Filter-based image encoding apparatus and method

Abstract

According to the embodiments described herein, sub-pictures and / or virtual boundaries can be used for encoding a picture. For example, sub-pictures in a current picture can be used for prediction, reconstruction and / or filtering of the current picture. Virtual boundaries can be used for filtering reconstructed samples of the current picture. By sub-picture and / or virtual boundary based picture encoding according to the embodiments described herein, subjective / objective picture quality can be improved and hardware resource consumption required for encoding can be reduced.

Description

Technical Field

[0001] This document relates to a device and method for image encoding based on 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, in-loop filtering is performed to increase subjective / objective visual quality, and a scheme for increasing the signaling efficiency of information for performing in-loop filtering based on virtual boundaries is discussed. In addition, the application of sub-pictures in image coding to improve prediction and reconstruction performance is being discussed. Summary of the Invention

[0006] Technical Solution

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

[0008] According to the embodiments of this document, a high-efficiency filtering application method and apparatus are provided.

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

[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, whether a sequence parameter set (SPS) includes additional virtual boundary related information (eg, information on the location and number of virtual boundaries) is determined based on whether resampling of reference pictures is enabled.

[0012] According to an embodiment of this document, image encoding may be performed on a sub-picture basis.

[0013] According to an embodiment of this document, sub-pictures used in image encoding can be independently encoded.

[0014] According to an embodiment of the present document, a picture may include only one sub-picture. In addition, the sub-picture may be encoded independently.

[0015] According to the embodiment of this document, a picture can be generated based on a merging process of sub-pictures. In addition, the sub-pictures can be independently coded sub-pictures.

[0016] According to an embodiment of this document, each sub-picture used in image encoding can be regarded as a picture.

[0017] According to an embodiment of this document, there is provided an encoding device for performing video / image encoding.

[0018] 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.

[0019] 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.

[0020] Beneficial effects

[0021] According to the embodiments of this document, the overall image / video compression efficiency can be improved.

[0022] According to the embodiments of this document, subjective / objective visual quality can be improved through efficient filtering.

[0023] According to the embodiments of this document, a virtual boundary-based in-loop filtering process can be efficiently performed, and filtering performance can be improved.

[0024] According to the embodiments of this document, information for virtual boundary-based in-loop filtering can be efficiently signaled.

[0025] According to the embodiments of this document, sub-picture related information can be efficiently signaled, thereby improving subjective / objective image quality and reducing hardware resource consumption required for encoding. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 An example of a video / image encoding system to which embodiments of the present disclosure are applicable is schematically shown.

[0027] Figure 2 is a diagram schematically showing a configuration of a video / image encoding apparatus to which an embodiment of the present disclosure can be applied.

[0028] Figure 3 is a diagram schematically illustrating a configuration of a video / image decoding device to which an embodiment of the present disclosure can be applied.

[0029] Figure 4 The layered architecture of coded video / images is shown as an example.

[0030] Figure 5 is a flowchart illustrating a filtering-based encoding method in an encoding device.

[0031] Figure 6 is a flowchart illustrating a filtering-based decoding method in a decoding device.

[0032] Figure 7 and Figure 8 An example of a video / image encoding method and related components according to an embodiment of this document is schematically shown.

[0033] Figure 9 and Figure 10 An example of an image / video decoding method and related components according to an embodiment of this document is schematically shown.

[0034] Figure 11 An example of a content streaming system to which the embodiments disclosed in this document can be applied is shown. DETAILED DESCRIPTION

[0035] The present disclosure can be modified in various forms, and its specific embodiments will be described and shown in the accompanying drawings. However, these embodiments are not intended to limit the present disclosure. The terms used in the following description are only used to describe specific embodiments and are not intended to limit the present disclosure. Singular expressions include plural expressions as long as they are clearly read differently. Terms such as "including" and "having" are intended to indicate the presence of features, quantities, steps, operations, elements, components, or combinations thereof used in the following description, so it should be understood that the possibility of the presence or addition of one or more different features, quantities, steps, operations, elements, components, or combinations thereof is not excluded.

[0036] In addition, the various configurations described in the drawings in this document are independent illustrations of functions that are different from each other, and do not mean that the various configurations are implemented by different hardware or different software. For example, two or more configurations can be combined to form a single configuration, and a single 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.

[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] 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.

[0040] 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.

[0041] 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.

[0042] 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.

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

[0044] 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."

[0045] 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”.

[0046] 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.”

[0047] 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."

[0048] In this specification, technical features described separately in one drawing may be implemented separately or simultaneously.

[0049] Figure 1 An example of a video / image encoding system to which the disclosure of this document can be applied is shown.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The renderer may render the decoded video / image, and the rendered video / image may be displayed on a display.

[0057] Figure 2 Schematically shows the configuration of a video / image encoding device to which the disclosure of this document can be applied. Hereinafter, the so-called video encoding device may include an image encoding device.

[0058] 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.

[0059] 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) based on a quadtree, binary tree, and / or ternary tree (QTBTTT) structure. For example, a coding unit may be divided into multiple coding units of greater 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 the present disclosure 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 greater 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.

[0060] 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).

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] Furthermore, luma mapping with chroma scaling (LMCS) may be applied during the picture coding and / or reconstruction process.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] Figure 3 This is a diagram for schematically illustrating the configuration of a video / image decoding device to which the disclosure of this document can be applied.

[0073] 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.

[0074] 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.

