Video coding method and apparatus using motion vector difference

Abstract

To provide a method and apparatus for increasing image / video coding efficiency.SOLUTION: According to embodiments of the present document, a prediction procedure can be performed for image / video coding, and the prediction procedure can comprise merge mode motion vector differences (MMVD) and symmetric motion vector differences (SMVD) according to inter prediction. The inter prediction can be performed on the basis of reference pictures of a current picture, and types of the reference pictures (e.g., a long-term reference picture, a short-term reference picture, etc.) can be taken into account for the inter prediction. Accordingly, performance and coding efficiency in the prediction procedure can be increased.SELECTED DRAWING: Figure 20

Description

[Technical Field]

[0001] This document relates to a video coding method and apparatus using motion vector differentials. [Background technology]

[0002] In recent years, demand for high-resolution, high-quality images / videos, such as 4K or 8K or higher UHD (Ultra High Definition) images / videos, has been increasing in various fields. As the resolution and quality of image / video data increases, the amount of information or bits to be transmitted increases relatively compared to existing image / video data. Therefore, when transmitting image data using existing media such as wired or wireless broadband lines or storing image / video data using existing storage media, transmission costs and storage costs increase.

[0003] In addition, interest in and demand for immersive media such as VR (Virtual Reality), AR (Artificial Reality) content, and holograms have been increasing in recent years, and the broadcast of images / videos with different image characteristics from real images, such as game images, has been increasing.

[0004] This necessitates the development of highly efficient image / video compression technologies to effectively compress and transmit, store, and play back high-resolution, high-quality image / video information that has the various characteristics described above.

[0005] In particular, inter prediction in image / video coding can utilize motion vector differentials. In connection with the above procedure, there is discussion of deriving motion vector differentials based on the reference picture type (e.g., shot-term or long-term reference picture). Summary of the Invention [Means for solving the problem]

[0006] According to one embodiment of this document, a method and apparatus for increasing video coding efficiency are provided.

[0007] According to one embodiment of this document, a method and apparatus for performing efficient inter prediction in a video coding system are provided.

[0008] According to one embodiment of this document, a method and apparatus for signaling information related to motion vector difference in inter prediction are provided.

[0009] According to one embodiment of this document, when dual prediction is applied to a current block, a method and apparatus for signaling information related to L0 motion vector difference and L1 motion vector difference are provided.

[0010] According to an embodiment of this document, a method and apparatus for signaling an SMVD flag are provided.

[0011] According to one embodiment of this document, a specific reference picture type is used for the derivation of symmetric motion vector difference.

[0012] According to one embodiment of this document, a procedure for deriving an SMVD reference index is performed using a short-term reference picture (a picture marked as being used for short-term reference).

[0013] According to one embodiment of this document, a video decoding method executed by a decoding apparatus is provided.

[0014] According to one embodiment of this document, a decoding apparatus for performing video decoding is provided.

[0015] According to one embodiment of this document, a video encoding method executed by an encoding apparatus is provided.

[0016] According to an embodiment of this document, an encoding device that performs video / video encoding is provided.

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

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

Advantages of the Invention

[0019] According to this document, the overall video / video compression efficiency can be increased.

[0020] According to this document, information regarding the motion vector difference can be efficiently signaled.

[0021] According to this document, when dual prediction is applied to the current block, the L1 motion vector difference can be efficiently derived.

[0022] According to this document, the information used for the derivation of the L1 motion vector difference is signaled based on the type of the reference picture, and thus the complexity of the coding system can be reduced.

[0023] According to an embodiment of this document, efficient inter prediction can be performed by using a specific reference picture type for the derivation of the reference picture index for SMVD. <L

[0024] The effects that can be obtained through a specific example of this document are not limited to the effects listed above. For example, there can be various technical effects that can be understood or induced by a person having ordinary skill in the related art from this document. Accordingly, the specific effects of this document can include various effects that can be understood or induced from the technical features of this document, rather than being limited to those explicitly described in this document.

Brief Description of the Drawings

[0025]

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Embodiments for Carrying Out the Invention

[0026] The disclosure of this document can be modified in various ways and can have various embodiments. However, specific embodiments will be illustrated in the drawings and described in detail. This is not, however, intended to limit the present disclosure to the specific embodiments. The terms used in this document are merely used to describe specific embodiments and are not intended to limit the technical idea of the embodiments in this document. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this document, terms such as "including" or "having" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the document, and should be understood not to preclude in advance the possibility of the presence or addition of one or more different features, numbers, steps, operations, components, parts, or combinations thereof.

[0027] On the other hand, each configuration in the drawings described in this document is shown independently for the convenience of explaining different characteristic functions, and does not mean that each configuration is implemented by separate hardware or separate software. For example, among the respective configurations, two or more configurations may be combined to form one configuration, or one configuration may be divided into a plurality of configurations. Embodiments in which each configuration is integrated and / or separated are also included in the disclosure scope of this document.

[0028] Hereinafter, embodiments of this document will be described with reference to the accompanying drawings. Hereinafter, the same reference numerals may be used for the same components in the drawings, and duplicate descriptions of the same components may be omitted.

[0029] FIG. 1 schematically shows an example of a video / video coding system to which the embodiments of this document can be applied.

[0030] As shown in FIG. 1, a video / image coding system can include a first device (source device) and a second device (receiving device). The source device can transmit encoded video / image information or data to the receiving device in a file or streaming form via a digital storage medium or a network.

[0031] The source device can include a video source, an encoding device, and a transmitting unit. The receiving device can include a receiving unit, a decoding device, and a renderer. The encoding device can be referred to as a video / image encoding device, and the decoding device can be referred to as a video / image decoding device. A transmitter can be provided in the encoding device. A receiver can be provided in the decoding device. The renderer can include a display unit, and the display unit can also be composed of a separate device or an external component.

[0032] The video source can obtain video / images through processes such as video / image capture, synthesis, or generation. The video source can include a video / image capture device and / or a video / image generation device. The video / image capture device can include, for example, one or more cameras, a video / image archive containing previously captured video / images, etc. The video / image generation device can include, for example, a computer, a tablet, and a smartphone, etc., and can (electronically) generate video / images. For example, virtual video / images can be generated via a computer, etc., and in this case, the video / image capture process can be replaced by the process of generating related data.

[0033] The encoding device can encode the input video / image. The encoding device can perform a series of procedures such as prediction, transformation, quantization, etc. for compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0034] The transmitting unit can transmit the encoded video / image information or data output in the form of a bitstream to the receiving unit of the receiving device via a digital storage medium or a network in the form of a file or streaming. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitting unit can include elements for generating a media file via a predetermined file format and can include elements for transmission via a broadcast / communication network. The receiving unit can receive / extract the bitstream and transmit it to the decoding device.

[0035] The decoding device can decode the video / image by performing a series of procedures such as inverse quantization, inverse transformation, prediction, etc. corresponding to the operation of the encoding device.

[0036] The renderer can render the decoded video / image. The rendered video / image can be displayed via the display unit.

[0037] This document relates to video / video coding. For example, the methods / embodiments disclosed in this document can be applied to the methods disclosed in the VVC (versatile video coding) standard. Also, the methods / embodiments disclosed in this document can be applied to the methods disclosed in the EVC (essential video coding) standard, the AV1 (AOMedia Video 1) standard, the AVS2 (2nd generation of audio video coding standard), or the next-generation video / video coding standard (e.g., 267 or H.268, etc.).

[0038] This document presents various embodiments related to video / video coding, and unless otherwise noted, the embodiments may be combined with each other.

[0039] In this document, video can mean a collection of a series of images over time. A picture generally means a unit indicating one image in a specific time period, and a slice / tile is a unit that constitutes a part of a picture in coding. A slice / tile can include one or more CTUs (coding tree units). One picture can be composed of one or more slices / tiles. A tile is a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. The tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements in the picture parameter set. The tile row is a rectangular region of CTUs having a height specified by syntax elements in the picture parameter set and a width equal to the width of the picture.A tile scan may indicate a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a tile whereas tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture. A slice may include an integer number of complete tiles or an integer number of consecutive complete CTU rows within a tile of a picture that may be exclusively contained in a single NAL unit.

[0040] On the other hand, one picture can be divided into two or more sub - pictures. A sub - picture may be an rectangular region of one or more slices within a picture.

[0041] A pixel or pel can mean the smallest unit that constitutes one picture (or video). Also, as a term corresponding to a pixel, "sample" can be used. A sample can generally indicate a pixel or a pixel value, can indicate only the pixel / pixel value of the luma component, or can also indicate only the pixel / pixel value of the chroma component.

[0042] A unit can indicate the basic unit of video processing. A unit can include at least one of a specific region of a picture and information related to that region. One unit can include one luma block and two chroma (e.g., cb, cr) blocks. A unit can, in some cases, be used interchangeably with terms such as "block" or "area". In general, an M×N block can include a set (or array) of samples (or sample array) or transform coefficients consisting of M columns and N rows.

[0043] In this document, "A or B" can mean "only A", "only B", or "both A and B". In other words, in this document, "A or B" can be interpreted as "A and / or B". For example, in this document, "A, B or C" can mean "only A", "only B", "only C", or "any combination of A, B and C".

[0044] The slash ( / ) or comma used in this document can mean "and / or". For example, "A / B" can mean "A and / or B". Thus, "A / B" can mean "only A", "only B", or "both A and B". For example, "A, B, C" can mean "A, B or C".

[0045] In this document, "at least one of A and B" can mean "only A", "only B", or "both A and B". Also, in this document, expressions such as "at least one of A or B" and "at least one of A and / or B" can be interpreted in the same way as "at least one of A and B".

[0046] Also, in this document, "at least one of A, B and C" can mean "only A", "only B", "only C", or "any combination of A, B and C". Also, "at least one of A, B or C" and "at least one of A, B and / or C" can mean "at least one of A, B and C".

[0047] Also, the parentheses used in this document can mean "for example". Specifically, when it is shown as "prediction (intra prediction)", "intra prediction" can be proposed as an example of "prediction". In other words, "prediction" in this document is not limited to "intra prediction", and "intra prediction" can be proposed as an example of "prediction". Also, when it is shown as "prediction (i.e., intra prediction)", "intra prediction" can be proposed as an example of "prediction".

[0048] In this document, the technical features separately described within one drawing may be embodied separately or simultaneously.

[0049] FIG. 2 is a diagram schematically illustrating the configuration of a video / video encoding apparatus to which the embodiments of this document can be applied. Hereinafter, the encoding apparatus can include a video encoding apparatus and / or a video encoding apparatus.

[0050] As shown in FIG. 2, the encoding apparatus 200 can be configured to include an image partitioner 210, a predictor 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The predictor 220 can include an inter-predictor 221 and an intra-predictor 222. The residual processor 230 can include a transformer 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235. The residual processor 230 can further include a subtractor (231). The adder 250 can be called a reconstructor or a reconstructed block generator. The above-described image partitioner 210, predictor 220, residual processor 230, entropy encoder 240, adder 250, and filter 260 can be configured by one or more hardware components (e.g., an encoder chipset or a processor) according to an embodiment. Also, the memory 270 can include a DPB (decoded picture buffer) and can also be configured by a digital storage medium. The hardware component can further include the memory 270 as an internal / external component.

[0051] The video segmentation unit 210 can divide the input video (or picture, frame) input to the encoding device 200 into one or more processing units. As an example, the processing unit can be called a coding unit (CU). In this case, the coding unit can be recursively divided from a coding tree unit (CTU) or a largest coding unit (LCU) by a QTBTTT (Quad-tree binary-tree ternary-tree) structure. For example, one coding unit can be divided into multiple coding units with a deeper depth based on a quad-tree structure, a binary-tree structure, and / or a ternary structure. In this case, for example, the quad-tree structure can be applied first, and then the binary-tree structure and / or the ternary structure can be applied. Or, the binary-tree structure can also be applied first. The coding procedure according to the present disclosure can be performed based on the final coding unit that is no longer divided. In this case, based on the coding efficiency according to the video characteristics, etc., the largest coding unit can be used as the final coding unit, or, if necessary, the coding unit can be recursively divided into coding units with a deeper depth, and the coding unit with the optimal size can be used as the final coding unit. Here, the coding procedure can include procedures such as prediction, conversion, and restoration described later. As another example, the processing unit can further include a prediction unit (PU: Prediction Unit) or a transform unit (TU: Transform Unit). In this case, the prediction unit and the transform unit can be divided or partitioned from the above-mentioned final coding unit, respectively.The prediction unit can be a unit of sample prediction, and the conversion unit can be a unit for deriving a conversion coefficient and / or a unit for deriving a residual signal from the conversion coefficient.

[0052] The term "unit" can, in some cases, be used interchangeably with terms such as "block" or "area". In a general case, an M×N block can represent a set of samples or transform coefficients, etc., consisting of M columns and N rows. A sample can generally represent a pixel or a pixel value, and can represent only the pixel / pixel value of the luma component, or only the pixel / pixel value of the chroma component. A sample can be used as a term corresponding to a pixel or a pel in one picture (or video).

[0053] The encoding device 200 can subtract the prediction signal (predicted block, predicted sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from the input video signal (original block, original sample array) to generate a residual signal (residual signal, residual block, residual sample array), and the generated residual signal is transmitted to the conversion unit 232. In this case, as shown in the figure, the unit that subtracts the prediction signal (predicted block, predicted sample array) from the input video signal (original block, original sample array) within the encoder 200 can be called the subtraction unit 231. The prediction unit can perform prediction on the block to be processed (hereinafter referred to as the current block) and generate a predicted block including the predicted samples for the current block. The prediction unit can determine whether intra prediction or inter prediction is applied in units of the current block or CU. The prediction unit can generate various pieces of information related to prediction, such as prediction mode information, and transmit them to the entropy encoding unit 240 as described later in the description of each prediction mode. The information related to prediction can be encoded by the entropy encoding unit 240 and output in the form of a bit stream.

[0054] The intra prediction unit 222 can predict the current block by referring to samples within the current picture. The samples to be referred to can be located adjacent to the current block or remotely located depending on the prediction mode. In intra prediction, the prediction mode can include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes can include, for example, the DC mode and the Planar mode. The directional modes can include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the level of detail of the prediction direction. However, this is an example, and more or fewer directional prediction modes can be used depending on the setting. The intra prediction unit 222 can also determine the prediction mode to be applied to the current block using the prediction mode applied to the adjacent block.

