KR20230063314A - Method for encoding/decoding a video signal and recording medium storing a bitsteram generated based on the method - Google Patents

Abstract

An image decoding method according to the present disclosure includes determining whether Geometry Partitioning with Merge mode (GPM) is applied to a current block, and when it is determined that the GPM is applied to the current block, a partition type for the current block. Determining, obtaining motion information of each of the first prediction unit and the second prediction unit in the current block, and based on the motion information of each of the first prediction unit and the second prediction unit, the current block Obtaining a prediction block for . In this case, the obtaining of the motion information may include determining whether merge mode with motion vector difference (MMVD) is applied to each of the first prediction unit and the second prediction unit.

Description

Video signal encoding/decoding method and recording medium for storing a bitstream generated based thereon

The present disclosure relates to a video signal encoding/decoding method and a recording medium storing a bitstream generated based thereon.

As display panels become larger and larger, higher quality video services are increasingly required. The biggest problem of high-definition video service is the large increase in the amount of data, and in order to solve this problem, research to improve video compression rate is being actively conducted. 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) formed a Joint Collaborative Team on Video Coding (JCT-VC). JCT-VC proposed HEVC (High Efficiency Video Coding), which is a video compression standard having compression performance about twice that of H.264/AVC, and was approved as a standard on January 25, 2013. With the rapid development of high-definition video services, the performance of HEVC is gradually revealing its limitations.

The present disclosure provides a method of predicting a block based on a merge mode involving geometric segmentation in encoding/decoding a video signal.

The present disclosure provides a method of modifying a motion vector using an offset vector when a merge mode involving geometric segmentation is applied in encoding/decoding a video signal.

The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below. You will be able to.

An image decoding method according to the present disclosure includes determining whether Geometry Partitioning with Merge mode (GPM) is applied to a current block, and when it is determined that the GPM is applied to the current block, a partition type for the current block. Determining, obtaining motion information of each of the first prediction unit and the second prediction unit in the current block, and based on the motion information of each of the first prediction unit and the second prediction unit, the current block Obtaining a prediction block for . In this case, the obtaining of the motion information may include determining whether merge mode with motion vector difference (MMVD) is applied to each of the first prediction unit and the second prediction unit.

An image encoding method according to the present disclosure includes determining whether Geometry Partitioning with Merge mode (GPM) is applied to a current block, and when it is determined that the GPM is applied to the current block, a partition type for the current block. Determining, obtaining motion information of each of the first prediction unit and the second prediction unit in the current block, and based on the motion information of each of the first prediction unit and the second prediction unit, the current block Obtaining a prediction block for . In this case, the obtaining of the motion information may include determining whether merge mode with motion vector difference (MMVD) is applied to each of the first prediction unit and the second prediction unit.

In the method for encoding/decoding a video signal according to the present disclosure, the obtaining of the motion information may include selecting a first merge candidate for the first prediction unit based on a first merge index; The method may include selecting a second merge candidate for the second prediction unit based on the index.

In the video signal encoding/decoding method according to the present disclosure, whether the MMVD is applied to the first prediction unit is determined based on a result of comparing the index of the first merge candidate with a threshold value, and the second Whether or not the MMVD is applied to the prediction unit may be determined based on a result of comparing the index of the second merge candidate with a threshold value.

In the video signal encoding/decoding method according to the present disclosure, the first merge index is signaled through a bitstream, while the second merge index is applied to both the first prediction unit and the second prediction unit. It may be selectively signaled based on whether MMVD is applied.

In the video signal encoding/decoding method according to the present disclosure, when the signaling of the second merge index is omitted, a default value or a value obtained by adding or subtracting an offset from the first merge index is inferred as the second merge index It can be.

In the video signal encoding/decoding method according to the present disclosure, when the MMVD is applied to both the first prediction unit and the second prediction unit, the signaling of the second merge index is omitted, and the second merge candidate may be set identically to the first merge candidate.

In the video signal encoding/decoding method according to the present disclosure, the MMVD is assigned to one of the first prediction unit and the second prediction unit according to a comparison result of the index of the first merge candidate and the index of the second merge candidate. may be applied.

In the video signal encoding/decoding method according to the present disclosure, when the index of the first merge candidate is smaller than the index of the second merge candidate, the MMVD is applied to the first prediction unit, and the second merge candidate When the index is smaller than the index of the first merge candidate, the MMVD may be applied to the second prediction unit.

In the video signal encoding/decoding method according to the present disclosure, the number of merge candidates indicated by the first merge index may be different between a case where MMVD is applied to the first prediction unit and a case where MMVD is not applied. .

In the video signal encoding/decoding method according to the present disclosure, when MMVD is applied to the first prediction unit, a motion vector of the first prediction unit is obtained by adding a first offset vector to a motion vector of the first merge candidate , and when MMVD is applied to the second prediction unit, the motion vector of the second prediction unit is derived by adding a second offset vector to the motion vector of the first merge candidate, and the first offset vector And the second offset vector may be determined based on separate index information.

In the video signal encoding/decoding method according to the present disclosure, when the first offset vector and the second offset vector are the same, the first merge candidate is different from the second merge candidate, and the first offset vector and the second merge candidate are different. When the second offset vectors are different, the first merge candidate and the second merge candidate may be the same.

The features briefly summarized above with respect to the disclosure are merely exemplary aspects of the detailed description of the disclosure that follows, and do not limit the scope of the disclosure.

According to the present disclosure, block prediction accuracy can be improved by using a merge mode involving geometric segmentation.

According to the present disclosure, when a merge mode involving geometric segmentation is applied, prediction accuracy of a block can be improved by modifying a motion vector using an offset vector.

Effects obtainable in the present disclosure are not limited to the effects mentioned above, and other effects not mentioned may be clearly understood by those skilled in the art from the description below. will be.

1 is a block diagram of an image encoder (encoder) according to an embodiment of the present disclosure.
2 is a block diagram of an image decoder (decoder) according to an embodiment of the present disclosure.
3 is a diagram illustrating a basic coding tree unit according to an embodiment of the present disclosure.
4 is a diagram illustrating various division types of a coding block.
5 is a diagram illustrating a splitting aspect of a coding tree unit.
6 is a flowchart of an inter prediction method according to an embodiment of the present disclosure.
7 is a flowchart of a process of deriving motion information of a current block under merge mode.
8 is an exemplary diagram illustrating merge candidate blocks.
9 is a diagram illustrating types of dividing lines dividing a coding block.
10 is a flowchart of an intra prediction method according to an embodiment of the present disclosure.
11 is a diagram illustrating intra prediction modes.
12 shows locations of neighboring blocks used to derive an intra prediction mode of a current block.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

Encoding and decoding of an image is performed in units of blocks. For example, encoding/decoding processing such as transform, quantization, prediction, in-loop filtering, or restoration may be performed on a coding block, a transform block, or a prediction block.

Hereinafter, a block to be encoded/decoded will be referred to as a 'current block'. For example, the current block may represent a coding block, a transform block, or a prediction block according to a current encoding/decoding process.

In addition, the term 'unit' used in this specification may be understood to denote a basic unit for performing a specific encoding/decoding process, and 'block' to denote a sample array of a predetermined size. Unless otherwise specified, 'block' and 'unit' may be used in the same sense. For example, in an embodiment to be described later, a coding block and a coding unit may be understood to have mutually equivalent meanings.

1 is a block diagram of an image encoder (encoder) according to an embodiment of the present disclosure.

Referring to FIG. 1 , an image encoding apparatus 100 includes a picture division unit 110, prediction units 120 and 125, a transform 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.

Each component shown in FIG. 1 is shown independently to represent different characteristic functions in the video encoding device, and does not mean that each component is made of separate hardware or a single software component. That is, each component is listed and included as each component for convenience of explanation, and at least two components of each component can be combined to form one component, or one component can be divided into a plurality of components to perform a function, and each of these components can be divided into a plurality of components. Integrated embodiments and separated embodiments of components are also included in the scope of the present disclosure unless departing from the essence of the present disclosure.

In addition, some of the components may be optional components for improving performance rather than essential components that perform essential functions in the present disclosure. The present disclosure may be implemented by including only components essential to implement the essence of the present disclosure, excluding components used for performance improvement, and a structure including only essential components excluding optional components used for performance enhancement. Also included in the scope of the present disclosure.

The picture division unit 110 may divide an input picture 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 picture divider 110 divides one picture into a plurality of combinations of coding units, prediction units, and transformation units, and combines one coding unit, prediction unit, and transformation unit according to a predetermined criterion (eg, a cost function). You can encode a picture by selecting .

For example, one picture may be divided into a plurality of coding units. In order to divide coding units in a picture, a recursive tree structure such as a quad tree structure can be used. Coding that is divided into different coding units with one image or largest coding unit as the root A unit may be divided with as many child nodes as the number of divided coding units. A coding unit that is not further divided according to a certain limit becomes a leaf node. That is, when it is assumed that only square division is possible for one coding unit, one coding unit can be divided into up to four different coding units.

Hereinafter, in an embodiment of the present disclosure, a coding unit may be used as a unit for performing encoding or a unit for performing decoding.

The prediction unit may be divided into at least one square or rectangular shape having the same size within one coding unit, and one of the prediction units divided within one coding unit predicts another prediction unit. It may be divided to have a shape and/or size different from the unit.

When generating a prediction unit for performing intra prediction based on a coding unit, if the coding unit is not a minimum coding unit, intra prediction may be performed without dividing into a plurality of prediction units NxN.

The prediction units 120 and 125 may include the inter prediction unit 120 performing inter prediction and the intra prediction unit 125 performing intra prediction. It is possible to determine whether to use inter prediction or intra prediction for a prediction unit, and determine specific information (eg, intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. In this case, a processing unit in which prediction is performed and a processing unit in which a prediction method and specific details are determined may be different. For example, a prediction method and a prediction mode may be determined in a prediction unit, and prediction may be performed in a transformation unit. A residual value (residual block) between the generated prediction block and the original block may be input to the transform unit 130 . In addition, prediction mode information and motion vector information used for prediction may be encoded in the entropy encoder 165 together with residual values and transmitted to the decoder. When a specific encoding mode is used, it is also possible to encode an original block as it is and transmit it to a decoder without generating a prediction block through the prediction units 120 and 125 .

