Image encoding / decoding method, method for transmitting bit stream, and recording medium for storing bit stream

Abstract

Provided are an image encoding / decoding method, a bitstream transmission method, and a computer-readable recording medium storing a bitstream. An image decoding method according to the present disclosure may be an image decoding method performed by an image decoding device, the image decoding method comprising the steps of: obtaining a supplemental enhancement information (SEI) message for an extended related random access point (EDRAP) picture from a bitstream; and identifying, based on the SEI message, a preamble picture after the EDRAP picture in the decoding order and before the EDRAP picture in the output order, where the preamble picture includes at least one of a decodable preamble picture and a non-decodable preamble picture.

Description

Technical Field

[0001] The present disclosure relates to an image encoding / decoding method, a method for transmitting a bitstream, and a recording medium for storing the bitstream, and more particularly, to an image encoding / decoding method and apparatus based on a method for identifying a leading picture, a method for transmitting a bitstream, and a recording medium for storing the bitstream. 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, an object of the present disclosure is to propose a method for identifying a leading picture.

[0007] In addition, one object of the present disclosure is to apply various constraints on the decoding order and output order of leading pictures.

[0008] In addition, one object of the present disclosure is to propose a definition for a decodable leading picture and an undecodable leading picture.

[0009] Additionally, one object of the present disclosure is to provide a mix of decodable leading pictures and non-decodable leading pictures.

[0010] 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 apparatus according to the present disclosure and used to reconstruct an image.

[0011] In addition, an object of the present disclosure is to provide a method of transmitting a bit stream generated by the image encoding method according to the present disclosure.

[0012] 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.

[0013] Technical Solution

[0014] An image decoding method according to one aspect of the present disclosure is an image decoding method performed by an image decoding device. The image decoding method may include the following steps: obtaining a supplemental enhancement information (SEI) message for an extended related random access point (EDRAP) picture from a bitstream; and identifying a leading picture that is after the EDRAP picture in a decoding order and before the EDRAP picture in an output order based on the SEI message. The leading picture may include at least one of a decodable leading picture or an undecodable leading picture.

[0015] According to another aspect of the present disclosure, an image encoding method is an image encoding method performed by an image encoding device. The image encoding method may include the following steps: identifying a leading picture that is after an extended related random access point (EDRAP) picture in decoding order and before the EDRAP picture in output order; and encoding a supplemental enhancement information (SEI) message for the EDRAP picture based on the result of identifying the leading picture. The leading picture may include at least one of a decodable leading picture or an undecodable leading picture.

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

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

[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] Beneficial Effects

[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, the method of identifying whether it is a leading screen can be simplified.

[0022] In addition, according to the present disclosure, a mixture of decodable leading pictures and undecodable leading pictures may be allowed.

[0023] Furthermore, according to the present disclosure, there may be provided a non-transitory computer-readable recording medium storing a bit stream generated by the image encoding method according to the present disclosure.

[0024] Furthermore, according to the present disclosure, there may be provided a non-transitory computer-readable recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0025] Furthermore, according to the present disclosure, a method of transmitting a bit stream generated by the image encoding method according to the present disclosure may be provided.

[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 coding layer and structure to which one embodiment of the present disclosure is applicable is shown.

[0031] Figure 5 is a flowchart illustrating an image encoding method according to one embodiment of the present disclosure.

[0032] Figure 6 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0033] Figure 7 is a flowchart illustrating an image encoding method according to another embodiment of the present disclosure.

[0034] Figure 8 is a flowchart illustrating an image decoding method according to another embodiment of the present disclosure.

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

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

[0037] Fig.11 is a diagram showing a content streaming system to which one embodiment of the present disclosure is applicable. 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 may 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 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).

[0046] In the present disclosure, "pixel" or "pel" may refer to the smallest unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, or may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0047] 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 ​​the 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.

[0048] 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".

[0049] 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".

[0050] In the present disclosure, the slash " / " or "," should be interpreted as indicating "and / or". For example, the expressions "A / B" and "A, B" may mean "A and / or B". In addition, "A / B / C" and "A, B, C" may mean "at least one of A, B and / or C".

[0051] 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".

[0052] Video Coding System Overview

[0053] Figure 1 is a diagram showing a video encoding system to which an embodiment of the present disclosure can be applied.

[0054] 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.

[0055] 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.

[0056] The video source generator 11 can obtain the video / image by the process of capturing, synthesizing or generating the video / image. The video source generator 11 may include a video / image capturing device and / or a video / image generating device. The video / image capturing device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generating device may include, for example, a computer, a tablet computer, and a smart phone, and may generate the video / image (electronically). For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process of generating relevant data.

[0057] 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.

[0058] The transmitter 13 can obtain the encoded video / image information or data output in the form of a bit stream and forward it to the receiver 21 of the decoding device 20 or another external object in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter 13 may include an element for generating a media file in a predetermined file format and may include an element for transmitting through a broadcast / communication network. The transmitter 13 may be set as a transmitting device separated from the encoding device 10, and in this case, the transmitting device may include at least one processor and a transmitting unit, the at least one processor obtaining the encoded video / image information or data output in the form of a bit stream, and the transmitting unit is used to transmit the encoded video / image information or data in the form of a file or stream. The receiver 21 may extract / receive a bit stream from a storage medium or a network and send the bit stream to the decoding unit 22.

[0059] 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.

[0060] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0061] Overview of Image Coding Equipment

[0062] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure can be applied.

[0063] like Figure 2 As 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.

[0064] 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.

[0065] The image segmenter 110 may segment the input image (or picture or frame) input to the image encoding device 100 into one or more processing units. For example, the processing unit may be referred to as a coding unit (CU). The coding unit may be obtained by recursively 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, the quadtree structure may be applied first, and then the binary tree structure and / or the 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 the 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 prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the encoding process may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit. The prediction unit may be a sample prediction unit, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0066] 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.

