Image encoding / decoding method for performing reference picture marking process at sub-picture level, method for transmitting bitstream, and recording medium for storing bitstream

Abstract

Provided are an image encoding / decoding method, a bitstream transmission method, and a computer-readable recording medium for storing a bitstream. An image decoding method performed by an image decoding device according to an embodiment of the present disclosure may comprise the steps of: receiving information on a reference picture set for inter prediction of a current sub-picture; deriving a reference sub-picture of the current sub-picture based on information on the reference picture set; and performing a process of marking whether to refer to the reference sub-picture.

Description

Technical Field

[0001] The present disclosure relates to an image encoding / decoding method that performs a reference picture marking process at a sub-picture level, a method of transmitting a bitstream, and a recording medium that stores the bitstream. Background Art

[0002] Recently, the demand for high-resolution and high-quality images, such as high-definition (HD) images and ultra-high-definition (UHD) images, is increasing in various fields. As the resolution and quality of image data are improved, the amount of information or bit volume transmitted is relatively increased compared to existing image data. The increase in the amount of information or bit volume transmitted leads to an increase in transmission cost and storage cost.

[0003] Therefore, efficient image compression technology is needed to effectively transmit, store, and reproduce information about high-resolution and high-quality images. Summary of the invention

[0004] Technical issues

[0005] An object of the present disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0006] An object of the present disclosure is to provide an image encoding / decoding method and apparatus that performs a reference picture marking process at a sub-picture level.

[0007] An object of the present disclosure is to provide a method for marking a reference picture as a single state through a reference picture marking process.

[0008] An object of the present disclosure is to provide a non-transitory recording medium storing a bit stream generated by an image encoding method according to the present disclosure.

[0009] An object of the present disclosure is to provide a non-transitory recording medium storing a bit stream received and decoded by an image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0010] An object of the present disclosure is to provide a method of transmitting a bit stream generated by an image encoding method according to the present disclosure.

[0011] The technical problems solved by the present disclosure are not limited to the above-mentioned technical problems, and other technical problems not described herein will be apparent to those skilled in the art through the following description.

[0012] Technical Solution

[0013] According to one embodiment of the present disclosure, an image decoding method performed by an image decoding device may include the following steps: receiving information about a reference picture set for inter-frame prediction of a current sub-picture; deriving a reference sub-picture of the current sub-picture based on the information about the reference picture set; and performing a reference marking process for the reference sub-picture.

[0014] Furthermore, the reference marking process may include a process of marking the reference sub-picture as one of a short-term reference, a long-term reference, or an unused reference.

[0015] Furthermore, based on the reference sub-picture being marked as a short-term reference picture, the reference sub-picture may be identified based on at least one of a layer identifier or a picture order count value.

[0016] Furthermore, based on the reference sub-picture being marked as a long-term reference picture, the reference sub-picture may be identified based on at least one of a layer identifier or a picture order count value.

[0017] Furthermore, based on the current picture including the current sub-picture being of a specific picture type, the reference sub-picture having the same layer identifier as the current picture may be marked as unused for reference.

[0018] Furthermore, the specific picture type may be a coding layer video sequence start (CLVSS) picture type.

[0019] Furthermore, the reference marking process may be performed before decoding slice data for a first slice in the current sub-picture.

[0020] Furthermore, the reference marking process may be performed after decoding a slice header of a first slice in the current sub-picture.

[0021] Furthermore, the reference marking process for the first slice in the current sub-picture may be applied only to collocated reference sub-pictures.

[0022] Furthermore, the reference sub-picture may include a collocated sub-picture included in the reference picture.

[0023] According to another embodiment of the present disclosure, an image encoding method performed by an image encoding device may include the following steps: deriving a reference picture set based on a reference sub-picture of a current sub-picture, performing a reference marking process for the reference sub-picture, and encoding information about the reference picture set of the current sub-picture.

[0024] A computer-readable storage medium according to another aspect of the present disclosure may store a bit stream generated by the image encoding method or apparatus of the present disclosure.

[0025] A transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding method or apparatus of the present disclosure.

[0026] The features briefly summarized above with respect to the present disclosure are merely exemplary aspects of the following detailed description of the present disclosure and do not limit the scope of the present disclosure.

[0027] Beneficial Effects

[0028] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0029] In addition, according to the present disclosure, by constructing a reference picture set at a sub-picture level, content characteristics can be more accurately reflected for each sub-picture.

[0030] In addition, according to the present disclosure, by performing a reference picture marking process at a sub-picture level, image quality may be improved.

[0031] In addition, according to the present disclosure, a method of performing a reference picture marking process at a sub-picture level may be provided.

[0032] In addition, according to the present disclosure, a method of marking a reference picture as a single state through a reference picture marking process may be provided.

[0033] In addition, according to the present disclosure, a non-transitory computer-readable recording medium for storing a bit stream generated by the image encoding method according to the present disclosure may be provided.

[0034] According to the present disclosure, there may be provided a non-transitory recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0035] According to the present disclosure, a method of transmitting a bit stream generated by the image encoding method according to the present disclosure may be provided.

[0036] Those skilled in the art will understand that the effects that can be achieved through the present disclosure are not limited to what has been specifically described above, and other advantages of the present disclosure will be more clearly understood from the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 FIG. 4 is a diagram schematically showing a video encoding system to which an embodiment of the present disclosure is applicable.

[0038] Figure 2 is a view schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0039] Figure 3is a view schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0040] Figure 4 is a diagram schematically showing an inter-frame prediction unit of an image encoding device.

[0041] Figure 5 is a flowchart illustrating a method of encoding an image based on inter-frame prediction.

[0042] Figure 6 is a diagram schematically showing an inter-frame prediction unit of an image decoding device.

[0043] Figure 7 is a flowchart illustrating a method of decoding an image based on inter-frame prediction.

[0044] Figure 8 is a flowchart illustrating an inter-frame prediction method.

[0045] Fig. 9 is a diagram illustrating a method of performing a reference picture marking process according to one embodiment of the present disclosure.

[0046] Fig.10 is a diagram illustrating an image decoding method that can be performed by an image decoding device according to one embodiment of the present disclosure.

[0047] Fig.11 is a diagram illustrating an image encoding method that can be performed by an image encoding device according to one embodiment of the present disclosure.

[0048] Fig.12 is a view illustrating a content streaming system to which an embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0049] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to facilitate implementation by those skilled in the art. However, the present disclosure may be implemented in various forms and is not limited to the embodiments described herein.

[0050] When describing the present disclosure, if it is determined that the detailed description of related known functions or configurations makes the scope of the present disclosure unnecessarily ambiguous, the detailed description thereof will be omitted. In the drawings, parts irrelevant to the description of the present disclosure are omitted, and like reference numerals are given to like parts.

[0051] In the present disclosure, when a component is "connected", "coupled" or "linked" to another component, it may include not only a direct connection relationship but also an indirect connection relationship with intermediate components. In addition, when a component "includes" or "has" other components, unless otherwise specified, it means that other components may also be included, rather than excluding other components.

[0052] In the present disclosure, the terms first, second, etc. may be used only for the purpose of distinguishing one component from other components, and do not limit the order or importance of the components, unless otherwise specified. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0053] In the present disclosure, components that are distinguished from each other are intended to clearly describe each feature and do not mean that the components must be separated. That is, multiple components can be integrated and implemented in one hardware or software unit, or one component can be distributed and implemented in multiple hardware or software units. Therefore, even if not otherwise specified, these embodiments in which the components are integrated or the components are distributed are also included in the scope of the present disclosure.

[0054] In the present disclosure, the components described in each embodiment are not necessarily indispensable components, and some components may be optional components. Therefore, the embodiments consisting of a subset of the components described in the embodiments are also included in the scope of the present disclosure. In addition, the embodiments including other components in addition to the components described in the various embodiments are included in the scope of the present disclosure.

[0055] The present disclosure relates to encoding and decoding of images. Unless otherwise defined in the present disclosure, terms used in the present disclosure may have general meanings commonly used in the technical field to which the present disclosure belongs.

