WO2019199152A1

WO2019199152A1 - Method and device for processing video signal by using affine prediction

Info

Publication number: WO2019199152A1
Application number: PCT/KR2019/004528
Authority: WO
Inventors: 남정학; 박내리; 이재호
Original assignee: 엘지전자 주식회사
Priority date: 2018-04-14
Filing date: 2019-04-15
Publication date: 2019-10-17

Abstract

A method for decoding a video signal and a device therefor are disclosed. Particularly, a method for decoding a video signal on the basis of an affine prediction mode can comprise the steps of: searching for a block encoded in an affine prediction mode, from among blocks neighboring a current block; deriving a first control point motion vector of an upper left side control point of the current block and a second control point motion vector of an upper right side control point of the current block, by using an affine motion model of the block encoded in the affine prediction mode; determining a motion compensation area for an affine prediction in a reference picture of the current block; updating the first control point motion vector and the second control point motion vector on the basis of the motion compensation area; and deriving a motion vector of sub block units in the current block by using the updated first control point motion vector and the updated second control point motion vector.

Description

Method and apparatus for processing video signal using affine prediction

The present invention relates to a method and apparatus for encoding / decoding a video signal, and more particularly, to a method and apparatus for adaptively performing affine prediction.

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.

In a conventional compression technique of a still image or a video, motion prediction is performed in units of prediction blocks during inter prediction. However, even if a prediction block of various sizes is supported to find an optimal prediction block for the current block, only the parallel-based block-based prediction method is applied, thereby lowering the prediction accuracy.

An object of the present invention is to propose an affine motion prediction method that performs encoding / decoding using an affine motion model.

It is also an object of the present invention to propose a method for limiting the motion compensation region of affine motion prediction in order to reduce the memory bandwidth in terms of hardware.

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 a video signal based on an Affine prediction mode, comprising: searching for a block encoded in an affine prediction mode among blocks neighboring a current block; A first control point motion vector of the upper left control point of the current block and an upper right control point of the current block by using an affine motion model of the block encoded in the affine prediction mode Deriving a second control point motion vector; Determining a motion compensation region for affine prediction within a reference picture of the current block; Updating the first control point motion vector and the second control point motion vector based on the motion compensation region; And using the updated one control point motion vector and the updated second control point motion vector, deriving a motion vector of a sub-block unit within the current block.

The determining of the motion compensation region may include: deriving a third control point motion vector at the center position of the current block by using the first control point motion vector and the second control point motion vector; And determining the motion compensation region by using the third control point motion vector and the motion compensation bandwidth threshold.

Preferably, the motion compensation bandwidth threshold value is a header of a sequence parameter set, a picture parameter set, a tile group header, or a network abstract layer unit. Signaled from the encoder via.

Preferably, the updating of the first control point motion vector and the second control point motion vector may be performed such that a position specified by at least one of the first control point motion vector and the second control point motion vector is outside the motion compensation region. In this case, the operation may be performed by updating at least one of the first control point motion vector and the second control point motion vector to be included in the motion compensation region.

Preferably, the determining of the motion compensation region may further include determining the motion compensation region by using the first control point motion vector and the motion compensation bandwidth threshold.

Preferably, the motion compensation region is determined to be a block having a predefined size specified by the first control point motion vector, and updating the first control point motion vector and the second control point motion vector comprises: When the position specified by the second control point motion vector is out of the motion compensation region, the second control point motion vector may be updated to be included in the motion compensation region.

Another aspect of the present invention provides a method of decoding a video signal based on an affine prediction mode, wherein the affine searches for a block encoded in an affine prediction mode among blocks neighboring a current block. A coding block search unit; A first control point motion vector of the upper left control point of the current block and an upper right control point of the current block by using an affine motion model of the block encoded in the affine prediction mode A control point motion vector derivation unit for deriving a second control point motion vector; A motion compensation region determiner configured to determine a motion compensation region for affine prediction within a reference picture of the current block; A control point motion vector updating unit which updates the first control point motion vector and the second control point motion vector based on the motion compensation region; And a sub-block motion vector derivation unit for deriving a motion vector of a sub-block unit in the current block by using the updated one control point motion vector and the updated second control point motion vector.

Preferably, the motion compensation region determiner is configured to derive a third control point motion vector at a central position of the current block by using the first control point motion vector and the second control point motion vector, and the third control point motion vector and motion The compensation region threshold may be used to determine the motion compensation region.