[0067] The intra prediction unit (intra predictor) 185 can predict the current block by referring to the samples in the current picture. Depending on the intra prediction mode and / or intra prediction technology, the reference samples can be located in the neighbors of the current block or can be placed separately. The intra prediction mode may include multiple non-directional modes and multiple directional modes. The non-directional mode may include, for example, a DC mode and a plane mode. Depending on the level of detail of the prediction direction, the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used according to the settings. The intra prediction unit 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0068] 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, motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter 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 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.

[0069] The prediction unit may generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit may not only apply intra prediction or inter prediction, but may also apply intra prediction and inter prediction simultaneously to predict the current block. The prediction method of applying both intra prediction and inter prediction simultaneously to predict the current block may be referred to as combined inter and intra prediction (CIIP). In addition, the prediction unit may perform intra block copying (IBC) to predict the current block. Intra block copying may be used for content image / video encoding of games, etc., such as screen content coding (SCC). IBC is a method of predicting the current picture using a previously reconstructed reference block in the current picture at a position separated by a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to a predetermined distance. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one inter prediction technique described in the present disclosure.

[0070] The prediction signal generated by the prediction unit can be used to generate a reconstruction signal or to generate a residual signal. The subtractor 115 can generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (prediction block or prediction sample array) output from the prediction unit from the input image signal (original block or original sample array). The generated residual signal can be transmitted to the transformer 120.

[0071] The transformer 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT refers to a transform obtained from a graph when relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to square pixel blocks of the same size or may be applied to blocks of variable size instead of square.

[0072] 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.

[0073] 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.

[0074] The bitstream may be transmitted over 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) for transmitting a signal output from the entropy encoder 190 and / or a storage unit (not shown) for storing 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] Overview of Image Decoding Equipment

[0081] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure can be applied.

[0082] 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.

[0083] 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.

[0084] The image decoding device 200 having received a bit stream including video / image information may perform the same Figure 2 The image encoding device 100 may reconstruct the image 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).

[0085] 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 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the neighboring block and the decoding target block, or the information of the symbol / bin decoded in the previous stage to determine the context model, perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. The information related to the prediction in the information decoded by the entropy decoder 210 can be provided to the prediction unit (inter-frame predictor 260 and intra-frame prediction unit 265), and the residual value of the entropy decoding performed on it in the entropy decoder 210, that is, the quantized transform coefficient and related parameter information can be input to the dequantizer 220. In addition, the information about filtering in the information decoded by the entropy decoder 210 can be provided to the filter 240. In addition, a receiver (not shown) for receiving a signal output from the image encoding apparatus may be further configured as an internal / external element of the image decoding apparatus 200 , or the receiver may be a component of the entropy decoder 210 .

[0086] In addition, the image decoding device according to the present disclosure may be referred to as a video / image / picture decoding device. The image decoding device may be divided into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, or at least one of an intra-frame prediction unit 265.

[0087] The dequantizer 220 may dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 220 may rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may dequantize the quantized transform coefficients by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficients.

[0088] The inverse transformer 230 may inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0089] 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).

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] The (modified) reconstructed picture stored in the DPB of the memory 250 can be used as a reference picture in the inter-frame predictor 260. The memory 250 can store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information can be transmitted to the inter-frame predictor 260 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 250 can store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0096] 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.

[0097] Coding layers and structure

[0098] The encoded video / image of the present disclosure may be processed according to, for example, the encoding layers and structures to be described later.

[0099] Figure 4 is a diagram illustrating a hierarchical structure for a coded image.

[0100] The coded image is classified into a video coding layer (VCL) for the image decoding process and handling itself, a lower system for transmitting and storing coded information, and a network abstraction layer (NAL) existing between the VCL and the lower system and responsible for a network adaptation function.

[0101] In the VCL, VCL data including compressed image data (slice data) can 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 the decoding process of the image can be generated.

[0102] 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.

[0103] like Figure 4 As shown, NAL units can be classified into VCL NAL units and non-VCL NAL units according to the RBSP generated in the VCL. A VCL NAL unit may refer to a NAL unit including information about an image (slice data), and a non-VCL NAL unit may refer to a NAL unit including information required for decoding an image (parameter set or SEI message).

[0104] The VCL NAL unit and the non-VCL NAL unit may be attached with header information and transmitted through a network according to the data format of a lower system. For example, the NAL unit may be modified into data having a predetermined data format (e.g., H.266 / VVC file format, RTP (Real-time Transport Protocol) or TS (Transport Stream)) and transmitted through various networks.

[0105] As described above, in a NAL unit, a NAL unit type may be specified according to an RBSP data structure included in a corresponding NAL unit, and information on the NAL unit type may be stored in a NAL unit header and signaled.

[0106] For example, NAL units can be broadly classified into VCL NAL unit types and non-VCL NAL unit types according to whether they contain information about a picture (slice data). VCL NAL unit types can be classified according to the nature and type of the picture included in the VCL NAL unit, and non-VCL NAL unit types can be classified according to the type of parameter set, etc.

[0107] The following are examples of NAL unit types specified according to the type of parameter sets included in a non-VCL NAL unit type.

[0108] -APS (Adaptation Parameter Set) NAL unit: Type for NAL units containing APS

[0109] -DPS (Decoding Parameter Set) NAL unit: Type for the NAL unit containing the DPS

[0110] -VPS (Video Parameter Set) NAL unit: Type for the NAL unit containing the VPS

[0111] -SPS (Sequence Parameter Set) NAL unit: Type for the NAL unit containing the SPS

[0112] -PPS (Picture Parameter Set) NAL unit: Type for the NAL unit containing the PPS

[0113] The above-mentioned NAL unit type may have syntax information about the NAL unit type, and the syntax information may be stored in the NAL unit header and signaled. For example, the syntax information may include nal_unit_type, and the NAL unit type may be specified by the nal_unit_type value.

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

[0115] In the present disclosure, the image / video information encoded and signaled in the form of a bit stream from the image encoding device 100 to the image decoding device 200 may include information related to segmentation within a picture, intra-frame / inter-frame prediction information, residual information, in-loop filtering information, etc., as well as information included in a slice header, information included in an APS, information included in a PPS, information included in an SPS, and / or information included in a VPS.

