RU2800133C2 - Method and device for coding/decoding image signals - Google Patents

Abstract

FIELD: video encoding.

SUBSTANCE: line of reference readings of the current block is defined. It is determined whether there is a candidate internal prediction mode that is the same as the internal prediction mode of the current block. Internal prediction is performed on the current block based on the reference sample line and the internal prediction mode. At least one of the candidate internal prediction modes is obtained by adding or subtracting an offset to the maximum value from the top neighbouring block internal prediction mode of the current block and the left neighbouring internal prediction mode of the current block. The transformation type in the horizontal direction of the sub-block is determined based on the width of the sub-block, and the transformation type in the vertical direction of the sub-block is determined based on the height of the sub-block.

EFFECT: increased efficiency of video coding.

8 cl, 30 dwg, 11 tbl

Description

BACKGROUND OF THE INVENTION

The field of technology to which the invention belongs

[01] The present invention relates to a method and apparatus for encoding and decoding a video signal.

Prior Art

[02] As display panels get bigger, more and more higher quality video services are needed. The biggest problem of high-definition video services is a significant increase in data volume, and to solve this problem, research is being actively conducted to improve the degree of video compression. As an illustrative example, the Motion Picture Experts Group (MPEG) and the Video Coding Experts Group (VCEG) within the Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T) formed the Joint Video Coding Team (JCT-VC) in 2009. JCT-VC proposed High Efficiency Video Coding (HEVC), which is a video compression standard that has a compression efficiency about twice that of H.264/AVC, and it was approved as a standard on January 25, 2013. With the rapid development of high-definition video services, the efficiency of HEVC is gradually discovering its limitations.

SUMMARY OF THE INVENTION

[03] An object of the present invention is to provide a method for obtaining a candidate intra prediction mode based on the intra prediction mode of an adjacent block adjacent to the current block when encoding/decoding a video signal, and an apparatus for performing the method.

[04] Yet another object of the present invention is to provide a method for partitioning an encoding block or a transformation block into a plurality of subblocks and performing intra prediction on each of the subblocks when encoding/decoding a video signal, and an apparatus for performing the method.

[05] Yet another object of the present invention is to provide a method for splitting an encoding block or a transformation block into a plurality of subblocks and performing transformation on only some of the subblocks when encoding/decoding a video signal, and a device for performing the method.

[06] The technical problems to be solved 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.

[07] The method for decoding/encoding a video signal according to the present invention includes the following steps: determining a reference sample line of the current block; determining whether there is a candidate intra prediction mode that is the same as the intra prediction mode of the current block; obtaining an intra prediction mode of the current block based on the determination; and performing intra prediction on the current block based on the reference sample line and the intra prediction mode. In this case, at least one of the candidate intra prediction modes can be obtained by adding or subtracting an offset to the maximum value from the top neighbor block intra prediction mode of the current block and the left neighbor intra prediction mode of the current block.

[08] In the video decoding/coding method according to the present invention, at least one of the candidate intra prediction modes can be obtained by adding 2 to or subtracting from the maximum value when the difference between the intra prediction mode of the upper neighbor block and the intra prediction mode of the left neighbor block is 64.

[09] In the video decoding/coding method according to the present invention, the number of candidate intra prediction modes may vary according to the reference sample line index.

[10] The video decoding/coding method according to the present invention may further include the step of determining whether the current block should be divided into a plurality of subblocks, and when the current block is divided into a plurality of subblocks, the plurality of subblocks may share one intra prediction mode.

[11] In the video decoding/coding method according to the present invention, the inverse transform may be skipped for some of the plurality of sub-blocks.

[12] In the video decoding/coding method according to the present invention, a transformation type in the horizontal direction of a subblock may be determined based on the width of the subblock, and a transformation type in the vertical direction of the subblock may be determined based on the height of the subblock.

[13] In the video decoding/coding method according to the present invention, a transformation type in the horizontal direction and a transformation type in the vertical direction of a sub-block may be determined based on the shape of the sub-block.

[14] The features summarized above in relation to the present invention are merely illustrative aspects of the detailed description of the present invention, which will be described below, and do not limit the scope of the present invention.

[15] According to the present invention, the performance of intra prediction can be improved by obtaining a candidate intra prediction mode similar to the intra prediction mode of an adjacent block adjacent to the current block.

[16] According to the present invention, the performance of intra prediction can be improved by dividing a coding block or a transform block into a plurality of sub-blocks and performing intra prediction on each of the sub-blocks.

[17] According to the present invention, encoding and decoding efficiency can be improved by dividing an encoding block or a transformation block into a plurality of subblocks and performing transformation on only some of the subblocks.

[18] 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 GRAPHICS

[19] FIG. 1 is a block diagram showing a video encoder according to one embodiment of the present invention.

[20] FIG. 2 is a block diagram showing a video decoder according to one embodiment of the present invention.

[21] FIG. 3 is a view showing a base element of a code tree according to one embodiment of the present invention.

[22] Fig. 4 is a view showing various types of partitioning of a coding block.

[23] Fig. 5 is a view showing a partitioning scheme of a code tree element.

[24] FIG. 6 is a flowchart showing a prediction method performed between images according to one embodiment of the present invention.

[25] FIG. 7 is a view showing a matching block.

[26] FIG. 8 is a flowchart showing an intra prediction method according to one embodiment of the present invention.

[27] Fig. 9 is a view showing reference samples included in each reference sample line.

[28] Fig. 10 is a view showing intra prediction modes.

[29] Figures 11 and 12 are views showing an example of a one-dimensional array placing reference samples in a line.

[30] FIG. 13 is a view showing an example of angles formed between angle information-based intra prediction modes and a straight line parallel to the x-axis.

[31] Fig. 14 is a view showing an embodiment of obtaining prediction samples when the current block is non-square.

[32] Fig. 15 is a view showing wide-angle intra prediction modes.

[33] Fig. 16 is a view showing an example of splitting in the vertical direction and splitting in the horizontal direction.

[34] FIG. 17 is a view showing an example of determining a split type of a coding block.

[35] FIG. 18 is a view showing an example of determining a splitting type of a coding block.

[36] FIG. 19 is a view showing an example in which a split type of a coding block is determined based on the intra prediction mode of the coding block.

[37] FIG. 20 is a view for describing a coding block split scheme.

[38] FIG. 21 is a view showing an example in which the predictive coding mode is set differently for each sub-block.

[39] FIG. 22 is a view showing an embodiment of applying PDPC.

[40] FIGS. 23 and 24 are views showing a sub-block on which the second transformation will be performed.

[41] FIG. 25 is a view for describing examples of determining the conversion type of the current block.

[42] FIG. 26 is a view showing an example of determining a sub-block conversion type.

[43] Fig. 27 is a view for describing an example in which the subblock residual coefficients are set to 0.

[44] FIG. 28 is a view showing an example in which the position of a sub-block on which transformation and/or quantization has been performed is indicated based on information transmitted by the bitstream.

[45] FIG. 29 is a flowchart showing a block quality determination process.

[46] FIG. 30 is a view showing predefined candidate filters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[47] Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[48] Video encoding and decoding is performed by the block element. For example, an encoding/decoding process such as transformation, quantization, prediction, loop filtering, reconstruction, and the like may be performed on an encoding block, a transformation block, or a prediction block.

[49] Hereinafter, the block to be encoded/decoded will be referred to as the "current block". For example, the current block may represent an encoding block, a transformation block, or a prediction block according to the current stage of the encoding/decoding process.

[50] In addition, it should be understood that the term "element" used in the present description denotes a basic element for performing a particular encoding/decoding process, and the term "block" denotes an array of samples of a predetermined size. Unless otherwise noted, "block" and "element" may be used with the same meaning. For example, in the embodiment described below, it should be understood that a coding block and a coding unit have the same meaning.

[51] FIG. 1 is a block diagram showing a video encoder according to one embodiment of the present invention.

[52] As shown in FIG. 1, the video encoding apparatus 100 may comprise an image splitting part 110, prediction parts 120 and 125, a transform part 130, a quantization part 135, a permutation part 160, an entropy coding part 165, an inverse quantization part 140, an inverse transform part 145, a filtering part 150, and a storage device 15 5.

[53] Each of the components shown in FIG. 1 is shown independently to represent the characteristic functions that distinguish them from each other in the video encoding device, but this does not mean that each component is formed by a configuration element of a separate hardware or one software. That is, each component is listed as a component for convenience of explanation, and at least two of the components may be combined to form a single component, or one component may be broken into multiple components to perform a function. Embodiments with integration and embodiments with separation of components are also included in the scope of the present invention, if they do not go beyond the essence of the present invention.

[54] In addition, some of the components are not essential components that perform the main functions in the present invention, but may be optional components only to improve efficiency. The present invention can be implemented by including only the components necessary to realize the essence of the present invention, excluding components used to improve efficiency, and a structure containing only the necessary components, excluding optional components used to improve efficiency, is also included in the scope of the present invention.

[55] The image splitting part 110 may split the input image into at least one processing element. In this case, the processing element may be a prediction element (PU), a transform element (TU), or a coding element (CU). The image splitting part 110 may partition an image into a plurality of coding elements, prediction elements, and transform elements, and encode the image by selecting a plurality of coding element, prediction element, and transform element based on a predetermined criterion (e.g., a cost function).

[56] For example, one image may be split into multiple coding units. A recursive tree structure, such as a quaternary tree structure, may be used to partition the coding elements in an image. A video or coding unit split into different coding units using the largest coding unit as the root can be split to have the same number of child nodes as the split coding units. An encoding element that no longer splits according to a predetermined constraint becomes a leaf node. That is, if it is assumed that only square splitting is possible for one coding unit, one coding unit can be split into no more than four different coding units.

[57] Further, in an embodiment of the present invention, an encoding element can be used in the value of an element that performs encoding, or in the meaning of an element that performs decoding.

[58] A prediction element may be an element that is partitioned into at least one square, rectangle, or the like of the same size within one coding element, or it can be any prediction element of prediction elements partitioned within one coding element that is partitioned such that it has a shape and/or size that is different from those of another prediction element.

[59] If a coding unit is not the smallest coding unit, when a prediction unit that performs intra prediction based on the coding unit is generated, intra prediction can be performed without splitting an image into a plurality of N×N prediction units.

[60] The prediction portions 120 and 125 may comprise an inter-picture prediction portion 120 that performs inter-picture prediction and an intra prediction portion 125 that performs intra prediction. It can be determined whether to use inter-picture prediction or perform intra prediction on a prediction element and determine specific information (eg, intra prediction mode, motion vector, reference picture, or the like) according to each prediction method. In this case, the processing element for performing prediction may be different from the processing element for determining the prediction method and specifically the content. For example, a prediction method and a prediction mode may be defined in the prediction element, and prediction may be performed in the transform element. The residual coefficient (residual block) between the generated prediction block and the original block may be input to the transform portion 130. In addition, prediction mode information, motion vector information, and the like used for prediction may be encoded by the entropy encoding portion 165 together with the residual coefficient and transmitted to the decoder. When a particular coding mode is used, the original block may be encoded as is and transmitted to the decoder without generating a prediction block by prediction portions 120 and 125.

[61] The inter-picture prediction portion 120 may predict a prediction element based on information about at least one image from images before or after the current image, and in some cases, it may predict the prediction element based on information about a partial area that has been encoded in the current image. The inter-picture prediction portion 120 may include a reference picture interpolation portion, a motion prediction portion, and a motion compensation portion.

[62] The reference picture interpolation portion may receive reference picture information from the storage device 155 and generate pixel information for an integer number of pixels or less from the reference picture. In the case of a luminance pixel, an 8-tap interpolation filter based on a DCT with a variable filter coefficient may be used to generate pixel information of an integer number of pixels or less by an element consisting of 1/4 pixels. In the case of a color difference signal, a 4-tap interpolation filter based on a DCT with a variable filter coefficient may be used to generate pixel information of an integer number of pixels or less by an element consisting of 1/8 pixels.

[63] The motion prediction part may perform motion prediction based on the reference image interpolated by the reference image interpolation part. Various methods such as full search block matching algorithm (FBMA), three-step search (TSS), new three-step search (NTS) algorithm, and the like can be used as a motion vector calculation method. The motion vector may have a 1/2 or 1/4 pixel motion vector value based on the interpolated pixels. The motion prediction part can predict the current prediction item by changing the motion prediction method. Various methods such as a skip method, a merge method, an advanced motion vector prediction (AMVP) method, an intra-block copy method, and the like, can be used as a motion prediction method.

[64] Part 125 for intra prediction may generate a prediction element based on information about reference pixels located in the vicinity of the current block, which is information about a pixel in the current image. When a block in the vicinity of the current prediction element is a block on which inter-picture prediction has been performed, and thus the reference pixel is a pixel on which inter-picture prediction has been performed, the reference pixel included in the block on which inter-picture prediction has been performed may be used instead of the reference pixel information of a nearby block on which intra prediction has been performed. That is, when the reference pixel is unavailable, at least one reference pixel of the available reference pixels may be used in place of the unavailable reference pixel information.

