Image encoding / decoding method and device based on available slice type information for GDR or IRPA pictures, and recording medium for storing bitstreams

Abstract

To provide a method and an apparatus for encoding / decoding an image.SOLUTION: There are disclosed a method and an apparatus for encoding / decoding an image. The method includes the steps of: determining whether an inter-slice type is to be allowed for a current picture including a current block; determining whether an intra-slice type is to be allowed for the current picture on the basis of whether the inter-slice type is allowed for the current picture; and decoding the current block on the basis of the slice type allowed for the current picture. Whether the inter-slice type is allowed for the current picture can be determined on the basis of whether the picture type of the current picture and the current layer including the current picture can use an inter-layer prediction.SELECTED DRAWING: Figure 18

Description

[Technical field]

[0001] The present disclosure relates to an image encoding / decoding method and apparatus, and more particularly, to an image encoding / decoding method and apparatus based on available slice type information for GDR or IRPA pictures, and a recording medium for storing a bitstream generated by the image encoding method / apparatus of the present disclosure. [Background technology]

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

[0003] This requires a highly efficient image compression technique 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] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus based on available slice type information for a GDR or IRPA picture.

[0006] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus that skips signaling of reference picture list information for an IRPA picture.

[0007] Another object of the present disclosure is to provide a recording medium for storing a bitstream generated by the image encoding method or apparatus according to the present disclosure.

[0008] Another object of the present disclosure is to provide a recording medium for storing a bitstream that is received by the image decoding device according to the present disclosure, decoded, and used to restore an image.

[0009] Another object of the present disclosure is to provide a method for transmitting a bitstream generated by the image encoding method or apparatus according to the present disclosure.

[0010] The technical problems to be solved by the present disclosure are not limited to the above-mentioned technical problems, and other technical problems not described above will be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the following description. [Means for solving the problem]

[0011] An image decoding method according to one aspect of the present disclosure includes a step of determining whether an inter slice type is allowed for a current picture including a current block, a step of determining whether an intra slice type is allowed for the current picture based on whether the inter slice type is allowed for the current picture, and a step of decoding the current block based on the slice type allowed for the current picture, where whether the inter slice type is allowed for the current picture can be determined based on the picture type of the current picture and whether the current layer including the current picture can utilize inter-layer prediction.

[0012] An image decoding device according to another aspect of the present disclosure includes a memory and at least one processor, where the at least one processor determines whether an inter slice type is allowed for a current picture including a current block, determines whether an intra slice type is allowed for the current picture based on whether the inter slice type is allowed for the current picture, and decodes the current block based on the slice type allowed for the current picture, where whether the inter slice type is allowed for the current picture can be determined based on the picture type of the current picture and whether a current layer including the current picture can utilize inter-layer prediction.

[0013] An image encoding method according to another aspect of the present disclosure includes a step of encoding first information regarding whether an inter slice type is allowed for a current picture including a current block, and a step of encoding second information regarding whether an intra slice type is allowed for the current picture based on whether the inter slice type is allowed for the current picture, where whether the inter slice type is allowed for the current picture can be determined based on the picture type of the current picture and whether the current layer including the current picture can utilize inter-layer prediction.

[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 image encoding device 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 image coding device of the present disclosure.

[0016] The features described above in the brief summary of the present disclosure are merely exemplary embodiments of the detailed description of the present disclosure that follows and are not intended to limit the scope of the present disclosure. Effect 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] In addition, according to the present disclosure, an image encoding / decoding method and apparatus based on available slice type information for a GDR or IRPA picture can be provided.

[0019] Furthermore, according to the present disclosure, an image encoding / decoding method and apparatus can be provided that skips signaling of reference picture list information for an IRPA picture.

[0020] According to the present disclosure, a recording medium storing a bitstream generated by the image encoding method or apparatus according to the present disclosure can be provided.

[0021] Furthermore, according to the present disclosure, it is possible to provide a recording medium storing a bitstream that is received by the image decoding device according to the present disclosure, decoded, and used to restore an image.

[0022] According to the present disclosure, there can also be provided a method for transmitting a bitstream generated by the image encoding method or apparatus according to the present disclosure.

[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 description of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram illustrating a video coding system to which an embodiment of the present disclosure can be applied. [Diagram 2] 1 is a diagram illustrating an image encoding device to which an embodiment of the present disclosure can be applied; [Diagram 3]1 is a diagram illustrating an image decoding device to which an embodiment of the present disclosure can be applied; [Figure 4] FIG. 2 shows an example of a hierarchical structure for coded images / video. [Diagram 5] FIG. 13 is a diagram illustrating an example of a picture header. [Figure 6] FIG. 13 is a diagram illustrating an example of a slice header. [Figure 7] FIG. 2 illustrates a picture header according to one embodiment of the present disclosure. [Figure 8] A diagram showing a picture header including idr_pic_flag according to one embodiment of the present disclosure. [Figure 9] A diagram showing a picture header including idr_pic_flag according to one embodiment of the present disclosure. [Figure 10] FIG. 2 illustrates a picture header according to one embodiment of the present disclosure. [Figure 11] FIG. 2 illustrates a picture header according to one embodiment of the present disclosure. [Figure 12] FIG. 2 illustrates a picture header according to one embodiment of the present disclosure. [Figure 13] FIG. 2 illustrates a picture header according to one embodiment of the present disclosure. [Figure 14] FIG. 2 illustrates a picture header according to one embodiment of the present disclosure. [Figure 15] FIG. 2 illustrates a picture header according to one embodiment of the present disclosure. [Figure 16] FIG. 2 illustrates a picture header according to one embodiment of the present disclosure. [Figure 17] 1 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure. [Figure 18] 1 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure. [Figure 19] FIG. 1 is a diagram illustrating an example of a content streaming system to which an embodiment of the present disclosure can be applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 specific description of a known configuration or function may make the gist of the present disclosure unclear, the detailed description thereof will be omitted. In addition, in the drawings, parts that are not related to the description of the present disclosure are omitted, and similar parts are denoted by similar reference numerals.

[0027] In the present disclosure, when a certain component is "connected," "coupled," or "connected" to another component, this includes not only a direct connection relationship, but also an indirect connection relationship in which another component exists between them. Furthermore, when a certain component is described as "including" or "having" another component, this does not mean that the other component is excluded, but that the other component can be further included, unless otherwise specified.

[0028] In this disclosure, terms such as "first" and "second" are used only for the purpose of distinguishing 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 called a second component in another embodiment, and similarly, a second component in one embodiment may be called 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 and configured as a single hardware or software unit, or one component may be distributed and configured as multiple hardware or software units. Thus, even if not otherwise stated, such integrated or distributed embodiments are also included in the scope of the present disclosure.

[0030] In the present disclosure, the components described in the 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 included in the scope of the present disclosure. In addition, an embodiment including other components in addition to the components described in the various embodiments is also included in the scope of the present disclosure.

[0031] The present disclosure relates to image encoding and decoding, and terms used in this disclosure may have ordinary meanings 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 means a unit indicating any one image in a particular time period, 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. Also, a slice / tile may include one or more coding tree units (CTUs).

[0033] In this disclosure, a "pixel" or a "pel" may refer to the smallest unit constituting one picture (or image). A term corresponding to a pixel may be a "sample." A sample may generally indicate a pixel or a pixel value, 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, a "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 the region. A unit may be used interchangeably with terms such as "sample array," "block," or "area," depending on the case. In a general case, 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." If prediction is performed, a "current block" may refer to a "current predicted block" or a "block to be predicted." If transformation (inverse transformation) / quantization (inverse quantization) is performed, a "current block" may refer to a "current transformed block" or a "block to be transformed." If filtering is performed, a "current block" may refer to a "block to be filtered."

[0036] Furthermore, in this disclosure, unless there is an explicit reference to a chroma block, a "current block" may refer to a block including both a luma component block and a chroma component block, or a "luma block of the current block." The luma component block of the current block may be expressed by explicitly including the reference to a luma component block, such as a "luma block" or a "current luma block." Furthermore, the chroma component block of the current block may be expressed by explicitly including the reference to a chroma component block, such as a "chroma block" or a "current chroma 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 schematic diagram of a video coding system to which embodiments of the present disclosure can be applied.

[0041] A video coding system according to an 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] The encoding device 10 according to an embodiment may include a video source generating unit 11, an encoding unit 12, and a transmitting unit 13. The decoding device 20 according to an embodiment may include a receiving 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 transmitting unit 13 may be included in the encoding unit 12. The receiving 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 generating unit 11 can obtain videos / images through a process of capturing, synthesizing, or generating videos / images. The video source generating 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 videos / images, etc. The video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate videos / images. For example, a virtual video / image can be generated through a computer, etc., in which case the video / image capture process can be replaced by 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, quantization, etc. for compression and encoding efficiency. The encoder 12 may output the encoded data (encoded video / image information) in a bitstream format.

