Image encoding / decoding apparatus and apparatus for transmitting data of image

Abstract

The application relates to an image encoding / decoding apparatus and an apparatus for transmitting data of an image. An image decoding method according to the present document comprises the steps of: decoding a current block on the basis of image information, in which an MVP candidate list of the current block is derived on the basis of an inter prediction mode derived on the basis of image information and peripheral blocks of the current block; and deriving motion information of the current block based on the MVP candidate list, in which the peripheral blocks include a lower left corner peripheral block, a left peripheral block, an upper right corner peripheral block, an upper peripheral block, and an upper left corner peripheral block of the current block, the motion information including an L0 motion vector for L0 prediction and / or an L1 motion vector for L1 prediction, the L0 motion vector is derived based on the L0 motion vector predictor and the L0 motion vector difference, and the L1 motion vector is derived based on the L1 motion vector predictor and the L1 motion vector difference.

Description

[0001] This application is a divisional application of the invention patent application with the original application number 202080050204.X (international application number: PCT / KR2020 / 007744, application date: June 15, 2020, invention name: Image / video encoding method and device based on motion vector prediction). Technical Field

[0002] The present document relates to an image / video encoding method based on motion vector prediction and a device used for the method. Background Art

[0003] Recently, there is an increasing demand for high-resolution, high-quality images / videos such as 4K or 8K ultra-high definition (UHD) images / videos in various fields. As the image / video resolution or quality becomes higher, relatively more information or bits are transmitted compared to conventional image / video data. Therefore, if the image / video data is transmitted via a medium such as an existing wired / wireless broadband line or is stored in a conventional storage medium, the cost of transmission and storage is easily increased.

[0004] In addition, there is growing interest and demand for virtual reality (VR) and artificial reality (AR) content and immersive media such as holograms; and there is also growing broadcasting of images / videos that exhibit image / video characteristics that are different from actual images / videos (e.g., game images / videos).

[0005] Therefore, highly efficient image / video compression technology is required to effectively compress and transmit, store, or play high-resolution, high-quality images / videos showing various characteristics as described above. Summary of the invention

[0006] Technical Solution

[0007] According to the embodiments of this document, a method and apparatus for improving image / video encoding efficiency are provided.

[0008] According to an embodiment of this document, a method and apparatus for efficiently performing inter-frame prediction in an image / video encoding system are provided.

[0009] According to an embodiment of this document, a method and apparatus for performing inter-frame prediction based on motion vector prediction are provided.

[0010] According to an embodiment of this document, a method and apparatus for signaling information about a motion vector difference in inter-frame prediction are provided.

[0011] According to an embodiment of this document, a method and apparatus for signaling prediction-related information when bidirectional prediction is applied to a current block are provided.

[0012] According to an embodiment of this document, a method and apparatus for signaling an L1 motion vector difference zero flag and / or an SMVD flag are provided.

[0013] According to an embodiment of this document, a video / image decoding method performed by a decoding device is provided.

[0014] According to an embodiment of this document, a decoding device for performing video / image decoding is provided.

[0015] According to an embodiment of this document, a video / image encoding method performed by an encoding device is provided.

[0016] According to an embodiment of this document, an encoding device for performing video / image encoding is provided.

[0017] According to an embodiment of the present document, a computer-readable digital storage medium is provided that stores encoded video / image information generated according to a video / image encoding method disclosed in at least one of the embodiments of the present document.

[0018] According to an embodiment of the present document, there is provided a computer-readable digital storage medium storing encoding information or encoded video / image information for causing a decoding device to perform a video / image decoding method disclosed in at least one of the embodiments of the present document.

[0019] Technical Effects

[0020] According to this document, the overall image / video compression efficiency can be improved.

[0021] According to this document, information about motion vector differences can be efficiently signaled.

[0022] According to this document, when bidirectional prediction is applied to a current block, an L1 motion vector difference can be efficiently derived.

[0023] According to this document, the complexity of the encoding system can be reduced by efficiently signaling information for deriving the L1 motion vector difference.

[0024] According to this document, bit waste that may occur in information signaling about inter-frame prediction modes can be avoided, and overall coding efficiency can be improved.

[0025] The effects that can be obtained through the detailed examples of this document are not limited to the effects listed above. For example, there may be various technical effects that a person of ordinary skill in the relevant field can understand or derive from this document. Therefore, the detailed effects of this document are not limited to the effects clearly set forth in this document, but may include various effects that can be understood or derived from the technical features of this document. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 An example of a video / image encoding system to which this document is applicable is schematically illustrated.

[0027] Figure 2 is a diagram schematically illustrating the configuration of a video / image encoding device to which this document is applied.

[0028] Figure 3 is a diagram schematically illustrating the configuration of a video / image decoding device to which this document is applied.

[0029] Figure 4 An example of video / image encoding based on inter-frame prediction is shown.

[0030] Figure 5 An example of a video / image decoding method based on inter-frame prediction is shown.

[0031] Figure 6 The inter-frame prediction process is exemplarily shown.

[0032] Figure 7 The spatial neighboring blocks used to derive motion information candidates in the MVP mode are exemplarily shown.

[0033] Figure 8 The method for constructing an MVP candidate list according to this document is schematically represented.

[0034] Fig. 9 is a diagram for explaining symmetric MVD.

[0035] Fig.10 and Fig.11 An example of a video / image encoding method and related components according to an embodiment of the present document is schematically shown.

[0036] Fig.12 and Fig.13 An example of a video / image decoding method and related components according to an embodiment of this document is schematically shown.

[0037] Fig.14 An example of a content streaming system to which the embodiments disclosed in this document can be applied is shown. DETAILED DESCRIPTION

[0038] The disclosure of this document can be modified in various forms, and its specific embodiments will be described and illustrated in the accompanying drawings. However, these embodiments are not intended to limit the present disclosure. The terms used in the following description are used to describe only specific embodiments, and are not intended to limit the embodiments of this document. The singular expression includes the plural expression, as long as it is clearly read out differently. Terms such as "including" and "having" are intended to indicate the presence of features, numbers, steps, operations, elements, parts or combinations thereof used in this document, so it should be understood that there is no possibility of excluding the presence or addition of one or more different features, numbers, steps, operations, elements, parts or combinations thereof.

[0039] In addition, each configuration of the drawings described in this document is an independent illustration for explaining the functions of features that are different from each other, and does not mean that each configuration is implemented by different hardware or different software. For example, two or more of the configurations can be combined to form one configuration, and one configuration can also be divided into multiple configurations. Implementations of combined and / or separated configurations are included in the scope of the disclosure of this document.

[0040] This document relates to video / image coding. For example, the methods / implementations disclosed in this document may relate to the Versatile Video Coding (VVC) standard. In addition, the methods / implementations disclosed in this document may relate to the Basic Video Coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the second generation audio video coding standard (AVS2), or the next generation video / image coding standard (e.g., H.267 or H.268, etc.).

[0041] This document proposes various embodiments of video / image coding, and unless otherwise specified, the above embodiments may also be performed in combination with each other.

[0042] Hereinafter, embodiments of the present document will be described with reference to the accompanying drawings. Hereinafter, the same reference numerals may be used for the same components in the accompanying drawings, and repeated description of the same components may be omitted.

[0043] Figure 1 An example of a video / image encoding system to which embodiments of this document can be applied is illustrated.

[0044] Reference Figure 1 The video / image coding system may include a first device (source device) and a second device (receiving device). The source device may send the coded video / image information or data to the receiving device in the form of a file or stream transmission via a digital storage medium or a network.

[0045] The source device may include a video source, an encoding device, and a transmitter. The receiving device may include a receiver, a decoding device, and a renderer. The encoding device may be referred to as a video / image encoding device, and the decoding device may be referred to as a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display, and the display may be configured as a separate device or an external component.

[0046] The video source may acquire the video / image by capturing, synthesizing or generating a video / image process. The video source may include a video / image capturing device, and / or a video / image generating device. For example, the video / image capturing device may include one or more cameras, a video / image archive including previously captured videos / images, etc. For example, the video / image generating device may include a computer, a tablet computer, and a smart phone, and may generate the video / image (electronically). For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process that generates relevant data.

[0047] The encoding device can encode the input video / image. For compression and encoding efficiency, the encoding device can perform a series of processes such as prediction, transformation and quantization. The encoded data (encoded video / image information) can be output in the form of a bit stream.

[0048] The transmitter may transmit the encoded image / image information or data output in the form of a bit stream to a receiver of a receiving device in the form of a file or stream via 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 may include an element for generating a media file in a predetermined file format, and may include an element for transmission via a broadcast / communication network. The receiver may receive / extract a bit stream and transmit the received bit stream to a decoding device.

[0049] The decoding device may decode a video / image by performing a series of processes corresponding to the operations of the encoding device, such as inverse quantization, inverse transformation, and prediction.

[0050] The renderer may render the decoded video / image. The rendered video / image may be displayed through a display.

[0051] In this document, video may refer to a series of images over time. A picture generally refers to a unit representing an image at a specific time frame, and a slice / tile refers to a unit that constitutes a part of a picture from the perspective of coding. A slice / tile may include one or more coding tree units (CTUs). A picture may be composed of one or more slices / tiles. A tile is a rectangular area of ​​a CTU within a specific tile column and a specific tile row in a picture. A tile column is a rectangular area of ​​a CTU whose height is equal to the height of the picture and whose width is specified by a syntax element in a picture parameter set. A tile row is a rectangular area of ​​a CTU whose height is specified by a syntax element in a picture parameter set and whose width is equal to the width of the picture. Tile scanning is a specific ordering of CTUs of the following partitioned pictures: CTUs are continuously sorted in a tile by a CTU raster scan, and tiles in a picture are continuously sorted by a raster scan of tiles of a picture. A slice includes an integer number of complete tiles of a picture that can be exclusively contained in a single NAL unit or an integer number of continuous complete CTU rows within a tile.

[0052] In addition, a picture can be divided into two or more sub-pictures. A sub-picture can be a rectangular area of ​​one or more slices within a picture.

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

[0054] A unit may represent a basic unit of image processing. A unit may include at least one of a specific area of ​​a picture and information related to the area. A unit may include a luminance block and two chrominance (e.g., cb, cr) blocks. In some cases, a unit may be used interchangeably with terms such as a block or an 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. Alternatively, a sample may mean a pixel value in a spatial domain, and when such a pixel value is transformed into a frequency domain, it may mean a transform coefficient in a frequency domain.

[0055] In this document, the term "A or B" may mean "only A", "only B", or "both A and B". In other words, "A or B" in this document may be interpreted as "A and / or B". For example, it should be interpreted as indicating "and / or". For example, in this document, "A, B, or C" may mean "only A", "only B", "only C", or "any combination of A, B, and C".

[0056] In this document, the terms " / " and "," may mean "and / or". For example, the expression "A / B" may mean "A and / or B". Thus, "A / B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B, or C".

[0057] In this document, "at least one of A and B" may mean "only A", "only B", or "both A and B". In addition, in this document, the expression "at least one of A or B" or "at least one of A and / or B" may be interpreted as the same as "at least one of A and B".

[0058] In addition, in this document, "at least one of A, B, and C" may mean "only A", "only B", "only C", or "any combination of A, B, and C". In addition, "at least one of A, B, or C" or "at least one of A, B and / or C" may mean "at least one of A, B, and C".

[0059] In addition, brackets used in this document may mean "for example". Specifically, in the case of expressing "prediction (intra-frame prediction)", it may indicate that "intra-frame prediction" is proposed as an example of "prediction". In other words, the term "prediction" in this document is not limited to "intra-frame prediction", and it may indicate that "intra-frame prediction" is proposed as an example of "prediction". In addition, even in the case of expressing "prediction (i.e., intra-frame prediction)", it may indicate that "intra-frame prediction" is proposed as an example of "prediction".

[0060] In this document, technical features independently described in one drawing may be implemented independently or may be implemented simultaneously.

