Method for coding or decoding video signal and apparatus used for the same

Abstract

To provide a method for coding or decoding and a video decoding apparatus which refine a motion vector derived from merge candidates on the basis of an offset vector when a video signal is coded or decoded.SOLUTION: A method for decoding a video includes the steps of: generating a merge candidate list of a current block; specifying a merge candidate of the current block from merge candidates in the merge candidate list; deriving an offset vector from the current block; and deriving a motion vector of the current block by adding a motion vector of the merge candidate to the offset vector.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a video signal encoding / decoding method and an apparatus used in said method. [Background technology]

[0002] As display panels become larger and larger, video services with higher image quality are required. The biggest problem with high-definition video services is the large increase in data volume. To solve this problem, active studies on improving video compression rates are underway. As a representative example, in 2009, the Motion Picture Experts Group (MPEG) and the Video Coding Experts Group (VCEG) under the International Telecommunication Union-Telecommunication (ITU-T) established the Joint Collaborative Team on Video Coding (JCT-VC). JCT-VC proposed a video compression standard called HEVC (High Efficiency Video Coding), which was approved on January 25, 2013. Its compression performance is about twice that of H.264 / AVC. With the rapid growth of high-definition video services, the performance limitations of HEVC are gradually emerging. Summary of the Invention [Problem to be solved by the invention]

[0003] It is an object of the present invention to provide a method and an apparatus for implementing the method for refining motion vectors derived from merging candidates based on offset vectors when encoding / decoding a video signal.

[0004] It is an object of the present invention to provide a method for signalling an offset vector when encoding / decoding a video signal, and an apparatus for implementing said method.

[0005] The technical problems that the present invention aims to achieve are not limited to the technical problems mentioned above, and a person having ordinary skill in the art to which the present invention pertains can clearly understand other technical problems not mentioned from the following description. [Means for solving the problem]

[0006] The video signal decoding / encoding method of the present invention includes the steps of generating a merge candidate list for a current block, selecting a merge candidate for the current block from among the merge candidates included in the merge candidate list, deriving an offset vector for the current block, and deriving a motion vector for the current block by adding a motion vector of the merge candidate to the offset vector.

[0007] In the video signal decoding / encoding method according to the present invention, the magnitude of the offset vector may be determined based on first index information specifying any one of motion magnitude candidates.

[0008] In the video signal decoding / encoding method according to the present invention, at least one of the maximum or minimum values ​​of the motion magnitude candidates can be set to be different based on the value of a flag indicating the range of the motion magnitude candidates.

[0009] In the video signal decoding / encoding method according to the invention, the flag can be signaled at a picture level.

[0010] In the video signal decoding / encoding method according to the present invention, at least one of the maximum value or the minimum value of the motion magnitude candidates may be set to be different depending on the motion vector accuracy of the current block.

[0011] In the video signal decoding / encoding method according to the present invention, the magnitude of the offset vector can be obtained by applying a shift operation to a value represented by the motion magnitude candidate designated by the first index information.

[0012] In the video signal decoding / encoding method according to the present invention, the direction of the offset vector can be determined based on second index information specifying any one of vector direction candidates.

[0013] The above brief summary features of the present invention are merely exemplary embodiments of the detailed description of the invention that follows and are not intended to limit the scope of the invention. Effect of the Invention

[0014] According to the present invention, the efficiency of inter prediction can be improved by refining the motion vectors of merging candidates based on the offset vectors.

[0015] According to the present invention, the efficiency of inter prediction can be improved by adaptively determining the magnitude and direction of the offset vector.

[0016] The effects obtainable by the present invention are not limited to the above effects, and a person having ordinary skill in the art to which the present invention pertains can clearly understand other effects not mentioned from the following description. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a block diagram illustrating a video encoder according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram illustrating a video decoder according to an embodiment of the present invention. [Diagram 3] FIG. 2 illustrates a basic coding tree unit according to an embodiment of the present invention. [Figure 4]A diagram showing multiple division types of a coding block. [Diagram 5] FIG. 1 illustrates division of a coding tree unit. [Figure 6] 2 is a flowchart illustrating an inter prediction method according to an embodiment of the present invention. [Figure 7] FIG. 2 illustrates non-linear motion of an object. [Figure 8] 2 is a flowchart illustrating an affine motion based inter prediction method according to an embodiment of the present invention. [Figure 9] FIG. 2 is a diagram showing examples of affine seed vectors for each affine motion model. [Figure 10] FIG. 2 is a diagram showing examples of affine vectors of sub-blocks in a four-parameter motion model. [Figure 11] 11 is a flowchart illustrating a process of deriving motion information for a current block in merge mode. [Figure 12] FIG. 13 illustrates an example of candidate blocks for deriving merging candidates. [Figure 13] FIG. 13 illustrates the location of a reference sample. [Figure 14] FIG. 13 illustrates an example of candidate blocks for deriving merging candidates. [Figure 15a] 13A and 13B are diagrams illustrating an example of a change in the position of a reference sample. [Figure 15b] 13A and 13B are diagrams illustrating an example of a change in the position of a reference sample. [Figure 16] 13A and 13B are diagrams illustrating an example of a change in the position of a reference sample. [Figure 17] 13 is a diagram showing an offset vector based on the values ​​of distance_idx indicating the magnitude of the offset vector and direction_idx indicating the direction of the offset vector. FIG. [Figure 18] 13 is a diagram showing an offset vector based on the values ​​of distance_idx indicating the magnitude of the offset vector and direction_idx indicating the direction of the offset vector. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0019] Video encoding and decoding is performed on a block-by-block basis. For example, encoding / decoding operations such as transform, quantization, prediction, loop filtering, or reconstruction may be performed on a coding block, a transform block, or a predictive block.

[0020] Hereinafter, the block to be coded / decoded is called a “current block.” For example, according to a current coding / decoding process step, the current block can represent a coding block, a transformation block or a prediction block.

[0021] In addition, the term "unit" as used in this specification may be understood to represent a basic unit for performing a specific encoding / decoding process, and "block" may be understood to represent a sample array of a certain size. Unless otherwise specified, "block" and "unit" are used interchangeably. For example, in the embodiments described below, a coding block and a coding unit may be understood to have the same meaning.

[0022] FIG. 1 is a block diagram illustrating a video encoder according to an embodiment of the present invention.

[0023] Referring to FIG. 1, the video encoding device 100 may include an image division unit 110, a prediction unit 120, 125, a transformation unit 130, a quantization unit 135, a rearrangement unit 160, an entropy encoding unit 165, an inverse quantization unit 140, an inverse transform unit 145, a filter unit 150 and a memory 155.

[0024] Each component shown in Fig. 1 is shown alone to represent different characteristic functions in a video encoding device, but does not represent that each component is composed of separate hardware or a single software assembly. That is, for ease of explanation, each component is arranged so that at least two of the components are combined to form one component, or one component is divided into multiple components to perform the function. As long as it does not deviate from the essence of the present invention, such an embodiment in which each component is integrated and an embodiment in which each component is separated also fall within the scope of the present invention.

[0025] In addition, some of the components are not essential components for performing the essential functions of the present invention, but are only optional components for improving performance. The present invention may be implemented by including only the members necessary to realize the essence of the present invention other than the components used only to improve performance, and a structure including only essential components other than the optional components used only to improve performance also falls within the scope of the present invention.

[0026] The image division unit 110 can divide an input image into at least one processing unit. In this case, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). The image division unit 110 divides one image into a combination of multiple coding units, prediction units, and transform units. The image can be coded by selecting a combination of a coding unit, a prediction unit, and a transform unit based on a predetermined criterion (e.g., a cost function).

[0027] For example, an image can be divided into multiple coding units. To divide an image into coding units, a recursive tree structure such as a quad tree structure can be used to divide a video or largest coding unit into other coding units as a root. The other coding units may have child nodes whose number is equal to the number of divided coding units. A coding unit that is not divided due to some restrictions becomes a leaf node. That is, if it is assumed that a coding unit can only realize a square division, a coding unit can be divided into a maximum of four other coding units.

[0028] Hereinafter, in the embodiments of the present invention, the encoding unit may refer to a unit that performs encoding, or may refer to a unit that performs decoding.

[0029] The prediction units in one coding unit may be divided into shapes such as at least one of a square or a rectangle of the same size, and one prediction unit in one coding unit may also be divided into a shape and / or size that differs from another prediction unit.

[0030] Performing intra prediction based on a coding unit When a prediction unit is not the smallest coding unit, intra prediction can be performed without the need to divide into multiple prediction units NxN.

[0031] The prediction units 120 and 125 may include an inter prediction unit 120 that performs inter prediction and an intra prediction unit 125 that performs intra prediction. It may be determined whether to use inter prediction or intra prediction for a prediction unit, and specific information (e.g., intra prediction mode, motion vector, reference image, etc.) may be determined based on each prediction method. In this case, the processing unit that performs the prediction may be different from the processing unit that determines the prediction method and specific content. For example, the prediction method and prediction mode may be determined by the prediction unit, and the prediction may be performed by the transformation unit. A residual value (residual block) between the generated prediction block and the original block may be input to the transformation unit 130. In addition, prediction mode information, motion vector information, etc. for prediction may be encoded together with the residual value in the entropy encoding unit 165 and transmitted to the decoder. When a specific encoding mode is used, the original block may be directly encoded and transmitted to the decoder without generating a prediction block by the prediction units 120 and 125.

[0032] The inter prediction unit 120 may predict a prediction unit based on information of at least one image, either an image immediately before or an image immediately after the current image. In some cases, the prediction unit may be predicted based on information of a part of an encoded region in the current image. The inter prediction unit 120 may include a reference image interpolation unit, a motion prediction unit, and a motion compensation unit.

[0033] The reference image interpolation unit receives reference image information from the memory 155, and can generate pixel information of integer pixels or less from the reference image. For luminance pixels, an 8-tap interpolation filter based on DCT with different filter coefficients can be used to generate pixel information of integer pixels or less in units of 1 / 4 pixels. For chrominance signals, a 4-tap interpolation filter based on DCT with different filter coefficients can be used to generate pixel information of integer pixels or less in units of 1 / 8 pixels.

