Method and apparatus for image encoding / decoding based on related random access point picture, and method for bit stream transmission

Abstract

A method and apparatus for image encoding / decoding are provided. An image decoding method according to the present disclosure may comprise the steps of: in response to a random access request for a first picture, acquiring a second picture associated with the first picture and having been decoded before the first picture; and decoding the first picture by referring to a second picture, where the first picture is an associated random access point picture and the second picture is a progressive coded refresh (GDR) picture having a zero recovery point picture.

Description

Technical Field

[0001] The present disclosure relates to an image encoding / decoding method and a recording medium storing a bitstream, and more particularly, to an image encoding / decoding method and apparatus based on a related random access point picture and a method of transmitting a bitstream generated by the image encoding method / apparatus of the present disclosure. Background Art

[0002] Recently, in various fields, the demand for high-resolution and high-quality images such as high-definition (HD) images and ultra-high-definition (UHD) images is increasing. As the resolution and quality of image data are improved, the amount of information or the amount of bits transmitted is relatively increased compared to existing image data. The increase in the amount of information or the amount of bits 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] In addition, the object of the present disclosure is to provide an image encoding / decoding method and device based on a related random access point picture.

[0007] In addition, an object of the present disclosure is to provide an image encoding / decoding method and apparatus for performing random access on a related random access point picture based on a GDR picture having a zero recovery point picture.

[0008] In addition, an object of the present disclosure is to provide a non-transitory computer-readable recording medium that stores a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0009] In addition, an object of the present disclosure is to provide a non-transitory computer-readable recording medium storing a bit stream received and decoded by the image decoding device according to the present disclosure and used to reconstruct an image.

[0010] In addition, an object of the present disclosure is to provide a method of transmitting a bit stream generated by the image encoding method or apparatus 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 here will be clear to those skilled in the art through the following description.

[0012] Technical Solution

[0013] An image decoding method according to an aspect of the present disclosure may include: in response to a random access request for a first picture, obtaining a second picture associated with the first picture and decoded before the first picture, and decoding the first picture by referring to the second picture. The first picture may be a related random access point (RAP) picture, and the second picture may be a progressive decoding refresh (GDR) picture with a zero recovery point picture.

[0014] An image decoding device according to another aspect of the present disclosure may include a memory and at least one processor. The at least one processor may obtain a second picture associated with the first picture and decoded before the first picture in response to a random access request for a first picture, and decode the first picture by referring to the second picture. The first picture may be a related random access point (RAP) picture, and the second picture may be a progressive decoding refresh (GDR) picture with a zero recovery point picture.

[0015] According to another aspect of the present disclosure, an image encoding method may include deriving a second picture associated with a first picture as a starting point of random access, and encoding information about the first picture and the second picture. The first picture may be a related random access point (RAP) picture, and the second picture may be a progressive decoding refresh (GDR) picture with a zero recovery point picture.

[0016] A computer-readable recording medium according to another aspect of the present disclosure can store a bit stream generated by the image encoding method or the image encoding device of the present disclosure.

[0017] A transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding method or the image encoding device of the present disclosure.

[0018] The above briefly summarized features of 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.

[0019] Effect of the Invention

[0020] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0021] In addition, according to the present disclosure, a method and apparatus for image encoding / decoding based on a correlated random access point picture can be provided.

[0022] In addition, according to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus for performing random access on a related random access point picture based on a GDR picture having a zero recovery point picture.

[0023] Furthermore, according to the present disclosure, it is possible to provide a non-transitory computer-readable recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0024] Furthermore, according to the present disclosure, it is possible to provide a non-transitory computer-readable recording medium storing a bit stream received and decoded by the image decoding device according to the present disclosure and used to reconstruct an image.

[0025] Furthermore, according to the present disclosure, it is possible to provide a method of transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0026] 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

[0027] Figure 1 is a diagram schematically showing a video encoding system to which one embodiment of the present disclosure can be applied.

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

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

[0030] Figure 4 An example of a schematic picture decoding process to which embodiments of the present disclosure may be applied is illustrated.

[0031] Figure 5 An example of an exemplary picture encoding process to which embodiments of the present disclosure may be applied is illustrated.

[0032] Figure 6 is a diagram illustrating a hierarchical structure of an image used for compilation.

[0033] Figure 7 2 is a diagram for explaining a decoding process of a DRAP picture according to an embodiment of the present disclosure.

[0034] Figure 8 is a diagram for explaining a decoding process of an EDRAP picture according to an embodiment of the present disclosure.

[0035] Fig. 9 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure.

[0036] Fig.10 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure.

[0037] Fig.11 is a view showing a content streaming system to which an embodiment of the present disclosure can be applied. DETAILED DESCRIPTION

[0038] Hereinafter, 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 can be implemented in various forms and is not limited to the embodiments described herein.

[0039] 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.

[0040] 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.

[0041] In the present disclosure, the terms first, second, etc. are 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.

[0042] 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 specifically stated, implementations in which these components are integrated or distributed are also included in the scope of the present disclosure.

[0043] 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.

[0044] 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.

[0045] In this disclosure, “video” may mean a collection of images over time.

[0046] In the present disclosure, "picture" generally means a basis for representing an image in a specific time period, and a slice / tile is a coding basis constituting a part of a picture. 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).

[0047] In the present disclosure, "pixel" or "pel" may mean 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.

[0048] 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. A unit may include a luminance block and two chrominance (e.g., Cb, Cr) blocks. 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.

[0049] 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".

[0050] In addition, in the present disclosure, unless explicitly stated as a chroma block, a "current block" may mean a block including both a luma component block and a chroma component block or a "luma block of the current block". A "luma component block of the current block" may be represented by an explicit description including a luma component block such as a "luma block" or a "current luma block". In addition, a "chroma component block of the current block" may be represented by an explicit description including a chroma component block such as a "chroma block" or a "current chroma block".

[0051] In the present disclosure, the term " / " 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".

[0052] 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".

[0053] In the present disclosure, "at least one of A, B, and C" may mean "only A", "only B", "only C", or "any and all combinations of A, B, and C". In addition, "at least one of A, B, or C" or "at least one of A, B and / or C" may mean "at least one of A, B, and C".

[0054] The brackets used in the present disclosure may mean "for example". For example, if "prediction (intra-frame prediction)" is indicated, "intra-frame prediction" may be proposed as an example of "prediction". In other words, "prediction" in the present disclosure is not limited to "intra-frame prediction", and "intra-frame prediction" may be proposed as an example of "prediction". In addition, even when "prediction (ie, intra-frame prediction)" is indicated, "intra-frame prediction" may be proposed as an example of "prediction".

