BR122025000828A2 - VIDEO DECODING METHOD, VIDEO CODING METHOD, VIDEO DECODER AND VIDEO ENCODER - Google Patents

Abstract

An image decoding method according to the present invention comprises the steps of: generating a list of fusion candidates in a current block; specifying one of a plurality of fusion candidates included in the list of fusion candidates; deriving a first affine seed vector and a second affine seed vector of the current block based on a first affine seed vector and a second affine seed vector of the specified fusion candidate; deriving an affine vector for a sub-block in the current block using the first affine seed vector and the second affine seed vector of the current block; and performing motion compensation prediction for the sub-block based on the affine vector.

Description

This patent application consists of a split application of the invention patent application BR 112021004922-3, dated 09/20/2019. BACKGROUND OF THE INVENTION FIELD OF INVENTION

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

BACKGROUND OF THE RELATED ART

[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 Experts Group (MPEG) and the Video Coding Experts Group (VCEG) under the International Telecommunication Union-Telecommunication (ITU-T) formed the Joint Collaborative 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 OF THE INVENTION

[003] An object of the present invention is to provide an interprediction method using an affine model, and an apparatus for the same, in encoding/decoding a video signal.

[004] Another object of the present invention is to provide a method of deriving an affine source vector using a translational motion vector of a sub-block, and an apparatus for performing the method, in encoding/decoding a video signal.

[005] Another object of the present invention is to provide a method of deriving an affine source vector by transforming a distance between a neighboring block and a current block into a power-of-2 series, and an apparatus for performing the method, in encoding/decoding a video signal.

[006] The technical problems to be achieved in the present invention 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 and encoding a video signal according to the present invention includes the steps of: generating a list of fusion candidates for a current block; specifying one of a plurality of fusion candidates included in the list of fusion candidates; deriving a first affine source vector and a second affine source vector of the current block based on a first affine source vector and a second affine source vector of the specified fusion candidate; deriving an affine vector for a sub-block in the current block by using the first affine source vector and the second affine source vector of the current block; and performing a motion compensation prediction for the sub-block based on the affine vector. At this point, the sub-block is a region of a size smaller than that of the current block. Furthermore, the first affine source vector and the second affine source vector of the fusion candidate may be derived based on motion information of a neighboring block adjacent to the current block.

[008] In the method of decoding and encoding a video signal according to the present invention, when the neighboring block is included in a coding tree unit other than a coding tree unit of the current block, the first affine source vector and the second affine source vector of the fusion candidate may be derived based on motion vectors of a lower left sub-block and a lower right sub-block of the neighboring block.

[009] In the method of decoding and encoding a video signal according to the present invention, the lower left sub-block may include a lower left reference sample positioned at a lower left corner of the neighboring block, and the lower right sub-block may include a lower right reference sample positioned at a lower left corner of the neighboring block.

[0010] In the method of decoding and encoding a video signal according to the present invention, the first affine source vector and the second affine source vector of the fusion candidate may be derived based on a value obtained based on a compensation operation performed on a difference value between motion vectors of the lower left sub-block and the lower right sub-block using a scaling factor, and the scaling factor may be derived based on a value obtained by adding a horizontal distance between the lower left reference sample and the lower right reference sample and an offset.

[0011] In the method of decoding and encoding a video signal according to the present invention, the first affine source vector and the second affine source vector of the fusion candidate may be derived based on a value obtained based on a compensation operation performed on a difference value between motion vectors of the lower left sub-block and the lower right sub-block using a scaling factor, and the scaling factor may be derived based on a distance between a neighboring sample adjacent to a right side of the lower right reference sample and the lower left reference sample.

[0012] In the method of decoding and encoding a video signal according to the present invention, the list of fusion candidates includes a first fusion candidate derived based on an upper neighbor block determined as a first available block among upper neighbor blocks positioned on a top of the current block, and a second fusion candidate derived based on a left neighbor block determined as a first available block among left neighbor blocks positioned on a left side of the current block.

[0013] In the method of decoding and encoding a video signal according to the present invention, when the neighboring block is included in a coding tree unit equal to a coding tree unit of the current block, the first affine source vector and the second affine source vector of the fusion candidate may be derived based on a first affine source vector and a second affine source vector of the neighboring block.

[0014] The features briefly summarized above in relation to the present invention are merely exemplary aspects of the detailed description of the present invention that will be described below and do not limit the scope of the present invention.

[0015] According to the present invention, there is an effect of improving prediction efficiency through an interprediction method using an affine model.

[0016] According to the present invention, there is a coding efficiency improvement effect by deriving an affine source vector using a translational motion vector of a sub-block.

[0017] According to the present invention, there is a coding efficiency improvement effect by deriving an affine source vector by transforming a distance between a neighboring block and a current block to a power-of-2 series.

[0018] The effects that can be obtained from the present invention 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 FIGURES

[0019] Figure 1 is a block diagram showing a video encoder in accordance with one embodiment of the present invention.

[0020] Figure 2 is a block diagram showing a video decoder in accordance with one embodiment of the present invention.

[0021] Figure 3 is a view showing a basic coding tree unit in accordance with an embodiment of the present invention.

[0022] Figure 4 is a view showing various types of partitioning of a coding block.

[0023] Figure 5 is a view showing a partition pattern of a coding tree unit.

[0024] Figure 6 is a flowchart illustrating an interprediction method in accordance with an embodiment of the present invention.

[0025] Figure 7 is a view showing non-linear motion of an object.

[0026] Figure 8 is a flowchart illustrating an interprediction method based on an affine motion in accordance with an embodiment of the present invention.

[0027] Figure 9 is a view showing an example of affine source vectors for each affine motion model.

[0028] Figure 10 is a view showing an example of sub-block affine vectors in a 4-parameter motion model.

[0029] Figure 11 is a view showing a neighboring block that can be used to derive a fusion candidate.

[0030] Figure 12 is a view showing an example of deriving an affine source vector of a current block based on an affine source vector of an affine neighboring block.

[0031] Figure 13 is a view showing an example of adjusting a motion vector of a sub-block as an affine source vector of an affine neighboring block.

[0032] Figures 14 to 16 are views showing positions of reference samples.

[0033] Figure 17 is a view showing an example application of a modified affine fusion vector derivation method.

[0034] Figure 18 is a view showing an example of deriving an affine source vector of a current block based on a non-affine neighboring block.

[0035] Figure 19 is a view showing an example of replacing a neighboring block with another neighboring block.

[0036] Figures 20 and 21 are views showing the flow of a motion compensation prediction method using a plurality of fusion candidates.

[0037] Figure 22 is a flowchart illustrating an intraprediction method in accordance with an embodiment of the present invention.

[0038] Figure 23 is a view showing reference samples included in each reference sample line.

[0039] Figure 24 is a view showing intraprediction modes.

[0040] Figures 25 and 26 are views showing an example of a one-dimensional array arranging reference samples in a row.

[0041] Figure 27 is a view showing an example of angles formed between angular intraprediction modes and a straight line parallel to the x-axis.

[0042] Figure 28 is a view showing an embodiment of acquiring prediction samples when the current block is a non-square shape.

[0043] Figure 29 is a view showing wide-angle intraprediction modes.

[0044] Figure 30 is a flowchart illustrating a block resistance determination process.

[0045] Figure 31 is a view showing predefined filter candidates.

[0046] Figure 32 is a view showing an example of partitioning a figuration into a plurality of tiles.

[0047] Figure 33 is a view showing a pattern of partitioning a figuration according to a flexible tiling technique.

[0048] Figure 34 is a view showing an example of assigning a tile ID to each coding tree unit.

[0049] Figure 35 is a view showing an example of selectively determining whether or not to apply a circuit filter to each tile.

DETAILED DESCRIPTION OF THE PREFERENTIAL MODALITY

[0050] Hereinafter in this document, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0051] Encoding and decoding of a video are performed by the block unit. For example, an encoding/decoding process such as transform, quantization, prediction, in-loop filtering, reconstruction or the like may be performed in a coding block, a transform block or a prediction block.

[0052] Hereinafter in this document, a block to be encoded/decoded will be referred to as ‘current block’. For example, the current block may represent an encoding block, a transform block or a prediction block according to a current encoding/decoding process step.

[0053] Furthermore, it can 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 array of a predetermined size. Unless otherwise stated, ‘block’ and ‘unit’ can be used as having the same meaning. For example, in an embodiment described below, it can be understood that a coding block and a coding unit have the same meaning.

[0054] Figure 1 is a block diagram showing a video encoder in accordance with one embodiment of the present invention.

[0055] Referring to Figure 1, a video coding apparatus 100 may include a figuring partition part 110, a partition 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, an inverse transform part 145, a filter part 150, and a memory 155.

[0056] Each of the components shown in Figure 1 is independently shown to represent different characteristic functions 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 simple hardware. 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 simple component, or a component can be divided into a plurality of components to realize a function. Integrated embodiments and separate embodiments of the components are also included in the scope of the present invention, if they do not depart from the essence of the present invention.

[0057] Furthermore, some of the components are not essential components that perform essential functions in the present invention, but may be optional components only to improve performance. The present invention may be implemented by including only essential components to implement the essence of the present invention, excluding the 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 invention.

[0058] The pattern partitioning portion 110 may partition an input pattern into at least one processing unit. At this point, the processing unit may be a prediction unit (PU), a transform unit (TU), or an encoding unit (CU). The pattern partitioning portion 110 may partition a pattern into a combination of a plurality of encoding units, prediction units, and transform units, and encode a pattern by selecting a combination of a coding unit, a prediction unit, and a transform unit based on a predetermined criterion (e.g., a cost function).

[0059] For example, a figuration may be partitioned into a plurality of coding units. In order to partition the coding units in a figuration, a recursive tree structure such as a quad tree structure may be used. A coding unit partitioned into different coding units using a video or 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, that coding unit may be partitioned into up to four different coding units.

[0060] Hereinafter in the present document, in one embodiment of the present invention, the coding unit can be used as a meaning of a unit that performs encoding or a meaning of a unit that performs decoding.

[0061] The prediction unit may be one that is partitioned into a shape of at least one square, rectangle or the like of the same size in a coding unit, or it may be any prediction unit, among the prediction units partitioned in a coding unit, that is partitioned to have a different shape and/or size than that of another prediction unit.

[0062] If the coding unit is not the smallest coding unit when a prediction unit that performs intraprediction based on the coding unit is generated, intraprediction can be performed without partitioning a figuration into a plurality of N x N prediction units.

[0063] The partition part 120 and 125 may include an inter-partition part 120 that performs inter-prediction and an intra-partition part 125 that performs intra-prediction. It may be determined whether to use inter-prediction or perform intra-prediction for a prediction unit, and determine specific information (e.g., intra-prediction mode, motion vector, reference figure, 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. Furthermore, 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 it is transmitted to a decoder without generating a prediction block through the partition part 120 and 125.

[0064] The inter-partition portion 120 may predict a prediction unit based on information in at least one picture among pictures before or after the current picture, and in some cases may predict a prediction unit based on information in a partial area that has been encoded in the current picture. The inter-partition portion 120 may include a reference picture interpolation portion, a motion partition portion, and a motion compensation portion.

[0065] The reference picture interpolation part may receive reference picture information from memory 155 and generate pixel information of an integer number of pixels or less of the reference picture. In the case of a luminance pixel, a DCT-based 8-tap interpolation filter with a variable filter coefficient may be used to generate pixel information of an integer number of pixels or less by the unit of 1/4 pixel. In the case of a color difference signal, a DCT-based 4-tap interpolation filter with a variable filter coefficient may be used to generate pixel information of an integer number of pixels or less by the unit of 1/8 pixel.

[0066] The motion partitioning part may perform motion prediction based on the reference picture interpolated by the reference picture 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 1/2 or 1/4 pixel unit based on interpolated pixels. The motion partitioning part may predict a current prediction unit by varying the motion prediction method. Various methods, such as a skip method, a fusion method, an advanced motion vector prediction (AMVP) method, an intra-block copy method, and the like, may be used as the motion prediction method.

[0067] The intra-partition portion 125 may generate a prediction unit based on information about reference pixels around the current block, which are pixel information in the current figure. When a block in the neighborhood of the current prediction unit is a block on which interprediction has been performed, and thus the reference pixel is a pixel on which interprediction has been performed, the reference pixel included in the block on which interprediction has been performed may be used in place of reference pixel information of a block in the neighborhood on which intraprediction has been performed. That is, when the reference pixel is unavailable, at least one reference pixel among available reference pixels may be used in place of unavailable reference pixel information.

[0068] In intraprediction, the prediction mode may have an angular prediction mode that uses reference pixel 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 color difference information.

[0069] If the size of the prediction unit is the same as the size of the transform unit when intra-prediction is performed, intra-prediction can be performed for the prediction unit based on a pixel on the left side, a pixel on the top left side, and a pixel 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 intra-prediction is performed, intra-prediction can be performed using a reference pixel based on the transform unit. Furthermore, intra-prediction using N x N partition can be used only for the smallest coding unit.

[0070] The intra-prediction method may generate a prediction block after applying an Adaptive Intra Smoothing (AIS) filter to the reference pixel according to a prediction mode. The type of AIS filter applied to the reference pixel may vary. In order to perform the intra-prediction method, the intra-prediction mode of the current prediction unit may be predicted from the intra-prediction mode of the existing prediction unit in the neighborhood of the current prediction unit. When a prediction mode of the current prediction unit is predicted using the predicted mode information of the neighboring prediction unit, if the intra-prediction 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 marking information, and if the prediction modes of the current prediction unit and the prediction unit in the neighborhood are different from each other, prediction mode information of the current block may be encoded by performing entropy coding.

[0071] Furthermore, a residual block may be generated that includes a prediction unit that performed prediction based on the prediction unit generated by the partition part 120 and 125 and residual coefficient information, which is a difference value of the prediction unit with the original block. The generated residual block may be input to the transform part 130.

[0072] The transform part 130 may transform the residual block that includes the original block and the residual coefficient information of the prediction unit generated through the partition part 120 and 125 using a transform method such as Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), or jump transform. The application of DCT, DST, or KLT to transform the residual block may be determined based on the intra-prediction mode information of a prediction unit used to generate the residual block.

[0073] 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.

[0074] The rearrangement part 160 may rearrange coefficient values for the quantized residual coefficients.

[0075] The rearrangement part 160 may change coefficients of a two-dimensional block format into a one-dimensional vector format through a coefficient scanning method. For example, the rearrangement part 160 may scan coefficients from DC to high-frequency domain coefficients using a zigzag scanning method, and change the coefficients into a one-dimensional vector format. According to the size of the transform unit and the intra-prediction mode, a vertical sweep of scanning the coefficients of a two-dimensional block format in the column direction and a horizontal sweep of scanning the coefficients of a two-dimensional block format in the row direction may be used instead of the zigzag scanning. That is, according to the size of the transform unit and the intra-prediction mode, a scanning method to be used may be determined from among the zigzag scanning, the vertical direction scanning, and the horizontal direction scanning.

[0076] The entropy coding part 165 may perform entropy coding based on 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.

[0077] 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, partition 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.

[0078] The entropy coding part 165 may entropy encode the coefficient value of an input coding unit of the rearrangement part 160.

[0079] The inverse quantization part 140 and 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 by a motion estimation part, a motion compensation part, and an intra-partition part included in the partition part 120 and 125 to generate a reconstructed block.

[0080] The filter portion 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

[0081] The deblocking filter can remove block distortion generated by the boundary between blocks in the reconstructed figure. 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 pixels included in several columns or rows included in the block. A strong filter or a weak filter can be applied according to the required deblocking filtration strength when the deblocking filter is applied to a block. Furthermore, when both vertical direction filtration and horizontal direction filtration are performed when applying the deblocking filter, the horizontal direction filtration and vertical direction filtration can be processed in parallel.

[0082] The displacement correction unit may correct a displacement for the original video by the pixel unit for a video on which deblocking has been performed. In order to perform displacement correction for a specific figuration, it is possible to use a method of dividing pixels 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 that considers edge information of each pixel.

[0083] Adaptive Loop Filtering (ALF) can be performed based on a value obtained by comparing the reconstructed and filtered video and the original video. After dividing the pixels included in the video into predetermined groups, a filter to be applied to a corresponding group can be determined, and the filtering can be performed differently for each group. A luminance signal, which is the information related to whether or not ALF is applied, can be output 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.

[0084] The memory 155 may store the reconstructed block or pattern calculated by the filter part 150, the reconstructed and stored block or pattern may be provided to the partition part 120 and 125 when interprediction is performed.

