Image decoding method and apparatus for coding image information including picture header

Abstract

To provide a video decoding method and apparatus for adaptively coding a PHNAL unit in a video coding system.SOLUTION: A video decoding method performed by a decoding apparatus includes obtaining a flag indicating whether a PictureHeader (PH) NetworkAbstractionLayer (NAL) unit is present, obtaining a PH based on the flag, and decoding a current picture related to the PH based on the PH.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] This document relates to video coding technology, and more particularly to a video decoding method and apparatus for adaptively coding PH NAL units in a video coding system. [Background technology]

[0002] Recently, demand for high-resolution, high-quality images such as HD (High Definition) images and UHD (Ultra High Definition) images has been increasing in various fields. As the resolution and quality of image data increases, the amount of information or bits to be transmitted increases relatively compared to existing image data. Therefore, when image data is transmitted using a medium such as an existing wired or wireless broadband line or when image data is stored using an existing recording medium, transmission costs and storage costs increase.

[0003] Therefore, highly efficient image compression techniques are required to effectively transmit, store and reproduce high-resolution, high-quality image information. Summary of the Invention [Problem to be solved by the invention]

[0004] The technical problem of this document is to provide a method and apparatus for increasing image coding efficiency.

[0005] Another technical problem of this document is to provide a method and apparatus for coding a flag indicating whether a PH NAL unit exists. [Means for solving the problem]

[0006] According to one embodiment of the present document, there is provided a video decoding method performed by a decoding device, the method including the steps of: obtaining a flag indicating whether a Picture Header (PH) Network Abstraction Layer (NAL) unit exists; obtaining the PH based on the flag; and decoding a current picture associated with the PH based on the PH.

[0007] According to another embodiment of the present document, there is provided a decoding device for performing video decoding, which includes an entropy decoding unit that acquires a flag indicating whether a Picture Header (PH) Network Abstraction Layer (NAL) unit exists, acquires a PH based on the flag, and a prediction unit that decodes a current picture associated with the PH based on the PH.

[0008] According to another embodiment of the present document, there is provided a video encoding method performed by an encoding apparatus, the method including the steps of: determining whether a Network Abstraction Layer (NAL) unit including a Picture Header (PH) associated with a current picture exists; generating a flag indicating whether the PH NAL unit exists based on the result of the determination; and encoding video information including the flag.

[0009] According to another embodiment of the present document, there is provided a video encoding apparatus, which includes an entropy encoding unit that determines whether a Network Abstraction Layer (NAL) unit including a Picture Header (PH) associated with a current picture exists, generates a flag indicating whether the PH NAL unit exists based on the determination result, and encodes video information including the flag.

[0010] According to another embodiment of the present document, there is provided a computer-readable digital storage medium storing a bitstream including video information for performing a video decoding method, wherein the video decoding method in the computer-readable digital storage medium includes the steps of: obtaining a flag indicating whether a Picture Header (PH) Network Abstraction Layer (NAL) unit exists; obtaining the PH based on the flag; and decoding a current picture associated with the PH based on the PH. [Effects of the Invention]

[0011] According to this document, a flag indicating whether a PH NAL unit exists can be signaled, and based on the flag, the NAL unit can be adaptively adjusted to the bit rate of the bitstream, thereby improving overall coding efficiency.

[0012] According to this document, based on a flag indicating whether a PH NAL unit exists, constraints on the number of slices in the current picture and constraints on the existence of PH NAL units for related pictures can be set, thereby adaptively adjusting NAL units to the bitrate of the bitstream to improve overall coding efficiency. [Brief explanation of the drawings]

[0013] [Figure 1] 1 illustrates schematically an example of a video / image coding system to which embodiments of the present document may be applied. [Figure 2] 1 is a diagram illustrating a schematic configuration of a video / image encoding device to which embodiments of the present document can be applied; [Figure 3] 1 is a diagram illustrating the configuration of a video / image decoding device to which the embodiments of the present document can be applied; [Figure 4] 1 illustrates an exemplary hierarchical structure of coded video information. [Figure 5] 1 illustrates an exemplary encoding procedure according to an embodiment of the present document. [Figure 6] 1 illustrates an exemplary decoding procedure according to an embodiment of the present document. [Figure 7] 10 shows an example of a picture header structure in a NAL unit depending on whether a PH NAL unit is present or not. [Figure 8] 1 illustrates a schematic diagram of an image encoding method using an encoding device according to the present document. [Figure 9] 1 shows a schematic diagram of an encoding device for performing the image encoding method according to the present document; [Figure 10] 1 illustrates an image decoding method using a decoding device according to the present document. [Figure 11] 1 shows a schematic diagram of a decoding device for performing the image decoding method according to the present document; [Figure 12] 1 exemplarily illustrates a structural diagram of a content streaming system to which an embodiment of the present document is applied. DETAILED DESCRIPTION OF THE INVENTION

[0014] This document may be modified in various ways and may have various embodiments. Specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit this document to the specific embodiment. Common terms used in this document are used merely to describe specific embodiments and are not intended to limit the technical ideas of this document. A singular expression includes a plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0015] Meanwhile, each component in the drawings described in this document is illustrated independently for the convenience of explaining the different characteristic functions, and does not mean that each component is realized by separate hardware or software. For example, two or more components may be combined to form a single component, or a single component may be divided into multiple components. Embodiments in which each component is integrated and / or separated are also within the scope of this document as long as they do not deviate from the essence of this document.

[0016] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals will be used to refer to the same components in the drawings, and duplicated descriptions of the same components may be omitted.

[0017] FIG. 1 illustrates schematically an example of a video / image coding system in which embodiments of the present document may be applied.

[0018] As shown in Figure 1, a video / image coding system may include a first device (source device) and a second device (receiving device). The source device may transmit encoded video / image information or data to the receiving device in a file or streaming format via a digital recording medium or a network.

[0019] The source device may include a video source, an encoding device, and a transmitting unit. The receiving device may include a receiving unit, a decoding device, and a renderer. The encoding device may be called a video / image encoding device, and the decoding device may be called a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display unit, which may be a separate device or an external component.

[0020] A video source can acquire video / images through a video / image capture, synthesis, or generation process. A video source can include a video / image capture device and / or a video / image generation device. A video / image capture device can include, for example, one or more cameras, a video / image archive containing previously captured video / images, etc. A video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate video / images. For example, virtual video / images can be generated via a computer, etc., in which case the video / image capture process can be replaced by a process in which the associated data is generated.

[0021] An encoding device can encode input video / images. The encoding device can perform a series of steps such as prediction, transformation, and quantization for compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0022] The transmitter can transmit the encoded video / image information or data output in the form of a bitstream to a receiver of a receiving device via a digital recording medium or a network in the form of a file or streaming. The digital recording medium can include various recording media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD. The transmitter can include elements for generating a media file in a predetermined file format and elements for transmission via a broadcasting / communication network. The receiver can receive / extract the bitstream and transmit it to a decoding device.

[0023] The decoding device can decode the video / image by performing a series of steps such as inverse quantization, inverse transform, prediction, etc., which correspond to the operations of the encoding device.

[0024] The renderer can render the decoded video / image, and the rendered video / image can be displayed via a display unit.

[0025] This document relates to video / image coding. For example, the methods / embodiments disclosed in this document can be applied to methods disclosed in the versatile video coding (VVC) standard, the essential video coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the second generation of audio video coding standard (AVS2), or next generation video / image coding standards (e.g., H.267 or H.268).

[0026] This document presents various embodiments relating to video / image coding, which, unless otherwise stated, may also be implemented in combination with one another.