Preferably, the control point motion vector updating unit, when the position specified by at least one of the first control point motion vector and the second control point motion vector is out of the motion compensation region, the first control point motion vector and the first At least one of two control point motion vectors may be updated to be included in the motion compensation region.

Preferably, the motion compensation region determiner may determine the motion compensation region by using the first control point motion vector and the motion compensation bandwidth threshold.

Preferably, the motion compensation region is set to a block having a predefined size specified by the first control point motion vector, and the control point motion vector updating unit is configured to position the motion specified by the second control point motion vector. When leaving the compensation region, the second control point motion vector may be updated to be included in the motion compensation region.

According to an exemplary embodiment of the present invention, the prediction accuracy may be improved by reflecting image distortion by processing an inter prediction based image using an affine transform.

In addition, according to an embodiment of the present invention, by effectively setting a motion compensation region for affine motion prediction, it is possible to improve the memory bandwidth.

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.

FIG. 15 is a diagram for describing an affine motion model as an embodiment to which the present invention is applied.

16 and 17 illustrate embodiments to which the present invention is applied and illustrate an affine motion prediction method using a control point motion vector.

FIG. 18 is a diagram for describing a motion vector field indicating a motion vector set of a coding block according to an embodiment to which the present invention is applied.

19 is a flowchart illustrating a method of encoding an image based on an inter prediction mode according to an embodiment to which the present invention is applied.

20 is a flowchart illustrating a method of decoding an image based on an inter prediction mode according to an embodiment to which the present invention is applied.

21 and 22 are diagrams for describing a method of determining a control point motion vector prediction value candidate when an affine inter mode is applied as an embodiment to which the present invention is applied.

23 and 24 are diagrams for explaining a motion estimation / compensation method when an affine merge mode is applied as an embodiment to which the present invention is applied.

FIG. 25 is a diagram illustrating a method of performing affine prediction using a defined motion compensation region according to an embodiment to which the present invention is applied.

FIG. 26 is a flowchart illustrating a motion compensation method through affine prediction according to an embodiment to which the present invention is applied.

FIG. 27 is a diagram for describing a method of deriving a control point motion vector of a center position of a current block according to an embodiment to which the present invention is applied.

FIG. 28 is a diagram for explaining a method of determining a motion compensation region defined using a control point motion vector at a central position according to an embodiment to which the present invention is applied.

FIG. 29 is a diagram for describing a method of performing affine prediction using a defined motion compensation region according to an embodiment to which the present invention is applied.

30 is a view illustrating a method of limiting a motion compensation region based on a control point motion vector as an embodiment to which the present invention is applied.

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

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

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

34 is a diagram illustrating the 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 samples. 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 (reconstructed 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, 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 it as a 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 coordinate 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, if the coordinates of the temporal neighboring block are (xTnb, yTnb), the modified positions ((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.

A general image coding technique uses a translation motion model to represent the motion of a coding block. Here, the translation motion model represents a parallel-based block-based prediction method. That is, the motion information of the coding block is represented using one motion vector. However, the optimal motion vector for each pixel in the actual coding block may be different. If the optimal motion vector can be determined for each pixel or subblock unit with only a little information, coding efficiency can be increased.

Accordingly, the present invention proposes an inter prediction based image processing method that reflects various motions of an image as well as a block based prediction method that is parallel moved to increase the performance of the inter prediction.

In addition, the present invention proposes a method of increasing the accuracy of the prediction and the compression performance by reflecting the motion information in the sub-block or pixel unit.

In addition, the present invention proposes an affine motion prediction method that performs coding / decoding using an affine motion model. The affine motion model represents a prediction method of deriving a motion vector on a pixel basis or a sub block basis using a motion vector of a control point.

Referring to FIG. 15, various methods may be used to represent distortion of an image as motion information. In particular, the affine motion model may express four motions illustrated in FIG. 5.

For example, the affine motion model can model any image distortion caused, including translation of the image, scaling of the image, rotation of the image, and shear of the image. have.

The affine motion model can be represented in various ways, but in the present invention, the distortion is displayed (or identified) using motion information at a specific reference point (or reference pixel / sample) of the block, and the inter prediction is used using the same. Suggest how to do it. Here, the reference point may be referred to as a control point (CP) (or control pixel, control sample), and the motion vector at this reference point may be referred to as a control point motion vector (CPMV). The degree of distortion that can be expressed may vary depending on the number of such control points.

The affine motion model can be expressed using six parameters (a, b, c, d, e, f) as shown in Equation 1 below.

Here, (x, y) represents the position of the upper left pixel of the coding block. And v_x and v_y represent the motion vector in (x, y), respectively.

