Image decoding and encoding method, data transmission method, and storage medium

Abstract

The invention discloses an image decoding and encoding method, a data transmission method, and a storage medium. According to an image encoding method according to an embodiment of the present document, information related to in-loop filtering may be effectively signaled, and a repeated process of signalling sub-picture related information may be reduced.

Description

[0001] This application is a divisional application of the invention patent application with the original application number 202080096369.0 (International application number: PCT / KR2020 / 018163, application date: December 11, 2020, invention name: Image encoding device and method for controlling loop filtering). Technical Field

[0002] The present document relates to an image encoding device and method for controlling loop filtering. Background Art

[0003] Recently, the demand for high-resolution, high-quality images / videos such as 4K or 8K or higher ultra-high-definition (UHD) images / videos has increased in various fields. As image / video data has high resolution and high quality, the amount of information or the amount of bits to be transmitted increases relative to existing image / video data, and therefore, transmitting image data using a medium such as an existing wired / wireless broadband line or an existing storage medium or storing image / video data using an existing storage medium increases transmission costs and storage costs.

[0004] In addition, interest in and demand for immersive media such as virtual reality (VR) and artificial reality (AR) content or holograms have recently increased, and broadcasting of images / videos having characteristics different from real images (e.g., game images) has increased.

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

[0006] In particular, sub-pictures and / or loop filtering may be used for image / video compression. A method of efficiently signaling information for controlling loop filtering and / or using sub-pictures is discussed. Summary of the invention

[0007] Technical Solution

[0008] According to an embodiment of this document, a method and apparatus for increasing image encoding efficiency are provided.

[0009] According to the embodiments of this document, a high-efficiency filtering application method and device are provided.

[0010] According to an embodiment of this document, a method and apparatus for efficiently applying deblocking, sample adaptive offset (SAO), and adaptive loop filtering (ALF) are provided.

[0011] According to an embodiment of the present document, in-loop filtering may be performed based on a virtual boundary.

[0012] According to an embodiment of the present document, whether a sequence parameter set (SPS) includes additional virtual boundary related information (eg, information about the location and number of virtual boundaries) is determined based on whether resampling of reference pictures is enabled.

[0013] According to an embodiment of this document, image encoding may be performed on a sub-picture basis.

[0014] According to an embodiment of the present document, sub-pictures used in image encoding can be independently encoded.

[0015] According to an embodiment of the present document, a picture may include only one sub-picture. In addition, the sub-picture may be independently encoded.

[0016] According to the embodiment of the present document, a picture can be generated based on the merging process of sub-pictures. In addition, the sub-picture can be a sub-picture that is independently encoded.

[0017] According to an embodiment of this document, each sub-picture used in image encoding can be regarded as a picture.

[0018] According to an embodiment of this document, there is provided an encoding device for performing video / image encoding.

[0019] According to one embodiment of the present document, a computer-readable digital storage medium is provided, in which encoded video / image information generated according to the video / image encoding method disclosed in at least one embodiment of the present document is stored.

[0020] According to an embodiment of the present document, a computer-readable digital storage medium is provided, in which encoded information or encoded video / image information is stored for enabling a decoding device to execute a video / image decoding method disclosed in at least one embodiment of the present document.

[0021] Beneficial Effects

[0022] According to the embodiments of this document, the overall image / video compression efficiency can be improved.

[0023] According to the embodiments of this document, subjective / objective visual quality can be improved through efficient filtering.

[0024] According to the embodiments of this document, a virtual boundary-based in-loop filtering process can be efficiently performed, and filtering performance can be improved.

[0025] According to the embodiments of this document, information for virtual boundary-based in-loop filtering can be efficiently signaled.

[0026] According to the embodiments of this document, sub-picture related information can be effectively signaled. Therefore, subjective / objective image quality can be improved, and hardware resource consumption required for encoding can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 An example of a video / image encoding system to which embodiments of the present disclosure can be applied is schematically shown.

[0028] Figure 2 is a diagram schematically showing a configuration of a video / image encoding device to which an embodiment of the present disclosure can be applied.

[0029] Figure 3 is a diagram schematically showing a configuration of a video / image decoding device to which an embodiment of the present disclosure can be applied.

[0030] Figure 4 The layered architecture of coded video / images is shown exemplarily.

[0031] Figure 5 Examples of adaptive loop filtering (ALF) filter shapes are shown.

[0032] Figure 6 An example of ALF processing using a virtual boundary according to an embodiment of this document is shown.

[0033] Figure 7 is a flow chart illustrating an encoding method based on filtering in an encoding device.

[0034] Figure 8 is a flow chart illustrating a filtering-based decoding method in a decoding device.

[0035] Fig. 9 and Fig.10 An example of a video / image encoding method and related components according to an embodiment of the present document is schematically shown.

[0036] Fig.11 and Fig.12 An example of an image / video decoding method and related components according to an embodiment of this document is schematically shown.

[0037] Fig.13 An example of a content streaming system to which the embodiments disclosed in this document can be applied is shown. DETAILED DESCRIPTION

[0038] The present disclosure can be modified in various forms, and its specific embodiments will be described and shown in the accompanying drawings. However, these embodiments are not intended to limit the present disclosure. The terms used in the following description are only used to describe specific embodiments and are not intended to limit the present disclosure. Singular expressions include plural expressions as long as they are clearly read differently. Terms such as "including" and "having" are intended to indicate the presence of features, quantities, steps, operations, elements, components, or combinations thereof used in the following description, so it should be understood that the possibility of the presence or addition of one or more different features, quantities, steps, operations, elements, components, or combinations thereof is not excluded.

[0039] In addition, the various configurations of the drawings described in this document are independent illustrations of functions that are different from each other, and do not mean that the various configurations are implemented by different hardware or different software. For example, two or more configurations can be combined to form one configuration, and one configuration can also be divided into multiple configurations. Without departing from the main purpose of this document, embodiments in which the configurations are combined and / or separated are included in the scope of the claims.

[0040] Hereinafter, examples of the present embodiment will be described in detail with reference to the accompanying drawings. In addition, like reference numerals are used to indicate like elements throughout the drawings, and the same description about the like elements will be omitted.

[0041] This document relates to video / image coding. For example, the methods / implementations disclosed in this document may relate to the Versatile Video Coding (VVC) standard (ITU-T Rec. H.266), the next generation video / image coding standard after VVC, or other video coding related standards (e.g., High Efficiency Video Coding (HEVC) standard (ITU-T Rec. H.265), Basic Video Coding (EVC) standard, AVS2 standard, etc.).

[0042] This document proposes various embodiments of video / image coding, and unless otherwise specified, the above embodiments may also be performed in combination with each other.

[0043] In this document, video may refer to a series of images over time. A picture generally refers to a unit representing an image for a specific time range, and a slice / tile refers to a unit that constitutes a part of a picture in terms of coding. A slice / tile may include one or more coding tree units (CTUs). A picture may consist of one or more slices / tiles. A picture may consist of one or more tile groups. A tile group may include one or more tiles.

[0044] A pixel or picture element may refer to the smallest unit constituting a picture (or image). In addition, a "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, and may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0045] A unit may represent a basic unit of image processing. A unit may include at least one of a specific area of ​​a picture and information related to the area. A unit may include a luminance block and two chrominance (e.g., cb, cr) blocks. In some cases, a unit may be used interchangeably with terms such as a block or an area. In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients. Alternatively, a sample may refer to a pixel value in a spatial domain, and when such a pixel value is transformed to a frequency domain, it may refer to a transform coefficient in a frequency domain.

[0046] 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".

[0047] Furthermore, in this document, the term "or" should be interpreted as indicating "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 indicating "additionally or alternatively".

[0048] In the present specification, "at least one of A and B" may mean "only A", "only B", or "both A and B". In addition, in the present specification, the expression "at least one of A or B" or "at least one of A and / or B" may be interpreted the same as "at least one of A and B".

[0049] Furthermore, in the present specification, “at least one of A, B, and C” may mean “only A”, “only B”, “only C”, or “any combination of A, B, and C”. Furthermore, “at least one of A, B, or C” or “at least one of A, B and / or C” may mean “at least one of A, B, and C”.

[0050] In addition, brackets used in this specification may mean "for example". Specifically, in the case of expressing "prediction (intra-frame prediction)", it may indicate that "intra-frame prediction" is proposed as an example of "prediction". In other words, the term "prediction" in this specification is not limited to "intra-frame prediction", and it may indicate that "intra-frame prediction" is proposed as an example of "prediction". In addition, even in the case of expressing "prediction (i.e., intra-frame prediction)", it may indicate that "intra-frame prediction" is proposed as an example of "prediction".

[0051] In this specification, technical features described separately in one drawing may be implemented separately or may be implemented simultaneously.

[0052] Figure 1 An example of a video / image encoding system to which the disclosure of this document can be applied is shown.

[0053] Reference Figure 1 The video / image coding system may include a source device and a receiving device. The source device may send the coded video / image information or data in the form of a file or stream to the receiving device via a digital storage medium or a network.

[0054] 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.

[0055] The video source may acquire the video / image by capturing, synthesizing or generating the video / image process. The video source may include a video / image capture device and / or a video / image generation device. For example, the video / image capture device may include one or more cameras, a video / image archive including previously captured videos / images, etc. For example, the video / image generation device may include a computer, a tablet computer, and a smart phone, and may generate the video / image (electronically). For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capture process may be replaced by a process that generates relevant data.

[0056] The encoding device can encode the input video / image. For compression and encoding efficiency, the encoding device can perform a series of processes such as prediction, transformation and quantization. The encoded data (encoded video / image information) can be output in the form of a bit stream.