[0034] The motion prediction unit can perform motion prediction based on the reference image interpolated by the reference image interpolation unit. As a method for calculating a motion vector, multiple methods such as a full search-based block matching algorithm (FBMA), a three step search method (TSS), a new three-step search algorithm (NTS), etc. can be used. According to the interpolated pixel, the motion vector may have a motion vector value in units of 1 / 2 pixel or 1 / 4 pixel. In the motion prediction unit, a current prediction unit can be predicted by using different motion prediction methods. As a motion prediction method, multiple methods such as a skip method, a merge method, an advanced motion vector prediction method (AMVP), an intra block copy method, etc. can be used.

[0035] The intra prediction unit 125 can generate a prediction unit based on the neighboring reference pixel information of the current block, which is pixel information in the current image. When the neighboring block of the current prediction unit is a block on which inter prediction has been performed, and the reference pixel is a pixel on which inter prediction has been performed, the reference pixel included in the block on which inter prediction has been performed can be the reference pixel information of the neighboring block on which intra prediction has been performed. In other words, when the reference pixel is unavailable, at least one reference pixel of the available reference pixels can be used instead of the unavailable reference pixel information.

[0036] In intra prediction, the prediction mode may include an angular prediction mode that uses reference pixel information based on the prediction direction and a non-angular mode that does not use direction information when performing prediction. The mode for predicting luma information may be different from the mode for predicting chroma information. To predict chroma information, intra prediction mode information for predicting luma information or predicted luma signal information may be used.

[0037] When performing intra prediction, if the size of prediction unit is the same as the size of transform unit, intra prediction can be performed on prediction unit based on the pixel located on the left side, the pixel located on the top left, and the pixel located on the top.However, when performing intra prediction, if the size of prediction unit is different from the size of transform unit, intra prediction can be performed based on the reference pixel of transform unit.Note that intra prediction using N×N division can be applied only to the minimum coding unit.

[0038] After applying an Adaptive Intra Smoothing (AIS) filter to the reference pixels based on the prediction mode, a prediction block can be generated by an intra prediction method. The type of the adaptive intra smoothing filter applied to the reference pixels can be different. To perform the intra prediction method, the intra prediction mode of the current prediction unit can be predicted based on the intra prediction mode of a prediction unit located in the vicinity of the current prediction unit. When predicting the prediction mode of the current prediction unit using mode information predicted from the surrounding prediction units, if the intra prediction mode of the current prediction unit is the same as the intra prediction mode of the surrounding prediction units, information indicating that the prediction mode of the current prediction unit is the same as the surrounding prediction units can be transmitted using predetermined flag information. If the prediction mode of the current prediction unit is different from the prediction mode of the surrounding prediction units, the prediction mode information of the current block can be encoded by performing entropy encoding.

[0039] In addition, a residual block including residual value information that is a difference value between a prediction unit that performs prediction based on the prediction unit generated by the prediction unit 120, 125 and an original block of the prediction unit can be generated. The generated residual block can be input to the conversion unit 130.

[0040] The transform unit 130 may perform transform on the original block and the residual block including residual value information between the prediction units generated by the prediction units 120 and 125 using a transform method such as a discrete cosine transform (DCT) or a discrete sine transform (DST). Here, the DCT transform kernel includes at least one of DCT2 or DCT8, and the DSTc includes DST7. Whether to apply DCT or DST to transform the residual block may be determined based on intra prediction mode information of the prediction unit for generating the residual block. Transformation of the residual block may also be skipped. A flag indicating whether to skip transformation of the residual block may be coded. Transformation may be skipped for residual blocks whose magnitude is equal to or less than a threshold, luma component, or chroma component (4:4:4 format or less).

[0041] The quantization unit 135 may quantize the values ​​transformed into the frequency domain by the transformation unit 130. The quantization coefficient may vary depending on the importance of the block or image. The values ​​calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the rearrangement unit 160.

[0042] The rearrangement unit 160 may perform rearrangement of coefficient values ​​on the quantized residual values.

[0043] The rearrangement unit 160 may change two-dimensional block shape coefficients into one-dimensional vector form using a coefficient scanning method. For example, the rearrangement unit 160 may scan DC coefficients or high-frequency region coefficients using a zig-zag scan method and convert them into one-dimensional vector form. Depending on the size of the transform unit and the intra prediction mode, instead of zig-zag scanning, vertical scanning for scanning two-dimensional block shape coefficients along a column direction and horizontal scanning for scanning two-dimensional block shape coefficients along a row direction may be used. That is, it is possible to determine which of zig-zag scanning, vertical scanning, and horizontal scanning to use, depending on the size of the transform unit and the intra prediction mode.

[0044] The entropy coding unit 165 may perform entropy coding based on the value calculated by the rearrangement unit 160. For example, the entropy coding may use a plurality of coding methods such as Exponential Golomb code, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).

[0045] The entropy coding unit 165 can code a variety of information such as residual value coefficient information and block type information of the coding unit from the rearrangement unit 160 and the prediction units 120 and 125, prediction mode information, division unit information, prediction unit information and transmission unit information, motion vector information, reference frame information, block interpolation information, and filtering information.

[0046] The entropy coding unit 165 may perform entropy coding on the coefficient values ​​of the coding unit input from the rearrangement unit 160 .

[0047] The inverse quantization unit 140 and the inverse transform unit 145 perform inverse quantization on the multiple values ​​quantized by the quantization unit 135, and perform inverse transform on the values ​​transformed by the transform unit 130. A reconstructed block can be generated by merging residual values ​​generated by the inverse quantization unit 140 and the inverse transform unit 145 with prediction units predicted by the motion prediction unit, motion compensation unit, and intra prediction unit included in the prediction units 120 and 125.

[0048] The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

[0049] The deblocking filter can remove block artifacts generated in a reconstructed image due to boundaries between blocks. In order to determine whether to perform deblocking, it can be determined whether to apply a deblocking filter to a current block based on pixels included in several columns or rows included in the block. When applying a deblocking filter to a block, a strong filter or a weak filter can be applied based on a required deblocking filtering strength. In addition, when performing vertical filtering or horizontal filtering in the process of using the deblocking filter, horizontal filtering and vertical filtering can be performed synchronously.

[0050] The offset correction unit can correct the offset between the deblocked video and the original video on a pixel-by-pixel basis. The offset correction can be performed on a specified image in the following manner: After dividing the pixels included in the video into a predetermined number of regions, the regions that require offset execution are determined, and an offset is applied to the corresponding region or an offset is applied taking into account edge information of each pixel.

[0051] Adaptive loop filtering (ALF) can be performed based on a comparison value between the filtered reconstructed image and the original video. After dividing the pixels included in the video into predetermined groups, a filter to be used for the corresponding group is determined, so that filtering can be performed differentially for each group. Information regarding whether adaptive loop filtering is applied and luminance information can be transmitted according to a coding unit (CU). The shape and filter coefficients of the adaptive loop filter to be applied vary depending on each block. It is also possible to apply the same type (constant type) of adaptive loop filter regardless of the characteristics of the block to which it is applied.

[0052] The memory 155 can store the reconstructed block or image calculated by the filter unit 150 and can provide the stored reconstructed block or image to the prediction units 120, 125 when performing inter prediction.

[0053] FIG. 2 is a block diagram illustrating a video decoder according to an embodiment of the present invention.

[0054] Referring to FIG. 2, the video decoder 200 may include an entropy decoding unit 210, a rearrangement unit 215, an inverse quantization unit 220, an inverse transform unit 225, a prediction unit 230, a prediction unit 235, a filter unit 240, and a memory 245.

[0055] When a video bitstream is input from a video encoder, the input bitstream can be decoded in steps that are the reverse of those taken by the video encoder.

[0056] The entropy decoding unit 210 may perform entropy decoding in a step that is the reverse of the step of performing entropy encoding in the entropy encoding unit of the video encoder. For example, a number of methods such as Exponential Golomb coding, Context-Adaptive Variable Length Coding (CAVLC), Context-Adaptive Binary Arithmetic Coding (CABAC), etc. may be applied to correspond to the method performed in the video encoder.

[0057] The entropy decoding unit 210 can perform decoding on information related to intra prediction and inter prediction performed by the encoder.

[0058] The rearrangement unit 215 may perform rearrangement by rearranging a bitstream entropy decoded by the entropy decoding unit 210 in the encoding unit. The rearrangement may be performed by reconstructing a plurality of coefficients represented in a one-dimensional vector form into coefficients in a two-dimensional block shape. The rearrangement unit 215 may perform rearrangement by receiving information related to a coefficient scan performed by the encoding unit and performing a reverse scan according to the scan order performed by the corresponding encoding unit.

[0059] The inverse quantization unit 220 may perform inverse quantization based on the quantization parameter provided by the encoder and the coefficient values ​​of the rearranged block.

[0060] The inverse transform unit 225 may perform an inverse discrete cosine transform and an inverse discrete sine transform on the quantization result performed by the video encoder. The inverse discrete cosine transform and the inverse discrete sine transform are inverse transforms of the transform performed by the transform unit, that is, inverse transforms of the discrete cosine transform and the discrete sine transform. Here, the DCT transform kernel may include at least one of DCT2 and DCT8, and the DST transform kernel may include DST7. Alternatively, if the transform is skipped in the video encoder, the inverse transform unit 225 may not perform the inverse transform. The inverse transform may be performed by a transmission unit determined by the video encoder. The inverse transform unit 225 of the video decoder may selectively perform a transform method (e.g., DCT or DST) based on a plurality of pieces of information such as a prediction method, a size of a current block, and a prediction direction.

[0061] The prediction units 230, 235 can generate a prediction block based on information related to the generation of the prediction block provided by the entropy decoding unit 210 and previously decoded block or image information provided by the memory 245.