[0055] The inter prediction unit 221 can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between adjacent blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can further include inter prediction direction (L0 prediction, L1 prediction, BI prediction, etc.) information. In the case of inter prediction, the adjacent blocks can 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 can be the same or different. The temporal neighboring block can be called by names such as a collocated reference block, a collocated CU (col CU), etc., and the reference picture including the temporal neighboring block can also be called a collocated picture (colPic). For example, the inter prediction unit 221 can construct a motion information candidate list based on adjacent blocks, and generate information indicating which candidate is used to derive the motion vector and / or the reference picture index of the current block. Inter prediction can be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter prediction unit 221 can use the motion information of adjacent blocks as the motion information of the current block. In the case of the skip mode, unlike the merge mode, a residual signal may not be transmitted.In the case of the motion information prediction (motion vector prediction, MVP) mode, the motion vector of an adjacent block is used as a motion vector predictor, and the motion vector difference is signaled to indicate the motion vector of the current block.

[0056] The prediction unit 220 can generate a prediction signal based on various prediction methods described later. For example, for the prediction of one block, the prediction unit can apply not only intra prediction or inter prediction, but also apply intra prediction and inter prediction simultaneously. This can be called combined inter and intra prediction (CIIP). Also, the prediction unit can be based on the intra block copy (IBC) prediction mode or the palette mode for the prediction of the block. The IBC prediction mode or the palette mode can be used for content video / motion video coding such as games, for example, like SCC (screen content coding). IBC basically performs prediction within the current picture, but can be performed in the same way as inter prediction in terms of deriving a reference block within 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, the sample values in the picture can be signaled based on the information regarding the palette table and the palette index.

[0057] The prediction signal generated via the prediction unit (including the inter prediction unit 221 and / or the intra prediction unit 222) can be used to generate a restored signal or can be used to generate a residual signal. The conversion unit 232 can apply a conversion technique to the residual signal to generate transform coefficients. For example, the conversion technique can include at least one of DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), GBT (Graph-Based Transform), or CNT (Conditionally Non-linear Transform). Here, GBT means the conversion obtained from this graph when expressing the relationship information between pixels as a graph. CNT means the conversion obtained based on generating a prediction signal using all previously reconstructed pixels. Also, the conversion process may be applied to a pixel block having the same size of a square or may be applied to a block of a variable size that is not a square.

[0058] The quantization unit 233 quantizes the transform coefficients and transmits them to the entropy encoding unit 240. The entropy encoding unit 240 can encode the quantized signal (information regarding the quantized transform coefficients) and output it as a bitstream. The information regarding the quantized transform coefficients can be called residual information. The quantization unit 233 can reorder the block-form quantized transform coefficients in a one-dimensional vector form based on the coefficient scan order, and can also generate the information regarding the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoding unit 240 can perform various encoding methods such as, for example, exponential Golomb, CAVLC (context-adaptive variable length coding), CABAC (context-adaptive binary arithmetic coding), etc. The entropy encoding unit 240 can encode, together or separately, information necessary for video / image restoration (e.g., values of syntax elements, etc.) in addition to the quantized transform coefficients. The encoded information (e.g., encoded video / video information) can be transmitted or stored in units of NAL (network abstraction layer) units in bitstream form. The video / video information can further include information regarding 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). Also, the video / video information can further include general constraint information. In this document, the information and / or syntax elements transmitted / signaled from the encoding device to the decoding device can be included in the video / video information.The video / video information can be encoded through the encoding procedure described above and included in the bitstream. The bitstream can be transmitted via a network or stored in a digital storage medium. Here, the network can include a broadcast network and / or a communication network, etc., and the digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The signal output from the entropy encoding unit 240 can be configured such that a transmission unit (not shown) for transmission and / or a storage unit (not shown) for storage are internal / external elements of the encoding apparatus 200, or the transmission unit can be included in the entropy encoding unit 240.

[0059] The quantized transform coefficients output from the quantization unit 233 can be used to generate a prediction signal. For example, by applying inverse quantization and inverse transformation to the quantized transform coefficients via the inverse quantization unit 234 and the inverse transform unit 235, a residual signal (residual block or residual sample) can be restored. The addition unit 155 can generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the restored residual signal to the prediction signal output from the inter prediction unit 221 or the intra prediction unit 222. When there is no residual for the block to be processed, as in the case where the skip mode is applied, the predicted block can be used as the reconstructed block. The addition unit 250 can be called a restoration unit or a reconstructed block generation unit. The generated reconstructed signal can be used for intra prediction of the next block to be processed within the current picture and, as will be described later, can also be used for inter prediction of the next picture after passing through filtering.

[0060] On the other hand, LMCS (luma mapping with chroma scaling) can also be applied in the picture encoding and / or restoration process.

[0061] The filtering unit 260 can apply filtering to the restored signal to improve the subjective / objective image quality. For example, the filtering unit 260 can apply various filtering methods to the restored picture to generate a modified restored picture, and store the modified restored picture in the memory 270, specifically, in the DPB of the memory 270. The various filtering methods can include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like. The filtering unit 260 can generate various information related to filtering and transmit it to the entropy encoding unit 240 as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoding unit 240 and output in the form of a bit stream.

[0062] The modified restored picture transmitted to the memory 270 can be used as a reference picture in the inter prediction unit 221. Through this, when inter prediction is applied, the encoding apparatus can avoid prediction mismatches between the encoding apparatus 100 and the decoding apparatus, and can also improve the encoding efficiency.

[0063] The DPB of the memory 270 can store the corrected reconstructed picture for use as a reference picture in the inter prediction unit 221. The memory 270 can store the motion information of the blocks for which the motion information in the current picture has been derived (or encoded) and / or the motion information of the blocks in the already reconstructed picture. The stored motion information can be transmitted to the inter prediction unit 221 for utilization as the motion information of spatially adjacent blocks or temporally adjacent blocks. The memory 270 can store the reconstructed samples of the reconstructed blocks in the current picture and can transmit them to the intra prediction unit 222.

[0064] FIG. 3 is a diagram schematically illustrating the configuration of a video / video decoding device to which the embodiments of this document can be applied. Hereinafter, the decoding device can include a video decoding device and / or a video decoding device.

[0065] As shown in FIG. 3, the decoding apparatus 300 can be configured to include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filtering unit 350, and a memory 360. The predictor 330 can include an intra predictor 331 and an inter predictor 332. The residual processor 320 can include a dequantizer 321 and an inverse transformer 321. The entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filtering unit 350 described above can be configured by one hardware component (e.g., a decoder chipset or a processor) according to an embodiment. Also, the memory 360 can include a DPB (decoded picture buffer) and can also be configured by a digital storage medium. The hardware component can further include the memory 360 as an internal / external component.

[0066] If a bitstream including video / video information is input, the decoding device 300 can restore the video corresponding to the process in which the video / video information is processed by the encoding device in FIG. 3. For example, the decoding device 300 can derive units / blocks based on the block splitting related information obtained from the bitstream. The decoding device 300 can perform decoding using the processing units applied in the encoding device. Therefore, the processing unit for decoding can be, for example, a coding unit, and the coding unit can be split according to a quad tree structure, a binary tree structure, and / or a ternary tree structure from a coding tree unit or a maximum coding unit. One or more transform units can be derived from the coding unit. Then, the restored video signal decoded and output via the decoding device 300 can be played back via a playback device.

[0067] The decoding device 300 can receive the signal output from the encoding device in FIG. 3 in the form of a bitstream, and the received signal can be decoded via the entropy decoding unit 310. For example, the entropy decoding unit 310 can parse the bitstream to derive information (e.g., video / video information) necessary for video restoration (or picture restoration). The video / video information can further include information regarding 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). Also, the video / video information can further include general constraint information. The decoding device can further decode a picture based on the information regarding the parameter set and / or the general constraint information. The signaling / received information and / or syntax elements described later in this document can be decoded via the decoding procedure and obtained from the bitstream. For example, the entropy decoding unit 310 can decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output the value of the syntax element necessary for video restoration and the quantized value of the transform coefficient regarding the residual. More specifically, the CABAC entropy decoding method receives the bin corresponding to each syntax element in the bitstream, determines a context model using the syntax element information to be decoded, the information adjacent to the decoding target block, and the decoding information of the decoding target block or the information of the symbol / bin decoded in the previous step, predicts the occurrence probability of the bin according to the determined context model, performs arithmetic decoding of the bin, and can generate a symbol corresponding to the value of each syntax element.At this time, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. Among the information decoded by the entropy decoding unit 310, the information related to prediction is provided to the prediction unit (inter prediction unit 332 and intra prediction unit 331), and the residual value obtained by performing entropy decoding in the entropy decoding unit 310, that is, the quantized transform coefficient and related parameter information, can be input to the residual processing unit 320. The residual processing unit 320 can derive a residual signal (residual block, residual sample, residual sample array). Also, among the information decoded by the entropy decoding unit 310, the information related to filtering can be provided to the filtering unit 350. On the other hand, a receiving unit (not shown) that receives the signal output from the encoding device can be further configured as an internal / external element of the decoding device 300, or the receiving unit can be a component of the entropy decoding unit 310. On the other hand, the decoding device according to the present document can be called a video / video / picture decoding device, and the decoding device can be classified into an information decoder (video / video / picture information decoder) and a sample decoder (video / video / picture sample decoder). The information decoder can include the entropy decoding unit 310, and the sample decoder can include at least one of the inverse quantization unit 321, inverse transform unit 322, addition unit 340, filtering unit 350, memory 360, inter prediction unit 332, and intra prediction unit 331.

[0068] In the inverse quantization unit 321, the quantized transform coefficients can be inverse quantized to output the transform coefficients. The inverse quantization unit 321 can reorder the quantized transform coefficients in a two-dimensional block form. In this case, the reordering can be performed based on the coefficient scan order performed by the encoding device. The inverse quantization unit 321 can perform inverse quantization on the quantized transform coefficients using quantization parameters (e.g., quantization step size information) to obtain the transform coefficients.

[0069] In the inverse transform unit 322, the transform coefficients are inversely transformed to obtain a residual signal (residual block, residual sample array).

[0070] The prediction unit can perform prediction on the current block and generate a predicted block including the predicted samples for the current block. The prediction unit can determine whether intra prediction or inter prediction is applied to the current block based on the information regarding the prediction output from the entropy decoding unit 310, and can determine a specific intra / inter prediction mode.

[0071] The prediction unit 330 can generate a prediction signal based on various prediction methods described below. For example, the prediction unit can apply intra prediction or inter prediction for predicting a single block, and can also apply intra prediction and inter prediction simultaneously. This can be called combined inter and intra prediction (CIIP). Further, the prediction unit can be based on the intra block copy (IBC) prediction mode or the palette mode for predicting a block. The IBC prediction mode or the palette mode can be used for content video / moving picture coding such as games, for example, like SCC (screen content coding). IBC basically performs prediction within the current picture, but can be performed in the same way as inter prediction in terms of deriving a reference block within the current picture. That is, IBC can utilize 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 regarding the palette table and the palette index can be included in and signaled in the video / video information.

[0072] The intra prediction unit 331 can predict the current block by referring to samples within the current picture. The samples to be referred to can be located adjacent to or away from the current block depending on the prediction mode. In intra prediction, the prediction mode can include a plurality of non-directional modes and a plurality of directional modes. The intra prediction unit 331 can also determine the prediction mode to be applied to the current block using the prediction mode applied to the adjacent block.

[0073] The inter prediction unit 332 can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between adjacent blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can further include inter prediction direction (L0 prediction, L1 prediction, BI prediction, etc.) information. In the case of inter prediction, the adjacent blocks can include spatial neighboring blocks existing in the current picture and temporal neighboring blocks existing in the reference picture. For example, the inter prediction unit 332 can construct a motion information candidate list based on adjacent blocks, and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter prediction can be performed based on various prediction modes, and the information regarding the prediction can include information indicating the mode of inter prediction for the current block.

[0074] The adder 340 can generate a restored signal (restored picture, restored block, restored sample array) by adding the obtained residual signal to the prediction signal (predicted block, predicted sample array) output from the prediction unit (including the inter prediction unit 332 and / or the intra prediction unit 331). When there is no residual for the processing target block, as in the case where the skip mode is applied, the predicted block can be used as the restored block.

[0075] The addition unit 340 can be called a restoration unit or a restoration block generation unit. The generated restoration signal can be used for intra prediction of the next processing target block within the current picture, and as will be described later, can be output after filtering, or can also be used for inter prediction of the next picture.

[0076] On the other hand, LMCS (luma mapping with chroma scaling) can also be applied during the picture decoding process.

[0077] The filtering unit 350 can apply filtering to the restoration signal to improve the subjective / objective image quality. For example, the filtering unit 350 can apply various filtering methods to the restored picture to generate a modified restored picture, and can transmit the modified restored picture to the memory 360, specifically, to the DPB of the memory 360. The various filtering methods can include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0078] The (modified) restored picture stored in the DPB of the memory 360 can be used as a reference picture in the inter prediction unit 332. The memory 360 can store the motion information of the blocks for which the motion information within the current picture has been derived (or decoded) and / or the motion information of the blocks within the already restored picture. The stored motion information can be transmitted to the inter prediction unit 260 for utilization as the motion information of spatially adjacent blocks or temporally adjacent blocks. The memory 360 can store the restored samples of the restored blocks within the current picture and can transmit them to the intra prediction unit 331.

[0079] In this specification, the examples described in the filtering unit 260, the inter prediction unit 221, and the intra prediction unit 222 of the encoding device 200 can be applied to the filtering unit 350, the inter prediction unit 332, and the intra prediction unit 331 of the decoding device 300 in the same or corresponding manner, respectively.

[0080] As described above, in performing video coding, prediction is executed to increase the compression efficiency. Through this, a predicted block including prediction samples for the current block, which is the block to be coded, can be generated. Here, the predicted block includes prediction samples in the spatial domain (or pixel domain). The predicted block is also derived in the encoding device and the decoding device, and the encoding device can increase the video coding efficiency by signaling information (residual information) about the residual between the original block, which is not the original sample value of the original block itself, and the predicted block to the decoding device. The decoding device can derive a residual block including residual samples based on the residual information, and combine the residual block and the predicted block to generate a restored block including restored samples, and can generate a restored picture including the restored block.

