WO2019199071A1

WO2019199071A1 - Image decoding method and device in accordance with inter-prediction in image coding system

Info

Publication number: WO2019199071A1
Application number: PCT/KR2019/004346
Authority: WO
Inventors: 박내리; 남정학; 장형문
Original assignee: 엘지전자 주식회사
Priority date: 2018-04-13
Filing date: 2019-04-11
Publication date: 2019-10-17

Abstract

An image decoding method carried out by means of a decoding device according to the present invention comprises the steps of: forming a motion information candidate list on the basis of a neighboring block of a current block; deriving costs with respect to motion information candidates comprised in the motion information candidate list; deriving a modified motion information candidate list on the basis of the costs with respect to the motion information candidates; deriving a motion vector of the current block on the basis of the modified motion information candidate list; and performing prediction of the current block on the basis of the motion vector.

Description

Method and apparatus for image decoding according to inter prediction in image coding system

The present invention relates to an image coding technique, and more particularly, to an image decoding method and apparatus according to inter prediction in an image coding system.

Recently, the demand for high resolution and high quality images such as high definition (HD) images and ultra high definition (UHD) images is increasing in various fields. The higher the resolution and the higher quality of the image data, the more information or bit rate is transmitted than the existing image data. Therefore, the image data can be transmitted by using a medium such as a conventional wired / wireless broadband line or by using a conventional storage medium. In the case of storage, the transmission cost and the storage cost are increased.

Accordingly, a high efficiency image compression technique is required to effectively transmit, store, and reproduce high resolution, high quality image information.

An object of the present invention is to provide a method and apparatus for improving image coding efficiency.

Another technical problem of the present invention is to derive a cost for a motion information candidate and to reconstruct the motion information candidate list based on the cost based on the modified motion information candidate list derived to perform the prediction on the current block. And providing an apparatus.

Another object of the present invention is to provide a method and an apparatus for decoding an image for deriving a candidate group for a motion information candidate and coding index information for the candidate group.

According to an embodiment of the present invention, there is provided an image decoding method performed by a decoding apparatus. The method includes constructing a motion information candidate list based on neighboring blocks of a current block, deriving costs for motion information candidates included in the motion information candidate list, and based on the costs for the motion information candidates. Deriving a modified motion information candidate list, deriving a motion vector of the current block based on the modified motion information candidate list, and performing prediction of the current block based on the motion vector Characterized in that.

According to another embodiment of the present invention, a decoding apparatus for performing image decoding is provided. The decoding apparatus constructs a motion information candidate list based on neighboring blocks of the current block, derives costs for motion information candidates included in the motion information candidate list, and corrects based on the costs for the motion information candidates. And a prediction unit for deriving a modified motion information candidate list, deriving a motion vector of the current block based on the modified motion information candidate list, and performing prediction of the current block based on the motion vector. do.

According to another embodiment of the present invention, a video encoding method performed by an encoding apparatus is provided. The method includes constructing a motion information candidate list based on neighboring blocks of a current block, deriving costs for motion information candidates included in the motion information candidate list, and based on the costs for the motion information candidates. Deriving a modified motion information candidate list, determining a motion vector of the current block based on the modified motion information candidate list, performing a prediction of the current block based on the motion vector, and the And encoding information on inter prediction of the current block.

According to another embodiment of the present invention, a video encoding apparatus is provided. The encoding apparatus constructs a motion information candidate list based on neighboring blocks of the current block, derives costs for motion information candidates included in the motion information candidate list, and corrects based on the costs for the motion information candidates. A prediction unit for deriving a modified motion information candidate list, determining a motion vector of the current block based on the modified motion information candidate list, and performing prediction of the current block based on the motion vector, and the current block And an entropy encoding unit that encodes information on inter prediction of the N-P.

According to the present invention, the optimal motion information candidates for the current block may be rearranged in the order indicated by the small values of the motion information indexes in consideration of the cost, thereby reducing the amount of bits for prediction and improving the overall coding efficiency. Can be.

According to the present invention, motion information candidates of the current block can be classified into candidate groups, a best candidate group can be derived, and a motion information index indicating one of the motion information candidates included in the candidate group can be coded. Therefore, the amount of bits for coding the motion information index can be reduced and the overall coding efficiency can be improved.

1 is a diagram schematically illustrating a configuration of a video encoding apparatus to which the present invention may be applied.

2 is a diagram schematically illustrating a configuration of a video decoding apparatus to which the present invention may be applied.

3 illustrates an example of deriving motion information of the current block using a motion vector predictor (MVP) index.

4 shows an example of a spatial neighboring block and a temporal neighboring block.

5A to 5B illustrate an example of a decoding process in which a processing order is changed.

6 illustrates an example of performing a reordering process for only some MVP candidates among MVP candidates.

7 illustrates an example of deriving a cost for an MVP candidate of the current block through the template matching method.

8 illustrates an example of deriving a cost of an MVP candidate through a bi-lateral matching method.

9 illustrates an example of deriving bi-prediction motion information for an MVP candidate including uni-prediction motion information.

10 shows an example of a template according to a processing order for a block.

11 illustrates an example of grouping MVP candidates for the current block and determining the MVP for the current block based on the MVP index for the grouped candidates.

12 illustrates an example of grouping MVP candidates for the current block and determining the MVP for the current block based on the MVP index for the grouped candidates.

13 illustrates an example of grouping MVP candidates for a current block and determining an MVP for the current block based on an MVP group index indicating a candidate group.

14 schematically illustrates an image encoding method by an encoding apparatus according to the present invention.

15 schematically illustrates an encoding apparatus for performing an image encoding method according to the present invention.

16 schematically illustrates an image decoding method by a decoding apparatus according to the present invention.

17 schematically illustrates a decoding apparatus for performing an image decoding method according to the present invention.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the invention to the specific embodiments. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the spirit of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. The terms "comprise" or "having" in this specification are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features It is to be understood that the numbers, steps, operations, components, parts or figures do not exclude in advance the presence or possibility of adding them.

On the other hand, each configuration in the drawings described in the present invention are shown independently for the convenience of description of the different characteristic functions, it does not mean that each configuration is implemented by separate hardware or separate software. For example, two or more of each configuration may be combined to form one configuration, or one configuration may be divided into a plurality of configurations. Embodiments in which each configuration is integrated and / or separated are also included in the scope of the present invention without departing from the spirit of the present invention.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and redundant description of the same components is omitted.

On the other hand, the present invention relates to video / image coding. For example, the method / embodiment disclosed herein may be applied to the method disclosed in the versatile video coding (VVC) standard or the next generation video / image coding standard.

In the present specification, a picture generally refers to a unit representing one image of a specific time zone, and a slice is a unit constituting a part of a picture in coding. One picture may be composed of a plurality of slices, and if necessary, the picture and the slice may be mixed with each other.

A pixel or a pel may refer to a minimum unit constituting one picture (or image). Also, 'sample' may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a value of a pixel, and may only represent pixel / pixel values of the luma component, or only pixel / pixel values of the chroma component.

A unit represents the basic unit of image processing. The unit may include at least one of a specific region of the picture and information related to the region. 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.

Referring to FIG. 1, the video encoding apparatus 100 may include a picture splitter 105, a predictor 110, a residual processor 120, an entropy encoder 130, an adder 140, and a filter 150. ) And memory 160. The residual processing unit 120 may include a subtraction unit 121, a conversion unit 122, a quantization unit 123, a reordering unit 124, an inverse quantization unit 125, and an inverse conversion unit 126.

The picture divider 105 may divide the input picture into at least one processing unit.

As an example, the processing unit may be called a coding unit (CU). In this case, the coding unit may be recursively split from the largest coding unit (LCU) according to a quad-tree binary-tree (QTBT) structure. 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 include a coding unit (CU) prediction unit (PU) or a transform unit (TU). The coding unit may be split from the largest coding unit (LCU) into coding units of deeper depths along the quad tree structure. 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. If a smallest coding unit (SCU) is set, the coding unit may not be split into smaller coding units than the minimum coding unit. Here, the final coding unit refers to a coding unit that is the basis of partitioning or partitioning into a prediction unit or a transform unit. The prediction unit is a unit partitioning from the coding unit and may be a unit of sample prediction. In this case, the prediction unit may be divided into sub blocks. The transform unit may be divided along the quad tree structure from the coding unit, and may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient. Hereinafter, a coding unit may be called a coding block (CB), a prediction unit is a prediction block (PB), and a transform unit may be called a transform block (TB). A prediction block or prediction unit may mean a specific area in the form of a block within a picture, and may include an array of prediction samples. In addition, a transform block or a transform unit may mean a specific area in a block form within a picture, and may include an array of transform coefficients or residual samples.

The prediction unit 110 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 of the current block. The unit of prediction performed by the prediction unit 110 may be a coding block, a transform block, or a prediction block.

The prediction unit 110 may determine whether intra prediction or inter prediction is applied to the current block. As an example, the prediction unit 110 may determine whether intra prediction or inter prediction is applied on a CU basis.

In the case of intra prediction, the prediction unit 110 may derive a prediction sample for the current block based on reference samples outside the current block in the picture to which the current block belongs (hereinafter, referred to as the current picture). In this case, the prediction unit 110 may (i) derive the prediction sample based on the average or interpolation of neighboring reference samples of the current block, and (ii) the neighbor reference of the current block. The prediction sample may be derived based on a reference sample present in a specific (prediction) direction with respect to the prediction sample among the samples. In case of (i), it may be called non-directional mode or non-angle mode, and in case of (ii), it may be called directional mode or angular mode. In intra prediction, the prediction mode may have, for example, 33 directional prediction modes and at least two non-directional modes. The non-directional mode may include a DC prediction mode and a planner mode (Planar mode). The prediction unit 110 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

In the case of inter prediction, the prediction unit 110 may derive the prediction sample for the current block based on the sample specified by the motion vector on the reference picture. The prediction unit 110 may apply one of a skip mode, a merge mode, and a motion vector prediction (MVP) mode to derive a prediction sample for the current block. In the skip mode and the merge mode, the prediction unit 110 may use the motion information of the neighboring block as the motion information of the current block. In the skip mode, unlike the merge mode, the difference (residual) between the prediction sample and the original sample is not transmitted. In the MVP mode, the motion vector of the current block may be derived using the motion vector of the neighboring block as a motion vector predictor.