[0062] As mentioned above, when performing intra prediction in the same manner as the operation manner in the video encoder, if the size of the prediction unit is the same as the size of the transform unit, intra prediction is performed on the prediction unit based on the pixel located to the left of the prediction unit, the pixel located to the upper left, and the pixel located above.When performing intra prediction, if the size of the prediction unit is different from the size of the transform unit, intra prediction can be performed based on the reference pixel of the transform unit.Note that intra prediction using N×N division can be applied only to the minimum coding unit.

[0063] The prediction unit 230, 235 may include a prediction unit determination unit, an inter prediction unit, and an intra prediction unit. The prediction unit determination unit receives a plurality of pieces of information, such as prediction unit information input from the entropy decoding unit 210, prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, and classifies the prediction unit based on the current encoding unit, and determines whether the prediction unit is performing inter prediction or intra prediction. The inter prediction unit 230 can perform inter prediction on the current prediction unit based on information included in at least one image of the image immediately before or immediately after the current image to which the current prediction unit belongs, using information necessary for performing inter prediction of the current prediction unit provided by the video encoder. Alternatively, inter prediction can be performed based on information of a reconstructed part of the area in the current image to which the current prediction unit belongs.

[0064] To perform inter prediction, it is possible to determine, based on the coding unit, whether the motion prediction method of the prediction unit included in the corresponding coding unit is skip mode, merge mode, advanced motion vector prediction mode (AMVP mode), or intra block duplication mode.

[0065] The intra prediction unit 235 may generate a prediction block based on pixel information in the current image. If the prediction unit is a prediction unit that has performed intra prediction, the intra prediction may be performed based on intra prediction mode information of the prediction unit provided from the video encoder. The intra prediction unit 235 may include an adaptive intra smoothing (AIS) filter, a reference pixel interpolation unit, and a DC filter. The adaptive intra smoothing filter is a part that performs filtering on reference pixels of the current block, and may determine whether to apply a filter based on the prediction mode of the current prediction unit. Adaptive intra smoothing filtering may be performed on reference pixels of the current block using the prediction mode of the prediction unit and adaptive intra smoothing filter information provided from the video encoder. If the prediction mode of the current block is a mode that does not perform adaptive intra smoothing filtering, the adaptive intra smoothing filter may not be applied.

[0066] Regarding the reference pixel interpolation unit, if the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on pixel values ​​to be interpolated for the reference pixels, the reference pixels can be generated by performing interpolation on the reference pixels. If the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without performing interpolation on the reference pixels, the reference pixels do not need to be interpolated. If the prediction mode of the current block is a DC mode, the DC filter can generate a prediction block by filtering.

[0067] The reconstructed block or image may be provided to a filter unit 240. The filter unit 240 may include a deblocking filter, an offset correction unit, and an ALF.

[0068] From the video encoder, information regarding whether to apply a deblocking filter to a corresponding block or image and information regarding whether to use a strong filter or a weak filter when applying the deblocking filter may be received. The deblocking filter of the video decoder may receive the information regarding the deblocking filter provided by the video encoder, and the video decoder may perform deblocking filtering on the corresponding block.

[0069] The offset compensation unit may perform offset compensation on the reconstructed image based on the offset information and the type of offset compensation applied to the video when encoding.

[0070] An ALF may be applied to a coding unit based on information provided by the encoder regarding whether to apply an ALF, ALF coefficient information, etc. Such ALF information may be provided by being included in a particular parameter set.

[0071] The memory 245 is capable of storing the reconstructed image or block, making said image or block available as a reference image or block, and of providing the reconstructed image to an output.

[0072] FIG. 3 is a diagram illustrating a basic coding tree unit according to an embodiment of the present invention.

[0073] The largest coding block can be defined as a coding tree block. An image may be divided into multiple coding tree units (a coding tree unit is a coding tree unit (CTU) in size). The largest coding unit may be called a largest coding unit (LCU). Figure 3 shows an example of dividing an image into multiple coding tree units.

[0074] The size of the coding tree unit may be defined at the picture level or at the sequence level, so that the picture parameter set or the sequence parameter set can be used to signal the information indicating the size of the coding tree unit.

[0075] For example, the size of the coding tree unit for all images in a sequence may be 128 x 128. Alternatively, the size of the coding tree unit may be determined to be one of 128 x 128 or 256 x 256 at the image level. For example, the size of the coding tree unit in a first image may be 128 x 128, and the size of the coding tree unit in a second image may be 256 x 256.

[0076] A coding block can be generated by dividing the coding tree unit. The coding block represents a basic unit for performing coding / decoding processing. For example, prediction or transformation can be performed according to different coding blocks, or a predictive coding mode can be determined according to different coding blocks. Here, the predictive coding mode represents a method for generating a predicted image. For example, the predictive coding mode may include intra prediction (Intra Prediction), inter prediction (Inter Prediction), current picture referencing (CPR), intra block copy (IBC), or combined prediction (Combined Prediction). For a coding block, a predictive block related to the coding block can be generated using at least one predictive coding mode among intra prediction, inter prediction, current picture referencing, or combined prediction.

[0077] Information indicating the predictive coding mode of the current block may be signaled via the bitstream. For example, the information may be a 1-bit flag indicating whether the predictive coding mode is an intra mode or an inter mode. Only if it is determined that the predictive coding mode of the current block is an inter mode, can current image reference or combined prediction be used.

[0078] The current image reference is used to obtain a prediction block of the current block from an encoded / decoded area in the current image by using the current image as a reference image. Here, the current image means an image including the current block. Information indicating whether the current image reference is applied to the current block may be signaled via the bitstream. For example, the information may be a 1-bit flag. If the flag is true, the prediction coding mode of the current block may be determined as the current image reference. If the flag is false, the prediction mode of the current block may be determined as the inter prediction.

[0079] Alternatively, the predictive coding mode of the current block may be determined based on the reference image index. For example, if the reference image index points to the current image, the predictive coding mode of the current block may be determined as current image reference. If the reference image index points to an image other than the current image, the predictive coding mode of the current block may be determined as inter prediction. That is, the current image reference is a prediction method that uses information of an encoded / decoded area in the current image, and the inter prediction is a prediction method that uses information of another encoded / decoded image.

[0080] The combined prediction is a coding mode formed by combining two or more of intra prediction, inter prediction, and current image reference. For example, when the combined prediction is applied, a first predicted block may be generated based on one of intra prediction, inter prediction, and current image reference, and a second predicted block may be generated based on the other. When the first predicted block and the second predicted block are generated, a final predicted block may be generated by averaging and weighted addition of the first predicted block and the second predicted block. Information indicating whether the combined prediction is applied may be signaled via the bitstream. The information may be a 1-bit flag.

[0081] FIG. 4 is a diagram showing a number of division types of a coding block.

[0082] A coding block can be divided into a plurality of coding blocks based on a quadtree division, a binary tree division, or a ternary tree division. Also, a divided coding block can be further divided into a plurality of coding blocks based on a quadtree division, a binary tree division, or a ternary tree division.

[0083] Quadtree partitioning is a partitioning technique that divides the current block into four blocks. As a result of the quadtree partitioning, the current block can be divided into four square partitions (see “SPLIT_QT” in (a) of FIG. 4).

[0084] Binary tree partitioning is a partitioning technique that divides a current block into two blocks. The process of dividing the current block into two blocks along the vertical direction (i.e., using a vertical line that crosses the current block) can be called vertical binary tree partitioning, and the process of dividing the current block into two blocks along the horizontal direction (i.e., using a horizontal line that crosses the current block) can be called horizontal binary tree partitioning. After binary tree partitioning, the current block can be divided into two non-square partitions. "SPLIT_BT_VER" in (b) of FIG. 4 represents the vertical binary tree partitioning result, and "SPLIT_BT_HOR" in (c) of FIG. 4 represents the horizontal binary tree partitioning result.

[0085] Ternary tree partitioning is a partitioning technique that partitions the current block into three blocks. The process of partitioning the current block into three blocks along the vertical direction (i.e., using two vertical lines that cross the current block) can be called vertical ternary tree partitioning, and the process of partitioning the current block into three blocks along the horizontal direction (i.e., using two horizontal lines that cross the current block) can be called horizontal ternary tree partitioning. After ternary tree partitioning, the current block can be partitioned into three non-square partitions. In this case, the width / height of the partition located at the center of the current block may be twice the width / height of the other partitions. "SPLIT_TT_VER" in FIG. 4(d) represents the vertical ternary tree partitioning result, and "SPLIT_TT_HOR" in FIG. 4(e) represents the horizontal ternary tree partitioning result.

[0086] The number of times a coding tree unit is divided can be defined as a partitioning depth. The maximum partitioning depth of a coding tree unit can be determined at a sequence or image level. Therefore, the maximum partitioning depth of a coding tree unit may differ depending on a sequence or image.

[0087] Alternatively, a maximum partitioning depth can be determined for each of multiple partitioning techniques independently. For example, the maximum partitioning depth that allows for quadtree partitioning may be different from the maximum partitioning depth that allows for binary tree partitioning and / or ternary tree partitioning.

[0088] The encoder may signal information indicative of at least one of the partition shape or partition depth of the current block via the bitstream, and the decoder may determine the partition shape and partition depth of the coding tree unit based on the information parsed from the bitstream.

[0089] FIG. 5 is a diagram illustrating an example of division of a coding tree unit.

[0090] The process of dividing a coding block using a division technique such as quad-tree division, binary-tree division and / or ternary-tree division can be called multi-tree partitioning.

[0091] The coding blocks generated by applying the multi-tree partitioning to the coding block can be called sub-coding blocks. If the partitioning depth of the coding block is k, the partitioning depth of the sub-coding blocks is k+1.

[0092] On the other hand, for a plurality of coding blocks with a division depth of k+1, a coding block with a division depth of k can be called a higher-order coding block.

[0093] A partition type of a current coding block may be determined based on at least one of a partition shape of an upper coding block or a partition type of an adjacent coding block, where the adjacent coding block is adjacent to the current coding block and may include at least one of an upper adjacent block, a left adjacent block, or an adjacent block adjacent to an upper left corner of the current coding block, where the partition type may include at least one of whether to perform quadtree partitioning, whether to perform binary tree partitioning, a binary tree partitioning direction, whether to perform ternary tree partitioning, or a ternary tree partitioning direction.

