BR122024024714A2 - VIDEO DECODING METHOD, VIDEO CODING METHOD, VIDEO DECODING DEVICE AND VIDEO CODING DEVICE - Google Patents

Abstract

An image decoding method according to the present invention may comprise the steps of: dividing a coding block into a first prediction unit and a second prediction unit; deriving a merge candidate list for the coding block; deriving first motion information for the first prediction unit and second motion information for the second prediction unit by means of the merge candidate list; and based on the first motion information and the second motion information, acquiring a prediction sample within the coding block.

Description

This patent application consists of a split application of the invention patent application BR 112021008654-4, dated 11/08/2019. FIELD OF TECHNIQUE

[001] The present disclosure relates to a method of encoding and decoding video signal and an apparatus for the same.

FUNDAMENTALS

[002] As display panels are getting larger and larger, even higher quality video services are increasingly required. The biggest problem of high-definition video services is the significant increase in data volume, and in order to solve this problem, studies to improve the video compression rate are actively carried out. As a representative example, the Motion Picture Expert Group (MPEG) and the Video Coding Expert Group (VCEG) under the International Telecommunication Union-Telecommunications (ITU-T) formed the Joint Collaboration Team on Video Coding (JCT-VC) in 2009. JCT-VC proposed High Efficiency Video Coding (HEVC), which is a video compression standard with a compression performance about twice that of H.264/AVC, and was approved as a standard on January 25, 2013. With the rapid advancement of high-definition video services, the performance of HEVC gradually reveals its limitations.

SUMMARY

[003] An object of the present disclosure is to provide a method of applying partitioning to a coding block to obtain a plurality of prediction blocks in encoding/decoding a video signal and an apparatus for performing the method.

[004] Another object of the present disclosure is to provide a method for deriving motion information from each of a plurality of prediction blocks, in encoding/decoding a video signal.

[005] Another object of the present disclosure is to provide a method of deriving a merging candidate using a list of motion information between regions, in encoding/decoding a video signal.

[006] The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

[007] A method of decoding/encoding a video signal according to the present disclosure may include the steps of: applying partitioning to a coding block to obtain a first prediction unit and a second prediction unit; deriving a merge candidate list for the coding block by deriving first motion information for the first prediction unit and second motion information for the second prediction unit using the merge candidate; and obtaining a prediction sample in the coding block based on the first motion information and the second motion information. At this point, whether or not to apply partitioning to the coding block is determined based on a size of the coding block, and the first motion information for the first prediction unit is derived from a first merge candidate in the merge candidate list, and the second motion information for the second prediction unit is derived from a second merge candidate other than the first merge candidate.

[008] In the video signal encoding and decoding method according to the present disclosure, when at least one of a width and a height of the coding block is greater than a threshold value, partitioning of the coding block may not be allowed.

[009] In the video signal encoding and decoding method according to the present disclosure, the method may further include the step of decoding the first index information for specifying the first merging candidate and the second index information for specifying the second merging candidate from a bit stream, and when a value of the second index information is equal to or greater than a value of the first index information, the value of the second index information specifying the second merging candidate is obtained by adding 1 to the value of the first index information specifying the first merging candidate.

[010] In the video signal encoding and decoding method according to the present disclosure, when the prediction sample is included in the boundary region between the first prediction unit and the second prediction unit, the prediction sample may be derived based on a weighted sum operation of a first prediction sample derived based on the first motion information and a second predicted sample derived based on the second motion information.

[011] In the video signal encoding and decoding method according to the present disclosure, a first weighting value applied to the first prediction sample may be determined based on an x-axis coordinate and a y-axis coordinate of the prediction sample.

[012] In the video signal encoding and decoding method according to the present disclosure, a second weighting value applied to the second prediction sample can be derived by subtracting the first weighting value from a constant value.

[013] In the video signal encoding and decoding method according to the present disclosure, the maximum number of merging candidates which the merging candidate list may include may be determined based on whether the coding block is partitioned into the first prediction unit and the second prediction unit.

[014] The features briefly summarized above with respect to the present disclosure are merely exemplary aspects of the detailed description of the present disclosure that will be described below and do not limit the scope of the present disclosure.

[015] In Accordance With The Present Disclosure, Interprediction Efficiency Can Be Improved By Providing A Method Of Applying Partitioning To A Coding Block To Obtain A Plurality Of Prediction Blocks And Deriving Motion Information From Each Of The Prediction Blocks

[016] In accordance with the present disclosure, inter-prediction efficiency can be improved by providing a method of deriving a merge candidate using a list of inter-region movement information.

[017] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[018] Figure 1 is a block diagram showing a video encoder in accordance with one embodiment of the present disclosure.

[019] Figure 2 is a block diagram showing a video decoder in accordance with one embodiment of the present disclosure.

[020] Figure 3 is a view showing a basic coding tree unit in accordance with an embodiment of the present disclosure.

[021] Figure 4 is a view showing various types of partitioning of a coding block.

[022] Figure 5 is a view showing a partitioning pattern of a coding tree unit.

[023] Figure 6 is a flowchart illustrating an interforecasting method in accordance with one embodiment of the present disclosure.

[024] Figure 7 is a view showing non-linear motions of an object.

[025] Figure 8 is a flowchart illustrating an interprediction method based on an affine motion in accordance with an embodiment of the present disclosure.

[026] Figure 9 is a view showing an example of affine seed vectors for each affine motion model.

[027] Figure 10 is a view showing an example of affine vector subblocks in a 4-parameter motion model.

[028] Figure 11 is a flowchart illustrating a process of deriving motion information from a current block using a blending mode.

[029] Figure 12 is a view showing an example of candidate blocks used to derive a merge candidate.

[030] Figure 13 is a view showing reference sample positions.

[031] Figure 14 is a view showing an example of candidate blocks used to derive a merge candidate.

[032] Figure 15 is a flowchart illustrating a process for updating a list of inter-region movement information.

[033] Figure 16 is a view showing one embodiment of updating an inter-region merge candidate list.

[034] Figure 17 is a view showing an example where an index of a previously stored inter-region merge candidate is updated.

[035] Figure 18 is a view showing the position of a representative sub-block.

[036] Figure 19 is a view showing an example where a list of inter-region motion information is generated for each interprediction mode.

[037] Figure 20 is a view showing an example where an inter-region merge candidate included in a long-term motion information list is added to a merge candidate list.

[038] Figure 21 is a view showing an example where a redundancy check is performed on only some of the merge candidates.

[039] Figure 22 is a view showing an example where a redundancy check is omitted for a specific merge candidate.

[040] Figure 23 is a view showing examples of applying partitioning to a coding block to obtain a plurality of prediction units using a diagonal line.

[041] Figure 24 is a view showing examples of applying partitioning to a coding block to obtain two prediction units.

[042] Figure 25 is a view showing examples of applying partitioning to a coding block to obtain a plurality of prediction blocks of different sizes.

[043] Figure 26 is a view showing neighboring blocks used to derive a triangular merge candidate.

[044] Figure 27 is a view to describe examples of determining the availability of a neighboring block for each triangular prediction unit.

[045] Figures 28 and 29 are views showing examples of deriving a forecast sample based on a weighted sum operation of a first forecast sample and a second forecast sample.

DETAILED DESCRIPTION

[046] In the following, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[047] Encoding and decoding of a video are performed by the block unit. For example, an encoding/decoding process such as transform, quantization, prediction, loop filtering, reconstruction, or the like may be performed in an encoding block, a transform block, or a prediction block.

[048] Next, a block to be encoded/decoded will be referred to as a “current block”. For example, the current block may represent an encoding block, a transform block, or a prediction block according to a step of the current encoding/decoding process.

[049] Furthermore, it may be understood that the term “unit” used in this specification indicates a basic unit for performing a specific encoding/decoding process, and the term “block” indicates a sample matrix of a predetermined size. Unless otherwise indicated, “block” and “unit” may be used to have the same meaning. For example, in an embodiment described below, it may be understood that a coding block and a coding unit have the same meaning.

[050] Figure 1 is a block diagram showing a video encoder in accordance with one embodiment of the present disclosure.

[051] Referring to Figure 1, a video coding apparatus 100 may include a picture partitioning part 110, a prediction part 120 and 125, a transform part 130, a quantization part 135, a rearrangement part 160, an entropy coding part 165, an inverse quantization part 140, and inverse transform part 145, a filter part 150, and a memory 155.

[052] Each of the components shown in Figure 1 is shown independently to represent characteristic functions different from each other in a video encoding apparatus, and it does not mean that each component is formed by the separate hardware configuration unit or single software. That is, each component is included to be listed as a component for convenience of explanation and at least two of the components can be combined to form a single component, or a component can be divided into a plurality of components to perform a function. Integrated embodiments and separate embodiments of the components are also included in the scope of the present disclosure if they do not depart from the essence of the present disclosure.

[053] Furthermore, some of the components are not essential components that perform essential functions in the present disclosure, but may be optional components only to improve performance. The present disclosure may be implemented by including only essential components to implement the essence of the present disclosure, excluding components used to improve performance, and a structure including only the essential components, excluding the optional components used to improve performance is also included in the scope of the present disclosure.

[054] The image partitioning part 110 may apply partitioning to an input image to obtain at least one processing unit. At this point, the processing unit may be a prediction unit (PU), a transform unit (TU), or an coding unit (CU). The image partitioning part 110 may apply partitioning to an image to obtain a combination of a plurality of coding units, prediction units, and transform units, and encode a selected image from a combination of a coding unit, a prediction unit, and a transform unit based on a predetermined criterion (e.g., a cost function).

[055] For example, an image may be partitioned into a plurality of coding units. In order to partition the coding units in an image, a recursive tree structure, such as a quad tree structure, may be used. A video or a coding unit partitioned into different coding units using the largest coding unit as a root may be partitioned to have as many child nodes as the number of partitioned coding units. A coding unit that is no longer partitioned according to a predetermined constraint becomes a leaf node. That is, when it is assumed that only square partitioning is possible for a coding unit, the coding unit may be partitioned into up to four different coding units.

[056] Next, in one embodiment of the present disclosure, the coding unit may be used as a meaning of a unit performing the encoding or a meaning of a unit performing the decoding.

[057] The prediction unit may be one that is partitioned into a shape of at least one square, rectangle or similar of the same size within a coding unit, or it may be any prediction unit, among the prediction units partitioned within a coding unit, that is partitioned to have a different shape and/or size than those of another prediction unit.

[058] If the coding unit is not a smaller coding unit when a prediction unit that performs intraprediction based on the coding unit is generated, intraprediction can be performed without partitioning an image into a plurality of N x N prediction units.

[059] The prediction part 120 and 125 may include an interprediction part 120 that performs interprediction and an intraprediction part 125 that performs intraprediction. It may be determined whether to use interprediction or perform intraprediction for a prediction unit, and determine specific information (e.g., intraprediction mode, motion vector, reference image, etc.) according to each prediction method. At this point, a processing unit for performing prediction may be different from a processing unit for determining a prediction method and specific content. For example, a prediction method and a prediction mode may be determined in a prediction unit, and prediction may be performed in a transform unit. A residual coefficient (residual block) between the generated prediction block and the original block may be input to the transform part 130. Further, prediction mode information, motion vector information and the like used for prediction may be encoded by the entropy coding part 165 together with the residual coefficient and passed to a decoder. When a specific coding mode is used, an original block may be encoded as is and transmitted to a decoder without generating a prediction block through the prediction part 120 and 125.

[060] The interprediction part 120 may predict a prediction unit based on information from at least one picture among the pictures before or after the current picture, and in some cases, may predict a prediction unit based on information from a partial area that has been encoded in the current picture. The interprediction part 120 may include a reference picture interpolation part, a motion prediction part, and a motion compensation part.

[061] The reference image interpolation part may receive reference image information from memory 155 and generate sample information of an integer number of samples or less from the reference image. In the case of a luminance sample, a DCT-based 8-tap interpolation filter with a variable filter coefficient may be used to generate sample information of an integer number of samples or less by the unit of 1/4 samples. In the case of a color difference signal, a DCT-based 4-coefficient interpolation filter with a variable filter coefficient may be used to generate sample information of an integer number of samples or less by the unit of 1/8 samples.

[062] The motion prediction part may perform motion prediction based on the reference image interpolated by the reference image interpolation part. Various methods, such as a full search-based block matching algorithm (FBMA), a three-step search (TSS), and a novel three-step search (NTS) algorithm, may be used as a method of calculating a motion vector. The motion vector may have a motion vector value of a unit of 1/2 or 1/4 samples based on interpolated samples. The motion prediction part may predict a current prediction unit by varying the motion prediction method. Various methods, such as a skip method, a merge method, an advanced motion vector prediction method (AMVP), an intra-block copy method, and the like, may be used as the motion prediction method.

[063] The intra-prediction part 125 may generate a prediction unit based on information about reference samples in the neighborhood of the current block, which is the sample information in the current image. When a block in the neighborhood of the current prediction unit is a block on which inter-prediction has been performed, and therefore the reference sample is a sample on which inter-prediction has been performed, the reference sample included in the block on which inter-prediction has been performed may be used in place of the reference sample information of a block in the neighborhood on which intra-prediction has been performed. That is, when a reference sample is not available, at least one reference sample among the available reference samples may be used in place of the unavailable reference sample information.

[064] In intraprediction, the prediction mode may have an angular prediction mode that uses reference sample information according to a prediction direction and a non-angular prediction mode that does not use directional information when performing prediction. A mode for predicting luminance information may be different from a mode for predicting color difference information, and intraprediction mode information used to predict luminance information or predicted luminance signal information may be used to predict the color difference information.

[065] If the size of the prediction unit is the same as the size of the transform unit when intraprediction is performed, intraprediction can be performed for the prediction unit based on a sample on the left side, a sample on the top of the left side, and a sample on the top of the prediction unit. However, if the size of the prediction unit is different from the size of the transform unit when intraprediction is performed, intraprediction can be performed using a reference sample based on the transform unit. Furthermore, intraprediction using N x N partitioning can be used only for the smallest coding unit.

[066] The intraprediction method may generate a prediction block after applying an Intra-Adaptive Smoothing (AIS) filter to the reference sample according to a prediction mode. The type of AIS filter applied to the reference sample may vary. In order to perform the intraprediction method, the intraprediction mode of the current prediction unit may be predicted from the intraprediction mode of the prediction unit existing in the neighborhood of the current prediction unit. When a prediction mode of the current prediction unit is predicted using the prediction mode information of the neighboring prediction unit, if the intraprediction modes of the current prediction unit are the same as the prediction unit in the neighborhood, information indicating that the prediction modes of the current prediction unit are the same as the prediction unit in the neighborhood may be transmitted using predetermined flag information, and if the prediction modes of the current prediction unit and the prediction unit in the neighborhood are different from each other, the prediction mode information of the current block may be encoded by performing entropy encoding.

