WO2019194462A1

WO2019194462A1 - Inter prediction mode-based video processing method and apparatus therefor

Info

Publication number: WO2019194462A1
Application number: PCT/KR2019/003605
Authority: WO
Inventors: 남정학; 김승환; 이재호
Original assignee: 엘지전자 주식회사
Priority date: 2018-04-01
Filing date: 2019-03-27
Publication date: 2019-10-10

Abstract

Disclosed are a method for decoding a video signal and an apparatus therefor. Specifically, a method for decoding a video on the basis of an inter prediction mode comprises the steps of: in the case where a bidirectional prediction is applied to a current block, deriving a first initial motion vector and a second initial motion vector of the current block; deriving a first final motion vector and a second final motion vector by improving the first initial motion vector and the second initial motion vector on the basis of a motion vector offset value that is symmetric with respect to a reference list direction; generating a first prediction block by using the first final motion vector and a second prediction block by using the second final motion vector; and generating a third prediction block indicating a prediction block of the current block, by using the first prediction block and the second prediction block.

Description

Inter prediction mode based image processing method and apparatus therefor

The present invention relates to a still image or moving image processing method, and more particularly, to a method for encoding / decoding a still image or moving image based on an inter prediction mode and an apparatus supporting the same.

Compression coding refers to a series of signal processing techniques for transmitting digitized information through a communication line or for storing in a form suitable for a storage medium. Media such as an image, an image, an audio, and the like may be a target of compression encoding. In particular, a technique of performing compression encoding on an image is called video image compression.

Next-generation video content will be characterized by high spatial resolution, high frame rate and high dimensionality of scene representation. Processing such content would result in a tremendous increase in terms of memory storage, memory access rate, and processing power.

Accordingly, there is a need to design coding tools for more efficiently processing next generation video content.

An object of the present invention is to propose a method for generating an adaptive prediction template based on an inter prediction direction (or reference direction) in applying a DMVR.

It is also an object of the present invention to propose a method for generating an adaptive prediction template based on a cost function in applying a DMVR.

It is also an object of the present invention to propose a method for generating an inter prediction sample by applying an adaptive weighted average based on a cost function.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

An aspect of the present invention provides a method of decoding an image based on an inter prediction mode, comprising: deriving a first initial motion vector and a second initial motion vector of the current block when bidirectional prediction is applied to a current block; Deriving a first final motion vector and a second final motion vector by improving the first initial motion vector and the second initial motion vector based on a motion vector offset value symmetric with respect to a reference list direction; Generating a first prediction block by using the first final motion vector, and generating a second prediction block by using the second final motion vector; And generating a third prediction block representing the prediction block of the current block by using the first prediction block and the second prediction block.

Preferably, the deriving of the first final motion vector and the second final motion vector comprises: a fourth prediction block specified by the first initial motion vector and a fifth prediction specified by the second initial motion vector. Weighting the blocks to generate a first prediction template for the reference list 0 direction and a second prediction template for the reference list 1 direction; And improving the first initial motion vector using the first prediction template, and improving the second initial motion vector using the second prediction template.

Preferably, the first prediction template is generated through a weighted sum that is weighted higher to the fourth prediction block than the fifth prediction block, and the second prediction template is the fifth prediction block than the fourth prediction block. The weighted sum may be generated by applying a higher weight to the prediction block.

Preferably, the deriving of the first final motion vector and the second final motion vector comprises: a fourth prediction block specified by the first initial motion vector and a fifth prediction specified by the second initial motion vector. Generating a prediction template by weighting the blocks; And improving the first initial motion vector and the second initial motion vector in each reference list direction based on the difference value with the prediction template.

Preferably, the weight applied to generating the prediction template may be determined based on a difference value between the fourth prediction block and the prediction template and a difference value between the fifth prediction block and the prediction template.

Preferably, the third prediction block is generated by weighting the first prediction block and the second prediction block, and weights applied to the first prediction block and the second prediction block are respectively applied to the first prediction block and the second prediction block. It may be determined according to a cost function value of the second prediction block.

According to another aspect of the present invention, in an apparatus for decoding an image based on an inter prediction mode, when bidirectional prediction is applied to a current block, an initial value for deriving a first initial motion vector and a second initial motion vector of the current block is provided. A motion vector induction part; A final motion vector derivation unit for deriving a first final motion vector and a second final motion vector by improving the first initial motion vector and the second initial motion vector based on a motion vector offset value symmetric with respect to a reference list direction; And generating a first prediction block using the first final motion vector, generating a second prediction block using the second final motion vector, and using the first prediction block and the second prediction block. It may include a prediction block generator for generating a third prediction block representing a prediction block of the current block.

Preferably, the final motion vector derivation unit weights a fourth prediction block specified by the first initial motion vector and a fifth prediction block specified by the second initial motion vector, thereby weighting the reference list 0 direction. Generate a second prediction template for a first prediction template and a reference list 1 direction, improve the first initial motion vector using the first prediction template, and use the second prediction template to generate the second prediction template It is possible to improve the initial motion vector.

Preferably, the final motion vector derivation unit generates a prediction template by weighting a fourth prediction block specified by the first initial motion vector and a fifth prediction block specified by the second initial motion vector, The first initial motion vector and the second initial motion vector may be improved in each reference list direction based on the difference value with the prediction template.

According to the embodiment of the present invention, it is possible to increase the precision of motion prediction and improve the compression performance without additional signaling information.

In addition, according to an embodiment of the present invention, the DMVR prediction performance can be improved by improving the template generation and weighted average method of the DMVR.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description. .

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, included as part of the detailed description in order to provide a thorough understanding of the present invention, provide embodiments of the present invention and together with the description, describe the technical features of the present invention.

1 is a schematic block diagram of an encoding apparatus in which an encoding of a video / image signal is performed, according to an embodiment to which the present invention is applied.

2 is a schematic block diagram of a decoding apparatus in which an embodiment of the present invention is applied and decoding of a video / image signal is performed.

3 is a diagram illustrating an example of a multi-type tree structure as an embodiment to which the present invention can be applied.

FIG. 4 is a diagram illustrating a signaling mechanism of partition partition information of a quadtree with nested multi-type tree structure according to an embodiment to which the present invention may be applied.

FIG. 5 is a diagram illustrating a method of dividing a CTU into multiple CUs based on a quadtree and accompanying multi-type tree structure as an embodiment to which the present invention may be applied.

FIG. 6 is a diagram illustrating a method of limiting ternary-tree splitting as an embodiment to which the present invention may be applied.

FIG. 7 is a diagram illustrating redundant division patterns that may occur in binary tree division and ternary tree division, as an embodiment to which the present invention may be applied.

8 and 9 illustrate an inter prediction based video / image encoding method and an inter prediction unit in an encoding apparatus according to an embodiment of the present invention.

10 and 11 illustrate an inter prediction based video / image decoding method and an inter prediction unit in a decoding apparatus according to an embodiment of the present invention.

FIG. 12 is a diagram for describing a neighboring block used in a merge mode or a skip mode as an embodiment to which the present invention is applied.

13 is a flowchart illustrating a merge candidate list construction method according to an embodiment to which the present invention is applied.

14 is a flowchart illustrating a merge candidate list construction method according to an embodiment to which the present invention is applied.

15 is a diagram illustrating a motion vector refinement method according to an embodiment to which the present invention is applied.

16 is a diagram illustrating a motion vector refinement method according to an embodiment to which the present invention is applied.

17 is a flowchart illustrating a method of generating a predictive block using weighted sum based on a cost function according to an embodiment of the present invention.

18 is a flowchart illustrating a method of generating an inter prediction block according to an embodiment to which the present invention is applied.

19 is a diagram illustrating an inter prediction apparatus according to an embodiment to which the present invention is applied.

20 shows a video coding system to which the present invention is applied.

21 is a diagram illustrating a structure of a content streaming system according to an embodiment to which the present invention is applied.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details.

In some instances, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention.

In addition, the terminology used in the present invention was selected as a general term widely used as possible now, in a specific case will be described using terms arbitrarily selected by the applicant. In such a case, since the meaning is clearly described in the detailed description of the part, it should not be interpreted simply by the name of the term used in the description of the present invention, and it should be understood that the meaning of the term should be understood and interpreted. .

Specific terms used in the following description are provided to help the understanding of the present invention, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present invention. For example, signals, data, samples, pictures, frames, blocks, etc. may be appropriately replaced and interpreted in each coding process.

Hereinafter, in the present specification, the 'processing unit' refers to a unit in which a process of encoding / decoding such as prediction, transformation, and / or quantization is performed. Hereinafter, for convenience of description, the processing unit may be referred to as a 'processing block' or 'block'.

The processing unit may be interpreted to include a unit for the luma component and a unit for the chroma component. For example, the processing unit may correspond to a Coding Tree Unit (CTU), a Coding Unit (CU), a Prediction Unit (PU), or a Transform Unit (TU).

In addition, the processing unit may be interpreted as a unit for a luma component or a unit for a chroma component. For example, the processing unit may be a coding tree block (CTB), a coding block (CB), a prediction block (PU), or a transform block (TB) for a luma component. May correspond to. Or, it may correspond to a coding tree block (CTB), a coding block (CB), a prediction block (PU), or a transform block (TB) for a chroma component. In addition, the present invention is not limited thereto, and the processing unit may be interpreted to include a unit for a luma component and a unit for a chroma component.

In addition, the processing unit is not necessarily limited to square blocks, but may also be configured in a polygonal form having three or more vertices.

In the following specification, a pixel, a pixel, and the like are referred to collectively as a sample. In addition, using a sample may mean using a pixel value or a pixel value.