[0094] To determine the partition shape of the coding block, information indicating whether the coding block is partitioned can be signaled via the bitstream. The information is a 1-bit flag "split_cu_flag", which indicates that the coding block is partitioned using a multi-tree partitioning technique if the flag is true.

[0095] If 'split_cu_flag' is true, information indicating whether the coding block has been quadtree split can be signaled via the bitstream, which is a 1-bit flag 'split_qt_flag', and if the flag is true, the coding block may be split into 4 blocks.

[0096] For example, in the example shown in Fig. 5, the coding tree unit is quadtree-divided to generate four coding blocks with a division depth of 1. Note that the diagram illustrates the application of quadtree division to the first and fourth coding blocks among the four coding blocks generated as a result of the quadtree division. Finally, four coding blocks with a division depth of 2 can be generated.

[0097] In addition, by applying quadtree partitioning again to a coding block with a partition depth of 2, a coding block with a partition depth of 3 can be generated.

[0098] If quadtree partitioning has not been applied to the coding block, it may be determined whether to perform binary tree partitioning or ternary tree partitioning on the coding block by considering at least one of the following: the size of the coding block, whether the coding block is located on the boundary of the image, the maximum partition depth, or the partition shape of the neighboring blocks. If it is determined to perform binary tree partitioning or ternary tree partitioning on the coding block, information indicating a partitioning direction may be signaled via a bitstream. The information may be a one-bit flag "mtt_split_cu_vertical_flag". Based on the flag, it may be determined whether the partitioning direction is vertical or horizontal. It is to be noted that information indicating whether binary tree partitioning or ternary tree partitioning is applied to the coding block may be signaled via a bitstream. The information may be a one-bit flag "mtt_split_cu_binary_flag". Based on the flag, it may be determined whether binary tree partitioning or ternary tree partitioning is applied to the coding block.

[0099] For example, in the example shown in Fig. 5, vertical binary tree partitioning is applied to a coding block with a partition depth of 1. Of the coding blocks generated as a result of the partitioning, vertical ternary tree partitioning is applied to the left coding block, and vertical binary tree partitioning is applied to the right coding block.

[0100] Inter prediction is a predictive coding mode that predicts a current block using information of a previous image. For example, a block in the previous image at the same position as the current block (hereinafter, referred to as a collocated block) can be used as a prediction block for the current block. Hereinafter, a prediction block generated based on a block that is located at the same position as the current block is referred to as a collocated prediction block.

[0101] On the other hand, if an object in the previous image moves to another position in the current image, the current block can be effectively predicted based on the object's motion. For example, if the moving direction and size of the object can be understood by comparing the previous image with the current image, a predicted block (or predicted image) of the current block can be generated taking into account the object's motion information. Hereinafter, the predicted block generated using the motion information can be referred to as a motion predicted block.

[0102] A residual block can be generated by subtracting the predictive block from the current block. In this case, in the presence of target motion, the energy of the residual block can be reduced by using a motion predictive block instead of a co-located predictive block, improving the compression performance of the residual block.

[0103] As described above, a process of generating a prediction block using motion information may be called motion compensated prediction. In most inter predictions, a prediction block may be generated based on motion compensated prediction.

[0104] The motion information may include at least one of a motion vector, a reference image index, a prediction direction, or a bidirectional weight index. The motion vector represents the moving direction and size of an object. The reference image index specifies a reference image of the current block among a plurality of reference images included in a reference image list. The prediction direction indicates one of unidirectional L0 prediction, unidirectional L1 prediction, or bidirectional prediction (L0 prediction and L1 prediction). At least one of the motion information in the L0 direction or the motion information in the L1 direction can be used based on the prediction direction of the current block. The bidirectional weight index specifies a weight applied to the L0 prediction block and a weight applied to the L1 prediction block.

[0105] FIG. 6 is a flowchart illustrating an inter prediction method according to an embodiment of the present invention.

[0106] Referring to FIG. 6, the inter prediction method includes a step of determining an inter prediction mode of a current block (S601), a step of obtaining motion information of the current block based on the determined inter prediction mode (S602), and a step of performing motion compensation prediction on the current block based on the obtained motion information (S603).

[0107] Here, the inter prediction mode represents a number of techniques for determining motion information of the current block, and may include an inter prediction mode using translation motion information and an inter prediction mode using affine motion information. For example, the inter prediction mode using translation motion information may include a merge mode and an advanced motion vector prediction mode. The inter prediction mode using affine motion information may include an affine merge mode and an affine motion vector prediction mode. According to the inter prediction mode, the motion information of the current block may be determined based on information analyzed from a neighboring block or a bitstream adjacent to the current block.

[0108] The inter prediction method using affine motion information will now be described in detail.

[0109] FIG. 7 is a diagram illustrating the nonlinear movement of an object.

[0110] The motion of an object in a video may be nonlinear. For example, as shown in the example of FIG. 7, nonlinear motion of an object may occur, such as camera zoom-in, zoom-out, rotation, or affine transformation. When nonlinear motion of an object occurs, the motion of the object cannot be effectively represented by a translational motion vector. Therefore, in the part where nonlinear motion of an object occurs, affine motion is used instead of translational motion, thereby improving coding efficiency.

[0111] FIG. 8 is a flow chart illustrating an affine motion based inter prediction method according to an embodiment of the present invention.

[0112] According to the information analyzed from the bitstream, it can determine whether to apply an affine motion-based inter prediction technique to the current block. Specifically, it can determine whether to apply an affine motion-based inter prediction technique to the current block according to at least one of a flag indicating whether to apply an affine merge mode to the current block or a flag indicating whether to apply an affine motion vector prediction mode to the current block.

[0113] When applying an affine motion-based inter prediction technique to a current block, an affine motion model of the current block can be determined (S801). The affine motion model may be determined by at least one of a six-parameter affine motion model or a four-parameter affine motion model. The six-parameter affine motion model represents affine motion with six parameters, and the four-parameter affine motion model represents affine motion with four parameters.

[0114] Equation 1 is a case where affine motion is expressed by six parameters. The affine motion represents the translational motion of a given region determined by an affine seed vector.

number

[0115] When affine motion is represented by six parameters, complex motion can be represented, but the number of bits required for coding each parameter increases, which reduces coding efficiency. Therefore, affine motion can also be represented by four parameters. Equation 2 is the case when affine motion is represented by four parameters.

number

[0116] Information for determining an affine motion model of a current block may be coded and signaled via a bitstream. For example, the information may be a 1-bit flag "affine_type_flag". When the value of the flag is 0, it indicates that a 4-parameter affine motion model is applied. When the value of the flag is 1, it indicates that a 6-parameter affine motion model is applied. The flag may be coded in units of slices, image blocks, or blocks (e.g., coding blocks or coding tree units). When a flag is transmitted using a signal at a slice level, the affine motion model determined at the slice level may be applied to all blocks belonging to the slice.

[0117] Alternatively, an affine motion model of the current block may be determined based on an affine inter prediction mode of the current block. For example, when an affine merge mode is applied, an affine motion model of the current block may be determined as a four-parameter motion model. On the other hand, when an affine motion vector prediction mode is applied, information for determining an affine motion model of the current block may be coded and signaled via a bitstream. For example, when an affine motion vector prediction mode is applied to the current block, an affine motion model of the current block may be determined based on a 1-bit flag "affine_type_flag".

[0118] Next, an affine seed vector for the current block may be derived (S802). If a four-parameter affine motion model is selected, motion vectors may be derived at two control points of the current block. However, if a six-parameter affine motion model is selected, motion vectors may be derived at three control points of the current block. The motion vectors at the control points may be referred to as affine seed vectors. The control points may include at least one of the top left corner, the top right corner, or the bottom left corner of the current block.

[0119] FIG. 9 is a diagram showing examples of affine seed vectors for each affine motion model.

[0120] In a four-parameter affine motion model, an affine seed vector related to two of the upper left corner, the upper right corner, or the lower left corner can be derived. For example, as shown in the example of FIG. 9(a), when a four-parameter affine motion model is selected, an affine vector can be derived using an affine seed vector sv0 related to the upper left corner of the current block (e.g., the upper left sample (x0, y0)) and an affine seed vector sv1 related to the upper right corner of the current block (e.g., the upper right sample (x1, y1)). Also, instead of the affine seed vector related to the upper left corner, an affine seed vector related to the lower left corner can be used. Or, instead of the affine seed vector related to the upper right corner, an affine seed vector related to the lower left corner can be used.

[0121] In the six-parameter affine motion model, affine seed vectors related to the upper left corner, the upper right corner, and the lower left corner can be derived. For example, as shown in the example of FIG. 9B, when the six-parameter affine motion model is selected, the affine vector can be derived using the affine seed vector sv0 related to the upper left corner of the current block (e.g., the upper left sample (x0, y0)), the affine seed vector sv1 related to the upper right corner of the current block (e.g., the upper right sample (x1, y1)), and the affine seed vector sv2 related to the upper left corner of the current block (e.g., the upper left sample (x2, y2)).

[0122] In the embodiment described below, in the four-parameter affine motion model, the affine seed vectors of the top-left control point and the top-right control point are referred to as the first affine seed vector and the second affine seed vector, respectively. In the embodiment described below that uses the first affine seed vector and the second affine seed vector, at least one of the first affine seed vector and the second affine seed vector can be replaced with the affine seed vector of the bottom-left control point (the third affine seed vector) or the affine seed vector of the bottom-right control point (the fourth affine seed vector).

[0123] In the six-parameter affine motion model, the affine seed vectors of the top-left control point, the top-right control point, and the bottom-left control point are referred to as the first affine seed vector, the second affine seed vector, and the third affine seed vector, respectively. In an embodiment using the first affine seed vector, the second affine seed vector, and the third affine seed vector, described below, at least one of the first affine seed vector, the second affine seed vector, and the third affine seed vector can be replaced with the affine seed vector of the bottom-right control point (fourth affine seed vector).