[067] Further, a residual block including a prediction unit that has performed prediction based on the prediction unit generated by the prediction part 120 and 125 and residual coefficient information, which is a difference value of the prediction unit with the original block, may be generated. The generated residual block may be input to the transform part 130.

[068] The transform part 130 may transform the residual block including the original block and the residual coefficient information of the prediction unit generated through the prediction part 120 and 125 using a transform method such as Discrete Cosine Transform (DCT) or Discrete Sine Transform (DST). Here, the DCT transform kernel includes at least one of DCT2 and DCT8, and the DST transform kernel includes DST7. Whether or not to apply DCT or DST to transform the residual block may be determined based on the intraprediction mode information of a prediction unit used to generate the residual block. The transform in the residual block may be skipped. A flag indicating whether or not to skip the transform in the residual block may be encoded. Transform skipping may be allowed for a residual block with a size less than or equal to a threshold, a luma component, or a chroma component under the 4:4:4 format.

[069] Quantization part 135 may quantize values transformed into the frequency domain by transform part 130. Quantization coefficients may vary depending on the block or importance of a video. A value calculated by quantization part 135 may be provided to inverse quantization part 140 and rearrangement part 160.

[070] The rearrangement part 160 may rearrange the coefficient values for the quantized residual coefficients.

[071] The rearrangement part 160 can change the coefficients of a two-dimensional block shape into a one-dimensional vector shape by means of a coefficient scanning method. For example, the rearrangement part 160 can scan coefficients from DC to high-frequency domain coefficients using a zigzag scanning method and change the coefficients into a one-dimensional vector shape. According to the size of the transform unit and the intraprediction mode, a vertical scan of scanning the coefficients of a two-dimensional block shape in the column direction and a horizontal scan of scanning the coefficients of a two-dimensional block shape in the row direction can be used instead of the zigzag scanning. That is, according to the size of the transform unit and the intraprediction mode, a scanning method to be used can be determined among the zigzag scanning, the scanning in the vertical direction, and the scanning in the horizontal direction.

[072] The entropy coding part 165 may perform entropy coding based on the values calculated by the rearrangement part 160. The entropy coding may use various coding methods, such as Exponential Golomb, Context Adaptive Variable Length Coding (CAVLC), Context Adaptive Binary Arithmetic Coding (CABAC), and the like.

[073] The entropy coding part 165 may encode various information such as residual coefficient information and block type information of a coding unit, prediction mode information, partitioning unit information, prediction unit information and transmission unit information, motion vector information, reference frame information, block interpolation information, and filtering information input from the rearrangement part 160 and the prediction parts 120 and 125.

[074] The entropy coding part 165 may entropy encode the coefficient value of a coding unit input of the rearrangement part 160.

[075] The inverse quantization part 140 and the inverse transform part 145 inversely quantize the values quantized by the quantization part 135 and inversely transform the values transformed by the transform part 130. The residual coefficient generated by the inverse quantization part 140 and the inverse transform part 145 may be combined with the prediction unit predicted through a motion estimation part, a motion compensation part, and an intraprediction part included in the prediction part 120 and 125 to generate a reconstructed block.

[076] The filter portion 150 may include at least one of a deblocking filter, an offset correction unit, and an Adaptive Loop Filter (ALF).

[077] The deblocking filter can remove the block distortion generated by the boundary between blocks in the reconstructed image. In order to determine whether or not to perform deblocking, whether or not to apply the deblocking filter to the current block can be determined based on the samples included in multiple columns or rows included in the block. A strong filter or a weak filter can be applied according to the required deblocking filtering strength when the deblocking filter is applied to a block. In addition, when vertical direction filtering and horizontal direction filtering are performed in applying the deblocking filter, horizontal direction filtering and vertical direction filtering can be processed in parallel.

[078] The displacement correction unit can correct a displacement for the original video by the sampling unit for a video on which deblocking has been performed. To perform displacement correction for a specific picture, it is possible to use a method of dividing samples included in the video into a certain number of areas, determining an area to perform displacement, and applying the displacement to the area, or a method of applying a displacement considering the edge information of each sample.

[079] Adaptive Loop Filtering (ALF) can be performed based on a value obtained by comparing the reconstructed and filtered video with the original video. After dividing the samples included in the video into predetermined groups, a filter to be applied to a corresponding group can be determined, and filtering can be performed differently for each group. A luminance signal, which is the information related to whether or not to apply ALF, can be transmitted to each coding unit (CU), and the shape and filter coefficient of an ALF filter to be applied can vary according to each block. In addition, an ALF filter of the same type (fixed type) can be applied regardless of the characteristic of the block to be applied.

[080] The memory 155 may store the reconstructed block or image calculated through the filter part 150, and the reconstructed and stored block or image may be provided to the prediction part 120 and 125 when interprediction is performed.

[081] Figure 2 is a block diagram showing a video decoder in accordance with one embodiment of the present disclosure.

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

[083] When a video bitstream is received from a video encoder, the input bitstream may be decoded in a procedure opposite to that of the video encoder.

[084] The entropy decoding part 210 may perform entropy decoding in a procedure opposite to that of performing entropy coding in the entropy decoding part of the video encoder. For example, various methods corresponding to the method performed by the video encoder, such as Exponential Golomb, Context Adaptive Variable Length Coding (CAVLC), and Context Adaptive Binary Arithmetic Coding (CABAC), may be applied.

[085] The entropy decoding part 210 can decode information related to the intraprediction and interprediction performed by the encoder.

[086] The rearrangement part 215 may perform rearrangement on the bit stream entropy decoded by the entropy decoding part 210 based on the rearrangement method performed by the encoder. The coefficients expressed in a one-dimensional vector form may be reconstructed and rearranged as two-dimensional block form coefficients. The rearrangement part 215 may receive information related to the coefficient scan performed by the coding part and perform reconstruction by a backward scan method based on the scan order performed by the corresponding coding part.

[087] The inverse quantization part 220 may perform inverse quantization based on a quantization parameter provided by the encoder and a coefficient value of the rearranged block.

[088] The inverse transform part 225 may perform the inverse transform on the transform, i.e., DCT or DST, performed by the transform part on a quantization result performed by the video encoder, i.e., inverse DCT or inverse DST. Here, the DCT transform core may include at least one of DCT2 and DCT8, and the DST transform core may include DST7. Alternatively, when the transform is skipped in the video encoder, even the inverse transform part 225 may not perform the inverse transform. The inverse transform may be performed based on a transmission unit determined by the video encoder. The inverse transform part 225 of the video decoder may selectively perform a transform technique (e.g., DCT or DST) according to a plurality of pieces of information, such as a prediction method, a size of a current block, a prediction direction, and the like.

[089] The prediction part 230 and 235 may generate a prediction block based on information related to generating a prediction block provided by the entropy decoder 210 and information about a previously decoded block or image provided by the memory 245.

[090] As described above, if the size of the prediction unit and the size of the transform unit are the same when intraprediction is performed in the same manner as the video encoder operation, intraprediction is performed on the prediction unit based on the sample existing on the left side, the sample on the upper left side, and the sample on the upper side of the prediction unit. However, if the size of the prediction unit and the size of the transform unit are different when intraprediction is performed, intraprediction can be performed using a reference sample based on a transform unit. Furthermore, intraprediction using N x N partitioning can be used only for the smallest coding unit.

[091] The prediction part 230 and 235 may include a prediction unit determination part, an inter-prediction part, and an intra-prediction part. The prediction unit determination part may receive various information, such as prediction unit information input from the entropy decoding part 210, prediction mode information from the intra-prediction method, motion prediction-related information from an inter-prediction method, and the like, identify the prediction unit from the current coding unit, and determine whether the prediction unit performs inter-prediction or intra-prediction. The inter-prediction part 230 may perform inter-prediction on the current prediction unit based on information included in at least one picture among the pictures before or after the current picture including the current prediction unit, using information necessary for inter-prediction of the current prediction unit provided by the video encoder. Alternatively, the interprediction part 230 may perform interprediction based on information in a previously reconstructed partial area in the current image including the current prediction unit.

[092] In order to perform inter-prediction, it can be determined, based on the coding unit, whether the motion prediction method of the prediction unit included in a corresponding coding unit is a hopping mode, a merging mode, a motion vector prediction mode (AMVP mode), or an intra-block copy mode.

[093] The intra-prediction part 235 may generate a prediction block based on information about the sample in the current picture. When the prediction unit is a prediction unit that has performed intra-prediction, the intra-prediction may be performed based on the intra-prediction mode information of the prediction unit provided by the video encoder. The intra-prediction part 235 may include an Intra-Adaptive Smoothing (AIS) filter, a reference sample interpolation part, and a DC filter. The AIS filter is a part that performs filtering on the reference sample of the current block, and may determine whether or not to apply the filter according to the prediction mode of the current prediction unit and apply the filter. AIS filtering may be performed on the reference sample of the current block using the prediction mode and AIS filter information of the prediction unit provided by the video encoder. When the prediction mode of the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

[094] When the prediction mode of the prediction unit is a prediction unit that performs intraprediction based on a sample value obtained by interpolating the reference sample, the reference sample interpolation part may generate a reference sample of a sample unit with an integer value or less by interpolating the reference sample. When the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without interpolating the reference sample, the reference sample may not be interpolated. The DC filter may generate a prediction block by filtering when the prediction mode of the current block is the DC mode.

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

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

[097] The displacement correction unit can perform displacement correction on the reconstructed video based on the displacement correction type and displacement value information applied to the video when encoding is performed.

[098] ALF may be applied to a coding unit based on information about whether or not ALF is applied and information about ALF coefficients provided by the encoder. ALF information may be provided to be included in a specific parameter set.

[099] Memory 245 may store the reconstructed image or block and use it as a reference image or a reference block and may provide the reconstructed image to an output unit.

[100] Figure 3 is a view showing a basic coding tree unit in accordance with an embodiment of the present disclosure.

[101] A coding block of a maximum size can be defined as a coding tree block. An image is partitioned into a plurality of coding tree units (CTUs). The coding tree unit is a coding unit with a maximum size and can be referred to as a Large Coding Unit (LCU). Figure 3 shows an example in which an image is partitioned into a plurality of coding tree units.

[102] The size of the coding tree unit may be defined at a picture level or a sequence level. To this end, information indicating the size of the coding tree unit may be signaled via a set of picture parameters or a set of sequence parameters.

[103] For example, the coding tree unit size for the entire image in a sequence may be set to 128 x 128. Alternatively, at the image level, any of 128 x 128 and 256 x 256 may be determined as the coding tree unit size. For example, the coding tree unit size may be set to 128 x 128 on a first image, and the coding tree unit size may be set to 256 x 256 on a second image.

[104] Coding blocks may be generated by partitioning a coding tree unit. The coding block indicates a basic unit for performing encoding/decoding. For example, prediction or transform may be performed for each coding block, or a prediction coding mode may be determined for each coding block. Here, the prediction coding mode indicates a method of generating a prediction image. For example, the prediction coding mode may include prediction within an image (intra-prediction), prediction between images (inter-prediction), current image reference (CPR) or intra-block copy (IBC), or combined prediction. For the coding block, a prediction block may be generated using at least one prediction coding mode among intra-prediction, inter-prediction, current image reference, and combined prediction.

[105] Information indicating the prediction coding mode of the current block may be signaled by means of a bit stream. For example, the information may be a 1-bit flag indicating whether the prediction coding mode is an intra mode or an inter mode. Only when the prediction coding mode of the current block is determined to be the inter mode, the current picture reference or the combined prediction may be used.

[106] The current picture reference is to set the current picture as a reference picture and obtain a prediction block of the current block from an area that has already been coded/decoded in the current picture. Here, the current picture means a picture including the current block. The information indicating whether the current picture reference is applied to the current block can be signaled via a bit stream. For example, the information can be a 1-bit flag. When the flag is true, the prediction coding mode of the current block can be determined as the current picture reference, and when the flag is false, the prediction mode of the current block can be determined as interprediction.

[107] Alternatively, the prediction coding mode of the current block may be determined based on a reference picture index. For example, when the reference picture index indicates the current picture, the prediction coding 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 interprediction. That is, current picture reference is a prediction method using information in an area where encoding/decoding has been completed in the current picture, and interprediction is a prediction method using information in another picture in which encoding/decoding has been completed.

[108] Combined prediction represents a coding mode in which two or more of the intra prediction, inter prediction and the current reference image are combined. For example, when combined prediction is applied, a first prediction block may be generated based on one of the intra prediction, inter prediction and the current reference image, and a second prediction block may be generated based on another. When the first prediction block and the second prediction block are generated, a final prediction block may be generated by means of an average operation or a weighted sum operation of the first prediction block and the second prediction block. Information indicating whether or not combined prediction is applied may be signaled by means of a bit stream. The information may be a 1-bit flag.

[109] Figure 4 is a view showing various types of partitioning of a coding block.

[110] The coding block may be partitioned into a plurality of coding blocks based on quad tree partitioning, binary tree partitioning, or ternary tree partitioning. The partitioned coding block may be partitioned again into a plurality of coding blocks based on quad tree partitioning, binary tree partitioning, or ternary tree partitioning.

[111] Quad-tree partitioning refers to a partitioning technique that partitions a current block into four blocks. As a result of quad-tree partitioning, the current block can be partitioned into four square partitions (see “SPLIT_QT” of Figure 4(a)).

[112] Binary tree partitioning refers to a partitioning technique that partitions a current block into two blocks. Partitioning a current block into two blocks along the vertical direction (i.e., using a vertical line crossing the current block) can be termed as vertical direction binary tree partitioning and partitioning a current block into two blocks along the horizontal direction (i.e., using a horizontal line crossing the current block) can be termed as horizontal direction binary tree partitioning. As a result of binary tree partitioning, the current block can be partitioned into two non-square partitionings. “SPLIT_BT_VER” of Figure 4(b) shows a result of vertical direction binary tree partitioning and “SPLIT_BT_HOR” of Figure 4(c) shows a result of horizontal direction binary tree partitioning.