[0056] In the present disclosure, a "picture" generally refers to a unit representing an image within a specific time period, and a slice / tile is a coding unit constituting a part of a picture, and a picture may be composed of one or more slices / tiles. In addition, a slice / tile may include one or more coding tree units (CTUs).

[0057] In the present disclosure, "pixel" or "pel" may refer to the smallest unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, or may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0058] In the present disclosure, a "unit" may refer to a basic unit of image processing. The unit may include at least one of a specific area of ​​a picture and information related to the area. In some cases, the unit may be used interchangeably with terms such as "sample array", "block" or "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.

[0059] In the present disclosure, "current block" may mean one of "current coding block", "current coding unit", "coding target block", "decoding target block" or "processing target block". When prediction is performed, "current block" may mean "current prediction block" or "prediction target block". When transform (inverse transform) / quantization (dequantization) is performed, "current block" may mean "current transform block" or "transform target block". When filtering is performed, "current block" may mean "filtering target block".

[0060] In addition, in the present disclosure, unless explicitly stated as a chroma block, "current block" may mean a block including both a luma component block and a chroma component block or a "luminance block of the current block". The luma component block of the current block may be expressed by an explicit description including a luma component block such as "luminance block" or "current luma block". In addition, "chroma component block of the current block" may be expressed by an explicit description including a chroma component block such as "chroma block" or "current chroma block".

[0061] In the present disclosure, the slash " / " or "," should be interpreted as indicating "and / or". For example, the expressions "A / B" and "A, B" may mean "A and / or B". In addition, "A / B / C" and "A, B, C" may mean "at least one of A, B and / or C".

[0062] In the present disclosure, the term "or" should be interpreted as indicating "and / or". For example, the expression "A or B" may include 1) only "A", 2) only "B", and / or 3) both "A and B". In other words, in the present disclosure, the term "or" should be interpreted as indicating "additionally or alternatively".

[0063] Overview of Video Coding Systems

[0064] Figure 1 is a diagram showing a video encoding system to which an embodiment according to the present disclosure is applicable.

[0065] The video encoding system according to the embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may deliver the encoded video and / or image information or data to the decoding device 20 via a digital storage medium or a network in the form of a file or a stream.

[0066] The encoding device 10 according to the embodiment may include a video source generator 11, an encoding unit 12, and a transmitter 13. The decoding device 20 according to the embodiment may include a receiver 21, a decoding unit 22, and a renderer 23. The encoding unit 12 may be called a video / image encoding unit, and the decoding unit 22 may be called a video / image decoding unit. The transmitter 13 may be included in the encoding unit 12. The receiver 21 may be included in the decoding unit 22. The renderer 23 may include a display and the display may be configured as a separate device or an external component.

[0067] The video source generator 11 can obtain the video / image by the process of capturing, synthesizing or generating the video / image. The video source generator 11 may include a video / image capturing device and / or a video / image generating device. The video / image capturing device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generating device may include, for example, a computer, a tablet computer, and a smart phone, and may generate the video / image (electronically). For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process of generating relevant data.

[0068] The encoding unit 12 may encode the input video / image. For compression and encoding efficiency, the encoding unit 12 may perform a series of processes such as prediction, transformation, and quantization. The encoding unit 12 may output the encoded data (encoded video / image information) in the form of a bitstream.

[0069] The transmitter 13 can obtain the encoded video / image information or data output in the form of a bit stream and forward it to the receiver 21 of the decoding device 20 or another external object in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter 13 may include an element for generating a media file in a predetermined file format and may include an element for transmitting through a broadcast / communication network. The transmitter 13 may be set as a transmitting device separated from the encoding device 10, and in this case, the transmitting device may include at least one processor and a transmitting unit, the at least one processor obtaining the encoded video / image information or data output in the form of a bit stream, and the transmitting unit is used to transmit the encoded video / image information or data in the form of a file or stream. The receiver 21 may extract / receive a bit stream from a storage medium or a network and send the bit stream to the decoding unit 22.

[0070] The decoding unit 22 may decode a video / image by performing a series of processes corresponding to the operations of the encoding unit 12, such as dequantization, inverse transformation, and prediction.

[0071] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0072] Overview of Image Coding Equipment

[0073] Figure 2 is a view schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0074] like Figure 2 As shown, the image source device (image encoding apparatus) 100 may include an image segmenter 110, a subtractor 115, a transformer 120, a quantizer 130, a dequantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter-frame prediction unit 180, an intra-frame prediction unit 185, and an entropy encoder 190. The inter-frame prediction unit 180 and the intra-frame prediction unit 185 may be collectively referred to as a "prediction unit". The transformer 120, the quantizer 130, the dequantizer 140, and the inverse transformer 150 may be included in a residual processor. The residual processor may also include a subtractor 115.

[0075] In some embodiments, all or at least some of the components configuring the image source device 100 may be configured by one hardware component (eg, an encoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium.

[0076] The image divider 110 may divide the input image (or picture or frame) input to the image source device 100 into one or more processing units. For example, the processing unit may be referred to as a coding unit (CU). The coding unit may be obtained by recursively dividing a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QT / BT / TT) structure. For example, a coding unit may be divided into a plurality of coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the division of the coding unit, the quadtree structure may be applied first, and the binary tree structure and / or the ternary tree structure may be applied later. The encoding process according to the present disclosure may be performed based on the final coding unit that is no longer divided. The maximum coding unit may be used as the final coding unit, and the coding unit of a deeper depth obtained by dividing the maximum coding unit may also be used as the final coding unit. Here, the encoding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the encoding process may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit. The prediction unit may be a sample prediction unit, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0077] The prediction unit (inter prediction unit 180 or intra prediction unit 185) may perform prediction on the block to be processed (current block) and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction based on the current block or CU. The prediction unit may generate various information related to the prediction of the current block and send the generated information to the entropy encoder 190. The information about the prediction may be encoded in the entropy encoder 190 and output in the form of a bitstream.

[0078] The intra prediction unit 185 can predict the current block by referring to the samples in the current picture. Depending on the intra prediction mode and / or the intra prediction technology, the reference samples can be located in the neighbors of the current block or can be placed separately. The intra prediction mode may include multiple non-directional modes and multiple directional modes. The non-directional mode may include, for example, a DC mode and a plane mode. Depending on the level of detail of the prediction direction, the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used according to the settings. The intra prediction unit 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0079] The inter prediction unit 180 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information sent in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc. The reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter prediction unit 180 may configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter prediction unit 180 may use the motion information of the neighboring block as the motion information of the current block. In the case of skip mode, unlike the merge mode, a residual signal may not be sent. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled by encoding the motion vector difference and an indicator of the motion vector predictor. The motion vector difference may mean the difference between the motion vector of the current block and the motion vector predictor.

[0080] The prediction unit may generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit may apply not only intra prediction or inter prediction, but also both intra prediction and inter prediction at the same time to predict the current block. The prediction method of applying both intra prediction and inter prediction to predict the current block may be referred to as combined inter and intra prediction (CIIP). In addition, the prediction unit may perform intra block copying (IBC) to predict the current block. Intra block copying may be used for content image / video encoding of games, etc., such as screen content coding (SCC). IBC is a method of predicting the current picture using a previously reconstructed reference block in the current picture at a position separated by a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to a predetermined distance. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described in the present disclosure.

[0081] The prediction signal generated by the prediction unit can be used to generate a reconstruction signal or to generate a residual signal. The subtractor 115 can generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (prediction block or prediction sample array) output from the prediction unit from the input image signal (original block or original sample array). The generated residual signal can be sent to the transformer 120.

[0082] The transformer 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT refers to a transform obtained from a graph when relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to square pixel blocks of the same size or may be applied to blocks of variable size rather than square.

