Image decoding method, image encoding method, and bit stream transmission method

Abstract

The invention provides an image decoding method, an image encoding method, and a bit stream transmission method. An image decoding method according to the present disclosure may comprise the steps of: obtaining a current block corresponding to a leaf node having a segmentation tree structure on the basis of a predetermined prediction mode type; reconfiguring the prediction mode type of the current block; obtaining prediction mode information of the current block based on the reconfigured prediction mode type; and generating a prediction block of the current block based on the prediction mode information, in which the step of reconfiguring the prediction mode type of the current block is performed based on at least one of a slice type or a size of the current block.

Description

[0001] This application is a divisional application of the invention patent application with the original application number 202080097605.0 (International application number: PCT / KR2020 / 019287, application date: December 31, 2020, invention name: Image encoding / decoding method and device for performing prediction based on reconfigured prediction mode type of leaf nodes and bit stream transmission method). Technical Field

[0002] The present disclosure relates to an image encoding / decoding method and device and a method for sending a bit stream, and more specifically, to an image encoding / decoding method and device for performing prediction based on a preset prediction mode type of a leaf node and a method for sending a bit stream generated by the image encoding method / device of the present disclosure. Background Art

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

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

[0005] Technical issues

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

[0007] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus for resetting a prediction mode type based on at least one of a slice type or a size of a current block.

[0008] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus for encoding / decoding prediction mode information based on a reset prediction mode type of a current block.

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

[0010] Another object of the present disclosure is to provide a recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0011] Another object of the present disclosure is to provide a recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

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

[0013] Technical Solution

[0014] An image decoding method performed by an image decoding device according to an aspect of the present disclosure may include: obtaining a current block corresponding to a leaf node of a partition tree structure based on a predetermined prediction mode type; resetting the prediction mode type of the current block; obtaining prediction mode information of the current block based on the reset prediction mode type; and generating a prediction block of the current block based on the prediction mode information. The step of resetting the prediction mode type of the current block may be performed based on at least one of a slice type or a size of the current block.

[0015] According to another aspect of the present disclosure, an image decoding device may include a memory and at least one processor. The at least one processor may: obtain a current block corresponding to a leaf node of a partition tree structure based on a predetermined prediction mode type; reset the prediction mode type of the current block; obtain prediction mode information of the current block based on the reset prediction mode type; and generate a prediction block of the current block based on the prediction mode information. The prediction mode type of the current block may be reset based on at least one of a slice type or a size of the current block.

[0016] An image encoding method performed by an image encoding device according to another aspect of the present disclosure may include: obtaining a current block corresponding to a leaf node of a partition tree structure based on a predetermined prediction mode type; resetting the prediction mode type of the current block; and encoding prediction mode information of the current block based on the reset prediction mode type. The step of resetting the prediction mode type of the current block may be performed based on at least one of a slice type or a size of the current block.

[0017] In addition, a transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding device or the image encoding method of the present disclosure.

[0018] In addition, a computer-readable recording medium according to another aspect of the present disclosure may store a bit stream generated by the image encoding device or the image encoding method of the present disclosure.

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

[0020] Beneficial Effects

[0021] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency may be provided.

[0022] According to the present disclosure, an image encoding / decoding method and apparatus for resetting a prediction mode type based on at least one of a slice type or a size of a current block may be provided.

[0023] According to the present disclosure, an image encoding / decoding method and apparatus for encoding / decoding prediction mode information based on a reset prediction mode type of a current block may be provided.

[0024] According to the present disclosure, an image encoding / decoding method and apparatus for limiting signaling of prediction mode information of a skip mode when a reset prediction mode type of a current block is an intra type may be provided.

[0025] In addition, according to the present disclosure, a method of transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure may be provided.

[0026] In addition, according to the present disclosure, a recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure may be provided.

[0027] In addition, according to the present disclosure, there may be provided a recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0028] Those skilled in the art will understand that the effects that can be achieved through the present disclosure are not limited to what has been specifically described above, and other advantages of the present disclosure will be more clearly understood from the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a diagram schematically showing a video encoding system to which an embodiment of the present disclosure is applicable.

[0030] Figure 2 is a view schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0031] Figure 3 is a view schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0032] Figure 4 is a view illustrating a segmentation structure of an image according to an embodiment.

[0033] Figure 5 is a view showing an embodiment of a partition type of a block according to a multi-type tree structure.

[0034] Figure 6 is a diagram illustrating a signaling mechanism of block partitioning information in a quadtree having a nested multi-type tree structure according to the present disclosure.

[0035] Figure 7is a view showing an example of splitting a CTU into a plurality of CUs by applying a multi-type tree after applying a quadtree.

[0036] Figure 8 Redundant partitioning patterns that can occur in binary tree partitioning and ternary tree partitioning are shown.

[0037] Figure 9a is a view illustrating an intra prediction direction according to an embodiment of the present disclosure.

[0038] Figure 9b is a view illustrating an intra prediction direction according to another embodiment of the present disclosure.

[0039] Fig.10 is a flowchart illustrating a video / image encoding method based on inter-frame prediction.

[0040] Fig.11 is a view illustrating a configuration of the inter prediction unit 180 according to the present disclosure.

[0041] Fig.12 is a flowchart illustrating a video / image decoding method based on inter-frame prediction.

[0042] Fig.13 is a view illustrating a configuration of the inter prediction unit 260 according to the present disclosure.

[0043] Fig.14 is a view illustrating an example of a coding_unit syntax including prediction mode information.

[0044] Fig.15 is a view illustrating a prediction mode applicable to a current block according to a slice type and size of the current block.

[0045] Figures 16 to 19 is a view illustrating a coding_unit syntax according to an embodiment of the present disclosure.

[0046] Fig. 20 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure.

[0047] Fig.21 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure.

[0048] Fig. 22 is a diagram showing a content streaming system to which an embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0049] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to facilitate implementation by those skilled in the art. However, the present disclosure can be implemented in various forms and is not limited to the embodiments described herein.

[0050] When describing the present disclosure, if it is determined that the detailed description of related known functions or configurations makes the scope of the present disclosure unnecessarily ambiguous, the detailed description thereof will be omitted. In the drawings, parts irrelevant to the description of the present disclosure are omitted, and like reference numerals are given to like parts.

[0051] In the present disclosure, when a component is "connected", "coupled" or "linked" to another component, it may include not only a direct connection relationship but also an indirect connection relationship with intermediate components. In addition, when a component "includes" or "has" other components, unless otherwise specified, it means that other components may also be included, rather than excluding other components.

[0052] In the present disclosure, the terms first, second, etc. are used only for the purpose of distinguishing one component from other components, and do not limit the order or importance of the components unless otherwise specified. Accordingly, within the scope of the present disclosure, the first component in one embodiment may be referred to as the second component in the embodiment, and similarly, the second component in one embodiment may be referred to as the first component in the embodiment.

[0053] In the present disclosure, components that are distinguished from each other are intended to clearly describe each feature and do not mean that the components must be separated. That is, multiple components can be integrated and implemented in one hardware or software unit, or one component can be distributed and implemented in multiple hardware or software units. Therefore, even if not specifically stated, embodiments in which these components are integrated or distributed are also included in the scope of the present disclosure.

[0054] In the present disclosure, the components described in the various embodiments are not necessarily essential components, and some components may be optional components. Therefore, embodiments consisting of a subset of the components described in the embodiments are also included in the scope of the present disclosure. In addition, embodiments that include other components in addition to the components described in the various embodiments are included in the scope of the present disclosure.

[0055] The present disclosure relates to encoding and decoding of images. Unless otherwise defined in the present disclosure, terms used in the present disclosure may have general meanings commonly used in the technical field to which the present disclosure belongs.

[0056] In the present disclosure, a "picture" generally refers to a unit representing an image within a specific time period, and a slice / tile is a coding unit that constitutes a part of a picture. A picture may be composed of one or more slices / tiles. In addition, a slice / tile may include one or more coding tree units (CTUs).

[0057] In the present disclosure, "pixel" or "pel" may mean the smallest single element constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, or may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0058] In the present disclosure, a "unit" may refer to a basic unit of image processing. The unit may include at least one of a specific area of ​​a picture and information related to the area. In some cases, the unit may be used interchangeably with terms such as "sample array", "block" or "area". In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients.

[0059] In the present disclosure, "current block" may mean one of "current coding block", "current coding unit", "coding target block", "decoding target block" or "processing target block". When prediction is performed, "current block" may mean "current prediction block" or "prediction target block". When transform (inverse transform) / quantization (dequantization) is performed, "current block" may mean "current transform block" or "transform target block". When filtering is performed, "current block" may mean "filtering target block".

[0060] In addition, in the present disclosure, "current block" may mean a block including both a luma component block and a chroma component block, or, unless explicitly stated as a chroma block, means "a luma block of a current block". The chroma component block of the current block may be expressed by an explicit description including a luma component block such as "a luma block" or "a current luma block". In addition, the chroma component block of the current block may be explicitly expressed by an explicit description including a chroma component block such as "a chroma block" or "a current chroma block".

[0061] In the present disclosure, the slash " / " or "," may be interpreted as indicating "and / or". For example, "A / B" and "A, B" may mean "A and / or B". In addition, "A / B / C" and "A, B, C" may mean "at least one of A, B and / or C".

[0062] In the present disclosure, the term "or" should be interpreted to indicate "and / or". For example, the expression "A or B" may include 1) only "A", 2) only "B", or 3) both "A and B". In other words, in the present disclosure, "or" should be interpreted to indicate "additionally or alternatively".

[0063] Video Coding System Overview

[0064] Figure 1 is a diagram schematically illustrating a video encoding system according to the present disclosure.

[0065] The video encoding system according to the embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may deliver the encoded video and / or image information or data to the decoding device 20 via a digital storage medium or a network in the form of a file or a stream.

[0066] The encoding device 10 according to the embodiment may include a video source generator 11, an encoding unit 12, and a transmitter 13. The decoding device 20 according to the embodiment may include a receiver 21, a decoding unit 22, and a renderer 23. The encoding unit 12 may be called a video / image encoding unit, and the decoding unit 22 may be called a video / image decoding unit. The transmitter 13 may be included in the encoding unit 12. The receiver 21 may be included in the decoding unit 22. The renderer 23 may include a display and the display may be configured as a separate device or an external component.

[0067] The video source generator 11 can obtain the video / image by the process of capturing, synthesizing or generating the video / image. The video source generator 11 may include a video / image capturing device and / or a video / image generating device. The video / image capturing device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generating device may include, for example, a computer, a tablet computer, and a smart phone, and may (electronically) generate the video / image. For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process of generating relevant data.

[0068] The encoding unit 12 may encode the input video / image. For compression and encoding efficiency, the encoding unit 12 may perform a series of processes such as prediction, transformation, and quantization. The encoding unit 12 may output encoded data (encoded video / image information) in the form of a bitstream.

[0069] The transmitter 13 may transmit the encoded video / image information or the data output in the form of a bit stream to the receiver 21 of the decoding device 20 in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter 13 may include an element for generating a media file in a predetermined file format and may include an element for transmitting through a broadcast / communication network. The receiver 21 may extract / receive a bit stream from a storage medium or a network and transmit the bit stream to the decoding unit 22.

[0070] The decoding unit 22 may decode a video / image by performing a series of processes corresponding to the operations of the encoding unit 12, such as dequantization, inverse transformation, and prediction.

[0071] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0072] Overview of Image Coding Device

[0073] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0074] like Figure 2 As shown, the image encoding device 100 may include an image segmenter 110, a subtractor 115, a transformer 120, a quantizer 130, a dequantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter-frame prediction unit 180, an intra-frame prediction unit 185, and an entropy encoder 190. The inter-frame prediction unit 180 and the intra-frame 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 also include a subtractor 115.

[0075] In some embodiments, all or at least some of the components configuring the image encoding apparatus 100 may be configured by one hardware component (eg, an encoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium.

[0076] The image segmenter 110 may segment the input image (or picture or frame) input to the image encoding device 100 into one or more processing units. For example, the processing unit may be referred to as a coding unit (CU). The coding unit may be obtained by recursively segmenting a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree, binary tree, ternary tree (QT / BT / TT) structure. For example, a coding unit may be segmented into a plurality of coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the segmentation of the coding unit, the quadtree structure may be applied first, and then the binary tree structure and / or the ternary tree structure may be applied. The encoding process according to the present disclosure may be performed based on the final coding unit that is no longer segmented. The maximum coding unit may be used as the final coding unit, and the coding unit of a deeper depth obtained by segmenting the maximum coding unit may also be used as the final coding unit. Here, the encoding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the encoding process may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit. The prediction unit may be a sample prediction unit, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from a transform coefficient.

[0077] The prediction unit (inter prediction unit 180 or intra prediction unit 185) may perform prediction on the block to be processed (current block) and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction based on the current block or CU. The prediction unit may generate various information related to the prediction of the current block and transmit the generated information to the entropy encoder 190. The information about the prediction may be encoded in the entropy encoder 190 and output in the form of a bitstream.

[0078] The intra prediction unit 185 can predict the current block by referring to the samples in the current picture. Depending on the intra prediction mode and / or the intra prediction technology, the reference samples can be located in the neighbors of the current block or can be placed separately. The intra prediction mode may include multiple non-directional modes and multiple directional modes. The non-directional mode may include, for example, a DC mode and a plane mode. Depending on the level of detail of the prediction direction, the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used according to the settings. The intra prediction unit 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0079] The inter prediction unit 180 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc. The reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter prediction unit 180 may configure a motion information candidate list based on the neighboring blocks and generate information specifying which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter prediction unit 180 may use the motion information of the neighboring block as the motion information of the current block. In the case of skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled by encoding the motion vector difference and an indicator of the motion vector predictor. The motion vector difference may mean the difference between the motion vector of the current block and the motion vector predictor.