[0085] Figure 2 is a block diagram showing a video decoder in accordance with one embodiment of the present invention.

[0086] 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 partition part 230 and 235, a filter part 240, and a memory 245.

[0087] When a video bitstream is input from a video encoder, the input bitstream may be decoded in a procedure opposite to that of the video encoder.

[0088] 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 that correspond 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.

[0089] The entropy decoding part 210 may decode information related to the intraprediction and interprediction performed by the encoder.

[0090] The rearrangement part 215 may perform rearrangement on the bit stream decoded by entropy 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.

[0091] 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.

[0092] The inverse transform part 225 may perform inverse transform, i.e., inverse DCT, inverse DST, or inverse KLT, to the transform, i.e., DCT, DST, or KLT, performed by the transform part on the quantization result performed by the video encoder. 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, DST, KLT) 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.

[0093] The partition portion 230 and 235 may generate a prediction block based on information related to the generation of a prediction block provided by the entropy decoder 210 and information about a previously decoded block or pattern provided by the memory 245.

[0094] As described above, if the size of the prediction unit and the size of the transform unit are the same when intra-prediction is performed in the same manner as the video encoder operation, intra-prediction is performed on the prediction unit based on the pixel on the left side, the pixel on the top left side, and the pixel on the top of the prediction unit. However, if the size of the prediction unit and the size of the transform unit are different when intra-prediction is performed, intra-prediction can be performed using a reference pixel based on a transform unit. Furthermore, intra-prediction using N x N partition can be used only for the smallest coding unit.

[0095] The partitioning part 230 and 235 may include a prediction unit determination part, an inter-partition part, and an intra-partition 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, information related to motion prediction from an inter-prediction method, and the like, identify the prediction unit of the current coding unit, and determine whether the prediction unit performs inter-prediction or intra-prediction. The inter-partition part 230 may perform inter-prediction on the current prediction unit based on information included in at least one picture among pictures before or after the current picture that includes the current prediction unit by using information necessary for inter-prediction of the current prediction unit provided by the video encoder. Alternatively, the inter-partition portion 230 may perform inter-prediction based on information in a previously reconstructed partial area in the current picture including the current prediction unit.

[0096] In order to perform interprediction, it may 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 intrablock copy mode.

[0097] The intra-partition portion 235 may generate a prediction block based on information about the pixel 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 intra-prediction mode information of the prediction unit provided by the video encoder. The intra-partition portion 235 may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolation portion, and a CC filter. The AIS filter is a portion that performs filtering on the reference pixel 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 pixel 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.

[0098] When the prediction mode of the prediction unit is a prediction unit that performs intra-prediction based on a pixel value obtained by interpolating the reference pixel, the reference pixel interpolation part may generate a reference pixel of a pixel unit that has an integer value or less by interpolating the reference pixel. When the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without interpolating the reference pixel, the reference pixel may not be interpolated. The CC filter may generate a prediction block by filtering when the prediction mode of the current block is the DC mode.

[0099] The reconstructed block or figuration may be provided to the filter portion 240. The filter portion 240 may include a deblocking filter, an offset correction unit, and an ALF.

[00100] Information whether or not a deblocking filter is applied to a corresponding block or figure and information whether or not 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 deblocking filter-related information provided by the video encoder, and the video decoder may perform deblocking filtering on a corresponding block.

[00101] The offset correction unit may perform offset correction on the reconstructed video based on the offset correction type and offset value information applied to the video when encoding is performed.

[00102] 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. The ALF information may be provided to be included in a specific set of parameters.

[00103] Memory 245 may store the reconstructed picture or block and use it as a reference picture or reference block and may provide the reconstructed picture to an output unit.

[00104] Figure 3 is a view showing a basic coding tree unit in accordance with an embodiment of the present invention.

[00105] A coding block of a maximum size may be defined as a coding tree block. A figuration is partitioned into a plurality of coding tree units (CTUs). The coding tree unit is a coding unit that has a maximum size and may be referred to as a Large Coding Unit (LCU). Figure 3 shows an example in which a figuration is partitioned into a plurality of coding tree units.

[00106] The size of the coding tree unit may be set at a figuration level or a sequence level. For this purpose, information indicating the size of the coding tree unit may be signaled via a set of figuration parameters or a set of sequence parameters.

[00107] For example, the coding tree unit size for all the drawing in a sequence may be set to 128 x 128. Alternatively, at the drawing 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 in a first drawing, and the coding tree unit size may be set to 256 x 256 in a second drawing.

[00108] Coding blocks may be generated by partitioning a coding tree unit. The coding block denotes 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 denotes a method of generating a prediction video. For example, the prediction coding mode may include prediction within a screen (intra-prediction), prediction between screens (inter-prediction), current picture reference (CPR) or intra-block copy (IBC), or combined prediction. For the coding block, a prediction block may be generated by using at least one prediction coding mode among intra-prediction, inter-prediction, current picture reference, and combined prediction.

[00109] Information indicating the prediction coding mode of the current block may be signaled via 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 figuration reference or combined prediction may be used.

[00110] The current figuration reference is to set the current figuration as a reference figuration and obtain a prediction block of the current block from an area that has already been coded/decoded in the current figuration. Here, the current figuration means a figuration that includes the current block. Information indicating whether the current figuration reference is applied to the current block may be signaled by a bit stream. For example, the information may be a 1-bit flag. When the flag is true, the prediction coding mode of the current block may be determined as the current figuration reference, and when the flag is false, the prediction mode of the current block may be determined as interprediction.

[00111] 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 inter-prediction. That is, the current picture reference is a prediction method using information about an area in which encoding/decoding has been completed in the current picture, and inter-prediction is a prediction method using information about another picture in which encoding/decoding has been completed.

[00112] Combined prediction represents a coding mode in which two or more of the intra-prediction, the inter-prediction, and the current figuration reference are combined. For example, when combined prediction is applied, a first prediction block may be generated based on one of the intra-prediction, the inter-prediction, and the current figuration reference, 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 an average operation or a weighted sum operation of the first prediction block and the second prediction block. Information indicating whether or not the combined prediction is applied may be signaled by a bit stream. The information may be a 1-bit flag.

[00113] Figure 4 is a view showing various types of partitioning of a coding block.

[00114] The coding block may be partitioned into a plurality of coding blocks based on quad tree partition, binary tree partition, or quad tree partition. The partitioned coding block may be partitioned again into a plurality of coding blocks based on quad tree partition, binary tree partition, or quad tree partition.

[00115] 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-shaped partitions (see ‘SPLIT_QT’ of Figure 4(a)).

[00116] Binary tree partition refers to a partition 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 referred to as vertical direction binary tree partition, and partitioning a current block into two blocks along the horizontal direction (i.e., using a horizontal line crossing the current block) can be referred to as horizontal direction binary tree partition. As a result of binary tree partition, the current block can be partitioned into two non-square-shaped partitions. ‘SPLIT_BT_VER’ of Figure 4(b) shows a result of vertical direction binary tree partition, and ‘SPLIT_BT_HOR’ of Figure 4(c) shows a result of horizontal direction binary tree partition.

[00117] Quad-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 that intersect the current block) can be referred to as vertical-direction quad-tree partitioning, and partitioning a current block into three blocks along the horizontal direction (i.e., using two horizontal lines that intersect the current block) can be referred to as horizontal-direction quad-tree partitioning. As a result of triple-tree partitioning, the current block can be partitioned into three non-square-shaped 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’ of Figure 4(d) shows a result of vertical direction quadruple tree partition and ‘SPLIT_TT_HOR’ of Figure 4(e) shows a result of horizontal direction quadruple tree partition.

[00118] The number of times a coding tree unit can be partitioned may be defined as a partition depth. The maximum partition depth of a coding tree unit may be determined at the sequence or picture level. Accordingly, the maximum partition depth of a coding tree unit may be different for each sequence or picture.

[00119] Alternatively, the maximum partition depth for each partition technique may be individually determined. For example, the maximum partition depth allowed for quad tree partitioning may be different from the maximum partition depth allowed for binary tree partitioning and/or quad tree partitioning.

[00120] The encoder may signal information indicating at least one of the partition type and partition depth of the current block via a bit stream. The decoder may determine the partition type and partition depth of a coding tree unit based on information parsed from the bit stream.

[00121] Figure 5 is a view showing a partition pattern of a coding tree unit.

[00122] Partitioning a cipher block using a partitioning technique such as quad tree partitioning, binary tree partitioning, and/or quad tree partitioning may be referred to as multi-tree partitioning.

[00123] The coding blocks generated by applying multiple tree partitioning to a coding block may be referred to as lower coding blocks. When the partition depth of a coding block is k, the partition depth of the lower coding blocks is set to k + 1.

[00124] In contrast, for coding blocks that have a partition depth of k + 1, a coding block that has a partition depth of k may be referred to as an upper coding block.

[00125] The partition type of the current coding block may be determined based on at least one of a partition type of a top coding block and a partition 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 neighboring block adjacent to the top left corner. Here, the partition type may include at least one of a quad tree partition or not, a binary tree partition or not, binary tree partition direction, a quad tree partition or not, and quad tree partition direction.

[00126] In order to determine a partition type of a coding block, information indicating whether or not the coding block can be partitioned may be signaled via a bit stream. The information is a 1-bit ‘split_cu_flag’ flag, and when the flag is true, it indicates that the coding block is partitioned by a head-tree (^quad) partitioning technique.

[00127] When split_cu_flag is true, information indicating whether the cipher block is quad-tree partitioned may be signaled via a bitstream. The information is a 1-bit split_qt_flag flag, and when the flag is true, the cipher block may be partitioned into four blocks.

[00128] For example, in the example shown in Figure 5, as a coding tree unit is quad-tree partitioned, four coding blocks are generated that have a partition depth of 1. 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 that have a partition depth of 2 can be generated.

[00129] Furthermore, coding blocks that have a partition depth of 3 may be generated by applying the quad tree partition again to a coding block that has a partition depth of 2.

[00130] When quad tree partitioning is not applied to the coding block, whether binary tree partitioning or quad tree partitioning is performed on the coding block can be determined by considering at least one of the size of the coding block, whether or not the coding block is positioned on the drawing boundary, the maximum partition depth, and the partition type of a neighboring block. When binary tree partitioning or quad tree partitioning is determined to be performed on the coding block, information indicating the partition 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, it can be determined whether the partition direction is a vertical direction or a horizontal direction. Additionally, information indicating whether binary tree partitioning or quad tree partitioning is applied to the coding block can be signaled via a bit stream. The information can be a 1-bit flag of mtt_split_cu_binary_flag. Based on the flag, it can be determined whether binary tree partitioning or quad tree partitioning is applied to the cipher block.

[00131] For example, in the example shown in Figure 5, it is shown that the vertical direction binary tree partition is applied to a coding block that has a partition depth of 1, the vertical direction quad tree partition is applied to the left-hand coding block among the coding blocks generated as a result of the partition, and the vertical direction binary tree partition is applied to the right-hand coding block.

[00132] Interprediction is a prediction coding mode that predicts a current block by using information from the previous figure. For example, a block at the same position as the current block in the previous figure (hereinafter in this document, a co-allocated block) can be set as the prediction block of the current block. Hereinafter in this document, a prediction block generated based on a block at the same position as the current block will be referred to as a co-allocated prediction block.

[00133] On the other hand, when an object in the previous picture has moved to another position in the current picture, the current block can be effectively predicted by using a motion of the object. For example, when the moving direction and size of an object can be known by comparing the previous picture and the current picture, a prediction block (or a prediction video) of the current block can be generated considering motion information of the object. Hereinafter in this document, the prediction block generated using motion information can be referred to as a motion prediction block.

[00134] A residual block may 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 may be reduced by using the motion prediction block instead of the co-allocated prediction block, and therefore the compression performance of the residual block may be improved.

[00135] As described above, generating a prediction block using motion information may be referred to as motion compensation prediction. In most interprediction, a prediction block may be generated based on motion compensation prediction.

[00136] The motion information may include at least one of a motion vector, a reference figure index, a prediction direction, and a bidirectional weight index. The motion vector represents the motion direction and size of an object. The reference figure index specifies a reference figure of the current block from among reference figures included in a reference figure 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 motion information in the L0 direction and 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.

[00137] Figure 6 is a flowchart illustrating an interprediction method in accordance with an embodiment of the present invention.

[00138] 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).

[00139] Here, the interprediction mode represents various techniques for determining motion information of the current block, and may include an interprediction mode using translational motion information and an interprediction mode using affine motion information. For example, the interprediction mode using translational motion information may include a fusion mode and a motion vector prediction mode, and the interprediction mode using affine motion information may include an affine fusion 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.

[00140] Hereinafter in this document, the interprediction method using affine motion information will be described in detail.

[00141] Figure 7 is a view showing non-linear motion of an object.

[00142] 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 may occur, such as zooming in, out, rotating, affine transforming, or the like of a camera. When a non-linear motion of an object occurs, the motion of the object cannot be effectively expressed with a translational motion vector. Accordingly, coding efficiency may be improved by using an affine motion instead of a translational motion in an area where a non-linear motion of an object occurs.

[00143] Figure 8 is a flowchart illustrating an interprediction method based on an affine motion in accordance with an embodiment of the present invention.

[00144] Whether an affine motion-based interprediction technique can be applied to the current block can be determined based on information analyzed from a bit stream. Specifically, whether the affine motion-based interprediction technique can be applied to the current block can be determined based on at least one of a flag indicating whether the affine fusion mode is applied to the current block and a flag indicating whether the affine motion vector prediction mode is applied to the current block.

[00145] When the interprediction technique based on an affine motion is applied to the current block, an affine motion model of the current block may be determined (S801). The affine motion model may 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.

[00146] Equation 1 expresses an affine motion using six parameters. The affine motion represents a translational motion for a predetermined area determined by affine source vectors.

[00147] [150] 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.

[00148] Information for determining an affine motion model of the current block may be encoded and flagged via a bit stream. For example, the information may be a 1-bit flag of ‘affine_type_flag’. When the flag value is 0, this may indicate that a 4-parameter affine motion model is applied, and when the flag value is 1, this may indicate that a 6-parameter affine motion model is applied. The flag may be encoded by the slice, tile, or block unit (e.g., by the coding block or coding tree unit). When a flag is flagged at the slice level, an affine motion model determined at the slice level may be applied to all blocks belonging to the slice.

[00149] 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 fusion 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, 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’.

[00150] Subsequently, an affine source vector of the current block may be derived (S802). When a 4-parameter affine motion model is selected, motion vectors at two control points of the current block may be derived. Conversely, when a 6-parameter affine motion model is selected, motion vectors at three control points of the current block may be derived. The motion vector at a control point may be referred to as an affine source vector. The control point may include at least one of the upper left corner, the upper right corner, and the lower left corner of the current block.

[00151] Figure 9 is a view showing an example of affine source vectors for each affine motion model.

[00152] In the affine 4-parameter motion model, affine source vectors can be derived for two of the top left corner, the top right corner, and the bottom left corner. For example, as shown in the example of Figure 9(a), when an affine 4-parameter motion model is selected, an affine vector can be derived using the affine source vector sv0 for the top left corner of the current block (e.g., top left sample (x1, y1)) and the affine source 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 source vector for the bottom left corner instead of the affine source vector for the top left corner, or to use an affine source vector for the bottom left corner instead of the affine source vector for the top right corner.

[00153] In the affine 6-parameter motion model, affine source 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 of Figure 9(b), when a 6-parameter affine motion model is selected, an affine vector can be derived using the affine source vector sv0 for the top left corner of the current block (e.g., top left sample (x1, y1)), the affine source vector sv1 for the top right corner of the current block (e.g., top right sample (x1, y1)), and the affine source vector sv2 for the top left corner of the current block (e.g., top left sample (x2, y2)).

[00154] In the embodiment described below, in the affine 4-parameter motion model, the affine source vectors of the top left control point and the top right control point will be referred to as a first affine source vector and a second affine source vector, respectively. In embodiments using the first affine source vector and the second affine source vector described below, at least one of the first affine source vector and the second affine source vector may be replaced by the affine source vector of the bottom left control point (a third affine source vector) or the affine source vector of the bottom right control point (a fourth affine source vector).

[00155] Furthermore, in the 6-parameter affine motion model, the affine source vectors of the top left control point, the top right control point, and the bottom left control point will be referred to as a first affine source vector, a second affine source vector, and a third affine source vector, respectively. In embodiments using the first affine source vector, the second affine source vector, and the third affine source vector described below, at least one of the first affine source vector, the second affine source vector, and the third affine source vector may be replaced by the affine source vector of the bottom right control point (a fourth affine source vector).