[0055] Video Coding System Overview

[0056] Figure 1 is a diagram showing a video encoding system to which an embodiment of the present disclosure can be applied.

[0057] 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.

[0058] The encoding device 10 according to the embodiment may include a video source generator 11, an encoding unit (encoder) 12, and a transmitter 13. The decoding device 20 according to the embodiment may include a receiver 21, a decoding unit (decoder) 22, and a renderer 23. The encoding unit 12 may be referred to as a video / image encoding device, and the decoding unit 22 may be referred to as a video / image decoding device. 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.

[0059] The video source generator 11 may acquire a video / image by a process of capturing, synthesizing or generating a 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 (electronically) generate a video / image. 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.

[0060] 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 encoded data (encoded video / image information) in the form of a bitstream.

[0061] The transmitter 13 may forward the encoded video / image information or data output in the form of a bit stream to the receiver 21 of the decoding device 20 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 transmission through a broadcast / communication network. 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.

[0062] 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.

[0063] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0064] Overview of Image Coding Equipment

[0065] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure can be applied.

[0066] like Figure 2As shown, the image encoding device 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.

[0067] In some embodiments, all or at least some of the components configuring the image encoding apparatus 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.

[0068] The image segmenter 110 may segment an input image (or picture or frame) input to the image encoding device 100 into one or more processing units. For example, a processing unit may be referred to as a coding unit (CU). A coding unit may be obtained by recursively segmenting 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 segmented 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 segmentation of the coding unit, a quadtree structure may be applied first, and then a binary tree structure and / or a ternary tree structure may be applied. The encoding process according to the present disclosure may be performed based on the final coding unit that is no longer segmented. The maximum coding unit may be used as the final coding unit, and a coding unit of a deeper depth obtained by segmenting the maximum coding unit may also be used as the final coding unit. Here, the encoding process may include the processes of prediction, transformation, and reconstruction to be described later. As another example, the processing unit of the encoding process may be a prediction unit (PU) or a transform 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 a transform coefficient.

[0069] 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 transmit 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.

[0070] The intra prediction unit (intra predictor) 185 can predict the current block by referring to samples in the current picture. Depending on the intra prediction mode and / or intra prediction technology, the reference samples may be located in the neighborhood of the current block or may 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 depending on the setting. 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.

[0071] The inter prediction unit (inter predictor) 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 transmitted 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, dual 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 construct 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-frame 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, the residual signal may not be transmitted. 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 signal the motion vector of the current block by encoding the motion vector difference and the 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.

[0072] 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 intra prediction and inter prediction simultaneously 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 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 inter prediction technique described in the present disclosure.

[0073] The prediction signal generated by the prediction unit may be used to generate a reconstruction signal or to generate a residual signal. The subtractor 115 may 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 may be transmitted to the transformer 120.

[0074] The transformer 120 may generate a transform coefficient by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-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 instead of square.

[0075] The quantizer 130 may quantize the transform coefficients and transmit 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.

[0076] The entropy encoder 190 may perform various encoding methods, such as exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 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 signaling information, the transmitted information, and / or the syntax elements described in the present disclosure may be encoded and included in the bitstream through the above-mentioned encoding process.

[0077] 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 encoding device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0078] 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.

[0079] 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 when 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.

[0080] At the same time, luminance mapping and chroma scaling (LMCS) is applicable during the picture encoding process and reconstruction process.

[0081] 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 transmit 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.

[0082] The modified reconstructed picture transferred 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 encoding apparatus 100, prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus may be avoided and encoding efficiency may be improved.

[0083] 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 from which the motion information in the current picture is derived (or encoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be transmitted 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.

[0084] Overview of Image Decoding Equipment

[0085] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure can be applied.

[0086] like Figure 3 As shown, the image decoding 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 predictor 260, and an intra-frame prediction unit 265. The inter-frame predictor (inter-frame prediction unit) 260 and the intra-frame predictor (intra-frame prediction unit) 265 may be collectively referred to as a "prediction unit (predictor)". The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0087] According to an embodiment, all or at least some of the plurality of components configuring the image decoding apparatus 200 may be configured by hardware components (eg, a decoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

[0088] The image decoding device 200 having received a bit stream including video / image information may perform the same Figure 2 The image is reconstructed by processing corresponding to the processing performed by the image encoding device 100. For example, the image decoding device 200 may perform decoding using a processing unit applied in the image encoding device. Therefore, the processing unit of decoding may be, for example, a coding unit. The coding unit may be obtained by partitioning the coding tree unit or the maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 may be reproduced by a reproduction device (not shown).

[0089] The image decoding device 200 may 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 decodes the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and outputs 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 may receive a bin corresponding to each syntax element in the bitstream, determine a context model using information of a decoding target syntax element, information of a neighboring block and a decoding target block, or information of a symbol / bin decoded at a previous stage, perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. Information related to prediction in the information decoded by the entropy decoder 210 may be provided to the prediction unit (inter-frame predictor 260 and intra-frame prediction unit 265), and the residual value for which entropy decoding is performed in the entropy decoder 210, that is, the quantized transform coefficient and related parameter information may be input to the dequantizer 220. In addition, information about filtering in the information decoded by the entropy decoder 210 may 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 decoding apparatus 200 , or the receiver may be a component of the entropy decoder 210 .

[0090] 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 at least one of a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, or an intra-frame prediction unit 265.

[0091] 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 a coefficient scanning order performed in an 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.

[0092] The inverse transformer 230 may inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0093] 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).

[0094] The same as described in the prediction unit of the image encoding device 100 , the prediction unit can generate a prediction signal based on various prediction methods (techniques) described later.

[0095] The intra predictor 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.

[0096] The inter-frame predictor 260 can 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 transmitted 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, dual 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 predictor 260 may configure a motion information candidate list based on the neighboring blocks, and derive a motion vector and / or a reference picture index of the current block based on the received candidate selection information. Inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0097] 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 predictor 260 and / or the intra-frame prediction unit 265). If the block to be processed has no residual (for example, when the skip mode is applied), the prediction block can be used as a 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.

[0098] 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.

[0099] The (modified) reconstructed picture stored in the DPB of the memory 250 may be used as a reference picture in the inter-frame predictor 260. The memory 250 may store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame predictor 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 may store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0100] In the present disclosure, the embodiments described in the filter 160, the inter-frame prediction unit 180 and the intra-frame prediction unit 185 of the image encoding device 100 can be equally or correspondingly applied to the filter 240, the inter-frame predictor 260 and the intra-frame predictor 265 of the image decoding device 200.

[0101] Meanwhile, the prediction unit of the above-mentioned image encoding / decoding device 100 or 200 may derive a reference sample among neighboring reference samples of the current block according to the intra prediction mode of the current block, and generate a prediction sample of the current block based on the reference sample.