[0083] The quantizer 130 may quantize the transform coefficients and send them to the entropy encoder 190. The entropy encoder 190 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 130 may rearrange the quantized transform coefficients of the block type into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0084] The entropy encoder 190 may perform various encoding methods, such as, for example, exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 190 may encode information required for video / image reconstruction other than quantized transform coefficients together or separately (e.g., values ​​of syntax elements, etc.). The encoded information (e.g., encoded video / image information) may be transmitted or stored in units of a network abstraction layer (NAL) in the form of a bitstream. The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The signaled information, transmitted information, and / or syntax elements described in the present disclosure may be encoded and included in a bitstream through the above-described encoding process.

[0085] The bit stream may be transmitted through a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits a signal output from the entropy encoder 190 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the image source device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0086] The quantized transform coefficients output from the quantizer 130 may be used to generate a residual signal. For example, the residual signal (residual block or residual sample) may be reconstructed by applying dequantization and inverse transformation to the quantized transform coefficients through the dequantizer 140 and the inverse transformer 150.

[0087] The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame prediction unit 180 or the intra-frame prediction unit 185 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If the block to be processed has no residual, such as the case where the skip mode is applied, the prediction block can be used as a reconstructed block. The adder 155 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0088] The filter 160 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 160 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc. The filter 160 can generate various information related to filtering and send the generated information to the entropy encoder 190, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 190 and output in the form of a bit stream.

[0089] The modified reconstructed picture transmitted to the memory 170 may be used as a reference picture in the inter prediction unit 180. When inter prediction is applied by the image source device 100, prediction mismatch between the image source device 100 and the image decoding apparatus may be avoided and encoding efficiency may be improved.

[0090] The DPB of the memory 170 may store the modified reconstructed picture for use as a reference picture in the inter-frame prediction unit 180. The memory 170 may store the motion information of the block for deriving (or encoding) the motion information in the current picture and / or the motion information of the reconstructed block in the picture. The stored motion information may be sent to the inter-frame prediction unit 180 and used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 170 may store the reconstructed samples of the reconstructed blocks in the current picture and may transmit the reconstructed samples to the intra-frame prediction unit 185.

[0091] Overview of Image Decoding Equipment

[0092] Figure 3 is a view schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0093] like Figure 3 As shown, the image receiving device 200 may include an entropy decoder 210, a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, and an intra-frame prediction unit 265. The inter-frame prediction unit 260 and the intra-frame prediction unit 265 may be collectively referred to as a "prediction unit". The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0094] According to an embodiment, all or at least some of the components configuring the image receiving apparatus 200 may be configured by hardware components (eg, decoders or processors). In addition, the memory 250 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

[0095] The image receiving apparatus 200 having received a bit stream including video / image information may perform the same operation as that performed by Figure 2 The image receiving device 200 may reconstruct the image by processing corresponding to the processing performed by the image source device 100. For example, the image receiving device 200 may perform decoding using a processing unit applied in an image encoding device. Therefore, the processing unit of decoding may be, for example, a coding unit. The coding unit may be obtained by dividing a coding tree unit or a maximum coding unit. The reconstructed image signal decoded and output by the image receiving device 200 may be reproduced by a reproduction device (not shown).

[0096] The image receiving device 200 can receive the image in the form of a bit stream from Figure 2The received signal may be decoded by the entropy decoder 210. For example, the entropy decoder 210 may parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The image decoding device may also decode the picture based on the information about the parameter set and / or the general constraint information. The signaled / received information and / or syntax elements described in the present disclosure may be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the neighboring block and the decoding target block, or the information of the symbol / bin decoded in the previous stage to determine the context model, perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. The information related to prediction among the information decoded by the entropy decoder 210 can be provided to the prediction unit (inter-frame prediction unit 260 and intra-frame prediction unit 265), and the residual value (ie, quantized transform coefficient and related parameter information) for which entropy decoding is performed in the entropy decoder 210 can be input to the dequantizer 220. In addition, the information about filtering among the information decoded by the entropy decoder 210 can be provided to the filter 240. In addition, a receiver (not shown) for receiving a signal output from the image encoding apparatus may be further configured as an internal / external element of the image receiving device 200 , or the receiver may be a component of the entropy decoder 210 .

[0097] In addition, the image decoding device according to the present disclosure may be referred to as a video / image / picture decoding device. The image decoding device may be divided into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, or at least one of an intra-frame prediction unit 265.

[0098] The dequantizer 220 may dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 220 may rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may dequantize the quantized transform coefficients by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficients.

[0099] The inverse transformer 230 may perform an inverse transformation on the transformation coefficients to obtain a residual signal (residual block, residual sample array).

[0100] The prediction unit may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction to the current block based on the information about prediction output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0101] The same as described in the prediction unit of the image source device 100 , the prediction unit may generate a prediction signal based on various prediction methods (techniques) to be described later.

[0102] The intra prediction unit 265 may predict the current block by referring to samples in the current picture. The description of the intra prediction unit 185 is also applicable to the intra prediction unit 265.

[0103] The inter-frame prediction unit 260 can derive the prediction block of the current block based on the reference block (reference sample array) specified by the motion vector on the reference picture. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information can be predicted in units of blocks, sub-blocks or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks existing in the current picture and temporal neighboring blocks existing in the reference picture. For example, the inter-frame prediction unit 260 may configure a motion information candidate list based on the neighboring blocks, and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0104] The adder 235 can generate a reconstruction signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the prediction unit (including the inter-frame prediction unit 260 and / or the intra-frame prediction unit 265). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as the reconstructed block. The description of the adder 155 also applies to the adder 235. The adder 235 can be called a reconstructor or a reconstructed block generator. The generated reconstruction signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0105] The filter 240 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 240 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 250, specifically, in the DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc.

[0106] The (modified) reconstructed picture stored in the DPB of the memory 250 can be used as a reference picture in the inter-frame prediction unit 260. The memory 250 can store the motion information of the block for deriving (or decoding) the motion information in the current picture and / or the motion information of the reconstructed block in the picture. The stored motion information can be sent to the inter-frame prediction unit 260 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 250 can store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0107] In the present disclosure, the embodiments described in the filter 160 , the inter prediction unit 180 , and the intra prediction unit 185 of the image source device 100 may be equally or correspondingly applied to the filter 240 , the inter prediction unit 260 , and the intra prediction unit 265 of the image receiving device 200 .

[0108] Inter prediction

[0109] The prediction unit of the image encoding device 100 and the image decoding device 200 may derive prediction samples by performing inter-frame prediction block by block. 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 may be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. In this article, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block may be predicted on a per-block, sub-block or sample basis based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, dual prediction, etc.) information. When inter-frame prediction is applied, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block or collocated CU (colCU). 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. 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 the case of skip mode and merge mode, the motion information of the current block may be the same as the motion information of the selected neighboring block. In the case of skip mode, unlike merge mode, a residual signal may not be sent. In the case of motion information prediction (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 sum of the motion vector predictor and the motion vector difference may be used to derive the motion vector of the current block.

[0110] Depending on the inter-frame prediction type (L0 prediction, L1 prediction, dual prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. The motion vector in the L0 direction may be referred to as the L0 motion vector or MVL0, and the motion vector in the L1 direction may be referred to as the L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as L0 prediction. Prediction based on the L1 motion vector may be referred to as L1 prediction. Prediction based on the L0 motion vector and the L1 motion vector may be referred to as bidirectional prediction. In this document, the L0 motion vector may refer to a motion vector associated with the reference picture list L0 (L0), and the L1 motion vector may refer to a motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include a picture before the current picture in output order as a reference picture. The reference picture list L1 may include a picture after the current picture in output order. The previous picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. The reference picture list L0 may also include a picture after the current picture in output order as a reference picture. In this case, within the reference picture list L0, the previous picture may be indexed first, and the subsequent picture may be indexed next. The reference picture list L1 may also include a picture preceding the current picture in output order as a reference picture. In this case, within the reference picture list 1, the subsequent picture may be indexed first, and the previous picture may be indexed next. Herein, the output order may correspond to a picture order count (POC) order.

[0111] Figure 4 is a diagram schematically showing the inter-frame prediction unit 180 of the image encoding device 100, and Figure 5 is a flowchart illustrating a method of encoding an image based on inter-frame prediction.