[0124] The affine seed vector can be used to derive affine vectors according to different sub-blocks (S803), where the affine vectors represent translational motion vectors derived based on the affine seed vectors. The affine vectors of a sub-block can be called affine sub-block motion vectors or sub-block motion vectors.

[0125] FIG. 10 is a diagram showing an example of affine vectors of sub-blocks in a four-parameter motion model.

[0126] The affine vector of the sub-block can be derived based on the control point position, the sub-block position, and the affine seed vector. For example, Equation 3 shows an example of derivation of the affine sub-block vector.

number

[0127] In the above formula 3, (x, y) represents the position of a sub-block. Here, the position of the sub-block represents the position of a reference sample included in the sub-block. The reference sample may be a sample located at the upper left corner of the sub-block, or at least one sample located at a central position in the x-axis or y-axis coordinate. (x0, y0) represents the position of the first control point, and (sv0x, sv0y) represents the first affine seed vector. Note that (x1, y1) represents the position of the second control point, and (sv1x, sv1y) represents the second affine seed vector.

[0128] If the first and second control points correspond to the upper left and upper right corners of the current block, respectively, x1-x0 may be set to a value equal to the width of the current block.

[0129] Then, motion compensation prediction may be performed for each subblock using the affine vector of each subblock (S804). After performing motion compensation prediction, a prediction block for each subblock may be generated. The prediction block of the subblock may be set as the prediction block of the current block.

[0130] Next, the inter prediction method using translational motion information will be described in detail.

[0131] The motion information of the current block may be derived from the motion information of another block of the current block. Here, the other block may be a block that is preferentially encoded / decoded by inter prediction rather than the current block. A merge mode may be defined as a case where the motion information of the current block is the same as the motion information of another block. Also, a motion vector prediction mode may be defined as a case where the motion vector of the other block is set as a predicted value of the motion vector of the current block.

[0132] FIG. 11 is a flow chart illustrating a process of deriving motion information for a current block in merge mode.

[0133] Merge candidates for a current block may be derived (S1101). The merging candidates for the current block are derived from a block that is before the current block and that is coded / decoded using inter prediction.

[0134] FIG. 12 is a diagram showing examples of candidate blocks for deriving merging candidates.

[0135] The candidate block may include at least one of an adjacent block including samples adjacent to the current block or a non-adjacent block including samples not adjacent to the current block. Hereinafter, a sample for determining the candidate block is designated as a reference sample. Note that a reference sample adjacent to the current block is called an adjacent reference sample, and a reference sample not adjacent to the current block is called a non-adjacent reference sample.

[0136] The neighboring reference sample may be included in the neighboring column of the leftmost column of the current block or the neighboring row of the topmost row of the current block. For example, if the coordinates of the top left sample of the current block are (0,0), one of the block including the reference sample at the (-1,H-1) position, the block including the reference sample at the (W-1,-1) position, the block including the reference sample at the (W,-1) position, the block including the reference sample at the (-1,H) position, or the block including the reference sample at the (-1,-1) position may be used as a candidate block. As shown in the drawing, the neighboring blocks with indexes 0 to 4 may be used as candidate blocks.

[0137] The non-adjacent reference sample represents a sample having at least one of the x-axis distance or y-axis distance from a reference sample adjacent to the current block having a predefined value. For example, one of a block including a reference sample having a predefined x-axis distance from a left reference sample, a block including a non-adjacent sample having a predefined y-axis distance from an upper reference sample, or a block including a non-adjacent sample having predefined x-axis and y-axis distances from an upper left reference sample can be used as a candidate block. The predefined value may be an integer such as 4, 8, 12, 16, etc. As shown in the drawing, at least one of blocks having indexes from 5 to 26 can be used as a candidate block.

[0138] A non-adjacent reference sample may be a sample that is not located on the same vertical, horizontal, or diagonal line as an adjacent reference sample.

[0139] FIG. 13 is a diagram showing the positions of the reference samples.

[0140] As shown in the example of Fig. 13, the x coordinate of the upper non-adjacent reference sample may be set to be different from the x coordinate of the upper adjacent reference sample. For example, when the position of the upper adjacent reference sample is (W-1, -1), the position of the upper non-adjacent reference sample that is N away from the upper adjacent reference sample along the y axis may be ((W / 2)-1, -1-N), and the position of the upper non-adjacent reference sample that is 2N away from the upper adjacent reference sample along the y axis may be (0, -1-2N). That is, the position of the non-adjacent reference sample may be determined based on the position of the adjacent reference sample and the distance from the adjacent reference sample.

[0141] Hereinafter, among the candidate blocks, a candidate block including adjacent reference samples will be referred to as an adjacent block, and a block including non-adjacent reference samples will be referred to as a non-adjacent block.

[0142] If the distance between the current block and the candidate block is equal to or greater than a threshold, the candidate block may be set as unavailable as a merging candidate. The threshold may be determined according to the size of the coding tree unit. For example, the threshold may be the height of the coding tree unit (ctu_height) or a value obtained by adding or subtracting an offset value to the height of the coding tree unit (e.g., ctu_height ± N). The offset value N is a value predefined in the encoder and decoder, and may be 4, 8, 16, 32, or ctu_height.

[0143] If the difference value between the y-axis coordinate of the current block and the y-axis coordinate of a sample included in the candidate block is greater than a threshold, the candidate block may be determined to be unavailable as a merging candidate.

[0144] Alternatively, a candidate block that does not belong to the same coding tree unit as the current block can be set as unavailable as a merging candidate, for example, if the reference sample is beyond the upper boundary of the coding tree unit to which the current block belongs, the candidate block containing the reference sample can be set as unavailable as a merging candidate.

[0145] When the upper boundary of the current block is adjacent to the upper boundary of a coding tree unit, if multiple candidate blocks are set as unavailable as merge candidates, the encoding / decoding efficiency of the current block will be reduced. To solve the above problem, the number of candidate blocks located above the current block can be made greater than the number of candidate blocks located to the left of the current block by setting the candidate blocks.

[0146] FIG. 14 is a diagram showing examples of candidate blocks for deriving merging candidates.

[0147] 14, the candidate blocks can be an upper block belonging to the N block rows above the current block and a left block belonging to the M block rows to the left of the current block. In this case, by making M larger than N, the number of left candidate blocks can be made larger than the number of above candidate blocks.

[0148] For example, the difference between the y-axis coordinate of a reference sample in the current block and the y-axis coordinate of an upper block that can be used as a candidate block can be set to N times the height of the current block or less, while the difference between the x-axis coordinate of a reference sample in the current block and the x-axis coordinate of a left block that can be used as a candidate block can be set to M times the width of the current block or less.

[0149] For example, in the example shown in FIG. 14, the blocks belonging to the two block columns above the current block and the blocks belonging to the five block columns to the left of the current block are set as candidate blocks.

[0150] As another example, if a candidate block does not belong to the same coding tree unit as the current block, a merging candidate can be derived instead of the candidate block using a block that belongs to the same coding tree unit as the current block or a block that contains reference samples adjacent to the boundary of the coding tree unit.

[0151] FIG. 15 is a diagram showing an example of a change in the position of the reference sample.

[0152] If a reference sample is included in a different coding tree unit from the current block and the reference sample is not adjacent to the boundary of the coding tree unit, a candidate block reference sample can be determined using a reference sample adjacent to the boundary of the coding tree unit instead of the reference sample.

[0153] For example, in the examples shown in Figures 15(a) and 15(b), when the upper boundary of the current block and the upper boundary of the coding tree unit touch each other, the reference samples above the current block belong to a coding tree unit different from the current block, and the samples adjacent to the upper boundary of the coding tree unit can replace the reference samples that do not adjacent to the upper boundary of the coding tree unit among the reference samples that belong to a coding tree unit different from the current block.

[0154] For example, as shown in the example of FIG. 15(a), the reference sample at position 6 is replaced with a sample located at position 6' of the upper boundary of the coding tree unit. As shown in the example of FIG. 15(b), the reference sample at position 15 is replaced with a sample located at position 15' of the upper boundary of the coding tree unit. In this case, the y coordinate of the replacement sample may be changed to an adjacent position of the coding tree unit, and the x coordinate of the replacement sample may be set to be the same as the reference sample. For example, the sample at position 6' may have the same x coordinate as the sample at position 6, and the sample at position 15' may have the same x coordinate as the sample at position 15.

[0155] Alternatively, the x-coordinate of the replacement sample may be obtained by adding or subtracting an offset value to or from the x-coordinate of the reference sample. For example, if the x-coordinates of an adjacent reference sample and a non-adjacent reference sample located above the current block are the same, the x-coordinate of the replacement sample may be obtained by adding or subtracting an offset value to or from the x-coordinate of the reference sample. The purpose is to prevent a replacement sample for a non-adjacent reference sample from being in the same position as other non-adjacent or adjacent reference samples.

[0156] FIG. 16 is a diagram showing an example of a change in the position of the reference sample.

[0157] When replacing a reference sample that is located at the boundary of a coding tree unit and is included in a coding tree unit different from the current block and is not adjacent to the boundary of the coding tree unit, the value obtained by adding or subtracting an offset value to the x coordinate of the reference sample can be used as the x coordinate of the replacement sample.

[0158] For example, in the example shown in Figure 16, the reference sample at position 6 and the reference sample at position 15 may be replaced with a sample at position 6' and a sample at position 15', respectively, that have the same y coordinate as the row adjacent to the upper boundary of the coding tree unit. In this case, the x coordinate of the sample at position 6' may be set to have a difference value of W / 2 from the x coordinate of the reference sample at position 6, and the x coordinate of the sample at position 15' may be set to have a difference value of W-1 from the x coordinate of the reference sample at position 15.

[0159] Different from the examples shown in Figures 15 and 16, the y coordinate of the row located above the top row of the current block or the y coordinate of the upper boundary of the coding tree unit may further be set as the y coordinate of the replacement sample.