Referring to FIG. 1, the encoding apparatus 100 may include an image splitter 110, a subtractor 115, a transformer 120, a quantizer 130, an inverse quantizer 140, an inverse transformer 150, The adder 155, the filter 160, the memory 170, the inter predictor 180, the intra predictor 185, and the entropy encoder 190 may be configured. The inter predictor 180 and the intra predictor 185 may be collectively referred to as a predictor. In other words, the predictor may include an inter predictor 180 and an intra predictor 185. The transform unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transform unit 150 may be included in the residual processing unit. The residual processing unit may further include a subtracting unit 115. As an example, the image divider 110, the subtractor 115, the transformer 120, the quantizer 130, the inverse quantizer 140, the inverse transformer 150, and the adder 155 may be described. The filtering unit 160, the inter prediction unit 180, the intra prediction unit 185, and the entropy encoding unit 190 may be configured by one hardware component (eg, an encoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

The image divider 110 may divide the input image (or picture or frame) input to the encoding apparatus 100 into one or more processing units. For example, the processing unit may be called a coding unit (CU). In this case, the coding unit may be recursively divided according to a quad-tree binary-tree (QTBT) structure from a coding tree unit (CTU) or a largest coding unit (LCU). For example, one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad tree structure and / or a binary tree structure. In this case, for example, the quad tree structure may be applied first and the binary tree structure may be applied later. Alternatively, the binary tree structure may be applied first. The coding procedure according to the present invention may be performed based on the final coding unit that is no longer split. In this case, the maximum coding unit may be used as the final coding unit immediately based on coding efficiency according to the image characteristic, or if necessary, the coding unit is recursively divided into coding units of lower depths and optimized. A coding unit of size may be used as the final coding unit. Here, the coding procedure may include a procedure of prediction, transform, and reconstruction, which will be described later. As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be partitioned or partitioned from the aforementioned final coding unit, respectively. The prediction unit may be a unit of sample prediction, and the transformation unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

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

The encoding apparatus 100 subtracts the prediction signal (predicted block, prediction sample array) output from the inter prediction unit 180 or the intra prediction unit 185 from the input image signal (original block, original sample array). A signal may be generated (residual signal, residual block, residual sample array), and the generated residual signal is transmitted to the converter 120. In this case, as shown, a unit that subtracts a prediction signal (prediction block, prediction sample array) from an input image signal (original block, original sample array) in the encoder 100 may be called a subtraction unit 115. The prediction unit may perform a prediction on a block to be processed (hereinafter, referred to as a current block) and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied on a current block or CU basis. As described later in the description of each prediction mode, the prediction unit may generate various information related to prediction, such as prediction mode information, and transmit the generated information to the entropy encoding unit 190. The information about the prediction may be encoded in the entropy encoding unit 190 and output in the form of a bitstream.

The intra predictor 185 may predict the current block by referring to the samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located apart according to the prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. Non-directional mode may include, for example, DC mode and planner mode (Planar mode). The directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes according to the degree of detail of the prediction direction. However, as an example, more or less directional prediction modes may be used depending on the setting. The intra predictor 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

The inter predictor 180 may derive the predicted block with respect to the current block based on the reference block (reference sample array) specified by the motion vector on the reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of the motion information between the neighboring block and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), and the like, and a reference picture including the temporal neighboring block is called a collocated picture (colPic). It may be. For example, the inter prediction unit 180 constructs a motion information candidate list based on neighboring blocks and provides information indicating which candidates are used to derive a motion vector and / or a reference picture index of the current block. Can be generated. Inter prediction may be performed based on various prediction modes. For example, in case of a skip mode and a merge mode, the inter prediction unit 180 may use motion information of a neighboring block as motion information of a current block. In the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the motion vector prediction (MVP) mode, the motion vector of the neighboring block is used as a motion vector predictor and the motion vector difference is signaled by signaling a motion vector difference. Can be directed.

The prediction signal generated by the inter predictor 180 or the intra predictor 185 may be used to generate a reconstruction signal or to generate a residual signal.

The transformer 120 may apply transform techniques to the residual signal to generate transform coefficients. For example, the transformation technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loeve transform (KLT), a graph-based transform (GBT), or a conditionally non-linear transform (CNT). It may include. Here, GBT means a conversion obtained from this graph when the relationship information between pixels is represented by a graph. CNT refers to a transform that is generated based on and generates a prediction signal using all previously reconstructed pixels. In addition, the conversion process may be applied to pixel blocks having the same size as the square, or may be applied to blocks of variable size rather than square.

The quantization unit 130 quantizes the transform coefficients and transmits them to the entropy encoding unit 190. The entropy encoding unit 190 encodes the quantized signal (information about the quantized transform coefficients) and outputs the bitstream. have. The information about the quantized transform coefficients may be referred to as residual information. The quantization unit 130 may rearrange block quantized transform coefficients into a one-dimensional vector form based on a coefficient scan order, and quantize the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. Information about transform coefficients may be generated. The entropy encoding unit 190 may perform various encoding methods such as, for example, exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), and the like. The entropy encoding unit 190 may encode information necessary for video / image reconstruction other than quantized transform coefficients (for example, values of syntax elements) together or separately. Encoded information (eg, encoded video / image information) may be transmitted or stored in units of NALs (network abstraction layer) in the form of a bitstream. The bitstream may be transmitted over a network or may be stored in a digital storage medium. The network may include a broadcasting network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. The signal output from the entropy encoding unit 190 may include a transmitting unit (not shown) for transmitting and / or a storing unit (not shown) for storing as an internal / external element of the encoding apparatus 100, or the transmitting unit It may be a component of the entropy encoding unit 190.

The quantized transform coefficients output from the quantization unit 130 may be used to generate a prediction signal. For example, the quantized transform coefficients may be reconstructed in the residual signal by applying inverse quantization and inverse transform through inverse quantization unit 140 and inverse transform unit 150 in a loop. The adder 155 adds the reconstructed residual signal to the predicted signal output from the inter predictor 180 or the intra predictor 185 so that a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) is added. Can be generated. If there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block may be used as the reconstructed block. The adder 155 may be called a restoration unit or a restoration block generation unit. The generated reconstruction signal may be used for intra prediction of a next processing target block in a current picture, and may be used for inter prediction of a next picture through filtering as described below.

The filtering unit 160 may improve subjective / objective image quality by applying filtering to the reconstruction signal. For example, the filtering unit 160 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and the modified reconstructed picture is stored in the memory 170, specifically, the DPB of the memory 170. Can be stored in The various filtering methods may include, for example, deblocking filtering, a sample adaptive offset, an adaptive loop filter, a bilateral filter, and the like. As described below in the description of each filtering method, the filtering unit 160 may generate various information about the filtering and transmit the generated information to the entropy encoding unit 190. The filtering information may be encoded in the entropy encoding unit 190 and output in the form of a bitstream.

The modified reconstructed picture transmitted to the memory 170 may be used as the reference picture in the inter predictor 180. When the inter prediction is applied through the encoding apparatus, the encoding apparatus may avoid prediction mismatch between the encoding apparatus 100 and the decoding apparatus, and may improve encoding efficiency.

The memory 170 DPB may store the modified reconstructed picture for use as a reference picture in the inter predictor 180. The memory 170 may store the motion information of the block from which the motion information in the current picture is derived (or encoded) and / or the motion information of the blocks in the picture that have already been reconstructed. The stored motion information may be transmitted to the inter predictor 180 to use the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 170 may store reconstructed samples of reconstructed blocks in the current picture, and transfer the reconstructed samples to the intra predictor 185.

Referring to FIG. 2, the decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantizer 220, an inverse transform unit 230, an adder 235, a filter 240, a memory 250, and an inter The prediction unit 260 and the intra prediction unit 265 may be configured. The inter predictor 260 and the intra predictor 265 may be collectively called a predictor. That is, the predictor may include an inter predictor 180 and an intra predictor 185. The inverse quantization unit 220 and the inverse transform unit 230 may be collectively called a residual processing unit. That is, the residual processing unit may include an inverse quantization unit 220 and an inverse transformation unit 230. The entropy decoder 210, the inverse quantizer 220, the inverse transformer 230, the adder 235, the filter 240, the inter predictor 260, and the intra predictor 265 are described in the embodiment. Can be configured by one hardware component (eg, decoder or processor). In addition, the memory 170 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

When a bitstream including video / image information is input, the decoding apparatus 200 may reconstruct an image corresponding to a process in which video / image information is processed in the encoding apparatus of FIG. 1. For example, the decoding apparatus 200 may perform decoding using a processing unit applied in the encoding apparatus. Thus the processing unit of decoding may be a coding unit, for example, which may be split along a quad tree structure and / or a binary tree structure from a coding tree unit or a maximum coding unit. The reconstructed video signal decoded and output through the decoding apparatus 200 may be reproduced through the reproducing apparatus.

The decoding apparatus 200 may receive a signal output from the encoding apparatus of FIG. 1 in the form of a bitstream, and the received signal may be decoded through the entropy decoding unit 210. For example, the entropy decoding unit 210 may parse the bitstream to derive information (eg, video / image information) necessary for image reconstruction (or picture reconstruction). For example, the entropy decoding unit 210 decodes information in a bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, quantized values of syntax elements required for image reconstruction, and transform coefficients for residuals. Can be output. More specifically, the CABAC entropy decoding method receives a bin corresponding to each syntax element in a bitstream, and decodes syntax element information and decoding information of neighboring and decoding target blocks or information of symbols / bins decoded in a previous step. The context model may be determined using the context model, the probability of occurrence of a bin may be predicted according to the determined context model, and arithmetic decoding of the bin may be performed to generate a symbol corresponding to the value of each syntax element. have. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bean after determining the context model. The information related to the prediction among the information decoded by the entropy decoding unit 2110 is provided to the prediction unit (the inter prediction unit 260 and the intra prediction unit 265), and the entropy decoding performed by the entropy decoding unit 210 is performed. Dual values, that is, quantized transform coefficients and related parameter information, may be input to the inverse quantizer 220. In addition, information on filtering among information decoded by the entropy decoding unit 210 may be provided to the filtering unit 240. Meanwhile, a receiver (not shown) that receives a signal output from the encoding apparatus may be further configured as an internal / external element of the decoding apparatus 200, or the receiver may be a component of the entropy decoding unit 210.

The inverse quantization unit 220 may dequantize the quantized transform coefficients and output the transform coefficients. The inverse quantization unit 220 may rearrange the quantized transform coefficients in the form of a two-dimensional block. In this case, the reordering may be performed based on the coefficient scan order performed by the encoding apparatus. The inverse quantization unit 220 may perform inverse quantization on quantized transform coefficients using a quantization parameter (for example, quantization step size information), and may obtain transform coefficients.