Referring to FIG. 16, the upper left control point (CP0) 1602 (hereinafter, referred to as a first control point) of the current block 1601, and the upper right control point (CP1) 1603 (hereinafter, referred to as the first control point). , A second control point) and a lower left control point (CP2) 1604 (hereinafter referred to as a third control point) may each have independent motion information. This may be expressed as CP0, CP1, and CP2, respectively. However, this corresponds to one embodiment of the present invention, and the present invention is not limited thereto. For example, various control points may be defined, such as a lower right control point, a center control point, and other control points for each position of a subblock.

In an embodiment, at least one of the first to third control points may be a pixel included in the current block. Alternatively, as another example, at least one of the first to third control points may be a pixel adjacent to the current block not included in the current block.

Motion information for each pixel or sub-block of the current block 1601 may be derived using motion information of one or more of the control points.

For example, an affine motion model using motion vectors of the upper left control point 1602, the upper right control point 1603, and the lower left control point 1604 of the current block 1601 may be defined as in Equation 2 below. .

Here, v_0 is a motion vector of the upper left control point 1602, v_1 is a motion vector of the upper right control point 1603, and v_2 is a motion vector of the lower left control point 1604, and v_0 = {v_0x, v_0y}, v_1 = {v_1x, v_1y}, v_2 = {v_2x, v_2y}. In Equation 2, w denotes a width of the current block 1601 and h denotes a height of the current block 1601. And v = {v_x, v_y} represents a motion vector at the {x, y} position.

According to another embodiment of the present invention, an affine motion model that expresses three motions of translation, scale, and rotation among motions that can be expressed by an affine motion model may be defined. In this specification, this is referred to as a simplified affine motion model or a simple affine motion model.

The simple affine motion model may be expressed using four parameters (a, b, c, d) as shown in Equation 3 below.

Here, {v_x, v_y} represents a motion vector at the {x, y} position, respectively. In this way, an affine motion model using four parameters can be called AF4. The present invention is not limited thereto, and when six parameters are used, it is called AF6, and the above embodiments may be applied in the same manner.

Referring to FIG. 17, when v_0 is a motion vector of the upper left control point 1701 of the current block, and v_1 is a motion vector of the right upper control point 1702, v_0 = {v_0x, v_0y}, v_1 = {v_1x, v_1y } Can be defined. In this case, the affine motion model of AF4 may be defined as in Equation 4 below.

In Equation 4, w denotes the width of the current block, and h denotes the height of the current block. And v = {v_x, v_y} represents the motion vector of the {x, y} position, respectively.

The encoder or decoder may determine (or derive) the motion vector of each pixel position using the control point motion vector (eg, the motion vectors of the upper left control point 1701 and the upper right control point 1702).

In the present invention, a set of motion vectors determined through affine motion prediction may be defined as an affine motion vector field. The affine motion vector field may be determined using at least one of Equations 1 to 4.

In the encoding / decoding process, the motion vector through the affine motion prediction may be determined in units of pixels or in units of predefined (or preset) blocks (or subblocks). For example, when determined in units of pixels, a motion vector may be derived based on each pixel in a block, and when determined in units of subblocks, a motion vector may be derived based on units of each subblock in a current block. As another example, when it is determined in units of sub blocks, the motion vector of the corresponding sub block may be derived based on the upper left pixel or the center pixel.

Hereinafter, in the description of the present invention, for convenience of description, the case where the motion vector through the affine motion prediction is determined in units of 4x4 blocks will be described. However, the present invention is not limited thereto, and the present invention is not limited thereto. It can be applied in units of blocks of different sizes.

Referring to FIG. 18, it is assumed that the size of the current block is 16 × 16. The encoder or decoder may determine the motion vector in units of 4 × 4 subblocks using the motion vectors of the upper left control point 1801 and the upper right control point 1802 of the current block. The motion vector of the corresponding subblock may be determined based on the central pixel value of each subblock.

In FIG. 18, an arrow displayed at the center of each subblock indicates a motion vector obtained by an Affine motion model.

Affine motion prediction may be used in an affine merge mode (hereinafter referred to as an "AF merge mode") and an affine inter mode (hereinafter referred to as an "AF inter mode"). Similar to the skip mode or the merge mode, the AF merge mode is a method of encoding or decoding two control point motion vectors without encoding motion vector differences. The AF inter mode is a method of encoding or decoding a control point motion vector difference after determining a control point motion vector predictor and a control point motion vector.