[0160] Although not shown, a sample to replace the reference sample may be determined based on the left boundary of the coding tree unit. For example, if the reference sample is not included in the same coding tree unit as the current block and is not adjacent to the left boundary of the coding tree unit, the reference sample may be replaced with a sample adjacent to the left boundary of the coding tree unit. In this case, the replacement sample may have the same y coordinate as the reference sample, or may have a y coordinate obtained by adding or subtracting an offset value to the y coordinate of the reference sample.

[0161] Subsequently, the blocks containing the replacement samples are taken as candidate blocks, based on which merging candidates for the current block can be derived.

[0162] Merging candidates can also be derived from temporally neighboring blocks in a different image than the current block, for example, from collocated blocks in a collocated image.

[0163] The motion information of the merging candidate may be set to be the same as the motion information of the candidate block, for example, at least one of the motion vector, the reference image index, the prediction direction, or the bidirectional weight index of the candidate block may be the motion information of the merging candidate.

[0164] A merge candidate list including merge candidates may be generated (S1102). The merge candidates may be classified into adjacent merge candidates derived from adjacent blocks adjacent to the current block and non-adjacent merge candidates derived from non-adjacent blocks.

[0165] Indices of the merge candidates in the merge candidate list may be assigned according to a predetermined order. For example, indices assigned to adjacent merge candidates may have lower values ​​than indices assigned to non-adjacent merge candidates. Alternatively, an index may be assigned to each merge candidate based on the index of each block shown in FIG. 12 or FIG. 14.

[0166] If the merge candidate list includes multiple merge candidates, at least one of the multiple merge candidates may be selected (S1103). In this case, information indicating whether motion information of the current block is derived from an adjacent merge candidate may be signaled via the bitstream. The information may be a 1-bit flag. For example, a syntax element isAdjancentMergeFlag indicating whether motion information of the current block is derived from an adjacent merge candidate may be signaled via the bitstream. If the syntax element isAdjancentMergeFlag has a value of 1, the motion information of the current block may be derived based on the adjacent merge candidate. On the other hand, if the syntax element isAdjancentMergeFlag has a value of 0, the motion information of the current block may be derived based on a non-adjacent merge candidate.

[0167] Table 1 shows a syntax table including the syntax element isAdjancentMergeFlag. [Table 1(1)]

[0168] [Table 1(2)]

[0169] Information for specifying one of the multiple merging candidates may be signaled via the bitstream, for example, information indicating an index of one of the merging candidates included in the merging candidate list may be signaled via the bitstream.

[0170] When isAdjacentMergeflag is 1, a signal may be used to transmit a syntax element merge_idx for determining one of the adjacent merge candidates. The maximum value of the syntax element merge_idx may be a value whose difference value from the number of adjacent merge candidates is 1.

[0171] If isAdjacentMergeflag is 0, the signal may be used to send a syntax element NA_merge_idx for determining one of the non-adjacent merge candidates. The syntax element NA_merge_idx indicates a value obtained by subtracting the index of the non-adjacent merge candidate from the number of adjacent merge candidates. The decoder may select the non-adjacent merge candidate by adding the number of adjacent merge candidates to the index based on NA_merge_idx.

[0172] If the number of merging candidates included in the merging candidate list is less than a threshold, merging candidates included in the inter motion information list may be added to the merging candidate list, where the threshold may be the maximum number of merging candidates included in the merging candidate list or the maximum number of merging candidates minus an offset value. The offset value may be an integer such as 1 or 2. The inter motion information list may include merging candidates derived based on blocks encoded / decoded before the current block.

[0173] The inter motion information list includes merge candidates derived from blocks encoded / decoded based on inter prediction in a current image. For example, the motion information of the merge candidates included in the inter motion information list may be set to be equal to the motion information of the blocks encoded / decoded based on inter prediction. Here, the motion information may include at least one of a motion vector, a reference image index, a prediction direction, or a bidirectional weight index. For convenience of interpretation, the merge candidates included in the inter motion information list are referred to as inter merge candidates.

[0174] When a merge candidate for the current block is selected, the motion vector of the merge candidate is set as an initial motion vector. In addition, the motion compensation prediction of the current block can be performed by adding or subtracting an offset vector to or from the initial motion vector. Deriving a new motion vector by adding or subtracting an offset vector to or from the motion vector of the merge candidate may be defined as a merge motion differential coding method.

[0175] Information indicating whether the merge offset coding method is used may be signaled via the bitstream. The information may be a 1-bit flag, merge_offset_vector_flag. For example, a value of merge_offset_vector_flag of 1 indicates that the merge motion differential coding method is applied to the current block. When the merge motion differential coding method is applied to the current block, the motion vector of the current block may be derived by adding or subtracting an offset vector to or from the motion vector of the merge candidate. A value of merge_offset_vector_flag of 0 indicates that the merge motion differential coding method is not applied to the current block. When the merge offset coding method is not applied, the motion vector of the merge candidate may be used as the motion vector of the current block.

[0176] It can be signaled only when the value of the skip flag indicating whether to apply the skip mode is true or the value of the merge flag indicating whether to apply the merge mode is true. For example, when the value of the skip_flag indicating whether to apply the skip mode to the current block is 1 or the value of the merge_flag indicating whether to apply the merge mode to the current block is 1, the merge_offset_vector_flag can be coded and signaled.

[0177] If it is determined that the merge offset encoding method is applied to the current block, at least one of information specifying one of the merge candidates included in the merge candidate list, information indicating the magnitude of the offset vector, and information indicating the direction of the offset vector can be separately signaled.

[0178] Information may be signaled via the bitstream to determine the maximum number of merge candidates that may be included in a merge candidate list, for example, the maximum number of merge candidates that may be included in a merge candidate list may be 6 or a smaller integer.

[0179] When it is determined that the merge offset coding method is applied to the current block, only a predetermined maximum number of merge candidates can be set as the initial motion vector of the current block. That is, the number of merge candidates available for the current block can be adaptively determined based on whether the merge offset coding method is applied. For example, when the value of merge_offset_vector_flag is set to 0, the maximum number of merge candidates available for the current block can be set to M. When the value of merge_offset_vector_flag is set to 1, the maximum number of merge candidates available for the current block can be set to N. Here, M represents the maximum number of merge candidates included in the merge candidate list, and N represents an integer equal to or less than M.

[0180] For example, if M is 6 and N is 2, two merging candidates with the smallest indexes among the merging candidates included in the merging candidate list may be set as available for the current block. Thus, the motion vector of the merging candidate with index value 0 or the motion vector of the merging candidate with index value 1 may be set as the initial motion vector of the current block. If M and N are the same (e.g., M and N are 2), all merging candidates included in the merging candidate list may be set as available for the current block.

[0181] Alternatively, it may be determined whether the neighboring blocks are available as merge candidates based on whether the merge motion differential coding method is applied to the current block. For example, if the value of merge_offset_vector_flag is 1, at least one of the neighboring blocks adjacent to the upper right corner, the lower left corner, and the lower left corner of the current block may be set as unavailable as merge candidates. Therefore, when the merge motion differential coding method is applied to the current block, at least one motion vector of the neighboring blocks adjacent to the upper right corner, the lower left corner, and the lower left corner of the current block may not be set as an initial motion vector. Alternatively, if the value of merge_offset_vector_flag is 1, the temporal neighboring blocks of the current block may be set as unavailable as merge candidates.

[0182] When applying the merge motion differential coding method to the current block, at least one of the paired merge candidate and the zero merge candidate may be set to not be used. Thus, when the value of merge_offset_vector_flag is 1, at least one of the paired merge candidate or the zero merge candidate may not be added to the merge candidate list even if the number of merge candidates included in the merge candidate list is less than the maximum number.

[0183] The motion vector of the merge candidate may be set as an initial motion vector of the current block. In this case, if there are multiple merge candidates available for the current block, information specifying any one of the multiple merge candidates may be signaled via the bitstream. For example, if the maximum number of merge candidates included in the merge candidate list is greater than 1, information merge_idx indicating any one of the multiple merge candidates may be signaled via the bitstream. That is, in the merge offset encoding method, a merge candidate may be specified by information merge_idx for specifying any one of the multiple merge candidates. The initial motion vector of the current block may be set as the motion vector of the merge candidate indicated by merge_idx.

[0184] On the other hand, when the number of merge candidates available for the current block is one, signaling of information for specifying a merge candidate may be omitted. For example, when the maximum number of merge candidates that can be included in the merge candidate list is one or less, signaling of information merge_idx for specifying a merge candidate may be omitted. That is, in the merge offset encoding method, when one merge candidate is included in the merge candidate list, encoding of information merge_idx for specifying a merge candidate may be omitted, and an initial motion vector may be determined based on the merge candidate included in the merge candidate list. The motion vector of the merge candidate may be set as the initial motion vector of the current block.

[0185] As another example, after determining the merge candidate for the current block, it may be determined whether to apply the merge motion differential coding method to the current block. For example, if the maximum number of merge candidates that can be included in the merge candidate list is greater than 1, information merge_idx for specifying any one of the merge candidates may be signaled. After selecting the merge candidate based on merge_idx, decoding may be performed on merge_offset_vector_flag, which indicates whether to apply the merge motion differential coding method to the current block. Table 2 illustrates a syntax table according to the above embodiment. [Table 2(1)]

[0186] [Table 2(2)]

[0187] As another example, after determining merge candidates for the current block, it may be determined whether to apply the merge motion differential coding method to the current block only if the determined merge candidate index is smaller than the maximum number of merge candidates available when applying the merge motion differential coding method. For example, only if the value of index information merge_idx is less than N, it may be coded and signaled for merge_offset_vector_flag, which indicates whether to apply the merge motion differential coding method to the current block. If the value of index information merge_idx is equal to or greater than N, coding for merge_offset_vector_flag may be omitted. If coding for merge_offset_vector_flag is omitted, it may be determined that the merge motion differential coding method is not applied to the current block.

