Image encoding device and method based on filtering

Abstract

A picture can be divided into sub-pictures / slices / tiles. For example, a picture can be divided into sub-pictures, and sub-picture-related information can be used for encoding. Sub-picture-related information can be generated by an encoding device and sent to a decoding device. According to embodiments of this document, sub-picture-related information can be efficiently signaled.

Description

Technical Field

[0001] This document relates to an image encoding device and method based on in-loop filtering. Background Art

[0002] 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 bit volume to be transmitted increases relative to existing image / video data. Therefore, transmitting image data using a medium such as an existing wired / wireless broadband line or an existing storage medium or storing image / video data using an existing storage medium increases transmission costs and storage costs.

[0003] 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.

[0004] 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.

[0005] Specifically, for image quality improvement, an in-loop filtering process may be performed on a reconstructed picture (sample). A decoding device performs signaling of information used for the in-loop filtering process. A scheme for efficient signaling of in-loop filtering related information is discussed. Summary of the Invention

[0006] Technical Solution

[0007] According to an embodiment of this document, a method and apparatus for enhancing image / video coding efficiency are provided.

[0008] According to embodiments of this document, a method and apparatus for efficient filtering applications are provided.

[0009] According to an embodiment of this document, a method and apparatus for efficiently applying deblocking, sample adaptive loop filtering (SAO), and adaptive loop filtering (ALF) are provided.

[0010] According to embodiments of this document, in-loop filtering may be performed based on a virtual boundary.

[0011] According to an embodiment of this document, a decoded picture may be composed of sub-pictures.

[0012] According to an embodiment of this document, a signaling position of information about a position of a virtual boundary may be determined based on signaling of information about a sub-picture.

[0013] According to an embodiment of this document, signaling of information related to a virtual boundary may be performed based on signaling of information related to a sub-picture.

[0014] According to an embodiment of this document, there is provided an encoding device for performing video / image encoding.

[0015] According to one embodiment of this document, a computer-readable digital storage medium is provided, in which encoded video / image information generated according to the video / image encoding method disclosed in at least one embodiment of this document is stored.

[0016] According to an embodiment of this document, a computer-readable digital storage medium is provided, in which encoded information or encoded video / image information is stored, which enables a decoding device to execute the video / image decoding method disclosed in at least one embodiment of this document.

[0017] Beneficial effects

[0018] According to the embodiments of this document, the overall image / video compression efficiency can be improved.

[0019] According to the embodiments of this document, subjective / objective visual quality can be improved through efficient filtering.

[0020] According to the embodiments of this document, efficient encoding can be achieved by omitting a process of rewriting a bitstream through signaling-based virtual boundary signaling of a sub-picture. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 An example of a video / image coding system to which embodiments of this document can be applied is schematically shown.

[0022] Figure 2 is a diagram schematically showing the configuration of a video / image encoding device to which an embodiment of this document can be applied.

[0023] Figure 3 is a diagram schematically showing the configuration of a video / image decoding device to which an embodiment of this document can be applied.

[0024] Figure 4 The layered architecture of coded video / images is shown as an example.

[0025] Figure 5 A screen showing an embodiment according to this document.

[0026] Figure 6 A sub-picture / slice / tile-based encoding method according to an embodiment of this document is shown.

[0027] Figure 7 A sub-picture / slice / tile-based decoding method according to an embodiment of this document is shown.

[0028] Figure 8 is a flowchart illustrating a filtering-based encoding method in an encoding device.

[0029] Figure 9 is a flowchart illustrating a filtering-based decoding method in a decoding device.

[0030] Figure 10 and Figure 11 An example of a video / image encoding method and related components according to an embodiment of this document is schematically shown.

[0031] Figure 12 and Figure 13 An example of an image / video decoding method and related components according to an embodiment of this document is schematically shown.

[0032] Figure 14 An example of a content streaming system to which the embodiments disclosed in this document can be applied is shown. DETAILED DESCRIPTION

[0033] 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.

[0034] In this document, video may refer to a series of images over time. A picture generally refers to a unit representing an image within a specific time range, and a slice / tile refers to a unit that constitutes a portion of a picture for coding purposes. A slice / tile may include one or more coding tree units (CTUs). A picture may be composed of one or more slices / tiles. A picture may be composed of one or more tile groups. A tile group may include one or more tiles.

[0035] The various configurations of the drawings described in this document are independent illustrations used to illustrate functions as different features 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 a configuration, and a configuration can also be divided into multiple configurations. Without departing from the main purpose of this document, embodiments in which configurations are combined and / or separated are included within the scope of the claims.

[0036] In addition, this document 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 this document. The terms used in the following description are only used to describe specific embodiments and are not intended to limit this document. Singular expressions include plural expressions as long as they are clearly 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.

[0037] 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.

[0038] This document relates to video / image coding. For example, the methods / implementations disclosed herein may relate to the Versatile Video Coding (VVC) standard (ITU-T Rec. H.266), next-generation video / image coding standards following VVC, or other video coding-related standards (e.g., the High Efficiency Video Coding (HEVC) standard (ITU-T Rec. H.265), the Essential Video Coding (EVC) standard, the AVS2 standard, etc.).

[0039] A pixel or picture element may refer to the smallest unit that constitutes a picture (or image). Furthermore, "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 the pixel / pixel value of the luma component or only the pixel / pixel value of the chroma component.

[0040] 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 the spatial domain, and when such a pixel value is transformed into the frequency domain, it may refer to a transform coefficient in the frequency domain.

[0041] 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".

[0042] Furthermore, in this document, the term "or" should be interpreted as meaning "and / or." For example, the expression "A or B" may include 1) only A, 2) only B, and / or 3) both A and B. In other words, the term "or" in this document should be interpreted as meaning "additionally or alternatively."

[0043] 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”.

[0044] In addition, in this specification, “at least one of A, B, and C” may mean “only A,” “only B,” “only C,” or “any combination of A, B, and C.” In addition, “at least one of A, B, or C” or “at least one of A, B, and / or C” may mean “at least one of A, B, and C.”

[0045] Furthermore, brackets used in this specification may mean "for example." Specifically, when "prediction (intra-frame prediction)" is expressed, 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 may indicate that "intra-frame prediction" is proposed as an example of "prediction." Furthermore, even when "prediction (i.e., intra-frame prediction)" is expressed, it may indicate that "intra-frame prediction" is proposed as an example of "prediction."

[0046] In this specification, technical features described separately in one drawing may be implemented separately or simultaneously.

[0047] Figure 1 An example of a video / image encoding system to which the document of this document can be applied is shown.

[0048] 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.

[0049] 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.

[0050] A video source may acquire video / images through a process of capturing, synthesizing, or generating video / images. A video source may include a video / image capture device and / or a video / image generation device. For example, a video / image capture device may include one or more cameras, a video / image archive including previously captured video / images, etc. A video / image generation device may include, for example, a computer, a tablet computer, and a smartphone, and may (electronically) generate video / images. 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 of generating relevant data.

[0051] An encoding device can encode input video / images. For compression and coding efficiency, the encoding device can perform a series of processes such as prediction, transformation, and quantization. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0052] The transmitter can transmit the encoded image / image information or data, output as a bitstream, in the form of a file or stream to a receiver in a receiving device via a digital storage medium or network. Digital storage media can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter can include components for generating a media file in a predetermined file format and can also include components for transmission via a broadcast / communication network. The receiver can receive / extract the bitstream and transmit the received bitstream to a decoding device.

[0053] 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.

[0054] The renderer may render the decoded video / image, and the rendered video / image may be displayed on a display.

[0055] Figure 2 Schematically shows the configuration of a video / image encoding device to which the document of this document can be applied. Hereinafter, the so-called video encoding device may include an image encoding device.

[0056] 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, predictor 220, residual processor 230, entropy encoder 240, adder 250, and 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 components may also include the memory 270 as an internal / external component.

