Encoding / decoding device and data transmission device

Abstract

The invention relates to an encoding / decoding apparatus and a data transmission apparatus. An image decoding method according to the present disclosure comprises the steps of: acquiring, from a bitstream, video coding layer (VCL) network abstraction layer (NAL) unit type information on a current picture and first flag information on whether a sub-picture included in the current picture is considered as a single picture; determining an NAL unit type of each of the plurality of slices in the current picture based on the acquired VCL NAL unit type information; and decoding the plurality of slices based on the determined NAL unit type and the first flag information, in which the current picture includes two or more sub-pictures based on at least some of the plurality of slices having different NAL unit types from each other, and the current picture includes two or more sub-pictures based on at least some of the plurality of slices having different NAL unit types from each other. The first flag information may have a prescribed value indicating that each of the two or more sub-pictures is considered as a single picture.

Description

[0001] This application is a divisional application of the invention patent application with the original application number 202180019013.1 (international application number: PCT / KR2021 / 002772, application date: March 5, 2021, invention name: Image encoding / decoding method and device based on hybrid NAL unit type and method for sending bit stream). Technical Field

[0002] The present disclosure relates to an image encoding / decoding method and apparatus, and more particularly, to an image encoding and decoding method and apparatus based on a hybrid NAL unit type, and a recording medium for storing a bit stream generated by the image encoding method / apparatus of the present disclosure. Background Art

[0003] Recently, the demand for high-resolution and high-quality images, such as high-definition (HD) images and ultra-high-definition (UHD) images, is increasing in various fields. As the resolution and quality of image data are improved, the amount of information or bit volume transmitted is relatively increased compared to existing image data. The increase in the amount of information or bit volume transmitted leads to an increase in transmission cost and storage cost.

[0004] Therefore, efficient image compression technology is needed to effectively transmit, store, and reproduce information about high-resolution and high-quality images. Summary of the invention

[0005] Technical issues

[0006] An object of the present disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0007] Another object of the present disclosure is to provide an image encoding / decoding method and device based on a hybrid NAL unit type.

[0008] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus based on two or more sub-pictures having different NAL unit types.

[0009] Another object of the present disclosure is to provide a non-transitory decoder-readable recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0010] Another object of the present disclosure is to provide a recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0011] Another object of the present disclosure is to provide a method for transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0012] The technical problems solved by the present disclosure are not limited to the above-mentioned technical problems, and other technical problems not described here will be clear to those skilled in the art through the following description.

[0013] Technical Solution

[0014] An image decoding method according to one aspect of the present disclosure includes the following steps: obtaining video coding layer (VCL) network abstraction layer (NAL) unit type information of a current picture and first flag information specifying whether a sub-picture included in the current picture is regarded as one picture from a bitstream; determining a NAL unit type of each of a plurality of slices included in the current picture based on the obtained VCL NAL unit type information; and decoding the plurality of slices based on the determined NAL unit type and the first flag information. The current picture may include two or more sub-pictures based on at least some of the plurality of slices having different NAL unit types, and based on at least some of the plurality of slices having different NAL unit types, the first flag information may have a predetermined value specifying that each of the two or more sub-pictures is regarded as one picture.

[0015] According to another aspect of the present disclosure, an image decoding device includes a memory and at least one processor. The at least one processor can obtain video coding layer (VCL) network abstraction layer (NAL) unit type information of a current picture and first flag information specifying whether a sub-picture included in the current picture is regarded as one picture from a bitstream, determine the NAL unit type of each of a plurality of slices included in the current picture based on the obtained VCL NAL unit type information, and decode the plurality of slices based on the determined NAL unit type and the first flag information. The current picture may include two or more sub-pictures based on at least some of the plurality of slices having different NAL unit types, and based on at least some of the plurality of slices having different NAL unit types, the first flag information may have a predetermined value specifying that each of the two or more sub-pictures is regarded as one picture.

[0016] According to another aspect of the present disclosure, an image encoding method includes the following steps: dividing a current picture into one or more sub-pictures; determining a network abstraction layer (NAL) unit type of each of a plurality of slices included in the one or more sub-pictures; and encoding the plurality of slices based on the determined NAL unit type. The current picture may be divided into two or more sub-pictures based on at least some of the plurality of slices having different NAL unit types, and each of the two or more sub-pictures may be regarded as one picture based on at least some of the plurality of slices having different NAL unit types.

[0017] In addition, a computer-readable recording medium according to another aspect of the present disclosure may store a bit stream generated by the image encoding device or the image encoding method of the present disclosure.

[0018] In addition, a transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding device or the image encoding method of the present disclosure.

[0019] The features described above in brief summary of the present disclosure are merely exemplary aspects of the following detailed description of the present disclosure and do not limit the scope of the present disclosure.

[0020] Beneficial Effects

[0021] According to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0022] Furthermore, according to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus based on a hybrid NAL unit type.

[0023] Furthermore, according to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus based on two or more sub-pictures having different mixed NAL unit types.

[0024] Furthermore, according to the present disclosure, it is possible to provide a method of transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure.

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

[0026] Furthermore, according to the present disclosure, it is possible to provide a recording medium that stores a bit stream received and decoded by the image decoding device according to the present disclosure and used to reconstruct an image.

[0027] Those skilled in the art will understand that the effects that can be achieved through the present disclosure are not limited to what has been specifically described above, and other advantages of the present disclosure will be more clearly understood from the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 FIG. 4 is a diagram schematically illustrating a video encoding system to which an embodiment of the present disclosure is applicable.

[0029] Figure 2 is a view schematically illustrating an image encoding device to which an embodiment of the present disclosure is applicable.

[0030] Figure 3 is a view schematically illustrating an image decoding device to which an embodiment of the present disclosure is applicable.

[0031] Figure 4 is a flowchart illustrating an image decoding process to which an embodiment of the present disclosure is applicable.

[0032] Figure 5 : is a flowchart illustrating an image encoding process to which an embodiment of the present disclosure is applicable.

[0033] Figure 6 is a view illustrating an example of a layer structure of a coded image / video.

[0034] Figure 7 is a view illustrating a picture parameter set (PPS) according to an embodiment of the present disclosure.

[0035] Figure 8 is a view illustrating a slice header according to an embodiment of the present disclosure.

[0036] Fig. 9 is a view illustrating an example of a sub-screen.

[0037] Fig.10 is a view illustrating an example of a picture with mixed NAL unit types.

[0038] Fig.11 is a view illustrating an example of a picture parameter set (PPS) according to an embodiment of the present disclosure.

[0039] Fig.12 is a view illustrating an example of a sequence parameter set (SPS) according to an embodiment of the present disclosure.

[0040] Fig.13 It is a view illustrating the decoding order and output order of each picture type.

[0041] Fig.14 is a flowchart illustrating a method for determining a NAL unit type of a current picture according to an embodiment of the present disclosure.

[0042] Fig.15 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure.

[0043] Fig.16 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure.

[0044] Fig.17 is a diagram illustrating a content streaming system to which an embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0045] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to facilitate implementation by those skilled in the art. However, the present disclosure can be implemented in various forms and is not limited to the embodiments described herein.

[0046] When describing the present disclosure, if it is determined that the detailed description of related known functions or configurations makes the scope of the present disclosure unnecessarily ambiguous, the detailed description thereof will be omitted. In the drawings, parts irrelevant to the description of the present disclosure are omitted, and like reference numerals are given to like parts.

[0047] In the present disclosure, when a component is "connected", "coupled" or "linked" to another component, it may include not only a direct connection relationship but also an indirect connection relationship with intermediate components. In addition, when a component "includes" or "has" other components, unless otherwise specified, it means that other components may also be included, rather than excluding other components.

[0048] In the present disclosure, the terms first, second, etc. are used only for the purpose of distinguishing one component from other components, and do not limit the order or importance of the components unless otherwise specified. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0049] In the present disclosure, components that are distinguished from each other are intended to clearly describe each feature and do not mean that the components must be separated. That is, multiple components can be integrated and implemented in one hardware or software unit, or one component can be distributed and implemented in multiple hardware or software units. Therefore, even if not specifically stated, implementations in which these components are integrated or distributed are also included in the scope of the present disclosure.

[0050] In the present disclosure, the components described in each embodiment are not necessarily indispensable components, and some components may be optional components. Therefore, the embodiments consisting of a subset of the components described in the embodiments are also included in the scope of the present disclosure. In addition, the embodiments including other components in addition to the components described in the various embodiments are included in the scope of the present disclosure.

[0051] The present disclosure relates to encoding and decoding of images. Unless otherwise defined in the present disclosure, terms used in the present disclosure may have general meanings commonly used in the technical field to which the present disclosure belongs.

[0052] In the present disclosure, a "picture" generally refers to a unit representing an image within a specific time period, and a slice / tile is a coding unit constituting a part of a picture, and a picture may be composed of one or more slices / tiles. In addition, a slice / tile may include one or more coding tree units (CTUs).

[0053] In the present disclosure, "pixel" or "pel" may refer to the smallest unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, or may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0054] In the present disclosure, a "unit" may refer to a basic unit of image processing. The unit may include at least one of a specific area of ​​a picture and information related to the area. In some cases, the unit may be used interchangeably with terms such as "sample array", "block" or "area". In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients.

[0055] In the present disclosure, "current block" may mean one of "current coding block", "current coding unit", "coding target block", "decoding target block" or "processing target block". When prediction is performed, "current block" may mean "current prediction block" or "prediction target block". When transform (inverse transform) / quantization (dequantization) is performed, "current block" may mean "current transform block" or "transform target block". When filtering is performed, "current block" may mean "filtering target block".

[0056] In addition, in the present disclosure, unless explicitly stated as a chroma block, a "current block" may mean a block including both a luma component block and a chroma component block or a "luma block of the current block". The luma component block of the current block may be represented by an explicit description including a luma component block such as "luma block" or "current luma block". In addition, a "chroma component block of the current block" may be represented by an explicit description including a chroma component block such as "chroma block" or "current chroma block".

[0057] In the present disclosure, the term " / " or "," may be interpreted as indicating "and / or". For example, "A / B" and "A, B" may mean "A and / or B". In addition, "A / B / C" and "A / B / C" may mean "at least one of A, B, and / or C".

[0058] In the present disclosure, the term "or" should be interpreted to indicate "and / or". For example, the expression "A or B" may include 1) only "A", 2) only "B", or 3) both "A and B". In other words, in the present disclosure, "or" should be interpreted to indicate "additionally or alternatively".

[0059] Overview of Video Coding Systems

[0060] Figure 1 is a diagram schematically illustrating a video encoding system according to the present disclosure.