[0027] In this document, video may refer to a collection of a series of images over time. A picture generally refers to a unit that shows an image at a specific time, and a subpicture, slice, or tile is a unit that constitutes part of a picture in coding. A subpicture, slice, or tile may contain one or more coding tree units (CTUs). A picture may be composed of one or more subpictures, slices, or tiles. A picture may be composed of one or more groups of tiles. A tile group may contain one or more tiles. A brick may represent a rectangular region of CTU rows within a tile in a picture. A tile may be partitioned into multiple bricks, each consisting of one or more CTU rows within the tile. A tile that is not partitioned into multiple bricks may also be referred to as a brick.A brick scan refers to a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a brick, bricks within a tile are ordered consecutively in a raster scan of the bricks of the tile, and tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture. Also, a subpicture may represent a rectangular region of one or more slices within a picture. That is, a subpicture contains one or more slices that collectively cover a rectangular region of a picture. A tile is a rectangular region of CTUs within a particular tile column and a particular tile row in a picture.The tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements in the picture parameter set. The tile row is a rectangular region of CTUs having a height specified by syntax elements in the picture parameter set and a width equal to the height of the picture. A tile scan refers to a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in a CTU raster scan in a tile whereas tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture.A slice includes an integer number of bricks of a picture that maybe exclusively contained in a single NAL unit. A slice may consist of either a number of complete tiles or only a consecutive sequence of complete bricks of one tile. In this document, the terms tile group and slice may be used interchangeably. For example, in this document, tile group / tile group header may be called slice / slice header.

[0028] A pixel or a pel may refer to the smallest unit that constitutes one picture (or image). A "sample" may also be used as a term corresponding to a pixel. A sample may generally refer to a pixel or a pixel value, or may refer to only a pixel / pixel value of a luma component, or may refer to only a pixel / pixel value of a chroma component.

[0029] A unit may refer to a basic unit of image processing. A unit may include at least one of a specific region of a picture and information related to that region. One unit may include one luma block and two chroma (e.g., cb, cr) blocks. The term unit may be used interchangeably with terms such as block or area. In a general case, an M×N block may include samples (or a sample array) consisting of M columns and N rows, or a set (or an array) of transform coefficients.

[0030] As used herein, "A or B" may mean "A only," "B only," or "both A and B." In other words, as used herein, "A or B" may be interpreted as "A and / or B." For example, as used herein, "A, B, or C" may mean "A only," "B only," "C only," or "any combination of A, B, and C."

[0031] As used herein, a slash ( / ) or a comma may mean "and / or." For example, "A / B" may mean "A and / or B." Thus, "A / B" may mean "A only," "B only," or "both A and B." For example, "A, B, C" may mean "A, B, or C."

[0032] As used herein, "at least one of A and B" can mean "A only," "B only," or "both A and B." Furthermore, as used herein, the expressions "at least one of A or B" and "at least one of A and / or B" can be interpreted in the same way as "at least one of A and B."

[0033] Furthermore, in this specification, "at least one of A, B and C" can mean "A only," "B only," "C only," or "any combination of A, B and C." Furthermore, "at least one of A, B or C" and "at least one of A, B and / or C" can mean "at least one of A, B and C."

[0034] Furthermore, parentheses used in this specification may mean "for example." Specifically, when "prediction (intra prediction)" is displayed, "intra prediction" may be proposed as an example of "prediction." In other words, "prediction" in this specification is not limited to "intra prediction," and "intra prediction" may be proposed as an example of "prediction." Furthermore, when "prediction (i.e., intra prediction)" is displayed, "intra prediction" may be proposed as an example of "prediction."

[0035] Technical features described separately in one drawing in this specification may be realized separately or simultaneously.

[0036] The following drawings are created to explain a specific example of the present specification. The names of specific devices and names of specific signals / messages / fields shown in the drawings are provided for illustrative purposes only, and the technical features of the present specification are not limited to the specific names used in the following drawings.

[0037] 2 is a diagram for explaining the configuration of a video / image encoding device to which the embodiments of this document can be applied. Hereinafter, the video encoding device may include an image encoding device.

[0038] As shown in FIG. 2, the encoding device 200 may include an image partitioner 210, a predictor 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The predictor 220 may include an inter predictor 221 and an intra predictor 222. The residual processor 230 may include a transformer 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235. The residual processor 230 may further include a subtractor 231. The adder 250 may be referred to as a reconstructor or a reconstructed block generator. The image dividing unit 210, the predicting unit 220, the residual processing unit 230, the entropy encoding unit 240, the adding unit 250, and the filtering unit 260 may be configured by one or more hardware components (e.g., an encoder chipset or a processor) depending on the embodiment. Also, the memory 270 may include a decoded picture buffer (DPB) and may be configured by a digital recording medium. The hardware components may further include the memory 270 as an internal / external component.

[0039] The image division unit 210 may divide an input image (or picture, frame) input to the encoding device 200 into one or more processing units. For example, the processing units may be called coding units (CUs). In this case, the coding units may be recursively divided from a coding tree unit (CTU) or a largest coding unit (LCU) according to a quad-tree, binary-tree, ternary-tree (QTBTTT) structure. For example, one coding unit may be divided into multiple coding units of deeper depths based on a quad-tree structure, a binary tree structure, and / or a ternary structure. In this case, for example, the quad-tree structure may be applied first, and then the binary tree structure and / or the ternary structure may be applied later. Alternatively, the binary tree structure may be applied first. The coding procedure according to this document may be performed based on the final coding unit that is not further divided. In this case, the largest coding unit may be immediately used as the final coding unit based on coding efficiency according to image characteristics, or the coding unit may be recursively divided into coding units of lower depths as needed, and the coding unit of the optimal size may be used as the final coding unit. Here, the coding procedure may include procedures such as prediction, transformation, and restoration, which will be described later. As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may each be divided or partitioned from the final coding unit.The prediction unit is a unit of sample prediction, and the transform unit is a unit for deriving transform coefficients and / or a unit for deriving a residual signal from the transform coefficients.

[0040] The term "unit" can be used interchangeably with terms such as "block" or "area." In general, an MxN block can refer to a set of samples or transform coefficients consisting of M columns and N rows. A sample can generally refer to a pixel or pixel value, and can refer to only a pixel / pixel value of the luma component, or only a pixel / pixel value of the chroma component. A sample can also be used as a term corresponding to one pixel or pel of a picture (or image).

[0041] The encoding apparatus 200 may generate a residual signal (residual block, residual sample array) by subtracting a prediction signal (predicted block, prediction sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from an input image signal (original block, original sample array), and the generated residual signal is transmitted to the conversion unit 232. In this case, as shown in the figure, a unit in the encoder 200 that subtracts the prediction signal (predicted block, prediction sample array) from the input image signal (original block, original sample array) may be referred to as a subtraction unit 231. The prediction unit may perform prediction on a current block to be processed (hereinafter, referred to as a current block) and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied on a current block or CU basis. The prediction unit may generate various information related to prediction, such as prediction mode information, and transmit the information to the entropy encoding unit 240, as will be described later in the description of each prediction mode. The prediction information can be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0042] The intra prediction unit 222 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located far away, depending on the prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes may include, for example, DC mode and planar mode. The directional modes may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the granularity of the prediction direction. However, this is merely an example, and more or less directional prediction modes may be used depending on the settings. The intra prediction unit 222 may also determine the prediction mode to be applied to the current block using the prediction modes applied to neighboring blocks.

[0043] The inter prediction unit 221 may derive a predicted block for a current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on an inter prediction direction (such as L0 prediction, L1 prediction, or Bi prediction). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks in the current picture and temporal neighboring blocks in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be called a collocated reference block, a collocated CU (colCU), or the like, and the reference picture including the temporal neighboring block may be called a collocated picture (colPic). For example, the inter predictor 221 may configure a motion information candidate list based on neighboring blocks and generate information indicating which candidates are used to derive a motion vector and / or a reference picture index for the current block. Inter prediction may be performed based on various prediction modes, and for example, in the case of a skip mode or a merge mode, the inter predictor 221 may use motion information of neighboring blocks as motion information of the current block. In the case of the skip mode, unlike in the merge mode, a residual signal may not be transmitted.In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block is used as a motion vector predictor, and the motion vector of the current block can be indicated by signaling the motion vector difference.