[65] In intra prediction, the prediction mode may include a prediction mode based on angle information that uses reference pixel information according to the prediction direction, and a prediction mode not based on angle information that does not use direction information when performing prediction. The mode for predicting luminance information may be different from the mode for predicting color difference information, and intra prediction mode information used for predicting luminance information or predicted luminance signal information may be used for predicting color difference information.

[66] If the prediction element size is the same as the transform element size when intra prediction is performed, intra prediction can be performed on the prediction element based on a pixel on the left side, a pixel on the upper left side, and a pixel above the prediction element. However, if the size of the prediction element is different from the size of the transform element when intra prediction is performed, intra prediction can be performed using the reference pixel based on the transform element. In addition, intra prediction using N×N partitioning can only be used for the smallest bin.

[67] By means of the intra prediction method, it is possible to generate a prediction block after applying an adaptive intra-smoothing (AIS) filter to a reference pixel according to the prediction mode. The type of AIS filter applied to the reference pixel may vary. To perform the intra prediction method, the intra prediction mode of the current prediction element may be predicted from the intra prediction mode of the prediction element existing in the vicinity of the current prediction element. When the prediction regime of the current prediction element is predicted using the information about the regime predicted from the neighboring element of prediction, if the internal prediction modes of the current prediction element are the same as the element of prediction nearby, then the information indicating that the prediction of the current prediction element of the close -ups can be transmitted using information about the preliminary certain flavor Ge, and if the predictions of the current element of prediction and the element of prediction nearby differ from each other, information about the prediction of the current block can be encoded by performing entropy coding.

[68] In addition, a residual block may be generated containing a prediction element that performed prediction based on the prediction element generated by the prediction portions 120 and 125 and the residual coefficient information, which is the difference value of the prediction element from the original block. The generated residual block may be input to part 130 for transformation.

[69] The transform part 130 may transform the residual block containing the original block and information about the residual coefficient of the prediction element generated by the prediction parts 120 and 125 with a transform method such as discrete cosine transform (DCT), discrete sine transform (DST), or KLT. The use of DCT, DST, or KLT to transform the residual block may be determined based on information about the intra prediction mode of the prediction element used to generate the residual block.

[70] The quantization part 135 may quantize the values converted into the frequency domain by the transform part 130. The quantization factors may vary depending on the block or importance of the video. The value calculated by the quantization part 135 may be provided to the inverse quantization part 140 and the permutation part 160.

[71] The permutation part 160 may perform permutation of coefficient values for the quantized residual coefficients.

[72] The permutation part 160 may change the coefficients of a two-dimensional block shape to a one-dimensional vector shape by a coefficient scanning method. For example, the permutation part 160 may scan from the DC coefficients to the high frequency region coefficients using a zigzag scanning method and change the coefficients into a one-dimensional vector form. According to the transform element size and the intra prediction mode, instead of zigzag scanning, vertical scanning of the 2D block shape coefficients in the column direction and horizontal scanning of the 2D block shape coefficients in the row direction can be used. That is, according to the transform element size and the intra prediction mode, the scanning method to be used can be determined from zigzag scanning, scanning in the vertical direction, and scanning in the horizontal direction.

[73] The entropy encoding part 165 may perform entropy encoding based on the values calculated by the permutation part 160. Various coding methods can be used for entropy coding, such as exponential Golomb coding, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and the like.

[74] The entropy encoding part 165 can encode various information such as residual coefficient information and coding element block type information, prediction mode information, split element information, prediction element information and transmission element information, motion vector information, reference frame information, block interpolation information, and filtering information which is input from the permutation part 160 and the prediction parts 120 and 125.

[75] The entropy encoding part 165 may perform entropy encoding of the coefficient value of the coding element inputted from the permutation part 160.

[76] The inverse quantization part 140 and the inverse transform part 145 perform inverse quantization of the values quantized by the quantization part 135 and inverse transformation of 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 element predicted by the motion estimation part, the motion compensation part, and the intra prediction part included in the prediction parts 120 and 125 to generate a reconstructed block.

[77] The filtering portion 150 may comprise at least one of a deblocking filter, an element for offset compensation, and an adaptive loop filter (ALF).

[78] A deblock filter can remove block distortion generated at a boundary between blocks in a reconstructed image. The determination of whether to perform deblocking, whether to apply a deblocking filter to the current block, may be based on the pixels contained in multiple columns or rows contained in the block. A strong filter or a weak filter can be applied according to the required degree of filtering to remove blockiness when applying a deblocking filter to a block. In addition, when vertical direction filtering and horizontal direction filtering are performed by applying the deblocking filter, vertical direction filtering and horizontal direction filtering can be performed in parallel.

[79] The offset correction element may correct the offset of the original video by the pixel element for the video that has been deblocked. To perform the offset correction for a specific image, a method of dividing the pixels included in the video into a certain number of areas, determining an area to perform the offset, and applying the offset to the area, or a method of applying the offset taking into account the edge information of each pixel, can be used.

[80] Adaptive loop filtering (ALF) may be performed based on a value obtained by comparing the reconstructed and filtered video with the original video. After dividing the pixels included in the video into predefined groups, one filter can be defined to be applied to the corresponding group, and filtering can be performed differently for each group. The luminance signal, which is information related to whether or not to apply ALF, may be transmitted for each coding unit (CU), and the shape and filter factor of the ALF to be applied may vary depending on each block. Also, the ALF filter of the same type (fixed type) can be applied regardless of the characteristic of the applied block.

[81] The memory 155 may store the reconstructed block or image computed by the filtering portion 150, and the reconstructed and stored block or image may be provided in the prediction portions 120 and 125 when performing inter-picture prediction.

[82] FIG. 2 is a block diagram showing a video decoder according to one embodiment of the present invention.

[83] As shown in FIG. 2, video decoder 200 may include an entropy decoding part 210, a permutation part 215, an inverse quantization part 220, an inverse transform part 225, prediction parts 230 and 235, a filtering part 240, and a memory 245.

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

[85] The entropy decoding part 210 may perform entropy decoding according to a procedure opposite to that of performing entropy encoding in the entropy decoding part of the video encoder. For example, various methods may be applied corresponding to the method performed by the video encoder, such as exponential Golomb coding, context adaptive variable length coding (CAVLC), and context adaptive binary arithmetic coding (CABAC).

[86] The entropy decoding part 210 may decode information related to intra prediction and prediction performed between pictures performed by the encoder.

[87] The permutation part 215 may perform permutation on the bitstream subjected to entropy decoding by the entropy decoding part 210 based on the permutation method performed by the encoder. Coefficients expressed in one-dimensional vector form can be retrieved and rearranged as coefficients in two-dimensional block form. The permutation part 215 may receive information related to the coefficient scan performed by the encoding part, and perform reconstruction by the inverse scanning method based on the scan order performed by the corresponding encoding part.

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

[89] The inverse transformation part 225 may perform inverse transformation, i. e. reverse DCT, reverse DST, or reverse KLT, to convert i.e. DCT, DST or KLT performed by the transformation part with respect to the quantization result performed by the video encoder. The inverse transformation may be performed based on the transmission element determined by the video encoder. The video decoder inverse transformation part 225 may selectively perform a transformation method (eg, DCT, DST, KLT) according to a plurality of pieces of information such as a prediction method, a current block size, a prediction direction, and the like.

[90] The prediction parts 230 and 235 can generate a prediction block based on information related to generating a prediction block provided by the entropy decoder 210 and information about a previously decoded block or picture provided by the memory 245.

[91] As described above, if the prediction element size and the transform element size are the same when intra prediction is performed in the same manner as the operation in the video encoder, intra prediction is performed on the prediction element based on the pixel on the left side, the pixel on the upper left side, and the pixel above the prediction element. However, if the prediction element size and the transform element size are different from each other when intra prediction is performed, intra prediction can be performed using a reference pixel based on the transform element. In addition, intra prediction using N×N partitioning can only be used for the smallest bin.

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

[93] To perform inter-picture prediction, it can be determined based on the coding unit whether the motion prediction method of the prediction unit included in the corresponding coding unit is a skip mode, a merge mode, a motion vector prediction mode (AMVP mode), or an intra-block copy mode.

[94] The intra prediction part 235 may generate a prediction block based on pixel information in the current image. When the prediction element is a prediction element that has performed intra prediction, intra prediction may be performed based on information about the intra prediction mode of the prediction element provided by the video encoder. The intra prediction portion 235 may comprise an adaptive intra-smoothing (AIS) filter, a reference pixel interpolation portion, and a DC filter. The AIS filter is a part that performs filtering on the reference pixel of the current block, and can determine whether or not to apply the filter according to the prediction mode of the current prediction element, and apply the filter. The AIS filtering can be performed on the reference pixel of the current block by using the prediction mode and the prediction element AIS filter information 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.

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

[96] The restored block or image may be provided to part 240 for filtering. The filtering portion 240 may include a deblocking filter, an element for offset correction, and an ALF.

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

[98] The offset correction element 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.

[99] ALF may be applied to a coding element based on information about whether or not to apply ALF and information about ALF coefficients provided by the encoder. ALF information may be provided for inclusion in a set of specific parameters.

[100] The storage device 245 may store the reconstructed image or block and use it as a reference image or reference block, and may provide the reconstructed image to an output element.

[101]

[102] FIG. 3 is a view showing a base element of a code tree according to one embodiment of the present invention.

[103] A maximum size coding block may be defined as a code tree block. The image is split into multiple code tree elements (CTUs). A code tree element is a coding element having a maximum size, and may be referred to as a large coding unit (LCU). 3 shows an example in which an image is split into a plurality of code tree elements.

[104] The size of the element of the code tree can be determined at the image level or the sequence level. For this, information indicating the size of the element of the code tree may be transmitted by a set of picture parameters or a set of sequence parameters.

[105] For example, the size of the code tree element for the entire image in the sequence may be set to 128×128. Alternatively, at the image level, any size between 128x128 and 256x256 can be defined as the size of a code tree element. For example, the code tree element size may be set to 128×128 in the first picture, and the code tree element size may be set to 256×256 in the second picture.

[106] Encoding blocks may be generated by splitting an element of a code tree. The encoding block specifies the base element to perform encoding/decoding. For example, prediction or transformation may be performed for each coding block, or a predictive coding mode may be determined for each coding block. Here, the predictive coding mode indicates a prediction image generation method. For example, the predictive coding mode may include intra-picture prediction (intra prediction), inter-picture prediction (inter-picture prediction), current picture referencing (CPR), or intra-block copying (IBC), or combined prediction. For a coding block, a prediction block may be generated by using at least one predictive coding mode of intra prediction, inter-picture prediction, current picture anchoring, and combined prediction.

[107] Information indicating the predictive coding mode of the current block may be transmitted via a bitstream. For example, the information may be a 1-bit flag indicating whether the predictive coding mode is an intra mode or an inter-picture mode. Only when the prediction coding mode of the current block is determined to be an inter-picture mode, current picture anchoring or combined prediction can be used.

[108] Linking to the current picture is for setting the current picture as a reference picture and obtaining a prediction block of the current block from an area that has already been coded/decoded in the current picture. In this case, the current image means the image containing the current block. Information indicating whether the current picture anchor is applied to the current block may be transmitted via a bitstream. 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 defined as anchoring to the current picture, and when the flag is false, the prediction mode of the current block may be defined as inter-picture prediction.

[109] Alternatively, the predictive coding mode of the current block may be determined based on the reference picture index. For example, when the reference picture index indicates the current picture, the predictive coding mode of the current block may be defined as anchoring to the current picture. When the reference picture index indicates a picture different from the current picture, the prediction coding mode of the current block may be defined as a prediction performed between pictures. That is, linking to the current image is a prediction method using information about an area in which encoding/decoding has been performed in the current image, and prediction performed between images is a prediction method using information about another image in which encoding/decoding has been performed.

[110] Combined prediction represents a coding mode in which two or more of intra prediction, inter-picture prediction, and the current reference picture are combined. For example, when applying combined prediction, a first prediction block may be generated based on one of intra prediction, inter-picture prediction, and current picture anchoring, and a second prediction block may be generated based on the other of them. When the first prediction block and the second prediction block are generated, the final prediction block may be generated by an averaging operation or a weighted summation operation of the first prediction block and the second prediction block. Information indicating whether or not combined prediction is applied may be transmitted via a bitstream. The information may be a 1-bit flag.

[111] FIG. 4 is a view showing various types of partitioning of a coding block.

[112] A coding block may be partitioned into a plurality of coding blocks based on a quaternary tree partition, a binary tree partition, or a ternary tree partition. The split coding block may be split again into a plurality of coding units based on a quaternary tree split, a binary tree split, or a ternary tree split.