[0057] The transmitter may transmit the encoded image / image information or data output in the form of a bit stream to a receiver of a receiving device in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter may include an element for generating a media file in a predetermined file format, and may include an element for transmission through a broadcast / communication network. The receiver may receive / extract a bit stream and transmit the received bit stream to a decoding device.

[0058] The decoding device may decode a video / image by performing a series of processes such as dequantization, inverse transformation, and prediction corresponding to the operations of the encoding device.

[0059] The renderer may render the decoded video / image. The rendered video / image may be displayed through a display.

[0060] Figure 2 is a diagram schematically showing the configuration of a video / image encoding device to which the disclosure of this document can be applied. Hereinafter, the so-called video encoding device may include an image encoding device.

[0061] Reference Figure 2 , the encoding device 200 may include and be configured with 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, a dequantizer 234, and an inverse transformer 235. The residual processor 230 may also include a subtractor 231. The adder 250 may be referred to as a reconstructor or a reconstructed block generator. According to an embodiment, the above-mentioned image segmenter 210, the predictor 220, the residual processor 230, the entropy encoder 240, the adder 250, and the filter 260 may be configured by 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 also be configured by a digital storage medium. The hardware component may also include a memory 270 as an internal / external component.

[0062] The image divider 210 may divide the input image (or picture, frame) input to the encoding device 200 into one or more processing units. As an example, the processing unit may be referred to as a coding unit (CU). In this case, the coding unit may be recursively divided from a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QTBTTT) structure. For example, one coding unit may be divided into a plurality of coding units with a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. In this case, for example, the quadtree structure is applied first, and the binary tree structure and / or the ternary tree structure may be applied later. Alternatively, the binary tree structure may also be applied first. The encoding process according to the present disclosure may be performed based on the final coding unit that is no longer divided. In this case, based on encoding efficiency according to image characteristics, etc., the maximum coding unit may be directly used as the final coding unit, or if necessary, the coding unit may be recursively divided into coding units with a deeper depth so that a coding unit with an optimal size may be used as the final coding unit. Here, the encoding process may include processes such as prediction, transformation, and reconstruction (described later). As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, each of the prediction unit and the transform unit may be split or divided from the above-mentioned final coding unit. The prediction unit may be a unit for sample prediction, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0063] In some cases, a unit may be used interchangeably with terms such as a block or a region. In general, an M×N block may represent a sample or a set of transform coefficients consisting of M columns and N rows. A sample may generally represent a pixel or a pixel value, and may also represent only a pixel / pixel value of a luminance component, and may also represent only a pixel / pixel value of a chrominance component. A sample may be used as a term corresponding to a pixel or a picture element configuring one screen (or image).

[0064] The subtractor 231 may generate a residual signal (residual block, residual sample, or residual sample array) by subtracting a prediction signal (prediction block, prediction sample, or prediction sample array) output from the predictor 220 from an input image signal (original block, original sample, or original sample array), and the generated residual signal is sent to the transformer 232. The predictor 220 may perform prediction on a processing target block (hereinafter, referred to as a "current block") and generate a prediction block including prediction samples of the current block. The predictor 220 may determine whether intra prediction or inter prediction is applied to the current block or in units of CUs. As described later in the description of each prediction mode, the predictor may generate various types of information related to prediction (e.g., prediction mode information) and transmit the generated information to the entropy encoder 240. Information about the prediction may be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0065] The intra-frame predictor 222 may predict the current block with reference to samples within the current picture. Depending on the prediction mode, the referenced sample may be located near the current block, or may be far away from the current block. The prediction mode in the intra-frame prediction may include multiple non-directional modes and multiple directional modes. For example, the non-directional mode may include a DC mode or a plane mode. For example, depending on the degree of refinement of the prediction direction, the directional mode may include 33 directional prediction modes or 65 directional prediction modes. However, this is exemplary, and more or less directional prediction modes than the above number may be used according to the settings. The intra-frame predictor 222 may also use the prediction mode applied to the neighboring blocks to determine the prediction mode applied to the current block.

[0066] The inter-frame predictor 221 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. At this time, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may also be the same as each other, and may also be different from each other. The temporal neighboring block may be referred to as a name such as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may also be referred to as a collocated picture (colPic). For example, the inter-frame predictor 221 may configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter prediction may be performed based on various prediction modes, for example, in the case of skip mode and merge mode, the inter predictor 221 may use motion information of a neighboring block as motion information of a current block. In skip mode, unlike merge mode, a residual signal may not be transmitted. A motion vector prediction (MVP) mode may indicate a motion vector of a current block by using a motion vector of a neighboring block as a motion vector predictor and signaling a motion vector difference.

[0067] The predictor 220 may generate a prediction signal based on various prediction methods described below. For example, the predictor may apply not only intra prediction or inter prediction to predict a block, but also both intra prediction and inter prediction at the same time. This may be referred to as combined inter and intra prediction (CIIP). In addition, the predictor may perform intra block copy (IBC) for predicting blocks. Intra block copy may be used for content image / motion image coding of games, etc., such as screen content coding (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction so that a reference block is derived in the current picture. That is, IBC may use at least one inter prediction technique described in this document.

[0068] The prediction signal generated by the inter-frame predictor 221 and / or the intra-frame predictor 222 can be used to generate a reconstruction signal or to generate a residual signal. The transformer 232 can generate a transform coefficient by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, when the relationship information between pixels is represented by a graph, GBT means a transform obtained from a 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 other than squares.

[0069] The quantizer 233 may quantize the transform coefficients and send them to the entropy encoder 240, and the entropy encoder 240 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 233 may rearrange the block type quantized transform coefficients into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoder 240 may 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 may encode information required for video / image reconstruction together with or separately from the quantized transform coefficients (e.g., the value of a syntax element, etc.). The encoded information (e.g., encoded video / image information) may be transmitted or stored in units of a network abstraction layer (NAL) in the form of a bitstream. The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. In this document, the information and / or syntax elements that are signaled / sent described later may be encoded by the above-mentioned encoding process and included in the bitstream. The bitstream may be sent over a network or may be stored in a digital storage medium. Here, the network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that sends a signal output from the entropy encoder 240 and / or a storage unit (not shown) that stores the signal may be configured as an internal / external element of the encoding device 200, and alternatively, the transmitter may be included in the entropy encoder 240.

[0070] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, a residual signal (residual block or residual sample) can be reconstructed by applying dequantization and inverse transformation to the quantized transform coefficients via the dequantizer 234 and the inverse transformer 235. The adder 250 adds the reconstructed residual signal to the prediction signal output from the predictor 220 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample or reconstructed sample array). If there is no residual in the processing target block (for example, in the case of applying skip mode), the prediction block can be used as a reconstructed block. As described below, the generated reconstructed signal can be used for intra-frame prediction of the next processing target block in the current picture and can be used for inter-frame prediction of the next picture by filtering.

[0071] Furthermore, luma mapping with chroma scaling (LMCS) may be applied during the picture encoding and / or reconstruction process.

[0072] The filter 260 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 260 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture and store the modified reconstructed picture in the memory 270 (specifically, the DPB of the memory 270). For example, various filtering methods may include deblocking filtering, sample adaptive offset (SAO), adaptive loop filter, bilateral filter, etc. The filter 260 can generate various types of information related to filtering and transmit the generated information to the entropy encoder 290, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 290 and output in the form of a bitstream.

[0073] The modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter predictor 221. When inter prediction is applied by the encoding apparatus, prediction mismatch between the encoding apparatus 200 and the decoding apparatus 300 may be avoided and encoding efficiency may be improved.

[0074] The DPB of the memory 270 may store a modified reconstructed picture used as a reference picture in the inter-frame predictor 221. The memory 270 may store motion information of a block from which motion information in the current picture is derived (or encoded) and / or motion information of a block that has been reconstructed in the picture. The stored motion information may be transmitted to the inter-frame predictor 221 to be used as motion information of a spatially adjacent block or motion information of a temporally adjacent block. The memory 270 may store reconstructed samples of a reconstructed block in the current picture and may transmit the reconstructed samples to the intra-frame predictor 222.

[0075] Figure 3 This is a diagram for schematically illustrating the configuration of a video / image decoding device to which the disclosure of this document can be applied.

[0076] Reference Figure 3 , the decoding device 300 may include and be configured with an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter-frame predictor 331 and an intra-frame predictor 332. The residual processor 320 may include a dequantizer 321 and an inverse transformer 322. 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 configured by one or more hardware components (e.g., a decoder chipset or a processor). In addition, the memory 360 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium. The hardware component may also include a memory 360 as an internal / external component.

[0077] When a bit stream including video / image information is input, the decoding device 300 may respond to the Figure 2The image is reconstructed by processing video / image information in the encoding device shown. For example, the decoding device 300 may derive a unit / block based on block partition related information obtained from the bitstream. The decoding device 300 may perform decoding using a processing unit applied to the encoding device. Thus, for example, the processing unit for decoding may be a coding unit, and the coding unit may be divided from a coding tree unit or a maximum coding unit according to a quadtree structure, a binary tree structure, and / or a ternary tree structure. One or more transform units may be derived from the coding unit. In addition, the reconstructed image signal decoded and output by the decoding device 300 may be reproduced by a reproduction device.

