IMAGE ENCODING / DECODING METHOD AND DEVICE FOR SIGNALING INFORMATION RELATED TO SUB-IMAGE AND IMAGE HEADER, AND METHOD FOR TRANSMITTING BITSTREAM

Abstract

The present invention relates to a method and apparatus for encoding and decoding an image to signal information about an image header and sub-image, and a method for transmitting a bitstream. The image decoding method according to the present description may include acquiring a first flag that specifies whether information about a sub-image is present in a bitstream, acquiring a second flag that specifies whether image header information is present in a segment header, and decoding the bitstream based on the first and second flags. When the first flag specifies that information about the sub-image is present in the bitstream, the second flag may have a value that specifies that image header information is not present in the image header.

Description

The present description relates to an image encoding / decoding method and apparatus, and, more particularly, to an image encoding and decoding method and apparatus for indicating information about a sub-image and image header, and a method for transmitting a bitstream generated by the image encoding method / apparatus of the present description. Background of the Invention Recently, the demand for high-resolution, high-quality images, such as high-definition (HD) and ultra-high-definition (UHD) images, has been increasing in various fields. As the resolution and quality of image data improve, the amount of information, or bits, transmitted increases relatively compared to existing image data. This increase in the amount of information, or bits, transmitted leads to an increase in both transmission and storage costs. Therefore, there is a need for highly efficient image compression technology to effectively transmit, store, and reproduce information in high-resolution, high-quality images. Summary of the Invention Technical Problem One objective of the present description is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency. Another objective of the present description is to provide a method and encoding / decoding apparatus to improve encoding / decoding efficiency by efficiently signaling information about a sub-image and image header. Another objective of the present description is to provide a method for transmitting a bit stream generated by an image encoding method or apparatus in accordance with the present description. Another objective of the present description is to provide a recording medium that stores a bitstream generated by an image encoding method or apparatus in accordance with the present description. Another objective of the present description is to provide a recording medium that stores a received bit stream, which is decoded and used to reconstruct an image by an image decoding apparatus in accordance with the present description. ML / t / ZUZZ / U / l rzi The technical problems solved by the present description are not limited to the above technical problems and other technical problems which are not described herein will become apparent to those skilled in the art, from the following description. Technical Solution An image decoding method performed by an image decoding apparatus in accordance with one aspect of this description may include acquiring a first flag specifying whether sub-image information is present in a bitstream, acquiring a second flag specifying whether image header information is present in a segment header, and decoding the bitstream based on the first and second flags. When the first flag specifies that sub-image information is present in the bitstream, the second flag may have a value specifying that image header information is not present in the image header. In the image decoding method according to the present description, when the first flag specifies that sub-image information is present in the bitstream, the segment header may include a sub-image identifier that includes a MA / t / ZUZZ / U / l rzi segment related to the segment header. The image decoding method in accordance with this description may further include acquiring the image header information from the segment header when the second flag specifies that the image header information is present in the segment header. In the image decoding method according to the present description, the second flag can have the same value with respect to all segments in a coded layer video sequence (CLVS). In the image decoding method according to the present description, when the second flag specifies that the image header information is present in the segment header, a network abstraction layer (NAL) unit to transmit the image header information may not be present in a coded layer video sequence (CLVS). In the image decoding method according to the present description, when the second flag specifies that the image header information is not present in the image header, the image header information can be acquired from a network abstraction layer (NAL) unit with a NAL unit type equal to PH NUT. (TO In the image decoding method according to the present description, the first flag can be signaled at a high level of a segment, and the second flag can be included and signaled in the segment header. An image decoding apparatus according to another aspect of this description may include a memory and at least one processor. At least one processor may be configured to acquire a first flag specifying whether sub-image information is present in a bitstream, to acquire a second flag specifying whether image header information is present in a segment header, and to decode the bitstream based on the first and second flags. When the first flag specifies that sub-image information is present in the bitstream, the second flag may have a value specifying that image header information is not present in the image header. An image encoding method conforming to another aspect of this description may include encoding a first flag that specifies whether sub-image information is present in a bitstream, encoding a second flag that specifies whether image header information is present in a segment header, and encoding the bitstream based on the first and second flags. When the first flag specifies that sub-image information is present in the bitstream, the second flag may have a value that specifies that image header information is not present in the image header. In the image encoding method according to the present description, when the first flag specifies that information about the subimage is present in the bitstream, the segment header may include an identifier of a subimage that includes a segment related to the segment header. The image encoding method in accordance with this description may further include encoding the image header information in the segment header when the second flag specifies that the image header information is present in the segment header. In the image coding method according to the present description, the second flag can have the same value with respect to all segments in a coded layer video sequence (CLVS). In the image encoding method according to the present description, when the second flag specifies that the image header information is not present in the image header, the image header information can be signaled through a network abstraction layer (NAL) unit with a NAL unit type equal to PH NUT. In the image encoding method according to the present description, the first flag can be signaled at a high level of a segment, and the second flag can be included and signaled in the segment header. Furthermore, a transmission method conforming to another aspect of this description may transmit a bit stream generated by the image encoding apparatus or the image encoding method of this description. In addition, a computer-readable recording medium in accordance with another aspect of this description may store the bitstream generated by the image encoding apparatus or image encoding method of this description. The features briefly summarized above with respect to this description are only exemplary aspects of the detailed description that follows, and do not limit the scope of this description. MA / t / ZUZZ / U / l rzi Advantageous Effects In accordance with the present description, it is possible to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency. Also, in accordance with the present description, it is possible to provide an image encoding / decoding method and apparatus to improve encoding / decoding efficiency by efficiently signaling information about an image header and sub-image. Also, in accordance with this description, it is possible to provide a method for transmitting a bit stream generated by an image encoding method or apparatus in accordance with this description. Also, in accordance with this description, it is possible to provide a recording medium that stores a bitstream generated by an image encoding method or apparatus in accordance with this description. Also, in accordance with the present description, it is possible to provide a recording medium that stores a received bit stream, decoded and used to reconstruct an image by an image decoding apparatus in accordance with the present description. (TO It will be appreciated by people skilled in the technique that the effects that can be achieved through the present description are not limited to what has been particularly described here above, and other advantages of the present description will be more clearly understood from the detailed description. Brief Description of the Figures Figure 1 is a schematic view of a video coding system, to which one modality of the present description is applicable; Figure 2 is a schematic view of an image encoding device, to which one modality of the present description is applicable; Figure 3 is a schematic view of an image decoding device, to which one modality of the present description is applicable; Figure 4 is a view showing a partitioning structure of an image according to a modality; Figure 5 is a view showing one modality of a block partitioning type in accordance with a multi-type tree structure; Figure 6 is a view showing a block partitioning information signaling mechanism in a quadruple tree with nested tree structure of various types in accordance with the present description; MA / t / ZUZZ / U / l rzi Figure 7 is a view showing a mode in which a CTU is partitioned into multiple CUs; Figure 8 is a flowchart illustrating a method for encoding an image using a segment / tile by an image encoding apparatus in accordance with one modality of the present description; Figure 9 is a flowchart illustrating a method for decoding an image using a segment / tile by an image decoding apparatus in accordance with one modality of the present description; Figure 10 is a view showing an example of the present description of a syntax and signaling element in a segment header; Figure 11 is a view showing a syntax structure of a segment header in accordance with one modality of the present description; Figure 12 is a flowchart illustrating a method for parsing and decoding the segment header in Figure 11; Figure 13 is a flowchart illustrating a method for decoding the segment header of Figure 11; Figure 14 is a view showing the syntax structure of a segment header in accordance with another modality of the present description; (TO Figure 15 is a flowchart illustrating a method for parsing and decoding the segment header in Figure 14; Figure 16 is a flowchart illustrating a method for decoding the segment header in Figure 14; Figure 17 is a view showing the syntax structure of a segment header in accordance with another modality of the present description; Figure 18 is a flowchart illustrating a method for parsing and decoding the segment header in Figure 17; Figure 19 is a flowchart illustrating a method for decoding the segment header of Figure 17; and Figure 20 is a view showing a continuous content transmission system, to which a modality of the present description is applicable. Method for the Invention Subsequently, the methods described herein will be described in detail with reference to the accompanying drawings to facilitate their implementation by those skilled in the technique. However, this description can be implemented in several different ways and is not limited to the methods listed. ΜΛ / t / ZUZZ / U / l rzi described herein. In the description of this product, if it is determined that a detailed description of a related known function or construction would make the scope of this description unnecessarily ambiguous, that detailed description will be omitted. In the drawings, parts not related to the description of this product will be omitted, and similar reference numbers will be attached to similar parts. In this description, when a component connects, couples, or links to another component, it may include not only a direct connection relationship but also an indirect connection relationship in which an intervening component is present. Furthermore, when a component includes or contains other components, it means that other components may also be included, rather than excluding other components unless otherwise stated. In this description, the terms first, second, etc., may be 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 stated. Accordingly, within the scope of this description, a first component in one modality may be referred to as a second component in another modality, and similarly, a second component in one modality may be referred to as a first component in another modality. In this description, the components that are distinguished from one another are intended to clearly describe each characteristic, and do not necessarily mean that the components are separate. That is, a plurality of components may be integrated and implemented in a single hardware or software unit, or a single component may be distributed and implemented in a plurality of hardware or software units. Therefore, unless otherwise stated, such modes in which the components are integrated or the component is distributed are also included within the scope of this description. In this description, components described under various modalities do not necessarily mean essential components, and some components may be optional. Therefore, a modality consisting of a subset of components described under one modality is also included within the scope of this description. Furthermore, modalities that include components other than those described under the various modalities are also included within the scope of this description. This description refers to coding and ML / t / ZUZZ / U / l rzi image decoding, and the terms used in this description may have a general meaning commonly used in the technical field to which this description belongs, unless otherwise defined in this description. In this description, an image generally refers to a unit that represents an image at a specific point in time, and a segment / tile is an encoding unit that constitutes a part of an image. An image can be composed of one or more segments / tiles. Furthermore, a segment / tile can include one or more encoding tree units (CTUs). In this description, a pixel or a pei can mean the smallest unit that makes up a frame (or image). Additionally, sample can be used as a term corresponding to a pixel. A sample can generally represent a