[113] Quaternary tree splitting refers to a splitting method that splits the current block into four blocks. As a result of splitting based on a quaternary tree, the current block can be split into four square-shaped partitions (see "SPLIT_QT" in FIG. 4(a)).

[114] Binary tree splitting refers to a splitting method that splits the current block into two blocks. Splitting the current block into two blocks along the vertical direction (i.e. using a vertical line crossing the current block) may be referred to as binary tree splitting in the vertical direction, and splitting the current block into two blocks along the horizontal direction (i.e. using a horizontal line crossing the current block) may be referred to as binary tree splitting in the horizontal direction. As a result of splitting based on a binary tree, the current block can be split into two non-square sections. "SPLIT_BT_VER" in Fig. 4(b) represents the split result based on the binary tree in the vertical direction, and "SPLIT_BT_HOR" in Fig. 4(c) represents the result of the split based on the binary tree in the horizontal direction.

[115] Ternary tree splitting refers to a splitting method that splits the current block into three blocks. Splitting the current box into three boxes along the vertical direction (i.e. using two vertical lines crossing the current box) may be referred to as ternary tree splitting in the vertical direction, and splitting the current box into three boxes along the horizontal direction (i.e. using two horizontal lines crossing the current box) may be referred to as ternary tree splitting in the horizontal direction. As a result of splitting based on a ternary tree, the current block can be split into three non-square sections. In this case, the width/height of the section located in the center of the current block can be twice the width/height of other sections. "SPLIT_TT_VER" in Fig. 4(d) represents a ternary tree split result in the vertical direction, and "SPLIT_TT_HOR" in Fig. 4(e) represents a ternary tree split result in the horizontal direction.

[116] The number of splits of the element of the code tree can be defined as the split depth. The maximum splitting depth of a code tree element can be defined at the sequence level or the image level. Accordingly, the maximum splitting depth of a code tree element may differ for each sequence or image.

[117] Alternatively, the maximum splitting depth for each splitting method can be determined separately. For example, the maximum split depth allowed for a quad tree split may be different from the maximum split depth allowed for a binary tree split and/or a ternary tree split.

[118] The encoder may transmit information indicative of at least one of the split type and split depth of the current block via the bitstream. The decoder may determine the split type and split depth of the code tree element based on the information parsed from the bitstream.

[119] FIG. 5 is a view showing a partitioning scheme of a code tree element.

[120] Partitioning a coding block using a partitioning technique such as quaternary tree partitioning, binary tree partitioning, and/or ternary tree partitioning may be referred to as multi-tree partitioning.

[121] Encoding blocks generated by applying partitioning based on multiple trees to a coding block may be referred to as lower coding blocks. When the split depth of a coding block is k, the split depth of lower coding blocks is set to k+1.

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

[123] A split type of a current coding block may be determined based on at least one of a split type of an upper coding block and a split type of an adjacent coding block. In this case, an adjacent coding block is a coding block adjacent to the current coding block, and may include at least one of the top neighboring block and the left neighboring block of the current coding block, and the neighboring block adjacent to the upper left corner. Here, the split type may include at least one of whether a quaternary tree split was applied, whether a binary tree based split was applied, a binary tree split direction, a ternary tree split, and a ternary tree split direction.

[124] To determine the splitting type of a coding block, information indicating whether a coding block can be split can be transmitted via a bitstream. The information is a 1-bit flag "split_cu_flag", and when the flag is true, it indicates that the coding block has been split using a quad tree splitting method.

[125] When the split_cu_flag is true, information indicating whether the coding block is split based on a quaternary tree may be transmitted via a bitstream. The information is a 1-bit flag in the form of split_qt_flag, and when the flag is true, the coding block may be split into four blocks.

[126] For example, in the example shown in FIG. 5, when a coding tree element is split based on a quaternary tree, four coding blocks having a split depth of 1 are generated. In addition, it is shown that splitting based on a quaternary tree is applied again to the first and fourth coding units of the four coding blocks generated as a result of splitting based on a quaternary tree. As a result, four coding blocks having a split depth of 2 can be generated.

[127] In addition, coding blocks having a split depth of 3 can be generated by re-applying a quaternary tree split to a coding block having a split depth of 2.

[128] When quaternary tree splitting is not applied to a coding block, whether binary tree splitting or ternary tree splitting is performed on the coding block can be determined based on at least one of the coding block size, whether the coding block is located on an image boundary, the maximum splitting depth, and the neighboring block splitting type. When it is determined that binary tree splitting or ternary tree splitting is to be performed on a coding block, information indicating the splitting direction may be transmitted via a bitstream. The information may be a 1-bit flag in the form mtt_split_cu_vertical_flag. Based on the flag, it can be determined whether the splitting direction is the vertical direction or the horizontal direction. Additionally, information indicating whether binary tree splitting or ternary tree splitting has been applied to a coding block may be transmitted via a bitstream. The information may be a 1-bit flag in the form mtt_split_cu_binary_flag. Based on the flag, it can be determined whether binary tree splitting or ternary tree splitting is applied to the coding block.

[129] For example, in the example shown in FIG. 5, vertical direction binary tree splitting is applied to a coding block having a split depth of 1, vertical direction ternary tree splitting is applied to the left coding block of the coding blocks generated by the splitting, and vertical direction binary tree splitting is applied to the right coding block.

[130]

[131] Inter-picture prediction is a predictive coding mode that predicts the current block by using information about the previous picture. For example, a block at the same position as the current block in the previous picture (hereinafter referred to as the matching block) may be set as the current block prediction block. Hereinafter, a prediction block generated based on a block at the same position as the current block will be referred to as a matching prediction block.

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

[133] A residual block may be generated by subtracting a prediction block from the current block. In this case, when there is motion of an object, the energy of the residual block can be reduced by using a motion prediction block instead of a co-located prediction block, and thus the compression efficiency of the residual block can be improved.

[134] As described above, generating a prediction block by using motion information may be referred to as motion-compensated prediction. In most inter-picture predictions, a prediction block may be generated based on motion-compensated prediction.

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

[136] Figure 6 is a flowchart depicting a prediction method performed between pictures, according to one embodiment of the present invention.

[137] As shown in FIG. 6, the inter-picture prediction method includes the steps of determining (S601) an inter-picture prediction mode of the current block, obtaining (S602) motion information of the current block according to the determined inter-picture prediction mode, and performing (S603) motion compensation prediction for the current block based on the acquired motion information.

[138] Here, the inter-picture prediction mode represents various methods for determining motion information of the current block, and may include an inter-picture prediction mode that uses translational motion information and an inter-picture prediction mode that uses affine motion information. For example, an inter-picture prediction mode that uses translational motion information may include a fusion mode and a motion vector prediction mode, and an inter-picture prediction mode that uses 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 parsed from the bitstream according to the inter-picture prediction mode.

[139] For example, the motion information of the current block may be obtained based on the motion information of a spatially adjacent block included in the image that is the same as the current block, or a matching block included in the image that is different from the current block. A spatially adjacent block includes at least one of a neighboring block adjacent to the top side of the current block, a neighboring block adjacent to the left side, a neighboring block adjacent to the upper left corner, a neighboring block adjacent to the upper right corner, and a neighboring block adjacent to the lower left corner. The merged block can have the same position and size as the current block in the merged image. For example, Fig. 7 is a view showing a matching block. The matching image may be indicated by index information indicating any one of the reference images.

[140] Any of the plurality of candidate motion vector precision values may be determined as the motion vector precision value of the current block. For example, a candidate motion vector accuracy value may include at least one of one eighth of a pixel, a quarter of a pixel, a half of a pixel, an integer pixel, 2 integer pixels, and 4 integer pixels. The number or type of candidate motion vector accuracy values may be determined by a sequence element, slice, or block. For example, information for determining the number or type of candidate motion vector accuracy values may be transmitted via a bitstream. Alternatively, the number or type of candidate motion vector accuracy values may be determined based on whether an inter-picture prediction mode or an affine motion model is used. Information for indicating any of a plurality of candidate motion vector accuracy values may be transmitted via a bitstream.

[141] Intra prediction is for predicting the current block using recovered samples that have been coded/decoded in the vicinity of the current block. In this case, the samples recovered before the application of the filter in the loop can be used for intra-prediction of the current block.

[142] The intra prediction method includes matrix-based intra prediction and general intra prediction considering directionality with respect to neighboring recovered samples. Information indicating the intra prediction method of the current block may be transmitted via a bitstream. The information may be a 1-bit flag. Alternatively, the intra prediction method of the current block may be determined based on at least one of the position of the current block, the size of the current block, the shape of the current block, and the intra prediction method of the neighboring block. For example, when the current block is on an image boundary, it may be determined that there is no need to apply matrix-based intra prediction to the current block.

[143] Matrix-based intra prediction is a method for deriving a prediction block of a current block by an encoder and a decoder based on a matrix product between a previously stored matrix and reconstructed samples in the vicinity of the current block. Information for specifying any of a plurality of previously stored matrices may be transmitted via a bit stream. The decoder may determine a matrix for intra prediction of the current block based on the information and the size of the current block.

[144] General intra prediction is a method for obtaining a prediction block for the current block based on an intra prediction mode not based on angle information or an intra prediction mode based on angle information. Next, the process of performing intra prediction based on the total intra prediction will be described in more detail with reference to the drawings.

[145] FIG. 8 is a flowchart showing an intra prediction method according to one embodiment of the present invention.

[146] A reference sample line of the current block can be determined (S801). Reference line means a set of reference points included in the k-th line from the top and/or left side of the current block. Reference samples may be derived from reconstructed samples that have been coded/decoded in the vicinity of the current block.

[147] Index information for identifying a reference sample line of a current block from a plurality of reference sample lines may be transmitted via a bitstream. For example, information about indexes intra_luma_ref_idx to indicate the reference sample line of the current block may be transmitted via a bitstream. The index information may be conveyed by the coding block element.

[148] The plurality of reference sample lines may comprise at least one of a first line, a second line, a third line, and a fourth line from above and/or to the left of the current block. A reference line consisting of a row adjacent to the top side of the current block and a column adjacent to the left side of the current block of the plurality of reference lines is referred to as an adjacent reference line, and other reference lines may be referred to as non-adjacent reference lines.

[149] Fig. 9 is a view showing reference samples.

[150] Figure 9 shows one adjacent reference line consisting of rows and columns adjacent to the current block and three non-adjacent reference lines consisting of rows and columns not adjacent to the current block.

[151] Only some of the plurality of reference sample lines may be selected as the reference sample line of the current block. For example, the rest of the reference lines except for the second non-adjacent reference line of the reference lines shown in FIG. 9 can be set as candidate reference lines. Table 1 shows the indexes respectively assigned to candidate reference sample lines.

[152] Table 1

[153] More candidate reference sample lines or fewer candidate reference sample lines than the number of candidate reference sample lines described above may be set. In addition, the number or positions of non-adjacent reference sample lines set as candidate reference sample lines are not limited to the example described above. For example, the first non-adjacent reference line and the third non-adjacent reference line may be set as candidate reference lines, or the second non-adjacent reference line and the third non-adjacent reference line may be set as candidate reference lines. Alternatively, all of the first non-adjacent reference sample line, the second non-adjacent reference sample line, and the third non-adjacent reference sample line may be set as candidate reference sample lines.

[154] The number or types of candidate reference sample lines may be determined based on at least one of the current block size, the shape of the current block, the position of the current block, whether the current block is subblocked, and the intra prediction mode of the current block.

[155] The reference sample line of the current block may be determined based on at least one of the position of the current block, the size of the current block, the shape of the current block, and the neighboring block predictive coding mode. For example, when the current block is in contact with the border of an image, tile, slice, or code tree element, an adjacent reference sample line may be defined as the reference sample line of the current block.

[156] Alternatively, when the current block has a non-square shape, an adjacent reference sample line may be defined as the reference sample line of the current block. Alternatively, when the width-to-height ratio of the current block is greater than the threshold value or less than the threshold value, the adjacent reference sample line may be determined as the reference sample line of the current block.

[157] The reference sample line may include top reference samples located above the current block and left reference samples located to the left of the current block. The top reference points and the left reference points can be obtained from the reconstructed samples in the vicinity of the current block. The recovered samples may be in the state prior to applying the filter to the loop.

[158] The number of reference samples included in the reference sample line may be determined based on the distance between the reference sample lines. For example, the number of reference samples included in the reference line having distance i from the current block may be greater than the number of reference samples included in the reference line having distance i-1 from the current block. Accordingly, the number of reference samples included in a non-adjacent reference sample line may be greater than the number of reference samples included in an adjacent reference sample line.

[159] The difference between the number of reference samples included in a non-adjacent reference sample line having a distance i from the current block and the number of reference samples included in the adjacent reference sample line can be defined as a reference sample number offset. In this case, the difference in the number of top reference samples located above the current block may be defined as offsetX[i], and the difference in the number of left reference samples located to the left of the current block can be defined as offsetY[i]. offsetX and offsetY may be determined based on the distance between the current block and a non-adjacent reference sample line. For example, offsetX and offsetY can be set to an integer multiple of i. For example, offsetX[i] and offset[i] may be 2i.