[00156] An affine vector may be derived for each sub-block by use of the affine source vectors (S803). Here, the affine vector represents a translational motion vector derived based on the affine source vectors. The affine vector of a sub-block may be referred to as an affine sub-block motion vector or a sub-block motion vector.

[00157] Figure 10 is a view showing an example of sub-block affine vectors in a 4-parameter motion model.

[00158] The subblock affine vector can be derived based on the control point position, the subblock position, and the affine source vector. For example, Equation 3 shows an example of deriving an affine subblock vector.

[00159] In Equation 3, (x, y) denotes the position of a subblock. Here, the position of a subblock denotes the position of a reference sample included in the subblock. The reference sample may be a sample positioned in 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.

[00160] When the first control point and the second control point correspond to the upper left corner and upper right corner of the current block, respectively, x1-x0 can be set to a value equal to the width of the current block.

[00161] Subsequently, motion compensation prediction for each sub-block may be performed using the affine vector of each sub-block (S804). As a result of performing motion compensation prediction, a prediction block for each sub-block may be generated. The prediction blocks of the sub-blocks may be adjusted as the prediction blocks of the current block.

[00162] The affine seed vector of the current block may be derived based on the affine seed vector of a neighboring block adjacent to the current block. When the interprediction mode of the current block is an affine fusion mode, the affine seed vector of a fusion candidate included in the fusion candidate list may be determined as the affine seed vector of the current block. Further, when the interprediction mode of the current block is an affine fusion mode, motion information including at least one of the reference figuration index of the current block, a prediction flag of a specific direction, and a bidirectional weighting value may be adjusted to be equal to that of the fusion candidate.

[00163] The merge candidate may be derived based on a neighboring block of the current block. The neighboring block may include at least one of a spatial neighboring block spatially adjacent to the current block, and a temporal neighboring block included in a figuration other than the current figuration.

[00164] Figure 11 is a view showing a neighboring block that can be used to derive a fusion candidate.

[00165] A neighboring block of the current block may include at least one of a neighboring block (A) adjacent to the left side of the current block, a neighboring block (B) adjacent to the top of the current block, a neighboring block (C) adjacent to the top right corner of the current block, a neighboring block (D) adjacent to the bottom left corner of the current block, and a neighboring block (E) adjacent to the top left corner of the current block. When the coordinates of the top left sample of the current block are (x0, y0), the left neighboring block A includes a sample at the position of (x0-1, y0 + H-1), and the top neighboring block B includes a sample at the position of (x0 + W-1, y0-1). Here, W and H denote the width and height of the current block, respectively. The top right neighboring block C includes a sample at the position of (x0 + W, y0-1), and the bottom left neighboring block D includes a sample at the position of (x0-1, y0 + H). The upper left neighboring block E includes a sample at the position of (x0-1, y0-1).

[00166] When a neighboring block is encoded in the affine interprediction mode, an affine seed vector of a fusion candidate may be derived based on the affine seed vector of the neighboring block. Hereinafter in this document, the neighboring block encoded in an affine interprediction mode will be referred to as an affine neighboring block.

[00167] A merge candidate for the current block may be generated by searching neighboring blocks in a predefined scan order. The scan order may be predefined in the encoder and decoder. For example, neighboring blocks may be searched in the order of A, B, C, and D. Furthermore, merge candidates may be sequentially derived from the searched affine neighboring blocks. Alternatively, the scan order may be adaptively determined based on at least one of the size, shape, and affine motion model of the current block. That is, the scan orders of blocks of which at least one of the size, shape, and affine motion model is different may be different from each other.

[00168] Alternatively, blocks positioned on top of the current block are sequentially searched, and a merge candidate is derived from a first-found affine neighboring block, and blocks positioned on the left side of the current block are sequentially searched, and a merge candidate may be derived from a first-found affine neighboring block. Here, the neighboring blocks positioned on top of the current block include at least one of neighboring block E, neighboring block B, and neighboring block C, and the blocks positioned on the left side of the current block may include at least one of block A and block D. At this point, neighboring block E may also be classified as a block positioned on the left side of the current block.

[00169] Although not shown, a fusion candidate may be derived from a temporal neighboring block of the current block. Here, the temporal neighboring block may include a block at a position equal to that of the current block in a co-located figuration or a block adjacent thereto. Specifically, when a temporal neighboring block of the current block is coded in an affine interprediction mode, a fusion candidate may be derived based on an affine seed vector of a temporal fusion candidate.

[00170] A merge candidate list including merge candidates may be generated, and an affine seed vector of one of the merge candidates included in the merge candidate list may be determined as an affine seed vector of the current block. For this purpose, index information for identifying any of the merge candidates may be encoded and transmitted via a bit stream.

[00171] As another example, neighboring blocks are searched according to a scan order, and an affine seed vector of the current block may be derived from the affine seed vector of a first encountered affine neighboring block.

[00172] As described above, in affine fusion mode, an affine seed vector of the current block may be derived using an affine seed vector of a neighboring block.

[00173] When the interprediction mode of the current block is an affine motion vector prediction mode, the affine seed vector of a motion vector prediction candidate included in a list of motion vector prediction candidates may be determined as an affine seed vector prediction value of the current block. The affine seed vector of the current block may be derived by adding an affine seed vector difference value to the affine source vector prediction value.

[00174] An affine source vector prediction candidate may be derived based on a neighboring block of the current block. Specifically, neighboring blocks positioned on top of the current block are searched according to a predetermined scan order, and a first affine source vector prediction candidate may be derived from a first-encountered affine neighboring block. Furthermore, neighboring blocks positioned on the left side of the current block are searched according to a predetermined scan order, and a second affine source vector prediction candidate may be derived from a first-encountered affine neighboring block.

[00175] Information for determining an affine source vector difference value may be encoded and transmitted via a bit stream. The information may include size information indicating the magnitude of the affine source vector difference value, and encode information indicating a sign of the affine source vector difference value. The affine source vector difference value for each control point may be set to be the same. Alternatively, the affine source vector difference value may be set differently for each control point.

[00176] As described above, an affine seed vector of a merge candidate or an affine seed vector prediction candidate may be derived from an affine seed vector of an affine neighboring block, and an affine seed vector of the current block may be derived using the affine seed vector derived from the merge candidate or the affine seed vector prediction candidate. Alternatively, after searching affine neighboring blocks according to a predetermined scan order, the affine seed vector of the current block may be derived from the affine seed vector of a first-encountered affine neighboring block.

[00177] Hereinafter in this document, a method of deriving an affine seed vector of the current block, a fusion candidate, or an affine seed vector prediction candidate from an affine seed vector of an affine neighboring block will be described in detail. In the embodiments described below, it can be understood that the derivation of an affine seed vector of the current block is the derivation of an affine seed vector of a fusion candidate or the derivation of an affine seed vector from an affine seed vector prediction candidate.

[00178] Figure 12 is a view showing an example of deriving an affine source vector of a current block based on an affine source vector of an affine neighboring block.

[00179] When a first affine source vector nv0 for the top left control point and a second affine source vector nv1 for the top right control point are stored for an affine neighboring block, a third affine source vector nv2 for the bottom left control point of the affine neighboring block can be derived based on the first affine source vector and the second affine source vector. Equation 4 shows an example of deriving the third affine source vector.

[00180] In Equation 4, (nv0x, nv0y) denotes a first affine source vector nv0, (nv1x, nv1y) denotes a second affine source vector nv1, and (nv2x, nv2y) denotes a third affine source vector nv2. Furthermore, (xn0, xn0) denotes the position of the first control point, (xn1, xn1) denotes the position of the second control point, and (xn2, xn2) denotes the position of the third control point.

[00181] Subsequently, an affine source vector of the current block can be derived using the first affine source vector, the second affine source vector, and the third affine source vector. Equation 5 shows an example of deriving the first affine source vector vo of the current block, and Equation 6 shows an example of deriving the second affine source vector v1 of the current block.

[00182] In Equations 5 and 6, (v0x, v0y) denotes the first affine source vector SVO of the current block and (VIX, VIY) denotes the second affine source vector sv1 of the current block. Additionally, (XO, YO) denotes the position of the first control point and (XI, YI) denotes the position of the second control point. For example, the first control point denotes the top left corner of the current block and the second control point denotes the top right corner of the current block.

[00183] In the example described above, it was described that affine source vectors of the current block are derived using three affine source vectors for an affine neighboring block. As another example, the affine source vectors of the current block may be derived using only two of the affine source vectors of an affine neighboring block.

[00184] Alternatively, the affine seed vectors of the current block may be derived using a fourth affine seed vector for the lower right corner, instead of the first affine seed vector for the upper left corner, the second affine seed vector for the upper right corner, or the third affine seed vector for the lower left corner of an affine neighboring block.

[00185] In particular, when the upper boundary of the current block is in contact with the upper boundary of a coding tree unit, and it is desired to use an affine source vector for an upper control point (e.g., the upper left corner or the upper right corner) of an affine neighboring block adjacent to the top of the current block (hereinafter referred to as the upper affine neighboring block), these should be stored in memory in advance, and a problem of increasing the number of line buffers may occur. Accordingly, when the upper boundary of the current block is in contact with the upper boundary of the coding tree unit, this may be adjusted to use an affine source vector of a lower control point (e.g., the lower left corner or the lower right corner), instead of the affine source vector of the upper control point, for the upper affine neighboring block. For example, affine source vectors of the current block can be derived using the third affine source vector for the lower left corner and the fourth affine source vector for the lower right corner of the upper affine neighboring block. At this point, the affine source vectors for the lower corners can be copied from the affine source vectors for the upper corners or derived from the affine source vectors for the upper corners. For example, the first affine source vector, the second affine source vector, or the third affine source vector can be converted to or replaced by the fourth affine source vector for the lower right corner.

[00186] Equations 7 and 8 show an example of deriving the first affine source vector and the second affine source vector of the current block using the third affine source vector for the lower left control point and the fourth affine source vector for the lower right control point of a neighboring affine vector.

[00187] In Equations 7 and 8, (xn2, yn2) denotes the coordinates of the lower left control point of an affine neighboring block, and (xn3, yn3) denotes the coordinates of the lower right control point of the affine neighboring block. (x0, y0) denotes the coordinates of the upper left control point of the current block, and (x1, y1) denotes the coordinates of the upper right control point of the current block. (nv2x, nv2y) denotes the affine seed vector of the lower left control point of an affine neighboring block (i.e., the third affine seed vector), and (nv3x, nv3y) denotes the affine seed vector of the lower right control point of the affine neighboring block (i.e., the fourth affine seed vector). (v0x, v0y) denotes the affine source vector of the top left control point of the current block (i.e., the first affine source vector), and (v1x, v1y) denotes the affine source vector of the top right control point of the current block (i.e., the second affine source vector).

[00188] The division operation included in Equations 7 and 8 may be changed to a compensation operation. The compensation operation may be performed based on a value derived by the width between the lower left control point and the lower right control point (i.e., (xn3-xn2)).

[00189] As shown in the example described above, affine source vectors of the current block can be derived from affine source vectors of an affine neighboring block that has been encoded/decoded. For this purpose, affine source vectors of the affine neighboring block that has been encoded/decoded should be stored in memory. However, since the affine source vectors of the affine neighboring block are stored in memory in addition to translational motion vectors (i.e., affine vectors) of sub-blocks included in the affine neighboring block, there is a problem of increased memory usage. In order to solve this problem, the affine source vector of the current block can be derived using the motion vector of a sub-block adjacent to the control point of the affine neighboring block, instead of the affine source vector of the affine neighboring block. That is, a motion vector of a sub-block adjacent to the control point of an affine neighboring block can be set as the affine source vector of the affine neighboring block. Here, the sub-block is a block that has a predefined size/shape in the encoder and decoder, and can be a block that has a basic size/shape for storing a motion vector. For example, the sub-block can be a square block of a size of 4x4. Alternatively, a motion vector for a specific sample position can be set as the affine seed vector of the affine neighboring block.

[00190] Figure 13 is a view showing an example of adjusting a motion vector of a sub-block as an affine source vector of an affine neighboring block.

[00191] A motion vector of a subblock adjacent to a control point may be set as an affine source vector of the control point. For example, in the example shown in Figure 13, a motion vector (nv4x, nv4y) of a subblock (bottom left subblock) adjacent to the bottom left corner of an affine neighboring block may be set as the affine source vector (nv2x, nv2x) of the bottom left control point, and a motion vector (nv5x, nv5y) of a subblock (bottom right subblock) adjacent to the bottom right corner may be set as the affine source vector (nv3x, nv3y) of the control point in the bottom right corner. Here, the bottom left sub-block may mean a sub-block that includes a sample (e.g., a sample at the position of (xn2, yn2-1)) adjacent to the bottom left control point (xn2, yn2) in the neighboring affine block, and the bottom right sub-block may mean a block that includes a sample (e.g., a sample at the position of (xn3-1, yn3-1)) adjacent to the bottom right control point (xn3, yn3) in the neighboring affine block. When affine source vectors of the current block are derived based on Equations 7 and 8, the third affine source vector of the neighboring affine block may be replaced by the motion vector of the bottom left sub-block, and the fourth affine source vector may be replaced by the motion vector of the bottom right sub-block.

[00192] Hereinafter in this document, in the embodiment described below, a sub-block used as the affine source vector of an affine neighboring block will be referred to as an affine sub-block.

[00193] According to one embodiment of the present invention, an affine subblock can be determined based on a sample at a specific position. For example, a subblock that includes a sample at a specific position can be set as an affine subblock. Hereinafter, a sample at a specific position will be referred to as an affine reference sample. Furthermore, a reference sample used to determine an affine subblock of the lower left control point is referred to as a lower left reference sample, and a reference sample used to determine an affine subblock of the lower right control point is referred to as a lower right reference sample.

[00194] The lower left reference sample and the lower right reference sample may be selected from samples included in the affine neighboring block. For example, at least one of the upper left sample, the lower left sample, the upper right sample, and the lower left sample of the lower left sub-block may be set as the lower left reference sample, and at least one of the upper left sample, the lower left sample, the upper right sample, and the lower left sample of the lower right sub-block may be set as the lower right reference sample. Accordingly, motion vectors of the lower left sub-block including the lower left reference sample and of the lower right sub-block including the lower right reference sample may be set as an affine seed vector for the lower left control point and an affine seed vector for the lower right control point, respectively.

[00195] As a further example, at least one of the lower left reference sample and the lower right reference sample may be set as a sample positioned outside of the neighboring affine block. This will be described in detail with reference to Figures 14 to 16.

[00196] Figures 14 to 16 are views showing positions of reference samples.

[00197] As shown in the example of Figure 14(a), the upper left sample of the lower left sub-block can be set as the reference sample (xn4, yn4) for the lower left control point. Accordingly, the lower left sub-block including the reference sample (xn4 and yn4) can be set as the affine sub-block for the lower left control point.

[00198] A sample positioned on the right side of the upper right sample of the lower right sub-block may be set as the reference sample (xn5, yn5) for the lower right control point. Accordingly, a sub-block adjacent to the right side of the lower right sub-block including the reference sample (xn5 and yn5) may be set as an affine sub-block for the lower right control point.

[00199] Alternatively, as shown in the example of Figure 14(b), a sample positioned on the left side of the upper left sample of the lower left sub-block may be set as the reference sample (xn4, yn4) for the lower left control point. Accordingly, a sub-block adjacent to the left side of the lower left sub-block including the reference sample (xn4 and yn4) may be set as the affine sub-block for the lower left control point.

[00200] The upper right sample of the lower right sub-block may be set as the reference sample (xn5, yn5) for the lower right control point. Accordingly, the lower right sub-block including the reference sample (xn5 and yn5) may be set as the affine sub-block for the lower right control point.

[00201] Alternatively, as shown in the example of Figure 15(a), the lower left sample of the lower left sub-block may be set as the reference sample (xn4, yn4) for the lower left control point. Accordingly, the lower left sub-block including the reference sample (xn4 and yn4) may be set as the affine sub-block for the lower left control point.

[00202] The sample positioned on the right side of the lower right sample of the lower right sub-block may be set as the reference sample (xn5, yn5) for the lower right control point. Accordingly, a sub-block adjacent to the right side of the lower right sub-block including the reference sample (xn5 and yn5) may be set as the affine sub-block for the lower right control point.

[00203] Alternatively, as shown in the example of Figure 15(b), a sample positioned on the left side of the lower left sample of the lower left sub-block may be set as the reference sample (xn4, yn4) for the lower left control point. Accordingly, a sub-block adjacent to the left side of the lower left sub-block including the reference sample (xn4 and yn4) may be set as the affine sub-block for the lower left control point.