[0061] The video encoding system according to the embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may deliver the encoded video and / or image information or data to the decoding device 20 via a digital storage medium or a network in the form of a file or a stream.

[0062] The encoding device 10 according to the embodiment may include a video source generator 11, an encoding unit 12, and a transmitter 13. The decoding device 20 according to the embodiment may include a receiver 21, a decoding unit 22, and a renderer 23. The encoding unit 12 may be called a video / image encoding unit, and the decoding unit 22 may be called a video / image decoding unit. The transmitter 13 may be included in the encoding unit 12. The receiver 21 may be included in the decoding unit 22. The renderer 23 may include a display and the display may be configured as a separate device or an external component.

[0063] The video source generator 11 can obtain the video / image by the process of capturing, synthesizing or generating the video / image. The video source generator 11 may include a video / image capturing device and / or a video / image generating device. The video / image capturing device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generating device may include, for example, a computer, a tablet computer, and a smart phone, and may generate the video / image (electronically). For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process of generating relevant data.

[0064] The encoding unit 12 may encode the input video / image. For compression and encoding efficiency, the encoding unit 12 may perform a series of processes such as prediction, transformation, and quantization. The encoding unit 12 may output encoded data (encoded video / image information) in the form of a bitstream.

[0065] The transmitter 13 transmits the encoded video / image information or data output in the form of a bit stream to the receiver 21 of the decoding device 20 in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter 13 may include an element for generating a media file in a predetermined file format and may include an element for transmission through a broadcast / communication network. The receiver 21 may extract / receive a bit stream from a storage medium or a network and transmit the bit stream to the decoding unit 22.

[0066] The decoding unit 22 may decode a video / image by performing a series of processes corresponding to the operations of the encoding unit 12, such as dequantization, inverse transformation, and prediction.

[0067] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0068] Overview of Image Coding Equipment

[0069] Figure 2 is a view schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0070] like Figure 2 As shown, the image encoding device 100 may include an image segmenter 110, a subtractor 115, a transformer 120, a quantizer 130, a dequantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter-frame predictor 180, an intra-frame predictor 185, and an entropy encoder 190. The inter-frame predictor 180 and the intra-frame predictor 185 may be collectively referred to as a "predictor". The transformer 120, the quantizer 130, the dequantizer 140, and the inverse transformer 150 may be included in a residual processor. The residual processor may also include a subtractor 115.

[0071] In some embodiments, all or at least some of the components configuring the image encoding apparatus 100 may be configured by one hardware component (eg, an encoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium.

[0072] The image segmenter 110 may segment the input image (or picture or frame) input to the image encoding device 100 into one or more processing units. For example, the processing unit may be referred to as a coding unit (CU). The coding unit may be obtained by recursively segmenting a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QT / BT / TT) structure. For example, a coding unit may be segmented into a plurality of coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the segmentation of the coding unit, the quadtree structure may be applied first, and then the binary tree structure and / or the ternary tree structure may be applied. The encoding process according to the present disclosure may be performed based on the final coding unit that is no longer segmented. The maximum coding unit may be used as the final coding unit, and the coding unit of a deeper depth obtained by segmenting the maximum coding unit may also be used as the final coding unit. Here, the encoding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the encoding process may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit. The prediction unit may be a sample prediction unit, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0073] The predictor (inter predictor 180 or intra predictor 185) may perform prediction on the block to be processed (current block) and generate a prediction block including prediction samples of the current block. The predictor may determine whether to apply intra prediction or inter prediction based on the current block or CU. The predictor may generate various information related to the prediction of the current block and transmit the generated information to the entropy encoder 190. Information about the prediction may be encoded in the entropy encoder 190 and output in the form of a bitstream.

[0074] The intra-frame predictor 185 can predict the current block by referring to the samples in the current picture. Depending on the intra-frame prediction mode and / or the intra-frame prediction technology, the reference samples can be located in the neighbors of the current block or can be placed separately. The intra-frame prediction mode may include multiple non-directional modes and multiple directional modes. The non-directional mode may include, for example, a DC mode and a plane mode. Depending on the level of detail of the prediction direction, the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used according to the settings. The intra-frame predictor 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0075] The inter-frame predictor 180 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, dual prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc. The reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter-frame predictor 180 may configure a motion information candidate list based on the neighboring blocks and generate information specifying which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame predictor 180 may use the motion information of the neighboring blocks as the motion information of the current block. In the case of skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled by encoding the motion vector difference and an indicator of the motion vector predictor. The motion vector difference may mean the difference between the motion vector of the current block and the motion vector predictor.

[0076] The predictor can generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the predictor can apply not only intra prediction or inter prediction, but also intra prediction and inter prediction at the same time to predict the current block. The prediction method that applies both intra prediction and inter prediction to predict the current block can be called combined inter and intra prediction (CIIP). In addition, the predictor can perform intra block copy (IBC) to predict the current block. Intra block copy can be used for content image / video encoding of games, etc., for example, screen content coding (SCC). IBC is a method of predicting the current picture using a previously reconstructed reference block in the current picture at a position separated by a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current picture can be encoded as a vector (block vector) corresponding to a predetermined distance. IBC basically performs prediction in the current picture, but can be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC can use at least one inter prediction technique described in the present disclosure.

[0077] The prediction signal generated by the predictor can be used to generate a reconstruction signal or to generate a residual signal. The subtractor 115 can generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (prediction block or prediction sample array) output from the predictor from the input image signal (original block or original sample array). The generated residual signal can be transmitted to the transformer 120.

[0078] The transformer 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT refers to a transform obtained from a graph when relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to square pixel blocks of the same size or may be applied to blocks of variable size instead of square.

[0079] The quantizer 130 may quantize the transform coefficients and transmit them to the entropy encoder 190. The entropy encoder 190 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 130 may rearrange the quantized transform coefficients of the block type into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0080] The entropy encoder 190 may perform various encoding methods, such as exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 190 may encode information required for video / image reconstruction other than quantized transform coefficients together or separately (e.g., values ​​of syntax elements, etc.). The encoded information (e.g., encoded video / image information) may be transmitted or stored in units of a network abstraction layer (NAL) in the form of a bitstream. The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The signaled information, transmitted information, and / or syntax elements described in the present disclosure may be encoded and included in a bitstream through the above-described encoding process.

[0081] The bitstream may be transmitted over a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) for transmitting a signal output from the entropy encoder 190 and / or a storage unit (not shown) for storing the signal may be included as an internal / external element of the image encoding device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0082] The quantized transform coefficients output from the quantizer 130 may be used to generate a residual signal. For example, the residual signal (residual block or residual sample) may be reconstructed by applying dequantization and inverse transformation to the quantized transform coefficients through the dequantizer 140 and the inverse transformer 150.

[0083] The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame predictor 180 or the intra-frame predictor 185 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as a reconstructed block. The adder 155 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0084] The filter 160 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 160 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc. The filter 160 can generate various information related to filtering and transmit the generated information to the entropy encoder 190, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 190 and output in the form of a bit stream.

[0085] The modified reconstructed picture transferred to the memory 170 may be used as a reference picture in the inter predictor 180. When inter prediction is applied by the image encoding apparatus 100, prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus may be avoided and encoding efficiency may be improved.

[0086] The DPB of the memory 170 may store the modified reconstructed picture for use as a reference picture in the inter-frame predictor 180. The memory 170 may store the motion information of the block from which the motion information in the current picture is derived (or encoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame predictor 180 and used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 170 may store the reconstructed samples of the reconstructed blocks in the current picture and may transmit the reconstructed samples to the intra-frame predictor 185.

[0087] Overview of Image Decoding Equipment

[0088] Figure 3 is a view schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0089] like Figure 3 As shown, the image decoding device 200 may include an entropy decoder 210, a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame predictor 260, and an intra-frame predictor 265. The inter-frame predictor 260 and the intra-frame predictor 265 may be collectively referred to as a "predictor". The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0090] According to an embodiment, all or at least some of the plurality of components configuring the image decoding apparatus 200 may be configured by hardware components (eg, a decoder or a processor). In addition, the memory 250 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

[0091] The image decoding device 200 having received a bit stream including video / image information may perform the same Figure 2 The image encoding device 100 may reconstruct the image by processing corresponding to the processing performed by the image encoding device 100. For example, the image decoding device 200 may perform decoding using a processing unit applied in the image encoding device. Therefore, the processing unit of decoding may be, for example, a coding unit. The coding unit may be obtained by partitioning the coding tree unit or the maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 may be reproduced by a reproduction device (not shown).

[0092] The image decoding device 200 may receive the image in the form of a bit stream from Figure 2The received signal may be decoded by the entropy decoder 210. For example, the entropy decoder 210 may parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The image decoding device may also decode the picture based on the information about the parameter set and / or the general constraint information. The information and / or syntax elements signaled / received described in the present disclosure may be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the neighboring block and the decoding target block, or the information of the symbol / bin decoded in the previous stage to determine the context model, perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. The information related to the prediction in the information decoded by the entropy decoder 210 can be provided to the predictor (inter-frame predictor 260 and intra-frame predictor 265), and the residual value of the entropy decoding performed on it in the entropy decoder 210, that is, the quantized transform coefficient and the related parameter information can be input to the dequantizer 220. In addition, the information about filtering in the information decoded by the entropy decoder 210 can be provided to the filter 240. In addition, a receiver (not shown) for receiving a signal output from the image encoding apparatus may be further configured as an internal / external element of the image decoding apparatus 200 , or the receiver may be a component of the entropy decoder 210 .

[0093] In addition, the image decoding device according to the present disclosure may be referred to as a video / image / picture decoding device. The image decoding device may be divided into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include at least one of a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame predictor 260, or an intra-frame predictor 265.

[0094] The dequantizer 220 may dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 220 may rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may dequantize the quantized transform coefficients by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficients.

[0095] The inverse transformer 230 may inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0096] The predictor may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The predictor may determine whether to apply intra prediction or inter prediction to the current block based on the information about prediction output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0097] The same as described in the predictor of the image encoding device 100 , the predictor can generate a prediction signal based on various prediction methods (techniques) described later.

[0098] The intra predictor 265 may predict the current block by referring to samples in the current picture. The description of the intra predictor 185 is also applicable to the intra predictor 265.

[0099] The inter-frame predictor 260 can derive the prediction block of the current block based on the reference block (reference sample array) specified by the motion vector on the reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter-frame prediction mode, the motion information can be predicted in units of blocks, sub-blocks or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, dual prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks existing in the current picture and temporal neighboring blocks existing in the reference picture. For example, the inter-frame predictor 260 may configure a motion information candidate list based on the neighboring blocks, and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information specifying the inter-frame prediction mode of the current block.