The inter-prediction unit 120 may predict a prediction unit based on information on at least one picture among pictures before or after the current picture, and in some cases, prediction based on information on a partially coded region within the current picture. Units can also be predicted. The inter prediction unit 120 may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

The reference picture interpolator may receive reference picture information from the memory 155 and generate pixel information of an integer pixel or less in the reference picture. In the case of luminance pixels, a DCT-based 8-tap interpolation filter with different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/4 pixels. In the case of a color difference signal, a DCT-based 4-tap interpolation filter with different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/8 pixels.

The motion predictor may perform motion prediction based on the reference picture interpolated by the reference picture interpolator. As a method for calculating the motion vector, various methods such as Full search-based Block Matching Algorithm (FBMA), Three Step Search (TSS), and New Three-Step Search Algorithm (NTS) may be used. The motion vector may have a motion vector value in units of 1/2 or 1/4 pixels based on interpolated pixels. The motion prediction unit may predict the current prediction unit by using a different motion prediction method. Various methods such as a skip method, a merge method, an advanced motion vector prediction (AMVP) method, and an intra block copy method may be used as motion prediction methods.

The intra prediction unit 125 may generate a prediction unit based on reference pixel information around the current block, which is pixel information in the current picture. If a block adjacent to the current prediction unit is a block on which inter prediction is performed, and the reference pixel is a pixel on which inter prediction is performed, the reference pixel of the block on which intra prediction is performed surrounding the reference pixel included in the block on which inter prediction is performed information can be used instead. That is, when a reference pixel is unavailable, information on the unavailable reference pixel may be replaced with at least one reference pixel among available reference pixels.

In intra prediction, a prediction mode may include a directional prediction mode in which reference pixel information is used according to a prediction direction and a non-directional prediction mode in which directional information is not used during prediction. A mode for predicting luminance information and a mode for predicting chrominance information may be different, and intra prediction mode information or predicted luminance signal information used to predict luminance information may be used to predict chrominance information.

When intra prediction is performed, if the size of the prediction unit and the size of the transformation unit are the same, intra prediction of the prediction unit is based on the pixel on the left, the top left, and the top of the prediction unit. can be performed. However, when performing intra prediction, when the size of a prediction unit and the size of a transformation unit are different, intra prediction may be performed using a reference pixel based on the transformation unit. In addition, intra prediction using NxN division may be used only for the smallest coding unit.

In the intra prediction method, a prediction block may be generated after applying an adaptive intra smoothing (AIS) filter to a reference pixel according to a prediction mode. The type of AIS filter applied to the reference pixel may be different. In order to perform the intra prediction method, the intra prediction mode of the current prediction unit may be predicted from the intra prediction modes of prediction units existing around the current prediction unit. When predicting the prediction mode of the current prediction unit using the mode information predicted from the neighboring prediction unit, if the intra-prediction mode of the current prediction unit and the neighboring prediction unit are identical, the current prediction unit and the neighboring prediction unit use predetermined flag information It is possible to transmit information that the prediction modes of are the same, and if the prediction modes of the current prediction unit and the neighboring prediction unit are different, entropy encoding may be performed to encode the prediction mode information of the current block.

In addition, a residual block may be generated that includes residual information that is a difference between a prediction unit performed prediction based on the prediction unit generated by the prediction units 120 and 125 and an original block of the prediction unit. The generated residual block may be input to the transform unit 130 .

The transform unit 130 transforms the original block and the residual block including the residual information of the prediction unit generated through the predictor units 120 and 125 into DCT (Discrete Cosine Transform) or DST (Discrete Sine Transform). method can be used to transform. Here, the DCT conversion core includes at least one of DCT2 and DCT8, and the DST conversion core includes DST7. Whether to apply DCT or DST to transform the residual block may be determined based on intra prediction mode information of a prediction unit used to generate the residual block. Transformation on the residual block may be skipped. A flag representing whether or not to skip transformation of a residual block may be encoded. Transform skipping may be allowed for residual blocks whose size is less than or equal to the threshold, luma components, or chroma components under the 4:4:4 format.

The quantization unit 135 may quantize the values converted to the frequency domain by the transform unit 130 . A quantization coefficient may change according to a block or an importance of an image. The value calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the rearrangement unit 160 .

The rearrangement unit 160 may rearrange the coefficient values for the quantized residual values.

The reordering unit 160 may change a 2D block-type coefficient into a 1-D vector form through a coefficient scanning method. For example, the reordering unit 160 may scan DC coefficients to high-frequency coefficients using a zig-zag scan method and change them into a one-dimensional vector form. Depending on the size of the transform unit and the intra prediction mode, instead of zig-zag scan, a vertical scan for scanning 2D block-type coefficients in a column direction and a horizontal scan for scanning 2-dimensional block-type coefficients in a row direction may be used. That is, it is possible to determine which scan method among zig-zag scan, vertical scan, and horizontal scan is used according to the size of the transform unit and the intra prediction mode.

The entropy encoding unit 165 may perform entropy encoding based on the values calculated by the reordering unit 160 . Entropy encoding may use various encoding methods such as, for example, exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC).

The entropy encoding unit 165 receives residual value coefficient information and block type information of a coding unit from the reordering unit 160 and the prediction units 120 and 125, prediction mode information, division unit information, prediction unit information and transmission unit information, motion Various information such as vector information, reference frame information, block interpolation information, and filtering information can be encoded.

The entropy encoding unit 165 may entropy-encode the coefficient value of the coding unit input from the reordering unit 160 .

The inverse quantization unit 140 and the inverse transform unit 145 inversely quantize the values quantized by the quantization unit 135 and inverse transform the values transformed by the transform unit 130 . The residual generated by the inverse quantization unit 140 and the inverse transform unit 145 is combined with the prediction unit predicted through the motion estimation unit, the motion compensation unit, and the intra prediction unit included in the prediction units 120 and 125 and restored. You can create a Reconstructed Block.

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

The deblocking filter can remove block distortion caused by a boundary between blocks in a reconstructed picture. In order to determine whether to perform deblocking, it may be determined whether to apply the deblocking filter to the current block based on pixels included in several columns or rows included in the block. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, when vertical filtering and horizontal filtering are performed, horizontal filtering and vertical filtering may be processed in parallel.

The offset correction unit may correct an offset of the deblocked image from the original image in units of pixels. In order to perform offset correction for a specific picture, pixels included in the image are divided into a certain number of areas, then the area to be offset is determined and the offset is applied to the area, or the offset is performed considering the edge information of each pixel method can be used.

Adaptive Loop Filtering (ALF) may be performed based on a value obtained by comparing the filtered reconstructed image with the original image. After dividing the pixels included in the image into predetermined groups, filtering may be performed differentially for each group by determining one filter to be applied to the corresponding group. Information related to whether or not to apply ALF may be transmitted for each coding unit (CU) of a luminance signal, and the shape and filter coefficients of an ALF filter to be applied may vary according to each block. In addition, the ALF filter of the same form (fixed form) may be applied regardless of the characteristics of the block to be applied.

The memory 155 may store a reconstructed block or picture calculated through the filter unit 150, and the stored reconstructed block or picture may be provided to the predictors 120 and 125 when inter prediction is performed.

2 is a block diagram of an image decoder (decoder) according to an embodiment of the present disclosure.

Referring to FIG. 2 , the image decoder 200 includes an entropy decoding unit 210, a rearrangement unit 215, an inverse quantization unit 220, an inverse transform unit 225, a prediction unit 230 and 235, a filter unit ( 240), memory 245 may be included.

When a video bitstream is input from the video encoder, the input bitstream may be decoded by a procedure opposite to that of the video encoder.

The entropy decoding unit 210 may perform entropy decoding by a procedure opposite to that performed by the entropy encoding unit of the image encoder. For example, various methods such as exponential Golomb, CAVLC (Context-Adaptive Variable Length Coding), and CABAC (Context-Adaptive Binary Arithmetic Coding) may be applied corresponding to the method performed by the image encoder.

The entropy decoding unit 210 may decode information related to intra prediction and inter prediction performed by the encoder.

The rearrangement unit 215 may perform rearrangement based on a method in which the encoding unit rearranges the entropy-decoded bitstream in the entropy decoding unit 210 . Coefficients expressed in the form of one-dimensional vectors may be reconstructed into coefficients in the form of two-dimensional blocks and rearranged. The rearrangement unit 215 may perform rearrangement through a method of receiving information related to the coefficient scanning performed by the encoder and performing reverse scanning based on the scanning order performed by the corresponding encoder.

The inverse quantization unit 220 may perform inverse quantization based on the quantization parameter provided by the encoder and the rearranged coefficient value of the block.

The inverse transform unit 225 may perform inverse transform, that is, inverse DCT or inverse DST, on the transform, that is, DCT or DST, performed by the transform unit on the quantization result performed by the video encoder. Here, the DCT conversion core may include at least one of DCT2 or DCT8, and the DST conversion core may include DST7. Alternatively, when transform is skipped in the video encoder, the inverse transform unit 225 may also not perform inverse transform. Inverse transformation may be performed based on the transmission unit determined by the video encoder. In the inverse transform unit 225 of the video decoder, a transform technique (eg, DCT or DST) may be selectively performed according to a plurality of pieces of information such as a prediction method, a size of a current block, and a prediction direction.

The prediction units 230 and 235 may generate a prediction block based on information related to prediction block generation provided from the entropy decoding unit 210 and previously decoded block or picture information provided from the memory 245 .

