary based on the bs of the boundary ( S650 ).

[0103] At this time, based on the determined bs value, a filter applied to the boundary between blocks can be determined. Filters can be divided into strong filters and weak filters. The encoding device / decoding device can use different filters to filter the boundaries of positions where block distortion is likely to occur in the reconstructed picture and the boundaries of positions where block distortion is unlikely to occur, thereby improving coding efficiency.

[0104] The encoding device / decoding device may use the determined filter (eg, a strong filter or a weak filter) to perform deblocking filtering on the boundary between blocks. If the deblocking filtering process is performed on all boundaries between blocks in the reconstructed picture, the deblocking filtering process may be terminated.

[0105] Hereinafter, this document proposes a method for determining a boundary strength (bs) in consideration of characteristics of a current picture reference (CPR) block in performing deblocking filtering and determining whether to perform boundary filtering on the CPR block based on the determined boundary strength.

[0106] Furthermore, CPR is a method for performing prediction with reference to the current picture and can be a concept included in the intra-block copy (IBC) prediction mode. In other words, IBC basically performs prediction in the current picture and can therefore also be referred to as CPR. In addition, IBC can be performed similarly to inter-frame prediction because the reference block is derived in the current picture. In other words, IBC can use at least one of the inter-frame prediction techniques described in this document and, for example, use at least one of the aforementioned methods to derive motion information (motion vectors).

[0107] For example, whether IBC is applied to the current block may be indicated based on an IBC flag (eg, pred_mode_ibc_flag). The IBC flag (eg, pred_mode_ibc_flag) may be coded with a syntax element and generated in the form of a bitstream, and signaled from the encoding device to the decoding device through the bitstream.

[0108] For IBC prediction, the encoding device can derive the optimal block vector (or motion vector) for the current block (e.g., CU) by performing block matching (BM). The derived block vector (or motion vector) can be signaled to the decoding device via the bitstream using a method similar to the signaling of motion information (motion vector) described above in inter-frame prediction. The decoding device can derive the reference block for the current block in the current picture using the signaled block vector (motion vector), and as a result, derive the prediction signal (prediction block or prediction sample) for the current block. Here, the block vector corresponds to the aforementioned motion vector, representing the displacement from the current block to the reference block located in the already reconstructed area of ​​the current picture. Therefore, the block vector (or motion vector) may also be referred to as a displacement vector. Hereinafter, the motion vector in IBC may correspond to the block vector or displacement vector. Furthermore, the MVD in IBC may be referred to as a block vector difference (BVD). The motion vector of the current block may include the motion vector of the luma component (luminance motion vector) or the motion vector of the chroma component (chroma motion vector). For example, the luma motion vector of a CU coded in IBC mode may be in integer sample units (i.e., integer precision). The chroma motion vector may also be clipped in integer sample units. As described above, IBC may use at least one of the inter-frame prediction techniques, and for example, if IBC is applied like AMVR, 1-pel and 4-pel motion vector precision may be switched.

[0109] At the CU level, the IBC prediction mode can be signaled by a flag and signaled in either IBC(A)MVP mode or IBC skip / merge mode.

[0110] For example, in IBC skip / merge mode, a merge candidate index can be used to derive a block vector for the current block. Here, the merge candidate index can indicate whether any of the block vectors in the list configured based on the neighboring candidate blocks coded in IBC mode is used to predict the current block. The merge candidate list can be configured to include spatial candidates, historical motion vector prediction (HMVP) candidates, and paired candidates.

[0111] In IBC(A)MVP mode, the block vector difference (BVD) can be coded in the same way as the MVD method. The block vector prediction method can use two candidates as predictors, and can derive the two candidates from the left neighboring block (coded in IBC mode) and the top neighboring block (coded in IBC mode). In this case, if the left neighboring block or the top neighboring block is unavailable, a default block vector can be used as the predictor. A flag can be signaled as index information for indicating the block vector predictor.

[0112] Hereinafter, a method is proposed for performing deblocking filtering by determining a boundary strength (bs) based on the prediction mode of two blocks (block P and block Q) adjacent to a boundary on which deblocking filtering is performed in a reconstructed picture. In particular, a method is provided for determining the boundary strength (bs) by considering whether block P and block Q are CPR blocks on which prediction is performed with reference to the current picture.