[0100] The adder 235 can generate a reconstruction signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the predictor (including the inter-frame predictor 260 and / or the intra-frame predictor 265). If the block to be processed has no residual (for example, when the skip mode is applied), the prediction block can be used as the reconstructed block. The description of the adder 155 is also applicable to the adder 235. The adder 235 can be called a reconstructor or a reconstructed block generator. The generated reconstruction signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0101] The filter 240 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 240 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 250, specifically, in the DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc.

[0102] The (modified) reconstructed picture stored in the DPB of the memory 250 can be used as a reference picture in the inter-frame predictor 260. The memory 250 can store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information can be transmitted to the inter-frame predictor 260 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 250 can store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame predictor 265.

[0103] In the present disclosure, the embodiments described in the filter 160 , the inter-frame predictor 180 , and the intra-frame predictor 185 of the image encoding device 100 may be equally or correspondingly applied to the filter 240 , the inter-frame predictor 260 , and the intra-frame predictor 265 of the image decoding device 200 .

[0104] General image / video encoding process

[0105] In image / video coding, the pictures configuring the image / video can be encoded / decoded according to the decoding order. The picture order corresponding to the output order of the decoded pictures can be set differently from the decoding order, and based on this, not only forward prediction but also backward prediction can be performed during inter-frame prediction.

[0106] Figure 4 is a flowchart illustrating an image decoding process to which an embodiment of the present disclosure is applicable.

[0107] Figure 4The various processes shown can be Figure 3 For example, step S410 may be performed by the entropy decoder 210, step S420 may be performed by a predictor including predictors 265 and 260, step S430 may be performed by residual processors 220 and 230, step S440 may be performed by the adder 235, and step S450 may be performed by the filter 240. Step S410 may include the information decoding process described in the present disclosure, step S420 may include the inter / intra prediction process described in the present disclosure, step S430 may include the residual processing process described in the present disclosure, step S440 may include the block / picture reconstruction process described in the present disclosure, and step S450 may include the in-loop filtering process described in the present disclosure.

[0108] Reference Figure 4 , the picture decoding process may schematically include a process (S410) for obtaining image / video information (by decoding) from a bitstream, a picture reconstruction process (S420 to S440), and an in-loop filtering process (S450) for the reconstructed picture. The picture reconstruction process may be performed based on the prediction samples and residual samples obtained by the inter / intra prediction (S420) and residual processing (S430) described in the present disclosure (dequantization and inverse transformation of quantized transform coefficients). A modified reconstructed picture may be generated by an in-loop filtering process for the reconstructed picture generated by the picture reconstruction process. In this case, the modified reconstructed picture may be output as a decoded picture, stored in a decoded picture buffer (DPB) of the memory 250, and used as a reference picture in an inter-frame prediction process when the picture is decoded later. The in-loop filtering process (S450) may be omitted. In this case, the reconstructed picture may be output as a decoded picture, stored in a DPB of the memory 250, and used as a reference picture in an inter-frame prediction process when the picture is decoded later. As described above, the in-loop filtering process (S450) may include a deblocking filtering process, a sample adaptive offset (SAO) process, an adaptive loop filter (ALF) process, and / or a bilateral filter process, some or all of which may be omitted. In addition, one or some of the deblocking filtering process, the sample adaptive offset (SAO) process, the adaptive loop filter (ALF) process, and / or the bilateral filter process may be applied sequentially, or all of them may be applied sequentially. For example, after applying the deblocking filtering process to the reconstructed picture, the SAO process may be performed. Alternatively, after applying the deblocking filtering process to the reconstructed picture, the ALF process may be performed. This may even be performed similarly in an encoding device.

[0109] Figure 5 : is a flowchart illustrating an image encoding process to which an embodiment of the present disclosure is applicable.

[0110] Figure 5 The various processes shown can be Figure 2 For example, step S510 may be performed by the predictors 185 and 180, step S520 may be performed by the residual processors 115, 120 and 130, and step S530 may be performed in the entropy encoder 190. Step S510 may include the inter / intra prediction process described in the present disclosure, step S520 may include the residual processing process described in the present disclosure, and step S530 may include the information encoding process described in the present disclosure.

[0111] Reference Figure 5 , the picture encoding process may schematically include not only the process of encoding information for picture reconstruction (e.g., prediction information, residual information, segmentation information, etc.) and outputting it in the form of a bitstream, but also the process of generating a reconstructed picture for the current picture and the process of applying in-loop filtering to the reconstructed picture (optional). The encoding device may derive (modified) residual samples from the quantized transform coefficients through the dequantizer 140 and the inverse transformer 150, and generate a reconstructed picture based on the prediction samples and (modified) residual samples output as step S510. The reconstructed picture generated in this way may be equal to the reconstructed picture generated in the decoding device. The modified reconstructed picture may be generated by an in-loop filtering process for the reconstructed picture. In this case, the modified reconstructed picture may be stored in a decoded picture buffer of the memory 170, and similar to the decoding device, may be used as a reference picture in an inter-frame prediction process when the picture is encoded later. As described above, in some cases, some or all in-loop filtering processes may be omitted. When an in-loop filtering process is performed, (in-loop) filtering-related information (parameters) can be encoded in the entropy encoder 190 and output in the form of a bit stream, and the decoding device can perform the in-loop filtering process based on the filtering-related information using the same method as the encoding device.

[0112] By this in-loop filtering process, noise (e.g., block artifacts and ringing artifacts) occurring during image / video encoding can be reduced, and subjective / objective visual quality can be improved. In addition, by performing the in-loop filtering process in both the encoding device and the decoding device, the encoding device and the decoding device can derive the same prediction result, picture encoding reliability can be increased, and the amount of data to be transmitted for picture encoding can be reduced.

[0113] As described above, the picture reconstruction process can be performed not only in the image decoding device, but also in the image encoding device. Reconstructed blocks can be generated in units of blocks based on intra-frame prediction / inter-frame prediction, and a reconstructed picture including the reconstructed blocks can be generated. When the current picture / slice / patchwork group is an I picture / slice / patchwork group, the blocks included in the current picture / slice / patchwork group can be reconstructed based only on intra-frame prediction. On the other hand, when the current picture / slice / patchwork group is a P or B picture / slice / patchwork group, the blocks included in the current picture / slice / patchwork group can be reconstructed based on intra-frame prediction or inter-frame prediction. In this case, inter-frame prediction can be applied to some blocks in the current picture / slice / patchwork group, and intra-frame prediction can be applied to the remaining blocks. The color components of the picture may include luminance components and chrominance components, and unless explicitly limited in the present disclosure, the methods and embodiments of the present disclosure are applicable to both luminance components and chrominance components.

[0114] Example of encoding a layer structure

[0115] The encoded video / image of the present disclosure may be processed according to, for example, the encoding layers and structures described later.

[0116] Figure 6 It is a view illustrating the layer structure of a coded image.

[0117] The coded image is classified into a video coding layer (VCL) for image decoding processing and processing itself, a lower system for transmitting and storing coding information, and a network abstraction layer (NAL) that exists between the VCL and the lower system and is responsible for network adaptation functions.

[0118] In the VCL, VCL data including compressed image data (slice data) can be generated, or a parameter set including information such as a picture parameter set (PPS), a sequence parameter set (SPS) or a video parameter set (VPS) or a supplemental enhancement information (SEI) message additionally required for the decoding process of the image can be generated.

[0119] In NAL, header information (NAL unit header) can be added to the raw byte sequence payload (RBSP) generated in the VCL to generate a NAL unit. In this case, RBSP refers to slice data, parameter sets, SEI messages generated in the VCL. The NAL unit header can include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0120] like Figure 6As shown, NAL units can be classified into VCL NAL units and non-VCL NAL units according to the type of RBSP generated in VCL. A VCL NAL unit may refer to a NAL unit including information about an image (slice data), and a non-VCL NAL unit may refer to a NAL unit including information required for decoding an image (parameter set or SEI message).

[0121] The VCL NAL unit and the non-VCL NAL unit may be attached with header information according to the data format of the lower layer system and sent over the network. For example, the NAL unit may be modified into data having a predetermined data format (e.g., H.266 / VVC file format, RTP (Real-time Transport Protocol) or TS (Transport Stream)) and sent over various networks.

[0122] As described above, in the NAL unit, the NAL unit type can be specified according to the RBSP data structure included in the corresponding NAL unit, and information about the NAL unit type can be stored in the NAL unit header and signaled. For example, this can be roughly classified into VCL NAL unit types and non-VCL NAL unit types based on whether the NAL unit includes information about the image (slice data). VCL NAL unit types can be classified according to the nature and type of the picture, and non-VCL NAL unit types can be classified according to the type of parameter set.

[0123] Examples of NAL unit types specified according to the types of parameter sets / information included in non-VCL NAL unit types will be listed below.

[0124] -DCI (Decoding Capability Information) NAL Unit Type (NUT): NAL unit type including DCI

[0125] -VPS (Video Parameter Set) NUT: includes the NAL unit type of VPS

[0126] -SPS (Sequence Parameter Set) NUT: NAL unit type including SPS

[0127] -PPS (Picture Parameter Set) NUT: NAL unit type including PPS

[0128] -APS (Adaptation Parameter Set) NUT: NAL unit type including APS

[0129] -PH (picture header) NUT: includes the NAL unit type of PH

[0130] The above-mentioned NAL unit type may have syntax information about the NAL unit type, and the syntax information may be stored in the NAL unit header and notified by a signal. For example, the syntax information may include nal_unit_type, and the NAL unit type may be specified by the value of nal_unit_type.

[0131] In addition, as described above, a picture may include multiple slices, and a slice may include a slice header and slice data. In this case, a picture header may be further added to multiple slices (slice headers and slice data sets) in a picture. The picture header (picture header syntax) may include information / parameters that are commonly applicable to the picture. The slice header (slice header syntax) may include information / parameters that are commonly applicable to the slice. APS (APS syntax) or PPS (PPS syntax) may include information / parameters that are commonly applicable to one or more slices or pictures. SPS (SPS syntax) may include information / parameters that are commonly applicable to one or more sequences. VPS (VPS syntax) may be information / parameters that are commonly applicable to multiple layers. DCI (DCI syntax) may include information / parameters related to decoding capabilities.

[0132] In the present disclosure, the high-level syntax (HLS) may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DCI syntax, picture header syntax, or slice header syntax. In addition, in the present disclosure, the low-level syntax (LLS) may include, for example, slice data syntax, CTU syntax, coding unit syntax, transform unit syntax, etc.