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. A reference picture including the temporal neighboring block may be called a collocated picture (colPic). The motion information may include a motion vector and a reference picture index. Information such as prediction mode information and motion information may be encoded (entropy) and output in the form of a bitstream.

When the motion information of the temporal neighboring block is used in the skip mode and the merge mode, the highest picture on the reference picture list may be used as the reference picture. Reference pictures included in a reference picture list may be sorted based on a difference in a picture order count (POC) between a current picture and a corresponding reference picture. The POC corresponds to the display order of the pictures and may be distinguished from the coding order.

The subtraction unit 121 generates a residual sample which is a difference between the original sample and the prediction sample. When the skip mode is applied, residual samples may not be generated as described above.

The transform unit 122 generates transform coefficients by transforming the residual sample in units of transform blocks. The transform unit 122 may perform the transform according to the size of the transform block and the prediction mode applied to the coding block or the prediction block that spatially overlaps the transform block. For example, if intra prediction is applied to the coding block or the prediction block that overlaps the transform block, and the transform block is a 4 × 4 residual array, the residual sample is configured to perform a discrete sine transform (DST) transform kernel. The residual sample may be transformed using a discrete cosine transform (DCT) transform kernel.

The quantization unit 123 may quantize the transform coefficients to generate quantized transform coefficients.

The reordering unit 124 rearranges the quantized transform coefficients. The reordering unit 124 may reorder the quantized transform coefficients in the form of a block into a one-dimensional vector form through a coefficient scanning method. Although the reordering unit 124 has been described in a separate configuration, the reordering unit 124 may be part of the quantization unit 123.

The entropy encoding unit 130 may perform entropy encoding on the quantized transform coefficients. Entropy encoding may include, for example, encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), and the like. The entropy encoding unit 130 may encode information necessary for video reconstruction other than the quantized transform coefficient (for example, a value of a syntax element) together or separately. Entropy encoded information may be transmitted or stored in units of network abstraction layer (NAL) units in the form of bitstreams.

The inverse quantization unit 125 inverse quantizes the quantized values (quantized transform coefficients) in the quantization unit 123, and the inverse transformer 126 inverse transforms the inverse quantized values in the inverse quantization unit 125 to obtain a residual sample. Create

The adder 140 reconstructs the picture by combining the residual sample and the predictive sample. The residual sample and the predictive sample may be added in units of blocks to generate a reconstructed block. Although the adder 140 has been described in a separate configuration, the adder 140 may be part of the predictor 110. On the other hand, the adder 140 may be called a restoration unit or a restoration block generation unit.

The filter unit 150 may apply a deblocking filter and / or a sample adaptive offset to the reconstructed picture. Through deblocking filtering and / or sample adaptive offset, the artifacts of the block boundaries in the reconstructed picture or the distortion in the quantization process can be corrected. The sample adaptive offset may be applied on a sample basis and may be applied after the process of deblocking filtering is completed. The filter unit 150 may apply an adaptive loop filter (ALF) to the reconstructed picture. ALF may be applied to the reconstructed picture after the deblocking filter and / or sample adaptive offset is applied.

The memory 160 may store reconstructed pictures (decoded pictures) or information necessary for encoding / decoding. Here, the reconstructed picture may be a reconstructed picture after the filtering process is completed by the filter unit 150. The stored reconstructed picture may be used as a reference picture for (inter) prediction of another picture. For example, the memory 160 may store (reference) pictures used for inter prediction. In this case, pictures used for inter prediction may be designated by a reference picture set or a reference picture list.

Referring to FIG. 2, the video decoding apparatus 200 may include an entropy decoding unit 210, a residual processor 220, a predictor 230, an adder 240, a filter 250, and a memory 260. It may include. Here, the residual processor 220 may include a rearrangement unit 221, an inverse quantization unit 222, and an inverse transform unit 223.

When a bitstream including video information is input, the video decoding apparatus 200 may restore video in response to a process in which video information is processed in the video encoding apparatus.

For example, the video decoding apparatus 200 may perform video decoding using a processing unit applied in the video encoding apparatus. Thus, the processing unit block of video decoding may be, for example, a coding unit, and in another example, a coding unit, a prediction unit, or a transform unit. The coding unit may be split along the quad tree structure and / or binary tree structure from the largest coding unit.

The prediction unit and the transform unit may be further used in some cases, in which case the prediction block is a block derived or partitioned from the coding unit and may be a unit of sample prediction. At this point, the prediction unit may be divided into subblocks. The transform unit may be divided along the quad tree structure from the coding unit, and may be a unit for deriving a transform coefficient or a unit for deriving a residual signal from the transform coefficient.

The entropy decoding unit 210 may parse the bitstream and output information necessary for video 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 necessary for video reconstruction, and residual coefficients. 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 210 is provided to the prediction unit 230, and the residual value on which the entropy decoding has been performed by the entropy decoding unit 210, that is, the quantized transform coefficient, is used as a reordering unit ( 221 may be input.

The reordering unit 221 may rearrange the quantized transform coefficients in a two-dimensional block form. The reordering unit 221 may perform reordering in response to coefficient scanning performed by the encoding apparatus. Here, the rearrangement unit 221 has been described in a separate configuration, but the rearrangement unit 221 may be part of the inverse quantization unit 222.

The inverse quantization unit 222 may dequantize the quantized transform coefficients based on the (inverse) quantization parameter and output the transform coefficients. In this case, information for deriving a quantization parameter may be signaled from the encoding apparatus.

The inverse transform unit 223 may inversely transform transform coefficients to derive residual samples.

The prediction unit 230 may perform prediction on the current block and generate a predicted block including prediction samples for the current block. The unit of prediction performed by the prediction unit 230 may be a coding block, a transform block, or a prediction block.

The prediction unit 230 may determine whether to apply intra prediction or inter prediction based on the information about the prediction. In this case, a unit for determining which of intra prediction and inter prediction is to be applied and a unit for generating a prediction sample may be different. In addition, the unit for generating a prediction sample in inter prediction and intra prediction may also be different. For example, whether to apply inter prediction or intra prediction may be determined in units of CUs. In addition, for example, in inter prediction, a prediction mode may be determined and a prediction sample may be generated in PU units, and in intra prediction, a prediction mode may be determined in PU units and a prediction sample may be generated in TU units.

In the case of intra prediction, the prediction unit 230 may derive the prediction sample for the current block based on the neighbor reference samples in the current picture. The prediction unit 230 may derive the prediction sample for the current block by applying the directional mode or the non-directional mode based on the neighbor reference samples of the current block. In this case, the prediction mode to be applied to the current block may be determined using the intra prediction mode of the neighboring block.

In the case of inter prediction, the prediction unit 230 may derive the prediction sample for the current block based on the sample specified on the reference picture by the motion vector on the reference picture. The prediction unit 230 may apply any one of a skip mode, a merge mode, and an MVP mode to derive a prediction sample for the current block. In this case, motion information required for inter prediction of the current block provided by the video encoding apparatus, for example, information about a motion vector, a reference picture index, and the like may be obtained or derived based on the prediction information.

In the skip mode and the merge mode, the motion information of the neighboring block may be used as the motion information of the current block. In this case, the neighboring block may include a spatial neighboring block and a temporal neighboring block.

The prediction unit 230 may construct a merge candidate list using motion information of available neighboring blocks, and may use information indicated by the merge index on the merge candidate list as a motion vector of the current block. The merge index may be signaled from the encoding device. The motion information may include a motion vector and a reference picture. When the motion information of the temporal neighboring block is used in the skip mode and the merge mode, the highest picture on the reference picture list may be used as the reference picture.

In the skip mode, unlike the merge mode, the difference (residual) between the prediction sample and the original sample is not transmitted.

In the MVP mode, the motion vector of the current block may be derived using the motion vector of the neighboring block as a motion vector predictor. In this case, the neighboring block may include a spatial neighboring block and a temporal neighboring block.

For example, when the merge mode is applied, a merge candidate list may be generated by using a motion vector of a reconstructed spatial neighboring block and / or a motion vector corresponding to a Col block, which is a temporal neighboring block. In the merge mode, the motion vector of the candidate block selected from the merge candidate list is used as the motion vector of the current block. The information about the prediction may include a merge index indicating a candidate block having an optimal motion vector selected from candidate blocks included in the merge candidate list. In this case, the prediction unit 230 may derive the motion vector of the current block by using the merge index.

As another example, when the Motion Vector Prediction (MVP) mode is applied, a motion vector predictor candidate list may be generated using a motion vector of a reconstructed spatial neighboring block and / or a motion vector corresponding to a Col block which is a temporal neighboring block. Can be. That is, the motion vector of the reconstructed spatial neighboring block and / or the Col vector, which is a temporal neighboring block, may be used as a motion vector candidate. The prediction information may include a prediction motion vector index indicating an optimal motion vector selected from the motion vector candidates included in the list. In this case, the prediction unit 230 may select the predicted motion vector of the current block from the motion vector candidates included in the motion vector candidate list using the motion vector index. 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 230 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 may also obtain or derive a reference picture index or the like indicating a reference picture from the information about the prediction.

The adder 240 may reconstruct the current block or the current picture by adding the residual sample and the predictive sample. The adder 240 may reconstruct the current picture by adding the residual sample and the predictive sample in block units. Since the residual is not transmitted when the skip mode is applied, the prediction sample may be a reconstruction sample. Although the adder 240 has been described in a separate configuration, the adder 240 may be part of the predictor 230. On the other hand, the adder 240 may be called a restoration unit or a restoration block generation unit.

The filter unit 250 may apply the deblocking filtering sample adaptive offset, and / or ALF to the reconstructed picture. In this case, the sample adaptive offset may be applied in units of samples and may be applied after deblocking filtering. ALF may be applied after deblocking filtering and / or sample adaptive offset.