[0078] The decoding device 300 may receive Figure 2The received signal may be decoded by the entropy decoder 310. For example, the entropy decoder 310 may parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The decoding device may also decode the picture based on the information about the parameter set and / or the general constraint information. The information and / or syntax elements signaled / received described later in this document may be decoded and obtained from the bitstream by a decoding process. For example, the entropy decoder 310 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output 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 may receive a bin corresponding to each syntax element in the bitstream, determine a context model using information of a decoding target syntax element, decoding information of a decoding target block, or information of a symbol / bin decoded in a previous stage, and perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. Information related to prediction among the information decoded by the entropy decoder 310 may be provided to the predictor 330, and information about the residual (i.e., quantized transform coefficients and related parameter information) on which entropy decoding is performed in the entropy decoder 310 may be input to the dequantizer 321. In addition, information about filtering among the information decoded by the entropy decoder 310 may be provided to the filter 350. In addition, a receiver (not shown) for receiving a signal output from the encoding device may also be configured as an internal / external element of the decoding device 300, or the receiver may be a constituent element 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 classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 310, and the sample decoder may include at least one of a dequantizer 321, an inverse transformer 322, a predictor 330, an adder 340, a filter 350, and a memory 360.

[0079] The dequantizer 321 may dequantize the quantized transform coefficient to output the transform coefficient. The dequantizer 321 may rearrange the quantized transform coefficient in a two-dimensional block form. In this case, the rearrangement may be performed based on the coefficient scanning order performed by the encoding device. The dequantizer 321 may perform dequantization on the quantized transform coefficient using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficient.

[0080] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0081] The predictor 330 may perform prediction of the current block and generate a prediction block including prediction samples of the current block. The predictor may determine whether to apply intra prediction or inter prediction to the current block based on information on prediction output from the entropy decoder 310 and determine a specific intra / inter prediction mode.

[0082] The predictor may generate a prediction signal based on various prediction methods described below. For example, the predictor may not only apply intra prediction or inter prediction to predict a block, but may also apply intra prediction and inter prediction at the same time. This may be referred to as combined inter and intra prediction (CIIP). In addition, the predictor may perform intra block copying (IBC) for predicting blocks. Intra block copying may be used for content image / motion image coding of games, etc., such as screen content coding (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction so that a reference block is derived in the current picture. That is, IBC may use at least one inter prediction technique described in this document.

[0083] The intra-frame predictor 332 may predict the current block with reference to samples in the current picture. Depending on the prediction mode, the referenced samples may be located near the current block or may be far away from the current block. In intra-frame prediction, the prediction mode may include multiple non-directional modes and multiple directional modes. The intra-frame predictor 332 may use the prediction mode applied to the neighboring blocks to determine the prediction mode to be applied to the current block.

[0084] The inter-frame predictor 331 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include information about the inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter-frame predictor 331 may construct a motion information candidate list based on neighboring blocks and derive a motion vector and / or a reference picture index of the current block based on the received candidate selection information. Inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0085] The adder 340 may generate a reconstructed signal (reconstructed picture, reconstructed block, and reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block or prediction sample array) output from the predictor 330. If there is no residual in the processing target block, such as when the skip mode is applied, the prediction block may be used as the reconstructed block.

[0086] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next block to be processed in the current picture, and as described later, may also be output through filtering, or may also be used for inter prediction of the next picture.

[0087] In addition, luma mapping with chroma scaling (LMCS) may also be applied in the picture decoding process.

[0088] The filter 350 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture and store the modified reconstructed picture in the memory 360 (specifically, the DPB of the memory 360). For example, the various filtering methods may include deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0089] The (modified) reconstructed picture stored in the DPB of the memory 360 may be used as a reference picture in the inter-frame predictor 331. The memory 360 may store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame predictor 331 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 360 may store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame predictor 332.

[0090] In the present specification, the implementations described in the predictor 330, dequantizer 321, inverse transformer 322, and filter 350 of the decoding device 300 may also be applied in the same or corresponding manner as the predictor 220, dequantizer 234, inverse transformer 235, and filter 260 of the encoding device 200.

[0091] In addition, as described above, when performing video encoding, prediction is performed to improve compression efficiency. Thus, a prediction block including prediction samples of a current block as a block to be encoded (i.e., an encoding target block) can be generated. Here, the prediction block includes prediction samples in a spatial domain (or a pixel domain). The prediction block is derived in the same manner as in the encoding device and the decoding device, and the encoding device can signal the decoding device with information about the residual between the original block and the prediction block (residual information) instead of the original sample value of the original block, thereby increasing the image coding efficiency. The decoding device can derive a residual block including residual samples based on the residual information, add the residual block and the prediction block to generate a reconstructed block including reconstructed samples, and generate a reconstructed picture including the reconstructed block.

[0092] The residual information may be generated by transform and quantization processing. For example, the encoding device may derive a residual block between the original block and the prediction block, perform a transform process on the residual samples (residual sample array) included in the residual block to derive a transform coefficient, perform a quantization process on the transform coefficient to derive a quantized transform coefficient, and notify the decoding device of the relevant residual information (through a bitstream) with a signal. Here, the residual information may include value information, position information, transform technology, transform kernel, quantization parameter, etc. of the quantized transform coefficient. The decoding device may perform a dequantization / inverse transform process based on the residual information and derive a residual sample (or residual block). The decoding device may generate a reconstructed picture based on the prediction block and the residual block. In addition, as a reference for inter-frame prediction of a later picture, the encoding device may also dequantize / inverse transform the quantized transform coefficient to derive a residual block, and generate a reconstructed picture based on it.

[0093] In this document, at least one of quantization / dequantization and / or transform / inverse transform may be omitted. When quantization / dequantization is omitted, the quantized transform coefficient may be referred to as a transform coefficient. When transform / inverse transform is omitted, the transform coefficient may be referred to as a coefficient or a residual coefficient, or may still be referred to as a transform coefficient for consistency of expression.

[0094] In this document, the quantized transform coefficient and the transform coefficient may be referred to as a transform coefficient and a scaled transform coefficient, respectively. In this case, the residual information may include information about the transform coefficient, and the information about the transform coefficient may be signaled by a residual coding syntax. The transform coefficient may be derived based on the residual information (or information about the transform coefficient), and the scaled transform coefficient may be derived by inverse transforming (scaling) the transform coefficient. The residual sample may be derived based on an inverse transform (transform) of the scaled transform coefficient. This may also be applied / expressed in other parts of this document.

[0095] The predictor of the encoding device / decoding device can derive prediction samples by performing inter-frame prediction in units of blocks. Inter-frame prediction may be a prediction derived in a manner that depends on data elements (e.g., sample values ​​or motion information) of a picture other than the current picture. When inter-frame prediction is applied to the current block, a prediction block (prediction sample array) of the current block may be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture pointing to a reference picture index. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block may be predicted in units of blocks, sub-blocks, or samples based on the correlation between the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When inter-frame prediction is applied, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. A temporally neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and a reference picture including a temporally neighboring block may be referred to as a collocated picture (colPic). For example, a motion information candidate list may be constructed based on the neighboring blocks of the current block, and a flag or index information indicating which candidate is selected (used) to derive the motion vector and / or reference picture index of the current block may be signaled. Inter-frame prediction may be performed based on various prediction modes. For example, in skip mode and merge mode, the motion information of the current block may be the same as the motion information of the selected neighboring block. In skip mode, unlike merge mode, a residual signal may not be sent. In the case of a motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor, and the motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0096] According to the inter prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. The motion vector in the L0 direction may be referred to as the L0 motion vector or MVL0, and the motion vector in the L1 direction may be referred to as the L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as the L0 prediction, prediction based on the L1 motion vector may be referred to as the L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as the dual prediction. Here, the L0 motion vector may indicate a motion vector associated with the reference picture list L0 (L0), and the L1 motion vector may indicate a motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include a picture that is earlier than the current picture in the output order as a reference picture, and the reference picture list L1 may include a picture that is later than the current picture in the output order. The previous picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. The reference picture list L0 may also include a picture that is later than the current picture in the output order as a reference picture. In this case, in the reference picture list L0, the previous picture may be indexed first and the subsequent picture may be indexed next. The reference picture list L1 may also include a picture that is earlier than the current picture in the output order as a reference picture. In this case, the subsequent picture may be indexed first in the reference picture list 1 and the previous picture may be indexed next. Here, the output order may correspond to a picture order count (POC) order.

[0097] Figure 4 The hierarchical structure of the encoded image / video is shown exemplarily.

[0098] Reference Figure 4 The coded image / video is divided into the VCL (Video Coding Layer) that handles the image / video decoding process and itself, the subsystem that sends and stores the coded information, and the Network Abstraction Layer (NAL) that exists between the VCL and the subsystem and is responsible for the network adaptation function.

[0099] VCL can generate VCL data including compressed image data (slice data), or generate parameter sets including picture parameter sets (picture parameter set: PSP), sequence parameter sets (sequence parameter set: SPS), video parameter sets (Video Parameter Set: VPS), etc., or supplementary enhancement information (SEI) messages required for image decoding processing.

[0100] In NAL, a NAL unit may be generated by adding header information (NAL unit header) to a raw byte sequence payload (RBSP) generated in a VCL. In this case, the RBSP refers to slice data, parameter sets, SEI messages, etc. generated in the VCL. The NAL unit header may include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0101] As shown in the figure, the NAL unit can be divided into a VCL NAL unit and a non-VCL NAL unit according to the RBSP generated in the VCL. The VCL NAL unit may refer to a NAL unit including information about the image (slice data), and the non-VCL NAL unit may refer to a NAL unit containing information required for decoding the image (parameter set or SEI message).

[0102] The above-mentioned VCL NAL unit and non-VCL NAL unit can be sent through the network by adding header information according to the data standard of the subsystem. For example, the NAL unit can be converted into a data form of a predetermined standard such as H.266 / VVC file format, real-time transport protocol (RTP), transport stream (TS), etc. and sent through various networks.

[0103] As described above, a NAL unit type may be specified in a NAL unit according to an RBSP data structure included in a corresponding NAL unit, and information about the NAL unit type may be stored in a NAL unit header and signaled.