[0081] The residual information can be generated through conversion and quantization procedures. For example, an encoding device derives a residual block between the original block and the predicted block, executes a conversion procedure on the residual samples (residual sample array) included in the residual block to derive conversion coefficients, and executes a quantization procedure on the conversion coefficients to derive quantized conversion coefficients, thereby being able to signal the relevant residual information (via a bitstream) to a decoding device. Here, the residual information can include information such as the value information, position information, conversion technique, conversion kernel, quantization parameter, etc. of the quantized conversion coefficients. The decoding device can execute an inverse quantization / inverse conversion procedure based on the residual information to derive residual samples (or a residual block). The decoding device can generate a restored picture based on the predicted block and the residual block. Also, the encoding device can inverse quantize / inverse transform the quantized conversion coefficients for reference in the inter prediction of subsequent pictures to derive a residual block and generate a restored picture based on this.

[0082] In this document, at least one of quantization / inverse quantization and / or conversion / inverse conversion can be omitted. When the quantization / inverse quantization is omitted, the quantized conversion coefficients can be called conversion coefficients. When the conversion / inverse conversion is omitted, the conversion coefficients can also be called coefficients or residual coefficients, or, for the sake of uniformity of expression, can still be called conversion coefficients.

[0083] In this document, the quantized transform coefficient and the transform coefficient can each be referred to as a transform coefficient and a scaled transform coefficient, respectively. In this case, the residual information can include information regarding the transform coefficient, and the information regarding the transform coefficient can be signaled via a residual coding syntax. The transform coefficient can be derived based on the residual information (or the information regarding the transform coefficient), and the scaled transform coefficient can be derived via an inverse transform (scaling) for the transform coefficient. The residual sample can be derived based on an inverse transform (transformation) for the scaled transform coefficient. This can be similarly applied / expressed in other parts of this document.

[0084] Intra prediction can indicate a prediction that generates a predicted sample for a current block based on reference samples within a picture to which the current block belongs (hereinafter referred to as the current picture). When intra prediction is applied to the current block, adjacent reference samples used for intra prediction of the current block can be derived. The adjacent reference samples of the current block can include samples adjacent to the left boundary of the current block having a size of nW×nH and a total of 2×nH samples adjacent to the bottom-left, samples adjacent to the top boundary of the current block and a total of 2×nW samples adjacent to the top-right, and 1 sample adjacent to the top-left of the current block. Alternatively, the adjacent reference samples of the current block can also include a plurality of rows of upper adjacent samples and a plurality of columns of left adjacent samples. Further, the adjacent reference samples of the current block can also include a total of nH samples adjacent to the right boundary of the current block having a size of nW×nH, a total of nW samples adjacent to the bottom boundary of the current block, and 1 sample adjacent to the bottom-right of the current block.

[0085] However, some of the neighboring reference samples of the current block may not have been decoded yet or may not be available. In this case, the decoder can form neighboring reference samples for prediction by substituting samples that are not available with samples that are available, or can form neighboring reference samples for prediction through interpolation of available samples.

[0086] When the neighboring reference samples are derived, (i) prediction samples can be derived based on the average or interpolation of the neighboring reference samples of the current block, and (ii) the prediction samples can also be derived based on the reference samples that exist in a specific (prediction) direction with respect to the prediction samples among the neighboring reference samples of the current block. In the case of (i), it is called a non-directional mode or a non-angular mode, and in the case of (ii), it can be called a directional mode or an angular mode.

[0087] Also, among the neighboring reference samples, based on the prediction samples of the current block, the prediction samples can be generated through interpolation between a first neighboring sample located in the prediction direction of the intra prediction mode of the current block and a second neighboring sample located in the direction opposite to the prediction direction. The above-mentioned case can be called linear interpolation intra prediction (LIP). Also, chroma prediction samples can be generated based on luma samples using a linear model. In this case, it can be called the LM mode.

[0088] Also, a temporary prediction sample of the current block is derived based on the filtered adjacent reference samples, and a weighted sum of at least one reference sample derived by the intra prediction mode among the existing adjacent reference samples, i.e., the unfiltered adjacent reference samples, and the temporary prediction sample is calculated to derive a prediction sample of the current block. In the above-described case, it can be called PDPC (Position dependent intra prediction).

[0089] Also, the reference sample line with the highest prediction accuracy is selected from among the adjacent multiple reference sample lines of the current block, and a prediction sample is derived using the reference sample located in the prediction direction on the corresponding line. At this time, intra prediction coding can be performed by indicating (signaling) the used reference sample line to the decoding device. In the above-described case, it can be called multi-reference line intra prediction or MRL-based intra prediction.

[0090] Also, the current block is divided into vertical or horizontal sub-partitions, and intra prediction is performed based on the same intra prediction mode. Adjacent reference samples can be derived and used in units of the sub-partitions. That is, in this case, the intra prediction mode for the current block is also applied to the sub-partitions, and by deriving and using adjacent reference samples in units of the sub-partitions, in some cases, the intra prediction performance can be improved. Such a prediction method can be called ISP (intra sub-partitions)-based intra prediction.

[0091] The intra prediction method described above can be called an intra prediction type, which is distinguished from the intra prediction mode. The intra prediction type can be called by various terms such as an intra prediction technique or an additional intra prediction mode. For example, the intra prediction type (or an additional intra prediction mode, etc.) can include at least one of the above-described LIP, PDPC, MRL, and ISP. A general intra prediction method excluding specific intra prediction types such as the above-described LIP, PDPC, MRL, and ISP can be called a normal intra prediction type. The normal intra prediction type can be generally applied when the above-described specific intra prediction types are not applied, and prediction can be performed based on the above-described intra prediction mode. On the other hand, if necessary, post-processing filtering on the derived prediction sample can also be performed.

[0092] Specifically, the intra prediction procedure can include an intra prediction mode / type determination step, an adjacent reference sample derivation step, and an intra prediction mode / type-based prediction sample derivation step. Also, if necessary, a post-processing filtering step on the derived prediction sample can be performed.

[0093] When intra prediction is applied, the intra prediction mode applied to the current block can be determined using the intra prediction modes of adjacent blocks. For example, the decoding device can select one of the MPM (most probable mode) candidates in the MPM list derived based on the intra prediction modes of the adjacent blocks (e.g., left and / or upper adjacent blocks) of the current block and additional candidate modes, based on the received MPM index, or can select one of the remaining intra prediction modes not included in the MPM candidates (and the planar mode), based on the remaining intra prediction mode information. The MPM list can be configured with or without including the planar mode as a candidate. For example, when the MPM list includes the planar mode as a candidate, the MPM list can have 6 candidates, and when the MPM list does not include the planar mode as a candidate, the MPM list can have 5 candidates. When the MPM list does not include the planar mode as a candidate, a not planar flag (e.g., intra_luma_not_planar_flag) indicating whether the intra prediction mode of the current block is not the planar mode can be signaled. For example, the MPM flag can be signaled first, and the MPM index and the not planar flag can be signaled when the value of the MPM flag is 1. Also, the MPM index can be signaled when the value of the not planar flag is 1. Here, configuring the MPM list not to include the planar mode as a candidate is for checking first whether it is the planar mode by signaling the flag (not planar flag) first, rather than meaning that the planar mode is not an MPM, because the planar mode is always considered as an MPM.

[0094] For example, whether the intra prediction mode currently applied to a block is within the MPM candidates (and the planar mode), or within the remaining modes, can be indicated based on an MPM flag (e.g., intra_luma_mpm_flag). A value of 1 for the MPM flag can indicate that the intra prediction mode for the current block is within the MPM candidates (and the planar mode), and a value of 0 for the MPM flag can indicate that the intra prediction mode for the current block is not within the MPM candidates (and the planar mode). A value of 0 for the not planar flag (e.g., intra_luma_not_planar_flag) can indicate that the intra prediction mode for the current block is the planar mode, and a value of 1 for the not planar flag can indicate that the intra prediction mode for the current block is not the planar mode. The MPM index can be signaled in the form of the mpm_idx or intra_luma_mpm_idx syntax element, and the remaining intra prediction mode information can be signaled in the form of the rem_intra_luma_pred_mode or intra_luma_mpm_remainder syntax element. For example, the remaining intra prediction mode information can index, in prediction mode number order, the remaining intra prediction modes not included in the MPM candidates (and the planar mode) among the overall intra prediction modes and point to one of them. The intra prediction mode is the intra prediction mode for the luma component (samples). Hereinafter, the intra prediction mode information can include at least one of the MPM flag (e.g., intra_luma_mpm_flag), the not planar flag (e.g., intra_luma_not_planar_flag), the MPM index (e.g., mpm_idx or intra_luma_mpm_idx), and the remaining intra prediction mode information (rem_intra_luma_pred_mode or intra_luma_mpm_remainder).In this document, the MPM list can be referred to by various terms such as the MPM candidate list, candModeList, etc. When MIP is currently applied to a block, a separate mpm flag (e.g., intra_mip_mpm_flag), mpm index (e.g., intra_mip_mpm_idx), and remaining intra prediction mode information (e.g., intra_mip_mpm_remainder) for MIP can be signaled, and the not planar flag is not signaled.

[0095] That is, generally when it comes to block partitioning for video, the current block to be coded and neighboring blocks tend to have similar video characteristics. Therefore, the current block and neighboring blocks are highly likely to have the same or similar intra prediction modes. Thus, the encoder can utilize the intra prediction modes of neighboring blocks to encode the intra prediction mode of the current block.

[0096] For example, the encoder / decoder can construct an MPM (most probable modes) list for the current block. The MPM list can also be referred to as the MPM candidate list. Here, MPM can be meant as a mode that is utilized to improve coding efficiency by considering the similarity between the current block and neighboring blocks during intra prediction mode coding. As described above, the MPM list can be constructed to include the planar mode or can be constructed to exclude the planar mode. For example, when the MPM list includes the planar mode, the number of candidates in the MPM list is 6. And when the MPM list does not include the planar mode, the number of candidates in the MPM list is 5.

[0097] The encoder / decoder can construct an MPM list including 5 or 6 MPMs.

[0098] To construct the MPM list, three types of modes can be considered: Default intra modes, Neighbour intra modes, and Derived intra modes.

[0099] For the Neighbour intra modes, two neighbouring blocks, namely, the left neighbouring block and the upper neighbouring block can be considered.

[0100] As described above, if the MPM list is configured to not include the planar mode, the planar mode is excluded from the list and the number of candidates for the MPM list can be set to five.

[0101] Also, among the intra prediction modes, the non-directional mode (or non-angle mode) can include the DC mode based on the average of the neighboring reference samples of the current block or the planar mode based on interpolation.

[0102] When inter prediction is applied, the prediction unit of the encoding device / decoding device can perform inter prediction in block units to derive prediction samples. Inter prediction can indicate a prediction derived in a method that depends on data elements (e.g., sample values or motion information) of pictures other than the current picture. When inter prediction is applied to the current block, a predicted block (prediction sample array) for the current block can be induced based on a reference block (reference sample array) specified by a motion vector on a reference picture pointed to by the index of the reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter 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 adjacent block and the current block. The motion information can include a motion vector and an index of a reference picture. The motion information can further include information on the inter prediction type (L0 prediction, L1 prediction, BI prediction, etc.). When inter prediction is applied, the adjacent block can include a spatial neighboring block existing in the current picture and a temporal neighboring block 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 or different. The temporal neighboring block can be called by names such as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may also be called a collocated picture (colPic). For example, a candidate list of motion information can be configured based on the adjacent blocks of the current block, and flag or index information indicating which candidate is selected (used) can be signaled to derive the motion vector and / or the index of the reference picture of the current block.Inter prediction is performed based on various prediction modes. For example, in the case of skip mode and merge mode, the motion information of the current block may be the same as that of the selected adjacent block. In the case of skip mode, different from merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the selected adjacent block is used as a motion vector predictor, and the motion vector difference can be signaled. In this case, the motion vector of the current block can be derived using the sum of the motion vector predictor and the motion vector difference.

[0103] The motion information can include L0 motion information and / or L1 motion information according to an inter prediction type (such as L0 prediction, L1 prediction, BI prediction, etc.). The motion vector in the L0 direction may be called an L0 motion vector or MVL0, and the motion vector in the L1 direction may be called an L1 motion vector or MVL1. The prediction based on the L0 motion vector may be called L0 prediction, the prediction based on the L1 motion vector may be called L1 prediction, and the prediction based on both the L0 motion vector and the L1 motion vector may be called bi (Bi) prediction. Here, the L0 motion vector can indicate a motion vector related to the reference picture list L0 (L0), and the L1 motion vector can indicate a motion vector related to the reference picture list L1 (L1). The reference picture list L0 can include, as reference pictures, pictures that are earlier in output order than the current picture, and the reference picture list L1 can include pictures that are later in output order than the current picture. The earlier picture may be called a forward (reference) picture, and the later picture may be called a backward (reference) picture. The reference picture list L0 can further include, as reference pictures, pictures that are later in output order than the current picture. In this case, the earlier picture may be indexed first within the reference picture list L0, and the later picture may be indexed thereafter. The reference picture list L1 can further include, as reference pictures, pictures that are earlier in output order than the current picture. In this case, the later picture may be indexed first within the reference picture list 1, and the earlier picture may be indexed thereafter. Here, the output order may correspond to the POC (picture order count) order (order).

[0104] Video / video encoding procedures based on inter prediction generally include, for example, the following.

[0105] FIG. 4 shows an example of an inter prediction-based video / video encoding method.