[0045] The transmitting unit 13 may transmit the encoded video / image information or data output in a bitstream format to the receiving unit 21 of the decoding device 20 via a digital storage medium or a network in a file or streaming format. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitting unit 13 may include an element for generating a media file via a predetermined file format and may include an element for transmitting via a broadcasting / communication network. The receiving unit 21 may 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. The rendered video / images can be displayed via a display unit.

[0048] Overview of the image encoding device

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

[0050] As shown in Fig. 2, the image coding device 100 may include an image division unit 110, a subtraction unit 115, a transformation unit 120, a quantization unit 130, an inverse quantization unit 140, an inverse transformation 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 coding unit 190. The inter prediction unit 180 and the intra prediction unit 185 may be collectively referred to as a "prediction unit." The transformation unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transformation unit 150 may be included in a residual processing unit. The residual processing unit may further include a subtraction unit 115.

[0051] 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) depending on the embodiment. 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) according to a QT / BT / TT (Quad-tree / Binary-tree / Ternal-tree) structure. For example, one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad-tree structure, a binary-tree structure, and / or a ternary-tree structure. For dividing the coding units, a quad-tree structure may be applied first, and a binary-tree structure and / or a ternary-tree structure may be applied later. A coding procedure according to the present disclosure may be performed based on a final coding unit that is not further divided. The maximum coding unit may be used as the final coding unit, and 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 restoration, 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 block to be processed (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 in units of a current block or a CU. The prediction unit may generate various information related to prediction of the current block and transmit it to the entropy encoding unit 190. The information related to prediction may be encoded by the entropy encoding 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 away from the current block according to an intra prediction mode and / or an intra prediction technique. The intra prediction mode may include a plurality of non-directional modes and a plurality of directional modes. The non-directional mode may include, for example, a DC mode and a planar mode. The directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the fineness of the prediction direction. However, this is merely an example, and more or less directional prediction modes may be used depending on the setting. The intra prediction unit 185 may also determine a prediction mode to be applied to the current block using 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. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of a block, a sub-block, or a sample based on the correlation of motion information between a neighboring block and a current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring block may include a spatial neighboring block present in the current picture and a temporal neighboring block 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 from each other. 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 prediction unit 180 may generate information indicating which candidate is used to derive a motion vector and / or a reference picture index of the current block by forming a motion information candidate list based on neighboring blocks. Inter prediction may be performed based on various prediction modes, and for example, in the case of a skip mode and a merge mode, the inter prediction unit 180 may use motion information of neighboring blocks as motion information of the current block. In the case of the skip mode, unlike the merge mode, a residual signal may not be transmitted.In the case of a motion vector prediction (MVP) mode, the motion vector of the current block can be signaled by using the motion vector of a neighboring block as a motion vector predictor and encoding a motion vector difference and an indicator for the motion vector predictor. The motion vector difference can mean the difference between the motion vector of the current block and the motion vector predictor.

[0056] The prediction unit may generate a prediction signal based on various prediction methods and / or prediction techniques, which will be described later. For example, the prediction unit may apply intra prediction or inter prediction for prediction of the current block, and may simultaneously apply intra prediction and inter prediction. A prediction method that simultaneously applies intra prediction and inter prediction for prediction of the current block may be called combined inter and intra prediction (CIIP). The prediction unit may also perform intra block copy (IBC) for prediction of the current block. Intra block copy can be used for content image / video coding such as games, for example, as in screen content coding (SCC). IBC is a method of predicting a current block using an already restored 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 is basically performed in the current picture, but may be performed similarly to inter prediction in that a reference block is derived in 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, prediction sample array) output from the prediction unit from the input image signal (original block, original sample array) to generate a 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 when the relationship information between pixels is represented by a graph. 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 may be applied to non-square, variable-sized blocks.

[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 code the quantized signal (information on the quantized transform coefficients) and output the coded signal in a bitstream format. The information on 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 on 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 required for video / image restoration (e.g., values ​​of syntax elements, etc.) together or separately in addition to the quantized transform coefficients. The coded information (e.g., coded video / image information) may be transmitted or stored in a network abstraction layer (NAL) unit unit in a bitstream format. 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 further include general constraint information. The signaling information, transmitted information and / or syntax elements referred to in this disclosure may be encoded through the above-mentioned encoding procedures and included in the bitstream.

[0061] The bitstream may be transmitted via a network or may be 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) for transmitting the signal output from the entropy encoding unit 190 and / or a storing unit (not shown) for storing the signal 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 quantized transform coefficients are subjected to inverse quantization and inverse transformation via the inverse quantization unit 140 and the inverse transformation unit 150, so that a residual signal (residual block or residual sample) can be restored.

[0063] The adder 155 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the reconstructed residual signal to a 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, a predicted block may be used as a 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 described below.

[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 may 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, and the like. The filtering unit 160 may generate various information related to filtering, as will be described later in the description of each filtering method, and transmit the information to the entropy coding unit 190. The information related to filtering 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 may be used as a reference picture in the inter prediction unit 180. When inter prediction is applied through this, the image encoding device 100 may avoid a prediction mismatch between the image encoding device 100 and the image decoding device, and may also improve encoding efficiency.

[0066] The DPB in the memory 170 may store modified reconstructed pictures to be used as reference pictures in the inter prediction unit 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 prediction unit 180 to be used as motion information of spatial surrounding blocks or motion information of temporal surrounding blocks. The memory 170 may store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra prediction unit 185.

[0067] Overview of the image decoding device

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

[0069] 3, the image decoding device 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] All or at least some of the components constituting the image decoding device 200 may be realized by one hardware component (e.g., a decoder or a processor) depending on the embodiment. 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 executing 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. Thus, the processing unit for decoding can be, for example, a coding unit. The coding unit can be obtained by dividing a coding tree unit or a maximum coding unit. Then, 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 the form of a bitstream. The received signal may be decoded via the entropy decoding unit 210. For example, the entropy decoding unit 210 may derive information (e.g., video / image information) required for image restoration (or picture restoration) by parsing the bitstream. 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). In addition, the video / image information may further include general constraint information. The image decoding apparatus may further use information on the parameter set 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 the residual. More specifically, the CABAC entropy decoding method may receive bins corresponding to each syntax element from the bitstream, determine a context model using syntax element information to be decoded and decoded information of neighboring blocks and a block to be decoded, or information of a symbol / bin decoded in a previous step, predict the occurrence probability of the bin based on the determined context model, and perform arithmetic decoding of the bin to generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method may update the context model using information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model.Among the information decoded by the entropy decoding unit 210, information related to prediction is provided to a prediction unit (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 device according to the present disclosure may be called a video / image / picture decoding device. The image decoding device 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 to output 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 a coefficient scan 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 a prediction sample for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on the prediction information 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 has been described in the explanation of the prediction unit of the image encoding device 100.

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

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

[0080] The adder 235 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the acquired residual signal to a prediction signal (predicted block, predicted sample array) output from a prediction unit (including the inter prediction unit 260 and / or the 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 may also be applied 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 the 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 may be used as a reference picture in the inter prediction unit 260. The memory 250 may 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 may be transmitted to the inter prediction unit 260 to be used as motion information of a spatial surrounding block or motion information of a temporal surrounding block. The memory 250 may store a reconstructed sample of a reconstructed block in the current picture and transmit it to the intra prediction unit 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] Example of 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 an example of a hierarchical structure for coded images / video.

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

[0088] In VCL, it is possible to generate VCL data including compressed image data (slice data), or to generate parameter sets including information such as a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), and a Video Parameter Set (VPS), or a Supplemental Enhancement Information (SEI) message that is additionally required for image decoding processing.

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

[0090] As shown in Fig. 4, NAL units can be classified into VCL NAL units and non-VCL NAL units according to the type of RBSP generated in the VCL. The VCL NAL unit can refer to a NAL unit that includes information (slice data) on an image, and the non-VCL NAL unit can refer to a NAL unit that includes information (parameter set or SEI message) required for decoding an image.

[0091] The above-mentioned VCL NAL unit and non-VCL NAL unit can be transmitted over a network with header information 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), TS (Transport Stream), etc., and transmitted over various networks.

[0092] As described above, the NAL unit type of an NAL unit can be identified according to an RBSP data structure included in the NAL unit, and information on the NAL unit type can be stored and signaled in a NAL unit header. For example, NAL units can be largely classified into VCL NAL unit types and Non-VCL NAL unit types depending on whether the NAL unit includes information on an image (slice data). The VCL NAL unit types can be classified according to the nature and type of a picture included in the VCL NAL unit, and the Non-VCL NAL unit types can be classified according to the type of parameter set.

[0093] Below, examples of NAL unit types identified by the types of parameter sets / information contained in the Non-VCL NAL unit types are listed.