[0044] The predictor 220 may generate a prediction signal based on various prediction methods, which will be described later. For example, the predictor may apply intra prediction or inter prediction for prediction of a block, or may simultaneously apply intra prediction and inter prediction. This may be referred to as combined inter and intra prediction (CIIP). The predictor may also use an intra block copy (IBC) prediction mode or a palette mode for prediction of a block. The IBC prediction mode or palette mode may be used for content image / video coding, such as games, such as screen content coding (SCC). IBC basically performs prediction within a current picture, but may be performed similarly to inter prediction in deriving a reference block within the current picture. That is, IBC may use at least one of the inter prediction techniques described herein. The palette mode may be seen as an example of intra coding or intra prediction. When the palette mode is applied, sample values ​​within a picture may be signaled based on information about a palette table and a palette index.

[0045] The prediction signal generated by the prediction unit (including the inter prediction unit 221 and / or the intra prediction unit 222) may be used to generate a reconstructed signal or a residual signal. The transform unit 232 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a Karhunen-Loeve transform (KLT), a graph-based transform (GBT), or a conditionally non-linear transform (CNT). Here, GBT refers to a transform obtained from a graph representing inter-pixel relationship information. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. The transform process may be applied to pixel blocks having the same square size or non-square blocks of variable size.

[0046] The quantizer 233 quantizes the transform coefficients and transmits them to the entropy encoder 240. The entropy encoder 240 encodes the quantized signal (information about the quantized transform coefficients) and outputs it as a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 233 may rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and may generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoder 240 may perform various encoding methods, such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. In addition to the quantized transform coefficients, the entropy encoder 240 may also encode information required for video / image restoration (e.g., values ​​of syntax elements, etc.) together with or separately from the quantized transform coefficients. The encoded information (e.g., encoded video / image information) may be transmitted or stored in the form of a bitstream in units of network abstraction layer (NAL) units. The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. Information and / or syntax elements transmitted / signaled from an encoding device to a decoding device in this document may be included in the video / image information. The video / image information may be encoded through the above-described encoding procedure and included in the bitstream.The bitstream may be transmitted via a network or stored on a digital recording medium. Here, the network may include a broadcasting network and / or a communication network, and the digital recording medium may include various recording media such as a USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) for transmitting the signal output from the entropy encoding unit 240 and / or a storage unit (not shown) for storing the signal may be configured as an internal / external element of the encoding device 200, or the transmitter may be included in the entropy encoding unit 240.

[0047] The quantized transform coefficients output from the quantization unit 233 may be used to generate a prediction signal. For example, a residual signal (residual block or residual sample) may be reconstructed by applying inverse quantization and inverse transform to the quantized transform coefficients via the inverse quantization unit 234 and the inverse transform unit 235. The adder 250 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the reconstructed residual signal to the prediction signal output from the inter prediction unit 221 or the intra prediction unit 222. When there is no residual for the current block, such as when skip mode is applied, a predicted block may be used as the reconstructed block. The adder 250 may be referred to as a reconstruction unit or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next block to be processed in the current picture, or may be used for inter prediction of the next picture after filtering, as described below.

[0048] Meanwhile, luma mapping with chroma scaling (LMCS) can be applied during picture encoding and / or reconstruction.

[0049] The filtering unit 260 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 260 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture and store the modified reconstructed picture in the memory 270, specifically, in the DPB of the memory 270. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc. The filtering unit 260 may generate various information related to filtering and transmit it to the entropy encoding unit 240, as will be described later in connection with each filtering method. The filtering information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0050] The modified reconstructed picture transmitted to the memory 270 can be used as a reference picture in the inter prediction unit 221. When inter prediction is applied through this, the encoding apparatus can avoid prediction mismatch between the encoding apparatus 200 and the decoding apparatus 300 and can also improve encoding efficiency.

[0051] The memory 270DPB may store modified reconstructed pictures for use as reference pictures in the inter predictor 221. The memory 270 may store motion information of blocks from which motion information in the current picture is derived (or encoded) and / or motion information of blocks in already reconstructed pictures. The stored motion information may be transmitted to the inter predictor 221 to be used as motion information of spatially neighboring blocks or temporally neighboring blocks. The memory 270 may store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 222.

[0052] FIG. 3 is a diagram illustrating the configuration of a video / image decoding device to which the embodiments of this document can be applied.

[0053] As shown in FIG. 3, the decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter-predictor 331 and an intra-predictor 332. The residual processor 320 may include a dequantizer 321 and an inverse transformer 322. The entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 may be configured as a single hardware component (e.g., a decoder chipset or processor) according to an embodiment. The memory 360 may include a decoded picture buffer (DPB) or may be configured as a digital recording medium. The hardware components may further include a memory 360 as an internal / external component.

[0054] When a bitstream including video / image information is input, the decoding device 300 can reconstruct an image corresponding to the process by which the video / image information was processed by the encoding device of FIG. 2. For example, the decoding device 300 can derive units / blocks based on block division-related information obtained from the bitstream. The decoding device 300 can perform decoding using a processing unit applied by the encoding device. Accordingly, the processing unit for decoding is, for example, a coding unit, and the coding unit can be divided from a coding tree unit or a maximal coding unit according to a quad tree structure, a binary tree structure, and / or a ternary tree structure. One or more transform units can be derived from the coding unit. The reconstructed image signal decoded and output by the decoding device 300 can be reproduced through a playback device.

[0055] The decoding device 300 may receive a signal output from the encoding device of FIG. 2 in the form of a bitstream, and the received signal may be decoded via the entropy decoding unit 310. For example, the entropy decoding unit 310 may parse the bitstream to derive information (e.g., video / image information) necessary for image restoration (or picture restoration). The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. The decoding device may further decode pictures based on the information on the parameter sets and / or the general constraint information. Signaling / received information and / or syntax elements, which will be described later in this document, may be decoded via the decoding procedure and obtained from the bitstream. For example, the entropy decoding unit 310 may decode information in a bitstream based on a coding method such as Exponential-Golomb coding, CAVLC, or CABAC, and output values ​​of syntax elements required for image restoration, quantized values ​​of transform coefficients related to residuals, etc. More specifically, the CABAC entropy decoding method receives bins corresponding to each syntax element in the bitstream, determines a context model using information on the syntax element to be decoded and decoded information on neighboring and current blocks, or information on symbols / bins decoded in previous steps, predicts the occurrence probability of the bins according to the determined context model, and performs arithmetic decoding of the bins to generate symbols corresponding to the values ​​of each syntax element. After determining the context model, the CABAC entropy decoding method may update the context model using information on the decoded symbols / bins for the context model of the next symbol / bin.Among the information decoded by the entropy decoding unit 310, information related to prediction is provided to a prediction unit (inter prediction unit 332 and intra prediction unit 331), and residual values ​​entropy decoded by the entropy decoding unit 310, i.e., quantized transform coefficients and related parameter information, may be input to a residual processing unit 320. The residual processing unit 320 may derive a residual signal (residual block, residual sample, residual sample array). In addition, among the information decoded by the entropy decoding unit 310, information related to filtering may be provided to a filtering unit 350. Meanwhile, a receiving unit (not shown) that receives a signal output from the encoding device may be further configured as an internal / external element of the decoding device 300, or the receiving unit may be a component of the entropy decoding unit 310. Meanwhile, the decoding device according to this document may be called a video / image / picture decoding device, and the 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 the entropy decoding unit 310, and the sample decoder may include at least one of the inverse quantization unit 321, the inverse transform unit 322, the addition unit 340, the filtering unit 350, the memory 360, the inter prediction unit 332, and the intra prediction unit 331.