[0075] The decoding device 300 may receive Figure 2The signal outputted in the form of a bitstream by the encoding apparatus, and the received signal can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information can further include information on 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 can further include general constraint information. The decoding apparatus can also decode a picture based on the information on the parameter sets and / or the general constraint information. The information and / or the syntax elements signaled / received later described in this document can be decoded by the decoding process and obtained from the bitstream. For example, the entropy decoder 310 decodes information in the bitstream based on an encoding method such as exponential Golomb encoding, CAVLC, or CABAC, and outputs syntax elements and quantized values of transform coefficients of a residual required for image reconstruction. More specifically, the CABAC entropy decoding method can receive bins corresponding to each syntax element in the bitstream, determine a context model using information of a decoding target syntax element, decoding information of a decoding target block, or a symbol / bin decoded in a previous stage, and generate a symbol corresponding to a value of each syntax element by performing arithmetic decoding on a bin by predicting a probability of bin occurrence according to the determined context model. In this case, the CABAC entropy decoding method can update the context model by using information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. Among the information decoded by the entropy decoder 310, information related to prediction can be provided to the predictor 330, and information on a residual for which entropy decoding is performed in the entropy decoder 310 (i.e., quantized transform coefficients and related parameter information) can be input to the dequantizer 321. In addition, among the information decoded by the entropy decoder 310, information on filtering can be provided to the filter 350. Furthermore, a receiver (not shown) for receiving a signal outputted from the encoding apparatus can also be configured as an internal / external element of the decoding apparatus 300, or the receiver can be a constituent element of the entropy decoder 310. Furthermore, the decoding apparatus according to this document can be referred to as a video / image / picture decoding apparatus, and the decoding apparatus can be classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder can include the entropy decoder 310, and the sample decoder can include at least one of the dequantizer 321, the inverse transformer 322, the predictor 330, the adder 340, the filter 350, and the memory 360.

[0076] 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.

[0077] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] In addition, luma mapping with chroma scaling (LMCS) can also be applied in the picture decoding process.

[0085] 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.

[0086] 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.

[0087] In this specification, the embodiments described in the predictor 330, the dequantizer 321, the inverse transformer 322, and the filter 350 of the decoding device 300 can also be applied in the same or corresponding manner as the predictor 220, the dequantizer 234, the inverse transformer 235, and the filter 260 of the encoding device 200.

[0088] Further, as described above, when performing video encoding, prediction is performed to improve compression efficiency. Thereby, a prediction block including prediction samples of a current block as a block to be encoded (i.e., an encoding target block) can be generated. Here, the prediction block includes prediction samples in a spatial domain (or a pixel domain). The prediction block is derived in the same manner in the encoding device and the decoding device, and the encoding device can signal the decoding device about information of a residual between the original block and the prediction block (residual information) rather than original sample values of the original block, thereby increasing image encoding 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.

[0089] The residual information can be generated through a transform and quantization process. For example, the encoding device can derive a residual block between the original block and the prediction block, perform a transform process on residual samples (a residual sample array) included in the residual block to derive transform coefficients, perform a quantization process on the transform coefficients to derive quantized transform coefficients, and signal the decoding device about the relevant residual information (through a bitstream). Here, the residual information can include value information of the quantized transform coefficients, position information, a transform technique, a transform kernel, a quantization parameter, and the like. The decoding device can perform dequantization / inverse transform processes based on the residual information and derive the residual samples (or the residual block). The decoding device can generate a reconstructed picture based on the prediction block and the residual block. In addition, the encoding device can also dequantize / inverse transform the quantized transform coefficients to derive a residual block for inter prediction of a later picture as a reference, and generate a reconstructed picture based thereon.

[0090] In this document, at least one of quantization / dequantization and / or transform / inverse transform can be omitted. When quantization / dequantization is omitted, the quantized transform coefficients can be referred to as transform coefficients. When transform / inverse transform is omitted, the transform coefficients can be referred to as coefficients or residual coefficients, or still be referred to as transform coefficients for consistency of expression.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Figure 4 The layered structure of the encoded image / video is shown as an example.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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).

[0099] The VCL NAL units and non-VCL NAL units can be sent over the network by adding header information according to the data standard of the subsystem. For example, the NAL unit can be converted into a data form of a predetermined standard such as the H.266 / VVC file format, the Real-time Transport Protocol (RTP), or the Transport Stream (TS) and sent over various networks.

[0100] 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.

[0101] 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.

[0102] The following are examples of NAL unit types specified according to the type of parameter sets included in non-VCL NAL unit types.

[0103] -APS (Adaptation Parameter Set) NAL unit: type of NAL unit including APS

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

[0105] -VPS (Video Parameter Set) NAL unit: Type of NAL unit containing VPS

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

[0107] -PPS (Picture Parameter Set) NAL unit: type of NAL unit including PPS

[0108] - PH (Picture Header) NAL unit: the type of NAL unit containing PH

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] Below, picture reconstruction and filtering will be described in detail. In image / video encoding, reconstructed blocks can be generated based on intra-frame prediction / inter-frame prediction in each block unit, and a reconstructed picture including the reconstructed blocks can be generated. When the current picture / slice is an I picture / slice, the blocks included in the current picture / slice can be reconstructed based only on intra-frame prediction. In addition, when the current picture / slice is a P or B picture / slice, the blocks included in the current picture / slice can be reconstructed based on intra-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.

[0115] 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.

[0116] 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.