[160] Alternatively, the offset of the number of reference samples may be determined based on the ratio of the width and height of the current block. Equation 1 shows an example of calculating the ratio of the width and height of the current box.

[161] [Equation 1]

[162] It is also possible to calculate the ratio of the width and height of the current box in a manner other than that expressed in Equation 1.

[163] The values of offsetX and offsetY may be determined based on the ratio of the width and height of the current block. For example, when the value of whRatio is greater than 1, the value of offsetX may be set to be greater than the value of offsetY. For example, the offsetX value may be set to 1, and the offsetY value may be set to 0. On the other hand, when the whRatio value is less than 1, the offsetY value may be set to be greater than the offsetX value. For example, the offsetX value may be set to 0 and the offsetY value may be set to 1.

[164] With the exception of the upper left reference sample having the same x-axis and y-axis coordinates, a non-adjacent reference sample line having a distance i from the current block may consist of up to (refW+offsetX[i]) upper reference samples and up to (refH+offsetY[i]) left reference samples. In this case, refW and refH denote the length of the adjacent reference sample line and can be set as shown in Equations 2 and 3, respectively.

[165] [Equation 2]

[166] [Equation 3]

[167] In Equations 2 and 3, nTbW indicates the width of the coding block or transform block on which intra prediction is performed, and nTbH indicates the height of the coding block or transform block on which intra prediction is performed.

[168] As a result, a reference sample line that is at a distance i from the current block may consist of up to (refW+refH+offsetX[i]+offsetY[i]+1) reference samples.

[169] According to the intra prediction mode of the current block, a prediction sample can be obtained by using at least one of the reference samples belonging to the reference sample line.

[170] Next, the intra prediction mode of the current block can be determined (S802). As for the intra prediction mode of the current block, at least one of the intra prediction mode not based on angle information and the intra prediction mode based on angle information can be defined as the intra prediction mode of the current block. The non-angle information intra prediction mode includes planar mode and DC mode, and the angle information based intra prediction mode includes 33 or 65 modes between diagonal down and left and diagonal up and right.

[171] Fig. 10 is a view showing intra prediction modes.

[172] FIG. 10(a) shows 35 intra prediction modes, and FIG. 10(b) shows 67 intra prediction modes.

[173] More or fewer intra prediction modes may be defined than shown in FIG.

[174] The most probable mode (MPM) may be set based on the intra prediction mode of an adjacent block adjacent to the current block. In this case, the adjacent block may include a left adjacent block adjacent to the left side of the current block and a top adjacent block adjacent to the top side of the current block. When the coordinates of the top left reference of the current block are (0, 0), the left adjacent block may contain the reference at position (-1, 0), (-1, H-1) or (-1, (H-1)/2). In this case, H is the height of the current block. The top adjacent block may contain a count at position (0, -1), (W-1, -1) or ((W-1)/2, -1). In this case, W is the width of the current block.

[175] When a neighboring block is encoded with normal intra prediction, the MPM may be obtained based on the intra block mode of the neighboring block. Specifically, the left neighbor intra prediction mode may be set as the variable candIntraPredModeA, and the intra prediction mode of the upper neighbor block may be set as the variable candIntraPredModeB.

[176] In this case, when a neighboring block is unavailable (for example, when a neighboring block has not yet been coded/decoded or when the position of a neighboring block is outside a picture boundary), when a neighboring block is encoded with matrix-based intra prediction, when a neighboring block is encoded with inter-picture prediction, or when a neighboring block is included in a code tree element other than the current block, the variable candIntraPredModeX (in this case, X is A or B) obtained based on the intra prediction neighbor mode block, can be set as the default mode. Here, the default mode may comprise at least one of planar mode, DC mode, vertical direction mode, and horizontal direction mode.

[177] Alternatively, when a neighboring block is encoded with matrix-based intra prediction, the intra prediction mode corresponding to an index value for indicating any of the matrices may be set to candIntraPredModeX. To this end, a lookup table showing the relationship between index values for indicating matrix and intra prediction modes may be previously stored in the encoder and decoder.

[178] The MPMs can be obtained based on the candIntraPredModeA variable and the candIntraPredModeB variable. For example, candIntraPredModeA and candIntraPredModeB may be set to MPM, or an intra prediction mode like greater or lesser value of candIntraPredModeA or candIntraPredModeB may be set to MPM. Here, an intra prediction mode like candIntraPredModeX (X is A or B) may be an intra prediction mode whose index difference value with candIntraPredModeX is ±1 or ±2.

[179] The number of MPMs included in the MPM list may be preset in the encoder and decoder. The number of MPMs included in the MPM list may be set in 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 transmitted via a bitstream. Alternatively, the number of MPMs may be determined based on at least one of the adjacent block predictive coding mode and the size, shape, and reference sample line index of the current block. For example, when an adjacent reference line is defined as the current block reference line, N MPMs can be used, while when a non-adjacent reference sample line is defined as the current block reference line, M MPMs can be used. M is a natural number less than N, and for example, N may be 6, and M may be 5, 4, or 3. Accordingly, when the reference sample line index of the current block is 0 and the MPM flag is true, any of the 6 candidate intra prediction modes can be determined as the intra prediction mode of the current block, while when the reference sample line index of the current block is greater than 0 and the MPM flag is true, any of the 5 candidate intra prediction modes may be defined as the intra prediction mode of the current block.

[180] Alternatively, a fixed number (eg, 6 or 5) of MPM candidates may be used regardless of the reference sample line index of the current block.

[181] In the embodiments described below, the number of MPMs is assumed to be 6, and the 6 MPMs are called MPM[0], MPM[1], MPM[2], MPM[3], MPM[4], and MPM[5]. An embodiment in which the number of MPMs is less than 6 can be realized by using only some of the 6 MPMs described in the embodiments described below. Alternatively, an embodiment in which the number of MPMs is greater than 6 may be implemented to include the 6 MPMs described in the embodiments described below.

[182] The initial MPM values may be set to an intra prediction mode not based on angle information or an intra prediction mode based on angle information other than candIntraPredModeA and candIntraPredModeA. Here, the angle information-based intra prediction mode, which can be set to MPM, may include at least one of the vertical intra prediction mode, the horizontal intra prediction mode, the down and left diagonal intra prediction mode, the up and left diagonal intra prediction mode, and the up and right diagonal intra prediction mode. For example, initial MPM values can be set as follows.

[183] MPM[0]=candIntraPredModeA

[184] MPM[1]=(candIntraPredModeA=INTRA_PLANAR) ? INTRA_DC: INTRA_PLANAR

[185] MPM[2]=INTRA_ANGULAR50

[186] MPM[3]=INTRA_ANGULAR18

[187] MPM[4]=INTRA_ANGULAR2

[188] MPM[5]=INTRA_ANGULAR34

[189] In the example above, ((A) ? B: C) represents a function that returns the value B when the condition expanded in A is true, and returns the value C when the condition expanded in A is false.

[190] When candIntraPredModeA and candIntraPredModeB are the same, and candIntraPredModeA is an intra prediction mode based on angle information, MPM[0] may be set to candIntraPredModeA, and MPM may be set to intra prediction modes like candIntraPredModeA. An intra prediction mode like candIntraPredModeA may be an intra prediction mode whose index difference value with candIntraPredModeA is ±1 or ±2. The modulo (%) operation and offset can be used to obtain an intra prediction mode like candIntraPredModeA. Further, the MPM may be set to at least one of an intra prediction mode not based on angle information and an intra prediction mode whose angle difference from candIntraPredModeA is a predetermined value. Here, the intra prediction mode whose angle difference from candIntraPredModeA is a predetermined value may be an intra prediction mode perpendicular to candIntraPredModeA or an intra prediction mode in a direction opposite to that of candIntraPredModeA. For example, MPM can be obtained as follows.

[191] MPM[0]=candIntraPredModeA

[192] MPM[1]=INTRA_PLANAR

[193] MPM[2]=INTRA_DC

[194] MPM[3]=2+((candIntraPredModeA+62) % 65)

[195] MPM[4]=2+((candIntraPredModeA - 1) % 65)

[196] MPM[5]=2+((candIntraPredModeA+94) % 65)

[197] MPM[3] matches (candIntraPredModeA-1) and MPM[4] matches (candIntraPredModeA+1). MPM[5] indicates the intra prediction mode perpendicular to candIntraPredModeA.

[198] When candIntraPredModeA and candIntraPredModeB differ from each other, candIntraPredModeA and candIntraPredModeB can be set to MPM[0] and MPM[1], respectively. Alternatively, candIntraPredA is compared to candIntraPredModeB and the maximum value may be set to MPM[0] and the minimum value may be set to MPM[1]. Conversely, you can also set the minimum value as MPM[0] and the maximum value as MPM[1].

[199] In this case, when both candIntraPredModeA and candIntraPredModeB are angle information based intra prediction modes, the angle information not based intra prediction mode can be set to MPM. For example, planar mode and DC mode can be set to MPM[2] and MPM[3] respectively.

[200] Additionally, an intra prediction mode like any of candIntraPredModeA and candIntraPredModeB having a larger or smaller value can be set to MPM. An intra prediction mode like candIntraPredModeX can be obtained by adding an offset to or subtracting from candIntraPredModeX. In this case, the maximum offset value may be determined based on the difference between the maximum value and the minimum value of candIntraPredModeA and candIntraPredModeB. For example, the offset can be a natural number such as 1 or 2.

[201] For example, when the difference value obtained by subtracting MIN(candIntraPredModeA, candIntraPredModeB) from MAX(candIntraPredModeA, candIntraPredModeB) is not 64 or 1, MPM[4] and MPM[5] can be obtained as follows.

[202] MPM[4]=2+((MAX(MPM[0], MPM[1])+62) % 65

[203] MPM[5]=2+((MAX(MPM[0], MPM[1]) - 1) % 65

[204] In this case, the MAX(A, B) function is a function that returns the larger value from A and B, and the MIN(A, B) function is a function that returns the smaller value from A and B. MPM[4] corresponds to (MAX(MPM[0], MPM[1]) - 1), and MPM[5] corresponds to (MAX(MPM[0], MPM[1])+1). On the other hand, when the difference value obtained by subtracting MIN (candIntraPredModeA, candIntraPredModeB) from MAX (candIntraPredModeA, candIntraPredModeB) is 64 or 1, MPM[4] and MPM[5] can be obtained as follows.

[205] MPM[4]=2+(MAX(MPM[0], MPM[1])+61) % 65

[206] MPM[5]=2+MAX(MPM[0], MPM[1]) % 65

[207] MPM[4] corresponds to (MAX(MPM[0], MPM[1]) - 2), and MPM[5] corresponds to (MAX(MPM[0], MPM[1])+2).

[208] When one of candIntraPredModeA and candIntraPredModeB is an intra prediction mode based on angle information, while the other is an intra prediction mode not based on angle information, at least one of the intra prediction mode not based on angle information that is not equal to MIN(candIntraPredModeA, candIntraPredModeB), an intra prediction mode based on angle information, which is like It is MAX(candIntraPredModeA, candIntraPredModeB), and the intra prediction mode whose angle difference from MAX(candIntraPredModeA, candIntraPredModeB) is a preset value can be set as MPM. For example, MPM[2]-MPM[5] can be obtained as follows.

[209] MPM[2]=! MIN(MPM[0], MPM[1])

[210] MPM[3]=2+((MAX(MPM[0], MPM[1])+62) % 65

[211] MPM[4]=2+((MAX(MPM[0], MPM[1]) - 1) % 65

[212] MPM[5]=2+((MAX(MPM[0], MPM[1])+94) % 65

[213] MPM[2] indicates an intra prediction mode not based on angle information, which is not the same as MPM[0] or MPM[1]. For example, when MIN(MPM[0], MPM[1]) is the DC mode, MPM[2] is set to the planar mode, and when MIN(MPM[0], MPM[1]) is the planar mode, MPM[2] is set to the DC mode. MPM[3] corresponds to ((MAX(MPM[0], MPM[1]) - 1), and MPM[4] corresponds to ((MAX(MPM[0], MPM[1])+1). MPM[5] indicates an intra prediction mode perpendicular to (MAX(MPM[0], MPM[1]). Unlike the examples listed above, an MPM obtained by adding 2 to or subtracting from MAX(MPM[0], MPM[1]) can be added to the list M P.M.

[214] When either of candIntraPredA and candIntraPredB is an intra mode not based on angle information and the other is an intra prediction mode based on angle information, i. e. either of candIntraPredA and PredIntraPredB is less than 2 and the other is equal to or greater than 2, the maximum value of candIntraPredA and candIntraPredB can be set to MPM. In addition, an intra prediction mode like the maximum value or an intra prediction mode perpendicular to the maximum value may be set to MPM. For example, MPM[0]-MPM[5] can be obtained as follows.

