Image encoding / decoding method and device for signaling information on sub-pictures and picture headers, and method for transmitting bitstreams - Patents.com

Abstract

To provide an image encoding / decoding method and device for signaling information related to a sub picture and picture header, and a method for transmitting a bitstream.SOLUTION: An image decoding method according to the present disclosure includes the steps of: acquiring a first flag specifying whether information related to a sub picture is present in a bitstream; acquiring a second flag specifying whether picture header information is present in a slice header; and decoding the bitstream on the basis of the first flag and the second flag. When the first flag specifies that the information related to the sub picture is present in the bitstream, the second flag may have a value specifying that the picture header information is not present in the slice header.SELECTED DRAWING: Figure 12

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 for signaling information regarding sub-pictures and picture headers, and a method for transmitting 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 that improves encoding / decoding efficiency by efficiently signaling information related to sub-pictures and picture headers.

[0006] 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.

[0007] Another object of the present disclosure is to provide a recording medium 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 storing a bitstream that is received by the image decoding device according to the present disclosure, decoded, and used to restore an image.

[0009] 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]

[0010] An image decoding method performed by an image decoding device according to an aspect of the present disclosure may include the steps of obtaining a first flag indicating whether information about a sub-picture is present in a bitstream, obtaining a second flag indicating whether picture header information is present in a slice header, and decoding the bitstream based on the first flag and the second flag. If the first flag indicates that information about the sub-picture is present in the bitstream, the second flag may have a value indicating that the picture header information is not present in the slice header.

[0011] In an image decoding method according to the present disclosure, if the first flag indicates that information about the sub-picture is present in the bitstream, the slice header may include an identifier of the sub-picture that includes the slice associated with the slice header.

[0012] In the image decoding method according to the present disclosure, if the second flag indicates that the picture header information is present in the slice header, the method may further include a step of obtaining the picture header information from the slice header.

[0013] In the image decoding method according to the present disclosure, the second flag may have the same value for all slices in a Coded Layer Video Sequence (CLVS).

[0014] In the image decoding method according to the present disclosure, when the second flag indicates that the picture header information is present in the slice header, a NAL unit transmitting the picture header information may not be present in a CLVS.

[0015] In the image decoding method according to the present disclosure, if the second flag indicates that the picture header information is not present in the slice header, the picture header information can be obtained from a NAL unit whose NAL unit type is PH_NUT.

[0016] In the image decoding method according to the present disclosure, the first flag may be signaled at an upper level of a slice, and the second flag may be signaled by being included in the slice header.

[0017] An image decoding device according to another aspect of the present disclosure includes a memory and at least one processor, the at least one processor being capable of obtaining a first flag indicating whether information about a sub-picture is present in a bitstream, obtaining a second flag indicating whether picture header information is present in a slice header, and decoding the bitstream based on the first flag and the second flag. When the first flag indicates that information about the sub-picture is present in the bitstream, the second flag may have a value indicating that the picture header information is not present in the slice header.

[0018] An image encoding method according to another aspect of the present disclosure may include the steps of: encoding a first flag indicating whether information about a sub-picture is present in a bitstream; encoding a second flag indicating whether picture header information is present in a slice header; and encoding the bitstream based on the first flag and the second flag. If the first flag indicates that information about the sub-picture is present in the bitstream, the second flag may have a value indicating that the picture header information is not present in the slice header.

[0019] In an image encoding method according to the present disclosure, if the first flag indicates that information about the sub-picture is present in the bitstream, the slice header may include an identifier of a sub-picture that includes the slice associated with the slice header.

[0020] In the image encoding method according to the present disclosure, if the second flag indicates that the picture header information is present in the slice header, the method may further include a step of encoding the picture header information into the slice header.

[0021] In the image coding method according to the present disclosure, the second flag may have the same value for all slices in a Coded Layer Video Sequence (CLVS).

[0022] In the image coding method according to the present disclosure, if the second flag indicates that the picture header information is not present in the slice header, the picture header information can be signaled via a NAL unit whose NAL unit type is PH_NUT.

[0023] In the image coding method according to the present disclosure, the first flag may be signaled at an upper level of a slice, and the second flag may be signaled by being included in the slice header.

[0024] Furthermore, a transmission method according to another aspect of the present disclosure can transmit a bitstream generated by the image encoding device or image encoding method of the present disclosure.

[0025] 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.

[0026] 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

[0027] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0028] Furthermore, according to the present disclosure, an image encoding / decoding method and apparatus can be provided that can improve encoding / decoding efficiency by efficiently signaling information related to sub-pictures and picture headers.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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]

[0033] [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 is a diagram showing an image division structure according to an embodiment. [Diagram 5] FIG. 11 is a diagram showing an example of a block division type according to a multi-type tree structure. [Figure 6] FIG. 13 is an exemplary diagram illustrating a signaling mechanism of block partition information in a quadtree with nested multi-type tree structure according to the present disclosure. [Figure 7] FIG. 1 illustrates an embodiment in which a CTU is divided into multiple CUs. [Figure 8] 1 is a flowchart illustrating a method for encoding an image using slices / tiles by an image encoding device according to an embodiment of the present disclosure. [Figure 9] 11 is a flowchart illustrating a method for an image decoding device according to an embodiment of the present disclosure to decode an image using slices / tiles. [Figure 10] FIG. 2 illustrates an example of signaling and syntax elements in a picture header according to the present disclosure. [Figure 11] A diagram showing a syntax structure of a slice header according to one embodiment of the present disclosure. [Figure 12] 12 is a flowchart illustrating a method for parsing and decoding the slice header of FIG. 11. [Figure 13] 12 is a flowchart illustrating a method for encoding the slice header of FIG. 11. [Figure 14] A diagram showing a syntax structure of a slice header according to another embodiment of the present disclosure. [Figure 15] 15 is a flowchart illustrating a method for parsing and decoding the slice header of FIG. 14. [Figure 16] 15 is a flowchart illustrating a method for encoding the slice header of FIG. 14. [Figure 17] A diagram showing a syntax structure of a slice header according to another embodiment of the present disclosure. [Figure 18] 18 is a flowchart illustrating a method for parsing and decoding the slice header of FIG. 17. [Figure 19] 18 is a flowchart illustrating a method for encoding the slice header of FIG. 17. [Figure 20] 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

[0034] 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.

[0035] 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.

[0036] 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 exclude another component, but means that the component can further include another component, unless otherwise specified to the contrary.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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).

[0042] 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.

[0043] In this disclosure, a "unit" refers 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 general, an M×N block may include a set (or array) of samples or transform coefficients consisting of M columns and N rows.

[0044] 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."

[0045] In this disclosure, "current block" may mean "luma block of the current block" unless there is an explicit mention of a chroma block. "Chroma block of the current block" may be expressed explicitly as "chroma block" or "current chroma block" including the explicit mention of a chroma block.

[0046] 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."

[0047] 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." Or, in this disclosure, "or" can mean "additionally or alternatively."

[0048] Video Coding System Overview

[0049] FIG. 1 illustrates a video coding system according to this disclosure.

[0050] 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.

[0051] 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.

[0052] The video source generating unit 11 can obtain the video / images through a process of capturing, synthesizing, or generating the video / 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 the video / 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 the associated data is generated.

[0053] 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.

[0054] 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 through 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.

[0055] 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.

[0056] The rendering unit 23 can render the decoded video / images. The rendered video / images can be displayed via a display unit.

[0057] Overview of the image encoding device

[0058] FIG. 2 is a diagram illustrating an image encoding device to which an embodiment of the present disclosure can be applied.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 prediction information may be encoded by the entropy encoding unit 190 and output in a bitstream format.

[0063] 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.

[0064] The inter prediction unit 180 may derive a predicted block for a current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of 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), or the like. 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 skip mode and 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 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.

