Image encoding / decoding method, bitstream transmission method, and recording medium storing bitstream

Abstract

An image encoding / decoding method, a bitstream transmission method, and a computer-readable recording medium for storing a bitstream are provided. An image decoding method according to the present disclosure may be an image decoding method performed by an image decoding device, including the steps of: obtaining a supplemental enhancement information (SEI) message for an extended dependent random access point (EDRAP) picture from a bitstream; and identifying, based on the SEI message, a leading picture that follows the EDRAP picture in decoding order but precedes the EDRAP picture in output order, wherein the leading picture includes at least one of a decodable leading picture and a non-decodable leading 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 storing the bitstream, and more particularly to an image encoding / decoding method based on a method for identifying a leading picture, a method for transmitting a bitstream, and a recording medium storing the bitstream. [Background technology]

[0002] Recently, demand for high-resolution, high-quality images, such as HD (High Definition) images and UHD (Ultra High Definition) images, has been increasing in various fields. As image data becomes higher in resolution and quality, the amount of information or bits to be transmitted increases relatively compared to conventional image data. The increase in the amount of information or bits to be transmitted results in an increase in transmission costs and storage costs.

[0003] This requires highly efficient image compression techniques for effectively transmitting, storing, and reproducing high-resolution, high-quality image information. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0005] The present disclosure also aims to propose a method for identifying a leading picture.

[0006] The present disclosure also aims to apply various restrictions to the decoding order and output order of leading pictures.

[0007] This disclosure also aims to propose definitions for decodable and non-decodable leading pictures.

[0008] The present disclosure also aims to provide a mix of decodable and non-decodable leading pictures.

[0009] Another object of the present disclosure is to provide a non-transitory computer-readable recording medium for storing a bitstream that is received by an image decoding device according to the present disclosure, decoded, and used to restore an image.

[0010] Another object of the present disclosure is to provide a method for transmitting a bitstream generated by the image encoding method according to the present disclosure.

[0011] The technical problems to be solved by the present disclosure are not limited to the above-mentioned technical problems, and other technical problems not mentioned above will be clearly understood by a person having ordinary skill in the technical field to which the present disclosure pertains from the following description. [Means for solving the problem]

[0012] An image decoding method according to one aspect of the present disclosure is an image decoding method performed by an image decoding device, and includes the steps of obtaining an SEI (supplemental enhancement information) message for an EDRAP (extended dependent random access point) picture from a bitstream, and identifying, based on the SEI message, a leading picture that follows the EDRAP picture in decoding order but precedes the EDRAP picture in output order, wherein the leading picture may include at least one of a leading picture that can be decoded and a leading picture that cannot be decoded.

[0013] An image encoding method according to another aspect of the present disclosure may be an image encoding method performed by an image encoding device, comprising: a step of identifying a leading picture that follows an EDRAP (extended dependent random access point) picture in decoding order but precedes the EDRAP picture in output order; and a step of encoding an SEI (supplemental enhancement information) message for the EDRAP picture based on the identification result of the leading picture, wherein the leading picture includes at least one of a leading picture that can be decoded and a leading picture that cannot be decoded.

[0014] A computer-readable recording medium according to another aspect of the present disclosure can store a bitstream generated by the image encoding method or apparatus of the present disclosure.

[0015] A transmission method according to another aspect of the present disclosure can transmit a bitstream generated by the image coding method or apparatus of the present disclosure.

[0016] The features described above in this brief summary of the present disclosure are merely exemplary aspects of the detailed description of the present disclosure that follows and are not intended to limit the scope of the present disclosure. [Effects of the Invention]

[0017] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0018] Furthermore, according to the present disclosure, the method for identifying whether or not a character is a leading character can be simplified.

[0019] Additionally, according to this disclosure, a mix of decodable and non-decodable leading pictures may be allowed.

[0020] According to the present disclosure, a non-transitory computer-readable recording medium for storing a bitstream generated by the image encoding method according to the present disclosure can also be provided.

[0021] Furthermore, according to the present disclosure, a non-transitory computer-readable recording medium can be provided that stores a bitstream that is received by an image decoding device according to the present disclosure, decoded, and used to restore an image.

[0022] Furthermore, the present disclosure can provide a method for transmitting a bitstream generated by an image coding method.

[0023] The effects obtained by the present disclosure are not limited to the effects described above, and other effects not described above will be clearly understood by those having ordinary skill in the art to which the present disclosure pertains from the following description. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a diagram illustrating a video coding system to which embodiments of the present disclosure can be applied; [Figure 2] 1 is a diagram schematically illustrating an image encoding device to which an embodiment of the present disclosure can be applied. [Figure 3] FIG. 1 is a diagram schematically illustrating an image decoding device to which an embodiment of the present disclosure can be applied. [Figure 4] 1 illustrates an example of a coding hierarchy and structure to which an embodiment of the present disclosure can be applied. [Figure 5] 1 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure. [Figure 6] 1 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure. [Figure 7] 10 is a flowchart illustrating an image encoding method according to another embodiment of the present disclosure. [Figure 8] 10 is a flowchart illustrating an image decoding method according to another embodiment of the present disclosure. [Figure 9]10 is a flowchart illustrating an image encoding method according to another embodiment of the present disclosure. [Figure 10] 10 is a flowchart illustrating an image decoding method according to another embodiment of the present disclosure. [Figure 11] 1 is a diagram illustrating an exemplary content streaming system to which an embodiment of the present disclosure can be applied; DETAILED DESCRIPTION OF THE INVENTION

[0025] The present disclosure will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the present disclosure. However, the present disclosure may be embodied in various different forms and is not limited to the embodiments described herein.

[0026] In describing the embodiments of the present disclosure, if it is determined that a detailed description of a known configuration or function may obscure the gist of the present disclosure, the detailed description thereof will be omitted. In addition, in the drawings, parts that are not related to the description of the present disclosure will be omitted, and similar parts will be designated by similar reference numerals.

[0027] In this disclosure, when a component is referred to as being "coupled," "coupled," or "connected" to another component, this includes not only a direct connection, but also an indirect connection where another component exists between them. Furthermore, when a component is referred to as "including" or "having" another component, this does not mean that the other component is excluded, but that the component can further include the other component, unless otherwise specified.

[0028] In this disclosure, terms such as "first" and "second" are used only to distinguish one component from another component, and do not limit the order or importance of the components unless otherwise specified. Therefore, within the scope of this 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.

[0029] In this disclosure, components that are distinguished from one another are used to clearly describe the characteristics of each component and do not necessarily mean that the components are separate. In other words, multiple components may be integrated into a single hardware or software unit, or a single component may be distributed into multiple hardware or software units. Therefore, even if not otherwise specified, such integrated or distributed embodiments are also included within the scope of this disclosure.

[0030] In this disclosure, the components described in various embodiments are not necessarily essential components, and some may be optional components. Therefore, an embodiment consisting of a subset of the components described in one embodiment is also within the scope of this disclosure. Furthermore, an embodiment including other components in addition to the components described in various embodiments is also within the scope of this disclosure.

[0031] The present disclosure relates to image encoding and decoding, and terms used in this disclosure may have their ordinary meaning in the technical field to which the present disclosure belongs unless they are newly defined in this disclosure.

[0032] In this disclosure, a "picture" generally refers to a unit representing any one image in a specific time period, and a slice / tile is a coding unit constituting a part of a picture, and one picture may be composed of one or more slices / tiles. Furthermore, a slice / tile may include one or more coding tree units (CTUs).

[0033] In this disclosure, "pixel" or "pel" may refer to the smallest unit constituting one picture (or image). Also, "sample" may be used as a term corresponding to pixel. A sample may generally indicate a pixel or a pixel value, and may indicate only a pixel / pixel value of a luma component, or may indicate only a pixel / pixel value of a chroma component.

[0034] In this disclosure, the term "unit" may refer to a basic unit of image processing. A unit may include at least one of a specific region of a picture and information related to that region. The term "unit" may be used interchangeably with terms such as "sample array," "block," or "area," depending on the situation. In general, an M×N block may include a set (or array) of samples or transform coefficients consisting of M columns and N rows.