[0080] The prediction unit may generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit may not only apply intra prediction or inter prediction, but may also apply intra prediction and inter prediction simultaneously to predict the current block. The prediction method of applying both intra prediction and inter prediction simultaneously to predict the current block may be referred to as combined inter and intra prediction (CIIP). In addition, the prediction unit may perform intra block copying (IBC) to predict the current block. Intra block copying may be used for content image / video encoding of games, etc., such as screen content coding (SCC). IBC is a method of predicting the current picture using a previously reconstructed reference block in the current picture at a position separated by a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to a predetermined distance. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described in the present disclosure. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one of the inter-frame prediction techniques described in this disclosure.

[0081] The prediction signal generated by the prediction unit can be used to generate a reconstruction signal or to generate a residual signal. The subtractor 115 can generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (prediction block or prediction sample array) output from the prediction unit from the input image signal (original block or original sample array). The generated residual signal can be transmitted to the transformer 120.

[0082] The transformer 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT refers to a transform obtained from a graph when relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to square pixel blocks of the same size or may be applied to blocks of variable size rather than square.

[0083] The quantizer 130 may quantize the transform coefficients and transmit them to the entropy encoder 190. The entropy encoder 190 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 130 may rearrange the quantized transform coefficients in the block form into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0084] The entropy encoder 190 may perform various encoding methods, such as exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 190 may encode information required for video / image reconstruction (e.g., values ​​of syntax elements, etc.) together or separately in addition to quantized transform coefficients. The encoded information (e.g., encoded video / image information) may be transmitted or stored in units of a network abstraction layer (NAL) in the form of a bitstream. The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The signaled information, the transmitted information, and / or the syntax elements described in the present disclosure may be encoded and included in the bitstream through the above-mentioned encoding process.

[0085] The bitstream may be transmitted over a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits a signal output from 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 device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0086] The quantized transform coefficients output from the quantizer 130 may be used to generate a residual signal. For example, the residual signal (residual block or residual sample) may be reconstructed by applying dequantization and inverse transformation to the quantized transform coefficients through the dequantizer 140 and the inverse transformer 150.

[0087] The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame prediction unit 180 or the intra-frame prediction unit 185 to generate a reconstructed signal (reconstructed image, reconstructed block, reconstructed sample array). If there is no residual in the block to be processed, such as when the skip mode is applied, the prediction block can be used as a reconstructed block. The adder 155 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0088] The filter 160 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 160 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc. The filter 160 can generate various information related to filtering and transmit the generated information to the entropy encoder 190, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 190 and output in the form of a bit stream.

[0089] The modified reconstructed picture transferred to the memory 170 may be used as a reference picture in the inter prediction unit 180. When inter prediction is applied by the image encoding device 100, prediction mismatch between the image encoding device 100 and the image decoding device may be avoided and encoding efficiency may be improved.

[0090] The DPB of the memory 170 may store the modified reconstructed picture for use as a reference picture in the inter-frame prediction unit 180. The memory 170 may store the motion information of the block from which the motion information in the current picture is derived (or encoded) and / or the motion information of the previously reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame prediction unit 180 and used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 170 may store the reconstructed samples of the reconstructed blocks in the current picture and may transmit the reconstructed samples to the intra-frame prediction unit 185.

[0091] Overview of image decoding device

[0092] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0093] like Figure 3As shown, the image decoding device 200 may include an entropy decoder 210, a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, and an intra-frame prediction unit 265. The inter-frame prediction unit 260 and the intra-frame prediction unit 265 may be collectively referred to as a "prediction unit". The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0094] According to an embodiment, all or at least some of the plurality of components configuring the image decoding apparatus 200 may be configured by hardware components (eg, a decoder or a processor). In addition, the memory 250 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

[0095] The image decoding apparatus 200 having received a bit stream including video / image information may perform the same operation as that performed by Figure 2 The image may be reconstructed by processing corresponding to the processing performed by the image encoding device 100. For example, the image decoding device 200 may perform decoding using a processing unit applied in the image encoding device. Therefore, the processing unit of decoding may be, for example, a coding unit. The coding unit may be obtained by splitting a coding tree unit or a maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 may be reproduced by a reproduction device (not shown).

[0096] The image decoding apparatus 200 may receive the image in the form of a bit stream from Figure 2The received signal may be decoded by the entropy decoder 210. For example, the entropy decoder 210 may parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The image decoding device may also decode the picture based on the parameter set information and / or the general constraint information. The information and / or syntax elements signaled / received described in the present disclosure may be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the neighboring block and the decoding target block, or the information of the symbol / bin decoded in the previous stage to determine the context model, and perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. The information related to the prediction in the information decoded by the entropy decoder 210 can be provided to the prediction unit (inter-frame prediction unit 260 and intra-frame prediction unit 265), and the residual value on which entropy decoding is performed in the entropy decoder 210, that is, the quantized transform coefficient and related parameter information can be input to the dequantizer 220. In addition, information about filtering among the information decoded by the entropy decoder 210 can be provided to the filter 240. Meanwhile, a receiver (not shown) for receiving a signal output from the image encoding device may be further configured as an internal / external element of the image decoding device 200 , or the receiver may be a component of the entropy decoder 210 .

[0097] Meanwhile, the image decoding device according to the present disclosure may be referred to as a video / image / picture decoding device. The image decoding device may be divided into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include at least one of a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, or an intra-frame prediction unit 265.

[0098] The dequantizer 220 may dequantize the quantized transform coefficient and output the transform coefficient. The dequantizer 220 may rearrange the quantized transform coefficient in the form of a two-dimensional block. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may perform dequantization on the quantized transform coefficient by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficient.

[0099] The inverse transformer 230 may inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0100] The prediction unit may perform prediction on the current block and generate a prediction block including a prediction sample of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction to the current block based on the information about the prediction output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0101] The same as described in the prediction unit of the image encoding device 100 , the prediction unit can generate a prediction signal based on various prediction methods (techniques) described later.

[0102] The intra prediction unit 265 may predict the current block by referring to samples in the current picture. The description of the intra prediction unit 185 is also applicable to the intra prediction unit 265.

[0103] The inter prediction unit 260 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter prediction unit 260 may configure a motion information candidate list based on neighboring blocks, and derive a motion vector and / or a reference picture index of the current block based on the received candidate selection information. Inter prediction may be performed based on various prediction modes, and information about the prediction may include information indicating an inter prediction mode of the current block.

[0104] The adder 235 can generate a reconstructed block by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the prediction unit (including the inter-frame prediction unit 260 and / or the intra-prediction unit 265). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as the reconstructed block. The description of the adder 155 is also applicable to the adder 235. The adder 235 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0105] The filter 240 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 240 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 250, specifically, in the DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc.

[0106] The (modified) reconstructed picture stored in the DPB of the memory 250 may be used as a reference picture in the inter-frame prediction unit 260. The memory 250 may store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the previously reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame prediction unit 260 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 250 may store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0107] In the present disclosure, the embodiments described in the filter 160, the inter-frame prediction unit 180 and the intra-frame prediction unit 185 of the image encoding device 100 can be equally or correspondingly applied to the filter 240, the inter-frame prediction unit 260 and the intra-frame prediction unit 265 of the image decoding device 200.

[0108] Overview of Image Segmentation

[0109] The video / image encoding method according to the present disclosure can be performed based on the image segmentation structure as follows. Specifically, the prediction, residual processing ((inverse) transform, (de)quantization, etc.), syntax element encoding and filtering processes described later can be performed based on the CTU, CU (and / or TU, PU) derived from the image segmentation structure. The image can be segmented in units of blocks and the block segmentation process can be performed in the image segmentor 110 of the encoding device. The segmentation related information can be encoded by the entropy encoder 190 and sent to the decoding device in the form of a bitstream. The entropy decoder 210 of the decoding device can derive the block segmentation structure of the current picture based on the segmentation related information obtained from the bitstream, and based on this, a series of processes (e.g., prediction, residual processing, block / picture reconstruction, in-loop filtering, etc.) can be performed for image decoding. The CU size and the TU size can be the same, or there can be multiple TUs in the CU area. At the same time, the CU size can generally represent the luminance component (sample) CB size. The TU size can generally represent the luminance component (sample) TB size. The chroma component (sample) CB or TB size can be derived based on the luminance component (sample) CB or TB size according to the chroma format (color format, such as 4:4:4, 4:2:2, 4:2:0, etc.) of the picture / image according to the component ratio. The TU size can be derived based on the maxTbSize that specifies the maximum available TB size. For example, when the CU size is larger than maxTbSize, multiple TUs (TBs) of maxTbSize can be derived from the CU, and transform / inverse transform can be performed in units of TU (TB). In addition, for example, when intra prediction is applied, the intra prediction mode / type can be derived in units of CU (or CB), and the neighboring reference sample derivation and prediction sample generation process can be performed in units of TU (or TB). In this case, one or more TUs (or TBs) may exist in a CU (or CB) area, and in this case, multiple TUs (or TBs) may share the same intra prediction mode / type.

[0110] In addition, in the image encoding and decoding according to the present disclosure, the image processing unit may have a hierarchical structure. For example, a picture may be divided into one or more tiles or tile groups. A tile group may include one or more tiles. A tile may include one or more CTUs. As described above, a CTU may be divided into one or more CUs. A tile may consist of a rectangular area including a CTU assembled in a specific row and a specific column in a picture. According to a tile raster scan, a tile group may include an integer number of tiles. A tile group header may signal information / parameters applicable to a corresponding tile group. When the encoding / decoding device has a multi-core processor, the encoding / decoding process of a tile or a tile group may be performed in parallel. Here, a tile group may have one of the tile group types including an intra (I) tile group, a prediction (P) tile group, and a dual prediction (B) tile group. For blocks in an I tile group, inter-frame prediction may not be used, and only intra-frame prediction may be used for prediction. Of course, even in this case, the original sample value may be encoded and signaled without prediction. For blocks in P mosaic groups, intra prediction or inter prediction can be used, and only uni-prediction can be used when inter prediction is used. Meanwhile, for blocks in B mosaic groups, intra prediction or inter prediction can be used, and up to bi-prediction can be used when inter prediction is used.

[0111] In the encoding device, the patch / patch group, slice, and maximum and minimum coding unit sizes can be determined according to the characteristics of the image (e.g., resolution) and taking into account coding efficiency or parallel processing, and information about them or information that can derive them can be included in the bitstream.

[0112] In the decoding device, information specifying that a slice, a tile / tile group, or a CTU in a tile of a current picture is partitioned into a plurality of coding units may be obtained. When such information is obtained (transmitted) only under certain conditions, efficiency may be increased.

[0113] A slice header or a tile group header (tile group header syntax) may include information / parameters that are commonly applicable to a slice or a tile group. APS (APS syntax) or PPS (PPS syntax) may include information / parameters that are commonly applicable to one or more pictures. SPS (SPS syntax) may include information / parameters that are commonly applicable to one or more sequences. VPS (VPS syntax) may include information / parameters that are commonly applicable to the entire video. In the present disclosure, the highest level syntax may include at least one of APS syntax, PPS syntax, SPS syntax, or VPS syntax.

[0114] In addition, for example, information on the partitioning and construction of patches / patch groups may be constructed by a high-level syntax during the encoding stage and sent to a decoding device in the form of a bitstream.

[0115] Split structure

[0116] A picture may be partitioned into a sequence of coding tree units (CTUs). A CTU may correspond to a coding tree block (CTB). Alternatively, a CTU may include a coding tree block of luma samples and two corresponding coding tree blocks of chroma samples. For example, for a picture containing three sample arrays, a CTU may include one N×N block of luma samples and two corresponding blocks of chroma samples. Figure 4 An example in which a picture is divided into CTUs is shown.

[0117] The maximum allowed size of a CTU for encoding and prediction may be different from that of a CTU for transform. For example, even when the maximum size of a luma block in a CTU for transform is 64×64, the maximum size of a luma block of a CTU for encoding and prediction may be 128×128.

[0118] In addition, the picture may be partitioned into one or more tile rows and one or more tile columns.A tile may be a sequence of CTUs covering a rectangular area in the picture.

[0119] A patch may be partitioned into one or more tiles, and each tile may be composed of multiple CTU rows in the patch. In the present disclosure, a patch that is not partitioned into multiple tiles may be referred to as a tile.

[0120] A slice can include multiple tiles in a picture or multiple tiles in a tile. Two slicing modes can be supported. One can be a raster scan slicing mode and the other can be a rectangular slicing mode.

[0121] In the raster slice mode, a slice may include multiple consecutive tiles within a picture according to a raster scan order. In the present disclosure, a slice according to the raster scan slice mode may be referred to as a raster scan slice.

[0122] In the rectangular slice mode, a slice may include a plurality of tiles constituting a rectangular area within a picture. In the present disclosure, a slice according to the rectangular slice mode may be referred to as a rectangular slice. According to the tile raster scan order of the slice, there may be a plurality of tiles included in the rectangular slice.

[0123] Overview of CTU Segmentation

[0124] As described above, a coding unit may be obtained by recursively partitioning a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree / binary tree / ternary tree (QT / BT / TT) structure. For example, a CTU may be first partitioned into a quadtree structure. Thereafter, the leaf nodes of the quadtree structure may be further partitioned by a multi-type tree structure.

[0125] Partitioning according to the quadtree means that the current CU (or CTU) is equally divided into four. By partitioning according to the quadtree, the current CU can be partitioned into four CUs with the same width and the same height. When the current CU is no longer partitioned into a quadtree structure, the current CU corresponds to a leaf node of the quadtree structure. The CU corresponding to the leaf node of the quadtree structure may no longer be partitioned and may be used as the above-mentioned final coding unit. Alternatively, the CU corresponding to the leaf node of the quadtree structure may be further partitioned by a multi-type tree structure.

[0126] Figure 5 is a view showing an embodiment of partition types of a block according to a multi-type tree structure. The partition according to the multi-type tree structure may include two types of partitions according to a binary tree structure and two types of partitions according to a ternary tree structure.