[0065] 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.

[0066] 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.

[0067] 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 expressed as 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.

[0068] 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.

[0069] The entropy coding unit 190 can 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., syntax elements (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 bitstream format in network abstraction layer (NAL) unit units. The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. The signaling information, information to be transmitted, and / or syntax elements mentioned in the present disclosure may be coded through the above-mentioned coding procedures and included in the bitstream.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] Overview of the image decoding device

[0077] FIG. 3 is a diagram illustrating an image decoding device to which an embodiment of the present disclosure can be applied.

[0078] 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.

[0079] 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 250 may include a DPB and may be realized by a digital storage medium.

[0080] 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).

[0081] 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.

[0082] 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.

[0083] 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.

[0084] The inverse transform unit 230 can inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0085] 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).

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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 a current block to be processed, such as when a skip mode is applied, the predicted block may be used as a reconstructed block. The description of the adder 155 may be similarly applied to the adder 235. The adder 235 may be referred to as a reconstruction unit or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of a next current block to be processed in a current picture, and may also be used for inter prediction of a next picture after filtering as described below.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] Image Segmentation Overview

[0094] The video / image coding method according to the present disclosure may be performed based on the following image partition structure. Specifically, procedures such as prediction, residual processing ((inverse) transform, (inverse) quantization, etc.), syntax element coding, filtering, etc., described below, may be performed based on CTU, CU (and / or TU, PU) derived based on the image partition structure. An image may be partitioned in units of blocks, and the block partition procedure may be performed in the image partition unit 110 of the encoding device described above. Partition-related information may be coded by the entropy coding unit 190 and transmitted to the decoding device in the form of a bitstream. The entropy decoding unit 210 of the decoding device may derive a block partition structure of a current picture based on the partition-related information obtained from the bitstream, and perform a series of procedures for image decoding (e.g., prediction, residual processing, block / picture reconstruction, in-loop filtering, etc.) based on the block partition structure.

[0095] A picture may be divided into a sequence of coding tree units (CTUs). FIG. 4 shows an example of a picture being divided into CTUs. A CTU may correspond to a coding tree block (CTB). Alternatively, a CTU may include a coding tree block of luma samples and two coding tree blocks of corresponding chroma samples. For example, for a picture containing three sample arrays, a CTU may include an N×N block of luma samples and two corresponding blocks of chroma samples.

[0096] Overview of CTU division

[0097] As mentioned above, a coding unit can be obtained by recursively splitting 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, a CTU can be first split into a quad-tree structure. Then, the leaf nodes of the quad-tree structure can be further split by a multi-type tree structure.

[0098] Partitioning by a quadtree means dividing a current CU (or CTU) into four equal parts. By partitioning by a quadtree, the current CU can be divided into four CUs having the same width and height. If the current CU is not further divided into a quadtree structure, the current CU corresponds to a leaf node of the quadtree structure. The CU corresponding to the leaf node of the quadtree structure is not further divided and can be used as the above-mentioned final coding unit. Alternatively, the CU corresponding to the leaf node of the quadtree structure can be further divided by a multi-type tree structure.

[0099] 5 is a diagram showing the types of division of a block by a multi-type tree structure. Division by a multi-type tree structure can include two divisions by a binary tree structure and two divisions by a ternary tree structure.

[0100] The two divisions according to the binary tree structure may include vertical binary splitting (SPLIT_BT_VER) and horizontal binary splitting (SPLIT_BT_HOR). Vertical binary splitting (SPLIT_BT_VER) refers to a division in which the current CU is divided into two equal parts vertically. As shown in FIG. 4, two CUs having the same height as the height of the current CU and half the width of the current CU may be generated by the vertical binary splitting. Horizontal binary splitting (SPLIT_BT_HOR) refers to a division in which the current CU is divided into two equal parts horizontally. As shown in FIG. 5, two CUs having the same width as the width of the current CU and half the height of the current CU may be generated by the horizontal binary splitting.

[0101] The two divisions according to the ternary tree structure may include vertical ternary splitting (SPLIT_TT_VER) and horizontal ternary splitting (SPLIT_TT_HOR). The vertical ternary splitting (SPLIT_TT_VER) divides the current CU vertically at a ratio of 1:2:1. As shown in FIG. 5, the vertical ternary splitting may generate two CUs having the same height as the current CU and a width 1 / 4 of the current CU, and a CU having the same height as the current CU and a width half the current CU. The horizontal ternary splitting (SPLIT_TT_HOR) divides the current CU horizontally at a ratio of 1:2:1. As shown in FIG. 5, the horizontal ternary splitting may generate two CUs having a height 1 / 4 of the current CU and a width equal to the current CU, and a CU having a height half the current CU and a width equal to the current CU.

[0102] FIG. 6 is a diagram illustrating an example of a signaling mechanism for block partition information in a quadtree with nested multi-type tree structure according to the present disclosure.

[0103] Here, the CTU is treated as a root node of the quadtree, and the CTU is first split into a quadtree structure. Information (e.g., qt_split_flag) indicating whether or not quadtree splitting is performed on the current CU (CTU or quadtree node (QT_node)) is signaled. For example, if qt_split_flag is a first value (e.g., "1"), the current CU can be split into a quadtree. Also, if qt_split_flag is a second value (e.g., "0"), the current CU is not split into a quadtree and becomes a leaf node (QT_leaf_node) of the quadtree. The leaf node of each quadtree can then be further split into a multitype tree structure. That is, the leaf node of the quadtree can become a node (MTT_node) of the multitype tree. A first flag (e.g., mtt_split_cu_flag) is signaled to indicate whether the current node is further split in the multitype tree structure. If the node is further split (e.g., the first flag is 1), a second flag (e.g., mtt_split_cu_vertical_flag) is signaled to indicate the splitting direction. For example, if the second flag is 1, the splitting direction may be vertical, and if the second flag is 0, the splitting direction may be horizontal. Then, a third flag (e.g., mtt_split_cu_binary_flag) is signaled to indicate whether the splitting type is a binary split type or a ternary split type. For example, if the third flag is 1, the splitting type may be a binary split type, and if the third flag is 0, the splitting type may be a ternary split type. The nodes of the multitype tree obtained by binary splitting or ternary splitting may be further partitioned into a multitype tree structure. However, the nodes of the multitype tree cannot be partitioned into a quadtree structure.If the first flag is 0, the corresponding node of the multitype tree is not further divided and becomes a leaf node (MTT_leaf_node) of the multitype tree. The CU corresponding to the leaf node of the multitype tree can be used as the final coding unit described above.

[0104] Based on the above mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, a multi-type tree splitting mode (MttSplitMode) of a CU can be derived as shown in Table 1. In the following description, the multi-type tree splitting mode may be abbreviated as a multi-tree splitting type or a splitting type.

[0105] [Table 1]

[0106] 7 shows an example of a CTU being split into multiple CUs by applying a multi-type tree after applying a quadtree. In FIG. 7, a bold block edge 710 indicates a quadtree split, and the remaining edges 720 indicate a multi-type tree split. A CU may correspond to a coding block CB. In one embodiment, a CU may include a coding block of luma samples and two coding blocks of chroma samples corresponding to the luma samples.

[0107] The chroma component (sample) CB or TB size may be derived based on the luma component (sample) CB or TB size according to the component ratio according to the color format (chroma format, e.g., 4:4:4, 4:2:2, 4:2:0, etc.) of the picture / image. If the color format is 4:4:4, the chroma component CB / TB size may be set to be the same as the luma component CB / TB size. If the color format is 4:2:2, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB, and the height of the chroma component CB / TB may be set to the height of the luma component CB / TB. If the color format is 4:2:0, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB, and the height of the chroma component CB / TB may be set to half the height of the luma component CB / TB.