[0102] For example, the prediction sample may be derived based on the average or interpolation of the neighboring reference samples of the current block, and (ii) the prediction sample may be derived based on the reference sample existing in a specific (prediction) direction relative to the prediction sample among the neighboring reference samples of the current block. The case of (i) may be referred to as a non-directional mode or a non-angle mode, and the case of (ii) may be referred to as a directional mode or an angle mode. In addition, the prediction sample may be generated by interpolating the second neighboring sample and the first neighboring sample positioned in the opposite direction of the prediction direction of the intra-frame prediction mode of the current block based on the prediction sample of the current block among the neighboring reference samples. The above case may be referred to as linear interpolation intra-frame prediction (LIP). In addition, the temporary prediction sample of the current block may be derived based on the filtered neighboring reference samples, and the prediction sample of the current block may be derived by the weighted sum of at least one reference sample derived according to the intra-frame prediction mode among the existing neighboring reference samples, that is, the unfiltered neighboring reference samples and the temporary prediction sample. The above case may be referred to as position-dependent intra-frame prediction (PDPC). In addition, a reference sample row with the highest prediction accuracy is selected from a plurality of adjacent reference sample rows of the current block to derive a prediction sample using a reference sample in a prediction direction located in the corresponding row, and at this time, intra-frame prediction coding can be performed by indicating (sending with a signal) the reference sample row used to the decoding device. The above situation may be referred to as multi-reference row (MRL) intra-frame prediction or MRL-based intra-frame prediction. In addition, by partitioning the current block into vertical or horizontal sub-partitions, intra-frame prediction is performed based on the same intra-frame prediction mode, and adjacent reference samples may be derived and used in units of sub-partitions. That is, in this case, the intra-frame prediction mode for the current block is also applied to the sub-partitions, but in some cases, the intra-frame prediction performance may be improved by deriving and using adjacent reference samples in units of sub-partitions. This prediction method may be referred to as intra-frame sub-partitioning (ISP) or intra-frame prediction based on ISP. The specific details will be described later. In addition, if the prediction direction based on the prediction sample indicates between adjacent reference samples, that is, if the prediction direction indicates a fractional sample position, the value of the prediction sample may also be derived by interpolation of multiple reference samples located around the corresponding prediction direction (around the corresponding fractional sample position).

[0103] The above-mentioned intra-frame prediction method may be referred to as an intra-frame prediction type to distinguish it from an intra-frame prediction mode. The intra-frame prediction type may be referred to as various terms, such as an intra-frame prediction technique or an additional intra-frame prediction mode. For example, the intra-frame prediction type (or additional intra-frame prediction mode, etc.) may include at least one of the aforementioned LIP, PDPC, MRL, or ISP. Information about the intra-frame prediction type may be encoded in an encoding device, included in a bitstream, and sent to a decoding device with a signal. Information about the intra-frame prediction type may be implemented in various forms, such as flag information indicating whether each intra-frame prediction type is applied or index information indicating one of several intra-frame prediction types.

[0104] Inter prediction

[0105] The prediction unit of the image encoding device 100 and the image decoding device 200 may derive a prediction sample by performing inter-frame prediction on a per-block basis. Inter-frame prediction may be a prediction derived in a manner that depends on data elements (e.g., sample values ​​or motion information) of a picture other than the current picture. When inter-frame prediction is applied to the current block, a prediction block (prediction sample array) for the current block 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. Here, 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 based on each block, sub-block, or sample based on the correlation of 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 further include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When inter-frame prediction is applied, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. 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 motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0106] According to the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. 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 both the L0 motion vector and the L1 motion vector may be referred to as dual prediction. Here, 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 pictures that precede the current picture in output order as reference pictures. The reference picture list L1 may include pictures that follow 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 further include pictures that follow the current picture in output order as reference pictures. 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 further 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. Here, the output order may correspond to a picture order count (POC) order.

[0107] General image / video compilation process

[0108] In image / video coding, the pictures configuring the image / video can be encoded / decoded according to the decoding order. The picture order corresponding to the output order of the decoded pictures can be set to be different from the decoding order, and based on this, not only forward prediction but also backward prediction can be performed during inter-frame prediction.

[0109] Figure 4 An example of a schematic picture decoding process to which the embodiments of the present disclosure are applicable is shown. Figure 4 In 4, S400 may be performed in the entropy decoder 310 of the decoding device, S410 may be performed in the prediction unit 310, S420 may be performed in the residual processor 320, S430 may be performed in the adder 340, and S440 may be performed in the filter 350. S400 may include the information decoding process described in the present disclosure, S410 may include the inter / intra prediction process described in the present disclosure, S420 may include the residual processing process described in the present disclosure, S430 may include the block / picture reconstruction process described in the present disclosure, and S440 may include the loop filtering process described in the present disclosure.

[0110] refer to Figure 4 , the image decoding process may schematically include a process (S400) of obtaining image / video information from a bitstream (by decoding), a picture reconstruction process (S410 to S430), and a loop filtering process (S440) for reconstructing the picture. The picture reconstruction process may be performed based on the prediction samples and residual samples obtained by inter / intra prediction (S410) and residual processing (S420) (dequantization and inverse transformation of quantized transform coefficients) described in the present disclosure. A modified reconstructed picture may be generated by a loop filtering process for the reconstructed picture generated by the picture reconstruction process, and the modified reconstructed picture may be output as a decoded picture, stored in a decoded picture buffer or memory 360 of a decoding device, and used as a reference picture in an inter-frame prediction process when the picture is decoded later. In some cases, the loop filtering process may be omitted. In this case, the reconstructed picture may be output as a decoded picture, stored in a decoded picture buffer or memory 360 of a decoding device, and used as a reference picture in an inter-frame prediction process when the picture is decoded later. The loop filtering process (S440) may include a deblocking filtering process, a sample adaptive offset (SAO) process, an adaptive loop filter (ALF) process, and / or a bilateral filter process as described above, some or all of which may be omitted. In addition, one or some of the deblocking filtering process, the sample adaptive offset (SAO) process, the adaptive loop filter (ALF) process, and / or the bilateral filter process may be applied sequentially, or all of them may be applied sequentially. For example, after applying the deblocking filtering process to the reconstructed picture, the SAO process may be performed. Alternatively, for example, after applying the deblocking filtering process to the reconstructed picture, the ALF process may be performed. This operation may be similarly performed even in an encoding device.

[0111] Figure 5 An example of a schematic picture encoding process to which the embodiments of the present disclosure are applicable is shown. Figure 5 S500 can be found in the above Figure 2 The above-described encoding device may be performed in the prediction unit 220, S510 may be performed in the residual processor 230, and S520 may be performed in the entropy encoder 240. S500 may include the inter / intra prediction process described in the present disclosure, S510 may include the residual processing process described in the present disclosure, and S520 may include the information encoding process described in the present disclosure.