[0061] Figure 2 Schematic diagram of the configuration of a video / image encoding device to which the embodiments of the present document can be applied. Hereinafter, the so-called encoding device may include an image encoding device and / or a video encoding device. In addition, the so-called image encoding method / device may include a video encoding method / device. Alternatively, the so-called video encoding method / device may include an image encoding method / device.

[0062] Reference Figure 2, the encoding device 200 includes an image segmenter 210, a predictor 220, a residual processor 230 and an entropy encoder 240, an adder 250, a filter 260 and a memory 270. The predictor 220 may include an inter-frame predictor 221 and an intra-frame predictor 222. The residual processor 230 may include a transformer 232, a quantizer 233, an inverse quantizer 234 and an inverse transformer 235. The residual processor 230 may also include a subtractor 231. The adder 250 may be referred to as a reconstructor or a reconstructed block generator. According to an embodiment, the image segmenter 210, the predictor 220, the residual processor 230, the entropy encoder 240, the adder 250 and the filter 260 may be configured by at least one hardware component (e.g., an encoder chipset or processor). In addition, the memory 270 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium. The hardware component may also include the memory 270 as an internal / external component.

[0063] The image divider 210 may divide the input image (or picture or frame) input to the encoding device 200 into one or more processors. For example, the processor may be referred to as a coding unit (CU). In this case, the coding unit may be recursively divided from a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QTBTTT) structure. For example, one coding unit may be divided into a plurality of coding units with a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary structure. In this case, for example, a quadtree structure may be applied first, and a binary tree structure and / or a ternary structure may be applied later. Alternatively, a binary tree structure may be applied first. The encoding process according to the present disclosure may be performed based on a final coding unit that is no longer divided. In this case, the maximum coding unit may be used as the final coding unit based on coding efficiency, etc. according to image characteristics, or if necessary, the coding unit may be recursively divided into coding units with a deeper depth and a coding unit with an optimal size may be used as the final coding unit. Here, the encoding process may include a process of prediction, transformation, and reconstruction (to be described later). As another example, the processor may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be split or divided from the above-mentioned final coding unit. The prediction unit may be a unit for sample prediction, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0064] In some cases, a unit may be used interchangeably with terms such as a block or region. In general, an M×N block may represent a set of samples or transform coefficients consisting of M columns and N rows. A sample may generally represent a pixel or a pixel value, and may represent only a pixel / pixel value of a luma component or only a pixel / pixel value of a chroma component. A sample may be used as a term corresponding to one picture (or image) of a pixel or a pixel element.

[0065] The encoding device 200 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 inter predictor 221 or the intra predictor 222 from the input image signal (original block or original sample array), and the generated residual signal is transmitted to the transformer 232. In this case, as shown, the unit for subtracting the prediction signal (prediction block or prediction sample array) from the input image signal (original block or original sample array) in the encoding device 200 can be referred to as a subtractor 231. The predictor can perform prediction on the processing target block (hereinafter, referred to as "current block") and generate a prediction block including the prediction sample of the current block. The predictor can determine whether to apply intra prediction or inter prediction to the current block or in units of CUs. As described later in the description of each prediction mode, the predictor can generate various types of information related to prediction such as prediction mode information, and transmit the generated information to the entropy encoder 240. Information about the prediction can be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0066] The intra-frame predictor 222 may predict the current block with reference to samples in the current picture. Depending on the prediction mode, the referenced samples may be located near the current block or may be spaced apart. In intra-frame prediction, the prediction mode may include multiple non-directional modes and multiple directional modes. For example, the non-directional mode may include a DC mode and a plane mode. For example, depending on the level of detail of the prediction direction, the directional mode may include 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 depending on the settings. The intra-frame predictor 222 may use the prediction mode applied to the neighboring blocks to determine the prediction mode applied to the current block.

[0067] The inter-frame predictor 221 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. Here, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter-frame predictor 221 may configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame predictor 221 may use the motion information of the neighboring block as the motion information of the current block. In the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of the 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 indicated by signaling the motion vector difference.

[0068] The predictor 220 may generate a prediction signal based on various prediction methods described below. For example, the predictor may not only apply intra prediction or inter prediction to predict a block, but may also apply both intra prediction and inter prediction at the same time. This may be referred to as a combination of inter and intra prediction (CIIP). In addition, the predictor may predict a block based on an intra-block copy (IBC) prediction mode or based on a palette mode. The IBC prediction mode or the palette mode may be used for content image / motion image encoding of games, etc., such as screen content coding (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction in terms of reference blocks being derived in the current picture. That is, IBC may use at least one of the inter prediction techniques described in this document. The palette mode may be considered an example of intra coding or intra prediction. When the palette mode is applied, the sample values ​​in the picture may be signaled based on information about the palette table and the palette index.

[0069] The prediction signal generated by the predictor (including the inter-frame predictor 221 and / or the intra-frame predictor 222) can be used to generate a reconstruction signal or to generate a residual signal. The transformer 232 can generate a transform coefficient 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 graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT means a transform obtained from a curve graph when the relationship information between pixels is represented by a curve graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process can be applied to square pixel blocks of the same size, or can be applied to blocks of variable size rather than square.

[0070] The quantizer 233 may quantize the transform coefficients and send them to the entropy encoder 240, and the entropy encoder 240 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 233 may rearrange the quantized transform coefficients of the block type into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoder 240 may perform various encoding methods such as (for example) exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 240 may encode the information necessary for video / image reconstruction together with the quantized transform coefficients (for example, the value of the syntax element, etc.) or separately. The encoding information (for example, the encoded image / video information) may be transmitted or stored in the form of a bitstream in units of a network abstraction layer (NAL). The image / video information may also include information about various parameter sets such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the image / video information may also include conventional constraint information. In this document, information and / or syntax elements transmitted / signaled to a decoding device from an encoding device may be included in the image / video information. The image / video information may be encoded by the above encoding process and may be included in a bitstream. The bitstream may be sent over a network or may be stored in a digital storage medium. Here, 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 illustrated) that transmits a signal output from the entropy encoder 240 or a storage unit (not illustrated) that stores the signal may be configured as an internal / external element of the encoding device 200, and alternatively, the transmitter may be included in the entropy encoder 240.

[0071] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, the residual signal (residual block or residual sample) can be reconstructed by applying inverse quantization and inverse transformation to the quantized transform coefficients via the inverse quantizer 234 and the inverse transformer 235. The adder 250 adds the reconstructed residual signal to the prediction signal output from the inter-frame predictor 221 or the intra-frame predictor 222 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If there is no residual of the processing target block (such as, when the skip mode is applied), the prediction block can be used as a reconstructed block. The adder 250 can be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next processing target block in the current picture, and as described below, can be used for inter-frame prediction of the next picture performed by filtering.

[0072] Furthermore, luminance mapping with chroma scaling (LMCS) may be applied during the picture encoding and / or reconstruction process.

[0073] The filter 260 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 260 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 270, specifically, in the DPB of the memory 270. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filter 260 can generate various types of information related to filtering, and transmit the generated information to the entropy encoder 290, as described later when each filtering method is described. The information related to filtering can be encoded by the entropy encoder 290 and output in the form of a bit stream.

[0074] The modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter predictor 221. When inter prediction is applied by the encoding device, prediction mismatch between the encoding device 200 and the decoding device may be avoided, and encoding efficiency may be improved.

[0075] The DPB of the memory 270 may store the modified reconstructed picture for use as a reference picture in the inter-frame predictor 221. The memory 270 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 block in the reconstructed picture. The stored motion information may be transmitted to the inter-frame predictor 221 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 270 may store the reconstructed samples of the reconstructed block in the current picture and may transmit the reconstructed samples to the intra-frame predictor 222.

[0076] Figure 3Schematically illustrates the configuration of a video / image decoding device to which the disclosure of this document can be applied. Hereinafter, the so-called decoding device may include an image decoding device and / or a video decoding device. In addition, the so-called image decoding method / device may include a video decoding method / device. Alternatively, the so-called video decoding method / device may include an image decoding method / device.

[0077] Reference Figure 3 , the decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter-frame predictor 332 and an intra-frame predictor 331. The residual processor 320 may include an inverse quantizer 321 and an inverse transformer 322. According to an embodiment, the entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 may be configured by a hardware component (e.g., a decoder chipset or a processor). In addition, the memory 360 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware component may also include a memory 360 as an internal / external component.

[0078] When a bit stream including image / video information is input, the decoding device 300 may respond to the Figure 2 The image is reconstructed by processing the image / video information in the encoding device illustrated in . For example, the decoding device 300 can derive the unit / block based on the information related to the block segmentation obtained from the bit stream. The decoding device 300 can perform decoding using a processing unit applied to the encoding device. Therefore, the processing unit for decoding can be, for example, a coding unit, and the coding unit can be divided from the coding tree unit or the maximum coding unit according to a quadtree structure, a binary tree structure and / or a ternary tree structure. One or more transform units can be derived from the coding unit. In addition, the reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a reproduction device.

[0079] The decoding device 300 may receive the Figure 2The received signal can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive information (e.g., image / video information) necessary for image reconstruction (or picture reconstruction). The image / video information may also include information about various parameter sets such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the image / video information may also include conventional constraint information. The decoding device may also decode the picture based on the information about the parameter set and / or the conventional constraint information. The signaled / received information and / or syntax elements described in this document may then be decoded by a decoding process and obtained from the bitstream. For example, the entropy decoder 310 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CABAC, or CAVLC, and output syntax elements required for image reconstruction and quantized values ​​of transform coefficients for the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in a bitstream, determine a context model by using information of a decoded target syntax element, information of a decoded target block, or information of a symbol / bin decoded in a previous stage, perform arithmetic decoding on the bin by predicting the probability of the 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 information of a symbol / bin decoded by a context model for the next symbol / bin after determining the context model. Information related to prediction among the information decoded by the entropy decoder 310 can be provided to the inter-frame predictor 332 and the intra-frame predictor 331, and the residual value (ie, the quantized transform coefficient and related parameter information) that has been entropy decoded in the entropy decoder 310 can be input to the residual processor 320. The residual processor 320 can derive a residual signal (residual block, residual sample, residual sample array). In addition, information about filtering among the information decoded by the entropy decoder 310 can be provided to the filter 350. In addition, a receiver (not illustrated) for receiving a signal output from the encoding device may also be configured as an internal / external element of the decoding device 300, or the receiver may be a constituent element of the entropy decoder 310. In addition, the decoding device according to the present document may be referred to as a video / image / picture decoding device, and the decoding device may be divided into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include the entropy decoder 310, and the sample decoder may include at least one of the inverse quantizer 321, the inverse transformer 322, the adder 340, the filter 350, the memory 360, the inter-frame predictor 332, and the intra-frame predictor 331.

[0080] The dequantizer 321 may dequantize the quantized transform coefficient and output the transform coefficient. The dequantizer 321 may rearrange the quantized transform coefficient in a two-dimensional block form. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the encoding device. The dequantizer 321 may perform dequantization on the quantized transform coefficient using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficient.

[0081] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0082] The predictor 330 may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The predictor may determine whether to apply intra prediction or inter prediction to the current block based on information on prediction output from the entropy decoder 310 and may determine a specific intra / inter prediction mode.

[0083] The predictor 330 can generate a prediction signal based on various prediction methods described below. For example, the predictor can not only apply intra prediction or inter prediction to predict a block, but also apply intra prediction and inter prediction at the same time. This can be called a combination of inter and intra prediction (CIIP). In addition, the predictor can predict the block based on an intra-block copy (IBC) prediction mode or based on a palette mode. The IBC prediction mode or the palette mode can be used for content image / motion image coding of games, etc., for example, screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter prediction in terms of deriving a reference block in the current picture. That is, IBC can use at least one of the inter prediction techniques described in this document. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, information about the palette table and the palette index can be included in the image / video information and signaled.