[00204] The upper right sample of the upper right sub-block may be set as the reference sample (xn5, yn5) for the lower right control point. Accordingly, the lower right sub-block including the reference sample (xn5 and yn5) may be set as the affine sub-block for the lower right control point.

[00205] Alternatively, as shown in the example of Figure 16(a), a sample positioned between the top left sample and bottom left sample of the bottom left sub-block (e.g., a middle left sample) may be set as the reference sample (xn4, yn4) for the bottom left control point. Accordingly, the bottom left sub-block including the reference sample (xn4 and yn4) may be set as the affine sub-block for the bottom left control point.

[00206] The sample positioned on the right side of a sample positioned between the upper right sample and the lower right sample of the lower right subblock (e.g., a right intermediate sample) may be set as the reference sample (xn5, yn5) for the lower right control point. Accordingly, a subblock adjacent to the right side of the lower right subblock including the reference sample (xn5 and yn5) may be set as the affine subblock for the lower right control point.

[00207] Alternatively, as shown in the example of Figure 16(b), a sample positioned on the left side of a sample positioned between the upper left sample and the lower left sample of the lower left sub-block may be set as the reference sample (xn4, yn4) for the lower left control point. Accordingly, a sub-block adjacent to the left side of the lower left sub-block including the reference sample (xn4 and yn4) may be set as the affine sub-block for the lower left control point.

[00208] A sample positioned between the upper right sample and the lower right sample of the lower right sub-block may be set as the reference sample (xn5, yn5) for the lower right control point. Accordingly, the lower right sub-block including the reference sample (xn5 and yn5) may be set as the affine sub-block for the lower right control point.

[00209] When the affine source vectors of the current block are derived based on Equations 7 and 8, the third affine source vector of an affine neighboring block may be replaced by the motion vector of the affine sub-block for the lower left control point, and the fourth affine source vector may be replaced by the motion vector of the affine sub-block for the lower right control point. Furthermore, the position of the lower left control point may be replaced by the position of the lower left reference sample, and the position of the lower right control point may be replaced by the position of the lower right reference sample.

[00210] Different from the embodiments described with reference to Figures 14-16, a subblock that includes a sample adjacent to a reference sample may be set as an affine subblock. Specifically, a sample positioned outside of an affine neighboring subblock may be set as a reference sample, and a subblock included in an affine neighboring block may be set as an affine subblock. For example, in the example shown in Figure 14(a), the sample positioned on the right side of the top right sample of the bottom right subblock may be set as the reference sample (xn5, yn5), and the bottom right subblock may be set as the affine subblock for the bottom right corner. Alternatively, in the example shown in Figure 14(b), the sample positioned to the left of the top left sample of the bottom left sub-block can be set as the reference sample (xn4, yn4) and the bottom left sub-block can be set as the affine sub-block for the bottom left.

[00211] The embodiments described above may be equally applied to Figures 15 and 16. That is, in the example shown in Figure 15(a) or 16(a), the sample positioned on the right side of the bottom right sample or the middle right sample of the bottom right subblock may be set as the reference sample (xn5, yn5) and the bottom right subblock may be set as the affine subblock for the bottom right corner. Alternatively, in the example shown in Figure 15(b) or 16(b), the sample positioned on the left side of the bottom left sample or the middle left sample of the bottom left subblock may be set as the reference sample (xn4, yn4) and the bottom left subblock may be set as the affine subblock for the bottom left corner.

[00212] As shown in the examples described above, an affine source vector of an affine neighboring block may be derived using the motion vector of an affine sub-block. For this purpose, in the case of a block that has been encoded/decoded, the motion vector may be stored by the sub-block unit.

[00213] As another example, after storing a minimum number of affine source vectors for an affine neighboring block, a motion vector of an affine sub-block can be derived using the stored affine source vectors.

[00214] Equations 9 and 10 show an example of deriving a motion vector of an affine sub-block using affine source vectors from a neighboring affine block.

[00215] In Equations 9 and 10, (nv4x, nv4y) denotes a motion vector from an affine subblock to the lower left control point and (nv5x, nv5y) denotes a motion vector from an affine subblock to the lower right control point. Since the motion vector of an affine subblock and the affine source vector of a control point are adjusted equally, (nv4x, nv4y) can be replaced by the affine source vector (nv2x, nv2y) for the lower left control point or (nv5x, nv5y) can be replaced by the affine source vector (nv3x, nv3y) for the lower right control point.

[00216] (xn4, yn4) denotes the position of the reference sample for the lower left sub-block. Alternatively, the center position of the lower left sub-block or the position of the lower left control point may be used instead. (xn5, yn5) denotes the position of the reference sample for the lower right sub-block. Alternatively, the center position of the lower right sub-block or the position of the lower right control point may be used instead.

[00217] Equations 9 and 10 may be applied when the current block is not in contact with the boundary of a coding tree unit. When the current block is in contact with the upper boundary of a coding tree unit, instead of using Equations 9 and 10, a translational motion vector of an affine sub-block determined based on the lower left reference sample may be set as the third affine seed vector, and a translational motion vector of an affine sub-block determined based on the lower right reference sample may be set as the fourth affine seed vector.

[00218] In Equations 7 and 8, (xn3-xn2) denotes the width between the lower left control point and the lower right control point. As described above, xn3 may be replaced by the position xn5 of the lower right reference sample, and xn2 may be replaced by the position xn4 of the lower left reference sample. Hereinafter, (xn3-xn2) or a value obtained by replacing the positions of the above equation with the positions of reference samples (e.g., (xn5-xn4)) is defined as the Wseed variable, and the variable is referred to as a suborigin vector width.

[00219] Depending on the reference sample positions, a case may occur where the suborigin vector width is not a power-of-2 series (e.g., 2n). For example, when the bottom left sample of the bottom left subblock is set as the bottom left reference sample, and the bottom right sample of the bottom right subblock is set as the bottom right reference sample, the suborigin vector width is not a multiple of 2. As described above, when the suborigin vector width is not a power-of-2 series, the suborigin vector width may be transformed to be a power-of-2 series. The transform may include adding or subtracting an offset to or from the suborigin vector width, or using a sample position adjacent to the reference sample instead of the reference sample position. For example, a transformed suborigin vector width can be derived by adding 1 to the width between the lower left reference sample and the lower right reference sample. Alternatively, a width between a neighboring reference sample adjacent to the right side of the lower right reference sample and a lower left reference sample can be set as the transformed suborigin vector width. Subsequently, an affine source vector of the current block can be derived by applying the transformed suborigin vector width to Equations 7 and 8.

[00220] The division operation included in Equations 7 and 8 may be changed to a compensation operation. The compensation operation may be performed based on a value derived by the transformed suborigin vector width (i.e., a value expressed as a power-of-2 series).

[00221] When the reference sample used to determine the affine sub-block does not belong to the affine neighboring block, the affine source vector of the affine neighboring block may be derived based on a sample adjacent to the reference sample among the samples included in the affine neighboring block. Specifically, a translational motion vector of a sub-block that includes a sample adjacent to the reference sample in the affine neighboring block (hereinafter referred to as a neighboring reference sample) may be set as the affine source vector of the affine neighboring block. In this way, a method of deriving an affine source vector using a neighboring reference sample may be defined as a modified affine fusion vector derivation method.

[00222] Figure 17 is a view showing an example application of a modified affine fusion vector derivation method.

[00223] When the lower right reference sample (xn5, yn5) of the affine neighboring block E does not belong to the affine neighboring block, an affine seed vector may be derived based on a sample (xn5-1, yn5) adjacent to the left side of the lower right reference sample from among the samples included in the affine neighboring block. Specifically, a translational motion vector of a sub-block that includes the neighboring reference sample (xn5-1, yn5) may be set as the affine seed vector of the lower right control point.

[00224] In the example shown in Figure 17, it is shown that a sample adjacent to the right side of the top right sample of the bottom right sub-block is the bottom right reference sample. Even when a sample adjacent to the right side of the bottom right sample of the bottom right sub-block or a sample adjacent to the right side of the middle right sample of the bottom right sub-block is set as the bottom right reference sample, an affine seed vector can be derived based on a sample adjacent to the left side of the neighboring reference sample.

[00225] Furthermore, even when the lower left reference sample does not belong to the affine neighboring block, according to the embodiment described above, the affine seed vector may be derived based on a sample adjacent to the right side of the lower left reference sample.

[00226] Since the position of the reference sample and the sub-block for deriving an affine source vector are adjusted differently, the sub-source vector width can be adjusted to a power-of-2 series.

[00227] A fusion candidate, an affine seed vector prediction candidate, or an affine seed vector of the current block may be derived using a neighboring block that has not been encoded in an inter-affine mode in the neighborhood of the current block. Specifically, blocks not encoded in the inter-affine mode may be combined and a combination thereof may be set as a fusion candidate or an affine seed vector prediction candidate. For example, a combination of at least one of a motion vector of any of neighboring blocks adjacent to the upper left corner of the current block, a motion vector of any of neighboring blocks adjacent to the upper right corner of the current block, and a motion vector of any of neighboring blocks adjacent to the lower left corner of the current block may be set as a fusion candidate or an affine seed vector prediction candidate. At this point, a motion vector of a neighboring block adjacent to the upper left corner, a motion vector of a neighboring block adjacent to the upper right corner, and a motion vector of a neighboring block adjacent to the lower left corner can be set as a first affine source vector for the upper left control point, a second affine source vector for the upper right control point, and a third affine source vector for the lower left control point, respectively.

[00228] Alternatively, a fusion candidate, an affine seed vector prediction candidate, or an affine seed vector of the current block may be derived using a neighboring block that is not encoded in the inter-affine mode in the modified affine fusion vector derivation method described above. Hereinafter in this document, a neighboring block that is not encoded in the inter-affine mode will be referred to as a non-affine neighboring block.

[00229] Figure 18 is a view showing an example of deriving an affine source vector of a current block based on a non-affine neighboring block.

[00230] In the example shown in Figure 18, it is assumed that all neighboring blocks adjacent to the current block are non-affine neighboring blocks.

[00231] When it is desired to derive an affine seed vector of the current block from the non-affine neighboring block A among the neighboring blocks adjacent to the current block, a lower left reference sample and a lower right reference sample may be set for block A. For example, a sample adjacent to the left side of the lower left sample of block A may be set as the lower left reference sample, and the lower right sample of block A may be set as the lower right reference sample. Since the lower left reference sample is outside of block A, the motion vector of a sub-block that includes a sample adjacent to the right side of the lower left reference sample can be set as a third affine source vector of block A. Furthermore, the motion vector of a sub-block that includes the lower right reference sample can be set as a fourth affine source vector of block A. Subsequently, a first affine source vector and a second affine source vector for the current block can be derived from block A based on Equations 9 and 10.

[00232] A method of deriving an affine source vector from a non-affine neighboring block may be used only when motion compensation prediction for a non-affine neighboring block is performed by the sub-block unit. Here, the prediction technique for performing motion compensation prediction by the sub-block unit may include at least one of STMVP, ATMVP, Bi-Directional Optical Flow (BIO), Overlapped Block Motion Compensation (OBMC), and Decoder side Motion Vector Refinement (DMVR).

[00233] In the embodiment described above, it has been described that when the upper boundary of the current block is in contact with the boundary of a coding tree unit, a fusion candidate, an affine seed vector prediction candidate, or an affine seed vector of the current block is derived using the third affine seed vector for the lower left control point and the fourth affine source vector for the lower right control point of the affine neighboring block positioned at the top of the current block.

[00234] As another example, when the upper boundary of the current block is in contact with the boundary of a coding tree unit, and a neighboring block positioned at the top of the current block belongs to a different coding tree unit than that of the current block, a fusion candidate, an affine seed vector prediction candidate, or an affine seed vector of the current block may be derived using a neighboring block closest to the neighboring block among the blocks included in the coding tree unit to which the current block belongs, instead of the neighboring block.

[00235] In the example shown in Figure 19, it is shown that the current block is in contact with the upper boundary of a coding tree unit, and the blocks B, C and E positioned at the top of the current block belong to a different coding tree unit than that of the current block. Consequently, instead of using block E, an affine seed vector of the current block can be derived using block F adjacent to a block E among the blocks included in the coding tree unit to which the current block belongs.

[00236] Due to the motion compensation prediction of the current block, affine source vectors from a plurality of blocks may be used. For example, it is possible to select a plurality of fusion candidates from the list of fusion candidates, and derive an affine source vector or a sub-block vector for the current block based on the affine source vectors of the selected fusion candidates. Encoding/decoding the current block using the affine source vectors from a plurality of blocks may be referred to as a multiple affine fusion coding method.

[00237] Information indicating whether or not the multiple affine fusion coding method is applied to the current block may be encoded and transmitted via a bit stream. Alternatively, whether or not the multiple affine fusion coding method is applied to the current block may be determined based on at least one of the number of affine neighboring blocks among the neighboring blocks adjacent to the current block, the number of fusion candidates included in the fusion candidate list, and the affine motion model of the current block.

[00238] Figures 20 and 21 are views showing the flow of a motion compensation prediction method using a plurality of fusion candidates.

[00239] Figure 20 is a view showing an example of deriving affine source vectors of the current block using affine source vectors of a plurality of fusion candidates. Figure 21 is a view showing an example of deriving a motion vector of each sub-block using affine source vectors of a plurality of fusion candidates.

[00240] The affine seed vectors of the current block may be generated based on a sum, difference, average, or weighted sum operation of affine seed vectors of two merge candidates.

[00241] Equations 11 and 12 show an example of deriving an affine seed vector of the current block by summing affine seed vectors of merge candidates.

[00242] In Equations 11 and 12, sv4 denotes a first affine source vector of the current block, sv0 denotes a first affine source vector of a first merge candidate, and sv2 denotes a first affine source vector of a second merge candidate. Additionally, sv5 denotes a second affine source vector of the current block, sv1 denotes a second affine source vector of the first merge candidate, and sv3 denotes a second affine source vector of the second merge candidate.

[00243] Furthermore, Equations 13 and 14 show an example of deriving an affine seed vector of the current block through a weighted sum operation of affine seed vectors of merge candidates.

[00244] As another example, a first sub-block motion vector and a second sub-block motion vector may be generated for each sub-block in the current block, based on the affine seed vectors of the first defusion candidate and the affine seed vectors of the second defusion candidate. Thereafter, a final sub-block motion vector may be generated based on a sum, difference, average, or weighted sum operation of the first sub-block motion vector and the second sub-block motion vector.

[00245] Equation 15 shows an example of deriving a final sub-block motion vector by summing the first sub-block motion vector and the second sub-block motion vector.

[00246] In Equation 15, V0 denotes a first sub-block motion vector, V1 denotes a second sub-block motion vector, and V2 denotes a final sub-block motion vector.

[00247] Furthermore, Equation 16 shows an example of deriving a final sub-block motion vector via a weighted sum operation of the first sub-block motion vector and the second sub-block motion vector.

[00248] Intraprediction is to predict a current block using reconstructed samples that were encoded/decoded around the current block. At this point, samples reconstructed before an in-loop filter was applied can be used for intraprediction of the current block.

[00249] 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 location, size, and shape of the current block, or based on an intraprediction technique of a neighboring block. For example, when the current block exists in a figuration boundary, this may be adjusted to not apply matrix-based intraprediction to the current block.

[00250] Matrix-based intraprediction 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 around the current block. Information for specifying any 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.

[00251] 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. Hereinafter in this document, a process of performing intraprediction based on general intraprediction will be described in more detail with reference to the drawings.

[00252] Figure 22 is a flowchart illustrating an intraprediction method in accordance with an embodiment of the present invention.

[00253] A reference sample line of the current block may be determined (S2201). The reference sample line means a set of reference samples included in a k-th separate line from the top and/or left side of the current block. The reference samples may be derived from reconstructed samples that were encoded/decoded around the current block.

[00254] Index information for identifying the reference sample line of the current block from among a plurality of reference sample lines may be signaled via a bit stream. The plurality of reference sample lines may include at least one of a first line, a second line, a third line, and a fourth line at the top and/or left side of the current block. Table 1 shows indices assigned to the reference sample lines, respectively. In Table 1, it is assumed that the first line, the second line, and the fourth line are used as reference sample line candidates.[TABLE 1]

[00255] The reference sample line of the current block may be determined based on at least one of the location, size, and shape of the current block, or based on a predictive coding mode of a neighboring block. For example, when the current block is in contact with the boundary of a figuration, a tile, a slice, or a coding tree unit, the first reference sample line may be determined as the reference sample line of the current block.