[0108] In one embodiment, when the size of the CTU is 128 based on the luma sample unit, the size of the CU can have a size from 128×128, which is the same size as the CTU, to 4×4. In one embodiment, in the case of a 4:2:0 color format (or chroma format), the chroma CB size can have a size from 64×64 to 2×2.

[0109] Meanwhile, in one embodiment, the CU size and the TU size may be the same, or there may be multiple TUs in a CU region. The TU size generally refers to the luma component (sample) TB (Transform Block) size.

[0110] The TU size may be derived based on a maximum allowable TB size (maxTbSize) that is a preset value. For example, if the CU size is larger than the maxTbSize, multiple TUs (TBs) having the maxTbSize may be derived from the CU, and transform / inverse transform may be performed in units of the TUs (TBs). For example, the maximum allowable luma TB size may be 64×64, and the maximum allowable chroma TB size may be 32×32. If the width or height of a CB divided by the tree structure is larger than the maximum transform width or height, the CB may be automatically (or implicitly) divided until the horizontal and vertical TB size restrictions are satisfied.

[0111] Also, for example, when intra prediction is applied, the intra prediction mode / type may be derived in units of the CU (or CB), and the procedure of deriving neighboring reference samples and generating predicted samples may be performed in units of TU (or TB). In this case, one or more TUs (or TBs) may exist within one CU (or CB) region, and in this case, the multiple TUs (or TBs) may share the same intra prediction mode / type.

[0112] Meanwhile, for a quadtree coding tree scheme with a multi-type tree, the following parameters can be signaled from the encoding device to the decoding device as SPS syntax elements, for example, at least one of CTUsize, a parameter indicating the size of a root node of a quadtree, MinQTSize, a parameter indicating the minimum allowable size of a leaf node of a quadtree, MaxBTSize, a parameter indicating the maximum allowable size of a root node of a binary tree, MaxTTSize, a parameter indicating the maximum allowable size of a root node of a ternary tree, MaxMttDepth, a parameter indicating the maximum allowed hierarchy depth of a multitype tree split from a leaf node of a quadtree, MinBtSize, a parameter indicating the minimum allowable leaf node size of a binary tree, and MinTtSize, a parameter indicating the minimum allowable leaf node size of a ternary tree, is signaled.

[0113] In one embodiment using a 4:2:0 chroma format, the CTU size may be set to a 128x128 luma block and two 64x64 chroma blocks corresponding to the luma block. In this case, MinQTSize may be set to 16x16, MaxBtSize may be set to 128x128, MaxTtSzie may be set to 64x64, MinBtSize and MinTtSize may be set to 4x4, and MaxMttDepth may be set to 4. A quadtree split may be applied to the CTU to generate quadtree leaf nodes. The quadtree leaf nodes may be referred to as leaf QT nodes. The quadtree leaf nodes may have a size from 16x16 (e.g., the MinQTSize) to 128x128 (e.g., the CTU size). If the leaf QT node is 128x128, it may not be further split into a binary / ternary tree. This is because even if the division is performed in this case, it will exceed MaxBtsize and MaxTtsize (e.g., 64×64). In other cases, the leaf QT node may be further divided into a multitype tree. Thus, the leaf QT node is a root node for the multitype tree, and the leaf QT node may have a multitype tree depth (mttDepth) value of 0. If the multitype tree depth reaches MaxMttdepth (e.g., 4), no further additional division may be considered. If the width of the multitype tree node is equal to MinBtSize and equal to or less than 2×MinTtSize, no further additional horizontal division may be considered. If the height of the multitype tree node is equal to MinBtSize and equal to or less than 2×MinTtSize, no further additional vertical division may be considered. In this case, if division is not considered, the encoding device may omit signaling of division information. In such a case, the decoding device may induce the division information to a predetermined value.

[0114] Meanwhile, one CTU may include a coding block of luma samples (hereinafter referred to as a "luma block") and two coding blocks of corresponding chroma samples (hereinafter referred to as "chroma blocks"). The above coding tree scheme may be applied to the luma blocks and chroma blocks of a current CU in the same manner, or may be applied separately. Specifically, the luma blocks and chroma blocks in one CTU may be divided into the same block tree structure, and the tree structure in this case is referred to as a single tree (SINGLE_TREE). Alternatively, the luma blocks and chroma blocks in one CTU may be divided into separate block tree structures, and the tree structure in this case is referred to as a dual tree (DUAL_TREE). In other words, when a CTU is divided into a dual tree, a block tree structure for the luma blocks and a block tree structure for the chroma blocks may exist separately. In this case, the block tree structure for the luma block may be called a dual tree luma (DUAL_TREE_LUMA), and the block tree structure for the chroma block may be called a dual tree chroma (DUAL_TREE_CHROMA). For P and B slice / tile groups, the luma block and the chroma block in one CTU may be restricted to have the same coding tree structure. However, for I slice / tile groups, the luma block and the chroma block may have separate block tree structures. If the separate block tree structure is applied, the luma coding tree block (CTB) may be divided into CUs based on a specific coding tree structure, and the chroma CTB may be divided into chroma CUs based on another coding tree structure. That is, it may mean that a CU in an I slice / tile group to which a separate block tree structure is applied may be composed of a coding block of a luma component or a coding block of two chroma components, and a CU in a P or B slice / tile group may be composed of blocks of three color components (a luma component and two chroma components).

[0115] Although the quadtree coding tree structure with the multi-type tree has been described above, the structure in which the CU is divided is not limited thereto. For example, the BT structure and the TT structure can be interpreted as concepts included in a multiple partitioning tree (MPT) structure, and the CU can be interpreted as being divided by the QT structure and the MPT structure. In an example in which the CU is divided by the QT structure and the MPT structure, a syntax element (e.g., MPT_split_type) including information on whether the leaf node of the QT structure is divided into several blocks and a syntax element (e.g., MPT_split_mode) including information on which direction the leaf node of the QT structure is divided in, vertically or horizontally, are signaled, so that the division structure can be determined.

[0116] In another example, the CUs may be divided in a manner different from that of the QT structure, the BT structure, or the TT structure, that is, unlike the QT structure in which the CUs of the lower depth are divided into 1 / 4 size of the CUs of the higher depth, or the BT structure in which the CUs of the lower depth are divided into 1 / 2 size of the CUs of the higher depth, or the TT structure in which the CUs of the lower depth are divided into 1 / 4 or 1 / 2 size of the CUs of the higher depth, the CUs of the lower depth may be divided into 1 / 5, 1 / 3, 3 / 8, 3 / 5, 2 / 3, or 5 / 8 size of the CUs of the higher depth, as the case may be, and the manner in which the CUs are divided is not limited thereto.

[0117] In this way, the quadtree coding block structure with the multi-type tree can provide a very flexible block partition structure. Meanwhile, due to the partition types supported by the multi-type tree, different partition patterns can potentially result in the same coding block structure in some cases. The encoding device and the decoding device can reduce the amount of data of partition information by limiting the occurrence of such redundant partition patterns.

[0118] Subpicture-based image encoding / decoding

[0119] A picture to be coded may be divided into a number of CTUs, slices, tiles, or brick units, and the picture may also be divided into a number of sub-picture units.

[0120] Within a picture, a sub-picture may be encoded or decoded independently of the encoding or decoding of the sub-pictures that precede it, for example, different quantizations may be applied to the sub-pictures, or different resolutions may be applied to the sub-pictures.

[0121] Furthermore, each sub-picture can be treated like an individual picture, for example, the picture to be coded can be a projected picture or a packed picture in a 360 degree image / video or an omnidirectional image / video.