[113] Ternary tree partitioning refers to a partitioning technique that partitions a current block into three blocks. Partitioning a current block into three blocks along the vertical direction (i.e., using two vertical lines crossing the current block) can be termed as ternary tree partitioning in the vertical direction, and partitioning a current block into three blocks along the horizontal direction (i.e., using two horizontal lines crossing the current block) can be termed as ternary tree partitioning in the horizontal direction. As a result of ternary tree partitioning, the current block can be partitioned into three non-square partitions. At this point, the width/height of a partition positioned at the center of the current block can be twice as large as the width/height of the other partitions. “SPLIT_TT_VER” in Figure 4(d) shows a result of ternary tree partitioning in the vertical direction, and “SPLIT_TT_HOR” in Figure 4(e) shows a result of ternary tree partitioning in the horizontal direction.

[114] The number of times of partitioning of a coding tree unit can be defined as a partitioning depth. The maximum partitioning depth of a coding tree unit can be determined at the sequence or image level. Consequently, the maximum partitioning depth of a coding tree unit can be different for each sequence or image.

[115] Alternatively, the maximum partitioning depth for each partitioning technique may be determined individually. For example, the maximum allowable partitioning depth for quad tree partitioning may be different from the maximum allowable partitioning depth for binary tree partitioning and/or ternary tree partitioning.

[116] The encoder may signal information indicating at least one of the partitioning type and partitioning depth of the current block via a bit stream. The decoder may determine the partitioning type and partitioning depth of a coding tree unit based on information parsed from the bit stream.

[117] Figure 5 is a view showing a partitioning pattern of a coding tree unit.

[118] Partitioning a cipher block using a partitioning technique such as quad tree partitioning, binary tree partitioning, and/or ternary tree partitioning can be referred to as multi-tree partitioning.

[119] The coding blocks generated by applying multiple tree partitioning to a coding block can be referred to as lower coding blocks. When the partitioning depth of a coding block is k, the partitioning depth of the lower coding blocks is set to k + 1.

[120] Conversely, for coding blocks with a partitioning depth of k + 1, a coding block with a partitioning depth of k can be termed as an upper coding block.

[121] The partitioning type of the current coding block may be determined based on at least one of a partitioning type of a top coding block and a partitioning type of a neighboring coding block. Here, the neighboring coding block is a coding block adjacent to the current coding block and may include at least one of a top neighboring block and a left neighboring block of the current coding block and a top-left neighboring block. Here, the partitioning type may include at least one of whether a quad tree partitioning is applied, whether a binary tree partitioning is applied, a binary tree partitioning direction, whether a ternary tree partitioning is applied, and ternary tree partitioning direction.

[122] In order to determine a partitioning type of a cipher block, information indicating whether or not the cipher block can be partitioned can be signaled via a bit stream. The information is a 1-bit flag “split_cu_flag”, and when the flag is true, it indicates that the cipher block is partitioned by a quad-tree partitioning technique.

[123] When split_cu_flag is true, information indicating whether the cipher block is quad-tree partitioned can be signaled via a bit stream. The information is a 1-bit flag of split_qt_flag, and when the flag is true, the cipher block can be partitioned into four blocks.

[124] For example, in the example shown in Figure 5, as a coding tree unit is quad-tree partitioned, four coding blocks with a partitioning depth of 1 are generated. Furthermore, it is shown that quad-tree partitioning is applied again to the first and fourth coding blocks among the four coding blocks generated as a result of quad-tree partitioning. As a result, four coding blocks with a partitioning depth of 2 can be generated.

[125] Additionally, cipher blocks with a partitioning depth of 3 can be generated by applying quad tree partitioning again to a cipher block with a partitioning depth of 2.

[126] When quad tree partitioning is not applied to the coding block, whether binary tree partitioning or ternary tree partitioning is performed on the coding block can be determined by considering at least one of the size of the coding block, whether the coding block is positioned on the image boundary, the maximum partitioning depth, and the partitioning type of a neighboring block. When it is determined to perform binary tree partitioning or ternary tree partitioning on the coding block, information indicating the partitioning direction can be signaled via a bit stream. The information can be a 1-bit flag of mtt_split_cu_vertical_flag. Based on the flag, whether the partitioning direction is a vertical direction or a horizontal direction can be determined. In addition, information indicating whether binary tree partitioning or ternary tree partitioning is applied to the coding block can be signaled via a bit stream. The information can be a 1-bit flag from mtt_split_cu_binary_flag. Based on the flag, it can be determined whether binary tree partitioning or ternary tree partitioning is applied to the cipher block.

[127] For example, in the example shown in Figure 5, it is shown that vertical-direction binary tree partitioning is applied to a coding block with a partitioning depth of 1, vertical-direction ternary tree partitioning is applied to the left-hand coding block among the coding blocks generated as a result of the partitioning, and vertical-direction binary tree partitioning is applied to the right-hand coding block.

[128] Interprediction is a prediction coding mode that predicts a current block using information from a previous image. For example, a block at the same position as the current block in the previous image (hereinafter, a placed block) can be defined as the prediction block of the current block. Hereinafter, a prediction block generated based on a block at the same position as the current block will be referred to as a placed prediction block.

[129] On the other hand, when an object existing in the previous image has moved to another position in the current image, the current block can be effectively predicted using a motion of the object. For example, when the motion direction and size of an object can be known by comparing the previous image and the current image, a prediction block (or a prediction image) of the current block can be generated considering the motion information of the object. Hereinafter, the prediction block generated using motion information can be referred to as a motion prediction block.

[130] A residual block can be generated by subtracting the prediction block from the current block. At this point, when there is a motion of an object, the energy of the residual block can be reduced by using the motion prediction block instead of the placed prediction block, and thus the compression performance of the residual block can be improved.

[131] As described above, generating a prediction block using motion information can be referred to as motion compensation prediction. In most interpredictions, a prediction block can be generated based on the motion compensation prediction.

[132] The motion information may include at least one of a motion vector, a reference image index, a prediction direction, and a bidirectional weight index. The motion vector indicates the motion direction and size of an object. The reference image index specifies a reference image of the current block among the reference images included in a reference image list. The prediction direction indicates any one of unidirectional L0 prediction, unidirectional L1 prediction, and bidirectional prediction (L0 prediction and L1 prediction). According to the prediction direction of the current block, at least one of the motion information in the L0 direction and the motion information in the L1 direction may be used. The bidirectional weight index specifies a weighting value applied to an L0 prediction block and a weighting value applied to an L1 prediction block.

[133] Figure 6 is a flowchart illustrating an interprediction method in accordance with one embodiment of the present disclosure.

[134] Referring to Figure 6, the interprediction method includes the steps of determining an interprediction mode of a current block (S601), acquiring motion information of the current block according to the determined interprediction mode (S602), and performing motion compensation prediction for the current block based on the acquired motion information (S603).

[135] Here, the interprediction mode represents various techniques for determining motion information of the current block, and may include an interprediction mode that uses translational motion information and an interprediction mode that uses affine motion information. For example, the interprediction mode using translational motion information may include a blending mode and a motion vector prediction mode, and the interprediction mode using affine motion information may include an affine blending mode and an affine motion vector prediction mode. The motion information of the current block may be determined based on a neighboring block adjacent to the current block or information analyzed from a bit stream according to the interprediction mode.

[136] Next, the interprediction method using affine motion information will be described in detail.

[137] Figure 7 is a view showing nonlinear motions of an object.

[138] A non-linear motion of an object may be generated in a video. For example, as shown in the example in Figure 7, a non-linear motion of an object, such as zooming, zooming, rotation, affine transformation, or the like of a camera, may occur. When a non-linear motion of an object occurs, the motion of the object cannot be effectively expressed with a translational motion vector. Consequently, coding efficiency can be improved by using an affine motion instead of a translational motion in an area where a non-linear motion of an object occurs.

[139] Figure 8 is a flowchart illustrating an interprediction method based on an affine motion in accordance with an embodiment of the present disclosure.

[140] Whether an affine motion-based interprediction technique is applied to the current block may be determined based on information parsed from a bit stream. Specifically, whether the affine motion-based interprediction technique is applied to the current block may be determined based on at least one of a flag indicating whether affine blending mode is applied to the current block and a flag indicating whether affine motion vector prediction mode is applied to the current block.

[141] When the interprediction technique based on an affine motion is applied to the current block, an affine motion model of the current block can be determined (S1101 → S801). The affine motion model can be determined as at least one of a six-parameter affine motion model and a four-parameter affine motion model. The six-parameter affine motion model expresses an affine motion using six parameters, and the four-parameter affine motion model expresses an affine motion using four parameters.

[142] Equation 1 expresses an affine motion using six parameters. The affine motion represents a translational motion to a predetermined area determined by affine seed vectors. [Equation 1]

[143] When an affine motion is expressed using six parameters, a complicated motion can be expressed. However, as the number of bits required to encode each of the parameters increases, the coding efficiency may be reduced. Consequently, the affine motion can be expressed using four parameters. Equation 2 expresses an affine motion using four parameters. [Equation 2]

[144] Information for determining an affine motion model for the current block may be encoded and signaled via a bit stream. For example, the information may be a 1-bit “affine_type_flag” flag. When the flag value is 0, it may indicate that a 4-parameter affine motion model is applied, and when the flag value is 1, it may indicate that a 6-parameter affine motion model is applied. The flag may be encoded by the slice, block, or block unit (e.g., by the coding block unit or coding tree). When a flag is signaled at the slice level, an affine motion model determined at the slice level may be applied to all blocks belonging to the slice.

[145] Alternatively, an affine motion model of the current block may be determined based on an affine interprediction mode of the current block. For example, when the affine blending mode is applied, the affine motion model of the current block may be determined as a 4-parameter motion model. On the other hand, when the affine motion vector prediction mode is applied, the information for determining the affine motion model of the current block may be encoded and signaled via a bit stream. For example, when the affine motion vector prediction mode is applied to the current block, the affine motion model of the current block may be determined based on the 1-bit flag of “affine_type_flag”.

[146] Then, an affine seed vector of the current block can be derived (S1102^S802). When a 4-parameter affine motion model is selected, motion vectors at two control points of the current block can be derived. On the other hand, when a 6-parameter affine motion model is selected, motion vectors at three control points of the current block can be derived. The motion vector at a control point can be termed as an affine seed vector. The control point can include at least one of the top-left corner, the top-right corner, and the bottom-left corner of the current block.

[147] Figure 9 is a view showing an example of affine seed vectors for each affine motion model.

[148] In the 4-parameter affine motion model, affine seed vectors can be derived for two between the top-left corner, the top-right corner, and the bottom-left corner. For example, as shown in the example in Figure 9(a), when a 4-parameter affine motion model is selected, an affine vector can be derived using the affine seed vector sv0 for the top-left corner of the current block (e.g., top-left sample (x1, y1)) and the affine seed vector sv1 for the top-right corner of the current block (e.g., top-right sample (x1, y1)). It is also possible to use an affine seed vector for the bottom-left corner instead of the affine seed vector for the top-left corner, or to use an affine seed vector for the bottom-left corner instead of the affine seed vector for the top-right corner.

[149] In the 6-parameter affine motion model, affine seed vectors can be derived for the top-left corner, the top-right corner, and the bottom-left corner. For example, as shown in the example in Figure 9(b), when a 6-parameter affine motion model is selected, an affine vector can be derived using the affine seed vector sv0 for the top-left corner of the current block (e.g., top-left sample (x1, y1)), the affine seed vector sv1 for the top-right corner of the current block (e.g., top-right sample (x1, y1)), and the affine seed vector sv2 for the top-left corner of the current block (e.g., top-left sample (x2, y2)).

[150] In the embodiment described below, in the 4-parameter affine motion model, the affine seed vectors of the upper left control point and the upper right control point will be referred to as a first affine seed vector and a second affine seed vector, respectively. In embodiments using the first affine seed vector and the second affine seed vector described below, at least one of the first affine seed vector and the second affine seed vector may be replaced by the affine seed vector of the lower left control point (a third affine seed vector) or the affine seed vector of the lower right control point (a fourth affine seed vector).

[151] Furthermore, in the 6-parameter affine motion model, the affine seed vectors of the upper left control point, the upper right control point, and the lower left control point will be referred to as a first affine seed vector, a second affine seed vector, and a third affine seed vector, respectively. In embodiments using the first affine seed vector, the second affine seed vector, and the third affine seed vector described below, at least one of the first affine seed vector, the second affine seed vector, and the third affine seed vector may be replaced by the affine seed vector of the lower right control point (a fourth affine seed vector).

[152] An affine vector can be derived for each sub-block using the affine seed vectors (S803). Here, the affine vector represents a translational motion vector derived based on the affine seed vectors. The affine vector of a sub-block can be termed as an affine sub-block motion vector or a sub-block motion vector.

[153] Figure 10 is a view showing an example of affine vector subblocks in a 4-parameter motion model.

[154] The subblock affine vector can be derived based on the control point position, the subblock position, and the affine seed vector. For example, Equation 3 shows an example of deriving an affine subblock vector. [Equation 3]

[155] In Equation 3, (x, y) denotes the position of a subblock. Here, the position of a subblock indicates the position of a reference sample included in the subblock. The reference sample can be a sample positioned at the upper left corner of the subblock or a sample of which at least one of the x-axis and y-axis coordinates is a center point. (x0, y0) denotes the position of the first control point and (sv0x, sv0y) denotes the first affine seed vector. Furthermore, (x1, y1) denotes the position of the second control point and (sv1x, sv1y) denotes the second affine seed vector.

[156] When the first control point and second control point correspond to the top left corner and top right corner of the current block, respectively, x1-x0 can be set to a value equal to the width of the current block.

[157] After that, motion compensation prediction for each sub-block can be performed using the affine vector of each sub-block (S1104^S804). As a result of performing motion compensation prediction, a prediction block for each sub-block can be generated. The prediction blocks of the sub-blocks can be set as the prediction blocks of the current block.

[158] Next, an interprediction method using translational motion information will be described in detail.

[159] The motion information of the current block may be derived from the motion information of another block. Here, another block may be an interprediction encoded/decoded block before the current block. Setting the motion information of the current block to be equal to the motion information of another block may be defined as a blending mode. Furthermore, setting the motion vector of another block as the prediction value of the motion vector of the current block may be defined as a motion vector prediction mode.

[160] Figure 11 is a flowchart illustrating a process of deriving motion information from a current block using a blending mode.

[161] A merge candidate for the current block may be derived (S1101). The merge candidate for the current block may be derived from an interprediction encoded/decoded block before the current block.

[162] Figure 12 is a view showing an example of candidate blocks used to derive a merge candidate.

[163] Candidate blocks may include at least one of neighboring blocks, including a sample adjacent to the current block, or non-neighboring blocks, including a sample not adjacent to the current block. Hereinafter, samples for determining candidate blocks are defined as reference samples. In addition, a reference sample adjacent to the current block is referred to as a neighboring reference sample, and a reference sample not adjacent to the current block is referred to as a non-neighboring reference sample.