[00256] The reference sample line may include top reference samples positioned at the top of the current block and left reference samples positioned on the left side of the current block. The top reference samples and the left reference samples may be derived from reconstructed samples around the current block. The reconstructed samples may be in a state before the in-loop filter is applied.

[00257] Figure 23 is a view showing reference samples included in each reference sample line.

[00258] According to the intra-prediction mode of the current block, a prediction sample may be acquired by using at least one of the reference samples belonging to a reference sample line.

[00259] Subsequently, the intra-prediction mode of the current block may be determined (S2202). As for the intra-prediction mode of the current block, at least one of a non-angular intra-prediction mode and an angular intra-prediction mode may be determined as the intra-prediction mode of the current block. The non-angular intra-prediction mode includes a flat mode and a DC mode, and the angular intra-prediction mode includes 33 or 65 modes between the lower left diagonal direction and the lower right diagonal direction.

[00260] Figure 24 is a view showing intraprediction modes.

[00261] Figure 24(a) shows 35 intra-prediction modes and Figure 24(b) shows 67 intra-prediction modes.

[00262] A greater or lesser number of intraprediction modes than those shown in Figure 24 may be defined.

[00263] A Most Likely Mode (MPM) may be adjusted based on the intraprediction mode of a neighboring block adjacent to the current block. Here, the neighboring block may include a left neighboring block adjacent to the left side of the current block and an upper neighboring block adjacent to the top of the current block. When the coordinates of the upper left sample of the current block are (0, 0), the left neighboring block may include a sample at the position of (-1, 0), (-1, H-1), or (-1, (H-1)/2). Here, H denotes the height of the current block. The upper neighboring block may include a sample at the position of (0, -1), (W-1, -1), or ((W-1)/2, -1). Here, W denotes the width of the current block.

[00264] When the neighboring block is coded by intraprediction normal, the MPM may be derived based on the intraprediction mode of the neighboring block. Specifically, the intraprediction mode of the left neighboring block may be set to variable candIntraPredModeA, and the intraprediction mode of the upper neighboring block may be set to variable candIntraPredModeB.

[00265] At this point, when the neighboring block is unavailable (e.g., when the neighboring block is not yet coded/decoded or when the position of the neighboring block is outside the figuration boundary), when the neighboring block is coded by matrix-based intraprediction, when the neighboring block is coded by interprediction, or when the neighboring block is included in a different coding tree unit than the current block, the variable candIntraPredModeX (here, X is A or B) derived based on the intraprediction mode of the neighboring block may be set as a default mode. Here, the default mode may include at least one of a flat mode, a DC mode, a vertical direction mode, and a horizontal direction mode.

[00266] Alternatively, when the neighboring block is coded by matrix-based intraprediction, an intraprediction mode that corresponds to an index value for specifying either matrix may be set to candIntraPredModeX. For this purpose, a lookup table showing the mapping relationship between index values for specifying a matrix and intraprediction modes may be previously stored in the encoder and decoder.

[00267] MPMs may be derived based on the candIntraPredModeA variable and the candIntraPredModeB variable. The number of MPMs included in an MPM list may be pre-set at the encoder and decoder. The number of MPMs included in the MPM list may be pre-set at the encoder and decoder. For example, the number of MPMs may be 3, 4, 5, or 6. Alternatively, information indicating the number of MPMs may be signaled via a bit stream. Alternatively, the number of MPMs may be determined based on at least one of the neighbor block prediction coding mode and the current block size and format.

[00268] In the embodiments described below, it is assumed that the number of MPMs is three, and the three MPMs will be referred to as MPM[0], MPM[1], and MPM[2]. When the number of MPMs is more than three, the MPMs may be configured to include three MPMs described in the embodiments described below.

[00269] When candIntraPredA and candIntraPredB are equal, and candIntraPredA is a flat mode or a DC mode, MPM[0] and MPM[1] can be set to a flat mode and a DC mode, respectively. MPM[2] can be set to a vertical direction intra-prediction mode, a horizontal direction intra-prediction mode, or a diagonal direction intra-prediction mode. The diagonal direction intra-prediction mode can be a lower-left diagonal direction intra-prediction mode, an upper-right direction intra-prediction mode, or an upper-right direction intra-prediction mode.

[00270] When candIntraPredA and candIntraPredB are equal, and candIntraPredA is an angular intraprediction mode, MPM[0] may be set to be equal to candIntraPredA. MPM[1] and MPM[2] may be set to an intraprediction mode similar to candIntraPredA, respectively. The intraprediction mode similar to candIntraPredA may be an intraprediction mode in which the difference between candIntraPredA and an index is ±1 or ±2. A modulo (%) operation and an offset may be used to derive the intraprediction mode similar to candIntraPredA.

[00271] When candIntraPredA and candIntraPredB are different, MPM[0] may be set to be equal to candIntraPredA, and MPM[1] may be set to be equal to candIntraPredB. At this point, when both candIntraPredA and candIntraPredB are non-angular intra-prediction mode, MPM[2] may be set to a vertical direction intra-prediction mode, a horizontal direction intra-prediction mode, or a diagonal direction intra-prediction mode. Alternatively, when at least one of candIntraPredA and candIntraPredB is an angular intra-prediction mode, MPM[2] may be set to an intra-prediction mode derived by adding or subtracting the offset of a planar mode, a DC mode, or the one of candIntraPredA and candIntraPredB that has a larger value. Here, the offset may be 1 or 2.

[00272] An MPM list including a plurality of MPMs is generated, and information indicating whether an MPM that is equal to the intraprediction mode of the current block is included in the MPM list may be signaled via a bit stream. The information is a 1-bit tag and may be referred to as an MPM tag. When the MPM tag indicates that an MPM equal to that of the current block is included in the MPM list, index information identifying one of the MPMs may be signaled via a bit stream. The MPM specified by the index information may be set as the intraprediction mode of the current block. When the MPM tag indicates that an MPM equal to that of the current block is not included in the MPM list, residual mode information indicating any of the residual intraprediction modes other than MPMs may be signaled via a bit stream. The residual mode information indicates an index value that corresponds to the intraprediction mode of the current block when indices are reassigned to the residual intraprediction modes excluding the MPMs. The decoder can arrange the MPMs in ascending order and determine the intraprediction mode of the current block by comparing the residual mode information with the MPMs. For example, when the residual mode information is equal to or less than the MPM, the intraprediction mode of the current block can be derived by adding 1 to the residual mode information.

[00273] Instead of setting the default mode for MPM, information indicating whether or not the intraprediction mode of the current block is the default mode may be signaled via a bit stream. The information is a 1-bit tag, and the tag may be referred to as a default mode tag. The default mode tag may be signaled only when the MPM tag indicates that an MPM equal to that of the current block is included in the MPM list. As described above, the default mode may include at least one of a flat mode, a DC mode, a vertical direction mode, and a horizontal direction mode. For example, when the flat mode is set as the default mode, the default mode tag may indicate whether or not the intraprediction mode of the current block is a flat mode. When the default mode tag indicates that the intraprediction mode of the current block is not the default mode, one of the MPMs indicated by the index information may be set as the intraprediction mode of the current block.

[00274] When a plurality of intraprediction modes are set as default modes, index information indicating any of the default modes may be additionally signaled. The intraprediction mode of the current block may be set as the default mode indicated by the index information.

[00275] When the reference sample line index of the current block is not 0, this may be set to not use the default mode. Accordingly, when the reference sample line index is not 0, the default mode flag is not signaled, and the value of the default mode flag may be set to a predefined value (i.e., false).

[00276] When the intraprediction mode of the current block is determined, prediction samples may be acquired for the current block based on the determined intraprediction mode (S2203).

[00277] When DC mode is selected, prediction samples are generated for the current block based on an average value of reference samples. Specifically, values of all samples in a prediction block may be generated based on an average value of the reference samples. The average value may be derived using at least one of the top reference samples positioned at the top of the current block and left reference samples positioned on the left side of the current block.

[00278] Depending on the shape of the current block, the number or range of reference samples used to derive the mean value may vary. For example, when the current block is a non-square shaped block of which the width is greater than the height, the mean value may be calculated using only the top reference samples. Conversely, when the current block is a non-square shaped block of which the width is less than the height, the mean value may be calculated using only the left reference samples. That is, when the width and height of the current block are different, the mean value may be calculated using only the reference samples adjacent to the longest one. Alternatively, based on the ratio of the width to height of the current block, it may be determined whether to calculate the mean value using only the top reference samples or whether to not calculate the mean value using only the left reference samples.

[00279] When the planar mode is selected, a prediction sample may be acquired using a horizontal direction prediction sample and a vertical direction prediction sample. Here, the horizontal direction prediction sample is acquired based on a left reference sample and a right reference sample positioned on a horizontal line equal to that of the prediction sample, and the vertical direction prediction sample is acquired based on an upper reference sample and a lower reference sample positioned on a vertical line equal to that of the prediction sample. Here, the right reference sample may be generated by copying a reference sample adjacent to the upper right corner of the current block, and the lower reference sample may be generated by copying a reference sample adjacent to the lower left corner of the current block. The horizontal direction prediction sample can be acquired based on a weighted sum operation of the left reference sample and the right reference sample, and the vertical direction prediction sample can be acquired based on a weighted sum operation of the upper reference sample and the lower reference sample. At this point, a weighting value assigned to each reference sample can be determined according to the position of the prediction sample. The prediction sample can be acquired based on an average operation or a weighted sum operation of the horizontal direction prediction sample and the vertical direction prediction sample. When the weighted sum operation is performed, weighting values applied to the horizontal direction prediction sample and the vertical direction prediction sample can be determined based on the position of the prediction sample.

[00280] When an angular prediction mode is selected, a parameter indicating the prediction direction (or prediction angle) of the selected angular prediction mode can be determined. Table 2 shows the intra direction parameter intraPredAng of each intraprediction mode.[TABLE 2]

[00281] When 35 intra-prediction modes are defined, Table 2 shows the intra-direction parameter of each intra-prediction mode having an index of any one of 2 to 34. When more than 33 angular intra-prediction modes are defined, Table 2 is further subdivided to adjust the intra-direction parameter of each angular intra-prediction mode.

[00282] After arranging top reference samples and left reference samples of the current block in a row, a prediction sample may be acquired based on the value of the intra direction parameter. At this point, when the value of the intra direction parameter is a negative value, the left reference samples and top reference samples may be arranged in a row.

[00283] Figures 25 and 26 are views showing an example of a one-dimensional array arranging reference samples in a row.

[00284] Figure 25 is a view showing an example of a one-dimensional vertical direction array arranging reference samples in the vertical direction, and Figure 26 is a view showing an example of a one-dimensional horizontal direction array arranging reference samples in the horizontal direction. The embodiments of Figures 25 and 26 will be described on the assumption that 35 intra-prediction modes are defined.

[00285] When the intra-prediction mode index is any one of 11 to 18, a horizontal direction one-dimensional array in which top reference samples are rotated counterclockwise can be applied, and when the intra-prediction mode index is any one of 19 to 25, a vertical direction one-dimensional array in which left reference samples are rotated clockwise can be applied. In arranging the reference samples in a row, an intra-prediction mode angle can be considered.

[00286] A reference sample determination parameter may be determined based on an intra-direction parameter. The reference sample determination parameter may include a reference sample index for specifying the reference sample and a weighting value parameter for determining a weighting value applied to the reference sample.

[00287] The reference sample index iIdx and the weighting value parameter ifact can be acquired via Equations 17 and 18 shown below, respectively.

[00288] In Equations 17 and 18, Pang denotes an intra-direction parameter. The reference sample specified by the reference sample index iIdx corresponds to an integer pel.

[00289] At least one or more reference samples may be specified to derive a prediction sample. Specifically, the position of the reference sample used to derive a prediction sample may be specified considering the slope of the prediction mode. For example, a reference sample used to derive a prediction sample may be specified using the reference sample index iIdx.

[00290] At this point, when the slope of the intra-prediction mode is not expressed by a reference sample, a prediction sample may be generated by interpolating a plurality of reference samples. For example, when the slope of the intra-prediction mode is a value between a slope between a prediction sample and a first reference sample and a slope between the prediction sample and a second reference sample, the prediction sample may be acquired by interpolating the first reference sample and the second reference sample. That is, when an angled line following an intra-prediction angle does not cross a reference sample positioned at an integer pel, the prediction sample may be acquired by interpolating reference samples adjacent to the left and right of or above and below a position where the angled line crosses.

[00291] Equation 19 shows an example of acquiring a prediction sample based on reference samples.

[00292] In Equation 19, P denotes a prediction sample, and Ref_1D denotes any of the one-dimensionally arranged reference samples. At this point, the position of the reference sample can be determined by the position (x, y) of the prediction sample and index iIdx of the reference sample.

[00293] When the intraprediction mode slope can be expressed as a reference sample, the weighting value parameter ifact is set to 0. Consequently, Equation 19 can be simplified as shown in Equation 20.

[00294] Intraprediction for the current block may be performed based on a plurality of intraprediction modes. For example, an intraprediction mode may be derived for each prediction sample, and the prediction sample may be derived based on an intraprediction mode assigned to each prediction sample.

[00295] Alternatively, an intra-prediction mode may be derived for each region, and intra-prediction for each region may be performed based on the intra-prediction mode assigned to each region. Here, the region may include at least one sample. At least one of the size and shape of the region may be adaptively determined based on at least one of the size, shape, and intra-prediction mode of the current block. Alternatively, at least one of the size and shape of the region may be predefined in the encoder and decoder to be independent of the size or shape of the current block.

[00296] Alternatively, intra-prediction may be performed based on each of a plurality of intra-predictions, and a final prediction sample may be derived based on an average operation or a weighted sum operation of a plurality of prediction samples acquired through the plurality of intra-predictions. For example, a first prediction sample may be acquired by performing intra-prediction based on a first intra-prediction mode, and a second prediction sample may be acquired by performing intra-prediction based on a second intra-prediction mode. Thereafter, a final prediction sample may be acquired based on an average operation or a weighted sum operation of the first prediction sample and the second prediction sample. At this point, a weighting value assigned to each of the first prediction sample and the second prediction sample can be determined by considering at least one of the possibilities of whether or not the first intra-prediction mode is a non-angular/angular prediction mode, whether or not the second intra-prediction mode is a non-angular/angular prediction mode, and an intra-prediction mode of a neighboring block.

[00297] The plurality of intra-prediction modes may be a combination of a non-angular intra-prediction mode and an angular prediction mode, a combination of angular prediction modes, or a combination of non-angular prediction modes.

[00298] Figure 27 is a view showing an example of angles formed between angular intraprediction modes and a straight line parallel to the x-axis.

[00299] As shown in the example of Figure 27, angular prediction modes may exist between the lower left diagonal direction and the lower right diagonal direction. Describing in terms of an angle formed by the x-axis and the angular prediction mode, angular prediction modes may exist between 45 degrees (lower left diagonal direction) and -135 degrees (lower right diagonal direction).

[00300] When the current block is a non-square shape, according to the intra-prediction mode of the current block, there may be a case of deriving a prediction sample by using the reference sample farthest from the prediction sample, instead of the reference sample even closer to the prediction sample, among the reference samples positioned on the angular line following the intra-prediction angle.

[00301] Figure 28 is a view showing an embodiment of acquiring prediction samples when the current block is a non-square shape.

[00302] For example, as shown in the example of Figure 28(a), it is assumed that the current block is a non-square shape of which the width is greater than the height, and the intra-prediction mode of the current block is an angular intra-prediction mode that has an angle between 0 and 45 degrees. In the above case, when the prediction sample A next to the right column of the current block is derived, there may be a use case of left reference sample L far from the prediction sample, instead of top reference sample T close to the prediction sample, among the reference samples positioned in an angular mode following the angle.

[00303] As another example, as shown in the example of Figure 28(b), it is assumed that the current block is a non-square shape of which the height is greater than the width, and the intra-prediction mode of the current block is an angular intra-prediction mode that has an angle between -90 and -135 degrees. In the above case, when prediction sample A next to the bottom row of the current block is derived, there may be a case of using top reference sample T away from the prediction sample, instead of left reference sample L next to the prediction sample, among the reference samples positioned in an angular mode following the angle.