[215] MPM[0]=MAX(candIntraPredA, candIntraPredB)

[216] MPM[1]=INTRA_PLANAR

[217] MPM[2]=INTRA_DC

[218] MPM[3]=2+((MAX(candIntraPredA, candIntraPredB)+62) % 65

[219] MPM[4]=2+((MAX(candIntraPredA, candIntraPredB]) - 1) % 65

[220] MPM[5]=2+((MAX(candIntraPredA, candIntraPredB)+94) % 65

[221] MPM[3] matches (MAX(candIntraPredA, candIntraPredB) - 1) and MPM[4] matches (MAX(candIntraPredA, candIntraPredB)+1). MPM[5] specifies the intra prediction mode perpendicular to MAX(candIntraPredA, candIntraPredB). Unlike the examples listed above, an MPM obtained by adding or subtracting 2 to MAX(candIntraPredA, candIntraPredB) can be added to the MPM list.

[222] The MPMs may be obtained given the reference sample line index of the current block. In particular, when a non-adjacent reference sample line is determined to be the reference sample line of the current block, a prediction mode not based on angle information such as planar mode or DC mode may not be set to MPM. For example, the initial MPM values may be set as follows according to whether an adjacent reference sample line is determined to be the reference sample line of the current block.

[223] MPM[0]=(IntraLumaRefLineIdx=0) ? candIntraPredModeA: INTRA_ANGULAR2

[224] MPM[1]=(IntraLumaRefLineIdx=0) ? (candIntraPredModeA:=INTRA_PLANAR ? INTRA_DC: INTRA_PLANAR): INTRA_ANGULAR18

[225] MPM[2]=INTRA_ANGULAR50

[226] MPM[3]=(IntraLumaRefLineIdx=0) ? INTRA_ANGULAR18: INTRA_ANGULAR34

[227] MPM[4]=(IntraLumaRefLineIdx=0) ? INTRA_ANGULAR2: INTRA_ANGULAR66

[228] MPM[5]=(IntraLumaRefLineIdx=0) ? INTRA_ANGULAR34: INTRA_ANGULAR42

[229] When the reference sample line of the current block is a non-adjacent reference sample line, and both candIntraPredModeA and candIntraPredModeB are angle information-based intra prediction modes, the MPM can be obtained as follows.

[230] MPM[0]=candIntraPredModeA

[231] MPM[1]=candIntraPredModeB

[232] MPM[2]=INTRA_ANGULAR2

[233] MPM[3]=INTRA_ANGULAR18

[234] MPM[4]=INTRA_ANGULAR50

[235] MPM[5]=INTRA_ANGULAR34

[236] When the reference sample line of the current block is a non-contiguous reference sample line, and either of candIntraPredModeA and candIntraPredModeB is an intra prediction mode not based on angle information, and the other is an intra prediction mode based on angle information, MPMs can be obtained as follows.

[237] MPM[0]=MAX(candIntraPredModeA, candIntraPredModeB)

[238] MPM[1]=INTRA_ANGULAR2

[239] MPM[2]=INTRA_ANGULAR18

[240] MPM[3]=INTRA_ANGULAR50

[241] MPM[4]=INTRA_ANGULAR34

[242] MPM[5]=INTRA_ANGULAR66

[243] An MPM list containing a plurality of MPMs is generated, and information indicating whether an MPM that is the same as the intra prediction mode of the current block is included in the MPM list can be transmitted via a bitstream. The information is a 1-bit flag and may be referred to as the MPM flag. When the MPM flag indicates that an MPM that is the same as that of the current block is included in the MPM list, index information indicating one of the MPMs may be transmitted via a bitstream. For example, index information mpm_idx indicating any one of a plurality of MPMs may be transmitted via a bitstream. The MPM indicated by the index information may be set as the intra prediction mode of the current block. When the MPM flag indicates that an MPM that is the same as that of the current block is not included in the MPM list, residual mode information indicating any of the non-MPM residual intra prediction modes may be transmitted via a bitstream. The residual mode information indicates an index value corresponding to the intra prediction mode of the current block when the indices are reassigned to the residual intra prediction modes except for MPM. The decoder may arrange the MPM in ascending order and determine the intra prediction mode of the current block by comparing the residual mode information with the MPM. For example, when the residual mode information is less than or equal to MPM, the intra prediction mode of the current block can be obtained by adding 1 to the residual mode information.

[244] When the intra prediction mode of the current block is obtained, the comparison between some of the MPMs and the residual mode information may be skipped. For example, the MPM of the angle information-free intra prediction mode of the MPM may be excluded from comparison purposes. When the intra prediction modes not based on the angle information are set to MPM, it is obvious that the residual mode information indicates the intra prediction mode based on the angle information, and thus the intra prediction mode of the current block can be obtained by comparison between the residual MPMs except for the intra prediction modes not based on the angle information and the residual mode information. Instead of excluding intra prediction modes not based on angle information from comparison purposes, the number of intra prediction modes not based on angle information is added to the residual mode information, and then the resulting comparison value can be compared with the residual MPMs.

[245] Instead of setting the default mode as MPM, information indicating whether the intra prediction mode of the current block is the default mode may be transmitted via a bitstream. The information is a 1-bit flag, and the flag may be referred to as the default mode flag. The default mode flag can only be transmitted when the MPM flag indicates that an MPM that is the same as the current block is included in the MPM list. As described above, the default mode may comprise at least one of planar mode, DC mode, vertical direction mode, and horizontal direction mode. For example, when the planar mode is set as the default mode, the default mode flag may indicate whether the intra prediction mode of the current block is the planar mode. When the default mode flag indicates that the intra prediction mode of the current block is not the default mode, one of the MPMs indicated by the index information may be set as the intra prediction mode of the current block.

[246] When using the default mode flag, it can be set to not set the intra prediction mode, which is the same as the default mode as MPM. For example, when the default mode flag indicates whether the intra prediction mode of the current block is the planar mode, the MPM corresponding to the planar mode of the 6 MPMs described above is replaced by another mode, or the intra prediction mode of the current block can be obtained by using 5 MPMs except for the MPM corresponding to the planar mode.

[247] When a plurality of intra prediction modes are set as default modes, index information indicating any of the default modes can be passed on. The intra prediction mode of the current block may be set as the default mode indicated by the index information.

[248] When the reference sample line index of the current block is not equal to 0, it may be set not to use the default mode. For example, it may be set not to use an intra prediction mode not based on angle information such as DC mode or planar mode when a non-adjacent reference sample line is determined to be the reference sample line of the current block. Accordingly, when the reference sample line index is not 0, the default mode flag is not transmitted, and the value of the default mode flag can be set to the same as a preset value (ie, false).

[249] When the intra prediction mode of the current block is determined, prediction samples can be obtained for the current block based on the determined intra prediction mode (S803).

[250] When the DC mode is selected, prediction samples are generated for the current block based on the average value of the reference samples. In particular, the values of all samples in the prediction block may be generated based on the average value of the reference samples. The average value can be obtained using at least one of the top reference samples located on top of the current block and the left reference samples located on the left of the current block.

[251] Depending on the shape of the current block, the number or range of reference samples used to obtain the average may vary. For example, when the current block is a non-square block whose width is greater than its height, the average value may be calculated using only the top reference samples. On the other hand, when the current block is a non-square block whose width is smaller than the height, the average value can be calculated using only the left reference samples. That is, when the width and height of the current block are different, the average can be calculated using only the reference samples adjacent to the one that is larger. Alternatively, based on the ratio of the width and height of the current block, it can be determined whether the average value should be calculated using only the top reference samples, or whether the average value should be calculated using only the left reference samples.

[252] When the planar mode is selected, the prediction sample can be obtained using the prediction sample in the horizontal direction and the prediction sample in the vertical direction. In this case, the horizontal direction prediction sample is obtained based on the left reference sample and the right reference sample located on the same horizontal line as the prediction sample, and the vertical direction prediction sample is obtained based on the upper reference sample and the lower reference sample located on the same vertical line as the prediction sample. In this case, the right reference may be generated by copying the reference adjacent to the upper right corner of the current block, and the lower reference may be generated by copying the reference adjacent to the lower left corner of the current block. The horizontal direction prediction sample may be obtained based on the weighted sum operation of the left reference sample and the right reference sample, and the vertical direction prediction sample may be obtained based on the weighted sum operation of the upper reference sample and the lower reference sample. In this case, the weighting value assigned to each reference sample can be determined according to the position of the prediction sample. The prediction sample may be obtained based on an averaging operation or a weighted summing operation of the horizontal direction prediction sample and the vertical direction prediction sample. When the weighted sum operation is performed, the weighting values applied to the prediction sample in the horizontal direction and the prediction sample in the vertical direction may be determined based on the position of the prediction sample.

[253] When a prediction mode based on angle information is selected, a parameter indicating a prediction direction (or a prediction angle) of the selected prediction mode based on angle information can be determined. Table 2 shows the intraPredAng parameter of the intra direction of each intra prediction mode.

[254] [Table 2]

[255] When 35 intra prediction modes are defined, Table 2 shows the intra direction parameter of each intra prediction mode having any index from 2 to 34. When more than 33 intra prediction modes based on angle information are defined, Table 2 is further divided to set the intra direction parameter of each intra prediction mode based on angle information.

[256] After placing the top reference samples and left reference samples of the current block in a line, a prediction sample can be obtained based on the value of the inner direction parameter. In this case, when the value of the inside direction parameter is a negative value, the left reference samples and the upper reference samples may be aligned.

[257] Figures 11 and 12 are views showing an example of a one-dimensional array placing reference samples in a line.

[258] FIG. 11 is a view showing an example of a one-dimensional array in the vertical direction arranging reference samples in the vertical direction, and FIG. 12 is a view showing an example of a 1-dimensional array in the horizontal direction arranging reference samples in the horizontal direction. The embodiments shown in FIGS. 11 and 12 will be described with the assumption that 35 intra prediction modes are defined.

[259] When the intra prediction mode index is any of 11-18, a one-dimensional array in the horizontal direction in which the top reference samples are rotated counterclockwise can be applied, and when the intra prediction mode index is any of 19-25, a one-dimensional array in the vertical direction can be applied in which the left reference samples are rotated clockwise. When arranging the reference readings in a line, the angle of the intra prediction mode can be taken into account.

[260] The reference sample determination parameter may be determined based on the internal direction parameter. The reference value determination parameter may comprise a reference value index for specifying the reference value and a weighting value parameter for determining a weighting value applied to the reference value.

[261] The index iIdx of the reference sample and the parameter ifact of the weighting value can be obtained using Equations 4 and 5 shown below, respectively.

[262] [Equation 4]

[263] [Equation 5]

[264] In Equations 4 and 5, Pang denotes the internal direction parameter. The reference sample indicated by index iIdx of the reference sample corresponds to an integer pixel.

[265] At least one or more reference samples may be specified to obtain a prediction sample. In particular, the position of the reference sample used to obtain the prediction sample may be indicated in view of the slope of the prediction mode. For example, the reference sample used to obtain the prediction sample may be indicated using the index iIdx of the reference sample.

[266] In this case, when the slope of the intra prediction mode is not expressed by one reference sample, the prediction sample can be generated by interpolating a plurality of reference samples. For example, when the slope of the intra prediction mode is a value between the slope between the prediction sample and the first reference sample and the slope between the prediction sample and the second reference sample, the prediction sample can be obtained by interpolating the first reference sample and the second reference sample. That is, when the corner line passing at the intra prediction angle does not pass through the reference sample located in the whole pixel, the prediction sample can be obtained by interpolating the reference samples adjacent to the left and right or upper or lower side of the position where the corner line passes through.

[267] Equation 6 shows an example of obtaining a prediction sample based on reference samples.

[268] [Equation 6]

[269] In Equation 6, P denotes a prediction sample, and Ref_1D denotes any one of the one-dimensionally placed reference samples. In this case, the position of the reference sample can be determined by the position (x, y) of the prediction sample and the index iIdx of the reference sample.

[270] When the slope of the intra prediction mode can be expressed as one reference sample, the weighting value parameter ifact is set to 0. Accordingly, Equation 6 can be simplified as shown in Equation 7.

[271] [Equation 7]

[272] Intra prediction for the current block may be performed based on a plurality of intra prediction modes. For example, the intra prediction mode may be obtained for each prediction sample, and the prediction sample may be obtained based on the intra prediction mode assigned to each prediction sample.

[273] Alternatively, an intra prediction mode may be obtained for each section, and intra prediction for each section may be performed based on the intra prediction mode assigned to each section. In this case, the patch may comprise at least one sample. At least one of the size and shape of the patch 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 chunk size and shape may be predetermined at the encoder and decoder to be independent of the size or shape of the current block.