[0057] The image splitter 210 may divide the input image (or picture, frame) input to the encoding device 200 into one or more processing units. For example, a 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, and / or ternary tree (QTBTTT) structure. For example, a coding unit may be divided into multiple coding units of increasing depth based on a quadtree, binary tree, and / or ternary tree structure. In this case, for example, the quadtree structure may be applied first, followed by the binary tree and / or ternary tree structure. Alternatively, the binary tree structure may be applied first. The encoding process according to this document may be performed based on the final coding unit that is no longer divided. In this case, based on coding efficiency, such as image characteristics, 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 of increasing depth so that the coding unit of the optimal size can be used as the final coding unit. The encoding process may include processes such as prediction, transform, and reconstruction (described later). As another example, a 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 partitioned from the final coding unit. A prediction unit may be a unit for sample prediction, and a transform unit may be a unit for deriving transform coefficients and / or a unit for deriving a residual signal from the transform coefficients.

[0058] In some cases, the term "unit" may be used interchangeably with terms such as "block" or "region." Generally, an M×N block may represent a sample consisting of M columns and N rows or a set of transform coefficients. A sample may generally represent a pixel or pixel value, but may also represent only the pixel / pixel value of the luma component or only the pixel / pixel value of the chroma component. A sample may be used as a term corresponding to a pixel or picture element configuring a screen (or image).

[0059] The subtractor 231 can generate a residual signal (residual block, residual sample, or residual sample array) by subtracting the prediction signal (prediction block, prediction sample, or prediction sample array) output from the predictor 220 from the input image signal (original block, original sample, or original sample array), and the generated residual signal is sent to the transformer 232. The predictor 220 can 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 can determine whether to apply intra-frame prediction or inter-frame prediction to the current block or in units of CUs. As described later in the description of each prediction mode, the predictor can generate various types of information related to the prediction (e.g., prediction mode information) and transmit the generated information to the entropy encoder 240. The information about the prediction can be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0060] The intra-frame predictor 222 can predict the current block with reference to samples within the current picture. Depending on the prediction mode, the referenced samples may be located near the current block or may be located 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 planar 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 illustrative, and more or fewer directional prediction modes than the above number may be used depending on 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.

[0061] The inter-frame predictor 221 can derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. It may also include information about the inter-frame prediction direction (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks within the current picture and temporally neighboring blocks within a reference picture. The reference picture including the reference block and the reference picture including the temporally neighboring block may be the same or different. Temporally neighboring blocks may be referred to by names such as collocated reference blocks or collocated CUs (colCUs), and reference pictures including temporally neighboring blocks may be referred to as collocated pictures (colPics). 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 for the current block. Inter-frame prediction can be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame predictor 221 can use the motion information of the neighboring block as the motion information of the current block. In skip mode, unlike merge mode, a residual signal may not be transmitted. The motion vector prediction (MVP) mode can indicate the motion vector of the current block by using the motion vector of the neighboring block as a motion vector predictor and signaling the motion vector difference.

[0062] The predictor 220 can generate a prediction signal based on various prediction methods described below. For example, the predictor can apply not only intra-frame prediction or inter-frame prediction to predict a block, but also both intra-frame prediction and inter-frame prediction simultaneously. This may be referred to as combined inter-frame and intra-frame prediction (CIIP). In addition, the predictor can perform intra-frame block copying (IBC) to predict the block. Intra-frame block copying can be used for content image / moving image coding such as games, such as screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter-frame prediction so that a reference block is derived in the current picture. That is, IBC can use at least one of the inter-frame prediction techniques described in this document.

[0063] 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 the 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 to blocks of variable size other than square.

[0064] The quantizer 233 may quantize the transform coefficients and transmit them to the entropy encoder 240. 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 implement various encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy encoder 240 may encode information required for video / image reconstruction (e.g., syntax element values) together with or separately from the quantized transform coefficients. 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 adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. In this document, the information and / or syntax elements to be signaled / transmitted described later may be encoded by the above-mentioned encoding process and included in the bitstream. The bitstream may be transmitted 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 transmits the 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.

[0065] 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 transform 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, when skip mode is applied), the prediction block can be used as the 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 through filtering.

[0066] Furthermore, luma mapping with chroma scaling (LMCS) may be applied during the picture coding and / or reconstruction process.

[0067] 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, the 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.

[0068] 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.

[0069] 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 reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame predictor 221 for use as motion information of a spatially neighboring block or motion information of a temporally neighboring 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.

[0070] Figure 3 This is a diagram for schematically illustrating the configuration of a video / image decoding device to which the document of this document can be applied.

[0071] 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 processor). In addition, the memory 360 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium. The hardware components may also include the memory 360 as an internal / external component.

[0072] When a bit stream including video / image information is input, the decoding apparatus 300 may generate a signal in response to the bit stream received in the video / image processing. Figure 2 The image is reconstructed by processing video / image information in the encoding device shown. For example, the decoding device 300 can derive a unit / block based on block division related information obtained from the bit stream. The decoding device 300 can perform decoding using a processing unit applied to the encoding device. Therefore, for example, the processing unit for decoding can be a coding unit, and the coding unit can 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 can be derived from the coding unit. In addition, the reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a reproduction device.

[0073] The decoding device 300 may receive Figure 2The received signal is output by the encoding device in the form of a bitstream, and the entropy decoder 310 can decode the received signal. For example, the entropy decoder 310 can parse the bitstream to derive information required for image reconstruction (or picture reconstruction) (e.g., video / image information). The video / image information may also include information about various parameter sets, such as the Adaptive Parameter Set (APS), Picture Parameter Set (PPS), Sequence Parameter Set (SPS), or Video Parameter Set (VPS). In addition, the video / image information may also include general constraint information. The decoding device can also decode the picture based on the information about the parameter sets and / or the general constraint information. The signaled / received information and / or syntax elements described later in this document can be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 310 decodes the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and outputs the syntax elements required for image reconstruction and the quantized values of the residual transform coefficients. More specifically, the CABAC entropy decoding method may receive bins corresponding to various syntax elements in a bitstream, determine a context model using information about the target syntax element to be decoded, information about the decoded target block, or information about symbols / cells decoded in a previous stage, perform arithmetic decoding on the bins by predicting the probability of their occurrence based on the determined context model, and generate symbols corresponding to the values of the various syntax elements. In this case, after determining the context model, the CABAC entropy decoding method may update the context model by applying information about the decoded symbol / cell to the context model for the next symbol / cell. Information related to prediction from the information decoded by the entropy decoder 310 may be provided to the predictor 330, and information regarding the residual entropy-decoded by the entropy decoder 310 (i.e., quantized transform coefficients and related parameter information) may be input to the dequantizer 321. Furthermore, information related to filtering from the information decoded by the entropy decoder 310 may be provided to the filter 350. Furthermore, a receiver (not shown) for receiving a signal output from the encoding device may be configured as an internal / external component of the decoding device 300, or the receiver may be a component of the entropy decoder 310. In addition, the decoding device according to this document may be referred to as a video / image / picture decoding device, and the decoding device may be classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 310, and the sample decoder may include at least one of a dequantizer 321, an inverse transformer 322, a predictor 330, an adder 340, a filter 350, and a memory 360.

[0074] The dequantizer 321 may dequantize the quantized transform coefficients to output the transform coefficients. The dequantizer 321 may rearrange the quantized transform coefficients 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 dequantize the quantized transform coefficients using quantization parameters (e.g., quantization step size information) and obtain the transform coefficients.

[0075] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0076] 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 and determine a specific intra / inter prediction mode based on the information on prediction output from the entropy decoder 310.

[0077] The predictor can generate a prediction signal based on various prediction methods described below. For example, the predictor can apply not only intra-frame prediction or inter-frame prediction to predict a block, but also intra-frame prediction and inter-frame prediction simultaneously. This can be referred to as combined inter-frame and intra-frame prediction (CIIP). In addition, the predictor can perform intra-frame block copying (IBC) to predict the block. Intra-frame block copying can be used for content image / moving image coding of games, such as screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter-frame prediction so that a reference block is derived in the current picture. That is, IBC can use at least one inter-frame prediction technique described in this document.