[0056] The inverse quantization unit 321 may inverse quantize the quantized transform coefficients and output the transform coefficients. The inverse quantization unit 321 may rearrange the quantized transform coefficients in a two-dimensional block format. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the encoding device. The inverse quantization unit 321 may perform inverse quantization on the quantized transform coefficients using a quantization parameter (e.g., quantization step size information) to obtain transform coefficients.

[0057] The inverse transform unit 322 performs inverse transform on the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0058] The prediction unit may perform prediction on a current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on information about the prediction output from the entropy decoding unit 310, and may determine a specific intra / inter prediction mode.

[0059] The predictor 320 may generate a prediction signal based on various prediction methods, which will be described later. For example, the predictor may apply intra prediction or inter prediction for predicting a block, or may simultaneously apply intra prediction and inter prediction. This may be referred to as combined inter and intra prediction (CIIP). The predictor may also use an intra block copy (IBC) prediction mode or a palette mode for predicting a block. The IBC prediction mode or palette mode may be used for content image / video coding, such as games, such as screen content coding (SCC). IBC basically performs prediction within a current picture, but may be performed similarly to inter prediction in deriving a reference block within the current picture. That is, IBC may use at least one of the inter prediction techniques described in this document. The palette mode may be seen as an example of intra coding or intra prediction. When the palette mode is applied, information regarding a palette table and a palette index may be included in the video / image information and signaled.

[0060] The intra prediction unit 331 may predict a current block by referring to samples in a current picture. The referenced samples may be located in the neighborhood of the current block or may be located far away from the current block depending on the prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The intra prediction unit 331 may also determine a prediction mode to be applied to the current block using prediction modes applied to neighboring blocks.

[0061] The inter prediction unit 332 may derive a predicted block for the current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted from the inter 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 further include information on the inter prediction direction (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks in the current picture and temporal neighboring blocks in the reference picture. For example, the inter prediction unit 332 may construct a motion information candidate list based on the neighboring blocks and derive a motion vector and / or a reference picture index for the current block based on received candidate selection information. Inter prediction may be performed based on various prediction modes, and the prediction information may include information indicating the inter prediction mode for the current block.

[0062] The adder 340 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the acquired residual signal to a predicted signal (predicted block, predicted sample array) output from a prediction unit (including the inter prediction unit 332 and / or the intra prediction unit 331). When there is no residual for the current block, such as when a skip mode is applied, the predicted block may be used as a reconstructed block.

[0063] The adder 340 may be referred to as a reconstruction unit or a reconstruction block generator. The generated reconstruction signal may be used for intra prediction of a next block to be processed in the current picture, may be output after filtering as described below, or may be used for inter prediction of a next picture.

[0064] Meanwhile, LMCS (luma mapping with chroma scaling) can be applied during the picture decoding process.

[0065] The filtering unit 350 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 350 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and may transmit the modified reconstructed picture to the memory 360, specifically, to the DPB of the memory 360. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc.

[0066] The (modified) reconstructed picture stored in the DPB of the memory 360 may be used as a reference picture in the inter predictor 332. The memory 360 may store motion information of a block from which motion information in the current picture is derived (or decoded) and / or motion information of a block in an already reconstructed picture. The stored motion information may be transmitted to the inter predictor 260 to be used as motion information of a spatially neighboring block or a temporally neighboring block. The memory 360 may store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 331.

[0067] In this specification, the embodiments described for the filtering unit 260, inter prediction unit 221, and intra prediction unit 222 of the encoding device 200 can also be applied identically or correspondingly to the filtering unit 350, inter prediction unit 332, and intra prediction unit 331 of the decoding device 300, respectively.

[0068] In this document, at least one of quantization / dequantization and / or transform / inverse transform may be omitted. When the quantization / dequantization is omitted, the quantized transform coefficients may be referred to as transform coefficients. When the transform / inverse transform is omitted, the transform coefficients may be referred to as coefficients or residual coefficients, or may still be referred to as transform coefficients for consistency of expression.

[0069] In this document, quantized transform coefficients and transform coefficients may be referred to as transform coefficients and scaled transform coefficients, respectively. In this case, residual information may include information about the transform coefficient(s), and the information about the transform coefficient(s) may be signaled via a residual coding syntax. Transform coefficients may be derived based on the residual information (or information about the transform coefficient(s)), and scaled transform coefficients may be derived through an inverse transform (scaling) of the transform coefficient(s). Residual samples may be derived based on an inverse transform (transform) of the scaled transform coefficient(s). This may be similarly applied / expressed in other parts of this document.

[0070] FIG. 4 shows an example of a hierarchical structure of coded video information.

[0071] 4 may exemplarily show a video / image coded according to the coding layer and structure of this document. Referring to FIG. 4, the coded video / image may be divided into a Video Coding Layer (VCL) that processes the video / image and the video / image decoding process, a subsystem that transmits and stores coded information, and a Network Abstraction Layer (NAL) that exists between the VCL and the subsystem and performs functions.

[0072] For example, in VCL, VCL data including compressed image data (slice data) can be generated, or a parameter set including a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), a Video Parameter Set (VPS), or an SEI (Supplemental Enhancement Information) message that is additionally required for the video decoding process can be generated.

[0073] For example, in NAL, a NAL unit can be generated by adding header information (NAL unit header) to a Raw Byte Sequence Payload (RBSP) generated by a VCL. In this case, the RBSP can refer to slice data, a parameter set, an SEI message, etc. generated by the VCL. The NAL unit header can include NAL unit type information specified by the RBSP data included in the corresponding NAL unit.

[0074] Also, for example, as shown in Figure 4, NAL units can be classified into VCL NAL units and non-VCL NAL units according to the RBSP generated by the VCL. A VCL NAL unit can refer to a NAL unit containing information (slice data) about an image, and a non-VCL NAL unit can refer to a NAL unit containing information (parameter set or SEI message) necessary for video decoding.

[0075] The VCL NAL units and non-VCL NAL units can be transmitted over a network by attaching header information according to the subsystem's data standard. For example, the NAL units can be converted into a predetermined standard data format such as H.266 / VVC file format, real-time transport protocol (RTP), transport stream (TS), etc., and can be transmitted over various networks.

[0076] Also, as mentioned above, the NAL unit type of an NAL unit can be specified by the RBSP data structure included in the corresponding NAL unit, and information about the NAL unit type can be stored and signaled in the NAL unit header.

[0077] For example, NAL units can be classified into VCL NAL unit types and non-VCL NAL unit types depending on whether they contain information about a video (slice data). In addition, VCL NAL unit types can be classified according to the characteristics and type of a picture included in the VCL NAL unit, and non-VCL NAL unit types can be classified according to the type of parameter set.

[0078] The following are examples of NAL unit types specified by the types of parameter sets contained in the Non-VCL NAL unit types:

[0079] -APS (Adaptation Parameter Set) NAL unit: Type for NAL units containing APS

[0080] -DPS (Decoding Parameter Set) NAL unit: Type for NAL units containing DPS

[0081] -VPS (Video Parameter Set) NAL unit: Type for NAL units containing VPS

[0082] -SPS (Sequence Parameter Set) NAL unit: Type for NAL units containing SPS

[0083] -PPS (Picture Parameter Set) NAL unit: Type for NAL units containing PPS

[0084] -PH (Picture header) NAL unit: Type for NAL units containing PH

[0085] The above-mentioned NAL unit type may have syntax information for the NAL unit type, and the syntax information may be stored and signaled in a NAL unit header. For example, the syntax information may be nal_unit_type, and the NAL unit type may be specified as a nal_unit_type value.