[0116] SEI news

[0117] DRAP (Related Random Access Point)

[0118] A DRAP picture may simply refer to a previous IRAP (Intra Random Access Point) picture and may be an inter-coded picture that provides a random access point to the bitstream of a DRAP picture when an IRAP picture is available. A DRAP picture may be indicated in the bitstream by a SEI message.

[0119] A picture associated with the DRAP indication SEI message may be referred to as a DRAP picture, and an example of the DRAP indication SEI message is shown in Table 1.

[0120] [Table 1]

[0121] dependent_rap_indication(payloadSize){ Descriptors }

[0122] The presence of the DRAP indication SEI message may indicate constraints on the reference and order of the picture. These constraints may enable the image decoding device 200 to properly decode the DRAP picture. In addition, these constraints may enable the image decoding device 200 to properly decode the pictures after both the decoding order and the output order while existing in the same layer without decoding any other pictures of the same layer except the IRAP picture associated with the DRAP picture.

[0123] The constraints for the presence indication of the SEI message through the DRAP indication may be as follows:

[0124] -DRAP screen is the trailing screen.

[0125] - A DRAP picture has a temporal sublayer identifier equal to 0.

[0126] - A DRAP picture does not include any picture in the same layer that is present in a valid entry in the reference picture list, except its associated IRAP picture.

[0127] - Any picture present in the same layer and following the DRAP picture in both decoding order and output order does not include any picture present in the same layer and preceding the DRAP picture in decoding order or output order in the valid entries of the reference picture list (except the associated IRAP picture of the DRAP picture).

[0128] EDRAP (Extended DRAP)

[0129] An EDRAP picture may be a DRAP picture based on only some of the pictures in a picture set. A picture set may consist of an associated IRAP picture and a specific EDRAP picture between the associated IRAP picture and the specific EDRAP picture in decoding order. An EDRAP picture may be used as a random access point as long as an associated IRAP picture or an EDRAP picture is provided.

[0130] A picture associated with the EDRAP indication SEI message may be referred to as an EDRAP picture.

[0131] The presence of the EDRAP indication SEI message may indicate constraints on the reference to the picture and the order of the pictures. These constraints may enable the image decoding device 200 to properly decode the EDRAP picture. In addition, these constraints may enable the image decoding device 200 to properly decode the pictures that are later in the decoding order and output order while existing in the same layer, without having to decode any other pictures of the same layer except for the list of picture referenceablePictures. Here, the list of picture referenceablePictures may consist of a list of IRAP or EDRAP pictures in decoding order that are present in the same coding layer video sequence (CLVS) and identified by the edrap_ref_rap_id[i] syntax element.

[0132] The constraints for the presence indication of the SEI message via EDRAP may be as follows:

[0133] -EDRAP picture is the trailing picture.

[0134] - EDRAP pictures have a temporal sub-layer identifier equal to 0.

[0135] - EDRAP pictures do not include any pictures in the same layer that are present in a valid entry in the reference picture list except referenceablePictures.

[0136] - Any picture present in the same layer and following the EDRAP picture in decoding order and output order does not include any picture in the same layer and preceding the EDRAP picture in decoding order or output order, except referenceablePictures.

[0137] - The pictures included in referenceablePictures do not include pictures at earlier positions in the valid entry of the reference picture list that exist in the same layer but do not exist in referenceablePictures. Therefore, even if the first picture in referenceablePictures is an EDRAP picture rather than an IRAP picture, the picture does not include pictures from the same layer in the valid entry of the reference picture list.

[0138] An example of the EDRAP indication SEI message is shown in Table 2.

[0139] [Table 2]

[0140] extended_drap_indication(payloadSize){ Descriptors edrap_rap_id_minus1 u(16) edrap_leading_pictures_decodable_flag u(1) edrap_reserved_zero_12bits u(12) edrap_num_ref_rap_pics_minus1 u(3) for(i=0;i<=edrap_num_ref_rap_pics_minus1;i++) edrap_ref_rap_id[i] u(16) }

[0141] The value of edrap_rap_id_minus1 plus 1 represents the RAP picture identifier RapPicId of the EDRAP picture. Each IRAP or EDRAP picture is associated with a RapPicId. The RapPicId value of an IRAP picture may be inferred to be 0. The RapPicId values ​​of any two EDRAP pictures associated with the same IRAP picture shall be different.

[0142] edrap_leading_pictures_decodable_flag equal to 1 indicates that all of the constraints below apply.

[0143] - Pictures present in the same layer and following the EDRAP picture in decoding order shall follow in output order the pictures present in the same layer and preceding the EDRAP picture in decoding order.

[0144] - Pictures present in the same layer and following the EDRAP picture in decoding order but preceding the EDRAP picture in output order shall not include pictures in the same layer and preceding the EDRAP picture in decoding order that are present in valid entries in the reference picture list other than referenceablePictures.

[0145] When edrap_leading_pictures_decodable_flag is equal to 0, the above constraints are not imposed.

[0146] In the bitstream, the value of edrap_reserved_zero_12bits shall be equal to 0. Other values ​​of edrap_reserved_zero_12bits are reserved for future definition, and the image decoding device 200 shall ignore the value of edrap_reserved_zero_12bits.

[0147] The value of edrap_num_ref_rap_pics_minus1 plus 1 represents the number of IRAPs or EDRAP pictures that exist in the same CLVS as the EDRAP picture and that can be included in the valid entries of the reference picture list of the EDRAP picture.

[0148] edrap_ref_rap_id[i] represents the RapPicId of the i-th RAP picture that may be included in a valid entry in the reference picture list of the EDRAP picture. The i-th RAP picture shall be an IRAP picture associated with the current EDRAP picture, or an EDRAP picture associated with the same IRAP picture as the current EDRAP picture.

[0149] Implementation

[0150] According to the current EDRAP SEI message, a picture indicated as an EDRAP picture may be associated with a leading picture. A leading picture is a picture that follows the EDRAP picture in decoding order but precedes the EDRAP picture in output order. An associated leading picture indicated as an EDRAP picture may be a decodable leading picture or a non-decodable leading picture. Whether an EDRAP picture is decodable may be indicated by a flag edrap_leading_pictures_decodable_flag signaled in the EDRAP SEI message.