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

The prediction unit may perform prediction on the current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on the information about the prediction output from the entropy decoding unit 210, and may determine a specific intra / inter prediction mode.

The intra predictor 265 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the neighborhood of the current block or may be located apart according to the prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The intra predictor 265 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

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

The adder 235 adds the obtained residual signal to the predictive signal (predicted block, predictive sample array) output from the inter predictor 260 or the intra predictor 265 to restore the reconstructed signal (restored picture, reconstructed block). , Restore sample array). If there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block may be used as the reconstructed block.

The adder 235 may be called a restoration unit or a restoration block generation unit. The generated reconstruction signal may be used for intra prediction of a next processing target block in a current picture, and may be used for inter prediction of a next picture through filtering as described below.

The filtering unit 240 may improve subjective / objective image quality by applying filtering to the reconstruction signal. For example, the filtering unit 240 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and the modified reconstructed picture may be stored in the memory 250, specifically, the DPB of the memory 250. Can be sent to. The various filtering methods may include, for example, deblocking filtering, a sample adaptive offset, an adaptive loop filter, a bilateral filter, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 250 may be used as the reference picture in the inter predictor 260. The memory 250 may store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the blocks in the picture that are already reconstructed. The stored motion information may be transmitted to the inter predictor 260 to use the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 170 may store reconstructed samples of reconstructed blocks in the current picture, and transfer the reconstructed samples to the intra predictor 265.

In the present specification, the embodiments described by the filtering unit 160, the inter prediction unit 180, and the intra prediction unit 185 of the encoding apparatus 100 are respectively the filtering unit 240 and the inter prediction of the decoding apparatus 200. The same may also apply to the unit 260 and the intra predictor 265.

Block PartitioningBlock Partitioning

The video / image coding method according to this document may be performed based on various detailed techniques, and each detailed technique will be described as follows. Techniques described below include prediction, residual processing ((inverse) transformation, (inverse) quantization, etc.), syntax element coding, filtering, partitioning / division, etc. in the video / image encoding / decoding procedures described above and / or described below. It will be apparent to those skilled in the art that they may be involved in related procedures.

The block partitioning procedure according to this document may be performed by the image splitter 110 of the encoding apparatus described above, and the partitioning related information may be processed (encoded) by the entropy encoding unit 190 and transmitted to the decoding apparatus in the form of a bitstream. . The entropy decoding unit 210 of the decoding apparatus derives a block partitioning structure of the current picture based on the partitioning related information obtained from the bitstream, and based on this, a series of procedures (eg, prediction and residual) for image decoding. Processing, block reconstruction, in-loop filtering, etc.).

Partitioning of picture into CTUs

Pictures can be divided into a sequence of coding tree units (CTUs). The CTU may correspond to a coding tree block (CTB). Alternatively, the CTU may include a coding tree block of luma samples and two coding tree blocks of corresponding chroma samples. In other words, for a picture that includes three sample arrays, the CTU may include an N × N block of luma samples and two corresponding blocks of chroma samples.

The maximum allowable size of the CTU for coding and prediction may be different from the maximum allowable size of the CTU for transform. For example, the maximum allowable size of the luma block in the CTU may be 128x128.

Partitionig of the CTUs using a tree structure

The CTU may be divided into CUs based on a quad-tree (QT) structure. The quadtree structure may be referred to as a quaternary tree structure. This is to reflect various local characteristics. Meanwhile, in the present document, the CTU may be divided based on a multitype tree structure partition including a binary tree (BT) and a ternary tree (TT) as well as a quad tree. Hereinafter, the QTBT structure may include a quadtree and binary tree based partition structure, and the QTBTTT may include a quadtree, binary tree, and ternary tree based partition structure. Alternatively, the QTBT structure may include a quadtree, binary tree and ternary tree based partitioning structure. In a coding tree structure, a CU may have a square or rectangular shape. The CTU may first be divided into quadtree structures. After that, the leaf nodes of the quadtree structure may be further divided by the multitype tree structure.

In one embodiment of the present invention, the multitype tree structure may include four partition types as shown in FIG. The four types of split include vertical binary splitting (SPLIT_BT_VER), horizontal binary splitting (SPLIT_BT_HOR), vertical ternary splitting (SPLIT_TT_VER), and horizontal ternary splitting (SPLIT_TT_HOR). ) May be included. Leaf nodes of the multitype tree structure may be called CUs. These CUs can be used for prediction and transform procedures. In general, CU, PU, and TU may have the same block size in this document. However, when the maximum supported transform length is smaller than the width or height of the color component of the CU, the CU and the TU may have different block sizes.

Here, the CTU is treated as the root of the quadtree, and is partitioned for the first time into a quadtree structure. Each quadtree leaf node may then be further partitioned into a multitype tree structure. In the multitype tree structure, a first flag (ex. Mtt_split_cu_flag) is signaled to indicate whether the node is additionally partitioned. If the node is additionally partitioned, a second flag (ex. Mtt_split_cu_verticla_flag) may be signaled to indicate the splitting direction. Thereafter, a third flag (ex. Mtt_split_cu_binary_flag) may be signaled to indicate whether the partition type is binary partition or ternary partition. For example, based on the mtt_split_cu_vertical_flag and the mtt_split_cu_binary_flag, a multi-type tree splitting mode (MttSplitMode) of a CU may be derived as shown in Table 1 below.

Here, bold block edges represent quadtree partitioning and the remaining edges represent multitype tree partitioning. Quadtree partitions involving a multitype tree can provide a content-adapted coding tree structure. The CU may correspond to a coding block (CB). Alternatively, the CU may include a coding block of luma samples and two coding blocks of corresponding chroma samples. The size of a CU may be as large as CTU, or may be cut by 4 × 4 in luma sample units. For example, in the 4: 2: 0 color format (or chroma format), the maximum chroma CB size may be 64x64 and the minimum chroma CB size may be 2x2.

For example, in this document, the maximum allowable luma TB size may be 64x64 and the maximum allowable chroma TB size may be 32x32. If the width or height of the CB divided according to the tree structure is larger than the maximum transform width or height, the CB may be automatically (or implicitly) split until the TB size limit in the horizontal and vertical directions is satisfied.

Meanwhile, for a quadtree coding tree scheme involving a multitype tree, the following parameters may be defined and identified as SPS syntax elements.

CTU size: the root node size of a quaternary tree

MinQTSize: the minimum allowed quaternary tree leaf node size

MaxBtSize: the maximum allowed binary tree root node size

MaxTtSize: the maximum allowed ternary tree root node size

MaxMttDepth: the maximum allowed hierarchy depth of multi-type tree splitting from a quadtree leaf

MinBtSize: the minimum allowed binary tree leaf node size

MinTtSize: the minimum allowed ternary tree leaf node size

As an example of a quadtree coding tree structure involving a multitype tree, the CTU size may be set to 64x64 blocks of 128x128 luma samples and two corresponding chroma samples (in 4: 2: 0 chroma format). In this case, MinOTSize can be set to 16x16, MaxBtSize to 128x128, MaxTtSzie to 64x64, MinBtSize and MinTtSize (for both width and height) to 4x4, and MaxMttDepth to 4. Quarttree partitioning may be applied to the CTU to generate quadtree leaf nodes. The quadtree leaf node may be called a leaf QT node. Quadtree leaf nodes may have a 128x128 size (i.e. the CTU size) from a 16x16 size (i.e. the MinOTSize). If the leaf QT node is 128x128, it may not be additionally divided into a binary tree / a ternary tree. This is because in this case, even if split, it exceeds MaxBtsize and MaxTtszie (i.e. 64x64). In other cases, leaf QT nodes may be further partitioned into a multitype tree. Therefore, the leaf QT node is the root node for the multitype tree, and the leaf QT node may have a multitype tree depth (mttDepth) 0 value. If the multitype tree depth reaches MaxMttdepth (ex. 4), further splitting may not be considered further. If the width of the multitype tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, then no further horizontal split may be considered. If the height of the multitype tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, no further vertical split may be considered.

With reference to FIG. 6, to allow for 64x64 luma blocks and 32x32 chroma pipeline designs in a hardware decoder, TT partitioning may be limited in certain cases. For example, when the width or height of the luma coding block is greater than a predetermined specific value (eg, 32 and 64), TT partitioning may be limited as shown in FIG. 6.

In this document, the coding tree scheme may support that the luma and chroma blocks have separate block tree structures. For P and B slices, luma and chroma CTBs in one CTU may be limited to have the same coding tree structure. However, for I slices, luma and chroma blocks may have a separate block tree structure from each other. If an individual block tree mode is applied, the luma CTB may be split into CUs based on a particular coding tree structure, and the chroma CTB may be split into chroma CUs based on another coding tree structure. This may mean that a CU in an I slice may consist of a coding block of a luma component or coding blocks of two chroma components, and a CU of a P or B slice may be composed of blocks of three color components.

In the above-described "Partitionig of the CTUs using a tree structure", a quadtree coding tree structure involving a multitype tree has been described, but a structure in which a CU is divided is not limited thereto. For example, the BT structure and the TT structure may be interpreted as a concept included in a multiple partitioning tree (MPT) structure, and the CU may be interpreted to be divided through the QT structure and the MPT structure. In one example where a CU is split through a QT structure and an MPT structure, a syntax element (eg, MPT_split_type) that contains information about how many blocks the leaf node of the QT structure is divided into and the leaf node of the QT structure are vertical The partition structure may be determined by signaling a syntax element (eg, MPT_split_mode) including information about which direction is divided into and horizontally.

In another example, the CU may be partitioned in a different way than the QT structure, BT structure or TT structure. That is, according to the QT structure, the CU of the lower depth is divided into 1/4 size of the CU of the upper depth, or the CU of the lower depth is divided into 1/2 size of the CU of the upper depth according to the BT structure, or according to the TT structure. Unlike the CU of the lower depth is divided into 1/4 or 1/2 size of the CU of the upper depth, the CU of the lower depth is sometimes 1/5, 1/3, 3/8, 3 of the CU of the upper depth. It can be divided into / 5, 2/3 or 5/8 size, the way in which the CU is divided is not limited to this.