[0127] The two types of splits according to the binary tree structure may include vertical binary split (SPLIT_BT_VER) and horizontal binary split (SPLIT_BT_HOR). Vertical binary split (SPLIT_BT_VER) means that the current CU is equally split into two in the vertical direction. Figure 5 As shown in FIG, through vertical binary splitting, two CUs with the same height as the current CU and half the width of the current CU can be generated. Horizontal binary splitting (SPLIT_BT_HOR) means that the current CU is equally divided into two in the horizontal direction. Figure 5 As shown, through horizontal binary partitioning, two CUs with a height half of the height of the current CU and the same width as the current CU can be generated.

[0128] The two types of splits according to the triad structure may include vertical triad split (SPLIT_TT_VER) and horizontal triad split (SPLIT_TT_HOR). In vertical triad split (SPLIT_TT_VER), the current CU is split in a vertical direction at a ratio of 1:2:1. Figure 5 As shown, through vertical trisection, two CUs with the same height as the current CU and a width of 1 / 4 of the width of the current CU, and a CU with the same height as the current CU and a width of half the width of the current CU can be generated. In horizontal trisection (SPLIT_TT_HOR), the current CU is split in the horizontal direction at a ratio of 1:2:1. Figure 4 As shown, through horizontal trifurcated division, two CUs whose height is 1 / 4 of the height of the current CU and whose width is the same as the current CU, and a CU whose height is half of the height of the current CU and whose width is the same as the current CU can be generated.

[0129] Figure 6is a diagram illustrating a signaling mechanism of block partitioning information in a quadtree having a nested multi-type tree structure according to the present disclosure.

[0130] Here, the CTU is regarded as the root node of the quadtree and is first split into a quadtree structure. Information (e.g., qt_split_flag) specifying whether to perform quadtree partitioning on the current CU (CTU or node (QT_node) of the quadtree) is signaled. For example, when qt_split_flag has a first value (e.g., "1"), the current CU can be split by the quadtree. In addition, when qt_split_flag has a second value (e.g., "0"), the current CU is not quadtree split, but becomes a leaf node (QT_leaf_node) of the quadtree. Each quadtree leaf node can then be further split into a multi-type tree structure. That is, the leaf node of the quadtree can become a node (MTT_node) of a multi-type tree. In the multi-type tree structure, a first flag (e.g., Mtt_split_cu_flag) is signaled to specify whether the current node is additionally split. If the corresponding node is additionally split (for example, if the first flag is 1), the second flag (for example, Mtt_split_cu_vertical_flag) may be signaled to specify the split direction. For example, the split direction may be a vertical direction when the second flag is 1, and a horizontal direction when the second flag is 0. Then, a third flag (for example, Mtt_split_cu_binary_flag) may be signaled to specify whether the split type is a binary split type or a ternary split type. For example, the split type may be a binary split type when the third flag is 1, and a ternary split type when the third flag is 0. The nodes of the multi-type tree obtained by binary splitting or ternary splitting may be further split into a multi-type tree structure. However, the nodes of the multi-type tree may not be split into a quadtree structure. If the first flag is 0, the corresponding node of the multi-type tree is no longer split, but becomes a leaf node (MTT_leaf_node) of the multi-type tree. The CU corresponding to the leaf node of the multi-type tree may be used as the above-mentioned final coding unit.

[0131] Based on mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, a multi-type tree partition mode (MttSplitMode) of a CU may be derived as shown in the following Table 1. In the following description, a multi-type tree partition mode may be referred to as a multi-tree partition type or a partition type.

[0132] [Table 1]

[0133] MttSplitMode mtt_split_cu_vertical_flag mtt_split_cu_binary_flag SPLIT_TT_HOR 0 0 SPLIT_BT_HOR 0 1 SPLIT_TT_VER 1 0 SPLIT_BT_VER 1 1

[0134] Figure 7 is a view showing an example of splitting a CTU into a plurality of CUs by applying a multi-type tree after applying a quadtree. Figure 7 , the bold block edge 710 represents a quadtree partition, while the remaining edges 720 represent a multi-type tree partition. A CU may correspond to a coding block (CB). In an embodiment, a CU may include a coding block of luma samples and two coding blocks of chroma samples corresponding to the luma samples.

[0135] The chroma component (sample) CB or TB size may be derived based on the luma component (sample) CB or TB size based on the component ratio according to the color format (chroma format, e.g., 4:4:4, 4:2:2, 4:2:0, etc.) of the picture / image. In the case of a 4:4:4 color format, the chroma component CB / TB size may be set equal to the luma component CB / TB size. In the case of a 4:2:2 color format, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB and the height of the chroma component CB / TB may be set to the height of the luma component CB / TB. In the case of a 4:2:0 color format, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB and the height of the chroma component CB / TB may be set to half the height of the luma component CB / TB.

[0136] In an embodiment, when the size of the CTU is 128 based on the luma sample unit, the size of the CU may have a size from 128x128 to 4x4, which is the same size as the CTU. In an embodiment, in the case of a 4:2:0 color format (or chroma format), the chroma CB size may have a size from 64x64 to 2x2.

[0137] Meanwhile, in an embodiment, the CU size and the TU size may be the same. Alternatively, there may be multiple TUs in a CU region. The TU size generally indicates the luma component (sample) transform block (TB) size.

[0138] The TU size can be derived based on the maximum allowed TB size maxTbSize as a predetermined value. For example, when the CU size is larger than maxTbSize, multiple TUs (TBs) with maxTbSize can be derived from the CU, and transform / inverse transform can be performed in units of TU (TB). For example, the maximum allowed luma TB size can be 64x64 and the maximum allowed chroma TB size can be 32x32. If the width or height of the CB split according to the tree structure is larger than the maximum transform width or height, the CB can be automatically (or implicitly) split until the TB size limits in the horizontal and vertical directions are met.

[0139] In addition, for example, when intra prediction is applied, the intra prediction mode / type may be derived in units of CU (or CB), and the neighboring reference sample derivation and prediction sample generation process may be performed in units of TU (or TB). In this case, there may be one or more TUs (or TBs) in a CU (or CB) region, and in this case, multiple TUs or (TBs) may share the same intra prediction mode / type.

[0140] Meanwhile, for a quadtree coding tree scheme with nested multi-type trees, the following parameters may be signaled from an encoding device to a decoding device as SPS syntax elements. For example, at least one of a CTU size as a parameter indicating a root node size of a quadtree, a MinQTSize as a parameter indicating a minimum allowed quadtree leaf node size, a MaxBtSize as a parameter indicating a maximum allowed binary tree root node size, a MaxTtSize as a parameter indicating a maximum allowed ternary tree root node size, a MaxMttDepth as a parameter indicating a maximum allowed hierarchical depth of multi-type tree partitioning from a quadtree leaf node, a MinBtSize as a parameter indicating a minimum allowed binary tree leaf node size, or a MinTtSize as a parameter indicating a minimum allowed ternary tree leaf node size is signaled.

[0141] As an embodiment using a 4:2:0 chroma format, the CTU size may be set to 128x128 luminance blocks and two 64x64 chroma blocks corresponding to these luminance blocks. In this case, MinOTSize may be set to 16x16, MaxBtSize may be set to 128x128, MaxTtSzie may be set to 64x64, MinBtSize and MinTtSize may be set to 4x4, and MaxMttDepth may be set to 4. Quadtree segmentation may be applied to a CTU to generate a quadtree leaf node. A quadtree leaf node may be referred to as a leaf QT node. The size of a quadtree leaf node may be from 16x16 size (e.g., MinOTSize) to 128x128 size (e.g., CTU size). If the leaf QT node is 128x128, it may not be additionally segmented into a binary tree / ternary tree. This is because, in this case, even if segmented, it exceeds MaxBtsize and MaxTtszie (e.g., 64x64). In other cases, the leaf QT node can be further split into a multi-type tree. Therefore, the leaf QT node is the root node of the multi-type tree, and the leaf QT node can have a multi-type tree depth (mttDepth) value of 0. If the multi-type tree depth reaches MaxMttdepth (for example, 4), further splitting can be ignored. If the width of the multi-type tree node is equal to MinBtSize and is less than or equal to 2xMinTtSize, further horizontal splitting can be ignored. If the height of the multi-type tree node is equal to MinBtSize and is less than or equal to 2xMinTtSize, further vertical splitting can be ignored. When splitting is not considered, the encoding device can skip the signaling of the splitting information. In this case, the decoding device can derive the splitting information with a predetermined value.

[0142] At the same time, one CTU may include a coding block of luma samples (hereinafter referred to as "luminance block") and two coding blocks of chroma samples corresponding thereto (hereinafter referred to as "chroma blocks"). The above coding tree scheme may be applied equally or individually to the luma block and chroma block of the current CU. Specifically, the luma block and chroma block in one CTU may be partitioned into the same block tree structure, and in this case, the tree structure is represented as SINGLE_TREE. Alternatively, the luma block and chroma block in one CTU may be partitioned into separate block tree structures, and in this case, the tree structure may be represented as DUAL_TREE. That is, when the CTU is divided into dual trees, a block tree structure for the luma block and a block tree structure for the chroma block may exist separately. In this case, the block tree structure for the luma block may be referred to as DUAL_TREE_LUMA, and the block tree structure for the chroma component may be referred to as DUAL_TREE_CHROMA. For P and B slices / block groups, the luma block and the chroma block in one CTU may be restricted to have the same coding tree structure. However, for I slices / patch groups, luma blocks and chroma blocks may have separate block tree structures from each other. If a separate block tree structure is applied, luma CTBs may be divided into CUs based on a specific coding tree structure, and chroma CTBs may be divided into chroma CUs based on another coding tree structure. That is, this means that a CU in an I slice / patch group to which a separate block tree structure is applied may include a coding block of a luma component or a coding block of two chroma components, and a CU of a P or B slice / patch group may include blocks of three color components (one luma component and two chroma components).

[0143] Although a quadtree coding tree structure with nested multi-type trees has been described, the structure for partitioning the CU is not limited thereto. For example, the BT structure and the TT structure may be interpreted as concepts included in a multi-partition tree (MPT) structure, and the CU may be interpreted as being partitioned by the QT structure and the MPT structure. In an example where the CU is partitioned by the QT structure and the MPT structure, a syntax element (e.g., MPT_split_type) including information about how many blocks a leaf node of the QT structure is partitioned into and a syntax element (e.g., MPT_split_mode) including information about which of the vertical and horizontal directions a leaf node of the QT structure is partitioned into may be signaled to determine the partition structure.

[0144] In another example, the CU may be partitioned in a manner different from the QT structure, the BT structure, or the TT structure. That is, instead of partitioning a CU of a lower depth into 1 / 4 of a CU of a higher depth according to the QT structure, partitioning a CU of a lower depth into 1 / 2 of a CU of a higher depth according to the BT structure, or partitioning a CU of a lower depth into 1 / 4 or 1 / 2 of a CU of a higher depth according to the TT structure, in some cases a CU of a lower depth may be partitioned into 1 / 5, 1 / 3, 3 / 8, 3 / 5, 2 / 3, or 5 / 8 of a CU of a higher depth, and the method of partitioning a CU is not limited thereto.

[0145] In this way, a quadtree coding block structure with a multi-type tree can provide a very flexible block segmentation structure. Due to the segmentation types supported in the multi-type tree, different segmentation patterns can potentially produce the same coding block structure in some cases. In the encoding device and the decoding device, by limiting the occurrence of such redundant segmentation patterns, the amount of data of the segmentation information can be reduced.

[0146] For example, Figure 8 The redundant partitioning patterns that may appear in binary tree partitioning and ternary tree partitioning are shown. Figure 8 As shown, the continuous binary partitions 810 and 820 for one direction of the two-step level have the same coding block structure as the binary partition for the center partition after the ternary partition. In this case, the binary tree partition for the center blocks 830 and 840 of the ternary tree partition can be prohibited. This prohibition applies to CUs of all pictures. When this particular partition is prohibited, the signaling of the corresponding syntax element can be modified by reflecting this prohibition, thereby reducing the number of bits for signaling the partition. For example, as Figure 9a and Figure 9b As shown in the example shown in , when binary tree partitioning for the center block of a CU is prohibited, the syntax element mtt_split_cu_binary_flag specifying whether the partition is binary partitioning or ternary partitioning is not signaled and its value may be derived as 0 by the decoding device.

[0147] Overview of intra prediction

[0148] Hereinafter, intra prediction according to the present disclosure will be described.

[0149] Intra-frame prediction may indicate a prediction of a prediction sample of a current block generated based on a reference sample in a picture to which the current block belongs (hereinafter referred to as the current picture). When intra-frame prediction is applied to the current block, neighboring reference samples to be used for intra-frame prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block of size nW×nH and a total of 2×nH samples adjacent to the lower left, samples adjacent to the upper boundary of the current block and a total of 2×nW samples adjacent to the upper right, and one sample adjacent to the upper left of the current block. Alternatively, the neighboring reference samples of the current block may include multiple columns of upper neighboring samples and multiple rows of left neighboring samples. In addition, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block of size nW×nH, a total of nW samples adjacent to the lower boundary of the current block, and one sample adjacent to the lower right of the current block.

[0150] Some neighboring reference samples of the current block have not been decoded or may not be available. In this case, the decoder can construct neighboring reference samples to be used for prediction by replacing unavailable samples with available samples. Alternatively, interpolation of available samples can be used to construct neighboring reference samples to be used for prediction.

[0151] When deriving neighboring reference samples, (i) the prediction sample may be derived based on an average or interpolation of neighboring reference samples of the current block, and (ii) the prediction sample may be derived based on reference samples existing in a specific (prediction) direction relative to the prediction sample among neighboring reference samples of the current block. The case of (i) may be referred to as a non-directional mode or a non-angular mode, and the case of (ii) may be referred to as a directional mode or an angular mode.