[0112] refer to Figure 5, the image encoding process may schematically include not only a process for encoding and outputting information for picture reconstruction (e.g., prediction information, residual information, partition information, etc.) in the form of a bitstream, but also a process for generating a reconstructed picture for the current picture and a process for applying loop filtering to the reconstructed picture (optional). The encoding device may derive (modified) residual samples from the quantized transform coefficients through a dequantizer 234 and an inverse transformer 235, and generate a reconstructed picture based on the prediction samples and (modified) residual samples as outputs of S500. The reconstructed picture generated in this manner may be equal to the reconstructed picture generated in the decoding device. The modified reconstructed picture may be generated by a loop filtering process for reconstructing the picture, may be stored in a decoded picture buffer or memory 270, and may be used as a reference picture in an inter-frame prediction process when the picture is later encoded, similar to the decoding device. As described above, in some cases, part or all of the loop filtering process may be omitted. When the loop filtering process is performed, the (loop) filtering related information (parameters) may be encoded in the entropy encoder 190 and output in the form of a bitstream, and the decoding device may perform the loop filtering process based on the filtering related information using the same method as the encoding device.

[0113] Through such a loop filtering process, noise such as block effect and ringing effect occurring during image / video coding can be reduced, and subjective / objective visual quality can be improved. In addition, by performing the loop filtering process in both the encoding device and the decoding device, the encoding device and the decoding device can derive the same prediction result, the reliability of picture coding can be increased, and the amount of data to be sent for picture coding can be reduced.

[0114] As described above, the picture reconstruction process can be performed not only in a decoding device but also in an encoding device. Reconstructed blocks can be generated based on intra prediction / inter prediction in units of blocks, and reconstructed pictures including reconstructed blocks can be generated. When the current picture / slice / tile group is an I picture / slice / tile group, the blocks included in the current picture / slice / tile group can be reconstructed based only on intra prediction. At the same time, when the current picture / slice / tile group is a P or B picture / slice / tile group, the blocks included in the current picture / slice / tile group can be reconstructed based on intra prediction or inter prediction. In this case, inter prediction can be applied to some blocks in the current picture / slice / tile group, while intra prediction can be applied to the remaining blocks. The color components of the picture may include luminance components and chrominance components, and unless explicitly limited by the present disclosure, the methods and embodiments of the present disclosure are applicable to luminance components and chrominance components.

[0115] Example of compilation layers and structures

[0116] The compiled video / image of the present disclosure may be processed according to, for example, the compilation layers and structures described later.

[0117] Figure 6 is a diagram illustrating a hierarchical structure of an image used for compilation.

[0118] The coded images are classified into a video coding layer (VCL) for the image decoding process and processing itself, a lower system for sending and storing coded information, and a network abstraction layer (NAL) that exists between the VCL and the lower system and is responsible for network adaptation functions.

[0119] In the VCL, VCL data including compressed image data (slice data) may be generated, or a parameter set including information such as a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS), or a supplemental enhancement information (SEI) message additionally required for an image decoding process may be generated.

[0120] In NAL, header information (NAL unit header) can be added to the raw byte sequence payload (RBSP) generated in the VCL to generate a NAL unit. In this case, RBSP refers to slice data, parameter sets, SEI messages generated in the VCL. The NAL unit header can include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0121] like Figure 6 As shown in , NAL units can be classified into VCL NAL units and non-VCL NAL units according to RBSP generated in VCL. A VCL NAL unit may mean a NAL unit including information about an image (slice data), and a non-VCL NAL unit may mean a NAL unit including information required for decoding an image (parameter set or SEI message).

[0122] The VCL NAL unit and the non-VCL NAL unit may be attached with header information and sent over a network according to the data format of a lower layer system. For example, the NAL unit may be modified into data having a predetermined data format, such as an H.266 / VVC file format, RTP (Real-time Transport Protocol), or TS (Transport Stream), and sent over various networks.

[0123] As described above, in the NAL unit, the NAL unit type can be specified according to the RBSP data structure included in the corresponding NAL unit, and information about the NAL unit type can be stored in the NAL unit header and transmitted by using a signal. For example, the NAL unit can be roughly classified into a VCL NAL unit type and a non-VCL NAL unit type based on whether it includes information about an image (slice data). The VCL NAL unit type can be classified according to the attributes and types of the picture, and the non-VCL NAL unit type can be classified according to the type of the parameter set.

[0124] Examples of VCL NAL unit types, depending on the picture type, are as follows:

[0125] - "IDR_W_RADL", "IDR_N_LP": VCL NAL unit type for IDR (Instantaneous Decoding Refresh) pictures, which is a type of IRAP (Intra Random Access Point) pictures

[0126] - "CRA_NUT": VCL NAL unit type for CRA (Clean Random Access) pictures, which is a type of IRAP pictures

[0127] - "GDR_NUT": VCL NAL unit type for GDR (Progressive Decoding Refresh) pictures that can be randomly accessed

[0128] - "STSA_NUT": VCL NAL unit type for STSA (Step-wise Temporal Sub-layer Access) pictures that can be randomly accessed

[0129] - "RADL_NUT": VCL NAL unit type for a RADL picture, which is the leading picture

[0130] - "RASL_NUT": VCL NAL unit type for a RASL picture, which is the leading picture

[0131] - "TRAIL_NUT": VCL NAL unit type for trailing pictures. A trailing picture is a non-IRAP picture and a trailing picture associated with an IRAP or GDR picture follows the IRAP or GDR picture in decoding order. Trailing pictures that follow the associated IRAP picture in output order but precede it in decoding order are not allowed.

[0132] Next, examples of non-VCL NAL unit types according to parameter set types are as follows.

[0133] - "DCI_NUT": non-VCL NAL unit type including DCI (decoding capability information)

[0134] - "VPS_NUT": non-VCL NAL unit type including VPS (Video Parameter Set)

[0135] - "SPS_NUT": non-VCL NAL unit type including SPS (Sequence Parameter Set)

[0136] - "PPS_NUT": non-VCL NAL unit type including PPS (Picture Parameter Set)

[0137] - "PREFIX_APS_NUT", "SUFFIX_APS_NUT": non-VCL NAL unit types including APS (Adaptation Parameter Set)

[0138] - "PH_NUT": non-VCL NAL unit type including picture header

[0139] The above-mentioned NAL unit type can be identified by certain syntax information (eg, nal_unit_type) included in the NAL unit header.