[0094] -DCI (Decoding capability information) NAL unit type (NUT): Type for NAL units containing DCI

[0095] -VPS (Video Parameter Set) NUT: Type for NAL units containing VPS

[0096] -SPS (Sequence Parameter Set) NUT: Type for NAL units containing SPS

[0097] -PPS (Picture Parameter Set) NUT: Type for NAL units containing PPS

[0098] -APS (Adaptation Parameter Set) NUT: Type for NAL units including APS

[0099] -PH(Picture header) NUT: Type for NUL units containing picture headers

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

[0101] Meanwhile, one picture may include a plurality of slices, and one slice may include a slice header and slice data. In this case, one picture header may be further added for a plurality of slices (slice header and slice data set) in one picture. The picture header (picture header syntax) may include information / parameters commonly applicable to the pictures. The slice header (slice header syntax) may include information / parameters commonly applicable to the slices. The APS (APS syntax) or PPS (PPS syntax) may include information / parameters commonly applicable to one or more slices or pictures. The SPS (SPS syntax) may include information / parameters commonly applicable to one or more sequences. The VPS (VPS syntax) may include information / parameters commonly applicable to multiple layers. The DCI may include information / parameters related to decoding capability.

[0102] In the present disclosure, the high level syntax (HLS) may include at least one of the APS syntax, the PPS syntax, the SPS syntax, the VPS syntax, the DCI syntax, the picture header syntax, and the slice header syntax. In addition, in the present disclosure, the low level syntax (LLS) may include, for example, a slice data syntax, a CTU syntax, a coding unit syntax, a transform unit syntax, and the like.

[0103] In the present disclosure, the image / video information encoded from the encoding device to the decoding device and signaled in a 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 the slice header information, the picture header information, the APS information, the PPS information, the SPS information, the VPS information, and / or the DCI information. In addition, the image / video information may further include general constraint information and / or NAL unit header information.

[0104] Overview of NAL unit types

[0105] Generally, one NAL unit type can be set for one picture. As described above, syntax information indicating the NAL unit type can be stored and signaled in a NAL unit header in the NAL unit. For example, the syntax information is nal_unit_type, and the NAL unit type can be specified using the nal_unit_type value. An example of the NAL unit type is shown in Table 1 below.

[0106] [Table 1-1]

[0107] [Table 1-2]

[0108] Referring to Table 1, VCL NAL unit types can be classified into NAL unit types 0 to 12 according to picture types. Also, non-VCL NAL unit types can be classified into NAL unit types 13 to 31 according to parameter types. The VCL NAL unit types are summarized by picture type as follows:

[0109] (1) IRAP (Intra Random Access Point) Picture

[0110] An IRAP picture may refer to a randomly accessible picture in which all VCL NAL units have the same NAL unit type within the range of IDR_W_RADL to CRA_NUT. An IRAP picture may include an Instantaneous Decoding Refresh (IDR) picture and a Clean Random Access (CRA) picture. An IRAP picture may not use inter prediction based on a reference picture in the same layer during decoding. The first picture in a bitstream in decoding order may be an IRAP picture or a Gradual Decoding Refresh (GDR) picture. For a single layer bitstream, if a parameter set that needs to be referenced is available, the IRAP picture and all non-Random Access Skipped Leading (RASL) pictures following the IRAP picture in decoding order in a coded layer video sequence (CLVS) can be correctly decoded without decoding any pictures preceding the IRAP picture in decoding order.

[0111] (2) CRA (Clean Random Access) Pictures

[0112] A CRA picture may refer to an IRAP picture in which each VCL NAL unit has a NAL unit type equal to CRA_NUT. A CRA picture may not use inter prediction during decoding. A CRA picture may be the first picture in a bitstream in decoding order, or may be a picture after the first picture. A CRA picture may be associated with a RADL or RASL picture. If NoOutputBeforeRecoveryFlag has a first value (e.g., 1) for a CRA picture, a RASL picture associated with the CRA picture cannot be decoded because it refers to a picture that does not exist in the bitstream, and therefore may not be output by the image decoding apparatus. Here, NoOutputBeforeRecoveryFlag may indicate whether a picture preceding a recovery point picture in decoding order is output before the recovery point picture. For example, a NoOutputBeforeRecoveryFlag with a first value (e.g., 1) may indicate that a picture preceding a recovery point picture in decoding order cannot be output before the recovery point picture. In this case, the CRA picture may be the first picture in the bitstream or the first picture following an End Of Sequence (EOS) NAL unit in decoding order, which may mean that random access has occurred. In contrast, a NoOutputBeforeRecoveryFlag with a second value (e.g., 0) may indicate that a picture preceding a recovery point picture in decoding order can be output before the recovery point picture. In this case, the CRA picture may not be the first picture in the bitstream or the first picture following an EOS NAL unit in decoding order, which may mean that random access has not occurred.

[0113] (3) IDR (Instantaneous Decoding Refresh) Picture

[0114] An IDR picture may refer to an IRAP picture in which each VCL NAL unit has a NAL unit type equal to IDR_W_RADL or IDR_N_LP. An IDR picture may not use inter prediction during decoding. An IDR picture may be the first picture in a bitstream in decoding order, or may be a picture after the first. Each IDR picture may be the first picture in a coded video sequence (CVS) in decoding order. If each VCL NAL unit for an IDR picture has a NAL unit type equal to IDR_W_RADL, the IDR picture may have an associated RADL picture. Alternatively, if each VCL NAL unit for an IDR picture has a NAL unit type equal to IDR_N_LP, the IDR picture may not have an associated leading picture. Meanwhile, an IDR picture may not have an associated RASL picture.

[0115] (4) RADL (Random Access Decodable Leading) Picture

[0116] A RADL picture may refer to a picture whose respective VCL NAL unit has a NAL unit type equal to RADL_NUT. All RADL pictures may be leading pictures.

[0117] (5) RASL (Random Access Skipped Leading) Picture

[0118] An RASL picture may refer to a picture in which at least one VCL NAL unit has a NAL unit type equal to RASL_NUT and the remaining VCL NAL units have NAL unit types equal to RASL_NUT or RADL_NUT. Every RASL picture may be a leading picture of an associated CRA picture.

[0119] (6) Trailing Picture

[0120] A trailing picture may refer to a picture whose respective VCL NAL unit has a NAL unit type equal to TRAIL_NUT. A trailing picture associated with an IRAP or GDR picture may follow the IRAP or GDR picture in decoding order. A picture following the associated IRAP picture in output order and preceding the associated IRAP picture in decoding order may not be allowed.

[0121] (7) GDR (Gradual Decoding Refresh) Picture

[0122] A GDR picture may refer to a randomly accessible picture in which each VCL NAL unit has a NAL unit type equal to GDR_NUT.

[0123] The GDR feature can mean that decoding starts from a picture where not all parts of the restored picture may be correctly decoded, but the correctly decoded parts of the restored picture in subsequent pictures gradually increase until the whole picture is correctly decoded. In this case, the picture where the decoding process can start with the GDR feature is called a GDR picture, and the first picture after the GDR picture where the whole picture is correctly decoded is called a recovery point picture.

[0124] (8) STSA (Step-wise Temporal Sublayer Access) Picture

[0125] An STSA picture may refer to a randomly accessible picture in which each VCL NAL unit has a NAL unit type equal to STSA_NUT.

[0126] High-Level Syntax

[0127] As described above, a high level syntax (HLS) may be encoded / signaled for image / video coding. Image / video information may include a high level syntax (HLS), and an image / video coding method may be performed based on the image / video information.

[0128] As an example of image / video information, reference picture list information (e.g., ref_pic_lists) may be signaled in a picture header or a slice header based on an rpl_info_in_ph_flag syntax signaled in a picture parameter set. Here, rpl_info_in_ph_flag may indicate whether reference picture list information is present in the picture header. For example, a first value (e.g., 1) of rpl_info_in_ph_flag may indicate that reference picture list information is present in the picture header but not in the slice header. Differently, a second value (e.g., 0) of rpl_info_in_ph_flag may indicate that reference picture list information is not present in the picture header but may be present in the slice header.

[0129] FIG. 5 is a diagram illustrating an example of a picture header.

[0130] Referring to FIG. 5, the picture header may include a syntax element gdr_or_irap_pic_flag. gdr_or_irap_pic_flag may indicate whether the current picture is a Gradual Decoding Refresh (GDR) or an Intra Random Access Point (IRAP) picture. For example, a first value (e.g., 1) of gdr_or_irap_pic_flag may indicate that the current picture is a GDR or an IRAP picture. In contrast, a second value (e.g., 0) of gdr_or_irap_pic_flag may indicate that the current picture is not a GDR picture but may be an IRAP picture.