[0035] In the present disclosure, a "current block" may refer to any one of a "current coding block," a "current coding unit," a "block to be coded," a "block to be decoded," or a "block to be processed." When prediction is performed, a "current block" may refer to a "current predicted block" or a "block to be predicted." When transformation (inverse transformation) / quantization (inverse quantization) is performed, a "current block" may refer to a "current transformed block" or a "block to be transformed." When filtering is performed, a "current block" may refer to a "block to be filtered."

[0036] Furthermore, in this disclosure, unless explicitly stated as a chroma block, the term "current block" may refer to a block including both a luma component block and a chroma component block, or the "luma block of the current block." The luma component block of the current block may be expressed explicitly as a "luma block" or a "current luma block," including the explicit description of the luma component block. Furthermore, the chroma component block of the current block may be expressed explicitly as a "chroma block" or a "current chroma block," including the explicit description of the chroma component block.

[0037] In the present disclosure, " / " and "," can be interpreted as "and / or." For example, "A / B" and "A, B" can be interpreted as "A and / or B." Also, "A / B / C" and "A, B, C" can mean "at least one of A, B, and / or C."

[0038] In this disclosure, "or" can be interpreted as "and / or." For example, "A or B" can mean 1) only "A," 2) only "B," or 3) "A and B." Alternatively, in this disclosure, "or" can mean "additionally or alternatively."

[0039] Video Coding System Overview

[0040] FIG. 1 is a diagram illustrating a video coding system to which embodiments of the present disclosure can be applied.

[0041] A video coding system according to one embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may transmit encoded video and / or image information or data to the decoding device 20 in a file or streaming format via a digital storage medium or a network.

[0042] An encoding device 10 according to an embodiment may include a video source generation unit 11, an encoding unit 12, and a transmission unit 13. A decoding device 20 according to an embodiment may include a reception unit 21, a decoding unit 22, and a rendering unit 23. The encoding unit 12 may be referred to as a video / image encoding unit, and the decoding unit 22 may be referred to as a video / image decoding unit. The transmission unit 13 may be included in the encoding unit 12. The reception unit 21 may be included in the decoding unit 22. The rendering unit 23 may include a display unit, which may be configured as a separate device or an external component.

[0043] The video source generation unit 11 can acquire video / images through a video / image capture, synthesis, or generation process. The video source generation unit 11 can include a video / image capture device and / or a video / image generation device. The video / image capture device can include, for example, one or more cameras, a video / image archive containing previously captured video / images, etc. The video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate video / images. For example, virtual video / images can be generated via a computer, etc., in which case the video / image capture process can be replaced with a process in which related data is generated.

[0044] The encoder 12 may encode the input video / image. The encoder 12 may perform a series of steps such as prediction, transformation, and quantization for compression and coding efficiency. The encoder 12 may output the encoded data (encoded video / image information) in a bitstream format.

[0045] The transmitting unit 13 can acquire coded video / image information or data output in a bitstream format and transmit it to the receiving unit 21 of the decoding device 20 or another external object in a file or streaming format via a digital storage medium or a network. Digital storage media can include various storage media such as USB, SD, CD, DVD, Blu-ray®, HDD, and SSD. The transmitting unit 13 can include elements for generating a media file in a predetermined file format and elements for transmitting it via a broadcasting / communication network. The transmitting unit 13 can be provided as a transmitting device separate from the encoding device 12. In this case, the transmitting device can include at least one processor for acquiring coded video / image information or data output in a bitstream format and a transmitting unit for transmitting it in a file or stream format. The receiving unit 21 can extract / receive the bitstream from the storage medium or network and transmit it to the decoding unit 22.

[0046] The decoding unit 22 can decode the video / image by performing a series of steps such as inverse quantization, inverse transformation, and prediction corresponding to the operations of the encoding unit 12.

[0047] The rendering unit 23 can render the decoded video / images, and the rendered video / images can be displayed via the display unit.

[0048] Overview of the image encoding device

[0049] FIG. 2 is a diagram schematically illustrating an image encoding device to which an embodiment of the present disclosure can be applied.

[0050] 2, the image encoding device 100 may include an image division unit 110, a subtraction unit 115, a transform unit 120, a quantization unit 130, an inverse quantization unit 140, an inverse transform unit 150, an addition unit 155, a filtering unit 160, a memory 170, an inter prediction unit 180, an intra prediction unit 185, and an entropy encoding unit 190. The inter prediction unit 180 and the intra prediction unit 185 may be collectively referred to as a "prediction unit." The transform unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transform unit 150 may be included in a residual processing unit. The residual processing unit may further include a subtraction unit 115.

[0051] Depending on the embodiment, all or at least some of the components constituting the image encoding device 100 may be realized by a single hardware component (e.g., an encoder or a processor). Also, the memory 170 may include a decoded picture buffer (DPB) and may be realized by a digital storage medium.

[0052] The image division unit 110 may divide an input image (or picture, frame) input to the image encoding device 100 into one or more processing units. As an example, the processing units may be called coding units (CUs). The coding units may be obtained by recursively dividing a coding tree unit (CTU) or a largest coding unit (LCU) using a QT / BT / TT (quad-tree / binary-tree / ternary-tree) structure. For example, one coding unit may be divided into multiple coding units at deeper depths based on a quad-tree structure, a binary-tree structure, and / or a ternary-tree structure. To divide the coding units, the quad-tree structure may be applied first, and then the binary-tree structure and / or the ternary-tree structure may be applied later. The coding procedure according to the present disclosure may be performed based on the final coding unit that is not further divided. The maximum coding unit may be used as the final coding unit, or a lower-depth coding unit obtained by dividing the maximum coding unit may be used as the final coding unit. Here, the coding procedure may include procedures such as prediction, transformation, and / or reconstruction, which will be described later. As another example, a processing unit of the coding procedure may be a prediction unit (PU) or a transform unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit, respectively. The prediction unit may be a unit of sample prediction, and the transform unit may be a unit for deriving transform coefficients and / or a unit for deriving a residual signal from the transform coefficients.

[0053] The prediction unit (inter prediction unit 180 or intra prediction unit 185) may perform prediction on a current block (current block) to generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block or CU. The prediction unit may generate various information related to prediction of the current block and transmit it to the entropy coding unit 190. The prediction information may be coded by the entropy coding unit 190 and output in a bitstream format.

[0054] The intra prediction unit 185 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located far away from the current block according to the intra prediction mode and / or intra prediction technique. The intra prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes may include, for example, DC mode and Planar mode. The directional modes may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the granularity of the prediction direction. However, this is merely an example, and more or less directional prediction modes may be used depending on the settings. The intra prediction unit 185 may also determine the prediction mode to be applied to the current block using the prediction modes applied to neighboring blocks.

[0055] The inter prediction unit 180 may derive a predicted block for a current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation between the motion information of neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on the inter prediction direction (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). 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 called a collocated reference block, a collocated CU (colCU), etc. The reference picture including the temporal neighboring block may be called a collocated picture (colPic). For example, the inter predictor 180 may construct a motion information candidate list based on neighboring blocks and generate information indicating which candidate is used to derive a motion vector and / or a reference picture index for 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 predictor 180 may use motion information of neighboring blocks as motion information for the current block. In the case of skip mode, unlike in merge mode, a residual signal may not be transmitted.In the case of a motion vector prediction (MVP) mode, the motion vector of a neighboring block is used as a motion vector predictor, and the motion vector of the current block can be signaled by encoding a motion vector difference and an indicator for 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.

[0056] The predictor may generate a prediction signal based on various prediction methods and / or prediction techniques, which will be described later. For example, the predictor may apply intra prediction or inter prediction to predict the current block, or may simultaneously apply intra prediction and inter prediction. A prediction method that simultaneously applies intra prediction and inter prediction to predict the current block may be referred to as combined inter and intra prediction (CIIP). The predictor may also perform intra block copy (IBC) to predict the current block. Intra block copy can be used for content image / video coding, such as screen content coding (SCC), for games. IBC is a method of predicting a current block using an already reconstructed reference block in a current picture that is located a predetermined distance away from the current block. When IBC is applied, the position of the reference block in the current picture may be coded as a vector (block vector) corresponding to the predetermined distance. IBC basically performs prediction within the current picture, but can be performed similarly to inter prediction in that a reference block is derived within the current picture. That is, the IBC may use at least one of the inter prediction techniques described in this disclosure.