pixel or a pixel value, and can represent only a pixel / pixel value of a luma component or only a pixel / pixel value of a chroma component. In this description, a unit may represent a basic image processing unit. The unit may include at least one sample from a specific region of the image and information related to that region. The unit may be used interchangeably with terms such as sample array, block, or area in some cases. In a general case, a block M×N may include samples (or sample arrays) or a series (or array) of transformation coefficients of columns M and rows N. In this description, "current block" can mean a current encoding block, current encoding unit, encoding target block, decoding target block, or processing target block. When prediction is performed, "current block" can mean a current prediction block or a prediction target block. When transformation (inverse transformation / quantization (dequantization)) is performed, "current block" can mean a current transformation block or a transformation target block. When filtering is performed, "current block" can mean a filtering target block. Furthermore, in this description, a current block may mean a luma block of a current block unless explicitly stated as a chroma block. The chroma block of the current block may be expressed by including an explicit description of a chroma block, such as chroma block or current chroma block. In this description, the term / and , should be interpreted to mean and / or. For example, the expression A / B and A, B can mean A and / or B. Furthermore, ML / t / ZUZZ / U / l rzi A / B / C and A / B / C can mean at least one of A, B, and / or C. In this description, the term "or" should be interpreted to mean "and / or." For example, the expression "A or B" may include 1) only A, 2) only B, and / or 3) both A and B. In other words, in this description, the term "or" should be interpreted to mean "in addition to" or "alternatively." Overview of the video encoding system Figure 1 is a view showing a video encoding system, in accordance with the present description. The video coding system in accordance with a modality may include an coding apparatus 10 and a decoding apparatus 20. The coding apparatus 10 may provide coded video and / or image information or data to the decoding apparatus 20 in the form of a file or bitstream via a network or digital storage medium. The encoding apparatus 10 in accordance with one modality may include a video source generator 11, an encoding unit 12, and a transmitter 13. The decoding apparatus 20 in accordance with one modality may include a receiver 21, a decoding unit 22, and a renderer 23. The encoding unit 12 may be MA / t / ZUZZ / U / l rzi may be named a video / image encoding unit, and the decoding unit 22 may be named 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. The video source generator 11 can acquire video / images through a video / image capture, synthesis, or generation process. The video source generator 11 can include a video / image capture device and / or a video / image generation device. The video / image capture device can include, for example, one or more cameras, video / image files containing previously captured video / images, and similar items. The video / image generation device can include computers, tablets, and smartphones, and can generate video / images electronically. For example, a virtual video / image can be generated using a computer or similar device. In this case, the video / image capture process can be replaced by a related data generation process. Encoding unit 12 can encode an input video / image. Encoding unit 12 can The ML / t / ZUZZ / UZ II performs a series of procedures such as prediction, transformation, and quantization for efficient compression and encoding. The encoding unit 12 can generate encoded data (encoded video / image information) in the form of a bitstream. Transmitter 13 can transmit the generated encoded video / image information or data as a bitstream to receiver 21 of the decoding unit 20 via a digital storage medium or network in the form of a file or bitstream. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and similar devices. Transmitter 13 can include a component for generating a media file in a predetermined file format and a component for transmission over a broadcast / communication network. Receiver 21 can extract / receive the bitstream from the storage medium or network and transmit the bitstream to the decoding unit 22. The decoding unit 22 can decode the video / image by performing a series of procedures such as dequantization, inverse transformation, and prediction that correspond to the operation of the encoding unit 12. ML / t / ZUZZ / U / l rzi Renderer 23 can render the decoded video / image. The rendered video / image can then be displayed on the screen. General information about the image encoding apparatus Figure 2 is a schematic view of an image encoding device, to which one modality of the present description is applicable. As shown in Figure 2, the image encoding apparatus 100 may include an image partitioner 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-predictor 180, an intra-predictor 185, and an entropy encoder 190. The inter-prediction unit 180 and the intra-prediction unit 185 may be collectively referred to as a prediction unit. 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 further include the subtractor 115. All or at least some of the multiple components that make up the image encoding apparatus 100 can be configured by a hardware component (for example, an encoder or a processor) in some modes. In addition, memory 170 can include an image buffer. ML / t / ZUZZ / U / l rzi decoded (DPB) and can be configured by a digital storage medium. The image partitioner 110 can partition an input image (or frame or frame) entering the image encoding apparatus 100 into one or more processing units. For example, the processing unit can be called an encoding unit (CU). The encoding unit can be obtained by recursively partitioning an encoding tree unit (CTU) or a larger encoding unit (LCU) according to a ternary-tree, binary-tree, or quaternary-tree (QT / BT / TT) structure. For example, an encoding unit can be partitioned into a plurality of encoding units of greater depth based on a quad-tree, binary-tree, and / or ternary-tree structure. For partitioning the encoding unit, a quad-tree structure can be applied first, and the binary-tree and / or ternary-tree structure can be applied afterward.The coding procedure described herein can be performed based on the final coding unit, which is no longer partitioned. The largest coding unit can be used as the final coding unit, or the deepest coding unit can be partitioned to become the final coding unit. The coding procedure may include prediction, transformation, and reconstruction, which will be described later. For example, the processing unit of the coding procedure can be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transformation unit can be divided or partitioned from the final coding unit.The prediction unit can be a sample prediction unit, and the transformation unit can be a unit for deriving a transformation coefficient and / or a unit for deriving a residual signal from the transformation coefficient. The predictor (either the inter-predictor 180 or the intra-predictor 185) can perform prediction on a block to be processed (the current block) and generate a predicted block that includes prediction samples for the current block. The predictor can determine whether the intra-prediction or inter-prediction applies to a current block or a CU base. The predictor can generate various information related to the prediction of the current block and transmit the generated information to the entropy encoder 190. The information in the prediction can be encoded in the entropy encoder 190 and output as a bitstream. The intra-predictor 185 can predict the current block by reference to samples in the current image. The reference samples can be located near the current block or further away, depending on the intra-prediction mode and / or technique. Intra-prediction modes can include multiple non-directional and directional modes. A non-directional mode might include, for example, a DC mode and a planar mode. A directional mode might include, for example, 33 or 65 directional prediction modes, depending on the level of detail required for the prediction direction. However, this is just one example; more or fewer directional prediction modes can be used depending on the setting. The intra-predictor 185 can determine the prediction mode applied to the current block using a prediction mode applied to a neighboring block. The Interpredictor 180 can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector in a reference image. In this case, to reduce the amount of motion information transmitted in interprediction mode, the motion information can be predicted in block, subblock, or sample units based on motion information correlation between the neighboring block and the current block. The motion information can include a motion vector and a reference image index. It can also include interprediction direction information (LO prediction, Ll prediction, Bi prediction, etc.). In interprediction mode, the neighboring block can include a spatial neighbor block present in the current image and a temporal neighbor block present in the reference image.The reference image that includes the reference block and the reference image that includes the temporary neighbor block can be the same or different. The temporary neighbor block can be called a colocalized reference block, a co-located CU (colCU), and similar terms. The reference image that includes the temporary neighbor block can be called a colocalized image (colPic). For example, the 180 interpredictor can configure a candidate list of motion information based on neighboring blocks and generate information indicating which candidate is used to derive a motion vector and / or a reference image index for the current block. Interprediction can be performed based on various prediction modes. For example, in the case of a jump mode and a merge mode, the 180 interpredictor can use motion information from the neighboring block as motion information for the current block.In the case of jump mode, as opposed to merge mode, the residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the neighboring block's motion vector can be used as a motion vector predictor, and the current block's motion vector can be signaled by encoding a motion vector difference and a flag for a motion vector predictor. The motion vector difference can represent a difference between the current block's motion vector and the motion vector predictor. The predictor can generate a prediction signal based on various prediction methods and techniques described below. For example, the predictor can apply not only intra-prediction or inter-prediction but also simultaneously apply both intra- and inter-prediction to predict the current block. A prediction method that simultaneously applies both intra- and inter-prediction to predict the current block can be called combined inter- and intra-prediction (CLIP). Additionally, the predictor can perform intra-block copying (IBC) to predict the current block. Intra-block copying can be used for image / video encoding of game content or similar applications, such as selected content coding (SCC). IBC is a method for predicting the current image using a reference block previously reconstructed within the current image at a specific location. ML / t / ZUZZ / U / l rzi apart from the current block by a predetermined distance. When IBC is applied, the location of the reference block in the current image can be encoded as a vector (block vector) that corresponds to the predetermined distance. IBC basically performs the prediction on the current image, but it can be performed similarly to interprediction, in which a reference block is derived within the current image. That is, IBC can use at least one of the interprediction techniques described herein. The prediction signal generated by the predictor can be used to generate a reconstructed signal or a residual signal. Subtractor 115 can generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (predicted block or prediction sample array) generated by the predictor from the input image signal (original block or original sample array). The generated residual signal can then be transmitted to transformer 120. Transformer 120 can generate transformation coefficients by applying a transformation technique to the residual signal. For example, the transformation technique can include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a Karhunen-Loéve transform (KLT), or a transformation to ML / t / ZUZZ / U / l rzi is a graph base (GBT), or a conditionally nonlinear transformation (CNT). Here, GBT means a transformation obtained from a graph when the information relating pixels is represented by the graph. CNT refers to a transformation acquired based on a prediction signal generated using all previously reconstructed pixels. Furthermore, the transformation process can be applied to square pixel blocks of the same size or to blocks of varying sizes other than square. Quantizer 130 can quantize the transformation coefficients and transmit them to entropy encoder 190. Entropy encoder 190 can encode the quantized signal (information about the quantized transformation coefficients) and generate a bit stream. The information about the quantized transformation coefficients can be referred to as residual information. Quantizer 130 can rearrange the quantized transformation coefficients into a block type in the form of a one-dimensional vector based on a coefficient sweep order and generate information about the quantized transformation coefficients based on the quantized transformation coefficients in the form of a one-dimensional vector. The entropy encoder 190 can perform several ML / t / ZUZZ / U / l rzi encoding methods such as, for example, exponential Golomb, adaptive context variable length coding (CAVLC), adaptive context binary arithmetic coding (CABAC), and the like. The entropy encoder 190 can encode information necessary for video / image reconstruction other than quantized transformation coefficients (for example, syntax element values, etc.) either together or separately. The encoded information (for example, encoded video / image information) can be transmitted or stored in Network Abstraction Layer (NAL) units as a bitstream. The video / image information can further include information about various set parameters such as an Adaptive Set Parameter (APS), an Image Set Parameter (PPS), a Sequence Set Parameter (SPS), or a Video Set Parameter (VPS).In addition, the video / image information may also include general restriction information. The indicated information, transmitted information, and / or syntax elements described herein may be encoded using the encoding procedure described above and included in the bitstream. The bitstream can be transmitted over a network or stored on a digital storage medium. The network may include a broadcast network and / or a communications network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. A transmitter (not shown) that transmits a signal generated by the entropy encoder 190 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the