As described above, when intra prediction is performed in the same way as the operation in the video encoder, when the size of the prediction unit and the size of the transformation unit are the same, the pixel existing on the left, the pixel existing on the upper left, and the pixel existing on the upper side of the prediction unit are the same. Intra prediction is performed on a prediction unit based on a pixel to perform intra prediction, but when performing intra prediction, when the size of the prediction unit and the size of the transformation unit are different, intra prediction is performed using a reference pixel based on the transformation unit. can In addition, intra prediction using NxN division may be used only for the smallest coding unit.

The prediction units 230 and 235 may include a prediction unit determining unit, an inter prediction unit, and an intra prediction unit. The prediction unit determination unit receives various 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, classifies the prediction unit from the current coding unit, and predicts It is possible to determine whether a unit performs inter prediction or intra prediction. The inter-prediction unit 230 uses information necessary for inter-prediction of the current prediction unit provided from the video encoder to make current prediction based on information included in at least one picture among pictures before or after the current picture including the current picture. Inter prediction can be performed on units. Alternatively, inter prediction may be performed based on information of a pre-reconstructed partial region in the current picture including the current prediction unit.

In order to perform inter prediction, the motion prediction method of the prediction unit included in the corresponding coding unit based on the coding unit is skip mode, merge mode, motion vector prediction mode (AMVP mode), intra block copy It is possible to determine which of the modes is used.

The intra prediction unit 235 may generate a prediction block based on pixel information in the current picture. When the prediction unit is a prediction unit that has undergone intra prediction, intra prediction may be performed based on intra prediction mode information of the prediction unit provided by the video encoder. The intra predictor 235 may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a part that performs filtering on reference pixels of the current block, and can be applied by determining whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering may be performed on reference pixels of the current block using the prediction mode of the prediction unit and AIS filter information provided by the image encoder. When the prediction mode of the current block is a mode in which AIS filtering is not performed, AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a pixel value obtained by interpolating the reference pixel, the reference pixel interpolator may interpolate the reference pixel to generate a reference pixel in pixel units having an integer value or less. When the prediction mode of the current prediction unit is a prediction mode for generating a prediction block without interpolating reference pixels, the reference pixels may not be interpolated. The DC filter may generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit 240 . The filter unit 240 may include a deblocking filter, an offset correction unit, and an ALF.

Information on whether a deblocking filter is applied to a corresponding block or picture and, when a deblocking filter is applied, information on whether a strong filter or a weak filter is applied may be provided from the video coder. The deblocking filter of the video decoder receives information related to the deblocking filter provided by the video encoder, and the video decoder may perform deblocking filtering on the corresponding block.

The offset correction unit may perform offset correction on the reconstructed image based on the type and offset value information of the offset correction applied to the image during encoding.

ALF may be applied to a coding unit based on ALF application information and ALF coefficient information provided from an encoder. Such ALF information may be included in a specific parameter set and provided.

The memory 245 may store a reconstructed picture or block so that it can be used as a reference picture or reference block, and may also provide the reconstructed picture to an output unit.

3 is a diagram illustrating a basic coding tree unit according to an embodiment of the present disclosure.

A coding block of the maximum size may be defined as a coding tree block. One picture is divided into a plurality of Coding Tree Units (CTUs). A coding tree unit is a coding unit having the largest size and may be referred to as a largest coding unit (LCU). 3 illustrates an example in which one picture is divided into a plurality of coding tree units.

The size of a coding tree unit can be defined at the picture level or sequence level. To this end, information indicating the size of a coding tree unit may be signaled through a picture parameter set or a sequence parameter set.

For example, the size of a coding tree unit for all pictures in a sequence may be set to 128x128. Alternatively, either 128x128 or 256x256 may be determined as the size of the coding tree unit at the picture level. For example, in the first picture, the size of the coding tree unit may be set to 128x128, and in the second picture, the size of the coding tree unit may be set to 256x256.

Coding tree units may be split to generate coding blocks. A coding block represents a basic unit for encoding/decoding processing. For example, prediction or transformation may be performed for each coding block, or a prediction coding mode may be determined for each coding block. Here, the prediction encoding mode indicates a method of generating a prediction image. For example, the prediction coding mode includes intra prediction (Intra Prediction), inter prediction (Inter Prediction), current picture referencing (Current Picture Referencing, CPR, or Intra Block Copy (IBC)). ) or combined prediction. For the coding block, a prediction block for the coding block may be generated using at least one prediction coding mode of intra prediction, inter prediction, current picture reference, or composite prediction.

Information indicating the prediction encoding mode of the current block may be signaled through a bitstream. For example, the information may be a 1-bit flag indicating whether the prediction encoding mode is an intra mode or an inter mode. Current picture reference or composite prediction may be used only when the prediction coding mode of the current block is determined to be the inter mode.

Current picture reference is for setting a current picture as a reference picture and obtaining a prediction block of a current block from an already encoded/decoded region within the current picture. Here, the current picture means a picture including the current block. Information indicating whether current picture reference is applied to the current block may be signaled through a 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 current picture reference, and if the flag is false, the prediction mode of the current block may be determined as inter prediction.

Alternatively, the prediction coding mode of the current block may be determined based on the reference picture index. For example, when the reference picture index indicates the current picture, the prediction encoding mode of the current block may be determined as the current picture reference. When the reference picture index indicates a picture other than the current picture, the prediction coding mode of the current block may be determined as inter prediction. That is, current picture reference is a prediction method using information of a coded/decoded region within the current picture, and inter prediction is a prediction method using information of another coded/decoded picture.

Complex prediction represents a coding mode in which two or more of intra prediction, inter prediction, and current picture reference are combined. For example, when compound prediction is applied, a first prediction block may be generated based on any one of intra prediction, inter prediction, or current picture reference, and a second prediction block may be generated based on the other one. When the first prediction block and the second prediction block are generated, a final prediction block may be generated through an average operation or a weighted sum operation of the first prediction block and the second prediction block. Information indicating whether compound prediction is applied may be signaled through a bitstream. The information may be a 1-bit flag.

4 is a diagram illustrating various division types of a coding block.

A coding block may be partitioned into a plurality of coding blocks based on quad tree partitioning, binary tree partitioning or triple tree partitioning. The divided coding block may also be further divided into a plurality of coding blocks based on quad tree partitioning, bitary tree partitioning, or triple tree partitioning.

Quad tree partitioning represents a partitioning technique that divides a current block into four blocks. As a result of quad tree splitting, the current block can be split into 4 square partitions (refer to 'SPLIT_QT' in (a) of FIG. 4).

Binary tree partitioning represents a partitioning technique that divides the current block into two blocks. Splitting the current block into two blocks along the vertical direction (ie, using a vertical line that crosses the current block) can be called vertical binary tree splitting, and along the horizontal direction (ie, using a vertical line that crosses the current block). Splitting the current block into two blocks may be referred to as horizontal binary tree splitting. As a result of binary tree partitioning, the current block can be partitioned into two non-square partitions. 'SPLIT_BT_VER' in FIG. 4 shows the result of vertical binary tree splitting, and 'SPLIT_BT_HOR' in FIG. 4 shows the result of horizontal binary tree splitting.

Triple tree partitioning represents a partitioning technique that divides a current block into three blocks. Splitting the current block into three blocks along the vertical direction (ie, using two vertical lines crossing the current block) can be called vertical triple tree splitting, and along the horizontal direction (ie, using two vertical lines crossing the current block). Splitting the current block into three blocks (using two horizontal lines crossing each other) may be referred to as horizontal triple tree splitting. As a result of triple tree partitioning, the current block can be partitioned into three non-square partitions. In this case, the width/height of the partition located in the center of the current block may be twice the width/height of other partitions. In (d) of FIG. 4, 'SPLIT_TT_VER' indicates a vertical triple tree split result, and in FIG. 4 (e) 'SPLIT_TT_HOR' indicates a horizontal triple tree split result.

The number of divisions of a coding tree unit may be defined as a partitioning depth. The maximum splitting depth of a coding tree unit at the sequence or picture level may be determined. Accordingly, the maximum split depth of a coding tree unit may be different for each sequence or each feature.

Alternatively, the maximum segmentation depth for each of the segmentation techniques may be individually determined. For example, the maximum splitting depth allowed for quad tree splitting may be different from the maximum splitting depth allowed for binary tree splitting and/or triple tree splitting.

The encoder may signal information indicating at least one of a division type and a division depth of the current block through a bitstream. The decoder may determine the splitting type and splitting depth of the coding tree unit based on the information parsed from the bitstream.

5 is a diagram illustrating a splitting aspect of a coding tree unit.

Partitioning a coding block using a partitioning technique such as quad tree partitioning, binary tree partitioning, and/or triple tree partitioning may be referred to as multi-tree partitioning.

Coding blocks generated by applying multi-tree partitioning to a coding block may be referred to as lower coding blocks. When the depth of division of a coding block is k, the depth of division of lower coding blocks is set to k+1.

Conversely, for coding blocks having a split depth of k+1, a coding block having a split depth of k may be referred to as an upper coding block.

The partition type of the current coding block may be determined based on at least one of a partition type of an upper coding block or a partition type of a neighboring coding block. Here, the neighboring coding block is adjacent to the current coding block and may include at least one of an upper neighboring block, a left neighboring block, and a neighboring block adjacent to the upper left corner of the current coding block. Here, the splitting type may include at least one of quad tree splitting, binary tree splitting, binary tree splitting direction, triple tree splitting, or triple tree splitting direction.

Information indicating whether the coding block is divided may be signaled through a bitstream in order to determine the division type of the coding block. The information is a 1-bit flag 'split_cu_flag', and when the flag is true, it indicates that the coding block is split by the head tree splitting technique.

When split_cu_flag is true, information indicating whether a coding block is quad-tree split may be signaled through a bitstream. The information is a 1-bit flag split_qt_flag, and if the flag is true, the coding block can be divided into 4 blocks.