[0113] Here, as described above, block P may represent a block including p0 samples adjacent to the boundary on which deblocking filtering is performed, and block Q may represent a block including q0 samples adjacent to the boundary on which deblocking filtering is performed. For example, p0 may represent samples of a block adjacent to the left portion of the boundary on which deblocking filtering is performed, and q0 may represent samples of a block adjacent to the right portion of the boundary on which deblocking filtering is performed. Alternatively, p0 may represent samples of a block adjacent to the top portion of the boundary on which deblocking filtering is performed, and q0 may represent samples of a block adjacent to the bottom portion of the boundary on which deblocking filtering is performed.

[0114] According to an exemplary embodiment, the boundary strength may be determined as shown in Table 1 below. Table 1 shows an example of deriving a boundary strength value based on the prediction mode of block P and block Q, the difference between their motion vectors, whether their reference pictures are the same, and whether there are non-zero significant coefficients therein. For example, as shown in Table 1, if at least one of block P and block Q is coded in CPR mode, the boundary strength may be determined to be 0.

[0115] [Table 1]

[0116]

[0117] According to another exemplary embodiment, the boundary strength may be determined as shown in Table 2 below. Table 2 shows an example of deriving a boundary strength value based on the prediction modes of blocks P and Q, the difference between their motion vectors, whether their reference pictures are the same, and whether there are non-zero significant coefficients therein. For example, as shown in Table 2, if both blocks P and Q are coded in the CPR mode, the boundary strength may be determined to be 0, whereas if only either block P or block Q is coded in the CPR mode, the boundary strength may be determined to be 1.

[0118] [Table 2]

[0119]

[0120]

[0121] Figure 7 is a flowchart schematically illustrating an encoding method that can be performed by an encoding device according to an exemplary embodiment of this document.

[0122] Figure 7 The method exemplified in can be Figure 2 Specifically, Figure 7 Step S700 illustrated in FIG. 1 may be performed by Figure 2 The adder 250 of the encoding device 200 illustrated in FIG. 1 performs, Figure 7 Steps S710 to S730 illustrated in FIG. 1 can be performed by Figure 2 The filter 260 of the encoding device 200 illustrated in FIG. 1 is executed, and Figure 7 Step S740 illustrated in FIG. 1 may be performed by Figure 2 The entropy encoder 240 of the encoding device 200 illustrated in FIG. Figure 7 The method exemplified in may include the aforementioned exemplary embodiments in this document. Figure 7 In the present invention, detailed descriptions of contents overlapping with the aforementioned exemplary embodiments will be omitted and simplified.

[0123] Reference Figure 7 , the encoding apparatus may generate a reconstructed picture based on the prediction samples of the coding block ( S700 ).

[0124] According to an exemplary embodiment, the encoding device may determine whether to perform inter prediction or intra prediction on a coding block, and may determine a specific inter prediction mode or a specific intra prediction mode based on an RD cost. The encoding device may derive a prediction sample for the coding block according to the determined mode.

[0125] In addition, the encoding device may generate a reconstructed picture based on the predicted samples of the coding block. In other words, the encoding device may derive residual samples by subtracting the original samples from the predicted samples of the coding block, and generate reconstructed samples based on the residual samples and the predicted samples. The encoding device may generate a reconstructed block based on the reconstructed samples of the coding block in the picture, and generate a reconstructed picture including the reconstructed block.

[0126] The encoding apparatus may derive a boundary strength (bs) of a boundary of a coding block in a reconstructed picture ( S710 ).

[0127] In other words, since the encoding device reconstructs a picture in units of blocks, block distortion may occur at the boundary between coding blocks in the reconstructed picture. Therefore, the encoding device may apply deblocking filtering to remove block distortion occurring at the boundary between coding blocks in the reconstructed picture, and at this time, determine the boundary strength according to the degree of block distortion.

[0128] According to an exemplary embodiment, the encoding apparatus may determine a boundary between coding blocks in a reconstructed picture, and derive a boundary strength based on a first block and a second block adjacent to the determined boundary.

[0129] Here, the boundary between coding blocks refers to the target boundary for which deblocking filtering is performed, and the target boundary may include a vertical boundary and a horizontal boundary. For example, the encoding device may derive a boundary strength of a vertical boundary and a boundary strength of a horizontal boundary, and perform deblocking filtering on the vertical boundary and the horizontal boundary based on each boundary strength.