[00304] To solve the problem described above, when the current block is a non-square shape, the intra-prediction mode of the current block can be replaced by an intra-prediction mode of the opposite direction. Accordingly, angular prediction modes that have an angle larger or smaller than that of the angular prediction modes shown in Figure 24 can be used for a non-square shaped block. Such an angular intra-prediction mode can be defined as a wide-angle intra-prediction mode. The wide-angle intra-prediction mode represents an angular intra-prediction mode that does not belong to the range of 45 to -135 degrees.

[00305] Figure 29 is a view showing wide-angle intraprediction modes.

[00306] In the example shown in Figure 29, intraprediction modes with an index of -1 to -14 and intraprediction modes with an index of 67 to 80 represent wide-angle intraprediction modes.

[00307] Although 14 wide-angle intra-prediction modes (-1 to -14) that have an angle greater than 45 degrees and 14 wide-angle intra-prediction modes (67 to 80) that have an angle less than -135 degrees are shown in Figure 29, a smaller or larger number of wide-angle intra-prediction modes may be defined.

[00308] When a wide-angle intra-prediction mode is used, the length of upper reference samples may be set to 2W+1, and the length of left reference samples may be set to 2H+1.

[00309] Since a wide-angle intra-prediction mode is used, sample A shown in Figure 28(a) can be predicted using reference sample T, and sample A shown in Figure 28(b) can be predicted using reference sample L.

[00310] By adding existing intraprediction modes and N wide-angle intraprediction modes, a total of 67+N intraprediction modes can be used. For example, Table 3 shows intradirection parameters of intraprediction modes when 20 wide-angle intraprediction modes are defined.[TABLE 3]

[00311] When the current block is a non-square shape and the intra-prediction mode of the current block acquired in step S2202 belongs to a transform range, the intra-prediction mode of the current block may be transformed into a wide-angle intra-prediction mode. The transform range may be determined based on at least one of the size, shape, and aspect ratio of the current block. Here, the aspect ratio may represent a ratio of the width to the height of the current block.

[00312] The current block is a non-square shape of which the width is greater than the height, the transform range may be adjusted by an intra-prediction mode index (e.g., 66) of the lower right diagonal direction (an intra-prediction mode index in the lower right diagonal direction - N). Here, N may be determined based on the ratio of the current block. When the intra-prediction mode of the current block belongs to the transform range, the intra-prediction mode may be transformed into a wide-angle intra-prediction mode. The transform may be a subtraction of a predefined value of the intra-prediction mode, and the predefined value may be the total number (e.g., 67) of intra-prediction modes excluding the wide-angle intra-prediction modes.

[00313] According to the above-described embodiment, 66-th to 53-th intra-prediction modes can be transformed into -1° to -14-th wide-angle intra-prediction modes, respectively.

[00314] When the current block is a non-square shape of which the height is greater than the width, the transform range may be adjusted by an intra-prediction mode index (e.g., 2) of the lower left diagonal direction (an intra-prediction mode index in the lower left diagonal direction + M). Here, M may be determined based on the ratio of the current block. When the intra-prediction mode of the current block belongs to the transform range, the intra-prediction mode may be transformed into a wide-angle intra-prediction mode. The transform may be the addition of a preset value to the intra-prediction mode, and the preset value may be the total number (e.g., 65) of angular intra-prediction modes excluding the wide-angle intra-prediction modes.

[00315] According to the above-described embodiment, 2nd to 15th intra-prediction modes can be transformed into 67th to 80th wide-angle intra-prediction modes, respectively.

[00316] Hereinafter in this document, intra-prediction modes that belong to the transform range will be referred to as wide-angle substitution prediction modes.

[00317] The transform range can be determined based on the current block ratio. For example, Tables 4 and 5 show a transform range when 35 intra-prediction modes and 67 intra-prediction modes are defined excluding the wide-angle intra-prediction modes, respectively.[TABLE 4] [TABLE 5]

[00318] As shown in the examples in Tables 4 and 5, the number of wide-angle replacement prediction modes that belong to the transform range may vary depending on the current block ratio.

[00319] As wide-angle intra-prediction modes are used in addition to existing intra-prediction modes, resources required to encode the wide-angle intra-prediction modes increase and thus coding efficiency may be decreased. Accordingly, coding efficiency may be improved by coding replacement intra-prediction modes for the wide-angle intra-prediction modes, rather than coding the wide-angle intra-prediction modes as is.

[00320] For example, when the current block is coded using the 67th wide-angle intra-prediction mode, the 2nd intra-prediction mode, which is the replacement intra-prediction mode of the 67th wide-angle intra-prediction mode, may be coded using the intra-prediction mode of the current block. Furthermore, when the current block is coded using the -1st wide-angle intra-prediction mode, the 66th intra-prediction mode, which is the replacement intra-prediction mode of the -1st wide-angle intra-prediction mode, may be coded using the intra-prediction mode of the current block.

[00321] The decoder may decode the intra-prediction mode of the current block and determine whether the decoded intra-prediction mode belongs to the transform range. When the decoded intra-prediction mode is a wide-angle substitution intra-prediction mode, the intra-prediction mode may be transformed into the wide-angle intra-prediction mode.

[00322] Alternatively, when the current block is encoded using the wide-angle intra-prediction mode, the wide-angle intra-prediction mode may be encoded as is.

[00323] Intra-prediction mode coding may be performed based on the MPM list described above. Hereinafter in this document, a method of configuring the MPM list will be described in detail. In the embodiments described below, it is assumed that 10 wide-angle intra-prediction modes (-1 to -10) with an angle greater than 45 degrees and 10 wide-angle intra-prediction modes (67 to 76) with an angle less than -135 degrees are defined.

[00324] When a neighboring block is coded using a wide-angle intra-prediction mode, the MPM may be adjusted based on a wide-angle substitution intra-prediction mode that corresponds to the wide-angle intra-prediction mode. For example, when a neighboring block is coded using a wide-angle intra-prediction mode, the variable candIntraPredX (X is either A or B) may be adjusted for the wide-angle substitution intra-prediction mode.

[00325] Alternatively, a method of deriving an MPM may be determined according to the shape of the current block. For example, when the current block is a square shape in which the width is equal to the height, candIntraPredX may be set to the wide-angle substitution intraprediction mode. Conversely, when the current block is a non-square shape, candIntraPredX may be set to the wide-angle intraprediction mode.

[00326] Alternatively, the possibility of setting candIntraPredX for the wide-angle intraprediction mode may be determined based on whether or not the wide-angle intraprediction mode of a neighboring block can be applied to the current block. For example, when the current block is a non-square shape of which the width is greater than the height, a wide-angle intraprediction mode of which the index is greater than that of the intraprediction mode of the lower right diagonal direction is set as candIntraPredX as is. However, a wide-angle replacement intraprediction mode that corresponds to this is set as candIntraPredX for a wide-angle intraprediction mode of which the index is less than that of the intraprediction mode of the lower left diagonal direction. On the other hand, when the current block is a non-square shape of which the height is greater than the width, a wide-angle intraprediction mode whose index is smaller than that of the intraprediction mode of the lower left diagonal direction is set as candIntraPredX as is. However, a wide-angle replacement intraprediction mode that corresponds to this is set as candIntraPredX for a wide-angle intraprediction mode whose index is larger than that of the intraprediction mode of the lower right diagonal direction.

[00327] That is, the possibility of deriving the MPM using the wide-angle intra-prediction mode as is, or the possibility of not deriving the MPM using the wide-angle substitution intra-prediction mode may be determined according to whether or not the neighboring block coded in the wide-angle intra-prediction mode has a shape equal to or similar to that of the current block.

[00328] Alternatively, the wide-angle intraprediction mode of the neighboring block may be set to candIntraPredX regardless of the current block shape.

[00329] In short, candIntraPredX can be set to a wide-angle intraprediction mode or a wide-angle replacement intraprediction mode of a neighboring block.

[00330] The MPM may be derived based on candIntraPredA and candIntraPredB. In this case, the MPM may be derived in an intraprediction mode similar to candIntraPredA or candIntraPredB. The intraprediction mode similar to candIntraPredA or candIntraPredB may be derived based on the modulo operation and an offset. At this point, the constant and offset used for the modulo operation may be determined differently according to the current block format.

[00331] Table 6 shows an example of deriving an MPM according to the current block format.[TABLE 6]

[00332] It is assumed that candIntraPredA and candIntraPredB are equal, and candIntraPredA is an angular intraprediction mode. When the current block is a square shape, an intraprediction mode similar to candIntraPredA can be obtained on the basis of a modular operation based on a value obtained by subtracting 1 from the total number of angular intraprediction modes excluding wide-angle intraprediction modes. For example, when the number of angular intraprediction modes other than wide-angle intraprediction modes is 65, the MPM can be derived on the basis of a value derived based on candIntraPredA and a modulo operation of 64. On the other hand, when the current block is a non-square shape, an intraprediction mode similar to candIntraPredA can be obtained on the basis of a modular operation based on a value obtained by subtracting 1 from the total number of angular intraprediction modes including wide-angle intraprediction modes. For example, when the number of wide-angle intraprediction modes is 20, the MPM can be derived on the basis of a value derived based on candIntraPredA and a modulo operation of 84.

[00333] Since the constant used for the modulo operation is set differently according to the current block format, the possibility that the wide-angle intra-prediction mode can be set to an angular intra-prediction mode similar to candIntraPredA can be determined. For example, the wide-angle intra-prediction mode may not be set to an angular intra-prediction mode similar to candIntraPredA in a modulo operation using 64, while the wide-angle intra-prediction mode may be set to an angular intra-prediction mode similar to candIntraPredA in a modulo operation using 84.

[00334] Alternatively, when candIntraPredA and candIntraPredB are equal, the MPM can be derived by considering the current block shape and the possibility that candIntraPredA is a wide-angle intraprediction mode.

[00335] Table 7 shows an example of deriving an MPM according to the current block format.[TABLE 7]

[00336] It is assumed that candIntraPredA and candIntraPredB are equal.

[00337] When the current block is a square shape and candIntraPredA is a wide-angle intraprediction mode, MPMs can be set to standard modes. For example, MPM[0], MPM[1], and MPM[2] can be set to a flat mode, a DC mode, and a vertical intraprediction mode, respectively.

[00338] When the current block is a square shape and candIntraPredA is not a wide-angle intraprediction mode but an angular intraprediction mode, MPMs can be set to candIntraPredA and an angular intraprediction mode similar to it. For example, MPM[0] can be set to candIntraPredA, and MPM[1] and MPM[2] can be set to candIntraPredA and an angular intraprediction mode similar to it.

[00339] When the current block is a non-square shape and candIntraPredA is an angular intraprediction mode, MPMs may be set to candIntraPredA and an angular intraprediction mode similar to it. For example, MPM[0] may be set to candIntraPredA, and MPM[1] and MPM[2] may be set to candIntraPredA and an angular intraprediction mode similar to it.

[00340] The angular intraprediction mode similar to candIntraPredA can be derived using a modulo operation and an offset. At this point, the constant used for the modulo operation can vary depending on the current block shape. Furthermore, the offset used to derive an angular intraprediction mode similar to candIntraPredA can be adjusted differently depending on the current block shape. For example, when the current block is a non-square shape of which the width is greater than the height, an angular intraprediction mode similar to candIntraPredA can be derived using an offset of 2. Conversely, when the current block is a non-square shape of which the height is greater than the width, an angular intraprediction mode similar to candIntraPredA can be derived using offsets of 2 and -8.

[00341] Alternatively, MPMs may be derived by considering whether or not candIntraPredX is a wide-angle intraprediction mode that has a larger or smaller index.

[00342] Table 8 shows an example of deriving an MPM considering the wide-angle intraprediction mode index.[TABLE 8]

[00343] It is assumed that candIntraPredA and candIntraPredB are equal. For ease of explanation, wide-angle intraprediction modes that have a smaller index value than that of the intraprediction mode of the lower left diagonal direction are referred to as lower-direction wide-angle intraprediction modes, and wide-angle intraprediction modes that have a larger index value than that of the intraprediction mode of the lower right diagonal direction are referred to as right-direction wide-angle intraprediction modes.

[00344] When candIntraPredA is a lower direction wide-angle intra-prediction mode, MPMs may be set to candIntraPredA and an angular intra-prediction mode similar thereto. At this point, when candIntraPredA is a lower direction wide-angle intra-prediction mode that has the smallest value, the MPM may be set to a lower direction wide-angle intra-prediction mode that has a predefined index value. Here, the predefined index may be an index that has the largest value among the indices of the lower direction wide-angle intra-prediction modes. For example, when candIntraPredA is -10, MPM[0], MPM[1], and MPM[2] may be set to -10, -1, and -9, respectively.

[00345] When candIntraPredA is a right-hand steering wide-angle intra-prediction mode, MPMs may be set to candIntraPredA and an angular intra-prediction mode similar thereto. At this point, when candIntraPredA is a right-hand steering wide-angle intra-prediction mode that has the largest value, the MPM may be set to a right-hand steering wide-angle intra-prediction mode that has a predefined index value. Here, the predefined index may be an index that has the smallest value among the indices of the right-hand steering wide-angle intra-prediction modes. For example, when candIntraPredA is 77, MPM[0], MPM[1], and MPM[2] may be set to 77, 76, and 67, respectively.

[00346] Alternatively, when an index derived by subtracting or adding 1 from or to the index of candIntraPredA is less than the smallest value or greater than the largest value among the indices of the intra-prediction modes, the MPM may be set to the default mode. Here, the default mode may include at least one of a flat mode, a DC mode, a vertical intra-prediction mode, a horizontal intra-prediction mode, and a diagonal intra-prediction mode.

[00347] Alternatively, when an index derived by subtracting or adding 1 from or to the index of candIntraPredA is less than the smallest value or greater than the largest value among the indices of the intraprediction modes, the MPM may be set to an intraprediction mode opposite to candIntraPredA or an intraprediction mode similar to the intraprediction mode opposite to candIntraPredA.

[00348] Alternatively, MPM candidates may be derived by considering the shape of the current block and the shape of a neighboring block. For example, the method of deriving MPMs when both the current block and the neighboring block are non-square shapes may be different from the method of deriving MPMs when the current block is a square shape and the neighboring block is a non-square shape.

[00349] MPMs in the MPM list may be rearranged (or reordered) considering at least one of the current block size, the current block shape, the neighboring block size, and the neighboring block shape. Here, rearrangement indicates reassignment of the indices assigned to each of the MPMs. For example, a smaller index may be assigned to an MPM equal to the intraprediction mode of a neighboring block that has a size or shape equal to that of the current block.

[00350] MPM[0] and MPM[1] are assumed to be set to left neighbor block intraprediction mode candIntraPredA and upper neighbor block intraprediction mode candIntraPredB, respectively.

[00351] When the current block and the upper neighboring block are non-square shapes of which the width is greater than the height, MPMs may be rearranged so that the intraprediction mode candIntraPredB of the upper neighboring block may have a smaller index. That is, candIntraPredB may be rearranged to MPM[0] and candIntraPredA may be rearranged to MPM[1].

[00352] Alternatively, when the current block and the upper neighboring block are non-square shapes of which the height is greater than the width, MPMs may be rearranged such that the intraprediction mode candIntraPredB of the upper neighboring block has a smaller index. That is, candIntraPredB may be rearranged to MPM[0] and candIntraPredA may be rearranged to MPM[1].

[00353] Alternatively, when the current block and the upper neighboring block are square shapes, MPMs may be rearranged such that the intraprediction mode candIntraPredB of the upper neighboring block has a smaller index. That is, candIntraPredB may be rearranged to MPM[0] and candIntraPredA may be rearranged to MPM[1].

[00354] Instead of rearranging the MPMs, when candIntraPredX is initially assigned to the MPM, at least one of the current block size, the current block format, the neighboring block size, and the neighboring block format may be considered.

[00355] MPMs may be rearranged based on the size or shape of the current block. For example, when the current block is a non-square shape of which the width is greater than the height, the MPMs may be rearranged in descending order. Conversely, when the current block is a non-square shape of which the height is greater than the width, the MPMs may be rearranged in ascending order.

[00356] A derived residual video may be derived by subtracting a prediction video from an original video. At this point, when the residual video is shifted to the frequency domain, subjective video quality of the video is not significantly decreased, although high frequency components among the frequency components are removed. Accordingly, when values of the high frequency components are converted to be smaller or values of the high frequency components are set to 0, there is an effect of increasing compression efficiency without generating significant visual distortion. Reflecting this characteristic, the current block may be transformed to decompose a residual video into two-dimensional frequency components. The transform may be performed using a transform technique such as Discrete Cosine Transform (DST) or Discrete Sine Transform (DST).