If a portion of a tree node block exceeds the bottom or right picture boundary, the tree node block is placed so that all samples of all coded CUs are located within the picture boundaries. May be limited. In this case, for example, the following division rule may be applied.

-If a portion of a tree node block exceeds both the bottom and the right picture boundaries,

-If the block is a QT node and the size of the block is larger than the minimum QT size, the block is forced to be split with QT split mode.

-Otherwise, the block is forced to be split with SPLIT_BT_HOR mode

-Otherwise if a portion of a tree node block exceeds the bottom picture boundaries,

-If the block is a QT node, and the size of the block is larger than the minimum QT size, and the size of the block is larger than the maximum BT size, the block is forced to be split with QT split mode.

-Otherwise, if the block is a QT node, and the size of the block is larger than the minimum QT size and the size of the block is smaller than or equal to the maximum BT size, the block is forced to be split with QT split mode or SPLIT_BT_HOR mode.

-Otherwise (the block is a BTT node or the size of the block is smaller than or equal to the minimum QT size), the block is forced to be split with SPLIT_BT_HOR mode.

-Otherwise if a portion of a tree node block exceeds the right picture boundaries,

-Otherwise, if the block is a QT node, and the size of the block is larger than the minimum QT size and the size of the block is smaller than or equal to the maximum BT size, the block is forced to be split with QT split mode or SPLIT_BT_VER mode.

-Otherwise (the block is a BTT node or the size of the block is smaller than or equal to the minimum QT size), the block is forced to be split with SPLIT_BT_VER mode.

On the other hand, the quadtree coded block structure with the multi-type tree described above can provide a very flexible block partitioning structure. Because of the partition types supported in a multitype tree, different partition patterns can sometimes lead to potentially identical coding block structure results. By limiting the occurrence of such redundant partition patterns, the data amount of partitioning information can be reduced. It demonstrates with reference to the following drawings.

As shown in FIG. 7, two levels of consecutive binary splits in one direction have the same coding block structure as the binary split for the center partition after the ternary split. . In this case, the binary tree split in the given direction for the center partition of the ternary tree split may be limited. This restriction can be applied for CUs of all pictures. If this particular partitioning is restricted, the signaling of the corresponding syntax elements can be modified to reflect this limited case, thereby reducing the number of bits signaled for partitioning. For example, as shown in FIG. 7, when the binary tree split for the center partition of the CU is restricted, the mtt_split_cu_binary_flag syntax element indicating whether the split is a binary split or a tenary split is not signaled, and its value is Can be inferred by the decoder to zero.

예측(prediction)Prediction

The decoded portion of the current picture or other pictures in which the current processing unit is included may be used to reconstruct the current processing unit in which decoding is performed.

Intra picture or I picture (slice), which uses only the current picture for reconstruction, i.e. performs only intra picture prediction, predicts a picture (slice) using at most one motion vector and reference index to predict each unit A picture using a predictive picture or P picture (slice), up to two motion vectors, and a reference index (slice) may be referred to as a bi-predictive picture or a B picture (slice).

Intra prediction means a prediction method that derives the current processing block from data elements (eg, sample values, etc.) of the same decoded picture (or slice). That is, a method of predicting pixel values of the current processing block by referring to reconstructed regions in the current picture.

Hereinafter, the inter prediction will be described in more detail.

Inter prediction (or inter screen prediction)

Inter prediction means a prediction method of deriving a current processing block based on data elements (eg, sample values or motion vectors, etc.) of pictures other than the current picture. That is, a method of predicting pixel values of the current processing block by referring to reconstructed regions in other reconstructed pictures other than the current picture.

Inter prediction (or inter picture prediction) is a technique for removing redundancy existing between pictures, and is mostly performed through motion estimation and motion compensation.

The present invention describes the detailed description of the inter prediction method described above with reference to FIGS. 1 and 2, and the decoder may be represented by the inter prediction-based video / image decoding method of FIG. 10 described later and the inter prediction unit in the decoding apparatus of FIG. 11. . In addition, the encoder may be represented by the inter prediction based video / video encoding method of FIG. 8 and the inter prediction unit in the encoding apparatus of FIG. 9. In addition, the data encoded by FIGS. 8 and 9 may be stored in the form of a bitstream.

The prediction unit of the encoding apparatus / decoding apparatus may derive the prediction sample by performing inter prediction on a block basis. Inter prediction may represent prediction derived in a manner dependent on data elements (e.g. sample values, motion information, etc.) of the picture (s) other than the current picture. When inter prediction is applied to the current block, a predicted block (prediction sample array) for the current block is derived based on a reference block (reference sample array) specified by a motion vector on the reference picture indicated by the reference picture index. Can be.

In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information of the current block may be predicted in units of blocks, subblocks, or samples based on the correlation of the motion information between the neighboring block and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information.

When inter prediction is applied, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), and the like, and a reference picture including the temporal neighboring block is called a collocated picture (colPic). It may be. For example, a motion information candidate list may be constructed based on neighboring blocks of the current block, and a flag indicating which candidate is selected (used) to derive a motion vector and / or a reference picture index of the current block. Or index information may be signaled.

Inter prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the motion information of the current block may be the same as the motion information of the selected neighboring block. In the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of a motion vector prediction (MVP) mode, a motion vector of a selected neighboring block is used as a motion vector predictor, and a motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

8 and 9, S801 may be performed by the inter prediction unit 180 of the encoding apparatus, and S802 may be performed by the residual processing unit of the encoding apparatus. In detail, S802 may be performed by the subtraction unit 115 of the encoding apparatus. In S803, the prediction information may be derived by the inter prediction unit 180 and encoded by the entropy encoding unit 190. In S803, the residual information may be derived by the residual processor and encoded by the entropy encoding unit 190. The residual information is information about the residual samples. The residual information may include information about quantized transform coefficients for the residual samples.

As described above, the residual samples may be derived as transform coefficients through the transform unit 120 of the encoding apparatus, and the transform coefficients may be derived as transform coefficients quantized through the quantization unit 130. Information about the quantized transform coefficients may be encoded by the entropy encoding unit 190 through a residual coding procedure.

The encoding apparatus performs inter prediction on the current block (S801). The encoding apparatus may derive inter prediction mode and motion information of the current block and generate prediction samples of the current block. In this case, the inter prediction mode determination, the motion information derivation, and the prediction samples generation procedure may be performed simultaneously, or one procedure may be performed before the other. For example, the inter prediction unit 180 of the encoding apparatus may include a prediction mode determination unit 181, a motion information derivation unit 182, and a prediction sample derivation unit 183, and the prediction mode determination unit 181. In FIG. 2, a prediction mode for the current block may be determined, motion information derivation unit 182 may derive motion information of the current block, and prediction sample derivation unit 183 may derive motion samples of the current block.

For example, the inter prediction unit 180 of the encoding apparatus searches for a block similar to the current block in a predetermined area (search area) of reference pictures through motion estimation, and a difference from the current block is determined. Reference blocks that are minimum or below a certain criterion may be derived. Based on this, a reference picture index indicating a reference picture in which the reference block is located may be derived, and a motion vector may be derived based on a position difference between the reference block and the current block. The encoding apparatus may determine a mode applied to the current block among various prediction modes. The encoding apparatus may compare RD costs for the various prediction modes and determine an optimal prediction mode for the current block.

For example, when a skip mode or a merge mode is applied to the current block, the encoding apparatus constructs a merge candidate list to be described later, and among the reference blocks indicated by merge candidates included in the merge candidate list. A reference block having a difference from the current block that is smaller than or equal to a predetermined criterion may be derived. In this case, a merge candidate associated with the derived reference block is selected, and merge index information indicating the selected merge candidate may be generated and signaled to the decoding apparatus. The motion information of the current block may be derived using the motion information of the selected merge candidate.

As another example, when the (A) MVP mode is applied to the current block, the encoding apparatus constructs a (A) MVP candidate list to be described later, and among the mvp (motion vector predictor) candidates included in the (A) MVP candidate list. The motion vector of the selected mvp candidate may be used as mvp of the current block. In this case, for example, a motion vector indicating a reference block derived by the above-described motion estimation may be used as the motion vector of the current block, and the difference with the motion vector of the current block is smallest among the mvp candidates. An mvp candidate with a motion vector may be the selected mvp candidate. A motion vector difference (MVD) which is a difference obtained by subtracting the mvp from the motion vector of the current block may be derived. In this case, the information about the MVD may be signaled to the decoding device. In addition, when the (A) MVP mode is applied, the value of the reference picture index may be configured with reference picture index information and separately signaled to the decoding apparatus.

The encoding apparatus may derive residual samples based on the prediction samples (S802). The encoding apparatus may derive the residual samples by comparing the original samples of the current block with the prediction samples.

The encoding apparatus encodes image information including prediction information and residual information (S803). The encoding apparatus may output the encoded image information in the form of a bitstream. The prediction information may include prediction mode information (eg, skip flag, merge flag or mode index) and information on motion information as information related to the prediction procedure. The information about the motion information may include candidate selection information (eg, merge index, mvp flag or mvp index) that is information for deriving a motion vector. In addition, the information about the motion information may include the above-described information about the MVD and / or reference picture index information.

The information about the motion information may include information indicating whether L0 prediction, L1 prediction, or bi prediction is applied. The residual information is information about the residual samples. The residual information may include information about quantized transform coefficients for the residual samples.

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

Meanwhile, as described above, the encoding apparatus may generate a reconstructed picture (including the reconstructed samples and the reconstructed block) based on the reference samples and the residual samples. This is because the encoding apparatus derives the same prediction result as that performed in the decoding apparatus, and thus the coding efficiency can be increased. Accordingly, the encoding apparatus may store a reconstructed picture (or reconstructed samples, a reconstructed block) in a memory and use the reference picture for inter prediction. As described above, an in-loop filtering procedure may be further applied to the reconstructed picture.