[0130] In addition, as described above, the first block and the second block may refer to block P and block Q. Block P may represent a block including p0 samples adjacent to the boundary on which deblocking filtering is performed, and block Q may represent a block including q0 samples adjacent to the boundary on which deblocking filtering is performed. For example, p0 may represent samples of a block adjacent to the left of the boundary on which deblocking filtering is performed, and q0 may represent samples of a block adjacent to the right of the boundary on which deblocking filtering is performed. Alternatively, p0 may represent samples of a block adjacent to the top of the boundary on which deblocking filtering is performed, and q0 may represent samples of a block adjacent to the bottom of the boundary on which deblocking filtering is performed. In other words, the first block may be a left block (block P) relative to the target boundary (i.e., vertical boundary), and the second block may be a right block (block Q) relative to the target boundary (i.e., vertical boundary). Alternatively, the first block may be a top block (block P) relative to the target boundary (i.e., horizontal boundary), and the second block may be a bottom block (block Q) relative to the target boundary (i.e., horizontal boundary).

[0131] In other words, the encoding device can derive the value of the boundary strength based on the prediction mode of the first block (block P) and the second block (block Q) adjacent to the target boundary, the difference between their motion vectors, whether their reference pictures are the same, and whether there are non-zero significant coefficients therein. In this case, the boundary strength can be derived as a value of 0 to 2 as expressed in Table 1 or Table 2 expressed above.

[0132] According to an exemplary embodiment, the encoding device may derive the boundary strength based on the prediction mode of the first block (block P) and the second block (block Q) adjacent to the target boundary. For example, the boundary strength may be derived based on whether the prediction mode of the first block (block P) and the second block (block Q) is the current picture reference (CPR) mode coded with reference to the current picture. If the prediction mode of the first block (block P) and the second block (block Q) are both CPR modes, the encoding device may derive the value of the boundary strength as 0. If the prediction mode of the first block (block P) and the second block (block Q) is not both coded in the CPR mode but any one of the first block (block P) and the second block (block Q) is coded in the CPR mode, the encoding device may derive the value of the boundary strength as 1. At this time, as an example, the prediction mode of the first block (block P) may be the CPR mode and the prediction mode of the second block (block Q) may be the inter-frame prediction mode, and in this case, the value of the boundary strength may be derived as 1. Alternatively, as another example, the prediction mode of the first block (block P) may be the CPR mode and the prediction mode of the second block (block Q) may be the palette mode, and in this case, the value of the boundary strength may be derived as 1. In other words, if the prediction modes of the first block (block P) and the second block (block Q) are different and either one of the first block (block P) and the second block (block Q) is the CPR mode, the value of the boundary strength may be derived as 1. If the prediction mode of neither the first block (block P) nor the second block (block Q) is the CPR mode and the prediction mode of the first block (block P) or the second block (block Q) is coded in the intra prediction mode, the encoding device may derive the value of the boundary strength as 2.

[0133] In addition, the encoding device can derive the boundary strength based on the prediction modes of the first block (block P) and the second block (block Q) adjacent to the target boundary, the difference between their motion vectors, whether their reference pictures are the same, and whether there are non-zero significant coefficients therein. For example, if the first block (block P) or the second block (block Q) is coded in the inter-frame prediction mode and there are non-zero residual coefficients in the first block (block P) and the second block (block Q), the encoding device can derive the boundary strength value as 1. Alternatively, if the first block (block P) or the second block (block Q) is coded in the inter-frame prediction mode and there are no residual coefficients in the first block (block P) and the second block (block Q), but the motion vectors of the first block (block P) and the second block (block Q) are different when rounded to integer unit samples (integer pixels), the encoding device can derive the boundary strength value as 1. Alternatively, if the first block (block P) or the second block (block Q) is coded in the inter prediction mode, there is no residual coefficient in the first block (block P) and the second block (block Q), and the motion vectors of the first block (block P) and the second block (block Q) are the same when rounded by integer-unit samples (integer pixels), but the first block (block P) and the second block (block Q) refer to different reference pictures, the encoding device may derive the value of the boundary strength as 1. In other cases, the encoding device may derive the value of the boundary strength as 0.

[0134] According to an exemplary embodiment, if a prediction mode that derives motion information in units of subblocks is applied to a coding block, for example, if the coding block is predicted in an affine mode or a subblock-based merge mode, the encoding device may determine a target boundary in units of subblocks and derive a boundary strength of the target boundary of the corresponding subblock. In this case, the encoding device may perform deblocking filtering based on the boundary strength derived with respect to the subblocks in the coding block.