[0122] In such an embodiment, a portion of a picture may be rendered or displayed based on a viewport of a user terminal (e.g., a head mounted display). Thus, to achieve low latency, at least one sub-picture that covers the viewport among the sub-pictures constituting a picture may be encoded or decoded preferentially or independently of the remaining sub-pictures.

[0123] The result of encoding a sub-picture may be called a sub-bitstream or a substream, or simply a bitstream. A decoding device may decode the sub-picture from the sub-bitstream or the substream or the bitstream. In such a case, a high level syntax (HLS), such as a PPS, SPS, VPS, and / or a decoding parameter set (DPS), may be used to encode / decode the sub-picture.

[0124] The high level syntax (HLS) in the present disclosure may include at least one of the APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, and SH syntax. For example, the APS (APS syntax) or the 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 DPS (DPS syntax) may include information / parameters commonly applicable to videos in general. For example, the DPS may include information / parameters related to concatenation of a coded video sequence (CVS).

[0125] A sub-picture may constitute a rectangular region of a coded picture. The size of the sub-pictures may be set to be different from each other within a picture. For all pictures belonging to one sequence, the size and position of a particular individual sub-picture may be set to be the same. Individual sub-picture sequences may be decoded independently. Tiles and slices (and CTBs) may be restricted not to span across sub-picture boundaries. For this purpose, the coding device may perform coding such that each sub-picture may be decoded independently. For this purpose, semantic restrictions in the bitstream may be required. Also, for each picture in one sequence, the arrangement of tiles, slices and bricks within a sub-picture may be configured to be different from each other.

[0126] The sub-picture design aims at abstraction or encapsulation on a scale smaller than the picture level but larger than the slice or tile group level. This allows processing such as extracting a VCL NAL unit of an MCTS (motion constraint tile set) subset from one VVC bitstream and relocating it to another VVC bitstream without the difficulty of modification at the VCL level. Here, MCTS is a coding technique that enables spatial and temporal independence between tiles. When MCTS is applied, it becomes impossible to refer to information of tiles that are not included in the MCTS to which the current tile belongs. Dividing an image into MCTSs and coding them allows independent transmission and decoding of the MCTSs.

[0127] Such a sub-picture design has advantages for changing viewing orientation in mixed resolution viewport dependent 360° streaming schemes.

[0128] Hereinafter, an image encoding / decoding method using slices / tiles will be described with reference to FIGS.

[0129] FIG. 8 is a flowchart showing a method in which an image encoding device according to an embodiment of the present disclosure encodes an image using slices / tiles.

[0130] The image coding apparatus may derive slices / tiles within the current picture by dividing the current picture (S810).

[0131] The image coding apparatus may code the current picture based on the slices / tiles derived in step S810 (S820).

[0132] FIG. 9 is a flowchart showing a method for an image decoding apparatus according to an embodiment of the present disclosure to decode an image using slices / tiles.

[0133] The image decoding device can obtain information about the video / image from the bitstream (S910).

[0134] The image decoding apparatus may then derive a slice / tile in the current picture based on the video / image information acquired in step S910 (S920). Here, the video / image information may include information about the slice / tile.

[0135] Next, the image decoding apparatus may decode the current picture based on the slice / tile derived in step S920 (S930).

[0136] In Figures 8 and 9, the information for a slice / tile may include various information and / or syntax elements mentioned in this disclosure. The video / image information may include a higher level syntax, and the higher level syntax may include information for a slice and / or information for a tile. The higher level syntax may include a picture header, and the information in the picture header may be included in a slice header described in this disclosure. The information for a slice may include information identifying one or more slices in the current picture, and the information for a tile may include information identifying one or more tiles in the current picture. There may be a slice including one or more tiles in a picture.

[0137] High level syntax (HLS) signaling

[0138] As described above, higher level syntax may be coded / signaled for video / image coding. In the following, signaling and syntax elements in picture headers and slice headers according to the present disclosure will be described.

[0139] Picture and slice headers

[0140] A coded picture may consist of one or more slices. Parameters for a coded picture may be signaled in a picture header (PH), and parameters for a slice may be signaled in a slice header (SH). A picture header may be transmitted in its own NAL unit form. A slice header may be present at the beginning of a NAL unit that contains the payload of a slice (i.e., slice data). Hereinafter, the syntax elements of the picture header and slice header and the meaning of each syntax element will be described with reference to Figures 10 and 11.

[0141] FIG. 10 is a diagram illustrating an example of signaling and syntax elements in a picture header according to the present disclosure.

[0142] The picture_header_rbsp() may include information that is common to all slices in the picture being coded that is associated with the picture header. For example, the picture_header_rbsp() may include information such as a reference picture flag (non_reference_picture_flag), a GDR picture identification (gdr_pic_flag), no_output_of_prior_pics_flag, recovery_poc_cnt, and ph_pic_parameter_set_id. Here, recovery_poc_cnt is signaled in the picture_header_rbsp() if gdr_pic_flag is 1.

[0143] A first value (e.g., 1) of non_reference_picture_flag indicates that the picture associated with the picture header is not used as a reference picture. A second value (e.g., 0) of non_reference_picture_flag indicates that the picture associated with the picture header may or may not be used as a reference picture.

[0144] A first value of gdr_pic_flag (e.g., 1) indicates that the picture associated with the picture header is a GDR picture. A second value of gdr_pic_flag (e.g., 0) indicates that the picture associated with the picture header is not a GDR picture.

[0145] The no_output_of_prior_pics_flag affects the output of previously decoded pictures in the DPB after decoding a CLVS (coded layer video sequence) picture that is not the first picture in the bitstream.

[0146] recovery_poc_cnt indicates the recovery point of a decoded picture in the output order.

[0147] ph_pic_parameter_set_id indicates the value of pps_pic_parameter_set_id for the picture parameter set in use. The pps_pic_parameter_set_id is a value used to identify the PPS so that it can be referenced in other syntax.

[0148] The syntax elements included in the picture_header_rbsp() syntax structure of Fig. 10 may be signaled by being included in the picture_header_structure() syntax structure. In this case, the picture_header_structure() syntax structure may be signaled by being included in the picture_header_rbsp() syntax structure.

[0149] FIG. 11 is a diagram illustrating a syntax structure of a slice header according to one embodiment of the present disclosure.

[0150] As shown in FIG. 11, picture_header_in_slice_header_flag, picture_header_structure(), slice_subpic_id, slice_address, num_tiles_in_slice_minus1, etc. can be signaled via the slice header.

[0151] In the example shown in Figure 11, picture_header_in_slice_header_flag may indicate whether a picture header syntax structure is present in the slice header syntax structure. A first value of picture_header_in_slice_header_flag (e.g., 1 or True) may indicate that a picture header is present in the slice header, and a second value of picture_header_in_slice_header_flag (e.g., 0 or False) may indicate that a picture header is not present in the slice header.

[0152] The picture_header_structure() may be obtained based on the picture_header_in_slice_header_flag. For example, the picture_header_structure() may be signaled when the picture_header_in_slice_header_flag is a first value. When the picture_header_in_slice_header_flag is a second value, the picture_header_structure() may be signaled in a separate NAL unit without being included in the slice header.

[0153] slice_subpic_id may be information on a subpicture identifier for identifying a subpicture in which a current slice is included. slice_subpic_id may be obtained based on subpics_present_flag. For example, slice_subpic_id may be signaled when subpics_present_flag is 1. subpics_present_flag may indicate whether a subpicture exists in the current picture, or whether information on the subpicture exists in the bitstream. For example, a first value of subpics_present_flag (e.g., 1 or True) may indicate that information on the subpicture exists in the bitstream or that one or more subpictures may exist in the current picture. A second value of subpics_present_flag (e.g., 0 or False) may indicate that information on the subpicture does not exist in the bitstream or that no subpicture exists in the current picture.