[0117] When deriving neighboring reference samples, there are two cases: case (i) where the prediction sample can be derived based on an average or interpolation of the neighboring reference samples of the current block, and case (ii) where 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) can be referred to as non-directional mode or non-angular mode, while case (ii) can be referred to as directional mode or angular mode. Alternatively, the prediction sample can be generated using first and second neighboring samples located in a direction opposite to the prediction direction of the intra prediction mode of the current block among the neighboring reference samples. This case is 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 is referred to as LM mode. Furthermore, the temporal prediction sample of the current block can be derived based on filtered neighboring reference samples. At least one reference sample derived according to the intra prediction mode and the temporal prediction sample among the existing neighboring reference samples (i.e., unfiltered neighboring reference samples) can be weighted summed to derive the prediction sample of the current block. This case is referred to as position-dependent intra prediction (PDPC). In addition, a reference sample line with the highest prediction accuracy among multiple reference sample lines adjacent to the current block can be selected to derive prediction samples using reference samples located in the prediction direction on the corresponding line. The reference sample lines used in this article can be indicated (notified by signal) to the decoding device, thereby performing intra-frame prediction encoding. The above situation can be referred to as multi-reference line (MRL) intra-frame prediction or MRL-based intra-frame prediction. In addition, intra-frame prediction can be performed based on the same intra-frame prediction mode by dividing the current block into vertical or horizontal sub-partitions, and adjacent reference samples can be derived and used in units of sub-partitions. That is, in this case, the intra-frame prediction mode of the current block is equally applied to the sub-partitions, and in some cases, the intra-frame prediction performance can be improved by deriving and using adjacent reference samples in units of sub-partitions. This prediction method can be referred to as intra-frame sub-partitioning (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 Section 1.2. The intra-frame prediction type can be referred to as various terms such as intra-frame prediction technology or additional intra-frame prediction mode. For example, the intra prediction type (or additional intra prediction mode, etc.) may include at least one of the aforementioned LIP, PDPC, MRL, and ISP. A general intra prediction method other than a specific intra prediction type such as LIP, PDPC, MRL, or ISP may be referred to as a normal intra prediction type. When a specific intra prediction type is not applied, a normal intra prediction type may generally be applied, and prediction may be performed based on the aforementioned intra prediction modes. Furthermore, post-processing filtering may optionally be performed on the derived prediction samples.

[0118] Specifically, the intra prediction process may include determining an intra prediction mode / type, deriving neighboring reference samples, and deriving prediction samples based on the intra prediction mode / type. In addition, a post-processing filtering operation may be optionally performed on the derived prediction samples.

[0119] A modified reconstructed picture can be generated by an in-loop filtering process, and the modified reconstructed picture can be output as a decoded picture in a decoding device, and can also be stored in a decoded picture buffer or memory of an encoding device / decoding device and used as a reference picture in an inter-frame prediction process at a later time when encoding / decoding the picture. The in-loop filtering process may include a deblocking filter process, a sample adaptive offset (SAO) process, and / or an adaptive loop filter (ALF) process as described above. In this case, one or some of the deblocking filter process, the SAO process, the ALF process, and the bilateral filtering process may be applied sequentially, or all of the processes may be applied sequentially. For example, the SAO process may be performed after the deblocking filter process is applied to the reconstructed picture. Alternatively, for example, the ALF process may be performed after the deblocking filter process is applied to the reconstructed picture. This can also be performed in the encoding device.

[0120] 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 can derive a target boundary in the reconstructed picture, determine the boundary strength (bS) of the target boundary, and perform deblocking filtering on the target boundary based on the bS. The bS can be determined based on the prediction mode, motion vector difference, whether the reference picture is the same, the presence of non-zero significant coefficients, and other factors of the two blocks adjacent to the target boundary.

[0121] SAO is a method that compensates for the offset difference between the reconstructed image and the original image based on samples. For example, SAO can be applied based on types such as band offset and edge offset. According to SAO, samples can be classified into different categories according to each SAO type, and an offset value can be added to each sample based on the category. SAO filter information may include information on whether SAO is applied, SAO type information, SAO offset value information, etc. SAO can be applied to the reconstructed image after deblocking filtering is applied.

[0122] ALF is a technique for filtering a reconstructed picture based on a filter shape, filter coefficients, and samples. The encoding device can determine whether to apply ALF, the ALF shape, and / or ALF filter coefficients by comparing the reconstructed picture with the original picture, and can signal the determination result to the decoding device. Specifically, ALF filter information may include information on whether to apply ALF, ALF filter shape information, ALF filter coefficient information, and so on. ALF can be applied to the reconstructed picture after deblocking filtering.

[0123] Figure 5 is a flowchart illustrating a filtering-based encoding method in an encoding device. Figure 5 The method may include steps S500 to S530.

[0124] In step S500 , the encoding apparatus may generate a reconstructed picture. Step S500 may be performed based on the above-described reconstructed picture (or reconstructed sample) generation process.

[0125] In step S510, the encoding device may determine whether to apply in-loop filtering (across a virtual boundary) based on in-loop filtering related information. Herein, in-loop filtering may include at least one of the above-mentioned deblocking filtering, SAO, and ALF.

[0126] In step S520, the encoding apparatus may generate a modified reconstructed picture (modified reconstructed samples) based on the determination of step S510. Herein, the modified reconstructed picture (modified reconstructed samples) may be a filtered reconstructed picture (filtered reconstructed samples).

[0127] In step S530 , the encoding apparatus may encode image / video information including in-loop filtering related information based on the in-loop filtering process.

[0128] Figure 6 is a flowchart illustrating a filtering-based decoding method in a decoding device. Figure 6 The method may include steps S600 to S630.

[0129] In step S600, the decoding apparatus may obtain image / video information including in-loop filtering related information from a bitstream. Herein, the bitstream may be based on encoded image / video information transmitted from an encoding apparatus.

[0130] In step S610 , the decoding apparatus may generate a reconstructed picture. Step S610 may be performed based on the reconstructed picture (or reconstructed sample).

[0131] In step S620, the decoding apparatus may determine whether to apply in-loop filtering (across a virtual boundary) based on in-loop filtering related information. Herein, in-loop filtering may include at least one of the above-mentioned deblocking filtering, SAO, and ALF.