The memory 260 may store reconstructed pictures (decoded pictures) or information necessary for decoding. Here, the reconstructed picture may be a reconstructed picture after the filtering process is completed by the filter unit 250. For example, the memory 260 may store pictures used for inter prediction. In this case, pictures used for inter prediction may be designated by a reference picture set or a reference picture list. The reconstructed picture can be used as a reference picture for another picture. In addition, the memory 260 may output the reconstructed picture in an output order.

Meanwhile, in the case of inter prediction, in order to derive motion information of a current block, a combination of the motion information of neighboring blocks or an affine transform method as well as the motion information of neighboring blocks spatially and temporally adjacent to the current block may be used. A method of deriving the motion information of the current block by using the same has been proposed. Accordingly, as candidates for the motion information of the current block increase, it is necessary to improve the efficiency of candidate selection for deriving the motion information of the current block. Accordingly, the present invention proposes a method for efficiently selecting candidates as the motion prediction candidates increase. Through the proposed method, candidates with high accuracy can be coded with a small number of bits, which can improve overall coding performance.

3 illustrates an example of deriving motion information of the current block using a motion vector predictor (MVP) index. Referring to FIG. 3, when there is an MVP candidate list composed of a plurality of MVP candidates, the decoding apparatus may derive one MVP candidate from the MVP candidate list as the MVP of the current block based on an MVP index. It is possible to perform motion compensation on the block. Meanwhile, the decoding apparatus may derive the motion vector of the spatial neighboring block and / or the temporal neighboring block of the current block as the MVP candidate of the current block.

4 shows an example of a spatial neighboring block and a temporal neighboring block. Referring to FIG. 4, the spatial peripheral block includes upper peripheral blocks, left peripheral blocks, upper left corner peripheral block 400, upper right corner peripheral block 425, and / or lower left corner peripheral block 450. can do. At least one of the motion vectors of the upper peripheral blocks, the left peripheral blocks, the upper left corner peripheral block 400, the upper right corner peripheral block 425, and the lower left corner peripheral block 450 may be determined. Can be derived as the MVP candidate of the current block. The upper peripheral blocks include an upper peripheral block 405 positioned at a left end of the upper peripheral blocks adjacent to an upper boundary of the current block, an upper peripheral block 410 located at the left of the center, and an upper peripheral block located at the right of the center. 415 and / or an upper peripheral block 420 located at the right end. In addition, the left peripheral blocks include a left peripheral block 430 located at the top of the left peripheral blocks adjacent to the left boundary of the current block, a left peripheral block 435 located at the center, and a left peripheral located at the bottom of the center. Block 440 and / or a left peripheral block 445 located at the bottom.

In addition, referring to FIG. 4, the temporal neighboring block includes a temporal upper left peripheral block 455 located at a position corresponding to the upper left position of the current block in a reference picture, and a temporal center upper left peripheral position positioned at a position corresponding to the center upper left position. Block 460, a temporal right bottom peripheral block 465 located at a location corresponding to the center bottom right position and / or a temporal right bottom peripheral block 470 located at a location corresponding to the bottom right position have. The motion vector of the temporal upper left peripheral block 455, the temporal center upper left peripheral block 460, the temporal center lower right peripheral block 465, or the temporal lower right peripheral block 470 is the MVP candidate of the current block. Can be derived.

In addition, the MVP candidates combined in the L0 direction and / or the L1 direction may be generated based on the motion vectors of the spatial neighboring block and the temporal neighboring block. That is, the L0 motion vector and / or the L1 motion vector generated based on the motion vectors may be derived as the MVP candidate of the current block. In addition, an average value or median value of MVP candidates for the current block may be derived and added as an MVP candidate.

Meanwhile, a fixed order (eg, raster scan order, etc.) may be used as the order of processing the coding units, but a method in which the order is adaptively changed to the coding unit may be applied. In this case, the raster scan order may indicate a scan order in which blocks are sequentially scanned in the upper row and scanned from the left to the right in each row.

5A to 5B illustrate an example of a decoding process in which a processing order is changed. Referring to FIG. 5A, coding units may be encoded / decoded in a structure in which a processing order may be changed in left and right directions. The number shown in FIG. 5A may indicate a processing order of the corresponding block. Since a motion vector of a spatially adjacent block may be used as an MVP candidate, an MVP candidate list for a fifth coding unit and an MVP candidate list for an eighth coding unit may be composed of different MVP candidates, respectively. Specifically, only the motion vectors of the coding units that are already encoded / decoded at the encoding / decoding time point of the coding unit may be used as the MVP candidate of the coding unit.

5B may indicate spatial neighboring blocks used to derive the MVP candidate of the fifth coding unit and spatial neighboring blocks used to derive the MVP candidate of the eighth coding unit. Referring to FIG. 5B, a motion vector of an upper left corner peripheral block, an upper peripheral block, an upper right corner peripheral block, a right peripheral block, or a lower right corner peripheral block of the fifth coding unit may be used as an MVP candidate of the fifth coding unit. Can be. The upper left corner peripheral block and the upper peripheral block may be included in a third coding unit, and the upper right corner peripheral block, the right peripheral block and the lower right corner peripheral block may be included in a first coding unit. The upper peripheral block may include an upper peripheral block positioned at a left end and an upper peripheral block positioned at a right end among upper peripheral blocks adjacent to an upper boundary of the fifth coding unit, and the right peripheral block may include the fifth peripheral block. The right peripheral block positioned at the top and the right peripheral block positioned at the bottom of the right peripheral blocks adjacent to the right boundary of the first coding unit may be included.

Referring to FIG. 5B, the MVP candidates of the eighth coding unit include motion vectors of the left neighboring block, the upper left corner neighboring block, the upper peripheral block, the upper right corner neighboring block, or the right peripheral block of the eighth coding unit. Can be used. The left peripheral block and the upper left corner peripheral block may be included in a fourth coding unit, the upper peripheral block may be included in a sixth coding unit, and the right upper corner peripheral block may be included in a fifth coding unit. The right peripheral block may be included in a seventh coding unit. The left peripheral block may include a left peripheral block positioned at an upper end and a left peripheral block positioned at a lower end among left peripheral blocks adjacent to a left boundary of the eighth coding unit, and the upper peripheral block may include the eighth peripheral block. And an upper peripheral block positioned at a left end and an upper peripheral block positioned at a right end among upper peripheral blocks adjacent to an upper boundary of a first coding unit, wherein the right peripheral block is a right adjacent to a right boundary of the eighth coding unit. The peripheral block may include a right peripheral block located at the top and a right peripheral block located at the bottom.

On the other hand, in the embodiment shown in FIG. 5, only a method of constructing an MVP candidate list using spatially neighboring neighboring blocks is described, but average values of motion vectors of temporally adjacent temporal neighboring blocks and motion vectors of neighboring blocks are shown. MVP candidate list is generated based on other MVP candidates such as MVP candidates generated by a median value or median value, MVP candidates generated by combining MVP candidates, and MVP candidates derived using the affine method. Of course, a different method (that is, a method of deriving an MVP candidate based on a block of a different position according to the position of each block) may also be applied to the method of configuring.

On the other hand, the use of a large number of MVP candidates for the current block may have an effect of increasing the accuracy of motion prediction for the current block, but information indicating the MVP candidate for the current block among the MVP candidates (for example, an MVP index) ), Which incurs a large amount of signaling overhead for encoding), which may be limited in improving compression efficiency. Therefore, in order to compensate for this, a method of limiting the number of candidates that can be represented by the MVP index can be proposed. For example, if the number of candidates that can be used as MVP candidates for the current block is 20, the MVP candidate list for the current block may be configured based on 10 MVP candidates in a predetermined order. Meanwhile, various MVP candidates may be configured by performing a duplicate check in the MVP candidate list construction process, and MVP candidates having a small difference from the MVP candidates derived in the previous order may be removed, and thus, other MVP candidates. May be checked as an MVP candidate for the current block.

In addition, when the MVP candidate list is configured in a fixed order for all blocks, it may be difficult to construct an optimal MVP candidate list for a specific sequence or a specific block. Therefore, a method of rearranging the configured MVP candidate list so that an MVP candidate having a high selection probability is located in front of the MVP candidate list (that is, in the preceding order) can be proposed, thereby improving compression performance.

Accordingly, the present invention proposes embodiments for reordering the MVP candidate list. Meanwhile, although the MVP candidate list is described as an example, the proposed embodiments may be applied to a motion information candidate list (for example, a merge candidate list) other than the MVP candidate list.

For example, a cost for each of the MVP candidates may be derived, and a method of rearranging the MVP candidates by comparing the costs of the MVP candidates may be proposed.

On the other hand, deriving and comparing the cost for all MVP candidates can cause an increase in the complexity of the decoding process, so it is important to find an appropriate trade-off. Accordingly, the following method may be applied before deriving the costs of the MVP candidates.

For example, in the process of constructing an MVP candidate list, a motion vector whose difference from the MVP candidates derived in the above order is smaller than a threshold value may not be added to the MVP candidate list. That is, a motion vector whose difference from the MVP candidates derived in the above order is smaller than the threshold value may not be derived as the MVP candidate for the current block. Through this configuration, the MVP candidate list may be formed of various MVP candidates, thereby improving the accuracy of prediction for the current block. The threshold value may vary depending on the type of the MVP candidate. That is, different threshold values may be derived according to the type of the motion vector. For example, in the case of a spatial candidate (ie, a motion vector of a spatial neighboring block), if the sum of the differences between MVx and MVy is less than 1 pel, the candidate is excluded from the MVP candidate list. Can be. In other words, when the motion vector is a motion vector of a spatial neighboring block, the threshold may be derived as 1 Pel. In this case, the difference between the x component (MVx) of the motion vector and the x component of the MVP candidate derived in the preceding order and the y component (MVy) of the motion vector and the y component of the MVP candidate derived in the preceding order When the sum of the difference between the x components and the difference between the y components is less than the 1pel, the motion vector may not be derived as the MVP candidate of the current block. In addition, for a candidate including a motion vector in a sub-block unit, such as an ATMVP or an affinity candidate, if the difference between the representative MVx and the representative MVy is smaller than half-pel, the candidate may be excluded. That is, when the motion vector includes motion vectors in sub-block units, such as ATMVP or affiliation candidate, the threshold may be derived as a half pel. In this case, the difference between the x component of the representative motion vector of the motion vector and the x component of the MVP candidate derived in the preceding order and the y component of the representative motion vector and the y component of the MVP candidate derived in the preceding order are If the sum of the difference between the x components and the difference between the y components is less than the 1 pel, the motion vector may not be derived as the MVP candidate of the current block.