[0140] Advanced Syntax

[0141] A coded picture can consist of one or more slices. Parameters describing the coded picture can be signaled in the picture header, while parameters describing the slices can be signaled in the slice header. The picture header is carried by a unique NAL unit type. In addition, the slice header is present at the beginning of the NAL unit containing the payload of the slice (i.e., the slice data).

[0142] Table 1 is a diagram showing an example of a picture header.

[0143] [Table 1]

[0144]

[0145] Referring to Table 1, the picture header may include a syntax element ph_gdr_or_irap_pic_flag. ph_gdr_or_irap_pic_flag may indicate whether the current picture is a GDR (progressive decoding refresh) or IRAP (intra-frame random access point) picture. For example, ph_gdr_or_irap_pic_flag equal to a first value (e.g., 1) may indicate that the current picture is a GDR or IRAP picture. Conversely, ph_gdr_or_irap_pic_flag equal to a second value (e.g., 0) may indicate that the current picture is not a GDR picture, but may be an IRAP picture.

[0146] In addition, the picture header may include a syntax element ph_gdr_pic_flag. ph_gdr_pic_flag may indicate whether the current picture is a GDR picture. For example, ph_gdr_pic_flag equal to a first value (e.g., 1) may indicate that the current picture is a GDR picture. Conversely, ph_gdr_pic_flag equal to a second value (e.g., 0) may indicate that the current picture is not a GDR picture. When the above-mentioned ph_gdr_or_irap_pic_flag has a first value (e.g., 1) and ph_gdr_pic_flag has a second value (e.g., 0), the current picture is determined to be an IRAP picture. Meanwhile, if ph_gdr_pic_flag does not exist, it may be inferred that the value of ph_gdr_pic_flag is the second value (e.g., 0).

[0147] In addition, the picture header may include a syntax element ph_recovery_poc_cnt. ph_recovery_poc_cnt may indicate a recovery point according to the output order of the decoded pictures. i) If the current picture is a GDR picture, and ii) ph_recovery_poc_cnt is 0, the current picture itself may be referred to as a recovery point picture. Conversely, if i) the current picture is a GDR picture, and ii) there is a subsequent picture in the CLVS that follows the current picture in decoding order and has a POC value equal to the POC value of the recovery point picture, the subsequent picture may be referred to as a recovery point picture. Alternatively, the first picture in the CLVS that has a POC value greater than the recovery point picture in output order may be referred to as a recovery point picture. The recovery point picture should not precede the current GDR picture in decoding order. A picture associated with the current GDR picture and having a POC value less than the POC value of the recovery point picture may be referred to as a recovery picture of the GDR picture.

[0148] Meanwhile, based on the pps_rpl_info_in_ph_flag having a first value (e.g., 1), ref_pic_lists() including reference picture list information may be called within a picture header. The pps_rpl_info_in_ph_flag is signaled / obtained via a picture parameter set and may indicate a calling location of ref_pic_lists(). For example, pps_rpl_info_in_ph_flag equal to a first value (e.g., 1) may indicate that ref_pic_lists() is called within a picture header instead of being called within a slice header. Conversely, pps_rpl_info_in_ph_flag equal to a second value (e.g., 0) may indicate that ref_pic_lists() is not called within a picture header but may be called within a slice header.

[0149] Random access and RAP pictures

[0150] Random access means that the decoding process for a bitstream starts from a point other than the starting point of the bitstream (i.e., the first picture in decoding order). A picture that can be a starting point for random access is called a random access point (RAP) picture, and can include an intra random access point (IRAP) picture and a gradual decoding refresh (GDR) picture.

[0151] (1) IRAP images

[0152] An IRAP picture is a random access picture and refers to a picture with a VCL NAL unit type in the range of IDR_W_RADL to CRA_NUT.

[0153] IRAP pictures may include Instantaneous Decoding Refresh (IDR) pictures and Clean Random Access (CRA) pictures. IRAP pictures may not use inter-frame prediction based on reference pictures in the same layer during the decoding process. The first picture in the bitstream in decoding order may be an IRAP picture or a Progressive Decoding Refresh (GDR) picture. For a single-layer bitstream, if the parameter set required for reference is available, the IRAP pictures in the CLVS (Coding Layer Video Sequence) and all non-RASL (Random Access Skip Leading) pictures that follow the IRAP pictures in decoding order can be correctly decoded even if the pictures that precede the IRAP pictures in decoding order are not decoded / referenced.

[0154] (2) CRA images

[0155] A CRA (Clean Random Access) picture is a kind of IRAP picture, and refers to a picture having a VCL NAL unit type such as CRA_NUT.

[0156] CRA pictures may not use inter-frame prediction during the decoding process. A CRA picture may be the first picture in the bitstream in decoding order, or may be the first or subsequent picture. A CRA picture may be associated with a RADL or RASL picture. If NoOutputBeforeRecoveryFlag has a first value (e.g., 1) for a CRA picture, RASL pictures associated with the CRA picture may not be decodable because they reference pictures that do not exist in the bitstream, and as a result, they may not be output by an image decoding device. Here, NoOutputBeforeRecoveryFlag may indicate whether a picture that precedes a recovery point picture in decoding order is output before a recovery point picture. For example, a NoOutputBeforeRecoveryFlag having a first value (e.g., 1) may indicate that a picture that precedes a recovery point picture in decoding order cannot be output before a recovery point picture. In this case, the CRA picture may be the first picture in the bitstream or the first picture following an EOS (end of sequence) NAL unit in decoding order, which may mean that random access has occurred. Conversely, NoOutputBeforeRecoveryFlag with a second value (e.g., 0) may indicate that pictures preceding the recovery point picture in decoding order may be output before the recovery point picture. In this case, the CRA picture may not be the first picture in the bitstream or the first picture following the EOS NAL unit in decoding order, which may mean that random access does not occur.

[0157] (3) IDR images

[0158] An IDR (Instantaneous Decoding Refresh) picture is a kind of IRAP picture, and refers to a picture having a VCL NAL unit type such as IDR_W_RADL or IDR_N_LP.

[0159] IDR pictures may not use inter-frame prediction during the decoding process. An IDR picture may be the first picture in the bitstream in decoding order, or may be the first or subsequent picture. Each IDR picture may be the first picture of a CVS (coded video sequence) in decoding order. If each VCL NAL unit for an IDR picture has a NAL unit type such as IDR_W_RADL, the IDR picture may have an associated RADL picture. On the other hand, if each VCL NAL unit for an IDR picture has a NAL unit type such as IDR_N_LP, the IDR picture may not have an associated leading picture. At the same time, an IDR picture may not have an associated RASL picture.

[0160] (4) GDR pictures

[0161] A GDR (Gradual Decoding Refresh) picture is a randomly accessible picture, and refers to a picture having a VCL NAL unit type such as GDR_NUT.