[0057] The prediction signal generated by the prediction unit may be used to generate a restored signal or a residual signal. The subtraction unit 115 may subtract the prediction signal (predicted block, predicted sample array) output from the prediction unit from the input image signal (original block, original sample array) to generate a residual signal (residual signal, residual block, residual sample array). The generated residual signal may be transmitted to the conversion unit 120.

[0058] The transform unit 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-Loeve transform (KLT), a graph-based transform (GBT), or a conditionally non-linear transform (CNT). Here, the GBT refers to a transform obtained from a graph representing inter-pixel relationship information. The CNT refers to a transform obtained based on a predicted signal generated using all previously reconstructed pixels. The transform process may be applied to pixel blocks having the same square size or to non-square blocks of variable size.

[0059] The quantization unit 130 may quantize the transform coefficients and transmit the quantized transform coefficients to the entropy coding unit 190. The entropy coding unit 190 may encode the quantized signal (information about the quantized transform coefficients) and output the encoded signal in a bitstream format. The information about the quantized transform coefficients may be referred to as residual information. The quantization unit 130 may rearrange the quantized transform coefficients in a block format into a one-dimensional vector format based on a coefficient scan order, and may generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector format.

[0060] The entropy coding unit 190 may perform various coding methods, such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy coding unit 190 may also code information necessary for video / image restoration (e.g., values ​​of syntax elements) together with or separately from the quantized transform coefficients. The coded information (e.g., coded video / image information) may be transmitted or stored in a bitstream format in network abstraction layer (NAL) units. The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. The signaling information, transmitted information and / or syntax elements mentioned in this disclosure may be encoded through the above-described encoding procedure and included in the bitstream.

[0061] The bitstream may be transmitted via a network or stored in a digital storage medium. Here, the network may include a broadcasting network and / or a communication network, and the digital storage medium may include various storage media such as a USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitting unit (not shown) that transmits and / or a storing unit (not shown) that stores the signal output from the entropy encoding unit 190 may be provided as an internal / external element of the image encoding device 100, or the transmitting unit may be provided as a component of the entropy encoding unit 190.

[0062] The quantized transform coefficients output from the quantization unit 130 can be used to generate a residual signal. For example, the residual signal (residual block or residual sample) can be reconstructed by applying inverse quantization and inverse transform to the quantized transform coefficients via the inverse quantization unit 140 and the inverse transform unit 150.

[0063] The adder 155 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the reconstructed residual signal to the prediction signal output from the inter prediction unit 180 or the intra prediction unit 185. When there is no residual for the current block to be processed, such as when a skip mode is applied, the predicted block may be used as the reconstructed block. The adder 155 may be referred to as a reconstruction unit or a reconstructed block generation unit. The generated reconstructed signal may be used for intra prediction of the next current block to be processed in the current picture, and may also be used for inter prediction of the next picture after filtering, as will be described later.

[0064] The filtering unit 160 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 160 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc. The filtering unit 160 may generate various information related to filtering and transmit it to the entropy coding unit 190, as will be described later in connection with each filtering method. The filtering information may be coded by the entropy coding unit 190 and output in a bitstream format.

[0065] The modified reconstructed picture transmitted to the memory 170 can be used as a reference picture in the inter prediction unit 180. When inter prediction is applied through this, the image encoding device 100 can avoid a prediction mismatch between the image encoding device 100 and the image decoding device, and can also improve encoding efficiency.

[0066] The DPB in the memory 170 may store modified reconstructed pictures for use as reference pictures in the inter predictor 180. The memory 170 may store motion information of blocks from which motion information in the current picture is derived (or coded) and / or motion information of already reconstructed intra-picture blocks. The stored motion information may be transmitted to the inter predictor 180 to be used as motion information of spatially surrounding blocks or temporally surrounding blocks. The memory 170 may store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 185.

[0067] Overview of the image decoding device

[0068] FIG. 3 is a diagram schematically illustrating an image decoding device to which an embodiment of the present disclosure can be applied.

[0069] 3, the image decoding apparatus 200 may include an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an adder 235, a filtering unit 240, a memory 250, an inter prediction unit 260, and an intra prediction unit 265. The inter prediction unit 260 and the intra prediction unit 265 may be collectively referred to as a "prediction unit." The inverse quantization unit 220 and the inverse transform unit 230 may be included in a residual processing unit.

[0070] Depending on the embodiment, all or at least some of the components constituting the image decoding device 200 may be realized by a single hardware component (e.g., a decoder or a processor). Also, the memory 170 may include a DPB and may be realized by a digital storage medium.

[0071] The image decoding device 200, which receives a bitstream including video / image information, can reconstruct an image by performing a process corresponding to the process performed by the image encoding device 100 of FIG. 2. For example, the image decoding device 200 can perform decoding using a processing unit applied in the image encoding device. Therefore, the decoding processing unit can be, for example, a coding unit. The coding unit can be obtained by dividing a coding tree unit or a maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 can be reproduced by a reproduction device (not shown).

[0072] The image decoding apparatus 200 may receive a signal output from the image encoding apparatus of FIG. 2 in a bitstream format. The received signal may be decoded via an entropy decoding unit 210. For example, the entropy decoding unit 210 may parse the bitstream to derive information (e.g., video / image information) necessary for image reconstruction (or picture reconstruction). The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. The image decoding apparatus may further use the information on the parameter sets and / or the general constraint information to decode an image. The signaling information, received information, and / or syntax elements referred to in the present disclosure may be obtained from the bitstream by being decoded via the decoding procedure. For example, the entropy decoding unit 210 may decode information in a bitstream based on a coding method such as Exponential-Golomb coding, CAVLC, or CABAC, and output values ​​of syntax elements required for image restoration and quantized values ​​of transform coefficients related to residuals. More specifically, the CABAC entropy decoding method receives bins corresponding to each syntax element from the bitstream, determines a context model using information on the syntax element to be decoded and decoded information on neighboring blocks and the block to be decoded, or information on symbols / bins decoded in a previous step, predicts the occurrence probability of the bins based on the determined context model, and performs arithmetic decoding of the bins to generate symbols corresponding to the values ​​of each syntax element. After determining the context model, the CABAC entropy decoding method may update the context model using information on the decoded symbol / bin for the context model of the next symbol / bin.Among the information decoded by the entropy decoding unit 210, information related to prediction is provided to the prediction units (inter prediction unit 260 and intra prediction unit 265), and residual values ​​entropy decoded by the entropy decoding unit 210, i.e., quantized transform coefficients and related parameter information, may be input to the inverse quantization unit 220. Also, among the information decoded by the entropy decoding unit 210, information related to filtering may be provided to the filtering unit 240. Meanwhile, a receiving unit (not shown) for receiving a signal output from the image encoding device may be further provided as an internal / external element of the image decoding device 200, or the receiving unit may be provided as a component of the entropy decoding unit 210.

[0073] Meanwhile, the image decoding apparatus according to the present disclosure may be referred to as a video / image / picture decoding apparatus. The image decoding apparatus may include an information decoder (video / image / picture information decoder) and / or a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoding unit 210, and the sample decoder may include at least one of an inverse quantization unit 220, an inverse transform unit 230, an adder 235, a filtering unit 240, a memory 250, an inter prediction unit 260, and an intra prediction unit 265.

[0074] The inverse quantization unit 220 may inverse quantize the quantized transform coefficients and output the transform coefficients. The inverse quantization unit 220 may rearrange the quantized transform coefficients in a two-dimensional block format. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The inverse quantization unit 220 may perform inverse quantization on the quantized transform coefficients using a quantization parameter (e.g., quantization step size information) to obtain transform coefficients.