For example, in the example shown in FIG. 5 , it is illustrated that 4 coding blocks having a split depth of 1 are generated as a coding tree unit is quad-tree split. Also, it is shown that quad tree splitting is applied again to the first and fourth coding blocks among four coding blocks generated as a result of quad tree splitting. As a result, 4 coding blocks with a split depth of 2 can be generated.

In addition, by applying quad tree partitioning to a coding block having a split depth of 2, a coding block having a split depth of 3 may be generated.

When quad tree partitioning is not applied to a coding block, binary tree partitioning is performed on the coding block in consideration of at least one of the size of the coding block, whether the coding block is located on a picture boundary, the maximum partition depth, or the partition type of a neighboring block. Alternatively, it may be determined whether to perform triple tree partitioning. When it is determined that binary tree splitting or triple tree splitting is performed on the coding block, information indicating a splitting direction may be signaled through a bitstream. The information may be a 1-bit flag mtt_split_cu_vertical_flag. Based on the flag, it can be determined whether the division direction is vertical or horizontal. Additionally, information indicating whether binary tree partitioning or triple tree partitioning is applied to the coding block may be signaled through a bitstream. The information may be a 1-bit flag mtt_split_cu_binary_flag. Based on the flag, it can be determined whether binary tree splitting or triple tree splitting is applied to the coding block.

For example, in the example shown in FIG. 5, vertical binary tree splitting is applied to a coding block having a split depth of 1, and vertical triple tree splitting is applied to a left coding block among coding blocks generated as a result of the splitting, It is shown that vertical binary tree partitioning is applied to the right coding block.

Inter prediction is a prediction coding mode in which a current block is predicted using information of a previous picture. For example, a block at the same position as the current block in the previous picture (hereinafter referred to as a collocated block) may be set as a prediction block of the current block. Hereinafter, a prediction block generated based on a block at the same location as the current block will be referred to as a collocated prediction block.

On the other hand, if an object existing in the previous picture moves to a different location in the current picture, the current block can be effectively predicted using the motion of the object. For example, if the movement direction and size of an object can be known by comparing the previous picture and the current picture, a prediction block (or prediction image) of the current block may be generated in consideration of motion information of the object. Hereinafter, a prediction block generated using motion information may be referred to as a motion prediction block.

A residual block may be generated by differentiating a prediction block from the current block. At this time, if the motion of the object exists, by using the motion prediction block instead of the collocated prediction block, the energy of the residual block can be reduced and, accordingly, the compression performance of the residual block can be improved.

As described above, generating a prediction block using motion information may be referred to as motion compensated prediction. In most inter-prediction, prediction blocks can be generated based on motion-compensated prediction.

The motion information may include at least one of a motion vector, a reference picture index, a prediction direction, or a bi-directional weight index. A motion vector indicates the direction and size of an object's movement. The reference picture index specifies the reference picture of the current block among the reference pictures included in the reference picture list. The prediction direction indicates any one of unidirectional L0 prediction, unidirectional L1 prediction, or bidirectional prediction (L0 prediction and L1 prediction). According to the prediction direction of the current block, at least one of L0-direction motion information and L1-direction motion information may be used. The bi-directional weight index specifies the weight applied to the L0 prediction block and the weight applied to the L1 prediction block.

6 is a flowchart of an inter prediction method according to an embodiment of the present disclosure.

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

Here, the inter prediction mode indicates various techniques for determining the 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. there is. For example, an inter prediction mode using translational motion information may include a merge mode and a motion vector prediction mode, and an inter prediction mode using affine motion information may include an affine merge mode and an affine motion vector prediction mode. . Motion information of the current block may be determined based on information parsed from a neighboring block or a bitstream neighboring the current block according to an inter prediction mode.

The motion information may include at least one of a motion vector, a reference picture index, a prediction flag, and a bi-directional weight index. In addition, motion information may be individually induced/set for each of the L0 and L1 directions.

Here, a motion vector represents a position difference between an object in the previous picture and an object in the current picture. A previous picture may be indicated by a reference picture index.

Also, information for determining the precision of a motion vector may be signaled through a bitstream. The information may be determined in units of sequences, slices, or blocks. Motion vector precision can be set to octopels, quarter pels, half pels, integer pels, 2 integer pels, or 4 integer pels. Alternatively, according to the inter prediction mode, the motion vector precision of the current block may be determined or the number/type of available motion vector precision candidates may be adaptively determined.

Motion information of the current block may be derived from motion information of other blocks of the current block. Here, the other block may be a block encoded/decoded by inter prediction prior to the current block. Setting motion information of the current block to be the same as motion information of another block may be defined as a merge mode. In addition, setting a motion vector of another block as a predicted value of a motion vector of a current block may be defined as a motion vector prediction mode.

7 is a flowchart of a process of deriving motion information of a current block under merge mode.

A merge candidate of the current block may be derived (S701). A merge candidate of the current block may be derived from a block encoded/decoded by inter prediction prior to the current block.

In this case, a block used to derive a merge candidate may be referred to as a 'merge candidate block'. The merge candidate block may include at least one of a block adjacent to the current block (adjacent merge candidate block) or a block not adjacent to the current block (non-adjacent merge candidate block). Motion information of a merge candidate may be set based on motion information of a merge candidate block. For example, motion information of a merge candidate may be set to be the same as motion information of a merge candidate block. Alternatively, only one of the L0 motion information and the L1 motion information of the merge candidate block may be set as the motion information of the merge candidate. Alternatively, the motion vector of the merge candidate block may be derived by scaling the motion vector of the merge candidate block.

8 is an exemplary diagram illustrating merge candidate blocks.

In FIG. 8, positions of samples for determining positions of merge candidate blocks are indicated. A position of a sample for determining merge candidate blocks may be referred to as a reference position sample.

The adjacent merge candidate block includes reference position samples belonging to a row adjacent to the top of the current block or a column adjacent to the left of the current block. For example, in the example of FIG. 8 , each of blocks including reference position samples marked with indices 1 to 5 may be set as an adjacent merge candidate block.

The non-adjacent merge candidate block includes a reference position sample belonging to a row not adjacent to the top of the current block or a column not adjacent to the left of the current blog. For example, in the example of FIG. 8 , each of blocks including reference position samples specified with indexes 6 to 23 may be set as non-adjacent merge candidate blocks.

Positions of adjacent merge candidate blocks and/or non-adjacent merge candidate blocks may be previously defined in an encoder and a decoder. For example, as in the example shown in FIG. 8 , reference position samples may be set at predetermined intervals between the boundary of the current block and the boundary of the CTU. For example, at least one of the x-axis coordinate and the y-axis coordinate is a non-adjacent block spaced apart by 2 ⁿ * N from an adjacent merge candidate block (ie, a reference position sample adjacent to the current block) as a non-adjacent merge candidate block. can be defined Here, n may be a natural number such as 1, 2, or 3. For example, when the coordinates of the top-left sample of the current block are (0,0) and the adjacent merge candidate block includes the reference position sample at the (-1, -1) position, (-1-4N, -1-4N ) may be defined as non-adjacent merge candidate blocks. In this case, the maximum value of N may be determined by at least one of a distance between the current block and the maximum CTU boundary or a value predefined in the encoder and decoder.

As in the example of FIG. 8 , reference position samples may be set outside the boundary of the CTU to which the current block belongs (indexes 19 to 23 of FIG. 8 ). Accordingly, a block belonging to a CTU different from the current block may be set as a merge candidate block.

However, in order to prevent the line buffer from indiscriminately increasing, samples not adjacent to the CTU boundary may not be used as reference position samples. Accordingly, a non-adjacent block adjacent to the CTU boundary can be used as a merge candidate block, but a non-adjacent block not adjacent to the CTU boundary cannot be used as a merge candidate block.

A merge candidate list including merge candidates may be generated (S702).

Indexes of merge candidates in the merge candidate list may be allocated in a predetermined order. For example, a merge candidate derived from a left neighboring block, a merge candidate derived from an upper neighboring block, a merge candidate derived from an upper right neighboring block, a merge candidate derived from a lower left neighboring block, and a merge candidate derived from an upper left neighboring block. And indexes may be assigned in the order of merge candidates derived from temporal neighboring blocks. Alternatively, indexes may be assigned in the order of merge candidates derived from adjacent merge candidate blocks, merge candidates derived from non-adjacent merge candidate blocks, and merge candidates derived from temporal neighboring blocks.

When a plurality of merge candidates are included in the merge candidate list, at least one of the plurality of merge candidates may be selected (S703). Specifically, information for specifying one of a plurality of merge candidates may be signaled through a bitstream. For example, information merge_idx indicating an index of any one of merge candidates included in the merge candidate list may be signaled through a bitstream.

A coding block may be divided into a plurality of prediction units, and prediction may be performed on each of the divided prediction units. Here, the prediction unit represents a basic unit for performing prediction. A method of performing prediction by dividing a coding block into a plurality of prediction units may be referred to as a geometric partition mode (GPM).

A coding block may be divided using at least one dividing line. For example, a coding block may be divided using at least one of a vertical line, a horizontal line, an oblique line, or a diagonal line.

9 is a diagram illustrating types of dividing lines dividing a coding block.

The number of prediction units generated by dividing the coding block may be 2, 3, 4 or more. For convenience of explanation, in the embodiments described below, it is assumed that a coding block is divided into two prediction units, and each of the two prediction units is referred to as a first prediction unit and a second prediction unit.

Information for determining a partition type of a coding block may be signaled through a bitstream. Specifically, at least one of the number of dividing lines dividing the coding block, the angle of the dividing line, or the position of the dividing line may be determined by the above information.

For example, syntax merge_gpm_partition_idx indicating one of combination candidates of the variable angleIdx representing the angle of the dividing line and the variable distanceIdx representing the position of the dividing line may be explicitly signaled through a bitstream.