[0154] slice_address may represent an address of the current slice in the current picture. slice_address may be obtained based on rect_slice_flag and / or NumTilesInPic. For example, when rect_slice_flag is a first value (e.g., 1 or True) or NumTilesInPic is greater than 1, slice_address may be signaled in the slice header. In this case, rect_slice_flag may be an indicator indicating whether a slice included in the current picture is a rectangular slice. For example, rect_slice_flag may be signaled at the picture level (PPS or picture header). In addition, NumTilesInPic may represent the number of tiles included in the current picture.

[0155] num_tiles_in_slice_minus1 may represent the number of tiles currently included in the slice. num_tiles_in_slice_minus1 may be obtained based on rect_slice_flag and NumTilesInPic. For example, when rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is greater than 1, num_tiles_in_slice_minus1 may be signaled in the slice header.

[0156] In the embodiment shown in FIG. 11, the bitstream conformance requirements related to picture_header_in_slice_header_flag may include the following:

[0157] To meet bitstream conformance, the value of picture_header_in_slice_header_flag is required to be the same for all slices in a CLVS.

[0158] Also, if picture_header_in_slice_header_flag is a first value (eg, 1), then to satisfy bitstream conformance, it is required that no NAL unit of the same NAL unit type as PH_NUT exists in the CLVS.

[0159] Also, when picture_header_in_slice_header_flag is a second value (eg, 0), to satisfy bitstream conformance, a NAL unit of the same NAL unit type as PH_NUT is required to be present in the PU prior to the first VCL NAL unit in the PU.

[0160] FIG. 12 is a flow chart illustrating a method for parsing and decoding the slice header of FIG.

[0161] First, the picture decoding apparatus can obtain a first flag (picture_header_in_slice_header_flag) included in the slice header (S1210).

[0162] The first flag may indicate whether a picture header is present within a slice header, and may also indicate whether the current picture includes only one slice.

[0163] If the first flag is a first value (e.g., 1 or True) (step S1220-Yes), the image decoding apparatus can obtain the picture header from the slice header (S1230). If the first flag is a second value (e.g., 0 or False) (step S1220-No), the picture header can be obtained from the picture header NAL unit instead of the slice header (not shown).

[0164] Thereafter, in step S1240, it may be determined whether subpics_present_flag is a first value (e.g., 1 or True). The subpics_present_flag may indicate whether the current picture includes a subpicture. The subpics_present_flag may also indicate whether information about the subpicture is included in the bitstream. The subpics_present_flag may be signaled at a higher level than the slice. For example, the subpics_present_flag may be signaled by being included in a sequence parameter set.

[0165] If the subpics_present_flag is a first value (e.g., 1 or True) (step S1240-Yes), the image decoding apparatus may obtain slice_subpic_id from the slice header (S1250). If the subpics_present_flag is a second value (e.g., 0 or False) (step S1240-No), the image decoding apparatus may omit (skip) parsing slice_subpic_id from the slice header.

[0166] Thereafter, in step S1260, it may be determined whether rect_slice_flag is a first value (e.g., 1 or True) and / or whether NumTilesInPic is greater than 1. rect_slice_flag may be an indicator of whether a slice included in the current picture is a rectangular slice. For example, rect_slice_flag may be signaled at the picture level (PPS or picture header). Also, NumTilesInPic may represent the number of tiles included in the current picture.

[0167] If the rect_slice_flag is a first value (e.g., 1 or True) or NumTilesInPic is greater than 1 (step S1260-Yes), the image decoding apparatus may obtain slice_address from the slice header (S1270). If the rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is not greater than 1 (step S1260-No), the image decoding apparatus may omit (skip) parsing slice_address from the slice header.

[0168] Thereafter, in step S1280, it may be determined whether rect_slice_flag is a first value (eg, 1 or True) and / or whether NumTilesInPic is greater than one.

[0169] If the rect_slice_flag is a first value (e.g., 1 or True) or NumTilesInPic is not greater than 1 (step S1280-No), the image decoding apparatus may omit (skip) parsing num_tiles_in_slice_minus1 from the slice header. If the rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is greater than 1 (step S1280-Yes), the image decoding apparatus may obtain num_tiles_in_slice_minus1 from the slice header (S1290).

[0170] Thereafter, the image decoding apparatus can decode the slice header by parsing subsequent syntax elements (not shown) from the slice header.

[0171] FIG. 13 is a flow chart illustrating a method for encoding the slice header of FIG.

[0172] First, the image coding apparatus determines the value of a first flag (picture_header_in_slice_header_flag) and codes the value in the slice header (S1310).

[0173] If the first flag is a first value (e.g., 1 or True) (step S1320-Yes), the image coding apparatus may code the picture header into a slice header (S1330). If the first flag is a second value (e.g., 0 or False) (step S1320-No), the picture header is not coded into a slice header and may be signaled by being included in a picture header NAL unit (not shown).

[0174] Thereafter, in step S1340, it may be determined whether subpics_present_flag is a first value (e.g., 1 or True). The subpics_present_flag may be determined and signaled at a higher level of the slice. For example, the subpics_present_flag may be included in a sequence parameter set and signaled.

[0175] If subpics_present_flag is a first value (e.g., 1 or True) (step S1340-Yes), the image coding apparatus may code slice_subpic_id in the slice header (S1350). If the subpics_present_flag is a second value (e.g., 0 or False) (step S1340-No), the image coding apparatus may omit (skip) coding slice_subpic_id in the slice header.

[0176] Thereafter, in step S1360, it may be determined whether rect_slice_flag is a first value (eg, 1 or True) and / or whether NumTilesInPic is greater than one.

[0177] If the rect_slice_flag is a first value (e.g., 1 or True) or NumTilesInPic is greater than 1 (step S1360-Yes), the image coding apparatus may code slice_address in the slice header (S1370). If the rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is not greater than 1 (step S1360-No), the image coding apparatus may omit (skip) coding slice_address in the slice header.

[0178] Thereafter, in step S1380, it may be determined whether rect_slice_flag is a first value (eg, 1 or True) and / or whether NumTilesInPic is greater than one.

[0179] If the rect_slice_flag is a first value (e.g., 1 or True) or NumTilesInPic is not greater than 1 (step S1380-No), the image coding apparatus may omit (skip) coding num_tiles_in_slice_minus1 in the slice header. If the rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is greater than 1 (step S1380-Yes), the image coding apparatus may code num_tiles_in_slice_minus1 in the slice header (S1390).

[0180] Thereafter, the image coding apparatus can code the slice header by coding subsequent syntax elements (not shown) into the slice header.

[0181] In the examples described with reference to Figures 12 and 13, some steps may be modified or omitted. For example, conditions related to the encoding / decoding of slice_address and / or num_tiles_in_slice_minus1 may be modified.

[0182] In the following, a method for improving the embodiment described with reference to Figs. 11 to 13 will be described, taking into account image encoding / decoding based on sub-pictures.

[0183] The image coding apparatus may code the current picture based on the sub-pictures, or may code at least one sub-picture constituting the current picture and generate a bitstream including coding information for the coded at least one sub-picture.

[0184] The image decoding apparatus is capable of decoding at least one sub-picture included in a current picture based on a bitstream containing coding information relating to the at least one sub-picture.

[0185] As described above, picture_header_in_slice_header_flag may indicate whether a picture header is present in a slice header. In addition, picture_header_in_slice_header_flag may be used to indicate whether the current picture includes only one slice or includes more slices. If the current picture includes only one slice, some syntax elements in the slice header have fixed values ​​because the slice is the only slice in the current picture. In this case, it may be efficient not to signal some syntax elements that have fixed values.

[0186] In the following, various configurations of the present disclosure for performing the above-mentioned efficient signaling will be described. The following configurations may be applied individually or in combination to the embodiments of the present disclosure.