[0075] The inverse transform unit 230 can inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0076] The prediction unit may perform prediction on a current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on information about the prediction output from the entropy decoding unit 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0077] The prediction unit can generate a prediction signal based on various prediction methods (techniques) described below, as described in the description of the prediction unit of the image encoding device 100.

[0078] The intra predictor 265 may predict the current block by referring to samples in the current picture. The description of the intra predictor 185 may also be applied to the intra predictor 265.

[0079] The inter prediction unit 260 may derive a predicted block for a current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on correlations between motion information of neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on an inter prediction direction (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks in the current picture and temporal neighboring blocks in the reference picture. For example, the inter prediction unit 260 may construct a motion information candidate list based on the neighboring blocks and derive a motion vector and / or a reference picture index for the current block based on received candidate selection information. Inter prediction may be performed based on various prediction modes (techniques), and the prediction information may include information indicating the inter prediction mode (technique) for the current block.

[0080] The adder 235 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to a prediction signal (predicted block, predicted sample array) output from a prediction unit (including the inter prediction unit 260 and / or intra prediction unit 265). When there is no residual for the current block, such as when a skip mode is applied, the predicted block can be used as the reconstructed block. The description of the adder 155 also applies to the adder 235. The adder 235 may also be referred to as a reconstruction unit or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next current block in the current picture, and may also be used for inter prediction of the next picture via filtering, as described below.

[0081] The filtering unit 240 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 240 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and may store the modified reconstructed picture in the memory 250, specifically, in a DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc.

[0082] The (modified) reconstructed picture stored in the DPB of the memory 250 can be used as a reference picture in the inter predictor 260. The memory 250 can store motion information of a block from which motion information in the current picture is derived (or decoded) and / or motion information of a block in an already reconstructed picture. The stored motion information can be transmitted to the inter predictor 260 to be used as motion information of a spatially surrounding block or a temporally surrounding block. The memory 250 can store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 265.

[0083] In this specification, the embodiments described for the filtering unit 160, inter prediction unit 180 and intra prediction unit 185 of the image encoding device 100 can also be applied in a similar or corresponding manner to the filtering unit 240, inter prediction unit 260 and intra prediction unit 265 of the image decoding device 200, respectively.

[0084] Coding hierarchy and structure

[0085] Video / images coded according to this document can be processed, for example, according to the coding hierarchy and structure described below.

[0086] FIG. 4 shows a hierarchical structure for a coded image.

[0087] The coded image is divided into the VCL (video coding layer), which handles the image decoding process and the image itself, the lower system, which transmits and stores the coded information, and the NAL (network abstraction layer), which exists between the VCL and the lower system and is responsible for network adaptation functions.

[0088] The VCL can generate VCL data containing compressed image data (slice data), or it can generate parameter sets containing information such as a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), and a Video Parameter Set (VPS), or an SEI (Supplemental Enhancement Information) message that is additionally required for the image decoding process.

[0089] In NAL, NAL units can be generated by adding header information (NAL unit header) to RBSP (Raw Byte Sequence Payload) generated by VCL. In this case, RBSP refers to slice data, parameter sets, SEI messages, etc. generated by VCL. The NAL unit header can include NAL unit type information identified by the RBSP data included in the NAL unit.

[0090] As shown in Figure 4, NAL units can be classified into VCL NAL units and non-VCL NAL units according to the RBSP generated by the VCL. A VCL NAL unit can refer to a NAL unit containing information about an image (slice data), and a non-VCL NAL unit can refer to a NAL unit containing information necessary for decoding an image (parameter set or SEI message).

[0091] The VCL NAL unit and non-VCL NAL unit described above can be transmitted over a network with header information attached according to the data standard of the lower system. For example, the NAL unit can be transformed into a data format of a predetermined standard such as H.266 / VVC file format, RTP (Real-time Transport Protocol), or TS (Transport Stream) and transmitted over various networks.

[0092] As described above, the NAL unit type of an NAL unit can be identified according to the RBSP data structure included in the NAL unit, and information about such NAL unit type can be stored and signaled in the NAL unit header.

[0093] For example, NAL units can be broadly classified into VCL NAL unit types and non-VCL NAL unit types depending on whether they contain information about an image (slice data). VCL NAL unit types can be classified according to the nature and type of pictures contained in the VCL NAL unit, and non-VCL NAL unit types can be classified according to the type of parameter set.

[0094] The following are examples of NAL unit types identified according to the types of parameter sets included in the non-VCL NAL unit types.

[0095] -APS (Adaptation Parameter Set) NAL unit: Type for NAL units containing APS

[0096] -DPS (Decoding Parameter Set) NAL unit: Type for NAL units containing DPS

[0097] -VPS (Video Parameter Set) NAL unit: Type for NAL units containing VPS

[0098] -SPS (Sequence Parameter Set) NAL unit: Type for NAL unit including SPS

[0099] -PPS (Picture Parameter Set) NAL unit: Type for NAL unit containing PPS

[0100] The above-mentioned NAL unit types have syntax information for the NAL unit type, and the syntax information can be stored and signaled in a NAL unit header. For example, the syntax information can be nal_unit_type, and the NAL unit type can be specified as a nal_unit_type value.

[0101] The slice header (slice header syntax) can include information / parameters commonly applicable to the slices. The APS (APS syntax) or PPS (PPS syntax) can include information / parameters commonly applicable to one or more slices or pictures. The SPS (SPS syntax) can include information / parameters commonly applicable to one or more sequences. The VPS (VPS syntax) can include information / parameters commonly applicable to multiple layers. The DPS (DPS syntax) can include information / parameters commonly applicable to video in general. The DPS can include information / parameters related to the concatenation of a coded video sequence (CVS). In this document, a high level syntax (HLS) can include at least one of the APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, and slice header syntax.

[0102] In the present disclosure, the image / video information encoded from the image encoding device 100 to the image decoding device 200 and signaled in bitstream format may include not only partitioning-related information within a picture, intra / inter prediction information, residual information, in-loop filtering information, etc., but also information contained in the slice header, information contained in the APS, information contained in the PPS, information contained in the SPS, and / or information contained in the VPS.

[0103] SEI Message

[0104] DRAP (Dependent Random Access Point)

[0105] A DRAP picture can be an inter-coded picture that can only reference a previous Intra Random Access Point (IRAP) picture and provides a random access point in the bitstream of the DRAP picture if the IRAP picture is available. Also, a DRAP picture can be indicated in the bitstream by an SEI message.

[0106] A picture associated with a DRAP indication SEI message can be referred to as a DRAP picture, and an example for a DRAP indication SEI message is shown in Table 1.

[0107] [Table 1]

[0108] The presence of the DRAP indication SEI message may indicate restrictions on picture referencing and picture order. These restrictions may enable the image decoding device 200 to properly decode the DRAP picture. These restrictions may also enable the image decoding device 200 to properly decode pictures that are in the same layer but are later in both the decoding order and the output order, without having to decode any other pictures in the same layer except for the DRAP picture's associated IRAP picture.

[0109] The restrictions indicated by the presence of the DRAP Indication SEI message may be as follows:

[0110] -DRAP pictures are trailing pictures.

[0111] -DRAP pictures have a temporal sub-layer identifier equal to 0.

[0112] A DRAP picture does not include any pictures that exist in the same layer in the active entries of the reference picture list, except for the DRAP picture's associated IRAP picture.

[0113] Any picture that exists in the same layer but follows the DRAP picture in both decoding order and output order does not include in the active entries of the reference picture list any pictures that exist in the same layer but precede the DRAP picture in decoding order or output order, except for the DRAP picture's associated IRAP picture.

[0114] EDRAP (Extended DRAP)

[0115] An EDRAP picture may be a DRAP picture that depends on only some pictures in a picture set. A picture set may consist of associated IRAP pictures and specific EDRAP pictures between the associated IRAP picture and the specific EDRAP picture in decoding order. As long as dependent IRAP pictures or EDRAP pictures are provided, one EDRAP picture can be used as a random access point.

[0116] A picture associated with an EDRAP indication SEI message can be referred to as an EDRAP picture.