[0104] For example, NAL units can be roughly classified into VCL NAL unit types and non-VCL NAL unit types according to whether the NAL unit includes information about an image (slice data). VCL NAL unit types can be classified according to the properties and types of pictures included in the VCL NAL unit, and non-VCL NAL unit types can be classified according to the types of parameter sets.

[0105] The following are examples of NAL unit types specified according to the type of parameter sets included in a non-VCL NAL unit type.

[0106] -APS (Adaptation Parameter Set) NAL unit: the type of NAL unit that includes APS

[0107] -DPS (Decoding Parameter Set) NAL unit: the type of NAL unit that includes the DPS

[0108] -VPS (Video Parameter Set) NAL unit: the type of NAL unit that contains the VPS

[0109] -SPS (Sequence Parameter Set) NAL unit: the type of NAL unit that includes SPS

[0110] -PPS (Picture Parameter Set) NAL unit: the type of NAL unit that includes the PPS

[0111] - PH (Picture Header) NAL unit: the type of NAL unit that includes PH

[0112] The above-mentioned NAL unit type has syntax information of the NAL unit type, and the syntax information may be stored in the NAL unit header and notified by a signal. For example, the syntax information may be nal_unit_type, and the NAL unit type may be specified by a nal_unit_type value.

[0113] In addition, as described above, a picture may include multiple slices, and a slice may include a slice header and slice data. In this case, a picture header may be further added to the multiple slices (slice header and slice data set) in a picture. The picture header (picture header syntax) may include information / parameters generally applicable to a picture. In this document, slices may be mixed with or replaced by tiling groups. In addition, in this document, slice headers may be mixed with tiling group headers or replaced by type group headers.

[0114] A slice header (slice header syntax or slice header information) may include information / parameters that are generally applicable to slices. APS (APS syntax) or PPS (PPS syntax) may include information / parameters that are generally applicable to one or more slices or pictures. SPS (SPS syntax) may include information / parameters that are generally applicable to one or more sequences. VPS (VPS syntax) may include information / parameters that are generally applicable to multiple layers. DPS (DPS syntax) may include information / parameters that are generally applicable to the entire video. DPS may include information / parameters related to the concatenation of a coded video sequence (CVS). In this document, a high-level syntax (HLS) may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, picture header syntax, and slice header syntax.

[0115] In this document, the image / video information encoded in the encoding device and notified to the decoding device in the form of a bitstream may include not only the segmentation related information, intra / inter prediction information, residual information, loop filtering information, etc. in the picture, but also the information included in the slice header, the information included in the picture header, the information included in the APS, the information included in the PPS, the information included in the SPS, the information included in the VPS and / or the information included in the DPS. In addition, the image / video information may also include the information of the NAL unit header.

[0116] In addition, in order to compensate for the difference between the original image and the reconstructed image due to errors occurring in the compression encoding process such as quantization, loop filtering processing may be performed on the reconstructed sample or the reconstructed picture as described above. As described above, loop filtering may be performed by a filter of an encoding device and a filter of a decoding device, and a deblocking filter, SAO and / or an adaptive loop filter (ALF) may be applied. For example, the ALF process may be performed after the deblocking filter process and / or the SAO process are completed. However, even in this case, the deblocking filter process and / or the SAO process may be omitted.

[0117] Hereinafter, picture reconstruction and filtering will be described in detail. In image / video encoding, a reconstructed block may be generated based on intra-frame prediction / inter-frame prediction in each block unit, and a reconstructed picture including the reconstructed block may be generated. When the current picture / slice is an I picture / slice, the blocks included in the current picture / slice may be reconstructed based only on intra-frame prediction. In addition, when the current picture / slice is a P or B picture / slice, the blocks included in the current picture / slice may be reconstructed based on intra-frame prediction or inter-frame prediction. In this case, intra-frame prediction may be applied to some blocks in the current picture / slice, and inter-frame prediction may be applied to the remaining blocks.

[0118] Intra-frame prediction may refer to a prediction of a prediction sample of a current block generated based on a reference sample in a picture to which the current block belongs (hereinafter, the current picture). In the case where intra-frame prediction is applied to the current block, neighboring reference samples to be used for intra-frame prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block of size nW×nH, a total of 2×nH samples adjacent to the lower left, samples adjacent to the upper boundary of the current block, a total of 2×nW samples adjacent to the upper right, and one sample adjacent to the upper left of the current block. Alternatively, the neighboring reference samples of the current block may include upper neighboring samples of multiple columns and left neighboring samples of multiple rows. Alternatively, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block of size nW×nH, a total of nH samples adjacent to the right boundary of the current block, a total of nW samples adjacent to the lower boundary of the current block, and one sample adjacent to the lower right of the current block.

[0119] However, some neighboring reference samples of the current block may not have been decoded or may not be available. In this case, the decoder can configure the neighboring reference samples to be used for prediction by replacing the unavailable samples with available samples. Alternatively, the neighboring reference samples to be used for prediction can be configured by interpolation of available samples.

[0120] When deriving neighboring reference samples, there are two cases, namely, case (i) in which the prediction sample can be derived based on the average or interpolation of the neighboring reference samples of the current block and case (ii) in which the prediction sample can be derived based on the reference sample existing in a specific (prediction) direction of the prediction sample among the neighboring reference samples of the current block. Case (i) may be referred to as a non-directional mode or a non-angular mode, and case (ii) may be referred to as a directional mode or an angular mode. In addition, the prediction sample may also be generated by the first neighboring sample and the second neighboring sample located in the direction opposite to the prediction direction of the intra-frame prediction mode of the current block among the neighboring reference samples. The above case may be referred to as linear interpolation intra-frame prediction (LIP). In addition, the chroma prediction sample may be generated based on the luminance sample using a linear model. This case may be referred to as LM mode. In addition, the temporal prediction sample of the current block may be derived based on the filtered neighboring reference samples. At least one reference sample derived according to the intra-frame prediction mode and the temporal prediction sample among the existing neighboring reference samples (i.e., the unfiltered neighboring reference samples) may be weighted summed to derive the prediction sample of the current block. The above case may be referred to as position-dependent intra-frame prediction (PDPC). In addition, a reference sample line with the highest prediction accuracy among multiple reference sample lines adjacent to the current block can be selected to derive a prediction sample using a reference sample located in the prediction direction on the corresponding line, and the reference sample line used in this article can be indicated (notified by signal) to the decoding device, thereby performing intra-frame prediction encoding. The above situation may be referred to as multi-reference line (MRL) intra-frame prediction or MRL-based intra-frame prediction. In addition, intra-frame prediction can be performed based on the same intra-frame prediction mode by dividing the current block into vertical or horizontal sub-partitions, and neighboring reference samples can be derived and used in units of sub-partitions. That is, in this case, the intra-frame prediction mode of the current block is equally applied to the sub-partitions, and the intra-frame prediction performance can be improved by deriving and using neighboring reference samples in units of sub-partitions in some cases. This prediction method may be referred to as intra-frame sub-partitioning (ISP) or intra-frame prediction based on ISP. The above intra-frame prediction method may be referred to as an intra-frame prediction type different from the intra-frame prediction mode in Section 1.2. The intra-frame prediction type may be referred to as various terms such as intra-frame prediction technology or additional intra-frame prediction mode. For example, the intra prediction type (or additional intra prediction mode, etc.) may include at least one of the above-mentioned LIP, PDPC, MRL, and ISP. A general intra prediction method other than a specific intra prediction type such as LIP, PDPC, MRL, or ISP may be referred to as a normal intra prediction type. When a specific intra prediction type is not applied, a normal intra prediction type may generally be applied, and prediction may be performed based on the above-mentioned intra prediction mode. In addition, post-processing filtering may be performed on the derived prediction sample, optionally.

[0121] Specifically, the intra prediction process may include an operation of determining an intra prediction mode / type, an operation of deriving neighboring reference samples, and an operation of deriving prediction samples based on the intra prediction mode / type. In addition, optionally, a post-processing filtering operation may be performed on the derived prediction samples.

[0122] A modified reconstructed picture may be generated by an in-loop filtering process, and the modified reconstructed picture may be output as a decoded picture in a decoding device, and may also be stored in a decoded picture buffer or memory of an encoding device / decoding device and used as a reference picture in an inter-frame prediction process when the picture is encoded / decoded at a later time. The in-loop filtering process may include a deblocking filtering process, a sample adaptive offset (SAO) process, and / or an adaptive loop filter (ALF) process as described above. In this case, one or some of the deblocking filtering process, the SAO process, the ALF process, and the bilateral filtering process may be applied sequentially, or all of the processes may be applied sequentially. For example, the SAO process may be performed after the deblocking filtering process is applied to the reconstructed picture. Alternatively, for example, the ALF process may be performed after the deblocking filtering process is applied to the reconstructed picture. This may also be performed in the encoding device in the same manner.

[0123] Deblocking filtering is a filtering technique that removes distortion that occurs at the boundaries between blocks in a reconstructed picture. For example, the deblocking filtering process may derive a target boundary in the reconstructed picture, determine a boundary strength (bS) of the target boundary, and perform deblocking filtering on the target boundary based on the bS. The bS may be determined based on the prediction mode of two blocks adjacent to the target boundary, the motion vector difference, whether the reference picture is the same, whether there are non-zero significant coefficients, etc.

[0124] SAO is a method of compensating for an offset difference between a reconstructed picture and an original picture based on samples. For example, SAO may be applied based on types such as band offset, edge offset, etc. According to SAO, samples may be classified into different categories according to respective SAO types, and an offset value may be added to each sample based on the category. Filter information of SAO may include information on whether SAO is applied, SAO type information, SAO offset value information, etc. SAO may be applied to the reconstructed picture after deblocking filtering is applied.