Alternatively, a method of reordering only some MVP candidates among MVP candidates may be proposed. For example, the reordering process may be performed only on a spatial candidate among the MVP candidates (that is, the MVP candidate which is the motion vector of the spatial neighboring block), or the motion vector of the block derived through the affine method (ie, the affine motion). The reordering process may be performed only for the MVP candidate, which is a vector). Also, the decoding apparatus may rearrange up to five MVP candidates added to the MVP candidate list in a check order. That is, for example, the reordering process may be performed only for the MVP candidates in the first order to the MVP candidates in the fifth order among the MVP candidates in the MVP candidate list. Meanwhile, the number of MVP candidates for which the reordering process is performed may be changed to a number other than five. In addition, an MVP candidate in which the reordering process is performed may be changed.

6 illustrates an example of performing a reordering process for only some MVP candidates among MVP candidates. The decoding apparatus may add a spatial candidate for the current block (S600). The decoding apparatus may derive an MVP candidate, that is, a spatial candidate, of the current block based on the motion vector of the spatial neighboring block with respect to the current block.

The decoding apparatus may perform a rearrangement process for the spatial candidates (S610). The decoding apparatus may derive the cost of the spatial candidate and may reorder the spatial candidate based on the cost. For example, the spatial candidates may be rearranged in order of decreasing cost. In the meantime, the details of the method for deriving the cost will be described later.

The decoding apparatus may add a temporal candidate for the current block (S620). The decoding apparatus may derive an MVP candidate, that is, a temporal candidate, of the current block based on the motion vector of the temporal neighboring block with respect to the current block. The temporal candidate may be added to the MVP candidate list in the order after the derived spatial candidate.

The decoding apparatus may add a combined bi-pred candidate for the current block (S630). The decoding apparatus may derive the combined pair prediction candidate based on the derived MVP candidate. The combined pair prediction candidate may represent a candidate including an L0 motion vector and an L1 motion vector generated based on the derived MVP candidate. The combined pair prediction candidate may be added to the MVP candidate list in the order after the derived spatial candidate and the temporal candidate.

The decoding apparatus may add an affiliate candidate for the current block (S640). The decoding apparatus may derive the affine candidate derived through the affine method. The affine candidate may be added to an MVP candidate list in the order after the derived spatial candidate, the temporal candidate, and the combined pair prediction candidate.

The decoding apparatus may parse the MVP index for the current block (S650). The MVP index may indicate one of MVP candidates of the MVP candidate list. The decoding apparatus may determine the MVP candidate indicated by the MVP index as the MVP for the current block (S660). The decoding apparatus may perform motion compensation on the current block based on the MVP (S670).

Meanwhile, the cost for the MVP candidate may be derived as follows.

For example, the cost may be calculated based on a template. In other words, the cost may be derived through a template matching method.

Referring to FIG. 7, a cost for the MVP candidate may be derived based on sample values of neighboring samples of the current block and sample values of neighboring samples of the candidate block indicated by the MVP candidate. Referring to FIG. 7, the peripheral samples of the current block may include left peripheral samples and upper peripheral samples that may be referenced in the current block. In addition, referring to FIG. 7, an arbitrary peripheral area of the current block may be set as a template of the current block, and the cost of the MVP candidate using the template of the candidate block indicated by the MVP candidate on a reference picture. Can be derived. Here, the template of the candidate block for the MVP candidate may have the same size as the template of the current block. In addition, the left neighboring samples and the upper neighboring samples of the current block may already be decoded at the decoding time of the current block, and thus may be used in the motion estimation process in the decoding apparatus. Upper peripheral samples may be included in the template of the current block. That is, the template of the current block may be a specific area including the left peripheral samples and the upper peripheral samples. Here, the cost may be derived as the sum of the absolute values of the differences between the templates of the current block and the corresponding samples of the template of the candidate block. For example, the cost may be derived based on the following equation.

Here, i and j represent positions (i, j) of samples in the template of the block, Cost _distortion is the cost, Temp _ref is the sample value of the template of the candidate block, Temp _cur is the sample value of the template of the current block Indicates. Differences between corresponding samples between the template of the reference block and the template of the current block can be accumulated, and the accumulation of the differences can be used as the cost for the MVP candidate.

Also, as an example, the cost may be derived through a bi-lateral matching method.

8 illustrates an example of deriving a cost of an MVP candidate through a bi-lateral matching method. Referring to FIG. 8, the cost of the MVP candidate may be derived as SAD between corresponding samples of a reference block P0 indicated by the L0 motion vector of the MVP candidate and P1 of the reference block indicated by the L1 motion vector of the MVP candidate.

On the other hand, when the MVP candidate includes only uni prediction motion information, that is, when the MVP candidate includes only the L0 motion vector or includes only the L1 motion vector, the encoding device / decoding device uses the MVP candidate as bi prediction motion information. The cost for the MVP candidate may be derived based on the derived double prediction motion information.

Specifically, for example, the MVP candidate may include an L0 motion vector, and an L0 reference block may be derived based on the L0 motion vector. In this case, the encoding device / decoding device may derive a reference block having a minimum cost with the L0 reference block indicated by the L0 motion vector among the reference blocks within a search range as the L1 reference block of the current block. In addition, a motion vector indicating the L1 reference block can be derived as an L1 motion vector. Here, the search range may be derived from eight peripheral positions within one integer pel range with respect to the position indicated by the L0 motion vector. Alternatively, the search range may be derived as peripheral positions within a half pel range around the position indicated by the LO motion vector.

In addition, the MVP candidate may include an L1 motion vector, and an L1 reference block may be derived based on the L1 motion vector. In this case, the encoding device / decoding device may derive a reference block having a minimum cost with the L1 reference block indicated by the L1 motion vector among the reference blocks within a search range as the L0 reference block of the current block. In addition, a motion vector indicating the L0 reference block can be derived as an L0 motion vector. Here, the search range may be derived from eight peripheral positions within a range of one integer pel with respect to the position indicated by the L1 motion vector. Alternatively, the search range may be derived as peripheral positions within a half pel range around the position indicated by the L1 motion vector. The number of the search range and the peripheral locations may be different from the above example.

Meanwhile, a method of applying reordering to MVP candidates possible in a structure in which encoding / decoding order of coding units are different may be proposed. That is, a scheme for rearranging the MVP candidates of the coding units in a structure in which the encoding / decoding order of the coding units may be changed may be proposed. In the structure, the candidates may be applied in different order according to the conditions, but the MVP including the candidates suitable for the characteristics of each block through the rearrangement while maintaining the same order (ie, the order of deriving the same MVP candidate). A scheme for constructing a candidate list may be proposed. In this case, the reordering process may be performed by deriving a cost for realigning the MVP candidates based on the template matching method described above, and thus, a modification to the template may be necessary according to the processing order of the coding units. That is, since the cost should be calculated for an available block at the time of encoding / decoding of the block, the template may be modified according to the processing order for the block.

10 shows an example of a template according to a processing order for a block. Referring to FIG. 10A, when the encoding / decoding process is performed from left to right, the template of the current block may include an upper peripheral region and a left peripheral region. Also, referring to FIG. 10B, when an encoding / decoding process is performed from right to left, the template of the current block may include an upper peripheral area and a right peripheral area. The template shown in FIG. 10 is an example, and another area may be used as a template of the current block. For example, when an encoding / decoding process is performed from the right to the left direction, when a block that is already encoded / decoded at the encoding / decoding time point for the current block exists on the left side of the current block, the template of the current block May include an upper peripheral region and a left peripheral region, and a cost for an MVP candidate may be derived based on the template.

Meanwhile, since many MVP candidates are used, a large amount of signaling overhead is generated in order to encode an MVP index indicating an MVP candidate for the current block among the MVP candidates. A method of grouping may be proposed.

Referring to FIG. 11, the decoding apparatus may generate a spatial candidate group (S1100), generate a temporal candidate group (S1105), and combine paired candidate prediction groups. A bi-pred candidate group may be generated (S1110), an affine candidate group may be generated (S1115), and an average candidate group may be generated (S1120). For example, the decoding apparatus may derive a plurality of MVP candidates and classify the MVP candidates into spatial candidate groups / temporal candidate groups / affin candidate groups / combined pair prediction candidate groups.

For example, each candidate list may be generated for the five groups. That is, MVP candidates derived based on the spatial neighboring blocks for the current block may be added to the spatial candidate group by the set number of candidates of the spatial candidate group. The spatial candidate group may be derived based on spatial neighboring blocks of the current block, and the number or order of MVP candidates included may be changed. That is, various embodiments may be proposed with respect to the number and order of MVP candidates included in the spatial candidate group. In addition, an MVP candidate derived based on a temporal neighboring block for the current block may be added to the temporal candidate group by the set number of candidates of the temporal candidate group. In addition, a combined pair prediction candidate for the current block may be added to the pair prediction candidate group combined by the set number of candidates of the combined pair prediction candidate group. Here, the combined pair prediction candidate is a combination of the L0 motion vector and the L1 motion vector generated based on the MVP candidate derived based on the spatial neighboring block and / or the MVP candidate derived based on the temporal neighboring block as described above. An MVP candidate may be included.

In addition, when the motion information of the neighboring block of the current block is generated through the affine method (that is, the motion information of the neighboring block is affine motion information), the affine candidate derived based on the neighboring block is included. The affine candidate group may be derived.