[0086] Meanwhile, as described above, one picture may include multiple slices, and each slice may include a slice header and slice data. In this case, one picture header may be added (embedded) for multiple slices (a set of slice headers and slice data). A picture header (picture header syntax) may include information / parameters that can be commonly applied to pictures. A slice header (slice header syntax) may include information / parameters that can be commonly applied to slices. An APS (APS syntax) or PPS (PPS syntax) may include information / parameters that can be commonly applied to one or more slices or pictures. An SPS (SPS syntax) may include information / parameters that can be commonly applied to one or more sequences. A VPS (VPS syntax) may include information / parameters that can be commonly applied to multiple layers. A DPS (DPS syntax) may include information / parameters that can be commonly applied to the entire image. The DPS may include information / parameters related to the concatenation of a coded video sequence (CVS). In this document, High Level Syntax (HLS) may include at least one of an APS syntax, a PPS syntax, an SPS syntax, a VPS syntax, a DPS syntax, a picture header syntax, and a slice header syntax.

[0087] Meanwhile, as described above, generally, one NAL unit type can be set for one picture, and the NAL unit type can be signaled via nal_unit_type in the NAL unit header of the NAL unit including the slice, as described above. The following table shows examples of NAL unit type codes and NAL unit type classes.

[0088] [Table 1-1]

[0089] [Table 1-2]

[0090] Meanwhile, as described above, a picture may be composed of one or more slices. Parameters describing the picture may be signaled in a picture header (PH), and parameters describing a slice may be signaled in a slice header (SH). The PH may be transmitted in its own NAL unit type. The SH may be present at the beginning of an NAL unit containing the payload of the slice (i.e., slice data).

[0091] For example, the syntax elements of the signaled PH are as follows:

[0092] [Table 2-1]

[0093] [Table 2-2]

[0094] [Table 2-3]

[0095] [Table 2-4]

[0096] [Table 2-5]

[0097] [Table 2-6]

[0098] On the other hand, the adoption of PH may mean that there should be at least two NAL units for every coded picture. For example, one of the two units is an NAL unit for the PH, and the other is an NAL unit for the coded slice including the slice header (SH) and slice data. This can be problematic for bitstreams with low bitrates because additional NAL units per picture can have a significant impact on the bitrate. Therefore, it is preferable that PH have a mode that does not consume new NAL units.

[0099] Therefore, this document proposes the following embodiments to solve the above-mentioned problems. The proposed embodiments can be applied individually or in combination.

[0100] As an example, we propose a scheme for signaling a flag in a high-level parameter set that indicates whether a PH NAL unit is present in a Coded Layer Video Sequence (CLVS). That is, the flag may indicate whether a picture header is present in an NAL unit (i.e., a PH NAL unit) or a slice header. Here, for example, the CLVS may refer to a sequence of picture units (PUs) having the same value of nuh_layer_id. The picture unit is a set of NAL units (and so on) for a coded picture. Also, for example, the high-level parameter set may be a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), or a slice header. The flag may be referred to as a ph_nal_present_flag. Alternatively, the flag may be referred to as a PH NAL present flag.

[0101] In addition, this document proposes an embodiment that constrains the value of ph_nal_present_flag to be the same for all SPSs referenced by pictures in the same CVS in relation to the PH NAL present flag. This constraint may mean that the value of ph_nal_present_flag must be the same for one coded video sequence in a multi-layer bitstream.

[0102] Also, as an example, it is proposed that if the value of ph_nal_present_flag is equal to 1, one PH NAL unit exists, and the PH NAL unit is associated with a VCL (Video Coding Layer) NAL unit of the picture.

[0103] Also, as an example, when the value of ph_nal_present_flag is equal to 0 (i.e., when a PH NAL unit does not exist for each picture), a solution is proposed in which the following constraints are applied:

[0104] For example, the constraints are as follows:

[0105] First, every picture in CLVS can contain only one slice.

[0106] Second, the PH NAL unit may not exist. The PH syntax table may exist in the slice layer RBSP together with the slice header (SH) and slice data. That is, the PH syntax table may exist in the slice header.

[0107] Third, the PH syntax table and the SH syntax table can start in a byte-aligned position. To achieve this, a byte alignment bit can be added between the PH and SH.

[0108] Fourth, the value of picture_header_extension_present_flag in all PPSs that reference an SPS is 0.

[0109] Fifth, all syntax elements that can be present in PH or SH can be present in PH that is not SH.

[0110] Also, as an example, a method for updating access unit detection may be proposed. That is, instead of checking the PH, all new VCL NAL units may indicate new Access Units (AUs). That is, if the value of ph_nal_present_flag indicates that the PH NAL unit does not exist, the VCL NAL unit including ph_nal_present_flag may indicate that a VCL NAL unit for a new AU (i.e., a picture for a new AU) is parsed, rather than a VCL NAL unit for a previous-order AU (i.e., a picture for a previous-order AU). Therefore, if the value of ph_nal_present_flag indicates that the PH NAL unit does not exist, the VCL NAL unit including ph_nal_present_flag is the first VCL NAL unit for a picture of a new AU (e.g., a current picture for which decoding is being performed). Here, an AU may refer to a set of Picture Units (PUs) including coded pictures that belong to different layers and are associated with the same time for output from a Decoded Picture Buffer (DPB). Also, the PU may refer to a set of NAL units including one coded picture that are related to each other and have consecutive decoding orders. That is, the PU may refer to a set of NAL units for one coded picture that are related to each other and have consecutive decoding orders. Meanwhile, if a bitstream is a single-layer bitstream rather than a multi-layer bitstream, the AU is the same as the PU.

[0111] The embodiments proposed in this document can be implemented as described below.

[0112] For example, the SPS syntax in which the ph_nal_present_flag proposed in the embodiment of this document is signaled is as follows:

[0113] [Table 3]

[0114] Referring to Table 3, the SPS may include a ph_nal_present_flag.

[0115] For example, the semantic of the syntax element ph_nal_present_flag is as shown in the table below.

[0116] [Table 4]

[0117] For example, referring to Table 4, the syntax element ph_nal_present_flag may indicate whether there is a NAL unit with a nal_unit_type equal to PH_NUT for each coded picture of a CLVS, etc. (CLVSs) that references an SPS. For example, ph_nal_present_flag equal to 1 may indicate that there is a NAL unit with a nal_unit_type equal to PH_NUT for each coded picture of a CLVS, etc. (CLVSs) that references an SPS. Also, for example, ph_nal_present_flag equal to 0 may indicate that there is no NAL unit with a nal_unit_type equal to PH_NUH for each coded picture of a CLVS, etc. (CLVSs) that references an SPS.

[0118] Also, for example, if the ph_nal_present_flag is 1, the following content may be applied.

[0119] NAL units whose -nal_unit_type is PH_NUT (i.e., PH NAL units) do not exist in the CLVS that references the SPS.

[0120] Each picture in a CLVS that references an SPS can contain one slice.

[0121] -PH can be present in the slice layer RBSP.

[0122] On the other hand, Tables 3 and 4 propose a method in which ph_nal_present_flag is signaled to an SPS, but the method shown in Tables 3 and 4 is only one embodiment proposed in this document, and an embodiment in which ph_nal_present_flag is signaled to a PPS or slice header other than an SPS can also be proposed.

[0123] Meanwhile, for example, according to one embodiment proposed in this document, the picture header syntax table and the picture header RBSP can be signaled separately as shown in the table below.

[0124] [Table 5]

[0125] The signaled picture header syntax table is as follows:

[0126] [Table 6-1]

[0127] [Table 6-2]

[0128] [Table 6-3]

[0129] [Table 6-4]

[0130] [Table 6-5]

[0131] [Table 6-6]

[0132] Also, for example, according to one embodiment proposed in this document, the slice layer RBSP can be signaled as follows:

[0133] [Table 7]

[0134] Also, for example, according to one embodiment proposed in this document, one or more of the constraints shown in the following table may be applied.

[0135] [Table 8]

[0136] For example, referring to Table 8, if ph_nal_present_flag is 0, the value of picture_header_extension_present_flag can be 0.