[0188] Alternatively, after determining a merge candidate for the current block, it may be determined whether to apply the merge motion differential coding method to the current block, taking into consideration whether the determined merge candidate has bidirectional motion information or unidirectional motion information. For example, only if the value of the index information merge_idx is less than N and the merge candidate selected based on the index information has bidirectional motion information, a merge_offset_vector_flag indicating whether to apply the merge motion differential coding method to the current block may be coded and signaled. Optionally, only if the value of the index information merge_idx is less than N and the merge candidate selected based on the index information has unidirectional motion information, a merge_offset_vector_flag indicating whether to apply the merge motion differential coding method to the current block may be coded and signaled.

[0189] Alternatively, it may be determined whether to apply the merge motion differential coding method based on at least one of the size of the current block, the shape of the current block, and whether the current block touches a boundary of a coding tree unit. If at least one of the size of the current block, the shape of the current block, and whether the current block touches a boundary of a coding tree unit does not satisfy a predetermined condition, coding of merge_offset_vector_flag, which indicates whether to apply the merge motion differential coding method to the current block, may be omitted.

[0190] When selecting a merging candidate, the motion vector of the merging candidate may be set as the initial motion vector of the current block. Then, the offset vector may be determined by decoding information indicating the magnitude of the offset vector and information indicating the direction of the offset vector. The offset vector may have a horizontal component or a vertical component.

[0191] The information indicating the magnitude of the offset vector may be index information indicating one of the motion magnitude candidates. For example, index information distance_idx indicating one of the motion magnitude candidates may be signaled via a bitstream. Table 3 shows the binarization of the index information distance_idx and the value of the variable DistFromMergeMV for determining the magnitude of the offset vector based on distance_idx. [Table 3]

[0192] The magnitude of the offset vector can be derived by dividing the variable DistFromMergeMV by a predetermined value. Equation 4 shows an example of determining the magnitude of the offset vector.

number

[0193] According to Equation 4, the value obtained by dividing the variable DistFromMegeMV by 4 or the value obtained by shifting the variable DistFromMergeMV by 2 to the left can be set as the magnitude of the offset vector.

[0194] More or fewer motion magnitude candidates may be used than the example shown in Table 3, or the range of motion vector offset magnitude candidates may be set differently than the example shown in Table 3. For example, the magnitude of the horizontal or vertical component of the offset vector may be less than or equal to two sample distances. Table 4 shows the binarization of the index information distance_idx and the value of the variable DistFromMergeMV for determining the magnitude of the offset vector based on distance_idx. [Table 4]

[0195] Alternatively, the range of motion vector offset magnitude candidates may be set differently based on the motion vector precision. For example, if the motion vector precision of the current block is fractional-pel, the value of the variable DistFromMergeMV corresponding to the value of the index information distance_idx may be 1, 2, 4, 8, 16, etc. Here, the fractional pel includes at least one of 1 / 16 pixel, 1 / 8 pixel (octo-pel), 1 / 4 pixel (quarter-pel), or 1 / 2 pixel (half-pel). On the other hand, if the motion vector precision of the current block is integer pixel, the value of the variable DistFromMergeMV corresponding to the value of the index information distance_idx may be 4, 8, 16, 32, 64, etc. That is, the table for determining the variable DistFromMergeMV may be set differently based on the motion vector precision of the current block.

[0196] For example, when the motion vector precision of the current block or merging candidate is 1 / 4 pixel, the variable DistFromMergeMV represented by distance_idx can be derived using Table 3. On the other hand, when the motion vector precision of the current block or merging candidate is integer pixel, the value of the variable DistFromMergeMV represented by distance_idx in Table 3 can be multiplied by N (for example, 4 times) to obtain a value as the value of the variable DistFromMergeMV.

[0197] Information for determining the motion vector accuracy can be signaled via the bitstream. For example, information can be sent by a signal at a sequence level, an image level, a slice level, or a block level. Thus, the range of motion magnitude candidates can be set differently based on the information related to the motion vector accuracy signaled via the bitstream. Alternatively, the motion vector accuracy can be determined based on the merging candidate of the current block. For example, the motion vector accuracy of the current block can be set to be the same as the motion vector accuracy of the merging candidate.

[0198] Alternatively, information for determining a search range of an offset vector may be signaled via a bitstream. At least one of the number of motion magnitude candidates, the minimum value of the motion magnitude candidates, and the maximum value of the motion magnitude candidates may be determined based on the search range. For example, a flag for determining a search range of an offset vector, merge_offset_vector_flag, may be signaled via a bitstream. The information may be signaled via a sequence header, a picture header, or a slice header.

[0199] For example, if the value of merge_offset_extend_range_flag is 0, the magnitude of the offset vector can be 2 or less. Thus, the maximum value of DistFromMergeMV can be 8. On the other hand, if the value of merge_offset_extend_range_flag is 1, the magnitude of the offset vector can be 32 sample distances. Thus, the maximum value of DistFromMergeMV can be 128.

[0200] A flag indicating whether the magnitude of the offset vector is greater than a threshold may be used to determine the magnitude of the offset vector. For example, a flag distance_flag indicating whether the magnitude of the offset vector is greater than a threshold may be signaled via the bitstream. The threshold may be 1, 2, 4, 8, or 16. For example, when distance_flag is 1, it indicates that the magnitude of the offset vector is greater than 4. On the other hand, when distance_flag is 0, it indicates that the magnitude of the offset vector is equal to or less than 4.

[0201] If the magnitude of the offset vector is greater than the threshold, the index information distance_idx can be used to derive a difference value between the magnitude of the offset vector and the threshold. Alternatively, if the magnitude of the offset vector is equal to or less than the threshold, the index information distance_idx can be used to determine the magnitude of the offset vector. Table 5 shows a syntax table of the process of encoding distance_flag and distance_idx. [Table 5(1)]

[0202] [Table 5(2)]

[0203] Equation 5 shows an example of deriving a variable DistFromMergeMV for determining the magnitude of the offset vector using distance_flag and distance_idx.

number

[0204] In Equation 5, the value of distance_flag can be 1 or 0. The value of distance_idx can be 1, 2, 4, 8, 16, 32, 64, 128, etc. N represents a factor determined by a threshold. For example, if the threshold is 4, N can be 16.

[0205] The information indicating the direction of the offset vector may be index information indicating one of vector direction candidates. For example, index information direction_idx indicating one of the vector direction candidates may be signaled via a bit stream. Table 6 shows the binarization of the index information direction_idx and the direction of the offset vector according to the direction_idx. [Table 6]

[0206] In Table 6, sign[0] indicates the horizontal direction, and sign[1] indicates the vertical direction. +1 indicates that the value of the x or y component of the offset vector is a positive number (+), and -1 indicates that the value of the x or y component of the offset vector is a negative number (-). Equation 6 shows an example of determining an offset vector based on the magnitude and direction of the offset vector.

number

[0207] In Equation 6, offsetMV[0] indicates the vertical component of the offset vector, and offsetMV[1] indicates the horizontal component of the offset vector.

[0208] FIG. 17 is a diagram showing offset vectors based on the values ​​of distance_idx, which indicates the magnitude of the offset vector, and direction_idx, which indicates the direction of the offset vector.

[0209] In the example shown in FIG. 7, the magnitude and direction of the offset vector may be determined based on the values ​​of distance_idx and direction_idx. The maximum magnitude of the offset vector may be set to be equal to or less than a threshold, where the threshold may have a value predefined by the encoder and decoder. For example, the threshold may be a distance of 32 samples. Alternatively, the threshold may be determined based on the magnitude of the initial motion vector. For example, a horizontal threshold may be set based on the magnitude of the horizontal component of the initial motion vector, and a vertical threshold may be set based on the vertical component of the initial motion vector.

[0210] When a merge candidate has bidirectional motion information, the L0 motion vector of the merge candidate can be the L0 initial motion vector of the current block, and the L1 motion vector of the merge candidate can be the L1 initial motion vector of the current block. In this case, the L0 offset vector and the L1 offset vector can be determined by considering the output order difference value (hereinafter referred to as the L0 difference value) between the L0 reference image of the merge candidate and the current image, and the output order difference value (hereinafter referred to as the L1 difference value) between the L1 reference image of the merge candidate and the current image.

[0211] First, if the symbols of the L0 differential value and the L1 differential value are the same, the L0 offset vector and the L1 offset vector can be set to be the same, whereas if the symbols of the L0 differential value and the L1 differential value are different, the L1 offset vector can be set in a direction opposite to that of the L0 offset vector.

[0212] The magnitude of the L0 offset vector and the magnitude of the L1 offset vector can be set to be the same, or alternatively, the magnitude of the L1 offset vector can be determined by shrinking the L0 offset vector based on the L0 difference value and the L1 difference value.

[0213] For example, Equation 7 shows the L0 offset vector and the L1 offset vector when the symbols of the L0 difference value and the L1 difference value are the same.

number

[0214] In Equation 7, offsetMVL0[0] indicates the horizontal component of the L0 offset vector, offsetMVL0[1] indicates the vertical component of the L0 offset vector, offsetMVL1[0] indicates the horizontal component of the L1 offset vector, and offsetMVL1[1] indicates the vertical component of the L1 offset vector.

[0215] Equation 8 shows the L0 offset vector and the L1 offset vector when the symbols of the L0 differential value and the L1 differential value are different.

number

[0216] It is also possible to define four or more vector direction candidates. Tables 7 and 8 show examples of defining eight vector direction candidates. [Table 7] [Table 8]

[0217] In Tables 7 and 8, if the absolute values ​​of sign[0] and sign[1] are greater than 0, it indicates that the offset vector is in the diagonal direction. When Table 6 is used, the magnitude of the x-axis component and the y-axis component of the diagonal offset vector is abs(offsetMV), and when Table 7 is used, the magnitude of the x-axis component and the y-axis component of the diagonal offset vector is abs(offsetMV / 2).

[0218] FIG. 18 is a diagram showing offset vectors based on the values ​​of distance_idx, which indicates the magnitude of the offset vector, and direction_idx, which indicates the direction of the offset vector.