[0112] The image encoding device 100 may perform inter prediction on the current block (S510). The image encoding device 100 may derive the inter prediction mode and motion information of the current block, and may generate a prediction sample of the current block. In this article, the process of determining the inter prediction mode, deriving the motion information, and generating the prediction sample may be performed simultaneously, or any one process may be performed before the other process. For example, the inter prediction unit 180 of the image encoding device 100 may include a prediction mode determination unit 181, a motion information derivation unit 182, and a prediction sample derivation unit 183. The prediction mode determination unit 181 may determine a prediction mode for the current block. The motion information derivation unit 182 may derive the motion information of the current block. The prediction sample derivation unit 183 may derive the prediction sample of the current block. For example, the inter prediction unit 180 of the image encoding device 100 may search for a predetermined area (search area) of a reference picture of a block similar to the current block through motion estimation, and may derive a reference block whose difference with the current block is the smallest or less than or equal to a predetermined standard. Based on this, a reference picture index indicating a reference picture where the reference block is located can be derived, and a motion vector can be derived based on a position difference between the reference block and the current block. The image encoding apparatus 100 can determine a mode applied to the current block among various prediction modes. The image encoding apparatus 100 can compare RD costs for various prediction modes, and can determine an optimal prediction mode for the current block.

[0113] For example, when the skip mode or merge mode is applied to the current block, the image encoding device 100 may construct a merge candidate list described later, and may derive a reference block whose difference with the current block is the smallest or less than or equal to a predetermined standard among the reference blocks indicated by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information indicating the selected merge candidate may be generated and signaled to the decoding device. The motion information of the current block may be derived using the motion information of the selected merge candidate.

[0114] As another example, when the (A)MVP mode is applied to the current block, the image encoding device 100 may construct the (A)MVP candidate list described later, and may use the motion vector of the MVP candidate selected from the motion vector predictor (MVP) candidates included in the (A)MVP candidate list as the MVP of the current block. In this case, for example, a motion vector indicating a reference block derived by the above-mentioned motion estimation may be used as the motion vector of the current block. Among the MVP candidates, the MVP candidate having a motion vector with the smallest difference from the motion vector of the current block may be the selected MVP candidate. A motion vector difference (MVD) as the difference obtained by subtracting the MVP from the motion vector of the current block may be derived. In this case, information about the MVD may be signaled to the image decoding device 200. In addition, when the (A)MVP mode is applied, the value of the reference picture index may be constructed as reference picture index information, and may be signaled separately to the image decoding device 200.

[0115] The image encoding apparatus 100 may induce a residual sample based on the prediction sample (S520). The image encoding apparatus 100 may compare the prediction sample with an original sample of the current block to induce the residual sample.

[0116] The image encoding device 100 may encode the image information including prediction information and residual information (S530). The image encoding device 100 may output the encoded image information in the form of a bitstream. The prediction information is information related to the prediction process, and may include prediction mode information (e.g., a skip flag, a merge flag, or a mode index) and information about motion information. The information about the motion information may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index) as information for deriving a motion vector. In addition, the information about the motion information may include the above-mentioned reference picture index information and / or information about the MVD. In addition, the information about the motion information may include information indicating whether L0 prediction, L1 prediction, or bidirectional prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients of the residual sample.

[0117] The output bit stream may be stored in a (digital) storage medium and sent to a decoding device, or may be sent to the image decoding device 200 via a network.

[0118] In addition, as described above, the image encoding device 100 can generate a reconstructed picture (including a reconstructed sample and a reconstructed block) based on the reference sample and the residual sample. This is to derive the same prediction result as the prediction result performed in the image decoding device 200 through the image encoding device 100, and thereby, the encoding efficiency can be improved. Therefore, the image encoding device 100 can store the reconstructed picture (or reconstructed sample, reconstructed block) in a memory, and can use it as a reference picture for inter-frame prediction. As described above, the loop filtering process can also be applied to the reconstructed picture.

[0119] Figure 6 is a diagram schematically showing the inter-frame prediction unit 260 of the image decoding device 200, and Figure 7 is a flow chart showing a method of decoding an image based on inter-frame prediction.

[0120] The image decoding apparatus 200 may perform an operation corresponding to the operation performed by the image encoding apparatus 100. The image decoding apparatus 200 may perform prediction on the current block based on the received prediction information, and may derive a prediction sample.

[0121] Specifically, the image decoding apparatus 200 may determine a prediction mode for a current block based on the received prediction information (S710). The image decoding apparatus 200 may determine which inter prediction mode is applied to the current block based on prediction mode information in the prediction information.

[0122] For example, based on the merge flag, it can be determined whether to apply the merge mode to the current block or to determine the (A) MVP mode. Alternatively, one of various inter-frame prediction mode candidates can be selected based on the mode index. The inter-frame prediction mode candidate may include a skip mode, a merge mode, and / or an (A) MVP mode, or may include various inter-frame prediction modes described later.

[0123] The image decoding device 200 may derive motion information of the current block based on the determined inter-frame prediction mode (S720). For example, when the skip mode or the merge mode is applied to the current block, the image decoding device 200 may construct a merge candidate list described later, and may select a merge candidate from among the merge candidates included in the merge candidate list. The selection may be performed based on the above-mentioned selection information (merge index). The motion information of the selected merge candidate may be used to derive the motion information of the current block. The motion information of the selected merge candidate may be used as the motion information of the current block.

[0124] As another example, when the (A)MVP mode is applied to the current block, the image decoding device 200 may construct an (A)MVP candidate list described later, and may use the motion vector of the motion vector predictor (MVP) candidate selected from the motion vector predictor (MVP) candidates included in the (A)MVP candidate list as the MVP of the current block. The selection may be performed based on the above-mentioned selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the MVP and MVD of the current block. In addition, the reference picture index of the current block may be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list associated with the current block may be derived as a reference picture, which is referenced for inter-frame prediction of the current block.

[0125] In addition, as will be described later, the motion information of the current block can be derived without constructing a candidate list. In this case, the motion information of the current block can be derived according to the process described in the prediction mode described later. In this case, the candidate list configuration as described above can be omitted.

[0126] The image decoding apparatus 200 may generate a prediction sample for the current block based on the motion information of the current block (S730). In this case, a reference picture may be derived based on a reference picture index of the current block, and a sample of the reference block indicated on the reference picture by a motion vector of the current block may be used to derive the prediction sample of the current block. In this case, as described below, in some cases, a prediction sample filtering process may also be performed on all or part of the prediction samples of the current block.

[0127] For example, the inter prediction unit 260 of the image decoding device 200 may include a prediction mode determination unit 261, a motion information derivation unit 262, and a prediction sample derivation unit 263. The prediction mode determination unit 181 may determine a prediction mode for a current block based on the received prediction mode information. The motion information derivation unit 182 may derive motion information (motion vector and / or reference picture index) of the current block based on the received information about motion information. The prediction sample derivation unit 183 may derive a prediction sample of the current block.

[0128] The image decoding device 200 may generate residual samples for the current block based on the received residual information (S740). The image decoding device 200 may generate reconstructed samples for the current block based on the predicted samples and the residual samples, and may generate a reconstructed picture based thereon (S750). Thereafter, as described above, a loop filtering process may also be applied to the reconstructed image.

[0129] Reference Figure 8, the inter-frame prediction process may include the following steps: determining an inter-frame prediction mode (S810), deriving motion information according to the determined prediction mode (S820), and performing prediction (generating prediction samples) based on the derived motion information (S830). The inter-frame prediction process may be performed in the image encoding apparatus 100 and the image decoding apparatus 200 as described above.

[0130] Inter prediction mode determination

[0131] Various inter prediction modes can be used to predict the current block in the picture. For example, various modes such as merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub-block merge mode, and merge with MVD (MMVD) mode can be used. Decoder-side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, bidirectional prediction (BCW) with CU-level weights, bidirectional optical flow (BDOF), etc. can also be used as additional modes in addition or alternatively. Affine mode can be referred to as affine motion prediction mode. MVP mode can be referred to as advanced motion vector prediction (AMVP) mode. In this document, some modes and / or motion information candidates derived by some modes can be included as one of the motion information candidates of other modes. For example, an HMVP candidate can be added as a merge candidate in merge / skip mode, or can be added as an MVP candidate in MVP mode.