[0152] In addition, the prediction sample can be generated by interpolation using the first neighboring sample located in the prediction direction of the intra prediction mode of the current block among the neighboring reference samples and the second neighboring sample located in the opposite direction based on the prediction target sample of the current block. The above situation can be called linear interpolation intra prediction (LIP).

[0153] In addition, a linear model can be used to generate chrominance prediction samples based on luma samples. This case can be called linear model (LM) mode.

[0154] In addition, the temporary prediction sample of the current block can be derived based on the filtered neighboring reference sample, and the prediction sample of the current block can be derived by weighted summing the temporary prediction sample and at least one reference sample derived according to the intra prediction mode among the existing neighboring reference samples (i.e., the unfiltered neighboring reference sample). This situation can be called position-dependent intra prediction (PDPC).

[0155] In addition, a reference sample row with the highest prediction accuracy can be selected from multiple neighboring reference sample rows of the current block to derive a prediction sample using a reference sample located in the prediction direction in the corresponding row, and at this time, information about the reference sample row used (e.g., intra_luma_ref_idx) can be encoded and signaled in the bitstream. This situation can be called multi-reference row (MRL) intra prediction or MRL-based intra prediction.

[0156] In addition, the current block can be divided into vertical sub-partitions or horizontal sub-partitions to perform intra-frame prediction for each sub-partition based on the same intra-frame prediction mode. At this time, the neighboring reference samples for intra-frame prediction can be derived in units of sub-partitions. That is, the reconstructed samples of the previous sub-partition in the encoding / decoding order can be used as neighboring reference samples of the current sub-partition. In this case, the intra-frame prediction mode of the current block is also applied to the sub-partition, and the neighboring reference samples are derived and used in units of sub-partitions, thereby increasing the intra-frame prediction performance. This prediction method can be referred to as intra-frame sub-partitioning (ISP) or intra-frame prediction based on ISP.

[0157] The intra prediction technique may be referred to as various terms such as intra prediction type or additional intra prediction mode to distinguish from directional or non-directional intra prediction mode. For example, the intra prediction technique (intra prediction type or additional intra prediction mode) may include at least one of LIP, LM, PDPC, MRL, ISP, or MIP.

[0158] The intra prediction process may include an intra prediction mode / type determination step, a neighboring reference sample derivation step, and a prediction sample derivation step based on the intra prediction mode / type. In addition, if necessary, post filtering may be further performed on the derived prediction samples.

[0159] Figure 9a is a view illustrating an intra prediction direction according to an embodiment of the present disclosure.

[0160] The intra prediction mode may include two non-directional intra prediction modes and 33 directional intra prediction modes. The non-directional intra prediction mode may include a planar mode and a DC mode, and the directional intra prediction mode may include intra prediction modes #2 to #34. The planar intra prediction mode may be referred to as a planar mode, and the DC intra prediction mode may be referred to as a DC mode.

[0161] Alternatively, to capture any edge directions present in natural videos, such as Figure 9aAs shown, the intra prediction mode may include two non-directional intra prediction modes and 65 extended directional intra prediction modes. The non-directional intra prediction mode may include a plane prediction mode and a DC prediction mode, and the extended directional intra prediction mode may include intra prediction modes #2 to #66. The intra prediction mode is applicable to blocks of all sizes and both luminance components (luminance blocks) and chrominance components (chrominance blocks).

[0162] Alternatively, the intra prediction modes may include two non-directional intra prediction modes and 129 directional intra prediction modes. The non-directional intra prediction modes may include a planar prediction mode and a DC prediction mode, and the directional intra prediction modes may include intra prediction modes #2 to #130.

[0163] In addition, in addition to the above intra prediction modes, the intra prediction mode may also include a cross component linear model (CCLM) mode for chroma samples. The CCLM mode may be divided into L_CCLM, T_CCLM, LT_CCLM according to whether the left sample, the upper sample, or both are considered according to the LM parameter derivation, and may be applied only to the chroma component.

[0164] For example, the intra prediction modes may be indexed as shown in Table 2 below.

[0165] [Table 2]

[0166] Intra prediction mode Association Name 0 INTRA_PLANAR 1 INTRA_DC 2..66 INTRA_ANGULAR2..INTRA_ANGULAR66 81..83 INTRA_LT_CCLM, INTRA_L_CCLM, INTRA_T_CCLM

[0167] Referring to Table 2, as a non-directional intra prediction mode, the mode number of the planar mode may be 0, and the mode number of the DC mode may be 1. In addition, the mode numbers of the plurality of directional intra prediction modes may be 2 to 66. In addition, the mode numbers of the additional intra prediction mode, the LT_CCLM mode, the L_CCLM mode, and the T_CCLM mode may be 81 to 83.

[0168] Figure 9b FIG. 2 is a diagram illustrating an intra prediction direction according to another embodiment of the present disclosure. Figure 9b In the figure, the dotted direction indicates the wide-angle mode which is only applicable to non-square blocks.

[0169] In order to capture any edge directions present in natural videos, such as Figure 9b As shown, the intra prediction mode according to the embodiment may include two non-directional intra prediction modes and 93 directional intra prediction modes. The non-directional intra prediction mode may include a plane prediction mode and a DC prediction mode, and the directional intra prediction mode may include intra prediction modes #2 to #80 to #-1 to #-14, as shown in FIG. Figure 9bThe planar mode may be represented by INTRA_PLANAR, and the DC mode may be represented by INTRA_DC. In addition, the directional intra prediction mode may be represented by INTRA_ANGULAR-14 to INTRA_ANGULAR-1 and INTRA_ANGULAR2 to INTRA_ANGULAR80.

[0170] The image encoding device may encode the intra prediction mode / type information specifying the intra prediction mode applied to the current block and signal it through the bitstream. In an example, the intra prediction mode / type information may include flag information (e.g., intra_luma_mpm_flag and / or intra_chroma_mpm_flag) specifying whether the most probable mode (MPM) or the residual mode is applied to the current block. When MPM is applied to the current block, the intra prediction mode / type information may include index information (e.g., intra_luma_mpm_idx and / or intra_chroma_mpm_idx) specifying one of the intra prediction mode candidates (MPM candidates). On the contrary, when MPM is not applied to the current block, the intra prediction mode / type information may also include residual mode information (e.g., intra_luma_mpm_remainder and / or intra_chroma_mpm_remainder) specifying one of the remaining intra prediction modes other than the intra prediction mode candidate (MPM candidate). The image decoding apparatus may determine an intra prediction mode of a current block based on intra prediction mode / type information received through a bitstream.

[0171] The intra-frame prediction mode / type information can be encoded / decoded by various encoding methods described in the present disclosure. For example, the intra-frame prediction mode / type information can be encoded / decoded by entropy encoding (e.g., CABAC, CAVLC) based on truncated (rice) binary code.

[0172] Overview of Inter Prediction

[0173] Hereinafter, inter prediction according to the present disclosure will be described.

[0174] The prediction unit of the image encoding device / image decoding device according to the present disclosure may perform inter-frame prediction in units of blocks to derive prediction samples. Inter-frame prediction may refer to prediction derived in a manner that depends on data elements (e.g., sample values, motion information, etc.) of a picture other than the current picture. When inter-frame prediction is applied to the current block, the prediction block (prediction block or prediction sample array) of the current block may be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When inter-frame prediction is applied, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. A temporally neighboring block may be referred to as a collocated reference block, a collocated CU (ColCU), or a colBlock, and a reference picture including a temporally neighboring block may be referred to as a collocated picture (colPic) or a colPicture. For example, a motion information candidate list may be constructed based on neighboring blocks of a current block, and a flag or index information specifying which candidate is selected (used) may be signaled in order to derive a motion vector and / or a reference picture index of the current block.

[0175] Inter-frame prediction can be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the motion information of the current block can be equal to the motion information of the selected neighboring block. In the case of skip mode, unlike merge mode, a residual signal may not be sent. In the case of motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor and the motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference. In the present disclosure, MVP mode may have the same meaning as advanced motion vector prediction (AMVP).

[0176] According to the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. The motion vector in the L0 direction may be referred to as the L0 motion vector or MVL0, and the motion vector in the L1 direction may be referred to as the L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as the L0 prediction, prediction based on the L1 motion vector may be referred to as the L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as the Bi prediction. Here, the L0 motion vector may specify a motion vector associated with the reference picture list L0 (L0), and the L1 motion vector may specify a motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include a picture before the current picture in the output order as a reference picture, and the reference picture list L1 may include a picture after the current picture in the output order. The previous picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. The reference picture list L0 may also include a picture after the current picture in the output order as a reference picture. In this case, within the reference picture list L0, the previous picture may be indexed first, and then the subsequent picture may be indexed. The reference picture list L1 may also include a picture preceding the current picture in the output order as a reference picture. In this case, within the reference picture list L1, the subsequent picture may be indexed first, and then the previous picture may be indexed. Here, the output order may correspond to a picture order count (POC) order.

[0177] Fig.10 is a flowchart illustrating a video / image encoding method based on inter-frame prediction, Fig.11 is a view illustrating a configuration of the inter prediction unit 180 according to the present disclosure.

[0178] Fig.10 The encoding method can be Figure 2 The image encoding device of the present invention may be performed. Specifically, step S1010 may be performed by the inter-frame prediction unit 180, and step S1020 may be performed by the residual processor. Specifically, step S1020 may be performed by the subtractor 115. Step S1030 may be performed by the entropy encoder 190. The prediction information of step S1030 may be derived by the inter-frame prediction unit 180, and the residual information of step S1030 may be derived by the residual processor. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficient for the residual sample. As described above, the residual sample may be derived as a transform coefficient by the transformer 120 of the image encoding device, and the transform coefficient may be derived as a quantized transform coefficient by the quantizer 130. The information about the quantized transform coefficient may be encoded by the entropy encoder 190 through the residual encoding process.

[0179] Refer to Fig.10 and Fig.11 , the image encoding device may perform inter-frame prediction on the current block (S1010). The image encoding device may derive the inter-frame prediction mode and motion information of the current block and generate a prediction sample of the current block. Here, the inter-frame prediction mode determination, motion information derivation, and prediction sample generation processes may be performed simultaneously or any one of them may be performed before the other processes. For example, Fig.11 As shown, the inter-frame prediction unit 180 of the image encoding device may include a prediction mode determination unit 181, a motion information derivation unit 182, and a prediction sample derivation unit 183. The prediction mode determination unit 181 may determine the prediction mode of the current block, the motion information derivation unit 182 may derive the motion information of the current block, and the prediction sample derivation unit 183 may derive the prediction sample of the current block. For example, the inter-frame prediction unit 180 of the image encoding device may search for a block similar to the current block in a predetermined area (search area) of the reference picture through motion estimation, and derive a reference block whose difference with the current block is equal to or less than a predetermined criterion or a minimum value. Based on this, a reference picture index of a reference picture in which the designated reference block is located may be derived, and a motion vector may be derived based on the position difference between the reference block and the current block. The image encoding device may determine a mode applied to the current block among various prediction modes. The image encoding device may compare rate-distortion (RD) costs for various prediction modes, and determine the best prediction mode for the current block. However, the method of determining the prediction mode of the current block by the image encoding device is not limited to the above example, and various methods may be used.

[0180] For example, when the skip mode or merge mode is applicable to the current block, the image encoding device may derive a merge candidate from a neighboring block of the current block, and use the derived merge candidate to construct a merge candidate list. In addition, the image encoding device may derive a reference block whose difference with the current block is equal to or less than a predetermined criterion or a minimum value from the reference blocks specified by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information specifying the selected merge candidate may be generated and signaled to the image decoding device. The motion information of the selected merge candidate may be used to derive the motion information of the current block.

[0181] As another example, when the MVP mode is applied to the current block, the image encoding device may derive a motion vector predictor (MVP) candidate from a neighboring block of the current block, and use the derived MVP candidate to construct an MVP candidate list. In addition, the image encoding device may use the motion vector of the MVP candidate selected from the MVP candidates included in the MVP candidate list as the MVP of the current block. In this case, for example, the motion vector indicating the reference block derived by the above-mentioned motion estimation may be used as the motion vector of the current block, and the current block having the motion vector with the smallest difference from the motion vector of the current block among the MVP candidates may be the selected MVP candidate. A motion vector difference (MVD) as the difference obtained by subtracting the MVP from the motion vector of the current block may be derived. In this case, index information specifying the selected MVP candidate and information about the MVD may be signaled to the image decoding device. In addition, when the MVP mode is applied, the value of the reference picture index may be constructed as reference picture index information and signaled separately to the image decoding device.

[0182] The image encoding device may derive residual samples based on the predicted samples (S1020). The image encoding device may derive residual samples by comparing the original samples of the current block with the predicted samples. For example, the residual samples may be derived by subtracting the corresponding predicted samples from the original samples.

[0183] The image encoding device may encode the image information including the prediction information and the residual information (S1030). The image encoding device may output the encoded image information in the form of a bitstream. The prediction information may include prediction mode information (e.g., a skip flag, a merge flag, or a mode index, etc.) and information about motion information as information related to the prediction process. Among the prediction mode information, the skip flag specifies whether the skip mode is applicable to the current block, and the merge flag specifies whether the merge mode is applicable to the current block. Alternatively, the prediction mode information may specify one of a plurality of prediction modes, such as a mode index. When the skip flag and the merge flag are 0, it can be determined that the MVP mode is applicable to the current block. The information about the motion information may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index) as information for deriving a motion vector. Among the candidate selection information, the merge index may be signaled when the merge mode is applicable to the current block and may be information for selecting one of the merge candidates included in the merge candidate list. Among the candidate selection information, the mvp flag or the mvp index may be signaled when the MVP mode is applicable to the current block and may be information for selecting one of the mvp candidates in the mvp candidate list. In addition, the information about the motion information may include information about the above-mentioned MVD and / or reference picture index information. In addition, the information about the motion information may include information specifying whether L0 prediction, L1 prediction or Bi prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficient for the residual sample.