image encoding apparatus 100. Alternatively, the transmitter may be provided as the component of the entropy encoder 190. The quantized transformation coefficients generated from quantizer 130 can be used to generate a residual signal. For example, the residual signal (residual block or residual samples) can be reconstructed by applying dequantization and inverse transformation to the quantized transformation coefficients via dequantizer 140 and inverse transformer 150. Adder 155 adds the reconstructed residual signal to the prediction signal generated from inter-predictor 180 or intra-predictor 185 to generate a reconstructed signal (reconstructed image, reconstructed block, reconstructed sample array). If no residual exists for the block to be processed, such as in a case where skip mode is applied, the predicted block can be used as the reconstructed block. Adder 155 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-prediction of the next block to be processed in the current image and can be used for inter-prediction of the next image through filtering as described below. Filter 160 can improve subjective / objective image quality by applying filtering to the reconstructed signal. For example, Filter 160 can generate a modified reconstructed image by applying various filtering methods and store the modified reconstructed image in memory 170, specifically, a DPB of memory 170. The various filtering methods can include, for example, unblocking filtering, adaptive sample compensation, an adaptive loop filter, a bilateral filter, and similar methods. Filter 160 can generate various filtering-related information and transmit this information to the entropy encoder 190, as described later in the description of each filtering method. The filtering-related information can be encoded by the entropy encoder 190 and output as a bitstream. The modified reconstructed image transmitted to memory 170 can be used as the reference image in the interpredictor 180. When interprediction is applied to (through the image encoding apparatus 100), the prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus can be avoided and the encoding efficiency can be improved. The DPB of memory 170 can store the modified reconstructed image for use as a reference image in inter-predictor 180. Memory 170 can store the motion information of the block from which the motion information in the current image is derived (or encoded) and / or the motion information of blocks in the image that have already been reconstructed. The stored motion information can be transmitted to inter-predictor 180 and used as the motion information of the spatially neighboring block or the motion information of the temporally neighboring block. Memory 170 can store reconstructed samples of reconstructed blocks in the current image and can transfer the reconstructed samples to intra-predictor 185. General information about the image decoding device Figure 3 is a schematic view of an image decoding device, to which one modality of the present description is applicable. As shown in Figure 3, the image decoding apparatus 200 may include an entropy decoder 210, a dequantizer 220, an inverting transformer 230, an adder 235, a filter 240, a memory 250, an inter-predictor 260, and an intra-predictor 265. The inter-predictor 260 and the intra-predictor 265 may be collectively referred to as a predictor. The dequantizer 220 and the inverting transformer 230 may be included in a residual processor. All or at least some of a plurality of components that make up the image decoding apparatus 200 may be configured by a hardware component (for example, a decoder or a processor) in accordance with a mode. In addition, the memory 250 may include a decoded image buffer (DPB) or may be configured by a digital storage medium. The image decoding device 200, which has received a bitstream containing video / image information, can reconstruct an image by performing a process that corresponds to a process performed by the image encoding device 100 in Figure 2. For example, the image decoding device 200 can perform decoding using a processing unit applied in the image encoding device. Thus, the decoding processing unit can be an encoding unit, for example. The encoding unit can be obtained by partitioning a tree unit of ML / t / ZUZZ / U / l rzi encoding or a larger encoding unit. The reconstructed image signal decoded and generated through the image decoding apparatus 200 can be reproduced through a playback apparatus (not shown). The image decoding apparatus 200 can receive a signal generated from the image encoding apparatus of Figure 2 in the form of a bitstream. The received signal can be decoded by the entropy decoder 210. For example, the entropy decoder 210 can analyze the bitstream to derive the information (e.g., video / image information) required for image reconstruction. The video / image information can also include information about various set parameters, such as an adaptation set parameter (APS), an image set parameter (PPS), a sequence set parameter (SPS), or a video set parameter (VPS). Furthermore, the video / image information can also include general constraint information.The image decoding device can also decode the image based on information about the set parameter and / or general restriction information. The signaled / received information and / or syntax elements described herein may be. ML / t / ZUZZ / U / l rzi decoded through the decoding procedure and obtained from the bitstream. For example, the entropy decoder 210 decodes the information in the bitstream based on an encoding method such as exponential Golomb encoding, CAVLC, or CABAC, and generates syntax element values ​​required for image reconstruction and quantized transformation coefficient values ​​for the residual.More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, determine a context model using information from the target decoding syntax element, decoding information from a neighboring block and a target decoding block, or information from a symbol / bin decoded in a previous step, and perform arithmetic decoding on the bin by predicting a probability of occurrence of a bin according to the determined context model, and generate a symbol that corresponds to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model using information from the decoded symbol / bin for a context model of the next symbol / bin after determining the context model.The information related to the prediction among the information decoded by the entropy decoder. 210 can be provided to the predictor (the inter-predictor 260 and the intra-predictor 265), and the residual value on which the entropy decoding is performed in the entropy decoder 210, i.e., the quantized transformation coefficients and related parameter information, can be input to the dequantizer 220. In addition, filtering information between the information decoded by the entropy decoder 210 can be provided to the filter 240. Meanwhile, a receiver (not shown) for receiving a signal generated from the image encoding apparatus can be further configured as an internal / external element of the image decoding apparatus 200, or the receiver can be a component of the entropy decoder 210. Meanwhile, the image decoding apparatus described herein may be referred to as a video / image / frame decoding apparatus. The image decoding apparatus may be classified into an image decoder (video / image / frame information decoder) and a sample decoder (video / image / frame sample decoder). The information decoder may include the entropy decoder 210. The sample decoder may include at least one of the following: the dequantizer 220, the inverting transformer 230, the adder 235, the filter 240, the memory 250, the inter-predictor 160, or the intra-predictor 265. The dequantizer 220 can dequantize quantized transformation coefficients and generate the transformation coefficients. The dequantizer 220 can rearrange the quantized transformation coefficients into a two-dimensional block. In this case, the rearrangement can be based on the coefficient sweep order performed in the image encoding apparatus. The dequantizer 220 can perform dequantization on quantized transformation coefficients using a quantization parameter (e.g., quantization step size information) and obtain transformation coefficients. The inverting transformer 230 can inversely transform the transformation coefficients to obtain a residual signal (residual block, residual sample array). The predictor can make predictions about the current block and generate a predicted block that includes prediction samples for the current block. The predictor can thus determine whether to apply intra-prediction or inter-prediction to the current block based on the prediction information generated from the entropy decoder 210, and can determine a specific intra / inter-prediction mode (prediction technique). This is the same as described in the image coding apparatus predictor 100, that the predictor can generate the prediction signal based on various description methods (techniques) which will be described later. Intra predictor 265 can predict the current block by reference to the samples in the current image. The description of intra predictor 185 also applies to intra predictor 265. The interpredictor 260 can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector in a reference image. In this case, to reduce the amount of motion information transmitted in interprediction mode, the motion information can be predicted in block units, subblocks, or samples based on motion information correlation between the neighboring block and the current block. The motion information can include a motion vector and a reference image index. The motion information can also include interprediction direction information (LO prediction, Ll prediction, Bi prediction, etc.). In the case of interprediction, the neighboring block can include a spatial neighbor block present in the current image and a temporal neighbor block present in the reference image. For example, the inter ML / t / ZUZZ / U / l rzi predictor 260 can configure a candidate list of motion information based on neighboring blocks and derive a motion vector of the current block and / or a reference image index based on the received candidate selection information. Interprediction can be performed based on various prediction modes, and the prediction information can include details indicating an interprediction mode for the current block. Adder 235 can generate a reconstructed signal (reconstructed image, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the prediction signal (predicted block, predicted sample array) generated from the predictor (which includes the inter-predictor 260 and / or the intra-predictor 265). If there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block can be used as the reconstructed block. The description of adder 155 is equally applicable to adder 235. Adder 235 can be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for the inter-prediction of a subsequent block to be processed in the current image and can be used for the inter-prediction of a subsequent image through filtering as described below. Filter 240 can improve subjective / objective image quality by applying filtering to the reconstructed signal. For example, Filter 240 can generate a modified reconstructed image by applying various filtering methods to the reconstructed image and store the modified reconstructed image in memory 250, specifically, a DPB of memory 250. The various filtering methods can include, for example, unblocking filtering, adaptive sample compensation, an adaptive loop filter, a bilateral filter, and similar methods. The reconstructed (modified) image stored in the DPB of memory 250 can be used as a reference image in inter-predictor 260. Memory 250 can store the motion information of the block from which the motion information in the current image is derived (or decoded) and / or the motion information of blocks in the image that have already been reconstructed. The stored motion information can be transmitted to inter-predictor 260 to be used as the motion information of the spatially neighboring block or the motion information of the temporally neighboring block. Memory 250 can store reconstructed samples of reconstructed blocks in the current image and transfer the reconstructed samples to intra-predictor 265. In the present description, the modalities described in filter 160, inter-predictor 180, and intra-predictor 185 of the image coding apparatus 100 may be equally or correspondingly applied to filter 240, inter-predictor 260, and intra-predictor 265 of the image decoding apparatus 200. General information on image partitioning The video / image coding method described herein can be implemented based on an image partitioning structure as follows. Specifically, the prediction, residual processing (transformation (inverse), (de)quantization, etc.), syntax element encoding, and filtering procedures, which will be described later, can be implemented based on a CTU, CU (and / or TU, PU) derived from the image partitioning structure. The image can be partitioned into block units, and the block partitioning procedure can be performed in the image partitioner 110 of the encoding apparatus. The partitioning information can be encoded by the entropy encoder 190 and transmitted to the decoding apparatus as a bitstream.The entropy decoder 210 of the decoding apparatus can derive a block partitioning structure of the current image based on partitioning-related information obtained from the bitstream, and based on this, it can perform a number of procedures (e.g., prediction, residual processing, image blocking / reconstruction, in-loop filtering, etc.) for image decoding. Images can be partitioned into a sequence of encoding tree units (CTUs). Figure 4 shows an example where an image is partitioned into CTUs. A CTU can correspond to a coding tree block (CTB). Alternatively, a CTU can include one lumen sample coding tree block and two corresponding chroma sample coding tree blocks. For example, for an image containing three sets of samples, the CTU might include one NxN lumen sample block and two corresponding chroma sample blocks. Generalities of CTU partitioning As described above, the coding unit (CU) can be acquired by recursively partitioning the coding tree unit (CTU) or the larger coding unit (LCU) according to a quad-tree / binary-tree / ternary-tree (QT / BT / TT) structure. For example, the CTU can first be partitioned into quad-tree structures. Subsequently, the leaf nodes of the quad-tree structure can be further partitioned by a multi-tree structure. Quad tree-conformance partitioning means that a current CU (or CTU) is partitioned into ML / t / ZUZZ / U / l rzi is also four. By partitioning according to the quad-tree structure, the current CU can be partitioned into four CUs that have the same width and height. When the current CU is no longer partitioned in the quad-tree structure, the current CU corresponds to the leaf node of the quad-tree structure. The CU corresponding to the leaf node of the quad-tree structure can no longer be partitioned and can be used as the final encoding unit described above. Alternatively, the CU corresponding to the leaf node of the quad-tree structure can be further partitioned by a multi-type tree