10 and 11, the decoding apparatus may perform an operation corresponding to the operation performed by the encoding apparatus. The decoding apparatus may perform prediction on the current block and derive prediction samples based on the received prediction information.

S1001 to S1003 may be performed by the inter prediction unit 260 of the decoding apparatus, and the residual information of S1004 may be obtained from the bitstream by the entropy decoding unit 210 of the decoding apparatus. The residual processor of the decoding apparatus may derive residual samples for the current block based on the residual information. In detail, the inverse quantization unit 220 of the residual processing unit performs dequantization on the basis of the quantized transform coefficients derived based on the residual information to derive transform coefficients and inverse transform unit of the residual processing unit ( 230 may derive residual samples for the current block by performing an inverse transform on the transform coefficients. S1005 may be performed by the adder 235 or the reconstruction unit of the decoding apparatus.

In detail, the decoding apparatus may determine a prediction mode for the current block based on the received prediction information (S1001). The decoding apparatus may determine which inter prediction mode is applied to the current block based on the prediction mode information in the prediction information.

For example, it may be determined whether the merge mode is not applied to the current block or (A) MVP mode is determined based on the merge flag. Alternatively, one of various inter prediction mode candidates may be selected based on the mode index. The inter prediction mode candidates may include a skip mode, a merge mode, and / or (A) MVP mode, or may include various inter prediction modes described below.

The decoding apparatus derives motion information of the current block based on the determined inter prediction mode (S1002). For example, when a skip mode or a merge mode is applied to the current block, the decoding apparatus may construct a merge candidate list to be described later, and select one merge candidate among merge candidates included in the merge candidate list. The selection may be performed based on the above merge information. The motion information of the current block may be derived using the motion information of the selected merge candidate. The motion information of the selected merge candidate may be used as motion information of the current block.

As another example, when (A) MVP mode is applied to the current block, the decoding apparatus constructs (A) MVP candidate list to be described later, and among (m) mvp (motion vector predictor) candidates included in the (A) MVP candidate list. The motion vector of the selected mvp candidate may be used as mvp of the current block. The selection may be performed based on the above-described selection information (mvp flag or mvp index). In this case, the MVD of the current block may be derived based on the information on the MVD, and the motion vector of the current block may be derived based on mvp and the MVD of the current block. In addition, a reference picture index of the current block may be derived based on the reference picture index information. A picture indicated by the reference picture index in the reference picture list for the current block may be derived as a reference picture referred for inter prediction of the current block.

Meanwhile, as described below, motion information of the current block may be derived without constructing a candidate list, and in this case, motion information of the current block may be derived according to a procedure disclosed in a prediction mode to be described later. In this case, the candidate list structure as described above may be omitted.

The decoding apparatus may generate prediction samples for the current block based on the motion information of the current block (S1003). In this case, the reference picture may be derived based on the reference picture index of the current block, and the prediction samples of the current block may be derived using the samples of the reference block indicated by the motion vector of the current block on the reference picture. In this case, as described below, a prediction sample filtering procedure for all or some of the prediction samples of the current block may be further performed.

For example, the inter prediction unit 260 of the decoding apparatus may include a prediction mode determination unit 261, a motion information derivation unit 262, and a prediction sample derivation unit 263, and the prediction mode determination unit 261 may be used. Determining a prediction mode for the current block based on the prediction mode information received in the step, and based on the information on the motion information received from the motion information derivation unit 262, motion information (motion vector and / or A reference picture index, etc.), and the prediction sample derivation unit 263 may derive the prediction samples of the current block.

The decoding apparatus generates residual samples for the current block based on the received residual information (S1004). The decoding apparatus may generate reconstructed samples for the current block based on the prediction samples and the residual samples, and may generate a reconstructed picture based on the prediction samples (S1005). After that, the in-loop filtering procedure may be further applied to the reconstructed picture as described above.

As described above, the inter prediction procedure may include determining an inter prediction mode, deriving motion information according to the determined prediction mode, and performing prediction based on the derived motion information (prediction sample generation).

Determination of inter prediction mode

Various inter prediction modes may be used for prediction of the current block in the picture. For example, various modes, such as merge mode, skip mode, MVP mode, and affine mode, may be used. Decoder side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, and the like may be further used as a secondary mode. The affine mode may be called an affine motion prediction mode. MVP mode may be referred to as advanced motion vector prediction (AMVP) mode.

Prediction mode information indicating the inter prediction mode of the current block may be signaled from the encoding device to the decoding device. The prediction mode information may be included in the bitstream and received by the decoding apparatus. The prediction mode information may include index information indicating one of a plurality of candidate modes. Alternatively, the inter prediction mode may be indicated through hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags.

For example, a skip flag is signaled to indicate whether a skip mode is applied, and if a skip mode is not applied, a merge flag is signaled to indicate whether a merge mode is applied, and if a merge mode is not applied, an MVP mode is applied. Or may further signal a flag for additional classification. The affine mode may be signaled in an independent mode, or may be signaled in a mode dependent on a merge mode or an MVP mode. For example, the affine mode may be configured with one candidate of a merge candidate list or an MVP candidate list as described below.

Derivation of motion information according to inter prediction mode

Inter prediction may be performed using motion information of the current block. The encoding apparatus may derive optimal motion information for the current block through a motion estimation procedure. For example, the encoding apparatus may search for a similar reference block having a high correlation using the original block in the original picture for the current block in fractional pixel units within a predetermined search range in the reference picture, thereby deriving motion information. Can be. Similarity of blocks can be derived based on the difference of phase based sample values. For example, the similarity of the blocks may be calculated based on the SAD between the current block (or template of the current block) and the reference block (or template of the reference block). In this case, motion information may be derived based on a reference block having the smallest SAD in the search area. The derived motion information may be signaled to the decoding apparatus according to various methods based on the inter prediction mode.

Merge mode and skip mode

When the merge mode is applied, the motion information of the current prediction block is not directly transmitted, and the motion information of the current prediction block is derived using the motion information of the neighboring prediction block. Accordingly, the motion information of the current prediction block can be indicated by transmitting flag information indicating that the merge mode is used and a merge index indicating which neighboring prediction blocks are used.

The encoder may search for merge candidate blocks used to derive motion information of the current prediction block to perform the merge mode. For example, up to five merge candidate blocks may be used, but the present invention is not limited thereto. The maximum number of merge candidate blocks may be transmitted in a slice header (or tile group header), but the present invention is not limited thereto. After finding the merge candidate blocks, the encoder may generate a merge candidate list, and select the merge candidate block having the smallest cost among them as the final merge candidate block.

The present invention provides various embodiments of a merge candidate block constituting the merge candidate list.

The merge candidate list may use, for example, five merge candidate blocks. For example, four spatial merge candidates and one temporal merge candidate may be used. As a specific example, in the case of the spatial merge candidate, the blocks shown in FIG. 12 may be used as the spatial merge candidate.

Referring to FIG. 13, the coding apparatus (encoder / decoder) inserts spatial merge candidates derived by searching for spatial neighboring blocks of the current block to the merge candidate list (S1301). For example, the spatial neighboring blocks may include a lower left corner peripheral block, a left peripheral block, a right upper corner peripheral block, an upper peripheral block, and an upper left corner peripheral block of the current block. However, as an example, in addition to the above-described spatial peripheral blocks, additional peripheral blocks such as a right peripheral block, a lower peripheral block, and a lower right peripheral block may be further used as the spatial peripheral blocks. The coding apparatus may search for the spatial neighboring blocks based on priority, detect available blocks, and derive motion information of the detected blocks as the spatial merge candidates. For example, the encoder and the decoder may search the five blocks shown in FIG. 12 in the order of A1, B1, B0, A0, and B2, and index the available candidates sequentially to form a merge candidate list.

The coding apparatus inserts the temporal merge candidate derived by searching the temporal neighboring block of the current block into the merge candidate list (S1302). The temporal neighboring block 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 in which the temporal neighboring block is located may be called a collocated picture or a col picture. The temporal neighboring block may be searched in the order of the lower right corner peripheral block 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 may be stored as representative motion information for each predetermined storage unit in the col picture. In this case, it is not necessary to store the motion information for all the blocks in the predetermined storage unit, thereby obtaining a motion data compression effect. In this case, the constant storage unit may be predetermined, for example, 16x16 sample units, 8x8 sample units, or the like, or size information about the constant storage unit may be signaled from the encoder to the decoder. When the motion data compression is applied, motion information of the temporal neighboring block may be replaced with representative motion information of the predetermined storage unit in which the temporal neighboring block is located.

That is, in this case, in terms of implementation, a position that is arithmetically shifted after arithmetic right shift by a predetermined value based on the coordinates (upper left sample position) of the temporal neighboring block, rather than the prediction block located at the coordinates of the temporal neighboring block The temporal merge candidate may be derived based on the motion information of the covering prediction block. For example, when the constant storage unit is 2nx2n sample units, assuming that the coordinates of the temporal neighboring block are (xTnb, yTnb), the modified positions are ((xTnb >> n) << n) and (yTnb >> The motion information of the prediction block located at n) << n)) may be used for the temporal merge candidate.

Specifically, for example, when the constant storage unit is a 16x16 sample unit, when the coordinates of the temporal neighboring block are (xTnb, yTnb), the modified position is ((xTnb >> 4) << 4), ( The motion information of the prediction block located at yTnb >> 4) << 4)) may be used for the temporal merge candidate. Or, for example, when the constant storage unit is an 8x8 sample unit, if the coordinates of the temporal neighboring block are (xTnb, yTnb), the modified position is ((xTnb >> 3) << 3), (yTnb> The motion information of the prediction block located at > 3) < 3) can be used for the temporal merge candidate.

The coding apparatus may check whether the number of current merge candidates is smaller than the number of maximum merge candidates (S1303). The maximum number of merge candidates may be predefined or signaled at the encoder to the decoder. For example, the encoder may generate information about the maximum number of merge candidates, encode the information, and transmit the encoded information to the decoder in the form of a bitstream. If the maximum number of merge candidates is filled up, the subsequent candidate addition process may not proceed.