[0084] The intra-frame predictor 331 can predict the current block by referencing samples in the current picture. Depending on the prediction mode, the referenced sample may be located in a neighbor of the current block, or its location may be separated from the current block. In intra-frame prediction, the prediction mode may include a plurality of non-directional modes and a plurality of directional modes. The intra-frame predictor 331 may determine the prediction mode to be applied to the current block by using the prediction mode applied to the neighboring blocks.

[0085] The inter-frame predictor 332 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 sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include information about the inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter-frame predictor 332 may construct a motion information candidate list based on the neighboring blocks, and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating a mode of inter-frame prediction for the current block.

[0086] The adder 340 can generate a reconstructed signal (reconstructed picture, reconstructed block, or reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block or prediction sample array) output from the inter-frame predictor 332 and / or the intra-frame predictor 331. If the residual of the target block is not processed (such as when the skip mode is applied), the prediction block can be used as the reconstructed block.

[0087] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next block to be processed in the current picture, and as described later, may also be output through filtering or may also be used for inter prediction of the next picture.

[0088] In addition, luminance mapping with chroma scaling (LMCS) can also be applied to the picture decoding process.

[0089] The filter 350 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 360, specifically, in the DPB of the memory 360. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0090] The (modified) reconstructed picture stored in the DPB of the memory 360 may be used as a reference picture in the inter-frame predictor 332. The memory 360 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 block in the reconstructed picture. The stored motion information may be transmitted to the inter-frame predictor 332 so as to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 360 may store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame predictor 331.

[0091] In this document, the embodiments described with respect to the filter 260 , the inter predictor 221 , and the intra predictor 222 of the encoding apparatus 200 may be commonly or correspondingly applied to the filter 350 , the inter predictor 332 , and the intra predictor 331 , respectively.

[0092] In addition, as described above, when performing video encoding, prediction is performed to improve compression efficiency. Accordingly, a prediction block including prediction samples for a current block as a block to be encoded (i.e., an encoding target block) can be generated. Here, the prediction block includes prediction samples in a spatial domain (or a pixel domain). The prediction block is derived in the same manner in the encoding device and the decoding device, and the encoding device can signal information about the residual between the original block and the prediction block (residual information) rather than the original sample value of the original block to the decoding device, thereby improving the image coding efficiency. The decoding device can derive a residual block including residual samples based on the residual information, add the residual block and the prediction block to generate a reconstructed block including reconstructed samples, and generate a reconstructed picture including the reconstructed block.

[0093] Residual information can be generated through a transformation and quantization process. For example, the encoding device can derive a residual block between the original block and the prediction block, perform a transformation process on the residual samples (residual sample array) included in the residual block to derive a transformation coefficient, perform a quantization process on the transformation coefficient to derive a quantized transformation coefficient, and signal the relevant residual information to the decoding device (through a bitstream). Here, the residual information may include value information, position information, transformation technology, transformation kernel, quantization parameter, etc. of the quantized transformation coefficient. The decoding device can perform an inverse quantization / inverse transformation process based on the residual information and derive residual samples (or residual blocks). The decoding device can generate a reconstructed picture based on the prediction block and the residual block. In addition, in order to provide a reference for inter-frame prediction of subsequent pictures, the encoding device can also perform inverse quantization / inverse transformation on the quantized transformation coefficient to derive a residual block and generate a reconstructed picture based on this.

[0094] The predictor of the encoding device / decoding device can perform inter-frame prediction and derive prediction samples in units of blocks. Inter-frame prediction can be a prediction derived in a manner that depends on data elements (e.g., sample values ​​or motion information) of pictures other than the current picture. When inter-frame prediction is applied to the current block, the prediction block (prediction sample array) of the current block can be derived based on the reference block (reference sample array) specified by the motion vector on the reference picture indicated by the reference picture index. At this time, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block can be predicted in units of blocks, sub-blocks or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When inter-frame prediction is applied, the neighboring blocks may include spatial neighboring blocks existing in the current picture and temporal neighboring blocks existing in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same as or different from each other. A temporally neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and a reference picture including a temporally neighboring block may be referred to as a collocated picture (colPic). For example, a motion information candidate list may be configured based on a neighboring block of the current block, and a flag or index information indicating which candidate is selected (used) to derive a motion vector and / or a reference picture index of the current block may be signaled. Inter-frame prediction may be performed based on various prediction modes. For example, in skip mode and merge mode, the motion information of the current block may be the same as the motion information of the selected neighboring block. In skip mode, unlike merge mode, a residual signal cannot be sent. In the case of motion information prediction (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.

[0095] According to the inter 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 an L0 motion vector or MVL0, and the motion vector in the L1 direction may be referred to as an L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as an L0 prediction; prediction based on the L1 motion vector may be referred to as an L1 prediction; and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as a bidirectional prediction. Here, the L0 motion vector may indicate a motion vector (L0) associated with the reference picture list L0, and the L1 motion vector may indicate a motion vector (L1) associated with the reference picture list L1. The reference picture list L0 may include a picture earlier than the current picture in output order as a reference picture, and the reference picture list L1 may include a picture later than the current picture in 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 later than the current picture in output order as a reference picture. In this case, in 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 further include a picture earlier than the current picture in the output order as a reference picture. In this case, in the reference picture list 1, 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.

[0096] The video / image encoding process based on inter-frame prediction may schematically include, for example, the following contents.

[0097] Figure 4 An example of video / image encoding based on inter-frame prediction is shown.

[0098] The encoding device performs inter prediction on the current block (S400). The encoding device may derive the inter prediction mode and motion information of the current block, and generate a prediction sample of the current block. Here, the processes for determining the inter prediction mode, deriving motion information, and generating prediction samples may be performed simultaneously, or another process may be performed after performing one process. For example, the inter predictor of the encoding device may include a prediction mode determiner, a motion information deriver, and a prediction sample deriver, the prediction mode determiner determines the prediction mode of the current block, the motion information deriver derives the motion information of the current block, and the prediction sample deriver derives the prediction sample of the current block. For example, the inter predictor of the encoding device searches for a block similar to the current block in a predetermined area (search area) of a reference picture through motion estimation, and derives a reference block with the smallest difference from the current block or within a predetermined standard. Based on this, a reference picture index indicating the reference picture where the 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 encoding device may determine a mode applied to the current block among various prediction modes. The encoding device may compare the RD costs of various prediction modes and determine an optimal prediction mode for the current block.

[0099] For example, when a skip mode or a merge mode is applied to the current block, the encoding device constructs a merge candidate list to be described later, and among the reference blocks indicated by the merge candidates included in the merge candidate list, a reference block having a minimum difference with the current block or being equal to or less than a predetermined standard can be derived. In this case, a merge candidate associated with the derived reference block can be selected, and merge index information indicating the selected merge candidate can be generated and signaled to the decoding device. The motion information of the selected merge candidate can be used to derive the motion information of the current block.

[0100] As another example, when the (A)MVP mode is applied to the current block, the encoding device constructs an (A)MVP candidate list to be described later, and among the motion vector predictor (MVP) candidates included in the (A)MVP candidate list, the motion vector of the selected MVP candidate can be used as the MVP of the current block. In this case, for example, a motion vector pointing to a reference block derived by the above-mentioned motion estimation can be used for the motion vector of the current block, and the MVP candidate with the smallest difference from the motion vector of the current block among the MVP candidates can become the selected MVP candidate. A motion vector difference (MVD) as a difference obtained by subtracting the MVP from the motion vector of the current block can be derived. In this case, information about the MVD can be signaled to the decoding device. In addition, when the (A)MVP mode is applied, the value of the reference picture index can be signaled to the decoding device separately by configuring the reference picture index information.

[0101] The encoding apparatus may induce residual samples based on the prediction samples (S410). The encoding apparatus may induce residual samples by comparing original samples of the current block with the prediction samples.

[0102] The encoding device encodes the image information including prediction information and residual information (S420). The encoding device can output the encoded image information in the form of a bitstream. The prediction information is information related to the prediction process, and may include prediction mode information (e.g., a skip flag, a merge flag, or a mode index, etc.) and information about motion information. 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. In addition, the information about the motion information may include the above-mentioned information about the MVD and / or reference picture index information. In addition, the information about the motion information may include information indicating whether L0 prediction, L1 prediction, or bidirectional prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients for the residual sample.

[0103] The output bitstream may be stored in a (digital) storage medium and sent to the decoding device, or may be sent to the decoding device over a network.

[0104] In addition, as described above, the encoding device can generate a reconstructed picture (including a reconstructed sample and a reconstructed block) based on the reference sample and the residual sample. This is because the encoding device can derive the same prediction result as the prediction result performed by the decoding device, and accordingly, the encoding efficiency can be improved. Therefore, the encoding device can store the reconstructed picture (or reconstructed sample, reconstructed block) in a memory and use it as a reference picture for inter-frame prediction. As described above, an in-loop filtering process can also be applied to the reconstructed picture.

[0105] The video / image decoding process based on inter-frame prediction may schematically include, for example, the following contents.

[0106] Figure 5 An example of a video / image decoding method based on inter-frame prediction is shown.

[0107] Reference Figure 5 The decoding device may perform an operation corresponding to the operation performed by the encoding device. The decoding device may perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0108] Specifically, the decoding device may determine a prediction mode of the current block based on the received prediction information (S500). The decoding device may determine which inter prediction mode to apply to the current block based on prediction mode information in the prediction information.

[0109] For example, based on the merge flag, it can be determined whether to apply the merge mode or the (A) MVP mode to the current block. Alternatively, one of the various inter-frame prediction mode candidates can be selected based on the mode index. The inter-frame prediction mode candidate may include a skip mode, a merge mode, and / or an (A) MVP mode, or may include various inter-frame prediction modes to be described later.

[0110] The decoding device derives the motion information of the current block based on the determined inter prediction mode (S510). For example, when the skip mode or merge mode is applied to the current block, the decoding device may configure a merge candidate list to be described later, and may select a merge candidate from the merge candidates included in the merge candidate list. The selection may be performed based on the above-mentioned selection information (merge index). The motion information of the selected merge candidate may be used to derive the motion information of the current block. The motion information of the selected merge candidate may be used as the motion information of the current block.

[0111] As another example, when the (A)MVP mode is applied to the current block, the decoding device constructs the (A)MVP candidate list to be described later, and among the motion vector predictor (MVP) candidates included in the (A)MVP candidate list, the motion vector of the selected MVP candidate can be used as the MVP of the current block. The selection can be performed based on the above-mentioned selection information (MVP flag or MVP index). In this case, the MVD of the current block can be derived based on the information about the MVD, and the motion vector of the current block can be derived based on the MVP and MVD of the current block. In addition, the reference picture index of the current block can 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 can be derived as the reference picture referenced by the inter-frame prediction of the current block.

[0112] In addition, as will be described later, the motion information of the current block can be derived without configuring the candidate list, and in this case, the motion information of the current block can be derived according to the process disclosed in the prediction mode to be described later. In this case, the candidate list configuration as described above can be omitted.

[0113] The decoding device may generate a prediction sample of the current block based on the motion information of the current block (S520). In this case, the reference picture may be derived based on the reference picture index of the current block, and the prediction sample of the current block may be derived by using the sample of the reference block indicated by the motion vector of the current block on the reference picture. In this case, as described later, a filtering process may also be performed on all or some of the prediction samples in the samples of the current block as appropriate.

[0114] For example, the inter-frame predictor of the decoding device may include a prediction mode determiner, a motion information deriver and a prediction sample deriver, and the prediction mode determiner determines the prediction mode of the current block based on the received prediction mode information, the motion information deriver derives the motion information based on the received information about the motion information of the current block (motion vector and / or reference picture index, etc.), and the prediction sample deriver derives the prediction sample of the current block.