[0117] The presence of the EDRAP indication SEI message may indicate restrictions on picture references and picture order. These restrictions may enable the image decoding device 200 to properly decode EDRAP pictures. These restrictions may also enable the image decoding device 200 to properly decode pictures that are in the same layer but that are later in both decoding order and output order, without having to decode any other pictures in the same layer except for the list of pictures referenceablePictures. Here, the list of pictures referenceablePictures may consist of a list of IRAP or EDRAP pictures in the same coded layer video sequence (CLVS) and in decoding order identified by the edrap_ref_rap_id[i] syntax element.

[0118] The restrictions indicated by the presence of the ERAP indication SEI message may be as follows:

[0119] -EDRAP pictures are trailing pictures.

[0120] -EDRAP pictures have a temporal sub-layer identifier equal to 0.

[0121] - The EDRAP picture does not contain any pictures that exist in the same layer in the active entries of the reference picture list, except for referenceablePictures.

[0122] -Any picture that exists in the same layer but follows the EDRAP picture in both decoding order and output order, except for referenceablePictures, does not include pictures that exist in the same layer but precede the EDRAP picture in decoding order or output order in the active entries of the reference picture list.

[0123] A picture included in referenceablePictures does not include in its active entry of the reference picture list any picture that exists in the same layer but does not exist in an earlier position in referenceablePictures. Therefore, the first picture in referenceablePictures does not include any picture from the same layer in its active entry of the reference picture list, even if the picture is an EDRAP picture rather than an IRAP picture.

[0124] An example for the EDRAP Indication SEI message is shown in Table 2.

[0125] [Table 2]

[0126] The value of edrap_rap_id_minus1 plus 1 indicates the RAP picture identifier RapPicId of the EDRAP picture. Each IRAP or EDRAP picture is associated with a RapPicId. The value of RapPicId for an IRAP picture can be inferred to be 0. The RapPicId values ​​for any two EDRAP pictures associated with the same IRAP picture should be different from each other.

[0127] A value of 1 for edrap_leading_pictures_decodable_flag indicates that all of the following restrictions apply.

[0128] A picture that exists in the same layer and follows an EDRAP picture in decoding order should be later in output order than a picture that exists in the same layer but precedes the EDRAP picture in decoding order.

[0129] - Pictures that exist in the same layer but follow the EDRAP picture in decoding order and precede the EDRAP picture in output order should not be included in the active entries of the reference picture list, except for referenceablePictures.

[0130] A value of 0 for edrap_leading_pictures_decodable_flag does not impose the above restrictions.

[0131] The value of edrap_reserved_zero_12bits must be equal to 0 in the bitstream. Other values ​​of edrap_reserved_zero_12bits are reserved for future definition, and the image decoding device 200 must ignore the value of edrap_reserved_zero_12bits.

[0132] The value of edrap_num_ref_rap_pics_minus1 plus 1 indicates the number of IRAP or EDRAP pictures that exist in the same CLVS as the EDRAP picture and can be included in the active entries of the reference picture list of the EDRAP picture.

[0133] edrap_ref_rap_id[i] indicates the RapPicId of the ith RAP picture that can be included in the active entry of the reference picture list of the EDRAP picture. The ith RAP picture must be an IRAP picture related to the current EDRAP picture or an EDRAP picture related to the same IRAP picture as the current EDRAP picture.

[0134] Example

[0135] According to the current EDRAP SEI message, a picture indicated by an EDRAP picture can be related to a leading picture. A leading picture corresponds to a picture that follows the EDRAP picture in decoding order but precedes the EDRAP picture in output order. The related leading picture indicated by an EDRAP picture can be a decodable leading picture or a non-decodable leading picture. Whether an EDRAP picture is decodable or non-decodable can be indicated by a flag signaled in the EDRAP SEI message, edrap_leading_pictures_decodable_flag.

[0136] When the decoding process starts from an EDRAP picture (i.e., random access from an EDRAP picture), leading pictures associated with the non-decodable EDRAP picture need to be removed from the bitstream for decoding. Considering this, the current design for leading pictures associated with EDRAP pictures may have the following problems.

[0137] 1. The flag edrap_leading_pictures_decodable_flag only indicates that the leading pictures associated with the EDRAP picture are decodable, but does not indicate how many leading pictures are associated with the EDRAP picture. When performing random access from an EDRAP picture from which non-decodable leading pictures are to be removed, the only way to identify whether a picture following the EDRAP picture in decoding order is a leading picture is to navigate the POC of the picture until the first non-leading picture associated with the EDRAP is found. This is completely different from removing non-decodable pictures associated with a CRA (i.e., RSAL pictures), because such pictures are easily recognized from the NAL unit header.

[0138] 2. In the current design, whether all leading pictures associated with an EDRAP picture are decodable or not is expressed in binary. It is preferable to allow a mixture of non-decodable and decodable leading pictures, as in the design of RASL and RADL pictures associated with a CRA picture. If the leading pictures associated with an EDRAP picture can be identified without deriving a POC value, no cost would be required to allow a mixture of non-decodable and decodable leading pictures associated with an EDRAP picture.

[0139] 3. Furthermore, signaling information in the EDRAP SEI message to indicate the type of leading picture associated with the EDRAP picture can be problematic when bitstream thinning occurs. For example, a picture in a higher temporal sublayer may be removed from the bitstream, and the removed picture may include a leading picture associated with the EDRAP picture. In this situation, after removing some pictures, the EDRAP SEI message must be updated to ensure that the correct information for the associated leading picture is included.

[0140] In order to solve the problems described above, the present application proposes various embodiments. The embodiments described below can be implemented individually or in combination of two or more embodiments.

[0141] First, the embodiments proposed in this application are summarized as follows.

[0142] 1. When random access is performed from an EDRAP memory picture, the EDRAP picture can be associated with zero or more leading pictures, which may be decodable or non-decodable.

[0143] a. A decodable leading picture associated with an EDRAP picture can be referred to as a DADL picture (DRAP-decodable leading picture).

[0144] b. A non-decodable leading picture associated with an EDRAP picture can be referred to as a DASL picture (DRAP-skipped leading picture).

[0145] 2. Any DASL picture associated with an EDRAP picture should precede in output order the DADL picture associated with the EDRAP picture.

[0146] 3. Any DADL picture associated with an EDRAP picture should not reference the DASL picture associated with the EDRAP picture or any picture preceding the EDRAP picture in decoding order, except for referenceablePictures.

[0147] 4. Any picture that follows the EDRAP picture in both decoding order and output order must not reference any DASL picture associated with the EDRAP picture or any picture that precedes the EDRAP picture in decoding order, except for referenceablePictures.

[0148] 5. A new SEI message is used to represent a picture as a DASL picture. This SEI message can be called the DASL Display SEI message.

[0149] 6. A new SEI message is used to represent a picture as a DADL picture. This SEI message can be called the DADL indication SEI message.

[0150] 7. Alternatively, a new SEI message is used to represent a picture as a leading picture associated with an EDRAP picture. This SEI message can be referred to as an EDRAP leading picture SEI message. The SEI message includes a flag indicating the leading picture type of the picture (i.e., DADL picture or DASL picture).

[0151] 8. Instead of signaling edrap_leading_pictures_decodable_flag, this flag is changed to indicate whether the displayed EDRAP picture has an associated leading picture or not. The flag can be changed to edrap_leading_pictures_present_flag.

[0152] 9. If edrap_leading_pictures_present_flag is 1, the following information may be additionally signaled:

[0153] a. Number of leading pictures associated with the EDRAP picture

[0154] b. Number of undecodable leading pictures

[0155] c. Number of decodable leading pictures

[0156] d. When decodable and non-decodable leading pictures are mixed, a flag to identify the type of the leading picture

[0157] 10. Alternatively, a two-bit representation may be used to indicate:

[0158] a. First value: The displayed EDRAP picture does not have an associated leading picture

[0159] b. Second value: The displayed EDRAP picture has one or more associated leading pictures, and all associated leading pictures are decodable leading pictures.

[0160] c. Third value: The displayed EDRAP picture has one or more associated leading pictures, and all associated leading pictures are non-decodable leading pictures.