[0131] The picture header may also include a syntax element gdr_pic_flag. The gdr_pic_flag may indicate whether the current picture is a GDR picture. For example, a first value (e.g., 1) of gdr_pic_flag may indicate that the current picture is a GDR picture. In contrast, a second value (e.g., 0) of gdr_pic_flag may indicate that the current picture is not a GDR picture. If gdr_pic_flag is not present (i.e., not signaled), the value of gdr_pic_flag may be inferred to be the second value (e.g., 0). If a GDR picture is unavailable and not present in the coded layer video sequence (CLVS) (e.g., sps_gdr_enabled_flag==0), the value of gdr_pic_flag may be restricted to the second value (e.g., 0). On the other hand, if the above-mentioned gdr_or_irap_pic_flag has a first value (eg, 1) and gdr_pic_flag has a second value (eg, 0), the current picture can be determined to be an IRAP picture.

[0132] The picture header may also include a syntax element ph_inter_slice_allowed_flag. The ph_inter_slice_allowed_flag may indicate whether one or more slices in the current picture may have an inter slice type (e.g., B slice type or P slice type). For example, a first value (e.g., 1) of ph_inter_slice_allowed_flag may indicate that there may be one or more coded slices in the current picture that have a B slice type (i.e., sh_slice_type=0) or a P slice type (i.e., sh_slice_type=1). In contrast, a second value (e.g., 0) of ph_inter_slice_allowed_flag may indicate that all coded slices in the current picture have an I slice type (i.e., sh_slice_type=2).

[0133] The picture header may also include a syntax element ph_intra_slice_allowed_flag. The ph_intra_slice_allowed_flag may indicate whether one or more slices in the current picture may have an intra slice type (e.g., an I slice type). For example, a first value (e.g., 1) of ph_intra_slice_allowed_flag may indicate that one or more coded slices having an I slice type (i.e., sh_slice_type=2) may exist in the current picture. In contrast, a second value (e.g., 0) of ph_intra_slice_allowed_flag may indicate that all coded slices in the current picture have a B slice type (i.e., sh_slice_type=0) or a P slice type (i.e., sh_slice_type=1). The ph_intra_slice_allowed_flag may be signaled only if the ph_intra_slice_allowed_flag has a first value (e.g., 1). If ph_intra_slice_allowed_flag is not present, the value of ph_intra_slice_allowed_flag may be inferred to be a first value (eg, 1).

[0134] On the other hand, if the above-mentioned rpl_info_in_ph_flag has a first value (eg, 1), the reference picture list information ref_pic_lists can be signaled in the picture header.

[0135] As described above, the picture header may include two syntax elements (e.g., ph_inter_slice_allowed_flag and ph_intra_slice_allowed_flag) that indicate whether signaling of syntax elements for inter-predicted slices and intra-predicted slices is allowed in the picture header. However, in the case of a GDR picture, since the picture includes one or more slices having an inter-slice type in terms of picture attributes, there is no need to signal ph_inter_slice_allowed_flag for the GDR picture. However, in the picture header of FIG. 5, ph_inter_slice_allowed_flag is signaled unconditionally, which causes a problem of unnecessary increase in signaling overhead.

[0136] FIG. 6 is a diagram illustrating an example of a slice header.

[0137] 6, when the above-mentioned rpl_info_in_ph_flag has a second value (e.g., 0), the reference picture list information ref_pic_lists may be signaled in the slice header under a certain condition. Specifically, when the rpl_info_in_ph_flag has a second value (e.g., 0) and the NAL unit type is neither IDR_W_RADL nor IDR_N_LP (i.e., nal_unit_type!=IDR_W_RADL && nal_unit_type!=IDR_N_LP), or when the sps_idr_rpl_presetn_flag has a first value (e.g., 1), the ref_pic_lists may be signaled. Here, a first value (eg, 1) of sps_idr_rpl_present_flag may indicate that syntax elements related to reference picture lists may be present in the slice header of a slice having a NAL unit type equal to IDR_W_RADL or IDR_N_LP.

[0138] Generally, for an IDR picture having a NAL unit type equal to IDR_W_RADL or IDR_N_LP, reference picture list information is not required due to picture attributes. Therefore, in order to signal the reference picture list information ref_pic_list, it is necessary to check the nal_unit_type value, which is information on the NAL unit type signaled in the NAL unit header. On the other hand, even if nal_unit_type has a value related to an IDR picture, reference picture list information may be required in the case of bitstream extraction and merging scenarios. Therefore, in order to signal the reference picture list information ref_pic_list, it is necessary to check sps_idr_rpl_present_flag, which indicates whether or not a syntax element related to a reference picture list is present in the slice header.

[0139] However, in the picture header, the reference picture list information is signaled without considering the above-mentioned additional signaling conditions, i.e., in the picture header, the reference picture list information ref_pic_list is only signaled based on rpl_info_in_ph_flag, which causes a problem that the reference picture list information ref_pic_list can be unnecessarily signaled even for IDR pictures that do not involve bitstream extraction and merging.

[0140] In order to solve the above-mentioned problems, according to an embodiment of the present disclosure, a signaling condition of reference picture list information may be added to a picture header, or a flag indicating that a current picture is an IDR picture may be added to a picture header, or a signaling condition of an inter-slice related syntax element may be added to a picture header. Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[0141] Example 1

[0142] According to embodiment 1 of the present disclosure, within the picture header, reference picture list information can be signaled based on whether a syntax element related to the reference picture list of the IDR picture is present in the slice header (i.e., sps_idr_rpl_present_flag).

[0143] FIG. 7 is a diagram illustrating a picture header according to one embodiment of the present disclosure.

[0144] Referring to FIG 7, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR (Gradual Decoding Refresh) or IRAP (Intra Random Access Point) picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture. The picture header may also include a syntax element ph_inter_slice_allowed_flag indicating whether one or more slices in the current picture can have an inter slice type (e.g., B slice type or P slice type), and a syntax element ph_intra_slice_allowed_flag indicating whether one or more slices in the current picture can have an intra slice type (e.g., I slice type). The semantics of each of the syntax elements are as described above with reference to FIG 5.

[0145] In the picture header, the reference picture list information ref_pic_lists may be signaled based on a first predetermined condition (710). Specifically, ref_pic_lists may be signaled only if the reference picture list information exists in the picture header (i.e., rpl_info_in_ph_flag==1) and a syntax element related to the reference picture list exists in the slice header of a slice having a NAL unit type equal to IDR_N_LP or IDR_W_RADL (i.e., sps_idr_rpl_present_flag==1). Here, IDR_N_LP may refer to a NAL unit type of an IDR picture that does not have an associated leading picture (e.g., RASL and RADL pictures) in the bitstream. Also, IDR_W_RADL may refer to a NAL unit type of an IDR picture that does not have an associated RASL picture in the bitstream but may have an associated RADL picture.

[0146] The picture header of Figure 7 may differ from that of Figure 5 in that reference picture list information ref_pic_lists is signaled based on whether sps_idr_rpl_present_flag has a first value (e.g., 1). That is, if there is no syntax element related to reference picture lists in the slice header (i.e., sps_idr_rpl_present_flag==0), ref_pic_lists may not be signaled in the picture header. This can solve the problem of unnecessary signaling of reference picture list information for an IDR picture in the picture header.

[0147] Example 2

[0148] According to the second embodiment of the present disclosure, a syntax element indicating whether the current picture is an IDR picture or not can be newly defined in the picture header.

[0149] FIG. 8 is a diagram illustrating a picture header including idr_pic_flag according to one embodiment of the present disclosure.

[0150] Referring to FIG 8, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR or IRAP picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture. The picture header may also include a syntax element ph_inter_slice_allowed_flag indicating whether one or more slices in the current picture can have an inter slice type (e.g., B slice type or P slice type), and a syntax element ph_intra_slice_allowed_flag indicating whether one or more slices in the current picture can have an intra slice type (e.g., I slice type). The semantics of each of the syntax elements are as described above with reference to FIG 5.

[0151] The picture header may further include a syntax element idr_pic_flag (810). The idr_pic_flag may indicate whether the current picture is an IDR picture. For example, a first value (e.g., 1) of idr_pic_flag may indicate that the current picture is an IDR picture. Conversely, a second value (e.g., 0) of idr_pic_flag may indicate that the current picture is not an IDR picture. If idr_pic_flag is not present, the idr_pic_flag may be inferred to be the second value (e.g., 0).

[0152] idr_pic_flag may be conditionally signaled based on gdr_or_irap_pic_flag. For example, if gdr_or_irap_pic_flag has a first value (e.g., 1) indicating that the current picture is a GDR or IRAP picture, idr_pic_flag may be signaled. In contrast, if gdr_or_irap_pic_flag has a second value (e.g., 0) indicating that the current picture may be an IRAP picture rather than a GDR picture, idr_pic_flag may not be signaled. In this way, idr_pic_flag may be signaled under the same condition as gdr_pic_flag (i.e., gdr_or_irap_pic_flag==1).