[0132] In step S630, the decoding apparatus may generate a modified reconstructed picture (modified reconstructed samples) based on the determination of step S620. Herein, the modified reconstructed picture (modified reconstructed samples) may be a filtered reconstructed picture (filtered reconstructed samples).

[0133] As described above, in-loop filtering may be applied to the reconstructed picture. In this case, a virtual boundary may be defined to further improve the subjective / objective visual quality of the reconstructed picture, and in-loop filtering may be applied across the virtual boundary. For example, the virtual boundary may include discontinuous edges such as 360-degree images, VR images, boundaries, picture-in-picture (PIP), and the like. For example, a virtual boundary may exist at a predetermined position, and its existence and / or position may be notified by a signal. For example, the virtual boundary may be located at the fourth sample line above the CTU row (specifically, for example, above the fourth sample above the CTU row). As another example, information about the existence and / or position of the virtual boundary may be notified by a signal via HLS. The HLS may include an SPS, a PPS, a picture header, a slice header, and the like as described above.

[0134] Hereinafter, high-level syntax signaling and semantics will be described according to embodiments of the present disclosure.

[0135] Embodiments of this document may include methods for controlling loop filters. This method for controlling loop filters may be applied to reconstructed pictures. An in-loop filter (loop filter) may be used for decoding the encoding bit rate. The loop filters may include the above-mentioned deblocking, SAO, and ALF. The SPS may include flags related to each of deblocking, SAO, and ALF. The flags may indicate whether each tool can be used for encoding a coded layer video sequence (CLVS) or a coded video sequence (CVS) referenced by the SPS.

[0136] In an example, when a loop filter is enabled for encoding of a picture in a CVS, the loop filter may be controlled not to be applied across specific boundaries. For example, the loop filter may be controlled not to cross a sub-picture boundary, the loop filter may be controlled not to cross a patch boundary, the loop filter may be controlled not to cross a slice boundary, and / or the loop filter may be controlled not to cross a virtual boundary.

[0137] In-loop filtering related information may include information, syntax, syntax elements and / or semantics described in this document (or an embodiment included therein). In-loop filtering related information may include information related to whether in-loop filtering processing (all or part) is enabled across specific boundaries (e.g., virtual boundaries, sub-picture boundaries, slice boundaries and / or patch boundaries). The image information included in the bitstream may include high-level syntax (HLS), and the HLS may include in-loop filtering related information. Modified (or filtered) reconstructed samples (reconstructed pictures) may be generated based on a determination of whether in-loop filtering processing is applied across specific boundaries. In an example, when in-loop filtering processing is disabled for all blocks / boundaries, the modified reconstructed samples may be the same as the reconstructed samples. In another example, the modified reconstructed samples may include modified reconstructed samples derived based on in-loop filtering. However, in this case, some reconstructed samples (e.g., reconstructed samples across virtual boundaries) may not be subjected to in-loop filtering based on the above determination. For example, reconstructed samples that cross certain boundaries (at least one of a virtual boundary, a sub-picture boundary, a slice boundary, and / or a patch boundary for which in-loop filtering is enabled) may be in-loop filtered, but reconstructed samples that cross other boundaries (e.g., a virtual boundary, a sub-picture boundary, a slice boundary, and / or a patch boundary for which in-loop filtering is disabled) may not be in-loop filtered.

[0138] In an example, regarding whether to perform in-loop filtering processing across virtual boundaries, the in-loop filtering related information may include an SPS virtual boundary existence flag, a picture header virtual boundary existence flag, information about the number of virtual boundaries, information about the position of the virtual boundaries, etc.

[0139] In the embodiments included in this document, the information about the virtual boundary position may include information about the x-coordinate of the vertical virtual boundary and / or information about the y-coordinate of the horizontal virtual boundary. Specifically, the information about the virtual boundary position may include information about the x-coordinate of the vertical virtual boundary and / or information about the y-axis of the horizontal virtual boundary in units of luminance samples. In addition, the information about the virtual boundary position may include information about the number of pieces 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 position may include information about the number of pieces of information (syntax elements) about the y-coordinate of the horizontal virtual boundary present in the SPS. Alternatively, the information about the virtual boundary position may include information about the number of pieces of information (syntax elements) about the x-coordinate of the vertical virtual boundary present in the picture header. In addition, the information about the virtual boundary position may include information about the number of pieces of information (syntax elements) about the y-coordinate of the horizontal virtual boundary present in the picture header.

[0140] The following table shows exemplary syntax and semantics of SPS according to this embodiment.

[0141] [Table 1]

[0142]

[0143] [Table 2]

[0144]

[0145]

[0146]

[0147] The following table shows an exemplary syntax and semantics of a picture parameter set (PPS) according to the present embodiment.

[0148] [Table 3]

[0149]

[0150] [Table 4]

[0151]

[0152]

[0153] The following table shows an exemplary syntax and semantics of a picture header according to the present embodiment.

[0154] [Table 5]

[0155]

[0156]

[0157] [Table 6]

[0158]

[0159]

[0160]

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

[0162] [Table 7]

[0163]

[0164] [Table 8]

[0165]

[0166]

[0167]

[0168] 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.

[0169] Even if a picture includes multiple sub-pictures, when there is no sub-picture whose boundary is regarded as a picture boundary, the advantage of using sub-pictures cannot be utilized. In the embodiment of this document, image / video information used for image coding may include information for treating a sub-picture as a picture, which may be referred to as a picture processing flag (i.e., subpic_treated_as_pic_flag[i]).