[0115] The decoding device generates a residual sample of the current block based on the received residual information (S530). The decoding device can generate a reconstructed sample of the current block based on the predicted sample and the residual sample, and can generate a reconstructed picture based on this (S540). Thereafter, as described above, an in-loop filtering process can also be applied to the reconstructed picture.

[0116] Figure 6 The inter-frame prediction process is exemplarily shown.

[0117] Reference Figure 6 The inter-frame prediction process may include determining an inter-frame prediction mode, deriving motion information according to the determined prediction mode, and performing prediction (generating prediction samples) based on the derived motion information. The inter-frame prediction process may be performed by an encoding device and a decoding device as described above. In this document, an encoding device may include an encoding device and / or a decoding device.

[0118] Reference Figure 6 , the encoding device determines the inter prediction mode of the current block (S600). Various inter prediction modes can be used to predict the current block in the picture. For example, various modes such as merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub-block merge mode, merge with MVD (MMVD) mode, etc. can be used. Decoder side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, bidirectional prediction with CU level weight (VCW), bidirectional optical flow (OBDF), etc. can be used in addition or alternatively as auxiliary modes. Affine mode can be referred to as affine motion prediction mode. MVP mode can be referred to as advanced motion vector prediction (AMVP) mode. In this document, some modes and / or motion information candidates derived from some modes can be included as one of the candidates related to the motion information of another mode. For example, an HMVP candidate can be added as a merge candidate for a merge / skip mode, or can be added as an MVP candidate for an MVP mode. When an HMVP candidate is used as a motion information candidate for a merge mode or a skip mode, the HMVP candidate can be referred to as an HMVP merge candidate.

[0119] Prediction mode information indicating the inter-frame prediction mode of the current block may be signaled from the encoding device to the decoding device. The prediction mode information may be included in the bitstream and received at the decoding device. The prediction mode information may include index information indicating one of a plurality of candidate modes. In addition, the inter-frame prediction mode may be indicated by hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, whether the skip mode is applied may be indicated by signaling a skip flag; whether the merge mode is applied may be indicated by signaling a merge flag for not applying the skip mode; and when the merge mode is not applied, the application of the MVP mode may be indicated or a flag for further segmentation may also be signaled. The affine mode may be signaled as an independent mode, or may be signaled as depending on the merge mode, the MVP mode, or the like. For example, the affine mode may include an affine merge mode and an affine MVP mode.

[0120] The encoding apparatus derives motion information of a current block (S610). The motion information may be derived based on an inter prediction mode.

[0121] The encoding device can use the motion information of the current block to perform inter-frame prediction. The encoding device can derive the best motion information of the current block through a motion estimation process. For example, the encoding device can use the original block in the original picture of the current block to search for similar reference blocks with high correlation in a predetermined search range in the reference picture in units of fractional pixels, and can derive motion information based on this. The similarity of the blocks can be derived based on the difference between the sample values ​​based on the phase. For example, the similarity of the blocks can be calculated based on the SAD between the current block (or the template of the current block) and the reference block (or the template of the reference block). In this case, the motion information can be derived based on the reference block with the minimum SAD in the search area. The derived motion information can be signaled to the decoding device according to various methods based on the inter-frame prediction mode.

[0122] The encoding device performs inter prediction based on the motion information about the current block (S620). The encoding device may derive a prediction sample of the current block based on the motion information. The current block including the prediction sample may be referred to as a prediction block.

[0123] In addition, information indicating whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction, or bidirectional prediction is used in the current block (current coding unit) may be signaled to the current block. This information may be referred to as motion prediction direction information, inter-frame prediction direction information, or inter-frame prediction indication information, and may be constructed / encoded / signaled in the form of, for example, an inter_pred_idc syntax element. That is, the inter_pred_idc syntax element may indicate whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction, or bidirectional prediction is used for the current block (current coding unit). In this document, for ease of description, the inter-frame prediction type (L0 prediction, L1 prediction, or BI prediction) indicated by the inter_pred_idc syntax element may be represented as a motion prediction direction. L0 prediction may be represented by pred_L0; L1 prediction may be represented by pred_L1; and bidirectional prediction may be represented by pred_BI.

[0124] A picture may include one or more slices. A slice may have one of slice types including an intra (I) slice, a predicted (P) slice, and a bidirectional predicted (B) slice. The slice type may be indicated based on slice type information. For blocks in an I slice, inter prediction is not used for prediction, but only intra prediction may be used. Of course, even in this case, the original sample values ​​may be encoded and signaled without prediction. For blocks in a P slice, intra prediction or inter prediction may be used, and when inter prediction is used, only unidirectional prediction may be used. In addition, for blocks in a B slice, intra prediction or inter prediction may be used, and when inter prediction is used, up to a maximum bidirectional prediction may be used.

[0125] L0 and L1 may include reference pictures that are encoded / decoded before the current picture. For example, L0 may include reference pictures that are before and / or after the current picture in POC order, and L1 may include reference pictures that are after and / or before the current picture in POC order. In this case, a lower reference picture index relative to a reference picture that is earlier than the current picture in POC order may be assigned to L0, and a lower reference picture index relative to a reference picture that is later than the current picture in POC order may be assigned to L1. In the case of a B slice, bidirectional prediction may be applied, and in this case, unidirectional bidirectional prediction may be applied, or bidirectional bidirectional prediction may be applied. Bidirectional bidirectional prediction may be referred to as true bidirectional prediction.

[0126] Specifically, for example, information about the inter prediction mode of the current block may be encoded and signaled at the CU (CU syntax) level, etc., or may be implicitly determined according to conditions. In this case, some modes may be explicitly signaled, while other modes may be implicitly derived.

[0127] Figure 7 The spatial neighboring blocks used to derive motion information candidates in the MVP mode are exemplarily shown.

[0128] The motion vector prediction (MVP) mode may be referred to as the advanced motion vector prediction (AMVP) mode. When the MVP mode is applied, the reconstructed spatial neighboring blocks (e.g., blocks that may include Figure 5 The motion vector predictor (MVP) candidate list is generated based on the motion vector of the reconstructed spatial neighboring block (or the neighboring block of the current block) and / or the motion vector corresponding to the temporal neighboring block (or Col block). That is, the motion vector of the reconstructed spatial neighboring block and / or the motion vector corresponding to the temporal neighboring block can be used as the motion vector predictor candidate. The spatial neighboring blocks may include the lower left neighboring block A0, the left neighboring block A1, the upper right neighboring block B0, the upper neighboring block B1 and the upper left neighboring block B2 of the current block.

[0129] When bidirectional prediction is applied, an MVP candidate list for deriving L0 motion information and an MVP candidate list for deriving L1 motion information may be generated and used respectively. The above-mentioned prediction information (or information about prediction) may include selection information (e.g., an MVP flag or an MVP index) indicating the best motion vector predictor candidate selected from the motion vector predictor candidates included in the list. In this case, the predictor can select the motion vector predictor of the current block from the motion vector predictor candidates included in the motion vector candidate list by using the selection information. The predictor of the encoding device may obtain the motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, encode it and output it in the form of a bitstream. That is, the MVD may be obtained by subtracting the motion vector predictor from the motion vector of the current block. In this case, the predictor of the decoding device may obtain the motion vector difference included in the information about the prediction, and derive the motion vector of the current block by adding the motion vector difference to the motion vector predictor. The predictor of the decoding device may obtain or derive a reference picture index indicating a reference picture from the information about the prediction.

[0130] Figure 8 The method for constructing an MVP candidate list according to this document is schematically represented.

[0131] Reference Figure 8As an embodiment, by searching for spatial neighboring blocks for motion vector prediction, available spatial (mvp) candidates can be inserted into a prediction candidate list (mvp candidate list) (S810). In this case, candidates can be derived by dividing the neighboring blocks into two groups. For example, one (mvp) candidate is derived from group A including the lower left neighboring block A0 and the left neighboring block A1 of the current block, and one (mvp) candidate is derived from group B including the upper right neighboring block B0, the upper neighboring block B1, and the upper left neighboring block B2. The mvp candidate derived from group A can be referred to as mvpA, and the mvp candidate derived from group B can be referred to as mvpB. If all neighboring blocks in the group are unavailable or intra-coded, the (mvp) candidate cannot be derived from the group.

[0132] Thereafter, as an embodiment, it is determined whether the number of spatial candidates is less than 2 (S820). For example, according to an embodiment, when the number of spatial candidates is less than 2, a temporal candidate derived by searching a temporal neighboring block may be additionally inserted into the prediction candidate list (S630). The temporal candidate derived from the temporal neighboring block may be referred to as mvpCol.

[0133] In addition, when the MVP mode is applied, the reference picture index may be explicitly signaled. In this case, the reference picture index for L0 prediction (refidxL0) and the reference picture index for L1 prediction (refidxL1) may be signaled separately. For example, when the MVP mode is applied and bidirectional prediction is applied, both information about refidxL0 and information about refidxL1 may be signaled.

[0134] When bidirectional prediction is applied, an MVP candidate list for deriving L0 motion information and an MVP candidate list for deriving L1 motion information may be generated and used respectively. The above information (or information about prediction) may include selection information (e.g., an MVP flag or an MVP index) indicating the best motion vector predictor candidate selected from the motion vector predictor candidates included in the list. In this case, the predictor may select the motion vector predictor of the current block from the motion vector predictor candidates included in the motion vector candidate list by using the selection information. The predictor of the encoding device may obtain the motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, and may encode the MVD and output the encoded MVD in the form of a bitstream. That is, the MVD may be obtained by subtracting the motion vector predictor from the motion vector of the current block. In this case, the predictor of the decoding device may obtain the motion vector difference included in the information about the prediction, and derive the motion vector of the current block by adding the motion vector difference to the motion vector predictor. The predictor of the decoding device may obtain or derive a reference picture index indicating a reference picture from the information about the prediction, etc.

[0135] When the MVP mode is applied, as described above, information about the MVD derived from the encoding device may be signaled to the decoding device. The information about the MVD may include, for example, information indicating the absolute value of the MVD and the x and y components of the sign. In this case, information indicating whether the absolute value of the MVD is greater than 0, whether the absolute value of the MVD is greater than 1, and the remaining part of the MVD may be signaled step by step. For example, only when the value of the flag information indicating whether the absolute value of the MVD is greater than 0 is 1, the information indicating whether the absolute value of the MVD is greater than 1 may be signaled.

[0136] For example, the information about the MVD may be configured in the syntax shown in Table 1, encoded by the encoding device, and signaled to the decoding device.

[0137] [Table 1]

[0138]

[0139] For example, in Table 1, the abs_mvd_greater0_flag syntax element may indicate information about whether the difference MVD is greater than 0, and the abs_mvd_greater1_flag syntax element may indicate information about whether the difference MVD is greater than 1. In addition, the abs_mvd_minus2 syntax element may indicate information about a value obtained by subtracting 2 from the difference MVD, and the mvd_sign_flag syntax element may indicate information about the sign of the difference MVD. In addition, in Table 1, [0] of each syntax element may indicate that it is information about L0, and [1] may indicate that it is information about L1.

[0140] For example, MVD[compIdx] may be derived based on abs_mvd_greater0_flag[compIdx]*(abs_mvd_minus2[compIdx]+2)*(1-2*mvd_sign_flag[compIdx]). Here, compIdx (or cpIdx) indicates the index of each component and may have a value of 0 or 1. compIdx 0 may indicate an x ​​component, and compIdx 1 may indicate a y component. However, this is an example, and the value of each component may be expressed using a coordinate system other than the x and y coordinate systems.

[0141] In addition, the MVD (MVDL0) for L0 prediction and the MVD (MVDL1) for L1 prediction may be signaled separately, and the information about the MVD may include information about MVDL0 and / or information about MVDL1. For example, when the MVP mode is applied to the current block and the BI prediction is applied, both the information about MVDL0 and the information about MVDL1 may be signaled.

[0142] Fig. 9 is a diagram for explaining symmetric MVD.