In addition, an average value of MVP candidates of the current block may be derived as MVP candidates of the current block, and the average candidate group including the MVP candidates may be derived. For example, an average value of MVP candidates including motion vectors of upper neighboring blocks of the current block may be derived as an MVP candidate of the current block, and the average candidate group including the MVP candidate may be derived.

Thereafter, the decoding apparatus may derive a representative value for each candidate group (S1125). That is, the decoding apparatus may generate representative motion vector values of MVP candidates included in each candidate group. For example, the representative value of the candidate group may be derived as an average value of MVP candidates of the candidate group. Alternatively, the representative value of the candidate group may be derived as a median value of MVP candidates of the candidate group.

The decoding apparatus may derive costs for candidate groups based on representative values of candidate groups, and select one of the candidate groups by comparing the costs (S1130). For example, the decoding apparatus may derive a template matching based cost for the representative value of the candidate group, and may derive the derived cost as the cost for the candidate group. Specifically, the cost for the candidate group may be derived as the sum of the absolute values of the differences between the templates of the current block and the corresponding samples of the template of the candidate block indicated by the representative value.

In addition, the decoding apparatus may derive a bidirectional matching-based cost for the representative value of the candidate group, and may derive the derived cost as the cost for the candidate group. Specifically, the cost for the candidate group may be derived as SAD between the reference block indicated by the L0 motion vector representative value of the candidate group and the corresponding samples of the reference block indicated by the L1 motion vector representative value of the candidate group. The decoding apparatus may derive costs for the candidate groups, compare the costs, select an optimal representative value, and select a candidate group for the optimal representative value. For example, the decoding apparatus may select the representative value for the smallest cost as the optimal representative value. That is, the decoding apparatus may derive costs for candidate groups and select a candidate group having the smallest cost among the candidate groups.

The decoding apparatus may parse the MVP index for the current block (S1135), and determine an MVP candidate indicated by the MVP index among the MVP candidates included in the selected candidate group as the MVP of the current block (S1140). The MVP index may indicate one of MVP candidates included in the selected candidate group. Through this, the number of MVP candidates that can be represented by the MVP index can be reduced, and the overall coding efficiency can be improved by reducing the number of bits necessary for encoding the MVP index.

The number of candidate groups or the number of MVP candidates in a candidate group may be changed, and various methods may be applied to a method of determining a representative value. In addition, the process of reordering the MVP candidates in the candidate group based on the above-described cost may be performed, thereby changing the order in the candidate group.

The decoding apparatus may perform motion compensation on the current block based on the determined MVP (S1145).

Referring to FIG. 12, the decoding apparatus may derive a plurality of MVP candidates, and classify the MVP candidates into bi-prediction candidate groups / uni-prediction candidate groups and the like. Here, the bi-prediction candidate may represent an MVP candidate including bi-prediction motion information, and the short-prediction candidate may represent an MVP candidate including single-prediction motion information. The bi-predicted motion information may include an L0 motion vector and an L1 motion vector, and the uni-predictive motion information may include an L0 motion vector, or may include an L1 motion vector. L0 represents a reference picture list L0 (List 0), and L1 represents a reference picture list L1 (List 1). The L0 motion vector may be a motion vector for an L0 reference picture included in the L0, and the L1 motion vector may be a motion vector for an L1 reference picture included in the L1.

Referring to FIG. 12, the decoding apparatus may generate a bi-prediction candidate group (S1200), and generate a uni-prediction candidate group (S1205). For example, an MVP candidate including pair prediction motion information may be added to the pair prediction candidate group by the set number of candidates of the pair prediction candidate group. In addition, an MVP candidate including short prediction motion information may be added to the short prediction candidate group by the set number of candidates of the short prediction candidate group.

Thereafter, the decoding apparatus may derive a representative value for each candidate group (S1210). That is, the decoding apparatus may generate representative motion vector values of MVP candidates included in each candidate group. For example, the representative value of the candidate group may be derived as an average value of MVP candidates of the candidate group. Alternatively, the representative value of the candidate group may be derived as a median value of MVP candidates of the candidate group.

The decoding apparatus may derive costs for candidate groups based on representative values of candidate groups, and select one of the candidate groups by comparing the costs (S1215). For example, the decoding apparatus may derive a template matching based cost for the representative value of the candidate group, and may derive the derived cost as the cost for the candidate group. Specifically, the cost for the candidate group may be derived as the sum of the absolute values of the differences between the templates of the current block and the corresponding samples of the template of the candidate block indicated by the representative value.

The decoding apparatus may parse the MVP index for the current block (S1220), and determine an MVP candidate indicated by the MVP index among the MVP candidates included in the selected candidate group as the MVP of the current block (S1225). The MVP index may indicate one of MVP candidates included in the selected candidate group. Through this, the number of MVP candidates that can be represented by the MVP index can be reduced, and the overall coding efficiency can be improved by reducing the number of bits necessary for encoding the MVP index.

The decoding apparatus may perform motion compensation on the current block based on the determined MVP (S1230).

Also, as an example of grouping MVP candidates, a method of grouping MVP candidates based on similarity may be proposed. For example, the decoding apparatus may derive MVP candidates including similar motion vectors among available MVP candidates of the current block into one group, and divide the MVP candidates into a plurality of groups. In this case, the number of possible groups (that is, the number of groups that can be derived) may be preset, and the threshold for determining similarity may also be preset. Subsequently, a method of deriving a representative value for each of the candidate groups and selecting a candidate group based on the representative value may determine the MVP for the current block as described above.

In addition, another example of deriving an MVP for the current block by performing a grouping process on MVP candidates may be proposed.

According to the embodiments described above, the decoding apparatus classifies MVP candidates of the current block into a candidate group, selects a specific candidate group based on cost, and based on an MVP index indicating one of the MVP candidates included in the specific candidate group. The MVP for the current block can be determined. In this case, signaling overhead may occur when the number of MVP candidates in each group is large. In the embodiment illustrated in FIG. 13, candidate groups are indexed, and MVP candidates present in each candidate group are separately. We suggest not indexing.

For example, referring to FIG. 13, the decoding apparatus may classify the MVP candidates of the current block to generate one group (S1300), two groups (S1305), and three groups (S1310). Thereafter, the decoding apparatus may parse an MVP group index indicating one of the groups (S1315), and determine a group indicated by the MVP group index as a candidate group for the current block (S1320).

The decoding apparatus may derive costs for MVP candidates of the selected candidate group and derive an MVP candidate having the smallest cost among the costs as an MVP for the current block (S1325).

For example, the decoding apparatus may derive a template matching based cost for each MVP candidate of the selected candidate group. Specifically, the cost for each MVP candidate may be derived as the sum of the absolute values of the differences between the template of the current block and the corresponding samples of the template of the candidate block indicated by each MVP candidate.

In addition, the decoding apparatus may derive a bidirectional matching based cost for each MVP candidate of the selected candidate group. Specifically, the cost for each MVP candidate of the selected candidate group may be derived as SAD between the reference block indicated by the L0 motion vector of each MVP candidate and the corresponding samples of the reference block indicated by the L1 motion vector of each MVP candidate. have. The decoding apparatus may derive costs for MVP candidates of the selected candidate group and derive an MVP candidate for the smallest cost as an MVP for the current block.

Also, for example, the decoding apparatus may add a refined motion vector derived by refinement based on the MVP candidate for the smallest cost as the MVP candidate, thereby predicting accuracy of the current block. Can increase. The decoding apparatus may derive the refined motion vector derived by refinement based on the MVP candidate for the smallest cost as the MVP for the current block. For example, the decoding apparatus may derive a template having the smallest cost from the template of the current block among templates of reference blocks included in any peripheral region of the candidate block indicated by the MVP candidate. The decoding apparatus may derive the motion vector indicating the reference block of the derived template as the refined motion vector.

The decoding apparatus may perform motion compensation on the current block based on the determined MVP (S1330).

14 schematically illustrates an image encoding method by an encoding apparatus according to the present invention. The method disclosed in FIG. 14 may be performed by the encoding apparatus disclosed in FIG. 1. Specifically, for example, S1400 to S1440 of FIG. 14 may be performed by the prediction unit of the encoding apparatus, and S1450 may be performed by the entropy encoding unit of the encoding apparatus. In addition, although not shown, a process of deriving a residual sample for the current block based on the original sample and the prediction sample for the current block may be performed by a subtractor of the encoding apparatus, The generating of the information about the residual on the basis of the current block may be performed by a converter of the encoding apparatus, and the encoding of the information about the residual may be performed by an entropy encoding unit of the encoding apparatus. Can be performed.

The encoding apparatus constructs an MVP candidate list based on the neighboring blocks of the current block (S1400). The encoding apparatus may derive the motion vector of the neighboring block as an MVP candidate and construct the MVP candidate list including the MVP candidate. Also, the encoding apparatus may derive the motion vector derived by combining the motion vectors of the neighboring blocks as the MVP candidate of the current block, and construct the MVP candidate list including the MVP candidate. Meanwhile, the MVP candidate list may be referred to as a motion information candidate list or a merge candidate list, and the MVP candidate may be referred to as a motion information candidate or a merge candidate. In addition, the MVP index described later may be referred to as a motion information index or merge index, and the MVP group index may be referred to as a motion information group index or a merge group index.