[0153] However, in other embodiments, idr_pic_flag may be conditionally signaled based on gdr_or_irap_pic_flag and gdr_pic_flag.

[0154] FIG. 9 is a diagram illustrating a picture header including idr_pic_flag according to another embodiment of the present disclosure.

[0155] 9, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR or IRAP picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture. The picture header may also include a syntax element ph_inter_slice_allowed_flag indicating whether one or more slices in the current picture can have an inter slice type (e.g., B slice type or P slice type), and a syntax element ph_intra_slice_allowed_flag indicating whether one or more slices in the current picture can have an intra slice type (e.g., I slice type). The semantics of each of the syntax elements are as described above with reference to FIG. 5.

[0156] The picture header may further include a syntax element idr_pic_flag indicating whether the current picture is an IDR picture (910). The semantics of idr_pic_flag are as described above with reference to FIG.

[0157] idr_pic_flag may be conditionally signaled based on gdr_or_irap_pic_flag and gdr_pic_flag. For example, idr_pic_flag may be signaled if gdr_or_irap_pic_flag has a first value (e.g., 1) indicating that the current picture is a GDR or IRAP picture and gdr_pic_flag has a second value (e.g., 0) indicating that the current picture is not a GDR picture. Alternatively, idr_pic_flag may not be signaled if gdr_or_irap_pic_flag has a second value (e.g., 0) indicating that the current picture may be an IRAP picture rather than a GDR picture or if gdr_or_irap_pic_flag has a first value (e.g., 1) indicating that the current picture is a GDR picture. This allows idr_pic_flag to be signaled only if the current picture is an IRAP picture.

[0158] In this way, by explicitly signaling idr_pic_flag, which indicates whether the current picture is an IDR picture, the signaling conditions of various syntax elements that assume that the current picture is an IDR picture can be simplified.

[0159] Example 3

[0160] According to the third embodiment of the present disclosure, in the picture header, the reference picture list information can be signaled based on whether the current picture is an IDR picture or not.

[0161] FIG. 10 is a diagram illustrating a picture header according to one embodiment of the present disclosure.

[0162] Referring to FIG 10, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR or IRAP picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture. The picture header may also include a syntax element ph_inter_slice_allowed_flag indicating whether one or more slices in the current picture can have an inter slice type (e.g., B slice type or P slice type), and a syntax element ph_intra_slice_allowed_flag indicating whether one or more slices in the current picture can have an intra slice type (e.g., I slice type). The semantics of each of the syntax elements are as described above with reference to FIG 5.

[0163] In one embodiment, if gdr_or_irap_pic_flag has a first value (e.g., 1), gdr_pic_flag has a second value (e.g., 0) (i.e., the current picture is an IRAP picture), and vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] has a first value (e.g., 1), the value of ph_inter_slice_allowed_flag may be set to a second value (e.g., 0). Here, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] of the first value (e.g., 1) may indicate that a layer having index GeneralLayerIdx[nuh_layer_id] does not use inter-layer prediction.

[0164] The picture header may further include a syntax element idr_pic_flag indicating whether the current picture is an IDR picture. The semantics and signaling conditions of idr_pic_flag are as described above with reference to FIG.

[0165] In the picture header, reference picture list information ref_pic_lists may be signaled based on a predetermined second condition (1010). Specifically, ref_pic_lists may be signaled only if reference picture list information exists in the picture header (i.e., rpl_info_in_ph_flag==1) and the current picture is not an IDR picture (i.e., idr_pic_flag==0).

[0166] The picture header of Figure 10 may differ from that of Figure 5 in that reference picture list information ref_pic_lists is signaled based on whether the current picture is an IDR picture or not. That is, if the current picture is an IDR picture (i.e., idr_pic_flag==1), ref_pic_lists may not be signaled in the picture header. This can solve the problem of unnecessary signaling of reference picture list information for an IDR picture in the picture header.

[0167] Example 4

[0168] According to embodiment 4 of the present disclosure, within the picture header, reference picture list information can be signaled based on whether the current picture is an IDR picture and whether a syntax element for the reference picture list of the IDR picture is present in the slice header.

[0169] FIG. 11 is a diagram illustrating a picture header according to one embodiment of the present disclosure.

[0170] 11, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR or IRAP picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture. The picture header may also include a syntax element ph_inter_slice_allowed_flag indicating whether one or more slices in the current picture can have an inter slice type (e.g., B slice type or P slice type), and a syntax element ph_intra_slice_allowed_flag indicating whether one or more slices in the current picture can have an intra slice type (e.g., I slice type). The semantics of each of the syntax elements are as described above with reference to FIG. 5.

[0171] In one embodiment, if gdr_or_irap_pic_flag has a first value (e.g., 1), gdr_pic_flag has a second value (e.g., 0) (i.e., the current picture is an IRAP picture), and vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] has a first value (e.g., 1), the value of ph_inter_slice_allowed_flag may be set to a second value (e.g., 0). Here, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] of the first value (e.g., 1) may indicate that a layer having index GeneralLayerIdx[nuh_layer_id] does not use inter-layer prediction.

[0172] The picture header may further include a syntax element idr_pic_flag indicating whether the current picture is an IDR picture. The semantics and signaling conditions of idr_pic_flag are as described above with reference to FIG.

[0173] In the picture header, the reference picture list information ref_pic_lists may be signaled based on a predetermined third condition (1110). Specifically, ref_pic_lists may be signaled only if the reference picture list information exists in the picture header (i.e., rpl_info_in_ph_flag==1) and a syntax element related to the reference picture list exists in the slice header of a slice having a NAL unit type equal to IDR_N_LP or IDR_W_RADL, or the current picture is not an IDR picture (i.e., sps_idr_rpl_present_flag==1 or idr_pic_flag==0).

[0174] The picture header of Figure 11 may differ from that of Figure 5 in that reference picture list information ref_pic_lists is signaled based on whether sps_idr_rpl_present_flag has a first value (e.g., 1) or idr_pic_flag has a second value (e.g., 0). That is, if there is no syntax element related to a reference picture list of an IDR picture in the slice header (i.e., sps_idr_rpl_present_flag==0) and the current picture is an IDR picture (i.e., idr_pic_flag==1), ref_pic_lists may not be signaled in the picture header. This can solve the problem of unnecessary signaling of reference picture list information for an IDR picture in the picture header.

[0175] Example 5

[0176] According to embodiment 5 of the present disclosure, within the picture header, reference picture list information can be signaled based on whether the current picture is an IDR picture and whether a syntax element for a reference picture list of the IDR picture is present in the slice header.

[0177] FIG. 12 is a diagram illustrating a picture header according to one embodiment of the present disclosure.

[0178] 12, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR or IRAP picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture. The picture header may also include a syntax element ph_inter_slice_allowed_flag indicating whether one or more slices in the current picture can have an inter slice type (e.g., B slice type or P slice type), and a syntax element ph_intra_slice_allowed_flag indicating whether one or more slices in the current picture can have an intra slice type (e.g., I slice type). The semantics of each of the syntax elements are as described above with reference to FIG. 5.

[0179] The picture header may further include a syntax element idr_pic_flag indicating whether the current picture is an IDR picture. idr_pic_flag may differ from idr_pic_flag in FIG. 11 in that idr_pic_flag is signaled only if the current picture is not a GDR picture (i.e., gdr_pic_flag==0). That is, if gdr_pic_flag has a first value (e.g., 1), idr_pic_flag may not be signaled. On the other hand, idr_pic_flag may be signaled if gdr_pic_flag is not signaled but is set to a second value (e.g., 0).

[0180] In the picture header, the reference picture list information ref_pic_lists may be signaled based on a predetermined third condition (1210). Specifically, ref_pic_lists may be signaled only if reference picture list information exists in the picture header (i.e., rpl_info_in_ph_flag==1) and a syntax element related to reference picture list exists in the slice header of a slice having a NAL unit type equal to IDR_N_LP or IDR_W_RADL, or the current picture is not an IDR picture (i.e., sps_idr_rpl_present_flag==1 or idr_pic_flag==0).

[0181] The picture header of Figure 12 may differ from that of Figure 5 in that reference picture list information ref_pic_lists is signaled based on whether sps_idr_rpl_present_flag has a first value (e.g., 1) or idr_pic_flag has a second value (e.g., 0). That is, if there is no syntax element related to a reference picture list of an IDR picture in the slice header (i.e., sps_idr_rpl_present_flag==0) and the current picture is an IDR picture (i.e., idr_pic_flag==1), ref_pic_lists may not be signaled in the picture header. This can solve the problem of unnecessary signaling of reference picture list information for an IDR picture in the picture header.

[0182] Example 6

[0183] According to the sixth embodiment of the present disclosure, in the picture header, information indicating whether inter slices are allowed in the current picture can be signaled based on whether the current picture is a GDR picture.