As a result of the checking, when the number of the current merge candidates is smaller than the maximum merge candidates, the coding apparatus inserts an additional merge candidate into the merge candidate list (S1304). The additional merge candidate may include, for example, ATMVP, combined bi-predictive merge candidate (when the slice type of the current slice is B type) and / or zero vector merge candidate.

As a result of the checking, when the number of the current merge candidates is not smaller than the number of the maximum merge candidates, the coding apparatus may terminate the construction of the merge candidate list. In this case, the encoder may select an optimal merge candidate among merge candidates constituting the merge candidate list based on a rate-distortion (RD) cost, and signal selection information (ex. Merge index) indicating the selected merge candidate to the decoder. can do. The decoder may select the optimal merge candidate based on the merge candidate list and the selection information.

As described above, the motion information of the selected merge candidate may be used as the motion information of the current block, and the prediction samples of the current block may be derived based on the motion information of the current block. An encoder may derive residual samples of the current block based on the prediction samples, and may signal residual information about the residual samples to a decoder. The decoder may generate reconstructed samples based on the residual samples derived from the residual information and the prediction samples, and generate a reconstructed picture based on the same.

When the skip mode is applied, the motion information of the current block may be derived in the same manner as when the merge mode is applied. However, when the skip mode is applied, the residual signal for the corresponding block is omitted, and thus prediction samples may be used as reconstructed samples.

MVP mode

When the Motion Vector Prediction (MVP) mode is applied, the motion vector and / or the temporal neighboring block (or Col block) of the restored spatial neighboring block (for example, may be the neighboring block described above with reference to FIG. 12). Using the motion vector, a motion vector predictor candidate list may be generated. That is, the motion vector of the reconstructed spatial neighboring block and / or the motion vector corresponding to the temporal neighboring block may be used as a motion vector predictor candidate.

The information about the prediction may include selection information (eg, MVP flag or MVP index) indicating an optimal motion vector predictor candidate selected from the motion vector predictor candidates included in the list. At this time, the prediction unit may select the motion vector predictor of the current block from among the motion vector predictor candidates included in the motion vector candidate list using the selection information. The prediction unit of the encoding apparatus may obtain a motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, and may encode the output vector in a bitstream form. That is, MVD may be obtained by subtracting the motion vector predictor from the motion vector of the current block. In this case, the prediction unit of the decoding apparatus may obtain a motion vector difference included in the information about the prediction, and derive the motion vector of the current block by adding the motion vector difference and the motion vector predictor. The prediction unit of the decoding apparatus may obtain or derive a reference picture index or the like indicating the reference picture from the information about the prediction. For example, the motion vector predictor candidate list may be configured as shown in FIG. 14.

DMVR (Decoder side Motion Vector Refinement)

The DMVR is a method of performing motion prediction by refinementing motion information of neighboring blocks at the decoder side. When DMVR is applied, the decoder may refine the motion information refined through cost comparison based on a template (or prediction block or prediction sample array) generated by using motion information of neighboring blocks in merge / skip mode. Can be induced.

When the merge / skip mode using the motion vector of the neighboring block is applied as it is, an error may occur as the motion vector of the current block is represented by using the motion vector for each direction. The encoder / decoder may apply a DMVR process to improve the motion vector to correct this error. In other words, the DMVR process can be invoked to improve the accuracy of the initial motion compensation prediction (ie, motion compensation prediction through merge / skip mode).

An embodiment of the present invention proposes a method of generating an adaptive prediction template based on an inter prediction direction (or a reference direction) in applying a DMVR.

In addition, an embodiment of the present invention proposes a method of generating an adaptive prediction template based on a cost function in applying a DMVR.

In addition, an embodiment of the present invention proposes a method of generating an inter prediction sample by applying an adaptive weighted average based on a cost function in applying a DMVR.

Referring to FIG. 15, in the embodiment of the present invention, when bidirectional prediction is applied to the current block C, the encoder / decoder uses the initial prediction block P ′ using motion information MV0 and MV1 in each direction. (In the present invention, the initial prediction block may be referred to as a template, a prediction template, a temporary prediction block, etc.), and in terms of cost function in each reference picture based on the initial prediction block P '. By searching for blocks P0 'and P1' having a minimum error, the motion information MV0 and MV1 in each direction may be updated (or refined) (MV0 'and MV1').

In detail, the encoder / decoder generates the prediction block P0 in the L0 direction using the motion vector MV0 of the reference picture list 0 (L0) and uses the motion vector MV1 of the reference picture list 1 (L1). By doing so, the prediction block P1 in the L1 direction may be generated. The encoder / decoder may generate an initial prediction block P ′ using average values of the generated two prediction blocks P0 and P1. In one embodiment, the initial prediction block P ′ may be generated using Equation 1 below.

Here, O represents an offset value, and as an example, O may be set to a value of 1.

That is, when DMVR technology is applied, the encoder / decoder uses the initial prediction block P 'as a reference block or prediction template, and the minimum in terms of the cost function in terms of MV0 in the reference picture list (or reference list) L0 direction. The motion vector can be updated (MV0 ') by searching for blocks with errors, and the motion vector is updated (MV1') by searching for blocks with the smallest error in terms of cost functions around MV1 in the reference picture list L1 direction. can do.

In one embodiment, the sum of absolute difference (SAD), sum of square difference (SSD), mean sum of absolute difference (MRSAD), etc. may be the cost function. (Or cost).

The encoder / decoder may generate prediction blocks P0 'and P1' using the updated motion vectors MV0 'and MV1', respectively, and sum (eg, average or weight) the two blocks to generate a final prediction block. have. In this case, Equation 2 below may be used.

The encoder / decoder may generate a reconstructed signal by adding the last generated final predictive block and the residual signal.

In an embodiment, the encoder / decoder may generate an initial prediction block and then refine the initial motion vector by searching by integer pixel units through template matching. The above-described cost function may be used for the template matching. For example, the initial motion vector may be improved such that the cost (or sum of differences) value calculated using the cost function described above is minimized.

Also, for example, in the search phase, the encoder / decoder may perform motion compensation using bilinear interpolation filtering. If the initial motion vector is changed, the encoder / decoder may improve the changed motion vector by searching in subpixel units through template matching. In this case, the encoder / decoder may perform motion compensation using bidirectional linear interpolation filtering.

Thereafter, the encoder / decoder may perform motion compensation using the final motion vector (or the last updated motion vector, the last changed motion vector). As an example, after the DMVR process is completed, the encoder / decoder may generate a final prediction block by performing motion compensation using a regular interpolation filter. If the initial motion vector is not changed, the encoder / decoder may perform motion compensation using the initial motion vector. As an example, after the DMVR process is completed, the encoder / decoder may perform final motion compensation using a regular interpolation filter.

According to the above-described embodiment, the decoder may improve the motion vector by performing motion compensation in both directions again using the initial prediction block as the reference block. Hereinafter, a method of applying DMVR using an initial prediction block that is weighted based on the inter prediction direction (or reference list direction) will be described.

16 shows an example of a process of generating a weight-based prediction template. In other words, in an embodiment of the present invention, the encoder / decoder may adaptively generate (or determine) a prediction template, that is, an initial prediction block, according to the prediction direction (or reference direction).

By way of example, when searching for a block with a minimum error in terms of a given (or preset) cost function about the initial motion vector MV0 with respect to the reference list L0 direction, the encoder / decoder is specified by the initial motion vector MV0. An initial prediction block for the reference list L0 direction may be generated through a weighted sum with higher weights applied to the prediction block P0 (or identified). For example, the encoder / decoder may use the following Equation 3 to generate the initial prediction block P0 'for the reference list L0 direction.

Referring to Equation 3, the encoder / decoder may weight the prediction blocks P0 and P1 to improve an initial motion vector in the reference list L0 direction. Here, O is an offset value, for example, O may be set to a value of (a + b) / 2.

Similarly, when searching for a block with the minimum error in terms of a given cost function about the initial motion vector MV1 with respect to the direction for the reference list L1 direction, the encoder / decoder is further added to the motion prediction block P1 using the initial motion vector MV1. An initial prediction block for the reference list L1 direction may be generated through a weighted weighted sum. For example, the encoder / decoder may use the following Equation 4 to generate the initial prediction block P0 'for the reference list L1 direction.

Referring to Equation 4, the encoder / decoder may weight the prediction blocks P0 and P1 to improve an initial motion vector in the reference list L1 direction. Here, O is an offset value, for example, O may be set to a value of (a + b) / 2.

In an embodiment, in the above Equations 3 and 4, the values of a and b may have the form of (3, 1), (7, 1), (1, 3), (1, 7), or the like. . Also, a value of (a + b) may be used for shift operation instead of division for the convenience of encoder and decoder implementation. For example, the value of (a + b) may have the form 2 << k.

In addition, in one embodiment, the motion vector improvement process may be performed only within a specific region determined based on an initial MV value (in the present invention, the specific region may be referred to as a search region, a search range, a limited region, a limited range, etc.). Can be performed. Or, it may be performed only when the cost value is larger than a specific threshold.

Further, in one embodiment, the weight values for the prediction templates for each direction described above may be determined (or set) equally at the encoder and decoder. Alternatively, the weight value for the prediction template for each direction may include a sequence parameter set, a picture parameter set, a slice header (or a tile group header), a slice data unit, and the like. Signaled via

Also, in one embodiment, the syntax indicating whether to apply the weight may be transmitted in a sequence parameter set, a picture parameter set, a slice header (or a tile group header), and a slice data unit. Alternatively, the weight value may be determined based on the distance between the reference list L0 and the reference picture of the reference list L1. In addition, when the distance-based weight value is derived and used, the weighted distance sum may have a form of 2 << k.

In another embodiment of the present invention, a method for generating a prediction template based on a cost function is proposed. That is, the encoder / decoder may derive a weight value for generating the prediction template based on the cost (or difference) value of the prediction block specified by the motion vector of each reference direction (or prediction direction).