Here, the variable angleIdx may indicate one of a plurality of angle candidates, and the plurality of angle candidates may be defined as in the example shown in FIG. 9 . The variable distanceIdx may represent one of a plurality of distance candidates representing a distance from the center of the coding block to the dividing line. According to the variable distanceIdx, the coding block may be divided based on a dividing line passing through the center of the coding block or the coding block may be divided based on a dividing line not passing through the center of the coding block.

Table 1 shows an example in which different index values are assigned to respective combinations of the variable angleIdx and the variable distanceIdx.

merge_gpm_partition_idx 0 One 2 3 4 5 6 7 8 9 10 11 12 13 14 15 angleIdx 0 0 2 2 2 2 3 3 3 3 4 4 4 4 5 5 distanceIdx One 3 0 One 2 3 0 One 2 3 0 One 2 3 0 One merge_gpm_partition_idx 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 angleIdx 5 5 8 8 11 11 11 11 12 12 12 12 13 13 13 13 distanceIdx 2 3 One 3 0 One 2 3 0 One 2 3 0 One 2 3 merge_gpm_partition_idx 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 angleIdx 14 14 14 14 16 16 18 18 18 19 19 19 20 20 20 21 distanceIdx 0 One 2 3 One 3 One 2 3 One 2 3 One 2 3 One merge_gpm_partition_idx 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 angleIdx 21 21 24 24 27 27 27 28 28 28 29 29 29 30 30 30 distanceIdx 2 3 One 3 One 2 3 One 2 3 One 2 3 One 2 3

Unlike the above example, the syntax for determining the variable angleIdx representing the angle of the division line and the syntax for determining the variable distanceIdx representing the position of the division line may be separately signaled. Meanwhile, depending on the size and/or shape of a coding block, signaling of one of the two syntaxes may be omitted.

The number of angle candidates that can be indicated by the variable angleIdx and/or the number of distance candidates that can be indicated by the variable distanceIdx may be adaptively determined according to the size and/or shape of the coding block.

After dividing the coding block into a first prediction unit and a second prediction unit, motion information for each of the first prediction unit and the second prediction unit may be derived. For example, based on the merge candidate list derived based on the position and size of the coding block, a merge candidate for each of the first prediction unit and the second prediction unit is selected, and the motion of each of the first prediction unit and the second prediction unit is performed. information can be derived.

To this end, a first merge index indicating a merge candidate of the first prediction unit, eg, gpm_merge_idx0, and a second merge index, eg, gpm_merge_idx1, indicating a merge candidate of the second prediction unit may be signaled.

A merge candidate of the first prediction unit and a merge candidate of the second prediction unit may be different. Accordingly, when a merge candidate is selected by the first merge index, a merge candidate of the second prediction unit may be selected from among the remaining merge candidates excluding the merge candidates. That is, after reallocating indexes of the remaining merge candidates excluding the merge candidate indicated by the first merge index, the second merge index may be encoded to indicate one of the merge candidates having the reallocated index. As an example, as a result of reassignment, an index decreased by 1 may be assigned to merge candidates having a greater index than the merge candidate indicated by the first merge index.

In the decoding step, values of the first merge index and the second merge index may be compared to select a merge candidate of the second prediction unit. For example, when the value of the second merge index gpm_merge_idx1 is smaller than the value of the first merge index gpm_merge_idx0, a merge candidate having the value of the second merge index gpm_merge_idx1 as an index may be selected. On the other hand, when the value of the second merge index gpm_merge_idx1 is equal to or greater than the first merge index gpm_merge_idx0, a merge candidate having an index obtained by adding 1 to the second merge index gpm_merge_idx1 may be selected.

The motion information of the first merge candidate selected by the first merge index is set as the motion information of the first prediction unit, and the motion information of the second merge candidate selected by the second merge index is set as the motion information of the second prediction unit. can

Thereafter, a first prediction block may be obtained based on motion information of the first prediction unit, and a second prediction block may be obtained based on motion information of the second prediction unit. Thereafter, a final prediction block for the coding block may be obtained through a weighted sum operation of the first prediction block and the second prediction block. In this case, the weights applied to the prediction samples included in the first prediction block and the weights applied to the prediction samples included in the second prediction block may be adaptively determined according to the location of the final prediction sample.

Instead of using the merge candidate motion information as it is, the motion information of the merge candidate may be modified and the corrected motion information may be used. For example, when a merge candidate for the current block is selected, a motion vector obtained by adding or subtracting an offset vector to the motion vector of the selected merge candidate may be set as the motion vector of the current block. As described above, modifying the motion vector of the merge candidate using the offset vector may be referred to as Merge mode with Motion Vector Difference (MMVD).

Information for determining an offset vector may be signaled through a bitstream. Specifically, the syntax mvd_direction_idx indicating the direction of the offset vector and the syntax mvd_distance_idx indicating the size of the offset vector may be coded and signaled.

The syntax mvd_direction_idx represents one of a plurality of direction candidates. As an example, Table 2 shows an example in which different index values are assigned to each of a plurality of direction candidates.

mmvd_distance_idx[ x0 ][ y0 ] MmvdDistance[ x0 ][ y0 ] ph_mmvd_fullpel_only_flag = = 0 ph_mmvd_fullpel_only_flag = = One 0 One 4 One 2 8 2 4 16 3 8 32 4 16 64 5 32 128 6 64 256 7 128 512

The syntax mvd_distance_idx represents one of a plurality of distance candidates. As an example, Table 3 shows an example in which different index values are assigned to each of a plurality of distance candidates.

mmvd_direction_idx[ x0 ][ y0 ] MmvdSign[ x0 ][ y0 ][ 0 ] MmvdSign[ x0 ][ y0 ][ One ] 0 +1 0 One -One 0 2 0 +1 3 0 -One

When a direction candidate and a distance candidate are selected by the above two syntaxes, an offset vector can be derived based on Equation 1 below.

In Equation 1, MmvdOffset[x0][y0][0] represents the horizontal component of the offset vector, and MmvdOffset[x0][y0][1] represents the vertical component of the offset vector. MmvdDistance represents a value of a distance candidate selected by mvd_distance_idx, and MmvdSign represents a value of a direction candidate selected by mvd_direction_idx.

GPM mode and MMVD can be used in combination. For example, in deriving at least one of the motion information of the first prediction unit and the motion information of the second prediction unit, MMVD may be applied. That is, the motion vector of the first prediction unit or the motion vector of the second prediction unit may be derived by adding or subtracting the offset vector to the motion vector of the merge candidate.

Information indicating whether MMVD is applied under the GPM mode may be signaled through a bitstream. For example, the information may be a 1-bit flag. In addition, the information may be coded and signaled for each of the prediction units.

Table 4 shows an example in which a flag indicating whether MMVD is applied to each of the prediction units is signaled.

merge_data(　x0,　y0,　cbWidth,　cbHeight,　chType　) { Descriptor ... gpm_mmvd_flag0 ae(v) gpm_mmvd_flag1 ae(v) if (gpm_mmvd_flag0){ gpm_merge_idx0 ae(v) gpm_mmvd_idx0 ae(v) Else gpm_merge_idx0 ae(v) } if (gpm_mmvd_flag1) gpm_mmvd_idx1 ae(v) if (!gpm_mmvd_flag0) gpm_merge_idx1 ae(v) else gpm_merge_idx1 ae(v) ... }

In Table 4, syntax gpm_mmvd_flag0 indicates whether MMVD is applied to the first prediction unit. A value of 1 in the syntax gpm_mmvd_flag0 indicates that MMVD is applied to the first prediction unit. In this case, the motion vector of the first prediction unit may be derived by adding or subtracting the offset vector to the motion vector of the merge candidate. On the other hand, a value of 0 in the syntax gpm_mmvd_flag0 indicates that MMVD is not applied to the first prediction unit. In this case, the motion vector of the first prediction unit may be set equal to the motion vector of the merge candidate.

Also, syntax gpm_mmvd_flag1 indicates whether MMVD is applied to the second prediction unit. A value of 1 in the syntax gpm_mmvd_flag1 indicates that MMVD is applied to the second prediction unit. In this case, the motion vector of the second prediction unit may be derived by adding or subtracting the offset vector to the motion vector of the merge candidate. On the other hand, a value of 0 in the syntax gpm_mmvd_flag1 indicates that MMVD is not applied to the second prediction unit. In this case, the motion vector of the second prediction unit may be set equal to the motion vector of the merge candidate.

Unlike the example of Table 4, a 1-bit flag indicating whether MMVD is applied may be signaled at the coding block level. For example, at the coding block level, a syntax gpm_mmvd_flag indicating whether the MMVD mode is combined and applied to the GPM mode may be encoded and signaled.

When the value of the syntax gpm_mmvd_flag is 0, the motion vectors of each of the first prediction unit and the second prediction unit may be set equal to the motion vectors of their respective merge candidates.

A value of 1 in the syntax gpm_mmvd_flag indicates that MMVD is used in deriving a motion vector of at least one of the first prediction unit and the second prediction unit. In this case, information indicating whether MMVD is applied to each of the first prediction unit and the second prediction unit may be additionally encoded and signaled. For example, the information may be an index indicating one of a plurality of cases to which MMVD can be applied. For example, when MMVD is applied only to the first prediction unit, when MMVD is applied only to the second prediction unit, and when MMVD is applied to both the first prediction unit and the second prediction unit, different indexes are assigned to each, Information indicating one of these may be encoded and signaled.

Alternatively, the information may include a first MMVD flag indicating whether MMVD is applied to the first prediction unit and a second MMVD flag indicating whether MMVD is applied to the second prediction unit. The first MMVD flag and the second MMVD flag may be sequentially encoded/decoded. In this case, when the first MMVD flag indicates that MMVD is not applied to the first prediction unit, encoding/decoding of the second MMVD flag may be omitted and it may be determined that MMVD is applied to the second prediction unit.

Alternatively, when it is determined that MMVD is applied at the coding block level, it may be set as a default that MMVD is applied to both the first prediction unit and the second prediction unit.