[0184] FIG. 13 is a diagram illustrating a picture header according to one embodiment of the present disclosure.

[0185] 13, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR or IRAP picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture, the semantics of each of the syntax elements being as described above with reference to FIG.

[0186] The picture header may also include a syntax element ph_inter_slice_allowed_flag. The ph_inter_slice_allowed_flag may indicate whether one or more slices in the current picture can have an inter slice type (e.g., B slice type or P slice type). For example, a first value (e.g., 1) of ph_inter_slice_allowed_flag may indicate that there may be one or more coded slices in the current picture that have a B slice type (i.e., slice_type=0) or a P slice type (i.e., slice_type=1). In contrast, a second value (e.g., 0) of ph_inter_slice_allowed_flag may indicate that all coded slices in the current picture have an I slice type (i.e., slice_type=2).

[0187] ph_inter_slice_allowed_flag may be signaled only if the current picture is not a GDR picture (1310). For example, if gdr_pic_flag has a second value (e.g., 0) indicating that the current picture is not a GDR picture, ph_inter_slice_allowed_flag may be signaled. Alternatively, if gdr_pic_flag has a first value (e.g., 1) indicating that the current picture is a GDR picture, ph_inter_slice_allowed_flag may not be signaled. If ph_inter_slice_allowed_flag is not signaled, the value of ph_inter_slice_allowed_flag may be inferred to be the first value (e.g., 1).

[0188] The picture header may also include a syntax element ph_intra_slice_allowed_flag. The ph_intra_slice_allowed_flag may indicate whether one or more slices in the current picture can have an intra slice type (e.g., an I slice type). For example, a first value (e.g., 1) of ph_intra_slice_allowed_flag may indicate that one or more coded slices having an I slice type (i.e., slice_type=2) may exist in the current picture. In contrast, a second value (e.g., 0) of ph_intra_slice_allowed_flag may indicate that all coded slices in the current picture have a B slice type (i.e., slice_type=0) or a P slice type (i.e., slice_type=1).

[0189] ph_intra_slice_allowed_flag may be signaled only if inter slices are allowed for the current picture (1720). For example, if ph_inter_slice_allowed_flag has a first value (e.g., 1) indicating that there may be one or more coded slices having a B slice type or a P slice type in the current picture, ph_intra_slice_allowed_flag may be signaled. In contrast, if ph_inter_slice_allowed_flag has a second value (e.g., 0) indicating that all coded slices in the current picture have an I slice type, ph_inter_slice_allowed_flag may not be signaled. If ph_intra_slice_allowed_flag is not signaled, the value of ph_intra_slice_allowed_flag may be inferred to be the first value (e.g., 1).

[0190] Meanwhile, in another embodiment, ph_intra_slice_allowed_flag may be signaled only if the current picture is not a GDR picture and inter slice is allowed for the current picture.

[0191] Figure 14 is a diagram showing a picture header according to another embodiment of the present disclosure. The picture header in Figure 14 may have the same structure and semantics as the picture header in Figure 13, except for the signaling condition of ph_intra_slice_allowed_flag. Therefore, a duplicated description will be omitted.

[0192] 14, in the picture header, ph_intra_slice_allowed_flag may be signaled only if the current picture is not a GDR picture and inter slices are allowed for the current picture (1410). For example, ph_intra_slice_allowed_flag may be signaled if gdr_pic_flag has a second value (e.g., 0) indicating that the current picture is not a GDR picture and ph_inter_slice_allowed_flag has a first value (e.g., 1) indicating that there may be one or more coded slices with B slice type or P slice type in the current picture. Alternatively, ph_intra_slice_allowed_flag may not be signaled if gdr_pic_flag has a first value (e.g., 1) indicating that the current picture is a GDR picture or if ph_inter_slice_allowed_flag has a second value (e.g., 0) indicating that all coded slices in the current picture have an I-slice type. If ph_intra_slice_allowed_flag is not signaled, the value of ph_intra_slice_allowed_flag may be inferred to be the first value (e.g., 1).

[0193] As described above with reference to Figures 13 and 14, ph_inter_slice_allowed_flag can be signaled only when the current picture is not a GDR picture, thereby solving the problem that ph_inter_slice_allowed_flag is unnecessarily signaled for a GDR picture that can include an inter slice according to the picture attributes.

[0194] Example 7

[0195] According to embodiment 7 of the present disclosure, in the picture header, information indicating whether inter-slices are allowed in the current picture can be signaled based on whether the current layer containing the current picture can utilize inter-layer prediction and whether the current picture is an IRAP picture.

[0196] FIG. 15 is a diagram illustrating a picture header according to one embodiment of the present disclosure.

[0197] 15, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR or IRAP picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture, the semantics of each of the syntax elements being as described above with reference to FIG.

[0198] The picture header may also include a syntax element ph_inter_slice_allowed_flag indicating whether inter slices (e.g., B slices or P slices) are allowed for the current picture. The semantics of ph_inter_slice_allowed_flag are as described above with reference to FIG.

[0199] The ph_inter_slice_allowed_flag may be signaled based on a predetermined fourth condition (1510). Specifically, if vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] has a second value (e.g., 0) indicating that a current layer including the current picture can utilize inter-layer prediction, or gdr_or_irap_pic_flag has a second value (e.g., 0) indicating that the current picture is not a GDR picture and may be an IRAP picture, or gdr_pic_flag has a first value (e.g., 1) indicating that the current picture is a GDR picture (i.e., !(vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] && gdr_or_irap_pic_flag && !gdr_pic_flag)==1), the ph_inter_slice_allowed_flag may be signaled. Alternatively, if vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] has a first value (e.g., 1) indicating that the current layer including the current picture does not utilize inter-layer prediction, gdr_or_irap_pic_flag has a first value (e.g., 1) indicating that the current picture is a GDR or IRAP picture, and gdr_pic_flag has a second value (e.g., 0) indicating that the current picture is not a GDR picture (i.e., !(vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] && gdr_or_irap_pic_flag && !gdr_pic_flag) == 0), then ph_inter_slice_allowed_flag is not signaled and can be inferred to be the second value (e.g., 0) indicating that inter-slice is not allowed for the current picture.That is, if the current picture is an IRAP picture contained in an independent layer that does not utilize inter-layer prediction, ph_inter_slice_allowed_flag is not signaled and can be inferred to be a second value (e.g., 0) indicating that inter-slicing is not allowed for the current picture.

[0200] In another embodiment, if ph_inter_slice_allowed_flag is not signaled, then if the current picture is a GDR picture (i.e., gdr_or_irap_pic_flag==1 && gdr_pic_flag==1), then ph_inter_slice_allowed_flag may be inferred to have a first value (e.g., 1) indicating that inter slicing is allowed for the current picture. Alternatively, if the current picture is not a GDR picture (e.g., if the current picture is an IRAP picture included in an independent layer (i.e., gdr_or_irap_pic_flag==1 && gdr_pic_flag==0 && vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]==1), then ph_inter_slice_allowed_flag may be inferred to have a second value (e.g., 0) indicating that inter slicing is not allowed for the current picture.

[0201] Meanwhile, in one embodiment, if gdr_or_irap_pic_flag has a first value (e.g., 1), gdr_pic_flag has a second value (e.g., 0) (i.e., the current picture is an IRAP picture), and vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] has a first value (e.g., 1), the value of ph_inter_slice_allowed_flag may be set to a second value (e.g., 0). Here, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] of the first value (e.g., 1) may indicate that a layer having index GeneralLayerIdx[nuh_layer_id] does not use inter-layer prediction.

[0202] As described above with reference to FIG. 15, if the current picture belongs to an independent layer that does not use inter-layer prediction and the current picture is only an IRAP picture (i.e., !(vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] && gdr_or_irap_pic_flag && !gdr_pic_flag)==0), ph_inter_slice_allowed_flag may not be signaled. This solves the problem of ph_inter_slice_allowed_flag being unnecessarily signaled for an IRAP picture that can only contain intra slices according to the picture attributes.

[0203] Example 8

[0204] According to embodiment 8 of the present disclosure, in the picture header, information indicating whether inter-slices are allowed in the current picture can be signaled based on whether the current picture is a GDR picture, whether the current layer containing the current picture can utilize inter-layer prediction, and whether the current picture is an IRAP picture.

[0205] FIG. 16 is a diagram illustrating a picture header according to one embodiment of the present disclosure.

[0206] 16, the picture header may include a syntax element gdr_or_irap_pic_flag indicating whether the current picture is a GDR or IRAP picture, and a syntax element gdr_pic_flag indicating whether the current picture is a GDR picture, the semantics of each of the syntax elements being as described above with reference to FIG.

[0207] The picture header may also include a syntax element ph_inter_slice_allowed_flag indicating whether inter slices (e.g., B slices or P slices) are allowed for the current picture. The semantics of ph_inter_slice_allowed_flag are as described above with reference to FIG.