structure. Figure 5 shows one type of block partitioning according to a multi-tree structure. Partitioning according to a multi-tree structure can include two types of partitioning according to a binary tree structure and two types of partitioning according to a ternary tree structure. The two types of splitting according to the binary tree structure can include vertical binary splitting (SPLIT BT VER) and horizontal binary splitting (SPLIT BT HOR). Vertical binary splitting (SPLIT BT VER) means that the current CU is being split equally in two in the vertical direction. As shown in Figure 4, By vertical binary splitting, two CUs can be generated that have the same height as the current CU and a width that is half the width of the current CU. Horizontal binary splitting (SPLIT BT HOR) means that the current CU is being split equally in two in the horizontal direction. As shown in Figure 5, by horizontal binary splitting, two CUs can be generated that have a height that is half the height of the current CU and the same width as the current CU. Two types of splitting according to the ternary tree structure include vertical ternary splitting (SPLIT_TT_VER) and horizontal ternary splitting (SPLIT_TT_HOR). In vertical ternary splitting (SPLIT_TT_VER), the current CU is split vertically at a 1:2:1 ratio. As shown in Figure 5, vertical ternary splitting can generate two CUs that have the same height as the current CU but a width that is 1 / 4 the width of the current CU, and one CU that has the same height as the current CU but a width that is half the width of the current CU. In horizontal ternary splitting (SPLIT_TT_HOR), the current CU is split horizontally at a 1:2:1 ratio.As shown in Figure 5, by horizontal ternary division, two CUs having a height which is 1 / 4 of the height of the current CU and having the same width as the current CU and one CU having a height which is half the height of the current CU and having the same width as the current CU can be generated. Figure 6 is a view showing a block splitting information signaling mechanism in a quad tree with a nested multi-type tree structure in accordance with the present description. Here, the CTU is treated as the root node of the quad tree and is partitioned for the first time into a quad tree structure. Information (e.g., qt_split_flag) indicating whether the quad tree split is performed with respect to the current CU (CTU or QT_node of the quad tree) is flagged. For example, when qt_split_flag has a first value (e.g., 1), the current CU can be partitioned from the quad tree. Furthermore, when qt_split_flag has a second value (e.g., 0), the current CU is not partitioned from the quad tree but becomes the leaf node (QT_leaf node) of the quad tree. Each leaf node of the quad tree can then be further partitioned into multi-type tree structures. That is, the leaf node of the quad tree can become the MTT_node of the multi-type tree structure. In the multi-type tree structure, a first flag (e.g., Mtt_split_cu_flag) is flagged to indicate whether the current node is further partitioned.If the corresponding node is further partitioned (for example, if the first flag is 1), a second flag (for example, Mtt_split_cu_vertical_flag) can be set to indicate the split direction. For example, the split direction can be vertical if the second flag is 1 and horizontal if the second flag is 0. Then, a third flag (for example, Mtt_split_cu_binary_flag) can be set to indicate whether the split type is binary or ternary. For example, the split type can be binary when the third flag is 1 and ternary when the third flag is 0. The multi-type tree node acquired by binary or ternary splitting can be further partitioned into multi-type tree structures.However, the multi-type tree node may not be partitioned in quad-tree structures. If the first flag is 0, the corresponding multi-type tree node is not further partitioned but becomes the leaf node of the multi-type tree. The CU corresponding to the leaf node of the multi-type tree can be used as the final encoding unit described above. Based on the mtt_split_cu_vertical_flag and the mtt split cu binary flag, a multi-type tree split mode (MttSplitMode) of a CU can be split ML / t / ZUZZ / U / l rzi as shown in Table 1 below. In the following description, the multi-type tree splitting mode may be referred to as multi-tree splitting type or splitting type. [Table 1] ML / t / ZUZZ / U / l rzi MttSplitMode mtt split cu vertical flag mtt split cu binary flag SPL1T_TT_HOR 0 0 SPLIT_BT_HOR 0 1 SPLIT_TT_VER 1 0 SPLIT_BT_VER 1 1 Figure 7 shows an example where a CTU is partitioned into several CUs by applying a multitype tree after applying a quadtree. In Fig. 7, the bold block borders 710 represent a quadtree partition, and the remaining borders 720 represent a multitype tree partition. The CU may correspond to an encoding block (CB). In one modality, the CU may include a luma sample encoding block and two chroma sample encoding blocks corresponding to the luma samples. The CB or TB size of a chroma component (sample) can be derived based on the CB or TB size of a chroma component (sample) in accordance with the component ratio according to the color format (chroma format, for example, 4:4:4, 4:2:2, 4:2:0 or 6 similar) of the picture / image. In the case of the 4:4:4 color format, the CB / TB size of the chroma component can be set equal to the CB / TB size of the luma component. In the case of the 4:2:2 color format, the width of the CB / TB chroma component can be set to half the width of the CB / TB luma component, and the height of the CB / TB chroma component can be set to the height of the CB / TB luma component. In the case of the 4:2:0 color format, the width of the CB / TB chroma component can be set to half the width of the CB / TB luma component, and the height of the CB / TB chroma component can be set to half the width of the CB / TB luma component. In one mode, when the CTU size is 128 based on the luma sample unit, the CU size can range from 128x128 to 4x4, which is the same size as the CTU. In another mode, in the case of the 4:2:0 color format (or chroma format), a CB chroma size can range from 64x64 to 2x2. Meanwhile, in one modality, the CU size and TU size can be equal. Alternatively, there can be a plurality of TUs in a CU region. The TU size generally represents a luma component (sample) transform block (TB) size. The TU size can be derived based on the maximum allowed TB size, maxTbSize, which is a default value. For example, when the CU size is larger than maxTbSize, a plurality of TUs (TBs) with maxTbSize can be derived from CUs, and the inverse transformation can be performed in TU (TB) units. For example, the largest allowed luma TB size might be 64x64, and the largest allowed chroma TB size might be 32x32. If the width or height of the CB partitioned according to the tree structure is greater than the width or height of the largest transformation, the CB can be automatically (or implicitly) partitioned until the TB size limit is met in both the horizontal and vertical directions. Furthermore, for example, when intra-prediction is applied, an intra-prediction mode / type can be derived in CU (or CB) units, and a prediction sample generation and neighboring reference sample derivation procedure can be performed in TU (or TB) units. In this case, there may be one or more TU (or TB) units in a CU (or CB) region, and the plurality of TU or TB units may share the same intra-prediction mode / type. Meanwhile, for a quadtree encoding scheme with a nested multitype tree, the following parameters can be signaled as SPS syntax elements from the encoding apparatus to the apparatus. ML / t / ZUZZ / U / l rzi decoding. For example, at least one of a CTU size, which is a parameter representing the size of the root node of a quad tree, MinQTSize, which is a parameter representing the minimum allowed size of the leaf node of a quad tree, MaxBtSize, which is a parameter representing the maximum allowed size of the root node of a binary tree, MaxTtSize, which is a parameter representing the maximum allowed size of the root node of a ternary tree, MaxMttDepth, which is a parameter representing the maximum allowed hierarchy depth of the branching of multi-type trees from a leaf node of a quad tree, MinBtSize, which is a parameter representing the minimum allowed size of the leaf node of a binary tree, or MinTtSize, which is a parameter representing the minimum allowed size of the leaf node of a ternary tree. As a variation of using the 4:2:0 chroma format, the CTU size can be set in 128x128 luma blocks and two 64x64 chroma blocks corresponding to the luma blocks. In this case, MinOTSize can be set to 16x16, MaxBtSize to 128x128, MaxTtSize to 64x64, MinBtSize and MinTtSize to 4x4, and MaxMttDepth to 4. Quadtree partitioning can be applied to the CTU to generate quadtree leaf nodes. The quadtree leaf node can be called a QT leaf node. Quadtree leaf nodes can range in size from 16x16 (e.g., MinOTSize) to 128x128 (e.g., the CTU size). If the QT leaf node is 128x128, it cannot be further partitioned into a binary / ternary tree. This is because, in this case, even if partitioned, it exceeds MaxBtsize and MaxTtszie (e.g., 64x64).In other cases, QT leaf nodes can be further partitioned into a multitype tree. Therefore, the QT leaf node is the root node for the multitype tree, and the QT leaf node can have a multitype tree depth (mttDepth) of 0. If the multitype tree depth reaches MaxMtt (for example, 4), no further partitioning may be considered. If the width of the multitype tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, then no further horizontal partitioning can be considered. If the height of the multitype tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, no further vertical partitioning can be considered. When partitioning is not considered, the encoding apparatus can omit signaling of partitioning information. In this case, the decoding apparatus can derive partitioning information with a default value. Meanwhile, a CTU can include one luma sample encoding block (hereafter referred to as a luma block) and two corresponding chroma sample encoding blocks (hereafter referred to as chroma blocks). The encoding tree scheme described above can be applied equally or separately to the luma block and chroma block of the current CU. Specifically, the luma and chroma blocks in a CTU can be partitioned into the same block tree structure, in which case the tree structure is represented as SINGLE_TREE. Alternatively, the luma and chroma blocks in a CTU can be partitioned into separate block tree structures, in which case the tree structure can be represented as DUAL_TREE.That is, when the CTU is partitioned into dual trees, the block tree structure for the luma block and the block tree structure for the chroma block can be separate. In this case, the block tree structure for the luma block can be named DUAL TREE LUMA, and the block tree structure for the chroma component can be named DUAL TREE CHROMA. For P and B segment / mosaic groups, the luma and chroma blocks in a CTU can be restricted to having the same coding tree structure. However, for I segment / mosaic groups, the luma and chroma blocks can have separate block tree structures. If the separate block tree structure is applied, the chroma CTB can be partitioned into CUs. ML / t / ZUZZ / U / l rzi based on a particular encoding tree structure, and the chroma CTB can be partitioned into chroma CUs based on another encoding tree structure. That is, this means that a CU in a segment / mosaic group I, to which the separate block tree structure is applied, can include either a luma component encoding block or two chroma component encoding blocks, and a CU in a segment / mosaic group P or B can include three color component blocks (one luma component and two chroma components). Although a quad-tree encoding tree structure with a nested multitype tree has been described, a structure in which a CU is partitioned is not limited to this. For example, the BT structure and the TT structure can be interpreted as a concept included within a multi-partitioning (MPT) tree structure, and the CU can be interpreted as being partitioned through the QT structure and the MPT structure. In an example where the CU is partitioned through a QT structure and an MPT structure, a syntax element (e.g., MPT_split_type) that includes information on how many blocks of the leaf node of the QT structure are partitioned, and a syntax element (e.g., MPT split mode) that includes information on the vertical and horizontal direction of the leaf node of the QT structure, can be used to define a partitioning structure. In another example, the CU can be partitioned in a different way than the QT, BT, or TT structure. That is, unlike the lower depth CU being partitioned into 1 / 4 of the upper depth CU according to the QT structure, the lower depth CU being partitioned into 1 / 2 of the upper depth CU according to the BT structure, or the lower depth CU being partitioned into 1 / 4 or 1 / 2 of the upper depth CU according to the TT structure, the lower depth CU can be partitioned into 1 / 5, 1 / 3, 3 / 8, 3 / 5, 2 / 3, or 5 / 8 of the upper depth CU in some cases, and the method of partitioning the CU is not limited to this. The quad-tree encoding block structure with a multi-type tree can provide a highly flexible block partitioning structure. Due to the partitioning types supported in a multi-type tree, different partitioning patterns can result in the same encoding block structure in some cases. In the encoding and decoding apparatus, limiting the occurrence of such redundant partitioning patterns can reduce the amount of partitioning information data. ML / t / ZUZZ / U / l rzi Subimage-based image encoding / decoding A target encoding image can be partitioned into units of a plurality of CTUs, segments, tiles, or blocks, and an image can be partitioned into units of a plurality of sub-images. Within the image, a sub-image can be encoded or decoded independently of whether a preceding sub-image is encoded or decoded. For example, different quantization or different resolution can be applied to multiple sub-images. Furthermore, each sub-image can be processed as a separate image. For example, a target encoding image can be a projected image or an image packaged within an omnidirectional image / video or a 360-degree image / video. In this mode, a portion of an image can be provided or displayed based on the viewport of a user terminal (e.g., a head-mounted display). Therefore, in order to implement low latency among the sub-images that make up an image, at least one sub-image covering the viewport can be encoded or decoded, preferably or independently of the remaining sub-images. The result of encoding the sub-image can be referred to as a sub-bitstream, a substream, or simply a bitstream. The decoding apparatus can decode the sub-image from the sub-bitstream, substream, or bitstream. In this case, a high-level syntax (HLS) such as a PPS, SPS, VPS, and / or a decoding parameter set (DPS) can be used to encode / decode the sub-image. In this description, high-level syntax (HLS) may include at least one of the following syntaxes: APS, PPS, SPS, VPS, DPS, or SH. For example, APS (APS syntax) or PPS (PPS syntax) may include information / parameters that can be commonly applied to one or more segments or images. SPS (SPS syntax) may include