[0135] The encoding apparatus may perform deblocking filtering on the boundary of the coding block based on the boundary strength derived as described above ( S720 ).

[0136] According to an exemplary embodiment, the encoding apparatus may perform deblocking filtering on a vertical boundary based on a boundary strength derived for the vertical boundary, and perform deblocking filtering on a horizontal boundary based on a boundary strength derived for the horizontal boundary.

[0137] The encoding apparatus may derive a modified reconstructed picture for the reconstructed picture based on the deblocking filtering ( S730 ).

[0138] In other words, the encoding device can perform deblocking filtering on the boundaries of coding blocks in the reconstructed picture based on the boundary strength, thereby deriving reconstructed samples from which block artifacts are removed, and generating a modified reconstructed picture based on the reconstructed samples. As a result, block artifacts occurring at block boundaries due to prediction performed on a block basis (in units of coding blocks or coding sub-blocks) can be removed, and the visual quality of the reconstructed picture can be improved.

[0139] In addition, as described above, in order to improve subjective / objective image quality as necessary, the encoding device may also apply a loop filtering process such as an SAO process to the modified reconstructed picture.

[0140] The encoding apparatus may encode image information including information about the coding block (S740).

[0141] Here, the information about the coding block may include prediction-related information of the coding block. For example, the prediction-related information may include prediction mode information of the coding block (e.g., intra prediction mode, inter prediction mode, affine prediction mode, sub-block-based merge mode, or IBC mode with reference to the current picture). In addition, the information about the coding block may include information about residual samples derived based on the prediction samples of the coding block. For example, the information about the residual samples may include information such as value information, position information, transformation technique, transformation kernel, and quantization parameter of quantized transform coefficients derived by performing transformation and quantization on the residual samples.

[0142] That is, the encoding device may encode the image information including the information about the coding block to output the encoded image information in the form of a bitstream, and transmit the bitstream to the decoding device via a network or storage medium. In addition, the encoding device may encode the information derived in the aforementioned process (e.g., deblocking filter related information) to generate encoded information in the form of a bitstream.

[0143] Figure 8 is a flowchart schematically illustrating a decoding method that can be performed by a decoding device according to an exemplary embodiment of this document.

[0144] Figure 8 The method exemplified in can be Figure 3 Specifically, Figure 8 Step S800 illustrated in FIG. 1 can be performed by Figure 3 The adder 340 of the decoding device 300 illustrated in FIG. 1 performs, and Figure 8 Steps S810 to S830 illustrated in FIG. 1 can be performed by Figure 3 The filter 350 of the decoding device 300 illustrated in FIG. Figure 8 The method exemplified in may include the aforementioned exemplary embodiments in this document. Figure 8 In the present invention, detailed descriptions of contents overlapping with the aforementioned exemplary embodiments will be omitted or simplified.

[0145] Reference Figure 8 , the decoding apparatus may generate a reconstructed picture based on the prediction samples of the coding block ( S800 ).

[0146] According to an exemplary embodiment, a decoding device may receive image information about a coding block via a bitstream. For example, the decoding device may receive image information including prediction-related information about the coding block via a bitstream. In this case, the image information may include prediction-related information about the coding block. The prediction-related information may include information about an inter-frame prediction mode or an intra-frame prediction mode performed on the coding block. In other words, the decoding device may perform inter-frame prediction or intra-frame prediction on the coding block based on the prediction-related information received via the bitstream, and derive prediction samples for the coding block.

[0147] In addition, the decoding device may receive image information including residual information about a coding block via a bitstream. In this case, the image information may include residual information about the coding block. The residual information may include transform coefficients of residual samples. The decoding device may derive residual samples (or residual sample arrays) for the coding block based on the residual information.

[0148] The decoding device may generate a reconstructed sample based on the prediction sample and the residual sample, and generate a reconstructed block based on the reconstructed sample of the coding block in the picture. In addition, the decoding device may generate a reconstructed picture including the reconstructed block.

[0149] The decoding apparatus may derive a boundary strength (bs) of a boundary of a coding block in a reconstructed picture ( S810 ).

[0150] In other words, since the decoding device reconstructs a picture in units of blocks, block distortion may occur at the boundary between coding blocks in the reconstructed picture. Therefore, the decoding device may apply a deblocking filtering process to remove block distortion occurring at the boundary between coding blocks in the reconstructed picture, and in this case, the boundary strength may be determined according to the degree of block distortion.