[274] Alternatively, intra prediction may be performed based on each of the plurality of intra predictions, and the final prediction sample may be obtained based on an averaging operation or a weighted summation operation of the plurality of prediction samples obtained by the plurality of intra predictions. For example, the first prediction sample may be obtained by performing intra prediction based on the first intra prediction mode, and the second prediction sample may be obtained by performing intra prediction based on the second intra prediction mode. Thereafter, the final prediction sample may be obtained based on an averaging operation or a weighted summation operation of the first prediction sample and the second prediction sample. In this case, the weighting value assigned to each of the first prediction sample and the second prediction sample can be determined considering at least one of whether the first intra prediction mode is a non-angle information based prediction mode/angle information based prediction mode, whether the second intra prediction mode is a non-angle information based prediction mode/angle information based prediction mode, and a neighboring block intra prediction mode.

[275] The plurality of intra prediction modes may be a combination of an intra prediction mode not based on angle information and a prediction mode based on angle information, a combination of prediction modes based on angle information, or a combination of prediction modes not based on angle information.

[276] FIG. 13 is a view showing an example of angles formed between angle information-based intra prediction modes and a straight line parallel to the x-axis.

[277] As shown in the example of FIG. 13, prediction modes based on angle information can exist between diagonal down and left and diagonal up and right. When described with respect to the angle formed by the x-axis and the angle information based prediction mode, the angle information based prediction modes can exist between 45 degrees (diagonal down and left) and -135 degrees (diagonal up and right).

[278] When the current block has a non-square shape, according to the intra prediction mode of the current block, there may be a case of obtaining a prediction sample by using a reference sample further from the prediction sample instead of a reference sample even closer to the prediction sample from the reference samples located on the angular line passing at the angle of intra prediction.

[279] FIG. 14 is a view showing an embodiment of obtaining prediction samples when the current block has a non-square shape.

[280] For example, as shown in the example of FIG. 14(a), it is assumed that the current block has a non-square shape whose width is larger than the height, and the intra prediction mode of the current block is an intra prediction mode based on angle information having an angle of 0 to 45 degrees. In the above case, when a prediction sample A near the right column of the current block is obtained, there may be a case of using the left reference sample L away from the prediction sample instead of the upper reference sample T near the prediction sample from the reference samples located on the corner mode passing at the angle.

[281] As another example, as shown in the example of FIG. 14(b), it is assumed that the current block has a non-square shape whose height is greater than the width, and the intra prediction mode of the current block is an intra prediction mode based on angle information having an angle of -90 to -135 degrees. In the above case, when a prediction sample A near the bottom line of the current block is obtained, there may be a case of using the top reference sample T away from the prediction sample instead of the left reference sample L near the prediction sample from the reference samples located on the angular mode passing at the angle.

[282] To solve the problem described above, when the current block has a non-square shape, the intra prediction mode of the current block may be replaced by the intra prediction mode in the opposite direction. Accordingly, angle information based prediction modes having an angle greater than or smaller than the angle information based prediction modes shown in FIG. 10 can be used for a non-square shaped block. Such an intra prediction mode based on angle information may be defined as a wide-angle intra prediction mode. The wide-angle intra prediction mode represents an intra prediction mode based on angle information that does not belong to the range of 45 to -135 degrees.

[283] FIG. 15 is a view showing wide-angle intra prediction modes.

[284] In the example shown in FIG. 15, intra prediction modes with an index of -1 to -14 and intra prediction modes with an index of 67 to 80 represent wide-angle intra prediction modes.

[285] Although Fig. 15 shows 14 wide-angle intra prediction modes (-1 to -14) having an angle that is greater than 45 degrees and 14 wide-angle intra prediction modes (67 to 80) having an angle that is less than -135 degrees, more or fewer wide-angle intra prediction modes can be defined.

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

[287] Since the wide-angle intra prediction mode is used, the sample A shown in Fig. 14(a) can be predicted using the reference sample T, and the sample A shown in Fig. 14(b) can be predicted using the reference sample L.

[288] By adding the existing intra prediction modes and N wide-angle intra prediction modes, a total of 67+N intra prediction modes can be used. For example, Table 3 shows the intra direction parameters of the intra prediction modes when 20 wide-angle intra prediction modes are defined.

[289] [Table 3]

[290] When the current block has a non-square shape, and the intra prediction mode of the current block obtained in step S802 belongs to the transform range, the intra prediction mode of the current block can be converted to a wide-angle intra prediction mode. The transform range may be determined based on at least one of the size, shape, and ratio of the current block. In this case, the ratio can represent the ratio of the width and height of the current box.

[291] When the current block has a non-square shape whose width is larger than the height, the transform range can be set from the up and right diagonal intra prediction mode index (e.g., 66) (up and right diagonal intra prediction mode index - N). In this case, 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 can be converted to the wide-angle intra prediction mode. The transform may be a subtraction of a preset value from an intra prediction mode, and the preset value may be a total number (eg, 67) of intra prediction modes excluding wide-angle intra prediction modes.

[292] According to the embodiment described above, intra prediction modes 66 to 53 can be converted to wide-angle intra prediction modes -1 to -14, respectively.

[293] When the current block has a non-square shape whose height is greater than the width, the transform range may be set from the diagonal down-left intra prediction mode index (e.g., 2) (down-left diagonal intra prediction mode index+M). In this case, 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 can be converted to the wide-angle intra prediction mode. The transform may be an addition of a predetermined value to an intra prediction mode, and the predetermined value may be a total number (eg, 65) of intra prediction modes based on angle information, excluding wide-angle intra prediction modes.

[294] According to the embodiment described above, intra prediction modes 2 to 15 can be converted to wide-angle intra prediction modes 67 to 80, respectively.

[295] In the following, the intra prediction modes belonging to the transform range will be referred to as wide-angle replacement intra prediction modes.

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

[297] [Table 4]

[298] [Table 5]

[299] As shown in the examples of Tables 4 and 5, the number of wide-angle replacement intra prediction modes belonging to the transform range may vary according to the ratio of the current block.

[300] The conversion range, as shown in Table 6, can be set by subdividing the ratio of the current block.

[301] [Table 6]

[302] It may be set not to use the wide-angle intra prediction mode when a non-adjacent reference sample line is determined to be the reference sample line of the current block or when a multi-line intra prediction coding method is used to select any of the plurality of reference sample lines. That is, although the current block has a non-square shape and the intra prediction mode of the current block belongs to the transform range, the intra prediction mode of the current block may not be converted to the wide-angle intra prediction mode.

[303] Alternatively, non-adjacent reference sample lines may be set to not be available as the reference sample line of the current block, or may be set to not use the multi-line intra prediction coding method to select any of the plurality of reference sample lines when the intra prediction mode of the current block is determined to be the wide-angle intra prediction mode. When the multi-line intra prediction coding method is not used, an adjacent reference sample line may be determined as the reference sample line of the current block.

[304] When the wide-angle intra prediction mode is not used, the sum of nTbW and nTbH can be set as refW and refH. Accordingly, with the exception of the upper left reference sample, a non-adjacent reference sample at distance i from the current block may include up to (nTbW+nTbH+offsetX[i]) upper reference samples and up to (nTbW+nTbH+offsetY[i]) left reference samples. That is, a non-contiguous reference sample at distance i from the current block may include up to (2nTbW+2nTbH+offsetX[i]+offsetY[i]+1) reference samples. For example, when the value of whRatio is greater than 1, the value of offsetX may be set to be greater than the value of offsetY. For example, the offsetX value may be set to 1, and the offsetY value may be set to 0. On the other hand, when the whRatio value is less than 1, the offsetY value may be set to be greater than the offsetX value. For example, the offsetX value may be set to 0 and the offsetY value may be set to 1.

[305] Since wide-angle intra prediction modes are used in addition to the existing intra prediction modes, the resources required to encode the wide-angle intra prediction modes increase, and thus the coding efficiency can be reduced. Accordingly, coding efficiency can be improved by encoding substitute intra prediction modes for wide-angle intra prediction modes instead of encoding wide-angle intra prediction modes per se.

[306] For example, when the current block is encoded 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 encoded using the intra prediction mode of the current block. In addition, when the current block is encoded using the -1st wide-angle intra prediction mode, the 66th intra prediction mode, which is a substitute intra prediction mode of the -1st wide-angle intra prediction mode, can be encoded using the intra prediction mode of the current block.

[307] 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 the wide-angle intra-prediction substitute mode, the intra prediction mode can be converted to the wide-angle intra prediction mode.

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

[309] Intra prediction mode encoding may be performed based on the MPM list described above. Specifically, when a neighboring block is encoded using the wide-angle intra prediction mode, the MPM may be set based on the wide-angle intra-prediction replacement mode corresponding to the wide-angle intra prediction mode. For example, when a neighboring block is encoded in a wide-angle intra prediction mode, the variable candIntraPredModeX (X is A or B) may be set equal to the wide-angle intra prediction substitute mode.

[310] Alternatively, the MPM may be set based on the wide-angle mode of the adjacent block intra prediction. For example, when a neighboring block is encoded in the wide-angle intra prediction mode, the variable candIntraPredModeX may be set equal to the wide-angle intra prediction mode.

[311] The MPM may be obtained based on whether the reference sample line of the current block is a non-adjacent reference sample line, or whether the multi-line intra prediction coding method is applied to select one of the plurality of reference sample lines. For example, when the reference sample line of the current block is a non-adjacent reference sample line, and the intra prediction mode of an adjacent block adjacent to the current block is the wide-angle intra prediction mode, the default mode may be set to MPM of the current block.

[312] For example, when candIntraPredModeA obtained based on the intra prediction mode of the left neighboring block and candIntraPredModeB obtained based on the intra prediction mode of the upper neighboring block are the same, and candIntraPredModeA is a planar mode or a DC mode, MPMs can be obtained as follows considering whether the reference sample line index of the current block is 0.

[313] MPM[0]=(IntraLumaRefLineIdx=0) ? Intra_Planar: INTRA_ANGULAR 50

[314] MPM[1]=(IntraLumaRefLineIdx=0) ? Intra_DC: INTRA_ANGULAR 18

[315] MPM[2]=INTRA_ANGULAR 2

[316] That is, when the reference sample line index of the current block is 0, the planar mode and the DC mode are set to MPM, while when the reference sample line index of the current block is not 0, the vertical direction intra prediction mode (INTRA_ANGULAR 50) and the horizontal direction intra prediction mode (INTRA_ANGULAR 18) can be set to MPM.

[317] When the reference sample line index of the current block is not equal to 0, and candIntraPredModeA and candIntraPredModeB are the same, and candIntraPredModeA is a wide-angle intra prediction mode, MPMs can be obtained as follows.

[318] MPM[0]=INTRA_ANGULAR2

[319] MPM[1]=INTRA_ANGULAR18

[320] MPM[2]=INTRA_ANGULAR50

[321] Alternatively, MPMs can be obtained as follows.

[322] MPM[0]=INTRA_ANGULAR50

[323] MPM[1]=INTRA_ANGULAR18

[324] MPM[2]=INTRA_ANGULAR2

[325] That is, when the reference sample line index of the current block is not equal to 0, the wide-angle intra prediction mode may not be set to MPM.

[326] When candIntraPredModeA and candIntraPredModeB are the same, and candIntraPredModeA is an intra prediction mode based on angle information, MPMs can be obtained as follows.

[327] MPM[0]=candIntraPredModeA

[328] MPM[1]=2+((candIntraPredModeA+61) % 64)

[329] MPM[2]=2+((candIntraPredModeA - 1) % 64)

[330] When the reference sample line index of the current block is 0 and candIntraPredModeA and candIntraPredModeB are different, MPM[0] and MPM[1] may be set to candIntraPredModeA and candIntraPredModeB, respectively. MPM[2] can be set to any of planar mode, DC mode, or vertical mode, which is not the same as MPM[0] and MPM[1] modes.

[331] When the reference sample line index of the current block is not equal to 0, and one of candIntraPredModeA and candIntraPredModeB is planar mode and the other is DC mode, MPMs can be obtained as follows.

[332] MPM[0]=INTRA_ANGULAR2

[333] MPM[1]=INTRA_ANGULAR18

[334] MPM[2]=INTRA_ANGULAR50

[335] When the reference sample line index of the current block is not equal to 0, and both candIntraPredModeA and candIntraPredModeB are wide-angle intra prediction modes, MPMs can be obtained as follows.

[336] MPM[0]=INTRA_ANGULAR2

[337] MPM[1]=INTRA_ANGULAR18

[338] MPM[2]=INTRA_ANGULAR50

[339] When the reference sample line index of the current block is not equal to 0, and any of candIntraPredModeA and candIntraPredModeB is a wide-angle intra prediction mode, any that is not a wide-angle intra prediction mode of candIntraPredModeA and candIntraPredModeB can be set to MPM[0], and intra prediction modes like MPM[0] can be set to MPM[1] and MPM[2 ]. For example, when candIntraPredModeA is not a wide-angle intra prediction mode and candIntraPredModeB is a wide-angle intra prediction mode, the MPMs can be obtained as follows.