information / parameters that can be commonly applied to one or more sequences. VPS (VPS syntax) may include information / parameters that can be commonly applied to multiple layers. DPS (DPS syntax) may include information / parameters that can be commonly applied to the entire video. For example, DPS may include information / parameters related to the concatenation of a video-encoded sequence (CVS). The subimage can define a rectangular region of the encoded image. The size of the subimage can be set differently within the image. For all images belonging to a sequence, the size The location of a particular separate subimage can be established in the same way. The separate subimage sequence can be decoded independently. A tile and a segment (and CTBs) may not be restricted to traversing a subimage boundary. To this end, the encoding apparatus can perform encoding in such a way that the subimages are decoded independently. For this purpose, semantic restrictions on the bitstream may be required. Furthermore, for each image in a sequence, the arrangement of tiles, segments, and blocks in the subimage can be configured differently. Subimage designs aim at the abstraction or encapsulation of a range that is smaller than an image level but larger than a tile or segment group level.Therefore, a NAL VCL unit from a Motion Constraint Tile Set (MCTS) subset can be extracted from a VVC bitstream, and processing such as rearranging it into another VVC bitstream can be performed as easily as a modification at the VCL level. Here, MCTS is an encoding technology that allows for spatial and temporal independence between tiles. When MCTS is applied, information about tiles not included in the MCTS to which the current tile belongs can be disregarded. When the image is partitioned into MCTSs and encoded, independent transmission and encoding of the MCTSs are possible. Such a sub-image design has an advantage in changing the display orientation in 360° transmission schemes dependent on the combined resolution viewport. From now on, an image encoding / decoding method using a segment / mosaic will be described with reference to Figures 8 and 9. Figure 8 is a flowchart illustrating a method for encoding an image using a segment / tile by an image encoding apparatus in accordance with one modality of the present description. The image encoding apparatus can derive segment(s) / mosaic(s) in a current image by partitioning the current image (S810). The image encoding apparatus can encode the current image based on the derived segment(s) / mosaic(s) in step S810 (S820). Figure 9 is a flowchart illustrating a method for decoding an image using a segment / tile by an image decoding apparatus in accordance with one modality of the present description. The image decoding device can acquire information about a video / image from a bitstream (S910). Furthermore, the image decoding device can derive segment(s) / tile(s) in a current image based on the video / image information acquired in step S910 (S920). Here, the video / image information may include information about the segment(s) / tile(s). Afterwards, the image decoding apparatus can decode the current image based on the derived segment(s) / mosaic(s) in step S920 (S930). In Figures 8 and 9, the segment / tile information may include various information and / or syntax elements described herein. The video / image information may include high-level syntax, and this high-level syntax may include segment and / or tile information. The high-level syntax may include an image header, and the image header information may be included in the segment header described herein. The segment information may include information specifying one or more segments, and the tile information may include information specifying one or more tiles. A segment that includes one or more tiles may be present in the image. ML / t / ZUZZ / U / l rzi High-level syntax signaling (HLS) As described above, high-level syntax can be encoded / signaled for video / image encoding. The following sections will describe the signaling and syntax elements in a segment header and a segment header in accordance with this description. Image header and segment header An encoded image can consist of one or more segments. The parameters for an encoded image are specified within a segment header (SH), and the parameters for a segment are specified within a segment header (SH). The PH is carried in its own NAL unit type. The SH can be present at the beginning of a NAL unit containing a segment's payload (i.e., segment data). The syntax elements of the PH and SH, and the semantics of these syntax elements, will be described hereafter with reference to Figure 10 and Figure 11. Figure 10 is a view showing an example of the present description of a syntax and signaling element in a segment header. `picture_header_rbsp()` contains information that is common to all segments of the encoded image associated with the picture header (PH). For example, The `ml / t / ZUZZ / U / l rzi picture_header_rbsp()` function may include a reference image flag (`non_reference_picture_flag`), GDR image identification information (`gdr_pic_flag`), no output of prior pie flag, recovery poc cnt, ph_pic_parameter_set_id`, or similar. Here, `recovery_poc_cnt` is signaled in `picture header rbsp()` when the `gdr pie` flag is 1. A first value (for example, 1) of non_reference_picture_flag specifies that the image associated with the PH is not used as a reference image. A second value (for example, 0) of non_reference_picture_flag specifies that the image associated with the PH may or may not be used as a reference image. A first value (for example, 1) of gdr_pic_flag specifies that the image associated with the PH is a GDR image. A second value (for example, 0) of gdr_pic_flag specifies that the image associated with the PH is not a GDR image. no_output_of_prior_pics_flag affects the output of previously decoded images in the DPB after decoding a Coded Layer Video Sequence (CLVSS) image that is not the first image in the bitstream. recovery_poc_cnt specifies the recovery point of decoded images in output order. ph_pic_parameter_set_id specifies the value of pps_pic_parameter_set_id for the image parameter set (PPS) in use. pps_pic_parameter_set_id is a value to identify the PPS to be referenced in other syntax. The syntax elements included in the picture_header_rbsp() syntax structure in Figure 10 can be included and referenced in the picture_header_structure() syntax structure. In this case, the picture_header_structure() syntax structure can be included and referenced in the picture_header_rbsp() syntax structure. Figure 11 is a view showing a syntax structure of a segment header in accordance with one modality of the present description. As shown in Figure 11, picture header in slice header flag, picture_header_structure(), slice_subpic_id, slice_address, num_tiles_in_slice_minusl or similar can be signaled through a slice header. In the example shown in Figure 11, the `picture_header_in_slice_header_flag` specifies whether an image header syntax structure is present in a slice header syntax structure. A first value (for example, 1 or True) of `picture_header_in_slice_header_flag` specifies that the image header is present in the slice header, and a second value (for example, 0 or False) of `picture_header_in_slice_header_flag` specifies that the image header is not present in the slice header. `picture_header_structure()` can be acquired based on `picture_header_in_slice_header_flag`. For example, `picture_header_structure()` can be referenced when `picture_header_in_slice_header_flag` has a first value. When `picture_header_in_slice_header_flag` has a second value, `picture_header_structure()` may not be included in the slice header, but it can be included and referenced in a separate NAL unit. `slice_subpic_id` can be information about a sub-image identifier to identify a sub-image that includes a current segment. `slice_subpic_id` can be acquired based on `subpics_present_flag`. For example, `slice_subpic_id` can be flagged when `subpics_present_flag` is 1. The `subpics_present_flag` can specify whether a sub-image is present in the current image or whether information about a sub-image is present in the bitstream. For example, a first value (e.g., 1 or True) of `subpics_present_flag` can specify that information about a sub-image is present in the bitstream or that one or more sub-images are present in the current image. A second value (e.g., 0 or False) of `subpics_present_flag` can specify that the information ML / t / ZUZZ / U / l rzi about a subimage is not present in the bitstream or a subimage is not present in the current image. `slice_address` can specify the address of the current slice within the image. The slice address can be derived based on `rect_slice_flag` and / or `NumTilesInPic`. For example, when `rect_slice_flag` is a first value (e.g., 1 or True) or `NumTilesInPic` is greater than 1, `slice_address` can be referenced in the segment header. `rect_slice_flag` can also be used to indicate whether the included slice in the current image is rectangular. For example, `rect_slice_flag` can be referenced at an image level (PPS or image header). Additionally, `NumTilesInPic` can specify the number of tiles included in the current image. `num_tiles_in_slice_minusl` can specify the number of tiles included in the current slice. `num tiles in slice minusl` can be inferred based on `rect_slice_flag` and `NumTilesInPic`. For example, when `rect slice flag` is a second value (e.g., 0 or False) and `NumTilesInPic` is greater than 1, `num_tiles_in_slice_minusl` can be specified in the slice header. In the mode shown in Figure 11, as a requirement for compliance with the bitstream associated with the picture header in slice header flag, the following can be included. In order to satisfy bitstream conformity, the value of picture_header_in_slice_header_flag is required to be the same in all segments of a CLVS. Additionally, when picture_header_in_slice_header_flag is a first value (e.g., 1), in order to satisfy bitstream conformity, it is required that a NAL unit with NAL unit type equal to PH_NUT is not present in the CLVS. Additionally, when picture_header_in_slice_header_flag is a second value (e.g., 0), in order to satisfy bitstream conformity, it is required that a NAL unit with NAL unit type equal to PH_NUT be present in the PU, preceding the first NAL unit VCL of the PU. Figure 12 is a flowchart illustrating a method for analyzing and decoding the segment header in Figure 11. First, the picture decoding apparatus can acquire a first flag (picture_header_in_slice_header_flag) included in the segment header (S1210). The first flag can specify whether an image header is present in the segment header. Additionally, the first flag can specify whether the current image includes only one segment. 4 When the first flag is a first value (e.g., 1 or True) (step S1220-S1), the picture decoding apparatus can acquire a picture header from the segment header (S1230). When the first flag is a second value (e.g., 0 or False) (step S1220-No), the picture header can be acquired from the picture header NAL unit instead of the segment header (not shown). Subsequently, you can determine whether `subpics_present_flag` is a first value (for example, 1 or True) in step S1240. `subpics_present_flag` can specify whether the current image includes a subimage. Furthermore, `subpics_present_flag` can specify whether information about a subimage is included in the bitstream. `subpics_present_flag` can be signaled at a high level within a segment. For example, `subpics_present_flag` can be included and signaled within a sequence parameter set. When `subpics present flag` is a first value (e.g., 1 or True) (step S1240-S1), the image decoding apparatus can acquire `slice_subpic_id` from the segment header (S1250). When `subpics_present_flag` is a second value (e.g., 0 or False) (step S1240-No), the image decoding apparatus can skip (skip) parsing `slice_subpic_id`. ΜΛ / t / ZUZZ / U / l rzi from the segment header. Subsequently, in step S1260, it can be determined whether rect_slice_flag is a first value (for example, 1 or True) and / or NumTilesInPic is greater than 1. The rect slice flag can be an indicator that shows whether the segment included in the current image is a rectangular segment. For example, rect_slice_flag can be set at an image level (PPS or image header). Additionally, NumTilesInPic can specify the number of tiles included in the current image. When rect_slice_flag is a first value (e.g., 1 or True) or NumTilesInPic is greater than 1 (step S1260-YES), the image decoding appliance can acquire the slice address from the segment header (S1270). When rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is not greater than 1 (step S1260-NO), the image decoding appliance can skip the slice address analysis from the segment header. Subsequently, in step S1280, it can be determined whether rect_slice_flag is a first value (e.g., 1 or True) and / or whether NumTilesInPic is greater than 1. When rect_slice_flag is a first value (e.g., 1 or True) or NumTilesInPic is not greater than 1 (step S1280No), the image decoding apparatus can skip the parsing of num_tiles_in_slice_minusl from the segment header. When rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is greater than 1 (step S1280-S1), the image decoding apparatus can acquire num_tiles_in_slice_minusl from the segment header (S1290). Subsequently, the image decoding apparatus can decode the segment header by analyzing subsequent syntax elements, which are not shown, starting from the segment header. Figure 13 is a flowchart illustrating a method for decoding the segment header in Figure 11. First, the picture encoding device can determine the value of a first flag (picture_header_in_slice_header_flag) and encode the first flag in the segment header (S1310). When the first flag is a first value (e.g., 1 or True) (step S1320-S1), the picture encoding apparatus can encode the picture header in the segment header (S1330). When the first flag is a second value (e.g., 0 or False) (step S1320-No), the picture header is not encoded in the segment header but can be included and signaled in the picture header NAL unit (not shown). ML / t / ZUZZ / U / l rzi Subsequently, in step S1340, it can be determined whether subpics_present_flag is a first value (for example, 1 or True). subpics_present_flag can be determined and signaled at a higher level of the segment. For example, subpicS—present—flag can be included and signaled in the sequence parameter set. When subpics_present_flag is a first value (for example, 1 or True) (step S1340-S1), the image encoding appliance can encode slice_subpic_id in the segment header (S1350). When subpics_present_flag is a second value (for example, 0 or False) (step S1340-No), the image encoding appliance can omit (skip) encoding slice_subpic_id in the segment header. Subsequently, in step S1360, it can be determined whether rect_slice_flag is a first value (e.g., 1 or True) and / or whether NumTilesInPic is greater than 1. When rect slice flag is a first value (for example, 1 or True) or when NumTilesInPic is greater than 1 (step S1360-S1), the image encoding appliance can encode slice_address in the segment header (S1370). When rect_slice_flag is a second value (for example, 0 or False) and NumTilesInPic