[0151] If the decoding process starts from an EDRAP picture (i.e., random access from an EDRAP picture), the leading picture associated with the undecodable EDRAP picture needs to be removed from the bitstream for decoding. Considering this, the current design for the leading picture associated with the EDRAP picture may have the following problems:

[0152] 1. The flag edrap_leading_pictures_decodable_flag only indicates that the leading pictures associated with the EDRAP picture are decodable, not how many leading pictures are associated with the EDRAP picture. When performing random access from an EDRAP picture from which undecodable leading pictures should be removed, the only way to identify whether the picture following the EDRAP picture in decoding order is the leading picture is to derive the POC of the picture until the first non-leading picture associated with the EDRAP is found. This is quite different from removing undecodable pictures associated with CRA (i.e., RSAL pictures), because such pictures are easily identifiable from the NAL unit header.

[0153] 2. In the current design, all leading pictures associated with an EDRAP picture are indicated in binary whether they are decodable. It may be desirable to allow a mixture of decodable leading pictures and non-decodable leading pictures (such as RASL and RADL pictures associated with CRA pictures). Allowing the identification of leading pictures associated with an EDRAP picture without the need to derive a POC value may allow a mixture of decodable and non-decodable leading pictures associated with an EDRAP picture without any cost.

[0154] 3. In addition, in the case of bitstream reduction, signaling information in the EDRAP SEI message to indicate the type of leading picture associated with the EDRAP picture may be problematic. For example, pictures in higher temporal sublayers may be removed from the bitstream, and the removed pictures may include leading pictures associated with the EDRAP picture. In this case, after some pictures are removed, the EDRAP SEI message needs to be updated to ensure that it contains the correct information about the associated leading pictures.

[0155] In order to solve the above problems, the present disclosure proposes various embodiments. The embodiments described below can be performed individually or in combination of two or more embodiments.

[0156] First, embodiments proposed by the present disclosure are summarized as follows.

[0157] 1. When random access is performed starting from an EDRAP picture, the EDRAP picture may be associated with zero or more decodable leading pictures or undecodable leading pictures.

[0158] a. A decodable leading picture associated with an EDRAP picture may be referred to as a DADL picture (DRAP decodable leading picture).

[0159] b. A non-decodable leading picture associated with an EDRAP picture may be referred to as a DASL picture (DRAP Skipped Leading Picture).

[0160] 2. Any DASL picture associated with an EDRAP picture shall precede the DADL picture associated with the EDRAP picture in the output order.

[0161] 3. Any DADL picture associated with an EDRAP picture shall not reference any DASL picture associated with the EDRAP picture or any picture preceding the EDRAP picture in decoding order (except referenceablePictures).

[0162] 4. Any picture following an EDRAP picture in decoding order and output order shall not reference a DASL picture associated with the EDRAP picture or a picture preceding the EDRAP picture in decoding order, except referenceable Pictures.

[0163] 5. Use a new SEI message to indicate that the picture is a DASL picture. This SEI message may be referred to as a DASL indication SEI message.

[0164] 6. Use a new SEI message to indicate that the picture is a DADL picture. This SEI message may be called a DADL indication SEI message.

[0165] 7. Alternatively, a new SEI message is used to indicate a picture as a leading picture associated with an EDRAP picture. This SEI message may be referred to as an EDRAP leading picture SEI message. The SEI message includes a flag indicating the leading picture type of the picture (ie, DADL picture or DASL picture).

[0166] 8. Instead of signaling edrap_leading_pictures_decodable_flag, the flag is changed to indicate whether the indicated EDRAP picture has an associated leading picture. The flag may be changed to edrap_leading_pictures_present_flag.

[0167] 9. If edrap_leading_pictures_present_flag is 1, the following information may be additionally signaled:

[0168] a. The number of leading pictures associated with the EDRAP picture

[0169] b. Number of undecodable leading pictures

[0170] c. Number of decodable leading pictures

[0171] d. When decodable leading pictures and undecodable leading pictures are mixed, a flag used to identify the type of leading picture

[0172] 10. Alternatively, a 2-bit indication is used to indicate the following:

[0173] a. First value: indicates that the EDRAP picture does not have an associated leading picture

[0174] b. Second value: The indicated EDRAP picture has one or more associated leading pictures, and all associated leading pictures are decodable leading pictures.

[0175] c. Third value: The indicated EDRAP picture has one or more associated leading pictures, and all the associated leading pictures are undecodable leading pictures.

[0176] d. Fourth value: The indicated EDRAP picture has one or more associated leading pictures, and the associated leading pictures are a mixture of undecodable leading pictures and decodable leading pictures.

[0177] 10. If the value of the 2-bit indication is not the first value, the following information is additionally signaled:

[0178] a. Number of leading pictures

[0179] b. If the value indicated by the 2 bits is equal to the fourth value, the flag is used to indicate the type of the leading picture

[0180] 11. If the leading picture associated with an EDRAP picture is removed from the bitstream due to bitstream extraction / reduction (ie, pictures of higher temporal sub-layers are removed), the EDRAP SEI message associated with the EDRAP picture needs to be updated to ensure correct signaling of the leading picture.

[0181] Figure 5 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure, and Figure 6 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0182] Reference Figure 5 , the image encoding apparatus 100 may identify a leading picture (S510). The leading picture may be a picture associated with the EDRAP picture. In addition, the leading picture may be a picture that is before the EDRAP picture in the decoding order but after the EDRAP picture in the output order. The leading picture may include at least one of a decodable leading picture (DADL picture) or an undecodable leading picture (DASL picture).

[0183] The image encoding apparatus 100 may encode the SEI message based on the result of identifying the leading picture (S520). The SEI message may be an SEI message for the EDRAP picture. That is, the SEI message may be an EDRAP SEI message associated with the EDRAP picture. The result of identifying the leading picture may be a determination result on whether there is a leading picture, the number of leading pictures, the type of leading picture (DADL picture or DASL picture), etc.