[0106] The encoding device performs inter prediction on the current block (S400). The encoding device derives the inter prediction mode and motion information of the current block, and generates a predicted sample of the block. Here, the procedures of inter prediction mode determination, motion information derivation, and predicted sample generation may be performed simultaneously, or one procedure may be performed prior to the other procedures. For example, the inter prediction unit of the encoding device includes a prediction mode determination unit, a motion information derivation unit, and a predicted sample derivation unit. The prediction mode determination unit determines the prediction mode for the current block, the motion information derivation unit derives the motion information of the current block, and the predicted sample derivation unit derives the predicted sample of the current block. For example, the inter prediction unit of the encoding device searches for a block similar to the current block within a certain region (search region) of the reference picture by motion estimation, and derives a reference block whose difference from the current block is the smallest or below a certain criterion. Based on this, a reference picture index indicating the reference picture where the reference block is located can be derived, and a motion vector can be derived based on the positional difference between the reference block and the current block. The encoding device determines the mode applied to the current block among various prediction modes. The encoding device can compare the RD costs for the various prediction modes and determine the optimal prediction mode for the current block.

[0107] For example, when the skip mode or the merge mode is applied to the current block, the encoding device constructs a merge candidate list to be described later, and can derive a reference block whose difference from the current block is the smallest or below a certain criterion among the reference blocks pointed to by the merge candidates included in the merge candidate list. In this case, the merge candidate related to the derived reference block is selected, and merge index information indicating the selected merge candidate is generated and signaled to the decoding device. The motion information of the current block can be derived using the motion information of the selected merge candidate.

[0108] As another example, when the (A)MVP mode is applied to the current block, the encoding device configures an (A)MVP candidate list described later, and the motion vector of the selected mvp (motion vector predictor) candidate among the mvp candidates included in the (A)MVP candidate list can be used as the mvp of the current block. In this case, for example, the motion vector indicating the reference block derived by the above-described motion estimation can be used as the motion vector of the current block, and the mvp candidate having the motion vector with the smallest difference from the motion vector of the current block among the mvp candidates can be the selected mvp candidate. An MVD (motion vector difference), which is the difference obtained by subtracting the mvp from the motion vector of the current block, can be derived. In that case, information regarding the MVD can be signaled to the decoding device. Further, when the (A)MVP mode is applied, the value of the reference picture index is configured with reference picture index information and is separately signaled to the decoding device.

[0109] The encoding device derives a residual sample based on the prediction sample (S410). The encoding device can derive the residual sample by comparing the original sample of the current block with the prediction sample.

[0110] The encoding device encodes video information including prediction information and residual information (S420). The encoding device outputs the encoded video information in the form of a bitstream. The prediction information is information related to the prediction procedure and includes prediction mode information (e.g., skip flag, merge flag, or mode index, etc.) and information related to motion information. The information related to the motion information includes candidate selection information (e.g., merge index, mvp flag, or mvp index) which is information for deriving a motion vector. Also, the information related to the motion information includes information related to the aforementioned MVD and / or reference picture index information. Also, the information related to the motion information includes information indicating whether L0 prediction, L1 prediction, or bi-prediction is applied. The residual information is information related to the residual samples. The residual information includes information related to the quantized transform coefficients for the residual samples.

[0111] The output bitstream may be stored in a (digital) storage medium and transmitted to the decoding device, or may be transmitted to the decoding device via a network.

[0112] On the other hand, as described above, the encoding device generates a reconstructed picture (including reconstructed samples and reconstructed blocks) based on the reference samples and the residual samples. This is to derive from the encoding device the same prediction result as that performed by the decoding device, thereby enabling improvement of the coding efficiency. Therefore, the encoding device can store the reconstructed picture (or reconstructed samples, reconstructed blocks) in the memory and utilize it as a reference picture for inter prediction. As described above, an in-loop filtering procedure or the like can be further applied to the reconstructed picture.

[0113] The video / video decoding procedure based on inter prediction generally includes, for example, the following.

[0114] FIG. 5 shows an example of an inter-prediction based video / video decoding method.

[0115] As shown in FIG. 5, the decoding device performs operations corresponding to the operations performed by the encoding device. The decoding device can perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0116] Specifically, the decoding device determines a prediction mode for the current block based on the received prediction information (S500). The decoding device can determine which inter-prediction mode is applied to the current block based on the prediction mode information in the prediction information.

[0117] For example, based on the merge flag, it can be determined whether the merge mode is applied to the current block, or whether the (A)MVP mode is determined. Alternatively, based on the mode index, any one of various inter-prediction mode candidates can be selected. The inter-prediction mode candidates include a skip mode, a merge mode, and / or the (A)MVP mode, or various inter-prediction modes described later.

[0118] The decoding device derives motion information of the current block based on the determined inter-prediction mode (S510). For example, when the skip mode or the merge mode is applied to the current block, the decoding device constructs a merge candidate list described later and selects any one of the merge candidates included in the merge candidate list. The selection is performed based on the aforementioned selection information (merge index). The motion information of the selected merge candidate can be used to derive the motion information of the current block. The motion information of the selected merge candidate can be used as the motion information of the current block.

[0119] As another example, when the (A)MVP mode is applied to the current block, the decoding device configures the (A)MVP candidate list described below, and can use the motion vector of the selected mvp (motion vector predictor) candidate included in the (A)MVP candidate list as the mvp of the current block. The selection is performed based on the above-described selection information (mvp flag or mvp index). In this case, the MVD of the current block can be derived based on the information regarding the MVD, and the motion vector of the current block can be derived based on the mvp of the current block and the MVD. Also, the reference picture index of the current block can be derived based on the reference picture index information. In the reference picture list regarding the current block, the picture pointed to by the reference picture index can be derived as the reference picture to be referred to for the inter prediction of the current block.

[0120] On the other hand, as described below, the motion information of the current block can be derived without configuring a candidate list. In this case, the motion information of the current block can be derived according to the procedure disclosed in the prediction mode described below. In this case, the candidate list configuration as described above may be omitted.

[0121] The decoding device generates a prediction sample for the current block based on the motion information of the current block (S520). In this case, the reference picture can be derived based on the reference picture index of the current block, and the prediction sample of the current block can be derived using the sample of the reference block pointed to by the motion vector of the current block on the reference picture. In this case, as described below, in some cases, a prediction sample filtering procedure may be further performed on all or part of the prediction samples of the current block.

[0122] For example, the inter prediction unit of the decoding device includes a prediction mode determination unit, a motion information derivation unit, and a prediction sample derivation unit. The prediction mode for the current block is determined based on the prediction mode information received by the prediction mode determination unit. The motion information (such as a motion vector and / or a reference picture index) of the current block is derived based on information regarding the motion information received by the motion information derivation unit. The prediction sample of the current block can be derived from the prediction sample derivation unit.

[0123] The decoding device generates a residual sample for the current block based on the received residual information (S530). The decoding device generates a restored sample for the current block based on the prediction sample and the residual sample, and generates a restored picture based on this (S540). As described above, an in-loop filtering procedure or the like can be further applied to the restored picture hereafter.

[0124] FIG. 6 exemplarily shows an inter prediction procedure.

[0125] Referring to FIG. 6, as described above, the inter prediction procedure includes an inter prediction mode determination step, a motion information derivation step according to the determined prediction mode, and a prediction execution (prediction sample generation) step based on the derived motion information. The inter prediction procedure is performed in the encoding device and the decoding device as described above. In this document, the coding device includes the encoding device and / or the decoding device.

[0126] As shown in FIG. 6, the coding device determines an inter prediction mode for the current block (S600). Various inter prediction modes can be used for predicting the current block within a picture. For example, various modes such as a merge mode, a skip mode, an MVP (motion vector prediction) mode, an Affine mode, a sub-block merge mode, an MMVD (merge with MVD) mode, etc. can be used. A DMVR (Decoder side motion vector refinement) mode, an AMVR (adaptive motion vector resolution) mode, Bi-prediction with CU-level weight (BCW), Bi-directional optical flow (BDOF), etc. can be used additionally or alternatively as accompanying modes. The Affine mode may be referred to as an affine motion prediction mode. The MVP mode may be referred to as an “AMVP (advanced motion vector prediction) mode. In this document, some modes and / or motion information candidates derived by some modes may be included as one of the motion information related candidates of other modes. For example, an HMVP candidate may be added as a merge candidate of the merge / skip mode, or may be added as an mvp candidate of the MVP mode. When the HMVP candidate is used as a motion information candidate of the merge mode or the skip mode, the HMVP candidate may be referred to as an HMVP merge candidate.

[0127] Prediction mode information indicating the inter prediction mode of the current block can be signaled from an encoding device to a decoding device. The prediction mode information can be included in a bitstream and received by the decoding device. The prediction mode information includes index information indicating one of a number of candidate modes. Alternatively, the inter prediction mode can also be indicated via hierarchical signaling of flag information. In this case, the prediction mode information includes one or more flags. For example, a skip flag is signaled to indicate whether the skip mode is applied, and when the skip mode is not applied, a merge flag is signaled to indicate whether the merge mode is applied. When the merge mode is not applied, it can be indicated that the MVP mode is applied, or flags for additional classification can be further signaled. The affine mode may be signaled as an independent mode, or may be signaled as a mode subordinate to the merge mode or the MVP mode, etc. For example, the affine mode includes an affine merge mode and an affine MVP mode.

[0128] On the one hand, information indicating whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used for the current block (current coding unit) can be signaled. The said information may be referred to as motion prediction direction information, inter prediction direction information, or inter prediction indication information, and can be configured / encoded / signaled, for example, in the form of an inter_pred_idc syntax element. That is, the inter_pred_idc syntax element can indicate whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used for the current block (current coding unit). In this document, for the convenience of explanation, the inter prediction type (L0 prediction, L1 prediction, or BI prediction) indicated by the inter_pred_idc syntax element may be shown as the motion prediction direction. L0 prediction may be represented as pred_L0, L1 prediction as pred_L1, and bi-prediction as pred_BI. For example, the following prediction types can be indicated by the value of the inter_pred_idc syntax element.

[0129]

Table 1

[0130] As described above, one picture includes one or more slices. A slice can have one of the slice types including an I (intra) slice, a P (predictive) slice, and a B (bi-predictive) slice. The slice type is indicated based on slice type information. For blocks within an I slice, only intra prediction is used without using inter prediction for prediction. Of course, in this case, the original sample values can also be coded and signaled without prediction. For blocks within a P slice, either intra prediction or inter prediction is used, and when inter prediction is used, only uni (single) prediction can be used. On the other hand, for blocks within a B slice, either intra prediction or inter prediction is used, and when inter prediction is used, up to maximum bi (double) prediction can be used.

[0131] L0 and L1 include reference pictures that have been encoded / decoded before the current picture. For example, L0 includes reference pictures before and / or after the current picture in POC order, and L1 includes reference pictures after and / or before the current picture in POC order. In this case, a relatively lower reference picture index is assigned to L0 with respect to reference pictures before the current picture in POC order, and a relatively lower reference picture index is assigned to L1 with respect to reference pictures after the current picture in POC order. In the case of a B slice, double prediction is applied, and in this case, either uni-directional double prediction or bi-directional double prediction may be applied. Bi-directional double prediction is also called true double prediction.

[0132] The following table shows the syntax for a coding unit according to an embodiment of this document.

[0133]

Table 2-1

[0134]

Table 2-2

[0135] [Table 2-3]

[0136] [Table 2-4]

[0137] [Table 2-5]

[0138] Referring to Table 2, general_merge_flag indicates that general merging is available, and regular merge mode, mmvd mode, and merge subblock mode (subblock merge mode) are available when the value of general_merge_flag is 1. For example, when the value of general_merge_flag is 1, merge data syntax can be parsed from the encoded video / image information (or bitstream), and the merge data syntax is configured / coded to include information such as the following table.

[0139] [Table 3]

[0140] The coding apparatus derives motion information for the current block (S610). The motion information may be derived based on the inter prediction mode.

[0141] The coding device can perform inter prediction using the motion information of the current block. The coding device can derive optimal motion information for the current block through a motion estimation procedure. For example, the coding device can search for highly correlated similar reference blocks within a determined search range in the reference picture in fractional pixel units using the original block in the original picture for the current block, thereby deriving motion information. The similarity of the blocks can be derived based on the difference in phase-based sample values. For example, the similarity of the blocks can be calculated based on the SAD (sum of absolute differences) between the current block (or a template of the current block) and the reference block (or a template of the reference block). In this case, the motion information can be derived based on the reference block with the smallest SAD within the search area. The derived motion information is signaled to the decoding device in various ways based on the inter prediction mode.

[0142] The coding device performs inter prediction based on the motion information for the current block (S***). The coding device can derive a predicted sample for the current block based on the motion information. The current block including the predicted sample may be called a predicted block.

[0143] When the merge mode is applied, instead of directly transmitting the motion information of the current predicted block, the motion information of the current predicted block is induced using the motion information of the surrounding predicted blocks. Therefore, by transmitting flag information indicating the use of the merge mode and a merge index indicating which surrounding predicted block is used, the motion information of the current predicted block can be indicated. The merge mode may be called the regular merge mode.

[0144] The encoder must search for a merge candidate block that is used to derive the motion information of the current prediction block in order to perform the merge mode. For example, up to five merge candidate blocks can be used, but the embodiments of this document are not limited to this. And the maximum number of the merge candidate blocks is transmitted in the slice header or the tile group header. After finding the merge candidate block, the encoder can generate a merge candidate list and select the merge candidate block with the minimum cost among them as the final merge candidate block.

[0145] For example, five merge candidate blocks can be used in the merge candidate list. For example, four spatial merge candidates and one temporal merge candidate can be used. Hereinafter, the spatial merge candidate or the spatial MVP candidate described later may be referred to as SMVP, and the temporal merge candidate or the temporal MVP candidate described later may be referred to as TMVP.

[0146] Hereinafter, a method for constructing a merge candidate list according to this document will be described.

[0147] The coding device (encoder / decoder) inserts the spatial merge candidates derived by searching the spatial neighboring blocks of the current block into the merge candidate list. For example, the spatial neighboring blocks include the lower left corner neighboring block, the left neighboring block, the upper right corner neighboring block, the upper neighboring block, and the upper left corner neighboring block of the current block. However, this is an example, and in addition to the aforementioned spatial neighboring blocks, additional neighboring blocks such as the right neighboring block, the lower neighboring block, and the lower right corner neighboring block can also be used as the spatial neighboring blocks. The coding device can search the spatial neighboring blocks based on the priority to detect available blocks, and derive the motion information of the detected blocks as the spatial merge candidates.