[0187] Configuration 1

[0188] If the current picture includes only one slice, the signaling for some syntax elements in the slice header may be omitted, and the values ​​of the syntax elements for which the signaling is omitted may be derived or inferred by the image coding apparatus and / or the image decoding apparatus.

[0189] Whether the current picture includes only one slice can be indicated by a predetermined indicator. Therefore, for example, if the indicator indicates that the current picture includes only one slice, some of the above-mentioned syntax elements are not included in the slice header, and their values ​​can be inferred or derived. In this case, the indicator can be used as a condition indicating whether the some of the syntax elements are included in the slice header.

[0190] Configuration 2

[0191] The indicator described in configuration 1 above may be, for example, picture_header_in_slice_header_flag.

[0192] Configuration 3

[0193] Syntax elements in the slice header for which signaling can be omitted depending on the value of picture_header_in_slice_header_flag may include at least one of (a) or (b) below.

[0194] (a) Syntax elements that specify the subpicture in which a slice is contained

[0195] The reason why the signaling of syntax element (a) can be omitted is that it is obvious that no sub-pictures are specified when only one slice is included per picture. For example, if picture_header_in_slice_header_flag indicates that the current picture includes only one slice, the current picture is not coded / decoded based on sub-pictures, so the signaling of information about sub-pictures can be omitted.

[0196] (b) Syntax elements that specify the address of a slice

[0197] The signaling of syntax element (b) can be omitted because it is clear that the slice is the only first slice in the picture. For example, if picture_header_in_slice_header_flag indicates that the current picture contains only one slice, the signaling of the address for the current slice can be omitted because the current slice is the only slice in the current picture.

[0198] Configuration 4

[0199] If each picture in the sequence has only one slice, no subpictures are used. For example, the syntax element subpics_present_flag or subpic_info_present_flag related to subpictures can be restricted to a second value (e.g., 0 or False). The subpics_present_flag or subpic_info_present_flag can indicate whether or not a subpicture is present in the current picture, or whether or not information for the subpicture is present in the bitstream. The subpics_present_flag or subpic_info_present_flag can be signaled, for example, in a sequence parameter set.

[0200] Similarly, when subpics_present_flag or subpic_info_present_flag is a first value (e.g., 1 or True), a flag indicating whether each picture in the sequence includes only one slice or a flag indicating whether a picture header is present in a slice header (e.g., picture_header_in_slice_header_flag) cannot indicate that the current picture includes only one slice and cannot indicate that a picture header is present in a slice header. Thus, for example, when subpics_present_flag or subpic_info_present_flag is a first value (e.g., 1 or True), picture_header_in_slice_header_flag can be restricted to have a second value (e.g., 0 or False).

[0201] Configuration 5

[0202] If a picture header is not present in the picture header NAL unit but is present in the slice header, then within the CLVS of a particular layer (layer A), the picture headers of all layers that reference layer A (i.e., subordinate layers of layer A) and all layers referenced by layer A can be restricted to not be present in the picture header NAL unit but be present in the slice header. The above restriction can be added to simplify picture boundary detection within an access unit in the case of a multi-layer bitstream.

[0203] FIG. 14 is a diagram illustrating a syntax structure of a slice header according to another embodiment of the present disclosure.

[0204] The explanations of the same syntax elements and the same signaling conditions in the slice header structure according to the embodiment of Figure 14 and the slice header structure according to the embodiment of Figure 11 are the same, so duplicate explanations will be omitted.

[0205] According to the embodiment of FIG. 14, the condition for signaling slice_subpic_id can be changed. Specifically, the slice header can include slice_subpic_id based on subpics_present_flag and picture_header_in_slice_header_flag. For example, when subpics_present_flag is a first value (e.g., 1 or True) and picture_header_in_slice_header_flag is a second value (e.g., 0 or False), slice_subpic_id can be signaled in the slice header. This is because, as described above, if picture_header_in_slice_header_flag has the first value, the current picture includes only one slice and encoding / decoding based on the subpicture is not performed, so that there is no need to signal information about the subpicture.

[0206] Also, according to the embodiment of Fig. 14, the condition for signaling slice_address can be changed. Specifically, the slice header can include slice_address based on rect_slice_flag, NumTilesInPic, and picture_header_in_slice_header_flag. For example, if rect_slice_flag is a first value (e.g., 1 or True), or NumTilesInPic is greater than 1 and picture_header_in_slice_header_flag is a second value (e.g., 0 or False), slice_address can be signaled in the slice header. This is because, as described above, if picture_header_in_slice_header_flag has the first value, the current picture includes only one slice, and therefore, there is no need to signal information regarding the address of the slice.

[0207] In the embodiment of FIG. 14, the bitstream conformance requirement for picture_header_in_slice_header_flag can be improved as follows:

[0208] First, the value of picture_header_in_slice_header_flag is required to be the same for all slices in a CLVS.

[0209] Also, if picture_header_in_slice_header_flag is a first value (e.g., 1), it is required that no NAL unit whose NAL unit type is PH_NUT exists in the CLVS, because the picture header is signaled in the slice header, and therefore no separate NAL unit is required to transmit the picture header.

[0210] Also, if picture_header_in_slice_header_flag is a second value (e.g., 0), it is required that a NAL unit whose NAL unit type is PH_NUT exists in the PU prior to the first VCL NAL unit of the PU, that is, it is required that the current PU has a PH NAL unit, because a separate NAL unit is required to carry the picture header.

[0211] Also, if subpics_present_flag or subpic_info_present_flag is a first value (e.g., 1), picture_header_in_slice_header_flag is required not to be a first value (e.g., 1). In this case, picture_header_in_slice_header_flag can be restricted to have a second value (e.g., 0).

[0212] In the example of Figure 14, slice_subpic_id indicates the identifier of the subpicture that contains the slice. If slice_subpic_id is present, the variable SubPicIdx is guided so that SubpicIdList[SubPicIdx] is equal to slice_subpic_id. If slice_subpic_id is not present, the variable SubPicIdx may be guided to 0.

[0213] In the example of FIG. 14, the length (bit length) of slice_subpic_id can be derived as follows.

[0214] If sps_subpic_id_signalling_present_flag is 1, the length of slice_subpic_id may be derived as sps_subpic_id_len_minus1+1. Here, sps_subpic_id_signalling_present_flag may indicate whether the identifier of the subpicture is signaled in the sequence parameter set. sps_subpic_id_len_minus1 is length information of the subpicture identifier and may be signaled by being included in the sequence parameter set.

[0215] Otherwise (if sps_subpic_id_signalling_present_flag is not 1), if ph_subpic_id_signalling_present_flag is 1, the length of slice_subpic_id can be derived as ph_subpic_id_len_minus1+1. Here, ph_subpic_id_signalling_present_flag can indicate whether the subpicture identifier is signaled in the picture header. ph_subpic_id_len_minus1 is length information of the subpicture identifier and can be included in the picture header for signaling.

[0216] Otherwise (when neither sps_subpic_id_signalling_present_flag nor ph_subpic_id_signalling_present_flag is 1), the length of slice_subpic_id can be derived as pps_subpic_id_len_minus1+1 if pps_subpic_id_signalling_present_flag is 1. Here, pps_subpic_id_signalling_present_flag can indicate whether the subpicture identifier is signaled in the picture parameter set. pps_subpic_id_len_minus1 is length information of the subpicture identifier and can be signaled by being included in the picture parameter set.

[0217] Alternatively (if sps_subpic_id_signalling_present_flag, ph_subpic_id_signalling_present_flag and pps_subpic_id_signalling_present_flag are not all 1), the length of slice_subpic_id can be derived as Ceil(Log2(sps_num_subpics_minus1+1)). sps_num_subpics_minus1 indicates the number of subpictures of each picture in the CLVS and can be signaled in the sequence parameter set.