[0184] Reference Figure 6, the image decoding apparatus 200 may obtain an SEI message from the bitstream (S610). The SEI message may be an SEI message for an EDRAP picture. That is, the SEI message may be an EDRAP SEI message associated with the EDRAP picture. The result of identifying the leading picture may be a determination result on whether there is a leading picture, the number of leading pictures, the type of leading picture (DADL picture or DASL picture), etc.

[0185] The image decoding apparatus 200 may identify a leading picture based on the SEI message (S620). The leading picture may be a picture associated with the EDRAP picture. In addition, the leading picture may be a picture that is before the EDRAP picture in the decoding order but after the EDRAP picture in the output order. The leading picture may include at least one of a decodable leading picture (DADL picture) or an undecodable leading picture (DASL picture).

[0186] Implementation Method 1

[0187] The SEI message may include at least one of a second SEI message for indicating a DASL picture or a first SEI message for indicating a DADL picture.

[0188] Table 3 shows an example of a DASL indication SEI message (DRAP skip preamble indication SEI message) as the second SEI message for indicating a DASL picture.

[0189] [Table 3]

[0190] drap_skipped_indication(payloadSize){ Descriptors }

[0191] A picture associated with the second message may be referred to as a DASL picture.A DASL picture associated with an EDRAP picture may be constrained to follow the associated EDRAP picture in decoding order but precede the EDRAP picture in output order.

[0192] In addition, any picture that exists in the same layer and follows the EDRAP picture in both decoding order and output order may be constrained so that any picture associated with the EDRAP picture or any picture that exists in the same layer and precedes the EDRAP picture in decoding order is not included in the valid entries of the reference picture list. However, this constraint may not be applied to referenceablePictures.

[0193] Table 4 shows an example of a DADL indication SEI message (DADL decodable preamble indication SEI message) which is a first SEI message for indicating a DADL picture.

[0194] [Table 4]

[0195] drap_decodable_indication(payloadSize){ Descriptors }

[0196] A picture associated with the first message may be referred to as a DADL picture.A DADL picture associated with an EDRAP picture may be constrained to follow the associated EDRAP picture in decoding order but precede the EDRAP picture in output order.

[0197] In addition, a DADL picture associated with an EDRAP picture may be constrained to follow a DASL picture associated with the EDRAP picture in output order. In addition, it may be proposed that a DADL picture associated with an EDRAP picture does not reference a DASL picture associated with the EDRAP picture or any picture belonging to the same layer and preceding the EDRAP picture in decoding order. However, this constraint may not apply to referenceablePictures.

[0198] Implementation Method 2

[0199] The SEI message may include a single SEI message to indicate the type of the leading picture (DADL picture and DASL picture).

[0200] Table 5 shows an example of an EDRAP preamble indication SEI message as a SEI message for indicating a DADL picture and a DASL picture.

[0201] [Table 5]

[0202] edrap_leading_picture_indication(payloadSize){ Descriptors dasl_pictures_flag u(1) }

[0203] In Table 5, dasl_picture_flag may indicate the type of picture associated with the EDRAP preamble indication SEI message. dasl_picture_flag equal to 1 indicates that the picture associated with the EDRAP preamble indication SEI message is a DASL picture, and dasl_picture_flag equal to 0 indicates that the picture associated with the EDRAP preamble indication SEI message is a DADL picture.

[0204] A picture associated with the EDRAP leading indication SEI message may be referred to as a leading picture associated with the EDRAP picture. When random access is performed from the associated EDRAP picture, the leading picture associated with the EDRAP picture may be decodable or undecodable. A decodable leading picture associated with the EDRAP picture may be referred to as a DADL picture, and an undecodable leading picture associated with the EDRAP picture may be referred to as a DASL picture.

[0205] Additionally, the following constraints may be applied to the EDRAP Preamble Indication SEI message:

[0206] - Any DADL picture associated with an EDRAP picture may be constrained such that a DASL picture associated with the EDRAP picture or any picture belonging to the same layer and preceding the EDRAP picture in decoding order is not included in the valid entries of the reference picture list. However, this constraint may not apply to referenceablePictures.

[0207] - Any picture belonging to the same layer and preceding the EDRAP picture in decoding order and output order may be constrained so that a DASL picture associated with the EDRAP picture or any picture belonging to the same layer and preceding the EDRAP picture in decoding order is not included in the valid entries of the reference picture list. However, this constraint may not apply to referenceablePictures.

[0208] Implementation 3

[0209] Table 6 shows an example of an extended DRAP indication SEI message as a SEI message for indicating information about an EDRAP picture.

[0210] [Table 6]

[0211]

[0212] A picture associated with an EDRAP indication SEI message may be referred to as an EDRAP picture. The presence of an EDRAP indication SEI message may indicate constraints on the order of pictures and references to pictures. These constraints may enable the image decoding device 200 to properly decode an EDRAP picture (a decodable leading picture associated with an EDRAP picture). In addition, these constraints may enable the image decoding device 200 to properly decode pictures that follow and exist in the same layer at the same time in decoding order and output order without having to decode any other pictures of the same layer except for the list of picture referenceablePictures. Here, the list of picture referenceablePictures may consist of a list of IRAP or EDRAP pictures in decoding order that exist in the same CLVS and are identified by the edrap_ref_rap_id[i] syntax element.

[0213] The constraints for the presence indication of the SEI message via EDRAP may be as follows:

[0214] -EDRAP picture is the trailing picture.

[0215] - EDRAP pictures have a temporal sub-layer identifier equal to 0.

[0216] - Except for referenceablePictures, EDRAP pictures do not include any pictures that exist in the same layer as a valid entry in the reference picture list.

[0217] - Any picture present in the same layer and following the EDRAP picture in both decoding order and output order does not include pictures in the same layer and preceding the EDRAP picture in both decoding order or output order that are present in a valid entry in the reference picture list (except referenceablePictures).

[0218] In addition, the following constraints applied in the conventional method may be changed to not be applied.