[0137] Also, for example, if the following two conditions are all true, the value of pic_rpl_present_flag must be equal to 1, which is a bitstream conformance requirement:

[0138] - ph_nal_present_flag is 0 and the picture associated with PH is not an IDR picture.

[0139] - ph_nal_present_flag is 0, the picture associated with the PH is an IDR picture, and sps_id_rpl_present_flag is equal to 1.

[0140] Here, the rpl may refer to a reference picture list.

[0141] Also, for example, if the value of ph_nal_present_flag is 0, the value of pic_sao_enabled_present_flag must be the same as 1, which is a bitstream compatibility requirement.

[0142] Also, for example, if the value of ph_nal_present_flag is 0, the value of pic_alf_enabled_present_flag must be the same as 1, which is a bitstream compatibility requirement.

[0143] Also, for example, if the value of ph_nal_present_flag is 0, the value of pic_deblocking_filter_override_present_flag must be the same as 1, which is a bitstream compatibility requirement.

[0144] Meanwhile, for example, the embodiment (etc.) can be applied by the following procedure.

[0145] FIG. 5 exemplarily illustrates an encoding procedure according to an embodiment of the present document.

[0146] 5, an encoding device may generate a NAL unit (or the like) containing information about a picture (S500). The encoding device may determine whether a NAL unit for a picture header exists (S510), and may determine whether a NAL unit for the picture header exists (S520).

[0147] For example, if the NAL unit for the picture header exists, the encoding apparatus can generate a bitstream including a VCL NAL unit including a slice header and a PH NAL unit including a picture header (S530).

[0148] On the other hand, for example, if there is no NAL unit for the picture header, the encoding apparatus may generate a bitstream including a VCL NAL unit including a slice header and a picture header (S540). That is, for example, the picture header syntax structure may exist in the slice header.

[0149] FIG. 6 exemplarily illustrates a decoding procedure according to an embodiment of the present document.

[0150] 6, a decoding device may receive a bitstream including NAL units (etc.) (S600). Thereafter, the decoding device may determine whether an NAL unit for a picture header exists (S610).

[0151] For example, if a NAL unit for the picture header exists, the decoding device can decode / reconstruct the picture / slice / block / sample based on the slice header in the VCL NAL unit and the picture header in the PH NAL unit (S620).

[0152] On the other hand, for example, if there is no NAL unit for the picture header, the decoding device can decode / reconstruct the picture / slice / block / sample based on the slice header and picture header in the VCL NAL unit (S630).

[0153] Here, the (coded) bitstream may include one or more NAL units for decoding a picture. The NAL units may be VCL NAL units or non-VCL NAL units. For example, a VCL NAL unit may include information about a coded slice, and the VCL NAL unit may have a NAL unit type with the NAL unit type class "VCL" as described in Table 1 above.

[0154] Meanwhile, according to the embodiment proposed in this document, the bitstream may include a PH NAL unit (NAL unit for a picture header) or may not include a PH NAL unit for the current picture. Information indicating the presence or absence of a PH NAL unit (e.g., ph_nal_present_flag) can be signaled in the HLS (e.g., VPS, DPS, SPS, or slice header).

[0155] 7 exemplarily illustrates the structure of a picture header in an NAL unit depending on whether a PH NAL unit is present. For example, (a) of FIG. 7 illustrates a case where a PH NAL unit for the current picture is present, and (b) of FIG. 7 illustrates a case where a PH NAL unit for the current picture is not present but a picture header is included in the VCL NAL unit.

[0156] For example, if the PH NAL unit exists, the picture header may be included in the PH NAL unit. Conversely, if the PH NAL unit does not exist, the picture header may still be constructed but may be included in another NAL unit. For example, the picture header may be included in a VCL NAL unit. The VCL NAL unit may include information about a coded slice. A VCL unit may include a slice header for a coded slice. For example, if a specific slice header includes information that the coded / associated slice is the first slice in a picture or subpicture, the picture header may be included in the specific VCL NAL unit that includes the specific slice header. Alternatively, for example, if the PH NAL unit does not exist, the picture header may be included in a non-VCL NAL unit such as a PPS NAL unit, an APS NAL unit, etc.

[0157] Figure 8 schematically illustrates a video encoding method by the encoding device according to the present document. The method disclosed in Figure 8 may be performed by the encoding device disclosed in Figure 2. Specifically, for example, steps S800 to S820 in Figure 8 may be performed by an entropy encoding unit of the encoding device. Also, although not shown, the process of decoding the current picture may be performed by a prediction unit and a residual processing unit of the encoding device.

[0158] An encoding apparatus determines whether a Network Abstraction Layer (NAL) unit including a Picture Header (PH) associated with a current picture exists (S800). The encoding apparatus may generate a NAL unit for the current picture. For example, the NAL unit for the current picture may include a PH NAL unit including a PH associated with the current picture and / or a Video Coded Layer (VCL) NAL unit including information on a slice of the current picture (e.g., a slice header and slice data). The encoding apparatus may determine whether the PH NAL unit exists. For example, if the PH NAL unit exists, the encoding apparatus may generate a PH NAL unit including a PH associated with the current picture and / or a Video Coded Layer (VCL) NAL unit including information on a slice of the current picture (e.g., a slice header and slice data). Furthermore, for example, if the PH NAL unit does not exist, the encoding apparatus may generate a Video Coded Layer (VCL) NAL unit including a PH associated with the current picture and information on one slice of the current picture (e.g., a slice header and slice data). Also, for example, if the flag indicates that the PH NAL unit is not present, the current picture may include one slice, where, for example, the PH may include syntax elements indicating parameters for the current picture.

[0159] The encoding apparatus generates a flag indicating whether the PH NAL unit exists based on the result of the determination (S810). The encoding apparatus may generate a flag indicating whether the PH NAL unit exists based on the result of the determination. For example, the flag may indicate whether the PH NAL unit exists. For example, if the flag has a value of 1, the flag may indicate that the PH NAL unit exists, and if the flag has a value of 0, the flag may indicate that the PH NAL unit does not exist. Alternatively, if the flag has a value of 0, the flag may indicate that the PH NAL unit exists, and if the flag has a value of 1, the flag may indicate that the PH NAL unit does not exist. The syntax element of the flag is the above-mentioned ph_nal_present_flag.

[0160] The encoding apparatus encodes the video information including the flag (S820). The encoding apparatus may encode the video information including the flag. The video information may include the flag. Also, for example, the video information may include a high-level syntax, and the flag may be included in the high-level syntax. For example, the high-level syntax may be a Sequence Parameter Set (SPS). Or, for example, the high-level syntax may be a slice header (SH). That is, for example, the flag may be included in the slice header.

[0161] Meanwhile, for example, if the flag indicates that the PH NAL unit exists, the PH may be included in the PH NAL unit, and if the flag indicates that the PH NAL unit does not exist, the PH may be included in a slice header associated with the current picture. For example, if the flag indicates that the PH NAL unit exists, the PH may be included in the PH NAL unit, and if the flag indicates that the PH NAL unit does not exist, the PH may be included in a VCL NAL unit including a slice header. That is, for example, if the flag indicates that the PH NAL unit exists, the PH may be included in the PH NAL unit, and if the flag indicates that the PH NAL unit does not exist, the PH may be included in a slice header. For example, if the flag indicates that the PH NAL unit exists, the video information may include at least one VCL NAL unit including the PH NAL unit including the PH and a slice header associated with the current picture. If the flag indicates that the PH NAL unit does not exist, the video information may include a VCL NAL unit including the PH and a slice header. Also, for example, if the flag indicates that the PH NAL unit is not present, the video information may not include the PH NAL unit.