[0143] In addition, when bidirectional prediction (BI prediction) is applied, symmetric MVD can be used in consideration of coding efficiency. Here, symmetric MVD can be referred to as SMVD. In this case, the signaling of some motion information can be omitted. For example, when symmetric MVD is applied to the current block, information about refidxL0, information about refidxL1, and information about MVDL1 are not signaled from the encoding device to the decoding device, but can be derived internally. For example, when MVP mode and BI prediction are applied to the current block, flag information indicating whether symmetric MVD is applied (e.g., symmetric MVD flag information or sym_mvd_flag syntax element) can be signaled, and when the value of the flag information is 1, the decoding device can determine to apply symmetric MVD to the current block.

[0144] When the symmetric MVD mode is applied (i.e., when the value of the symmetric MVD flag information is 1), information about MVDL0 and mvp_l0_flag, mvp_l1_flag may be explicitly signaled, and as described above, signaling of information about refidxL0, information about refidxL1, and information about MVDL1 may be omitted and derived internally. For example, refidxL0 may be derived as an index indicating a previous reference picture closest to the current picture in POC order in reference picture list 0 (which may be referred to as list 0 or L0). refidxL1 may be derived as an index indicating a subsequent reference picture closest to the current picture in POC order in reference picture list 1 (which may be referred to as list 1 or L1). Or, for example, both refidxL0 and refidxL1 may be derived as 0, respectively. Alternatively, for example, refidxL0 and refidxL1 may be derived as the minimum index having the same POC difference relative to the current picture, respectively. Specifically, for example, when it is assumed that [POC of the current picture]-[POC of the first reference picture indicated by refidxL0] is the first POC difference, and [POC of the second reference picture indicated by refidxL1] is the second POC difference, and only when the first POC difference is the same as the second POC difference, the value of refidxL0 indicating the first reference picture is derived as the value of refidxL0 of the current block, and the value of refidxL1 indicating the second reference picture can be derived as the value of refidxL1 of the current block. In addition, for example, when there are multiple sets in which the first POC difference is equal to the second POC difference, refidxL0 and refidxL1 of one of the sets with the smallest difference value can be derived as refidxL0 and refidxL1 of the current block. When the symmetric MVD mode is applied, refidxL0 and refidxL1 can be referred to as RefIdxSymL0 and RefIdxSymL1, respectively. For example, RefIdxSymL0 and RefIdxSymL1 may be determined in units of slices. In this case, a block to which SMVD is applied in the current slice may use the same RefIdxSymL0 and RefIdxSymL1.

[0145] MVDL1 can be derived as -MVDL0. For example, the final MV of the current block can be derived in Equation 1.

[0146] [Formula 1]

[0147]

[0148] In formula 1, mvx 0 and mvy 0The x component and y component of the motion vector for L0 motion information or L0 prediction may be represented, and mvx 1 and mvy 1 It can represent the x component and y component of the motion vector used for L1 motion information or L1 prediction. 0 and mvpy 0 The x and y components of the motion vector predictor for L0 prediction may be indicated, and mvpx 1 and mvpy 1 The x and y components of the motion vector predictor used for L1 prediction can be indicated. 0 and mvdy 0 The x component and y component of the motion vector difference for L0 prediction may be indicated.

[0149] In addition, the prediction block of the current block can be derived based on the motion information derived according to the prediction mode. The prediction block may include the prediction sample (prediction sample array) of the current block. When the motion vector of the current block indicates a fractional sample unit, an interpolation process may be performed, and accordingly, the prediction sample of the current block may be derived based on the reference sample of the fractional sample unit in the reference picture. When affine inter prediction is applied to the current block, the prediction sample may be generated based on the sample / sub-block unit MV. When bidirectional prediction is applied, the prediction sample derived by the weighted sum (according to the phase) or weighted average of the prediction sample derived based on the L0 prediction (i.e., prediction using the reference picture in the reference picture list L0 and MVL0) and the prediction sample derived based on the L1 prediction (i.e., prediction using the reference picture in the reference picture list L1 and MVL1) may be used as the prediction sample of the current block. When bidirectional prediction is applied, and when the reference picture for L0 prediction and the reference picture for L1 prediction are located in different time directions relative to the current picture (i.e., in the case corresponding to bidirectional prediction and bidirectional), this may be referred to as true bidirectional prediction.

[0150] As described above, reconstructed samples and reconstructed pictures may be generated based on the derived prediction samples, and then processes such as in-loop filtering may be performed.

[0151] In addition, referring back to the configuration related to symmetric MVD (SMVD), the symmetric MVD flag is signaled only for the blocks to which the prediction is applied, and if the symmetric MVD flag is true, only the MVD for L0 is signaled, and the MVD for L1 can be used by mirroring the MVD signaled for L0. However, in this case, during the process of applying the symmetric MVD, problems may occur depending on the value of the mvd_l1_zero_flag syntax element (e.g., when the mvd_l1_zero_flag syntax element is true).

[0152] For example, the mvd_l1_zero_flag syntax element may be signaled based on the syntax shown in Tables 2 to 4. That is, when the current slice in the slice header is a B slice, the mvd_l1_zero_flag syntax element may be signaled. Here, Tables 2 to 4 may continuously represent one syntax (eg, slice header syntax).

[0153] [Table 2]

[0154]

[0155] [Table 3]

[0156]

[0157] [Table 4]

[0158]

[0159] For example, the semantics of the mvd_l1_zero_flag syntax element in Tables 2 to 4 may be as shown in Table 5 below.

[0160] [Table 5]

[0161]

[0162] Alternatively, for example, the mvd_l1_zero_flag syntax element may indicate information about whether the mvd_coding syntax for L1 prediction is parsed. For example, when the mvd_l1_zero_flag syntax element has a value of 1, it may indicate that the mvd_coding syntax according to L1 prediction is not parsed, and the MvdL1 value is determined to be 0. Alternatively, for example, when the mvd_l1_zero_flag syntax element has a value of 0, it may indicate that the mvd_coding syntax according to L1 prediction is parsed. That is, the MvdL1 value may be determined according to the mvd_l1_zero_flag syntax element.

[0163] For example, the decoding process of the symmetric motion vector difference reference index may be as shown in Table 6 below, but is not limited thereto. For example, the symmetric MVD reference index for L0 prediction may be represented as RefIdxSymL0, and the symmetric MVD reference index for L1 prediction may be represented as RefIdxSymL1.

[0164] [Table 6]

[0165]

[0166] For example, information about the symmetric MVD or the sym_mvd_flag syntax element may be signaled based on the syntaxes shown in the following Tables 7 to 10. Here, Tables 7 to 10 may consecutively represent one syntax (eg, coding unit syntax).

[0167] [Table 7]

[0168]

[0169] [Table 8]

[0170]

[0171] [Table 9]

[0172]

[0173] [Table 10]

[0174]

[0175] Alternatively, for example, information about the symmetric MVD or the sym_mvd_flag syntax element may be signaled based on the syntaxes shown in Tables 11 to 15. Here, Tables 11 to 15 may continuously represent one syntax (eg, coding unit syntax).

[0176] [Table 11]

[0177]

[0178] [Table 12]

[0179]

[0180] [Table 13]

[0181]

[0182] [Table 14]

[0183]

[0184] [Table 15]

[0185]

[0186] For example, information about the symmetric MVD or sym_mvd_flag syntax element may be signaled as shown in Tables 7 to 10 or Tables 11 to 15.

[0187] For example, referring to Tables 7 to 10 or Tables 11 to 15, when the current block is not an affine block but a block to which bidirectional prediction is applied, and when there is a symmetric MVD reference index derived by the above method, information about the symmetric MVD or sym_mvd_flag syntax element can be signaled regardless of the mvd_l1_zero_flag syntax element.

[0188] That is, even when the mvd_l1_zero_flag syntax element is 1, the sym_mvd_flag syntax element may be 1. In this case, even when the sym_mvd_flag syntax element is 1, MvdL1 may be derived as 0. Although this is not operated according to the sym_mvd_flag syntax element, the sym_mvd_flag syntax element is signaled, and thus there is a problem of unnecessary bit signaling.

[0189] Furthermore, according to an embodiment of the present document, when the value of the mvd_l1_zero_flag syntax element is 1, and when the value of the sym_mvd_flag syntax element is 1, the value of MvdL1 may be derived as a mirror value of the value of MvdL0 even when the mvd_l1_zero_flag syntax element is 1.

[0190] For example, information about the symmetric MVD or sym_mvd_flag syntax element may be signaled based on at least a portion of a coding unit syntax such as Table 16 and Table 17. Here, Table 16 and Table 17 may consecutively represent a portion of one syntax.

[0191] [Table 16]

[0192]

[0193] [Table 17]

[0194]

[0195] For example, referring to Table 16 and Table 17, the value of MvdL1 may be derived based on the value of the mvd_l1_zero_flag syntax element, the value of the sym_mvd_flag syntax element, and whether bidirectional prediction is applied. That is, based on the value of the mvd_l1_zero_flag syntax element, the value of the sym_mvd_flag syntax element, and whether bidirectional prediction is applied, the value of MvdL1 may be derived as 0 or -MvdL0 (a mirror value of MvdL0).

[0196] For example, the semantics of the mvd_l1_zero_flag syntax element in Table 16 and Table 17 may be as shown in Table 18.

[0197] [Table 18]

[0198]

[0199] In addition, according to an embodiment of the present document, when the value of the mvd_l1_zero_flag syntax element is 1, the sym_mvd_flag syntax element may not be parsed. That is, when the value of the mvd_l1_zero_flag syntax element is 1, symmetric MVD may not be allowed. In other words, when the value of the mvd_l1_zero_flag syntax element is 1, the decoding device may not parse the sym_mvd_flag syntax element, and the encoding device may configure the sym_mvd_flag syntax element to not be parsed (from the bitstream, image / video information, CU syntax, inter-prediction mode information, or prediction-related information). Alternatively, according to an embodiment, when the value of the mvd_l1_zero_flag syntax element is 0, a symmetric MVD index may be inferred or derived. Here, the symmetric MVD index may indicate a symmetric MVD reference (picture) index. For example, when symmetric MVD is applied to the current block (eg, sym_mvd_flag==1), L0 / L1 reference (picture) index information (eg, ref_idx_l0 and / or ref_idx_l1) for the current block may not be explicitly signaled and the symmetric MVD reference index may be inferred or derived.

[0200] For example, in this case, the decoding process of the symmetric motion vector difference reference index may be as shown in Table 19 below, but is not limited thereto. For example, the symmetric MVD reference index for L0 prediction may be represented as RefIdxSymL0, and the symmetric MVD reference index for L1 prediction may be represented as RefIdxSymL1.

[0201] [Table 19]

[0202]

[0203] Alternatively, for example, information about the symmetric MVD or the sym_mvd_flag syntax element may be signaled based on at least a portion of a coding unit syntax such as Table 20 and Table 21. Here, Table 20 and Table 21 may continuously show a portion of one syntax.

[0204] [Table 20]

[0205]

[0206] [Table 21]

[0207]

[0208] For example, referring to Tables 20 and 21, SMVD flag information (e.g., sym_mvd_flag syntax element) may be signaled based on at least one of inter-prediction type information indicating whether bidirectional prediction is applied to the current block (e.g., inter_pred_idc syntax element), L1 motion vector difference zero flag information (e.g., mvd_l1_zero_flag or ph_mvd_l1_zero_flag syntax element), SMVD enable flag information (e.g., sps_smvd_enabled_flag syntax element), and / or inter-affine flag information (e.g., inter_affine_flag syntax element).

[0209] Specifically, for example, based on the case where the inter-frame prediction type information indicates a bidirectional prediction type, the value of the L1 motion vector difference zero flag information is 0, the value of the SMVD enable flag information is 1, and the value of the inter-frame affine flag information is 0, the SMVD flag information may be explicitly signaled. That is, when the value of the L1 motion vector difference zero flag information is 1, the SMVD flag information may not be explicitly signaled. In this case, the decoding device may implicitly infer the value of the SMVD flag information to be 0. Not signaling the SMVD flag information may indicate that the SMVD flag information is not included in the prediction related information (or inter-frame prediction mode information) or the CU syntax or is not parsed.