[0132] Prediction mode information indicating the inter prediction mode of the current block may be signaled from the image encoding device 100 to the image decoding device 200. The prediction mode information may be included in a bitstream and received by the image decoding device 200. The prediction mode information may include index information indicating one of a plurality of candidate modes. Alternatively, the inter prediction mode may be indicated by hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, a skip flag may be signaled to indicate whether the skip mode is applied, and if the skip mode is not applied, a merge flag may be signaled to indicate whether the merge mode is applied, and if the merge mode is not applied, an MVP mode may be indicated to be applied or a flag for additional classification may be further signaled. The affine mode may be signaled in an independent mode, or the affine mode may be signaled in a mode dependent on the merge mode or the MVP mode. For example, the affine mode may include an affine merge mode and an affine MVP mode.

[0133] Derivation of motion information

[0134] Inter-frame prediction can be performed using the motion information of the current block. The image encoding device 100 can derive the best motion information for the current block through a motion estimation process. For example, the image encoding device 100 can use the original block in the original picture for the current block to search for a similar reference block with high correlation in units of fractional pixels within a predetermined search range in the reference picture, thereby deriving motion information. The similarity of the block can be derived based on the difference in the sample value based on the phase. For example, the similarity of the block can be calculated based on the SAD between the current block (or the template of the current block) and the reference block (or the template of the reference block). In this case, the motion information can be derived based on the reference block with the minimum SAD in the search area. The derived motion information can be signaled to the image decoding device 200 according to various methods based on the inter-frame prediction mode.

[0135] Generation of prediction samples

[0136] A prediction block for a current block may be derived based on motion information derived according to a prediction mode. The prediction block may include prediction samples (prediction sample arrays) of the current block. When a motion vector of the current block indicates a fractional sample unit, an interpolation process may be performed, by which prediction samples of the current block may be derived based on reference samples in fractional sample units within a reference picture. When affine inter prediction is applied to the current block, prediction samples may be generated based on sample / sub-block units MV. When bidirectional prediction is applied, prediction samples derived by weighting or weighted averaging (according to phase) prediction samples derived based on L0 prediction (that is, prediction using a reference picture and MVL0 in a reference picture list L0) and prediction samples derived based on L1 prediction (that is, prediction using a reference picture and MVL1 in a reference picture list L1) may be used as prediction samples of the current block. When bidirectional prediction is applied, if a reference picture for L0 prediction and a reference picture for L1 prediction are located in different temporal directions relative to the current picture (i.e., bidirectional prediction and bi-prediction), it may be referred to as true bidirectional prediction.

[0137] As described above, reconstructed samples and reconstructed pictures may be generated based on the derived prediction samples, and thereafter, processes such as in-loop filtering may be performed.

[0138] Reference picture marking process

[0139] To support inter prediction, one or more reference pictures may be stored in a buffer called a decoded picture buffer (DPB). Each reference picture may be in one of the following states: used for short-term reference, used for long-term reference, or not used for reference. The state of the reference picture in the DPB may be updated before decoding of the current picture. In the following, the reference picture marking process will be described in detail.

[0140] This process can be performed before decoding the slice data, but can be performed after decoding related to the RPL (reference picture list) configuration for the slice and decoding of the slice header, and can be performed once per picture. Through this process, one or more reference pictures in the DPB can be marked as "not used for reference" or "used for long-term reference".

[0141] A decoded picture in a DPB may be marked as "not used for reference", "used for short-term reference", or "used for long-term reference" during the decoding process, but may be marked as only one of these states. Assigning a single specific state to a picture and marking the picture as a single specific state in this manner may implicitly eliminate the possibility that other states may also be assigned, even when marking the picture as another state is applicable.

[0142] When a picture is marked as "used for reference", this may indicate that the picture is marked as "used for short-term reference" or "used for long-term reference", but a picture cannot be marked as both "used for short-term reference" and "used for long-term reference".

[0143] STRP (Short Term Reference Picture) and ILRP (Inter-Layer Reference Picture) can be identified by their nuh_layer_id and PicOrderCntVal values. LTRP (Long Term Reference Picture) can be identified by the nuh_layer_id value and PicOrderCntVal value or the Log2(MaxPicOrderCntLsb)LSB (Least Significant Bit) value of the PicOrderCntVal value.

[0144] If the current picture is a CLVSS picture, all reference pictures in the DPB with the same nuh_layer_id as the current picture (if present) may be marked as "unused for reference". Otherwise, the following may apply:

[0145] - For each LTRP entry in RefPicList[0] or RefPicList[1], a picture may be marked as "used for long-term reference" if it is marked as "used for short-term reference" and has the same nuh_layer_id as the current picture.

[0146] - Each reference picture in the DPB with the same nuh_layer_id as the current picture that is not referenced by an entry in RefPicList[0] or RefPicList[1] may be marked as "unused for reference".

[0147] - For each ILRP entry in RefPicList[0] or RefPicList[1], a picture may be marked as "used for long-term reference".

[0148] To support the design of the reference picture marking process described above, some constraints for signaling and handling reference pictures may be defined as follows:

[0149] The following constraints may apply to bitstream conformance:

[0150] NOTE - If bitstream consistency is checked for some of these constraints, it can be expected that such consistency will be checked after the decoding process for unavailable reference pictures has been invoked.

[0151] - If i is 0 or 1, num_ref_entries[i][RplsIdx[i]] shall be less than NumRefIdxActive[i].

[0152] - The picture referenced by each active entry in RefPicList[0] or RefPicList[1] shall exist in the DPB and the TemporalId value shall be less than or equal to the TemporalId of the current picture.

[0153] - The picture referenced by each active entry in RefPicList[0] or RefPicList[1] shall not be the current picture and the ph_non_ref_pic_flag value shall be 0.

[0154] - A STRP entry in RefPicList[0] or RefPicList[1] of a slice within a picture and a LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice within the same picture shall not refer to the same picture.

[0155] - The difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the LTRP entry is 2 24 LTRP entries of size 0 or greater shall not exist in RefPicList[0] or RefPicList[1].

[0156] - Let setOfRefPics be the unique set of pictures referenced by all entries in RefPicList[0] with the same nuh_layer_id as the current picture and all entries in RefPicList[1] with the same nuh_layer_id as the current picture. The number of pictures in setOfRefPics shall be less than or equal to MaxDpbSize-1, where MaxDpbSize may be as described in the standard document (e.g., A.4.2 of VVC), and setOfRefPics shall be the same for all slices of a picture.

[0157] - If the nal_unit_type of the current slice is STSA_NUT, an active entry with nuh_layer_id equal to the nuh_layer_id of the current picture and TemporalId equal to the TemporalId of the current picture shall not be present in RefPicList[0] or RefPicList[1].

[0158] - In decoding order, if the current picture follows a STSA (Step-by-Step Temporal Sub-layer Access) picture having the same nuh_layer_id as the nuh_layer_id of the current picture and the same TemporalId as the current picture, then there shall not be a picture having the same nuh_layer_id as the nuh_layer_id of the current picture and the same TemporalId as the current picture and preceding the STSA picture included as the active entry in RefPicList[0] or RefPicList[1] in decoding order.

[0159] - When the current sub-picture with TemporalId equal to a specific value tId, nuh_layer_id equal to a specific value layerId, and a sub-picture index equal to a specific value subpicIdx is a sub-picture that follows, in decoding order, a STSA sub-picture with TemporalId equal to tId, nuh_layer_id equal to layerId, and a sub-picture index equal to subpicIdx, there shall be no picture preceding the picture containing the STSA sub-picture that is included as the active entry in RefPicList[0] or RefPicList[1] in decoding order and has TemporalId equal to tId and nuh_layer_id equal to layerId.