[0170] In order to signal the layout of the sub-pictures, a flag related to whether a sub-picture exists (i.e., subpic_present_flag) is signaled. This may be referred to as a sub-picture present flag. When the value of subpic_present_flag is 1, information related to the number of sub-pictures used to split the picture (i.e., sps_num_subpics_minus1) is signaled. In an example, the number of sub-pictures used to split the picture may be equal to sps_num_subpics_minus1+1 (1 added to sps_num_subpics_minus1). Available values ​​for sps_num_subpics_minus1 include 0, which means that only one sub-picture can exist in the picture. If the picture includes only one sub-picture, the signaling of sub-picture related information may be considered redundant processing because the sub-picture itself is a picture.

[0171] In existing embodiments, if a picture includes only one sub-picture and sub-picture signaling is present, the value of the picture processing flag (i.e., subpic_treated_as_pic_flag[i]) and / or the value of the flag related to whether loop filtering is performed across sub-pictures (i.e., loop_filter_across_subpic_enabled_flag) may be 0 or 1. However, there is a problem in that the case where the value of subpic_treated_as_pic_flag[i] is 0 is inconsistent with the case where the sub-picture boundary is a picture boundary. This requires additional redundant processing to allow the decoder to confirm that the picture boundary is a sub-picture boundary.

[0172] When a picture is generated based on a merge process of two or more sub-pictures, all sub-pictures used in the merge process should be independently coded sub-pictures (sub-pictures for which the value of the picture processing flag (subpic_reated_as_pic_flag[i]) is 1). This is because, when a sub-picture other than an independently coded sub-picture (referred to as a "first sub-picture" in this paragraph) is merged, blocks in the first sub-picture are encoded with reference to reference blocks existing outside the first sub-picture, which may cause problems after merging.

[0173] In addition, when a picture is divided into sub-pictures, sub-picture ID signaling may or may not be present. When sub-picture ID signaling is present, it may be present in (included in) the SPS, PPS, and / or picture header (PH). The case where sub-picture ID signaling is not present in the SPS may include the case where a bitstream is generated as a result of sub-picture merging processing. Therefore, it is preferable that all sub-pictures are independently encoded when sub-picture ID signaling is not included in the SPS.

[0174] In an image coding process using a virtual boundary, information about the position of the virtual boundary can be signaled in an SPS or a picture header. The signaling of the information about the position of the virtual boundary in the SPS means that the position in the entire CLVS does not change. However, when reference picture resampling (RPR) is enabled for the CLVS, the pictures in the CLVS may have different sizes. Herein, RPR (also known as adaptive resolution change (ARC)) is performed for normal coding operations of pictures with different resolutions (spatial resolutions). For example, RPR may include upsampling and downsampling. High coding efficiency for adapting to bit rate and spatial resolution can be achieved through RPR. Taking into account RPR, it is necessary to ensure that all positions of the virtual boundary exist in one picture.

[0175] In existing ALF processing, k-order exponential Golomb codes (k=3) are used to signal the absolute values ​​of luma and chroma ALF coefficients. However, k-order exponential Golomb coding is problematic because it incurs significant computational overhead and complexity.

[0176] The embodiments described below may provide solutions to the above problems. The embodiments may be applied independently. Alternatively, at least two embodiments may be applied in combination.

[0177] In the embodiments of this document, when sub-picture signaling is present and a picture has only one sub-picture, the sub-picture is an independently coded sub-picture. For example, when a picture has only one sub-picture, the sub-picture is an independently coded sub-picture, and the picture processing flag (i.e., subpic_treated_as_pic_flag[i]) of the sub-picture is 1. Therefore, redundant processing related to the sub-picture can be omitted.

[0178] In an embodiment of the present document, when sub-picture signaling is present, the number of sub-pictures may be greater than 1. In an example, if sub-picture signaling is present (i.e., the value of subpics_present_flag is 1), the information about the number of sub-pictures (i.e., sps_num_subpics_minus1) may be greater than 0, and the number of sub-pictures may be sps_num_subpics_minus1+1 (1 added to sps_num_subpics_minus1). In another example, the information about the number of sub-pictures may be sps_num_subpics_minus2, and the number of sub-pictures may be sps_num_subpics_minus2+2 (2 added to sps_num_subpics_minus2). In another example, the sub-picture present flag (subpics_present_flag) may be replaced by the information about the number of sub-pictures (sps_num_subpics_minus1), so that sub-picture signaling may be present when sps_num_subpics_minus1 is greater than 0.

[0179] In an embodiment of this document, when a picture is divided into sub-pictures, at least one of the sub-pictures may be an independently coded sub-picture. Here, the value of the picture processing flag (ie, subpic_treated_as_pic_flag[i]) of the independently coded sub-picture may be 1.

[0180] In the embodiments of this document, the sub-pictures of a picture processed based on the merging of two or more sub-pictures may be independently coded sub-pictures.

[0181] In an embodiment of this document, when sub-picture identification (ID) signaling is present in a location other than the SPS (other syntax, other high-level syntax information), all sub-pictures can be independently coded sub-pictures, and the value of the picture processing flag (i.e., subpic_treated_as_pic_flag) of all sub-pictures can be 1. In an example, sub-picture ID signaling can be present in the PPS, and in this case, all sub-pictures can be independently coded sub-pictures. In another example, sub-picture ID signaling can be present in the picture header, and in this case, all sub-pictures are independently coded sub-pictures.

[0182] In an embodiment of this document, when virtual boundary signaling is present in the SPS of the CLVS and reference picture resampling is enabled, all horizontal virtual boundary positions can be within the minimum picture height of the picture of the reference SPS, and all vertical virtual boundary positions can be within the minimum picture width of the picture of the reference SPS.