[0078] The intra-frame predictor 332 may reference samples in the current picture to predict the current block. Depending on the prediction mode, the referenced samples may be located near or far from the current block. In intra-frame prediction, the prediction modes may include multiple non-directional modes and multiple directional modes. The intra-frame predictor 332 may use the prediction modes applied to neighboring blocks to determine the prediction mode to be applied to the current block.

[0079] The inter-frame predictor 331 can derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include information regarding the inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks in the current picture and temporally neighboring blocks in the reference picture. For example, the inter-frame predictor 331 may construct a motion information candidate list based on the neighboring blocks and derive the motion vector and / or reference picture index for the current block based on the received candidate selection information. Inter-frame prediction can be performed based on various prediction modes, and the prediction information may include information indicating the inter-frame prediction mode for the current block.

[0080] The adder 340 can 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 skip mode is applied, the prediction block can be used as the reconstructed block.

[0081] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra-frame prediction of the next block to be processed in the current picture, and as described later, may also be output through filtering or may also be used for inter-frame prediction of the next picture.

[0082] In addition, luma mapping with chroma scaling (LMCS) can also be applied in the picture decoding process.

[0083] 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.

[0084] The (modified) reconstructed picture stored in the DPB of the memory 360 can be used as a reference picture in the inter-frame predictor 331. The memory 360 can store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information can be transmitted to the inter-frame predictor 331 to be used as the motion information of the spatially adjacent block or the motion information of the temporally adjacent block. The memory 360 can store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame predictor 332.

[0085] In this specification, the embodiments 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.

[0086] 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 the spatial domain (or 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 values of the original block, thereby increasing 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.

[0087] Residual information can be generated through transformation and quantization processing. For example, the encoding device may derive a residual block between the original block and the prediction block, perform transformation processing on the residual samples (residual sample array) included in the residual block to derive transform coefficients, perform quantization processing on the transform coefficients to derive quantized transform coefficients, and signal the relevant residual information (via the bitstream) to the decoding device. Here, the residual information may include value information, position information, transformation technology, transformation kernel, quantization parameter, etc. of the quantized transform coefficients. The decoding device may perform dequantization / inverse transformation processing based on the residual information and derive residual samples (or residual blocks). 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 coefficients to derive a residual block and generate a reconstructed picture based on it.

[0088] In this document, at least one of quantization / dequantization and / or transform / inverse transform may be omitted. When quantization / dequantization is omitted, the quantized transform coefficient may be referred to as a transform coefficient. When transform / inverse transform is omitted, the transform coefficient may be referred to as a coefficient or a residual coefficient, or, for consistency of expression, may still be referred to as a transform coefficient.

[0089] In this document, quantized transform coefficients and transform coefficients may be referred to as transform coefficients and scaled transform coefficients, respectively. In this case, residual information may include information about the transform coefficients, and the information about the transform coefficients may be signaled via residual coding syntax. The transform coefficients may be derived based on the residual information (or information about the transform coefficients), and the scaled transform coefficients may be derived by inversely transforming (scaling) the transform coefficients. Residual samples may be derived based on the inverse transform (transform) of the scaled transform coefficients. This may also be applied / expressed in other parts of this document.

[0090] The predictor of the encoding / decoding device can derive prediction samples by performing inter-frame prediction on a block-by-block basis. Inter-frame prediction 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) for the current block is derived based on a reference block (reference sample array) specified by a motion vector on a reference picture that points to a reference picture index. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information for the current block may be predicted on a block, sub-block, or sample basis based on correlation between motion information between neighboring blocks and the current block. Motion information may include a motion vector and a reference picture index. Motion information may also include information on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.). When inter-frame prediction is applied, neighboring blocks may include spatially neighboring blocks in the current picture and temporally neighboring blocks in a reference picture. The reference picture comprising the reference block and the reference picture comprising the temporally neighboring blocks may be the same or different. Temporally neighboring blocks may be referred to as collocated reference blocks, collocated CUs (colCUs), etc., and a reference picture including temporally neighboring blocks may be referred to as a collocated picture (colPic). For example, a motion information candidate list may be constructed based on neighboring blocks of the current block, and a flag or index information indicating which candidate is selected (used) to derive the motion vector and / or reference picture index of the current block may be signaled. Inter-frame prediction may be performed based on various prediction modes. For example, in skip mode and merge mode, the motion information of the current block may be the same as that of the selected neighboring block. In skip mode, unlike merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the 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.

[0091] Depending on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. A motion vector in the L0 direction may be referred to as an L0 motion vector or MVL0, and a motion vector in the L1 direction may be referred to as an L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as L0 prediction, prediction based on the L1 motion vector may be referred to as L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as bi-prediction. Here, the L0 motion vector may indicate a motion vector associated with reference picture list L0 (L0), and the L1 motion vector may indicate a motion vector associated with reference picture list L1 (L1). Reference picture list L0 may include pictures preceding the current picture in output order as reference pictures, and reference picture list L1 may include pictures following the current picture in output order. The preceding picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. Reference picture list L0 may also include pictures following the current picture in output order as reference pictures. In this case, in reference picture list L0, the previous picture may be indexed first, and the subsequent picture may be indexed next. Reference picture list L1 may also include pictures that are earlier than the current picture in output order as reference pictures. In this case, the subsequent picture may be indexed first in reference picture list 1, and the previous picture may be indexed next. Here, the output order may correspond to the picture order count (POC) order.

[0092] Figure 4 The layered structure of the encoded image / video is shown as an example.

[0093] 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.

[0094] 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.

[0095] In NAL, a NAL unit can be generated by adding header information (NAL unit header) to the raw byte sequence payload (RBSP) generated in the VCL. In this case, RBSP refers to slice data, parameter sets, SEI messages, etc. generated in the VCL. The NAL unit header may include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0096] As shown in the figure, NAL units can be divided into VCL NAL units and non-VCL NAL units according to the RBSP generated in the VCL. VCL NAL units may refer to NAL units including information about images (slice data), and non-VCL NAL units may refer to NAL units containing information required for decoding images (parameter sets or SEI messages).

[0097] The VCL NAL units and non-VCL NAL units can be transmitted over a network by adding header information according to the data standard of the subsystem. For example, the NAL units can be converted into a data format of a predetermined standard such as the H.266 / VVC file format, the Real-time Transport Protocol (RTP), or the Transport Stream (TS) and transmitted over various networks.

[0098] 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.

[0099] 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 the image (slice data). VCL NAL unit types can be classified according to the nature and type of the picture included in the VCL NAL unit, and non-VCL NAL unit types can be classified according to the type of parameter set.

[0100] The following are examples of NAL unit types specified according to the type of parameter sets included in non-VCL NAL unit types.

[0101] -APS (Adaptation Parameter Set) NAL unit: type of NAL unit including APS

[0102] -DPS (Decoding Parameter Set) NAL unit: the type of NAL unit that includes DPS

[0103] -VPS (Video Parameter Set) NAL unit: Type of NAL unit containing VPS

[0104] -SPS (Sequence Parameter Set) NAL unit: the type of NAL unit that includes the SPS

[0105] -PPS (Picture Parameter Set) NAL unit: type of NAL unit including PPS

[0106] - PH (Picture Header) NAL unit: the type of NAL unit containing PH

[0107] The above-mentioned NAL unit type has syntax information of the NAL unit type, and the syntax information can be stored in the NAL unit header and notified by signaling. For example, the syntax information can be nal_unit_type, and the NAL unit type can be specified by the nal_unit_type value.

[0108] Furthermore, 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, a slice may be mixed with or replaced by a tile group. In addition, in this document, a slice header may be mixed with a tile group header or replaced by a type group header.

[0109] A slice header (slice header syntax or slice header information) may include information / parameters generally applicable to a slice. An APS (APS syntax) or a PPS (PPS syntax) may include information / parameters generally applicable to one or more slices or pictures. An SPS (SPS syntax) may include information / parameters generally applicable to one or more sequences. A VPS (VPS syntax) may include information / parameters generally applicable to multiple layers. A DPS (DPS syntax) may include information / parameters generally applicable to the entire video. A DPS may include information / parameters related to the concatenation of coded video sequences (CVS). In this document, a high-level syntax (HLS) may include at least one of an APS syntax, a PPS syntax, an SPS syntax, a VPS syntax, a DPS syntax, a picture header syntax, and a slice header syntax.