[0148] The coding device inserts the temporal merge candidates derived by searching the temporal neighboring blocks of the current block into the merge candidate list. The temporal neighboring blocks may be located on a reference picture that is a picture different from the current picture in which the current block is located. The reference picture on which the temporal neighboring blocks are located may be referred to as a collocated picture or a col picture. The temporal neighboring blocks can be searched in the order of the peripheral blocks of the lower right corner and the lower right center block of the co-located block with respect to the current block on the col picture. On the other hand, when motion data compression is applied, specific motion information is stored as representative motion information for each fixed storage unit in the col picture. In this case, it is not necessary to store the motion information for all blocks within the fixed storage unit, and thus the motion data compression effect can be obtained. In this case, the fixed storage unit may be predetermined, for example, in units of 16×16 samples or 8×8 samples, or the size information regarding the fixed storage unit may be signaled from the encoder to the decoder. When the motion data compression is applied, the motion information of the temporal neighboring blocks can be replaced with the representative motion information of the fixed storage unit in which the temporal neighboring blocks are located. That is, in this case, from the perspective of implementation, instead of the prediction block located at the coordinates of the temporal neighboring blocks, based on the coordinates (upper left sample position) of the temporal neighboring blocks, after arithmetic right shift by a certain value, the temporal merge candidate is derived based on the motion information of the prediction block covering the position after arithmetic left shift. For example, when the fixed storage unit is a 2n×2n sample unit, if the coordinates of the temporal neighboring blocks are (xTnb, yTnb), the motion information of the prediction block located at the corrected position ((xTnb>n)<<n), (yTnb>n)<<n)) is used for the temporal merge candidate.Specifically, for example, when the fixed storage unit is a 16×16 sample unit, if the coordinates of the temporal neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the corrected position ((xTnb>4)<<4),(yTnb>4)<<4)) is used for the temporal merge candidate. Or, for example, when the fixed storage unit is an 8×8 sample unit, if the coordinates of the temporal neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the corrected position ((xTnb>3)<<3),(yTnb>3)<<3)) is used for the temporal merge candidate.

[0149] The coding device can check whether the number of current merge candidates is less than the number of maximum merge candidates. The number of the maximum merge candidates can be predefined or signaled from the encoder to the decoder. For example, the encoder generates information regarding the number of the maximum merge candidates, encodes it, and transmits it to the decoder in the form of a bitstream. When the number of the maximum merge candidates is filled, the subsequent candidate addition process may not be performed.

[0150] As a result of the check, if the number of current merge candidates is less than the number of maximum merge candidates, the coding device inserts an additional merge candidate into the merge candidate list.

[0151] As a result of the check, if the number of current merge candidates is not less than the number of maximum merge candidates, the coding device terminates the configuration of the merge candidate list. In this case, the encoder can select the optimal merge candidate among the merge candidates that make up the merge candidate list based on the rate-distortion (RD) cost, and can signal selection information (for example, merge index) indicating the selected merge candidate to the decoder. The decoder selects the optimal merge candidate based on the merge candidate list and the selection information.

[0152] The motion information of the selected merge candidate can be used as the motion information of the current block, and as described above, a predicted sample of the current block can be derived based on the motion information of the current block. The encoder can derive a residual sample of the current block based on the predicted sample and signal residual information regarding the residual sample to the decoder. As described above, the decoder can generate a restored sample based on the residual sample derived based on the residual information and the predicted sample, and generate a restored picture based on this.

[0153] When the skip mode is applied, the motion information of the current block can be derived in the same way as when the above-described merge mode is applied. However, when the skip mode is applied, the residual signal for the corresponding block is omitted, and thus the predicted sample can be immediately used as the restored sample.

[0154] When the MVP mode is applied, a motion vector predictor (mvp) candidate list is generated using the motion vectors of the restored spatial neighboring blocks and / or the motion vectors corresponding to the temporal neighboring blocks (or, Col blocks). That is, the motion vectors of the restored spatial neighboring blocks and / or the motion vectors corresponding to the temporal neighboring blocks can be used as motion vector predictor candidates. When dual prediction is applied, an mvp candidate list for L0 motion information derivation and an mvp candidate list for L1 motion information derivation can be separately generated and used. The aforementioned prediction information (or, information related to prediction) includes selection information (e.g., MVP flag or MVP index) indicating the optimal motion vector predictor candidate selected from among the motion vector predictor candidates included in the list. Here, the prediction unit can use the selection information to select the motion vector predictor of the current block from among the motion vector predictor candidates included in the motion vector candidate list. The prediction unit of the encoding device can obtain the motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, and encode this and output it in the form of a bitstream. That is, the MVD is obtained as the value obtained by subtracting the motion vector predictor from the motion vector of the current block. Here, the prediction unit of the decoding device can obtain the motion vector difference included in the information related to the prediction, and derive the motion vector of the current block by adding the motion vector difference and the motion vector predictor. The prediction unit of the decoding device can obtain or derive from the information related to the prediction a reference picture index indicating a reference picture, etc.

[0155] Hereinafter, a method for constructing a motion vector predictor candidate list according to this document will be described.

[0156] One embodiment first searches for spatial candidate blocks for motion vector prediction and inserts them into the prediction candidate list. Thereafter, one embodiment determines whether the number of spatial candidate blocks is less than 2. For example, if the number of spatial candidate blocks is less than 2 in one embodiment, it searches for temporal candidate blocks and additionally inserts them into the prediction candidate list, and uses a zero motion vector if the temporal candidate blocks are unavailable. That is, a zero motion vector can be additionally inserted into the prediction candidate list. Thereafter, one embodiment ends the configuration of the preliminary candidate list. Or, if the number of spatial candidate blocks is not less than 2 in one embodiment, it ends the configuration of the preliminary candidate list. Here, the preliminary candidate list indicates the MVP candidate list.

[0157] On the other hand, when the MVP mode is applied, the reference picture index is explicitly signaled. In this case, it can be signaled separately as the reference picture index (refidxL0) for L0 prediction and the reference picture index (refidxL1) for L1 prediction. For example, when the MVP mode is applied and bi-prediction is applied, information regarding the refidxL0 and information regarding the refidxL1 can both be signaled.

[0158] When the MVP mode is applied, as described above, information regarding the MVD derived from the encoding device is signaled to the decoding device. The information regarding the MVD can include, for example, information indicating the x and y components of the MVD absolute value and the sign. In this case, information indicating whether the MVD absolute value is greater than 0 and whether it is greater than 1, and information indicating the remaining MVD can be signaled step by step. For example, information indicating whether the MVD absolute value is greater than 1 can be signaled only when the value of the flag information indicating whether the MVD absolute value is greater than 0 is 1.

[0159] For example, the information regarding the MVD is configured in a syntax as shown in the following table, encoded in the encoding device, and signaled to the decoding device.

[0160]

Table 4

[0161] For example, in Table 4, the abs_mvd_greater0_flag syntax element indicates information regarding whether the difference (MVD) is greater than 0, and the abs_mvd_greater1_flag syntax element indicates information regarding whether the difference (MVD) is greater than 1. Also, the abs_mvd_minus2 syntax element indicates information regarding the value obtained by subtracting 2 from the difference (MVD), and the mvd_sign_flag syntax element indicates information regarding the sign of the difference (MVD). Also, in Table 4, [0] of each syntax element indicates information regarding L0, and [1] indicates information regarding L1.

[0162] For example, MVD[compIdx] is 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 can have a value of 0 or 1. compIdx is such that 0 indicates the x component and compIdx1 indicates the 7 component. However, this is an example, and values can be represented for each component using other coordinate systems instead of the x, y coordinate system.

[0163] On the other hand, the MVD for L0 prediction (MVD L0) and the MVD for L1 prediction (MVD L1) may be signaled separately, and the information regarding the MVD may include information regarding MVD L0 and / or information regarding MVD L1. For example, when the MVP mode is applied to the current block and the BI prediction is applied, both the information regarding MVD L0 and the information regarding MVD L1 are signaled.

[0164] FIG. 7 is a diagram for explaining SMVD (symmetric motion vector differences).

[0165] When BI prediction is applied, SMVD (symmetric MVD) may be used in consideration of coding efficiency. In this case, some of the signaling of motion information may be omitted. For example, when SMVD is applied to the current block, information regarding refidxL0, information regarding refidxL1, and information regarding MVD L1 can be derived internally without being signaled from the encoding device to the decoding device. For example, when the MVP mode and BI prediction are applied to the current block, flag information (e.g., SMVD flag information or sym_mvd_flag syntax element) indicating whether SMVD can be applied is signaled, and when the value of the flag information is 1, the decoding device determines that SMVD is applied to the current block.

[0166] When the SMVD mode is applied (i.e., when the value of the SMVD flag information is 1), information regarding mvp_l0_flag, mvp_l1_flag, and MVD L0 (Motion Vector Difference L0) is explicitly signaled, and signaling of information regarding refidxL0, refidx1, and MVD L1 (Motion Vector Difference L1) as described above is omitted and can be derived internally. For example, refidxL0 can be derived as an index indicating the previous reference picture closest to the current picture in terms of the POC procedure within the reference picture list 0 (which may be called list0 or L0). refidxL1 can be derived as an index indicating the subsequent reference picture closest to the current picture in terms of the POC procedure within the reference picture list 1 (which may be called list1 or L1). Or, for example, both refidxL0 and refidxL1 can be derived as 0 respectively. Or, for example, the refidxL0 and refidxL1 can be derived as the minimum indices having the same POC difference in relation to the current picture respectively. Specifically, for example, when "[POC of the current picture] - [POC of the first reference picture indicated by refidxL0]" is called the first POC difference, and "[POC of the current picture] - [POC of the second reference picture indicated by refidxL1]" is called the second POC difference, the value of refidxL0 indicating the first reference picture is derived as the refidxL0 of the current block and the value of refidxL1 indicating the second reference picture is derived as the refidxL1 of the current block only when the first POC difference and the second POC difference are the same. Also, for example, when there are multiple sets where the first POC difference and the second POC difference are the same, refidxL0 and refidxL1 of the set with the smallest difference among them can be derived as the refidxL0 and refidxL1 of the current block.

[0167] As shown in FIG. 7, reference picture list 0, reference picture list 1, and MVD L0, MVD L1 are shown. Here, MVD L1 is symmetric to MVD L0.

[0168] MVD L1 can be derived as minus (-) MVD L0. For example, the final (improved or corrected) motion information (motion vector: MV) for the current block is derived based on the following formula.

[0169]

Equation

[0170] In Equation 1, mvx0 and mvy0 represent the x and y components of the motion vector for L0 motion information or L0 prediction, and mvx1 and mvy1 represent the x and y components of the motion vector for L1 motion information or L1 prediction. Also, mvpx0 and mvpy0 represent the x and y components of the motion vector predictor for L0 prediction, and mvpx1 and mvpy1 represent the x and y components of the motion vector predictor for L1 prediction. Further, mvdx0 and mvdy0 represent the x and y components of the motion vector difference for L0 prediction.

[0171] On the other hand, the MMVD mode is a method of applying MVD (motion vector difference) to the merge mode, and the motion information directly used for generating the prediction sample of the current block (i.e., the current CU) can be implicitly derived. For example, an MMVD flag (e.g., mmvd_flag) indicating whether to use MMVD for the current block (i.e., the current CU) is signaled, and MMVD can be performed based on this MMVD flag. When MMVD is applied to the current block (e.g., when mmvd_flag is 1), additional information for MMVD can be signaled.

[0172] Here, the additional information for the MMVD includes a merge candidate flag (e.g., mmvd_cand_flag) indicating whether the first or second candidate in the merge candidate list is used with the MVD, a distance index (e.g., mmvd_distance_idx) to indicate the motion magnitude, and a direction index (mmvd_direction_idx) to indicate the motion direction.

[0173] In the MMVD mode, two candidates (i.e., the first candidate or the second candidate) located in the first and second entries of the merge candidate list can be used, and either one of the two candidates (i.e., the first candidate or the second candidate) can be used as the base MV. For example, a merge candidate flag (e.g., mmvd_cand_flag) can be signaled to indicate either one of the two candidates (i.e., the first candidate or the second candidate) in the merge candidate list.

[0174] Furthermore, a distance index (e.g., mmvd_distance_idx) indicates motion magnitude information and may indicate a predetermined offset from the starting point. The offset may be added to the horizontal or vertical component of the starting motion vector. The relationship between the distance index and the predetermined offset may be shown in the following table.

[0175] [Table 5]

[0176] Referring to Table 5 above, the distance of the MVD (e.g., MmvdDistance) is determined by the value of the distance index (e.g., mmvd_distance_idx), and the distance of the MVD (e.g., MmvdDistance) can be derived using integer sample precision or fractional sample precision based on the value of tile_group_fpel_mmvd_enabled_flag. For example, when tile_group_fpel_mmvd_enabled_flag is 1, it indicates that the distance of the MVD is derived using integer sample precision in the current tile group (or picture header), and when tile_group_fpel_mmvd_enabled_flag is 0, it indicates that the distance of the MVD is derived using fractional sample precision in the tile group (or picture header). In Table 1, the information (flags) for the tile group can be replaced with the information for the picture header. For example, tile_group_fpel_mmvd_enabled_flag can be replaced with ph_fpel_mmvd_enabled_flag (or ph_mmvd_fullpel_only_flag).

[0177] Also, the direction index (e.g., mmvd_direction_idx) indicates the direction of the MVD with respect to the starting point and indicates 4 directions as shown in Table 5 below. Here, the direction of the MVD can indicate the sign of the MVD. The relationship between the direction index and the MVD sign is shown as follows in the table.

[0178] [Table 6]

[0179] Referring to Table 6 above, the sign of the MVD (e.g., MmvdSign) is determined by the value of the direction index (e.g., mmvd_direction_idx), and the sign of the MVD (e.g., MmvdSign) is derived for the L0 reference picture and the L1 reference picture.

[0180] Based on the distance index (e.g., mmvd_distance_idx) and the direction index (e.g., mmvd_direction_idx) as described above, the offset of the MVD can be calculated as follows.