[00357] The DCT decomposes (or transforms) a residual video into two-dimensional frequency components using a cosine transform, and the DST decomposes (or transforms) a residual video into two-dimensional frequency components using a sine transform. As a result of the transformation of the residual video, the frequency components can be expressed as a basis video. For example, when the DCT transform is performed on a block of size N x N, N2 basic pattern components can be acquired. The size of each of the basic pattern components included in a block of size N x N can be acquired through the transform. According to a transform technique used for this, the size of the basic pattern component can be referred to as a DCT coefficient or a DST coefficient.

[00358] The DCT transform technique is mainly used to transform a video in which many non-zero low frequency components are distributed. The DST transform technique is mainly used for videos in which many high frequency components are distributed.

[00359] The residual video may be transformed using a transform technique other than DCT or DST.

[00360] Hereinafter in this document, the transform of a residual video into two-dimensional frequency components will be referred to as two-dimensional video transform. Furthermore, the size of the basic pattern components acquired as a result of the transform is referred to as a transform coefficient. For example, the transform coefficient may mean a DCT coefficient or a DST coefficient. When both the first transform and the second transform described below are applied, the transform coefficient may mean the size of a basic pattern component generated as a result of the second transform.

[00361] The transform technique may be determined for each block. The transform technique may be determined based on at least one of the prediction coding mode of the current block, the current block size, and the current block size. For example, when the current block is coded in intra-prediction mode and the current block size is less than N x N, the transform may be performed using the DST transform technique. On the other hand, when the above conditions are not satisfied, the transform may be performed using the DCT transform technique.

[00362] The two-dimensional video transform may not be performed for some blocks of the residual video. Failure to perform the two-dimensional video transform may be referred to as a transform skip. When the transform skip is applied, quantization may be applied to residual coefficients that have not been transformed.

[00363] After the current block is transformed using DCT or DST, the current transformed block may be transformed again. At this point, the DCT or DST based transform may be defined as a first transform, and retransforming a block to which the first transform is applied may be defined as a second transform.

[00364] 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.

[00365] Different transform cores may 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 may be signaled via a bit stream.

[00366] Units for performing the first transform and the second transform may be different. For example, the first transform may be performed on an 8x8 block, and the second transform may be performed on a sub-block of size 4x4 within the transformed 8x8 block. At this point, the transform coefficients of the residual regions that were not performed the second transform may be set to 0.

[00367] Alternatively, the first transform may be performed on a 4 x 4 block, and the second transform may be performed on a region of size 8x8 including the transformed 4 x 4 block.

[00368] Information indicating the possibility that the second transform has been performed may be signaled via a bit stream.

[00369] The decoder may perform an inverse transform of the second transform (a second inverse transform), and may perform an inverse transform of the first transform (a first inverse transform) on a result of the inverse transform. As a result of performing the second inverse transform and the first inverse transform, residual signals for the current block may be acquired.

[00370] Quantization is to reduce the energy of a block, and the quantization process includes a process of dividing a transform coefficient by a specific constant value. The constant value may be derived by a quantization parameter, and the quantization parameter may be set to a value between 1 and 63.

[00371] When the encoder performs transform and quantization, the decoder may acquire a residual block through inverse quantization and inverse transform. The decoder may acquire a reconstructed block for the current block by adding a prediction block and the residual block.

[00372] When a block of the current reconstructed block is acquired, the information loss that occurs in the quantization and encoding process can be reduced by 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 in-loop filter (ALF). Hereinafter in this document, a block reconstructed before the in-loop filter is applied is referred to as a first reconstructed block, and a block reconstructed after the in-loop filter is applied is referred to as a second reconstructed block.

[00373] The second reconstructed block may be acquired by applying at least one of the unlocking filter, the SAO, and the ALF to the first reconstructed block. At this point, the SAO or the ALF may be applied after the unlocking filter is applied.

[00374] The deblocking filter is to mitigate video quality degradation (blocking artifact) at the boundary of a block, which occurs as quantization is performed on individual blocks. In order to apply the deblocking filter, a block resistance (BS) between the first reconstructed block and a neighboring reconstructed block may be determined.

[00375] Figure 30 is a flowchart illustrating a block resistance determination process.

[00376] In the example shown in Figure 30, P denotes a first reconstructed block and Q denotes a neighboring reconstructed block. Here, the neighboring reconstructed block may be a block adjacent to the left side or on the top side of the current block.

[00377] In the example shown in Figure 30, it is shown that the block resistance is determined considering the prediction coding modes of P and Q, the possibility of a transform coefficient other than ero being included, the possibility of interprediction being performed using the same reference figuration, and the possibility of the difference value of motion vectors being greater than or equal to a threshold value.

[00378] Whether or not to apply the deblocking filter may be determined based on the block resistance. For example, when the block resistance is 0, filtering may not be performed.

[00379] SAO is to mitigate a blur phenomenon (blur artifact) that occurs as quantization is performed in the frequency domain. SAO can be performed by adding or subtracting an offset determined by considering the pattern of the first reconstructed video. The method of determining the offset includes an edge offset (EO) or a band offset. EO denotes a method of determining an offset of a current sample according to the pattern of surrounding pixels. BO denotes a method of applying a common offset to a set of pixels that have similar brightness values in a region. Specifically, pixel brightness can be divided into 32 equal sections, and pixels that have similar brightness values can be adjusted as a set. For example, four adjacent bands out of 32 bands can be adjusted as a group, and the same offset value can be applied to the samples belonging to the four bands.

[00380] ALF is a method of generating a second reconstructed video by applying a filter that has a predefined size/shape to the first reconstructed video or a reconstructed video to which a deblocking filter has been applied. Equation 21 shows an example application of ALF.

[00381] Any of the predefined filter candidates may be selected by a representation unit, a coding tree unit, a coding block, a prediction block, or a transform block. Each of the filter candidates may differ in either size or shape.

[00382] Figure 31 is a view showing predefined filter candidates.

[00383] As shown in the example of Figure 31, at least one of 5 x 5, 7 x 7, and 9 x 9 diamond shapes may be selected.

[00384] Only a diamond shape of a size of 5 x 5 can be used for a chroma component.

[00385] For real-time or low-delay encoding of high-resolution videos, such as panoramic videos, 360-degree videos, or 4K/8K UHD (Ultra High Definition) videos, a method of partitioning a picture into a plurality of regions and encoding/decoding the plurality of regions in parallel may be considered. For this purpose, a picture may be partitioned into tiles, i.e., a basic parallel encoding/decoding unit, and the tiles may be processed in parallel.

[00386] Tiles may be constrained to have a rectangular shape. When encoding/decoding a tile, data from other tiles is not used. A context-adaptive binary arithmetic coding (CABAC) context probability table may be initialized by the tile unit and may be configured to not apply a loop filter at tile boundaries.

[00387] Figure 32 is a view showing an example of partitioning a figuration into a plurality of tiles.

[00388] A tile includes at least one coding tree unit, and the boundary of a tile overlaps the boundary of the coding tree unit.

[00389] As shown in the example of Figure 32, a picture may be partitioned into a plurality of tile sets. Information for partitioning a picture into a plurality of tile sets may be signaled via a bit stream.

[00390] Depending on the type of partition of a figuration, tiles may have the same size in all regions, except in the figuration boundaries.

[00391] Alternatively, a figuration may be partitioned so that adjacent tiles in the horizontal direction may have the same height, or the figuration may be partitioned so that adjacent tiles in the vertical direction may have the same width.

[00392] Since a pattern is partitioned using at least one of a vertical line and a horizontal line that intersects the pattern, each of the tiles belongs to a different column and/or row. In the embodiment described below, a column to which a tile belongs is referred to as a tile column, and a row to which a tile belongs is referred to as a tile row.

[00393] Information for determining a partition format of a tiled pattern may be signaled via a bit stream. The information may be encoded and signaled via a set of pattern parameters or a set of sequence parameters. The information is for determining the number of tiles in a pattern, and may include information indicating the number of tile rows and information indicating the number of tile columns. For example, the syntax element num_tile_columns_minus1 indicates a value obtained by subtracting 1 from the number of tile columns, and the syntax element num_tile_rows_minus1 indicates a value obtained by subtracting 1 from the number of tile rows.

[00394] In the example shown in Figure 32, since the number of tile columns is 4 and the number of tile rows is 3, num_tile_columns_minus1 could be 3 and num_tile_rows_minus1 could be 2.

[00395] When the picture is partitioned into a plurality of tiles, information indicating the size of a tile may be signaled via a bit stream. For example, when the picture is partitioned into a plurality of tile columns, information indicating the width of each tile column is signaled via a bit stream, and when the picture is partitioned into a plurality of tile rows, information indicating the height of each tile row is signaled via a bit stream. For example, the syntax element column_width_minus1 indicating the tile column width may be encoded and signaled for each tile column, and the syntax element row_height_minus1 indicating the tile row height may be encoded and signaled for each tile row.

[00396] Column_width_minus1 may indicate a value obtained by subtracting 1 from the width of a tile column, and row_height_minus1 may indicate a value obtained by subtracting 1 from the height of a tile row.

[00397] The encoding of column_width_minus1 may be omitted for the last tile column, and the encoding of row_height_minus1 may be omitted for the last tile row. The width of the last tile column and the height of the last tile row may be derived by considering a figuration size.

[00398] The decoder may determine a tile size based on column_width_minus1 and row_height_minus1.

[00399] Table 9 shows a syntax table for partitioning a figuration into tiles.[TABLE 9]

[00400] With reference to Table 9, the syntax element num_tile_columns_minus1 indicating the number of tile columns and the syntax element num_tile_rows_minus1 indicating the number of tile rows may be flagged.

[00401] Subsequently, the uniform_spacing_flag syntax element indicating whether the figuration is partitioned into equal-sized tiles may be flagged. When uniform_spacing_flag is true, tiles in the remaining area excluding the figuration boundaries may be partitioned into equal-sized tiles.

[00402] When uniform_spacing_flag is false, the column_width_minus1 syntax element indicating the width of each tile column and the row_height_minus1 syntax element indicating the height of each tile row may be flagged.

[00403] The loop_filter_across_tiles_enabled_flag syntax element indicates whether it is allowed to use a loop filter across tile boundaries.

[00404] A tile column that has the smallest width among the tile columns may be referred to as a minimum width tile, and a tile row that has the smallest height among the tile rows may be referred to as a minimum height tile. Information indicating the width of the minimum width tile and information indicating the height of the minimum height tile may be signaled via a bit stream. For example, the min_column_width_minus1 syntax element indicates a value obtained by subtracting 1 from the width of the minimum width tile, and the min_row_height_minus1 syntax element indicates a value obtained by subtracting 1 from the height of the minimum height tile.

[00405] Information indicating a difference value with the minimum tile width may be signaled for each tile column. For example, the diff_column_width syntax element indicates a difference value in width between the current tile column and the minimum tile column. The difference value in width may be expressed as a value of the difference in the number of coding tree unit columns. The decoder may derive the width of the current tile by adding the width of the minimum width tile derived based on min_column_width_minus1 and the difference value in width derived based on diff_column_width.

[00406] Additionally, information indicating a value of the difference with the minimum tile height may be flagged for each tile row. For example, syntax element diff_row_height indicates a value of the difference in height between the current tile row and the minimum tile row. The value of the difference in height may be expressed as a value of the difference in the number of coding tree unit rows. The decoder may derive the height of the current tile by adding the height of the minimum height tile derived based on min_row_height_minus1 and the value of the difference in height derived based on diff_row_height.

[00407] Table 10 shows a syntax table including information about the difference in size.[TABLE 10]

[00408] A figuration may be partitioned such that horizontally adjacent tiles may have different heights, or a figuration may be partitioned such that vertically adjacent tiles may have different widths. The method of partitioning such a figuration may be referred to as a flexible tile partitioning method, and tiles partitioned via the flexible tile partitioning method may be referred to as flexible tiles.

[00409] Figure 33 is a view showing a pattern of partitioning a figuration according to a flexible tiling technique.

[00410] The search order of the tiles generated by partitioning a figuration may follow a predetermined scan order. Furthermore, an index may be assigned to each of the tiles according to a predetermined scan order.

[00411] The tile scanning order may be any one of a raster scan, a diagonal scan, a vertical direction scan, and a horizontal direction scan. Figures 33(a) to 33(d) respectively show examples of assigning an index to each of the tiles according to a raster scan, a diagonal scan, a vertical direction scan, and a horizontal direction scan.

[00412] A next scan order may be determined according to the size or position of the current tile. For example, when the height of the current tile and the height of a tile adjacent to the right side of the current tile are different (e.g., when the height of the right neighboring tile is greater than the height of the current tile), a tile positioned on the leftmost side among the tiles placed in a vertical line equal to that of a tile adjacent to the bottom of the current tile may be determined as a scan target after the current tile.

[00413] The tile scanning order may be determined by the figuration unit or sequence.

[00414] Alternatively, the tile scan order may be determined by considering the size of the first tile in the drawing. For example, when the width of the first tile is greater than the height, the tile scan order may be adjusted for horizontal scanning. When the height of the first tile is greater than the width, the tile scan order may be adjusted for vertical scanning. When the width of the first tile is equal to the height, the tile scan order may be adjusted for raster scanning or diagonal scanning.

[00415] Information indicating the total number of tiles may be signaled via a bit stream. For example, when a flexible tiling technique is applied, the syntax element number_of_tiles_in_picture_minus2 derived by subtracting 2 from the total number of tiles in a picture may be signaled. The decoder may recognize the number of tiles included in the current picture based on number_of_tiles_in_picture_minus2.

[00416] Table 11 shows a syntax table including information about the number of tiles.[TABLE 11]

[00417] In order to reduce the number of bits required to encode the size of a tile, information indicating the size of a sub-tile may be encoded and signaled. The sub-tile is a basic unit that constitutes a tile, and each tile may be configured to include at least one sub-tile. The sub-tile may include one or more coding tree units.

[00418] For example, the syntax element subtile_width_minus1 indicates a value obtained by subtracting 1 from the width of a subtile. The syntax element subtile_height_minus1 indicates a value obtained by subtracting 1 from the height of a subtile.

[00419] Information indicating whether remaining tiles beyond the first tile have the same size as a previous tile may be encoded and flagged. For example, the syntax element use_previous_tile_size_flag indicates whether the size of the current tile is equal to the size of a previous tile. When use_previous_tile_size_flag is true, it indicates that the size of the current tile is equal to the size of a previous tile. When use_previous_tile_size_flag is false, information indicating the size of the current tile may be encoded and flagged. For the first tile, the encoding of use_previous_tile_size_flag may be omitted and a value of the flag may be set to false.

[00420] Information indicating the tile size may include tile_width_minus1[i] syntax element indicating the width of the ith tile and tile_height_minus1[i] syntax element indicating the height of the ith tile.

[00421] Information indicating the tile size may indicate a value of the difference with the size of a sub-tile. Since the size information of a sub-tile is used, the efficiency of encoding/decoding may be improved by reducing the number of bits required to encode the size of each tile. For example, the width of the i-th tile tileWidth may be derived based on Equation 22 shown below, and the height of the i-th tile tileHeight may be derived based on Equation 23 shown below.

[00422] Alternatively, encoding of sub-tile size information may be omitted, and the size of the ith tile may be encoded as tile size information. Sub-tile size information may optionally be encoded. Information indicating whether or not sub-tile size information is encoded may be signaled via a set of video parameters, a set of sequence parameters, or a set of figuration parameters.

[00423] Information related to the tile size described above may be encoded and flagged as indicating the number of coding tree units. For example, column_width_minus1, min_column_width_minus1, subtile_width_minus1, or tile_width_minus1 may indicate the number of coding tree unit columns included in a tile. Additionally, diff_column_width may indicate a value of the difference between the number of coding tree unit columns included in the minimum width tile and the number of coding tree unit columns included in the current tile.

[00424] Additionally, row_height_minus1, min_row_height_minus1, subtile_height_minus1, or tile_height_minus1 may indicate the number of coding tree unit rows included in a tile. Additionally, diff_row_height may indicate a value of the difference between the number of coding tree unit rows included in the minimum height tile and the number of coding tree unit rows included in the current tile.

[00425] The decoder may determine the size of a tile based on the number of coding tree unit columns and/or the number of coding tree unit rows derived based on the syntax elements and the coding tree unit size. For example, the width of the i-th tile may be set to (tile_width_minus1[i] + 1)*(coding tree unit width), and the height of the i-th tile may be set to (tile_height_minus1[i] + 1)*(coding tree unit height).

[00426] In the meantime, information indicating the size of the coding tree unit may be signaled via a set of sequence parameters or a set of figuration parameters.