[164] The neighboring reference sample may be included in a neighboring column of the leftmost column of the current block or a neighboring row of the topmost row of the current block. For example, when the coordinates of the top left sample of the current block are (0, 0), at least one of a block including a reference sample at the position of (-1, H-1), a block including a reference sample at the position of (W-1, -1), a block including a reference sample at the position of (W, -1), a block including a reference sample at the position of (-1, H), and a block including a reference sample at the position of (-1, -1) may be used as a candidate block. With reference to the drawing, neighboring blocks of index 0 to 4 may be used as candidate blocks.

[165] The non-neighboring reference sample represents a sample of which at least one of an x-axis distance and a y-axis distance from a reference sample adjacent to the current block has a predefined value. For example, at least one of a block including a reference sample of which the x-axis distance from the left reference sample is a predefined value, a block including a non-neighboring sample of which the y-axis distance from the top reference sample is a predefined value, and a block including a non-neighboring sample of which the x-axis distance and the y-axis distance from the top left reference sample are predefined values can be used as a candidate block. The predefined values can be a natural number such as 4, 8, 12, 16, or the like. Referring to the drawing, at least one of the blocks of index 5 to 26 can be used as a candidate block.

[166] A sample not positioned on the same vertical line, horizontal line, or diagonal line as the neighboring reference sample may be defined as a non-neighboring reference sample.

[167] Figure 13 is a view showing reference sample positions.

[168] As shown in the example of Figure 13, the x-coordinates of the top non-neighboring reference samples can be set to be different from the x-coordinates of the top neighboring reference samples. For example, when the position of the top neighboring reference sample is (W-1, -1), the position of a top non-neighboring reference sample separated as much as N from the top neighboring reference sample on the y-axis can be set to ((W/2)-1, -1-N), and the position of a top non-neighboring reference sample separated as much as 2N from the neighboring reference sample on the y-axis can be set to (0, -1-2N). That is, the position of a non-adjacent reference sample can be determined based on the position of an adjacent reference sample and a distance from the adjacent reference sample.

[169] Then, a candidate block including a neighboring reference sample among the candidate blocks is termed as a neighboring block, and a block including a non-neighboring reference sample is termed as a non-neighboring block.

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

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

[172] Alternatively, a candidate block that does not belong to the same cipher tree unit as the current block may be set to unavailable as a merge candidate. For example, when a reference sample deviates from the upper bound of a cipher tree unit to which the current block belongs, a candidate block including the reference sample may be set to unavailable as a merge candidate.

[173] When the upper boundary of the current block is adjacent to the upper boundary of the cipher tree unit, a plurality of candidate blocks are determined to be unavailable as a merge candidate, and therefore the encoding/decoding efficiency of the current block may decrease. To solve this problem, the candidate blocks may be configured so that the number of candidate blocks positioned on the left side of the current block is greater than the number of candidate blocks positioned on the top of the current block.

[174] Figure 14 is a view showing an example of candidate blocks used to derive a merge candidate.

[175] As shown in the example of Figure 14, the top blocks belonging to the top N block columns of the current block and the left-side blocks belonging to M left-side block columns of the current block can be set as candidate blocks. At this point, the number of left-side candidate blocks can be set to be greater than the number of top candidate blocks by setting M to be greater than N.

[176] For example, the difference between the y-axis coordinate of the reference sample in the current block and the y-axis coordinate of the top block that can be used as a candidate block can be set to not exceed N times the height of the current block. Furthermore, the difference between the x-axis coordinate of the reference sample in the current block and the x-axis coordinate of the left-hand block that can be used as a candidate block can be set to not exceed M times the width of the current block.

[177] For example, in the example shown in Figure 14, it is shown that the blocks belonging to the top two block columns of the current block and the blocks belonging to the left five block columns of the current block are defined as candidate blocks.

[178] A merge candidate can also be derived from a neighboring block temporarily included in a different image than the current block. For example, a merge candidate can be derived from a placed block included in a placed image.

[179] The motion information of the merge candidate may be set to be the same as the motion information of the candidate block. For example, at least one of a motion vector, a reference image index, a prediction direction, and a bidirectional weight index of the candidate block may be set as the motion information of the merge candidate.

[180] A list of merge candidates including merge candidates may be generated (S1102). The merge candidates may be divided into an adjacent merge candidate derived from a neighboring block adjacent to the current block and a non-adjacent merge candidate derived from a non-neighboring block.

[181] Indexes of the merge candidates in the merge candidate list may be assigned in a predetermined order. For example, an index assigned to an adjacent merge candidate may have a lower value than an index assigned to a non-adjacent merge candidate. Alternatively, an index may be assigned to each of the merge candidates based on the index of each block shown in Figure 12 or 14.

[182] 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 (S1103). At this point, information indicating whether the motion information of the current block is derived from an adjacent merge candidate may be signaled via a bit stream. The information may be a 1-bit flag. For example, a syntax element isAdjancentMergeFlag indicating whether the motion information of the current block is derived from an adjacent merge candidate may be signaled via a bit stream. When the value of the syntax element isAdjancentMergeFlag is 1, the motion information of the current block may be derived based on the adjacent merge candidate. Conversely, when the value of the syntax element isAdjancentMergeFlag is 0, the motion information of the current block may be derived based on a non-adjacent merge candidate.

[183] Information for specifying any of a plurality of merge candidates may be signaled via a bit stream. For example, information indicating an index of any of the merge candidates included in the list of merge candidates may be signaled via a bit stream.

[184] When isAdjacentMergeflag is 1, the merge_idx syntax element specifying any of the adjacent merge candidates may be flagged. The maximum value of the merge_idx syntax element may be set to a value obtained by subtracting 1 from the number of adjacent merge candidates.

[185] When isAdjacentMergeflag is 0, the NA_merge_idx syntax element specifying any of the non-adjacent merge candidates may be flagged. The NA_merge_idx syntax element represents a value obtained by subtracting the number of adjacent merge candidates from the index of the non-adjacent merge candidate. The decoder may select a non-adjacent merge candidate by adding the number of adjacent merge candidates to an index specified by NA_merge_idx.

[186] When the number of merge candidates included in the merge candidate list is less than a threshold value, the merge candidate included in the inter-region movement information list may be added to the merge candidate list. Here, the threshold value may be the maximum number of merge candidates that the merge candidate list may include, or a value obtained by subtracting an offset from the maximum number of merge candidates. The offset may be a natural number such as 1, 2, or the like. The inter-region movement information list may include a merge candidate derived based on a block encoded/decoded before the current block.

[187] The inter-region motion information list includes a merge candidate derived from an interprediction-based encoded/decoded block in the current picture. For example, the motion information of a merge candidate included in the inter-region motion information list may be set to be the same as the motion information of an interprediction-based encoded/decoded block. Here, the motion information may include at least one of a motion vector, a reference picture index, a prediction direction, and a bidirectional weight index.

[188] For Convenience of Explanation, a Merge Candidate Included in the Inter-Region Movement Information List Will Be Referred to as an Inter-Region Merge Candidate.

[189] The maximum number of merge candidates whose inter-region motion information list may include may be predefined by an encoder and a decoder. For example, the maximum number of merge candidates whose inter-region motion information list may include may be 1, 2, 3, 4, 5, 6, 7, 8, or more (e.g., 16).

[190] Alternatively, information indicating the maximum number of merge candidates in the inter-region motion information list may be signaled via a bit stream. The information may be signaled at the sequence, picture, or slice level.

[191] Alternatively, the maximum number of merge candidates from the inter-region motion information list may be determined according to the size of an image, the size of a slice, or the size of a coding tree unit.

[192] The inter-region motion information list may be initialized by the image unit, slice, block, brick, coding tree unit, or coding tree unit row (row or column). For example, when a slice is initialized, the inter-region motion information list is also initialized, and the inter-region motion information list may not include any merge candidates.

[193] Alternatively, information indicating whether or not to initialize the inter-region motion information list may be signaled via a bit stream. The information may be signaled at the slice, block, brick, or chunk level. Until the information indicates to initialize the inter-region motion information list, a previously configured inter-region motion information list may be used.

[194] Alternatively, information about the initial inter-region merge candidate may be signaled via a set of image parameters or a slice header. While the slice is initialized, the list of inter-region motion information may include the initial inter-region merge candidate. Consequently, an inter-region merge candidate may be used for a block that is the first encoding/decoding target in the slice.

[195] Blocks are encoded/decoded according to an encoding/decoding order, and the blocks encoded/decoded based on interprediction can be sequentially configured as an inter-region merge candidate according to an encoding/decoding order.

[196] Figure 15 is a flowchart illustrating a process for updating an inter-region movement information list.

[197] When interprediction is performed on the current block (S1501), an inter-region merge candidate may be derived based on the current block (S1502). The motion information of the inter-region merge candidate may be set to be the same as the motion information of the current block.

[198] When the inter-region movement information list is empty (S1503), the inter-region merge candidate derived based on the current block may be added to the inter-region movement information list (S1504).

[199] When the inter-region movement information list already includes the inter-region merge candidate (S1503), a redundancy check may be performed on the movement information of the current block (or the inter-region merge candidate derived based on the current block) (S1705). The redundancy check is to determine whether the movement information of an inter-region merge candidate previously stored in the inter-region movement information list and the movement information of the current block are the same. The redundancy check may be performed on all inter-region merge candidates previously stored in the inter-region movement information list. Alternatively, the redundancy check may be performed on inter-region merge candidates with an index greater than a threshold value or less than a threshold value among the inter-region merge candidates previously stored in the inter-region movement information list.

[200] When an inter-prediction merge candidate having the same motion information as the motion information of the current block is not included, the inter-region merge candidate derived based on the current block may be added to the inter-region motion information list (S1508). Whether the inter-region merge candidates are the same may be determined based on whether the motion information (e.g., a motion vector and/or a reference image index) of the inter-region merge candidates is the same.

[201] At this point, when the maximum number of inter-region merge candidates are already stored in the inter-region movement information list (S1506), the oldest prediction inter-region merge candidate is deleted (S1507) and the inter-region merge candidate derived based on the current block may be added to the inter-region movement information list (S1508).

[202] Each of the inter-region merge candidates can be identified by an index. When an inter-region merge candidate derived from the current block is added to the inter-region move information list, the lowest index (e.g., 0) is assigned to the inter-region merge candidate, and the indices of previously stored inter-region merge candidates can be increased by 1. At this point, when the maximum number of inter-region merge candidates is already stored in the inter-region move information list, an inter-region merge candidate with the highest index is removed.

[203] Alternatively, when the inter-region merge candidate derived from the current block is added to the inter-region movement information list, the largest index may be assigned to the inter-region merge candidate. For example, when the number of previously stored inter-region merge candidates in the inter-region movement information list is less than a maximum value, an index with the same value as the number of previously stored inter-region merge candidates may be assigned to the inter-region merge candidate. Alternatively, when the number of previously stored inter-region merge candidates in the inter-region movement information list is the same as the maximum value, an index subtracting 1 from the maximum value may be assigned to the inter-region merge candidate. Furthermore, an inter-region merge candidate with the smallest index is removed, and the indices of previously stored inter-region merge candidates may be decreased by 1.

[204] Figure 16 is a view showing one embodiment of updating an inter-region merge candidate list.

[205] It is assumed that as the inter-region merge candidate derived from the current block is added to the inter-region merge candidate list, the highest index is assigned to the inter-region merge candidate. Furthermore, it is assumed that the maximum number of inter-region merge candidates is already stored in the inter-region merge candidate list.

[206] When the inter-region merge candidate HmvpCand[n+1] derived from the current block is added to the inter-region merge candidate list HmvpCandList, the inter-region merge candidate HmvpCand[0] having the smallest index among the previously stored inter-region merge candidates is deleted, and the indices of the remaining inter-region merge candidates may be decreased by 1. Furthermore, the index of the inter-region merge candidate HmvpCand[n+1] derived from the current block may be set to a maximum value (n in the example shown in Figure 18).

[207] When an inter-region merge candidate equal to the inter-region merge candidate derived based on the current block is previously stored (S1705), the inter-region merge candidate derived based on the current block cannot be added to the inter-region movement information list (S1509).

[208] Alternatively, as the inter-region merge candidate derived based on the current block is added to the inter-region movement information list, a previously stored inter-region merge candidate that is the same as the inter-region merge candidate may be removed. In this case, an effect equal to that of recently updating the index of the previously stored inter-region merge candidate is achieved.

[209] Figure 17 is a view showing an example where an index of a previously stored inter-region merge candidate is updated.

[210] When the index of a previously stored inter-region merge candidate mvCand that is the same as the inter-region merge candidate mvCand derived based on the current block is hIdx, the previously stored inter-region merge candidate is deleted, and the indices of inter-region merge candidates with an index greater than hIdx may be decremented by 1. For example, in the example shown in Figure17, it is shown that HmvpCand[2] the same as mvCand is deleted from the inter-region movement information list HvmpCandList, and the indices from HmvpCand[3] to HmvpCand[n] are decremented by 1.

[211] Additionally, the inter-region merge candidate mvCand derived based on the current block may be added to the end of the inter-region move information list.

[212] Alternatively, the index assigned to the previously stored inter-region merge candidate that is the same as the inter-region merge candidate derived based on the current block may be updated. For example, the index of the previously stored inter-region merge candidate may be changed to a minimum or maximum value.

[213] It can be configured not to add motion information of blocks included in a predetermined area to the inter-region motion information list. For example, an inter-region merge candidate derived based on the motion information of a block included in the merge processing area cannot be added to the inter-region motion information list. Since an encoding/decoding order is not defined for the blocks included in the merge processing area, it is inappropriate to use motion information of any one of the blocks for interprediction of another block. Therefore, inter-region merge candidates derived based on the blocks included in the merge processing area cannot be added to the inter-region motion information list.

[214] When motion compensation prediction is performed by the sub-block unit, an inter-region merge candidate may be derived based on the motion information of a representative sub-block among a plurality of sub-blocks included in the current block. For example, when a sub-block merge candidate is used for the current block, an inter-region merge candidate may be derived based on the motion information of a representative sub-block among the sub-blocks.

[215] The motion vectors of the sub-blocks can be derived in the following order. First, any one of the merge candidates included in the merge candidate list of the current block is selected, and an initial displacement vector (shVector) can be derived based on the motion vector of the selected merge candidate. Then, a displacement sub-block, where the position of the reference sample is (xColSb, yColSb), can be derived as the initial displacement vector is added at the position (xSb, ySb) of the reference sample (e.g., the top-left corner sample or the sample in the center) of each sub-block in the coding block. Equation 4 shows an equation for deriving a displacement sub-block. [Equation 4]

[216] Then, the motion vector of a placed block corresponding to the center position of the sub-block including (xColSb, yColSb) can be defined as the motion vector of the sub-block including (xSb, ySb).