[0133] In the present disclosure, the image / video information encoded by the encoding device and notified to the decoding device in the form of a bitstream may include not only information related to intra-picture segmentation, intra-frame / inter-frame prediction information, residual information, and in-loop filtering information, but also information about a slice header, information about a picture header, information about an APS, information about a PPS, information about an SPS, information about a VPS, and / or information about a DCI. In addition, the image / video information may also include general constraint information and / or information about a NAL unit header.

[0134] Overview of Entry Point Signaling

[0135] As described above, the VCL NAL unit may include slice data as an RBSP (raw byte sequence payload). The slice data may be aligned in bytes in the VCL NAL unit and may include one or more subsets. At least one entry point for random access (RA) may be defined for the subset, and parallel processing may be performed based on the entry point.

[0136] The Versatile Video Coding (VVC) standard (ITU-T Rec. H.266) supports wavefront parallel processing (WPP), which is one of various parallel processing technologies. Multiple slices in a picture can be encoded / decoded in parallel based on WPP.

[0137] In order to enable parallel processing capabilities, entry point information may be signaled. The image decoding device may directly access the start point of the data segment included in the NAL unit based on the entry point information. Here, the start point of the data segment may mean the start point of a tile in a slice or the start point of a CTU row in a slice.

[0138] The entry point information may be signaled in a high-level syntax (eg, a picture parameter set (PPS)) and / or a slice header.

[0139] Figure 7 is a view illustrating a picture parameter set (PPS) according to an embodiment of the present disclosure, Figure 8 is a view illustrating a slice header according to an embodiment of the present disclosure.

[0140] First, refer to Figure 7 , a picture parameter set (PPS) may include entry_point_offsets_present_flag as a syntax element indicating whether entry point information is signaled.

[0141] entry_point_offsets_present_flag may indicate whether there is signaling of entry point information in a slice header of a reference picture parameter set (PPS). For example, entry_point_offsets_present_flag having a first value (e.g., 0) may indicate that there is no signaling of entry point information for a tile or a specific CTU row in a tile in the slice header. In contrast, entry_point_offsets_present_flag having a second value (e.g., 1) may indicate that there is signaling of entry point information for a tile or a specific CTU row in a tile in the slice header.

[0142] In addition, despite Figure 7 , entry_point_offsets_present_flag is included in a picture parameter set (PPS), but this is an example, and thus the embodiments of the present disclosure are not limited thereto. For example, entry_point_offsets_present_flag may be included in a sequence parameter set (SPS).

[0143] Next, refer to Figure 8, the slice header may include offset_len_minus1 and entry_point_offset_minus1[i] as syntax elements to identify the entry point.

[0144] offset_len_minus1 may indicate a value obtained by subtracting 1 from the bit length of entry_point_offset_minus1[i]. The value of offset_len_minus1 may have a range from 0 to 31. In an example, offset_len_minus1 may be signaled based on a variable NumEntryPoints indicating the total number of entry points. For example, offset_len_minus1 may be signaled only when NumEntryPoints is greater than 0. In addition, Figure 7 The described entry_point_offsets_present_flag signals offset_len_minus1. For example, offset_len_minus1 may be signaled only when entry_point_offsets_present_flag has the second value (eg, 1) (ie, signaling of entry point information is present in the slice header).

[0145] entry_point_offset_minus1[i] may indicate the i-th entry point offset in bytes, and may be represented by adding 1 bit to offset_len_minus1. The slice data in the NAL unit may include the same number of subsets as a value obtained by adding 1 to NumEntryPoints, and an index value specifying each subset may have a range from 0 to NumEntryPoints. The first byte of the slice data in the NAL unit may be represented by byte 0.

[0146] When entry_point_offset_minus1[i] is signaled, the imitation prevention byte included in the slice data in the NAL unit may be counted as a slice data portion for identifying a subset. Subset 0, which is the first subset of the slice data, may have a configuration from byte 0 to entry_point_offset_minus1[0]. Similarly, subset k, which is the kth subset of the slice data, may have a configuration from firstByte[k] to lastByte[k]. Here, firstByte[k] may be derived as shown in Equation 1 below, and lastByte[k] may be derived as shown in Equation 2 below.

[0147] [Formula 1]

[0148]

[0149] [Formula 2]

[0150] lastByte[k]=firstByte[k]+sh_entry_point_offset_minus1[k]

[0151] In Equation 1 and Equation 2, k may have a range from 1 to a value obtained by subtracting 1 from NumEntryPoints.

[0152] The last subset of the slice data (ie, the NumEntryPoints-th subset) may consist of the remaining bytes of the slice data.

[0153] In addition, if a predetermined synchronization process of context variables is not performed before decoding the CTU including the first CTB of the CTB row in each tile (e.g., sps_entropy_coding_sync_enabled_flag==0) and the slice includes one or more complete tiles, each subset of the slice header may consist of all coded bits of all CTUs in the same tile. In this case, the total number of subsets of slice data may be equal to the total number of tiles in the slice.

[0154] In contrast, when the predetermined synchronization process is not performed and the slice includes a subset of CTU rows in a single tile, NumEntryPoints may be 0. In this case, a subset of the slice data may consist of all coded bits of all CTUs in the slice.

[0155] In contrast, when a predetermined synchronization process is performed (e.g., sps_entropy_coding_sync_enabled_flag==1), each subset may consist of all coded bits of all CTUs of a CTU row in a tile. In this case, the total number of subsets of slice data may be equal to the total number of CTU rows of each tile in the slice.

[0156] Overview of mixed NAL unit types

[0157] Typically, one NAL unit type can be set for one picture. As described above, syntax information specifying the NAL unit type can be stored in a NAL unit header of the NAL unit and signaled. For example, the syntax information may include nal_unit_type, and the NAL unit type may be specified by the value of nal_unit_type.

[0158] Examples of NAL unit types to which embodiments of the present disclosure are applicable are shown in Table 1 below.

[0159] [Table 1]

[0160]

[0161]

[0162] Referring to Table 1, the VCL NAL unit type may be classified into NAL unit types 0 to 12 according to the attributes and types of pictures. In addition, the non-VCL NAL unit type may be classified into NAL unit types 13 to 31 according to the types of parameter sets.

[0163] Detailed examples of VCL NAL unit types are as follows.

[0164] - IRAP (Intra Random Access Point) NAL Unit Type (NUT): NAL unit type of IRAP pictures, which is set to the range from IDR_W_RADL to CRA_NUT.

[0165] - IDR (Instantaneous Decoding Refresh) NUT: NAL unit type for IDR pictures, which is set to IDR_W_RADL or IDR_N_LP.

[0166] - CRA (Clean Random Access) NUT: NAL unit type for CRA pictures, which is set to CRA_NUT.

[0167] - RADL (Random Access Decodable Preamble) NUT: NAL unit type of RADL pictures, which is set to RADL_NUT.

[0168] - RASL (Random Access Skip Leader) NUT: NAL unit type of RASL pictures, which is set to RASL_NUT.

[0169] - Trailing NUT: NAL unit type of the trailing picture, which is set to TRAIL_NUT.

[0170] - GDR (Gradual Decoding Refresh) NUT: NAL unit type for GDR pictures, which is GDR_NUT.

[0171] - STSA (Step-by-Step Temporal Sub-layer Access) NUT: NAL unit type for STSA pictures, which is set to STSA_NUT.

[0172] In addition, the VVC standard allows a picture to include multiple slices with different NAL unit types. For example, a picture may include at least one first slice with a first NAL unit type and at least one second slice with a second NAL unit type different from the first NAL unit type. In this case, the NAL unit type of the picture can be referred to as a mixed NAL unit type. When the VVC standard supports mixed NAL unit types, multiple pictures can be more easily reconstructed / synthesized in content synthesis processing, encoding / decoding processing, etc.

[0173] However, according to the existing scheme of mixed NAL unit types, it is limited to allow only two NAL unit types to be mixed. In addition, when a picture has mixed NAL unit types, it is limited that one or more VCL NAL units of the picture should have NAL unit types ranging from IDR_W_RADL to CRA_NUT, and the remaining VCL NAL units of the picture should have NAL unit types ranging from TRAIL_NUT value RSV_VCL_6. As a result, although the mixed NAL unit type is useful in the image processing process, there is a problem that the mixed NAL unit type is not generally used.

[0174] In order to solve such a problem, according to an embodiment of the present disclosure, two or more NAL unit types may be allowed to be mixed and more diverse mixed NAL unit types may be provided.

[0175] Hereinafter, embodiments of the present disclosure will be described in detail.

[0176] When a picture includes two or more slices and the NAL unit types of the slices are different, the picture may be limited to include two or more sub-pictures. That is, when a picture has a mixed NAL unit type, the picture may include two or more sub-pictures.

[0177] A sub-picture may include one or more slices and constitute a rectangular area in a picture. The sub-pictures included in a picture may have different sizes from each other. On the other hand, for all pictures belonging to a sequence, the size and position of a specific individual sub-picture may be set to be equal to each other.

[0178] Fig. 9 is a view illustrating an example of a sub-screen.

[0179] Reference Fig. 9, a picture can be divided into 18 tiles in total. 12 tiles among the 18 tiles can be arranged on the left side of the picture, and each of the 12 tiles can include a slice having a 4x4 CTU. In addition, 6 tiles can be arranged on the right side of the picture, and each of the 6 tiles can include two slices, each of which includes a 2x2 CTU and is stacked in the vertical direction. As a result, the picture can include 24 sub-pictures and 24 slices, and each sub-picture can include one slice.

[0180] In one embodiment, each sub-picture in a picture can be regarded as one picture to support mixed NAL unit types. When a sub-picture is regarded as one picture, the sub-picture can be encoded / decoded independently, regardless of the result of encoding / decoding another sub-picture. Here, independent encoding / decoding may mean that the block partition structure (e.g., single tree structure, dual tree structure, etc.), prediction mode type (e.g., intra-frame prediction, inter-frame prediction, etc.), decoding order, etc. of the sub-picture are different from another sub-picture. For example, when the first sub-picture is encoded / decoded based on the intra-frame prediction mode, the second sub-picture adjacent to the first sub-picture and regarded as one picture can be encoded / decoded based on the inter-frame prediction mode.

[0181] When one picture includes two or more independent sub-pictures and the sub-pictures have NAL unit types different from each other, the picture may have a mixed NAL unit type.

[0182] Fig.10 is a view illustrating an example of a picture with mixed NAL unit types.

[0183] Reference Fig.10 , one picture 1000 may include first to third sub-pictures 1010 to 1030. Each of the first sub-picture 1010 and the third sub-picture 1030 may include two slices. In contrast, the second sub-picture 1020 may include four slices.