[0162] The GDR function means that when the decoding process starts from a picture in which all parts of the reconstructed image may not be correctly decoded, the correctly decoded part of the reconstructed picture gradually increases in the pictures following the picture until the entire picture is correctly decoded. A picture with this GDR function is called a GDR picture, and the first picture in which the entire picture can be correctly decoded among the pictures following the GDR picture is called a recovery point picture.

[0163] GDR pictures may include refresh areas and dirty areas. A refresh area refers to an area that has an exact match of decoded sample values ​​when the decoding process starts from a GDR picture, compared to the case where the decoding process starts from the previous IRAP picture in decoding order. A refresh area may include blocks coded using intra-frame prediction and can be decoded without reference to other pictures. In contrast, a dirty area refers to an area that does not have an exact match of decoded sample values ​​when the decoding process starts from a GDR picture, compared to the case where the decoding process starts from the previous IRAP picture in decoding order. A dirty area may include blocks coded using inter-frame prediction and may not be decodable without reference to other pictures. As a result, a dirty area is decodable only when the corresponding GDR picture is not the starting point of random access.

[0164] Meanwhile, unlike the above-mentioned IRAP picture, the RAP picture may further include DRAP (Related Random Access Point) and EDRAP (Extended DRAP) pictures which cannot be decoded independently.

[0165] DRAP and EDRAP pictures refer to pictures that cannot be correctly decoded without reference to other pictures, but may be the starting point for random access. A DRAP picture can be correctly decoded if it can reference the nearest picture that precedes the DRAP picture in decoding order. On the other hand, an EDRAP picture can be correctly decoded if it can reference the nearest picture that precedes the EDRAP picture in decoding order and one or more other identified EDRAP pictures that precede the EDRAP picture in decoding order. DRAP and EDRAP pictures can be encoded and represented using significantly fewer bits than other RAP pictures (especially IRAP pictures), which has the advantage of increasing the total number of RAPs while maintaining the overall bit rate.

[0166] Information about DRAP pictures may be signaled via a DRAP indication SEI message specified in the generic supplemental enhancement information (VSEI) specification. Additionally, information about EDRAP pictures may be signaled via an EDRAP indication SEI message specified in the VSEI specification. Conversely, a picture associated with a DRAP indication SEI message is referred to as a DRAP picture, and a picture associated with an EDRAP indication SEI message is referred to as an EDRAP picture.

[0167] The DRAP or EDRAP picture indicated by the SEI message can be associated with an anchor picture, which is an actual independent picture used for random access. In the current design, the anchor picture only includes IRAP pictures, which are called associated IRAP (intra-frame random access point) pictures. The basic idea of ​​the current design is that random access can be performed from the DRAP picture as long as the associated IRAP picture is provided and decoded before decoding the DRAP picture. In this case, no other pictures (i.e., pictures between the associated IRAP picture and the DRAP picture) are required for random access from the DRAP picture. This concept can be similarly applied to EDRAP pictures when adding an EDRAP picture that can further refer to zero or more previous EDRAP pictures.

[0168] As described above, according to the current design, only IRAP pictures are designated and used as anchor pictures for DRAP and EDRAP pictures. However, GDR pictures with zero recovery point pictures (e.g., GDR pictures with ph_recovery_poc_cnt equal to 0) may also be random access points and can be correctly decoded without reference to other pictures. In this regard, the current design of using only IRAP pictures as associated pictures is problematic in that all other types of pictures that can be performed as actual anchor pictures cannot be utilized.

[0169] To solve this problem, according to the present disclosure, the following aspects regarding DRAP and EDRAP pictures may be provided.

[0170] - (Aspect 1): For DRAP and EDRAP pictures, anchor pictures associated with the DRAP and / or EDRAP pictures may be defined. Here, the anchor picture means a picture from which random access can be performed and which can be correctly decoded without referring to other pictures.

[0171] - (Aspect 2): The list of pictures that may be used / considered as anchor pictures for DRAP and / or EDRAP pictures may include the following.

[0172] a. IRAP images

[0173] b. IRAP-like pictures. Here, IRAP-like pictures mean pictures that are not existing IRAP pictures but from which random access can be performed. An example of such a picture is a GDR (Gradual Decoding Refresh) picture with a zero recovery point picture (i.e., a GDR picture with ph_recovery_poc_cnt equal to 0 in the H.266 / VVC standard).

[0174] Embodiments of the present disclosure may be provided based on the above aspects. According to the embodiment, the above configurations may be applied alone or in combination of two or more. Hereinafter, embodiments of the present disclosure will be described in detail.

[0175] 1. DRAP pictures

[0176] According to an embodiment of the present disclosure, in order to support random access from a DRAP picture, an anchor picture associated with the DRAP picture may be newly defined. In addition, when random access occurs, the DRAP picture may be correctly decoded by referring to the associated anchor picture.

[0177] In one embodiment, the associated anchor picture of the DRAP picture may be a GDR picture with a zero recovery point picture. In other words, the IRAP picture associated with the existing DRAP picture may be newly defined as a GDR picture with a zero recovery point picture.

[0178] Information about DRAP pictures may be signaled via a DRAP indication SEI message. For example, the DRAP indication SEI message may have a format as shown in Table 2.

[0179] [Table 2]

[0180]

[0181] The presence of a DRAP indication SEI message indicates the application of certain constraints on picture order and picture references. These constraints allow the decoder to correctly decode the DRAP picture and the pictures that are in the same layer and follow the DRAP picture in both decoding order and output order, without decoding any other pictures in the same layer, except for the pictures of the DRAP picture's related anchors.

[0182] The anchor image used for the association of a DRAP image should be one of the following images:

[0183] - The associated IRAP picture of the DRAP picture.

[0184] - The associated GDR picture of a DRAP picture has ph_recovery_poc_cnt equal to 0. This means that the GDR picture itself is a recovery point picture.

[0185] At the same time, all constraints indicated by the presence of the DRAP indication SEI message shall apply as follows:

[0186] - DRAP pictures are trailing pictures.

[0187] - A DRAP picture has a temporal sub-layer identifier equal to 0.

[0188] - A DRAP picture does not contain any other pictures of the same layer in its active entry in the reference picture list, except the DRAP picture's associated anchor pictures.

[0189] - In the active entry of the reference picture list, all pictures that are present in the same layer and that follow the DRAP picture in both decoding order and output order do not include any pictures that belong to the same layer and that precede the DRAP picture in both decoding order and output order, except the DRAP picture's associated anchor pictures.