[0219] - The pictures included in referenceablePictures do not include pictures in the same layer that exist in the valid entry of the reference picture list but do not exist at an earlier position in referenceablePictures. Therefore, even if the first picture in referenceablePictures is an EDRAP picture rather than an IRAP picture, the picture does not include pictures from the same layer in the valid entry of the reference picture list.

[0220] In Table 6, the value of edrap_rap_id_minus1 plus 1 represents the RAP picture identifier RapPicId of the EDRAP picture. Each IRAP or EDRAP picture is associated with a RapPicId. The RapPicId value of an IRAP picture may be inferred to be 0. The RapPicId values ​​for any two EDRAP pictures associated with the same IRAP picture shall be different from each other.

[0221] edrap_leading_pictures_present_flag may indicate whether an EDRAP picture has one or more associated leading pictures. edrap_leading_pictures_present_flag equal to 1 may indicate that the EDRAP picture has one or more associated leading pictures, and edrap_leading_pictures_present_flag equal to 0 may indicate that the EDRAP picture has no associated leading pictures.

[0222] edrap_num_dadl_pictures may indicate the number of DADL pictures associated with the EDRAP picture and may have a value between 0 and 255. edrap_num_dasl_pictures may indicate the number of DASL pictures associated with the EDRAP picture and may have a value between 0 and 255.

[0223] edrap_dasl_picture_flag[i] equal to 1 may indicate that the (i+1)th picture after the EDRAP picture in decoding order is a DASL picture, and edrap_dasl_picture_flag[i] equal to 0 may indicate that the (i+1)th picture after the EDRAP picture in decoding order is a DADL picture. When the value of edrap_num_dadl_pictures is 0, the value of edrap_dasl_picture_flag[i] may be inferred to be 1 for i having a value between 0 and edrap_num_dasl_pictures-1. When the value of edrap_num_dasl_pictures is 0, the value of edrap_dasl_picture_flag[i] may be inferred to be 0 for i having a value between 0 and edrap_num_dadl_pictures-1.

[0224] Additionally, the following constraints may apply:

[0225] - Any DASL picture associated with an EDRAP picture shall precede the DADL picture associated with the EDRAP picture in the output order.

[0226] - A DADL picture associated with an EDRAP picture shall not include any DASL picture associated with the EDRAP picture or any picture in a valid entry of a reference picture list belonging to the same layer and preceding the EDRAP picture in decoding order. However, this constraint may not apply to referenceablePictures.

[0227] - Any picture belonging to the same layer and following the EDRAP picture in both decoding order and output order shall not include any picture belonging to the same layer and preceding the EDRAP picture in decoding order in a valid entry of a DASL picture or reference picture list associated with the EDRAP picture. However, this constraint may not apply to referenceablePictures.

[0228] - If one or more leading pictures associated with an EDRAP picture are removed (ie, bitstream reduction is performed by removing pictures of a higher temporal sub-layer), the EDRAP SEI message needs to be updated to ensure accurate information about the leading pictures associated with the EDRAP picture.

[0229] In the bitstream, the value of edrap_reserved_zero_5bits shall be equal to 0. Other values ​​of edrap_reserved_zero_5bits are reserved for future definition, and the image decoding device 200 shall ignore the value of edrap_reserved_zero_5bits.

[0230] The value of edrap_num_ref_rap_pics_minus1 plus 1 indicates the number of IRAP pictures or EDRAP pictures that exist in the same CLVS as the EDRAP picture and that can be included in the valid entries of the reference picture list of the EDRAP picture.

[0231] edrap_ref_rap_id[i] represents the RapPicId of the i-th RAP picture that may be included in a valid entry in the reference picture list of the EDRAP picture. The i-th RAP picture shall be an IRAP picture associated with the current EDRAP picture, or an EDRAP picture associated with the same IRAP picture as the current EDRAP picture.

[0232] Figure 7 is a flowchart illustrating an image encoding method according to Embodiment 3, and Figure 8 This is a flowchart illustrating an image decoding method according to embodiment 3.

[0233] Reference Figure 7, the image encoding apparatus 100 may determine whether the EDRAP picture has one or more leading pictures (S710). If the EDRAP picture does not have one or more leading pictures, the image encoding apparatus 100 may encode the value of edrap_leading_pictures_present_flag as 0 (S770). Alternatively, if the EDRAP picture has one or more leading pictures, the image encoding apparatus 100 may encode the value of edrap_leading_pictures_present_flag as 1 (S720). In this case, the image encoding apparatus 100 may determine the number of DADL pictures and DASL pictures, and encode edrap_num_dadl_pictures indicating the number of DADL pictures and edrap_num_dasl_pictures indicating the number of DASL pictures (S720).

[0234] If both the number of DADL pictures and the number of DASL pictures are not 0 (S730), the image encoding apparatus 100 may determine the type of the picture following (after) the EDRAP picture. If the type of the subsequent picture is a DASL picture, the image encoding apparatus 100 may encode the value of edrap_dasl_picture_flag[i] as 1 (S750), and if the type of the subsequent picture is a DADL picture, the image encoding apparatus 100 may encode the value of edrap_dasl_picture_flag[i] as 0 (S760). Here, i may be 0 or greater, and may be less than the sum of the number of DADL pictures and the number of DASL pictures.

[0235] The image decoding apparatus 200 may obtain edrap_leading_pictures_present_flag from a bitstream (S810) and determine a value of edrap_leading_pictures_present_flag (S820). If the value of edrap_leading_pictures_present_flag is 1, the image decoding apparatus 200 may obtain edrap_num_dadl_pictures indicating the number of DADL pictures and edrap_num_dasl_pictures indicating the number of DASL pictures from the bitstream (S830).

[0236] The image decoding device 200 may determine whether the value of edrap_num_dadl_pictures is 0 and whether the value of edrap_num_dasl_pictures is 0 (S840). When both the value of edrap_num_dadl_pictures and the value of edrap_num_dasl_pictures are not 0, the image decoding device 200 may obtain edrap_dasl_picture_flag[i] from the bitstream (S850). Here, i may be greater than or equal to 0, and may be less than the sum of the value of edrap_num_dadl_pictures and the value of edrap_num_dasl_pictures.