Referring to FIG. 19, the encoder performs (or applies) a skip mode, a merge mode, and an inter mode with respect to a current processing block (S1901). The encoder performs an AF merge mode on the current processing block (S1902) and performs an AF inter mode (S1903). In this case, the execution order of steps S1901 to S1903 may be changed.

The encoder selects an optimal mode applied to the current processing block among the modes performed in steps S1901 to S1903 (S1904). In this case, the encoder can determine the optimal mode based on the minimum rate-distortion value.

The decoder determines whether the AF merge mode is applied to the current processing block (S2001). As a result of the determination in step S2001, when the AF merge mode is applied to the current processing block, decoding is performed based on the AF merge mode (S2002). When the AF merge mode is applied, the decoder may generate a control point motion vector predictor candidate and determine a candidate determined based on the index (or flag) value received from the encoder as the control point motion vector.

As a result of the determination in step S2001, when the AF merge mode is not applied to the current processing block, the decoder determines whether the AF inter mode is applied (S2003). As a result of the determination in step S2003, when the AF inter mode is applied to the current processing block, the decoder performs decoding based on the AF inter mode (S2004). When the AF inter mode is applied, the decoder generates a control point motion vector prediction value candidate, determines the candidate using an index (or flag) value received from the encoder, and then adds the difference values of the motion vector prediction values received from the encoder. The control point motion vector can be determined.

As a result of the determination in step S2003, when the AF inter mode is not applied to the current processing block, the decoder performs decoding based on a mode other than the AF merge / AF inter mode (S2005).

In the AF inter mode, the control point motion vector prediction value may be composed of two motion vector pairs of the first control point and the second control point, and two control point motion vector prediction value candidates may be configured. The encoder may signal an optimal control point motion vector prediction value index and control point motion vector difference value among two candidates to the decoder. A method of determining two control point motion vector prediction value candidates will be described in detail with reference to the following drawings.

Referring to FIG. 21, the encoder / decoder generates a combined motion vector prediction value combining motion vector prediction values of a first control point, a second control point, and a third control point (S2101). For example, the encoder / decoder may generate up to 12 combined motion vector prediction values by combining motion vectors of neighboring blocks adjacent to the control points, respectively.

Referring to FIG. 22, the encoder / decoder may use the motion vectors of the upper left neighboring block A, the upper neighboring block B, and the left neighboring block C of the first control point 2201 as the motion vector combination candidate of the first control point 2201. have. The encoder / decoder may use the upper neighboring block D and the right upper neighboring block E of the second control point 2202 as the motion vector combination candidates of the second control point 2202. The encoder / decoder may use the left neighboring block F and the lower left neighboring block G of the third control point 2203 as the motion vector combination candidate of the third control point 2203. Here, the neighboring blocks of each control point may be a 4x4 block. The motion vector combination of the neighboring blocks adjacent to the control points may be expressed by Equation 5 below.

Referring back to FIG. 21, the encoder / decoder lists (or arranges) the combined motion vector prediction values generated in step S2101 in order of decreasing divergence of the motion vectors of the control point (S2102). As the divergence degree of the motion vectors has a smaller value, the motion vectors of the control points may indicate the same or similar directions. In this case, the degree of divergence of the motion vectors may be determined using Equation 6 below.

The encoder / decoder determines (or adds) the upper two of the combined motion vector prediction values listed in step S2102 as a motion vector prediction value candidate list (hereinafter, may be referred to as a candidate list) (S2103).

If the number of candidates added to the candidate list is smaller than two, the encoder / decoder adds candidates of the AMVP candidate list to the candidate list (S2104). In detail, when the candidate added in step S2103 is 0, the encoder / decoder may add the top two candidates of the AMVP candidate list to the candidate list. When there is one candidate added in step S2103, the encoder / decoder may add the first candidate of the AMVP candidate list to the candidate list. The AMVP candidate list may be generated by applying the method described with reference to FIGS. 12 to 14.

In one embodiment, the encoder determines a control point motion vector for each of the two candidate lists, compares the RD cost, selects candidates and / or control point motion vectors with small values, and converts the index and control point motion vector differences to the decoder. Can transmit

Referring to FIG. 23, for convenience of description, an encoder will be mainly described. However, the encoding method in the AF merge mode proposed in this embodiment may be applied to the decoder in the same manner.

When the AF merge mode is applied, the encoder may scan blocks A, B, C, D, and E of size 4x4 around the current block in alphabetical order. The encoder searches for the block encoded in the first affine prediction mode based on the scanning order, and determines the found block as the AF merge candidate block. In another embodiment, the encoder may search / determine a plurality of AF merge candidates on a scanning order basis.