[217] The representative sub-block may mean a sub-block including the top left sample or the sample in the center of the current block.

[218] Figure 18 is a view showing the position of a representative subblock.

[219] Figure 18(a) shows an example where the sub-block positioned at the top-left corner of the current block is defined as the representative sub-block, and Figure 18(b) shows an example where the sub-block positioned at the center of the current block is defined as the representative sub-block. When motion compensation prediction is performed per sub-block unit, an inter-region merging candidate of the current block can be derived based on the motion vector of the sub-block including the top-left sample of the current block or the sub-block including the sample at the center of the current block.

[220] It may be determined whether or not to use the current block as an inter-region merge candidate based on the inter-prediction mode of the current block. For example, a block encoded/decoded based on an affine motion model may be set as unavailable as an inter-region merge candidate. Therefore, although the current block is encoded/decoded by inter-prediction, when the inter-prediction mode of the current block is affine prediction mode, the inter-region motion information list may not be updated based on the current block.

[221] Alternatively, the inter-region merge candidate may be derived based on at least one sub-block vector among the sub-blocks included in the encoded/decoded block based on the affine motion model. For example, the inter-region merge candidate may be derived using a sub-block positioned in the top left corner, a sub-block positioned in the center, or a sub-block positioned in the top right side of the current block. Alternatively, an average value of sub-block vectors of a plurality of sub-blocks may be defined as the motion vector of the inter-region merge candidate.

[222] Alternatively, the inter-region merge candidate may be derived based on an average value of affine seed vectors of the encoded/decoded block based on the affine motion model. For example, an average of at least one of the first affine seed vector, the second affine seed vector, and the third affine seed vector of the current block may be defined as the motion vector of the inter-region merge candidate.

[223] Alternatively, a list of inter-region motion information may be configured for each inter-prediction mode. For example, at least one of a list of inter-region motion information for a block encoded/decoded by intra-block copy, a list of inter-region motion information for a block encoded/decoded based on a translational motion model, and a list of inter-region motion information for a block encoded/decoded based on an affine motion model may be defined. According to the inter-prediction mode of the current block, any one of a plurality of lists of inter-region motion information may be selected.

[224] Figure 19 is a view showing an example where a list of inter-region motion information is generated for each interprediction mode.

[225] When a block is encoded/decoded based on a non-affine motion model, an inter-region merge candidate mvCand derived based on the block may be added to an inter-region non-affine motion information list HmvpCandList. Conversely, when a block is encoded/decoded based on an affine motion model, an inter-region merge candidate mvAfCand derived based on the block may be added to an inter-region affine motion information list HmvpAfCandList.

[226] Affine seed vectors of a block encoded/decoded based on the affine motion model may be stored in an inter-region merge candidate derived from the block. Therefore, the inter-region merge candidate may be used as a merge candidate to derive the affine seed vector of the current block.

[227] In addition to the above-described inter-region movement information list, an additional inter-region movement information list may be defined. In addition to the above-described inter-region movement information list (hereinafter, referred to as a first inter-region movement information list), a long-term movement information list (hereinafter, referred to as a second inter-region movement information list) may be defined. Here, the long-term movement information list includes long-term merge candidates.

[228] When both the first inter-region movement information list and the second inter-region movement information list are empty, first, inter-region merge candidates can be added to the second inter-region movement information list. Only after the number of available inter-region merge candidates reaches the maximum number in the second inter-region movement information list, inter-region merge candidates can be added to the first inter-region movement information list.

[229] Alternatively, an inter-region merge candidate may be added to both the second inter-region movement information list and the first inter-region movement information list.

[230] At this point, the second inter-region motion information list, whose setup has been completed, may no longer be updated. Alternatively, when the decoded region is greater than or equal to a predetermined proportion of the slice, the second inter-region motion information list may be updated. Alternatively, the second inter-region motion information list may be updated for every N coding tree unit lines.

[231] On the other hand, the first inter-region motion information list may be updated whenever an inter-prediction encoded/decoded block is generated. However, it may be configured not to use the inter-region merge candidate added to the second inter-region motion information list to update the first inter-region motion information list.

[232] Information for selecting any one of the first inter-region movement information list and the second inter-region movement information list may be signaled via a bit stream. When the number of merge candidates included in the merge candidate list is less than a threshold value, merge candidates included in the inter-region movement information list indicated by the information may be added to the merge candidate list.

[233] Alternatively, a list of inter-region motion information may be selected based on the current block size and shape, interprediction mode, whether bidirectional prediction is enabled, whether motion vector refinement is enabled, or whether triangular partitioning is enabled.

[234] Alternatively, although an inter-region merge candidate included in the first inter-region movement information list is added, when the number of merge candidates included in the merge candidate list is less than the maximum number of merges, the inter-region merge candidates included in the second inter-region movement information list may be added to the merge candidate list.

[235] Figure 20 is a view showing an example where an inter-region merge candidate included in a long-term motion information list is added to a merge candidate list.

[236] When the number of merge candidates included in the merge candidate list is less than the maximum number, the inter-region merge candidates included in the first inter-region movement information list HmvpCandList may be added to the merge candidate list. When the number of merge candidates included in the merge candidate list is less than the maximum number, although the inter-region merge candidates included in the first inter-region movement information list are added to the merge candidate list, the inter-region merge candidates included in the long-term movement information list HmvpLTCandList may be added to the merge candidate list.

[237] The inter-region merge candidate may be configured to include additional information in addition to movement information. For example, for the inter-region merge candidate, a size, shape, or partitioning information of a block may be additionally stored. When the merge candidate list of the current block is constructed, only inter-region merge candidates having a size, shape, or partitioning information equal to or similar to that of the current block are used among the inter-region merge candidates, or inter-region merge candidates having a size, shape, or partitioning information equal to or similar to that of the current block may be added to the merge candidate list first.

[238] Alternatively, a list of inter-region movement information may be generated for each of the size, shape, or partitioning information of a block. Among the plurality of lists of inter-region movement information, a list of merge candidates of the current block may be generated using a list of inter-region movement information corresponding to the shape, size, or partitioning information of the current block.

[239] When the number of merge candidates included in the current block's merge candidate list is less than the threshold value, inter-region merge candidates included in the inter-region movement information list may be added to the merge candidate list. The addition process is performed in ascending or descending order based on the index. For example, an inter-region merge candidate with the largest index may be added to the merge candidate list first.

[240] When it is desired to add an inter-region merge candidate included in the inter-region movement information list to the merge candidate list, a redundancy check may be performed between the inter-region merge candidate and the merge candidates previously stored in the merge candidate list.

[241] Redundancy checking may be performed on only some of the inter-region merge candidates included in the inter-region move information list. For example, redundancy checking may be performed on only inter-region merge candidates with an index greater than a threshold value or less than a threshold value. Alternatively, redundancy checking may be performed on only N merge candidates with the largest index or N merge candidates with the smallest index.

[242] Alternatively, the redundancy check may be performed only on some of the merge candidates previously stored in the merge candidate list. For example, the redundancy check may be performed only on a merge candidate with an index greater than a threshold value or less than a threshold value, or on a merge candidate derived from a block at a specific position. Here, the specific position may include at least one of a left neighboring block, an upper neighboring block, an upper right neighboring block, and a lower left neighboring block of the current block.

[243] Figure 21 is a view showing an example where a redundancy check is performed on only some of the merge candidates.

[244] When one wants to add the prediction inter-region merge candidate HmvpCand[j] to the merge candidate list, a redundancy check can be performed on the inter-region merge candidate with two merge candidates mergeCandList[NumMerge-2] and mergeCandList[NumMerge-1] having the largest indices. Here, NumMerge can represent the number of spatial merge candidates and temporal merge candidates that are available.

[245] Unlike the example shown in the drawing, when one wants to add an inter-region merge candidate HmvpCand[j] to the merge candidate list, a redundancy check can be performed on the inter-region merge candidate with up to two merge candidates having the lowest index. For example, one can check whether mergeCandList[0] and mergeCandList[1] are equal to HmvpCand[j]. Alternatively, a redundancy check can be performed only on merge candidates derived at a specific position. For example, the redundancy check can be performed on at least one of a merge candidate derived from a neighboring block positioned on the left side of the current block and a merge candidate derived from a neighboring block positioned on the top of the current block. When a merge candidate derived at a specific position does not exist in the merge candidate list, an inter-region merge candidate can be added to the merge candidate list without having a redundancy check.

[246] When a merge candidate equal to the first inter-region merge candidate is found and a redundancy check is performed on the second inter-region merge candidate, the redundancy check with a merge candidate equal to the first inter-region merge candidate may be omitted.

[247] Figure 22 is a view showing an example where a redundancy check is omitted for a specific merge candidate.

[248] When one wants to add an inter-region merge candidate HmvpCand[i] having index i to the merge candidate list, a redundancy check is performed between the inter-region merge candidate and the merge candidates previously stored in the merge candidate list. At this point, when a merge candidate mergeCandList[j] the same as the inter-region merge candidate HmvpCand[i] is found, the redundancy check can be performed between the inter-region merge candidate HmvpCand[i-1] with index i-1 and the merge candidates without adding the inter-region merge candidate HmvpCand[i] to the merge candidate list. At this point, the redundancy check between the inter-region merge candidate HmvpCand[i-1] and the merge candidate mergeCandList[j] can be omitted.

[249] For example, in the example shown in Figure 22, it is determined that HmvpCand[i] and mergeCandList[2] are equal. Consequently, HmvpCand[i] is not added to the merge candidate list, and a redundancy check can be performed on HmvpCand[i-1]. At this point, the redundancy check between HvmpCand[i-1] and mergeCandList[2] can be omitted.

[250] When the number of merge candidates included in the merge candidate list of the current block is less than the threshold value, at least one of a pairwise merge candidate and a zero merge candidate may be additionally included in addition to the inter-region merge candidate. The pairwise merge candidate means a merge candidate with an average value of motion vectors of two or more merge candidates as a motion vector, and the zero merge candidate means a merge candidate with a motion vector of 0.

[251] A merge candidate can be added to the current block's merge candidate list in the following order.

[252] Spatial merge candidate - Temporal merge candidate - Inter-region merge candidate - (inter-region affine merge candidate) - Pairwise merge candidate - Zero merge candidate

[253] The spatial merging candidate means a merging candidate derived from at least one of a neighboring block and a non-neighboring block, and the temporal merging candidate means a merging candidate derived from a previous reference image. The inter-region affine merging candidate represents an inter-region merging candidate derived from a block encoded/decoded with an affine motion model.

[254] The prediction region motion information list may also be used in motion vector prediction mode. For example, when the number of motion vector prediction candidates included in a motion vector prediction candidate list of the current block is less than a threshold value, a prediction region merge candidate included in the prediction region motion information list may be set as a prediction candidate motion vector for the current block. Specifically, the motion vector of the prediction region merge candidate may be set as a prediction candidate motion vector.

[255] When any one among the motion vector prediction candidates included in the motion vector prediction candidate list of the current block is selected, the selected candidate can be set as the motion vector predictor of the current block. Thereafter, after a residual coefficient of the motion vector of the current block is decoded, a motion vector of the current block can be obtained by adding the motion vector predictor and the residual coefficient of the motion vector.

[256] The motion vector prediction candidate list of the current block can be configured in the following order.

[257] Spatial motion vector prediction candidate - Temporal motion vector prediction candidate - Inter-region merging candidate - (inter-region affine merging candidate) - Zero motion vector prediction candidate.

[258] The spatial motion vector prediction candidate means a motion vector prediction candidate derived from at least one of a neighboring block and a non-neighboring block, and the temporal motion vector prediction candidate means a motion vector prediction candidate derived from a previous reference image. The inter-region affine merging candidate represents an inter-region motion vector prediction candidate derived from a block encoded/decoded with the affine motion model. The zero motion vector prediction candidate represents a candidate with a motion vector value of 0.

[259] A coding block may be partitioned into a plurality of prediction units, and prediction may be performed on each of the partitioned prediction units. Here, a prediction unit represents a basic unit for performing prediction.

[260] A coding block may be partitioned using at least one of a vertical line, a horizontal line, an oblique line, and a diagonal line. Information for determining at least one of the number, angles, and positions of the lines that partition a coding block may be signaled via a bit stream. For example, information indicating any of the candidates for the partitioning type of a coding block may be signaled via a bit stream, or information specifying any of a plurality of line candidates for partitioning a coding block may be signaled via a bit stream. Alternatively, information for determining the number or types of candidate lines that partition a coding block may be signaled via the bit stream. For example, whether an oblique line with an angle greater than that of a diagonal line and/or an oblique line with an angle less than that of a diagonal line may be used as a line candidate may be determined using a 1-bit flag.

[261] Alternatively, at least one of the number, angles, and positions of lines partitioning a coding block may be adaptively determined based on at least one of the intra-prediction mode of the coding block, the inter-prediction mode of the coding block, the position of an available merge candidate of the coding block, and a partitioning pattern of a neighboring block.

[262] When a coding block is partitioned into a plurality of prediction units, intraprediction or interprediction may be performed on each of the partitioned prediction units.

[263] Figure 23 is a view showing examples of applying partitioning to a coding block to obtain a plurality of prediction units using a diagonal line.

[264] As shown in the examples in Figures 23(a) and 23(b), a coding block can be partitioned into two triangular prediction units using a diagonal line.

[265] In Figures 23(a) and 23(b), it is shown that a coding block is partitioned into two prediction units using a diagonal line connecting two vertices of the coding block. However, the coding block can be partitioned into two prediction units using an oblique line, at least one end of which does not pass through a vertex of the coding block.

[266] Figure 24 is a view showing examples of applying partitioning to a coding block to obtain two prediction units.

[267] As shown in the examples of Figures 24(a) and 24(b), a coding block can be partitioned into two prediction units using an oblique line, both ends of which are in contact with the upper boundary and the lower boundary of the coding block, respectively.

[268] Alternatively, as shown in the examples of Figures 24(c) and 24(d), a coding block can be partitioned into two prediction units using an oblique line, both ends of which are in contact with the left boundary and the right boundary of the coding block, respectively.

[269] Alternatively, a coding block may be partitioned into two prediction blocks of different sizes. For example, a coding block may be partitioned into two prediction units of different sizes by defining an oblique line that partitions the coding block to contact two boundary surfaces that form a vertex.