[0161] d. Fourth value: The displayed EDRAP picture has one or more associated leading pictures, and the associated leading pictures are a mixture of non-decodable and decodable leading pictures.

[0162] If the value of the 10.2 bit representation is not the first value, the following information is additionally signaled:

[0163] a. Number of leading pictures

[0164] b. If the value of the 2-bit representation is the fourth value, a flag to indicate the type of leading picture

[0165] 11. If a leading picture associated with an EDRAP picture is removed from the bitstream due to bitstream extraction / thinning (i.e., removing a picture of a higher temporal sublayer), the EDRAP SEI message associated with the EDRAP picture needs to be updated to ensure accurate signaling for the leading picture.

[0166] FIG. 5 is a flowchart showing an image encoding method according to an embodiment of the present invention, and FIG. 6 is a flowchart showing an image decoding method according to an embodiment of the present invention.

[0167] 5, the image coding apparatus 100 may identify a leading picture (S510). A leading picture may be a picture associated with an EDRAP picture. Alternatively, a leading picture may be a picture that precedes the EDRAP picture in decoding order but follows the EDRAP picture in output order. A leading picture may include at least one of a decodable leading picture (DADL picture) and a non-decodable leading picture (DASL picture).

[0168] The image coding apparatus 100 may encode an SEI message based on the identification result of the leading picture (S520). 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 identification result of the leading picture may be a determination result regarding the presence or absence of a leading picture, the number of leading pictures, the type of the leading picture (DADL picture or DASL picture), etc.

[0169] 6, the image decoding apparatus 200 may obtain an SEI message from a 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 an EDRAP picture. The identification result of the leading picture may be a determination result regarding the presence or absence of a leading picture, the number of leading pictures, the type of the leading picture (DADL picture or DASL picture), etc.

[0170] The image decoding apparatus 200 may identify a leading picture based on the SEI message (S620). A leading picture may be a picture associated with an EDRAP picture. Alternatively, a leading picture may be a picture that precedes the EDRAP picture in decoding order but follows the EDRAP picture in output order. A leading picture may include at least one of a decodable leading picture (DADL picture) and a non-decodable leading picture (DASL picture).

[0171] Example 1

[0172] The SEI message may include at least one of a second SEI message for indicating a DASL picture and a first SEI message for indicating a DADL picture.

[0173] Table 3 shows an example of a DASL indication SEI message (DRAP-Skipped Leading Indication SEI Message), which is a second SEI message for indicating a DASL picture.

[0174] [Table 3]

[0175] The picture associated with the second message can be referred to as a DASL picture. A DASL picture associated with an EDRAP picture can be restricted to follow the associated EDRAP picture in decoding order but precede the EDRAP picture in output order.

[0176] In addition, any picture that is in the same layer but follows the EDRAP picture in both decoding order and output order may be restricted so that any picture associated with the EDRAP picture or any picture that is in the same layer but precedes the EDRAP picture in decoding order is not included in the active entry in the reference picture list, although such a restriction may not apply to refereceablePictures.

[0177] Table 4 shows an example of a DADL indication SEI message (DRAP-Decodable Leading Indication SEI Message) which is the first SEI message for indicating a DADL picture.

[0178] [Table 4]

[0179] The picture associated with the first message can be referred to as a DADL picture. A DADL picture associated with an EDRAP picture can be restricted to follow the associated EDRAP picture in decoding order but precede the EDRAP picture in output order.

[0180] In addition, a DADL picture associated with an EDRAP picture may be restricted to be later in output order than a DASL picture associated with the EDRAP picture. A DADL picture associated with an EDRAP picture may also be suggested not to reference the DASL picture associated with the EDRAP picture or any picture that belongs to the same layer but precedes the EDRAP picture in decoding order. However, this restriction may not apply to referenceablePictures.

[0181] Example 2

[0182] The SEI message can contain one single SEI message to indicate the type of the leading picture (DADL picture and DASL picture).

[0183] Table 5 shows an example of an EDRAP Leading Indication SEI message, which is an SEI message for indicating a DADL picture and a DASL picture.

[0184] [Table 5]

[0185] In Table 5, dasl_picture_flag may indicate the type of picture associated with the EDRAP leading indication SEI message. A value of 1 for dasl_picture_flag may indicate that the picture associated with the EDRAP leading indication SEI message is a DASL picture, and a value of 0 for dasl_picture_flag may indicate that the picture associated with the EDRAP leading indication SEI message is a DADL picture.

[0186] A picture associated with an EDRAP leading indication SEI message can be referred to as a leading picture associated with the EDRAP picture. A leading picture associated with an EDRAP picture can be decodable or non-decodable when random access is performed from the associated EDRAP picture. A decodable leading picture associated with an EDRAP picture can be referred to as a DADL picture, and a non-decodable leading picture associated with an EDRAP picture can be referred to as a DASL picture.

[0187] Additionally, the following restrictions apply to EDRAP reading indication SEI messages:

[0188] Any DADL picture associated with an EDRAP picture may be restricted so that it does not include in its active entry in the reference picture list any DASL picture associated with the EDRAP picture or any picture that precedes the EDRAP picture in decoding order while belonging to the same layer. However, this restriction may not apply to referenceablePictures.

[0189] Any picture that belongs to the same layer but follows the EDRAP picture in both decoding order and output order may be restricted so that the DASL picture associated with the EDRAP picture or any picture that belongs to the same layer but precedes the EDRAP picture in decoding order is not included in the active entry of the reference picture list. However, this restriction may not apply to referenceablePictures.

[0190] Example 3

[0191] An example of an extended DRAP indication SEI message, which is an SEI message for indicating information about an EDRAP picture, is shown in Table 6.

[0192] [Table 6]

[0193] A picture associated with an EDRAP indication SEI message may be referred to as an EDRAP picture. The presence of the EDRAP indication SEI message may indicate restrictions on picture order and picture referencing. These restrictions may enable the image decoding device 200 to properly decode the EDRAP picture (the decodable leading picture associated with the EDRAP picture). These restrictions may also enable the image decoding device 200 to properly decode a picture that exists in the same layer but is later in both decoding order and output order, without having to decode any other pictures in the same layer except for the picture list referenceablePictures. Here, the picture list referenceablePictures may consist of a list of IRAP or EDRAP pictures in the same CLVS and in decoding order identified by the edrap_ref_rap_id[i] syntax element.

[0194] The restrictions indicated by the presence of the EDRAP Indication SEI message may be as follows:

[0195] -EDRAP pictures are trailing pictures.

[0196] -EDRAP pictures have a temporal sub-layer identifier equal to 0.

[0197] - The EDRAP picture does not contain any pictures that exist in the same layer in the active entries of the reference picture list, except for referenceablePictures.

[0198] -Any picture that exists in the same layer but follows the EDRAP picture in both decoding order and output order, except for referenceablePictures, does not include pictures that exist in the same layer but precede the EDRAP picture in decoding order or output order in the active entries of the reference picture list.

[0199] In addition, the following restrictions that were previously applied may no longer be applied:

[0200] A picture included in referenceablePictures does not include pictures from the same layer in the active entries of the reference picture list that are not in an earlier position in referenceablePictures, even if the first picture in referenceablePictures is an EDRAP picture rather than an IRAP picture.

[0201] In Table 6, the value of edrap_rap_id_minus1 plus 1 indicates 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 can be inferred to be 0. The RapPicId values ​​for any two EDRAP pictures associated with the same IRAP picture should be different from each other.

[0202] The edrap_leading_pictures_present_flag may indicate whether the EDRAP picture has one or more associated leading pictures. A value of 1 for the edrap_leading_pictures_present_flag may indicate that the EDRAP picture has one or more associated leading pictures, and a value of 0 for the edrap_leading_pictures_present_flag may indicate that the EDRAP picture does not have any associated leading pictures.

[0203] edrap_num_dadl_pictures may indicate the number of DADL pictures associated with an EDRAP picture. edrap_num_dadl_pictures may have a value between 0 and 255. edrap_num_dasl_pictures may indicate the number of DASL pictures associated with an EDRAP picture. edrap_num_dasl_pictures may have a value between 0 and 255.