[340] MPM[0]=candIntraPredModeA

[341] MPM[1]=2+((candIntraPredModeA+61) % 64)

[342] MPM[2]=2+((candIntraPredModeA - 1) % 64)

[343] On the other hand, when candIntraPredModeA is a wide-angle intra prediction mode and candIntraPredModeB is not a wide-angle intra prediction mode, the MPMs can be obtained as follows.

[344] MPM[0]=candIntraPredModeB

[345] MPM[1]=2+((candIntraPredModeB+61) % 64)

[346] MPM[2]=2+((candIntraPredModeB - 1) % 64)

[347] When the reference sample line index of the current block is not equal to 0, and either of candIntraPredModeA and candIntraPredModeB is a planar mode or a DC mode, and the other is not a wide-angle intra prediction mode, any that is not a wide-angle intra prediction mode of candIntraPredModeA and candIntraPredModeB may be set to MPM[0], and intra prediction modes like MPM[0] may be set to MPM[1] and MPM[2]. For example, when candIntraPredModeA is not a wide-angle intra prediction mode and candIntraPredModeB is a planar mode or a DC mode, the MPMs can be obtained as follows.

[348] MPM[0]=candIntraPredModeA

[349] MPM[1]=2+((candIntraPredModeA+61) % 64)

[350] MPM[2]=2+((candIntraPredModeA - 1) % 64)

[351] On the other hand, when candIntraPredModeA is a planar mode or DC mode, and candIntraPredModeB is not a wide-angle intra prediction mode, the MPMs can be obtained as follows.

[352] MPM[0]=candIntraPredModeB

[353] MPM[1]=2+((candIntraPredModeB+61) % 64)

[354] MPM[2]=2+((candIntraPredModeB - 1) % 64)

[355] When the reference sample line index of the current block is not equal to 0, and both candIntraPredModeA and candIntraPredModeB are not wide-angle intra prediction modes, candIntraPredModeA and candIntraPredModeB may be set to MPM[0] and MPM[1], respectively. Any mode that does not overlap with MPM[0] and MPM[1], from the intra vertical direction prediction mode (INTRA_ANGULAR50), the horizontal intra prediction mode (INTRA_ANGULAR18), and the downward and left diagonal intra prediction mode (INTRA_ANGULAR2) can be set as MPM[2].

[356] An encoding block or a transform block may be divided into a plurality of subblocks (or subsections). When a coding block or a transform block is partitioned into a plurality of subblocks, prediction, transformation, and quantization can be performed on each subblock. Splitting a coding block or a transform block into a plurality of sub-blocks may be defined as a sub-partitioning intra-coding method.

[357] Information indicating whether an intra subdivision coding method is applied may be transmitted by a bitstream. The information may be a 1-bit flag. For example, the "intra_subpartitions_mode_flag" syntax element indicating whether a coding block or a transformation block is divided into a plurality of sub-blocks may be transmitted via a bitstream.

[358] Alternatively, whether the intra subdivision coding method is applied may be determined based on at least one of the size, shape, and intra prediction mode of the coding block or transform block. For example, when the intra prediction mode of a coding block is an intra prediction mode not based on angle information (e.g., planar mode or DC mode) or a predetermined intra prediction mode based on angle information (e.g., horizontal direction intra prediction mode, vertical direction intra prediction mode, or diagonal direction intra prediction mode), the subdivision intra coding method may not be applied. Alternatively, it may be set not to use the subdivision intra coding method when the coding block size is less than a threshold value.

[359] Alternatively, when intra prediction is performed on a subblock based on the intra prediction mode of a coding block, then whether the subdivision intra coding method should be applied may be determined based on whether a reconstructed sample included in an adjacent subblock should be used as a reference sample when intra prediction is performed on the subblock. For example, it may be set not to use the subdivision intra coding method when the intra prediction mode of the coding block is the diagonal direction intra prediction mode or the wide-angle intra prediction mode, and the neighboring subblock may not be used as a reference when intra prediction is performed on the subblock based on the intra prediction mode.

[360] Alternatively, it may be set not to use the subdivision intra-coding method when the height-to-width ratio of the coding block is greater than a threshold value or less than a threshold value. Alternatively, when at least one of the height and width of the coding block is less than or equal to the threshold value, the intra subdivision coding method may not be used. For example, when both the height and the width of the coding block are less than or equal to the threshold value, the subdivision intra coding method may not be used. The threshold value may be a value predefined in the encoder and decoder. Alternatively, the information for determining the threshold value may be transmitted via a bitstream.

[361] Alternatively, whether a flag indicating whether to apply the intra subdivision coding method should be transmitted may be determined based on at least one of the size, shape, and intra prediction mode of the coding block or transform block. For example, only when both the height and width of the coding block is less than or equal to the threshold value and/or the size of the coding block is greater than or equal to the threshold value, a flag indicating whether to apply the subdivision intra coding method may be encoded and transmitted. When a flag indicating whether or not to apply the intra subdivision coding method is not encoded, the intra subdivision coding method may not be applied.

[362] When the subdivision intra coding method is applied, the partition type of the coding block or the transform block can be determined. In this case, the split type indicates the splitting direction of the coding block or transform block. For example, splitting in the vertical direction may mean splitting a coding block or a transform block using at least one vertical line, and splitting in a horizontal direction may mean splitting a coding block or a transform block using at least one horizontal line.

[363] Fig. 16 is a view showing an example of splitting in the vertical direction and splitting in the horizontal direction.

[364] Fig. 16(a) shows an example in which the coding block is divided into two subblocks, and Fig. 16(b) shows an example in which the coding block is divided into four subblocks.

[365] Information for determining the split type of a coding block or a transform block may be transmitted via a bitstream. For example, information indicating whether splitting in the vertical direction or splitting in the horizontal direction is applied to a coding block or a transform block may be transmitted. The information may be an intra_subpart_type_flag of a 1-bit flag. When the flag value is 1, it indicates that the coding block or transform block is split in the horizontal direction, and when the flag value is 0, it indicates that the coding block or transform block is split in the vertical direction.

[366] Alternatively, the partition type of the coding block or transform block may be determined based on the size, shape, or intra prediction mode of the coding block or transform block. For example, the partition type of the coding block may be determined based on the ratio of the width and height of the coding block. For example, when the whRatio value indicating the ratio of the height and width of the coding block is greater than or equal to the first threshold value, splitting in the vertical direction may be applied to the coding block. Otherwise, splitting in the horizontal direction may be applied to the coding block.

[367] FIG. 17 is a view showing an example of determining a splitting type of a coding block.

[368] For convenience of explanation, the first threshold value is assumed to be 2. In the example shown in FIG. 17(a), the coding block whRatio is 1, which is less than the first threshold value. Accordingly, encoding of information indicating the type of partitioning of the coding block can be skipped, and partitioning in the horizontal direction can be applied to the coding block.

[369] In the example shown in FIG. 17(b), the whRatio of the coding block is 2, which is equal to the first threshold value. Accordingly, the encoding of information indicating the type of partitioning of the coding block can be skipped, and partitioning in the vertical direction can be applied to the coding block.

[370] The split type of the coding block may be determined using a second threshold having the opposite sign of the first threshold. For example, when the value of whRatio is less than or equal to the second threshold value, splitting in the horizontal direction may be applied to the coding block, and otherwise splitting in the vertical direction may be applied to the coding block. The absolute values of the first threshold value and the second threshold value are the same, and their signs may differ. For example, when the first threshold is N (in this case, N is an integer such as 1, 2, 4, or the like), the second threshold may be -N.

[371] Fig. 18 is a view showing an example of determining a splitting type of a coding block.

[372] For convenience of explanation, the second threshold is assumed to be -2. In the example shown in FIG. 18(a), the coding block whRatio is -1, which is greater than the second threshold value. Accordingly, the encoding of information indicating the type of partitioning of the coding block can be skipped, and partitioning in the vertical direction can be applied to the coding block.

[373] In the example shown in FIG. 18(b), the whRatio of the coding block is -2, which is equal to the second threshold value. Accordingly, encoding of information indicating the type of partitioning of the coding block can be skipped, and partitioning in the horizontal direction can be applied to the coding block.

[374] Alternatively, the splitting type of the coding block may be determined based on the first threshold and the second threshold. For example, when the value of whRatio is greater than or equal to the first threshold, splitting in the horizontal direction may be applied to the coding block, and when the value of whRatio is less than or equal to the second threshold, splitting in the vertical direction may be applied to the coding block. When the value of whRatio is between the first threshold value and the second threshold value, the partition type of the current block can be determined by parsing information from the bitstream.

[375] The first threshold and the second threshold may be predefined in the encoder and decoder. Alternatively, the first threshold and the second threshold may be determined for each sequence, picture, or slice.

[376] Alternatively, the partition type may be determined based on the size of the coding block or transform block. For example, when the coding block size is N×n, splitting in the vertical direction can be applied, and when the coding block size is n×N, splitting in the horizontal direction can be applied. In this case, n may be a natural number that is less than N. N and/or n may be values predefined in the encoder and decoder. Alternatively, information for determining N and/or n may be transmitted via a bitstream. For example, N may be 32, 64, 128, or 256. Accordingly, when the coding block size is 128×n (where n is a natural number such as 16, 32, or 64), splitting in the vertical direction can be applied, and when the coding block size is n×128, splitting in the horizontal direction can be applied.

[377] Alternatively, the partition type of the coding block or transform block may be determined based on the intra prediction mode of the coding block or transform block. For example, when the intra prediction mode of a coding block has a horizontal direction or a direction similar to the horizontal direction, splitting in the vertical direction may be applied to the coding block. Here, the intra prediction mode in the direction similar to the horizontal direction indicates an intra prediction mode whose index difference value from the intra prediction mode in the horizontal direction (for example, INTRA_ANGULAR18 as shown in FIG. 10(b)) is less than or equal to the threshold value (for example, INTRA_ANGULAR18(N). On the other hand, when the intra prediction mode of a coding block has a vertical direction or a direction similar to the vertical direction, splitting in the horizontal direction can be applied to the block In this case, the intra prediction mode in a direction like the vertical direction indicates an intra prediction mode whose index difference value from the intra prediction mode in the vertical direction (for example, INTRA_ANGULAR50, as shown in Fig. 10(b)) is less than or equal to the threshold value (for example, INTRA_ANGULAR50(N). Here, the threshold value N may be a value preset in the encoder and decoder. Alternatively, the information for determining the threshold N may be passed to the sequence, image, or slice level.

[378] FIG. 19 is a view showing an example in which a split type of a coding block is determined based on the intra prediction mode of the coding block.

[379] As shown in the example of FIG. 19(a), when the intra prediction mode of a coding block has a direction similar to the vertical direction, splitting in the horizontal direction can be applied to the coding block.

[380] On the other hand, as shown in the example of FIG. 19(b), when the intra prediction mode of a coding block has a direction similar to the horizontal direction, splitting in the vertical direction can be applied to the coding block.

[381] Unlike the example described above, when the intra prediction mode of a coding block has a horizontal direction or a direction similar to the horizontal direction, splitting in the horizontal direction is applied, and when the intra prediction mode of the coding unit has a vertical direction or a direction similar to the vertical direction, splitting in the vertical direction can be applied.

[382] When splitting is applied in the vertical or horizontal direction, the type of splitting of a coding block or a transform block can be determined based on whether at least one of the width and height of a subblock generated by splitting a coding block or a transform block is less than a threshold value. In this case, the threshold value may be an integer such as 2, 4, or 8.

[383] FIG. 20 is a view for describing a coding block partition scheme.

[384] When splitting in the horizontal direction is applied to a 4x8 coding block as shown in FIG. 20(a), the coding block is divided into 2x8 subblocks. In this case, since the sub-block width is smaller than the threshold value, splitting in the horizontal direction may not be allowed for the coding block. On the other hand, when splitting in the vertical direction is applied to a 4x8 coding block, the coding block is split into 4x4 subblocks. Since both the width and the height of the sub-block are equal to or greater than the threshold value, splitting in the vertical direction can be used for the coding block. Since only splitting in the vertical direction is allowed for a coding block, encoding information indicating a splitting type for a coding block can be skipped, and splitting in the vertical direction can be applied to the coding block.

[385] When splitting in the vertical direction is applied to an 8x4 coding block as shown in FIG. 20(b), the coding block is divided into 8x2 subblocks. In this case, since the sub-block height is smaller than the threshold value, splitting in the vertical direction may not be allowed for the coding block. On the other hand, when splitting in the horizontal direction is applied to an 8x4 coding block, the coding block is divided into 4x4 subblocks. Since both the width and the height of the sub-block are equal to or greater than the threshold value, splitting in the horizontal direction can be used for the coding block. Since only splitting in the horizontal direction is allowed for a coding block, encoding information indicating a splitting type for a coding block can be skipped, and splitting in the vertical direction can be applied to the coding block.