is not greater than 1 (step S1360-No), the image encoding appliance can omit (skip) the encoding of the slice address in the segment header. Subsequently, in step S1380, it can be determined whether rect_slice_flag is a first value (e.g., 1 or True) and / or whether NumTilesInPic is greater than 1. When rect_slice_flag is a first value (for example, 1 or True) or when NumTilesInPic is not greater than 1 (step S1380-No), the image encoding apparatus can omit (skip) the encoding of num_tiles_in_slice_minusl in the segment header. When rect_slice_flag is a second value (for example, 0 or False) and NumTilesInPic is greater than 1 (step S1380-S1), the image encoding apparatus can encode num_tiles_in_slice_minusl in the segment header (S1390). Subsequently, the image encoding apparatus can encode the segment header, encoding subsequent syntax elements, which are not shown, in the segment header. In the example described with reference to Figures 12 and 13, some steps can be changed or omitted. For example, the conditions related to encoding / decoding slice address and / or num_tiles_in_slice_minusl can be changed. In the future, a method will be described to improve the modality described with reference to Figures 11 to 13 in consideration of encoding / decoding an image based on a sub-image. The image coding device can encode the ML / t / ZUZZ / U / l rzi current image based on a sub-image. Alternatively, the image encoding apparatus can encode at least one sub-image by configuring the current image and generating a bitstream that includes encoded information from at least one encoded sub-image. The image decoding device can decode at least one sub-image included in the current image based on the bitstream that includes encoded information from at least one sub-image. As described above, `picture_header_in_slice_header_flag` can specify whether an image header is present in the segment header. Additionally, `picture_header_in_slice_header_flag` can be used to specify whether the current image includes only one segment or multiple segments. When the current image includes only one segment, since the segment is the only segment in the current image, some syntax elements in the segment header have fixed values. In this case, it can be efficient not to specify some syntax elements that have fixed values. The following sections will describe various configurations of the system described herein for efficient signaling. These configurations can be applied to the modes described herein individually or in combination. Configuration 1 When the current image includes only one segment, the signaling of some syntax elements in the segment header can be skipped (omitted). The value of the syntax element whose signaling is omitted can be derived or inferred by the image encoding and / or image decoding apparatus. If the current image includes only one segment, this can be indicated by a predefined indicator. Therefore, when the indicator shows that the current image includes only one segment, some syntax elements may not be included in the segment header, and their values ​​may be inferred or derived. In this case, the indicator can be used as a condition to determine whether certain syntax elements are included in the segment header. Configuration 2 The indicator described in Configuration 1 can be, for example, picture header in slice header flag. Configuration 3 A syntax element in the slice header, the signaling of which can be omitted in accordance with the value of picture_header_in_slice_header_flag, may include at least one of the following (a) or (b). (a) Syntax element(s) that specify the subimage that includes the segment The reason why the syntax element (a) flag can be omitted is that, when only one segment is included per image, it is obvious that the sub-image is not specified. For example, when `picture_header_in_slice_header_flag` indicates that the current image includes only one segment, since the current image is not encoded / decoded based on the sub-image, the flagging of the sub-image information can be omitted. (b) Syntax element(s) that specify the segment address The reason why the syntax element (b) signaling can be omitted is because it is obvious that the segment is the only first segment in the image. For example, when `picture header in slice header fia` indicates that the current image includes only one segment, since the current segment is the only segment in the current image, the direction signaling for the current segment can be omitted. Configuration 4 When each image in the sequence has only one segment, the sub-image is also unused. For example, `subpics_present_flag` or `subpic_info_present_flag`, which is a syntax element for the sub-image, can be limited to a second value (e.g., 0 or False). `subpics_present_flag` or `subpic_info_present_flag` can specify whether a sub-image is present in the current image or whether information about a sub-image is present in the bitstream. `subpics_present_flag` or `subpic_info_present_flag` can be included and referenced in the sequence parameter set, for example. Similarly, when `subpics_present_flag` or `subpic_info_present_flag` has a first value (e.g., 1 or True), a flag indicating whether each image in the sequence includes only one segment, or a flag (e.g., `picture_header_in_slice_header_flag`) indicating whether an image header is present in the segment header, may not indicate that the current image includes only one segment and may not indicate that an image header is present in the segment header. Therefore, for example, when `subpics_present_flag` or `subpic_info_present_flag` has a first value (e.g., 1 or True), `picture_header_in_slice_header_flag` may be restricted to having a second value (e.g., 0 or False). Configuration 5 When an image header is not present in the image header NAL unit but is present in the segment header, in a CLVS of a particular layer (layer A), the headers of all layers that refer to layer A (i.e., layers dependent on layer A) and all layers referenced by layer A can be restricted to being present in the segment header, not in the image header NAL unit. The above restriction is imposed to simplify the detection of the image boundary within an access unit for the case of multi-layer bitstreaming. Figure 14 is a view showing the syntax structure of a segment header in accordance with another modality of the present description. Since the description of the same syntax elements and the same signaling conditions are the same in the segment header structure conforming to the modality of Figure 14 and the segment header structure conforming to the modality of Figure 11, a repeated description will be omitted. In accordance with the modality shown in Figure 14, the condition for specifying `slice_subpic_id` can be changed. Specifically, the slice header can include the `slice_subpic_id` based on `subpics present flag` and `picture_header_in_slice_header_flag`. For example, when `subpics present flag` is a first value (e.g., 1 or Venadero) and `picture_header_in_slice_header_flag` is a second value. The ML / t / ZUZZ / U / l rzi value (e.g., 0 or False), slice_subpic_id can be signaled in the segment header. This is because, as described above, when the picture header in slice header flag has a first value, the current image includes only one segment and sub-image encoding / decoding is not performed; signaling the sub-image information is unnecessary. Furthermore, in accordance with the modality shown in Figure 14, the condition for signaling slice_address can be changed. Specifically, the segment header can include slice_address based on rect_slice_flag, NumTilesInPic, and picture_header_in_slice_header_flag. For example, when rect slice flag is a first value (e.g., 1 or True) or NumTilesInPic is greater than 1, and picture_header_in_slice_header_flag is a second value (e.g., 0 or False), slice address can be signaled in the segment header. This is because, as described above, when picture_header_in_slice_header_flag has a first value, since the current image includes only one slice, signaling the segment address information is unnecessary. In the mode of Figure 14, a bitstream conformance requirement for ML / t / ZUZZ / U / l rzi picture_header_in_slice_header_flag can be improved as follows. First, the value of the picture header in slice header flag is required to be the same in all slices in the CLVS. Furthermore, when the `picture header in slice header` flag is a first value (for example, 1), a NAL unit with NAL unit type PH_NUT is not required in the CLVS. This is because the picture header is included and referenced in the segment header, and therefore a separate NAL unit to transmit the picture header is not needed. Furthermore, when picture_header_in_slice_header_flag is a second value (for example, 0), a NAL unit with NAL unit type PH_NUT is required in the PU, preceding the first NAL unit VCL in the PU. That is, the current PU is required to have the NAL unit PH. This is because a separate NAL unit is needed to transmit the picture header. Furthermore, when `subpics_present_flag` or `subpic_info_present_flag` is a first value (e.g., 1), `picture header in slice header flag` is not required to be a first value (e.g., 1). In this case, `picture header in slice header flag` can be restricted to having a second value (e.g., 0). ML / t / ZUZZ / U / l rzi In the example in Figure 14, slice_subpic_id indicates the identifier of the subimage that includes the segment. When slice_subpic_id is present, a SubPicIdx variable is derived such that SubpicIdList[SubPicIdx] is equal to slice_subpic_id. When slice_subpic_id is not present, a SubPicIdx variable can be derived to be equal to 0. In the example in Figure 14, the length (bit length) of slice_subpic_id can be derived as follows. If sps_subpic_id_signalling_present_flag is equal to 1, the length of slice_subpic_id is derived to be equal to sps_subpic_id_len_minus1 + 1. Here, sps_subpic_id_signalling_present_flag can specify whether the subpic ID is signaled in the sequence parameter set. sps_subpic_id_len_minus1 is the length information of the subpic ID and can be included and signaled in the sequence parameter set. Otherwise (if sps_subpic_id_signalling_present_flag is not 1), if ph subpic id signalling present flag is 1, the length of slice_subpic_id can be derived to be equal to ph_subpic_id_len_minusl + 1. Here, ph subpic id signalling present flag can specify whether the sub-image identifier is signaled in the image header, ph subpic id len minusl is the length information of the sub-image identifier and can be included and signaled in the image header. Otherwise (if both sps_subpic_id_signalling_present_flag and ph subpic id signalling present flag are not 1), if pps_subpiC—id_signalling_present—flag is 1, the length of slice subpic id can be derived to be equal to pps_subpic_id_len_minusl + 1. Here, pps_subpic_id_signalling_present_flag can specify whether the subpic id is signaled in the image parameter set. pps_subpic_id_len_minusl is the length information of the subpic id and can be included and signaled in the image parameter set. Otherwise (if all sps_subpic_id_signalling_present_flag, ph_subpic_id_signalling_present_flag and pps subpic id signalling present flag are not 1), the length of slice_subpic_id can be derived to be equal to Ceil (Log2 (sps num subpics minusl + 1) ). sps num subpics minusl is the number of subimages of each image in the CLVS and can be included and pointed to in the sequence parameter set. slice_address specifies the segment address of the current segment. When slice address is not present, the slice address value is inferred to be 0. picture_header_structure() may include at least one syntax element included in picture_header_rbsp() described with reference to Figure 10. Figure 15 is a flowchart illustrating a method for analyzing and decoding the segment header in Figure 14. Steps S1510 to S1530 in Figure 15 are the same as steps S1210 to S1230 in Figure 12, respectively, and thus a repeated description of the same will be omitted. Steps S1540 to S1570 in Figure 15 may correspond to steps S1240 to S1270 in Figure 12, respectively. Therefore, a repeated description of the common portions will be omitted. In accordance with the modality of Figure 15, in step S1540, it can be determined whether subpics_present_flag is a first value (e.g., 1 or True) and whether a first flag is a second value (e.g., 0 or False). When `subpics_present_flag` is a first value and the first flag is a second value (step S1540-YES), the image decoding apparatus can acquire `slice_subpic_id` from the segment header (S1550). When `subpics present flag` is a second value (e.g., 0 or False) or the first flag is a first value (e.g., 1 or True) (step S1540-NO), the image decoding apparatus can skip (skip) parsing `slice_subpic_id` from the segment header. Subsequently, in step S1560, it can be determined whether rect_slice_flag is a first value (e.g., 1 or True) or if NumTilesInPic is greater than 1 and if the first flag is a second value (e.g., 0 or False). When the rect slice flag is a first value or NumTilesInPic is greater than 1 and the first flag is a second value (step S1560-YES), the image decoding apparatus can acquire slice_address from the segment header (S1570). When the rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is not greater than 1 or the first flag is a first value (e.g., 1 or True) (step S1560-NO), the image decoding apparatus can skip the analysis of slice_address from the segment header. Steps S1580 to S1590 in Figure 15 are the same as steps S1280 to S1290 in Figure 12, respectively, and thus a repeated description of the same will be omitted. As described with reference to Figure 12, the image decoding apparatus can decode the segment header by analyzing subsequent syntax elements, which are not shown, starting from the segment header. Figure 16 is a flowchart illustrating a method for decoding the segment header of the Figure 14. Steps S1610 to S1630 in Figure 16 are the same as steps S1310 to S1330 in Figure 13, respectively, and thus a repeated description of the same will be omitted. Steps S1640 to S1670 in Figure 16 may correspond to steps S1340 to S1370 in Figure 16, respectively. Therefore, a repeated description of the common portions will be omitted. In accordance with the modality of Figure 16, in step S1640, it can be determined whether subpics_present_flag is a first value (e.g., 1 or True) and a first flag is a second value (e.g., 0 or False). When `subpics_present_flag` is a first value and the first flag is a second value (step S1640-S1), the image encoding apparatus can encode `slice_subpic_id` in the segment header (S1650). When `subpics present flag` is a second value (e.g., 0 or False) or the first flag is a first value (e.g., 1 or True) (step S1640-No), the image encoding apparatus can omit (skip) encoding `slice_subpic_id` in the segment header. Subsequently, in step S1660, it can be determined whether rect_slice_flag is a first value (e.g., 1 or True) or if NumTilesInPic is greater than 1 and whether a first flag is a second value (e.g., 0 or False). When rect_slice_flag is a first value or NumTilesInPic is greater than 1 and the first flag is a second value (step S1660-S1), the image encoding apparatus can encode the slice address in the segment header (S1670). When rect_slice_flag is a second value (e.g., 