[0184] The output bit stream may be stored in a (digital) storage medium and transmitted to the image decoding device or may be transmitted to the image decoding device via a network.

[0185] As described above, the image encoding device may generate a reconstructed picture (a picture including reconstructed samples and reconstructed blocks) based on the reference samples and the residual samples. This is for the image encoding device to derive the same prediction result as the prediction result performed by the image decoding device, thereby improving the coding efficiency. Therefore, the image encoding device may store the reconstructed picture (or the reconstructed sample and the reconstructed block) in a memory and use it as a reference picture for inter-frame prediction. As described above, the in-loop filtering process is also applicable to the reconstructed picture.

[0186] Fig.12 is a flowchart illustrating a video / image decoding method based on inter-frame prediction, Fig.13 is a view illustrating a configuration of the inter prediction unit 260 according to the present disclosure.

[0187] The image decoding device may perform an operation corresponding to the operation performed by the image encoding device. The image decoding device may perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0188] Fig.12 The decoding method can be obtained by Figure 3 The image decoding device is performed. Specifically, steps S1210 to S1230 can be performed by the inter-frame prediction unit 260, and the prediction information of step S1210 and the residual information of step S1240 can be obtained from the bitstream by the entropy decoder 210. The residual processor of the image decoding device can derive the residual samples of the current block based on the residual information. For example, the dequantizer 220 of the residual processor can perform dequantization based on the dequantized transform coefficient derived according to the residual information to derive the transform coefficient, and the inverse transformer 230 of the residual processor can perform an inverse transform on the transform coefficient to derive the residual sample of the current block. Step S1350 can be performed by the adder 235 or the reconstructor.

[0189] Refer to Fig.12 and Fig.13 The image decoding apparatus may determine a prediction mode of the current block based on the received prediction information (S1210). The image decoding apparatus may determine which inter-frame prediction mode is applicable to the current block based on the prediction mode information in the prediction information.

[0190] For example, it may be determined whether the skip mode is applicable to the current block based on a skip flag. In addition, it may be determined whether the merge mode or the MVP mode is applicable to the current block based on a merge flag. Alternatively, one of various inter-frame prediction mode candidates may be selected based on a mode index. The inter-frame prediction mode candidate may include a skip mode, a merge mode, and / or an MVP mode or may include various inter-frame prediction modes to be described below.

[0191] The image decoding device may derive motion information of the current block based on the determined inter prediction mode (S1220). For example, when the skip mode or merge mode is applicable to the current block, the image decoding device may construct a merge candidate list to be described below, and select one of the merge candidates included in the merge candidate list. The selection may be performed based on the above-mentioned candidate selection information (merge index). The motion information of the selected merge candidate may be used to derive the motion information of the current block. For example, the motion information of the selected merge candidate may be used as the motion information of the current block.

[0192] As another example, when the MVP mode is applicable to the current block, the image decoding device may construct an MVP candidate list, and use the motion vector of the MVP candidate selected from the MVP candidates included in the MVP candidate list as the MVP of the current block. The selection may be performed based on the above-mentioned candidate selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the MVP and MVD of the current block. In addition, the reference picture index of the current block may be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list of the current block may be derived as a reference picture referenced for inter-frame prediction of the current block.

[0193] The image decoding apparatus may generate a prediction sample of the current block based on the motion information of the current block (S1230). In this case, a reference picture may be derived based on a reference picture index of the current block, and a sample of the reference block indicated by a motion vector of the current block on the reference picture may be used to derive the prediction sample of the current block. In some cases, a prediction sample filtering process may also be performed on all or some of the prediction samples of the current block.

[0194] For example, Fig.13 As shown, the inter-frame prediction unit 260 of the image decoding device may include a prediction mode determination unit 261, a motion information derivation unit 262, and a prediction sample derivation unit 263. In the inter-frame prediction unit 260 of the image decoding device, the prediction mode determination unit 261 may determine the prediction mode of the current block based on the received prediction mode information, the motion information derivation unit 262 may derive the motion information (motion vector and / or reference picture index, etc.) of the current block based on the received motion information, and the prediction sample derivation unit 263 may derive the prediction sample of the current block.

[0195] The image decoding device may generate residual samples of the current block based on the received residual information (S1240). The image decoding device may generate reconstructed samples of the current block based on the predicted samples and the residual samples and generate a reconstructed picture based thereon (S1250). Thereafter, the in-loop filtering process is applied to the reconstructed picture as described above.

[0196] As described above, the inter-frame prediction process may include a step of determining an inter-frame prediction mode, a step of deriving motion information according to the determined prediction mode, and a step of performing prediction (generating prediction samples) based on the derived motion information. As described above, the inter-frame prediction process may be performed by an image encoding device and an image decoding device.

[0197] Overview of Intra Block Copy (IBC) Prediction

[0198] Hereinafter, IBC prediction according to the present disclosure will be described.

[0199] IBC prediction can be performed by a prediction unit of an image encoding / decoding device. IBC prediction can be referred to as IBC for short. IBC can be used for content image / video encoding such as screen content coding (SCC). IBC prediction can basically perform IBC prediction in the current picture, but can be performed similarly to inter-frame prediction because the reference block is derived within the current picture. That is, IBC can use at least one of the inter-frame prediction techniques described in the present disclosure. For example, IBC can use at least one of the above-mentioned motion information (motion vector) derivation methods. It can be considered that IBC prediction partially modifies and uses at least one of the inter-frame prediction techniques. IBC can refer to the current picture and can therefore be called a current picture reference (CPR).

[0200] For IBC, the image encoding device may perform block matching (BM) and derive the best block vector (or motion vector) of the current block (or current CU). The derived block vector may be signaled to the image decoding device through the bitstream using a method similar to the signaling of the motion information (motion vector) in the above-mentioned inter-frame prediction. The image decoding device may derive the reference block of the current block in the current picture by the block vector signaled, and derive the prediction signal (prediction block or prediction sample) of the current block by this. Here, the block vector may specify the displacement from the current block to the reference block located in the previously reconstructed area in the current picture. Therefore, the block vector (or motion vector) may be referred to as a displacement vector. Hereinafter, in IBC, the motion vector may correspond to a block vector or a displacement vector. The motion vector of the current block may include a motion vector of a luminance component (luminance motion vector) or a motion vector of a chrominance component (chrominance motion vector). For example, the luminance motion vector of an IBC-encoded CU may be an integer sample unit (ie, integer precision). The chrominance motion vector may be cropped by integer sample units. As described above, IBC may use at least one inter-frame prediction technique, for example, the luma motion vector may be encoded / decoded using the above-described merge mode or MVP mode.

[0201] When the merge mode is applied to the luma IBC block, the merge candidate list of the luma IBC block may be constructed similarly to the merge candidate list in the inter prediction mode. However, unlike the merge candidate list in the inter prediction mode, the merge candidate list of the luma IBC block may not include a temporal candidate block.

[0202] When the MVP mode is applied to the luma IBC block, the mvp candidate list of the luma IBC block can be constructed similarly to the mvp candidate list in the inter prediction mode. However, unlike the mvp candidate list in the inter prediction mode, the merge candidate list of the luma IBC block may not include a temporal candidate block.

[0203] In IBC, the reference block is derived from a previously reconstructed area in the current picture. In this case, in order to reduce the memory consumption and complexity of the image decoding device, a predefined area among only the previously reconstructed areas in the current picture can be referenced. The predefined area may include the current CTU in which the current block is included. By limiting the referenceable reconstruction area to the predefined area, the IBC mode can be implemented in hardware using local on-chip memory.

[0204] An image encoding apparatus for performing IBC may search a predefined area to determine a reference block having a minimum RD cost and derive a motion vector (block vector) based on the positions of the reference block and the current block.

[0205] Prediction mode information about IBC may be signaled at the CU level. For example, flag information specifying whether IBC skip / merge mode is applied to the current block and / or flag information specifying whether IBC AMVP mode is applied to the current block may be signaled through the coding_unit syntax.

[0206] In the case of IBC skip / merge mode, a merge candidate index may be signaled to specify a block vector to be used for prediction of the current luma block among the block vectors included in the merge candidate list. In this case, the merge candidate list may include neighboring blocks encoded by IBC. As described above, the merge candidate list may include spatial merge candidates, but may not include temporal merge candidates. In addition, the merge candidate list may also include history-based motion vector predictor (HMVP) candidates and / or paired candidates.

[0207] In the case of the IBC MVP mode, the block vector difference can be encoded using the same method as the motion vector difference of the above-mentioned inter-frame prediction mode. In the IBC MVP mode, the block vector prediction method can be performed similarly to the MVP mode based on the MVP candidate list including two candidates as predictors. One of the two candidates can be derived from the left neighboring block of the current block, and the other candidate can be derived from the top neighboring block of the current block. In this case, the candidate can only be derived from the corresponding neighboring block when the left neighboring block or the top neighboring block is IBC encoded. If the left neighboring block or the top neighboring block is not available (for example, not IBC encoded), a predetermined default block vector can be included in the MVP candidate list as a predictor. In addition, in the case of the IBC MVP mode, block vector prediction similar to the MVP mode can be performed, so that information (for example, a flag) specifying one of the two block vector predictors is signaled as candidate selection information and used for image decoding. The MVP candidate list may include an HMVP candidate and / or a zero motion vector as a default block vector.

[0208] The HMVP candidate may be referred to as a history-based MVP candidate, and an MVP candidate, a merge candidate, or a block vector candidate used before encoding / decoding of the current block may be stored in the HMVP list as an HMVP candidate. Thereafter, when the merge candidate list or the mvp candidate list of the current block does not include the maximum number of candidates, the candidate stored in the HMVP list may be added as an HMVP candidate to the merge candidate list or the mvp candidate list of the current block.

[0209] The pair of candidates may mean candidates derived by averaging two candidates selected according to a predetermined order from among candidates included in the merge candidate list of the current block.

[0210] Prediction mode information (e.g., pred_mode_ibc_flag) specifying whether IBC is applied to the current block may be signaled at the CU level. For example, pred_mode_ibc_flag may be signaled through a coding_unit syntax. In this case, pred_mode_ibc_flag having a first value (e.g., 0) may specify that IBC is not applied to the current block. Conversely, pred_mode_ibc_flag having a second value (e.g., 1) may specify that IBC is applied to the current block.

[0211] At the same time, IBC may not support merge mode and skip mode. In addition, IBC has no limit on the maximum block size and may not be used for chroma blocks with less than 16 samples.

[0212] As described above, in order to generate a prediction block of the current block, various prediction modes such as an intra prediction mode, an inter prediction mode, or an IBC may be used. The image encoding device may encode predetermined prediction mode information and signal it through a bitstream so as to specify a prediction mode for the current block. In addition, the image decoding device may determine the prediction mode of the current block based on the predetermined prediction mode information obtained from the bitstream. Hereinafter, a method for encoding / decoding the prediction mode information will be described in detail.

[0213] Fig.14 is a view illustrating an example of a coding_unit syntax including prediction mode information, Fig.15 is a view illustrating a prediction mode applicable to a current block according to a slice type and size of the current block.

[0214] First, refer to Fig.14 , the coding_unit syntax may include cu_skip_flag, pred_mode_flag, pred_mode_ibc_flag, and pred_mode_plt_flag as prediction mode information.

[0215] Specifically, cu_skip_flag can specify whether the skip mode is applied to the current block. For example, a cu_skip_flag with a first value (e.g., 0) can specify that the skip mode is not applied to the current block. Conversely, a cu_skip_flag with a second value (e.g., 1) can specify that the skip mode is applied to the current block. In the case where cu_skip_flag has a second value (e.g., 1), when the current slice is a P or B slice, after parsing cu_skip_flag, no syntax elements can be parsed except pred_mode_ibc_flag and merge_data syntax structures. Conversely, in the case where cu_skip_flag has a second value (e.g., 1), when the current slice is an I slice, after parsing cu_skip_flag, no syntax elements can be parsed except merge_idx. In the absence of cu_skip_flag, cu_skip_flag can be inferred to be the first value (e.g., 0).

[0216] pred_mode_flag may specify which of the inter prediction mode and the intra prediction mode is applied to the current block. For example, a pred_mode_flag having a first value (e.g., 0) may specify that the inter prediction mode is applied to the current block. Conversely, a pred_mode_flag having a second value (e.g., 1) may specify that the intra prediction mode is applied to the current block. In the absence of pred_mode_flag, pred_mode_flag may be inferred as follows.

[0217] - First inference condition: When both the width cbWidth and the height cbHeight of the current block are 4, pred_mode_flag is inferred to be the second value (eg, 1).

[0218] - Second inference condition: When the first condition is not satisfied, when the prediction mode type modeType of the current block is MODE_TYPE_INTRA specifying that only intra prediction mode, IBC, and palette mode are available, pred_mode_flag is inferred to be a second value (eg, 1).

[0219] - Third inference condition: In a case where both the first and second conditions are not satisfied, when the prediction mode type modeType of the current block is MODE_TYPE_INTER specifying that only the inter prediction mode is available, pred_mode_flag is inferred to be the first value (eg, 0).

[0220] -Fourth inference condition: When all the first to third conditions are not satisfied, when the slice type slice_type of the current block is an I slice, pred_mode_flag is inferred to be the second value (e.g., 1); when the slice type slice_type of the current block is a P or B slice, pred_mode_flag is inferred to be the first value (e.g., 0).

[0221] pred_mode_ibc_flag may specify whether IBC is applied to the current block. For example, a pred_mode_ibc_flag having a first value (e.g., 0) may specify that IBC is not applied to the current block. Conversely, a pred_mode_ibc_flag having a second value (e.g., 1) may specify that IBC is applied to the current block. When pred_mode_ibc_flag is not present, pred_mode_ibc_flag may be inferred as follows.

[0222] - Fifth inference condition: when cu_skip_flag has the second value (eg, 1) and both the width cbWidth and the height cbHeight of the current block are 4, pred_mode_ibc_flag is inferred to be the second value (eg, 1).