[0181] [Equation]

[0182] [Equation]

[0183] In Equation 2 and Equation 3, the MMVD distance (MmvdDistance[x0][y0]) and the MMVD signs (MmvdSign[x0][y0][0], MmvdSign[x0][y0][1]) are derived based on Table 5 and / or Table 6. In summary, in the MMVD mode, among the merge candidate children of the merge candidate list derived based on the neighboring blocks, the merge candidate indicated by the merge candidate flag (e.g., mmvd_cand_flag) is selected, and the selected merge candidate can be used as the base candidate (e.g., MVP). Then, the motion information (i.e., the motion vector) of the current block can be derived by adding the MVD derived using the distance index (e.g., mmvd_distance_idx) and the direction index (e.g., mmvd_direction_idx) based on the base candidate.

[0184] A predicted block for the current block can be derived based on the motion information derived by the prediction mode. The predicted block includes a predicted sample (predicted sample array) of the current block. When the motion vector of the current block indicates a fractional sample unit, an interpolation procedure can be performed, whereby the predicted sample of the current block can be derived based on the reference samples of the fractional sample unit within the reference picture. When dual prediction is applied, the predicted sample derived by the weighted sum or weighted average (according to the phase) of the predicted sample derived based on L0 prediction (i.e., prediction using the reference picture within reference picture list L0 and MVL0) and the predicted sample derived based on L1 prediction (i.e., prediction using the reference picture within reference picture list L1 and MVL1) can be used as the predicted sample of the current block. When dual prediction is applied and the reference picture used for L0 prediction and the reference picture used for L1 prediction are located in different temporal directions with respect to the current picture (i.e., when it corresponds to bidirectional prediction while being dual prediction), this may be referred to as true dual prediction.

[0185] As described above, it is possible to generate a restored sample and a restored picture based on the derived predicted sample, and then procedures such as in-loop filtering can be executed.

[0186] As described above, according to this document, when dual prediction is applied to the current block, a predicted sample can be derived based on a weighted average. Conventionally, the dual prediction signal (i.e., the dual prediction sample) has been derived by the simple average of the L0 prediction signal (L0 prediction sample) and the L1 prediction signal (L1 prediction sample). That is, the dual prediction sample has been derived as the average of the L0 prediction sample based on the L0 reference picture and MVL0 and the L1 prediction sample based on the L1 reference picture and MVL1. However, according to this document, when dual prediction is applied, the dual prediction signal (dual prediction sample) can be derived by the weighted average of the L0 prediction signal and the L1 prediction signal as follows.

[0187] In the embodiments related to the foregoing MMVD, a method considering long-term reference pictures in the MVD induction process of MMVD can be proposed, so that the compression efficiency can be maintained and increased in various applications. Also, the method proposed in the embodiments of this document can be similarly applied not only to the MMVD technology used in MERGE but also to the symmetric MVD technology (SMVD) used in the inter mode (MVP mode).

[0188] FIG. 8 is a diagram for explaining a method of deriving a motion vector in inter prediction.

[0189] In an embodiment of this document, an MV induction method considering long-term reference pictures is used in the process of motion vector scaling (MV scaling) of temporal motion candidates (temporal merge candidate, or temporal mvp candidate). Temporal motion candidates can correspond to mvCol (mvLXCol). Temporal motion candidates may also be referred to as "TMVP".

[0190] The following table explains the definition of long-term reference pictures.

[0191]

Table 7

[0192] Referring to Table 7 above, when LongTermRefPic (aPic, aPb, refIdx, LX) is 1 (true), the corresponding reference picture is marked as being used for long - term reference. For example, a reference picture that is not marked as being used for long - term reference can be a reference picture that is marked as being used for short - term reference. In another example, a reference picture that is not marked as being used for long - term reference and is not marked as being unused can be a reference picture that is marked as being used for short - term reference. Hereinafter, a reference picture marked as being used for long - term reference may be referred to as a long - term reference picture, and a reference picture marked as being used for short - term reference may be referred to as a short - term reference picture.

[0193] The following table explains the derivation of TMVP (mvLXCol).

[0194]

Table 8

[0195] Referring to FIG. 8 and Table 8, when the type of the reference picture type pointed to by the current picture (e.g., indicating whether it is a long-term reference picture (LTRP) or a short-term reference picture (STRP)) is not the same as the type of the collocated reference picture pointed to by the collocated picture, the temporal motion vector (mvLXCol) is not used. That is, when all are long-term reference pictures or all are short-term reference pictures, colMV is derived, and when there are other types, colMV is not derived. Also, when all are long-term reference pictures and the POC difference between the current picture and the reference picture of the current picture is the same as the POC difference between the collocated picture and the reference picture of the collocated picture, the collocated motion vector can be used as it is without scaling. When it is a short-term reference picture and the POC differences are different, the motion vector of the scaled collocated block is used.

[0196] In the embodiments of this document, the MMVD used in the MERGE / SKIP mode signals the base motion vector index, distance index, and direction index for one coding block as information for deriving MVD information. When performing unidirectional prediction, the MVD is derived from the motion information, and when performing bidirectional prediction, symmetric MVD information is generated using mirroring and scaling methods.

[0197] When performing bidirectional prediction, the MVD information for L0 or L1 is scaled to generate the MVD for L1 or L0, but when referring to a long-term reference picture, changes in the MVD derivation process are required.

[0198] Figures 9 to 13 show the MVD derivation method of MMVD according to the embodiments of this document. The method shown in Figures 9 to 13 can be for blocks to which bidirectional prediction is applied.

[0199] In one embodiment according to Figure 9, if the distance to the L0 reference picture is the same as the distance to the L1 reference picture, the derived MmvdOffset can be used directly as the MVD. When the POC differences (the POC difference between the L0 reference picture and the current picture and the POC difference between the L1 reference picture and the current picture) are different, the MVD can be derived by scaling according to the POC difference and whether it is a long-term or short-term reference picture, or by simple mirroring (i.e., multiplying MmvdOffset by -1).

[0200] As an example, the method of deriving a symmetric MVD using MMVD for blocks to which bidirectional prediction is applied does not fit blocks that use long-term reference pictures. In particular, when the reference picture types in each direction are different, it is difficult to expect performance improvement when using MMVD. Therefore, in the following figures and embodiments, examples are introduced in which it is realized that MMVD is not applied when the reference picture types of L0 and L1 are different.

[0201] In one embodiment according to Figure 10, different MVD derivation methods are applied depending on whether the reference picture referred to by the current picture (or the current slice, current block) is a LTRP (long-term reference picture) or a STRP (short-term reference picture). In one example, when the method of the embodiment according to Figure 10 is applied, a part of the standard document according to this embodiment is described as follows in the following table.

[0202]

Table 9-1

[0203]

Table 9-2

[0204] In one embodiment according to FIG. 11, different MVD derivation methods are applied depending on whether the reference picture referred to by the current picture (or, current slice, current block) is an LTRP (long-term reference picture) or an STRP (short-term reference picture). In one example, when the method of the embodiment according to FIG. 11 is applied, a part of the standard document according to this embodiment is described as in the following table.

[0205] [Table 10-1]

[0206] [Table 10-2]

[0207] In summary, when the reference picture types in each direction are different, the MVD derivation process of MMVD that does not derive MVD is described.

[0208] In one embodiment according to FIG. 12, MVD is not derived in all cases where a long-term reference picture is referred to. That is, when at least one of the L0 and L1 reference pictures is a long-term reference picture, MVD is set to 0, and MVD can be derived only when there is a short-term reference picture.

[0209] In one example, based on the highest priority condition (RefPicL0!=LTRP && RefPicL1!=STRP), when the current picture (or, current slice, current block) refers to only short-term reference pictures, MVD for MMVD can be derived. In one example, when the method of the embodiment according to FIG. 12 is applied, a part of the standard document according to this embodiment is described as in the following table.

[0210]

Table 11-1

[0211]

Table 11-2

[0212] In one embodiment according to FIG. 13, when the reference picture types in each direction are different, if there is a short-term reference picture, MVD is induced, and if there is a long-term reference picture, MVD is induced to 0.

[0213] In one example, when the reference picture types in each direction are different, when referring to a reference picture close to the current picture (short-term reference picture), MmvdOffset is applied, and when referring to a reference picture far from the current picture (long-term reference picture), MVD has a value of 0. Here, a picture close to the current picture can be regarded as having a short-term reference picture, but if the close picture is a long-term reference picture, mmvdOffset can be applied to the motion vector of the list pointing to the short-term reference picture.

[0214]

Table 12

[0215] For example, the four paragraphs included in the said Table 12 can sequentially replace the bottom block (content) of the sequence diagram included in the said FIG. 13.

[0216] In one example, when the method of the embodiment according to FIG. 13 is applied, a part of the standard document according to this embodiment is described as follows in the following table.

[0217]

Table 13-1

[0218]

Table 13-2

[0219] The following table shows a comparison table among the examples included in this document.

[0220]

Table 14

[0221] Referring to Table 14, a comparison is shown between methods of applying an offset considering a reference picture type for MVD derivation of MMVD described in the examples according to FIGS. 9 to 13. In Table 14, Example A relates to an existing MMVD, Example B shows the examples according to FIGS. 9 to 11, Example C shows the example according to FIG. 12, and Example D shows the example according to FIG. 13.

[0222] That is, in the examples according to FIGS. 9, 10, and 11, a method of inducing MVD only when the reference picture types in both directions are the same is described. In the example according to FIG. 12, a method of inducing MVD only when both directions are short-term reference pictures is described. In the case of the example according to FIG. 12, if it is a long-term reference picture for unidirectional prediction, MVD is set to 0. Also, in the example according to FIG. 13, a method of inducing MVD in only one direction when the reference picture types in both directions are different is described. Such differences among the examples show various features of the technology described in this document, and those having ordinary knowledge in the technical field to which this document pertains can understand that the effects to be achieved by the examples according to this document can be realized based on the said features.

[0223] In the embodiments according to this document, when the reference picture type is a long-term reference picture, it has a separate process. When including a long-term reference picture, since the POC difference (POCDiff)-based scaling or mirroring has no impact on performance improvement, the MVD in the direction with a short-term reference picture is assigned the MmvdOffset value, and the MVD in the direction with a long-term reference picture is assigned a value of 0. In one example, when this embodiment is applied, a part of the standard document according to this embodiment is described as follows in the following table.

[0224]

Table 15-1

[0225]

Table 15-2

[0226] In other examples, a part of Table 15 can be replaced with the following table. Referring to Table 16, the Offset is applied based on the reference picture type instead of POCDiff.

[0227]

Table 16

[0228] In still other examples, a part of Table 15 can be replaced with the following table. Referring to Table 17, the MmvdOffset can always be set to L0 and -MmvdOffset to L1 without considering the reference picture type.

[0229]

Table 17

[0230] According to one embodiment of this document, SMVD in inter mode can be performed similarly to MMVD used in the aforementioned MERGE mode. When performing bidirectional prediction, whether symmetric MVD derivation is possible is signaled from the encoding device to the decoding device. When the related flag (e.g., sym_mvd_flag) is true (or its value is 1), the second-direction MVD (e.g., MVD L1) is induced by mirroring the first-direction MVD (e.g., MVD L0). In this case, scaling for the first-direction MVD may not be performed.

[0231] The following table shows the syntax for a coding unit according to one embodiment of this document.

[0232]

Table 18

[0233]

Table 19

[0234] Referring to Table 18 and Table 19 above, when inter_pred_idc == PRED_BI and the reference pictures of L0 and L1 are available (e.g., RefIdxSymL0 > -1 && RefIdxSymL1 > -1), sym_mvd_flag is signaled.

[0235] The following table shows the decoding procedure for MMVD reference indexes according to an example.

[0236]

Table 20

[0237] Referring to Table 20, the procedure for deriving the availability of the reference pictures of L0 and L1 is described. That is, if there is a reference picture in the forward direction among the L0 reference pictures, the reference picture index closest to the current picture is set to RefIdxSymL0, and the corresponding value is set to the reference index of L0. Also, if there is a reference picture in the backward direction among the L1 reference pictures, the reference picture index closest to the current picture is set to RefIdxSymL1, and the corresponding value is set to the reference index of L1.

[0238] The following Table 21 shows the decoding procedure for the MMVD reference index according to another example.

[0239]

Table 21

[0240] Referring to Table 21, when the L0 or L1 reference picture type is different as in the embodiments described with FIGS. 9, 10, and 11, that is, when a long-term reference picture and a short-term reference picture are used, after deriving the reference index for SMVD to prevent SMVD, if the L0 and L1 reference picture types are different, do not use SMVD (see the bottom paragraph of Table 20).

[0241] In one embodiment of this document, SMVD can be applied in inter mode similar to MMVD used in merge mode. As in the embodiment described with FIG. 12, when a long-term reference picture is used, the long-term reference picture can be excluded in the process of deriving the reference index for SMVD as shown in the following table to prevent SMVD.

[0242]

Table 22

[0243] The following table according to another example of this embodiment shows an example of processing such that the SMVD is not applied when using a long-term reference picture after the reference picture index derivation for SMVD.

[0244]

Table 23

[0245] In one embodiment of this document, when the reference picture type of the current picture and the reference picture type of the collocated picture are different in the colMV derivation process of TMVP, the motion vector MV is set to 0. However, since it is different from the derivation methods in the cases of MMVD and SMVD, this is made to be unified.

[0246] Even when the reference picture type of the current picture is a long-term reference picture and the reference picture type of the collocated picture is a long-term reference picture, the motion vector still uses the collocated motion vector value as it is. However, in MMVD and SMVD, in this case, the MV is set to 0. Here, TMVP also sets the MV to 0 without additional derivation.

[0247] Also, even if the reference picture types are different, since there may be a long-term reference picture close to the current picture, instead of setting the MV to 0 considering this, the colMV can be used as the MV without scaling.

[0248] FIG. 14 is a diagram for explaining SMVD according to one embodiment of this document.

[0249] For the derivation of SMVD, a method as shown in FIG. 14 can be used. That is, SMVD can be derived based on STRP (Short-Term Reference Picture) and / or LTRP (Long-Term Reference Picture). When using the mirrored L0 MVD for L1 MVD, if the types of reference pictures are different, an inaccurate MVD may be derived. This is because the ratio of distances (the distance between reference picture 0 and the current picture and the distance between reference picture 1 and the current picture) becomes large, and the correlation degree of the motion vectors in each direction decreases.