[0204] A value of 1 for edrap_dasl_picture_flag[i] may indicate that the (i+1)th picture after the EDRAP picture in decoding order is a DASL picture, and a value of 0 for edrap_dasl_picture_flag[i] may indicate that the (i+1)th picture after the EDRAP picture in decoding order is a DADL picture. If the value of edrap_num_dadl_pictures is 0, then the value of edrap_dasl_picture_flag[i] may be inferred to be 1 for i having values ​​between 0 and edrap_num_dasl_pictures-1. If the value of edrap_num_dasl_pictures is 0, then the value of edrap_dasl_picture_flag[i] may be inferred to be 0 for i having values ​​between 0 and edrap_num_dadl_pictures-1.

[0205] In addition, the following restrictions apply:

[0206] Any DASL picture associated with an EDRAP picture should precede in output order any DADL picture associated with the EDRAP picture.

[0207] A DADL picture associated with an EDRAP picture should not include in its active entry of the reference picture list a DASL picture associated with the EDRAP picture, or any picture that belongs to the same layer but precedes the EDRAP picture in decoding order. However, this restriction does not apply to referenceablePictures.

[0208] Any picture that belongs to the same layer but follows the EDRAP picture in both decoding order and output order should not include in the active entries of the reference picture list the DASL picture associated with the EDRAP picture or any picture that belongs to the same layer but precedes the EDRAP picture in decoding order, except that this restriction does not apply to referenceablePictures.

[0209] -If one or more leading pictures associated with an EDRAP picture are removed (i.e., bitstream thinning due to removal of pictures of higher temporal sublayers), the EDRAP SEI message must be updated to ensure accurate information about the leading pictures associated with the EDRAP picture.

[0210] The value of edrap_reserved_zero_5bits must be equal to 0 in the bitstream. Other values ​​of edrap_reserved_zero_5bits are reserved for future definition, and the image decoding device 200 must ignore the value of edrap_reserved_zero_5bits.

[0211] The value obtained by adding 1 to edrap_num_ref_rap_pics_minus1 indicates the number of IRAP or EDRAP pictures that exist in the same CLVS as the EDRAP picture and that can be included in the active entries of the reference picture list of the EDRAP picture.

[0212] edrap_ref_rap_id[i] indicates the RapPicId of the i-th RAP picture that can be included in the active entry of the reference picture list of the EDRAP picture. The i-th RAP picture must 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.

[0213] FIG. 7 is a flowchart showing an image encoding method according to the third embodiment, and FIG. 8 is a flowchart showing an image decoding method according to the third embodiment.

[0214] 7, the image coding device 100 may determine whether an EDRAP picture has one or more leading pictures (S710). If the EDRAP picture does not have one or more leading pictures, the image coding device 100 may code the value of edrap_leading_pictures_present_flag to 0 (S770). In contrast, if the EDRAP picture has one or more leading pictures, the image coding device 100 may code the value of edrap_leading_pictures_present_flag to 1 (S720). In this case, the image coding device 100 may determine the number of DADL pictures and DASL pictures, and code edrap_num_dadl_pictures indicating the number of DADL pictures and edrap_num_dasl_pictures indicating the number of DASL pictures (S720).

[0215] If both the number of DADL pictures and the number of DASL pictures are not 0 (S730), the image coding device 100 can determine the type of picture that follows (follows) the EDRAP picture (S740). If the type of the following picture is a DASL picture, the image coding device 100 can code the value of edrap_dasl_picture_flag[i] to 1 (S750), and if the type of the following picture is a DADL picture, the image coding device 100 can code the value of edrap_dasl_picture_flag[i] to 0 (S760). Here, i is equal to or greater than 0 and can be less than the sum of the number of DADL pictures and the number of DASL pictures.

[0216] The image decoding device 200 acquires edrap_leading_pictures_present_flag from the bitstream (S810) and can determine the value of edrap_leading_pictures_present_flag (S820). If the value of edrap_leading_pictures_present_flag is 1, the image decoding device 200 can acquire 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).

[0217] The image decoding device 200 can determine whether the value of edrap_num_dadl_pictures is 0 and whether the value of edrap_num_dasl_pictures is 0 (S840). If the values ​​of edrap_num_dadl_pictures and edrap_num_dasl_pictures are both not 0, the image decoding device 200 can acquire edrap_dasl_picture_flag[i] from the bitstream (S850). Here, i may be 0 or greater, and may be less than the sum of the values ​​of edrap_num_dadl_pictures and edrap_num_dasl_pictures.

[0218] The image decoding apparatus 200 may determine the type of a leading picture based on edrap_num_dadl_pictures, edrap_num_dasl_pictures, and edrap_dasl_picture_flag[i]. For example, when 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 to be DASL pictures. As another example, when 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 to be DADL pictures. As another example, when 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].

[0219] Example 4

[0220] Another example of an extended DRAP indication SEI message, which is an SEI message for indicating information about an EDRAP picture, is shown in Table 7.

[0221] [Table 7]

[0222] A picture associated with an EDRAP indication SEI message may be referred to as an EDRAP picture. The presence of the EDRAP indication SEI message may indicate restrictions on picture order and picture referencing. These restrictions may enable the image decoding device 200 to properly decode the EDRAP picture (the decodable leading picture associated with the EDRAP picture). These restrictions may also enable the image decoding device 200 to properly decode a picture that exists in the same layer but is later in both decoding order and output order, without having to decode any other pictures in the same layer except for the picture list referenceablePictures. Here, the picture list referenceablePictures may consist of a list of IRAP or EDRAP pictures in the same CLVS and in decoding order identified by the edrap_ref_rap_id[i] syntax element.

[0223] The restrictions indicated by the presence of the EDRAP Indication SEI message may be as follows:

[0224] -EDRAP pictures are trailing pictures.

[0225] -EDRAP pictures have a temporal sub-layer identifier equal to 0.

[0226] - The EDRAP picture does not contain any pictures that exist in the same layer in the active entries of the reference picture list, except for referenceablePictures.

[0227] -Any picture that exists in the same layer but follows the EDRAP picture in both decoding order and output order, except for referenceablePictures, does not include pictures that exist in the same layer but precede the EDRAP picture in decoding order or output order in the active entries of the reference picture list.

[0228] In addition, the following restrictions that have been applied in the conventional method may be changed so that they do not apply.

[0229] - Pictures included in referenceablePictures do not include pictures that exist in the same layer but do not exist in an earlier position in referenceablePictures in the active entries of the reference picture list. Therefore, the first picture in referenceablePictures does not include pictures from the same layer in the active entries of the reference picture list, even if the picture is an EDRAP picture rather than an IRAP picture.

[0230] In Table 7, the value of edrap_rap_id_minus1 plus 1 indicates 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 can be inferred to be 0. The RapPicId values ​​for any two EDRAP pictures associated with the same IRAP picture should be different from each other.

[0231] A value of 0 for edrap_leading_pictures_idc may indicate that the EDRAP picture has no associated leading pictures. A value of 1 for edrap_leading_pictures_idc may indicate that the EDRAP picture has one or more associated leading pictures, all of which are DADL pictures. A value of 2 for edrap_leading_pictures_idc may indicate that the EDRAP picture has one or more associated leading pictures, all of which are DASL pictures. A value of 3 for edrap_leading_pictures_idc may indicate that the EDRAP picture has one or more associated leading pictures, all of which are DASL pictures.

[0232] edrap_num_leading_pictures may indicate the number of leading pictures associated with the EDRAP picture. The value of edrap_num_leading_pictures may have a value between 0 and 255.

[0233] A value of 1 for edrap_dasl_picture_flag[i] indicates that the (i+1)th picture after the EDRAP picture in decoding order is a DASL picture, and a value of 0 for edrap_dasl_picture_flag[i] indicates that the (i+1)th picture after the EDRAP picture in decoding order is a DADL picture. If the value of edrap_leading_pictures_idc is 1, then the value of edrap_dasl_picture_flag[i] can be inferred to be 0 for i having values ​​between 0 and edrap_num_leading_pictures-1. If the value of edrap_leading_pictures_idc is 2, then the value of edrap_dasl_picture_flag[i] can be inferred to be 1 for i having values ​​between 0 and edrap_num_leading_pictures-1.