[0125] ALF is a technique for filtering a reconstructed picture based on a sample based on a filter coefficient according to a filter shape. The encoding device may determine whether to apply ALF, ALF shape, and / or ALF filter coefficients, etc. by comparing the reconstructed picture with the original picture, and may signal the determination result to the decoding device. That is, the filter information of ALF may include information on whether to apply ALF, ALF filter shape information, ALF filter coefficient information, etc. ALF may be applied to the reconstructed picture after deblocking filtering is applied.

[0126] Figure 5 An example of an ALF filter shape is shown.

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

[0128] Figure 6 An example of ALF processing using a virtual boundary according to an embodiment of this document is shown.

[0129] The virtual boundary may be a line defined by shifting the horizontal CTU boundary by N samples. In an embodiment, N may be 4 for luma components and / or 2 for chroma components.

[0130] Modified block classification may be applied to the luma component. For 1D Laplacian gradient calculations of 4×4 blocks above a virtual boundary, only samples above the virtual boundary may be used. Similarly, for 1D Laplacian gradient calculations of 4×4 blocks below a virtual boundary, only samples below the virtual boundary may be used. The quantization of the activity value A may be scaled accordingly by taking into account the reduction in the number of samples used in the 1D Laplacian gradient calculations.

[0131] For the filtering process, symmetric padding operations at virtual boundaries can be used for both luma and chroma components. Figure 6 , when the filtered sample is below the virtual boundary, the adjacent samples above the virtual boundary can be filled in. In addition, the corresponding samples on the other side can also be filled symmetrically.

[0132] When no filters are enabled across boundaries, according to Figure 6 The described process can also be used for slice, tile and / or patch boundaries. For ALF block classification, only samples included in the same slice, tile and / or patch can be used, and the activity value can be scaled accordingly. For ALF filtering, symmetric padding can be applied in both horizontal and vertical directions for horizontal and / or vertical boundaries, respectively.

[0133] Figure 7 is a flowchart illustrating a filtering-based encoding method in an encoding device. Figure 7 The method may include steps S700 to S730.

[0134] In step S700, the encoding apparatus may generate a reconstructed picture. Step S700 may be performed based on the above-described reconstructed picture (or reconstructed sample) generation process.

[0135] In step S710, the encoding device may determine whether to apply in-loop filtering (across a virtual boundary) based on in-loop filtering related information. Herein, in-loop filtering may include at least one of the above-mentioned deblocking filtering, SAO, and ALF.

[0136] In step S720, the encoding apparatus may generate a modified reconstructed picture (modified reconstructed sample) based on the determination of step S710. Herein, the modified reconstructed picture (modified reconstructed sample) may be a filtered reconstructed picture (filtered reconstructed sample).

[0137] In step S730, the encoding apparatus may encode image / video information including in-loop filtering related information based on the in-loop filtering process.

[0138] Figure 8 is a flow chart illustrating a filtering-based decoding method in a decoding device. Figure 8 The method may include steps S800 to S830.

[0139] In step S800, the decoding apparatus may obtain image / video information including in-loop filtering related information from a bitstream. Herein, the bitstream may be based on encoded image / video information transmitted from an encoding apparatus.

[0140] In step S810, the decoding apparatus may generate a reconstructed picture. Step S810 may be performed based on the above-mentioned reconstructed picture (or reconstructed sample).

[0141] In step S820, the decoding device may determine whether to apply in-loop filtering (across a virtual boundary) based on the in-loop filtering related information. Herein, the in-loop filtering may include at least one of the above-mentioned deblocking filtering, SAO, and ALF.

[0142] In step S830, the decoding apparatus may generate a modified reconstructed picture (modified reconstructed samples) based on the determination of step S820. Herein, the modified reconstructed picture (modified reconstructed samples) may be a filtered reconstructed picture (filtered reconstructed samples).

[0143] As described above, in-loop filtering may be applied to the reconstructed picture. In this case, a virtual boundary may be defined to further improve the subjective / objective visual quality of the reconstructed picture, and in-loop filtering may be applied across the virtual boundary. For example, the virtual boundary may include discontinuous edges such as 360-degree images, VR images, boundaries, picture-in-picture (PIP), etc. For example, a virtual boundary may exist at a predetermined position, and its existence and / or position may be notified by a signal. For example, the virtual boundary may be located at the fourth sample line above the CTU row (specifically, for example, above the fourth sample above the CTU row). As another example, information about the existence and / or position of the virtual boundary may be notified by a signal via HLS. HLS may include SPS, PPS, picture header, slice header, etc. as described above.

[0144] Hereinafter, high-level syntax signaling and semantics will be described according to embodiments of the present disclosure.

[0145] Embodiments of the present document may include methods for controlling loop filters. The present method for controlling loop filters may be applied to reconstructed pictures. An in-loop filter (loop filter) may be used for decoding of a coding bit rate. The loop filter may include deblocking, SAO, and ALF as described above. The SPS may include flags associated with each of deblocking, SAO, and ALF. The flags may indicate whether the respective tools may be used for coding of a coded layer video sequence (CLVS) or a coded video sequence (CVS) with reference to the SPS.

[0146] In an example, when a loop filter is enabled for encoding of a picture in a CVS, the loop filter may be controlled not to be applied across a specific boundary. For example, the loop filter may be controlled not to cross a sub-picture boundary, the loop filter may be controlled not to cross a tile boundary, the loop filter may be controlled not to cross a slice boundary, and / or the loop filter may be controlled not to cross a virtual boundary.

[0147] The information related to in-loop filtering may include information, syntax, syntax elements and / or semantics described in this document (or an embodiment included therein). The information related to in-loop filtering may include information related to whether (all or part of) in-loop filtering processing is enabled across specific boundaries (e.g., virtual boundaries, sub-picture boundaries, slice boundaries and / or patch boundaries). The image information included in the bitstream may include high-level syntax (HLS), and the HLS may include in-loop filtering related information. Modified (or filtered) reconstructed samples (reconstructed pictures) may be generated based on the determination of whether in-loop filtering processing is applied across specific boundaries. In an example, when in-loop filtering processing is disabled for all blocks / boundaries, the modified reconstructed samples may be the same as the reconstructed samples. In another example, the modified reconstructed samples may include modified reconstructed samples derived based on in-loop filtering. However, in this case, some reconstructed samples (e.g., reconstructed samples across virtual boundaries) may not be subjected to in-loop filtering based on the above determination. For example, reconstructed samples across certain boundaries (at least one of a virtual boundary, a sub-picture boundary, a slice boundary, and / or a patch boundary for enabling in-loop filtering) may be in-loop filtered, but reconstructed samples across other boundaries (e.g., a virtual boundary, a sub-picture boundary, a slice boundary, and / or a patch boundary for disabling in-loop filtering) may not be in-loop filtered.

[0148] In an example, regarding whether to perform in-loop filtering processing across a virtual boundary, the in-loop filtering related information may include an SPS virtual boundary existence flag, a picture header virtual boundary existence flag, information about the number of virtual boundaries, information about the position of the virtual boundary, etc.

[0149] In the embodiments included in this document, the information about the virtual boundary position may include information about the x-coordinate of the vertical virtual boundary and / or information about the y-coordinate of the horizontal virtual boundary. Specifically, the information about the virtual boundary position may include information about the x-coordinate of the vertical virtual boundary and / or information about the y-axis of the horizontal virtual boundary in units of brightness samples. In addition, the information about the virtual boundary position may include information about the number of pieces of information (syntactic elements) about the x-coordinate of the vertical virtual boundary present in the SPS. In addition, the information about the virtual boundary position may include information about the number of pieces of information (syntactic elements) about the y-coordinate of the horizontal virtual boundary present in the SPS. Alternatively, the information about the virtual boundary position may include information about the number of pieces of information (syntactic elements) about the x-coordinate of the vertical virtual boundary present in the picture header. In addition, the information about the virtual boundary position may include information about the number of pieces of information (syntactic elements) about the y-coordinate of the horizontal virtual boundary present in the picture header.

[0150] The following table shows an exemplary syntax and semantics of SPS according to the present embodiment.

[0151] [Table 1]

[0152]

[0153] [Table 2]

[0154]

[0155]

[0156] The following table shows an exemplary syntax and semantics of a picture parameter set (PPS) according to the present embodiment.

[0157] [Table 3]

[0158]

[0159] [Table 4]

[0160]

[0161] The following table shows an exemplary syntax and semantics of a picture header according to the present embodiment.

[0162] [Table 5]

[0163]

[0164]

[0165] [Table 6]

[0166]

[0167]

[0168] The following table shows an exemplary syntax and semantics of a slice header according to the present embodiment.

[0169] [Table 7]

[0170]

[0171] [Table 8]

[0172]

[0173]

[0174] Hereinafter, information related to a sub-picture, information related to a virtual boundary that can be used for in-loop filtering, and signaling thereof will be described.

[0175] When there is no sub-picture whose boundary is regarded as a picture boundary even if a picture includes a plurality of sub-pictures, the advantage of using sub-pictures cannot be utilized. In an embodiment of the present document, image / video information for image encoding may include information for treating a sub-picture as a picture, which may be referred to as a picture processing flag (i.e., subpic_treated_as_pic_flag[i]).

[0176] In order to signal the layout of the sub-picture, a flag related to whether a sub-picture exists (i.e., subpic_present_flag) is signaled. This may be referred to as a sub-picture presence flag. When the value of subpic_present_flag is 1, information related to the number of sub-pictures used to split the picture (i.e., sps_num_subpics_minus1) is signaled. In an example, the number of sub-pictures used to split the picture may be equal to sps_num_subpics_minus1+1 (1 added to sps_num_subpics_minus1). Available values ​​of sps_num_subpics_minus1 include 0, which means that only one sub-picture may be present in the picture. If the picture includes only one sub-picture, the signaling of sub-picture related information may be considered as redundant processing because the sub-picture itself is a picture.