Here, the neighboring block may include a spatial neighboring block and a temporal neighboring block. The neighboring block may be a block available at a decoding time of the current block. The available blocks of the current block may be changed according to the processing order for the current block. For example, the spatial peripheral block may include a left peripheral block, an upper peripheral block, an upper left corner peripheral block, a lower left corner peripheral block, and a right upper corner peripheral block of the current block. The spatial peripheral block may include an upper peripheral block, an upper left corner peripheral block, a right upper corner peripheral block, a right peripheral block, and a lower right corner peripheral block of the current block. The spatial peripheral block may include a left peripheral block, an upper peripheral block, an upper left corner peripheral block, a right upper corner peripheral block, and a right peripheral block of the current block. In addition, the temporal neighboring block may include the same position block including a position within a reference picture corresponding to an upper left position, a lower right position, a center upper right position, and / or a center lower left position of the current block. Meanwhile, the upper peripheral block may include an upper peripheral block located at the left end, an upper peripheral block located at the right side of the middle, and an upper peripheral block located at the middle left and / or right end of the upper peripheral blocks adjacent to the upper boundary of the current block. It may include an upper peripheral block located. The left peripheral block may include a left peripheral block positioned at an upper side, a left peripheral block positioned in an upper side of the left peripheral block adjacent to a left boundary of the current block, a left peripheral block positioned in a lower side of the center block, and / or It may include a left peripheral block located. The right peripheral block may include a right peripheral block positioned at an upper side, a right peripheral block positioned at an upper side of the right peripheral block adjacent to a right boundary of the current block, a right peripheral block positioned at a lower side of the center, and / or It may include a right peripheral block located.

Further, for example, when the size of the current block is WxH, and the x component of the top-left sample position of the current block is 0 and the y component is 0, the left neighboring block is (-1, H- 1) a block containing a sample of coordinates, wherein the upper peripheral block is a block containing a sample of (W-1, -1) coordinates, and the right upper corner peripheral block is a sample of (W, -1) coordinates And a block including a sample of (-1, H) coordinates, and the block near a top left corner, which is a block including a sample of (-1, -1) coordinates. have.

In addition, the encoding apparatus may construct an MVP candidate list including the MVP candidates of the maximum number of candidates based on the neighboring blocks. The maximum number of candidates may be preset. In addition, the MVP candidate may include a spatial candidate, a temporal candidate, an affine candidate, a combined candidate and / or an average candidate. The spatial candidate may represent an MVP candidate including a motion vector of the spatial neighboring block, and the temporal candidate may represent an MVP candidate including a motion vector of the temporal neighboring block. In addition, the affine candidate may represent an MVP candidate including an affine motion vector. When the motion vector of the neighboring block of the current block is an affine motion vector, the affine candidate may be derived based on the neighboring block. The affine motion vector may include a motion vector in units of subblocks.

In addition, the average candidate may include an MVP candidate indicating an average value of MVP candidates. For example, an average value of MVP candidates derived based on upper neighboring blocks of the current block may be derived as an average candidate of the current block.

Meanwhile, when the difference between the motion vector of the neighboring block and the MVP candidate derived in the previous order is smaller than the threshold value, the motion vector of the neighboring block may not be derived as the MVP candidate of the current block. The difference between the motion vector of the neighboring block and the MVP candidate may be derived as the sum of the difference between the x component of the motion vector and the x component of the MVP candidate and the difference between the y component of the motion vector and the y component of the MVP candidate. Can be. Also, for example, the threshold may be 1 pel. In addition, the threshold may be derived based on the type of the motion vector. For example, when the motion vector is a motion vector of a spatial neighboring block or a motion vector of a temporal neighboring block, the threshold may be derived as 1 pel, and when the motion vector is an affine motion vector, the threshold may be Can be derived as a half pel.

The encoding apparatus derives costs for MVP candidates included in the MVP candidate list (S1410). The encoding apparatus may derive a cost for each of the MVP candidates included in the MVP candidate list.

For example, the cost of the MVP candidate may be derived as a sum of absorptive difference (SAD) between the template of the current block and the template of the MVP candidate. That is, the cost may be derived as a sum of absolute difference (SAD) of the difference between the corresponding sample of the template of the current block and the template of the MVP candidate. The cost may be derived based on Equation 1 described above.

Here, the template of the current block may include an upper peripheral area and a left peripheral area of the current block. The template of the MVP candidate may include an upper peripheral region and a left peripheral region of the reference block indicated by the MVP candidate. In addition, the template of the current block may be changed according to the processing order for the current block. For example, when the processing order for the current block is from left to right, the template of the current block may include an upper peripheral area and a left peripheral area of the current block, and the processing order for the current block is In a right-to-left direction, the template of the current block may include an upper peripheral area and a right peripheral area of the current block.

The template of the current block may include an upper template (ie, the upper peripheral area of the current block) and a left template (ie, the left peripheral area of the current block), wherein the cost of the MVP candidate is an upper cost and a left side. It can be derived as the sum of costs. The upper cost may be derived as SAD between the upper template of the current block and the upper template of the MVP candidate, and the left cost may be derived as the SAD between the left template of the current block and the left template of the MVP candidate. have. Alternatively, the upper cost may be derived as a value obtained by normalizing a SAD between an upper template of the current block and an upper template of the MVP candidate to a size of the upper template, and the left cost is the current block. The SAD between the left template of and the left template of the MVP candidate may be derived as a value normalized to the size of the left template. The left cost and the upper cost may be derived based on the following equation.

Where costL 'represents the cost of the normalized left template, costA' represents the cost of the normalized upper template, costL represents the cost of the left template, and costA represents the cost of the upper template Where width represents the width of the current block and height represents the height of the current block. The cost may be a cost in a sample unit.

Alternatively, the upper cost may be derived as a value obtained by upscaling the SAD between the upper template of the current block and the upper template of the MVP candidate and normalizing the upscaled SAD to the size of the upper template. The left cost may be upscaled to the SAD between the left template of the current block and the left template of the MVP candidate, and derived as a value obtained by normalizing the upscaled SAD to the size of the left template. Can be. The left cost and the upper cost may be derived based on the following equation.

Where costL 'represents the cost of the normalized left template, costA' represents the cost of the normalized upper template, costL represents the cost of the left template, and costA represents the cost of the upper template Where width represents the width of the current block and height represents the height of the current block. In addition, scale represents a value for the upscaling. The scale may be derived as in the following equation.

Here, scale represents a value for the upscaling, width represents a width of the current block, and height represents a height of the current block.

Meanwhile, as another example, the cost of an MVP candidate may be derived as a sum of absorptive difference (SAD) between an L0 reference block of the MVP candidate and an L1 reference block of the MVP candidate. That is, the cost may be derived as a sum of absolute difference (SAD) of the difference between the L0 reference block and the corresponding samples of the L1 reference block. Here, the L0 reference block may be a reference block indicated by the L0 motion vector of the MVP candidate, and the L1 reference block may be a reference block indicated by the L1 motion vector of the MVP candidate.

Meanwhile, when the MVP candidate is unipredicted motion information including an L0 motion vector, it indicates a reference block having a minimum cost with the L0 reference block indicated by the L0 motion vector among reference blocks in a search range. The motion vector may be derived as an L1 motion vector. Thereafter, the cost of the MVP candidate may be derived as the cost of the L0 reference block and the L1 reference block indicated by the L1 motion vector. The search range may be a range of one integer pel around a position indicated by the L0 motion vector. Alternatively, the search range may be a two integer pel range around the location indicated by the LO motion vector. Alternatively, the search range may be a half integer pel range around a location indicated by the LO motion vector. In addition, the search range may be set to a range other than the above-described examples.

In addition, when the MVP candidate is unipredicted motion information including an L1 motion vector, it indicates a reference block having a minimum cost with the L1 reference block indicated by the L1 motion vector among the reference blocks in a search range. The motion vector may be derived as a L0 motion vector. Thereafter, the cost of the MVP candidate may be derived as the cost of the L1 reference block and the L0 reference block indicated by the L0 motion vector. Here, the search range may be a range of one integer pel around a position indicated by the L1 motion vector. Alternatively, the search range may be a two integer pel range around the position indicated by the L1 motion vector. Alternatively, the search range may be a half integer pel range around a position indicated by the L1 motion vector. In addition, the search range may be set to a range other than the above-described examples.

Meanwhile, the encoding apparatus may derive only the cost for a specific MVP candidate among the MVP candidates. That is, only costs for the MVP candidates that are the realignment targets among the MVP candidates may be derived. For example, the particular MVP candidate may be a spatial candidate and / or a temporal candidate.

The encoding apparatus derives a modified MVP candidate list based on the costs for the MVP candidates (S1420).

For example, the encoding apparatus may reorder the MVP candidates in order of decreasing cost to derive a rearranged MVP candidate list.

Also, as an example, the encoding apparatus may classify the MVP candidates to derive a plurality of candidate groups.

For example, the plurality of candidate groups may include a spatial candidate group, a temporal candidate group, a combined candidate group, an affine candidate group, and / or an average candidate group. The spatial candidate group may include a spatial candidate among the MVP candidates, the temporal candidate group may include a temporal candidate among the MVP candidates, and the combined candidate group includes a combined bi-pred candidate among the MVP candidates. The candidate candidate group may include an affiliate candidate among the MVP candidates, and the average candidate group may include an average candidate among the MVP candidates.

Alternatively, for example, the plurality of candidate groups may include a spatial candidate group, a temporal candidate group, a combined candidate group, an affine candidate group, and / or an average candidate group. The spatial candidate group may include a spatial candidate among the MVP candidates, the temporal candidate group may include a temporal candidate among the MVP candidates, and the combined candidate group includes a combined bi-pred candidate among the MVP candidates. The candidate candidate group may include an affiliate candidate among the MVP candidates, and the average candidate group may include an average candidate among the MVP candidates.

Or, for example, the plurality of candidate groups may include a pair prediction group and / or a single prediction group. The bi-prediction candidate group may include an MVP candidate including bi-prediction motion information among the MVP candidates, and the uni-prediction candidate group may include an MVP candidate including short-prediction motion information among the MVP candidates. The bi-predicted motion information may include an L0 motion vector and an L1 motion vector, and the unipredicted motion information may include an L0 motion vector or an L1 motion vector.

Alternatively, for example, the encoding apparatus may derive MVP candidates including similar motion vectors among MVP candidates into one candidate group, and divide the MVP candidates into a plurality of candidate groups. In this case, the maximum number of candidate groups may be preset. In addition, a threshold for determining similarity may be preset. For example, when the difference between MVP candidates is smaller than the threshold, the MVP candidates may be determined to be similar motion vectors and included in the same candidate group.