[0223] - Sixth inference condition: In case the fifth inference condition is not satisfied, when cu_skip_flag has the second value (eg, 1) and the prediction mode type modeType of the current block is MODE_TYPE_INTRA, pred_mode_ibc_flag may be inferred to be the second value (eg, 1).

[0224] - Seventh inference condition: In a case where both the fifth and sixth conditions are not satisfied, when the width cbWidth or the height cbHeight of the current block is 128, red_mode_ibc_flag is inferred to be the first value (eg, 0).

[0225] - Eighth inference condition: When all the fifth to seventh conditions are not satisfied, when the prediction mode type modeType of the current block is MODE_TYPE_INTER, pred_mode_ibc_flag is inferred to be the first value (eg, 0).

[0226] - Ninth inference condition: When all the fifth to eighth conditions are not satisfied, when the partition structure treeType of the current block is DUAL_TREE_CHROMA, pred_mode_ibc_flag is inferred to be the first value (eg, 0).

[0227] - Tenth inference condition: In the case where all the fifth to ninth conditions are not satisfied, when the slice type slice_type of the current block is an I slice, pred_mode_ibc_flag is inferred to be the same value as sps_ibc_enabled_flag obtained through a sequence parameter set (SPS), and when the slice type slice_type of the current block is a P or B slice, pred_mode_ibc_flag is inferred to be a first value (e.g., 0). Here, sps_ibc_enabled_flag specifies whether IBC is available at the sequence level. For example, sps_ibc_enabled_flag having a first value (e.g., 0) specifies that IBC is not available, and sps_ibc_enabled_flag having a second value (e.g., 1) specifies that IBC is available.

[0228] pred_mode_plt_flag may specify whether the palette mode is applied to the current block. For example, a pred_mode_plt_flag having a first value (e.g., 0) may specify that the palette mode is not applied to the current block. Conversely, a pred_mode_plt_flag having a second value (e.g., 1) may specify that the palette mode is applied to the current block. In the absence of pred_mode_plt_flag, pred_mode_plt_flag may be inferred to be the first value (e.g., 0).

[0229] At the same time, the above prediction mode information may be signaled based on the size cbWidth×cbHeight of the current block. For example, the signaling conditions 1420, 1430, and 1440 of each of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag may include detailed conditions on whether the size cbWidth×cbHeight of the current block is 4×4. In addition, the signaling conditions 1420, 1440, and 1450 of each of cu_skip_flag, pred_mode_ibc_flag, and pred_mode_plt_flag may include detailed conditions on whether the size cbWidth×cbHeight of the current block is less than or equal to 64×64.

[0230] In addition, the above-mentioned prediction mode information may be signaled based on the prediction mode type modeType of the current block. For example, the signaling conditions 1420 and 1440 of each of cu_skip_flag and pred_mode_ibc_flag may include detailed conditions on whether the prediction mode type modeType of the current block is MODE_TYPE_INTRA. In addition, the signaling condition 1450 of pred_mode_flag may include detailed conditions on whether the prediction mode type modeType of the current block is MODE_TYPE_ALL, which specifies that all prediction modes are available. In addition, the signaling condition 1450 of pred_mode_plt_flag may include detailed conditions on whether the prediction mode type modeType of the current block is MODE_TYPE_INTER, which specifies that only inter-frame prediction is available.

[0231] However, for the current block having a size of 4×4, the inter prediction mode may not be applied, and only the intra prediction mode and the palette mode may be applied. This means that the prediction mode type modeType of the current block having a size of 4×4 is defined only as MODE_TYPE_INTRA. Therefore, when the prediction mode information is signaled by separately determining whether the size cbWidth×cbHeight of the current block is 4×4 and whether the prediction mode type modeType of the current block is MODE_TYPE_INTRA, the signaling conditions become complicated, and the problem of repeatedly determining substantially the same conditions may occur.

[0232] At the same time, the inter prediction mode and IBC can be restrictively applied to the current block. Fig.15, as the case where IBC is available at the sequence level (1510 is "yes") and the slice type slice_type of the current block is not an I slice (1520 is "yes"), when the size CU size of the current block is greater than 64×64 (1540 is "no"), IBC may not be applied to the current block (1561). In addition, as the case where IBC is available at the sequence level (1510 is "yes") and the slice type slice_type of the current block is an I slice (1520 is "no"), when the size CU size of the current block is less than or equal to 64×64 (1550 is "yes"), the inter-frame prediction mode may not be applied to the current block (1571). On the contrary, when the size CU size of the current block is greater than 64×64 (1550 is "no"), both the inter-frame prediction mode and IBC may not be applied to the current block (1572). Meanwhile, when IBC is not available at the sequence level (No at 1510), IBC may not be applied to the current block (1581, 1582). In addition, as a case where IBC is not available at the sequence level (No at 1510), when the slice type slice_type of the current block is an I slice (No at 1530), the inter prediction mode may not be applied to the current block (1582). In this way, only when the slice type slice_type of the current block is not an I slice (No at 1520) and the size CU size of the current block is less than or equal to 64×64 (Yes at 1540), both the inter prediction mode and IBC may be applied to the current block.

[0233] However, as a common signaling condition 1410 of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag, in the case where IBC is available at the sequence level (sps_ibc_enabled_flag == 1), even when the slice type slice_type of the current block is an I slice or the size cbWidth×cbHeight of the current block is greater than 64×64, cu_skip_flag may be signaled according to a separate signaling condition 1420. For example, when the size cbWidth×cbHeight of the current block is not 4×4 and the prediction mode type modeType of the current block is not MODE_TYPE_INTRA, cu_skip_flag may be signaled. According to the signaling condition 1420 of cu_skip_flag, since cu_skip_flag may be signaled even for a current block to which inter-prediction mode and / or IBC may not be applied, transmission bits may be wasted unnecessarily. In addition, when cu_skip_flag having a second value (eg, 1) specifying application of skip mode is signaled for a current block to which inter prediction mode and / or IBC may not be applied, a problem may occur that the current block cannot be decoded.

[0234] To solve the above problem, the prediction mode type modeType of the current block can be reset to MODE_TYPE_INTRA based on at least one of the slice type of the current block or the size of the current block. In addition, based on the reset prediction mode type modeType, the prediction mode information of the current block can be signaled.

[0235] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0236] Example 1

[0237] Fig.16 1 is a view illustrating a coding_unit syntax according to an embodiment of the present disclosure. The prediction mode information (cu_skip_flag, pred_mode_flag, pred_mode_ibc_flag, and pred_mode_plt_flag) included in the coding_unit syntax is referred to above. Fig.14 Description has been made, and its repeated description will be omitted.

[0238] Reference Fig.16, the prediction mode type modeType of the current block may be set as a call input value of the coding_unit syntax. Here, the current block is an application target of the recursively called coding_unit syntax and may correspond to a leaf node of the partition tree structure. In addition, the prediction mode type modeType of the current block may be reset based on the size cbWidth×cbHeight of the current block (1610). For example, the prediction mode type modeType of the current block may be reset based on a comparison result of the size cbWidth×cbHeight of the current block with a predetermined reference.

[0239] The reference value may be determined as 4×4, which is a block size available only for intra prediction mode and palette mode, such as Fig.16 As shown. In this case, the prediction mode type modeType of the current block can be reset to MODE_TYPE_INTRA based on whether the size cbWidth×cbHeight of the current block is 4×4. For example, when both the width cbWidth and the height cbHeight of the current block are 4, the prediction mode type modeType of the current block can be reset to MODE_TYPE_INTRA. On the contrary, when at least one of the width cbWidth or the height cbHeight of the current block is not 4, the prediction mode type modeType of the current block can be reset to the calling input value of the coding_unit syntax (i.e., maintain the original value).

[0240] When whether the size cbWidth×cbHeight of the current block is 4×4 is reflected in the prediction mode type modeType, the detailed condition on whether the size cbWidth×cbHeight of the current block is 4×4 may be removed from the signaling conditions 1620, 1630, and 1640 of each of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag. That is, in the case of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag, it is not necessary to separately determine whether the size cbWidth×cbHeight of the current block is 4×4, and it may be signaled based on the prediction mode type modeType. For example, when the prediction mode type modeType of the current block is MODE_TYPE_INTRA, cu_skip_flag and pred_mode_flag are not signaled, and pred_mode_ibc_flag may be signaled according to other detailed conditions.

[0241] In another example, the reference value may be determined to be 64×64, which is the maximum block size available for IBC. In addition, based on whether the size cbWidth×cbHeight of the current block is greater than 64×64, the prediction mode type modeType of the current block may be reset to MODE_TYPE_INTRA. For example, when at least one of the width cbWidth or the height cbHeight of the current block is greater than 64, the prediction mode type modeType of the current block may be reset to MODE_TYPE_INTRA. On the contrary, when both the width cbWidth and the height cbHeight of the current block are less than or equal to 64, the prediction mode type modeType of the current block may be reset to the calling input value of the coding_unit syntax (i.e., maintaining the original value).

[0242] When whether the size cbWidth×cbHeight of the current block is greater than 64×64 is reflected in the prediction mode type modeType, signaling of cu_skip_flag of the current block greater than 64×64 may be restricted based on the prediction mode type modeType (1620). In this case, cu_skip_flag may be inferred to be a first value (eg, 0).

[0243] As described above, according to Embodiment 1 of the present disclosure, since it is not necessary to separately determine whether the size cbWidth×cbHeight of the current block is 4×4 in order to signal the prediction mode information of the current block, the signaling condition of the prediction mode information can be simplified (i.e., the cleaning of the coding_unit syntax). In addition, by resetting the prediction mode type modeType of the current block of 4×4 or greater than 64×64 to MODE_TYPE_INTRA, the signaling of cu_skip_flag can be limited to the current block to which the inter-frame prediction mode and / or IBC may not be applied.

[0244] Example 2

[0245] Fig.17 1 is a view illustrating a coding_unit syntax according to another embodiment of the present disclosure. The prediction mode information (cu_skip_flag, pred_mode_flag, pred_mode_ibc_flag, and pred_mode_plt_flag) included in the coding_unit syntax is referred to above. Fig.14 Described, its repeated description will be omitted.

[0246] Reference Fig.17, the prediction mode type modeType of the current block may be set as the calling input value of the coding_unit syntax. Here, the current block is the application target of the recursively called coding_unit syntax and may correspond to a leaf node of the partition tree structure. In addition, the prediction mode type modeType of the current block may be reset based on the slice type slice_type of the current block and the size cbWidth×cbHeight of the current block (1710). For example, the prediction mode type modeType of the current block may be reset based on whether the slice type slice_type of the current block is an I slice (a first reset condition) and a comparison result of the size cbWidth×cbHeight of the current block with a predetermined reference value (a second reset condition).

[0247] The reference value may be determined as 4×4, which is a block size available only for intra prediction mode and palette mode, such as Fig.17 In this case, when both the width cbWidth and the height cbHeight of the current block are 4, the second reset condition may be true. Conversely, when at least one of the width cbWidth or the height cbHeight of the current block is not 4, the second reset condition may be false.

[0248] In another example, the predetermined reference value may be determined as 64×64, which is the maximum block size available for IBC. In this case, when both the width cbWidth and the height cbHeight of the current block are less than or equal to 64, the second reset condition may be true. Conversely, when at least one of the width cbWidth or the height cbHeight of the current block is greater than 64, the second reset condition may be false.

[0249] The first reset condition and the second reset condition can form an OR condition, such as Fig.16 For example, when at least one of the first reset condition or the second reset condition is true, the prediction mode type modeType of the current block may be reset to MODE_TYPE_INTRA. On the contrary, when both the first reset condition and the second reset condition are false, the prediction mode type modeType of the current block may be reset to the calling input value of the coding_unit syntax. That is, in this case, the prediction mode type modeType of the current block may be maintained as the original value.

[0250] In another example, the first reset condition and the second reset condition may construct an AND condition. For example, when the first reset condition and the second reset condition are true, the prediction mode type modeType of the current block may be reset to MODE_TYPE_INTRA. On the contrary, when at least one of the first reset condition or the second reset condition is false, the prediction mode type modeType of the current block may be reset to the calling input value of the coding_unit syntax. That is, in this case, the prediction mode type modeType of the current block may be maintained as the original value.

[0251] When the slice type slice_type of the current block and the size cbWidth×cbHeight of the current block are reflected in the prediction mode type modeType, the first detailed condition about whether the slice type slice_type of the current block is an I slice and the second detailed condition about whether the size cbWidth×cbHeight of the current block is 4×4 may be removed from the signaling conditions 1720, 1730, and 1740 of each of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag. That is, in the case of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag, the first detailed condition and the second detailed condition do not need to be determined separately, and may be signaled based on the prediction mode type modeType of the current block. For example, when the prediction mode type modeType of the current block is MODE_TYPE_INTRA, cu_skip_flag and pred_mode_flag may not be signaled, and pred_mode_ibc_flag may be signaled according to other detailed conditions. In addition, for a current block to which inter prediction mode and / or IBC may not be applied, signaling of cu_skip_flag and pred_mode_ibc_flag may be limited (1720, 1740). In this case, each of cu_skip_flag and pred_mode_ibc_flag may be inferred to be a first value (eg, 0).

[0252] Meanwhile, when the signaling conditions 1720, 1730, and 1740 of each of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag are simplified, the above reference Fig.14 The semantics of each of the described pred_mode_flag and pred_mode_ibc_flag may be partially changed.

[0253] In the example, refer to Fig.14 Among the first to fourth inference conditions of pred_mode_flag described above, the first inference condition regarding whether the size cbWidth×cbHeight of the current block is 4×4 can be removed. Fig.14 The fifth to tenth inference conditions of pred_mode_ibc_flag described above may be replaced with the following conditions.