The encoder determines the affine motion model of the current block using the determined control point motion vector of the candidate block. The control point motion vector of the current block and the motion vector field of the current block may be determined according to the affine motion model of the candidate block.

For example, referring to FIG. 24, when block A is a block coded in an affine mode (affine prediction mode), the encoder may determine block A as a candidate block. The encoder may derive the affine motion model of the A block using the control point motion vectors of the A block, v_2 and v_3 (or v_2, v_3, v_4). The encoder may derive (or generate or determine) the control point motion vectors v_0 and v_1 of the current block based on the derived affine motion model. After determining the affine motion vector field, the encoder may encode syntax information indicating the AF merge mode.

As an example, the syntax used in the method described above with reference to FIGS. 15 to 23 may be represented as Table 2 below.

Referring to Table 2, in the isAffineMrgFlagCoded () syntax (or function), the decoder may check whether there is a block encoded in the affine mode (or the affine prediction mode) among neighboring blocks. In this case, if there is a block encoded in the affine mode, a true value may be returned and affine_flag may be parsed.

Referring to FIG. 25, as described above with reference to FIG. 18, the affine motion vector field may be determined in a pixel unit or a predefined block unit. If it is determined in units of pixels, the encoder / decoder can obtain a motion vector based on each pixel value. If it is determined in units of blocks, the motion vector of the corresponding subblock is determined based on the center pixel value of each subblock. Can be obtained.

As described above, the motion vector field of the current block may be determined using the motion vector of the first control point representing the upper left control point of the current block and the motion vector of the second control point representing the right upper control point.

In this case, when the motion vector of the first control point and the motion vector of the second control point are determined, the defined motion compensation region (defined MC region) representing the motion compensation region in the sub-block unit according to the affine prediction in the reference picture is defined. May be determined as shown in FIG. 25. In other words, the defined motion compensation region refers to the total memory size of the reference picture region required for performing motion compensation in the decoding process of the current block. In the present invention, the motion compensation region defined above is not limited to the name. For example, the defined motion compensation region may include a predefined motion compensation region, a motion compensation region, an affine motion compensation region, a search region (or search range), a defined search region (or search range), a predefined It may be referred to as a search region (or search range), an affine search region (or search range), a motion vector field, a defined motion vector field, a predefined motion vector field, and the like.

If the difference between the motion vector of the first control point and the motion vector of the second control point is large, the size of the above-described defined motion compensation region may increase. This has the problem of increasing hardware bandwidth (or memory bandwidth). Accordingly, the present invention proposes a method of limiting the range for deriving a motion vector when predicting affine motion in order to improve this problem.

Referring to Figure 26, it illustrates a method of limiting the motion compensation region proposed in the present invention.

The decoder first derives motion vectors of the first control point and the second control point in the AF merge mode or the AF inter mode (S2601). The control point motion vector derived in step S2601 may be referred to as an initial control point motion vector.

The decoder calculates a control point motion vector with respect to the center position (or the position of the center pixel) of the current block (S2602). Hereinafter, in the present invention, the control point motion vector of the central position may be referred to as a central control point and a fourth control point. The method for calculating the central control point will be described later with reference to the following drawings.

The decoder updates the motion compensation region defined using the motion vector of the central control point calculated in step S2602 (S2603). This will be described later in detail.

The decoder derives the first control point and the second control point by performing affine prediction in the motion compensation region updated in step S2603 (S2604). The decoder derives the motion vector of the current block in units of subblocks by using the affine motion model of the current block derived by the first control point and the second control point (S2605).

Referring to FIG. 27, in an embodiment of the present invention, the encoder / decoder is a control point motion vector of the center position of the current block, that is, the center of the current block based on the motion vectors of the first control point CP_0 and the second control point CP_1. The control point motion vector CPMV_C may be derived. In this case, the encoder / decoder may use Equation 7 below.

In Equation 7, h means the height of the current block, w means the width of the current block. In addition, v_0 represents a motion vector of the first control point, v_1 represents a motion vector of the second control point, v_2 represents a motion vector of the third control point representing the lower left control point, and each motion vector represents v_0 = {v_0x, v_0y} and v_1. = {v_1x, v_1y}, v_2 = {v_2x, v_2y}.

The encoder / decoder may set (or reset or update) a motion compensation region defined based on the calculated central control point motion vector.