Specifically, the encoder / decoder may derive a weight value for generating a prediction template by comparing the cost function value of the motion prediction block P0 using the initial motion vector MV0 with the cost function value of the motion prediction block P1 using the initial motion vector MV1. have. For example, when the value of the cost function for P0 is smaller than the value of the cost function for P1 as shown in Equation 5 below, it may mean that the prediction error of P0 is relatively small. In this case, the encoder / decoder can evaluate the reliability of P0 high. In an embodiment, the encoder / decoder may apply weights to the block using Equation 6 below.

In Equation 5, O represents an offset value and may be set to a value of (a + b) / 2. Also, as an example, the values of a and b may have the form of (3, 1), (7, 1), and the like. That is, since the value of the cost function for P0 is relatively smaller, the weight a value can be set to a value greater than the b value.

Also, in one embodiment, when the value of the cost function for P0 is smaller than the value of the cost function for P1 as shown in Equation 5, the P1 block is different from the above-described embodiment because the error of the block for P0 is small. More reflection may be required when predicting the motion of a camera. Therefore, the encoder / decoder may set the weight value for the P1 block relatively larger than the P1 block. For example, the values of a and b may have the form of (1, 3), (1, 7), or the like. That is, the weight b value may be set to a value larger than the a value.

Also, a value of (a + b) may be used for shift operation instead of division for the convenience of encoder and decoder implementation. For example, the value of (a + b) may have the form 2 << k.

Also, in one embodiment, the syntax indicating whether to apply the weight may be transmitted in a sequence parameter set, a picture parameter set, a slice header (or a tile group header), and a slice data unit. Alternatively, the weight value may be determined based on the distance between the reference list L0 and the reference picture of the reference list L1.

As described above, the DMVR technique improves (or updates) the motion vectors for both directions based on the prediction template, and uses the improved motion vectors MV0 'and motion vectors MV1' to respectively calculate the motion prediction blocks P0 'and P1'. After the generation, the final prediction block P ”may be generated using the average value of the two blocks. Hereinafter, in applying the DMVR technique, a method of generating a final prediction block by adaptively performing a weighted average (or weighted sum) based on a cost function is proposed.

Referring to FIG. 17, in an embodiment of the present invention, the encoder / decoder may generate a final prediction block by performing weighted sum based on a cost function. In other words, the encoder / decoder may refine the motion vector of each reference direction (or prediction direction) and weight the prediction blocks specific to the improved motion vector to generate a final prediction block.

In detail, the encoder / decoder generates the prediction block P0 using the motion vector MV0 (or the initial motion vector) in the direction of the reference picture list 0 (L0), and the motion vector MV1 (or the initial value in the direction of the reference picture list 1 (L1). A prediction block P1 is generated using the motion vector (S1701).

The encoder / decoder may improve the MV0 and MV1 by applying a DMVR process (S1702). Here, the DMVR technique represents a technique of correcting a motion vector in a decoder based on a symmetrical motion vector offset value. For example, the method described above with reference to FIGS. 15 and 16 may be used as the DMVR technique.

Further, in one embodiment, the motion vector may be improved (or updated) within a search region of ± 2 integer pixels around the received motion vector in consideration of the decoder computational complexity. In addition, a DCT based interpolation filter, a bi-linear interpolation filter, or the like may be used to more accurately search (or obtain) an optimal motion vector improvement position. As an embodiment, when the DCT based interpolation filter or bi-linear interpolation filter is used, the subpixel precision of 1/2, 1/4, and 1/16 positions may be provided. Between the prediction block P0 in the reference list 0 direction and the prediction block P1 in the reference list 1 direction, a position (or an improved motion vector) at which the difference value is minimum based on SAD or MR-SAD may be selected.

The encoder / decoder generates the improved prediction blocks P0 'and P1' using the improved motion vector (refined MV) (S1703).

The encoder / decoder may calculate (or derive) a weight value applied to each of the prediction blocks P0 'and P1' generated in step S1703 (S1704). As an embodiment, the encoder / decoder may derive a weight value for calculating the final prediction block by comparing the cost function value of the prediction block P0 using the motion vector MV0 with the cost function value of the motion prediction block P1 using the motion vector MV1. have. For example, when the value of the cost function for P0 is smaller than the value of the cost function for P1 as shown in Equation 7 below, it may mean that the prediction error of P0 is relatively small. In this case, the encoder / decoder can evaluate the reliability of P0 high. The encoder / decoder may use the weight value for the block as shown in Equation 8 below.

In Equation 7, O represents an offset value and may be set to a value of (a + b) / 2. Also, as an example, the values of a and b may have the form of (3, 1), (7, 1), and the like.

In addition, in one embodiment, when the value of the cost function for P0 is smaller than the value of the cost function for P1 as shown in Equation 7, the P1 block is different from the above-described embodiment because the error of the block for P0 is small. More reflection may be required when predicting the motion of a camera. Therefore, the encoder / decoder may set the weight value for the P1 block relatively larger than the P1 block. For example, the values of a and b may have the form of (1, 3), (1, 7), or the like. That is, the weight b value may be set to a value larger than the a value.

Or, in one embodiment, the encoder / decoder compares the cost function values of the prediction blocks P0 'and P1' specified by the improved motion vectors MV0 ', MV1' to obtain a weight value for generating the final prediction block. Can be induced. For example, when the value of the cost function for P0 'is smaller than the value of the cost function for P1' as shown in Equation 9 below, it may mean that the prediction error of P0 'is relatively small. In this case, the encoder / decoder can evaluate the reliability of P0 'highly. In this case, the values of a and b may have the form of (3, 1), (7, 1), or the like. That is, the weight a value may be set to a value larger than the b value.

In addition, in an embodiment, when the value of the cost function for P0 'is smaller than the value of the cost function for P1' as shown in Equation 9, the error of the block for P0 'is small. Alternatively, more reflection may be required when predicting the motion of the P1 'block. Therefore, the encoder / decoder may set the weight value for the P1 'block relatively larger than the P1' block. For example, the values of a and b may have the form of (1, 3), (1, 7), or the like. That is, the weight b value may be set to a value larger than the a value. Alternatively, the values of a and b may have the form of (3, 1), (7, 1), (1, 3), (1, 7), or the like.

Embodiments of the present invention described above may be implemented independently, or one or more embodiments may be implemented in combination.

Referring to FIG. 18, a decoder is mainly described for convenience of description, but the present invention is not limited thereto, and the method of generating an inter prediction block according to an embodiment of the present invention may be performed in the same manner in the encoder and the decoder.

When the bidirectional prediction is applied to the current block, the decoder derives a first initial motion vector and a second initial motion vector of the current block (S1801). According to an embodiment, when the bidirectional prediction is applied to the current block and the current picture is located between two reference picture lists based on a picture order count (POC) indicating an output order of the picture, the present invention The DMVR process according to the embodiment of FIGS. 15 to 18 may be applied. Also, in one embodiment, when the decoder applies bidirectional prediction to the current block, the current picture is located between two reference pictures based on the POC, and the distance between the two reference pictures and the current picture is the same, an embodiment of the present invention The DMVR process according to FIG. 15 to FIG. 18 may be applied.

The decoder improves the first initial motion vector and the second initial motion vector based on a motion vector offset value that is symmetrical with respect to the reference list direction so that the first final motion vector (or the improved motion vector) and the second final motion vector ( Or an improved motion vector) (S1802). The motion vector offset value represents a value added (or subtracted) to the initial motion vector and may be referred to as a motion vector difference value.

As described above with reference to FIG. 16, the decoder weights the fourth prediction block specified by the first initial motion vector and the fifth prediction block specified by the second initial motion vector, thereby removing the first reference motion relative to the reference list 0 direction. The second prediction template for the first prediction template and the reference list 1 direction may be generated. The decoder may improve the first initial motion vector using the first prediction template and may improve the second initial motion vector using the second prediction template. In this case, the first prediction template is generated through a weighted sum to which the fourth prediction block has a higher weight than the fifth prediction block, and the second prediction template has a higher weight to the fifth prediction block than the fourth prediction block. It can be generated through the weighting applied.

In addition, as described above with reference to FIG. 16, the decoder may generate a prediction template by weighting the fourth prediction block specified by the first initial motion vector and the fifth prediction block specified by the second initial motion vector. Can be. The decoder may improve the first initial motion vector and the second initial motion vector in each reference list direction based on the difference value with the prediction template. In this case, the weight applied to generating the prediction template may be determined based on a difference value between the fourth prediction block and the prediction template and a difference value between the fifth prediction block and the prediction template.

The decoder generates a first prediction block using the first final motion vector, and generates a second prediction block using the second final motion vector (S1803).

The decoder generates a third prediction block representing the prediction block of the current block by using the first prediction block and the second prediction block (S1804).

As described above with reference to FIG. 17, the decoder may generate the third prediction block by weighting the first prediction block and the second prediction block. In this case, a weight applied to each of the first prediction block and the second prediction block may be determined according to a cost function value of the first prediction block and the second prediction block.

In FIG. 19, the inter prediction unit is illustrated as one block for convenience of description, but the inter prediction unit may be implemented in a configuration included in the encoder and / or the decoder.

Referring to FIG. 19, the inter prediction unit implements the functions, processes, and / or methods proposed in FIGS. 8 to 18. In detail, the inter prediction unit may include an initial motion vector derivation unit 1901, a final motion vector derivation unit 1902, and a prediction block generator 1803.

When bidirectional prediction is applied to the current block, the initial motion vector deriving unit 1901 derives a first initial motion vector and a second initial motion vector of the current block. According to an embodiment, when the bidirectional prediction is applied to the current block and the current picture is located between two reference picture lists based on a picture order count (POC) indicating an output order of the picture, the present invention The DMVR process according to the embodiment of FIGS. 15 to 18 may be applied. Also, in one embodiment, when the decoder applies bidirectional prediction to the current block, the current picture is located between two reference pictures based on the POC, and the distance between the two reference pictures and the current picture is the same, an embodiment of the present invention The DMVR process according to FIG. 15 to FIG. 18 may be applied.

The final motion vector derivation unit 1902 improves the first initial motion vector and the second initial motion vector based on the motion vector offset value symmetrical with respect to the reference list direction, so that the first final motion vector (or the improved motion vector) and Derive a second final motion vector (or an improved motion vector). The motion vector offset value represents a value added (or subtracted) to the initial motion vector and may be referred to as a motion vector difference value.