[0237] The image decoding device 200 may determine the type of the leading picture based on edrap_num_dadl_pictures, edrap_num_dasl_pictures, and edrap_dasl_picture_flag[i]. For example, if the value of edrap_num_dadl_pictures is 0 and the value of edrap_num_dasl_pictures is not 0, all leading pictures may be determined as DASL pictures. As another example, if the value of edrap_num_dadl_pictures is not 0 and the value of edrap_num_dasl_pictures is 0, all leading pictures may be determined as DADL pictures. As another example, if the values ​​of edrap_num_dadl_pictures and edrap_num_dasl_pictures are both 0, the type of each leading picture may be determined by the value of edrap_dasl_picture_flag[i].

[0238] Implementation 4

[0239] Table 7 shows an example of an extended DRAP indication SEI message as a SEI message for indicating information about an EDRAP picture.

[0240] [Table 7]

[0241]

[0242] A picture associated with an EDRAP indication SEI message may be referred to as an EDRAP picture. The presence of an EDRAP indication SEI message may indicate constraints on the order of pictures and references to pictures. These constraints may enable the image decoding device 200 to properly decode an EDRAP picture (a decodable leading picture associated with an EDRAP picture). In addition, these constraints may enable the image decoding device 200 to properly decode pictures that follow and exist in the same layer at the same time in decoding order and output order without having to decode any other pictures of the same layer except for the list of picture referenceablePictures. Here, the list of picture referenceablePictures may consist of a list of IRAP or EDRAP pictures in decoding order that exist in the same CLVS and are identified by the edrap_ref_rap_id[i] syntax element.

[0243] The constraints for the presence indication of the SEI message via EDRAP may be as follows:

[0244] -EDRAP picture is the trailing picture.

[0245] - EDRAP pictures have a temporal sub-layer identifier equal to 0.

[0246] - An EDRAP picture does not include any picture in the same layer that is present in a valid entry in the reference picture list, except referenceablePictures.

[0247] - Any picture present in the same layer and following the EDRAP picture in both decoding order and output order does not include pictures in the same layer and preceding the EDRAP picture in both decoding order or output order that are present in a valid entry in the reference picture list (except referenceablePictures).

[0248] In addition, the following constraints applied in the conventional method may be changed to not be applied.

[0249] - The pictures included in referenceablePictures do not include pictures at earlier positions in the valid entry of the reference picture list that exist in the same layer but do not exist in referenceablePictures. Therefore, even if the first picture in referenceablePictures is an EDRAP picture rather than an IRAP picture, the picture does not include pictures from the same layer in the valid entry of the reference picture list.

[0250] In Table 7, the value of edrap_rap_id_minus1 plus 1 represents the RAP picture identifier RapPicId of the EDRAP picture. Each IRAP or EDRAP picture is associated with a RapPicId. The RapPicId value of an IRAP picture may be inferred to be 0. The RapPicId values ​​of any two EDRAP pictures associated with the same IRAP picture shall be different from each other.

[0251] edrap_leading_pictures_idc equal to 0 may indicate that the EDRAP picture has no associated leading pictures. edrap_leading_pictures_idc equal to 1 may indicate that the EDRAP picture has one or more associated leading pictures, and all associated leading pictures are DADL pictures. edrap_leading_pictures_idc equal to 2 may indicate that the EDRAP picture has one or more associated leading pictures, and all associated leading pictures are DASL pictures. edrap_leading_pictures_idc equal to 3 may indicate that the EDRAP picture has one or more associated leading pictures, and the associated leading pictures are a mixture of DADL pictures and DASL pictures.

[0252] edrap_num_leading_pictures may indicate the number of leading pictures associated with the EDRAP picture, and the value of edrap_num_leading_pictures may have a value between 0 and 255.

[0253] edrap_dasl_picture_flag[i] equal to 1 may indicate that the (i+1)th picture following the EDRAP picture in decoding order is a DASL picture, and edrap_dasl_picture_flag[i] equal to 0 may indicate that the (i+1)th picture following the EDRAP picture in decoding order is a DADL picture. When the value of edrap_leading_pictures_idc is 1, the value of edrap_dasl_picture_flag[i] may be inferred to be 0 for i having a value between 0 and edrap_num_leading_pictures-1. When the value of edrap_leading_pictures_idc is 2, the value of edrap_dasl_picture_flag[i] may be inferred to be 1 for i having a value between 0 and edrap_num_leading_pictures-1.

[0254] Additionally, the following constraints may apply:

[0255] - Any DASL picture associated with an EDRAP picture shall precede the DADL picture associated with the EDRAP picture in the output order.

[0256] - A DADL picture associated with an EDRAP picture shall not include any DASL picture associated with the EDRAP picture or any picture in a valid entry of a reference picture list belonging to the same layer and preceding the EDRAP picture in decoding order. However, this constraint may not apply to referenceablePictures.

[0257] - Any picture belonging to the same layer and following the EDRAP picture in both decoding order and output order shall not include any picture belonging to the same layer and preceding the EDRAP picture in decoding order in a valid entry of a DASL picture or reference picture list associated with the EDRAP picture. However, this constraint may not apply to referenceablePictures.

[0258] - If one or more leading pictures associated with an EDRAP picture are removed (ie, bitstream reduction is performed by removing pictures of a higher temporal sub-layer), the EDRAP SEI message needs to be updated to ensure accurate information about the leading pictures associated with the EDRAP picture.

[0259] In the bitstream, the value of edrap_reserved_zero_5bits shall be equal to 0. Other values ​​of edrap_reserved_zero_5bits are reserved for future definition, and the image decoding device 200 shall ignore the value of edrap_reserved_zero_5bits.

[0260] The value of edrap_num_ref_rap_pics_minus1 plus 1 indicates the number of IRAP pictures or EDRAP pictures that exist in the same CLVS as the EDRAP picture and that can be included in the valid entries of the reference picture list of the EDRAP picture.