[0177] In the existing embodiment, if a picture includes only one sub-picture and sub-picture signaling is present, the value of the picture processing flag (i.e., subpic_treated_as_pic_flag[i]) and / or the value of the flag related to whether loop filtering is performed across sub-pictures (i.e., loop_filter_across_subpic_enabled_flag) may be 0 or 1. Herein, there is a problem that the case where the value of subpic_treated_as_pic_flag[i] is 0 is inconsistent with the case where the sub-picture boundary is a picture boundary. This requires additional redundant processing that allows the decoder to confirm that the picture boundary is a sub-picture boundary.

[0178] When a picture is generated based on a merge process of two or more sub-pictures, all sub-pictures used in the merge process should be independently coded sub-pictures (sub-pictures for which the value of the picture processing flag (subpic_reated_as_pic_flag[i]) is 1). This is because, when a sub-picture other than an independently coded sub-picture (referred to as a "first sub-picture" in this paragraph) is merged, a block in the first sub-picture is encoded with reference to a reference block existing outside the first sub-picture, which may cause a problem after merging.

[0179] In addition, when a picture is divided into sub-pictures, sub-picture ID signaling may or may not exist. When sub-picture ID signaling exists, the sub-picture ID signaling may exist (included) in SPS, PPS and / or picture header (PH). The case where sub-picture ID signaling does not exist in SPS may include the case where a bitstream is generated as a result of sub-picture merging processing. Therefore, it is preferred that when sub-picture ID signaling is not included in SPS, all sub-pictures are independently encoded.

[0180] In an image encoding process using a virtual boundary, information about the position of the virtual boundary may be signaled in an SPS or a picture header. The signaling of information about the position of the virtual boundary in the SPS means that the position in the entire CLVS has not changed. However, when reference picture resampling (RPR) is enabled for CLVS, the pictures in the CLVS may have different sizes. Herein, RPR (also referred to as adaptive resolution change (ARC)) is performed for normal encoding operations of pictures with different resolutions (spatial resolutions). For example, RPR may include upsampling and downsampling. High coding efficiency for adapting to bit rate and spatial resolution can be achieved through RPR. Taking into account RPR, it is necessary to ensure that all positions of the virtual boundaries exist in one picture.

[0181] In existing ALF processing, k-order exponential Golomb codes (k=3) are used to signal the absolute values ​​of luma and chroma ALF coefficients. However, k-order exponential Golomb coding is problematic because it incurs significant computational overhead and complexity.

[0182] The embodiments described below may provide solutions to the above problems. The embodiments may be applied independently. Alternatively, at least two embodiments may be applied in combination.

[0183] In an embodiment of the present document, when sub-picture signaling is present and a picture has only one sub-picture, the only sub-picture is an independently coded sub-picture. For example, when a picture has only one sub-picture, the only sub-picture is an independently coded sub-picture, and the value of the picture processing flag (i.e., subpic_treated_as_pic_flag[i]) of the only sub-picture is 1. Therefore, redundant processing related to the sub-picture can be omitted.

[0184] In an embodiment of the present document, when sub-picture signaling is present, the number of sub-pictures may be greater than 1. In an example, if sub-picture signaling is present (i.e., the value of subpics_present_flag is 1), the information about the number of sub-pictures (i.e., sps_num_subpics_minus1) may be greater than 0, and the number of sub-pictures may be sps_num_subpics_minus1+1 (1 added to sps_num_subpics_minus1). In another example, the information about the number of sub-pictures may be sps_num_subpics_minus2, and the number of sub-pictures may be sps_num_subpics_minus2+2 (2 added to sps_num_subpics_minus2). In another example, the sub-picture present flag (subpics_present_flag) may be replaced by the information about the number of sub-pictures (sps_num_subpics_minus1), so sub-picture signaling may be present when sps_num_subpics_minus1 is greater than 0.

[0185] In an embodiment of the present document, when a picture is divided into sub-pictures, at least one of the sub-pictures may be an independently coded sub-picture. Here, the value of the picture processing flag (ie, subpic_treated_as_pic_flag[i]) of the independently coded sub-picture may be 1.

[0186] In the embodiments of this document, a sub-picture of a picture processed based on a merge of two or more sub-pictures may be an independently encoded sub-picture.

[0187] In an embodiment of the present document, when sub-picture identification (ID) signaling exists in a location other than SPS (other syntax, other high-level syntax information), all sub-pictures may be independently coded sub-pictures, and the values ​​of the picture processing flags (i.e., subpic_treated_as_pic_flag) of all sub-pictures may be 1. In an example, sub-picture ID signaling may exist in PPS, and in this case, all sub-pictures may be independently coded sub-pictures. In another example, sub-picture ID signaling may exist in the picture header, and in this case, all sub-pictures are independently coded sub-pictures.

[0188] In an embodiment of this document, when virtual boundary signaling is present in the SPS of the CLVS and reference picture resampling is enabled, all horizontal virtual boundary positions may be within the minimum picture height of the picture of the reference SPS, and all vertical virtual boundary positions may be within the minimum picture width of the picture of the reference SPS.

[0189] In an embodiment of the present document, when reference picture resampling (RPR) is enabled, virtual boundary signaling may be included in the picture header. That is, when RPR is enabled, virtual boundary signaling may not be included in the SPS.

[0190] In an embodiment of the present document, a fixed length code (FLC) having a number of bits (or a bit length) may be used to signal ALF data. In an example, the information about the ALF data may include information about the bit length of the absolute value of the ALF luminance coefficient (i.e., alf_luma_coeff_abs_len_minus1) and / or information about the bit length of the absolute value of the ALF chrominance coefficient (i.e., alf_chroma_coeff_abs_len_minus1). For example, the information about the bit length of the absolute value of the ALF luminance coefficient and / or the information about the bit length of the absolute value of the ALF chrominance coefficient may be ue(v) encoded.

[0191] The following table shows an exemplary syntax of an SPS according to the present embodiment.

[0192] [Table 9]

[0193]

[0194] The following table shows exemplary semantics of the syntax elements included in the syntax.

[0195] [Table 10]

[0196]

[0197] The following table shows an exemplary syntax of an SPS according to the present embodiment.

[0198] [Table 11]

[0199]

[0200] The following table shows exemplary semantics of the syntax elements included in the syntax.

[0201] [Table 12]

[0202]

[0203] The following table shows an exemplary syntax of ALF data according to the present embodiment.

[0204] [Table 13]

[0205]

[0206] The following table shows exemplary semantics of the syntax elements included in the syntax.

[0207] [Table 14]

[0208]

[0209]

[0210] According to the embodiments of this document described together with the above table, through image encoding based on sub-pictures and / or virtual boundaries, subjective / objective image quality can be improved and hardware resource consumption required for encoding can be reduced.

[0211] Fig. 9 and Fig.10 An example of a video / image encoding method and related components according to an embodiment of the present document is schematically shown.

[0212] Fig. 9 The method disclosed in Figure 2 or Fig.10 Specifically, for example, Fig. 9 S900 to S920 can be Fig.10 The residual processor 230 of the encoding device performs, Fig. 9 The S930 and S940 can be Fig.10 The predictor 220 of the encoding device performs, Fig. 9 The S950 can be Fig.10 The filter 260 of the encoding device performs, Fig. 9 The S960 can be Fig.10 The encoding is performed by the entropy encoder 240 of the encoding device. Fig. 9 The method disclosed in may include the above-mentioned embodiments in this document.

[0213] Reference Fig. 9 , the encoding device may derive residual samples. The encoding device may derive residual samples of the current block, and the residual samples of the current block may be derived based on the original samples and the predicted samples of the current block. Specifically, the encoding device may derive the predicted samples of the current block based on the prediction mode. In this case, various prediction methods disclosed in this document may be applied, such as inter-frame prediction or intra-frame prediction. Residual samples may be derived based on predicted samples and original samples. For inter-frame prediction, the encoding device may derive at least one reference picture. Inter-frame prediction may be performed based on at least one reference picture. Prediction samples may be generated based on inter-frame prediction. The encoding device may generate reference picture related information based on at least one reference picture.

[0214] The encoding device may derive residual samples (S900). The encoding device may derive residual samples of the current block, and may derive the residual samples of the current block based on the original samples and the predicted samples of the current block. Specifically, the encoding device may derive the predicted samples of the current block based on the prediction mode. In this case, various prediction methods disclosed in this document, such as inter-frame prediction or intra-frame prediction, may be applied. The residual samples may be derived based on the predicted samples and the original samples.

[0215] The encoding device may derive a transform coefficient (S910). The encoding device may derive the transform coefficient based on a transform process of the residual sample. For example, the transform process may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a graph-based transform (GBT), and a conditional nonlinear transform (CNT).

[0216] The encoding apparatus may induce a quantized transform coefficient. The encoding apparatus may induce a quantized transform coefficient based on a quantization process of the transform coefficient. The quantized transform coefficient may have a 1-dimensional vector form based on a coefficient scanning order.

[0217] The encoding device may generate residual information (S920). The encoding device may generate residual information based on the transform coefficient. The encoding device may generate residual information indicating the quantized transform coefficient. The residual information may be generated by various encoding methods such as exponential Golomb, CAVLC, CABAC, etc.

[0218] The encoding device may derive a prediction sample (S930). The encoding device may derive a prediction sample of the current block based on the prediction mode. The encoding device may derive a prediction sample of the current block based on the prediction mode. In this case, various prediction methods disclosed in this document, such as inter-frame prediction or intra-frame prediction, may be applied.