[00427] In Table 11, it is described that the use_previous_tile_size_flag syntax element is used to indicate whether the size of the current tile is equal to the size of a previous tile. As another example, information indicating whether the width of the current tile is equal to the width of a previous tile or information indicating whether the height of the current tile is equal to the height of a previous tile may be encoded and flagged.

[00428] Table 12 shows a syntax table including information indicating whether the width of the current tile is equal to the width of a previous tile.[TABLE 12]

[00429] The use_previous_tile_width_flag syntax element indicates whether the width of the current tile is equal to the width of a previous tile. When use_previous_tile_width_flag is true, the width of the current tile may be adjusted to be equal to the width of a previous tile. In this case, the encoding of the information indicating the width of the current tile may be omitted, and the width of the current tile may be derived from the width of a previous tile.

[00430] When use_previous_tile_width_flag is false, information indicating the width of the current tile may be flagged. For example, tile_width_minus1[i] may indicate a value obtained by subtracting 1 from the width of the i-th tile.

[00431] The use_previous_tile_width_flag syntax element may be encoded and flagged only when it is determined that the size of the current tile is different from the size of a previous tile (e.g., when the value of use_previous_tile_size_flag is 0).

[00432] Tile_width_minus1[i] may have a value obtained by subtracting 1 from the number of coding tree unit columns included in the i-th tile. The decoder may derive the number of coding tree unit columns belonging to the i-th tile by adding 1 to tile_width_minus1[i], and calculate the tile width by multiplying the derived value by the coding tree unit width.

[00433] Table 13 shows a syntax table that additionally includes information indicating whether the height of the current tile is equal to the height of a previous tile.[TABLE 13]

[00434] The use_previous_tile_height_flag syntax element indicates whether the height of the current tile is equal to the height of a previous tile. When use_previous_tile_height_flag is true, the height of the current tile may be adjusted to be equal to the height of a previous tile. In this case, the encoding of the information indicating the height of the current tile may be omitted, and the height of the current tile may be derived from the height of a previous tile.

[00435] When use_previous_tile_height_flag is false, information indicating the height of the current tile may be flagged. For example, tile_height_minus1[i] may indicate a value obtained by subtracting 1 from the height of the i-th tile.

[00436] The use_previous_tile_height_flag syntax element may be encoded and flagged only when it is determined that the size of the current tile is different from the size of a previous tile (for example, when the value of use_previous_tile_size_flag is 0). Additionally, the use_previous_tile_height_flag syntax element may be flagged only when use_previous_tile_width_flag is false.

[00437] Table 12 shows an example of a use case for use_previous_tile_width_flag and Table 13 shows an example of a use case for both use_previous_tile_width_flag and use_previous_tile_height_flag. Although not shown in the Tables above, the encoding of use_previous_tile_width_flag may be omitted and only use_previous_tile_height_flag may be used.

[00438] Which of use_previous_tile_height_flag and use_previous_tile_size_flag will be used may be determined based on at least one of a tile scan order, the width and height of the first tile, and the width and height of a previous tile. For example, when the tile scan order is vertical direction, use_previous_tile_height_flag may be used, while when the tile scan order is horizontal direction, use_previous_tile_width_flag may be used. Alternatively, when the first tile or a previous tile is a non-square shape of which the width is greater than the height, use_previous_tile_width_flag may be used, while when the first tile or a previous tile is a non-square shape of which the height is greater than the width, use_previous_tile_height_flag may be used.

[00439] When signaling the number of tiles included in a figuration, the encoding of information related to tile size may be omitted for the last tile.

[00440] Table 14 shows an example in which the encoding of tile size information is omitted for the last tile.[TABLE 14]

[00441] When the size of tiles beyond the last tile is specified, the remaining region in the figure can be adjusted as the last tile.

[00442] For each coding tree unit, an identifier may be assigned to identify a tile to which the coding tree unit belongs (hereinafter referred to as tile ID TileID).

[00443] Figure 34 is a view showing an example of assigning a tile ID to each coding tree unit.

[00444] The same tile ID may be assigned to coding tree units that belong to the same tile. Specifically, Nth TileID may be assigned to coding tree units that belong to Tile N.

[00445] Variables x and y indicating the position of a coding tree unit in a drawing may be determined to determine a tile ID assigned to each coding tree unit. Here, x denotes a value obtained by dividing the x-axis coordinate of the (x0, y0) position of the top left sample of the coding tree unit by the width of the coding tree unit, and y denotes a value obtained by dividing the y-axis coordinate of the (x0, y0) position of the top left sample of the coding tree unit by the height of the coding tree unit. Specifically, x and y may be derived by Equations 24 and 25 shown below.

[00446] Assigning a tile ID to each coding tree unit may be accomplished through the process described below.

[00447] i) Initialize tile ID

[00448] The tile ID of each coding tree unit may be initialized to a value obtained by subtracting 1 from the number of tiles in a figuration.[TABLE 15]

[00449] ii) Derive Tile ID[TABLE 16]

[00450] The value of the tile_id variable and the value of the two-dimensional array assignment CTU_tile are derived as follows:

[00451] for (ctu_y = 0; ctu_y < (tile_height_minus1[i] + 1)*(subtile_height_minus1 + 1) && (tile_coordinate_y + ctu_y) < PicHeightInCtbsY; ctu_y++)

[00452] - for (ctu_x = 0; ctu_x < (tile_width_minus1[i] + 1)*(subtile_width_minus1 + 1) && (tile_coordinate_x + ctu_x) < PicWidthInCtbsY; ctu_x++)

[00453] -- TileId[tile_coordinate_x + ctu_x] [tile_coordinate_y + ctu_y] = tile_id

[00454] tile_id++

[00455] In the embodiment described above, it has been described that a flag indicating whether it is permissible to apply a loop filter to tile boundaries is signaled via a set of imaging parameters. However, when it is set to not use a loop filter at all tile boundaries, a problem of decreased subjective image quality and decreased coding efficiency may occur.

[00456] Therefore, information indicating whether or not an in-circuit filter is allowed for each tile can be encoded and flagged.

[00457] Figure 35 is a view showing an example of selectively determining whether or not to apply a circuit filter to each tile.

[00458] As shown in the example in Figure 35, whether or not an in-loop filter (e.g., an unblocking, SAO, and/or ALF filter) is allowed on the horizontal or vertical boundary can be determined for each tile.

[00459] Table 17 shows an example in which information indicating whether or not an in-circuit filter is allowed is encoded for each tile.[TABLE 17]

[00460] In the example in Table 17, the syntax element loop_filter_across_tiles_flag[i] indicates whether a loop filter is allowed to be applied to the i-th tile. When the value of loop_filter_across_tiles_flag[i] is 1, it indicates that a loop filter may be used on the horizontal and vertical boundaries of a tile whose tile ID is i. When the value of loop_filter_across_tiles_flag[i] is 0, it indicates that a loop filter may not be used on the horizontal and vertical boundaries of a tile whose tile ID is i.

[00461] Information indicating whether or not an in-circuit filter is permitted for each of the horizontal and vertical directions may be encoded.

[00462] Table 18 shows an example in which information indicating whether or not an in-circuit filter is allowed is individually coded for the horizontal direction and the vertical direction.[TABLE 18]

[00463] In the example in Table 18, the syntax element loop_filter_hor_across_tiles_flag[i] indicates whether it is allowed to apply a filter in a loop that crosses the ith tile in the horizontal direction. The syntax element loop_filter_ver_across_tiles_flag[i] indicates whether it is allowed to apply a filter in a loop that crosses the ith tile in the vertical direction.

[00464] When the value of loop_filter_hor_across_tiles_flag[i] is 1, this indicates that a loop filter can be used on the horizontal bounding of a tile whose tile ID is i. When the value of loop_filter_hor_across_tiles_flag[i] is 0, this indicates that a loop filter cannot be used on the horizontal bounding of a tile whose tile ID is i.

[00465] When the value of loop_filter_ver_across_tiles_flag[i] is 1, this indicates that a loop filter can be used on the vertical bounding of a tile whose tile ID is i, and when the value of loop_filter_ver_across_tiles_flag[i] is 0, this indicates that a loop filter cannot be used on the vertical bounding of a tile whose tile ID is i.

[00466] Alternatively, information indicating whether an in-loop filter is allowed for a tile group including a plurality of tiles may be encoded and flagged. The possibility of allowing an in-loop filter for a plurality of tiles included in a tile group may be determined by means of the information.

[00467] In order to determine a tile group, at least one of the number of tiles belonging to the tile group, the size of the tile group, and partition information of a picture may be signaled via a bit stream. Alternatively, a region of a predefined size in the encoder and decoder may be set as a tile group.

[00468] Encoding information indicating whether a loop filter is allowed may be omitted, and whether a loop filter is allowed may be determined based on at least one of the number of coding tree units included in a tile, the tile width, and the tile height. For example, when the tile width is less than a reference value, a loop filter for the horizontal direction may be allowed, and when a tile height is less than a reference value, a loop filter for the vertical direction may be allowed.

[00469] When a loop filter is used on a tile boundary, reconstructed out-of-tile data can be generated based on the data included in the tile. At this point, a reconstructed out-of-tile video can be acquired by padding or interpolating the data included in the tile. Subsequently, a loop filter can be applied using the reconstructed out-of-tile data.

[00470] The application of the above described embodiments with focus on a decoding process or an encoding process to an encoding process or a decoding process is included in the scope of the present invention. Changing the described embodiments in a predetermined order into an order different from the described order is also included in the scope of the present invention.

[00471] 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 invention and can 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 embodiments described above can be implemented as a hardware or software device, or a plurality of components can be combined to be implemented as a single hardware or software device. The embodiments described above can be implemented in the form of program commands that can be executed by means of multiple computer components and recorded on a computer-readable recording medium. The computer-readable recording medium can include program commands, data files, data structures, and the like, independently or in combination. Computer-readable recording media include, 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 invention, and vice versa.

[00472] The present invention can be applied to an electronic device that encodes and decodes a video.

Claims (8)

1. A VIDEO DECODING METHOD comprising: generating a list of fusion candidates for a current block; specifying a fusion candidate among a plurality of fusion candidates included in the list of fusion candidates; deriving a first affine source vector (sv0) and a second affine source vector (sv1) of the current block based on a first affine source vector (nv0) and a second affine source vector (nv1) of a fusion candidate; deriving an affine vector for a sub-block in the current block using the first affine source vector (sv0) and the second affine source vector (sv1) of the current block, wherein the sub-block is a region of a size smaller than that of the current block; and perform a motion compensation prediction for the sub-block based on the affine vector, wherein the first affine source vector (nv0) and the second affine source vector (nv1) of the single fusion candidate are derived based on motion information of a neighboring block adjacent to the current block, wherein the neighboring block is included in a coding tree unit other than a coding tree unit of the current block, the first affine source vector (nv0) and the second affine source vector (nv1) of a fusion candidate are derived based on motion vectors of a bottom-left sub-block and a bottom-right sub-block of the neighboring block, the bottom-left sub-block includes a bottom-left affine reference sample control point (xn4, yn4) positioned at a bottom-left corner of the neighboring block, and the bottom-right sub-block joins a bottom-right affine reference sample control point (xn5, yn5) located at a right side of a sample from the bottom right of the bottom right subblock; wherein the first affine seed vector and the second affine seed vector of the single merge candidate are derived from a value obtained by applying a shift operation to a width between the bottom left subblock and the bottom right subblock, wherein the shift operation changes the width by a scale factor. 2. The method of claim 1, wherein the width between the lower left subblock and the lower right subblock is defined as a variable, the variable being a subseed vector width that is defined as a power series of 2. 3. A VIDEO CODING METHOD comprising: generating a list of fusion candidates for a current block; specifying a fusion candidate from among a plurality of fusion candidates included in the list of fusion candidates; deriving a first affine source vector (sv0) and a second affine source vector (sv1) of the current block based on a first affine source vector (nv0) and a second affine source vector (nv1) of a fusion candidate; deriving an affine vector for a sub-block in the current block using the first affine source vector (sv0) and the second affine source vector (sv1) of the current block, wherein the sub-block is a region of a size smaller than that of the current block; and perform a motion compensation prediction for the sub-block based on the affine vector, wherein the first affine source vector (nv0) and the second affine source vector (nv1) of the single fusion candidate are derived based on the motion information of a neighboring block adjacent to the current block, wherein the neighboring block is included in a coding tree unit other than a coding tree unit of the current block, the first affine source vector (nv0) and the second affine source vector (nv1) of a fusion candidate are derived based on motion vectors of a bottom-left sub-block and a bottom-right sub-block of the neighboring block, the bottom-left sub-block includes a bottom-left affine reference sample control point (xn4, yn4) positioned at a bottom-left corner of the neighboring block, and the bottom-right sub-block joins a bottom-right affine reference sample control point (xn5, yn5) located at a right side of a sample from the bottom right of the bottom right subblock; wherein the first affine seed vector and the second affine seed vector of the single merge candidate are derived from a value obtained by applying a shift operation to a width between the bottom left subblock and the bottom right subblock, wherein the shift operation changes the width by a scale factor. 4. The method of claim 3, wherein the width between the lower left sub-block and the lower right sub-block is defined as a variable, the variable being a sub-seed vector width that is defined as a power series of 2. 5. A VIDEO DECODER configured to perform the following operations: generating a list of merge candidates for a current block; specifying a merge candidate from among a plurality of merge candidates included in the list of merge candidates; deriving a first affine source vector (sv0) and a second affine source vector (sv1) of the current block based on a first affine source vector (nv0) and a second affine source vector (nv1) of a merge candidate; deriving an affine vector for a sub-block in the current block using the first affine source vector (sv0) and the second affine source vector (sv1) of the current block, wherein the sub-block is a region of a size smaller than that of the current block; and perform a motion compensation prediction for the sub-block based on the affine vector, wherein the first affine source vector (nv0) and the second affine source vector (nv1) of the single fusion candidate are derived based on the motion information of a neighboring block adjacent to the current block, wherein the neighboring block is included in a coding tree unit other than a coding tree unit of the current block, the first affine source vector (nv0) and the second affine source vector (nv1) of a fusion candidate are derived based on motion vectors of a bottom-left sub-block and a bottom-right sub-block of the neighboring block, the bottom-left sub-block includes a bottom-left affine reference sample control point (xn4, yn4) positioned at a bottom-left corner of the neighboring block, and the bottom-right sub-block joins a bottom-right affine reference sample control point (xn5, yn5) located at a right side of a sample from the bottom right of the bottom right subblock; wherein the first affine seed vector and the second affine seed vector of the single merge candidate are derived from a value obtained by applying a shift operation to a width between the bottom left subblock and the bottom right subblock, wherein the shift operation changes the width by a scale factor. 6. VIDEO DECODER, according to claim 5, characterized in that the width between the lower left sub-block and the lower right sub-block is defined as a variable, the variable is a sub-seed vector width that is defined as a power series of 2. 7. A VIDEO ENCODER configured to perform the following operations: generating a list of fusion candidates for a current block; specifying a fusion candidate from among a plurality of fusion candidates included in the list of fusion candidates; deriving a first affine source vector (sv0) and a second affine source vector (sv1) of the current block based on a first affine source vector (nv0) and a second affine source vector (nv1) of a fusion candidate; deriving an affine vector for a sub-block in the current block using the first affine source vector (sv0) and the second affine source vector (sv1) of the current block, wherein the sub-block is a region of a size smaller than that of the current block; and perform a motion compensation prediction for the sub-block based on the affine vector, wherein the first affine source vector (nv0) and the second affine source vector (nv1) of the single fusion candidate are derived based on the motion information of a neighboring block adjacent to the current block, wherein the neighboring block is included in a coding tree unit other than a coding tree unit of the current block, the first affine source vector (nv0) and the second affine source vector (nv1) of a fusion candidate are derived based on motion vectors of a bottom-left sub-block and a bottom-right sub-block of the neighboring block, the bottom-left sub-block includes a bottom-left affine reference sample control point (xn4, yn4) positioned at a bottom-left corner of the neighboring block, and the bottom-right sub-block joins a bottom-right affine reference sample control point (xn5, yn5) located at a right side of a sample from the bottom right of the bottom right subblock; wherein the first affine seed vector and the second affine seed vector of the single merge candidate are derived from a value obtained by applying a shift operation to a width between the bottom left subblock and the bottom right subblock, wherein the shift operation changes the width by a scale factor. 8. The video encoder of claim 7, wherein the width between the lower left subblock and the lower right subblock is defined as a variable, the variable being a subseed vector width that is defined as a power series of 2.