Alternatively, when it is determined that MMVD is applied at the coding block level, the first prediction unit and the second prediction unit are respectively based on the index of the merge candidate for the first prediction unit and the index of the merge candidate for the second prediction unit. It may be determined whether MMVD is applied to.

For example, after comparing the index of the merge candidate for the first prediction unit with the index of the merge candidate for the second prediction unit, MMVD may be applied only to a prediction unit using a merge candidate having a small index value.

Alternatively, it may be determined whether to apply MMVD to the prediction unit by comparing the index of the merge candidate with the threshold. For example, after comparing the index of the merge candidate for the first prediction unit with the threshold value, if the index is smaller than the threshold value, MMVD may be applied to the first prediction unit. On the other hand, if the index is equal to or greater than the threshold value, it may be determined that MMVD is not applied to the first prediction unit. Similarly, after comparing the index of the merge candidate for the second prediction unit with the threshold value, if the index is smaller than the threshold value, MMVD may be applied to the second prediction unit. On the other hand, if the index is equal to or greater than the threshold value, it may be determined that MMVD is not applied to the second prediction unit.

In a case where MMVD is applied and a case where MMVD is not applied, the maximum number of merge candidates that can be selected by a prediction unit may be set differently.

For example, when MMVD is applied to the first prediction unit, one of the N merge candidates included in the merge candidate list may be selected for the first prediction unit. On the other hand, when MMVD is applied, one of two merge candidates having a small index among N merge candidates included in the merge candidate list may be selected for the first prediction unit.

The above constraints may be equally applied to the second prediction unit.

When MMVD is applied to both the first prediction unit and the second prediction unit, encoding/decoding of the second merge index gpm_merge_idx1 for the second prediction unit may be omitted. For example, in Table 4, when MMVD is applied to both the first prediction unit and the second prediction unit, encoding/decoding of the second merge index gpm_merge_idx1 is omitted. In this case, the value of the second merge index gpm_merge_idx1 may be inferred to have a value derived based on the value of the first merge index explicitly signaled through the bitstream. For example, the value of the second merge index may be inferred according to Equation 2 below.

Alternatively, when MMVD is applied only to either the first prediction unit or the second prediction unit, encoding/decoding of the merge index is omitted for the prediction unit to which MMVD is applied, and the merge index is applied only to the prediction unit to which MMVD is not applied. You can also encode/decrypt.

For example, when MMVD is applied to the first prediction unit but MMVD is not applied to the second prediction unit, encoding/decoding of the first merge index merge_gpm_idx0 is omitted while the second merge index merge_gpm_idx1 is transmitted through a bitstream. Can be explicitly signaled. In this case, a merge candidate having a default value or a value obtained by adding or subtracting an offset from the second merge index as an index may be used for the first prediction unit. Similarly, when MMVD is not applied to the first prediction unit while MMVD is applied to the second prediction unit, the first merge index merge_gpm_idx0 is explicitly signaled through the bitstream, whereas the second merge index merge_gpm_idx1 is /decryption can be omitted. In this case, a merge candidate having a default value or a value obtained by adding or subtracting an offset from the first merge index as an index may be used for the second prediction unit. Here, the default value may be an integer such as 0 or 1, and the offset may be an integer such as 1 or 2.

For a prediction unit to which MMVD is applied, information for determining an offset vector may be additionally encoded/decoded. For example, when MMVD is applied to the first prediction unit, syntax gpm_mmvd_idx0 for determining a motion vector offset vector for the first prediction unit may be encoded/decoded. Similarly, when MMVD is applied to the second prediction unit, syntax gpm_mmvd_idx1 for determining a motion vector offset vector for the second prediction unit may be encoded/decoded. Here, gpm_mmvd_idxX (X is 0 or 1) may indicate one of a plurality of offset vector candidates. Furthermore, each of the plurality of offset vector candidates may be different from each other in at least one of a direction and a distance.

Alternatively, for a prediction unit to which MMVD is applied, information indicating one of a plurality of direction candidates, eg, gpm_mmvd_direction_idxX and information indicating one of a plurality of distance candidates, eg, gpm_mmvd_distance_idxX, may be coded and signaled.

When MMVD is applied to both the first prediction unit and the second prediction unit, the first prediction unit and the second prediction unit may be set to use the same merge candidate. Table 5 is an example of a syntax structure when the first prediction unit and the second prediction unit use the same merge candidate.

merge_data(　x0,　y0,　cbWidth,　cbHeight,　chType　) { Descriptor ... gpm_mmvd_flag0 ae(v) gpm_mmvd_flag1 ae(v) if (gpm_mmvd_flag0 ==1 && gpm_mmmvd_flag1==1){ gpm_mmvd_idx0 ae(v) gpm_mmvd_idx1 ae(v) if(gpm_mmvd_idx0 != gpm_mmvd_idx1 ) { gpm_merge_idx0 ae(v) } else { gpm_merge_idx0 ae(v) gpm_merge_idx1 ae(v) } } else if (gpm_mmvd_flag0 ==1 && gpm_mmmvd_flag1==0){ gpm_mmvd_idx0 ae(v) gpm_merge_idx0 ae(v) } else { gpm_mmvd_idx1 ae(v) gpm_merge_idx1 ae(v) } } ... }

When MMVD is applied to both the first prediction unit and the second prediction unit, the merge index (ie, merge_gpm_idx0) is signaled only for the first prediction unit, and the merge index (ie, merge_gpm_idx1) is added to the second prediction unit. / may not be decrypted.

Furthermore, after determining the offset vector for the MMVD of each of the prediction units, a merge candidate of each of the prediction units may be selected. That is, as in the example of Table 5, after encoding/decoding the syntax gpm_mmvd_idxX representing the offset vector of the prediction unit, the syntax gpm_merge_idxX indicating the merge candidate of the prediction unit can be encoded/decoded.

In this case, when the offset vector for the first prediction unit and the offset vector for the second prediction unit are the same, a merge candidate different from that of the first prediction unit may be selected for the second prediction unit. To this end, when the offset vector for the first prediction unit and the offset vector for the second prediction unit are the same (ie, gpm_mmvd_idx0 and gpm_mmvd_idx1 are the same), in addition to the first merge index gpm_merge_idx0 for the first prediction unit, the second The second merge index gpm_merge_idx1 for the prediction unit may also be encoded and signaled.

Alternatively, when the offset vector for the first prediction unit and the offset vector for the second prediction unit are the same (ie, gpm_mmvd_idx0 and gpm_mmvd_idx1 are the same), encoding/decoding of the second merge index gpm_merge_idx1 for the second prediction unit is omitted. And, according to Equation 2 described above, a merge candidate of the second prediction unit may be selected.

In the examples of Tables 4 and 5, it is exemplified that after decoding the syntax gpm_mmvd_flagX indicating whether MMVD is applied to the prediction unit, the syntax gpm_merge_idxX indicating the merge candidate of the prediction unit is decoded. Unlike the example, after encoding/decoding the syntax gpm_merge_idxX indicating the merge candidate of the prediction unit, the syntax gpm_mmvd_flagX indicating whether MMVD is applied may be encoded/decoded.

In this case, information indicating whether MMVD is applied may be encoded and signaled only to a prediction unit using a merge candidate having an index smaller than the threshold. For example, when the index of the merge candidate selected for the first prediction unit is smaller than the threshold value, a flag gpm_mmvd_flag0 indicating whether MMVD is applied to the first prediction unit may be encoded and signaled. On the other hand, if the index of the merge candidate selected for the first prediction unit is equal to or greater than the threshold, encoding/decoding of the flag gpm_mmvd_flag0 for the first prediction unit may be omitted and MMVD may not be applied. Similarly, when the index of the merge candidate selected for the second prediction unit is smaller than the threshold value, a flag gpm_mmvd_flag1 indicating whether MMVD is applied to the second prediction unit may be encoded and signaled. On the other hand, if the index of the merge candidate selected for the second prediction unit is equal to or greater than the threshold, encoding/decoding of the flag gpm_mmvd_flag1 may be omitted and MMVD may not be applied to the second prediction unit.

Furthermore, unlike in the example of Table 5, after determining the offset vector for the MMVD of each of the prediction units, a merge candidate of each of the prediction units may be selected. That is, after encoding/decoding the syntax gpm_mmvd_idxX indicating the offset vector of the prediction unit, the syntax gpm_merge_idxX indicating the merge candidate of the prediction unit may be encoded/decoded.

In this case, when the offset vector for the first prediction unit and the offset vector for the second prediction unit are the same, a merge candidate different from that of the first prediction unit may be selected for the second prediction unit.

Intra prediction is to predict the current block using reconstructed samples that have been encoded/decoded around the current block. In this case, the reconstructed sample before the in-loop filter is applied may be used for intra prediction of the current block.

Intra prediction techniques include intra prediction based on a matrix and normal intra prediction considering directionality with neighboring reconstructed samples. Information indicating an intra prediction technique of the current block may be signaled through a 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 location, size, and shape of the current block, or intra prediction techniques of neighboring blocks. For example, if the current block exists across picture boundaries, matrix-based intra prediction may not be applied to the current block.

Matrix-based intra prediction is a method of obtaining a prediction block of a current block based on matrix multiplication between a matrix pre-stored in an encoder and a decoder and a reconstructed sample around the current block. Information for specifying one of a plurality of pre-stored matrices may be signaled through a bitstream. The decoder may determine a matrix for intra prediction of the current block based on the information and the size of the current block.

Normal intra prediction is a method of acquiring a prediction block for a current block based on a non-directional intra prediction mode or a directional intra prediction mode. Hereinafter, a process of performing intra prediction based on general intra prediction will be described in more detail with reference to drawings.

10 is a flowchart of an intra prediction method according to an embodiment of the present disclosure.

A reference sample line of the current block may be determined (S1001). The reference sample line means a set of reference samples included in a line kth away from the top and/or left side of the current block. The reference sample may be derived from a reconstructed sample for which encoding/decoding around the current block has been completed.