[0210] Based on the above implementations of this document, the signaling of information about the symmetric MVD can be optimized, and unnecessary bit waste can be avoided, thereby improving the overall coding efficiency.

[0211] Fig.10 and Fig.11 An example of a video / image encoding method and related components according to an embodiment of the present document is schematically shown.

[0212] Fig.10 The method disclosed in can be Figure 2 or Fig.11 Specifically, for example, Fig.10 S1000 to S1010 in may be performed by the predictor 220 of the encoding device, and Fig.10 S1020 in can be performed by the entropy encoder 240 of the encoding device. Fig.10 The method disclosed in may include the embodiments described above in this document.

[0213] Reference Fig.10, the encoding device derives the MVP candidate list of the current block (S1000). The encoding device may derive the MVP candidate list based on the neighboring blocks of the current block and the inter-frame prediction mode of the current block. As described above, the neighboring blocks may include the spatial neighboring blocks and / or the temporal neighboring blocks of the current block. The neighboring blocks may include the lower left neighboring block, the left neighboring block, the upper right neighboring block, the upper neighboring block, and the upper left neighboring block of the current block.

[0214] The encoding device generates information for indicating the motion information of the current block based on the MVP candidate list (S1010). The information for indicating the motion information of the current block may include the above-mentioned selection information (e.g., mvp flag information or mvp index information, etc.). The mvp flag information may include the above-mentioned mvp_10_flag and / or mvp_11_flag. In addition, the information for indicating the motion information of the current block may include information about MVD. For example, the information about MVD may include at least one of abs_mvd_greater0_flag syntax element, abs_mvd_greater1_flag syntax element, abs_mvd_minus2 syntax element, or mvd_sign_flag syntax element, but it is not limited because it may also include other information. The motion information may include at least one of an L0 motion vector for L0 prediction and an L1 motion vector for L1 prediction. The L0 motion vector may be represented based on an L0 motion vector predictor and an L0 motion vector difference, and the L1 motion vector may be represented based on an L1 motion vector predictor and an L1 motion vector difference.

[0215] For example, the encoding device may perform inter prediction on the current block in consideration of rate distortion (RD) cost so as to generate a prediction sample of the current block. Alternatively, for example, the encoding device may determine the inter prediction mode that has been used to generate the prediction sample of the current block, and may derive motion information. Here, the inter prediction mode may be a motion vector prediction (MVP) mode, but is not limited thereto. Here, the MVP mode may be referred to as an advanced motion vector prediction (AMVP) mode.

[0216] The encoding device can derive the best motion information of the current block through motion estimation. For example, the encoding device can use the original block in the original picture of the current block to search for a similar reference block with high correlation in a predetermined search range in the reference picture in units of fractional pixels, and can derive motion information based on this.

[0217] The encoding device may construct a motion vector predictor candidate list using a motion vector predictor and / or a motion vector difference to represent the derived motion information. For example, the encoding device may construct a motion vector predictor candidate list based on spatial neighboring candidate blocks and / or temporal neighboring candidate blocks. For example, when bidirectional prediction is applied to the current block, an L0 motion vector predictor candidate list for L0 prediction and an L1 motion vector predictor candidate list for L1 prediction may be constructed respectively.

[0218] The encoding device may determine the motion vector predictor of the current block based on the motion vector predictor candidate list. For example, the encoding device may determine the motion vector predictor for the current block from the motion vector predictor candidates in the motion vector predictor candidate list based on the derived motion information (or motion vector). Alternatively, the encoding device may determine the motion vector predictor in the motion vector predictor candidate list that has the smallest difference with the derived motion information (or motion vector). For example, when bidirectional prediction is applied to the current block, the L0 motion vector predictor for L0 prediction and the L1 motion vector predictor for L1 prediction may be obtained from the L0 motion vector predictor candidate list and the L1 motion vector predictor candidate list, respectively.

[0219] The encoding device may generate selection information indicating a motion vector predictor in the motion vector predictor candidate list. For example, the selection information may also be referred to as index information, and may also be referred to as an MVP flag or an MVP index. That is, the encoding device may generate information indicating a motion vector predictor in the motion vector predictor candidate list that has been used to indicate a motion vector of the current block. For example, when bidirectional prediction is applied to the current block, selection information for an L0 motion vector predictor and selection information for an L1 motion vector predictor may be generated, respectively.

[0220] The encoding device may determine the motion vector difference of the current block based on the motion vector predictor. For example, the encoding device may determine the motion vector difference based on the motion information (or motion vector) derived for the current block and the motion vector predictor. Alternatively, the encoding device may determine the motion vector difference based on the difference between the motion information (or motion vector) derived for the current block and the motion vector predictor. For example, when bidirectional prediction is applied to the current block, the L0 motion vector difference and the L1 motion vector difference may be determined separately. Here, the L0 motion vector difference may be represented as MvdL0, and the L1 motion vector difference may be represented as MvdL1. The L0 motion vector may be represented based on the sum of the L0 motion vector predictor and the L0 motion vector difference, and the L1 motion vector may be represented based on the sum of the L1 motion vector predictor and the L1 motion vector difference.

[0221] In addition, the encoding device may derive motion information of the current block based on the inter prediction mode and generate a prediction sample. The motion information may include an L0 motion vector for L0 prediction and / or an L1 motion vector for L1 prediction.

[0222] When bidirectional prediction is applied, the encoding device may derive an L0 prediction sample and an L1 prediction sample, and may derive a prediction sample of the current block based on a weighted sum or a weighted average of the L0 prediction sample and the L1 prediction sample. The L0 motion vector may indicate an L0 prediction sample on an L0 reference picture, and the L1 motion vector may indicate an L1 prediction sample on an L1 reference picture.

[0223] The L1 motion vector difference may be derived from the L0 motion vector difference based on the case where the value of the L1 motion vector difference zero flag information is 0 and the value of the SMVD flag information is 1. In this case, the absolute value of the L1 motion vector difference may be the same as the absolute value of the L0 motion vector difference, and the sign of the L1 motion vector difference may be different from the sign of the L0 motion vector difference.

[0224] The encoding device may derive residual information based on the prediction sample of the current block. The encoding device may derive residual samples based on the prediction sample. The encoding device may derive residual samples based on the original sample of the current block and the prediction sample of the current block. The encoding device may derive residual information based on the residual sample. The residual information may include information about the quantized transform coefficient. The encoding device may derive the quantized transform coefficient by performing a transform / quantization process on the residual sample.

[0225] The encoding device encodes the video / image information (S1020). The video / image information may include at least one of information about the inter-frame prediction mode and information for indicating motion information of the current block. The video / image information may also include residual information. The encoded video / image information may be output in the form of a bit stream. The bit stream may be sent to a decoding device via a network or a storage medium. The bit stream may include the encoded (image / video) information.

[0226] The video / image information may include inter-frame prediction type information (e.g., inter_pred_idc), a general merge flag, SMVD flag information, L1 motion vector difference zero flag information, SMVD enable flag information, and / or inter-frame affine flag information. For example, when the value of the general merge flag is 0, it may indicate that the MVP mode is applied to the current block. The inter-frame prediction type information may indicate whether bidirectional prediction is applied to the current block. Specifically, for example, the inter-frame prediction type information may indicate whether L0 prediction, L1 prediction, or bidirectional prediction is applied to the current block.

[0227] For example, the image information includes L1 motion vector difference zero flag information, the image information includes a coding unit (CU) syntax for the current block, and based on the L1 motion vector difference zero flag information, it can be determined whether the CU syntax includes SMVD flag information indicating whether a symmetric motion vector difference (SMVD) is applied to the current block.

[0228] Specifically, for example, the image information may include header information. The header information may include a slice header or a picture header. The header information may include L1 motion vector difference zero flag information, and based on the case where the value of the L1 motion vector difference zero flag information is 0, the CU syntax may include SMVD flag information. For example, when the value of the mvd_l1_zero_flag syntax element is 1, the decoding device may not parse the sym_mvd_flag syntax element, and the encoding device may configure the sym_mvd_flag syntax element configuration not to be parsed (from the bitstream, video / image information, CU syntax, inter-frame prediction mode information, or prediction-related information).

[0229] In addition, as an example, based on the case where the value of the L1 motion vector difference zero flag information is 1, the CU syntax may not include the SMVD flag information. In this case, the decoding device may infer that the value of the SMVD flag information is 0 without parsing the SMVD flag information.

[0230] In addition, as an example, whether the SMVD flag information is included in the CU syntax is determined based on the value of the symmetric motion vector difference reference index of the current block, and based on the L1 motion vector difference zero flag information having a value of 1, the value of the symmetric motion vector difference reference index is derived as -1, and it is determined based on the symmetric motion vector difference reference index having a value of -1 that the SMVD flag information is not included in the CU syntax. For example, the symmetric motion vector difference reference index may include an L0 symmetric motion vector difference reference index and an L1 symmetric motion vector difference reference index, both of which may be determined to have a value of -1. Here, the L0 symmetric motion vector difference reference index may be expressed as RefIdxSymL0, and the L1 symmetric motion vector difference reference index may be expressed as RefIdxSymL1. For example, when RefIdxSymL0 and RefIdxSymL1 are respectively greater than -1, the SMVD flag information may be included in the inter-prediction mode information or the CU syntax. Alternatively, for example, the inter prediction mode information or the CU syntax may include a symmetric motion vector difference flag based on RefIdxSymL0 being greater than -1 and RefIdxSymL1 being greater than -1.

[0231] In addition, as an example, the image information includes a sequence parameter set (SPS), the SPS includes SMVD enable flag information, the CU syntax includes prediction type information and inter-frame affine flag information, the prediction type information indicates whether bidirectional prediction is applied to the current block, and the CU syntax can include SMVD flag information based on the SMVD enable flag information, the prediction type information, and the inter-frame affine flag information.

[0232] Specifically, for example, based on the case where the inter-frame prediction type information indicates bidirectional prediction, the value of the L1 motion vector difference zero flag information is 0, the value of the SMVD enable flag information is 1, and the value of the inter-frame affine flag information is 0, the SMVD flag information may be included in the CU syntax to be explicitly signaled. That is, when the value of the L1 motion vector difference zero flag information is 1, the SMVD flag information may not be explicitly signaled. In this case, the decoding device may implicitly infer the value of the SMVD flag information to be 0. Not signaling the SMVD flag information may indicate that the SMVD flag information is not included in the prediction related information (or inter-frame prediction mode information) or the CU syntax.

[0233] The video / image information may include information about the motion vector difference. For example, the information about the motion vector difference may include information indicating the motion vector difference. When SMVD is applied, the information about the motion vector difference may include only information about the L0 motion vector difference, and as described above, the L1 motion vector difference may be derived based on the L0 motion vector difference.

[0234] The zero flag of the L1 motion vector difference may indicate information about whether the L1 motion vector difference is 0, and may be referred to as an L1 motion vector difference zero flag, an L1 MVD zero flag, and an MVD L1 zero flag. In addition, the L1 motion vector difference zero flag may be expressed as an mvd_11_zero_flag syntax element or a ph_mvd_11_zero_flag syntax element. In addition, the SMVD flag information may indicate information about whether the L0 motion vector difference and the L1 motion vector difference are symmetrical, and may be expressed as a sym_mvd_flag syntax element.

[0235] In addition, the encoding device can derive (modified) residual samples based on the residual information, and can generate reconstructed samples based on the (modified) residual samples and the predicted samples. In addition, reconstructed blocks and reconstructed pictures can be derived based on the reconstructed samples. The derived reconstructed pictures can be used as references for inter-frame prediction of subsequent pictures.