[0151] According to an exemplary embodiment, the decoding apparatus may determine a boundary between coding blocks in a reconstructed picture, and derive a boundary strength based on a first block and a second block adjacent to the determined boundary.

[0152] Here, the boundary between coding blocks refers to the target boundary for which deblocking filtering is performed, and the target boundary may include a vertical boundary and a horizontal boundary. For example, the decoding device may derive a boundary strength of the vertical boundary and a boundary strength of the horizontal boundary, and perform deblocking filtering on the vertical boundary and the horizontal boundary based on each boundary strength.

[0153] In addition, as described above, the first block and the second block may refer to block P and block Q. Block P may represent a block including p0 samples adjacent to the boundary on which deblocking filtering is performed, and block Q may represent a block including q0 samples adjacent to the boundary on which deblocking filtering is performed. For example, p0 may represent samples of a block adjacent to the left of the boundary on which deblocking filtering is performed, and q0 may represent samples of a block adjacent to the right of the boundary on which deblocking filtering is performed. Alternatively, p0 may represent samples of a block adjacent to the top of the boundary on which deblocking filtering is performed, and q0 may represent samples of a block adjacent to the bottom of the boundary on which deblocking filtering is performed. In other words, the first block may be a left block (block P) relative to the target boundary (i.e., vertical boundary), and the second block may be a right block (block Q) relative to the target boundary (i.e., vertical boundary). Alternatively, the first block may be a top block (block P) relative to the target boundary (i.e., horizontal boundary), and the second block may be a bottom block (block Q) relative to the target boundary (i.e., horizontal boundary).

[0154] In other words, the decoding device can derive the value of the boundary strength based on the prediction mode of the first block (block P) and the second block (block Q) adjacent to the target boundary, the difference between their motion vectors, whether their reference pictures are the same, and whether there are non-zero significant coefficients therein. In this case, the boundary strength can be derived as a value of 0 to 2 as in Table 1 or Table 2 expressed above.

[0155] According to an exemplary embodiment, the decoding device may derive the boundary strength based on the prediction mode of the first block (block P) and the second block (block Q) adjacent to the target boundary. For example, the boundary strength may be derived based on whether the prediction mode of the first block (block P) and the second block (block Q) is the current picture reference (CPR) mode coded with reference to the current picture. When the prediction mode of the first block (block P) and the second block (block Q) are both CPR modes, the decoding device may derive the boundary strength value as 0. If the prediction modes of the first block (block P) and the second block (block Q) are not both coded in the CPR mode but either one of the first block (block P) and the second block (block Q) is coded in the CPR mode, the decoding device may derive the boundary strength value as 1. At this time, as an example, the prediction mode of the first block (block P) may be the CPR mode and the prediction mode of the second block (block Q) may be the inter-frame prediction mode, and in this case, the boundary strength value may be derived as 1. Alternatively, as another example, the prediction mode of the first block (block P) may be the CPR mode and the prediction mode of the second block (block Q) may be the palette mode, and in this case, the value of the boundary strength may be derived as 1. In other words, if the prediction modes of the first block (block P) and the second block (block Q) are different and either one of the first block (block P) and the second block (block Q) is the CPR mode, the value of the boundary strength may be derived as 1. If the prediction mode of neither the first block (block P) nor the second block (block Q) is the CPR mode and the prediction mode of the first block (block P) or the second block (block Q) is coded in the intra prediction mode, the decoding device may derive the value of the boundary strength as 2.

[0156] In addition, the decoding device can derive the boundary strength based on the prediction modes of the first block (block P) and the second block (block Q) adjacent to the target boundary, the difference between their motion vectors, whether their reference pictures are the same, and whether there are non-zero significant coefficients therein. For example, if the first block (block P) or the second block (block Q) is coded in inter-frame prediction mode and there are non-zero residual coefficients in the first block (block P) and the second block (block Q), the decoding device can derive the boundary strength value as 1. Alternatively, if the first block (block P) or the second block (block Q) is coded in inter-frame prediction mode and there are no residual coefficients in the first block (block P) and the second block (block Q), but the motion vectors of the first block (block P) and the second block (block Q) are different when rounded to integer unit samples (integer pixels), the decoding device can derive the boundary strength value as 1. Alternatively, if the first block (block P) or the second block (block Q) is coded in the inter prediction mode, there is no residual coefficient in the first block (block P) and the second block (block Q), and the motion vectors of the first block (block P) and the second block (block Q) are the same when rounded by integer-unit samples (integer pixels), but the first block (block P) and the second block (block Q) refer to different reference pictures, the decoding device may derive the value of the boundary strength as 1. In other cases, the decoding device may derive the value of the boundary strength as 0.