[0261] edrap_ref_rap_id[i] represents the RapPicId of the i-th RAP picture that may be included in a valid entry in the reference picture list of the EDRAP picture. The i-th RAP picture shall be an IRAP picture associated with the current EDRAP picture, or an EDRAP picture associated with the same IRAP picture as the current EDRAP picture.

[0262] Fig. 9 is a flowchart illustrating an image encoding method according to Embodiment 4, and Fig.10This is a flowchart illustrating an image decoding method according to embodiment 4.

[0263] Reference Fig. 9 , the image encoding apparatus 100 may determine the number and / or type of leading pictures that the EDRAP picture has, and encode edrap_leading_pictures_idc indicating the number and / or type of leading pictures (S910). For example, if the EDRAP picture has no associated leading picture, the value of edrap_leading_pictures_idc may be encoded as 0, and if the EDRAP picture has one or more associated leading pictures and all associated leading pictures are DADL pictures, the value of edrap_leading_pictures_idc may be encoded as 1. In addition, if the EDRAP picture has one or more associated leading pictures and all associated leading pictures are DASL pictures, the value of edrap_leading_pictures_idc may be encoded as 2, and if the EDRAP picture has one or more associated leading pictures and the associated leading pictures are a mixture of DADL pictures and DASL pictures, the value of edrap_leading_pictures_idc may be encoded as 3.

[0264] When the EDRAP picture has one or more associated leading pictures (S920, edrap_leading_pictures_idc!=0), the image encoding apparatus 100 may encode edrap_num_leading_pictures indicating the number of associated leading pictures (S930).

[0265] When the associated leading picture is a mixture of DADL pictures and DASL pictures (S940), the image encoding apparatus 100 may encode edrap_dasl_picture_flag[i] indicating the type of each leading picture (S950). Here, i may be greater than or equal to 0 and less than the value of edrap_num_leading_pictures.

[0266] Reference Fig.10 , the image decoding apparatus 200 may obtain edrap_leading_pictures_idc from the bitstream (S1010), and determine whether the value of edrap_leading_pictures_idc is 0 (S1020). If the value of edrap_leading_pictures_idc is not 0, the image decoding apparatus 200 may obtain edrap_num_leading_pictures from the bitstream (S1030).

[0267] The image decoding apparatus 200 may determine whether the value of edrap_leading_pictures_idc is 3 (S1040). If the value of edrap_leading_pictures_idc is 3, the image decoding apparatus 200 may obtain edrap_dasl_picture_flag[i] from the bitstream (S1050). Here, i may be greater than or equal to 0 and less than the value of edrap_num_leading_pictures.

[0268] The image decoding device 200 may determine the type of the leading picture based on edrap_leading_pictures_idc and edrap_dasl_picture_flag[i]. For example, if the value of edrap_leading_pictures_idc is 1, all leading pictures may be determined as DADL pictures. As another example, if the value of edrap_leading_pictures_idc is 2, all leading pictures may be determined as DASL pictures. As yet another example, if the value of edrap_leading_pictures_idc is 3, the type of each leading picture may be determined according to the value of edrap_dasl_picture_flag[i].

[0269] Fig.11 is a diagram showing a content streaming system to which an embodiment of the present disclosure can be applied.

[0270] 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.

[0271] 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.

[0272] 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.

[0273] 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.

[0274] 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.

[0275] 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.

[0276] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0277] 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.

[0278] Industrial Applicability

[0279] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising the following steps: Obtaining a supplemental enhancement information SEI message for an extended associated random access point EDRAP picture from a bitstream; as well as Identifying, based on the SEI message, a leading picture that follows the EDRAP picture in decoding order and precedes the EDRAP picture in output order, The leading picture includes at least one of a decodable leading picture and an undecodable leading picture.

2. The image decoding method according to claim 1, wherein: The non-decodable leading picture is constrained to precede the decodable leading picture in output order.

3. The image decoding method according to claim 1, in, The decodable leading picture is constrained not to refer to the undecodable leading picture except for a predetermined picture, and The predetermined picture includes an intra random access point IRAP picture or an EDRAP picture belonging to the same coded layer video sequence CLVS.

4. The image decoding method according to claim 1, in, The decodable leading picture is constrained not to reference a picture preceding the EDRAP picture in decoding order except for a predetermined picture, and The predetermined picture includes an intra random access point IRAP picture or an EDRAP picture belonging to the same coded layer video sequence CLVS.

5. The image decoding method according to claim 1, in, Pictures following the EDRAP picture in decoding order and output order are constrained not to reference undecodable pictures except for predetermined pictures, and The predetermined picture includes an intra random access point IRAP picture or an EDRAP picture belonging to the same coded layer video sequence CLVS.

6. The image decoding method according to claim 1, in, Pictures following the EDRAP picture in decoding order and output order are constrained not to reference pictures preceding the EDRAP picture in decoding order except for predetermined pictures, and The predetermined picture includes an intra random access point IRAP picture or an EDRAP picture belonging to the same coded layer video sequence CLVS.

7. The image decoding method according to claim 1, wherein: The SEI message includes a first SEI message for indicating the decodable leading picture.

8. The image decoding method according to claim 1, wherein: The SEI message includes a second SEI message for indicating the undecodable leading picture.

9. The image decoding method according to claim 1, wherein: The SEI message includes a syntax element indicating whether the EDRAP picture includes the leading picture.

10. An image encoding method performed by an image encoding device, the image encoding method comprising the following steps: Identify the leading picture that follows the extended associated random access point EDRAP picture in decoding order and precedes the EDRAP picture in output order; as well as encoding a supplemental enhancement information SEI message for the EDRAP picture based on the result of identifying the leading picture, The leading picture includes at least one of a decodable leading picture and an undecodable leading picture.

11. A method for transmitting a bit stream generated by an image encoding method, the image encoding method comprising the following steps: Identify the leading picture that follows the extended associated random access point EDRAP picture in decoding order and precedes the EDRAP picture in output order; as well as encoding a supplemental enhancement information SEI message for the EDRAP picture based on the result of identifying the leading picture, The leading picture includes at least one of a decodable leading picture and an undecodable leading picture.

Images