[0219] The encoding device may generate prediction related information (S940). The encoding device may generate prediction related information based on the prediction sample and / or the mode applied thereto. The prediction related information may include information about various prediction modes (e.g., merge mode, MVP mode, etc.), MVD information, etc.

[0220] The encoding device may generate a reconstructed sample. The encoding device may generate a reconstructed sample based on residual information. The reconstructed sample may be generated by adding the predicted sample and the residual sample based on the residual information. Specifically, the encoding device may perform prediction (intra-frame or inter-frame prediction) on the current block, and may generate a reconstructed sample based on the original sample and the predicted sample generated from the prediction.

[0221] The reconstructed samples may include reconstructed luma samples and reconstructed chroma samples. Specifically, the residual samples may include residual luma samples and residual chroma samples. The residual luma samples may be generated based on the original luma samples and the predicted luma samples. The residual chroma samples may be generated based on the original chroma samples and the predicted chroma samples. The encoding device may derive the transform coefficients (luminance transform coefficients) of the residual luma samples and / or the transform coefficients (chroma transform coefficients) of the residual chroma samples. The quantized transform coefficients may include quantized luma transform coefficients and / or quantized chroma transform coefficients.

[0222] The encoding device may generate information related to in-loop filtering of the reconstructed samples (S950). The encoding device may perform in-loop filtering processing on the reconstructed samples, and may generate information related to in-loop filtering based on the in-loop filtering processing. For example, the information related to in-loop filtering may include the above-mentioned information about the virtual boundary (SPS virtual boundary enable flag, picture header virtual boundary enable flag, SPS virtual boundary existence flag, picture header virtual boundary existence flag, information about the position of the virtual boundary, etc.).

[0223] The encoding device may encode the video / image information (S960). The encoding device may encode the video / image information including residual information, prediction related information, reference picture related information, sub-picture related information, in-loop filtering related information, and virtual boundary related information (and / or additional virtual boundary related information). The encoded video / image information may be output in the form of a bit stream. The bit stream may be transmitted to the decoding device via a network or a storage medium.

[0224] The image / video information may include various information according to the embodiments of this document. For example, the image / video may include information disclosed in at least one of Tables 1 to 14 above.

[0225] In an embodiment, the image information may include a sequence parameter set (SPS) and picture header information of the reference SPS. For example, whether the SPS or picture header information includes additional virtual boundary related information may be determined based on whether reference picture resampling is enabled. Herein, reference picture resampling may be performed according to the above-mentioned RPR. Additional virtual boundary related information may also be referred to as virtual boundary related information. The term "additional" is used to distinguish from virtual boundary related information such as an SPS virtual boundary presence flag and / or a PH virtual boundary presence flag.

[0226] In an embodiment, the additional virtual boundary related information may include the number of virtual boundaries and the positions of the virtual boundaries.

[0227] In an embodiment, the additional virtual border related information may include information about the number of vertical virtual borders, information about the positions of the vertical virtual borders, information about the number of horizontal virtual borders, and information about the positions of the horizontal virtual borders.

[0228] In an embodiment, the image information may include a reference picture resampling enable flag. For example, whether to enable reference picture resampling may be determined based on the reference picture resampling enable flag.

[0229] In an embodiment, the SPS may include an SPS virtual boundary existence flag related to whether the SPS includes additional virtual boundary related information. Based on enabling reference picture resampling, the value of the SPS virtual boundary existence flag may be determined to be 0.

[0230] In an embodiment, based on enabling reference picture resampling, additional virtual boundary related information may not be included in the SPS. In this case, for example, the picture header information may include the additional virtual boundary related information.

[0231] In an embodiment, the current picture may include a sub-picture as only one sub-picture. The sub-picture may be independently encoded. A reconstructed sample may be generated based on the sub-picture, and information related to the sub-picture may be generated based on the sub-picture. In addition, the image information may include information related to the sub-picture.

[0232] In an embodiment, the picture processing flag (subpicture_treated_as_picture flag) for the subpicture may not exist in the image information. Therefore, the value of the subpicture_treated_as_picture flag may be set by inference (estimation or prediction) at the decoding end. In an example, the value of the subpicture_treated_as_picture flag may be set to 1.

[0233] In an embodiment, the current picture may include a sub-picture. In an example, the sub-picture may be derived based on a merge process of two or more independently encoded sub-pictures. A reconstructed sample may be generated based on the sub-picture. Sub-picture related information may be generated based on the sub-picture. In addition, the image information may include sub-picture related information.

[0234] Fig.11 and Fig.12 An example of a video / image decoding method and related components according to an embodiment of this document is schematically shown.

[0235] Fig.11 The method disclosed in Figure 3 or Fig.12 Specifically, for example, Fig.11S1100 may be executed by the entropy decoder 310 of the decoding device, S1110 and S1120 may be executed by the residual processor 320 of the decoding device, S1130 may be executed by the predictor 330 of the decoding device, S1140 may be executed by the adder 340 of the decoding device, and S1150 may be executed by the filter 350 of the decoding device. Fig.11 The method disclosed in may include the above-mentioned embodiments in this document.

[0236] Reference Fig.11 , the decoding device may receive / obtain video / image information (S1100). The video / image information may include residual information, prediction related information, reference picture related information, sub-picture related information, in-loop filtering related information and / or virtual boundary related information (and / or additional virtual boundary related information). The decoding device may receive / obtain image / video information through a bitstream.

[0237] The image / video information may include various information according to the embodiments of this document. For example, the image / video may include information disclosed in at least one of Tables 1 to 14 above.

[0238] The decoding device may derive the quantized transform coefficient. The decoding device may derive the quantized transform coefficient based on the residual information. Based on the coefficient scanning order, the quantized transform coefficient may have a 1-dimensional vector form. The quantized transform coefficient may include a quantized luminance transform coefficient and / or a quantized chrominance transform coefficient.

[0239] The decoding device may derive a transform coefficient (S1110). The decoding device may derive the transform coefficient based on a dequantization process of the quantized transform coefficient. The decoding device may derive a luminance transform coefficient by dequantization based on the quantized luminance transform coefficient. The decoding device may derive a chrominance transform coefficient by dequantization based on the quantized chrominance transform coefficient.

[0240] The decoding device may generate / derive residual samples (S1120). The decoding device may derive residual samples based on an inverse transform process of the transform coefficient. The decoding device may derive residual luma samples through an inverse transform process based on the luma transform coefficient. The decoding device may derive residual chroma samples through an inverse transform based on the chroma transform coefficient.

[0241] The decoding apparatus may derive at least one reference picture based on the reference picture related information. The decoding apparatus may perform a prediction process based on the at least one reference picture.

[0242] The decoding device may generate a prediction sample (S1130). The decoding device may generate a prediction sample of the current block based on prediction related information and / or reference picture related information. The decoding device may generate a prediction sample of the current block in the current picture based on prediction related information and / or at least one reference picture. The decoding device may perform prediction based on image / video information, and may derive a prediction sample of the current block. The prediction related information may include prediction mode information. The decoding device may determine whether to apply inter-frame prediction to the current block based on the prediction mode information, and may perform prediction based on this. The prediction sample may include a predicted luminance sample and / or a predicted chrominance sample. For example, the decoding device may perform an inter-frame prediction process based on at least one reference picture, and may generate a prediction sample based on the inter-frame prediction process.

[0243] The decoding device may generate / derive reconstructed samples (S1140). For example, the decoding device may generate / derive reconstructed luma samples and / or reconstructed chroma samples. The decoding device may generate reconstructed luma samples and / or reconstructed chroma samples based on residual information. The decoding device may generate reconstructed samples based on residual information. The reconstructed samples may include reconstructed luma samples and / or reconstructed chroma samples. The luma component of the reconstructed sample may correspond to the reconstructed luma sample, and the chroma component of the reconstructed sample may correspond to the reconstructed chroma sample. The decoding device may generate predicted luma samples and / or predicted chroma samples through prediction processing. The decoding device may generate reconstructed luma samples based on the predicted luma samples and the residual luma samples. The decoding device may generate reconstructed chroma samples based on the predicted chroma samples and the residual chroma samples.

[0244] The decoding device may generate a modified (filtered) reconstructed sample (S1150). The decoding device may generate the modified reconstructed sample by performing an in-loop filtering process on the reconstructed sample of the current picture. The decoding device may generate the modified reconstructed sample based on the in-loop filtering related information (and / or the virtual boundary related information). The decoding device may use a deblocking process, an SAO process, and / or an ALF process to generate the modified reconstructed sample.

[0245] In an embodiment, step S1150 may include determining whether to perform in-loop filtering across a virtual boundary. That is, the decoding device may determine whether to perform in-loop filtering across a virtual boundary. The decoding device may determine whether to perform in-loop filtering based on in-loop filtering related information (and / or virtual boundary related information).

[0246] In an embodiment, the image information may include the SPS and the picture header information of the reference SPS. For example, whether the SPS or the picture header information includes additional virtual boundary related information may be determined based on whether the reference picture resampling is enabled. Herein, the reference picture resampling may be performed according to the above-mentioned RPR. The additional virtual boundary related information may also be referred to as virtual boundary related information. The term "additional" is used to distinguish from virtual boundary related information such as the SPS virtual boundary presence flag and / or the PH virtual boundary presence flag.

[0247] In an embodiment, the additional virtual boundary related information may include the number of virtual boundaries and the positions of the virtual boundaries.

[0248] In an embodiment, the additional virtual border related information may include information about the number of vertical virtual borders, information about the positions of the vertical virtual borders, information about the number of horizontal virtual borders, and information about the positions of the horizontal virtual borders.

[0249] In an embodiment, the image information may include a reference picture resampling enable flag. For example, whether to enable reference picture resampling may be determined based on the reference picture resampling enable flag.