[0183] In an embodiment of this document, when reference picture resampling (RPR) is enabled, virtual boundary signaling may be included in the picture header. That is, when RPR is enabled, virtual boundary signaling may not be included in the SPS.

[0184] In an embodiment of the present document, a fixed length code (FLC) having a number of bits (or bit length) may be used to signal ALF data. In an example, the information about the ALF data may include information about the bit length of the absolute value of the ALF luma coefficient (i.e., alf_luma_coeff_abs_len_minus1) and / or information about the bit length of the absolute value of the ALF chroma coefficient (i.e., alf_chroma_coeff_abs_len_minus1). For example, the information about the bit length of the absolute value of the ALF luma coefficient and / or the information about the bit length of the absolute value of the ALF chroma coefficient may be ue(v) encoded.

[0185] The following table shows an exemplary syntax of an SPS according to the present embodiment.

[0186] [Table 9]

[0187]

[0188] The following table shows exemplary semantics of the syntax elements included in the syntax.

[0189] [Table 10]

[0190]

[0191]

[0192] The following shows an exemplary syntax of SPS according to the present embodiment.

[0193] [Table 11]

[0194]

[0195] The following shows exemplary semantics of syntax elements included in the syntax.

[0196] [Table 12]

[0197]

[0198]

[0199] The following shows an exemplary syntax of ALF data according to the present embodiment.

[0200] [Table 13]

[0201]

[0202] The following shows exemplary semantics of syntax elements included in the syntax.

[0203] [Table 14]

[0204]

[0205]

[0206] According to the embodiments of the present document described together with the above table, by image encoding based on sub-pictures and / or virtual boundaries, subjective / objective image quality can be improved, and hardware resource consumption required for encoding can be reduced.

[0207] Figure 7 and Figure 8 An example of a video / image encoding method and related components according to the embodiments of the present document is schematically shown.

[0208] Figure 7 The method disclosed in the Figure 2 or Figure 8 The encoding device can be executed by the encoding device. Specifically, for example, Figure 7 S700 and S730 of the Figure 8 S700 and S730 of the Figure 7 S710 and S720 of the Figure 8 S710 and S720 of the Figure 7 S740 of the Figure 8 S750 of the Figure 7 S750 of the Figure 8 The entropy encoder 240 of the encoding device performs. In addition, although Figure 7 Not shown in the figure, the prediction samples or prediction related information can be obtained by Figure 7 The predictor 220 of the encoding device of the encoding apparatus derives the information, and the entropy encoder 240 of the encoding device can generate a bitstream from the residual information or the prediction-related information. Figure 7 The method disclosed in may include the above-mentioned embodiments in this document.

[0209] Reference Figure 7 , the encoding device may derive at least one reference picture (S700). The encoding device may perform a prediction process based on the at least one reference picture. Specifically, the encoding device may derive prediction samples for the current block based on a prediction mode. In this case, various prediction methods disclosed in this document (e.g., inter-frame prediction or intra-frame prediction) may be applied. The encoding device may generate prediction samples for the current block in the current picture based on the prediction process. For example, the encoding device may perform an inter-frame prediction process based on the at least one reference picture, and may generate prediction samples based on the inter-frame prediction process.

[0210] The encoding device may generate / derive residual samples (S710). The encoding device may derive residual samples for the current block, and may derive the residual samples for the current block based on the original samples and the predicted samples of the current block. Specifically, the encoding device may generate the residual samples based on the at least one reference picture of step S700. For example, the encoding device may generate predicted samples for the current block based on the at least one reference picture, and may generate the residual samples based on the predicted samples.

[0211] The encoding device may derive transform coefficients. The encoding device may derive transform coefficients based on a transform process performed on the residual samples. For example, the transform process may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a graph-based transform (GBT), and a conditional nonlinear transform (CNT).

[0212] The encoding apparatus may derive quantized transform coefficients. The encoding apparatus may derive quantized transform coefficients based on quantization processing of the transform coefficients. The quantized transform coefficients may have a 1-dimensional vector form based on a coefficient scanning order.

[0213] The encoding device may generate residual information (S720). The encoding device may generate residual information based on the transform coefficient. The encoding device may generate residual information indicating the quantized transform coefficient. The residual information may be generated by various encoding methods such as exponential Golomb, CAVLC, CABAC, etc.

[0214] 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 the predicted samples and the residual samples based on the residual information. Specifically, the encoding device may perform prediction (intra-frame or inter-frame prediction) on the current block and may generate reconstructed samples based on the original samples and the predicted samples generated from the prediction.

[0215] 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.

[0216] The encoding device may generate reference picture related information (S730). The encoding device may generate reference picture related information based on at least one reference picture. The reference picture related information may be used for inter-frame prediction of the decoding device.

[0217] The encoding device may generate information related to in-loop filtering of the reconstructed samples (S740). The encoding device may perform in-loop filtering on the reconstructed samples and may generate information related to the in-loop filtering based on the in-loop filtering. For example, the information related to the in-loop filtering may include the above-mentioned information about the virtual boundary (SPS virtual boundary enable flag, picture header virtual boundary enable flag, SPS virtual boundary presence flag, picture header virtual boundary presence flag, information about the position of the virtual boundary, etc.).

[0218] The encoding device may encode the video / image information (S750). The image information may include residual information, prediction-related information, reference picture-related information, virtual boundary-related information (and / or additional virtual boundary-related information), and / or in-loop filtering-related information. The encoded video / image information may be output in the form of a bitstream. The bitstream may be transmitted to the decoding device via a network or storage medium.

[0219] The image / video information may include various information according to the embodiments of this document. For example, the image / video may include the information disclosed in at least one of Tables 1 to 14 above.