[0160] - When the current picture with nuh_layer_id equal to a specific value layerId is an IRAP (Intra Random Access Picture) picture, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede the previous IRAP picture with nuh_layer_id equal to layerId in output order or decoding order (if any).

[0161] - When the current sub-picture with nuh_layer_id equal to a specific value layerId and a sub-picture index equal to a specific value subpicIdx is an IRAP picture, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede, in output order or decoding order, the picture containing the IRAP sub-picture with sub-picture index equal to subpicIdx and nuh_layer_id equal to layerId in decoding order.

[0162] - When the current sub-picture is not a RASL (Random Access Skip Leading) sub-picture associated with a CRA (Clean Random Access) sub-picture with NoOutputBeforeRecoveryFlag equal to 1, there shall be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] generated by the decoding process for generating reference pictures that are not available for the CRA picture containing the CRA sub-picture associated with the current sub-picture.

[0163] - There shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] generated by the decoding process for generating reference pictures that are unavailable for IRAP or CRA pictures associated with the current picture when the current picture with nuh_layer_id equal to a specific value layerId does not correspond to any of the following:

[0164] * IDR pictures with pps_rpl_info_in_ph_flag equal to 1 or sps_idr_rpl_present_flag equal to 1

[0165] * CRA screen with NoOutputBeforeRecoveryFlag equal to 1

[0166] * When sps_field_seq_flag is 1, as a picture associated with a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, the picture precedes all leading pictures associated with the same CRA picture in decoding order

[0167] *Boot screen associated with a CRA screen with NoOutputBeforeRecoveryFlag equal to 1

[0168] * GDR screen with NoOutputBeforeRecoveryFlag equal to 1

[0169] * Recovery screen for GDR screen with NoOutputBeforeRecoveryFlag equal to 1 and nuh_layer_id equal to layerId

[0170] - There shall be no pictures referenced by an entry in RefPicList[0] or RefPicList[1] generated by a decoding process for generating reference pictures for an IRAP or GDR picture that is unavailable for use with an IRAP or GDR sub-picture associated with the current sub-picture when the current sub-picture with nuh_layer_id equal to a specific value layerId and with a sub-picture index equal to a specific value subpicIdx does not correspond to any of the following:

[0171] * IDR sub-picture in an IDR picture with pps_rpl_info_in_ph_flag equal to 1 and sps_idr_rpl_present_flag equal to 1

[0172] * CRA sub-picture in a CRA picture with NoOutputBeforeRecoveryFlag equal to 1

[0173] * When sps_field_seq_flag is 1, as a sub-picture associated with a CRA sub-picture in a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, the sub-picture precedes all leading pictures associated with the same CRA picture.

[0174] * Boot screen associated with a CRA sub-screen in a CRA screen with NoOutputBeforeRecoveryFlag equal to 1

[0175] * A sub-picture in a recovery picture of a GDR picture with nuh_layer_id equal to layerId and NoOutputBeforeRecoveryFlag equal to 1

[0176] - When the current picture follows an IRAP picture with the same nuh_layer_id value in both decoding order and output order, there shall be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] that precede the IRAP picture in output order or decoding order.

[0177] - When the current sub-picture follows an IRAP sub-picture with the same nuh_layer_id value and the same sub-picture index value in both decoding order and output order, there shall be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] that precede the picture containing the IRAP picture in output order or decoding order.

[0178] - When the current picture follows, in decoding order and output order, all leading pictures associated with the IRAP picture (if any) and the IRAP picture with the same nuh_layer_id value, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede the IRAP picture in output order or decoding order.

[0179] - When the current sub-picture follows, in both decoding order and output order (if any), all leading sub-pictures associated with the IRAP sub-picture and the IRAP sub-picture with the same nuh_layer_id value and the same sub-picture index, a picture referenced by an entry in RefPicList[0] or RefPicList[1] that precedes the picture containing the IRAP sub-picture in output order or decoding order shall not exist.

[0180] - When the current picture is a RADL (Random Access Decodable Leading) picture, there shall be no active entry in RefPicList[0] or RefPicList[1] corresponding to one of the following:

[0181] * RASL (Random Access Skip Boot) picture with pps_mixed_nalu_types_in_pic_flag equal to 0

[0182] NOTE - The active entry in RefPicList[0] or RefPicList[1] of the current picture (which is a RADL picture) may reference a reference layer of the current layer or a RASL picture in that layer with pps_mixed_nalu_types_in_pic_flag equal to 1. However, such a RADL picture may still be correctly decoded when the decoding process starts from the associated CRA picture, because the RADL sub-pictures in the referenced RASL picture may be correctly decoded only by enabling the RADL picture to reference the RADL sub-pictures in the referenced RASL picture, as imposed by the following constraint that does not allow RADL sub-pictures to reference RASL sub-pictures:

[0183] *The picture that precedes the RADL picture's associated IRAP picture in decoding order

[0184] - The current sub-picture is a RADL sub-picture, the nuh_layer_id of the current sub-picture is a specific value layerId, the sub-picture index is a specific value subpicIdx, and an active entry corresponding to one of the following items shall not exist in RefPicList[0] or RefPicList[1]:

[0185] * The picture containing the RASL subpicture with a subpicture index equal to subpicIdx

[0186] * RASL pictures with sps_num_subpics_minus1 value equal to 0 and nuh_layer_id value not equal to layerId

[0187] * The picture that precedes, in decoding order, the picture containing the associated IRAP sub-picture of the RADL sub-picture

[0188] The following constraints may be applied to pictures referenced by each ILRP entry in RefPicList[0] or RefPicList[1] of the slice of the current picture (if any):

[0189] *The screen should be in the same AU as the current screen.

[0190] *The picture should be in DPB.

[0191] * The picture should have a nuh_layer_id refPicLayerId that is smaller than the nuh_layer_id of the current picture.

[0192] *One of the following conditions shall apply:

[0193] **Picture is an IRAP picture or a GDR picture with ph_recovery_poc_cnt equal to 0

[0194] ** The picture shall have a TemporalId less than vps_max_tid_il_ref_pics_plus1[currLayerIdx][refLayerIdx], where currLayerIdx and refLayerIdx are equal to GeneralLayerIdx[nuh_layer_id] and GeneralLayerIdx[refpicLayerId], respectively.

[0195] - Each ILRP entry in the slice's RefPicList[0] or RefPicList[1] (if present) will be the active entry.

[0196] - When sps_num_subpics_minus1 is greater than 0 and the current sub-picture with sub-picture index subpicIdx has sps_subpic_treated_as_pic_flag[subpicIdx] equal to 1, the bitstream conformance requirements require that both of the following conditions are true:

[0197] *Only one of the following conditions should be true:

[0198] **The picture referenced by each active entry in RefPicList[0] or RefPicList[1] has the same value as the current picture for each of the following:

[0199] ***pps_pic_width_in_luma_samples

[0200] ***pps_pic_height_in_luma_samples

[0201] ***sps_num_subpics_minus1

[0202] ***sps_log2_ctu_size_minus5

[0203] ***sps_subpic_ctu_top_left_x[i], sps_subpic_ctu_top_left_y[i], sps_subpic_width_minus1[i], sps_subpic_height_minus1[i], and sps_subpic_treated_as_pic_flag[i] (for each, i is a value in the range of 0 to sps_num_subpics_minus1)

[0204] ***SubpicIdVal[subpicIdx]

[0205] **The picture referenced by each active entry in RefPicList[0] or RefPicList[1] is the ILRP entry with sps_num_subpics_minus1 equal to 0.

[0206] * The current picture and all pictures contained in the active entry other than the current picture and having the current picture in RefPicList[0] or RefPicList[1] have the same value for each of the following items:

[0207] **pps_pic_width_in_luma_samples

[0208] **pps_pic_height_in_luma_samples

[0209] **sps_num_subpics_minus1

[0210] **sps_log2_ctu_size_minus5

[0211] **sps_subpic_ctu_top_left_x[i], sps_subpic_ctu_top_left_y[i], sps_subpic_width_minus1[i], sps_subpic_height_minus1[i], sps_subpic_treated_as_pic_flag[i], SubpicIdVal[i] (for each, i is in the range of 0 to sps_num_subpics_minus1)

[0212] In the current design, in the reference picture marking process, all sub-pictures of a picture can have the same reference picture set (here, the unique picture set referenced by all entries of RefPicList[0] with the same nuh_layer_id as the current picture and all entries of RefPicList[1] with the same nuh_layer_id as the current picture is called setOfRefPics). That is, a reference picture set can be generated per picture. This is because the reference picture marking process is only called / completed once when decoding of the current picture starts.