In an embodiment, the defined motion compensation region may be determined using a predefined motion compensation bandwidth threshold value MC_BW_TH or a current block size.

Referring to FIG. 28, when the defined motion compensation region is determined using the motion compensation bandwidth threshold value, the defined motion compensation region may be determined as shown in FIG. 28.

In detail, the upper left position of the defined motion compensation region may be derived (or determined) by the coordinates of Equation 8 below, and the lower right position may be derived by the coordinates of Equation 9 below.

In Equation 8, MC_BW_TH represents a motion compensation bandwidth threshold. In one embodiment, the MC_BW_TH is a Sequence Parameter Set (SPS), Picture Parameter Set (PPS), Slice Header (SH) (or Tile Group Header, TGH). Or may be transmitted through a header of a network abstract layer (NAL) unit, etc. Alternatively, in another embodiment, the MC_BW_TH may be defined as the same value in the encoder and the decoder.

In one embodiment, if the motion compensation region defined based on the current block size is determined, the MC_BW_TH value may be replaced with w (h) or w / 2 (h / 2) of the current block. The determination of w representing the width of the current block or h representing the height of the current block can be adaptively selected according to the shape of the current block.

Referring to FIG. 29, the encoder / decoder may derive (or update, adjust) motion vectors of the first control point and the second control point again based on the defined (or updated) defined motion compensation region. That is, the motion vectors of the first control point and the second control point may be limited not to exceed the defined motion compensation region.

In one embodiment, when the motion vector of the first control point and / or the motion vector of the second control point exceeds the defined motion compensation region, the encoder / decoder may not use the candidate for affine motion prediction.

Or, in one embodiment, when the motion vector of the first control point and / or the motion vector of the second control point exceeds the defined motion compensation region, the encoder / decoder clips to the control point motion vector to fall within the defined motion compensation region. Can be performed.

The encoder / decoder may calculate (or derive) an affine motion vector field in sub-block units using the updated motion vectors of the first control point and the second control point.

In the embodiment described with reference to FIGS. 27 to 29, the control point motion vector of the center position is derived using the initial first control point motion vector and the initial second control point motion vector, and a defined motion compensation region is set based thereon. (Or reset or update).

On the other hand, in an embodiment of the present invention, the AF merge candidate may be derived using a defined motion compensation region determined based on the motion vector of the first control point, which is the upper left control point.

When the AF merge mode is applied, as described above with reference to FIG. 23, the encoder / decoder may scan blocks A, B, C, D, and E of a neighboring 4x4 size of the current coding block in alphabetical order. The encoder may search for the block encoded in the first affine prediction mode based on the scanning order, and determine the searched block as an AF merge candidate block.

In an embodiment, the encoder / decoder may derive the motion vector of the first control point using an affine model of a block encoded in the affine prediction mode among neighboring blocks. The encoder / decoder may set (or define) a motion compensation region based on the derived first control point motion vector. After the encoder / decoder derives the second control point motion vector, when the region (or pixel) specified by the motion vector of the second control point is included in the set motion compensation region, the encoder / decoder is encoded in the affine prediction mode. A block can be added as an AF merge candidate.

In this case, the encoder / decoder may derive the upper left position of the defined motion compensation region using Equation 10 below. The encoder / decoder may derive the lower right position of the defined motion compensation region using Equation 11 below.

In Equations 10 and 11, MC_BW_TH represents a motion compensation bandwidth threshold. In one embodiment, the MC_BW_TH is a Sequence Parameter Set (SPS), Picture Parameter Set (PPS), Slice Header (SH) (or Tile Group Header, TGH). Or may be transmitted through a header of a network abstract layer (NAL) unit, etc. Alternatively, in another embodiment, the MC_BW_TH may be defined as the same value in the encoder and the decoder.

For example, in FIG. 30, it is assumed that the neighboring block A and the neighboring block C are blocks encoded in the affine prediction mode. In this case, when the motion compensation region defined based on the first control point motion vector by the affine model of block A is set, the position indicated by the second control point motion vector by the affine model of block A is defined above. It is not included in the compensation area. Thus, in this case, the affine model of block A may not be considered as an AF merge candidate.

If a motion compensation region defined based on the first control point motion vector by the affine model of block C to be searched is set, the position indicated by the second control point motion vector by the affine model of block C is defined above. It may be included in the motion compensation region. Thus, in this case, the affine model of block C can be used as an AF merge candidate.