0 or False) and NumTilesInPic is not greater than 1 or the first flag is a first value (e.g., 1 or True) (step S1660-S1), the image encoding apparatus can omit (skip) the encoding of the slice address in the segment header. Steps S1680 to S1690 in Figure 16 are the same as steps S1380 to S1390 in Figure 13, respectively, and thus a repeated description of the same will be omitted. As described with reference to Figure 13, the image encoding apparatus can encode the segment header, encoding subsequent syntax elements, which are not shown, in the segment header. In the example described with reference to Figures 15 and 16, some steps can be changed or omitted. For example, the conditions related to encoding / decoding slice address and / or num_tiles_in_slice_minusl can be changed. As a modified example of the modes described with reference to Figures 14 to 16, the improved restrictions on `picture_header_in_slice_header_flag` are applicable to the mode shown in Figure 11. In this case, at least some of the problems with conventional methods can be resolved. Specifically, for example, the value of `picture_header_in_slice_header_flag` can be restricted based on information about a sub-image (`subpics_present_flag` or `subpic_info_present_flag`) referenced at a higher level of the segment header. More specifically, when `subpics_present_flag` or `subpic_info_present_flag` is a first value, `picture_header_in_slice_header_flag` can be restricted to have a second value.Therefore, when `subpics_present_flag` (or `subpic_info_present_flag`) is a first value (when information about a subpic is present in a bitstream or the current image includes a subpic), `picture_header_in_slice_header_flag` may indicate that an image header is not present in the image header or that the current image does not include only a slice. In the mode shown in Figure 14, when `subpics_present_flag` is a first value and `picture_header_in_slice_header_flag` is a second value, the `slice subpic id` can be acquired from the slice header. However, when `subpics_present_flag` is a first value, since `picture_header_in_slice_header_flag` is restricted to having a second value, it may be... ML / t / ZUZZ / U / l rzi is sufficient to check subpics_present_flag as the analysis of the slice_subpic_id condition. That is, according to this modified example, in steps S1540 and S1640, a determination as to whether the first flag is a second value can be omitted. According to this modified example, the image encoding apparatus can encode picture_header_in_slice_header_flag, which has a second value, when subpics_present_flag or subpic_info_present_flag is a first value. Furthermore, the image decoding apparatus can acquire picture_header_in_slice_header_flag, which has a second value, when subpics_present_flag or subpic_info_present_flag is a first value. Figure 17 is a view showing the syntax structure of a segment header in accordance with another modality of the present description. Since the description of the same syntax elements and the same signaling conditions are the same in the segment header structure conforming to the modality of Figure 17 and the segment header structure conforming to the modality of Figure 14, a repeated description will be omitted. In accordance with the modality shown in Figure 17, the condition for setting the Picture Leader in Slice header flag can be changed. Specifically, the slice header ML / t / ZUZZ / U / l rzi can include the picture_header_in_slice_header_flag based on the subpics_present_flag. For example, when subpics_present_flag is a first value (e.g., 1 or True), the picture_header_in_slice_header_flag may not be flagged in the slice header. For example, when subpics_present_flag is a second value (e.g., 0 or False), the picture_header_in_slice_header_flag may be flagged in the slice header. This is because, as described above, when subpics_present_flag has a first value, since the current image cannot contain only one slice, the picture_header_in_slice_header_flag has a fixed (second) value. Therefore, flagging the picture_header_in_slice_header_flag is unnecessary. In this case, an image header which is indicated in the case where picture_header_in_slice_header_flag is a first value may not be indicated through the segment header. Furthermore, in accordance with the modality of Figure 17, when subpics present flag is a first value, slice_subpic_id can be pointed to in the segment header. From now on, for description of slice address and num_tiles_in_slice_minusl, refer to Figure 14. In the mode of Figure 17, a bitstream conformance requirement for ML / t / ZUZZ / U / l rzi picture_header_in_slice_header_flag may be the same as that described with reference to Figure 14. Figure 18 is a flowchart illustrating a method for analyzing and decoding the segment header in Figure 17. The method of conformity with Figure 18 and the method of conformity with Figure 15 are different in some conditions and order for analyzing the syntax element, and the description of the syntax elements which are commonly described may be the same. In accordance with the modality of Figure 18, the image decoding apparatus can determine if the value of subpics_present_flag is a second value (e.g., 0 or False) in step S1810. When the value of subpics_present_flag is a first value (for example, 1 or True) in step S1810, since encoding / decoding is performed on a sub-image basis, the actual image does not include only a segment. Therefore, in this case, the image decoding apparatus may not acquire picture_header_in_slice_header_flag and an image header from the segment header, but it may acquire slice_subpic_id (S1850). When the value of the `subpics present flag` is a second value in step S1810, the picture decoder acquires a first flag (`picture_header_in_slice_header_flag`) from the segment header (S1820). The picture decoder can determine if the first flag is a first value (S1830), and acquires a picture header from the segment header when the first flag is a first value (S1840). When the first flag is a second value, the picture decoder does not acquire the picture header from the segment header, and in this case, the picture decoder can acquire the picture header through a separate NAL unit.When the value of subpics_present_flag is a second value in step S1810, since no sub-image encoding / decoding is performed, the image decoding apparatus may not acquire information about a sub-image (slice_subpic_id). Steps S1860 to S1890 in Figure 18 are the same as steps S1560 to S1590 in Figure 15, respectively, and thus a repeated description of the same will be omitted. As described with reference to Figure 12, the image decoding apparatus can decode the segment header by analyzing subsequent syntax elements, which are not shown, starting from the segment header. Figure 19 is a flowchart illustrating a ΜΛ / t / ZUZZ / U / l rzi method to decode the segment header of Figure 17. The method of conformity with Figure 19 and the method of conformity with Figure 16 are different in some conditions and order for encoding the syntax element, and the description of the syntax elements which are commonly described may be the same. In accordance with the modality of Figure 19, the image encoding apparatus can determine if the value of subpics_present_flag is a second value (e.g., 0 or False) in step S1910. When the value of subpics_present_flag is a first value (for example, 1 or True) in step S1910, since encoding / decoding is performed on a sub-image basis, the actual image does not include only a segment. Therefore, in this case, the image encoding apparatus may not encode the picture header in the slice header flag and an image header in the segment header, but it may encode slice_subpic_id (S1950). When the value of subpics_present_flag is a second value in step S1910, the image encoding apparatus can determine the value of a first flag (picture_header_in_slice_header_flag) and encode the first flag in the segment header (S1920). The image encoding apparatus can determine if the first flag When the first flag is a first value (S1930), the image encoding apparatus may encode an image header in the segment header. In this case, the image encoding apparatus may signal the image header through a separate NAL unit. When the value of subpics_present_flag is a second value in step S1910, since no sub-image encoding / decoding is performed, the image encoding apparatus may not encode information about a sub-image (slice_subpic_id) in the segment header. Steps S1960 to S1990 in Figure 19 are the same as steps S1660 to S1690 in Figure 16, respectively, and thus a repeated description of them will be omitted. As described with reference to Figure 13, the image encoding apparatus can encode the segment header, encoding subsequent syntax elements, which are not shown, in the segment header. In the examples described with reference to Figures 18 and 19, some steps can be changed or omitted. For example, the conditions related to encoding / decoding slice address and / or num_tiles_in_slice_minusl can be changed. In accordance with the modality of the present description, it is possible to more efficiently indicate information about whether an image header is present in a segment header and / or information about whether an image includes only one segment. Furthermore, in accordance with the modality of the present description, since the information about whether the image header is present in the segment header is indicated based on whether encoding / decoding is performed based on a sub-image, it is possible to prevent unnecessary information from being indicated. The names of the syntax elements described herein may include information about the location where the corresponding syntax element is referenced. For example, a syntax element beginning with sps may mean that the corresponding syntax element is referenced in a sequence parameter set (SPS). Similarly, syntax elements beginning with pps_, ph_, sh_, etc., mean that the corresponding syntax elements are referenced, respectively, in an image parameter set (PPS), an image header, and a segment header. While the exemplary modes of the present description described above are represented as a The series of operations is presented for clarity of description; it is not intended to limit the order in which the steps are performed, and the steps may be performed simultaneously or in a different order as necessary. In order to implement the method in accordance with this description, the steps described may also include other steps, may include remaining steps except for some of the steps, or may include other additional steps except for some steps. In this description, the image encoding or image decoding apparatus that performs a predetermined operation (step) may perform a follow-up operation (step) to confirm a condition or status of the corresponding operation (step). For example, if the predetermined operation is described as being performed when a predetermined condition is met, the image encoding or image decoding apparatus may perform the predetermined operation after determining whether the predetermined condition is met. The various modalities in this description are not a list of all possible combinations and are intended to describe representative aspects of this description, and the topics described in the various modalities can be applied independently in ML / t / ZUZZ / U / l rzi combination of two or more. Several variations of this description can be implemented in hardware, firmware, software, or a combination thereof. If implemented in hardware, this description can be implemented using application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), general-purpose processors, controllers, microcontrollers, microprocessors, etc. Furthermore, the image decoding apparatus and the image encoding apparatus, to which the modalities of the present description apply, may be included in a multimedia broadcasting transmission and reception device, a mobile communication terminal, a home cinema video device, a digital cinema 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 video camera, a device providing video-on-demand (VoD) services, an OTT (over-the-top) video device, a device providing internet streaming services, a three-dimensional (3D) video device, a video telephony device, a medical video device, and the like.and can be used to process video signals into data signals. For example, OTT video devices can 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), or similar devices. Figure 20 is a view showing a continuous content transmission system, to which a modality of the present description is applicable. As shown in Figure 20, the continuous content transmission system, to which the modality of the present description applies, may broadly include an encoding server, a continuous transmission server, a network server, a media storage device, a user device, and a multimedia input device. The encoding server compresses the content coming in from multimedia input devices, such as smartphones, cameras, camcorders, etc., into digital data to generate a bitstream and transmits this bitstream to the streaming server. Alternatively, if multimedia input devices such as smartphones, cameras, camcorders, etc., directly generate a bitstream, the encoding server can be bypassed. The bitstream can be generated by a method that encodes an image or an image encoding device, to which the modality of the present description applies, and the streaming server can temporarily store the bitstream in the process of transmitting or receiving the bitstream. The streaming server transmits multimedia data to the user's device based on a user request via the network server, which in turn serves as a means of informing the user about the service. When the user requests a desired service from the network server, the network server can then provide it to a streaming server, which in turn can transmit the multimedia data to the user. In this case, the content streaming system may include a separate control server. The control server manages the command and response between devices within the content streaming system. The streaming server can receive content from a storage medium and / or an encoding server. For example, when content is received from the encoding server, it can be received in real time. In this case, to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined time. Examples of user devices may include a mobile phone, a smartphone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable media player (PMP), navigation, a slate PC, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, head-mounted devices), digital TVs, desktop computers, digital signatures, and the like. Each server in the continuous content transmission system can be operated as a distributed server, in which case the data received from each server can be distributed. The scope of the description includes software or machine-executable commands (e.g., an operating system, an application, firmware, a program, etc.) to enable operations in accordance with various methods to be executed on an apparatus or computer, a non-transient computer-readable medium having such software or commands stored therein and executable on the apparatus or computer. Industrial Applicability The methods described herein can be used to encode or decode an image.