[270] Figure 25 is a view showing examples of partitioning a coding block into a plurality of prediction blocks of different sizes.

[271] As shown in the examples of Figures 25(a) and 25(b), since a diagonal line connecting the upper-left and lower-right corners of the coding block is defined to pass through the left boundary, the right boundary, the upper boundary, or the lower boundary, instead of passing through the upper-left corner or the lower-right corner of the coding block, the coding block can be partitioned into two prediction units with different sizes.

[272] Alternatively, as shown in the examples of Figures 25(c) and 25(d), since a diagonal line connecting the upper-right and lower-left corners of the coding block is defined to pass through the left boundary, the right boundary, the upper boundary, or the lower boundary, instead of passing through the upper-left corner or the lower-right corner of the coding block, the coding block can be partitioned into two prediction units with different sizes.

[273] Each of the prediction units generated by partitioning a coding block will be referred to as an “nth prediction unit”. For example, in the examples shown in Figures 23 through 25, PU1 may be defined as a first prediction unit and PU2 may be defined as a second prediction unit. The first prediction unit means a prediction unit including a sample positioned at the bottom left or a sample positioned at the top left in the coding block, and the second prediction unit means a prediction unit including a sample positioned at the top right or a sample positioned at the bottom right in the coding block.

[274] Conversely, a prediction unit including a sample positioned in the upper right or a sample positioned in the lower right in the coding block may be defined as a first prediction unit, and a prediction unit including a sample positioned in the lower left or a sample positioned in the upper left in the coding block may be defined as a second prediction unit.

[275] The embodiments below are described with a focus on examples of partitioning a coding block using a diagonal line. In particular, partitioning a coding block into two prediction units using a diagonal line is referred to as diagonal partitioning or triangular partitioning, and a prediction unit generated based on diagonal partitioning is referred to as a triangular prediction unit. However, it is also possible to apply the embodiments described below to examples of partitioning a coding block using an oblique line from an angle other than a vertical line, a horizontal line, or a diagonal line.

[276] Whether or not diagonal partitioning is applied to a coding block may be determined based on at least one of a slice type, the maximum number of merge candidates that the merge candidate list may include, the size of the coding block, the shape of the coding block, the prediction coding mode of the coding block, and the partitioning pattern of the parent node.

[277] For example, whether or not diagonal partitioning applies to a coding block can be determined based on whether the current slice is of type B. Diagonal partitioning may be allowed only when the current slice is of type B.

[278] Alternatively, whether or not diagonal partitioning is applied to a cipher block may be determined based on whether the maximum number of merge candidates included in the merge candidate list is two or more. Diagonal partitioning may be allowed only when the maximum number of merge candidates included in the merge candidate list is two or more.

[279] Alternatively, when at least one of the width and height is greater than 64 in the hardware implementation, there is an issue where a data processing unit of size 64 x 64 is accessed redundantly. Therefore, when at least one of the width and height of the coding block is greater than a threshold value, partitioning of a coding block into a plurality of prediction blocks may not be allowed. For example, when at least one of the width and height of a coding block is greater than 64 (e.g., when at least one of the width and height is 128), diagonal partitioning cannot be used.

[280] Alternatively, diagonal partitioning may not be allowed for a coding block whose number of samples is greater than a threshold value, considering the maximum number of samples that can be processed simultaneously in the hardware implementation. For example, diagonal partitioning may not be allowed for a coding tree block whose number of samples is greater than 4,096.

[281] Alternatively, diagonal partitioning may not be allowed for a coding block whose number of samples included in the coding block is less than a threshold value. For example, it may be defined to not apply diagonal partitioning to a coding block when the number of samples included in the coding block is less than 64.

[282] Alternatively, whether or not diagonal partitioning applies to a coding block may be determined based on whether the width-to-height ratio of the coding block is less than a first threshold value or whether the width-to-height ratio of the coding block is greater than a second threshold value. Here, the width-to-height ratio whRatio of the coding block may be determined as a ratio of the width CbW to the height CbH of the coding block, as shown in Equation 5. [Equation 5] The second boundary value can be an inverse number of the first boundary value. For example, when the first boundary value is k, the second boundary value can be 1/k.

[283] Diagonal partitioning can be applied to a coding block only when the width-to-height ratio of the coding block is between the first boundary value and the second boundary value.

[284] Alternatively, triangular partitioning may be used only when the width-to-height ratio of the coding block is less than the first threshold value or greater than the second threshold value. For example, when the first threshold value is 16, diagonal partitioning may not be allowed for a coding block of size 64 x 4 or 4 x 64.

[285] Alternatively, whether or not to allow diagonal partitioning can be determined based on the partitioning pattern of the parent node. For example, when a parent node's coding block is partitioned based on quad tree partitioning, diagonal partitioning can be applied to a leaf node's coding block. Conversely, it can be configured to disallow diagonal partitioning for the leaf node's coding block when the parent node's coding block is partitioned based on binary tree or ternary tree partitioning.

[286] Alternatively, whether or not to allow diagonal partitioning may be determined based on the prediction coding mode of a coding block. For example, diagonal partitioning may be allowed only when the coding block is intra-prediction coded, when the coding block is inter-prediction coded, or when the coding block is coded by a predefined inter-prediction mode. Here, the predefined inter-prediction mode may represent at least one of a blending mode, a motion vector prediction mode, an affine blending mode, and an affine motion vector prediction mode.

[287] Alternatively, whether or not to allow diagonal partitioning can be determined based on the size of a parallel processing region. For example, when the size of a coding block is larger than the size of a parallel processing region, diagonal partitioning cannot be used.

[288] Whether or not diagonal partitioning applies to a coding block can be determined by considering two or more of the conditions listed above.

[289] As another example, information indicating whether or not to apply diagonal partitioning to a coding block may be signaled via a bit stream. The information may be signaled at a sequence, image, slice, or block level. For example, the flag triangle_partition_flag indicating whether triangular partitioning is applied to a coding block may be signaled at a coding block level.

[290] When it is determined to apply diagonal partitioning to a coding block, information indicating the number of lines that partition the coding block or the positions of the lines may be signaled via a bit stream.

[291] For example, when a coding block is partitioned by a diagonal line, information indicating the direction of the diagonal line that partitions the coding block can be signaled via a bit stream. For example, the triangle_partition_type_flag flag indicating the direction of the diagonal line can be signaled via a bit stream. The flag indicates whether the coding block is partitioned by a diagonal line connecting the upper-left corner and the lower-right corner or whether the coding block is partitioned by a diagonal line connecting the upper-right corner and the lower-left corner. Partitioning a coding block by a diagonal line connecting the upper-left corner and the lower-right corner can be termed as a left triangular partitioning type, and partitioning a coding block by a diagonal line connecting the upper-right corner and the lower-left corner can be termed as a right triangular partitioning type. For example, when the value of the flag is 0, it may indicate that the partitioning type of the encoding block is the left triangular partitioning type, and when the value of the flag is 1, it may indicate that the partitioning type of the encoding block is the right triangular partitioning type.

[292] In addition, information indicating whether the prediction units are of equal size or information indicating the position of a diagonal line for partitioning the coding block may be signaled via a bit stream. For example, when the information indicating the sizes of the prediction units indicates that the sizes of the prediction units are equal, the encoding of the information indicating the position of the diagonal is omitted and the coding block may be partitioned into two prediction units using a diagonal line passing through two vertices of the coding block. On the other hand, when the information indicating the sizes of the prediction units indicates that the sizes of the prediction units are not equal, the position of the diagonal line that partitions the coding block may be determined based on the information indicating the position of the diagonal line. For example, when the left triangular partitioning type is applied to a coding block, the position information may indicate whether the diagonal line is in contact with the left boundary and the lower boundary or the upper boundary and the right boundary of the coding block. Alternatively, when the right triangular partitioning type is applied to a coding block, the position information can indicate whether the diagonal line is in contact with the right boundary and the lower boundary or the upper boundary and the left boundary of the coding block.

[293] Information indicating the partitioning type of a coding block may be signaled at a coding block level. Consequently, the partitioning type may be determined for each coding block to which diagonal partitioning is applied.

[294] As another example, information indicating the partitioning type may be flagged for a sequence, an image, a slice, a block, or a coding tree unit. In this case, the partitioning types of coding blocks to which diagonal partitioning is applied in a sequence, an image, a slice, a block, or a coding tree unit may be set to be the same.

[295] Alternatively, information for determining the partitioning type may be encoded and signaled for the first coding unit to which diagonal partitioning is applied in the coding tree unit, and the second and subsequent coding units to which diagonal partitioning is applied may be defined to use a partitioning type equal to that of the first coding unit.

[296] As another example, the partitioning type of a coding block may be determined based on the partitioning type of a neighboring block. Here, the neighboring block may include at least one of a neighboring block adjacent to the top-left corner of the coding block, a neighboring block adjacent to the top-right corner, a neighboring block adjacent to the bottom-left corner, a neighboring block positioned on the top, and a neighboring block positioned on the left side. For example, the partitioning type of the current block may be set to be the same as the partitioning type of a neighboring block. Alternatively, the partitioning type of the current block may be determined based on whether the left triangular partitioning type is applied to the top-left neighboring block or whether the right triangular partitioning type is applied to the top-right neighboring block or the bottom-left neighboring block.

[297] In order to perform motion prediction compensation in a first triangular prediction unit and a second triangular prediction unit, motion information of each of the first triangular prediction unit and the second triangular prediction unit may be derived. At this point, motion information of the first triangular prediction unit and the second triangular prediction unit may be derived from merge candidates included in the merge candidate list. To distinguish a general merge candidate list from a merge candidate list used to derive motion information of triangular prediction units, the merge candidate list for deriving motion information of triangular prediction units is referred to as a triangular merge candidate list, and a merge candidate included in the triangular merge candidate list will be referred to as a triangular merge candidate. However, using the method of deriving a merge candidate and the method of constructing a merge candidate list described above for the benefit of triangular merge candidates and the method of constructing the triangular merge candidate list are also included in the spirit of the present disclosure.

[298] Information for determining the maximum number of triangular merge candidates that the triangular merge candidate list may include may be signaled via a bit stream. The information may indicate a difference between the maximum number of merge candidates that the merge candidate list may include and the maximum number of triangular merge candidates that the triangular merge candidate list may include.

[299] Triangular merge candidates can be derived from a spatially neighboring block and a temporally neighboring block of a coding block.

[300] Figure 26 is a view showing neighboring blocks used to derive a triangular merge candidate.

[301] A triangular merging candidate may be derived using at least one of a neighboring block positioned at the top of a coding block, a neighboring block positioned at the left side of the coding block, and a placed block included in a different picture than the coding block. The top neighboring block may include at least one of a block including a sample (xCb+CbW-1, yCb-1) positioned at the top of the coding block, a block including a sample (xCb+CbW, yCb-1) positioned at the top of the coding block, and a block including a sample (xCb-1, yCb-1) positioned at the top of the coding block. The left neighboring block may include at least one of a block including a sample (xCb-1, yCb+CbH-1) positioned at the left side of the coding block and a block including a sample (xCb-1, yCb+CbH) positioned at the left side of the coding block. The placed block can be determined as any one of a block including a sample (xCb + CbW, yCb + CbH) adjacent to the upper right corner of the coding block and a block including a sample (xCb/2, yCb/2) positioned at the center of the coding block, in a placed image.

[302] Neighboring blocks can be searched in a predefined order, and triangular merge candidates can be constructed as a list of triangular merge candidates according to a predefined order. For example, the list of triangular merge candidates can be constructed by searching the triangular merge candidates in the order of B1, A1, B0, A0, C0, B2, and C1.

[303] Neighboring blocks can be searched in a predefined order, and triangular merge candidates can be constructed as a list of triangular merge candidates according to a predefined order. For example, the list of triangular merge candidates can be constructed by searching the triangular merge candidates in the order of B1, A1, B0, A0, C0, B2, and C1.

[304] The motion information of the triangular prediction units can be derived based on the triangular merge candidate list. That is, the triangular prediction units can share a triangular merge candidate list.

[305] In order to derive motion information of the triangular merge unit, information for specifying at least one of the triangular merge candidates included in the triangular merge candidate list may be signaled via a bit stream. For example, merge_triangle_idx index information for specifying at least one of the triangular merge candidates may be signaled via a bit stream.

[306] The index information may specify a combination of a merge candidate from the first triangular prediction unit and a merge candidate from the second triangular prediction unit. For example, Table 1 shows an example of a combination of merge candidates according to the merge_triangle_idx index information. TABLE 1

[307] When the value of the merge_triangle_idx index information is 1, it indicates that the motion information of the first triangular prediction unit is derived from a merge candidate with an index of 1, and the motion information of the second triangular prediction unit is derived from a merge candidate with an index of 0. A triangular merge candidate for deriving motion information of the first triangular prediction unit and a triangular merge candidate for deriving motion information of the second triangular prediction unit can be determined through the merge_triangle_idx index information.

[308] A partitioning type of a coding block to which diagonal partitioning is applied may be determined based on index information. That is, the index information may specify a combination of a merge candidate of the first triangular prediction unit, a merge candidate of the second triangular prediction unit, and a partitioning direction of the coding block. When a partitioning type of the coding block is determined based on index information, the triangle_partition_type_flag information indicating the direction of a diagonal line partitioning the coding block may not be encoded. Table 2 expresses the partitioning types of a coding block with respect to the merge_triangle_idx index information. TABLE 2

[309] When the triangledir variable is 0, it indicates that the left triangle partitioning type is applied to the coding block, and when the triangledir variable is 1, it indicates that the right triangle partitioning type is applied to the coding block. When combining Table 1 and Table 2, it can be set to specify a combination of the merge candidate of the first triangle prediction unit, the merge candidate of the second triangle prediction unit, and the partitioning direction of the coding block by index information Merge_triangle_idx.

[310] As another example, index information only for any one of the first triangular prediction unit and the second triangular prediction unit may be flagged, and an index from one triangular merge candidate to the other one of the first triangular prediction unit and the second triangular prediction unit may be determined based on the index information. For example, a triangular merge candidate of the first triangular prediction unit may be determined based on the index information merge_triangle_idx indicating an index of any one of the triangular merge candidates. Furthermore, a triangular merge candidate of the second triangular prediction unit may be specified based on merge_triangle_idx. For example, the triangular merge candidate of the second triangular prediction unit may be derived by adding or subtracting an offset to or from the index information merge_triangle_idx. The offset can be an integer such as 1 or 2. For example, a triangular merge candidate having a value obtained by adding 1 to merge_traingle_idx as an index can be determined as the triangular merge candidate of the second triangular prediction unit. When merge_triangle_idx indicates a triangular merge candidate having the largest index value among the triangular merge candidates, the motion information of the second triangular prediction unit can be derived from a triangular merge candidate having an index of 0 or a triangular merge candidate having a value obtained by subtracting 1 from merge_triangle_idx as an index.