[0236] For example, the encoding device can generate a bit stream or coding information by encoding all or some of the image / video information including the above information (or syntax elements). Alternatively, it can be output in the form of a bit stream. In addition, the bit stream or coding information can be sent to a decoding device via a network or a storage medium. Alternatively, the bit stream or coding information can be stored in a computer-readable storage medium, and the bit stream or coding information can be generated by the above image / video coding method.

[0237] Fig.12 and Fig.13 An example of a video / image decoding method and related components according to an embodiment of this document is schematically shown.

[0238] Fig.12 The method disclosed in can be Figure 3 or Fig.13 Specifically, for example, Fig.12 S1200 in the above may be performed by the entropy decoder 310 of the decoding device. Fig.12 S1210 to S1240 in may be performed by the predictor 330 of the decoding device, and Fig.12 S1250 in may be performed by the adder 340 or the reconstructor of the decoding device. Fig.12 The method disclosed in may include the embodiments described above in this document.

[0239] Reference Fig.12 , the decoding device obtains video / image information from the bitstream (S1000). The video / image information may include at least one of information about an inter-frame prediction mode or information for indicating motion information of a current block. The video / image information also includes residual information. For example, the decoding device may obtain the video / image information by parsing or decoding the bitstream. For example, the prediction-related information may include information indicating a prediction mode and / or motion information for generating a prediction sample of the current block. The prediction-related information may include selection information or information about a motion vector difference.

[0240] The information indicating the motion information of the current block may include the above-mentioned selection information (eg, mvp flag information or mvp index information, etc.). The mvp flag information may include the above-mentioned mvp_10_flag and / or mvp_11_flag. In addition, the information indicating the motion information of the current block may include information about MVD.

[0241] For example, the selection information may also be referred to as index information, and may also be referred to as an MVP flag or an MVP index. That is, the selection information may indicate information for indicating a motion vector predictor of a current block in a motion vector predictor candidate list. For example, when bidirectional prediction is applied to the current block, the selection information may include selection information for L0 prediction and selection information for L1 prediction. The selection information for L0 prediction may indicate information indicating a motion vector predictor in an L0 motion vector predictor candidate list for L0 prediction, which will be described later, and the selection information for L1 prediction may indicate information indicating a motion vector predictor in an L1 motion vector predictor candidate list for L1 prediction, which will be described later.

[0242] For example, the information about the motion vector difference (MVD) may include information for deriving the motion vector difference. For example, the information about the motion vector difference may include at least one of an abs_mvd_greater0_flag syntax element, an abs_mvd_greater1_flag syntax element, an abs_mvd_minus2 syntax element, or an mvd_sign_flag syntax element, but is not limited thereto because it may also include other information. For example, when bidirectional prediction is applied to the current block, the information about the motion vector difference may include information about the motion vector difference for L0 prediction and information about the motion vector difference for L1 prediction.

[0243] For information about the inter-frame prediction mode, the video / image information may include inter-frame prediction type information (e.g., inter_pred_idc), a general merge flag, SMVD flag information, L1 motion vector difference zero flag information, SMVD enable flag information, and / or inter-frame affine flag information. For example, when the value of the general merge flag is 0, it may indicate that the MVP mode is applied to the current block. The inter-frame prediction type information may indicate whether bidirectional prediction is applied to the current block. Specifically, for example, the inter-frame prediction type information may indicate whether L0 prediction, L1 prediction, or bidirectional prediction is applied to the current block. The prediction-related information may include information about the motion vector difference.

[0244] For example, the image information includes L1 motion vector difference zero flag information, the image information includes a coding unit (CU) syntax for the current block, and based on the L1 motion vector difference zero flag information, it can be determined whether the CU syntax includes SMVD flag information indicating whether a symmetric motion vector difference (SMVD) is applied to the current block.

[0245] Specifically, for example, the image information may include header information. The header information may include a slice header or a picture header. The header information may include L1 motion vector difference zero flag information, and based on the case where the value of the L1 motion vector difference zero flag information is 0, the CU syntax may include SMVD flag information. For example, when the value of the mvd_l1_zero_flag syntax element is 1, the decoding device may not parse the sym_mvd_flag syntax element, and the encoding device may configure the sym_mvd_flag syntax element configuration not to be parsed (from the bitstream, video / image information, CU syntax, inter-frame prediction mode information, or prediction-related information).

[0246] In addition, as an example, based on the case where the value of the L1 motion vector difference zero flag information is 1, the CU syntax may not include the SMVD flag information. In this case, the decoding device may infer that the value of the SMVD flag information is 0 without parsing the SMVD flag information.

[0247] In addition, as an example, whether the SMVD flag information is included in the CU syntax is determined based on the value of the symmetric motion vector difference reference index of the current block, and based on the L1 motion vector difference zero flag information having a value of 1, the value of the symmetric motion vector difference reference index is derived as -1, and based on the symmetric motion vector difference reference index having a value of -1, it is determined that the SMVD flag information is not included in the CU syntax. For example, the symmetric motion vector difference reference index may include an L0 symmetric motion vector difference reference index and an L1 symmetric motion vector difference reference index, both of which may be determined to be values ​​of -1. Here, the L0 symmetric motion vector difference reference index may be expressed as RefIdxSymL0, and the L1 symmetric motion vector difference reference index may be expressed as RefIdxSymL1. For example, when RefIdxSymL0 and RefIdxSymL1 are respectively greater than -1, the SMVD flag information may be included in the inter-prediction mode information or the CU syntax. Alternatively, for example, the inter prediction mode information or the CU syntax may include a symmetric motion vector difference flag based on RefIdxSymL0 being greater than -1 and RefIdxSymL1 being greater than -1.

[0248] In addition, as an example, the image information includes a sequence parameter set (SPS), the SPS includes SMVD enable flag information, the CU syntax includes prediction type information and inter-frame affine flag information, the prediction type information indicates whether bidirectional prediction is applied to the current block, and the CU syntax can include SMVD flag information based on the SMVD enable flag information, the prediction type information, and the inter-frame affine flag information.

[0249] Specifically, for example, based on the case where the inter-frame prediction type information indicates bidirectional prediction, the value of the L1 motion vector difference zero flag information is 0, the value of the SMVD enable flag information is 1, and the value of the inter-frame affine flag information is 0, the SMVD flag information may be included in the CU syntax to be explicitly signaled. That is, when the value of the L1 motion vector difference zero flag information is 1, the SMVD flag information may not be explicitly signaled. In this case, the decoding device may implicitly infer the value of the SMVD flag information to be 0. Not signaling the SMVD flag information may indicate that the SMVD flag information is not included in the prediction related information (or inter-frame prediction mode information) or the CU syntax.

[0250] The video / image information may include information about the motion vector difference. For example, the information about the motion vector difference may include information indicating the motion vector difference. When SMVD is applied, the information about the motion vector difference may include only information about the L0 motion vector difference, and as described above, the L1 motion vector difference may be derived based on the L0 motion vector difference.

[0251] The zero flag of the L1 motion vector difference may indicate information about whether the L1 motion vector difference is 0, and may be referred to as an L1 motion vector difference zero flag, an L1 MVD zero flag, and an MVD L1 zero flag. In addition, the L1 motion vector difference zero flag may be expressed as an mvd_11_zero_flag syntax element or a ph_mvd_11_zero_flag syntax element. In addition, the SMVD flag information may indicate information about whether the L0 motion vector difference and the L1 motion vector difference are symmetrical, and may be expressed as a sym_mvd_flag syntax element.

[0252] Alternatively, for example, the L1 motion vector difference may be represented by the L0 motion vector difference based on the L1 motion vector difference zero flag being equal to 0 or the symmetric motion vector difference flag being equal to 1. That is, when the value of the L1 motion vector difference zero flag is 0 or the value of the symmetric motion vector difference flag is 1, the L1 motion vector difference may be represented by the L0 motion vector difference. Alternatively, the L1 motion vector difference may be represented as a mirror value of the L0 motion vector difference. For example, when the value of the mvd_11_zero_flag syntax element or the ph_mvd_11_zero_flag syntax element is 0 or the value of the sym_mvd_flag syntax element is 1, MvdL1 may be represented based on MvdL0. Alternatively, MvdL1 may be determined as -MvdL0. For example, when MvdL1 is -MvdL0, the absolute value, i.e., the magnitude, of the L1 motion vector difference is the same as the absolute value, i.e., the magnitude, of the L0 motion vector difference, and the sign of the L1 motion vector difference is different from the sign of the L0 motion vector difference.

[0253] The decoding device derives an inter prediction mode of the current block based on the image information (S1210). For example, the decoding device may derive the inter prediction mode based on information about the inter prediction mode included in the image information. For example, the inter prediction mode may be a motion vector prediction (MVP) mode, but is not limited thereto. Here, the MVP mode may be referred to as an advanced motion vector prediction (AMVP) mode.

[0254] The decoding device may derive an MVP candidate list based on the inter prediction mode and neighboring blocks of the current block (S1220). For example, the decoding device may configure the MVP candidate list based on spatial neighboring candidate blocks and / or temporal neighboring candidate blocks. The MVP candidate list configured here may be the same as the MVP candidate list configured in the encoding device. The neighboring blocks may include the lower left neighboring block, the left neighboring block, the upper right neighboring block, the upper neighboring block, and the upper left neighboring block of the current block. For example, when bidirectional prediction is applied to the current block, an L0 MVP candidate list for L0 prediction and an L1 MVP candidate list for L1 prediction may be configured respectively.

[0255] The decoding device may generate motion information of the current block based on the MVP candidate list (S1230). For example, the decoding device may derive the motion vector predictor candidate of the current block in the motion vector predictor candidate list based on the above-mentioned selection information, and may derive the motion information (or motion vector) of the current block based on the derived motion vector predictor candidate. Alternatively, the motion information (or motion vector) of the current block may be derived based on the motion vector difference derived by the above-mentioned information about the motion vector difference and the derived motion vector predictor candidate. For example, when bidirectional prediction is applied to the current block, the L0 motion vector predictor for L0 prediction and the L1 motion vector predictor for L1 prediction based on the selection information for L0 prediction and the selection information for L1 prediction may be derived from the L0 motion vector predictor candidate list and the L1 motion vector predictor candidate list, respectively. For example, when bidirectional prediction is applied to the current block, the L0 motion vector difference and the L1 motion vector difference may be derived based on the information about the motion vector difference, respectively. Here, the L0 motion vector difference may be expressed as MvdL0, and the L1 motion vector difference may be expressed as MvdL1. In addition, the motion vectors of the current block may be derived as the L0 motion vector and the L1 motion vector, respectively.

[0256] The decoding device generates a prediction sample of the current block based on the motion information (S1240). For example, when bidirectional prediction is applied to the current block, the decoding device may generate an L0 prediction sample for L0 prediction based on the L0 motion vector, and generate an L1 prediction sample for L1 prediction based on the L1 motion vector. In addition, the decoding device may generate a prediction sample of the current block based on the L0 prediction sample and the L1 prediction sample.

[0257] The decoding device generates a reconstructed sample based on the predicted sample (S1250). A reconstructed block or a reconstructed picture may be derived based on the reconstructed sample. As described above, an in-loop filtering process may also be applied to the reconstructed sample / block / picture.

[0258] The decoding device may generate a reconstructed sample based on the predicted sample and the residual sample. In this case, the decoding device may derive the residual sample based on the residual information. For example, the residual information may represent information for deriving the residual sample, and may include information about the residual sample, inverse transform related information, and / or inverse quantization related information. For example, the residual information may include information about the quantized transform coefficient.

[0259] For example, the decoding device can obtain video / image information including all or part of the above-mentioned multiple pieces of information (or syntax elements) by decoding the bit stream or coding information. In addition, the bit stream or coding information can be stored in a computer-readable storage medium, and can cause the above-mentioned decoding method to be executed.