Claims

1. An image decoding method comprising: acquiring a first flag specifying whether information about a sub-image is present in a bitstream; acquiring a second flag specifying whether image header information is present in a segment header; and decoding the bitstream based on the first flag and the second flag, wherein, when the first flag specifies that information about the sub-image is present in the bitstream, the second flag has a value specifying that image header information is not present in the image header.

2. The image decoding method of claim 1, wherein, when the first flag specifies that information about the sub-image is present in the bitstream, the segment header includes an identifier of a sub-image that includes a segment related to the segment header.

3. The image decoding method of claim 1, further comprising acquiring the image header information from the segment header when the second flag specifies that the image header information is present in the segment header.

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

5. The image decoding method of claim 1, wherein, when the second flag specifies that the image header information is present in the segment header, a network abstraction layer (NAL) unit for transmitting the image header information is not present in a coded layer video sequence (CLVS).

6. The image decoding method of claim 1, wherein, when the second flag specifies that the image header information is not present in the image header, the image header information is acquired from a network abstraction layer (NAL) unit with a NAL unit type equal to PH_NUT.

7. The image decoding method of claim 1, wherein the first flag is pointed at a high level of a segment, and wherein the second flag is included and pointed at the segment header.

8. An image decoding apparatus comprising a memory and at least one processor, wherein at least one processor is configured to: acquire a first flag specifying whether information about a sub-image is present in a bitstream; acquire a second flag specifying whether image header information is present in a segment header; and decode the bitstream based on the first flag and the second flag, wherein, when the first flag specifies that information about the sub-image is present in the bitstream, the second flag has a value specifying that image header information is not present in the image header.

9. An image encoding method comprising: encoding a first flag specifying whether information about a sub-image is present in a bitstream; encoding a second flag specifying whether image header information is present in a segment header; and encoding the bitstream based on the first flag and the second flag, wherein, when the first flag specifies that information about the sub-image is present in the bitstream, the second flag has a value specifying that image header information is not present in the image header.

10. The image encoding method of claim 9, wherein, when the first flag specifies that information about the subimage is present in the bitstream, the segment header includes an identifier of a subimage that includes a segment related to the segment header.

11. The image encoding method of claim 9, further comprising encoding the image header information in the segment header when the second flag specifies that the image header information is present in the segment header.

12. The image coding method of claim 9, wherein the second flag has the same value with respect to all segments in a coded layer video sequence (CLVS).

13. The image encoding method of claim 9, wherein, when the second flag specifies that the image header information is not present in the image header, the image header information is signaled through a network abstraction layer (NAL) unit with a NAL unit type equal to PH_NUT.

14. The image encoding method of claim 9, wherein the first flag is pointed at a high level of a segment, and wherein the second flag is included and pointed at the segment header.

15. A method for transmitting a bit stream generated by the image encoding method of claim 9.

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