[0184] When each of the first sub-picture 1010 to the third sub-picture 1030 is regarded as a picture, the first sub-picture 1010 to the third sub-picture 1030 can be independently encoded to constitute different bitstreams. For example, the coded slice data of the first sub-picture 1010 can be encapsulated into one or more NAL units having the same NAL unit type as RASL_NUT to constitute a first bitstream (bitstream 1). In addition, the coded slice data of the second sub-picture 1020 can be encapsulated into one or more NAL units having the same NAL unit type as RADL_NUT to constitute a second bitstream (bitstream 2). In addition, the coded slice data of the third sub-picture 1030 can be encapsulated into one or more NAL units having the same NAL unit type as RASL_NUT to constitute a third bitstream (bitstream 3). As a result, one picture 1000 can have a mixed NAL unit type of RASL_NUT and RADL_NUT.

[0185] In one embodiment, all slices included in each sub-picture in the picture may be restricted to have the same NAL unit type. For example, both slices included in the first sub-picture 1010 may have the same NAL unit type as RASL_NUT. In addition, all four slices included in the second sub-picture 1020 may have the same NAL unit type as RADL_NUT. In addition, both slices included in the third sub-picture 1030 may have the same NAL unit type as RASL_NUT.

[0186] Information about sub-pictures can be signaled in high-level syntax such as picture parameter set (PPS) and sequence parameter set (SPS). In addition, information specifying whether a mixed NAL unit type is applied can be signaled in high-level syntax such as picture parameter set (PPS).

[0187] Fig.11 is a view illustrating an example of a picture parameter set (PPS) according to an embodiment of the present disclosure, Fig.12 is a view illustrating an example of a sequence parameter set (SPS) according to an embodiment of the present disclosure.

[0188] First, refer to Fig.11 , a picture parameter set (PPS) may include pps_mixed_nalu_types_in_pic_flag as a syntax element indicating whether a mixed NAL unit type is applied.

[0189] pps_mixed_nalu_types_in_pic_flag may indicate whether the current picture has a mixed NAL unit type. For example, pps_mixed_nalu_types_in_pic_flag having a first value (e.g., 0) may indicate that the current picture does not have a mixed NAL unit type. In this case, the current picture may have the same NAL unit type for all VCL NAL units, e.g., the same NAL unit type as the coded slice NAL unit. In contrast, pps_mixed_nalu_types_in_pic_flag having a second value (e.g., 1) may indicate that the current picture has a mixed NAL unit type.

[0190] In an embodiment, when the current picture has a mixed NAL unit type (eg, pps_mixed_nalu_types_in_pic_flag==1), the VCL NAL unit of the current picture may be restricted to not have the same NAL unit type as GDR_NUT.

[0191] In an embodiment, when the current picture has a mixed NAL unit type (e.g., pps_mixed_nalu_types_in_pic_flag==1), if one VCL NAL unit of the current picture has the same NAL unit type (NAL unit type A) as IDR_W_RADL, IDR_N_LP, or CRA_NUT, then another VCL NAL unit of the current picture may be restricted to have the same NAL unit type as IDR_W_RADL, IDR_N_LP, CRA_NUT, or TRAIL_NUT.

[0192] When the current picture has a mixed NAL unit type (e.g., pps_mixed_nalu_types_in_pic_flag==1), each sub-picture in the current picture may have any one of the VCL NAL unit types described above with reference to Table 1. For example, when the sub-picture in the current picture is an IDR sub-picture, the sub-picture may have the same NAL unit type as IDR_W_RADL or IDR_N_LP. Alternatively, when the sub-picture in the current picture is a trailing sub-picture, the sub-picture may have the same NAL unit type as TRAIL_NUT.

[0193] Pps_mixed_nalu_types_in_pic_flag having a second value (e.g., 1) may indicate that a picture of a reference picture parameter set (PPS) may include slices with different NAL unit types. Here, the picture may originate from a sub-picture bitstream merge operation, where the encoder ensures the matching of the bitstream structure and the alignment between the parameters of the original bitstream. As an example of alignment, when there is no reference picture list (RPL) syntax element for a slice with the same NAL unit type as IDR_W_RADL or IDR_N_LP in the slice header (e.g., sps_idr_rpl_present_flag==0) and the current picture including the slice has a mixed NAL unit type (e.g., pps_mixed_nalu_types_in_pic_flag==1), the current picture may be restricted to not including a slice with the same NAL unit type as IDR_W_RADL or IDR_N_LP.

[0194] Furthermore, when it is restricted not to apply mixed NAL unit types to all pictures in an output layer set (OLS) (eg, gci_no_mixed_nalu_types_in_pic_constraint_flag==1), pps_mixed_nalu_types_in_pic_flag may have a first value (eg, 0).

[0195] In addition, a picture parameter set (PPS) may include pps_no_pic_partition_flag as a syntax element indicating whether picture partitioning is applied.

[0196] pps_no_pic_partition_flag may indicate whether picture partitioning is applicable to the current picture. For example, pps_no_pic_partition_flag having a first value (e.g., 0) may indicate that the current picture cannot be partitioned. In contrast, pps_no_pic_partition_flag having a second value (e.g., 1) may indicate that the current picture may be partitioned into two or more tiles or slices. When the current picture has a mixed NAL unit type (e.g., pps_mixed_nalu_types_in_pic_flag==1), the current picture may be restricted to having two or more tiles or slices (e.g., pps_no_pic_partition_flag=1).

[0197] In addition, the picture parameter set (PPS) may include pps_num_subpics_minus1 as a syntax element indicating the number of sub-pictures.

[0198] pps_num_subpics_minus1 may indicate a value obtained by subtracting 1 from the number of subpictures included in the current picture. pps_num_subpics_minus1 may be signaled only when picture partitioning is applicable to the current picture (e.g., pps_no_pic_partition_flag == 1). When pps_num_subpics_minus1 is not signaled, the value of pps_num_subpics_minus1 may be inferred to be 0. In addition, a syntax element indicating the number of subpictures may be signaled in a high-level syntax (e.g., a sequence parameter set (SPS)) other than a picture parameter set (PPS).

[0199] In an embodiment, when the current picture includes only one sub-picture (e.g., pps_num_subpics_minus1==0), the current picture may be restricted to not have a mixed NAL unit type (e.g., pps_mixed_nalu_types_in_pic_flag==0). That is, when the current picture has a mixed NAL unit type (e.g., pps_mixed_nalu_types_in_pic_flag==1), the current picture may be restricted to include two or more sub-pictures (e.g., pps_num_subpics_minus1>0).

[0200] Next, refer to Fig.12 , a sequence parameter set (SPS) may include sps_subpic_treated_as_pic_flag[i] as a syntax element related to the processing of sub-pictures during encoding / decoding.

[0201] sps_subpic_treated_as_pic_flag[i] may indicate whether each sub-picture in the current picture is considered as one picture. For example, sps_subpic_treated_as_pic_flag[i] having a first value (e.g., 0) may indicate that the i-th sub-picture in the current picture is not considered as one picture. In contrast, sps_subpic_treated_as_pic_flag[i] having a second value (e.g., 1) may indicate that the i-th sub-picture in the current picture is considered as one picture in an encoding / decoding process that does not include an in-loop filtering operation. When sps_subpic_treated_as_pic_flag[i] is not signaled, sps_subpic_treated_as_pic_flag[i] may be inferred to have the second value (e.g., 1).

[0202] In an embodiment, when the current picture includes two or more sub-pictures (e.g., pps_num_subpics_minus1>0) and at least one sub-picture is not treated as one picture (e.g., sps_subpic_treated_as_pic_flag[i]==0), the current picture may be restricted to not have a mixed NAL unit type (e.g., pps_mixed_nalu_types_in_pic_flag=0). That is, when the current picture has a mixed NAL unit type (e.g., pps_mixed_nalu_types_in_pic_flag==1), all sub-pictures in the current picture may be restricted to be treated as one picture (e.g., sps_subpic_treated_as_pic_flag[i]=1).

[0203] Hereinafter, the NAL unit type according to the embodiment of the present disclosure will be described in detail for each picture type.

[0204] (1) IRAP (Intra-frame Random Access Point) screen

[0205] An IRAP picture is a randomly accessible picture and may have the same NAL unit type described above with reference to Table 1, such as IDR_W_RADL, IDR_N_LP, or CRA_NUT. An IRAP picture may not refer to pictures other than the IRAP picture used for inter-frame prediction in the decoding process. An IRAP picture may include an IDR (Instantaneous Decoding Refresh) picture and a CRA (Clean Random Access) picture.

[0206] The first picture in the decoder order in the bitstream can be restricted to an IRAP picture or a GDR (progressive decoding refresh) picture. For a single-layer bitstream, when the basic parameter set to be referenced is available, the IRAP picture and all non-RASL pictures after the IRAP picture in decoding order can be correctly decoded, although the pictures before the IRAP picture in decoding order are not decoded at all.

[0207] In an embodiment, an IRAP picture may not have a mixed NAL unit type. That is, for an IRAP picture, pps_mixed_nalu_types_in_pic_flag may have a first value (e.g., 0), and all slices in the IRAP picture may have the same NAL unit type in the range from IDR_W_RADL to CRA_NUT. As a result, when the first slice to be decoded in the picture has a NAL unit type in the range from IDR_W_RADL to CRA_NUT, the picture may be determined to be an IRAP picture.

[0208] (2) CRA (Clean Random Access) screen

[0209] The CRA picture is one of the IRAP pictures, and may have the same NAL unit type as CRA_NUT, as described above with reference to Table 1. The CRA picture may not refer to pictures other than the CRA picture used for inter prediction in a decoding process.

[0210] A CRA picture may be the first picture or a picture after the first picture in decoding order in the bitstream. A CRA picture may be associated with a RADL or RASL picture.

[0211] When NoIncorrectPicOutputFlag has a second value (e.g., 1) for a CRA picture, the RASL picture associated with the CRA picture references a picture that does not exist in the bitstream, and therefore may not be decoded, and as a result, may not be output by the image decoding device. Here, NoIncorrectPicOutputFlag may indicate whether a picture before the recovery point picture in decoding order is output before the recovery point picture. For example, NoIncorrectPicOutputFlag having a first value (e.g., 0) may indicate that a picture before the recovery point picture in decoding order is output before the recovery point picture. In this case, the CRA picture may not be the first picture in the bitstream or the first picture after the end of sequence (EOS) NAL unit in decoding order, which may mean that random access does not occur. In contrast, NoIncorrectPicOutputFlag having a second value (e.g., 1) may indicate that a picture before the recovery point picture in decoding order cannot be output before the recovery point picture. In this case, the CRA picture may be the first picture in the bitstream or the first picture after the end of sequence (EOS) NAL unit in decoding order, which may mean that random access occurs. Furthermore, in some implementations, NoIncorrectPicOutputFlag may be referred to as NoOutputBeforeRecoveryFlag.