In another embodiment, the defined motion compensation region according to the embodiment proposed by the present invention may be set to a block of a predefined size specified by the first control point motion vector. That is, the defined motion compensation region may be set to a region of a predefined size, and the upper left pixel position of the region of the predefined size may be determined by the first control point motion vector. If the defined motion compensation region is set and the pixel (or region, sample) specified by the second control point motion vector is out of the defined motion compensation region, the second control point motion vector is the defined motion compensation region. It may be clipped (or modified, adjusted, updated) to be included within.

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

Referring to FIG. 31, a decoder is described for convenience of description, but the present invention is not limited thereto, and the method of generating an inter prediction block using affine prediction according to an embodiment of the present invention is performed in the same manner in the encoder and the decoder. Can be.

The decoder searches for blocks encoded in the affine prediction mode among blocks neighboring the current block (S3101).

The decoder uses an affine motion model of the block encoded in the affine prediction mode to form a first control point motion vector of a top left control point of the current block and a top right side of the current block. A second control point motion vector of the control point is derived (S3102).

The decoder determines a motion compensation region for affine prediction in the reference picture of the current block (S3103).

The decoder updates the first control point motion vector and the second control point motion vector based on the motion compensation region (S3104).

The decoder derives a motion vector of a sub-block unit in the current block by using the updated one control point motion vector and the updated second control point motion vector (S3105).

As described above with reference to FIGS. 27 and 28, the step S3103 may include: deriving a third control point motion vector of the center position of the current block by using the first control point motion vector and the second control point motion vector; And determining the motion compensation region by using the third control point motion vector and the motion compensation bandwidth threshold.

In addition, as described above with reference to FIG. 28, the motion compensation bandwidth threshold may include a sequence parameter set, a picture parameter set, a tile group header, or a network abstraction layer. Abstract Layer) may be signaled from an encoder through a header of a unit.

In addition, as described above with reference to FIGS. 29 and 30, in step S3104, when the position specified by at least one of the first control point motion vector and the second control point motion vector is out of the motion compensation region, The control may be performed by updating at least one of a first control point motion vector and the second control point motion vector to be included in the motion compensation region.

In addition, as described above with reference to FIG. 30, the step S3103 may further include determining the motion compensation region by using the first control point motion vector and the motion compensation bandwidth threshold.

In addition, as described above with reference to FIG. 30, the motion compensation bandwidth threshold may include a sequence parameter set, a picture parameter set, a tile group header, or a network abstraction layer. Abstract Layer) may be signaled from an encoder through a header of a unit.

In addition, as described above with reference to FIG. 30, the motion compensation region is determined as a block having a predetermined size specified by the first control point motion vector, and in step S3104, the motion compensation region is specified by the second control point motion vector. When the position becomes out of the motion compensation region, it may be performed by updating the second control point motion vector to be included in the motion compensation region.

In FIG. 32, 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. 32, the inter prediction unit implements the functions, processes, and / or methods proposed in FIGS. 8 to 31. Specifically, the inter prediction unit is the affine coded block search unit 3201, the control point motion vector derivation unit 3202, the motion compensation region determiner 3203, the control point motion vector updater 3204, and the sub block motion vector derivation unit 3205. It may be configured to include.

The affine coding block search unit 3201 searches for a block encoded in the affine prediction mode among blocks neighboring the current block.

The control point motion vector derivation unit 3202 is configured to generate a first control point motion vector of an upper left control point of the current block by using an affine motion model of the block encoded in the affine prediction mode, and A second control point motion vector of the right upper control point of the current block is derived.

The motion compensation region determiner 3203 determines a motion compensation region for affine prediction in the reference picture of the current block.

The control point motion vector updater 3204 updates the first control point motion vector and the second control point motion vector based on the motion compensation region.

The subblock motion vector derivation unit 3205 derives a motion vector of each subblock in the current block by using the updated one control point motion vector and the updated second control point motion vector.

As described above with reference to FIGS. 27 and 28, the motion compensation region determiner 3203 may use the first control point motion vector and the second control point motion vector to control the third control point motion vector at the center position of the current block. In addition, the motion compensation region may be determined using the third control point motion vector and the motion compensation bandwidth threshold.

In addition, as described above with reference to FIGS. 29 and 30, the control point motion vector updating unit 3204 may determine a position specified by at least one of the first control point motion vector and the second control point motion vector. In the case of, the at least one of the first control point motion vector and the second control point motion vector may be updated to be included in the motion compensation region.

In addition, as described above with reference to FIG. 30, the motion compensation region determiner 3203 may determine the motion compensation region by using the first control point motion vector and the motion compensation bandwidth threshold.