[0219] FIG. 18(a) is an example in which Table 6 is applied, and FIG. 18(b) is an example in which Table 7 is applied.

[0220] Information for determining at least one of the number or magnitude of vector direction candidates may be signaled via the bitstream. For example, a flag merge_offset_direction_range_flag for determining vector direction candidates may be signaled via the bitstream. The flag may be transmitted by a signal at the sequence level, image level, or slice level. For example, when the value of the flag is 0, the four vector direction candidates shown in Table 6 may be used. On the other hand, when the value of the flag is 1, the eight vector direction candidates shown in Table 7 or Table 8 may be used.

[0221] Alternatively, at least one of the number or magnitude of the vector direction candidates may be determined based on the magnitude of the offset vector. For example, when the value of the variable DistFromMergeMV for determining the magnitude of the offset vector is equal to or less than a threshold, the eight vector direction candidates shown in Table 7 or Table 8 may be used. On the other hand, when the value of the variable DistFromMergeMV is greater than the threshold, the four vector direction candidates shown in Table 6 may be used.

[0222] Alternatively, at least one of the number or magnitude of the vector direction candidates can be determined based on the value MVx of the x component and the value MVy of the y component of the initial motion vector. For example, when the difference or the absolute value of the difference between MVx and MVy is equal to or less than a threshold, the eight vector direction candidates shown in Table 7 or Table 8 can be used. On the other hand, when the difference or the absolute value of the difference between MVx and MVy is greater than the threshold, the four vector direction candidates shown in Table 6 can be used.

[0223] The motion vector of the current block can be derived by adding the initial motion vector to the offset vector. Equation 9 shows an example of determining the motion vector of the current block.

number

[0224] In Equation 9, mvL0 indicates the L0 motion vector of the current block, and mvL1 indicates the L1 motion vector of the current block. mergeMVL0 indicates the L0 initial motion vector of the current block (i.e., the L0 motion vector of the merge candidate), and mergeMVL1 indicates the L1 initial motion vector of the current block. [0] indicates the horizontal component of the motion vector, and [1] indicates the vertical component of the motion vector.

[0225] Intra prediction is to predict a current block using reconstructed samples that have been coded / decoded around the current block. In this case, the intra prediction of the current block can use reconstructed samples before applying an in-loop filter.

[0226] The intra prediction technique includes intra prediction based on a matrix and general intra prediction considering the directionality with surrounding reconstructed samples. Information indicating the intra prediction technique of the current block may be signaled via the bitstream. The information may be a 1-bit flag. Alternatively, the intra prediction technique of the current block may be determined based on at least one of the position, size, shape, or intra prediction techniques of the neighboring blocks of the current block. For example, if the current block is located across an image boundary, the current block is set to not apply intra prediction based on a matrix.

[0227] Matrix-based intra prediction is a method of obtaining a prediction block of a current block based on matrix multiplication of a matrix stored in an encoder and a decoder with a reconstructed sample around the current block. Information indicating one of a plurality of stored matrices can be signaled via a bitstream. The decoder can determine a matrix to be used for intra prediction of the current block based on the information and the size of the current block.

[0228] General intra prediction is a method of obtaining a predicted block related to a current block based on a non-angular intra prediction mode or an angular intra prediction mode.

[0229] A residual image can be derived by subtracting the original image from the predicted image. In this case, when the residual image is transformed into the frequency domain, removing high frequency components from the frequency components does not significantly degrade the subjective image quality of the video. Therefore, reducing the value of the high frequency components or setting the value of the high frequency components to 0 has the effect of improving compression efficiency without causing obvious visual distortion. In order to reflect the above characteristics, the residual image can be decomposed into two-dimensional frequency components by transforming the current block. The transformation can be performed using a transformation technique such as a Discrete Cosine Transform (DCT) or a Discrete Sine Transform (DST).

[0230] After transforming the current block using DCT or DST, a transformation can be performed again on the transformed current block. In this case, the transformation based on DCT or DST is defined as a first transformation, and the process of performing a transformation again on the block to which the first transformation has been applied is called a second transformation.

[0231] The first transform may be performed using any one of a number of candidate transform kernels, for example, the first transform may be performed using any one of DCT2, DCT8, or DCT7.

[0232] Different transform kernels can also be used for the horizontal and vertical directions. Information representing a combination of horizontal and vertical transform kernels can also be signaled via the bitstream.

[0233] The execution units of the first transform and the second transform are different. For example, the first transform can be performed on an 8×8 block, and the second transform can be performed on a sub-block of the transformed 8×8 block that has a size of 4×4. In this case, the transform coefficients of the surplus area where the second transform is not performed can be set to 0.

[0234] Alternatively, a first transform can be performed on a 4x4 block and a second transform can be performed on a region of size 8x8 that contains the transformed 4x4 block.

[0235] Information can be signaled via the bitstream indicating whether or not to perform a second transformation.

[0236] In the decoder, the inverse transform (second inverse transform) of the second transform can be performed, and the inverse transform (first inverse transform) of the first transform can be performed on the result. As a result of performing the second inverse transform and the first inverse transform, a residual signal of the current block can be obtained.

[0237] Quantization is used to reduce the energy of a block, and the quantization process involves dividing the transform coefficients by a certain constant, which may be derived from a quantization parameter, which may be defined as a value between 1 and 63.

[0238] After performing the transform and quantization in the encoder, the decoder can obtain the residual block by inverse quantization and inverse transform. At the decoder, the predictive block and the residual block can be added to obtain a reconstructed block of the current block.

[0239] Once a reconstructed block of the current block is obtained, in-loop filtering can be performed to reduce information loss that occurs in the quantization and encoding processes. The in-loop filter may include at least one of a deblocking filter, a sample adaptive offset filter (SAO), or an adaptive loop filter (ALF).

[0240] It is within the scope of the present invention to use the embodiments described with emphasis on a decoding or encoding process in an encoding or decoding process. It is also within the scope of the present invention to modify the embodiments described in a given order in a different order than that described.

[0241] Although the embodiments have been described based on a series of steps or flow charts, this does not limit the time order of the invention. Furthermore, the steps may be executed simultaneously or in a different order, as necessary. In the above embodiments, each of the components (e.g., units, modules, etc.) constituting the block diagrams may be realized as a hardware device or software. Furthermore, a plurality of components may be combined and executed as a single hardware device or software. The embodiments may be executed in the form of program instructions. The program instructions may be executed by various computer components and recorded on a computer-readable storage medium. The computer-readable storage medium may include program instructions, data files, data structures, etc., alone or in combination. Examples of computer-readable storage media may include magnetic media such as hard disks, flexible disks, and magnetic tapes, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, and hardware devices that are specifically arranged in a manner to store and execute program instructions, such as ROMs, RAMs, flash memories, etc. The hardware devices may be configured to operate as one or more software modules to execute the processes according to the present invention, or vice versa. [Industrial Applicability]

[0242] The present invention is applicable to electronic devices that perform encoding / decoding on video.

Claims

1. 1. A video decoding method, comprising: generating a merge candidate list for the current block; designating a merge candidate for the current block from among the merge candidates included in the merge candidate list; deriving an offset vector for the current block; deriving a motion vector of the current block by adding the motion vector of the merging candidate to the offset vector; the magnitude of the offset vector is determined based on first index information specifying one of the motion magnitude candidates; At least one of the maximum value and the minimum value of the motion magnitude candidate is set to be different based on a value of a flag indicating a range of the motion magnitude candidate; A video decoding method, wherein a range of motion vector offset magnitude candidates is set differently based on the motion vector accuracy of the current block, and the flag is signaled at a picture level.

2. The magnitude of the offset vector is obtained by applying a shift operation to a value represented by the motion magnitude candidate designated by the first index information. The video decoding method of claim 1.

3. The direction of the offset vector is determined based on second index information that designates one of vector direction candidates. The video decoding method of claim 1.

4. If the motion vector precision of the current block is a sub-pixel, the value of the variable corresponding to the value of the index information is 1, 2, 4, 8 or 16; or When the motion vector precision of the current block is integer pixels, the value of the variable corresponding to the value of the index information is set to 4, 8, 16, 32, or 64. The video decoding method of claim 1.

5. The sub-pixel is a 1 / 4 pixel. The video decoding method of claim 4.

6. The information for determining the motion vector accuracy is signaled at the picture level in the bitstream. The video decoding method of claim 1.

7. 1. A video encoding method, comprising: generating a merge candidate list for the current block; selecting a merging candidate for the current block from among the merging candidates included in the merging candidate list; deriving an offset vector for the current block; deriving a motion vector of the current block by adding the motion vector of the merging candidate to the offset vector; The method further includes a step of encoding first index information, the first index information being for specifying a motion magnitude candidate having a magnitude of the offset vector among a plurality of motion magnitude candidates; 11. The video encoding method, further comprising the step of: encoding a flag indicating a range of the motion magnitude candidates, wherein based on a value of the encoded flag, at least one of a maximum value or a minimum value of the motion magnitude candidates is set to be different, and a range of motion vector offset magnitude candidates is set to be different based on the motion vector accuracy of the current block, and the flag is signaled at a picture level.

8. The video encoding method further includes a step of encoding second index information, the second index information being for specifying a vector direction candidate indicating a direction of the offset vector among a plurality of vector direction candidates.

8. The video encoding method of claim 7.

9. 11. A video decoding device comprising: an inter predictor configured to generate a merge candidate list for a current block, specify a merge candidate for the current block from among the merge candidates included in the merge candidate list, derive an offset vector for the current block, and derive a motion vector for the current block by adding a motion vector of the merge candidate to the offset vector, wherein a magnitude of the offset vector is determined based on first index information specifying one of motion magnitude candidates, at least one of a maximum value or a minimum value of the motion magnitude candidates is set to be different based on a value of a flag indicating a range of the motion magnitude candidates, a range of motion vector offset magnitude candidates is set to be different based on a motion vector accuracy of the current block, and the flag is signaled at a picture level.

Images