[311] Alternatively, the motion information of the second triangular prediction unit may be derived from a triangular merge candidate having a reference image equal to that of the triangular merge candidate of the first triangular prediction unit specified by the index information. Here, the triangular merge candidate having a reference image equal to that of the triangular merge candidate of the first triangular prediction unit may indicate a triangular merge candidate having at least one of the L0 reference image and the L1 reference image equal to those of the triangular merge candidate of the first triangular prediction unit. When there are a plurality of triangular merge candidates having a reference image equal to that of the triangular merge candidate of the first triangular prediction unit, at least one of the triangular merge candidates may be selected based on whether the merge candidate includes bidirectional motion information or a difference value between the index of the merge candidate and the index information.

[312] As another example, index information may be signaled to each of the first triangular prediction unit and the second triangular prediction unit. For example, the first index information 1st_merge_idx for determining a triangular merge candidate of the first triangular prediction unit and the second index information 2nd_merge_idx for determining a triangular merge candidate of the second triangular prediction unit may be signaled via a bit stream. The motion information of the first triangular prediction unit may be derived from the triangular merge candidate determined based on the first index information 1st_merge_idx and the motion information of the second triangular prediction unit may be derived from the triangular merge candidate determined based on the second index information 2nd_merge_idx.

[313] The first index information 1st_merge_idx may indicate an index of any of the triangular merge candidates included in the triangular merge candidate list. The triangular merge candidate of the first triangular prediction unit may be determined as a triangular merge candidate indicated by the first index information 1st_merge_idx.

[314] The triangular merge candidate indicated by the first index information 1st_merge_idx may be set to not be used as a triangular merge candidate of the second triangular prediction unit. Therefore, the second index information 2nd_merge_idx of the second triangular prediction unit may indicate an index of any one of the remaining triangular merge candidates, excluding the triangular merge candidate indicated by the first index information. When the value of the second index information 2nd_merge_idx is smaller than the value of the first index information 1st_merge_idx, the triangular merge candidate of the second triangular prediction unit may be determined as a triangular merge candidate having the index information indicated by the second index information 2nd_merge_idx. On the other hand, when the value of the second index information 2nd_merge_idx is equal to or greater than the value of the first index information 1st_merge_idx, the triangular merge candidate of the second triangular prediction unit can be determined as a triangular merge candidate having a value obtained by adding 1 to the value of the second index information 2nd_merge_idx as an index.

[315] Alternatively, whether or not to flag the second index information may be determined according to the number of triangular merge candidates included in the triangular merge candidate list. For example, when the maximum number of triangular merge candidates that the triangular merge candidate list can include does not exceed 2, the flagging of the second index information may be omitted. When the flagging of the second index information is omitted, a second triangular merge candidate may be derived by adding or subtracting an offset to or from the first index information. For example, when the maximum number of triangular merge candidates that the triangular merge candidate list can include is 2 and the first index information indicates index 0, the second triangular merge candidate may be derived by adding 1 to the first index information. Alternatively, when the maximum number of triangular merge candidates that the triangular merge candidate list can include is 2 and the first index information indicates 1, the second triangular merge candidate may be derived by subtracting 1 from the first index information.

[316] Alternatively, when the flag of the second index information is omitted, the second index information may be set to a default value. Here, the default value may be 0. The second triangular merge candidate may be derived by comparing the first index information and the second index information. For example, when the second index information is less than the first index information, a merge candidate with index 0 may be defined as the second triangular merge candidate, and when the second index information is equal to or greater than the first index information, a merge candidate with index 1 may be defined as the second triangular merge candidate.

[317] When the triangular merge candidate has unidirectional motion information, the unidirectional motion information of the triangular merge candidate can be set as the motion information of the triangular prediction unit. On the other hand, when the triangular merge candidate has bidirectional motion information, only one of the L0 motion information and the L1 motion information can be set as the motion information of the triangular prediction unit. Which one of the L0 motion information and the L1 motion information will be obtained can be determined based on the index of the triangular merge candidate or motion information of another triangular prediction unit.

[318] For example, when the index of the triangular merge candidate is an even number, the L0 motion information of the triangular prediction unit can be set to 0, and the L1 motion information of the triangular merge candidate can be set to L1 motion information of the triangular prediction unit. Conversely, when the index of the triangular merge candidate is an odd number, the L1 motion information of the triangular prediction unit can be set to 0, and the L0 motion information of the triangular merge candidate can be set to 0. Contrarily, when the index of the triangular merge candidate is an even number, the L0 motion information of the triangular merge candidate can be set to L0 motion information of the triangular prediction unit, and when the index of the triangular merge candidate is an odd number, the L1 motion information of the triangular merge candidate can be set to L1 motion information of the triangular prediction unit. Alternatively, when the triangular merge candidate is an even number for the first triangular prediction unit, the L0 motion information of the triangular merge candidate can be defined as the L0 motion information of the first triangular prediction unit, while when the triangular merge candidate is an odd number for the second triangular prediction unit, the L1 motion information of the triangular merge candidate can be defined as the L1 motion information of the second triangular prediction unit.

[319] Alternatively, when the first triangular prediction unit has L0 motion information, L0 motion information of the second triangular prediction unit may be set to 0, and L1 motion information of the triangular merge candidate may be set as L1 motion information of the second triangular prediction unit. Conversely, when the first triangular prediction unit has L1 motion information, L1 motion information of the second triangular prediction unit may be set to 0, and L0 motion information of the triangular merge candidate may be set as L0 motion information of the second triangular prediction unit.

[320] A list of triangular merge candidates for deriving motion information from the first triangular prediction unit and a list of triangular merge candidates for deriving motion information from the second triangular prediction unit may be defined differently.

[321] For example, when a triangular merge candidate for deriving motion information of the first triangular prediction unit in the list of triangular merge candidates is specified based on the index information for the first triangular prediction unit, the motion information of the second triangular prediction unit may be derived using the list of triangular merge candidates, including the remaining triangular merge candidates, excluding the triangular merge candidate indicated by the index information. Specifically, the motion information of the second triangular prediction unit may be derived from any of the remaining triangular merge candidates.

[322] Accordingly, the maximum number of triangular merge candidates that the triangular merge candidate list of the first triangular prediction unit includes and the maximum number of triangular merge candidates that the triangular merge candidate list of the second triangular prediction unit includes may be different. For example, when the triangular merge candidate list of the first triangular prediction unit includes M merge candidates, the triangular merge candidate list of the second triangular prediction unit may include M-1 merge candidates excluding the triangular merge candidate indicated by the index information of the first triangular prediction unit.

[323] As another example, a merge candidate of each triangular prediction unit is derived based on neighboring blocks adjacent to a coding block, and the availability of neighboring blocks can be determined by considering the shape or position of the triangular prediction unit.

[324] Figure 27 is a view to describe examples of determining the availability of a neighboring block for each triangular forecast unit.

[325] A neighboring block not adjacent to the first triangular prediction unit may be defined as unavailable to the first triangular prediction unit and a neighboring block not adjacent to the second triangular prediction unit may be defined as unavailable to the second triangular prediction unit.

[326] For example, as shown in the example of Figure 27(a), when the left triangular partitioning type is applied to a coding block, it may be determined that blocks A1, A0, and A2 adjacent to the first triangular prediction unit among neighboring blocks adjacent to the coding block are available to the first triangular prediction unit, while blocks B0 and B1 are unavailable to the first triangular prediction unit. Accordingly, the list of triangular merge candidates for the first triangular prediction unit may include triangular merge candidates derived from blocks A1, A0, and A2, and may not include triangular merge candidates derived from blocks B0 and B1.

[327] As shown in the example of Figure 27(b), when the left triangular partitioning type is applied to a coding block, it can be determined that blocks B0 and B1 adjacent to the second triangular prediction unit are available to the second triangular prediction unit, while blocks A1, A0, and A2 are not available to the second triangular prediction unit. Therefore, the list of triangular merge candidates for the second triangular prediction unit may include triangular merge candidates derived from blocks B0 and B1, and may not include triangular merge candidates derived from blocks A1, A0, and A2.

[328] Accordingly, the number of triangular merge candidates or the range of triangular merge candidates that the triangular prediction unit can use can be determined based on at least one of the position of the triangular prediction unit or the partitioning type of the coding block.

[329] As another example, the blending mode may be applied to only one of the first triangular prediction unit and the second triangular prediction unit. Furthermore, the motion information of the other of the first triangular prediction unit and the second triangular prediction unit may be defined to be the same as the motion information of the triangular prediction unit to which the blending mode is applied, or may be derived by refining the motion information of the triangular prediction unit to which the blending mode is applied.

[330] For example, a motion vector and a reference image index of the first triangular prediction unit may be derived based on a triangular merge candidate, and a motion vector of the second triangular prediction unit may be derived by refining the motion vector of the first triangular prediction unit. For example, the motion vector of the second triangular prediction unit may be derived by adding or subtracting a refined motion vector {Rx, Ry} to or from the motion vector {mvD1LXx, mvD1LXy} of the first triangular prediction unit. The reference image index of the second triangular prediction unit may be set to be the same as the reference image index of the first triangular prediction unit.

[331] Information for determining a refined motion vector indicating the difference between the motion vector of the first triangular prediction unit and the motion vector of the second triangular prediction unit may be signaled via a bit stream. The information may include at least one of information indicating the size of the refined motion vector and information indicating the sign of the refined motion vector.

[332] Alternatively, the refined motion vector signal may be derived based on at least one of the position of the triangular prediction unit, the index of the triangular prediction unit, and the type of partitioning applied to the coding block.

[333] As another example, the motion vector and reference image index of either one of the first triangular prediction unit and the second triangular prediction unit may be signaled. The motion vector of the other one of the first triangular prediction unit and the second triangular prediction unit may be derived by refining the signaled motion vector.

[334] For example, the motion vector and reference picture index of the first triangular prediction unit may be determined based on the signaled information of a bit stream. Furthermore, the motion vector of the second triangular prediction unit may be derived by refining the motion vector of the first triangular prediction unit. For example, the motion vector of the second triangular prediction unit may be derived by adding or subtracting a refined motion vector {Rx, Ry} to or from the motion vector {mvD1LXx, mvD1LXy} of the first triangular prediction unit. The reference picture index of the second triangular prediction unit may be set to be the same as the reference picture index of the first triangular prediction unit.

[335] Motion prediction compensation prediction for each coding block may be performed based on the motion information of the first triangular prediction unit and the motion information of the second triangular prediction unit. At this point, video quality degradation may occur at the boundary between the first triangular prediction unit and the second triangular prediction unit. For example, video quality continuity may be degraded in the vicinity of an edge existing at the boundary between the first triangular prediction unit and the second triangular prediction unit. In order to reduce video quality degradation at the boundary, a prediction sample may be derived via a smoothing filter or a weighted prediction.

[336] Prediction samples in a coding block to which diagonal partitioning is applied may be derived based on a weighted sum operation of a first prediction sample obtained based on the motion information of the first triangular prediction unit and a second prediction sample obtained based on the motion information of the second triangular prediction unit. Alternatively, a prediction sample of the first triangular prediction unit is derived from a first prediction block determined based on the motion information of the first triangular prediction unit, and a prediction sample of the second triangular prediction unit is derived from a second prediction block determined based on the motion information of the second triangular prediction unit, and a prediction sample positioned in the boundary region of the first triangular prediction unit and the second triangular prediction unit may be derived based on a weighted sum operation of the first prediction sample included in the first prediction block and the second prediction sample included in the second prediction block. For example, Equation 6 shows an example of deriving prediction samples from the first triangular prediction unit and the second triangular prediction unit. [Equation 6]

[337] In Equation 6, P1 denotes a first forecast sample and P2 denotes a second forecast sample. w1 denotes a weighting value applied to the first forecast sample and (1-w1) denotes a weighting value applied to the second forecast sample. As shown in the example in Equation 6, the weighting value applied to the second forecast sample can be derived by subtracting the weighting value applied to the first forecast sample from a constant value.

[338] When the left triangular partitioning type is applied to a coding block, the boundary region may include prediction samples of which the x-axis coordinate and the y-axis coordinate are the same. Conversely, when the right triangular partitioning type is applied to a coding block, the boundary region may include prediction samples of which the sum of the x-axis coordinate and the y-axis coordinate is greater than or equal to a first boundary value and less than a second boundary value.

[339] A size of the boundary region may be determined based on at least one of the size of the coding block, the shape of the coding block, motion information of the triangular prediction units, a difference value between the motion vectors of the triangular prediction units, an output order of reference images, and a difference value between the first prediction sample and the second prediction sample at the diagonal boundary.

[340] Figures 28 and 29 are views showing examples of deriving a prediction sample based on a weighted sum operation of a first prediction sample and a second prediction sample. Figure 28 shows an example of applying the left triangular partitioning type to a coding block, and FIG. 29 shows an example of applying the right triangular partitioning type to a coding block. Further, Figures 28(a) and 29(a) are views showing prediction patterns for a luma component, and Figures 28(b) and 29(b) are views showing prediction patterns for a chroma component.

[341] In the drawings, numbers marked on the forecast samples positioned near the boundary between the first forecast unit and the second forecast unit indicate weighting values applied to the first forecast sample. For example, when a number marked on a forecast sample is N, the forecast sample may be derived by applying a weighting value of N/8 to the first forecast sample and applying a weighting value of (1-(N/8)) to the second forecast sample.

[342] In a non-threshold region, either the first prediction sample or the second prediction sample may be determined as a prediction sample. Referring to the example of Figure 28, in a region belonging to the first triangular prediction unit among regions in which the absolute value of the difference between the x-axis coordinate and the y-axis coordinate is greater than a threshold value, the first prediction sample derived based on the motion information of the first triangular prediction unit may be determined as a prediction sample. On the other hand, in a region belonging to the second triangular prediction unit among regions in which the value of the difference between the x-axis coordinate and the y-axis coordinate is greater than a threshold value, the second prediction sample derived based on the motion information of the second triangular prediction unit may be determined as a prediction sample.

[343] Referring to the example of Figure 29, in a region in which the sum of the x-axis coordinate and the y-axis coordinate is less than a first threshold value, the first prediction sample derived based on the motion information of the first triangular prediction unit may be determined as a prediction sample. Conversely, in a region in which the sum of the x-axis coordinate and the y-axis coordinate is greater than a second threshold value, the second prediction sample derived based on the motion information of the second triangular prediction unit may be determined as a prediction sample.