[0110] In this document, image / video information encoded in an encoding device and signaled to a decoding device in the form of a bitstream may include not only information related to segmentation in a picture, intra / inter prediction information, residual information, loop filtering information, etc., but also information included in a slice header, information included in a picture header, information included in an APS, information included in a PPS, information included in an SPS, information included in a VPS, and / or information included in a DPS. In addition, the image / video information may also include information in a NAL unit header.

[0111] Furthermore, to compensate for differences between the original image and the reconstructed image due to errors occurring during compression encoding processes such as quantization, loop filtering may be performed on the reconstructed samples or reconstructed pictures as described above. As described above, loop filtering may be performed by filters of an encoding device and a decoding device, and may include a deblocking filter, SAO, and / or an adaptive loop filter (ALF). 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.

[0112] Below, a detailed description of picture reconstruction and filtering will be described. In image / video encoding, reconstructed blocks can be generated in block units based on intra-frame prediction / inter-frame prediction, and a reconstructed picture including the reconstructed blocks can be generated. If the current picture / slice is an I picture / slice, the blocks included in the current picture / slice can be reconstructed based only on intra-frame prediction. In addition, if the current picture / slice is a P or B picture / slice, the blocks included in the current picture / slice can be reconstructed based on intra-frame prediction or inter-frame prediction. In this case, intra-frame prediction can be applied to some blocks in the current picture / slice, and inter-frame prediction can be applied to the remaining blocks.

[0113] Intra-frame prediction may refer to a prediction that generates prediction samples for the current block based on reference samples in a picture to which the current block belongs (hereinafter, the current picture). When intra-frame prediction is applied to the current block, neighboring reference samples to be used for intra-frame prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block 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 multiple columns of upper neighboring samples and multiple rows of left neighboring samples. 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.

[0114] However, some neighboring reference samples of the current block may not have been decoded or may be unavailable. 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.

[0115] When deriving neighboring reference samples, (i) the prediction sample can be derived based on the average or interpolation of the neighboring reference samples of the current block, and (ii) the prediction sample can be derived based on reference samples located 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 non-directional mode or non-angular mode, and case (ii) may be referred to as directional mode or angular mode. Furthermore, the prediction sample can be generated by interpolating a first neighboring sample located in a direction opposite to the prediction direction of the intra prediction mode of the current block and a second neighboring sample among the neighboring reference samples. This case may be referred to as linear interpolation intra prediction (LIP). Furthermore, chroma prediction samples can be generated based on luma samples using a linear model. This case may be referred to as LM mode. Furthermore, the temporal prediction sample of the current block can be derived based on filtered neighboring reference samples, and the prediction sample of the current block can be derived by calculating a weighted sum of the temporal prediction sample and at least one reference sample derived according to the intra prediction mode among existing neighboring reference samples (i.e., unfiltered neighboring reference samples). This case may be referred to as position-dependent intra prediction (PDPC). In addition, prediction samples can be derived using reference samples located in the prediction direction on the corresponding line by selecting the reference sample line with the highest prediction accuracy among multiple reference sample lines adjacent to the current block. In this case, intra-frame prediction encoding can be performed by indicating (signaling) the reference sample line to be used to the decoding device. The above situation can 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 sub-partitions or horizontal sub-partitions, and neighboring reference samples can be derived and used in units of sub-partitions. That is, in this case, since the intra-frame prediction mode of the current block is applied equally to the sub-partitions, and neighboring reference samples are derived and used in units of sub-partitions, intra-frame prediction performance can be enhanced in some cases. This prediction method can be referred to as intra sub-partition (ISP) or ISP-based intra-frame prediction. The above intra-frame prediction method can be referred to as an intra-frame prediction type different from the intra-frame prediction mode in Content 1.2. The intra-frame prediction type can be referred to by 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) may include at least one of the aforementioned LIP, PDPC, MRL, or 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. In the absence of a specific intra prediction type, a normal intra prediction type may generally be applied, and prediction may be performed based on the aforementioned intra prediction modes. Furthermore, post-filtering may be performed on the derived prediction samples as needed.

[0116] Specifically, the intra prediction process may include the steps of determining the intra prediction mode / type, deriving neighboring reference samples, and deriving prediction samples based on the intra prediction mode / type. In addition, a post-filtering step may be performed on the derived prediction samples as needed.

[0117] A reconstructed picture modified by the in-loop filtering process can be generated, and the modified reconstructed picture can be output from the decoding device as a decoded picture. In addition, the modified reconstructed picture can be stored in a decoded picture buffer or memory of the encoding device / decoding device, and can then be used as a reference picture in the inter-frame prediction process when encoding / decoding the picture. As described above, the in-loop filtering process may include deblocking filtering, sample adaptive offset (SAO) processing, and / or adaptive loop filter (ALF) processing. In this case, one or some of the deblocking filtering, sample adaptive offset (SAO), adaptive loop filter (ALF), and bilateral filtering processes may be applied sequentially, or all of them may be applied sequentially. For example, after applying deblocking filtering to the reconstructed picture, SAO processing may be performed. In addition, for example, after applying deblocking filtering to the reconstructed picture, ALF processing may be performed. This can even be performed in the same manner by the encoding device.

[0118] 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 from the reconstructed picture, determine the 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, motion vector difference, whether the reference picture is the same, and whether there are any non-zero significant coefficients of the two blocks adjacent to the target boundary.

[0119] SAO is a method for compensating for the offset difference between a reconstructed picture and an original picture on a sample-by-sample basis, and can be applied based on types such as band offset and edge offset. According to SAO, samples are classified into different categories based on the SAO type, and an offset value can be added to each sample based on the category. SAO filter information may include information on whether SAO is applied, SAO type information, and SAO offset value information. SAO can be applied to the reconstructed picture after deblocking filtering.

[0120] An adaptive loop filter (ALF) is a filtering technique that applies a filter shape to a reconstructed picture based on filter coefficients on a sample-by-sample basis. The encoding device can determine whether to apply the ALF, the ALF shape, and / or ALF filter coefficients by comparing the reconstructed picture with the original picture, and can signal this to the decoding device. Specifically, ALF filter information may include information on whether to apply the ALF, ALF filter shape information, and ALF filter coefficient information. The ALF may also be applied to the reconstructed picture after deblocking filtering has been applied.

[0121] Figure 5 A screen showing an embodiment according to this document. Figure 5 An exemplary picture of may be divided into sub-pictures, slices and tiles.

[0122] Reference Figure 5 , a picture can be divided into sub-pictures. For example, a sub-picture can include one or more slices. A slice can represent a rectangular area of a picture. In addition, a picture can be divided into tiles. For example, a rectangular slice can include only a portion (subset) of a tile. That is, in Figure 5 In , two rectangular slices are in the same tile, and these two rectangular slices may belong to different sub-pictures. Figure 5 The problems caused by this situation and their solutions will be described later.

[0123] In an example, a picture / sub-picture may be encoded based on a sub-picture / slice / patch. An encoding device may encode a current picture based on a sub-picture / slice / patch structure, or an encoding device may encode one or more sub-pictures (including slices / patch) of the current picture and may output a (sub) bitstream including (encoded) information about the sub-pictures. A decoding device may decode one or more sub-pictures in the current picture based on a (sub) bitstream including (encoded) information of the sub-picture / slice / patch.

[0124] Figure 6 A sub-picture / slice / tile-based encoding method according to an embodiment of this document is shown.

[0125] The encoder may divide the (input) picture into multiple (or one or more) sub-pictures / slices / tiles. Each sub-picture may be encoded separately / independently and a bitstream may be output. Here, the bitstream for a sub-picture may be referred to as a substream, subset, or sub-bitstream. Information about sub-pictures / slices / tiles may include the information / syntax elements described in this document. For example, information about slices may include information about the number of slices signaled for each picture / sub-picture and the width / height of the slices in the tile. For example, information about tiles may include information about the number of tiles (e.g., the number of tile columns and / or the number of tile rows) and information about the size (e.g., width and / or height) of each tile.