[0220] In an embodiment, the image information may include a sequence parameter set (SPS). For example, whether the SPS includes additional virtual boundary-related information may be determined based on whether resampling of at least one reference picture is enabled. Herein, resampling of at least one reference picture may be performed according to the aforementioned reference picture resampling (RPR). The additional virtual boundary-related information may also be referred to as simply virtual boundary-related information. The term "additional" is used to distinguish it from virtual boundary-related information such as an SPS virtual boundary presence flag and / or a PH virtual boundary presence flag.

[0221] In an embodiment, the additional virtual boundary-related information may include the number of virtual boundaries and the positions of the virtual boundaries.

[0222] 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.

[0223] In an embodiment, the image information may include a reference picture resampling enable flag. For example, whether to enable resampling of at least one reference picture may be determined based on the reference picture resampling enable flag.

[0224] In an embodiment, the SPS may include an SPS virtual boundary existence flag related to whether the SPS includes additional virtual boundary related information. Based on enabling resampling of at least one reference picture, the value of the SPS virtual boundary existence flag may be determined to be 0.

[0225] In an embodiment, based on enabling resampling of at least one reference picture, additional virtual boundary related information may not be included in the SPS. The image information may include picture header information. In addition, the picture header information may include additional virtual boundary related information.

[0226] In an embodiment, the current picture may include a sub-picture as only one sub-picture. The sub-picture may be independently encoded. Reconstructed samples may be generated based on the sub-picture. Sub-picture related information may be generated based on the sub-picture. The image information may include sub-picture related information.

[0227] In an embodiment, the subpicture_treated_as_picture flag may not be present in the picture information. Therefore, the value of the subpicture_treated_as_picture flag may be set by inference (estimation or prediction) at the decoding end. In an example, the value of the subpicture_treated_as_picture flag may be set to 1.

[0228] In an embodiment, the current picture may include a sub-picture. In an example, the sub-picture may be derived based on a merge process of two or more independently encoded sub-pictures. Reconstructed samples may be generated based on the sub-picture. Sub-picture related information may be generated based on the sub-picture. In addition, the image information may include sub-picture related information.

[0229] Figure 9 and Figure 10 An example of a video / image decoding method and related components according to an embodiment of this document is schematically shown.

[0230] Figure 9 The method disclosed in Figure 3 or Figure 10 Specifically, for example, Figure 9 S900 may be performed by the entropy decoder 310 of the decoding device, Figure 9 S910 may be performed by the predictor 330 of the decoding device, S920 may be performed by the residual processor 320 and / or the adder 340 of the decoding device, and S930 may be performed by the filter 350 of the decoding device. Figure 9 The method disclosed in may include the above-mentioned embodiments in this document.

[0231] Reference Figure 9 The decoding device may receive / obtain video / image information (S900). The video / image information may include residual information, prediction-related information, reference picture-related information, virtual boundary-related information (and / or additional virtual boundary-related information), and / or in-loop filtering-related information. The decoding device may receive / obtain image / video information through a bitstream.

[0232] The image / video information may include various information according to the embodiments of this document. For example, the image / video may include the information disclosed in at least one of Tables 1 to 14 above.

[0233] The decoding device may derive quantized transform coefficients. The decoding device may derive the quantized transform coefficients based on the residual information. The quantized transform coefficients may have a 1-dimensional vector form based on the coefficient scanning order. The quantized transform coefficients may include quantized luma transform coefficients and / or quantized chroma transform coefficients.

[0234] The decoding device may derive transform coefficients. The decoding device may derive transform coefficients based on dequantization of the quantized transform coefficients. The decoding device may derive luma transform coefficients based on the quantized luma transform coefficients by dequantization. The decoding device may derive chroma transform coefficients based on the quantized chroma transform coefficients by dequantization.

[0235] The decoding device may generate / derive residual samples. 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.

[0236] The decoding device may derive at least one reference picture based on the reference picture related information (S910). The decoding device may perform a prediction process based on the at least one reference picture. Specifically, the decoding device may derive prediction samples for the current block based on a prediction mode. In this case, various prediction methods disclosed in this document (e.g., inter-frame prediction or intra-frame prediction) may be applied. The decoding device may generate prediction samples for the current block in the current picture based on the prediction process. For example, the decoding device may perform an inter-frame prediction process based on the at least one reference picture, and may generate prediction samples based on the inter-frame prediction process.

[0237] The decoding device may generate / derive reconstructed samples (S920). The decoding device may generate the reconstructed samples based on the predicted samples and the residual samples. The decoding device may generate the reconstructed samples based on the sum of the predicted samples and the original samples. For example, the decoding device may generate / derive reconstructed luma samples and / or reconstructed chroma samples. The decoding device may generate the reconstructed luma samples and / or reconstructed chroma samples based on the residual information. The decoding device may generate the reconstructed samples based on the residual information. The reconstructed samples may include reconstructed luma samples and / or reconstructed chroma samples. The luma component of the reconstructed samples may correspond to the reconstructed luma samples, and the chroma component of the reconstructed samples may correspond to the reconstructed chroma samples. The decoding device may generate predicted luma samples and / or predicted chroma samples through a prediction process. The decoding device may generate the reconstructed luma samples based on the predicted luma samples and the residual luma samples. The decoding device may generate constructed chroma samples based on the predicted chroma samples and the residual chroma samples.

[0238] The decoding device may generate modified (filtered) reconstructed samples (S930). The decoding device may generate the modified reconstructed samples based on in-loop filtering processing on the reconstructed samples. The decoding device may generate the modified reconstructed samples based on in-loop filtering related information. The decoding device may use deblocking processing, SAO processing, and / or ALF processing to generate the modified reconstructed samples.