[0212] For all picture units (PUs) following the current picture in decoding order within a CLVS (coding layer video sequence), a reference picture list 0 (e.g., RefPicList[0]) and a reference picture list 1 (e.g., RefPicList[1]) of a slice included in a CRA sub-picture belonging to the picture unit (PU) may be restricted to not include any picture preceding the picture including the CRA sub-picture in decoding order within a valid entry. Here, a picture unit (PU) may mean a NAL unit set including a plurality of NAL units that are associated with each other according to a predetermined classification rule and are continuous in decoding order for one coded picture.

[0213] (3) IDR (Instantaneous Decoding Refresh) screen

[0214] The IDR picture is one of the IRAP pictures, and may have the same NAL unit type as IDR_W_RADL or IDR_N_LP, as described above with reference to Table 1. The IDR picture may not refer to pictures other than the IDR picture used for inter prediction in the decoding process.

[0215] An IDR picture may be the first picture in the bitstream in decoding order, or may be a picture after the first picture.Each IDR picture may be the first picture of a CVS (Coded Video Sequence) in decoding order.

[0216] When an IDR picture has the same NAL unit type as IDR_W_RADL for each NAL unit, the IDR picture may have an associated RADL picture. In contrast, when an IDR picture has the same NAL unit type as IDR_N_LP for each NAL unit, the IDR picture may not have an associated leading picture. In addition, an IDR picture may not be associated with a RASL picture.

[0217] For all picture units (PUs) following the current picture in decoding order within the CLVS (coding layer video sequence), reference picture list 0 (e.g., RefPicList[0]) and reference picture list 1 (e.g., RefPicList[1]) of a slice included in an IDR sub-picture belonging to the picture unit (PU) may be restricted to not include any picture that precedes the picture including the IDR sub-picture in decoding order within the valid entry.

[0218] (4) RADL (Random Access Decodable Lead) screen

[0219] The RADL picture is one of the leading pictures and may have the same NAL unit type as RADL_NUT, as described above with reference to Table 1.

[0220] In the decoding process of the trailing picture with the same associated IRAP picture, the RADL picture may not be used as a reference picture. When field_seq_flag has a first value (e.g., 0) for a RADL picture, the RADL picture may precede all non-leading pictures with the same associated IRAP picture in decoding order. Here, field_seq_flag may indicate whether CLVS (Coding Layer Video Sequence) transmits a picture indicating a field or a picture indicating a frame. For example, field_seq_flag having a first value (e.g., 0) may indicate that CLVS transmits a picture indicating a frame. In contrast, field_seq_flag having a second value (e.g., 1) may indicate that CLVS transmits a picture indicating a field.

[0221] (5) RASL (Random Access Skip Leader) screen

[0222] The RASL picture is one of the leading pictures and may have the same NAL unit type as RASL_NUT, as described above with reference to Table 1.

[0223] In an example, all RASL pictures may be leading pictures of an associated CRA picture. When NoIncorrectPicOutputFlag has a second value (eg, 1) for a CRA picture, the RASL picture references a picture that does not exist in the bitstream and thus may not be decoded and, as a result, may not be output by an image decoding apparatus.

[0224] In the decoding process of non-RASL pictures, RASL pictures may not be used as reference pictures. However, when there is a RADL picture belonging to the same layer as the RASL picture and associated with the same CRA picture, the RASL picture can be used as a collocated reference picture for inter-frame prediction of a RADL sub-picture included in the RADL picture.

[0225] When field_seq_flag has a first value (eg, 0) for a RASL picture, the RASL picture may precede all non-leading pictures of a CRA picture associated with the RASL picture in decoding order.

[0226] (6) Ending screen

[0227] The end picture is a non-IRAP picture that follows the associated IRAP picture or GDR picture in the output order, and may not be a STSA picture. In addition, the end picture may follow the associated IRAP picture in the decoding order. That is, an end picture that follows the associated IRAP picture in the output order but precedes the associated IRAP picture in the decoding order may not be allowed.

[0228] (7) GDR (Progressive Decoding Refresh) screen

[0229] The GDR picture is a randomly accessible picture and may have the same NAL unit type as GDR_NUT, as described above with reference to Table 1.

[0230] (8) STSA (Step-by-Step Temporal Sublayer Access) screen

[0231] The STSA picture is a randomly accessible picture and may have the same NAL unit type as STSA_NUT, as described above with reference to Table 1.

[0232] The STSA picture may not reference a picture having the same TemporalId as the STSA picture used for inter prediction. Here, TemporalId may be an identifier indicating a temporal layer (e.g., a temporal sublayer in scalable video coding). In an embodiment, the STSA picture may be restricted to have a TemporalId greater than 0.

[0233] For inter prediction, a picture having the same TemporalID as an STSA picture and following the STSA picture in decoding order may not reference a picture having the same TemporalID as the STSA picture and preceding the STSA picture in decoding order. An STSA picture may enable up-switching from the immediately lower sublayer of the current sublayer to which the STSA picture belongs to the current sublayer.

[0234] Fig.13 It is a view illustrating the decoding order and output order of each picture type.

[0235] A plurality of pictures may be classified into an I picture, a P picture, or a B picture according to a prediction method. An I picture may refer to a picture to which only intra-frame prediction is applicable, and may be decoded without reference to another picture. An I picture may be called an intra-frame picture and may include the above-mentioned IRAP picture. A P picture may refer to a picture to which intra-frame prediction and unidirectional inter-frame prediction are applicable, and may be decoded by reference to another picture. A B picture may refer to a picture to which intra-frame prediction and bidirectional / unidirectional inter-frame prediction are applicable, and may be decoded using one or two other pictures. P pictures and B pictures may be called inter-frame pictures, and may include the above-mentioned RADL pictures, RASL pictures, and end pictures.

[0236] Inter-frame pictures can be further classified into leading pictures (LP) or non-leading pictures (NLP) according to the decoding order and the output order. The leading picture may refer to a picture after the IRAP picture in the decoding order and before the IRAP picture in the output order, and may include the above-mentioned RADL picture and RASL picture. The non-leading picture may refer to a picture after the IRAP picture in the decoding order and the output order, and may include the above-mentioned ending picture.

[0237] exist Fig.13 In , the name of each picture can indicate its picture type. For example, the I5 picture can be an I picture, the B0, B2, B3, B4 and B6 pictures can be B pictures, and the P1 and P7 pictures can be P pictures. Fig.13 In FIG. 1 , each arrow may indicate a reference direction between pictures. For example, the B0 picture may be decoded by referring to the P1 picture.

[0238] Reference Fig.13, the I5 picture may be an IRAP picture (eg, a CRA picture). When random access to the I5 picture occurs, the I5 picture may be the first picture in decoding order.

[0239] B0 and P1 pictures may precede I5 picture in decoding order and constitute a video sequence separate from I5 picture. B2, B3, B4, B6 and P7 pictures may follow I5 picture in decoding order and constitute a video sequence together with I5 picture.

[0240] B2, B3 and B4 pictures are after the I5 picture in decoding order and before the I5 picture in output order, so they can be classified as leading pictures. The B2 picture can be decoded by referring to the P1 picture before the I5 picture in decoding order. Therefore, when random access occurs from the I5 picture, the B2 picture cannot be correctly decoded by referring to the P1 picture that does not exist in the bitstream. Picture types such as B2 pictures can be called RASL pictures. In contrast, the B3 picture can be decoded by referring to the I5 picture before the B3 picture in decoding order. Therefore, when random access occurs from the I5 picture, the B3 picture can be correctly decoded by referring to the pre-decoded I5 picture. In addition, B4 can be decoded by referring to the I5 picture and B3 picture before the B4 picture in decoding order. Therefore, when random access occurs from the I5 picture, the B4 picture can be correctly decoded by referring to the pre-decoded I5 picture and B3 picture. Picture types such as B3 and B4 pictures can be called RADL pictures.

[0241] In addition, the B6 and P7 pictures are after the I5 picture in the decoding order and the output order, and thus can be classified as non-leading pictures. The B6 picture can be decoded by referring to the I5 picture and the P7 picture preceding in the decoding order. Therefore, when random access occurs from the I5 picture, the B6 picture can be correctly decoded by referring to the pre-decoded I5 picture and the P7 picture.

[0242] In a video sequence, the decoding process and the output process can be performed in different orders based on the picture type. For example, when a video sequence includes an IRAP picture, a leading picture, and a non-leading picture, the decoding process can be performed in the order of the IRAP picture, the leading picture, and the non-leading picture, and the output process can be performed in the order of the leading picture, the IRAP picture, and the non-leading picture.

[0243] Fig.14 is a flowchart illustrating a method for determining a NAL unit type of a current picture according to an embodiment of the present disclosure.

[0244] Reference Fig.14, the image encoding device may determine whether the current picture includes two or more sub-pictures (S1410). One or more syntax elements in the high-level syntax may be used to signal the segmentation information of the current picture. For example, by referring to Figure 7 The picture parameter set (PPS) described herein may signal no_pic_partition_flag indicating whether the current picture is partitioned and pps_num_subpics_minus1 indicating the number of subpictures included in the current picture. When the current picture includes two or more subpictures, no_pic_partition_flag may have a first value (eg, 0) and pps_num_subpics_minus may have a value greater than 0.

[0245] When the current picture does not include two or more sub-pictures (S1410 is "No"), the image encoding apparatus may determine that the current picture has a single NAL unit type (S1450). That is, all slices in the current picture may have any one of the NAL unit types described above with reference to Table 1.

[0246] In contrast, when the current picture includes two or more sub-pictures (S1410 is "yes"), the image encoding apparatus may determine whether the respective sub-pictures in the current picture are regarded as one picture (S1420). Information indicating whether the sub-picture is regarded as one picture may be signaled using a predetermined syntax element in the high-level syntax, for example, by referring to Fig.12 The sequence parameter set (SPS) described in the present disclosure may signal sps_subpic_treated_as_pic_flag[i] indicating whether a sub-picture is regarded as one picture. When each sub-picture in the current picture is regarded as one picture, sps_subpic_treated_as_pic_flag[i] may have a second value (eg, 1).

[0247] When each sub-picture in the current picture is not regarded as one picture (No in S1420 ), the image encoding apparatus may determine that the current picture has a single NAL unit type ( S1450 ).

[0248] In contrast, when each sub-picture in the current picture is regarded as one picture (Yes in S1420 ), the image encoding apparatus may determine whether at least some of the plurality of slices in the current picture have different NAL unit types ( S1430 ).

[0249] When at least some of the plurality of slices in the current picture have different NAL unit types (Yes in S1430 ), the image encoding apparatus may determine that the current picture has a mixed NAL unit type ( S1440 ).