[0250] In an embodiment, the SPS may include an SPS virtual boundary existence flag related to whether the SPS includes additional virtual boundary related information. Based on enabling reference picture resampling, the value of the SPS virtual boundary existence flag may be determined to be 0.

[0251] In an embodiment, based on enabling reference picture resampling, additional virtual boundary related information may not be included in the SPS. In this case, for example, the picture header information may include the additional virtual boundary related information.

[0252] In an embodiment, the current picture may include a sub-picture as only one sub-picture. The sub-picture may be independently encoded. The reconstructed sample may be generated based on the sub-picture, and the information related to the sub-picture may be generated based on the sub-picture. In addition, the image information may include information related to the sub-picture.

[0253] In an embodiment, the picture processing flag (subpicture_treated_as_picture flag) for the subpicture may not exist in the image information. Therefore, the value of the subpicture_treated_as_picture flag may be set by inference (estimation or prediction) at the decoding end. In an example, the value of the subpicture_treated_as_picture flag may be set to 1.

[0254] In an embodiment, the current picture may include a sub-picture. In an example, the sub-picture may be derived based on a merge process of two or more independently encoded sub-pictures. A reconstructed sample may be generated based on the sub-picture. Sub-picture related information may be generated based on the sub-picture. In addition, the image information may include sub-picture related information.

[0255] In the case where there are residual samples of the current block, the decoding device may receive residual information of the current block. The residual information may include transform coefficients of the residual samples. The decoding device may derive residual samples (or residual sample arrays) of the current block based on the residual information. Specifically, the decoding device may derive quantized transform coefficients based on the residual information. Based on the coefficient scanning order, the quantized transform coefficients may have a 1-dimensional vector form. The decoding device may derive the transform coefficients based on a dequantization process of the quantized transform coefficients. The decoding device may derive residual samples based on the transform coefficients.

[0256] The decoding device may generate a reconstructed sample based on the (intra-frame) prediction sample and the residual sample, and may derive a reconstructed block or a reconstructed picture based on the reconstructed sample. Specifically, the decoding device may generate a reconstructed sample based on the sum between the (intra-frame) prediction sample and the residual sample. Thereafter, as described above, the decoding device may optionally apply an in-loop filtering process such as a deblocking filter and / or a SAO process to the reconstructed picture to improve subjective / objective image quality.

[0257] For example, the decoding device can obtain all or part of the image information including the above information (or syntax elements) by decoding the bitstream or coding information. In addition, the bitstream or coding information can be stored in a computer-readable storage medium, and the above decoding method can be executed.

[0258] Although the method is described based on a flowchart listing steps or blocks in sequence in the above embodiments, the steps of this document are not limited to a specific order, and specific steps may be performed in different steps or in a different order or simultaneously relative to the above content. In addition, it will be understood by a person of ordinary skill in the art that the steps of the flowchart are not exclusive, and another step may be included therein without affecting the scope of the present disclosure, or one or more steps in the flowchart may be deleted.

[0259] The above-mentioned method according to the present disclosure may be in the form of software, and the encoding device and / or decoding device according to the present disclosure may be included in an apparatus for image processing (e.g., TV, computer, smart phone, set-top box, display device, etc.).

[0260] When the embodiments of the present disclosure are implemented by software, the above methods can be implemented by modules (processes or functions) that perform the above functions. The module can be stored in a memory and executed by a processor. The memory can be installed inside or outside the processor and can be connected to the processor via various well-known 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. In other words, according to the embodiments of the present disclosure, it can be implemented and executed on a processor, a microprocessor, a controller or a chip. For example, the functional units shown in each figure can be implemented and executed on a computer, a processor, a microprocessor or a controller or a chip. In this case, information about the implementation (e.g., information about instructions) or an algorithm can be stored in a digital storage medium.

[0261] In addition, the decoding device and the encoding device to which the embodiments of the present document are applied may be included in a multimedia broadcast transceiver, a mobile communication terminal, a home theater video device, a digital theater video device, a surveillance camera, a video chat device, and a real-time communication device (e.g., video communication), a mobile streaming device, a storage medium, a camera, a video on demand (VoD) service provider, an over-the-top (OTT) video device, an Internet streaming service provider, a 3D video device, a virtual reality (VR) device, an augmented reality (AR) device, an image phone video device, a vehicle terminal (e.g., a vehicle (including an autonomous vehicle) terminal, an aircraft terminal, or a ship terminal) and a medical video device; and may be used to process image signals or data. For example, an OTT video device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smart phone, a tablet PC, and a digital video recorder (DVR).

[0262] In addition, the processing method to which the embodiments of the present document are applied can be generated in the form of a program executed by a computer and can be stored in a computer-readable recording medium. Multimedia data having a data structure according to the embodiments of the present document can also be stored in a computer-readable recording medium. Computer-readable recording media include all types of storage devices and distributed storage devices that store computer-readable data. For example, computer-readable recording media may include Blu-ray discs (BDs), universal serial buses (USBs), ROMs, PROMs, EPROMs, EEPROMs, RAMs, CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. Computer-readable recording media also include media specifically implemented in the form of carrier waves (e.g., transmission via the Internet). In addition, the bit stream generated by the encoding method can be stored in a computer-readable recording medium or sent via a wired or wireless communication network.

[0263] In addition, the embodiments of this document can be embodied as a computer program product based on a program code, and the program code can be executed on a computer according to the embodiments of this document. The program code can be stored on a computer readable carrier.

[0264] Fig.13 An example of a content streaming system to which the embodiments of this document can be applied is shown.

[0265] Reference Fig.13 A content streaming system to which the embodiments of this document are applied may generally include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0266] The encoding server is used to compress the content input from the multimedia input device (e.g., smart phone, camera, camcorder, etc.) into digital data to generate a bit stream and send it to the streaming server. As another example, in the case where the multimedia input device (e.g., smart phone, camera, camcorder, etc.) directly generates the bit stream, the encoding server can be omitted.

[0267] The bitstream may be generated by the encoding method or the bitstream generation method to which the embodiment of the present document is applied. Also, in the process of transmitting or receiving the bitstream, the streaming server may temporarily store the bitstream.

[0268] The streaming server sends multimedia data to the user device based on the user's request through the network server, and the network server is used as an instrument to inform the user of what services are available. When the user requests the service the user wants, the network server transmits the request to the streaming server, and the streaming server sends the multimedia data to the user. In this regard, the content streaming system may include a separate control server, and in this case, the control server is used to control the command / response between the various devices in the content streaming system.

[0269] The streaming server may receive content from a media storage device and / or an encoding server. For example, in the case of receiving content from an encoding server, the content may be received in real time. In this case, the streaming server may store the bitstream for a predetermined period of time to smoothly provide a streaming service.

[0270] For example, user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation, tablet computers, tablet PCs, ultrabooks, wearable devices (e.g., watch-type terminals (smart watches), glasses-type terminals (smart glasses), head-mounted displays (HMDs)), digital TVs, desktop computers, digital signage, etc.

[0271] Each server in the content streaming system may operate as a distributed server, and in this case, data received by each server may be processed in a distributed manner.

[0272] The claims in this specification may be combined in various ways. For example, the technical features in the method claims of this specification may be combined to be implemented or performed in a device, and the technical features in the device claims may be combined to be implemented or performed in a method. In addition, the technical features in the method claims and the device claims may be combined to be implemented or performed in a device. In addition, the technical features in the method claims and the device claims may be combined to be implemented or performed in a method.

Claims

1. An image decoding method performed by a decoding device, the image decoding method comprising the following steps: Obtaining image information including prediction related information and in-loop filtering related information through a bit stream; generating a prediction sample based on the prediction related information; generating reconstructed samples based on the predicted samples; and generating modified reconstructed samples by performing an in-loop filtering process on the reconstructed samples based on the in-loop filtering related information, The image information includes a sequence parameter set SPS and picture header information referring to the SPS. The additional virtual boundary related information is included in the SPS or the picture header information, and The additional virtual boundary related information includes at least one of information about the number of virtual boundaries and information about the positions of the virtual boundaries.

2. An image encoding method performed by an encoding device, the image encoding method comprising the following steps: Generate prediction samples for the current block; generating prediction related information based on the prediction sample; generating in-loop filtering related information for in-loop filtering processing of reconstructed samples; as well as encoding the image information including the prediction related information and the in-loop filtering related information, The image information includes a sequence parameter set SPS and picture header information referring to the SPS. The additional virtual boundary related information is included in the SPS or the picture header information, and The additional virtual boundary related information includes information about the number of virtual boundaries and information about the positions of the virtual boundaries.

3. A method for transmitting image data, the method comprising the following steps: Obtaining a bitstream for the image, wherein the bitstream is generated based on the following steps: generating prediction samples for a current block, generating prediction related information based on the prediction samples, generating in-loop filtering related information for in-loop filtering processing of reconstructed samples, and encoding image information including the prediction related information and the in-loop filtering related information; and sending said data comprising said bit stream, The image information includes a sequence parameter set SPS and picture header information referring to the SPS. The additional virtual boundary related information is included in the SPS or the picture header information, and The additional virtual boundary related information includes information about the number of virtual boundaries and information about the positions of the virtual boundaries.

4. A non-transitory computer-readable storage medium storing a bitstream generated by a method comprising the steps of: Generate prediction samples for the current block; generating prediction related information based on the prediction sample; generating in-loop filtering related information for in-loop filtering processing of reconstructed samples; as well as encoding the image information including the prediction related information and the in-loop filtering related information, The image information includes a sequence parameter set SPS and picture header information referring to the SPS. The additional virtual boundary related information is included in the SPS or the picture header information, and The additional virtual boundary related information includes information about the number of virtual boundaries and information about the positions of the virtual boundaries.

Images