[0157] According to an exemplary embodiment, if a prediction mode that derives motion information in units of subblocks is applied to a coding block, for example, if the coding block is predicted in an affine mode or a subblock-based merge mode, the decoding device may determine a target boundary in units of subblocks and derive a boundary strength of the target boundary of the corresponding subblock. In this case, the decoding device may perform deblocking filtering based on the boundary strength derived for the subblocks in the coding block.

[0158] The decoding apparatus may perform deblocking filtering on the boundary of the coding block based on the boundary strength derived as described above ( S820 ).

[0159] According to this exemplary embodiment, the decoding device may perform deblocking filtering on the vertical boundary based on the boundary strength derived for the vertical boundary, and perform deblocking filtering on the horizontal boundary based on the boundary strength derived for the horizontal boundary.

[0160] The decoding apparatus may derive a modified reconstructed picture for the reconstructed picture based on the deblocking filtering ( S830 ).

[0161] In other words, the decoding device can perform deblocking filtering on the boundaries of coding blocks in the reconstructed picture based on the boundary strength, thereby deriving reconstructed samples from which block artifacts are removed, and generating a modified reconstructed picture based on the reconstructed samples. As a result, block artifacts that occur at block boundaries due to prediction performed on a block basis (on a coding block or coding sub-block basis) can be removed, and the visual quality of the reconstructed picture can be improved.

[0162] In addition, as described above, in order to improve subjective / objective image quality as necessary, the decoding device may also apply a loop filtering process such as an SAO process to the modified reconstructed picture.

[0163] In the above-mentioned embodiments, although these methods have been described based on flowcharts in the form of a series of steps or units, the embodiments of this document are not limited to the order of these steps, and some of these steps may be performed in an order different from that of other steps or may be performed simultaneously with other steps. In addition, it will be understood by those skilled in the art that the steps shown in the flowcharts are not exclusive, and that these steps may include additional steps or may delete one or more steps in the flowcharts without affecting the scope of the rights of this document.

[0164] The above-mentioned method according to this document can be implemented in software form, and the encoding device and / or decoding device according to this document can be included in an apparatus for performing image processing, such as a TV, a computer, a smart phone, a set-top box, or a display device.

[0165] In this document, when the implementation is implemented in software form, the above-mentioned method can be implemented as a module (program, function, etc.) for performing the above-mentioned functions. The module can be stored in a memory and executed by a processor. The memory can be arranged inside or outside the processor and connected to the processor by various well-known means. The processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits and / or data processing 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. That is, the implementation described in this document can be implemented and executed on a processor, a microprocessor, a controller or a chip. For example, the functional units illustrated in the accompanying drawings can be implemented and executed on a computer, a processor, a microprocessor, a controller or a chip. In this case, the information (for example, information about instructions) or the algorithm used for this implementation can be stored in a digital storage medium.

[0166] In addition, the decoding device and the encoding device to which this document is applied may be included in a multimedia broadcast transmitting and receiving device, a mobile communication terminal, a home theater video device, a digital theater video device, a surveillance camera, a video chat device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camera, a video on demand (VoD) service providing device, an over-the-top (OTT) video device, an Internet streaming service providing device, a three-dimensional (3D) video device, a virtual reality (VR) device, an augmented reality (AR) device, a video phone video device, a transportation terminal (e.g., a vehicle (including an autonomous vehicle) terminal, an airplane terminal, and a ship terminal) and a medical video device, and may be used to process a video signal or a data signal. For example, an over-the-top (OTT) video device may include a game console, a Blueray player, an Internet access TV, a home theater system, a smart phone, a tablet PC, and a digital video recorder (DVR).

[0167] In addition, the processing method of the application file 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 file can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices storing computer-readable data. The computer-readable recording medium may include, for example, a Blueray 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. In addition, the computer-readable recording medium includes a medium implemented in the form of a carrier wave (for example, transmitted over the Internet). In addition, the bit stream generated using the encoding method can be stored in a computer-readable recording medium, or can be transmitted through a wired and wireless communication network.