[0208] The ph_inter_slice_allowed_flag may be signaled based on a predetermined fifth condition (1610). In this case, the fifth condition may consist of a 5-1 condition and a 5-2 condition. Specifically, the 5-1 condition may mean that the gdr_pic_flag has a second value (e.g., 0) indicating that the current picture is not a GDR picture (i.e., !(gdr_pic_flag)==1). Furthermore, the 5-2 condition may mean that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] has a second value (e.g., 0) indicating that the current layer including the current picture can use inter-layer prediction, or gdr_or_irap_pic_flag has a second value (e.g., 0) indicating that the current picture may be an IRAP picture and not a GDR picture, or gdr_pic_flag has a first value (e.g., 1) indicating that the current picture is a GDR picture (i.e., !(vps_independent_layer_flag[GeneralLayerIdex[nuh_layer_id]] && gdr_or_irap_pic_flag && !gdr_pic_flag)==1). If both the 5-1 condition and the 5-2 condition are true, ph_inter_slice_allowed_flag may be signaled. Alternatively, if at least one of the 5-1 condition and the 5-2 condition is false, ph_inter_slice_allowed_flag is not signaled and may be inferred to be a second value (e.g., 0) indicating that inter-slicing is not allowed for the current picture. That is, if the current picture is a GDR picture or an IRAP picture included in an independent layer that does not use inter-layer prediction, ph_inter_slice_allowed_flag is not signaled and may be inferred to be a second value (e.g., 0) indicating that inter-slicing is not allowed for the current picture.

[0209] In another embodiment, if ph_inter_slice_allowed_flag is not signaled, then if the current picture is a GDR picture (i.e., gdr_or_irap_pic_flag==1 && gdr_pic_flag==1), then ph_inter_slice_allowed_flag may be inferred to have a first value (e.g., 1) indicating that inter slicing is allowed for the current picture. Alternatively, if the current picture is not a GDR picture (e.g., if the current picture is an IRAP picture included in an independent layer (i.e., gdr_or_irap_pic_flag==1 && gdr_pic_flag==0 && vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]==1), then ph_inter_slice_allowed_flag may be inferred to have a second value (e.g., 0) indicating that inter slicing is not allowed for the current picture.

[0210] Meanwhile, in one embodiment, if gdr_or_irap_pic_flag has a first value (e.g., 1), gdr_pic_flag has a second value (e.g., 0) (i.e., the current picture is an IRAP picture), and vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] has a first value (e.g., 1), the value of ph_inter_slice_allowed_flag may be set to a second value (e.g., 0). Here, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] of the first value (e.g., 1) may indicate that a layer having index GeneralLayerIdx[nuh_layer_id] does not use inter-layer prediction.

[0211] As described above with reference to FIG. 16, ph_inter_slice_allowed_flag may not be signaled if the current picture is a GDR picture (i.e., !(gdr_pic_flag)==0), or if the current picture belongs to an independent layer that does not use inter-layer prediction and is only an IRAP picture (i.e., !(vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]] && gdr_or_irap_pic_flag && !gdr_pic_flag)==0). This solves the problem that ph_inter_slice_allowed_flag is unnecessarily signaled for GDR pictures that can include inter slices and IRAP pictures that can include only intra slices according to picture attributes.

[0212] Hereinafter, an image encoding / decoding method according to an embodiment of the present disclosure will be described in detail with reference to FIGS.

[0213] 17 is a flowchart showing an image encoding method according to an embodiment of the present disclosure. The image encoding method of FIG. 17 can be performed by the image encoding device of FIG.

[0214] Referring to FIG. 17, the image coding apparatus may code first information regarding whether the inter slice type is allowed for a current picture including a current block (S1710). The first information may be, for example, ph_inter_slice_allowed_flag described above with reference to FIGs. 7 to 16. In one example, the first information may be determined based on a slice type of a slice in the current picture. For example, if one or more slices in the current picture have a B slice type or a P slice type, the first information may have a first value (e.g., 1) indicating that the inter slice type is allowed for the current picture. In contrast, if all slices in the current picture have an I slice type, the first information may have a second value (e.g., 0) indicating that the inter slice type is not allowed for the current picture.

[0215] In one embodiment, whether the inter slice type is allowed for the current picture may be determined based on the picture type of the current picture and whether the current layer including the current picture can use inter layer prediction. For example, if the current picture has the same picture type as an Intra Random Access Point (IRAP) picture and the current layer including the current picture does not use inter layer prediction, the inter slice type may not be allowed for the current picture. Or, if the current picture has the same picture type as a Gradual Decoding Refresh (GDR) picture, the inter slice type may be allowed for the current picture. In this case, the encoding of the first information may be skipped.

[0216] Information on the picture type of the current picture may be coded in the picture header. The information on the picture type of the current picture may include third information on whether the current picture has the same picture type as a Gradual Decoding Refresh (GDR) or an Intra Random Access Point (IRAP) picture, and fourth information on whether the current picture has the same picture type as a GDR picture. The third information and the fourth information may be, for example, gdr_or_irap_pic_flag and gdr_pic_flag described above with reference to Figs. 7 to 16. If the current picture has the same picture type as an IRAP picture, the third information may have a first value (e.g., 1) indicating that the current picture has the same picture type as a GDR or IRAP picture. Also, the fourth information may have a second value (e.g., 0) indicating that the current picture has a different picture type from a GDR picture.

[0217] Meanwhile, fifth information (e.g., vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]) regarding whether the current layer can use inter-layer prediction (i.e., whether the current layer is an independent layer in a multi-layer structure) may be coded in the video parameter set. If the fifth information has a first value (e.g., 1), the current layer may not use inter-layer prediction. Conversely, if the fifth information has a second value (e.g., 0), the current layer may use inter-layer prediction.

[0218] Based on the inter slice type being allowed for the current picture, the image coding apparatus may code second information regarding whether the intra slice type is allowed for the current picture (S1720). The second information may be, for example, ph_intra_slice_allowed_flag described above with reference to FIG. 7 to FIG. 16. The second information may be determined based on the slice type of a slice in the current picture, similar to the first information. For example, if one or more slices in the current picture have an I slice type, the second information may have a first value (e.g., 1) indicating that the intra slice type is allowed for the current picture. In contrast, if all slices in the current picture have a B slice type or a P slice type, the second information may have a second value (e.g., 0) indicating that the intra slice type is not allowed for the current picture. The second information may be coded / signaled together with the first information in a picture header. Meanwhile, in the present disclosure, the first information and the second information may also be referred to as available slice type information.

[0219] 18 is a flowchart showing an image decoding method according to an embodiment of the present disclosure. The image decoding method of FIG. 18 can be performed by the image decoding device of FIG.

[0220] Referring to FIG. 18, the image decoding apparatus may determine whether the inter slice type is allowed for the current picture including the current block (S1810).

[0221] Whether the inter slice type is allowed for the current picture may be determined based on first information (e.g., ph_inter_slice_allowed_flag) obtained from a picture header. For example, if the first information has a first value (e.g., 1), the inter slice type may be allowed for the current picture. In contrast, if the second information has a second value (e.g., 0), the inter slice type may not be allowed for the current picture.

[0222] In one embodiment, whether the inter slice type is allowed for the current picture may be determined based on the picture type of the current picture and whether the current layer including the current picture can use inter layer prediction. For example, the inter slice type may not be allowed for the current picture based on the current picture having the same picture type as an Intra Random Access Point (IRAP) picture and the current layer not using inter layer prediction. Alternatively, the inter slice type may be allowed for the current picture if the current picture has the same picture type as a Gradual Decoding Refresh (GDR) picture. In this case, the parsing of the first information may be skipped.

[0223] The picture type of the current picture may be determined based on third information on whether the current picture has the same picture type as a GDR (Gradual Decoding Refresh) or IRAP (Intra Random Access Point) picture, and fourth information on whether the current picture has the same picture type as a GDR picture. The third information and the fourth information may be, for example, gdr_or_irap_pic_flag and gdr_pic_flag described above with reference to Figures 7 to 16. If the third information indicates that the current picture has the same picture type as a GDR or IRAP picture and the fourth information indicates that the current picture has a different picture type from a GDR picture, the picture type of the current picture may be determined to be the same picture type as an IRAP picture.

[0224] Meanwhile, whether the current layer can use inter-layer prediction (i.e., whether the current layer is an independent layer in a multi-layer structure) can be determined based on fifth information obtained from a video parameter set. For example, if the fifth information has a first value (e.g., 1), the current layer may not use inter-layer prediction. In contrast, if the fifth information has a second value (e.g., 0), the current layer may use inter-layer prediction.

[0225] Based on whether the inter slice type is allowed for the current picture, the image decoding apparatus may determine whether the intra slice type is allowed for the current picture (S1820).