[0254] -The eleventh inference condition: pred_mode_ibc_flag is inferred to be the second value (e.g., 1) when i) IBC is available at the sequence level (sps_ibc_enabled_flag == 1), ii) the size cbWidth×cbHeight of the current block is less than 128x128, iii) cu_skip_fla has a first value (e.g., 0), iv) the prediction mode type modeType of the current block is MODE_TYPE_INTRA, and v) the partition structure treeType of the current block is not DUAL_TREE_CHROMA.

[0255] - Twelfth inference condition: When the eleventh inference condition is not satisfied, pred_mode_ibc_flag is inferred to be the first value (eg, 0).

[0256] In another example, referring to Fig.14 The first to fourth inference conditions pred_mode_flag described may remove the first inference condition regarding whether the size cbWidth×cbHeight of the current block is 4×4, and the fourth inference condition may be changed to pred_mode_flag inferred as the first value (eg, 0) regardless of the slice type slice_type of the current block.

[0257] In another example, referring to Fig.14 The fifth to tenth inference conditions pred_mode_flag described may remove the fifth inference condition regarding whether the size cbWidth×cbHeight of the current block is 4×4, and the tenth inference condition may be changed to pred_mode_flag inferred as the first value (eg, 0) regardless of the slice type slice_type of the current block.

[0258] Meanwhile, when the signaling conditions 1720, 1730, and 1740 of each of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag are simplified, the third detailed condition about whether cu_skip_flag has a first value (e.g., 0) and the fourth detailed condition about whether the prediction mode type modeType of the current block is MODE_TYPE_INTER may be removed from the signaling condition 1750 of pred_mode_plt_flag. That is, in the case of pred_mode_plt_flag, the third detailed condition and the fourth detailed condition do not need to be determined separately, and may be signaled according to the value of the variable CuPredMode determined based on pred_mode_flag. Here, CuPredMode specifies the prediction mode of the current block, and may be determined as MODE_INTER or MODE_INTRA based on pred_mode_flag. For example, when pred_mode_flag has a first value (e.g., 0), CuPredMode may be determined as MODE_INTER specifying that the prediction mode of the current block is an inter-prediction mode. In contrast, when pred_mode_flag has the second value (eg, 1), CuPredMode may be determined as MODE_INTRA specifying that the prediction mode of the current block is the intra prediction mode.

[0259] As described above, according to Embodiment 2 of the present disclosure, since it is not necessary to separately determine whether the slice type slice_type of the current block is an I slice and whether the size cbWidth×cbHeight of the current block is 4×4 in order to signal the prediction mode information of the current block, the signaling condition of the prediction mode information can be simplified (i.e., the cleaning of the coding_unit syntax). In addition, by resetting the prediction mode type modeType of the current block of 4×4 or greater than 64×64 belonging to the I slice to MODE_TYPE_INTRA, the signaling of cu_skip_flag can be limited to the current block to which the inter-frame prediction mode and / or IBC may not be applied.

[0260] Example 3

[0261] Fig.18 1 is a view illustrating a coding_unit syntax according to another embodiment of the present disclosure. The prediction mode information (cu_skip_flag, pred_mode_flag, pred_mode_ibc_flag, and pred_mode_plt_flag) included in the coding_unit syntax is referred to above. Fig.14Description has been made, and its repeated description will be omitted.

[0262] Reference Fig.18 , the prediction mode type modeType of the current block can be set to the calling input value of the coding_unit syntax. Here, the current block is the application target of the recursively called coding_unit syntax and can correspond to the leaf node of the partition tree structure. In addition, the prediction mode type modeType of the current block can be reset based on the slice type slice_type of the current block (1810). For example, in the case where the slice type slice_type of the current block is an I slice, the prediction mode type modeType of the current block can be reset to MODE_TYPE_INTRA. On the contrary, in the case where the slice type slice_type of the current block is not an I slice (e.g., a P or B slice), the prediction mode type modeType of the current block can be reset to the calling input value of the coding_unit syntax. That is, in this case, the prediction mode type modeType of the current block can be maintained as the original value.

[0263] Therefore, even in the case where IBC is available at the sequence level (sps_ibc_enabled_flag==1) as the common signaling condition 1820 of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag, when the slice type slice_type of the current block is an I slice, since the prediction mode type modeType is MODE_TYPE_INTRA, the signaling of cu_skip_flag can be limited according to a separate signaling condition 1830.

[0264] Meanwhile, in the example, the reset condition 1810 of the prediction mode type modeType may further include a condition regarding the size cbWidth×cbHeight of the current block. For example, the prediction mode type modeType of the current block may be reset to MODE_TYPE_INTRA based on whether the slice type slice_type of the current block is an I slice and the comparison result of the size cbWidth×cbHeight of the current block with a predetermined reference value. Here, the predetermined reference value may be determined as 4×4 (a block size available only for intra prediction mode and palette mode) or 64×64 (a maximum block size available for IBC). In addition, the condition regarding the slice type slice_type of the current block and the condition regarding the size cbWidth×cbHeight of the current block may construct an OR condition or an AND condition. For example, when the slice type slice_type of the current block is an I slice or at least one of the width cbWidth or height cbHeight of the current block exceeds 64, the prediction mode type modeType of the current block may be reset to MODE_TYPE_INTRA. Alternatively, only when the slice type slice_type of the current block is an I slice and at least one of the width cbWidth or the height cbHeight of the current block exceeds 64, the prediction mode type modeType of the current block may be reset to MODE_TYPE_INTRA.

[0265] As described above, according to Embodiment 3 of the present disclosure, by resetting the prediction mode type modeType of the current block belonging to the I slice to MODE_TYPE_INTRA, the signaling of cu_skip_flag can be limited to the current block to which the inter-frame prediction mode may not be applied. In addition, by resetting the prediction mode type modeType of the current block of 4×4 or greater than 64×64 to MODE_TYPE_INTRA, the signaling of cu_skip_flag can be limited to the current block to which the inter-frame prediction mode and / or IBC may not be applied.

[0266] Example 4

[0267] Fig.19 1 is a view illustrating a coding_unit syntax according to another embodiment of the present disclosure. The prediction mode information (cu_skip_flag, pred_mode_flag, pred_mode_ibc_flag, and pred_mode_plt_flag) included in the coding_unit syntax is referred to above. Fig.14 Description has been made, and its repeated description will be omitted.

[0268] Reference Fig.19 , the prediction mode type modeType of the current block can be set as the calling input value of the coding_unit syntax. Here, the current block is the application target of the recursively called coding_unit syntax and can correspond to the leaf node of the partition tree structure. Unlike the above-mentioned embodiments 1 to 3 of the present disclosure, the reset processing of the prediction mode type modeType can be skipped.

[0269] The signaling condition 1920 of cu_skip_flag may include detailed conditions on whether the slice type slice_type of the current block is an I slice. For example, in the case where the slice type slice_type of the current block is an I slice, cu_skip_flag may not be signaled. On the contrary, in the case where the slice type slice_type of the current block is not an I slice (e.g., a P or B slice), cu_skip_flag may be signaled according to other detailed conditions. That is, cu_skip_flag may be explicitly signaled for a current block belonging to a P or B slice.

[0270] Therefore, even in the case where IBC is available at the sequence level (sps_ibc_enabled_flag==1) as a common signaling condition 1910 of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag, when the slice type slice_type of the current block is an I slice, since the slice type slice_type is an I slice, the signaling of cu_skip_flag can be limited according to a separate signaling condition 1920.

[0271] As described above, according to Embodiment 4 of the present disclosure, signaling of cu_skip_flag may be limited to a current block belonging to an I slice.

[0272] Image Coding Methods

[0273] Hereinafter, a method for encoding an image by an image encoding device will be described in detail based on the above embodiments. The image encoding device may include a memory and at least one processor, and the image encoding method may be executed by the at least one processor.

[0274] Fig. 20 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure.

[0275] Reference Fig. 20, the image encoding device can obtain the current block corresponding to the leaf node of the partition tree structure based on a predetermined prediction mode type (e.g., modeType) (S2010). Here, the predetermined prediction mode type is the prediction mode type of the current block, and can be determined based on the prediction mode characteristic information of the high-level block (e.g., modeTypeCondition). For example, in the case where the prediction mode characteristic information of the high-level block has a first value (e.g., 0), the predetermined prediction mode type can be determined as the prediction mode type of the high-level block. On the contrary, in the case where the prediction mode characteristic information of the high-level block has a second value (e.g., 1), the predetermined prediction mode type can be determined as MODE_TYPE_INTRA. On the contrary, in the case where the prediction mode characteristic information of the high-level block has a third value (e.g., 2), the predetermined prediction mode type can be determined as MODE_TYPE_INTRA or MODE_TYPE_INTER.

[0276] Meanwhile, the prediction mode characteristic information of the high-level block may have any one of first to third values ​​(eg, 0, 1, and 2) based on a predetermined condition.

[0277] Specifically, in a case where at least one of the following conditions 1-1 to 1-4 is satisfied, the prediction mode characteristic information of the high-level block may be determined to be a first value (eg, 0).

[0278] - Condition 1-1: A high-level block is included in an I slice, each CTU included in the corresponding slice is implicitly quadtree-divided into 64×64 luma sample CUs, and the luma sample CU is a root node of the dual tree.

[0279] - Condition 1-2: The prediction mode type (eg, modeTypeCurr) of the high-level block is not MODE_TYPE_ALL.

[0280] - Condition 1-3: The color format of the high-level block is a monochrome format (eg, sps_chroma_format_idc == 0).

[0281] - Condition 1-4: The color format of the high-layer block is the 4:4:4 format (eg, sps_chroma_format_idc == 3).

[0282] In a case where all of the above conditions are not satisfied and at least one of the following conditions 2-1 to 2-3 is satisfied, the prediction mode characteristic information of the high-level block may be determined to be the second value (eg, 1).

[0283] - Condition 2-1: The product of the width and height of the high-level block is 64 and the division mode of the high-level block is the quadtree division mode.

[0284] - Condition 2-2: The product of the width and height of the high-level block is 64 and the division mode of the high-level block is the horizontal ternary division mode or the vertical ternary division mode.

[0285] - Condition 2-3: The product of the width and height of the high-level block is 32 and the division mode of the high-level block is the horizontal binary division mode or the vertical binary division mode.

[0286] When all of the above conditions are not met and at least one of the following conditions 3-1 to 3-4 is met, the prediction mode characteristic information of the high-level block belonging to the I slice can be determined as the second value (e.g., 1), and the prediction mode characteristic information of the high-level block not belonging to the I slice can be determined as the third value (e.g., 2).

[0287] - Condition 3-1: The product of the width and height of the high-level block is 64 and the division mode of the high-level block is the horizontal binary division mode or the vertical binary division mode.

[0288] - Condition 3-2: The product of the width and height of the high-level block is 128 and the division mode of the high-level block is the horizontal ternary division mode or the vertical ternary division mode.

[0289] - Condition 3-3: The width of the high-level block is 8 and the division mode of the high-level block is the vertical binary division mode.

[0290] - Condition 3-4: The width of the high-level block is 16, quadtree partitioning of the high-level block is now allowed (eg, split_qt_flag == 0), and the partitioning mode of the high-level block is the vertical ternary partitioning mode.

[0291] Meanwhile, in the case that all of the above conditions are not satisfied, the prediction mode characteristic information of the high-level block may be determined as the first value (eg, 0).

[0292] The image encoding device may determine the prediction mode type of the current block based on the prediction mode characteristic information of the high-level block determined according to the above conditions. In addition, the image encoding device may obtain the current block by dividing the high-level block based on the determined prediction mode type. For example, when the prediction mode type of the current block is MODE_TYPE_INTRA, the image encoding device may obtain the current block by dividing the high-level block in a dual-tree structure. On the contrary, when the prediction mode type of the current block is not MODE_TYPE_INTRA (e.g., MODE_TYPE ALL or MODE_TYPE_INTER), the image encoding device may obtain the current block by dividing the high-level block according to the division structure of the high-level block.

[0293] The image encoding apparatus may reset the prediction mode type of the current block (S2020).

[0294] In an embodiment, the prediction mode type of the current block may be reset to an intra type (eg, MODE_TYPE_INTRA) based on the size of the current block.

[0295] For example, when at least one of the width or height of the current block is greater than 64, the prediction mode type of the current block may be reset to MODE_TYPE_INTRA. Conversely, when both the width and height of the current block are less than 64, the prediction mode type of the current block may be reset to the calling input value of the coding_unit syntax (i.e., the prediction mode type of S2010). In this way, when whether the size of the current block is greater than 64×64 is reflected in the prediction mode type, for a current block greater than 64×64, the signaling of cu_skip_flag may be limited based on the prediction mode type.

[0296] Alternatively, when both the width and height of the current block are 4, the prediction mode type of the current block may be reset to MODE_TYPE_INTRA. Conversely, when at least one of the width or height of the current block is not 4, the prediction mode type of the current block may be reset to the above-mentioned call input value of the coding_unit syntax (i.e., the prediction mode type of S2010). In this way, when whether the size of the current block is 4×4 is reflected in the prediction mode type, in the case of cu_skip_flag, pred_mode_flag, and pred_mode_ibc_flag, it is not necessary to separately determine whether the size of the current block is 4×4, and it may be signaled based on the prediction mode type.

[0297] In another example, the prediction mode type of the current block can be reset to an intra type (e.g., MODE_TYPE_INTRA) based on the slice type of the current block. For example, in the case where the slice type of the current block is an I slice, the prediction mode type of the current block can be reset to MODE_TYPE_INTRA. On the contrary, in the case where the slice type of the current block is not an I slice (e.g., a P or B slice), the prediction mode type of the current block can be reset to the above-mentioned call input value of the coding_unit syntax (i.e., the prediction mode type of S2010). In this way, when whether the slice type of the current block is an I slice is reflected in the prediction mode type, the signaling of the cu_skip_flag of the current block belonging to the I slice can be limited. For example, as described above with reference to Fig.18As described, when IBC is available at the sequence level (sps_ibc_enabled_flag==1), even when the common signaling condition 1820 of cu_skip_flag, pred_mode_flag and pred_mode_ibc_flag is true, the signaling of cu_skip_flag can be restricted according to a separate signaling condition 1830 when the prediction mode type modeType of the current block is MODE_TYPE_INTRA.