[0213] On the other hand, having all sub-pictures and all slices within a picture have the same reference picture may have the following disadvantages:

[0214] - The available reference pictures for a slice of a picture may lead to non-preferred inter prediction regardless of where the sub-picture belongs to. Here, it is assumed that a picture contains multiple sub-pictures, and the sub-pictures cover different areas within the picture and have different content characteristics (e.g., motion characteristics, spatial uniformity characteristics, etc.). In this case, different sub-pictures may require different reference picture sets in order to better represent different content characteristics.

[0215] - It can be a strong constraint for sub-picture coordination. Due to the existing constraints, the encoding of the sub-pictures to be coordinated may need to be highly coordinated, and these sub-pictures need to be encoded with the same coding conditions (e.g., the same reference structure for inter prediction) to satisfy the constraints. In some cases, it may be desirable to coordinate sub-pictures from different sources that are not well coordinated into one bitstream.

[0216] In order to solve these problems, the present disclosure proposes, for example, an image encoding / decoding method and apparatus for calling a reference picture marking process for each sub-picture, a method for transmitting a bitstream, and a recording medium for storing a bitstream. According to an embodiment of the present disclosure, instead of calling a reference picture marking process once per picture (i.e., after decoding of a slice header of the first slice of the picture and a decoding process for constructing a reference picture list (RPL) of the slice, and before decoding of slice data), a reference picture marking process may be called once per sub-picture. According to an embodiment of the present disclosure, the reference picture marking process may be called after decoding of a slice header of the first slice of the sub-picture and a decoding process for constructing a reference picture list of the slice, and may be called before decoding of slice data (i.e., the first slice data of the sub-picture). In addition, according to an embodiment of the present disclosure, the reference picture marking process may be performed on a sub-picture basis, rather than indicating the entire picture as being used for short-term reference, long-term reference, or not used for reference. That is, according to the present disclosure, a sub-picture may be marked as a single state in the reference picture marking process. That is, each sub-picture in a reference picture may be marked as being used for long-term reference, short-term reference, or not used for reference. In addition, according to an embodiment of the present disclosure, when the reference picture marking process is called when the first slice of a sub-picture is received, the reference picture marking process can be applied only to the corresponding / collocated sub-picture in the reference picture. Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0217] When describing the embodiments of the present disclosure, the reference picture marking process may be expressed as a reference marking process.

[0218] In describing the embodiments of the present disclosure, a sub-picture may include one or more slices.

[0219] When describing the embodiments of the present disclosure, a screen may include a sub-screen, but the term "screen" may also be used to collectively refer to a sub-screen. In other words, the description of a screen may also be applied to a sub-screen.

[0220] Furthermore, the embodiments of the present disclosure may be applied individually or in combination with each other.

[0221] Implementation

[0222] Fig. 9 is a diagram illustrating a method for performing a reference picture marking process according to one embodiment of the present disclosure. More specifically, it is a diagram for explaining the order in which a reference picture marking process is performed during image decoding. For example, Fig. 9 The method of the reference picture marking process may be included in the image decoding method and may also be performed by the image decoding device.

[0223] As an example, before performing the reference picture marking process, a first slice header of a sub-picture in a picture may be decoded (S901). Here, the first slice may be a first slice and may be any slice within the sub-picture. The first slice header may be a header for the first slice and may include information related to the first slice.

[0224] Thereafter, information about a reference picture list of the first slice may be decoded (S902). The information about the reference picture list of the first slice may include one or more reference pictures, wherein the reference picture may be a reference sub-picture. That is, the reference picture included in the reference picture list may also be in the form of a sub-picture, in which case the reference picture list may be a reference sub-picture list. The information about the reference picture list may include a reference picture index, etc.

[0225] Thereafter, it may be marked whether a sub-picture in the reference picture is referenced (S903). As an example, the process of marking whether it is referenced may include a process of marking a sub-picture in the reference picture (i.e., a reference sub-picture) according to whether it is used for reference. As an example, a reference sub-picture may be marked as one of "used for short-term reference", "used for long-term reference", or "not used for reference". Here, a reference sub-picture may be marked as only a single state, and may not correspond to two or more states among a plurality of states at the same time. As an example, if one of these marks is assigned to a sub-picture, another of these marks may be implicitly removed. As another example, a sub-picture may be marked as "used for reference" or "not used for reference", wherein the "used for reference" state may collectively refer to a sub-picture marked as "used for short-term reference" or "used for long-term reference". As an example, a short-term reference picture (STRP) and an inter-layer reference picture (ILRP) may be identified by a layer identifier (e.g., nuh_layer_id) and / or a picture order count (e.g., PicOrderCntVal) value. A long-term reference picture (LTRP) may be identified by a layer identifier (e.g., nuh_layer_id) value and / or a picture order count (e.g., PicOrderCntVal), wherein the picture order count value may be identified by the least significant bit (LSB) of Log2(MaxPicOrderCntLsb) or PicOrderCntVal. In addition, as an example, if a (current) picture (e.g., a current sub-picture) is a picture of a specific type (e.g., CLVVS: coding layer video sequence start), all collocated sub-pictures (i.e., sub-pictures with the same sub-picture identifier and / or collocated sub-pictures) in a plurality of reference pictures in a decoded picture buffer (DPB) having the same layer identifier (e.g., nuh_layer_id) as the picture may be marked as "unused for reference". Furthermore, as an example, for each LTRP (long-term reference picture) entry in a reference picture list (e.g., refPicList[0] or [1]), if a collocated sub-picture in the reference picture is marked as "used for short-term reference" and has the same layer identifier (e.g., nuh_layer_id) as the picture, the reference sub-picture may be marked as "used for long-term reference". Additionally, a collocated sub-picture in each reference picture in the DPB that has the same layer identifier (e.g., nuh_layer_id) as the current picture and is not referenced by each entry in the reference picture list (e.g., RefPicList[0] or [1]) may be marked as "not used for reference". Additionally, as another example, for each ILRP entry in a reference picture list (e.g., RefPicList[0] or [1]), a collocated sub-picture in the reference picture may be marked as "used for long-term reference".On the other hand, after all slices in the current sub-picture are decoded, if the currently decoded sub-picture is marked as "used for short-term reference", the collocated sub-picture referenced by each ILRP entry (if any) can be marked as "used for short-term reference" in the reference picture list (e.g., refPicList[0] or [1]).

[0226] Thereafter, the information about the first slice may be decoded (S904). As an example, the information about the slice may correspond to a payload of the slice and may include some information for slice decoding.

[0227] also, Fig. 9 This is an example shown in the order when executed in the image decoding device or when decoding an image, but for the sake of clarity of explanation, this is merely an example assumed and explained in terms of image decoding.

[0228] In addition, based on Fig. 9 In another embodiment, according to an image encoding device or an image encoding method, information in a first slice header of a sub-picture to be included in a picture is derived, information about a reference picture list of the first slice is derived, it is marked whether a sub-picture in a reference picture is referenced, and information about the first slice can be derived, and the information to be included in the first slice header, the information about the reference picture list of the first slice, and the information about the first slice can be encoded into a bitstream.

[0229] In addition, due to Fig. 9 and based on Fig. 9 The embodiment corresponds to one embodiment of the present disclosure, so the order of some steps may be changed or some steps may be added or deleted.

[0230] According to the present disclosure, by performing a reference picture marking process for each sub-picture, the characteristics (eg, motion characteristics, spatial uniformity characteristics, etc.) of each sub-picture can be expressed in more detail, thereby improving the quality of the image.