[0250] According to one embodiment of this document, the availability of the reference picture is checked, and if the conditions are met, sym_mvd_flag can be parsed. If, by any chance, sym_mvd_flag is true, the MVD of L1 (MVDL1) can be derived with the mirrored MVDL0 (the MVD of L0).

[0251] The following table shows a part of the coding unit syntax according to this embodiment.

[0252]

Table 24

[0253] Based on Table 24, the derivation procedure of sym_mvd_flag according to this embodiment can be described.

[0254] In this embodiment, the reference picture index for SMVD (RefIdxSymLX with X = 0, 1) can be derived. RefIdxSymL0 can indicate the index of the nearest reference picture having a POC smaller than the POC of the current picture. RefIdxSymL1 can indicate the index of the nearest reference picture having a POC larger than the POC of the current picture.

[0255] The following table describes, in the format of a standard document, the method for deriving the reference picture index for SMVD according to this embodiment.

[0256]

Table 25

[0257] The following table shows the comparison results among the embodiments. By considering the reference picture type according to the embodiments included in Table 26, the accuracy of MVD in SMVD can be improved. In Table 26, MVD can indicate MVD 0 (the MVD of L0).

[0258]

Table 26

[0259] Referring to Table 26, Example P shows the existing method for deriving SMVD. In Example Q, SMVD may be restricted when using a mixed reference picture type (ex. STRP / LTRP or LTRP / STRP) at L0 and L1. In Example R, SMVD may be restricted when referring to a long-term reference picture (LTRP).

[0260] The following table describes, in the format of a standard document, the method for deriving the reference picture index for SMVD according to Example Q of Table 26.

[0261]

Table 27

[0262] The following table describes, in the format of a standard document, the method for deriving the reference picture index for SMVD according to Example Q of Table 26.

[0263]

Table 28

[0264]

Table 29

[0265] Referring to Table 28 and / or Table 29, the SMVD may be restricted when referring to the Long-Term Reference Picture (LTRP). For example, referring to Table 28, the long-term reference picture can be excluded in the reference picture checking process. Thereby, other reference pictures (e.g., not the long-term reference picture) can be considered for SMVD. Referring to Table 29, the SMVD may not be executed when the reference picture closest to the current picture is the long-term reference picture. For example, even if the reference picture list includes short-term reference pictures, the SMVD may not be executed when the reference picture closest to the current picture is the long-term reference picture.

[0266] In an example according to an embodiment of this document, when the POC distance of L0 is greater than or equal to the POC of L1 in the MMVD procedure, the L1 MVD can be derived as a scaled or mirrored L0 MVD. When the POC distance of L0 is less than the POC of L1 in the MMVD procedure, the L0 MVD can be derived as a scaled or mirrored L1 MVD in the MMVD procedure.

[0267] FIG. 15 is a flowchart showing a method for deriving MMVD according to an embodiment of this document.

[0268] In one embodiment of this document, considering the POC difference and / or reference picture type, MVD can be derived by MMVD. Referring to FIG. 15, currPocDiffLX can mean the difference between the POC of the current picture and the POC of the reference picture LX. CurrPocDiffL0 and currPocDiffL1 can be compared with each other, and the type of the reference picture can be checked ("refPicList0!= LTRP" or "refPicList1!= LTRP"). Considering the conditions, MmvdOffset (derived using mmvd_cand_flag, mmvd_distance_idx, and / or mmvd_direction_idx) can be assigned as the same value as mMvdLX, a mirrored value, or a scaled value.

[0269] The following table shows a part of the standard document according to this embodiment.

[0270]

Table 30-1

[0271]

Table 30-2

[0272] When the current picture refers to one or more long-term reference pictures (LTRP), a mirroring procedure considering the POC distance may not be necessary. This is because the mirrored MVD obtained from a reference picture at a very far distance compared to other MVDs is not effective in terms of accuracy. A solution to this is described below.

[0273] The following table shows the comparison results between examples.

[0274]

Table 31

[0275] Referring to Table 31, Example X shows the existing method for deriving MMVD. In Example Y, the MMVD procedure can be restricted when one or more long-term reference pictures are referred to in the current block. That is, in Example Y, the procedure for comparing the POC distances for the long-term reference pictures can be omitted. In Example Z, for all cases, the derivation procedure of MMVD can be restricted. That is, in Example Z, for all cases, the procedure for comparing the POC distances can be omitted. In Table 31, offset may refer to MmvdOffset.

[0276] FIG. 16 is a flowchart showing a method for deriving MMVD according to an embodiment of this document. The flowchart of FIG. 16 can show the method for deriving MMVD according to the aforementioned Example Y.

[0277] Referring to FIG. 16, when the reference picture type is a long-term reference picture, the condition for comparing the POC difference can be removed, and the anchor MVD used for the mirroring procedure can be fixed to the L0 MVD.

[0278] The following table describes in the form of a standard document the method for deriving MMVD according to Example Y of Table 31.

[0279]

Table 32-1

[0280]

Table 32-2

[0281] FIG. 17 is a flowchart showing a method for deriving MMVD according to an embodiment of this document. The flowchart of FIG. 17 can show the method for deriving MMVD according to the aforementioned Example Z.

[0282] Referring to FIG. 17, in Example Z, for all cases, the derivation procedure of MMVD can be restricted. For all cases, the condition for comparing POC differences can be removed, and the anchor MVD used for the mirroring or scaling procedure can be fixed to the L0 MVD.

[0283] The following table describes in the form of a standard document the method for deriving MMVD according to Example Z of Table 31.

[0284]

Table 33-1

[0285]

Table 33-2

[0286] Also, in an example of this embodiment, for all cases, the condition for comparing POC differences can be removed, and only the case of mirroring may be used. The following table describes in the form of a standard document the method for deriving MMVD in this example.

[0287]

Table 34

[0288] The following drawings are created to illustrate a specific example of this specification. Since the names of specific devices and the names of specific signal message fields described in the drawings are presented exemplarily, the technical features of this specification are not limited to the specific names used in the following drawings.

[0289] Figures 18 and 19 schematically show an example of a video / image encoding method and related components according to an embodiment of this document. The method disclosed in FIG. 18 can be executed by the encoding device disclosed in FIG. 2. Specifically, for example, S1800 to S1850 in FIG. 18 can be executed by the prediction unit 220 of the encoding device, and S1860 can be executed by the residual processing unit 230 of the encoding device. S1870 can be executed by the entropy encoding unit 240 of the encoding device. The method disclosed in FIG. 18 can include the embodiments described above in this document.

[0290] Referring to FIG. 18, the encoding device derives an inter prediction mode for the current block within the current picture (S1800). Here, the inter prediction mode can include the merge mode, AMVP mode (mode using motion vector predictor candidates), MMVD, and SMVD described above.

[0291] The encoding device can derive a reference picture for the inter prediction mode. The encoding device can configure a reference picture list for the derivation of the reference picture. In one example, the reference picture list can include reference picture list 0 (or L0, reference picture list L0) or reference picture list 1 (or L1, reference picture list L1). For example, the encoding device can configure a reference picture list for each slice included in the current picture.

[0292] The encoding device constructs an MVP candidate list for the current block based on the surrounding blocks of the current block (S1810). The MVP candidate list can include an MVP candidate list L0 and an MVP candidate list L1. In one example, the surrounding blocks may be included in the current picture including the current block. In another example, the surrounding blocks may be included in a previous (reference) picture or a subsequent (reference) picture from the current picture. Here, the POC of the previous picture may be smaller than the POC of the current picture, and the POC of the subsequent picture may be larger than the POC of the current picture. According to one example, the POC difference between the current picture and the previous (reference) picture from the current picture may be greater than 0. In another example, the POC difference between the current picture and the subsequent (reference) picture from the current picture may be less than 0. However, this is only exemplary.

[0293] The encoding device can derive an MVP for the current block based on the MVP candidate list (S1820). The MVP can include an MVPL0 and an MVPL1. The MVPL0 can be derived from the MVP candidate list L0, and the MVPL1 can be derived from the MVP candidate list L1. The encoding device can derive an optimal motion vector predictor candidate among the motion vector predictor candidates included in the MVP candidate list. The encoding device can generate selection information (e.g., an MVP flag or an MVP index) indicating the optimal motion vector predictor candidate.

[0294] The encoding device generates prediction-related information including the inter prediction mode (S1830). In one example, the prediction-related information can include information regarding an MVD (motion vector difference) for the current block. Also, the prediction-related information can include information regarding an MMVD, information regarding an SMVD, etc.

[0295] The encoding device derives motion information for predicting the current block based on the information regarding the MVP and the MVD (S1840). For example, the motion information can include a reference index for SMVD (symmetric motion vector difference reference index). The reference index for SMVD can indicate a reference picture for the application of SMVD. The reference index for SMVD can include a reference index L0 (RefIdxSumL0) and a reference index L1 (RefIdxSumL1).

[0296] The encoding device generates a prediction sample based on the motion information (S1850). The encoding device can generate the prediction sample based on the motion vector and the reference picture index included in the motion information. For example, the prediction sample can be generated based on the block (or sample) indicated by the motion vector among the blocks (or samples) in the reference picture indicated by the reference picture index.

[0297] The encoding device derives residual information based on the prediction sample (S1860). Specifically, the encoding device can derive a residual sample based on the prediction sample and the original sample. The encoding device can derive residual information based on the residual sample. For the derivation of the residual information, the above-described transformation and quantization processes can be performed.

[0298] The encoding device encodes image / video information including the prediction-related information and the residual information (S1870). The encoded image / video information can be output in the form of a bitstream. The bitstream can be transmitted to a decoding device via a network or a (digital) storage medium.

[0299] The image / video information can include various information related to the embodiments of this document. For example, the image / video information can include the information disclosed in at least one of Tables 1 to 34 described above.

[0300] In one embodiment, the motion information can include an MV (motion vector) and a symmetric motion vector difference reference index. The MV can include MVL0 for L0 prediction and MVL1 for L1 prediction. The symmetric motion vector difference reference index can include a symmetric motion vector difference reference index L0 for the L0 prediction and a symmetric motion vector difference reference index L1 for the L1 prediction. The information regarding the MVD can include the information regarding MVDL0 for the L0 prediction. In one example, the information regarding MVDL1 for the L1 prediction can be derived based on the information regarding MVDL0. In another example, based on the peripheral blocks for predicting the current block, the information regarding MVDL0 and / or the information regarding MVDL1 can be derived. When encoding the image / video information, the encoding device may exclude the information regarding MVDL1. The MVL0 is derived based on the information regarding MVDL0, and the MVL1 can be derived based on the information regarding MVDL1. The symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 can be derived based on the short-term reference pictures among the reference pictures included in the reference picture list.

[0301] In one embodiment, the MVP can include MVPL0 for the L0 prediction and MVPL1 for the L1 prediction. The MVL0 can be derived based on the sum of the MVDL0 and the MVPL0. The MVL1 can be derived based on the sum of the MVDL1 and the MVPL1.

[0302] In one embodiment, the prediction-related information may include information related to the symmetric motion vector difference (information related to SMVD or SMVD flag information). When the symmetric motion vector difference reference indexes L0 and L1 are derived based on the POC (picture order count) difference between the short-term reference picture and the current picture including the current block, the value of the information related to the symmetric motion vector difference may be 1.

[0303] In one embodiment, the magnitude of the MVDL1 may be the same as the magnitude of the MVDL0. The sign of the MVDL1 may be opposite to the sign of the MVDL0.

[0304] In one embodiment, the short-term reference picture may include a short-term reference picture L0 and a short-term reference picture L1. For example, the symmetric motion vector difference reference index L0 may point to the short-term reference picture L0. Also, the symmetric motion vector difference reference index L1 may point to the short-term reference picture L1.

[0305] In one embodiment, the reference picture list may include a reference picture list 0. The reference picture list 0 may include the short-term reference picture L0. The symmetric motion vector difference reference index L0 can be derived based on the POC (picture order count) difference between each of the short-term reference pictures included in the reference picture list 0 and the current picture including the current block.

[0306] In one embodiment, the symmetric motion vector difference reference index L0 can be derived based on a comparison between the POC differences.

[0307] In one embodiment, the reference picture list 0 may further include other short-term reference pictures L0. The POC difference may include a first POC difference between the short-term reference picture L0 and the current picture, and a second POC difference between the other short-term reference picture L0 and the current picture. The first POC difference may be smaller than the second POC difference.

[0308] FIGs. 20 and 21 schematically show an example of an image / video decoding method and related components according to an embodiment of this document. The method disclosed in FIG. 20 can be executed by the decoding device disclosed in FIG. 3. Specifically, for example, S2000 in FIG. 20 can be executed by the entropy decoding unit 310 of the decoding device, and S2010 to S2050 can be executed by the prediction unit 330 of the decoding device. The method disclosed in FIG. 20 can include the embodiments described above in this document.

[0309] Referring to FIG. 20, the decoding device receives / obtains image / video information (S2000). The decoding device can receive / obtain the image / video information via a bitstream. The image / video information can include prediction-related information (including prediction mode information), information related to MVD, and / or residual information. The prediction-related information can include information related to MMVD, information related to SMVD, etc. Also, the image / video information can include various information according to the embodiments of this document. For example, the image / video information can include the information described with FIGS. 1 to 17 and / or the information disclosed in at least one of the aforementioned Tables 1 to 34.

[0310] The decoding device derives an inter prediction mode for the current block based on the prediction-related information (S2010). Here, the inter prediction mode can include the merge mode, the AMVP mode (a mode using a motion vector predictor candidate), MMVD, and SMVD described above.

[0311] The decoding device constructs an MVP candidate list for the current block based on the peripheral blocks of the current block (S2020). The MVP candidate list can include an MVP candidate list L0 and an MVP candidate list L1. In one example, the peripheral blocks may be included in the current picture including the current block. In another example, the peripheral blocks may be included in a previous (reference) picture or a subsequent (reference) picture from the current picture. Here, the POC of the previous picture may be smaller than the POC of the current picture, and the POC of the subsequent picture may be larger than the POC of the current picture. According to one example, the POC difference between the current picture and the previous (reference) picture from the current picture may be greater than 0. In another example, the POC difference between the current picture and the subsequent (reference) picture from the current picture may be less than 0. However, this is only exemplary.