The encoding apparatus derives the motion vector of the current block based on the modified MVP candidate list (S1430). The encoding apparatus may select one MVP candidate among the MVP candidates of the modified MVP candidate list, and derive the selected MVP candidate as the MVP of the current block. The encoding apparatus may generate an MVP index indicating the selected MVP candidate among the MVP candidates included in the modified MVP candidate list. The MVP index may be included in the information about the inter prediction.

Or, for example, when the candidate groups are derived, the encoding apparatus may derive costs for the candidate groups and select a candidate group for the smallest cost. The encoding apparatus may select one MVP candidate among the MVP candidates of the selected candidate group, and derive the selected MVP candidate as the MVP of the current block. The encoding apparatus may generate an MVP index indicating the selected MVP candidate among the MVP candidates included in the selected candidate group. The MVP index may be included in the information about the inter prediction.

Here, the cost for the candidate group may be derived as follows. For example, a representative value for a candidate group may be derived, and the cost for the candidate group may be derived as a sum of absolute difference (SAD) between the template of the current block and the template of the reference block indicated by the representative value. Can be. That is, the cost may be derived as a sum of absolute difference (SAD) of the difference between the template of the current block and the corresponding samples of the template of the reference block indicated by the representative value.

Alternatively, for example, a representative L0 motion vector and a representative L1 motion vector for a candidate group may be derived, and the cost for the candidate group may refer to an L0 reference block of the representative L0 motion vector and an L1 of the representative L1 motion vector. It can be derived as a sum of absolute difference (SAD) with the block. That is, the cost may be derived as a sum of absolute difference (SAD) of the difference between the L0 reference block and the corresponding samples of the L1 reference block. Here, the L0 reference block may be a reference block indicated by the representative L0 motion vector, and the L1 reference block may be a reference block indicated by the representative L1 motion vector.

Or, for example, when the candidate groups are derived, the encoding apparatus may select one candidate group among the candidate groups, derive costs for the selected candidate group, and MVP candidate for the smallest cost Can be derived as the MVP of the current block. The encoding apparatus may generate an MVP group index indicating the selected candidate group among the candidate groups. The MVP group index may be included in the information about the inter prediction.

The encoding apparatus may derive the motion vector of the current block based on the MVP of the current block. In addition, for example, the encoding apparatus may obtain a motion vector difference (MVD) between the motion vector of the current block and the MVP, encode the same, and output the encoded bitstream in the form of a bitstream. That is, MVD may be obtained by subtracting the MVP from the motion vector of the current block.

The encoding apparatus performs prediction of the current block based on the motion vector (S1440). A prediction block of the current block may be derived based on the motion vector, and a reconstruction block may be derived based on the prediction block. In detail, the encoding apparatus may derive a reference block within a reference picture based on the motion vector. The encoding apparatus may derive a reference picture for the current block among reference pictures, and may derive a block indicated by the motion vector in the reference picture as a reference block of the current block. The encoding apparatus may generate a prediction sample based on the reference block. The encoding apparatus may generate a reference picture index indicating the reference picture, encode the same, and output the encoded picture in the form of a bitstream.

In addition, the encoding apparatus may generate a residual sample based on the original sample and the generated prediction sample. The encoding apparatus may generate information about the residual based on the residual sample. The information about the residual may include transform coefficients related to the residual sample. The encoding apparatus may derive the reconstructed sample based on the prediction sample and the residual sample. That is, the encoding apparatus may derive the reconstructed sample by adding the prediction sample and the residual sample. In addition, the encoding apparatus may encode the information about the residual and output the bitstream. The bitstream may be transmitted to a decoding apparatus via a network or a storage medium.

The encoding device encodes information about inter prediction of the current block (S1450). The encoding apparatus may determine a prediction mode of the current block, and generate information indicating the prediction mode. In addition, the encoding apparatus may generate an MVP index indicating the MVP candidate selected to derive the motion information of the current block. The encoding device may encode and output the MVP index. The MVP index may be included in the information about the inter prediction. In addition, the encoding apparatus may generate an MVP group index indicating the selected candidate group. The encoding device may encode and output the MVP group index. The MVP group index may be included in the information about the inter prediction. In addition, the encoding apparatus may generate information about the residual based on the residual sample. The information about the residual may include transform coefficients related to the residual sample. The encoding device may encode the information about the residual and output the encoded information about the residual. The bitstream may be transmitted to a decoding apparatus via a network or a storage medium.

15 schematically illustrates an encoding apparatus for performing an image encoding method according to the present invention. The method disclosed in FIG. 14 may be performed by the encoding apparatus disclosed in FIG. 15. In detail, for example, the prediction unit of the decoding apparatus of FIG. 15 may perform S1400 to S1440 of FIG. 14, and the entropy encoding unit of the decoding apparatus of FIG. 15 may perform S1450 of FIG. 14. Although not shown, a process of deriving a residual sample for the current block based on the original sample and the prediction sample for the current block may be performed by the subtraction unit of the encoding apparatus of FIG. 15. The generating of the information about the residual for the current block based on the residual sample may be performed by the transform unit of the encoding apparatus of FIG. 15, and the encoding of the residual information may be performed in FIG. 15. May be performed by an entropy encoding unit of the encoding apparatus.

16 schematically illustrates an image decoding method by a decoding apparatus according to the present invention. The method disclosed in FIG. 16 may be performed by the decoding apparatus disclosed in FIG. 2. Specifically, for example, S1600 to S1640 of FIG. 16 may be performed by the prediction unit of the decoding apparatus. In addition, although not shown, the process of acquiring the information about the inter prediction and the residual information of the current block through the bitstream may be performed by an entropy decoding unit of the decoding apparatus, based on the residual information. Deriving the residual sample for the current block may be performed by an inverse transform unit of the decoding apparatus, and generating a reconstructed picture based on the prediction sample and the residual sample may be added by the decoding apparatus. Can be performed by wealth.

The decoding apparatus configures an MVP candidate list based on the neighboring blocks of the current block (S1600). The decoding apparatus may derive the motion vector of the neighboring block as an MVP candidate and construct the MVP candidate list including the MVP candidate. The decoding apparatus may derive the motion vector derived by combining the motion vectors of the neighboring blocks as the MVP candidate of the current block, and construct the MVP candidate list including the MVP candidate. Meanwhile, the MVP candidate list may be referred to as a motion information candidate list or a merge candidate list, and the MVP candidate may be referred to as a motion information candidate or a merge candidate. In addition, the MVP index described later may be referred to as a motion information index or merge index, and the MVP group index may be referred to as a motion information group index or a merge group index.

Also, the decoding apparatus may construct an MVP candidate list including the MVP candidates of the maximum number of candidates based on the neighboring blocks. The maximum number of candidates may be preset. In addition, the MVP candidate may include a spatial candidate, a temporal candidate, an affine candidate, a combined candidate and / or an average candidate. The spatial candidate may represent an MVP candidate including a motion vector of the spatial neighboring block, and the temporal candidate may represent an MVP candidate including a motion vector of the temporal neighboring block. In addition, the affine candidate may represent an MVP candidate including an affine motion vector. When the motion vector of the neighboring block of the current block is an affine motion vector, the affine candidate may be derived based on the neighboring block. The affine motion vector may include a motion vector in units of subblocks.

Meanwhile, when the difference between the motion vector of the specific neighboring block and the MVP candidate derived in the previous order is smaller than the threshold value, the motion vector of the specific neighboring block may not be derived as the MVP candidate of the current block. The difference between the motion vector of the specific neighboring block and the MVP candidate is derived as the sum of the difference between the x component of the motion vector and the x component of the MVP candidate and the difference between the y component of the motion vector and the y component of the MVP candidate. Can be. Also, for example, the threshold may be 1 pel. In addition, the threshold may be derived based on the type of the motion vector. For example, if the motion vector is a motion vector of a spatial neighboring block or a motion vector of a temporal neighboring block (i.e., the specific neighboring block is a spatial neighboring block or a temporal neighboring block), the threshold may be derived as 1 Pel. If the motion vector is an affinity motion vector, the threshold may be derived as a half pel.

The decoding apparatus derives costs for MVP candidates included in the MVP candidate list (S1610). The decoding apparatus may derive a cost for each of the MVP candidates included in the MVP candidate list.

The template of the current block may include an upper template (ie, the upper peripheral area of the current block) and a left template (ie, the left peripheral area of the current block), wherein the cost of the MVP candidate is an upper cost and a left side. It can be derived as the sum of costs. The upper cost may be derived as SAD between the upper template of the current block and the upper template of the MVP candidate, and the left cost may be derived as the SAD between the left template of the current block and the left template of the MVP candidate. have. Alternatively, the upper cost may be derived as a value obtained by normalizing a SAD between an upper template of the current block and an upper template of the MVP candidate to a size of the upper template, and the left cost is the current block. The SAD between the left template of and the left template of the MVP candidate may be derived as a value normalized to the size of the left template. The left cost and the upper cost may be derived based on Equation 2 described above.

Alternatively, the upper cost may be derived as a value obtained by upsizing the SAD between the upper template of the current block and the upper template of the MVP candidate and normalizing the upscaled SAD to the size of the upper template. The left cost may be upscaled to the SAD between the left template of the current block and the left template of the MVP candidate, and derived as a value obtained by normalizing the upscaled SAD to the size of the left template. Can be. The left cost and the upper cost may be derived based on Equation 3 described above. In addition, the scale of Equation 3 described above may be derived based on Equation 4 described above.

Meanwhile, the decoding apparatus may derive only the cost for a specific MVP candidate among the MVP candidates. That is, only costs for the MVP candidates that are the realignment targets among the MVP candidates may be derived. For example, the particular MVP candidate may be a spatial candidate and / or a temporal candidate.

The decoding apparatus derives a modified MVP candidate list based on the costs for the MVP candidates (S1620).

For example, the decoding apparatus may derive the rearranged MVP candidate list by rearranging the MVP candidates in descending order of cost.

Also, as an example, the decoding apparatus may classify the MVP candidates to derive a plurality of candidate groups.