As described above with reference to FIG. 16, the final motion vector deriving unit 1902 weights the fourth prediction block specified by the first initial motion vector and the fifth prediction block specified by the second initial motion vector, thereby referencing it. A first prediction template for the list 0 direction and a second prediction template for the reference list 1 direction may be generated. The final motion vector derivator 1902 may improve the first initial motion vector using the first prediction template and may improve the second initial motion vector using the second prediction template. In this case, the first prediction template is generated through a weighted sum to which the fourth prediction block has a higher weight than the fifth prediction block, and the second prediction template has a higher weight to the fifth prediction block than the fourth prediction block. It can be generated through the weighting applied.

In addition, as described above with reference to FIG. 16, the final motion vector deriving unit 1902 weights the fourth prediction block specified by the first initial motion vector and the fifth prediction block specified by the second initial motion vector. For example, a prediction template may be generated. The final motion vector derivator 1902 may improve the first initial motion vector and the second initial motion vector in each reference list direction based on the difference value with the prediction template. In this case, the weight applied to generating the prediction template may be determined based on a difference value between the fourth prediction block and the prediction template and a difference value between the fifth prediction block and the prediction template.

The prediction block generator 1903 generates a first prediction block by using the first final motion vector, and generates a second prediction block by using the second final motion vector. The prediction block generator 1903 generates a third prediction block representing the prediction block of the current block by using the first prediction block and the second prediction block.

As described above with reference to FIG. 17, the prediction block generator 1903 may generate the third prediction block by weighting the first prediction block and the second prediction block. In this case, a weight applied to each of the first prediction block and the second prediction block may be determined according to a cost function value of the first prediction block and the second prediction block.

20 shows a video coding system to which the present invention is applied.

The video coding system can include a source device and a receiving device. The source device may deliver the encoded video / image information or data to a receiving device through a digital storage medium or network in a file or streaming form.

The source device may include a video source, an encoding apparatus, and a transmitter. The receiving device may include a receiver, a decoding apparatus, and a renderer. The encoding device may be called a video / image encoding device, and the decoding device may be called a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display unit, and the display unit may be configured as a separate device or an external component.

The video source may acquire the video / image through a process of capturing, synthesizing, or generating the video / image. The video source may comprise a video / image capture device and / or a video / image generation device. The video / image capture device may include, for example, one or more cameras, video / image archives including previously captured video / images, and the like. Video / image generation devices may include, for example, computers, tablets and smartphones, and may (electronically) generate video / images. For example, a virtual video / image may be generated through a computer or the like. In this case, the video / image capturing process may be replaced by a process of generating related data.

The encoding device may encode the input video / image. The encoding apparatus may perform a series of procedures such as prediction, transform, and quantization for compression and coding efficiency. The encoded data (encoded video / image information) may be output in the form of a bitstream.

The transmitter may transmit the encoded video / video information or data output in the form of a bitstream to the receiver of the receiving device through a digital storage medium or a network in the form of a file or streaming. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. The transmission unit may include an element for generating a media file through a predetermined file format, and may include an element for transmission through a broadcast / communication network. The receiver may extract the bitstream and transmit the extracted bitstream to the decoding apparatus.

The decoding apparatus may decode the video / image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding apparatus.

The renderer may render the decoded video / image. The rendered video / image may be displayed through the display unit.

Referring to FIG. 21, a content streaming system to which the present invention is applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

The encoding server compresses content input from multimedia input devices such as a smart phone, a camera, a camcorder, etc. into digital data to generate a bitstream and transmit the bitstream to the streaming server. As another example, when multimedia input devices such as smart phones, cameras, camcorders, etc. directly generate a bitstream, the encoding server may be omitted.

The bitstream may be generated by an encoding method or a bitstream generation method to which the present invention is applied, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

The streaming server transmits the multimedia data to the user device based on the user's request through the web server, and the web server serves as a medium for informing the user of what service. When a user requests a desired service from the web server, the web server delivers it to a streaming server, and the streaming server transmits multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server plays a role of controlling a command / response between devices in the content streaming system.

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

Examples of the user device include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), navigation, a slate PC, Tablet PCs, ultrabooks, wearable devices, such as smartwatches, glass glasses, head mounted displays, digital TVs, desktops Computer, digital signage, and the like.

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

As described above, the embodiments described herein may be implemented and performed on a processor, microprocessor, controller, or chip. For example, the functional units shown in each drawing may be implemented and performed on a computer, processor, microprocessor, controller, or chip.

In addition, the decoder and encoder to which the present invention is applied include a multimedia broadcasting transmitting and receiving device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video chat device, a real time communication device such as video communication, a mobile streaming device, Storage media, camcorders, video on demand (VoD) service providing devices, OTT video (Over the top video) devices, Internet streaming service providing devices, three-dimensional (3D) video devices, video telephony video devices, and medical video devices. It can be used to process video signals or data signals. For example, the OTT video device may include a game console, a Blu-ray player, an internet access TV, a home theater system, a smartphone, a tablet PC, a digital video recorder (DVR), and the like.

In addition, the processing method to which the present invention is applied can be produced in the form of a program executed by a computer, and can be stored in a computer-readable recording medium. Multimedia data having a data structure according to the present invention can also be stored in a computer-readable recording medium. The computer readable recording medium includes all kinds of storage devices and distributed storage devices in which computer readable data is stored. The computer-readable recording medium may be, for example, a Blu-ray disc (BD), a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical disc. It may include a data storage device. The computer-readable recording medium also includes media embodied in the form of a carrier wave (eg, transmission over the Internet). In addition, the bitstream generated by the encoding method may be stored in a computer-readable recording medium or transmitted through a wired or wireless communication network.

In addition, embodiments of the present invention may be implemented as a computer program product by a program code, the program code may be performed on a computer by an embodiment of the present invention. The program code may be stored on a carrier readable by a computer.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in memory and driven by the processor. The memory may be located inside or outside the processor, and may exchange data with the processor by various known means.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

As mentioned above, preferred embodiments of the present invention are disclosed for the purpose of illustration, and those skilled in the art can improve and change various other embodiments within the spirit and technical scope of the present invention disclosed in the appended claims below. , Replacement or addition would be possible.

Claims

A method of decoding an image based on an inter prediction mode,

When bidirectional prediction is applied to a current block, deriving a first initial motion vector and a second initial motion vector of the current block;

Deriving a first final motion vector and a second final motion vector by improving the first initial motion vector and the second initial motion vector based on a motion vector offset value symmetric with respect to a reference list direction;

Generating a first prediction block by using the first final motion vector, and generating a second prediction block by using the second final motion vector; And

And generating a third prediction block representing a prediction block of the current block by using the first prediction block and the second prediction block.
The method of claim 1,

Deriving the first final motion vector and the second final motion vector,

By weighting the fourth prediction block specified by the first initial motion vector and the fifth prediction block specified by the second initial motion vector, the first prediction template and the reference list 1 direction for the reference list 0 direction are weighted. Generating a second prediction template for the; And

And improving the first initial motion vector using the first prediction template, and improving the second initial motion vector using the second prediction template.
The method of claim 2,

The first prediction template is generated through a weighted sum to which the fourth prediction block is weighted higher than the fifth prediction block.

And the second prediction template is generated through a weighted sum to which the fifth prediction block is weighted higher than the fourth prediction block.
The method of claim 1,

Deriving the first final motion vector and the second final motion vector,

Generating a prediction template by weighting a fourth prediction block specified by the first initial motion vector and a fifth prediction block specified by the second initial motion vector; And

And improving the first initial motion vector and the second initial motion vector in each reference list direction based on a difference value with the prediction template.
The method of claim 4, wherein

The weight applied to generating the prediction template is determined based on the difference between the fourth prediction block and the prediction template and the difference between the fifth prediction block and the prediction template.
The method of claim 1,

The third prediction block is generated by weighting the first prediction block and the second prediction block,

The weights applied to the first prediction block and the second prediction block are respectively determined according to cost function values of the first prediction block and the second prediction block.
An apparatus for decoding an image based on an inter prediction mode,

An initial motion vector derivation unit for deriving a first initial motion vector and a second initial motion vector of the current block when bidirectional prediction is applied to the current block;

A final motion vector derivation unit for deriving a first final motion vector and a second final motion vector by improving the first initial motion vector and the second initial motion vector based on a motion vector offset value symmetric with respect to a reference list direction; And

Generate a first prediction block using the first final motion vector, generate a second prediction block using the second final motion vector, and use the current prediction block and the second prediction block. An inter prediction mode based image decoding apparatus comprising a prediction block generator for generating a third prediction block representing a prediction block of the block.
The method of claim 7, wherein

The final motion vector derivation unit,

By weighting the fourth prediction block specified by the first initial motion vector and the fifth prediction block specified by the second initial motion vector, the first prediction template and the reference list 1 direction for the reference list 0 direction are weighted. Create a second prediction template for

And improving the first initial motion vector using the first prediction template and improving the second initial motion vector using the second prediction template.
The method of claim 8,

The first prediction template is generated through a weighted sum to which the fourth prediction block is weighted higher than the fifth prediction block.

And the second prediction template is generated through a weighted sum to which the fifth prediction block is weighted higher than the fourth prediction block.
The method of claim 7, wherein

The final motion vector derivation unit,

Generating a prediction template by weighting a fourth prediction block specified by the first initial motion vector and a fifth prediction block specified by the second initial motion vector, and

And an inter prediction mode based image decoding apparatus for improving the first initial motion vector and the second initial motion vector in each reference list direction based on the difference value with the prediction template.
The method of claim 10,

The weight applied to generating the prediction template is determined based on the difference between the fourth prediction block and the prediction template and the difference between the fifth prediction block and the prediction template.
The method of claim 7, wherein

The third prediction block is generated by weighting the first prediction block and the second prediction block,

And a weight applied to each of the first prediction block and the second prediction block is determined according to a cost function value of the first prediction block and the second prediction block.