Index information identifying a reference sample line of a current block among a plurality of reference sample lines may be signaled through a bitstream. For example, index information intra_luma_ref_idx for specifying the reference sample line of the current block may be signaled through a bitstream. The index information may be signaled in units of coding blocks.

The plurality of reference sample lines may include at least one of a first line, a second line, and a third line at the top and/or left of the current block. Among the plurality of reference sample lines, a reference sample line composed of a row adjacent to the top of the current block and a column adjacent to the left of the current block is referred to as an adjacent reference sample line, and other reference sample lines are referred to as non-adjacent reference sample lines. can also be called

Table 6 shows indexes assigned to each of the candidate reference sample lines.

index (intra_luma_ref_idx) reference sample line 0 adjacent reference sample line One First non-adjacent reference sample line 2 Second non-adjacent reference sample line

A reference sample line of the current block may be determined based on at least one of the position, size, and shape of the current block or the predictive coding mode of the neighboring block. For example, when the current block borders a picture, tile, slice, or coding tree unit, an adjacent reference sample line may be determined as a reference sample line of the current block.

The reference sample line may include upper reference samples located on top of the current block and left reference samples located on the left side of the current block. Top reference samples and left reference samples may be derived from reconstruction samples around the current block. The reconstructed samples may be in a state before the in-loop filter is applied.

Next, an intra prediction mode of the current block may be determined (S1002). As the intra prediction mode of the current block, at least one of a non-directional intra prediction mode and a directional intra prediction mode may be determined as the intra prediction mode of the current block. The non-directional intra prediction mode includes a planner and DC, and the directional intra prediction mode includes 33 or 65 modes from a lower left diagonal direction to an upper right diagonal direction.

11 is a diagram illustrating intra prediction modes.

(a) of FIG. 11 shows 35 intra prediction modes, and (b) of FIG. 11 shows 67 intra prediction modes.

More or fewer intra prediction modes than shown in FIG. 11 may be defined.

An intra-prediction mode of the current block may be determined or predicted using information of neighboring blocks adjacent to the current block. For example, the intra prediction mode of the current block may be derived based on the edge direction and/or angle of the neighboring block. For example, when an edge exists in a neighboring block, an intra-prediction mode having the same or most similar angle as the direction and/or angle formed by the edge may be set as the prediction mode of the current block.

The neighboring block may include at least one of a left neighboring block or an upper neighboring block of the current block. Accordingly, an intra prediction mode that is the same as or most similar to the edge direction and/or edge angle of the left neighboring block or an intra prediction mode that is the same as or most similar to the edge direction and/or edge angle of the top neighboring block is set as the prediction mode of the current block. can

As another example, the intra prediction mode of the neighboring block may be set to the intra prediction mode of the current block.

12 shows locations of neighboring blocks used to derive an intra prediction mode of a current block.

As in the example shown in FIG. 12, at least one of the left neighboring block 1, the upper neighboring block 2, the upper right neighboring block 3, the lower left neighboring block 4, or the upper left neighboring block 5 is used. Thus, the intra prediction mode of the current block can be derived.

Setting the intra prediction mode of a neighboring block to the intra prediction mode of the current block may be defined as an intra merge mode. In this case, the intra prediction mode of each of the neighboring blocks may be set as an intra merge candidate. When a plurality of intra merge candidates exist, index information identifying one of the plurality of intra merge candidates may be signaled through a bitstream. Alternatively, an intra prediction mode having the highest frequency among a plurality of intra merge candidates may be set as the intra prediction mode of the current block.

After selecting a plurality of intra-merge candidates, each of the plurality of selected intra prediction modes may be assigned to a sub-block. Accordingly, different intra prediction modes may be allocated for each sub-block within the current block. For example, the intra prediction mode of the first subblock in the current block is set to be the same as that of the first intra merge candidate, and the intra prediction mode of the second subblock in the current block is set to be the same as that of the second intra merge candidate. can

When the intra prediction mode of the current block is determined, prediction samples for the current block may be obtained based on the determined intra prediction mode (S1003).

When the DC mode is selected, prediction samples for the current block are generated based on the average value of reference samples. Specifically, values of all samples in the prediction block may be generated based on an average value of reference samples. The average value may be derived using at least one of upper reference samples located at the top of the current block and left reference samples located at the left side of the current block.

Depending on the shape of the current block, the number or range of reference samples used to derive the average value may vary. For example, when the current block is a non-square block having a width greater than a height, an average value may be calculated using only upper reference samples. On the other hand, if the current block is a non-square block whose width is smaller than its height, an average value can be calculated using only the left reference samples. That is, when the width and height of the current block are different, an average value may be calculated using only reference samples adjacent to the longer side. Alternatively, based on the width-to-height ratio of the current block, it may be determined whether to calculate the average value using only the upper reference samples or the average value using only the left reference samples.

When the planner mode is selected, a prediction sample may be obtained using the horizontal direction prediction sample and the vertical direction prediction sample. Here, the horizontal direction prediction sample is obtained based on the left reference sample and the right reference sample located on the same horizontal line as the prediction sample, and the vertical direction prediction sample includes the top reference sample and the bottom reference sample located on the same vertical line as the prediction sample. obtained on the basis of a reference sample. Here, the right reference sample may be generated by copying a reference sample adjacent to the upper right corner of the current block, and the lower reference sample may be generated by copying a reference sample adjacent to the lower left corner of the current block. The horizontal direction prediction sample may be obtained based on the weighted sum operation of the left reference sample and the right reference sample, and the vertical direction prediction sample may be obtained based on the weighted sum operation of the upper reference sample and the lower reference sample. In this case, a weight given to each reference sample may be determined according to a position of the predicted sample. The prediction sample may be obtained based on an average operation or a weighted sum operation of the horizontal direction prediction samples and the vertical direction prediction samples. When the weighted sum operation is performed, weights given to the horizontal direction prediction sample and the vertical direction prediction sample may be determined based on the position of the prediction sample.

When a directional prediction mode is selected, a parameter indicating a prediction direction (or prediction angle) of the selected directional prediction mode may be determined. Table 7 below shows the intra direction parameter intraPredAng for each intra prediction mode.

PredModeIntra One 2 3 4 5 6 7 IntraPredAng - 32 26 21 17 13 9 PredModeIntra 8 9 10 11 12 13 14 IntraPredAng 5 2 0 -2 -5 -9 -13 PredModeIntra 15 16 17 18 19 20 21 IntraPredAng -17 -21 -26 -32 -26 -21 -17 PredModeIntra 22 23 24 25 26 27 28 IntraPredAng -13 -9 -5 -2 0 2 5 PredModeIntra 29 30 31 32 33 34 IntraPredAng 9 13 17 21 26 32

Table 7 shows an intra direction parameter of each intra prediction mode having an index of any one of 2 to 34 when 35 intra prediction modes are defined. If more than 33 directional intra prediction modes are defined, Table 7 can be further subdivided to set the intra direction parameter of each directional intra prediction mode. Top reference samples and left reference samples of the current block are arranged in a row. After arranging, a prediction sample may be obtained based on the value of the intra-direction parameter. In this case, when the value of the intra direction parameter is a negative number, the left reference samples and the top reference samples may be arranged in a row. Based on the intra-direction parameter, a reference sample determination parameter may be determined. The reference sample determination parameter may include a reference sample index for specifying a reference sample and a weight parameter for determining a weight applied to the reference sample.

The reference sample index iIdx and the weight parameter ifact may be obtained through Equations 3 and 4, respectively.

In Equations 3 and 4, P _ang represents an intra-direction parameter. The reference sample specified by the reference sample index iIdx corresponds to an integer pel.

In order to derive a prediction sample, at least one or more reference samples may be specified. Specifically, the location of a reference sample used to derive a prediction sample may be specified by considering the gradient of the prediction mode. For example, a reference sample used to derive a prediction sample may be specified using the reference sample index iIdx.

In this case, when the slope of the intra prediction mode is not represented by one reference sample, a prediction sample may be generated by interpolating a plurality of reference samples. For example, when the slope of the intra prediction mode is a value between the slope between the prediction sample and the first reference sample and the slope between the prediction sample and the second reference sample, the prediction sample is obtained by interpolating the first reference sample and the second reference sample. can be obtained That is, when an angular line along the intra prediction angle does not pass through a reference sample located in an integer pel, a prediction sample may be obtained by interpolating reference samples located adjacent to the left or right or above and below the position through which the angular line passes there is.

Equation 5 below shows an example of obtaining prediction samples based on reference samples.

In Equation 5, P denotes a prediction sample, and Ref_1D denotes one of the one-dimensional arrayed reference samples. In this case, the location of the reference sample may be determined by the location (x, y) of the prediction sample and the reference sample index iIdx.

If the gradient of the intra prediction mode can be expressed by one reference sample, the weight parameter i _fact is set to 0. Accordingly, Equation 5 can be simplified as Equation 6 below.

A residual image derived by differentiating a predicted image from an original image may be derived. In this case, when the residual image is changed to the frequency domain, subjective image quality of the image does not significantly deteriorate even when high-frequency components among frequency components are removed. Accordingly, if the values of the high-frequency components are reduced or the values of the high-frequency components are set to 0, there is an effect of increasing compression efficiency without greatly generating visual distortion. Reflecting the above characteristics, the current block may be transformed to decompose the residual image into 2D frequency components. The transform may be performed using a transform technique such as Discrete Cosine Transform (DCT) or Discrete Sine Transform (DST).

DCT decomposes (or transforms) the residual image into 2D frequency components using cosine transform, and DST decomposes (or transforms) the residual image into 2D frequency components using sine transform. As a result of transforming the residual image, frequency components may be expressed as a basis image. For example, when DCT transform is performed on an NxN-sized block, N ² basic pattern components may be obtained. Through transformation, the size of each of the basic pattern components included in the NxN size block may be obtained. Depending on the transform technique used, the magnitude of the basic pattern component may be referred to as a DCT coefficient or a DST coefficient.