Or, for example, the decoding apparatus may derive MVP candidates including similar motion vectors among MVP candidates into one candidate group, and divide the MVP candidates into a plurality of candidate groups. In this case, the maximum number of candidate groups may be preset. In addition, a threshold for determining similarity may be preset. For example, when the difference between MVP candidates is smaller than the threshold, the MVP candidates may be determined to be similar motion vectors and included in the same candidate group.

The decoding apparatus derives a motion vector of the current block based on the modified MVP candidate list (S1630). The decoding apparatus may select one MVP candidate among the MVP candidates of the modified MVP candidate list, and derive the selected MVP candidate as a motion vector predictor (MVP) of the current block.

As an example, the decoding apparatus may obtain an MVP index indicating one MVP candidate among the MVP candidates included in the modified MVP candidate list through the bitstream. The MVP index may be included in the information about the inter prediction. The decoding apparatus may derive the MVP candidate indicated by the MVP index among the MVP candidates of the modified MVP candidate list as the MVP of the current block.

Or, for example, when the candidate groups are derived, the decoding apparatus may derive costs for the candidate groups and select a candidate group for the smallest cost. The decoding apparatus may obtain an MVP index indicating one MVP candidate among the MVP candidates included in the selected candidate group through the bitstream. The MVP index may be included in the information about the inter prediction. The decoding apparatus may derive the MVP candidate indicated by the MVP index among the MVP candidates of the selected candidate group as the MVP of the current block.

Here, the cost for the candidate group may be derived as follows. For example, a representative value for a candidate group may be derived, and the cost for the candidate group may be derived as a sum of absorptive difference (SAD) between a template of the current block and a template of a reference block indicated by the representative value. Can be. That is, the cost may be derived as a sum of absolute difference (SAD) of the difference between the template of the current block and the corresponding samples of the template of the reference block indicated by the representative value.

Or, as an example, when the candidate groups are derived, the decoding apparatus may obtain an MVP group index indicating one candidate group of the candidate groups through a bitstream. The MVP group index may be included in the information about the inter prediction. The decoding apparatus may select a candidate group indicated by the MVP group index among the candidate groups as a candidate group for the current block. The decoding apparatus may derive the MVP candidate having the lowest cost among the MVP candidates included in the selected candidate group as the MVP of the current block.

The decoding apparatus may derive the motion vector of the current block based on the MVP of the current block. For example, the decoding apparatus may obtain a motion vector difference (MVD) for the current block, and derive the motion vector of the current block based on the MVP and the MVD.

The decoding apparatus performs prediction of the current block based on the motion vector (S1640). A prediction block of the current block may be derived based on the motion vector, and a reconstruction block may be derived based on the prediction block. In detail, the decoding apparatus may derive a reference block within a reference picture based on the motion vector. For example, a reference picture index for the current block indicating the reference picture may be obtained through the bitstream, and the reference picture may be derived based on the reference picture index. The decoding apparatus may obtain a reference picture index for the current block through the bitstream, and may derive the reference picture indicated by the reference picture index among the reference pictures of the reference picture list as the reference picture of the current block. The block indicated by the motion vector in the reference picture may be derived as a reference block of the current block. The decoding apparatus may generate a prediction sample based on the reference block, and may directly use the prediction sample as a reconstruction sample according to a prediction mode, or generate a reconstruction sample by adding a residual sample to the prediction sample. . If there is a residual sample for the current block, the decoding apparatus may receive information about the residual for the current block from the bitstream. The information about the residual may include transform coefficients regarding the residual sample. The decoding apparatus may derive the residual sample (or residual sample array) for the current block based on the residual information. The decoding apparatus may generate a reconstructed sample based on the prediction sample and the residual sample, and may derive a reconstructed block or a reconstructed picture based on the reconstructed sample. Thereafter, as described above, the decoding apparatus may apply an in-loop filtering procedure, such as a deblocking filtering and / or SAO procedure, to the reconstructed picture in order to improve subjective / objective picture quality as necessary.

17 schematically illustrates a decoding apparatus for performing an image decoding method according to the present invention. The method disclosed in FIG. 16 may be performed by the decoding apparatus disclosed in FIG. 17. Specifically, for example, the prediction unit of the decoding apparatus of FIG. 17 may perform S1600 to S1640 of FIG. 16. In addition, although not shown, the process of obtaining the information about the inter prediction and the residual information of the current block through the bitstream may be performed by the entropy decoding unit of the decoding apparatus of FIG. 17. Deriving the residual sample for the current block based on information may be performed by an inverse transform unit of the decoding apparatus of FIG. 17, and generating a reconstructed picture based on a prediction sample and the residual sample. May be performed by the adder of the decoding apparatus of FIG.

According to the present invention described above, considering the cost, the optimal MVP candidates for the current block can be rearranged in the order indicated by the small value of the MVP index, thereby reducing the amount of bits for prediction and improving the overall coding efficiency. Can be.

In addition, according to the present invention, MVP candidates of the current block may be classified into candidate groups, an optimal candidate group may be derived, and an MVP index indicating one of the MVP candidates included in the candidate group may be coded. It is possible to reduce the amount of bits for coding the MVP index and to improve the overall coding efficiency.

In the above-described embodiment, the methods are described based on a flowchart as a series of steps or blocks, but the present invention is not limited to the order of steps, and any steps may occur in a different order or simultaneously from other steps as described above. have. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

The above-described method according to the present invention may be implemented in software, and the encoding device and / or the decoding device according to the present invention may perform image processing of, for example, a TV, a computer, a smartphone, a set-top box, a display device, and the like. It can be included in the device.

When embodiments of the present invention are implemented in software, the above-described method may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor by various well known means. The processor may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage device. That is, the embodiments described in the present invention may be implemented and performed on a processor, a microprocessor, a controller, or a 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 decoding apparatus and encoding apparatus 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, and mobile streaming. Devices, storage media, camcorders, video on demand (VoD) service providers, over the top video (OTT) devices, internet streaming service providers, 3D (3D) video devices, video telephony video devices, and medical video devices It may be included and used to process a video signal or a data signal. 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.

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

The encoding server compresses content input from multimedia input devices such as a smart phone, a camera, a camcorder, etc. into digital data to generate a bitstream and transmit the bitstream to the streaming server. As another example, when multimedia input devices such as smart phones, cameras, camcorders, etc. directly generate a bitstream, the encoding server may be omitted. The bitstream may be generated by an encoding method or a bitstream generation method to which the present invention is applied, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

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

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

Examples of the user device include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), navigation, a slate PC, Tablet PCs, ultrabooks, wearable devices (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.

Claims

In the image decoding method performed by the decoding apparatus,

Constructing a motion information candidate list based on neighboring blocks of the current block;

Deriving costs for motion information candidates included in the motion information candidate list;

Deriving a modified motion information candidate list based on the costs for the motion information candidates;

Deriving a motion vector of the current block based on the modified motion information candidate list; And

And predicting the current block based on the motion vector.
The method of claim 1,

Deriving the modified motion information candidate list based on the costs for the motion information candidates,

And rearranging the motion information candidates in order of decreasing cost to derive a rearranged motion information candidate list.
The method of claim 1,

Deriving the modified motion information candidate list based on the costs for the motion information candidates,

And classifying the motion information candidates to derive a plurality of candidate groups.
The method of claim 3,

The plurality of candidate groups includes a spatial candidate group and a temporal candidate group,

The spatial candidate group includes a spatial candidate among the motion information candidates,

The temporal candidate group includes a temporal candidate among the motion information candidates.
The method of claim 3,

The plurality of candidate groups includes a pair of predictive candidate groups and a single predictive candidate group,

The bi-prediction candidate group includes a motion information candidate including bi-prediction motion information among the motion information candidates,

The short prediction candidate group includes a motion information candidate including short prediction motion information among the motion information candidates.
The method of claim 3,

Deriving the motion vector of the current block based on the modified motion information candidate list,

Deriving costs for the candidate groups; And

Selecting a candidate group for the smallest cost of the candidate groups;

Obtaining a motion information index indicating one of the motion information candidates of the selected candidate group through a bitstream; And

And deriving the motion information candidate indicated by the motion information index as motion information of the current block.
The method of claim 3,

Deriving the motion vector of the current block based on the modified motion information candidate list,

Obtaining a motion information group index indicating one of the candidate groups through a bitstream;

Selecting the candidate group indicated by the motion information group index;

And deriving motion information candidates for the smallest cost among the motion information candidates of the selected candidate group as motion information of the current block.
The method of claim 1,

When the difference between the motion vector of the specific neighboring block and the motion information candidate derived in the previous order is smaller than the threshold, the motion vector of the specific neighboring block is not derived as the motion information candidate of the current block. Way.
The method of claim 8,

And the threshold value is derived based on the type of the motion vector.
The method of claim 1,

Deriving the costs for the motion information candidates included in the motion information candidate list,

And deriving only a cost for a specific motion information candidate among the motion information candidates.
12. The method of claim 10, wherein the specific motion information candidate is a spatial candidate.
The method of claim 1,

And a cost of a motion information candidate is derived as a sum of absolute difference (SAD) between a template of the current block and a template of a reference block indicated by the motion information candidate.
The method of claim 1,

The cost of the motion information candidate is derived as a sum of absolute difference (SAD) between the L0 reference block of the motion information candidate and the L1 reference block of the motion information candidate,

The L0 reference block is a reference block indicated by the L0 motion vector of the motion information candidate, and the L1 reference block is a reference block indicated by the L1 motion vector of the motion information candidate.
In the video encoding method performed by the encoding device,

Constructing a motion information candidate list based on neighboring blocks of the current block;

Deriving costs for motion information candidates included in the motion information candidate list;

Deriving a modified motion information candidate list based on the costs for the motion information candidates;

Determining a motion vector of the current block based on the modified motion information candidate list;

Performing prediction of the current block based on the motion vector; And

And encoding information on inter prediction of the current block.
The method of claim 14,

Deriving the modified motion information candidate list based on the costs for the motion information candidates,

And rearranging the motion information candidates in order of decreasing cost to derive a rearranged motion information candidate list.