[0298] In another example, the prediction mode type of the current block may be reset to an intra type (e.g., MODE_TYPE_INTRA) based on the slice type of the current block and the size of the current block. For example, when the slice type of the current block is an I slice and at least one of the width or height of the current block is greater than 64, the prediction mode type of the current block may be reset to MODE_TYPE_INTRA. On the contrary, when the slice type of the current block is not an I slice (e.g., a P or B slice) or both the width and height of the current block are less than or equal to 64, the prediction mode type of the current block may be reset to the above-mentioned call input value of the coding_unit syntax (i.e., the prediction mode type of S2010). In this way, when whether the slice type of the current block is an I slice and whether the size of the current block exceeds 64×64 is reflected in the prediction mode type, the signaling of cu_skip_flag may be limited to the current block to which the inter prediction mode and / or IBC may not be applied.

[0299] The image encoding device may encode the prediction mode information of the current block based on the prediction mode type reset according to the above method (S2030). Here, the prediction mode information of the current block may include cu_skip_flag specifying whether to apply the skip mode, pred_mode_flag specifying whether to apply the intra prediction mode or the inter prediction mode, pred_mode_ibc_flag specifying whether to apply the IBC, and pred_mode_plt_flag specifying whether to apply the palette mode. The details of the above prediction mode information are described above. Figures 14 to 19 Described.

[0300] As described above, according to the image encoding method of the embodiment of the present disclosure, the prediction mode type of the current block can be reset to a predetermined prediction mode type (e.g., MODE_TYPE_INTRA) based on at least one of the slice type or size of the current block. In addition, the prediction mode information of the current block can be encoded based on the reset prediction mode type. Therefore, the signaling condition of the prediction mode information can be simplified, and the signaling of cu_skip_flag can be limited to the current block to which the inter-frame prediction mode and / or IBC may not be applied.

[0301] Image decoding method

[0302] Hereinafter, a method for decoding an image by an image decoding device will be described in detail based on the above embodiments. The image decoding device may include a memory and at least one processor, and the image decoding method may be executed by the at least one processor.

[0303] Fig.21 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure.

[0304] Reference Fig.21 , the image decoding device can obtain the current block corresponding to the leaf node of the partition tree structure based on a predetermined prediction mode type (e.g., modeType) (S2110). Here, the predetermined prediction mode type is the prediction mode type of the current block and can be determined based on the prediction mode characteristic information of the high-level block (e.g., modeTypeCondition). For example, in a case where the prediction mode characteristic information of the high-level block has a first value (e.g., 0), the predetermined prediction mode type can be determined as the prediction mode type of the high-level block. On the contrary, in a case where the prediction mode characteristic information of the high-level block has a second value (e.g., 1), the predetermined prediction mode type can be determined as MODE_TYPE_INTRA. On the contrary, in a case where the prediction mode characteristic information of the high-level block has a third value (e.g., 2), the predetermined prediction mode type can be determined as MODE_TYPE_INTRA or MODE_TYPE_INTER. At the same time, the prediction mode characteristic information of the high-level block can have any one of the first to third values ​​(e.g., 0, 1, and 2) based on a predetermined condition, and the predetermined condition is referred to above. Fig. 20 Described.

[0305] In this way, the image decoding device can determine the prediction mode type of the current block based on the prediction mode characteristic information of the high-level block. In addition, the image decoding device can obtain the current block by dividing the high-level block based on the determined prediction mode type. For example, when the prediction mode type of the current block is MODE_TYPE_INTRA, the image decoding device can obtain the current block by dividing the high-level block in a dual tree structure. On the contrary, when the prediction mode type of the current block is not MODE_TYPE_INTRA (for example, MODE_TYPE ALL or MODE_TYPE_INTER), the image decoding device can obtain the current block by dividing the high-level block according to the division structure of the high-level block.

[0306] The image decoding apparatus may reset the prediction mode type of the current block (S2120).

[0307] In an embodiment, the prediction mode type of the current block may be reset to an intra type (eg, MODE_TYPE_INTRA) based on the size of the current block.

[0308] For example, when at least one of the width or height of the current block is greater than 64, the prediction mode type of the current block may be reset to MODE_TYPE_INTRA. On the contrary, when both the width and height of the current block are less than 64, the prediction mode type of the current block may be reset to the calling input value of the coding_unit syntax (i.e., the prediction mode type of S2110). Alternatively, when both the width and height of the current block are 4, the prediction mode type of the current block may be reset to MODE_TYPE_INTRA. On the contrary, when at least one of the width or height of the current block is not 4, the prediction mode type of the current block may be reset to the above-mentioned calling input value of the coding_unit syntax (i.e., the prediction mode type of S2110).

[0309] In another example, the prediction mode type of the current block may be reset to a predetermined prediction mode type (e.g., MODE_TYPE_INTRA) based on the slice type of the current block. For example, when the slice type of the current block is an I slice, the prediction mode type of the current block may be reset to MODE_TYPE_INTRA. On the contrary, when the slice type of the current block is not an I slice (e.g., a P or B slice), the prediction mode type of the current block may be reset to the above-mentioned call input value of the coding_unit syntax (i.e., the prediction mode type of S2110).

[0310] In another example, the prediction mode type of the current block may be reset to a predetermined prediction mode type (e.g., MODE_TYPE_INTRA) based on the slice type of the current block and the size of the current block. For example, when the slice type of the current block is an I slice and at least one of the width or height of the current block is greater than 64, the prediction mode type of the current block may be reset to MODE_TYPE_INTRA. On the contrary, when the slice type of the current block is not an I slice (e.g., a P or B slice) or both the width and height of the current block are less than or equal to 64, the prediction mode type of the current block may be reset to the above-mentioned call input value of the coding_unit syntax (i.e., the prediction mode type of S2110).

[0311] The image decoding device can obtain the prediction mode information of the current block based on the prediction mode type reset according to the above method (S2130). For example, the image decoding device can obtain the prediction mode information of the current block by parsing the coding_unit syntax included in the bitstream based on the reset prediction mode type. Here, the prediction mode information of the current block may include cu_skip_flag specifying whether to apply the skip mode, pred_mode_flag specifying whether to apply the intra-frame prediction mode or the inter-frame prediction mode, pred_mode_ibc_flag specifying whether to apply IBC, and pred_mode_plt_flag specifying whether to apply the palette mode. The details of the above prediction mode information refer to the above. Figures 14 to 19 Described.

[0312] The image decoding device may generate a prediction block of the current block based on the prediction mode information of the current block (S2140). Specifically, the image decoding device may determine the prediction mode of the current block based on the prediction mode information of the current block. In addition, the image decoding device may generate a prediction block of the current block by performing prediction based on the determined prediction mode.

[0313] As described above, according to the image decoding method of the embodiment of the present disclosure, the prediction mode type of the current block can be reset to a predetermined prediction mode type (e.g., MODE_TYPE_INTRA) based on at least one of the slice type or size of the current block. In addition, the prediction mode information of the current block can be obtained based on the reset prediction mode type. Therefore, the parsing condition of the prediction mode information can be simplified, and for the current block to which the inter-frame prediction mode and / or IBC may not be applied, cu_skip_fla can be inferred to be a first value (e.g., 0) without decoding.

[0314] Although the exemplary method of the present disclosure described above is represented as a series of operations for the sake of clarity of description, it is not intended to limit the order of executing the steps, and these steps can be performed simultaneously or in different orders when necessary. In order to implement the method according to the present disclosure, the steps described may further include other steps, may include the remaining steps except some steps, or may include other additional steps except some steps.

[0315] In the present disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) may perform an operation (step) of confirming an execution condition or situation of the corresponding operation (step). For example, if it is described that a predetermined operation is performed when a predetermined condition is met, the image encoding device or the image decoding device may perform the predetermined operation after determining whether the predetermined condition is met.

[0316] The various embodiments of the present disclosure are not a list of all possible combinations and are intended to describe representative aspects of the present disclosure, and matters described in the various embodiments may be applied independently or in combination of two or more.

[0317] Various embodiments of the present disclosure may be implemented in hardware, firmware, software or a combination thereof. In the case of implementing the present disclosure in hardware, the present disclosure may be implemented in an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a general purpose processor, a controller, a microcontroller, a microprocessor, etc.

[0318] In addition, the image decoding device and the image encoding device of the embodiment of the present disclosure can be included in multimedia broadcast transmission and reception equipment, mobile communication terminals, home theater video equipment, digital theater video equipment, surveillance cameras, video chat equipment, real-time communication equipment such as video communication, mobile streaming equipment, storage media, cameras, video on demand (VoD) service providing equipment, OTT video (over the top video) equipment, Internet streaming service providing equipment, three-dimensional (3D) video equipment, video phone video equipment, medical video equipment, etc., and can be used to process video signals or data signals. For example, OTT video equipment can include game consoles, Blu-ray players, Internet access TVs, home theater systems, smart phones, tablet PCs, digital video recorders (DVRs), etc.

[0319] Fig. 22 is a view showing a content streaming system to which an embodiment of the present disclosure can be applied.

[0320] like Fig. 22 As shown in , a content streaming transmission system to which an embodiment of the present disclosure is applied may mainly include an encoding server, a streaming transmission server, a network server, a media storage, a user device, and a multimedia input device.

[0321] The encoding server compresses the content input from a multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream and sends the bitstream to the streaming server. As another example, when a multimedia input device such as a smartphone, camera, camcorder, etc. directly generates a bitstream, the encoding server can be omitted.

[0322] A bitstream may be generated by applying the image encoding method or the image encoding device according to the embodiment of the present disclosure, and a streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0323] The streaming server sends multimedia data to the user device based on the user's request through the network server, and the network server serves as a medium to notify the user of the service. When the user requests the required service from the network server, the network server can deliver it to the streaming server, and the streaming server can send the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server serves as a command / response between devices in the control content streaming system.

[0324] The streaming server may receive content from a media storage and / or encoding server. For example, when content is received from an encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.

[0325] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, tablet PCs, tablet computers, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0326] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0327] The scope of the present disclosure includes software or executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling operations according to the methods of various embodiments to be performed on a device or computer, and a non-transitory computer-readable medium having such software or commands stored thereon and executable on a device or computer.

[0328] Industrial Applicability

[0329] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising the following steps: obtaining a current block corresponding to a leaf node of the partition tree structure based on a predetermined prediction mode type; Determine the prediction mode type of the current block as the intra-frame type MODE_TYPE_INTRA or the predetermined prediction mode type; Obtaining prediction mode information of the current block based on the determined prediction mode type; as well as generating a prediction block of the current block based on the obtained prediction mode information, wherein the step of determining the prediction mode type of the current block is performed based on the slice type and size of the current block, and The current block is obtained by dividing the block into four blocks having the same size as each other.

2. The image decoding method according to claim 1, wherein: Based on the fact that the slice type of the current block is an I slice and at least one of a width or a height of the current block is greater than 64, the prediction mode type of the current block is determined to be the intra type MODE_TYPE_INTRA.

3. The image decoding method according to claim 1, wherein: Based on whether the slice type of the current block is a P or B slice, the prediction mode type of the current block is determined to be the predetermined prediction mode type.

4. The image decoding method according to claim 1, wherein: Based on the width and height of the current block being less than or equal to 64, the prediction mode type of the current block is determined to be the predetermined prediction mode type.

5. The image decoding method according to claim 1, wherein: Based on the determined prediction mode type being the intra type MODE_TYPE_INTRA, the prediction mode information does not include information on a skip mode.

6. The image decoding method according to claim 5, wherein: The information about the skip mode is inferred to be a first value specifying that the skip mode is not applied to the current block.

7. The image decoding method according to claim 1, wherein: The predetermined prediction mode type is determined based on prediction mode characteristic information of a high-level block of the current block.

8. The image decoding method according to claim 1, wherein: The current block is obtained by determining a division structure based on the predetermined prediction mode type and dividing a high-level block of the current block based on the determined division structure.

9. The image decoding method according to claim 8, wherein: Based on the predetermined prediction mode type being the intra type MODE_TYPE_INTRA, the partition structure is determined to be a dual tree structure.

10. The image decoding method according to claim 8, wherein: Based on the fact that the predetermined prediction mode type is not the intra type MODE_TYPE_INTRA, the division structure is determined to be the same structure as that of the high-level block.

11. An image encoding method performed by an image encoding device, the image encoding method comprising the following steps: obtaining a current block corresponding to a leaf node of the partition tree structure based on a predetermined prediction mode type; Determine the prediction mode type of the current block as the intra-frame type MODE_TYPE_INTRA or the predetermined prediction mode type; as well as encoding prediction mode information of the current block based on the determined prediction mode type, wherein the step of determining the prediction mode type of the current block is performed based on the slice type and size of the current block, and The current block is obtained by dividing the block into four blocks having the same size as each other.

12. The image encoding method according to claim 11, wherein: Based on the slice type of the current block being an I slice and at least one of a width or a height of the current block being greater than 64, the prediction mode type of the current block is determined to be the intra type MODE_TYPE_INTRA.

13. The image encoding method according to claim 11, wherein: Based on the determined prediction mode type being the intra type MODE_TYPE_INTRA, the prediction mode information does not include information on a skip mode.

14. A method for transmitting a bit stream generated by an image encoding method, the image encoding method comprising the steps of: obtaining a current block corresponding to a leaf node of the partition tree structure based on a predetermined prediction mode type; Determine the prediction mode type of the current block as the intra-frame type MODE_TYPE_INTRA or the predetermined prediction mode type; as well as encoding prediction mode information of the current block based on the determined prediction mode type, wherein the step of determining the prediction mode type of the current block is performed based on the slice type and size of the current block, and The current block is obtained by dividing the block into four blocks having the same size as each other.

Images