[0162] Also, for example, if the flag indicates that the PH NAL unit does not exist, the PH NAL unit may not exist for all pictures in a Coded Layer Video Sequence (CLVS) including the current picture. That is, for example, the flag values ​​for the presence or absence of the PH NAL unit for all pictures in a Coded Layer Video Sequence (CLVS) are the same. Also, for example, if the flag indicates that the PH NAL unit does not exist, picture headers for all pictures in the CLVS may be included in slice headers of all pictures.

[0163] Meanwhile, for example, AU detection can be modified differently from the existing scheme. For example, a new VCL NAL unit can mean a new AU. That is, for example, if the flag indicates that the PH NAL unit does not exist, the VCL NAL unit including the slice header is the first VCL NAL unit of the current picture (for a new AU (i.e., an AU for the current picture)). For example, the flag can be included in the slice header of the VCL NAL unit. Or, for example, if the flag indicates that the PH NAL unit exists, it follows the PH NAL unit, i.e., it is the first VCL NAL unit of the current picture signaled after the PH NAL unit.

[0164] Meanwhile, an encoding device may decode the current picture. For example, the encoding device may decode the current picture based on the syntax elements of the PH. For example, the syntax elements of the PH are the syntax elements shown in Table 6 above. The PH may include syntax elements indicating parameters for the current picture, and the encoding device may decode the current picture based on the syntax elements. Also, for example, a VCL NAL unit including the slice header may include slice data for a slice in the current picture, and the encoding device may decode the slice of the current picture based on the slice data. For example, a decoding device may derive predicted samples and residual samples of the current picture and generate reconstructed samples / pictures for the current picture based on the predicted samples and the residual samples.

[0165] Meanwhile, for example, an encoding apparatus may generate and encode prediction information for a block of the current picture. In this case, various prediction methods disclosed herein, such as inter prediction or intra prediction, may be applied. For example, the encoding apparatus may determine whether to perform inter prediction or intra prediction on the block, and may determine a specific inter prediction mode or a specific intra prediction mode based on an RD cost. Depending on the determined mode, the encoding apparatus may derive prediction samples for the block. The prediction information may include prediction mode information for the block. The video information may include the prediction information.

[0166] Also, for example, the encoding apparatus may encode residual information for a block of the current picture.

[0167] For example, the encoding apparatus may derive the residual samples through subtraction of the original samples and the predicted samples for the block.

[0168] Thereafter, for example, the encoding apparatus may quantize the residual samples to derive quantized residual samples, derive transform coefficients based on the quantized residual samples, and generate and encode the residual information based on the transform coefficients. Alternatively, for example, the encoding apparatus may quantize the residual samples to derive quantized residual samples, transform the quantized residual samples to derive transform coefficients, and generate and encode the residual information based on the transform coefficients. The video information may include the residual information. Also, for example, the encoding apparatus may encode the video information and output it in the form of a bitstream.

[0169] The encoding apparatus may generate reconstructed samples and / or reconstructed pictures by adding the predicted samples and the residual samples. As described above, in-loop filtering procedures such as deblocking filtering, SAO, and / or ALF procedures may be applied to the reconstructed samples as needed to improve subjective / objective image quality.

[0170] Meanwhile, the bitstream containing the video information can be transmitted to the decoding device via a network or a (digital) storage medium, where the network can include a broadcasting network and / or a communication network, and the digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc.

[0171] Figure 9 schematically illustrates an encoding device that performs the video encoding method according to the present document. The method disclosed in Figure 8 can be performed by the encoding device disclosed in Figure 9. Specifically, for example, the entropy encoding unit of the encoding device of Figure 9 can perform steps S800 to S820. Also, although not shown, the process of decoding the current picture can be performed by a prediction unit and a residual processing unit of the encoding device.

[0172] Figure 10 schematically illustrates a video decoding method by a decoding device according to the present document. The method disclosed in Figure 10 can be performed by the decoding device disclosed in Figure 3. Specifically, for example, steps S1000 to S1010 of Figure 10 can be performed by an entropy decoding unit of the decoding device, and step S1020 of Figure 10 can be performed by a prediction unit and a residual processing unit of the decoding device.

[0173] A decoding apparatus acquires a flag indicating whether a Picture Header (PH) Network Abstraction Layer (NAL) unit is present (S1000). The decoding apparatus may acquire the flag indicating whether the PH NAL unit is present via a bitstream. For example, the decoding apparatus may acquire video information via a bitstream, and the video information may include the flag. Also, for example, the video information may include a high-level syntax, and the flag may be included in the high-level syntax. For example, the high-level syntax may be a Sequence Parameter Set (SPS). Or, for example, the high-level syntax may be a slice header (SH). That is, for example, the flag may be included in the slice header.

[0174] For example, the flag may indicate whether the PH NAL unit is present. For example, if the value of the flag is 1, the flag may indicate that the PH NAL unit is present, and if the value of the flag is 0, the flag may indicate that the PH NAL unit is not present. Or, for example, if the value of the flag is 0, the flag may indicate that the PH NAL unit is present, and if the value of the flag is 1, the flag may indicate that the PH NAL unit is not present. The syntax element of the flag is the above-mentioned ph_nal_present_flag.

[0175] The decoding device acquires the PH based on the flag (S1010). The decoding device can acquire the PH from the PH NAL unit or a VCL NAL unit including a slice header based on the flag. That is, for example, the decoding device can acquire the PH from the PH NAL unit or a slice header based on the flag.

[0176] For example, if the flag indicates that the PH NAL unit exists, the PH may be obtained in the PH NAL unit, and if the flag indicates that the PH NAL unit does not exist, the PH may be obtained in a slice header. For example, if the flag indicates that the PH NAL unit exists, the PH may be included in the PH NAL unit, and if the flag indicates that the PH NAL unit does not exist, the PH may be included in a VCL NAL unit including a slice header. That is, if the flag indicates that the PH NAL unit exists, the PH may be included in the PH NAL unit, and if the flag indicates that the PH NAL unit does not exist, the PH may be included in a slice header. For example, if the flag indicates that the PH NAL unit exists, the video information may include a VCL NAL unit including the PH NAL unit including the PH and a slice header, and if the flag indicates that the PH NAL unit does not exist, the video information may include a VCL NAL unit including the PH and a slice header. Also, for example, if the flag indicates that the PH NAL unit is not present, the video information may not include the PH NAL unit.

[0177] Also, for example, if the flag indicates that the PH NAL unit does not exist, the current picture associated with the PH may include one slice. That is, for example, if the flag indicates that the PH NAL unit does not exist, the video information may include a VCL NAL unit including a slice header for one slice in the current picture.

[0178] Furthermore, for example, if the flag indicates the presence of the PH NAL unit, at least one VCL NAL unit including the PH NAL unit and a slice header for the current picture can be obtained via a bitstream. That is, for example, if the flag indicates the presence of the PH NAL unit, the video information can include a VCL NAL unit including the PH NAL unit for the current picture and a slice header for at least one slice in the current picture.

[0179] Also, for example, if the flag indicates that the PH NAL unit does not exist, the PH NAL unit may not exist for all pictures in a Coded Layer Video Sequence (CLVS) including the current picture. That is, for example, the flag values ​​for the presence or absence of the PH NAL unit for all pictures in a Coded Layer Video Sequence (CLVS) are the same. Also, for example, if the flag indicates that the PH NAL unit does not exist, picture headers for all pictures in the CLVS may be included in slice headers of all pictures.

[0180] Meanwhile, for example, AU detection can be modified differently from the existing scheme. For example, a new VCL NAL unit can mean a new AU. That is, for example, if the flag indicates that the PH NAL unit does not exist, the VCL NAL unit including the slice header is the first VCL NAL unit of the current picture (for a new AU (i.e., an AU for the current picture)). For example, the flag can be included in the slice header of the VCL NAL unit. Or, for example, if the flag indicates that the PH NAL unit exists, it follows the PH NAL unit, i.e., it is the first VCL NAL unit of the current picture signaled after the PH NAL unit.