[0312] The decoding device can derive an MVP for the current block based on the MVP candidate list (S2030). The MVP can include MVPL0 and MVPL1. MVPL0 can be derived from the MVP candidate list L0, and MVPL1 can be derived from the MVP candidate list L1. The decoding device can derive an optimal motion vector predictor candidate among the motion vector predictor candidates included in the MVP candidate list. The encoding device can generate selection information (e.g., an MVP flag or an MVP index) indicating the optimal motion vector predictor candidate.

[0313] The decoding device derives motion information for the current block based on the information regarding the MVD and the MVP (S2040). For example, the motion information can include a reference index for the SMVD. The reference index for the SMVD can point to a reference picture for the application of the SMVD. The reference index for the SMVD can include a reference index L0 (RefIdxSumL0) and a reference index L1 (RefIdxSumL1).

[0314] The decoding device generates prediction samples based on the motion information (S2050). The decoding device can generate the prediction samples based on the motion vectors and reference picture indexes included in the motion information. For example, the prediction samples can be generated based on the block (or sample) indicated by the motion vector among the blocks (or samples) in the reference picture pointed to by the reference picture index.

[0315] The decoding device can generate residual samples based on the residual information. Specifically, the decoding device can derive quantized transform coefficients based on the residual information. The quantized transform coefficients can have the form of a one-dimensional vector based on the coefficient scan order. The decoding device can derive transform coefficients based on an inverse quantization procedure for the quantized transform coefficients. The decoding device can derive residual samples based on an inverse transform procedure for the transform coefficients.

[0316] The decoding device can generate restored samples of the current picture based on the prediction samples and the residual samples. The decoding device can also further execute a filtering procedure to generate (corrected) restored samples.

[0317] In one embodiment, the motion information may include an MV (motion vector) and a symmetric motion vector difference reference index. The MV may include an MVL0 for L0 prediction and an MVL1 for L1 prediction. The symmetric motion vector difference reference index may include a symmetric motion vector difference reference index L0 for the L0 prediction and a symmetric motion vector difference reference index L1 for the L1 prediction. The information regarding the MVD may include the information regarding the MVDL0 for the L0 prediction. In one example, the information regarding the MVDL1 for the L1 prediction may be derived based on the information regarding the MVDL0. In another example, the information regarding the MVDL0 and / or the information regarding the MVDL1 can be derived based on the neighboring blocks for predicting the current block. When encoding the image / video information, the encoding device may sometimes exclude the information regarding the MVDL1. The MVL0 is derived based on the information regarding the MVDL0, and the MVL1 can be derived based on the information regarding the MVDL1. The symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 can be derived based on the short-term reference pictures among the reference pictures included in the reference picture list.

[0318] In one embodiment, the MVP may include an MVPL0 for the L0 prediction and an MVPL1 for the L1 prediction. The MVL0 can be derived based on the sum of the MVDL0 and the MVPL0. The MVL1 can be derived based on the sum of the MVDL1 and the MVPL1.

[0319] In one embodiment, the prediction-related information can include information regarding the symmetric motion vector difference (information for SMVD or SMVD flag information). For example, when the value of the information regarding the symmetric motion vector difference is 1, based on the POC difference between the short-term reference picture and the current picture including the current block, the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 can be derived.

[0320] In one embodiment, the magnitude of the MVDL1 can be the same as the magnitude of the MVDL0. The sign of the MVDL1 can be opposite to the sign of the MVDL0.

[0321] In one embodiment, the short-term reference picture can include a short-term reference picture L0 and a short-term reference picture L1. For example, the symmetric motion vector difference reference index L0 can point to the short-term reference picture L0. Also, the symmetric motion vector difference reference index L1 can point to the short-term reference picture L1.

[0322] In one embodiment, the reference picture list can include a reference picture list 0. The reference picture list 0 can include the short-term reference picture L0. Based on the POC (picture order count) difference between each of the short-term reference pictures included in the reference picture list 0 and the current picture including the current block, the symmetric motion vector difference reference index L0 can be derived.

[0323] In one embodiment, based on the comparison between the POC differences, the symmetric motion vector difference reference index L0 can be derived.

[0324] In one embodiment, the reference picture list 0 may further include other short-term reference pictures L0. The POC difference may include a first POC difference between the short-term reference picture L0 and the current picture, and a second POC difference between the other short-term reference picture L0 and the current picture. The first POC difference may be smaller than the second POC difference.

[0325] In one embodiment, the symmetric motion vector difference reference indexes L0 and L1 (ex.ref_idx_l1[x0][y0], ref_idx_l1[x0][y0]) are not directly signaled and can be derived based on the information (ex.sym_mvd_flag) regarding the symmetric motion vector difference.

[0326] In the foregoing embodiments, the method is described based on a flowchart as a series of steps or blocks, but the corresponding embodiments are not limited to the order of the steps. A certain step may occur in a different order from the steps described above or simultaneously with different steps. Also, those skilled in the art can understand that the steps shown in the flowchart are not exclusive, and different steps may be included, or one or more steps of the flowchart may be deleted without affecting the scope of the embodiments of this document.

[0327] The method according to the foregoing embodiments of this document can be embodied in the form of software, and the encoding device and / or decoding device according to this document may be included in a device that performs video processing, such as a TV, a computer, a smartphone, a set-top box, a display device, etc.

[0328] In this document, when an embodiment is implemented in software, the above-described method can be implemented by modules (processes, functions, etc.) that perform the above-described functions. The modules can be stored in a memory and executed by a processor. The memory may be internal or external to the processor and may be connected to the processor by various well-known means. The processor can include an ASIC (application-specific integrated circuit), other chip sets, logic circuits, and / or data processing devices. The memory can include a ROM (read-only memory), a RAM (random access memory), a flash memory, a memory card, a storage medium, and / or other storage devices. That is, the embodiments described in this document can be implemented and performed on a processor, a microprocessor, a controller, or a chip. For example, the functional units shown in each drawing can be implemented and performed on a computer, a processor, a microprocessor, a controller, or a chip. In this case, information for implementation (e.g., information on instructions) or an algorithm can be stored in a digital storage medium.

[0329] In addition, the decoding device and the encoding device to which the embodiments of this document are applied may include a multimedia broadcast transmission / reception device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video conferencing device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camcorder, an on-demand video (VoD) service providing device, an OTT video (Over the top video) device, an Internet streaming service providing device, a three-dimensional (3D) video device, a VR (virtual reality) device, an AR (augmented reality) device, a videophone video device, a transportation means terminal (e.g., a vehicle terminal including an autonomous driving vehicle terminal, an airplane terminal, a ship terminal, etc.) and a medical video device, etc., and may be used to process video signals or data signals. For example, as an OTT video (Over the top video) device, it may include a game console, a Blu-ray player, an Internet access TV, a home theater system, a smartphone, a tablet PC, a DVR (Digital Video Recoder), etc.

[0330] In addition, the processing method to which the embodiments of this document are applied can be produced in the form of a program executed by a computer and can be stored in a recording medium readable by the computer. Multimedia data having a data structure according to the embodiments of this document can also be stored in a recording medium readable by the computer. The recording medium readable by the computer includes all types of storage devices and distributed storage devices in which data readable by the computer is stored. The recording medium readable by the computer can include, for example, Blu-ray Disc (BD), Universal Serial Bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical data storage devices. Also, the recording medium readable by the computer includes a medium embodied in the form of a carrier wave (e.g., transmission via the Internet). Also, a bitstream generated by an encoding method can be stored in a recording medium readable by the computer or can be transmitted via a wired or wireless communication network.

[0331] In addition, the embodiments of this document can be embodied in a computer program product by program code, and the program code can be executed by a computer according to the embodiments of this document. The program code can be stored on a carrier readable by a computer.

[0332] FIG. 22 shows an example of a content streaming system to which the embodiments disclosed in this document can be applied.

[0333] Referring to FIG. 22, the content streaming system to which the embodiments of this document are applied can include a large encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0334] The encoding server compresses the content input from a multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream, and serves to transmit this to the streaming server. As another example, when a multimedia input device such as a smartphone, camera, camcorder, etc. directly generates a bitstream, the encoding server may be omitted.

[0335] The bitstream can be generated by an encoding method or a bitstream generation method to which the embodiments of this document are applicable. The streaming server can temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0336] The streaming server transmits multimedia data to the user device based on a user request via a web server. The web server serves as a medium to inform the user of what services are available. If the user requests a desired service from the web server, the web server transmits this to the streaming server, and the streaming server transmits multimedia data to the user. At this time, the content streaming system can include another control server. In this case, the control server serves to control commands / responses between each device within the content streaming system.

[0337] The streaming server can receive content from a media repository and / or an encoding server. For example, when it comes to receiving content from the encoding server, the content can be received in real time. In this case, in order to provide a smooth streaming service, the streaming server can store the bitstream for a certain period of time.

[0338] In the example of the user device, there may be a mobile phone, a smart phone, a laptop computer, a digital broadcast terminal, a PDA (personal digital assistants), a PMP (portable multimedia player), a navigation device, a slate PC, a tablet PC, an ultrabook, a wearable device (for example, a smartwatch, a smart glass, an HMD (head mounted display)), a digital TV, a desktop computer, a digital signage, etc.

[0339] Each server in the content streaming system can be operated as a distributed server. In this case, the data received by each server can be distributedly processed.

[0340] The claims described in this specification can be combined in various ways. For example, the technical features of the method claims in this specification can be combined and embodied as a device, and the technical features of the device claims in this specification can be combined and embodied as a method. Also, the technical features of the method claims in this specification and the technical features of the device claims can be combined and embodied as a device, and the technical features of the method claims in this specification and the technical features of the device claims can be combined and embodied as a method.

Claims

Claim 1 In an image decoding method executed by a decoding apparatus, obtaining image information including prediction-related information and information regarding an MVD (motion vector difference) from a bitstream; deriving an inter prediction mode for a current block based on the prediction-related information; constructing a candidate list of MVPs (motion vector predictors) for the current block based on peripheral blocks of the current block; deriving an MVP for the current block based on the MVP candidate list; deriving an MV (motion vector) for the current block based on the MVD and the MVP; generating a prediction sample for the current block based on motion information including the MV and a symmetric motion vector difference reference index; and dual prediction is applied to the current block, the MV includes an MV_L0 for L0 prediction and an MV_L1 for L1 prediction, the symmetric motion vector difference reference index includes a symmetric motion vector difference reference index L0 for the L0 prediction and a symmetric motion vector difference reference index L1 for the L1 prediction, the information regarding the MVD includes information regarding an MVD_L0 for the L0 prediction, the MVD includes an MVD_L0 for the L0 prediction and an MVD_L1 for the L1 prediction, the MVD_L0 is derived based on the information regarding the MVD_L0, the MVD_L1 is derived based on the MVD_L0, the magnitude of the MVD_L1 is the same as the magnitude of the MVD_L0, the sign of the MVD_L1 is opposite to the sign of the MVD_L0, the MVP includes an MVP_L0 for the L0 prediction and an MVP_L1 for the L1 prediction, the MV_L0 is derived based on the sum of the MVD_L0 and the MVP_L0, the MV_L1 is derived based on the sum of the MVD_L1 and the MVP_L1. The method in which the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are derived based on the difference in POC (picture order count) between the short-term reference picture among the reference pictures included in the reference picture list and the current picture including the current block. Claim 2 In an image encoding method executed by an encoding device, a step of deriving an inter prediction mode for a current block; a step of constructing a MVP (motion vector predictor) candidate list for the current block based on peripheral blocks of the current block; a step of deriving an MVP for the current block based on the MVP candidate list; a step of deriving motion information for the current block including an MV (motion vector) and a symmetric motion vector difference reference index; a step of generating prediction-related information including information regarding the inter prediction mode and information regarding an MVD (motion vector difference) for the current block; a step of generating a prediction sample for the current block based on the motion information; a step of generating residual information based on the prediction sample; encoding image information including the prediction-related information and the residual information, bi-prediction is applied to the current block, the MVP includes an MVPL0 for L0 prediction and an MVPL1 for L1 prediction, the MV includes an MVL0 for the L0 prediction and an MVL1 for the L1 prediction, the symmetric motion vector difference reference index includes a symmetric motion vector difference reference index L0 for the L0 prediction and a symmetric motion vector difference reference index L1 for the L1 prediction, the information regarding the MVD includes information regarding an MVDL0 for the L0 prediction, the MVDL0 is derived by subtracting the MVPL0 from the MVL0, the MVDL1 is derived by subtracting the MVPL1 from the MVL1, the magnitude of the MVDL1 is the same as the magnitude of the MVDL0, the sign of the MVDL1 is opposite to the sign of the MVDL0, The method in which the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are derived based on the difference in POC (picture order count) between the short-term reference picture among the reference pictures included in the reference picture list and the current picture including the current block.

3. A method for transmitting data for an image, obtaining a bitstream for the image, wherein the bitstream deriving an inter prediction mode for a current block; constructing a MVP (motion vector predictor) candidate list for the current block based on the peripheral blocks of the current block; deriving an MVP for the current block based on the MVP candidate list; deriving motion information for the current block including an MV (motion vector) and a symmetric motion vector difference reference index; generating prediction-related information including information regarding the inter prediction mode and information regarding an MVD (motion vector difference) for the current block; generating a prediction sample for the current block based on the motion information; generating residual information based on the prediction sample; encoding image information including the prediction-related information and the residual information, and generating based on the steps; transmitting the data including the bitstream, including the steps; bi-prediction is applied to the current block, the MVP includes MVPL0 for L0 prediction and MVPL1 for L1 prediction, the MV includes MVL0 for the L0 prediction and MVL1 for the L1 prediction, the symmetric motion vector difference reference index includes the symmetric motion vector difference reference index L0 for the L0 prediction and the symmetric motion vector difference reference index L1 for the L1 prediction, the information regarding the MVD includes information regarding MVDL0 for the L0 prediction, MVDL0 is derived by subtracting MVPL0 from MVL0, MVDL1 is derived by subtracting MVPL1 from MVL1, The size of the MVDL1 is the same as the size of the MVDL0, the sign of the MVDL1 is opposite to the sign of the MVDL0, a method in which the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are derived based on the difference in POC (picture order count) between a short-term reference picture among the reference pictures included in the reference picture list and the current picture including the current block.

Images