[0126] The encoder may encode one or more sub-pictures as information about the sub-pictures.The encoder may encode one or more slices / patches as information about the slices / patches.

[0127] Figure 7 A sub-picture / slice / tile-based decoding method according to an embodiment of this document is shown.

[0128] The decoder can decode one or more sub-pictures (including slices / patches) and can output one or more decoded sub-pictures or a current picture including sub-pictures. The bitstream may include a substream or sub-bitstream for the sub-picture. As described above, information about the sub-picture / slice / patches can be configured in a high-level syntax (HLS) included in the bitstream. The decoder can derive one or more sub-pictures based on the information about the sub-pictures. The decoder can derive one or more slices / patches based on the information about the slices / patches. The decoder can decode all or some sub-pictures. The decoder can decode sub-pictures (including current blocks (or CUs)), CTUs, slices, and / or patches based on CABAC, prediction, residual processing (transformation and quantization), and in-loop filtering. Therefore, decoded sub-pictures can be output. The decoded sub-pictures may include reconstructed / decoded blocks. The decoded sub-pictures in the output sub-picture set (OPS) can be output together. For example, if the screen is related to a 360-degree or omnidirectional image / video, some of them may be rendered, and in this case, only some of all sub-pictures may be decoded, and some or all of the decoded sub-pictures may be rendered depending on the user's viewport or viewing position. In addition, if information indicating (indicating) whether in-loop filtering is enabled across sub-picture boundaries is enabled, the decoder may apply in-loop filtering processing (e.g., deblocking filtering) to the sub-picture boundary between two sub-pictures. For example, if the sub-picture boundary is the same as the picture boundary, in-loop filtering processing may be applied or may not be performed for the sub-picture boundary.

[0129] In an embodiment of the present document, the image / video information may include HLS, and the HLS may include information about sub-pictures / slices / tiles. The information about sub-pictures may include information representing one or more sub-pictures in the current picture. The information about slices may include information representing one or more slices in the current picture, sub-picture, or tile. The information about tiles may include information representing one or more tiles in the current picture, sub-picture, or slice. A picture may include a tile containing one or more slices and / or a slice containing one or more tiles. In addition, a picture may include a sub-picture containing one or more slices / tiles.

[0130] The following table shows the syntax related to the above picture division (sub-picture / slice / tile). Information about sub-picture / slice / tile may include the syntax elements in the following table.

[0131] The following table shows the syntax of the sequence parameter set (SPS) based on picture partitioning (sub-picture / slice / tile).

[0132] [Table 1]

[0133]

[0134] The following table shows the syntax of the picture parameter set (PPS) based on the picture partitioning (sub-picture / slice / tile).

[0135] [Table 2]

[0136]

[0137] The following table shows the syntax of the slice header based on the picture partitioning (sub-picture / slice / tile).

[0138] [Table 3]

[0139]

[0140] Figure 8 is a flow chart illustrating a filtering-based encoding method in an encoding device. Figure 8 The method may include steps S800 to S830.

[0141] In step S800 , the encoding apparatus may generate a reconstructed picture. Step S800 may be performed based on the above-described process of generating a reconstructed picture (or reconstructed sample).

[0142] In step S810, the encoding device may determine whether to apply in-loop filtering (across a virtual boundary) based on in-loop filtering related information. Here, in-loop filtering may include at least one of the above-mentioned deblocking filtering, SAO, or ALF.

[0143] In step S820, the encoding apparatus may generate a modified reconstructed picture (modified reconstructed sample) based on the determination in step S810. Here, the modified reconstructed picture (modified reconstructed sample) may be a filtered reconstructed picture (filtered reconstructed sample).

[0144] In step S830 , the encoding apparatus may encode image / video information including in-loop filtering related information based on the in-loop filtering process.

[0145] Figure 9 is a flow chart illustrating a filtering-based decoding method in a decoding device. Figure 9 The method may include steps S900 to S930.

[0146] In step S900, the decoding apparatus may obtain image / video information including in-loop filtering related information from a bitstream. Here, the bitstream may be based on encoded image / video information transmitted from the encoding apparatus.

[0147] In step S910 , the decoding apparatus may generate a reconstructed picture. Step S910 may be performed based on the above-described process of generating a reconstructed picture (or reconstructed sample).

[0148] In step S920, the decoding apparatus may determine whether to apply in-loop filtering (across a virtual boundary) based on in-loop filtering related information. Here, in-loop filtering may include at least one of the above-mentioned deblocking filtering, SAO, or ALF.

[0149] In step S930, the decoding apparatus may generate a modified reconstructed picture (modified reconstructed samples) based on the determination in step S920. Here, the modified reconstructed picture (modified reconstructed samples) may be a filtered reconstructed picture (filtered reconstructed samples).

[0150] As described above, in-loop filtering may be applied to the reconstructed picture. In this case, in order to further enhance the subjective / objective visual quality of the reconstructed picture, a virtual boundary may be defined, and in-loop filtering may be applied across the virtual boundary. For example, the virtual boundary may include discontinuous edges such as a 360-degree image, a VR image, or a picture-in-picture (PIP). For example, a virtual boundary may exist at a predetermined joint position, and its presence / absence and / or position may be notified by a signal. As an example, the virtual boundary may be located at the fourth sample line above the CTU row (specifically, for example, above the fourth sample line above the CTU row). As another example, information about the presence / absence and / or position of the virtual boundary may be notified by a signal via the HLS. As described above, the HLS may include an SPS, a PPS, a picture header, and a slice header.

[0151] In the following, high-level syntax signaling and semantics according to embodiments of this document will be described.

[0152] Embodiments of this document may include methods for controlling loop filters. The methods for controlling loop filters may be applied to reconstructed pictures. An in-loop filter (loop filter) may be used to decode the encoding bitrate. The loop filters may include the aforementioned deblocking, SAO, and ALF. The SPS may include flags related to deblocking, SAO, and ALF, respectively. The flags may indicate whether the respective tools are enabled for encoding the coded layer video sequence (CLVS) and coded video sequence (CVS) referenced by the SPS.

[0153] If the loop filter is enabled for CVS, you can control whether the loop filter is applied across specific boundaries. For example, you can control whether the loop filter crosses sub-picture boundaries. Additionally, you can control whether the loop filter crosses tile boundaries. Furthermore, you can control whether the loop filter crosses virtual boundaries. Here, virtual boundaries can be defined on the CTU based on the availability of line buffers.

[0154] Regarding whether to perform in-loop filtering across a virtual boundary, the in-loop filtering related information may include at least one of an SPS virtual boundary enable flag (virtual boundary enable flag in SPS), an SPS virtual boundary existence flag, a picture header virtual boundary existence flag, an SPS picture header virtual boundary existence flag, and information about the location of the virtual boundary.

[0155] In the embodiments included in this document, the information about the position of the virtual boundary may include information about the x-coordinate of the vertical virtual boundary and information about the y-coordinate of the horizontal virtual boundary. Specifically, the information about the position of the virtual boundary may include information about the x-coordinate of the vertical virtual boundary and / or the y-coordinate of the horizontal virtual boundary in units of luminance samples. In addition, the information about the position of the virtual boundary may include information about the number of information (syntax elements) about the x-coordinate of the vertical virtual boundary present in the SPS. In addition, the information about the virtual boundary may include information about the number of information (syntax elements) about the y-coordinate of the horizontal virtual boundary present in the SPS. In addition, the information about the position of the virtual boundary may include information about the number of information (syntax elements) about the x-coordinate of the vertical virtual boundary present in the picture header. In addition, the information about the position of the virtual boundary may include information about the number of information (syntax elements) about the y-coordinate of the horizontal virtual boundary present in the picture header.

[0156] The following table shows exemplary syntax and semantics of a sequence parameter set (SPS) according to this embodiment.