[0181] The decoding device decodes the current picture associated with the PH based on the PH (S1020). The decoding device may decode the current picture based on syntax elements of the PH. For example, the syntax elements of the PH are the syntax elements shown in Table 6 above. The PH may include syntax elements indicating parameters for the current picture, and the decoding device may decode the current picture based on the syntax elements. Also, for example, a VCL NAL unit including the slice header may include slice data for a slice in the current picture, and the decoding device may decode the slice of the current picture based on the slice data. For example, the decoding device may derive predicted samples and residual samples of the current picture and generate reconstructed samples / pictures for the current picture based on the predicted samples and the residual samples.

[0182] As mentioned above, in-loop filtering procedures such as deblocking filtering, SAO and / or ALF procedures can be applied to the reconstructed samples to improve the subjective / objective image quality, if necessary.

[0183] Figure 11 schematically illustrates a decoding device that performs the video decoding method according to the present document. The method disclosed in Figure 10 can be performed by the decoding device disclosed in Figure 11. Specifically, for example, the entropy decoding unit of the decoding device of Figure 11 can perform steps S1000 to S1010 of Figure 10, and the prediction unit and residual processing unit of the decoding device of Figure 11 can perform step S1020 of Figure 10.

[0184] According to the detailed description in this document, a flag indicating whether a PH NAL unit exists can be signaled, and based on the flag, the NAL unit can be adaptively adjusted to the bit rate of the bitstream, thereby improving overall coding efficiency.

[0185] In addition, according to this document, it is possible to set constraints on the number of slices in the current picture and constraints on the existence of PH NAL units for related pictures based on a flag indicating whether a PH NAL unit exists, thereby adaptively adjusting NAL units to the bitrate of the bitstream and improving overall coding efficiency.

[0186] In the above-described embodiments, the method is described based on a flow chart as a series of steps or blocks, but this document is not limited to the order of steps, and some steps may occur in a different order or simultaneously with other steps than those described above. Furthermore, those skilled in the art will understand that the steps shown in the flow chart are not exclusive, and other steps may be included, or one or more steps of the flow chart may be deleted without affecting the scope of this document.

[0187] The embodiments described herein may be implemented and executed on a processor, microprocessor, controller, or chip. For example, the functional units illustrated in the drawings may be implemented and executed on a computer, processor, microprocessor, controller, or chip. In this case, information (e.g., information on instructions) or algorithms for implementation may be stored in a digital recording medium.

[0188] In addition, the decoding device and encoding device to which the embodiments of this document are applied may be included in a multimedia broadcast transmitting / receiving device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video interaction device, a real-time communication device such as video communication, a mobile streaming device, a recording medium, a camcorder, a custom video (VoD) service providing device, an over-the-top (OTT) video (over-the-top) device, an internet streaming service providing device, a three-dimensional (3D) video device, an image telephone video device, a vehicle terminal (e.g., a vehicle terminal, an airplane terminal, a ship terminal, etc.), a medical video device, etc., and may be used to process video signals or data signals. For example, an over-the-top (OTT) video (over-the-top) device may include a game console, a Blu-ray player, an internet-connected TV, a home theater system, a smartphone, a tablet PC, a digital video recorder (DVR), etc.

[0189] In addition, a processing method to which an embodiment of this document is applied may be produced in the form of a computer-executable program and stored in a computer-readable recording medium. Multimedia data having a data structure according to this document may also be stored in a computer-readable recording medium. The computer-readable recording medium includes all types of storage devices and distributed storage devices in which computer-readable data is stored. The computer-readable recording medium may include, for example, a Blu-ray Disc (BD), a Universal Serial Bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. The computer-readable recording medium may also include media implemented in the form of a carrier wave (e.g., transmission via the Internet). The bitstream generated by the encoding method may be stored in a computer-readable recording medium or transmitted via a wired or wireless communication network.

[0190] Furthermore, the embodiments of the present document may be implemented in a computer program product by program code, which may be executed by a computer in accordance with the embodiments of the present document. The program code may be stored on a computer-readable carrier.

[0191] FIG. 12 exemplarily illustrates a structural diagram of a content streaming system to which the embodiments of this document are applied.

[0192] A content streaming system to which the embodiments of this document are applied can broadly include an encoding server, a streaming server, a web server, a media repository, a user device, and a multimedia input device.

[0193] The encoding server compresses content input from a multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, if a multimedia input device such as a smartphone, camera, camcorder, etc. directly generates a bitstream, the encoding server may be omitted.

[0194] The bitstream can be generated by an encoding method or a bitstream generation method to which an embodiment of this document is applied, and the streaming server can temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0195] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server acts as an intermediary to inform the user of available services. When a user requests a desired service from the web server, the web server transmits the request to the streaming server, which then transmits the multimedia data to the user. The content streaming system may include a separate control server, which controls commands and responses between devices in the content streaming system.

[0196] The streaming server can receive content from a media repository and / or an encoding server. For example, if content is received from the encoding server, the content can be received in real time. In this case, the streaming server can store the bitstream for a certain period of time to provide a smooth streaming service.

[0197] Examples of the user devices include mobile phones, smartphones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation systems, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, and head mounted displays (HMDs)), digital TVs, desktop computers, digital signage, etc. Each server in the content streaming system can be operated as a distributed server, and in this case, data received by each server can be processed in a distributed manner.

[0198] The claims described in this specification may be combined in various ways. For example, the technical features of the method claims in this specification may be combined to be realized as an apparatus, and the technical features of the apparatus claims in this specification may be combined to be realized as a method. Furthermore, the technical features of the method claims and the technical features of the apparatus claims in this specification may be combined to be realized as an apparatus, and the technical features of the method claims and the technical features of the apparatus claims in this specification may be combined to be realized as a method.

Claims

1. A video decoding method performed by a decoding device, comprising: obtaining a flag for whether a Picture Header (PH) Network Abstraction Layer (NAL) unit is present; obtaining a picture header for a current picture from the PH NAL unit based on the flag indicating that the PH NAL unit exists; obtaining the picture header for the current picture from a slice layer raw byte sequence payload (RBSP) of the current picture based on the flag indicating that the PH NAL unit is not present; decoding the current picture based on the picture header; Based on the flag indicating that the PH NAL unit is not present, the current picture includes only one slice; The method of claim 1, wherein the slice layer RBSP includes the picture header and slice data based on the flag indicating that the PH NAL unit is not present.

2. A video encoding method performed by an encoding device, comprising: determining whether a Picture Header (PH) Network Abstraction Layer (NAL) unit containing a picture header associated with the current picture exists; generating the PH NAL unit including the picture header based on the determination that the PH NAL unit exists; generating a slice layer raw byte sequence payload (RBSP) for the current picture including the picture header based on the determination that the PH NAL unit does not exist; generating a flag for whether the PH NAL unit exists based on the result of the determination; encoding video information including the flag; Based on the flag indicating that the PH NAL unit is not present, the current picture includes only one slice; The method of claim 1, wherein the slice layer RBSP includes the picture header and slice data based on the flag indicating that the PH NAL unit is not present.

3. A method for transmitting data relating to video, comprising: The bitstream of video information is determining whether a Picture Header (PH) Network Abstraction Layer (NAL) unit containing a picture header associated with the current picture exists; generating the PH NAL unit including the picture header based on the determination that the PH NAL unit exists; generating a slice layer raw byte sequence payload (RBSP) for the current picture including the picture header based on the determination that the PH NAL unit does not exist; generating a flag for whether the PH NAL unit exists based on the result of the determination; encoding the video information including the flag; transmitting the data including the bitstream; Based on the flag indicating that the PH NAL unit is not present, the current picture includes only one slice; The transmission method, wherein, based on the flag indicating that the PH NAL unit is not present, the slice layer RBSP includes the picture header and slice data.

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