In addition, as described above with reference to FIG. 30, the motion compensation region is set to a block having a predetermined size specified by the first control point motion vector, and the control point motion vector updating unit 3204 is configured to perform the second control operation. When the position specified by the control point motion vector is out of the motion compensation region, the second control point motion vector may be updated to be included in the motion compensation region.

33 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. 34, 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 smartphone, 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 (e.g., 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 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, an embodiment of the present invention may be implemented as a computer program product by program code, which 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 should 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 a video signal based on an Affine prediction mode,

Searching for a block encoded in the affine prediction mode among blocks neighboring the current block;

A first control point motion vector of the upper left control point of the current block and an upper right control point of the current block by using an affine motion model of the block encoded in the affine prediction mode Deriving a second control point motion vector;

Determining a motion compensation region for affine prediction within a reference picture of the current block;

Updating the first control point motion vector and the second control point motion vector based on the motion compensation region; And

And using the updated one control point motion vector and the updated second control point motion vector, deriving a motion vector in sub-block units within the current block.
The method of claim 1,

Determining the motion compensation region,

Deriving a third control point motion vector of a central position of the current block by using the first control point motion vector and the second control point motion vector; And

And determining the motion compensation region using the third control point motion vector and a motion compensation bandwidth threshold.
The method of claim 2,

The motion compensation bandwidth threshold value is obtained from an encoder through a sequence parameter set, a picture parameter set, a tile group header, or a header of a network abstract layer unit. Signaled, video signal decoding method.
The method of claim 1,

The updating of the first control point motion vector and the second control point motion vector may include:

When the position specified by at least one of the first control point motion vector and the second control point motion vector is out of the motion compensation region, at least one of the first control point motion vector and the second control point motion vector is moved. Performed by updating to be included in a compensation region.
The method of claim 1,

Determining the motion compensation region,

Determining the motion compensation region using the first control point motion vector and a motion compensation bandwidth threshold.
The method of claim 5,

The motion compensation bandwidth threshold value is obtained from an encoder through a sequence parameter set, a picture parameter set, a tile group header, or a header of a network abstract layer unit. Signaled, video signal decoding method.
The method of claim 1,

The motion compensation region is determined as a block of a predefined size specified by the first control point motion vector,

The updating of the first control point motion vector and the second control point motion vector may include:

And when the position specified by the second control point motion vector is out of the motion compensation region, updating the second control point motion vector to be included in the motion compensation region.
A method of decoding a video signal based on an Affine prediction mode,

An affine coded block searching unit searching for a block encoded in an affine prediction mode among blocks neighboring the current block;

A first control point motion vector of the upper left control point of the current block and an upper right control point of the current block by using an affine motion model of the block encoded in the affine prediction mode A control point motion vector derivation unit for deriving a second control point motion vector;

A motion compensation region determiner configured to determine a motion compensation region for affine prediction within a reference picture of the current block;

A control point motion vector updating unit which updates the first control point motion vector and the second control point motion vector based on the motion compensation region; And

And a sub-block motion vector derivation unit for deriving a motion vector of a sub-block unit in the current block by using the updated one control point motion vector and the updated second control point motion vector.
The method of claim 8,

The motion compensation region determiner,

Derive a third control point motion vector at the center position of the current block by using the first control point motion vector and the second control point motion vector,

And determine the motion compensation region by using the third control point motion vector and the motion compensation bandwidth threshold.
The method of claim 9,

The motion compensation bandwidth threshold value is obtained from an encoder through a sequence parameter set, a picture parameter set, a tile group header, or a header of a network abstract layer unit. Signaled, video signal decoding apparatus.
The method of claim 8,

The control point motion vector update unit,

When the position specified by at least one of the first control point motion vector and the second control point motion vector is out of the motion compensation region, at least one of the first control point motion vector and the second control point motion vector is moved. Updating to be included in the compensation region.
The method of claim 8,

The motion compensation region determiner,

And determine the motion compensation region by using the first control point motion vector and the motion compensation bandwidth threshold.
The method of claim 12,

The motion compensation bandwidth threshold value is obtained from an encoder through a sequence parameter set, a picture parameter set, a tile group header, or a header of a network abstract layer unit. Signaled, video signal decoding apparatus.
The method of claim 8,

The motion compensation region is set to a block of a predefined size specified by the first control point motion vector,

The control point motion vector update unit,

And when the position specified by the second control point motion vector is out of the motion compensation region, updating the second control point motion vector to be included in the motion compensation region.