[0218] slice_address indicates the slice address of the current slice. If slice_address does not exist, the value of slice_address can be inferred to be 0.

[0219] The picture_header_structure() may include at least one syntax element included in the picture_header_rbsp() described with reference to FIG.

[0220] FIG. 15 is a flow chart illustrating a method for parsing and decoding the slice header of FIG.

[0221] Steps S1510 to S1530 in FIG. 15 are the same as steps S1210 to S1230 in FIG. 12, respectively, and therefore will not be described again.

[0222] Steps S1540 to S1570 in Fig. 15 can respectively correspond to steps S1240 to S1270 in Fig. 12. Therefore, a duplicated description of common contents will be omitted.

[0223] According to the embodiment of FIG. 15, in step S1540, it may be determined whether the subpics_present_flag is a first value (eg, 1 or True) and whether the first flag is a second value (eg, 0 or False).

[0224] If the subpics_present_flag is a first value and the first flag is a second value (step S1540-Yes), the image decoding apparatus may obtain slice_subpic_id from the slice header (S1550). If the subpics_present_flag is a second value (e.g., 0 or False) or the first flag is a first value (e.g., 1 or True) (step S1540-No), the image decoding apparatus may omit (skip) parsing slice_subpic_id from the slice header.

[0225] Thereafter, in step S1560, it may be determined whether rect_slice_flag is a first value (eg, 1 or True) or NumTilesInPic is greater than 1 and the first flag is a second value (eg, 0 or False).

[0226] If the rect_slice_flag is a first value, or NumTilesInPic is greater than 1 and the first flag is a second value (step S1560-Yes), the image decoding apparatus may obtain slice_address from the slice header (S1570). If the rect_slice_flag is a second value (e.g., 0 or False), NumTilesInPic is not greater than 1, or the first flag is a first value (e.g., 1 or True) (step S1560-No), the image decoding apparatus may omit (skip) parsing slice_address from the slice header.

[0227] Steps S1580 to S1590 in Fig. 15 correspond to steps S1280 to S1290 in Fig. 12, respectively, and therefore a duplicated description will be omitted.

[0228] As described with reference to FIG. 12, the image decoding apparatus can decode the slice header by parsing the subsequent syntax elements (not shown) from the slice header.

[0229] FIG. 16 is a flow chart illustrating a method for encoding the slice header of FIG.

[0230] Steps S1610 to S1630 in FIG. 16 are the same as steps S1310 to S1330 in FIG. 13, respectively, and therefore will not be described again.

[0231] Steps S1640 to S1670 in Fig. 16 correspond to steps S1340 to S1370 in Fig. 13, respectively, so a duplicated description of the common contents will be omitted.

[0232] According to the embodiment of FIG. 16, in step S1640, it may be determined whether the subpics_present_flag is a first value (eg, 1 or True) and whether the first flag is a second value (eg, 0 or False).

[0233] If the subpics_present_flag is a first value and the first flag is a second value (step S1640-Yes), the image coding apparatus may code slice_subpic_id in the slice header (S1650). If the subpics_present_flag is a second value (e.g., 0 or False) or the first flag is a first value (e.g., 1 or True) (step S1640-No), the image coding apparatus may omit (skip) coding slice_subpic_id in the slice header.

[0234] Thereafter, in step S1660, it may be determined whether rect_slice_flag is a first value (eg, 1 or True) or whether NumTilesInPic is greater than 1 and the first flag is a second value (eg, 0 or False).

[0235] If the rect_slice_flag is a first value, or NumTilesInPic is greater than 1 and the first flag is a second value (step S1660-Yes), the image coding apparatus can code slice_address in the slice header (S1670). If the rect_slice_flag is a second value (e.g., 0 or False), NumTilesInPic is not greater than 1, or the first flag is a first value (e.g., 1 or True) (step S1660-No), the image coding apparatus can omit (skip) coding slice_address in the slice header.

[0236] Steps S1680 to S1690 in Fig. 16 can respectively correspond to steps S1380 to S1390 in Fig. 13. Therefore, a duplicated description will be omitted.

[0237] As described with reference to FIG. 13, the image coding apparatus can code the slice header by coding subsequent syntax elements (not shown) into the slice header.

[0238] In the examples described with reference to Figures 15 and 16, some steps may be modified or omitted. For example, conditions related to the encoding / decoding of slice_address and / or num_tiles_in_slice_minus1 may be modified.

[0239] As a modification of the embodiment described with reference to Figures 14 to 16, the improved restriction on picture_header_in_slice_header_flag described above can be applied to the embodiment shown in Figure 11. In this case, at least some of the problems of the conventional method described above can be resolved. Specifically, the value of picture_header_in_slice_header_flag can be restricted based on information on subpictures (subpics_present_flag or subpic_info_present_flag) signaled at a higher level of the slice header. More specifically, if subpics_present_flag or subpic_info_present_flag is a first value, picture_header_in_slice_header_flag can be restricted to have a second value. Thus, if subpics_present_flag (or subpic_info_present_flag) is a first value (if information about subpictures is present in the bitstream or the current picture contains a subpicture), picture_header_in_slice_header_flag may indicate that a picture header is not present in the slice header or that the current picture does not contain only one slice. In the embodiment shown in Fig. 14, slice_subpic_id can be obtained from the slice header when subpics_present_flag is a first value and picture_header_in_slice_header_flag is a second value. However, if subpics_present_flag is a first value, picture_header_in_slice_header_flag is restricted to have a second value, so that it is sufficient to check subpics_present_flag as a parsing condition for slice_subpic_id. That is, according to this modification, the determination as to whether the first flag is equal to the second value in steps S1540 and S1640 can be omitted.According to this modification, when subpics_present_flag or subpic_info_present_flag is a first value, the image coding device can code picture_header_in_slice_header_flag having a second value. Also, when subpics_present_flag or subpic_info_present_flag is a first value, the image decoding device can obtain picture_header_in_slice_header_flag having a second value.

[0240] FIG. 17 is a diagram illustrating a syntax structure of a slice header according to another embodiment of the present disclosure.

[0241] The explanations of the same syntax elements and the same signaling conditions in the slice header structure according to the embodiment of Figure 17 and the slice header structure according to the embodiment of Figure 14 are the same, so duplicate explanations will be omitted.

[0242] According to the embodiment of FIG. 17, the condition for signaling picture_header_in_slice_header_flag may be changed. Specifically, the slice header may include picture_header_in_slice_header_flag based on subpics_present_flag. For example, if subpics_present_flag is a first value (e.g., 1 or True), picture_header_in_slice_header_flag may not be signaled in the slice header. For example, if subpics_present_flag is a second value (e.g., 0 or False), picture_header_in_slice_header_flag may be signaled in the slice header. This is because, as described above, if subpics_present_flag has the first value, the current picture cannot include only one slice, and so picture_header_in_slice_header_flag has a fixed value (second value). Therefore, signaling of picture_header_in_slice_header_flag is unnecessary. In this case, if picture_header_in_slice_header_flag is the first value, the signaled picture header may not be signaled via the slice header.

[0243] Also, according to the embodiment of FIG. 17, when subpics_present_flag is a first value, slice_subpic_id can be signaled in the slice header.

[0244] Hereinafter, the explanation of slice_address and num_tiles_in_slice_minus1 is the same as that explained with reference to FIG.

[0245] In the embodiment of FIG. 17, the bitstream conformance requirements for picture_header_in_slice_header_flag are similar to those described with reference to FIG.

[0246] FIG. 18 is a flow chart illustrating a method for parsing and decoding the slice header of FIG.