[0234] In addition, the following restrictions apply:

[0235] Any DASL picture associated with an EDRAP picture should precede in output order any DADL picture associated with the EDRAP picture.

[0236] A DADL picture associated with an EDRAP picture should not include in its active entry of the reference picture list a DASL picture associated with the EDRAP picture, or any picture that belongs to the same layer but precedes the EDRAP picture in decoding order. However, this restriction does not apply to referenceablePictures.

[0237] Any picture that belongs to the same layer but follows the EDRAP picture in both decoding order and output order should not include in the active entries of the reference picture list the DASL picture associated with the EDRAP picture or any picture that belongs to the same layer but precedes the EDRAP picture in decoding order, except that this restriction does not apply to referenceablePictures.

[0238] -If one or more leading pictures associated with an EDRAP picture are removed (i.e., bitstream thinning due to removal of pictures of higher temporal sublayers), the EDRAP SEI message must be updated to ensure accurate information about the leading pictures associated with the EDRAP picture.

[0239] The value of edrap_reserved_zero_5bits must be equal to 0 in the bitstream. Other values ​​of edrap_reserved_zero_5bits are reserved for future definition, and the image decoding device 200 must ignore the value of edrap_reserved_zero_5bits.

[0240] The value obtained by adding 1 to edrap_num_ref_rap_pics_minus1 indicates the number of IRAP or EDRAP pictures that exist in the same CLVS as the EDRAP picture and that can be included in the active entries of the reference picture list of the EDRAP picture.

[0241] edrap_ref_rap_id[i] indicates the RapPicId of the i-th RAP picture that can be included in the active entry of the reference picture list of the EDRAP picture. The i-th RAP picture must 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.

[0242] FIG. 9 is a flowchart showing an image encoding method according to the fourth embodiment, and FIG. 10 is a flowchart showing an image decoding method according to the fourth embodiment.

[0243] 9, the image coding apparatus 100 may determine the number and / or type of leading pictures included in an EDRAP picture and encode edrap_leading_pictures_idc indicating the number and / or type of leading pictures (S910). For example, if an EDRAP picture does not have an associated leading picture, the value of edrap_leading_pictures_idc may be encoded as 0. If an EDRAP picture has one or more associated leading pictures and all of the associated leading pictures are DADL pictures, the value of edrap_leading_pictures_idc may be encoded as 1. In addition, if an EDRAP picture has one or more associated leading pictures and all of the associated leading pictures are DASL pictures, the value of edrap_leading_pictures_idc can be coded as 2, and if an 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 can be coded as 3.

[0244] If the EDRAP picture has one or more associated leading pictures (S920, edrap_leading_pictures_idc!=0), the image coding apparatus 100 can code edrap_num_leading_pictures indicating the number of associated leading pictures (S930).

[0245] When the associated leading pictures are a mixture of DADL and DASL pictures (S940), the image coding device 100 may code edrap_dasl_picture_flag[i] indicating the type of each leading picture (S950), where i may be greater than or equal to 0 and less than the value of edrap_num_leading_pictures.

[0246] 10, the image decoding device 200 can 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 device 200 can obtain edrap_num_leading_pictures from the bitstream (S1030).

[0247] The image decoding device 200 can 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 device 200 can acquire edrap_dasl_picture_flag[i] from the bitstream (S1050). Here, i may be equal to or greater than 0 and may be less than the value of edrap_num_leading_pictures.

[0248] The image decoding apparatus 200 can 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 can be determined as DADL pictures. As another example, if the value of edrap_leading_pictures_idc is 2, all leading pictures can be determined as DASL pictures. As another example, if the value of edrap_leading_pictures_idc is 3, the type of each leading picture can be determined by the value of edrap_dasl_picture_flag[i].

[0249] FIG. 11 is a diagram illustrating an exemplary content streaming system to which an embodiment of the present disclosure can be applied.

[0250] As shown in FIG. 11, a content streaming system to which an embodiment of the present disclosure is applied can broadly include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0251] The encoding server compresses content input from a multimedia input device such as a smartphone, camera, or camcorder into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, if a multimedia input device such as a smartphone, camera, or video camera directly generates a bitstream, the encoding server can be omitted.

[0252] The bitstream can be generated by an image encoding method and / or image encoding device to which an embodiment of the present disclosure is applied, and the streaming server can temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0253] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server serves as an intermediary for informing the user of available services. When a user requests a desired service from the web server, the web server transmits the request to the streaming server, which then transmits the multimedia data to the user. In this case, the content streaming system may include a separate control server, which may control commands and responses between devices in the content streaming system.

[0254] The streaming server may receive content from a media storage and / or an encoding server. For example, when receiving content from the encoding server, the content may be received in real time. In this case, the streaming server may store the bitstream for a certain period of time to provide a smooth streaming service.

[0255] Examples of the user device include a mobile phone, a smartphone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation system, a slate PC, a tablet PC, an ultrabook, a wearable device such as a smartwatch, smart glass, a head mounted display (HMD), a digital TV, a desktop computer, and digital signage.

[0256] Each server in the content streaming system can be operated as a distributed server, in which case data received from each server can be processed in a distributed manner.

[0257] The scope of the present disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) that cause operations according to the methods of various embodiments to be performed on a device or computer, and non-transitory computer-readable medium on which such software or commands can be stored and executed on a device or computer. [Industrial Applicability]

[0258] The embodiments of the present disclosure can be used to encode / decode images.

Claims

1. An image decoding method performed by an image decoding device, comprising: obtaining a supplemental enhancement information (SEI) message for an extended dependent random access point (EDRAP) picture from the bitstream; and identifying a leading picture that follows the EDRAP picture in decoding order but precedes the EDRAP picture in output order based on the SEI message; The image decoding method, wherein the leading picture includes at least one of a decodable leading picture and a non-decodable leading picture.

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

3. The decodable leading pictures are restricted so as not to refer to the non-decodable leading pictures except for a predetermined picture; The image decoding method according to claim 1 , wherein the predetermined picture includes an intra random access point (IRAP) picture or an EDRAP picture that belongs to the same coded layer video sequence (CLVS).

4. The decodable leading picture is restricted so as not to refer to any picture preceding the EDRAP picture in decoding order, except for a predetermined picture; The image decoding method according to claim 1 , wherein the predetermined picture includes an intra random access point (IRAP) picture or an EDRAP picture that belongs to the same coded layer video sequence (CLVS).

5. Pictures following the EDRAP picture in decoding order and output order except for a predetermined picture are restricted so as not to refer to the non-decodable picture; The image decoding method according to claim 1 , wherein the predetermined picture includes an intra random access point (IRAP) picture or an EDRAP picture that belongs to the same coded layer video sequence (CLVS).

6. A picture following the EDRAP picture in decoding order and output order is restricted not to refer to a picture preceding the EDRAP picture in decoding order, except for a predetermined picture; The image decoding method according to claim 1 , wherein the predetermined picture includes an intra random access point (IRAP) picture or an EDRAP picture that belongs 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 leading picture that can be decoded.

8. The image decoding method according to claim 1 , wherein the SEI message includes a second SEI message for indicating the leading picture that cannot be decoded.

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 coding method performed by an image coding device, comprising: identifying a leading picture that follows an extended dependent random access point (EDRAP) picture in decoding order but precedes the EDRAP picture in output order; encoding a supplemental enhancement information (SEI) message for the EDRAP picture based on the identification of the leading picture; The image coding method, wherein the leading picture includes at least one of a decodable leading picture and a non-decodable leading picture.

11. A method for transmitting a bitstream generated by an image coding method, comprising: The image encoding method includes: identifying a leading picture that follows an extended dependent random access point (EDRAP) picture in decoding order but precedes the EDRAP picture in output order; encoding a supplemental enhancement information (SEI) message for the EDRAP picture based on the identification of the leading picture; The method, wherein the leading picture comprises at least one of a decodable leading picture and a non-decodable leading picture.

Images