[0168] In addition, the embodiments of the present invention may be implemented as a computer program product using program code. The program code may be executed by a computer according to the embodiments of the present invention. The program code may be stored on a carrier wave readable by a computer.

[0169] Figure 9 An example of a content streaming system to which the embodiments disclosed in this document may be applied is illustrated.

[0170] Reference Figure 9 A content streaming system to which embodiments of the present document are applied may basically include an encoding server, a streaming server, a network server, a media storage, a user device, and a multimedia input device.

[0171] The encoding server compresses content input from a multimedia input device such as a smartphone, a camera, or a camcorder into digital data to generate a bitstream, and transmits the bitstream to the streaming server. As another example, when a multimedia input device such as a smartphone, a camera, or a camcorder directly generates a bitstream, the encoding server can be omitted.

[0172] A bitstream may be generated by applying the encoding method or the bitstream generation method of the embodiment of this document, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0173] The streaming server transmits multimedia data to user devices via a network server based on user requests. The network server serves as a medium for informing users of services. When a user requests a desired service from the network server, the network server transmits the requested service to the streaming server, which then transmits the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server is used to control commands and responses between devices in the content streaming system.

[0174] The streaming server can receive content from a media storage and / or encoding server. For example, when receiving content from an encoding server, the content can be received in real time. In this case, in order to provide a stable streaming service, the streaming server can store the bit stream for a predetermined time.

[0175] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigators, touch-screen PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital TVs, desktop computers, digital signage, etc.

[0176] The individual servers in the content streaming system may operate as distributed servers, in which case data received from the individual servers may be distributed.

Claims

1. A decoding device for image decoding, the decoding device comprising: Memory; as well as at least one processor connected to the memory, the at least one processor configured to: Generate a reconstructed picture based on the predicted samples of the coding block; deriving a boundary strength (bs) of a boundary of the coding block in the reconstructed picture; performing deblocking filtering on the boundary of the coding block based on the boundary strength; and deriving a modified reconstructed picture for the reconstructed picture based on the deblocking filtering, wherein the boundary strength is derived based on prediction modes of a first block and a second block adjacent to the boundary of the coding block, wherein, for the coding block to which the prediction mode for deriving motion information in units of subblocks is applied, the boundary strength of the subblock boundary in the coding block is derived, and Wherein, based on the fact that the prediction modes of the first block and the second block are different and the prediction mode of any one of the first block and the second block is a current picture reference (CPR) mode coded with reference to a current picture, the value of the boundary strength of the sub-block boundary is derived as 1.

2. A coding apparatus for image coding, the coding apparatus comprising: Memory; as well as at least one processor connected to the memory, the at least one processor configured to: Generate a reconstructed picture based on the predicted samples of the coding block; deriving a boundary strength (bs) of a boundary of the coding block in the reconstructed picture; performing deblocking filtering on the boundary of the coding block based on the boundary strength; deriving a modified reconstructed picture for the reconstructed picture based on the deblocking filtering; and encoding picture information including information about the coding block, wherein the boundary strength is derived based on prediction modes of a first block and a second block adjacent to the boundary of the coding block, wherein, for the coding block to which the prediction mode for deriving motion information in units of subblocks is applied, the boundary strength of the subblock boundary in the coding block is derived, and Wherein, based on the fact that the prediction modes of the first block and the second block are different and the prediction mode of any one of the first block and the second block is a current picture reference (CPR) mode coded with reference to a current picture, the value of the boundary strength of the sub-block boundary is derived as 1.

3. A device for transmitting image data, the device comprising: At least one processor configured to obtain a bitstream, wherein the bitstream is generated based on: generating a reconstructed picture based on prediction samples of a coding block; deriving a boundary strength (bs) of a boundary of the coding block in the reconstructed picture; performing deblocking filtering on the boundary of the coding block based on the boundary strength; deriving a modified reconstructed picture for the reconstructed picture based on the deblocking filtering; and encoding image information including information about the coding block; and a transmitter configured to transmit data comprising the bit stream, wherein the boundary strength is derived based on prediction modes of a first block and a second block adjacent to the boundary of the coding block, wherein, for the coding block to which the prediction mode for deriving motion information in units of subblocks is applied, the boundary strength of the subblock boundary in the coding block is derived, and Wherein, based on the fact that the prediction modes of the first block and the second block are different and the prediction mode of any one of the first block and the second block is a current picture reference (CPR) mode coded with reference to a current picture, the value of the boundary strength of the sub-block boundary is derived as 1.

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