[0190] As described above, according to an embodiment of the present disclosure, when random access occurs from a DRAP picture, a GDR picture with a zero recovery point picture can be used as an anchor picture associated with the DRAP picture. In this case, when random access occurs to a DRAP picture, the DRAP picture can be correctly decoded by referring to the GDR picture with a zero recovery point picture, such as Figure 7 As shown in the figure.

[0191] 2. EDRAP images

[0192] According to an embodiment of the present disclosure, in order to support random access from an EDRAP picture, an anchor picture associated with the EDRAP picture may be newly defined. Then, when random access occurs, the EDRAP picture may be correctly decoded by referring to the associated anchor picture and the previous EDRAP picture preceding it in the decoding order.

[0193] In one embodiment, the associated anchor picture of the EDRAP picture may be a GDR picture with a zero recovery point picture. In other words, the IRAP picture associated with the existing EDRAP picture may be newly defined as a GDR picture with a zero recovery point picture.

[0194] Information about EDRAP pictures may be signaled via an EDRAP indication SEI message. The presence of an EDRAP indication SEI message indicates that certain constraints on picture order and picture references apply. These constraints allow a decoder to correctly decode EDRAP pictures and pictures that are located in the same layer and follow the EDRAP picture in both decoding order and output order without decoding any other pictures in the same layer except for the referenceable picture list. Here, the referenceable picture list consists of associated anchor pictures or EDRAP pictures that belong to the same CLVS as the EDRAP picture and are indicated by the edrap_ref_rap_id[i] syntax element.

[0195] The associated anchor image of an EDRAP image should be one of the following images:

[0196] - The associated IRAP picture of the EDRAP picture.

[0197] - The associated GDR picture of the EDRAP picture has ph_recovery_poc_cnt equal to 0. This means that the GDR picture itself is the recovery point picture.

[0198] At the same time, all constraints indicated by the presence of the EDRAP indication SEI message shall apply as follows:

[0199] - EDRAP pictures are trailing pictures.

[0200] - EDRAP pictures have a temporal sub-layer identifier equal to 0.

[0201] - An EDRAP picture does not include any other pictures of the same layer, except for the reference pictures, in its active entry in the reference picture list.

[0202] - All pictures that are present in the same layer and that follow the EDRAP picture in both decoding order and output order, in the active entry of its reference picture list, do not include any pictures that belong to the same layer and that precede the EDRAP picture in both decoding order and output order, except for pictures that can be referenced.

[0203] - Any picture in the list of referenceable pictures does not include any picture in the active entry of the reference picture list that does not belong to the same layer and exists at an earlier position in the referenceable picture list. Therefore, the first picture in the referenceable picture list does not include any picture of the same layer in the active entry of the reference picture list, even if it is an EDRAP picture that is a non-anchor picture.

[0204] An example of the EDRAP indication SEI message is shown in Table 3.

[0205] [Table 3]

[0206]

[0207] Referring to Table 3, the EDRAP indication SEI message extended_drap_indication() may include syntax elements edrap_rap_id_minus1, edrap_leading_pictures_decodable_flag, edrap_reserved_zero_12bits, edrap_num_ref_rap_pics_minus1, and edrap_ref_rap_id[i].

[0208] edrap_rap_id_minus1 plus 1 may represent a RAP picture identifier, which is denoted as the RapPicId of the EDRAP picture. Each anchor picture or EDRAP picture may be associated with a RapPicId value. The RapPicId value for an anchor picture may be inferred to be 0. The RapPicId values ​​for two EDRAP pictures associated with the same anchor picture shall be different.

[0209] edrap_leading_pictures_decodable_flag may indicate whether certain constraints apply. Specifically, edrap_leading_pictures_decodable_flag equal to 1 may indicate that all of the following constraints apply:

[0210] - All pictures belonging to the same layer and following an EDRAP picture in decoding order shall follow in output order any picture belonging to the same layer and preceding the EDRAP picture in decoding order.

[0211] - All pictures belonging to the same layer and following the EDRAP picture in decoding order and preceding the EDRAP picture in output order shall not include any pictures belonging to the same layer and preceding the EDRAP picture in decoding order, except for referenceable pictures, in their active entries in the reference picture lists.

[0212] Conversely, edrap_leading_pictures_decodable_flag equal to 0 may indicate that the constraint does not apply.

[0213] In bitstreams conforming to video codec standards such as the H.266 / VVC standard, edrap_reserved_zero_12bits shall be equal to 0. Other values ​​of edrap_reserved_zero_12bits are reserved for future use and decoders shall ignore edrap_reserved_zero_12bits values.

[0214] edrap_num_ref_rap_pics_minus1 plus 1 may indicate the number of anchor or EDRAP pictures that belong to the same CLVS as the EDRAP picture and may be included in an active entry of a reference picture list of the EDRAP picture.

[0215] edrap_ref_rap_id[i] may indicate the RapPicId of the i-th RAP picture, which may be included in the active entry of the reference picture list of the EDRAP picture. The i-th RAP picture shall be an anchor picture associated with the current EDRAP picture or an EDRAP picture associated with the same IRAP picture as the current EDRAP picture.

[0216] As described above, when random access occurs from an EDRAP picture, a GDR picture with a zero recovery point picture can be used as an anchor picture associated with the EDRAP picture. In this case, when random access occurs to an EDRAP picture, the EDRAP picture can be correctly decoded by referring to another EDRAP picture that precedes the GDR picture with a zero recovery point picture in decoding order, such as Figure 8 As shown in the figure.

[0217] In the above, according to an embodiment of the present disclosure, an anchor picture can be newly defined as an associated picture of a DRAP and EDRAP picture. An anchor picture means a picture that can be correctly decoded without decoding any other pictures that precede it in the decoding order within the same layer, and can be a GDR picture with a zero recovery point picture. That is, a GDR picture that is itself a recovery point picture can be newly defined as an IRAP picture associated with a DRAP picture. Therefore, a GDR picture that can perform as an actual anchor picture can be used in random access, thereby achieving more flexible and extended random access support.

[0218] In the following, reference will be made to Fig. 9 and Fig.10 An image encoding / decoding method according to an embodiment of the present disclosure is described in detail.

[0219] Fig. 9 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure. Fig. 9 The image encoding method can be Figure 2The image encoding device is executed.

[0220] refer to Fig. 9 , the image encoding device may derive a second picture associated with a first picture as a starting point of random access (S910). Then, the image encoding device may encode information about the first picture and the second picture (S920). Here, the first picture may be a related random access point picture, and the second picture may be a GDR (Progressive Decoding Refresh) picture with a zero recovery point picture.

[0221] In one embodiment, the first picture may be a Dependent Random Access Point (DRAP) picture or an Extended DRAP (EDRAP) picture.