[0239] In an embodiment, the image information may include an SPS. For example, whether the SPS includes additional virtual boundary-related information may be determined based on whether resampling of at least one reference picture is enabled. Herein, resampling of at least one reference picture may be performed based on the aforementioned RPR. The additional virtual boundary-related information may also be referred to as simply virtual boundary-related information. The term "additional" is used to distinguish it from virtual boundary-related information such as an SPS virtual boundary presence flag and / or a PH virtual boundary presence flag.

[0240] In an embodiment, the additional virtual boundary-related information may include the number of virtual boundaries and the positions of the virtual boundaries.

[0241] 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.

[0242] In an embodiment, the image information may include a reference picture resampling enable flag. For example, whether to enable resampling of at least one reference picture may be determined based on the reference picture resampling enable flag.

[0243] In an embodiment, the SPS may include an SPS virtual boundary existence flag related to whether the SPS includes additional virtual boundary related information. Based on enabling resampling of at least one reference picture, the value of the SPS virtual boundary existence flag may be determined to be 0.

[0244] In an embodiment, based on enabling resampling of at least one reference picture, additional virtual boundary related information may not be included in the SPS. The image information may include picture header information. In addition, the picture header information may include additional virtual boundary related information.

[0245] In an embodiment, the current picture may include a sub-picture as only one sub-picture. The sub-picture may be independently encoded. The reconstructed sample may be generated based on the sub-picture, and the information related to the sub-picture may be generated based on the sub-picture. In addition, the image information may include information related to the sub-picture.

[0246] In an embodiment, the picture processing flag for the sub-picture (subpicture_treated_as_picture flag) may not be present in the image information. Therefore, the value of the subpicture_treated_as_picture flag may be set by inference (estimation or prediction) at the decoding end. In an example, the value of the subpicture_treated_as_picture flag may be set to 1.

[0247] In an embodiment, the current picture may include a sub-picture. In an example, the sub-picture may be derived based on a merge process of two or more independently encoded sub-pictures. Reconstructed samples may be generated based on the sub-picture. Sub-picture related information may be generated based on the sub-picture. In addition, the image information may include sub-picture related information.

[0248] When residual samples of a current block exist, the decoding device may receive residual information of the current block. The residual information may include transform coefficients of the residual samples. The decoding device may derive residual samples (or a residual sample array) 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 a 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.

[0249] 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 optionally apply in-loop filtering processing such as deblocking filtering and / or SAO processing to the reconstructed picture to improve subjective / objective image quality.

[0250] 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.

[0251] 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, it will be understood by those skilled in the art 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 the present disclosure.

[0252] The above-mentioned method according to the present disclosure may be in the form of software, and the encoding device and / or decoding device according to the present disclosure may be included in an apparatus for image processing (e.g., TV, computer, smart phone, set-top box, display device, etc.).

[0253] When the embodiments of the present disclosure 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 the present disclosure, it can be implemented and executed on a processor, a microprocessor, a controller or a chip. For example, the functional units shown in 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.

[0254] 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).

[0255] 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.

[0256] 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.

[0257] Figure 11 This shows an example of a content streaming system to which the embodiments of this document can be applied.

[0258] Reference Figure 11 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.

[0259] 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.

[0260] 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.

[0261] 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.

[0262] 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.

[0263] For example, user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation, tablet computers, tablet PCs, ultrabooks, wearable devices (e.g., watch-type terminals (smart watches), glasses-type terminals (smart glasses), head-mounted displays (HMDs)), digital TVs, desktop computers, digital signs, etc.

[0264] 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.

[0265] 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 and reference picture related information through a bit stream; deriving at least one reference picture based on the reference picture related information; generating a reconstructed sample of a current picture based on the residual information and the at least one reference picture; and generating modified reconstructed samples based on an in-loop filtering process on the reconstructed samples, The image information includes sequence parameter set SPS and picture header information. Wherein, based on whether reference picture resampling for the at least one reference picture is enabled, determining whether the SPS includes additional virtual boundary related information, and Wherein, based on enabling the reference picture resampling for the reference picture, the picture header information includes the additional virtual boundary related information and the SPS does not include the additional virtual boundary related information.

2. An image encoding method performed by an encoding device, the image encoding method comprising the following steps: Generate residual samples for the current block; generating residual information based on the residual samples for the current block; deriving at least one reference picture for reconstructed samples of the current picture; generating reference picture related information based on the at least one reference picture; generating in-loop filtering related information for the reconstructed samples of the current picture; as well as encoding the image information including the residual information, the reference picture related information, and the in-loop filtering related information, The image information includes sequence parameter set SPS and picture header information. Wherein, based on whether reference picture resampling for the at least one reference picture is enabled, determining whether the SPS includes additional virtual boundary related information, and Wherein, based on enabling the reference picture resampling for the reference picture, the picture header information includes the additional virtual boundary related information and the SPS does not include the additional virtual boundary related information.

3. A method for transmitting image data, the method comprising the following steps: Obtaining a bitstream for the image, wherein the bitstream is generated based on the following steps: generating residual samples for a current block, generating residual information based on the residual samples for the current block, deriving at least one reference picture for reconstructed samples of a current picture, generating reference picture related information based on the at least one reference picture, generating in-loop filtering related information for the reconstructed samples of the current picture, and encoding image information including the residual information, the reference picture related information, and the in-loop filtering related information; and sending said data comprising said bitstream, The image information includes sequence parameter set SPS and picture header information. Wherein, based on whether reference picture resampling for the at least one reference picture is enabled, determining whether the SPS includes additional virtual boundary related information, and Wherein, based on enabling the reference picture resampling for the reference picture, the picture header information includes the additional virtual boundary related information and the SPS does not include the additional virtual boundary related information.

Images