[0247] The method according to FIG. 18 and the method according to FIG. 15 only differ in some conditions and orders for parsing syntax elements, and the descriptions of commonly disclosed syntax elements may be the same.

[0248] According to the embodiment of FIG. 18, in step S1810, the image decoding apparatus can determine whether the value of subpics_present_flag is a second value (eg, 0 or False).

[0249] In step S1810, if the value of subpics_present_flag is a first value (e.g., 1 or True), the current picture does not include only one slice because subpicture-based encoding / decoding is performed. Therefore, in this case, the image decoding apparatus can obtain slice_subpic_id without obtaining picture_header_in_slice_header_flag and the picture header from the slice header (S1850).

[0250] If the value of subpics_present_flag is the second value in step S1810, the image decoding apparatus acquires a first flag (picture_header_in_slice_header_flag) from the slice header (S1820). The image decoding apparatus determines whether the first flag is the first value (S1830), and if the first flag is the first value, may acquire a picture header from the slice header (S1840). If the first flag is the second value, the image decoding apparatus does not acquire a picture header from the slice header, and in this case, the image decoding apparatus may acquire a picture header via a separate NAL unit. If the value of subpics_present_flag is the second value in step S1810, encoding / decoding based on a subpicture is not performed, and therefore the image decoding apparatus may not acquire information about the subpicture (slice_subpic_id).

[0251] Steps S1860 to S1890 in FIG. 18 are the same as steps S1560 to S1590 in FIG. 15, respectively, and therefore will not be described again.

[0252] As described with reference to FIG. 12, the image decoding apparatus can decode the slice header by parsing the subsequent syntax elements (not shown) from the slice header.

[0253] FIG. 19 is a flow chart illustrating a method for encoding the slice header of FIG.

[0254] The method according to FIG. 19 and the method according to FIG. 16 only differ in some conditions and orders for encoding syntax elements, and the descriptions of the commonly disclosed syntax elements may be the same.

[0255] According to the embodiment of FIG. 19, the image coding apparatus can determine in step S1910 whether the value of subpics_present_flag is a second value (eg, 0 or False).

[0256] If the value of subpics_present_flag is a first value (e.g., 1 or True) in step S1910, the current picture does not include only one slice because subpicture-based encoding / decoding is performed. Therefore, in this case, the image encoding apparatus can encode slice_subpic_id in the slice header without encoding picture_header_in_slice_header_flag and the picture header (S1950).

[0257] If the value of subpics_present_flag is the second value in step S1910, the image coding apparatus may determine the value of a first flag (picture_header_in_slice_header_flag) and encode the first flag in the slice header (S1920). The image coding apparatus may determine whether the first flag is the first value (S1930), and if the first flag is the first value, may encode the picture header in the slice header (S1940). If the first flag is the second value, the image coding apparatus may not encode the picture header in the slice header, and in this case, the image coding apparatus may signal the picture header through a separate NAL unit. If the value of subpics_present_flag is the second value in step S1910, encoding / decoding based on the subpicture is not performed, so the image coding apparatus may not encode information about the subpicture (slice_subpic_id) in the slice header.

[0258] Steps S1960 to S1990 in FIG. 19 are the same as steps S1660 to S1690 in FIG. 16, respectively, and therefore will not be described again.

[0259] As described with reference to FIG. 13, the image coding apparatus can code the slice header by coding subsequent syntax elements (not shown) into the slice header.

[0260] In the examples described with reference to Figures 18 and 19, some steps may be modified or omitted. For example, conditions related to the encoding / decoding of slice_address and / or num_tiles_in_slice_minus1 may be modified.

[0261] According to an embodiment of the present disclosure, the signaling of information regarding whether a picture header is present in a slice header and / or whether a picture contains only one slice may be performed more efficiently.

[0262] In addition, according to an embodiment of the present disclosure, the information regarding whether a picture header is present in a slice header is signaled based on whether encoding / decoding based on a sub-picture is performed, thereby preventing the signaling of unnecessary information.

[0263] The names of syntax elements described in this disclosure may include information about 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). Also, 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.

[0264] 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.

[0265] 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.

[0266] 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.

[0267] 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.

[0268] 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.

[0269] FIG. 20 is a diagram illustrating an example of a content streaming system to which an embodiment of the present disclosure can be applied.

[0270] As shown in FIG. 20, 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.

[0271] 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.

[0272] 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.

[0273] 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.

[0274] 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.

[0275] 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.

[0276] 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.

[0277] 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]

[0278] The embodiments of the present disclosure can be used for image encoding / decoding.

Claims

1. obtaining a first flag indicating whether information about a sub-picture is present in the bitstream; obtaining a second flag indicating whether picture header information is present in the slice header; and decoding the bitstream based on the first flag and the second flag; The first flag is obtained from a sequence parameter set (SPS); 11. A method for decoding an image, comprising: based on the first flag indicating that the information regarding the sub-picture is present in the bitstream, the second flag having a value indicating that the picture header information is not present in the slice header.

2. 2. The image decoding method of claim 1, wherein, based on the first flag indicating that the information regarding the sub-picture is present in the bitstream, the slice header includes an identifier of a sub-picture that includes a slice associated with the slice header.

3. The image decoding method of claim 1 , further comprising: obtaining the picture header information from the slice header based on the second flag indicating that the picture header information is present in the slice header.

4. The image decoding method of claim 1 , wherein the second flag has the same value for all slices in a coded layer video sequence (CLVS).

5. 2. The image decoding method of claim 1, wherein a network abstraction layer (NAL) unit for transmitting the picture header information is not present in a CLVS based on the second flag indicating that the picture header information is present in the slice header.

6. 2. The image decoding method of claim 1, wherein, based on the second flag indicating that the picture header information is not present in the slice header, the picture header information is obtained from a NAL unit whose NAL unit type is the same as PH_NUT.

7. The first flag is signaled at a higher level of a slice; The image decoding method according to claim 1 , wherein the second flag is signaled by being included in the slice header.

8. encoding a first flag indicating whether information about a sub-picture is present in the bitstream; encoding a second flag indicating whether picture header information is present in the slice header; encoding the bitstream based on the first flag and the second flag; The first flag is encoded in a sequence parameter set (SPS); 11. A method for encoding an image, comprising: based on the first flag indicating that the information regarding the sub-picture is present in the bitstream, the second flag having a value indicating that the picture header information is not present in the slice header.

9. 9. The image encoding method of claim 8, wherein, based on the first flag indicating that the information regarding the sub-picture is present in the bitstream, the slice header includes an identifier of a sub-picture that includes a slice associated with the slice header.

10. The image encoding method of claim 8 , further comprising: encoding the picture header information in the slice header based on the second flag indicating that the picture header information is present in the slice header.

11. The image coding method according to claim 8 , wherein the second flag has the same value for all slices in a coded layer video sequence (CLVS).

12. 9. The image coding method of claim 8, wherein, based on the second flag indicating that the picture header information is not present in the slice header, the picture header information is signaled via a network abstraction layer (NAL) unit whose NAL unit type is the same as PH_NUT.

13. The first flag is signaled at a higher level of a slice; The image coding method according to claim 8 , wherein the second flag is signaled by being included in the slice header.

14. 1. A method of transmitting a bitstream for an image, comprising: The method for transmitting the bitstream comprises: generating the bitstream by performing the steps of: encoding a first flag indicating whether information about a sub-picture is present in the bitstream; encoding a second flag indicating whether picture header information is present in a slice header; and encoding the bitstream based on the first flag and the second flag; transmitting the bitstream; The first flag is encoded in a sequence parameter set (SPS); A method of transmitting a bitstream, wherein, based on the first flag indicating that the information regarding the subpicture is present in the bitstream, the second flag has a value indicating that the picture header information is not present in the slice header.

Images