The transformation technique DCT is mainly used to transform an image in which a large number of non-zero low-frequency components are distributed. The conversion technique DST is mainly used for images in which high-frequency components are widely distributed.

The residual image may be transformed using a transformation technique other than DCT or DST.

Hereinafter, transforming the residual image into 2D frequency components will be referred to as 2D image conversion. In addition, the size of the basic pattern components obtained as a result of conversion will be referred to as a conversion coefficient. For example, the transform coefficient may mean a DCT coefficient or a DST coefficient. When both the first transform and the second transform, which will be described later, are applied, the transform coefficient may mean the size of a basic pattern component generated as a result of the second transform. In addition, the residual sample to which the transform skip is applied will also be referred to as a transform coefficient.

A conversion technique may be determined in units of blocks. A transform technique may be determined based on at least one of a prediction encoding mode of the current block, a size of the current block, or a shape of the current block. For example, when the current block is coded in intra prediction mode and the size of the current block is smaller than NxN, transformation may be performed using DST. On the other hand, if the above condition is not satisfied, conversion may be performed using the conversion technique DCT.

2D image conversion may not be performed on some blocks of the residual image. Not performing 2D image transformation may be referred to as a transform skip. Transform skip indicates that the first transform and the second transform are not applied to the current block. When transform skip is applied, quantization may be applied to residual values on which transform is not performed.

Whether or not to allow transform skip for the current block may be determined based on at least one of the size or shape of the current block. For example, transform skip may be applied only when the size of the current block is smaller than the threshold value. The threshold value is related to at least one of the width, height, or number of samples of the current block and may be defined as 32x32 or the like. Alternatively, transform skipping may be allowed only for square blocks. For example, transform skip may be allowed for a square block having a size of 32x32, 16x16, 8x8, or 4x4. Alternatively, transform skipping may be allowed only when the sub-partition intra-coding method is not used.

After converting the current block using DCT or DST, the converted current block may be converted again. In this case, a transform based on DCT or DST may be defined as a first transform, and transforming a block to which the first transform is applied may be defined as a second transform.

The first transformation may be performed using any one of a plurality of transformation core candidates. For example, the first conversion may be performed using any one of DCT2, DCT8, and DST7.

Different conversion cores may be used for horizontal and vertical directions. Information indicating a combination of a conversion core in a horizontal direction and a conversion core in a vertical direction may be signaled through a bitstream. For example, tu_mts_idx may indicate one of combinations of a horizontal conversion core and a vertical conversion core.

Performance units of the first transformation and the second transformation may be different. For example, a first transformation may be performed on an 8x8 block, and a second transformation may be performed on a subblock having a size of 4x4 among the transformed 8x8 blocks. Alternatively, the second transform may be performed on transform coefficients belonging to three 4x4 subblocks. The three sub-blocks may include a sub-block positioned at the upper left of the current block, a sub-block neighboring to the right of the sub-block, and a sub-block neighboring to the lower end of the sub-block. Alternatively, the second transformation may be performed on an 8x8 block.

Transformation coefficients of residual regions in which the second transform is not performed may be set to 0.

Alternatively, the first transformation may be performed on the 4x4 block, and the second transformation may be performed on an 8x8 area including the transformed 4x4 block.

Information representing the transform type of the current block may be signaled through a bitstream. The information may be index information tu_mts_idx indicating one of combinations of a transform type for the horizontal direction and a transform type for the vertical direction.

Whether to explicitly determine the transform type of the current block may be determined based on information signaled from the bitstream. The information may be signaled through a sequence, picture, or slice header. For example, at the sequence level, sps_explicit_intra_mts_flag indicates whether explicit transform type determination is allowed for blocks encoded in intra prediction and/or indicates whether explicit transform type determination is permitted for blocks encoded in inter prediction. Information sps_explicit_inter_mts_flag may be signaled.

When explicit transform type determination is allowed, the transform type of the current block may be determined based on index information tu_mts_idx signaled from the bitstream.

On the other hand, when explicit transformation type determination is not allowed, the transformation type is based on at least one of the size and shape of the current block, whether transformation in units of subblocks is allowed, or the location of a subblock including a non-zero transformation coefficient. this can be determined. For example, the horizontal conversion type of the current block may be determined based on the width of the current block, and the vertical conversion type of the current block may be determined based on the height of the current block.

For example, when the width of the current block is less than 4 or greater than 16, the conversion type in the horizontal direction may be determined as DCT2. Otherwise, the conversion type in the horizontal direction may be determined as DST7.

When the height of the current block is less than 4 or greater than 16, the conversion type in the vertical direction may be determined as DCT2. Otherwise, the conversion type in the vertical direction may be determined as DST7.

Here, in order to determine the transform type in the horizontal direction and the transform type in the vertical direction, the threshold values compared with the width and height are predefined in the encoder and decoder, or among the size, shape, or intra prediction mode of the current block. It may be adaptively determined based on at least one.

If the encoder performs transformation and quantization, the decoder may obtain a residual block through inverse quantization and inverse transformation. The decoder may obtain a reconstructed block for the current block by adding the prediction block and the residual block.

When a reconstructed block of the current block is acquired, loss of information occurring in quantization and encoding processes can be reduced through in-loop filtering. The in-loop filter may include at least one of a deblocking filter, a sample adaptive offset filter (SAO), and an adaptive loop filter (ALF).

Although the foregoing embodiments have been described based on a series of steps or flowcharts, this does not limit the chronological order of the invention, and may be performed simultaneously or in a different order as needed. In addition, each of the components (eg, units, modules, etc.) constituting the block diagram in the above-described embodiment may be implemented as a hardware device or software, or a plurality of components may be combined to form a single hardware device or software. may be implemented. The above-described embodiment may be implemented in the form of program instructions that can be executed through various computer components and recorded on a computer-readable recording medium. The computer readable recording medium may include program instructions, data files, data structures, etc. alone or in combination. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks and magnetic tapes, optical recording media such as CD-ROMs and DVDs, and magneto-optical media such as floptical disks. media), and hardware devices specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. The hardware device may be configured to act as one or more software modules to perform processing according to the present disclosure and vice versa.

Claims (13)

determining whether Geometry Partitioning with Merge mode (GPM) is applied to the current block;
determining a partition type for the current block when it is determined that the GPM is applied to the current block;
obtaining motion information of each of a first prediction unit and a second prediction unit within the current block; and
Obtaining a prediction block for the current block based on motion information of each of the first prediction unit and the second prediction unit,
Obtaining the motion information,
And determining whether merge mode with motion vector difference (MMVD) is applied to each of the first prediction unit and the second prediction unit. According to claim 1,
Obtaining the motion information,
selecting a first merge candidate for the first prediction unit based on a first merge index; and
And selecting a second merge candidate for the second prediction unit based on a second merge index. According to claim 2,
Whether or not the MMVD is applied to the first prediction unit is determined based on a result of comparing the index of the first merge candidate with a threshold value,
Whether or not the MMVD is applied to the second prediction unit is determined based on a result of comparing an index of the second merge candidate with a threshold value. According to claim 2,
While the first merge index is signaled through a bitstream,
The second merge index is selectively signaled based on whether the MMVD is applied to both the first prediction unit and the second prediction unit. According to claim 4,
When the signaling of the second merge index is omitted, a default value or a value obtained by adding or subtracting an offset from the first merge index is inferred as the second merge index. According to claim 4,
When the MMVD is applied to both the first prediction unit and the second prediction unit, the signaling of the second merge index is omitted, and the second merge candidate is set to be the same as the first merge candidate. Characterized by, video decoding method. According to claim 2,
Characterized in that, the MMVD is applied to one of the first prediction unit and the second prediction unit according to a comparison result of the index of the first merge candidate and the index of the second merge candidate. decryption method. According to claim 7,
When the index of the first merge candidate is smaller than the index of the second merge candidate, the MMVD is applied to the first prediction unit;
When the index of the second merge candidate is smaller than the index of the first merge candidate, the MMVD is applied to the second prediction unit. According to claim 2,
The video decoding method, characterized in that the number of merge candidates indicated by the first merge index is different between a case where MMVD is applied to the first prediction unit and a case where MMVD is not applied. According to claim 2,
When MMVD is applied to the first prediction unit, a motion vector of the first prediction unit is derived by adding a first offset vector to a motion vector of the first merge candidate;
When MMVD is applied to the second prediction unit, a motion vector of the second prediction unit is derived by adding a second offset vector to the motion vector of the first merge candidate;
The first offset vector and the second offset vector are determined based on separate index information. According to claim 10,
When the first offset vector and the second offset vector are the same, the first merge candidate is different from the second merge candidate;
When the first offset vector and the second offset vector are different, the first merge candidate and the second merge candidate are identical. determining whether Geometry Partitioning with Merge mode (GPM) is applied to the current block;
determining a partition type for the current block when it is determined that the GPM is applied to the current block;
obtaining motion information of each of a first prediction unit and a second prediction unit within the current block; and
Obtaining a prediction block for the current block based on motion information of each of the first prediction unit and the second prediction unit,
Obtaining the motion information,
And determining whether merge mode with motion vector difference (MMVD) is applied to each of the first prediction unit and the second prediction unit. determining whether Geometry Partitioning with Merge mode (GPM) is applied to the current block;
determining a partition type for the current block when it is determined that the GPM is applied to the current block;
obtaining motion information of each of a first prediction unit and a second prediction unit within the current block; and
Obtaining a prediction block for the current block based on motion information of each of the first prediction unit and the second prediction unit,
Obtaining the motion information,
Storing a bitstream generated by an image encoding method, comprising the step of determining whether merge mode with motion vector difference (MMVD) is applied to each of the first prediction unit and the second prediction unit A computer-readable recording medium.

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