[344] A threshold value for determining a non-threshold region may be determined based on at least one of the size of a coding block, the shape of the coding block, and a color component. For example, when the threshold value for a luma component is set to N, the threshold value for a chroma component may be set to N/2.

[345] The prediction samples included in the boundary region may be derived based on a weighted sum operation of the first prediction sample and the second prediction sample. At this point, the weighting values applied to the first prediction sample and the second prediction sample may be determined based on at least one of the position of a prediction sample, the size of a coding block, the shape of the coding block, and a color component.

[346] For example, as shown in the example of Figure 28(a), prediction samples at the position of the same x-axis coordinate and y-axis coordinate can be derived by applying the same weighting value to the first prediction sample and the second prediction sample. Prediction samples of which the absolute value of the difference between the x-axis coordinate and the y-axis coordinate is 1 can be derived by setting the ratio of the weighting value applied to the first prediction sample and the second prediction sample to (3:1) or (1:3). Furthermore, prediction samples of which the absolute value of the difference of the x-axis coordinate and the y-axis coordinate is 2 can be derived by setting the ratio of the weighting value applied to the first prediction sample and the second prediction sample to (7:1) or (1:7).

[347] Alternatively, as shown in the example of Figure 28(b), prediction samples at the position of the same x-axis coordinate and y-axis coordinate can be derived by applying the same weighting value to the first prediction sample and the second prediction sample, and prediction samples of which the absolute value of the difference between the x-axis coordinate and the y-axis coordinate is 1 can be derived by setting the ratio of the weighting value applied to the first prediction sample and the second prediction sample to (7:1) or (1:7).

[348] For example, as shown in the example of Figure 29(a), prediction samples of which the sum of the x-axis coordinate and the y-axis coordinate is less than the width or height of a coding block by 1 can be derived by applying the same weighting value to the first prediction sample and the second prediction sample. Prediction samples of which the sum of the x-axis coordinate and the y-axis coordinate is equal to or less than the width or height of the coding block by 2 can be derived by setting the ratio of weighting value applied to the first prediction sample and the second prediction sample to (3:1) or (1:3). Prediction samples of which the sum of the x-axis coordinates and the y-axis coordinates is greater or less than the width or height of the coding block by 1 or 3 can be derived by setting the ratio of the weighting value applied to the first prediction sample and the second prediction sample to (7:1) or (1:7).

[349] Alternatively, as shown in the example of Figure 29(b), prediction samples of which the sum of the x-axis coordinate and the y-axis coordinate is less than the width or height of the coding block by 1 can be derived by applying the same weighting value to the first prediction sample and the second prediction sample. Prediction samples of which the sum of the x-axis coordinate and the y-axis coordinate is equal to or less than the width or height of the coding block by 2 can be derived by setting the ratio of weighting value applied to the first prediction sample and the second prediction sample to (7:1) or (1:7).

[350] As another example, the weight value can be determined by considering the position of a prediction sample or the shape of a coding block. Equations 7 through 9 show an example of deriving a weight value when the left triangular partitioning type is applied to a coding block. Equation 7 shows an example of deriving a weight value applied to the first prediction sample when the coding block is a square shape. [Equation 7]

[351] In Equation 7, x and y denote the position of a prediction sample. When a coding block has a non-square shape, a weighting value applied to the first prediction sample can be derived as shown in Equation 8 or 9. Equation 8 shows a case where the width of a coding block is greater than the height, and Equation 9 shows a case where the width of a coding block is less than the height. [Equation 8] [Equation 9] [Equation 10]

[352] When the right triangular partitioning type is applied to a coding block, a weighting value applied to the first prediction sample can be determined as shown in Equations 10 through 12. Equation 10 shows an example of deriving a weighting value applied to the first prediction sample when the coding block is a square shape. [Equation 11] [Equation 12]

[353] In Equation 11, CbH denotes the height of the coding block.

[354] As shown in the example, among the forecast samples in the boundary region, the forecast samples included in the first triangular forecast unit are derived by assigning a weighting value greater than that of the second forecast sample to the first forecast sample, and the forecast samples included in the second triangular forecast unit are derived by assigning a weighting value greater than that of the first forecast sample to the second forecast sample.

[355] When diagonal partitioning is applied to a coding block, it can be configured to not apply a combined prediction mode by combining the intraprediction mode and the blending mode for the coding block.

[356] Intraprediction is to predict a current block using reconstructed samples that were encoded/decoded in the neighborhood of the current block. At this point, the reconstructed samples before an in-loop filter was applied can be used for intraprediction of the current block.

[357] The intraprediction technique includes matrix-based intraprediction and general intraprediction considering directionality with respect to neighboring reconstructed samples. Information indicating the intraprediction technique of the current block may be signaled via a bit stream. The information may be a 1-bit flag. Alternatively, the intraprediction technique of the current block may be determined based on at least one of the position of the current block, the size of the current block, the shape of the current block, and an intraprediction technique of a neighboring block. For example, when the current block exists across an image boundary, it may be configured to not apply matrix-based intraprediction to the current block.

[358] Intraprediction based on intraprediction matrix is a method of acquiring a prediction block of the current block by an encoder and a decoder based on a matrix product between a previously stored matrix and reconstructed samples in the neighborhood of the current block. Information for specifying any one of a plurality of previously stored matrices may be signaled via a bit stream. The decoder may determine a matrix for intraprediction of the current block based on the information and size of the current block.

[359] General intraprediction is a method of acquiring a prediction block for the current block based on a non-angular intraprediction mode or an angular intraprediction mode.

[360] A derived residual image can be derived by subtracting a prediction video from an original video. At this point, when the residual video is shifted to the frequency domain, the subjective quality of the video is not significantly reduced, although the high-frequency components among the frequency components are removed. Consequently, when the values of the high-frequency components are converted to small or the values of the high-frequency components are set to 0, there is an effect of increasing the compression efficiency without generating significant visual distortion. By reflecting this characteristic, the current block can be transformed to decompose a residual video into two-dimensional frequency components. The transform can be performed using a transform technique such as Discrete Cosine Transform (DCT) or Discrete Sine Transform (DST).

[361] The two-dimensional video transform may not be performed for some blocks of the residual video. Not performing the two-dimensional video transform can be referred to as a transform skip. When the transform skip is applied, quantization can be applied to the residual coefficients that were not transformed.

[362] After the current block is transformed using DCT or DST, the current transformed block can be transformed again. At this point, the DCT or DST-based transform can be defined as a first transform, and transforming again a block to which the first transform is applied can be defined as a second transform.

[363] The first transform may be performed using any of a plurality of transform kernel candidates. For example, the first transform may be performed using any of DCT2, DCT8, or DCT7.

[364] Different transform cores can be used for the horizontal direction and the vertical direction. Information indicating the combination of a horizontal direction transform core and a vertical direction transform core can be signaled via a bit stream.

[365] The units for performing the first transform and the second transform may be different. For example, the first transform may be performed on an 8 x 8 block and the second transform may be performed on a sub-block of size 4 x 4 within the transformed 8 x 8 block. At this point, the transform coefficients of the residual regions that were not performed in the second transform may be set to 0.

[366] Alternatively, the first transform can be performed on a 4 x 4 block, and the second transform can be performed on a region of size 8 x 8 including the transformed 4 x 4 block.

[367] Information indicating whether or not the second transform has been performed can be signaled by means of a bit stream.

[368] Alternatively, whether or not to perform the second transform can be determined based on whether the horizontal direction transform kernel and the vertical direction transform kernel are the same. For example, the second transform can be performed only when the horizontal direction transform kernel and the vertical direction transform kernel are the same. Alternatively, the second transform can be performed only when the horizontal direction transform kernel and the vertical direction transform kernel are different from each other.

[369] Alternatively, the second transform may be allowed only when both the horizontal direction transform and the vertical direction transform use a predefined transform kernel. For example, when a DCT2 transform kernel is used for both the horizontal direction transform and the vertical direction transform, the second transform may be allowed.

[370] Alternatively, whether or not to perform the second transform may be determined based on the number of non-zero transform coefficients of the current block. For example, it may be configured to not use the second transform when the number of non-zero transform coefficients of the current block is less than or equal to a threshold value, and it may be configured to use the second transform when the number of non-zero transform coefficients of the current block is greater than the threshold value. It may be configured to use the second transform only when the current block is intraprediction encoded.

[371] The decoder may perform inverse transform of the second transform (second inverse transform) and may perform inverse transform of the first transform (first inverse transform) on the result of the second inverse transform. As a result of performing the second inverse transform and the first inverse transform, the residual signals for the current block can be acquired.

[372] When the encoder performs transform and quantization, the decoder can acquire a residual block through inverse quantization and inverse transform. The decoder can acquire a reconstructed block for the current block by adding a prediction block and the residual block.

[373] When a reconstructed block of the current block is acquired, the information loss that occurs in the quantization and encoding process can be reduced by means of in-loop filtering. An in-loop filter can include at least one of a deblocking filter, an adaptive sample shift (SAO) filter, and an adaptive loop filter (ALF).

[374] Applying the above-described embodiments with a focus on a decoding process or an encoding process to an encoding process or a decoding process is included within the scope of the present disclosure. Changing the described embodiments in a predetermined order into an order other than the described order is also included within the scope of the present disclosure.

[375] Although the above embodiments have been described based on a series of steps or flowcharts, this does not limit the order of the time series of the present disclosure and may be performed simultaneously or in a different order as needed. Furthermore, each of the components (e.g., units, modules, etc.) that constitute the block diagram in the above-described embodiments may be implemented as a hardware or software device, or a plurality of components may be combined to be implemented as a single hardware or software device. The above-described embodiments may be implemented in the form of program commands that may be executed by means of multiple computer components and recorded on a computer-readable recording medium. The computer-readable recording medium may include program commands, data files, data structures, and the like, independently or in combination. The computer-readable recording medium includes, for example, magnetic media such as a hard disk, a floppy disk, and a magnetic tape, optical recording media such as a CD-ROM and a DVD, magneto-optical media such as a floppy disk, and hardware devices specially configured to store and execute program commands, such as ROM, RAM, flash memory, and the like. The hardware devices described above may be configured to operate using one or more software modules to perform the process of the present disclosure, and vice versa.

[376] The present disclosure may be applied to an electronic device that encodes and decodes a video.

Claims (15)

1. A VIDEO DECODING METHOD comprising the steps of: determining a first prediction unit and a second prediction unit; deriving a merge candidate list for the coding block; determining first motion information for the first prediction unit based on a first merge candidate in the merge candidate list; determining second motion information for the second prediction unit based on a second merge candidate in the merge candidate list; wherein the first merge candidate is determined as a merge candidate indicated by an index indicated by the first index information and the second merge candidate is determined based on the second index information, wherein when a value of the second index information is equal to or greater than a value of the first index information, the second merge candidate is determined as a merge candidate indicated by an index obtained by adding 1 to the value of the second index information; and determining a prediction sample of the coding block based on the first motion information and the second motion information. 2. The method of claim 1, wherein when the value of the second index information is less than the value of the first index information, the second merge candidate is determined to be a merge candidate indicated by an index indicated by the second index information. 3. The method of claim 2, wherein determining a prediction sample of the coding block based on the first motion information and the second motion information comprises: determining a first prediction sample based on the first motion information; determining a second prediction sample based on the second motion information; and determining the prediction sample of the coding block based on a weighted sum of the first prediction sample and the second prediction sample. 4. The method of claim 3, wherein determining the prediction sample of the coding block based on a weighted sum of the first prediction sample and the second prediction sample comprises: determining the prediction sample of the coding block based on the first prediction sample, a first weighted value, the second prediction sample, and a second weighted value, wherein the first weighted value is determined based on an x-axis coordinate and a y-axis coordinate of the prediction sample; and the second weighted value is derived by subtracting the first weighted value from a constant value. 5. The method of any one of claims 1 to 4, wherein partitioning is applied to the coding block to obtain the first prediction unit and the second prediction unit is determined based on at least one of a parcel type, a coding block size, a coding block format and a coding block prediction mode. 6. The method of any one of claims 1 to 4, wherein a maximum number of merge candidates that the merge candidate list includes is determined based on applying partitioning to the coding block to obtain the first prediction unit and the second prediction unit. 7. METHOD according to any one of claims 1 to 4, characterized in that the information of the first index and the information of the second index are obtained by decoding from a bit stream. 8. A VIDEO CODING METHOD comprising the steps of: determining a first prediction unit and a second prediction unit; deriving a merge candidate list for the coding block; determining first motion information for the first prediction unit based on a first merge candidate in the merge candidate list; determining second motion information for the second prediction unit based on a second merge candidate in the merge candidate list; determining a prediction sample of the coding block based on the first motion information and the second motion information; and encoding the first index information and the second index information into a bit stream, wherein the first index information indicates an index of the first merge candidate, the second index information indicates an index of the second merge candidate, and when the index of the second merge candidate is equal to or greater than the index of the first merge candidate, the second index information is encoded using a value obtained by subtracting 1 from the index of the second merge candidate. 9. The method of claim 8, wherein when the index of the second merge candidate is less than the index of the first merge candidate, the information of the second index is encoded using a value equal to the index of the second merge candidate. 10. The method of claim 9, wherein determining a prediction sample of the coding block based on the first motion information and the second motion information comprises: determining a first prediction sample based on the first motion information; determining a second prediction sample based on the second motion information; and determining the prediction sample of the coding block based on a weighted sum of the first prediction sample and the second prediction sample. 11. The method of claim 10, the determination of the prediction sample of the coding block based on a weighted sum of the first prediction sample and the second prediction sample comprising: determining the prediction sample of the coding block based on the first prediction sample, a first weighted value, the second prediction sample, and a second weighted value, wherein the first weighted value is determined based on an x-axis coordinate and a y-axis coordinate of the prediction sample; and the second weighted value is derived by subtracting the first weighted value from a value of a constant value. 12. The method of any one of claims 8 to 11, wherein partitioning is applied to the coding block to obtain the first prediction unit and the second prediction unit is determined based on at least one of a portion type, a coding block size, a coding block format, and a coding block prediction mode. 13. The method of any one of claims 8 to 11, wherein a maximum number of merge candidates that the merge candidate list includes is determined based on applying partitioning to the coding block to obtain the first prediction unit and the second prediction unit. 14. VIDEO DECODING APPARATUS, characterized by comprising an interprediction part configured to perform the method, as defined in any one of claims 1 to 7. 15. VIDEO CODING APPARATUS, characterized by comprising an interprediction part configured to perform the method, as defined in any one of claims 8 to 13.