[0157] [Table 4]

[0158]

[0159] [Table 5]

[0160]

[0161]

[0162]

[0163] The following table shows an exemplary syntax and semantics of a picture parameter set (PPS) according to the present embodiment.

[0164] [Table 6]

[0165]

[0166] [Table 7]

[0167]

[0168]

[0169] The following table shows an exemplary syntax and semantics of the picture header according to this embodiment.

[0170] [Table 8]

[0171]

[0172]

[0173] [Table 9]

[0174]

[0175]

[0176]

[0177] The following table shows an exemplary syntax and semantics of a slice header according to this embodiment.

[0178] [Table 10]

[0179]

[0180] [Table 11]

[0181]

[0182]

[0183]

[0184] 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.

[0185] In an example, two different rectangular slices may belong to different sub-pictures while sharing the same tile. In this case, the problem of increased coding complexity may arise.

[0186] To simplify picture partitioning, embodiments of this document may include example conditions where a picture is divided into two or more sub-pictures. In one example, all CTUs in a tile may belong to the same sub-picture. In another example, all CTUs in a sub-picture may belong to the same tile. These two examples may be applied to image / video coding individually, sequentially, or in combination. Furthermore, in embodiments of this document, when a sub-picture includes CTUs that are a subset of all CTUs in one tile, the sub-picture may not include CTUs belonging to another tile.

[0187] In the signaling for the current picture, if the value of subpic_present_flag is 1, the number of subpics in each picture of the reference SPS can be 1 (with the value of sps_num_subpics_minus1 being 0). This condition is in place to support a subpicture extraction use case where subpictures are encoded independently from a bitstream to form another bitstream, even without changing values less than the value of the parameter set. Therefore, even if the value of subpic_present_flag is 1 and the value of sps_num_subpics_minus1 is 0, subpic_ctu_top_left_x[0], subpic_ctu_top_left_y[0], subpic_width_minus1[0], subpic_height_minus1[0], subpic_treated_as_pic_flag[i], and / or loop_filter_across_subpic_enabled_flag[i] are still present. In this case, these syntax elements may overlap with each other and may make the operation of the decoder unpredictable if erroneous values are signaled in the corresponding syntax elements. For example, if the value of subpics_present_flag is 1 and the value of sps_num_subpics_minus1 is 0, this means that there is only one sub-picture (the picture itself) and the value of subpic_treat_as_pic_flag[0] is equal to 1. In this case, if the corresponding value is signaled as 0, a contradiction problem may occur in the decoding process.

[0188] To address the above issues, embodiments of this document include conditional examples that can be applied when sub-picture signaling is present (e.g., subpic_present_flag is set to 1) and there is only one sub-picture in a picture (e.g., sps_num_subpics_minus1 is set to 0). The above conditional examples may be as shown in the following table.

[0189] [Table 12]

[0190]

[0191]

[0192] In the example, if there is sub-picture signaling and the position of the virtual boundary is present in the picture header, there is a question whether the picture header should be rewritten in the sub-picture extraction and sub-picture merging scenarios to identify whether the signaling of the virtual boundary position is correct. This may violate the design purpose of sub-picture extraction / merging, where there is no need to rewrite the bitstream for NAL units of layers lower than the parameter set.

[0193] To address the above issues, according to an embodiment of this document, if sub-picture signaling is present (e.g., if sub-picture signaling is present in an SPS), the picture header may not include signaling of the virtual boundary position. As an example, if sub-picture signaling is present, information about the virtual boundary position may be included in an advanced parameter set. For example, if sub-picture signaling is present, information about the virtual boundary position may be included in the SPS. Furthermore, if sub-picture signaling is present, information about the virtual boundary position may be included in the PPS.

[0194] In the embodiments of this document, if sub-picture ID signaling is present (if the value of sps_subpic_id_present_flag is 1), all sub-pictures can be independently coded sub-pictures (the value of subpic_treated_as_pic_flag[i] is 1). In this case, the location of the sub-picture ID signaling (e.g., SPS, PPS, or picture header) may not matter.

[0195] According to the embodiments of this document and the above table, whether virtual boundary related information (e.g., virtual boundary position related information) is signaled in the sequence parameter set can be determined based on whether sub-picture information is present. For example, if sub-picture information is present in the corresponding sequence, virtual boundary related information (e.g., virtual boundary position related information) can be signaled in the sequence parameter set. Therefore, the virtual boundary-based encoding method according to the embodiments of this document can be efficiently implemented without rewriting or changing high-level syntax.

[0196] Furthermore, according to embodiments of this document, a (decoded) picture may be composed of sub-pictures. Information regarding the sub-pictures may be obtained by a decoding device, and decoding processing may be performed based on the information regarding the sub-pictures. In one example, based on the information regarding the sub-pictures, the decoding device may determine a location (e.g., SPS) for signaling information regarding the location of a virtual boundary used for in-loop filtering.

[0197] Figure 10 and Figure 11 An example of a video / image encoding method and related components according to an embodiment of this document is schematically shown.

[0198] Figure 10 The method disclosed in Figure 2 or Figure 11 Specifically, for example, Figure 10 S1000 to S1020 can be Figure 11 The residual processor 230 of the encoding device performs, Figure 10 The S1040 can be Figure 11 The filter 260 of the encoding device performs, Figure 10 The S1050 can be Figure 11 The entropy encoder 240 of the encoding device performs. In addition, although Figure 10 Not shown in the figure, the prediction sample or the prediction related information may be derived by the predictor 220 of the encoding apparatus, and a bitstream may be generated from the residual information or the prediction related information by the entropy encoder 240 of the encoding apparatus. Figure 10 The method disclosed in may include the above-mentioned embodiments of this document.

[0199] The encoding device may derive a sub-picture. The encoding device may divide a current picture into sub-pictures. The encoding device may determine the size (eg, height / width) of the sub-pictures. Furthermore, the encoding device may determine the number of sub-pictures included in the current picture.

[0200] The encoding device may generate sub-picture related information. For example, the encoding device may generate sub-picture related information based on the number of sub-pictures included in the current picture, the size (e.g., height / width) of the sub-picture, and / or the boundary of the sub-picture. The sub-picture related information may include information about whether a sub-picture exists, information about whether a sub-picture is treated as a picture, information about the number of sub-pictures included in the current picture, information about the size (e.g., height / width) of the sub-picture, information about whether the boundary of the sub-picture coincides with the boundary of the current picture, and / or information about the ID of the sub-picture.

[0201] Reference Figure 10 , the encoding device may derive residual samples (S1000). 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 predicted samples of the current block. Specifically, the encoding device may derive 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.

[0202] The encoding device may derive transform coefficients (S1010). The encoding device may derive transform coefficients based on a transform process on the residual sample. For example, the transform process may include at least one of DCT, DST, GBT, or CNT.

[0203] The encoding apparatus may derive quantized transform coefficients (S1020). The encoding apparatus may derive quantized transform coefficients based on the quantization process of the transform coefficients. The quantized transform coefficients may have a 1-dimensional vector form based on a coefficient scanning order.

[0204] The encoding device may generate residual information (S1030). The encoding device may generate residual information based on the residual samples of the current block. The encoding device may generate residual information representing quantized transform coefficients. The residual information may be generated by various encoding methods such as exponential Golomb, CAVLC, and CABAC.

[0205] The encoding device may generate reconstructed samples. The encoding device may generate reconstructed samples based on residual information. The reconstructed samples may be generated by adding residual samples based on the residual information to the predicted samples. Specifically, the encoding device may perform prediction (intra-frame or inter-frame prediction) on the current block and may generate reconstructed samples based on the predicted samples generated by the prediction and the original samples.

[0206] 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 a transform coefficient (luminance transform coefficient) of the residual luma sample and / or a transform coefficient (chroma transform coefficient) of the residual chroma sample. The quantized transform coefficient may include a quantized luma transform coefficient and / or a quantized chroma transform coefficient.