[0250] In contrast, when a plurality of slices in the current picture all have the same NAL unit type (No in S1430 ), the image encoding apparatus may determine that the current picture has a single NAL unit type ( S1450 ).

[0251] When the current picture has a mixed NAL unit type, the image encoding device can generate a sub-bitstream for each sub-picture included in the current picture. In this case, the multiple sub-bitstreams generated for the current picture can constitute one bitstream.

[0252] A predetermined syntax element in the high-level syntax may be used to signal information indicating whether the current picture has a mixed NAL unit type. Fig.11 The above-described picture parameter set (PPS) may signal pps_mixed_nalu_types_in_pic_flag indicating whether the current picture has a mixed NAL unit type. In this case, the image decoding device may determine whether the current picture has a mixed NAL unit type based on pps_mixed_nalu_types_in_pic_flag. For example, when pps_mixed_nalu_types_in_pic_flag has a first value (e.g., 0), the image decoding device may determine that the current picture has a single NAL unit type. In contrast, when pps_mixed_nalu_types_in_pic_flag has a second value (e.g., 1), the image decoding device may determine that the current picture has a mixed NAL unit type.

[0253] In addition, all slices in each sub-picture included in the current picture may have the same NAL unit type. That is, each sub-picture may have only a single NAL unit type. In addition, when the current picture has a mixed NAL unit type, at least some of the sub-pictures included in the current picture may have different NAL unit types. For example, a first sub-picture included in the current picture may have a first NAL unit type, and a second sub-picture included in the current picture may have a second NAL unit type different from the first NAL unit type.

[0254] The types of each sub-picture included in the current picture can be determined based on the NAL unit type of each sub-picture. For example, as described above with reference to Table 1, the type of a sub-picture with a NAL unit type such as TRAIL_NUT can be determined as a trailing sub-picture. In addition, the type of a sub-picture with a NAL unit type such as STSA NUT can be determined as an STSA sub-picture, and the type of a sub-picture with a NAL unit type such as GDR_NUT can be determined as a GDR sub-picture. In addition, the type of a sub-picture with a NAL unit type such as RADL_NUT can be determined as a RADL sub-picture, and the type of a sub-picture with a NAL unit type such as RASL_NUT can be determined as a RASL sub-picture. In addition, the type of a sub-picture with a NAL unit type such as IDR_W_RADL or IDR_N_LP can be determined as an IDR sub-picture, and the type of a sub-picture with a NAL unit type such as CRA_NUT can be determined as a CRA sub-picture.

[0255] According to an embodiment of the present disclosure, when a current picture includes two or more sub-pictures and each sub-picture is regarded as one picture, the current picture may have a mixed NAL unit type. Therefore, in various applications or use cases, image encoding / decoding efficiency may be further improved.

[0256] Below, we will refer to Fig.15 and Fig.16 An image encoding / decoding method according to an embodiment of the present disclosure is described in detail.

[0257] Fig.15 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure.

[0258] Fig.15 The image encoding method can be Figure 2 For example, step S1510 may be performed by the image segmenter 110 , and steps S1520 and S1530 may be performed by the entropy encoder 190 .

[0259] Reference Fig.15 , the image encoding apparatus may split the current picture into two or more sub-pictures (S1510).

[0260] In an embodiment, if the current picture has a mixed NAL unit type, the current picture may be limited to include two or more sub-pictures. That is, based on at least some of the multiple slices included in the current picture having different NAL unit types, the current picture may be divided into two or more sub-pictures.

[0261] One or more syntax elements in the high-level syntax may be used to signal the segmentation information of the current picture. Figure 7 The picture parameter set (PPS) described in the present invention may encode / signal flag information no_pic_partition_flag indicating whether the current picture is partitioned and flag information pps_num_subpics_minus1 indicating the number of sub-pictures included in the current picture. In this case, when the current picture is partitioned into two or more sub-pictures, no_pic_partition_flag may have a first value (e.g., 0) and pps_num_subpics_minus may have a value greater than 0.

[0262] In an embodiment, when the current picture has a mixed NAL unit type, each sub-picture included in the current picture may be regarded as one picture. For example, the current picture having a mixed NAL unit type may include a first sub-picture and a second sub-picture, and each of the first sub-picture and the second sub-picture may be independently encoded / decoded except for the in-loop filtering operation.

[0263] Information about whether a sub-picture included in the current picture is regarded as one picture can be encoded / signaled using a predetermined syntax element in the high-level syntax. For example, flag information sps_subpic_treated_as_pic_flag[i] indicating whether the i-th sub-picture included in the current picture is regarded as one picture can be obtained by referring to the above. Fig.12 In this case, when the i-th sub-picture included in the current picture is not regarded as one picture, sps_subpic_treated_as_pic_flag[i] may have a first value (e.g., 0). On the other hand, when the i-th sub-picture included in the current picture is regarded as one picture, sps_subpic_treated_as_pic_flag[i] may have a second value (e.g., 1).

[0264] The image encoding apparatus may determine a NAL unit type of each of a plurality of slices included in a current picture ( S1520 ).

[0265] In an embodiment, all slices included in each sub-picture in the current picture may have the same NAL unit type. For example, all slices included in the first sub-picture of the current picture may have a first NAL unit type, and all slices included in the second sub-picture of the current picture may have a second NAL unit type. In this case, when the current picture has a mixed NAL unit type, the second NAL unit type may be different from the first NAL unit type. Alternatively, when the current picture has a single NAL unit type, the second NAL unit type may be the same as the first NAL unit type.

[0266] In an embodiment, whether at least some of the multiple slices included in the current picture have different NAL unit types (i.e., whether the current picture has a mixed NAL unit type) can be encoded / signaled using a syntax element. For example, flag information pps_mixed_nalu_types_in_pic_flag indicating whether the current picture has a mixed NAL unit type can be encoded / signaled by referring to the above Fig.11 The pps_mixed_nalu_types_in_pic_flag may be encoded / signaled using the picture parameter set (PPS) described in the description. In this case, when the current picture has a single NAL unit type, pps_mixed_nalu_types_in_pic_flag may have a first value (e.g., 0). In contrast, when the current picture has a mixed NAL unit type, pps_mixed_nalu_types_in_pic_flag may have a second value (e.g., 1).

[0267] In an embodiment, the value of pps_mixed_nalu_types_in_pic_flag may be determined based on whether the mixed NAL unit type is applicable to all pictures in the output layer set (OLS). For example, when the mixed NAL unit type is not applicable to all pictures in the output layer set (OLS), pps_mixed_nalu_types_in_pic_flag may be restricted to have a first value (e.g., 0). In contrast, when the mixed NAL unit type is applicable to all pictures in the output layer set (OLS), pps_mixed_nalu_types_in_pic_flag may have a first value (e.g., 0) or a second value (e.g., 1).

[0268] In addition, whether the mixed NAL unit type is applicable to all pictures in the output layer set (OLS) can be encoded / signaled using a predetermined syntax element in the high-level syntax. For example, flag information gci_no_mixed_nalu_types_in_pic_constraint_flag indicating whether the mixed NAL unit type is restricted can be encoded / signaled by general_constraints_info including general constraint information. In this case, when the mixed NAL unit type is applicable to all pictures in the output layer set (OLS), gci_no_mixed_nalu_types_in_pic_constraint_flag can have a first value (e.g., 0). In contrast, when the mixed NAL unit type is not applicable to all pictures in the output layer set (OLS), gci_no_mixed_nalu_types_in_pic_constraint_flag can have a second value (e.g., 1).

[0269] In an embodiment, the value of pps_mixed_nalu_types_in_pic_flag may be determined based on whether the current picture includes only one sub-picture. For example, when the current picture includes only one sub-picture, pps_mixed_nalu_types_in_pic_flag may be limited to have a first value (e.g., 0). On the other hand, when the current picture includes two or more sub-pictures, pps_mixed_nalu_types_in_pic_flag may have a first value (e.g., 0) or a second value (e.g., 1).

[0270] In an embodiment, the value of pps_mixed_nalu_types_in_pic_flag may be determined based on whether each of all sub-pictures included in the current picture is regarded as one picture. For example, when at least one sub-picture included in the current picture is not regarded as one picture, pps_mixed_nalu_types_in_pic_flag may be limited to have a first value (e.g., 0). In contrast, when each of all sub-pictures included in the current picture is regarded as one picture, pps_mixed_nalu_types_in_pic_flag may have a first value (e.g., 0) or a second value (e.g., 1).

[0271] The image encoding device may encode the sub-picture in the current picture based on the NAL unit type determined in S1520 (S1530). At this time, as described above, the encoding process of each slice may be performed in the coding unit (CU) based on a predetermined prediction mode. In addition, each sub-picture may be independently encoded to constitute a different (sub-picture) bitstream. For example, a first sub-bitstream including encoding information of a first sub-picture may be constituted, and a second sub-bitstream including encoding information of a second sub-picture may be constituted.

[0272] Fig.16 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure.

[0273] Fig.16 The image decoding method can be Figure 3 For example, steps S1610 and S1620 may be performed by the entropy decoder 210 , and step S1630 may be performed by the dequantizer 220 to the intra predictor 265 .

[0274] Reference Fig.16 , the image decoding apparatus may obtain VCL NAL unit type information of a current picture and first flag information specifying whether a sub-picture included in the current picture is regarded as one picture from a bitstream (S1610).

[0275] The NAL unit type information of the current picture may include a NAL unit type value of a VCL NAL unit containing coded image data (eg, slice data) of the current picture. The NAL unit type value may be obtained by parsing a syntax element nal_unit_type included in a NAL unit header of the VCL NAL unit.

[0276] The first flag information may be obtained by parsing a high-level syntax (e.g., sps_subpic_treated_as_pic_flag[i] included in a sequence parameter set (SPS). In this case, when the i-th sub-picture included in the current picture is not regarded as one picture, sps_subpic_treated_as_pic_flag[i] may have a first value (e.g., 0). On the other hand, when the i-th sub-picture included in the current picture is regarded as one picture, sps_subpic_treated_as_pic_flag[i] may have a second value (e.g., 1).

[0277] The image decoding apparatus may determine a NAL unit type of each of a plurality of slices in the current picture based on VCL NAL unit type information of the current picture ( S1620 ).

[0278] In an embodiment, when at least some of the plurality of slices in the current picture have different NAL unit types (ie, when the current picture has mixed NAL unit types), the current picture includes two or more sub-pictures.

[0279] In an embodiment, when at least some of the plurality of slices in the current picture have different NAL unit types, each of all sub-pictures included in the current picture may be regarded as one picture. In this case, for all sub-pictures included in the current picture, the first flag information (e.g., sps_subpic_treated_as_pic_flag[i]) may have a second value (e.g., 1).