[0260] Although the method has been described based on a flowchart that lists steps or blocks in sequence in the above-mentioned embodiments, the steps of this document are not limited to a specific order, and specific steps can be performed in different steps or in a different order or simultaneously relative to the above-mentioned steps. In addition, it will be understood by a person of ordinary skill in the art that the steps in the flowchart are not exclusive, and another step may be included therein, or one or more steps in the flowchart may be deleted without affecting the scope of the present disclosure.

[0261] The above-mentioned method according to the present disclosure may be in the form of software, and the encoding device and / or decoding device according to the present disclosure may be included in a device for performing image processing (e.g., TV, computer, smart phone, set-top box, display device, etc.).

[0262] When the embodiments of the present disclosure are implemented by software, the above-mentioned methods can be implemented by modules (processing or functions) that perform the above-mentioned functions. The module can be stored in a memory and executed by a processor. The memory can be installed inside or outside the processor and can be connected to the processor via various well-known devices. The processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits and / or data processing devices. The memory may include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium and / or other storage devices. In other words, according to the embodiments of the present disclosure, it can be implemented and executed on a processor, a microprocessor, a controller or a chip. For example, the functional units illustrated in the corresponding figures can be implemented and executed on a computer, a processor, a microprocessor, a controller or a chip. In this case, information about the implementation (e.g., information about instructions) or an algorithm can be stored in a digital storage medium.

[0263] In addition, the decoding device and the encoding device of the embodiment of the present document can be included in a multimedia broadcast transceiver, a mobile communication terminal, a home theater video device, a digital theater video device, a surveillance camera, a video chat device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a portable camera, a video on demand (VoD) service provider, an over-the-top (OTT) video device, an Internet streaming service provider, a 3D video device, a virtual reality (VR) device, an augmented reality (AR) device, an image phone video device, a vehicle terminal (e.g., a vehicle (including an autonomous vehicle) terminal, an aircraft terminal or a ship terminal) and a medical video device; and can be used to process image signals or data. For example, an OTT video device can include a game console, a Blueray player, a networked TV, a home theater system, a smart phone, a tablet PC, and a digital video recorder (DVR).

[0264] In addition, the processing method of the embodiment of the application of this document can be generated in the form of a program executed by a computer and can be stored in a computer-readable recording medium. The multimedia data with a data structure according to the embodiment of this document can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices and distributed storage devices storing computer-readable data. The computer-readable recording medium may include, for example, a Blu-ray disc (BD), a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. The computer-readable recording medium also includes a medium implemented in the form of a carrier wave (e.g., transmission on the Internet). In addition, the bit stream generated by the encoding method can be stored in a computer-readable recording medium, or can be transmitted through a wired or wireless communication network.

[0265] In addition, the embodiments of the present document can be implemented as a computer program product based on a program code, and the program code can be executed on a computer according to the embodiments of the present document. The program code can be stored on a computer readable carrier.

[0266] Fig.14 An example of a content streaming system to which the embodiments of this document can be applied is shown.

[0267] Reference Fig.14 A content streaming system to which the embodiments of this document are applied may generally include an encoding server, a streaming server, a network server, a media storage, a user device, and a multimedia input device.

[0268] The encoding server is used to compress the content input from the multimedia input device such as a smart phone, a camera, a camcorder, etc. into digital data, generate a bit stream, and transmit it to the streaming server. As another example, in the case where the multimedia input device such as a smart phone, a camera, a camcorder, etc. directly generates a bit stream, the encoding server can be omitted.

[0269] The bitstream may be generated by the encoding method or the bitstream generating method to which the embodiments of this document are applied, and the streaming server may temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0270] The streaming server transmits multimedia data to the user device based on the user's request through the network server, which acts as a tool to inform the user of what services exist. When the user requests the service the user wants, the network server transfers the request to the streaming server, and the streaming server transmits the multimedia data to the user. In this regard, the content streaming system may include a separate control server, and in this case, the control server is used to control the commands / responses between the various devices in the content streaming system.

[0271] The streaming server may receive content from a media storage device and / or an encoding server. For example, in the case where the content is received from the encoding server, the content may be received in real time. In this case, the streaming server may store the bitstream for a predetermined period of time to smoothly provide a streaming service.

[0272] For example, user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation, tablet PCs, tablet PCs, ultrabooks, wearable devices (e.g., watch-type terminals (smart watches), glasses-type terminals (smart glasses), head-mounted displays (HMDs)), digital TVs, desktop computers, digital signage, etc.

[0273] Each server in the content streaming system may be operated as a distributed server, and in this case, data received by each server may be processed in a distributed manner.

[0274] The claims in this specification can be combined in various ways. For example, the technical features in the method claims of this specification can be combined to be implemented or performed in a device, and the technical features in the device claims can be combined to be implemented or performed in a method. In addition, the technical features in the method claims and the device claims can be combined to be implemented or performed in a device. In addition, the technical features in the method claims and the device claims can be combined to be implemented or performed in a method.

Claims

1. An image decoding device, the image decoding device comprising: Memory: and at least one processor connected to the memory, wherein the at least one processor is configured to: Obtain image information from a bitstream; deriving an inter-frame prediction mode for a current block based on the image information; Derived a motion vector predictor MVP candidate list of the current block based on neighboring blocks of the current block and the inter prediction mode; deriving motion information of the current block based on the MVP candidate list; generating a prediction sample of the current block based on the motion information; generating a reconstructed sample based on the predicted sample, The motion information includes at least one of an L0 motion vector for L0 prediction or an L1 motion vector for L1 prediction, wherein the L0 motion vector is derived based on an L0 motion vector predictor and an L0 motion vector difference, and the L1 motion vector is derived based on an L1 motion vector predictor and an L1 motion vector difference, Wherein, the image information includes an L1 motion vector difference zero flag, and The image information includes a coding unit CU syntax for the current block, The CU syntax includes a symmetric motion vector difference (SMVD) flag of the current block. wherein, based on the value of the SMVD flag being equal to 1, the L1 motion vector difference is derived from the L0 motion vector difference, wherein, based on the value of the L1 motion vector difference zero flag being equal to 1, the L1 motion vector difference is derived to be 0, and Among them, only when the value of the SMVD flag is not equal to 1, the L1 motion vector difference is derived as 0.

2. The image decoding device according to claim 1, wherein: The image information includes header information, Wherein, the header information includes the L1 motion vector difference zero flag, Wherein, based on the value of the L1 motion vector difference zero flag being equal to 0, the CU syntax includes the SMVD flag.

3. The image decoding device according to claim 1, wherein: Based on the value of the L1 motion vector difference zero flag being equal to 1, the CU syntax does not include the SMVD flag.

4. The image decoding device according to claim 1, wherein: determining whether the SMVD flag is included in the CU syntax based on a value of a symmetric motion vector difference reference index of the current block, Wherein, based on the value of the L1 motion vector difference zero flag being equal to 1, the value of the symmetric motion vector difference reference index is derived as -1, and Wherein, based on the value of the symmetric motion vector difference reference index being equal to -1, it is determined that the SMVD flag is not included in the CU syntax.

5. The image decoding device according to claim 1, wherein: The image information includes a sequence parameter set SPS, Wherein, the SPS includes an SMVD enable flag, The CU syntax includes inter-frame prediction type information and an inter-frame affine flag, wherein the inter-frame prediction type information indicates whether bidirectional prediction is applied to the current block, The CU syntax further includes the SMVD flag based on the SMVD enable flag, the inter prediction type information and the inter affine flag.

6. The image decoding device according to claim 1, wherein: Based on the value of the L1 motion vector difference zero flag being equal to 0 and the value of the SMVD flag being equal to 1, the L1 motion vector difference is derived from the L0 motion vector difference.

7. The image decoding device according to claim 6, wherein: The absolute value of the L1 motion vector difference is equal to the absolute value of the L0 motion vector difference, and The sign of the L1 motion vector difference is different from the sign of the L0 motion vector difference.

8. An image encoding device, the image encoding device comprising: Memory: and at least one processor connected to the memory, wherein the at least one processor is configured to: Derives a motion vector predictor MVP candidate list of the current block based on neighboring blocks and an inter-frame prediction mode of the current block; generating information indicating motion information of the current block based on the MVP candidate list; and encoding image information including at least one of the information about the inter prediction mode or the information indicating the motion information of the current block, The motion information includes at least one of an L0 motion vector for L0 prediction or an L1 motion vector for L1 prediction, wherein the L0 motion vector is derived based on an L0 motion vector predictor and an L0 motion vector difference, and the L1 motion vector is derived based on an L1 motion vector predictor and an L1 motion vector difference, Wherein, the image information includes an L1 motion vector difference zero flag, and The image information includes a coding unit CU syntax for the current block, The CU syntax includes a symmetric motion vector difference (SMVD) flag of the current block. wherein, based on the value of the SMVD flag being equal to 1, the L1 motion vector difference is derived from the L0 motion vector difference, wherein, based on the value of the L1 motion vector difference zero flag being equal to 1, the L1 motion vector difference is derived to be 0, and Among them, only when the value of the SMVD flag is not equal to 1, the L1 motion vector difference is derived as 0.

9. The image encoding device according to claim 8, wherein: The image information includes header information, Wherein, the header information includes the L1 motion vector difference zero flag, Wherein, based on the value of the L1 motion vector difference zero flag being equal to 0, the CU syntax includes the SMVD flag.

10. The image encoding device according to claim 8, wherein: Based on the value of the L1 motion vector difference zero flag being equal to 1, the CU syntax does not include the SMVD flag.

11. The image encoding device according to claim 8, wherein: determining whether the SMVD flag is included in the CU syntax based on a value of a symmetric motion vector difference reference index of the current block, Wherein, based on the value of the L1 motion vector difference zero flag being equal to 1, the value of the symmetric motion vector difference reference index is derived as -1, and Wherein, based on the value of the symmetric motion vector difference reference index being equal to -1, it is determined that the SMVD flag is not included in the CU syntax.

12. The image encoding device according to claim 8, wherein: The image information includes a sequence parameter set SPS, Wherein, the SPS includes an SMVD enable flag, The CU syntax includes inter-frame prediction type information and an inter-frame affine flag, wherein the inter-frame prediction type information indicates whether bidirectional prediction is applied to the current block, The CU syntax further includes the SMVD flag based on the SMVD enable flag, the inter prediction type information and the inter affine flag.

13. The image encoding device according to claim 8, wherein: Based on the value of the L1 motion vector difference zero flag being equal to 0 and the value of the SMVD flag being equal to 1, the L1 motion vector difference is derived from the L0 motion vector difference.

14. A device for transmitting image data, the device comprising: at least one processor configured to generate a bitstream for image information, wherein the bitstream is generated based on the following operations: deriving a motion vector predictor MVP candidate list of the current block based on neighboring blocks and an inter-frame prediction mode of the current block, generating information indicating motion information of the current block based on the MVP candidate list, and encoding image information to generate the bitstream, wherein the image information includes at least one of the information about the inter-frame prediction mode or the information indicating the motion information of the current block; and a transmitter configured to transmit data comprising the bit stream, The motion information includes at least one of an L0 motion vector for L0 prediction or an L1 motion vector for L1 prediction, wherein the L0 motion vector is derived based on an L0 motion vector predictor and an L0 motion vector difference, and the L1 motion vector is derived based on an L1 motion vector predictor and an L1 motion vector difference, Wherein, the image information includes an L1 motion vector difference zero flag, and The image information includes a coding unit CU syntax for the current block, wherein the CU syntax includes a symmetric motion vector difference SMVD flag of the current block, wherein, based on the value of the SMVD flag being equal to 1, the L1 motion vector difference is derived from the L0 motion vector difference, wherein, based on the value of the L1 motion vector difference zero flag being equal to 1, the L1 motion vector difference is derived to be 0, and Among them, only when the value of the SMVD flag is not equal to 1, the L1 motion vector difference is derived as 0.

Images