[0207] The encoding device may determine whether to perform in-loop filtering across virtual boundaries (S1040). Based on the above determination, the encoding device may generate information about the number of virtual boundaries and the positions of the virtual boundaries. For example, the encoding device may generate information about the number of virtual boundaries and the positions of the virtual boundaries. For example, the encoding device may generate information about the number of vertical virtual boundaries, information about the positions of vertical virtual boundaries, information about the number of horizontal virtual boundaries, and information about the positions of horizontal virtual boundaries.

[0208] The encoding device may generate in-loop filtering related information for the reconstructed samples of the current picture. The encoding device may perform in-loop filtering processing on the reconstructed samples, and may generate in-loop filtering related information based on the in-loop filtering processing. For example, the in-loop filtering related information may include the information about the virtual boundaries described above in this document (SPS virtual boundary enable flag, picture header virtual boundary enable flag, SPS virtual boundary existence flag, picture header virtual boundary existence flag, and information about the position of the virtual boundary). In the example, the encoding device may generate in-loop filtering related information based on information about the number of vertical virtual boundaries, information about the position of the vertical virtual boundaries, information about the number of horizontal virtual boundaries, and information about the position of the horizontal virtual boundaries.

[0209] The encoding device may encode the video / image information (S1050). The image information may include residual information, prediction-related information, sub-picture-related information, and / or in-loop filtering-related information. The encoded video / image information may be output as a bitstream. The bitstream may be transmitted to a decoding device via a network or storage medium.

[0210] The image / video information may include various information according to the embodiments of this document. For example, the image / video information may include the information disclosed in at least one of Tables 1 to 12 above.

[0211] In an embodiment, the image information may include a sequence parameter set (SPS). Based on whether the SPS includes sub-picture related information, it may be determined whether the SPS includes additional information related to the virtual boundary.

[0212] In an embodiment, the additional information related to the virtual boundaries may include the number of virtual boundaries and the positions of the virtual boundaries.

[0213] 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.

[0214] In an embodiment, the image information may include a sub-picture presence flag (eg, subpic_present_flag). Whether the SPS includes sub-picture related information may be determined based on the sub-picture presence flag.

[0215] In an embodiment, the image information may include a sub-picture ID existence flag. If the value of the sub-picture ID existence flag is 1, the sub-picture in the current picture may be an independently coded sub-picture.

[0216] In an embodiment, the current picture may include a sub-picture and a patch. Coding tree units (CTUs) in a patch may belong to the same sub-picture.

[0217] In an embodiment, the current picture may include a sub-picture and a patch. Coding tree units (CTUs) in a sub-picture may belong to the same patch.

[0218] In an embodiment, the SPS may include an SPS virtual boundary existence flag related to whether the SPS includes additional information related to the virtual boundary. Based on the SPS including the sub-picture related information, the value of the SPS virtual boundary existence flag may be determined to be 1.

[0219] In an embodiment, the image information may include picture header information. Based on the SPS including sub-picture related information, the picture header may not include additional information related to the virtual boundary.

[0220] In an embodiment, based on the SPS including the sprite-related information, the SPS may include additional information related to the virtual boundary.

[0221] Figure 12 and Figure 13 An example of a video / image decoding method and related components according to an embodiment of this document is schematically shown.

[0222] Figure 12 The method disclosed in Figure 12 or Figure 13 Specifically, for example, Figure 12 S1200 may be performed by the entropy decoder 310 of the decoding device, Figure 12 S1210 to S1230 may be performed by the residual processor 320 of the decoding device, S1240 may be performed by the residual processor 320 and / or the adder 340 of the decoding device, and S1250 may be performed by the filter 350 of the decoding device. Figure 12 The method disclosed in may include the above-mentioned embodiments as described above in this document.

[0223] Reference Figure 12 The decoding device may receive / obtain video / image information (S1200). The video / image information may include residual information, prediction-related information, sub-picture-related information, and / or in-loop filtering-related information. The decoding device may receive / obtain image / video information via a bitstream.

[0224] The image / video information may include various information according to the embodiments of this document. For example, the image / video information may include the information disclosed in at least one of Tables 1 to 12 above.

[0225] The decoding device can derive a sub-picture of the current picture. The decoding device can derive the sub-picture based on sub-picture related information obtained based on the bitstream. Based on the sub-picture related information, the number of sub-pictures, the size of the sub-pictures, and whether the sub-pictures are considered as pictures can be determined. Residual samples and / or prediction samples to be described later can be generated based on the sub-pictures.

[0226] The decoding apparatus may derive quantized transform coefficients (S1210). The decoding apparatus may derive quantized transform coefficients based on residual information. The quantized transform coefficients may have a 1-dimensional vector form based on a coefficient scanning order. The quantized transform coefficients may include quantized luma transform coefficients and / or quantized chroma transform coefficients.

[0227] The decoding apparatus may derive transform coefficients (S1220). The decoding apparatus may derive transform coefficients based on dequantization processing of the quantized transform coefficients. The decoding apparatus may derive luma transform coefficients based on the quantized luma transform coefficients by dequantization. The decoding apparatus may derive chroma transform coefficients based on the quantized chroma transform coefficients by dequantization.

[0228] The decoding device may generate / derive residual samples (S1230). The decoding device may derive residual samples based on an inverse transform process of the transform coefficients. The decoding device may derive residual luma samples based on the luma transform coefficients through an inverse transform process. The decoding device may derive residual chroma samples based on the chroma transform coefficients through an inverse transform process.

[0229] The decoding device may generate / derive reconstructed samples (S1240). For example, the decoding device may generate / derive reconstructed luma samples and / or reconstructed chroma samples. The decoding device may generate / derive 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. In addition, the decoding device may generate reconstructed samples of the current picture based on the residual samples, the predicted samples and / or the sub-picture.

[0230] The decoding device may generate modified (filtered) reconstructed samples (S1250). The decoding device may generate the modified reconstructed samples based on an in-loop filtering process for the reconstructed samples. The decoding device may generate the modified reconstructed samples based on in-loop filtering related information. To generate the modified reconstructed samples, the decoding device may use deblocking, SAO, and / or ALF processing.

[0231] In an embodiment, the image information may include a sequence parameter set (SPS). Based on whether the SPS includes sub-picture related information, it may be determined whether the SPS includes additional information related to the virtual boundary.

[0232] In an embodiment, the additional information related to the virtual boundaries may include the number of virtual boundaries and the positions of the virtual boundaries.

[0233] In an embodiment, the additional information related to the virtual border 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.

[0234] In an embodiment, the image information may include a sub-picture presence flag (eg, subpic_present_flag). Whether the SPS includes sub-picture related information may be determined based on the sub-picture presence flag.

[0235] In an embodiment, the image information may include a sub-picture ID existence flag. If the value of the sub-picture ID existence flag is 1, the sub-picture in the current picture may be an independently coded sub-picture.

[0236] In an embodiment, the current picture may include a sub-picture and a patch. Coding tree units (CTUs) in a patch may belong to the same sub-picture.

[0237] In an embodiment, the current picture may include a sub-picture and a patch. Coding tree units (CTUs) in a sub-picture may belong to the same patch.

[0238] In an embodiment, the SPS may include an SPS virtual boundary existence flag related to whether the SPS includes additional information related to the virtual boundary. Based on the SPS including the sub-picture related information, the value of the SPS virtual boundary existence flag may be determined to be 1.

[0239] In an embodiment, the image information may include picture header information. Based on the SPS including sub-picture related information, the picture header may not include additional information related to the virtual boundary.

[0240] In an embodiment, based on the SPS including the sprite-related information, the SPS may include additional information related to the virtual boundary.

[0241] If residual samples of the current block exist, the decoding device may receive information about the residual of the current block. The information about the residual 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 the residual samples based on the transform coefficients.

[0242] The decoding device may generate reconstructed samples based on the (intra-frame) prediction samples and the residual samples, and may derive a reconstructed block or a reconstructed picture based on the reconstructed samples. Specifically, the decoding device may generate the reconstructed samples based on the sum of the (intra-frame) prediction samples and the residual samples. Thereafter, as described above, the decoding device may apply in-loop filtering, such as deblocking filtering and / or SAO processing, to the reconstructed picture as needed to improve subjective / objective picture quality.