[0280] In an embodiment, all slices included in each sub-picture in the current picture may have the same NAL unit type. For example, all slices included in the first sub-picture of the current picture may have a first NAL unit type, and all slices included in the second sub-picture of the current picture may have a second NAL unit type. In this case, when the current picture has a mixed NAL unit type, the second NAL unit type may be different from the first NAL unit type. In contrast, when the current picture has a single NAL unit type, the second NAL unit type may be the same as the first NAL unit type.

[0281] In an embodiment, whether at least some of the multiple slices in the current picture have different NAL unit types may be determined based on a high-level syntax (e.g., second flag information (e.g., pps_mixed_nalu_types_in_pic_flag) obtained from a picture parameter set (PPS). For example, when the second flag information has a first value (e.g., 0), all slices in the current picture may have the same NAL unit type. In contrast, when the second flag information has a second value (e.g., 1), at least some of the multiple slices in the current picture may have different NAL unit types.

[0282] In an embodiment, based on whether the mixed NAL unit type is applicable to all pictures in the output layer set (OLS), the second flag information (e.g., pps_mixed_nalu_types_in_pic_flag) may have a predetermined value. For example, when the mixed NAL unit type is not applicable to all pictures in the output layer set (OLS), the second flag information may have a first value (e.g., 0). In this case, the image decoding device may infer the value of the second flag information to be the first value (e.g., 0) without separately parsing the second flag information. In contrast, when the mixed NAL unit type is applicable to all pictures in the output layer set (OLS), the second flag information may have a first value (e.g., 0) or a second value (e.g., 1).

[0283] In an embodiment, based on whether the current picture includes only one sub-picture, the second flag information (e.g., pps_mixed_nalu_types_in_pic_flag) may have a predetermined value. For example, when the current picture includes only one sub-picture, the second flag information may have only a first value (e.g., 0). In this case, the image decoding device may infer the value of the second flag information to be the first value (e.g., 0) without separately parsing the second flag information. In contrast, when the current picture includes two or more sub-pictures, the second flag information may have a first value (e.g., 0) or a second value (e.g., 1).

[0284] In an embodiment, based on whether each of all sub-pictures included in the current picture is regarded as one picture, the second flag information (e.g., pps_mixed_nalu_types_in_pic_flag) may have a predetermined value. For example, when at least one sub-picture included in the current picture is not regarded as one picture, pps_mixed_nalu_types_in_pic_flag may have only a first value (e.g., 0). In this case, the image decoding device may infer the value of the second flag information as the first value (e.g., 0) without separately parsing the second flag information. In contrast, when each of all sub-pictures included in the current picture is regarded as one picture, pps_mixed_nalu_types_in_pic_flag may have a first value (e.g., 0) or a second value (e.g., 1).

[0285] In addition, the types of each sub-picture included in the current picture can be determined based on the NAL unit type of each sub-picture. For example, as described above with reference to Table 1, the type of a sub-picture with a NAL unit type such as TRAIL_NUT can be determined as a trailing sub-picture. In addition, the type of a sub-picture with a NAL unit type such as STSA_NUT can be determined as an STSA sub-picture, and the type of a sub-picture with a NAL unit type such as GDR_NUT can be determined as a GDR sub-picture. In addition, the type of a sub-picture with a NAL unit type such as RADL_NUT can be determined as a RADL sub-picture, and the type of a sub-picture with a NAL unit type such as RASL_NUT can be determined as a RASL sub-picture. In addition, the type of a sub-picture with a NAL unit type such as IDR_W_RADL or IDR_N_LP can be determined as an IDR sub-picture, and the type of a sub-picture with a NAL unit type such as CRA_NUT can be determined as a CRA sub-picture.

[0286] The image decoding apparatus may decode multiple slices in the current picture based on the first flag information obtained in step S1610 and the NAL unit type determined in step S1620 (S1630). At this time, the decoding process of each slice may be performed in a coding unit (CU) based on a predetermined prediction mode as described above.

[0287] According to an embodiment of the present disclosure, the current picture may have two or more NAL unit types based on the sub-picture structure.

[0288] The names of the syntax elements described in the present disclosure may include information about the location of the corresponding syntax element being signaled. For example, a syntax element starting with "sps_" may mean that the corresponding syntax element is signaled in a sequence parameter set (SPS). In addition, a syntax element starting with "pps_", "ph_", "sh_" may mean that the corresponding syntax element is signaled in a picture parameter set (PPS), a picture header, and a slice header, respectively.

[0289] Although for the sake of clarity of description, the exemplary method of the present disclosure described above is represented as a series of operations, it is not intended to limit the order of executing the steps, and these steps can be performed simultaneously or in different orders when necessary. In order to implement the method according to the present invention, the steps described may further include other steps, may include the remaining steps except some steps, or may include other additional steps except some steps.

[0290] In the present disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) may perform an operation (step) of confirming an execution condition or situation of the corresponding operation (step). For example, if it is described that a predetermined operation is performed when a predetermined condition is met, the image encoding device or the image decoding device may perform the predetermined operation after determining whether the predetermined condition is met.

[0291] The various embodiments of the present disclosure are not a list of all possible combinations and are intended to describe representative aspects of the present disclosure, and matters described in the various embodiments may be applied independently or in combination of two or more.

[0292] Various embodiments of the present disclosure may be implemented in hardware, firmware, software or a combination thereof. In the case of implementing the present disclosure in hardware, the present disclosure may be implemented in an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a general purpose processor, a controller, a microcontroller, a microprocessor, etc.

[0293] 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 transmission and reception device, a mobile communication terminal, a home theater video device, a digital theater video device, a surveillance camera, a video chat device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camera, a video on demand (VoD) service provider, an OTT video (over the top video) device, an Internet streaming service provider, a three-dimensional (3D) video device, a video phone video device, a medical video device, etc., and may be used to process a video signal or a data signal. For example, an OTT video device may include a game console, a Blu-ray player, an Internet access TV, a home theater system, a smart phone, a tablet PC, a digital video recorder (DVR), etc.

[0294] Fig.17 is a diagram showing a content streaming system to which an embodiment of the present disclosure can be applied.

[0295] like Fig.17 As shown in , a content streaming system to which the embodiments of the present disclosure are applied may mainly include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0296] The encoding server compresses the content input from a multimedia input device such as a smart phone, camera, or camcorder into digital data to generate a bitstream and sends the bitstream to the streaming server. As another example, when a multimedia input device such as a smart phone, camera, or camcorder directly generates a bitstream, the encoding server can be omitted.

[0297] The bitstream may be generated by the image encoding method or the image encoding device to which the embodiments of the present disclosure are applied, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0298] The streaming server sends multimedia data to the user device based on the user's request through the network server, and the network server is used as a medium to inform the user of the service. When the user requests the required service from the network server, the network server can deliver it to the streaming server, and the streaming server can send the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server is used to control the command / response between the devices in the content streaming system.

[0299] The streaming server may receive content from a media storage device and / or an encoding server. For example, when receiving content from an encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream within a predetermined time.

[0300] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0301] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0302] The scope of the present disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling operations of methods according to various embodiments to be performed on a device or computer, and non-transitory computer-readable media having such software or commands stored thereon and executable on a device or computer.

[0303] Industrial Applicability

[0304] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. A decoding device for image decoding, the decoding device comprising: Memory; as well as at least one processor, the at least one processor connected to the memory, the at least one processor configured to: Get the video coding layer VCL network abstraction layer NAL unit type information of the current picture from the bitstream; determining, based on the obtained VCL NAL unit type information, a NAL unit type of each of a plurality of slices included in the current picture; and decoding the plurality of slices based on the determined NAL unit type, Wherein, based on that at least some of the multiple slices have different NAL unit types, the current picture includes two or more sub-pictures.

2. The decoding device according to claim 1, wherein: All slices in each sub-picture included in the current picture have the same NAL unit type.

3. The decoding device according to claim 1, wherein: Whether at least some of the plurality of slices have different NAL unit types is determined based on second flag information obtained from a picture parameter set PPS.

4. The decoding device according to claim 3, wherein: Based on the mixed NAL unit type not being applicable to all pictures in the output layer set OLS, the second flag information has a predetermined value specifying that the plurality of slices all have the same NAL unit type.

5. The decoding device according to claim 3, wherein: Based on the current picture including only one sub-picture, the second flag information has a predetermined value specifying that all of the plurality of slices have the same NAL unit type.

6. The decoding device according to claim 3, wherein: Based on that at least one of the sub-pictures included in the current picture is not regarded as one picture, the second flag information has a predetermined value specifying that all of the plurality of slices have the same NAL unit type.

7. The decoding device according to claim 1, wherein: A sub-picture type of each sub-picture included in the current picture is determined based on the NAL unit type of each sub-picture.

8. A coding device for image coding, the coding device comprising: Memory; as well as at least one processor, the at least one processor connected to the memory, the at least one processor configured to: Split the current screen into one or more sub-screens; determining a network abstraction layer (NAL) unit type for each of a plurality of slices included in the one or more sub-pictures; and encoding the plurality of slices based on the determined NAL unit type, Wherein, based on at least some of the multiple slices having different NAL unit types, the current picture is divided into two or more sub-pictures.

9. The encoding device according to claim 8, wherein: All slices in each sub-picture included in the current picture have the same NAL unit type.

10. The encoding device according to claim 8, wherein: Whether at least some of the plurality of slices have different NAL unit types is encoded based on predetermined flag information included in a picture parameter set PPS.

11. The encoding device according to claim 10, wherein: Based on the mixed NAL unit type not being applicable to all pictures in the output layer set OLS, the flag information has a predetermined value specifying that the plurality of slices all have the same NAL unit type.

12. The encoding device according to claim 10, wherein: Based on the current picture including only one sub-picture, the flag information has a predetermined value specifying that the plurality of slices all have the same NAL unit type.

13. The encoding device according to claim 10, wherein: Based on that at least one of sub-pictures included in the current picture is not regarded as one picture, the flag information has a predetermined value specifying that all of the plurality of slices have the same NAL unit type.

14. A device for transmitting data for an image, the device comprising: at least one processor configured to obtain a bit stream generated by a coding method performed by a coding device for image coding; as well as a transmitter configured to transmit the bit stream, The encoding method comprises the following steps: Split the current screen into one or more sub-screens; determining a network abstraction layer (NAL) unit type for each of a plurality of slices included in the one or more sub-pictures; and encoding the plurality of slices based on the determined NAL unit type, Wherein, based on at least some of the multiple slices having different NAL unit types, the current picture is divided into two or more sub-pictures.

Images