[0222] In one embodiment, when the first picture is a Dependent Random Access Point (DRAP) picture, the valid entries of the reference picture list for the first picture may not include any other pictures in the same layer except for GDR pictures with zero recovery point pictures.

[0223] In one embodiment, when the first picture is an extended DRAP (EDRAP) picture, a random access point (RAP) picture identifier indicating the second picture may be encoded in a supplemental enhancement information (SEI) message.

[0224] In one embodiment, for a GDR picture with a zero recovery point picture, the RAP picture identifier value may be determined to be 0.

[0225] A bit stream generated by the above-described image encoding method may be stored in a non-transitory computer-readable recording medium and transmitted to an image decoding apparatus.

[0226] Fig.10 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure. Fig.10 The image decoding method can be Figure 3 The image decoding device is executed.

[0227] refer to Fig.10 In response to a random access request for a first picture, the image decoding device may obtain a second picture associated with the first picture and decoded before the first picture (S1010). Then, the image decoding device may decode the first picture by referring to the second picture (S1020). Here, the first picture may be a related random access point picture, and the second picture may be a GDR (Progressive Decoding Refresh) picture with a zero recovery point picture.

[0228] In one embodiment, the first picture may be a Dependent Random Access Point (DRAP) picture or an Extended DRAP (EDRAP) picture.

[0229] In one embodiment, if the first picture is a Dependent Random Access Point (DRAP) picture, the active entry of the reference picture list for the first picture may not include any other pictures in the same layer except for GDR pictures with zero recovery point pictures.

[0230] In one embodiment, if the first picture is an extended DRAP (EDRAP) picture, the second picture may be identified based on a random access point (RAP) picture identifier obtained from a supplemental enhancement information (SEI) message.

[0231] In one embodiment, the RAP picture identifier value for a GDR picture with a zero recovery point picture may be determined to be 0.

[0232] Although the exemplary method of the present disclosure is represented as a series of operations for the sake of clarity, it is not intended to limit the order in which the steps are performed, and the steps are performed simultaneously or in different orders when necessary. In order to implement the method according to the present disclosure, the steps described may further include other steps, may include remaining steps other than some steps, or may include other additional steps other than some steps.

[0233] In the present disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) may perform an operation (step) of confirming an execution condition or situation of the corresponding operation (step). For example, if it is described that a predetermined operation is performed when a predetermined condition is satisfied, the image encoding device or the image decoding device may perform the predetermined operation after determining whether the predetermined condition is satisfied.

[0234] The various embodiments of the present disclosure are not a list of all possible combinations and are intended to describe representative aspects of the present disclosure, and matters described in the various embodiments may be applied independently or in combination of two or more.

[0235] Various embodiments of the present disclosure may be implemented in hardware, firmware, software, or a combination thereof. In the case of implementing the present disclosure in hardware, the present disclosure can be implemented using an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a general purpose processor, a controller, a microcontroller, a microprocessor, etc.

[0236] In addition, the image decoding device and the image encoding device to which the embodiments of the present disclosure are applied may be included in a multimedia broadcast sending and receiving device, a mobile communication terminal, a home theater video device, a digital theater video device, a surveillance camera, a video chat device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camera, a video on demand (VoD) service providing device, an OTT video (over the top video) device, an Internet streaming service providing device, a three-dimensional (3D) video device, a video phone video device, a medical video device, etc., and may be used to process a video signal or a data signal. For example, an OTT video device may include a game console, a Blu-ray player, an Internet access TV, a home theater system, a smart phone, a tablet computer, a digital video recorder (DVR), etc.

[0237] Fig.11 is a diagram showing a content streaming system to which an embodiment of the present disclosure can be applied.

[0238] like Fig.11 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.

[0239] The encoding server compresses the content input from a multimedia input device such as a smart phone, camera, or camcorder into digital data to generate a bitstream and sends the bitstream to the streaming server. As another example, when a multimedia input device such as a smart phone, camera, or camcorder directly generates a bitstream, the encoding server can be omitted.

[0240] The bitstream may be generated by the image encoding method or the image encoding device to which the embodiments of the present disclosure are applied, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0241] 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.

[0242] 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.

[0243] 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, tablet PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0244] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0245] 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.

[0246] Industrial Applicability

[0247] 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: In response to a random access request for a first picture, obtaining a second picture associated with the first picture and decoded before the first picture; as well as decoding the first picture by referring to the second picture, wherein the first picture is a related random access point (RAP) picture, and The second picture is a progressive decoding refresh (GDR) picture with a zero recovery point picture.

2. The image decoding method according to claim 1, wherein: The first picture is a Dependent Random Access Point (DRAP) picture or an Extended DRAP (EDRAP) picture.

3. The image decoding method according to claim 1, wherein: Based on the first picture being a dependent random access point (DRAP) picture, active entries of a reference picture list for the first picture do not include any other pictures in the same layer except the GDR picture with the zero recovery point picture.

4. The image decoding method according to claim 1, wherein: Based on the first picture being an extended DRAP (EDRAP) picture, the second picture is identified based on a random access point (RAP) picture identifier obtained from a supplemental enhancement information (SEI) message associated with the second picture.

5. The image decoding method according to claim 4, wherein: The RAP picture identifier value for the GDR picture having the zero recovery point picture is determined to be 0.

6. An image encoding method performed by an image encoding device, the image encoding method comprising: deriving a second picture, the second picture being associated with the first picture as a starting point of random access; as well as encoding information for the first picture and the second picture, wherein the first picture is a related random access point (RAP) picture, and The second picture is a progressive decoding refresh (GDR) picture with a zero recovery point picture.

7. The image encoding method according to claim 6, wherein: The first picture is a Dependent Random Access Point (DRAP) picture or an Extended DRAP (EDRAP) picture.

8. The image encoding method according to claim 6, wherein: Based on the first picture being a dependent random access point (DRAP) picture, active entries of a reference picture list for the first picture do not include any other pictures in the same layer except the GDR picture with the zero recovery point picture.

9. The image encoding method according to claim 6, wherein: Based on the first picture being an extended DRAP (EDRAP) picture, a random access point (RAP) picture identifier indicating the second picture is encoded in a supplemental enhancement information (SEI) message associated with the second picture.

10. The image encoding method according to claim 9, wherein: For the GDR picture with the zero recovery point picture, the RAP picture identifier value is determined to be 0.

11. A non-transitory computer-readable recording medium storing a bit stream generated by the image encoding method according to claim 6.

12. A method for transmitting a bit stream generated by an image encoding method, the image encoding method comprising: deriving a second picture, the second picture being associated with the first picture as a starting point of random access; as well as encoding information for the first picture and the second picture, wherein the first picture is a related random access point (RAP) picture, and The second picture is a progressive decoding refresh (GDR) picture with a zero recovery point picture.

Images