[0243] For example, a decoding device may obtain image information including all or part of the above information (or syntax elements) by decoding a bitstream or coding information. In addition, the bitstream or coding information may be stored in a computer-readable storage medium and may cause the above decoding method to be executed.

[0244] Although the methods are described in the above embodiments based on flowcharts that list steps or blocks in sequence, the steps of this document are not limited to a specific order, and specific steps may be performed in different steps, in a different order, or simultaneously relative to the above. In addition, those skilled in the art will understand that the steps of the flowcharts are not exclusive, and another step may be included, or one or more steps in the flowcharts may be deleted without affecting the scope of this document.

[0245] The above-mentioned method according to the present document may be in the form of software, and the encoding device and / or decoding device according to the present document may be included in an apparatus for image processing (e.g., TV, computer, smart phone, set-top box, display device, etc.).

[0246] When the embodiments of this document are implemented by software, the above method can be implemented by a module (process or function) that performs 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 this document, it can be implemented and executed on a processor, a microprocessor, a controller or a chip. For example, the functional units shown in the various figures 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 (for example, information about instructions) or the algorithm can be stored in a digital storage medium.

[0247] In addition, the decoding device and the encoding device to which the embodiments of the present document are applied may be included in multimedia broadcast transceivers, mobile communication terminals, home theater video devices, digital theater video devices, surveillance cameras, video chat devices and real-time communication devices (e.g., video communication), mobile streaming devices, storage media, cameras, video on demand (VoD) service providers, over-the-top (OTT) video devices, Internet streaming service providers, 3D video devices, virtual reality (VR) devices, augmented reality (AR) devices, image phone video devices, vehicle terminals (e.g., vehicle (including autonomous vehicle) terminals, aircraft terminals, or ship terminals), and medical video devices; and may be used to process image signals or data. For example, OTT video devices may include game consoles, Blu-ray players, Internet-connected TVs, home theater systems, smartphones, tablet PCs, and digital video recorders (DVRs).

[0248] In addition, the processing method of the embodiment of the present document is 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 embodiment 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.

[0249] 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.

[0250] Figure 14 This shows an example of a content streaming system to which the embodiments of this document can be applied.

[0251] Reference Figure 14 A content streaming system to which 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.

[0252] The encoding server is used to compress the content input from the multimedia input device (e.g., a smartphone, a camera, a camcorder, etc.) into digital data to generate a bitstream and send it to the streaming server. As another example, if the multimedia input device (e.g., a smartphone, a camera, a camcorder, etc.) directly generates the bitstream, the encoding server can be omitted.

[0253] The bitstream can be generated by applying the encoding method or bitstream generation method according to the embodiment of this document. In addition, the streaming server can temporarily store the bitstream during the transmission or reception of the bitstream.

[0254] The streaming server transmits multimedia data to a user device via a network server based on a user's request. The network server serves as a means of informing the user of available services. When a user requests a desired service, the network server transmits the request to the streaming server, which then transmits the multimedia data to the user. In this regard, the content streaming system may include a separate control server, which in this case is used to control commands and responses between the various devices in the content streaming system.

[0255] The streaming server may receive content from a media storage device and / or an encoding server. For example, when 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.

[0256] For example, user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., watch-type terminals (smart watches), glasses-type terminals (smart glasses), head-mounted displays (HMDs)), digital TVs, desktop computers, digital signs, etc.

[0257] The various servers in the content streaming system may operate as distributed servers, and in this case, data received by the various servers may be processed in a distributed manner.

[0258] 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. Furthermore, the technical features in method claims and device claims may be combined to be implemented or performed in a device. Furthermore, the technical features in method claims and 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 residual information through a bit stream; deriving quantized transform coefficients based on the residual information; deriving transform coefficients based on dequantization processing of the quantized transform coefficients; deriving residual samples based on an inverse transform process on the transform coefficients; generating a reconstructed sample of the current picture based on the residual sample; and generating modified reconstructed samples based on an in-loop filtering process on the reconstructed samples of the current picture, wherein determining whether the in-loop filtering process is performed across a virtual boundary, The image information includes a sequence parameter set SPS, Wherein, whether the SPS includes information about the number of the virtual boundaries is determined based on whether the SPS includes sub-picture related information, Wherein, based on the presence of multiple sub-pictures in the current picture, the sub-picture related information includes information about the position of at least one sub-picture, and Wherein, based on the existence of a sub-picture in the current picture, the information about the position of the sub-picture is determined to be a predetermined value.

2. The image decoding method according to claim 1, wherein: The information about the number of virtual boundaries includes information about the number of vertical virtual boundaries and information about the number of horizontal virtual boundaries.

3. The image decoding method according to claim 1, wherein: The image information includes a sub-picture existence flag, and Wherein, whether the SPS includes the sub-picture related information is determined based on the sub-picture existence flag.

4. The image decoding method according to claim 1, wherein: The SPS includes an SPS virtual boundary existence flag related to whether the SPS includes the information about the number of virtual boundaries, and Wherein, based on the SPS including the sub-picture related information, the value of the SPS virtual boundary existence flag is determined to be 1.

5. The image decoding method according to claim 1, wherein: The image information includes picture header information, and Wherein, based on the fact that the SPS includes the sub-picture related information, the picture header does not include the information about the number of the virtual boundaries. The image decoding method according to claim 5 , wherein: Based on the SPS including the sprite-related information, the SPS includes the information about the number of the virtual boundaries.

7. An image encoding method performed by an encoding device, the image encoding method comprising the following steps: Derive residual samples for the current block; deriving transform coefficients based on transform processing of the residual samples; deriving quantized transform coefficients based on quantizing the transform coefficients; generating residual information based on the quantized transform coefficients; determining whether to perform in-loop filtering on reconstructed samples of the current picture across a virtual boundary; as well as encoding image information based on the residual information and determining whether to perform in-loop filtering on reconstructed samples of the current picture across a virtual boundary, The image information includes a sequence parameter set SPS, Wherein, whether the SPS includes information about the number of the virtual boundaries is determined based on whether the SPS includes sub-picture related information, and Wherein, based on the presence of multiple sub-pictures in the current picture, the sub-picture related information includes information about the position of at least one sub-picture.

8. The image encoding method according to claim 7, wherein: The information about the number of virtual boundaries includes information about the number of vertical virtual boundaries and information about the number of horizontal virtual boundaries.

9. The image encoding method according to claim 7, wherein: The image information includes a sub-picture existence flag, and Wherein, whether the SPS includes the sub-picture related information is determined based on the sub-picture existence flag.

10. The image encoding method according to claim 7, wherein: The image information includes a sub-picture ID presence flag, and Wherein, based on the value of the sub-picture ID existence flag being 1, the sub-picture in the current picture is independently encoded.

11. The image encoding method according to claim 7, wherein: The SPS includes an SPS virtual boundary existence flag related to whether the SPS includes the information about the number of virtual boundaries, and Wherein, based on the SPS including the sub-picture related information, the value of the SPS virtual boundary existence flag is determined to be 1.

12. The image encoding method according to claim 7, wherein: The image information includes picture header information, and Wherein, based on the fact that the SPS includes the sub-picture related information, the picture header does not include the information about the number of the virtual boundaries.

13. The image encoding method according to claim 12, wherein: Based on the SPS including the sprite-related information, the SPS includes the information about the number of the virtual boundaries.

14. 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: deriving residual samples for a current block, deriving transform coefficients based on a transform process on the residual samples, deriving quantized transform coefficients based on a quantization process on the transform coefficients, generating residual information based on the quantized transform coefficients, determining whether to perform in-loop filtering on reconstructed samples of a current picture across a virtual boundary, and encoding image information based on the residual information and the determination of whether to perform in-loop filtering on reconstructed samples of the current picture across the virtual boundary; and sending said data comprising said bitstream, The image information includes a sequence parameter set SPS, Wherein, whether the SPS includes information about the number of the virtual boundaries is determined based on whether the SPS includes sub-picture related information, and Wherein, based on the presence of multiple sub-pictures in the current picture, the sub-picture related information includes information about the position of at least one sub-picture.

Images