[0226] Whether the intra slice type is allowed for the current picture may be determined based on second information (e.g., ph_intra_slice_allowed_flag) obtained from the picture header. For example, if the second information has a first value (e.g., 1), the intra slice type may be allowed for the current picture. Conversely, if the second information has a second value (e.g., 0), the intra slice type may not be allowed for the current picture. Meanwhile, in this disclosure, the first information and the second information may also be referred to as available slice type information.

[0227] Then, the image decoding apparatus may decode the current block based on slice types allowed for the current picture (S1830). For example, the image decoding apparatus may determine a slice type of a slice in the current picture based on slice types allowed for the current picture. If the current block is included in a slice having an inter slice type, the image decoding apparatus may decode the current block by performing inter prediction. In contrast, if the current block is included in a slice having an intra slice type, the image decoding apparatus may decode the current block by performing intra prediction.

[0228] As described above, according to the image encoding / decoding method according to an embodiment of the present disclosure, if the current picture belongs to an independent layer that does not use inter-layer prediction and the current picture is only an IRAP picture, the inter slice type may not be allowed for the current picture. As a result, the encoding stage does not need to signal information (e.g., ph_inter_slice_allowed_flag) indicating whether the inter slice type is allowed for the current picture, so that signaling overhead can be reduced and encoding efficiency can be improved. In addition, the decoding stage does not need to parse information (e.g., ph_inter_slice_allowed_flag) indicating whether the inter slice type is allowed for the current picture, so that calculation complexity can be reduced and decoding efficiency can be improved.

[0229] The names of syntax elements described in this disclosure may include information regarding the location where the syntax element is signaled. For example, a syntax element beginning with "sps_" may mean that the syntax element is signaled in a sequence parameter set (SPS). Furthermore, a syntax element beginning with "pps_", "ph_", "sh_", etc. may mean that the syntax element is signaled in a picture parameter set (PPS), a picture header, a slice header, etc., respectively.

[0230] Although the exemplary method of the present disclosure is expressed as a series of operations for clarity of explanation, this is not intended to limit the order in which the steps are performed, and each step may be performed simultaneously or in a different order, if necessary. To realize the method according to the present disclosure, the steps illustrated may include other steps, some steps may be omitted and the remaining steps may be omitted, or some steps may be omitted and additional steps may be included.

[0231] In the present disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) can perform the operation (step) to check the execution conditions or circumstances of the operation (step). For example, if it is described that a predetermined operation is performed when a predetermined condition is satisfied, the image encoding device or the image decoding device can perform the predetermined operation after performing an operation to check whether the predetermined condition is satisfied or not.

[0232] The various embodiments of the present disclosure are not intended to enumerate all possible combinations, but are intended to describe representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combination of two or more.

[0233] Additionally, various embodiments of the present disclosure may be implemented using hardware, firmware, software, or a combination thereof, etc. In the case of a hardware implementation, the implementation may be implemented using one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general processors, controllers, microcontrollers, microprocessors, etc.

[0234] In addition, the image decoding device and the image encoding device to which the embodiments of the present disclosure are applied may be included in a multimedia broadcast transmitting / receiving device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video conversation device, a real-time communication device such as a video communication, a mobile streaming device, a storage medium, a camcorder, a custom video (VoD) service providing device, an over-the-top video (OTT) device, an internet streaming service providing device, a three-dimensional (3D) video device, an image telephone video device, and a medical video device, and may be used to process a video signal or a data signal. For example, the over-the-top video (OTT) device may include a game console, a Blu-ray player, an internet-connected TV, a home theater system, a smartphone, a tablet PC, a digital video recorder (DVR), and the like.

[0235] FIG. 19 is a diagram illustrating a content streaming system to which an embodiment of the present disclosure can be applied.

[0236] As shown in FIG. 19, a content streaming system to which an embodiment of the present disclosure is applied may broadly include an encoding server, a streaming server, a Web server, a media storage, a user device, and a multimedia input device.

[0237] The encoding server compresses content input from a multimedia input device such as a smartphone, camera, camcorder, etc. 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, video camera, etc. directly generates a bitstream, the encoding server can be omitted.

[0238] The bitstream may 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 may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0239] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server can act as a medium to inform 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, and the streaming server can transmit the multimedia data to the user. At this time, the content streaming system can include a separate control server, and in this case, the control server can control commands / responses between devices in the content streaming system.

[0240] The streaming server may receive the content from a media storage and / or an encoding server. For example, when receiving the 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 in order to provide a smooth streaming service.

[0241] Examples of the user devices include mobile phones, smart phones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation systems, slate PCs, tablet PCs, ultrabooks, wearable devices such as smartwatches, smart glass, head mounted displays (HMDs), digital TVs, desktop computers, and digital signage.

[0242] 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.

[0243] 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 the 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]

[0244] The embodiments according to the present disclosure can be used to encode / decode images.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising: determining whether inter slice type is allowed for a current picture that includes the current block; determining whether an intra slice type is allowed for the current picture based on the inter slice type being allowed for the current picture; and decoding the current block based on slice types allowed for the current picture; Whether the inter slice type is allowed for the current picture is determined based on a picture type of the current picture and whether a current layer including the current picture is an independent layer that is decoded without referring to other layers; The picture type of the current picture is determined based on third information regarding whether the picture type of the current picture is a Gradual Decoding Refresh (GDR) or an Intra Random Access Point (IRAP) picture, and fourth information regarding whether the picture type of the current picture is the GDR picture; The image decoding method, wherein the fourth information is obtained based on the third information indicating that a picture type of the current picture is the GDR or IRAP picture.

2. 2. The image decoding method of claim 1, wherein whether or not the inter slice type is allowed for the current picture is determined based on first information obtained from a picture header, and whether or not the intra slice type is allowed for the current picture is determined based on second information obtained from the picture header.

3. The image decoding method of claim 1 , wherein the inter slice type is not allowed for the current picture based on the picture type of the current picture being the Intra Random Access Point (IRAP) and the current layer being the independent layer.

4. 2. The image decoding method according to claim 1, wherein the picture type of the current picture is determined to be the IRAP picture based on the third information indicating that the picture type of the current picture is the GDR or IRAP picture and the fourth information indicating that the picture type of the current picture is different from the GDR picture.

5. The image decoding method of claim 1 , wherein whether the current layer is the independent layer is determined based on fifth information obtained from a video parameter set.

6. An image coding method performed by an image coding device, the image coding method comprising: encoding first information regarding whether an inter slice type is allowed for a current picture including the current block; encoding second information regarding whether an intra slice type is allowed for the current picture based on the inter slice type being allowed for the current picture; Whether the inter slice type is allowed for the current picture is determined based on a picture type of the current picture and whether a current layer including the current picture is an independent layer that is decoded without referring to other layers; The information on the picture type of the current picture includes third information on whether the picture type of the current picture is a Gradual Decoding Refresh (GDR) or Intra Random Access Point (IRAP) picture, and fourth information on whether the picture type of the current picture is the GDR picture; The image coding method, wherein the fourth information is included in information about a picture type of the current picture based on the picture type of the current picture being the GDR or IRAP picture.

7. The image coding method according to claim 6 , wherein the inter slice type is not allowed for the current picture based on the picture type of the current picture being an Intra Random Access Point (IRAP) picture and the current layer being the independent layer.

8. The image coding method according to claim 6 , wherein, based on a picture type of the current picture being a Gradual Decoding Refresh (GDR) picture, the inter slice type is permitted for the current picture, and coding of the first information is skipped.

9. The image coding method according to claim 6 , wherein the information about the picture type of the current picture is coded in a picture header.

10. 7. The image encoding method according to claim 6, wherein, based on the picture type of the current picture being the IRAP picture, the third information has a first value indicating that the picture type of the current picture is the GDR or IRAP picture, and the fourth information has a second value indicating that the picture type of the current picture is different from the GDR picture.

11. The image encoding method of claim 7 , wherein the fifth information regarding whether the current layer is the independent layer is encoded in a video parameter set.

12. 1. A method for transmitting a bitstream, comprising the steps of: encoding first information about whether an inter slice type is allowed for a current picture including the current block; encoding second information about whether an intra slice type is allowed for the current picture based on the inter slice type being allowed for the current picture; generating the bitstream including the encoded first information and the encoded second information; transmitting data including the bitstream; Whether the inter slice type is allowed for the current picture is determined based on a picture type of the current picture and whether a current layer including the current picture is an independent layer that is decoded without referring to other layers; The information on the picture type of the current picture includes third information on whether the picture type of the current picture is a Gradual Decoding Refresh (GDR) or Intra Random Access Point (IRAP) picture, and fourth information on whether the picture type of the current picture is the GDR picture; The method of claim 1, wherein the fourth information is included in information about a picture type of the current picture based on the picture type of the current picture being the GDR or IRAP picture.

Images