[0231] Fig.10 is a diagram illustrating an image decoding method that can be performed by an image decoding device according to one embodiment of the present disclosure.

[0232] As an example, information about a reference picture set may be received (S1001). That is, information about a reference picture set of a current sub-picture may be received for inter-frame prediction. The information about the reference picture set may include information about a reference picture included in the reference picture set. The reference picture set may include one or more reference pictures. As an example, the information about the reference picture may include information about a reference sub-picture, and the information about the reference picture set may be used to derive a reference picture list. The information about the reference picture set may be included in the information about the reference picture list, in which case, the information about the reference picture set may be applied. Fig. 9 For example, since it is possible to partially apply Fig. 9 The description of step S902 in FIG. 1 is omitted, so the repeated description is omitted.

[0233] Thereafter, a reference picture may be derived based on the received information about the reference picture set (S1002). That is, a reference sub-picture of a current sub-picture may be derived based on the information about the reference picture set. As described above, since the information about the reference picture set may include information about one or more reference pictures, the reference picture may be derived based thereon. As described above, the reference picture may be a reference sub-picture, and may be a collocated sub-picture in the reference picture.

[0234] Thereafter, a reference marking process may be performed for the reference picture (S1003). As an example, the reference marking process may correspond to Fig. 9 The reference marking process of step S903 as the reference picture marking process can therefore be applied without change. Fig. 9 A description of the reference marking process. Fig. 9As described in , the reference marking process may include a process of marking a reference sub-picture as one of a short-term reference, a long-term reference, or a process of not being used for reference. As an example, if the reference sub-picture is marked as a short-term reference picture, the reference sub-picture may be identified based on at least one of a layer identifier and a picture sequence count value. As another example, if the reference sub-picture is marked as a long-term reference picture, the sub-picture of the reference picture may be identified based on at least one of a layer identifier and a maximum picture sequence count value, wherein the maximum picture sequence count value may be calculated based on a logarithmic function with a base of 2. In addition, based on the current picture including the current sub-picture having a specific picture type, the reference sub-picture having the same layer identifier as the current sub-picture may be marked as not being used for reference, wherein the specific picture type may be a coded layer video sequence start (CLVSS) picture type. In addition, the reference marking process may be performed before decoding slice data for the first slice in the current sub-picture. As an example, the reference marking process may be performed after decoding a slice header for the first slice in the current sub-picture. In addition, the reference marking process for the first slice in the current sub-picture may be applied only to a collocated reference sub-picture. As an example, the reference sub-picture may include a collocated sub-picture included in the reference picture.

[0235] In addition, due to Fig.10 Corresponding to one embodiment of the present disclosure, some steps may be added, deleted, or the order of the steps may be changed.

[0236] According to an embodiment of the present disclosure, a reference picture set may be configured for each sub-picture in a picture to improve image quality during image restoration.

[0237] Fig.11 is a diagram illustrating an image encoding method that can be performed by an image encoding device according to one embodiment of the present disclosure.

[0238] As an example, a reference picture set may be derived based on a reference sub-picture of a current sub-picture (S1101). Fig. 9 and Fig.10 The description of the reference picture set described above is omitted, and thus a repeated description is omitted.

[0239] Thereafter, a reference marking process may be performed on the reference sub-picture (S1102). Fig. 9 and Fig.10The description of the reference picture set described herein is as a reference picture marking process, and thus repeated description is omitted. However, the reference marking process may be performed before deriving slice data for the first slice in the current sub-picture. As an example, the reference marking process may be performed after deriving information in a slice header of the first slice in the current sub-picture. In addition, the reference marking process for the first slice in the current sub-picture may be applied only to a collocated reference sub-picture. As an example, the reference sub-picture may include a collocated sub-picture included in the reference picture.

[0240] Thereafter, information about the reference picture set of the current sub-picture may be encoded (S1103). As an example, the information about the reference picture set may include information about one or more reference pictures (i.e., reference sub-pictures) included in the reference picture set. In addition to the information about the reference picture set, slice data (e.g., a payload of a slice), information included in a slice header, etc. may be further encoded. Since the above reference picture set may be applied Fig. 9 and Fig.10 Description of information about reference picture sets is described above, and thus a repeated description is omitted.

[0241] In addition, due to Fig.11 Corresponding to the embodiments of the present disclosure, some steps may be added, deleted, or the order of the steps may be changed.

[0242] According to an embodiment of the present disclosure, by deriving reference picture set information for a sub-picture and performing a reference picture marking process, ie, a reference marking process, for each sub-picture, detailed image reconstruction may be performed by clearly reflecting characteristics of content.

[0243] Fig.12 is a diagram showing a content streaming system to which an embodiment of the present disclosure can be applied.

[0244] like Fig.12 As shown, the content streaming system to which the embodiments of the present disclosure are applied may mainly include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0245] The encoding server compresses the content input from the multimedia input device such as a smart phone, a camera, a camcorder, etc. into digital data to generate a bit stream and sends the bit stream to the streaming server. As another example, when the multimedia input device such as a smart phone, a camera, a camcorder, etc. directly generates a bit stream, the encoding server can be omitted.

[0246] A bitstream may be generated by an image encoding method or an image encoding device to which an embodiment of the present disclosure is applied, and a streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0247] The streaming server sends multimedia data to the user device based on the user's request through the network server, and the network server is used as a medium to inform the user of the service. When the user requests the required service from the network server, the network server can deliver it to the streaming server, and the streaming server can send the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server is used to control the command / response between the devices in the content streaming system.

[0248] 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, in order to provide a smooth streaming service, the streaming server may store the bitstream within a predetermined time.

[0249] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0250] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0251] The scope of the present disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling operations of methods according to various embodiments to be performed on a device or computer, and non-transitory computer-readable media having such software or commands stored thereon and executable on a device or computer.

[0252] Industrial Applicability

[0253] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising the following steps: Receiving information about a reference picture set for inter-frame prediction of a current sub-picture; deriving a reference sub-picture of the current sub-picture based on the information about the reference picture set; as well as A reference marking process is performed on the reference sub-picture.

2. The image decoding method according to claim 1, wherein: The reference marking process includes a process of marking the reference sub-picture as one of a short-term reference, a long-term reference, or an unused reference.

3. The image decoding method according to claim 2, wherein: Based on the reference sub-picture being marked as a short-term reference picture, the reference sub-picture is identified based on at least one of a layer identifier or a picture order count value.

4. The image decoding method according to claim 2, wherein: Based on the reference sub-picture being marked as a long-term reference picture, the reference sub-picture is identified based on at least one of a layer identifier or a picture order count value.

5. The image decoding method according to claim 2, wherein: Based on the current picture including the current sub-picture being of a specific picture type, the reference sub-picture having the same layer identifier as the current picture is marked as unused for reference.

6. The image decoding method according to claim 5, wherein: The specific picture type is a coding layer video sequence start CLVSS picture type.

7. The image decoding method according to claim 1, wherein: The reference marking process is performed before decoding slice data for a first slice in the current sub-picture.

8. The image decoding method according to claim 1, wherein: The reference marking process is performed after decoding a slice header of a first slice in the current sub-picture.

9. The image decoding method according to claim 1, wherein: The reference marking process for the first slice in the current sub-picture is applied only to collocated reference sub-pictures.

10. The image decoding method according to claim 1, wherein: The reference sub-picture includes a collocated sub-picture included in the reference picture.

11. An image encoding method performed by an image encoding device, the image encoding method comprising the following steps: deriving a reference picture set based on a reference sub-picture of the current sub-picture; performing a reference marking process on the reference sub-picture; as well as Information about the reference picture set of the current sub-picture is encoded.

12. A method for transmitting a bit stream, the method comprising the following steps: Sending the bit stream generated by the image encoding method; The image encoding method comprises the following steps: deriving a reference picture set based on a reference sub-picture of the current sub-picture; performing a reference marking process on the reference sub-picture; and Information about the reference picture set of the current sub-picture is encoded. 13 . A computer-readable storage medium storing a bit stream generated by the image encoding method according to claim 11 .

Images