[386] When both splitting in the vertical direction and splitting in the horizontal direction can be used, the type of splitting of the coding block can be determined by analyzing information indicating the type of splitting of the coding block.

[387] The number of subblocks may be determined based on at least one of the size and shape of the coding block or the transform block. For example, when either of the coding block width and height is 8 and the other is 4, the coding block may be split into two sub-blocks. On the other hand, when both the width and height of the coding block are 8 or more, or either of the width and height of the coding block is greater than 8, the coding block may be divided into 4 sub-blocks. As a result, when a coding block has a size of 4×4, the coding block may not be sub-blocked. When the coding block has a size of 4x8 or 8x4, the coding block may be split into two sub-blocks. In other cases, the coding block may be divided into four sub-blocks.

[388] Alternatively, information indicating the size, shape, or number of sub-blocks may be transmitted via a bitstream. The size or shape of the sub-blocks may be determined with information indicating the number of sub-blocks. Alternatively, the number of sub-blocks may be determined with information indicating the size or shape of the sub-blocks.

[389] When a subdivision intra coding method is applied, subblocks generated by splitting a coding block or a transform block can use the same intra prediction mode. For example, the MPMs for a coding block may be derived based on the intra prediction modes of adjacent blocks adjacent to the coding block, and the intra prediction mode for the coding block may be determined based on the obtained MPMs. When the intra prediction mode of a coding block is determined, each subblock can perform intra prediction using the determined intra prediction mode.

[390] When the subdivision intra coding method is applied, any of the MPMs may be defined as the coding block intra prediction mode. That is, when the subdivision intra-coding method is applied, the MPM flag may be considered to be true although the MPM flag is not transmitted.

[391] Alternatively, when the subdivision intra coding method is applied, any of the predefined candidate intra prediction modes may be determined as the coding block intra prediction mode. For example, any of the horizontal intra prediction mode, the vertical intra prediction mode, the diagonal intra prediction mode (e.g., at least one of the up and left intra prediction mode, the up and right intra prediction mode, and the down and left intra prediction mode), and the non-angle information based intra prediction mode (e.g., at least one of the planar mode and the DC mode) can be defined as a coding block intra prediction mode. Index information indicating any of the predefined candidate intra prediction modes may be transmitted via the bitstream.

[392] According to an embodiment of the present invention, the intra prediction mode of at least one of the sub-blocks may be set to be different from the modes of other sub-blocks. For example, the intra prediction mode of the Nth subblock can be obtained by adding an offset to or subtracting from the intra prediction mode of the N-1th subblock. The offset may be predefined in the encoder and decoder. Alternatively, the offset may be derived based on at least one of the size, shape, and intra prediction mode of the coding block, the size, shape, and number of sub-blocks, and the splitting direction of the coding block. Alternatively, the information to obtain the offset may be transmitted via a bitstream.

[393] Alternatively, when the intra prediction mode of the N-1st subblock has a mode not based on angle information, the intra prediction mode of the Nth subblock is also set to be the same as the intra prediction mode of the N-1st subblock, and when the intra prediction mode of the N-1st subblock has a mode based on angle information, the intra prediction mode obtained by adding an offset to or subtracting from the N-1st subblock intra prediction mode , may be set to be the same as the Nth subblock intra prediction mode.

[394] Alternatively, an intra prediction mode based on angle information may be applied to some of the plurality of sub-blocks, and an intra prediction mode not based on angle information may be applied to other sub-blocks. A sub-block to which an intra-prediction mode not based on angle information is applied can be determined in consideration of at least one of the size, shape, position, and number of sub-blocks. Alternatively, only when the angle information-based intra prediction mode applied to any of the plurality of sub-blocks is a predetermined value, the non-angle information-based intra prediction mode can be applied to another sub-block.

[395] Alternatively, the intra prediction mode of each subblock can be obtained from the MPM. For this, index information indicating any of the MPMs may be transmitted for each sub-block.

[396] Alternatively, the intra prediction mode of each sub-block may be derived from predefined candidate intra prediction modes. For this, index information indicating any of the predefined candidate intra prediction modes may be transmitted for each sub-block.

[397] Alternatively, information indicating whether intra subblock prediction modes are equally set may be transmitted via a bitstream.

[398] The quantization parameters of the sub-blocks may be individually determined. Accordingly, the value of the quantization parameter of each sub-block may be set differently. To determine the quantization parameter of each sub-block, information indicating the value of the difference from the quantization parameter of the previous sub-block may be encoded. For example, a difference value between the Nth subblock quantization parameter and the N-1st subblock quantization parameter may be encoded for the Nth subblock.

[399] Intra-subblock prediction may be performed using a reference sample. In this case, the reference sample can be obtained from the reconstructed neighboring block sample adjacent to the sub-block. When an adjacent block adjacent to a subblock is another subblock included in the coding block that is the same as that of the subblock, the subblock reference sample may be obtained based on the reconstructed sample of the other subblock. For example, when the first sub-block is located to the left or above the second sub-block, the reference sample of the second sub-block may be obtained from the reconstructed sample of the first sub-block. For this, parallel intra prediction may not be applied between sub-blocks. That is, encoding/decoding may be sequentially performed on the sub-blocks included in the encoding block. Accordingly, after the encoding/decoding of the first subblock is completed, intra prediction can be performed for the second subblock.

[400] When the intra subdivision coding method is applied, it may be set not to use the multi-line intra prediction coding method to select any one of the plurality of candidate reference sample lines. When the multi-line intra prediction coding method is not used, an adjacent reference sample line adjacent to each sub-block may be defined as the reference sample line of each sub-block.

[401] Alternatively, the multi-line intra prediction coding method can be used even when the subdivision intra coding method is applied. For this, index information for indicating a reference sample line may be transmitted for each sub-block. Alternatively, the index information for indicating the reference sample line may only be transmitted for any one of the plurality of sub-blocks, and the index information may also be applied to the remaining sub-blocks as is. Alternatively, it may be set to transmit index information for indicating a reference sample line for a coding block and share index information from a plurality of sub-blocks included in the coding block.

[402] Alternatively, it may be set to only allow a subblock having a predetermined position or a predetermined partition index of the subblocks to use the multi-line intra prediction coding method. For example, index information indicating any of the candidate reference sample lines may only be transmitted for a sub-block having a partition index of 0 out of a plurality of sub-blocks or a sub-block that is in contact with the top or left border of a coding block. The multi-line intra prediction coding method may not be applied to the rest of the sub-blocks. Accordingly, the remaining sub-blocks may perform intra prediction using adjacent reference sample lines.

[403] The predictive coding mode may be set differently for each sub-block. For example, intra-prediction may be applied to some sub-blocks, and inter-picture prediction, current-picture anchoring, or combined prediction may be applied to other sub-blocks.

[404] FIG. 21 is a view showing an example in which the predictive coding mode is set differently for each sub-block.

[405] The intra prediction mode may be set differently for each sub-block, or the predictive coding mode may be set differently. For example, in the example shown in FIG. 21, it is shown that intra prediction is applied to sub-block 0 and sub-block 1, and the current picture anchor is applied to sub-block 1 and sub-block 2.

[406] When the current picture anchor is used, the sub-block prediction block may be obtained from an already decoded portion of the current picture or slice (or group of tiles). When snapping is applied to the current picture, a motion vector may be obtained to indicate a sub-block prediction block. The motion vector associated with the current image may be referred to as a "block vector".

[407] A motion vector may be obtained based on a motion vector of an adjacent block adjacent to a coding block or subblock. Alternatively, the information for determining the motion vector may be transmitted via a bitstream.

[408] In this case, the maximum value of the motion vector of the subblock may be determined according to the size of the subblock, or the coding block, or the transform block to which the subblock belongs. For example, the motion vector of a subblock may be set so as not to deviate from the boundary of the coding block or transform block to which the subblock belongs. That is, a subblock prediction block can be obtained from a portion encoded/decoded before the subblock in the coding block to which the subblock belongs.

[409] Index information indicating any of the previously decoded sub-blocks in a coding block may be encoded and transmitted instead of a motion vector. A subblock prediction block may be defined as a previously decoded subblock indicated by the index information.

[410] As another example, the motion vector of the subblock may be allowed to deviate from the boundary of the coding block or transform block to which the subblock belongs.

[411] When a prediction block is generated as a result of performing intra prediction, the prediction samples may be updated based on the position of each of the prediction samples included in the prediction block. Such an update method may be referred to as an intra-weighted prediction based on sample position (or a position dependent prediction combination (PDPC)).

[412] Whether PDPC should be used may be determined based on the size, shape, and intra prediction mode of the current block, the reference sample line of the current block, the size of the current block, and the color component. For example, PDPC may be used when the intra prediction mode of the current block is at least one of a planar mode, a DC mode, a mode in the vertical direction, a mode in the horizontal direction, a mode having an index value that is smaller than the vertical direction mode, and a mode having an index value that is larger than the horizontal direction mode. Alternatively, PDPC may be used only when at least one of the width and height of the current block is greater than 4. Alternatively, PDPC may be used only when the reference picture line index of the current block is 0. Alternatively, PDPC may be used only when the reference picture line index of the current block is equal to or greater than a predetermined value. Alternatively, PDPC can only be used for the luma component. Alternatively, whether or not PDPC should be used may be determined according to whether two or more of the conditions listed above are satisfied.

[413] Alternatively, whether or not to use PDPC can be determined according to whether an intra subdivision coding method is used. For example, it may be set not to use PDPC when a subdivision intra coding method is applied to a coding block or a transform block. Alternatively, when a subdivision intra coding method is applied to a coding block or a transform block, PDPC may be applied to at least one of the plurality of subblocks. In this case, the sub-block to which PDPC is applied may be determined based on at least one of the size, shape, position, intra prediction mode, and reference sample line index of the coding block or sub-block. For example, PDPC may be applied to a subblock adjacent to the top and/or left coding block boundaries, or a subblock adjacent to the bottom and/or right coding block boundaries. Alternatively, based on the size or shape of the subblock, it may be determined that PDPC should be applied to all subblocks included in the coding block, or that PDPC should not be applied to all subblocks included in the coding block. As another example, PDPC may be applied to all sub-blocks in a coding block.

[414] Alternatively, whether PDPC should be applied to each subblock may be determined according to whether at least one of the size, shape, intra prediction mode, and reference picture index of the subblocks generated by splitting a coding block or a transform block satisfies a predetermined condition. For example, when at least one of the sub-block width and height is greater than 4, PDPC may be applied to the sub-block.

[415] As another example, information indicating whether PDPC is applied may be transmitted via a bitstream.

[416] Alternatively, the portion to which PDPC is applied may be determined based on at least one of the size, shape, and intra prediction mode of the current block and the prediction sample position. For example, when the intra prediction mode of the current block has an index that is greater than the vertical direction, prediction samples at least one of the x-coordinate and the y-coordinate of which are greater than the threshold value are not corrected, and correction can only be performed on prediction samples whose x-coordinate or y-coordinate is less than or equal to the threshold value. Alternatively, when the intra prediction mode of the current block has an index that is less than in the horizontal direction, the prediction samples at least one of the x-coordinate and the y-coordinate of which is greater than the threshold value are not corrected, and the correction can be performed only on prediction samples whose x-coordinate or y-coordinate is less than or equal to the threshold value. In this case, the threshold value may be determined based on at least one of the size, shape, and intra prediction mode of the current block.

[417] When the prediction sample is obtained by the intra prediction sample, the reference sample used to correct the prediction sample may be determined based on the position of the received prediction sample. For convenience of explanation, in the embodiments described below, the reference sample used to correct the prediction sample will be referred to as the PDPC reference sample. In addition, a prediction sample obtained by intra prediction is called a first prediction sample, and a prediction sample obtained by correcting the first prediction sample is called a second prediction sample.

[418] FIG. 22 is a view showing an embodiment of applying PDPC.

[419] The first prediction sample may be corrected using at least one PDPC reference sample. The PDPC reference sample may include at least one of the reference sample adjacent to the upper left corner of the current block, the upper reference sample located above the current block, and the left reference sample located to the left of the current block.

[420] At least one of the reference samples belonging to the reference sample line of the current block may be set as a PDPC reference sample. Alternatively, regardless of the reference sample line of the current block, at least one of the reference samples belonging to the reference sample line having index 0 may be set as the PDPC reference sample. For example, although the first prediction sample is obtained using the reference sample included in the reference sample line with index 1 or index 2, the second prediction sample can be obtained using the reference sample included in the reference sample line with index 0.

[421] The number or positions of the PDPC reference samples used to correct the first prediction sample may be determined based on at least one of the intra prediction mode of the current block, the size of the current block, the shape of the current block, and the position of the first prediction sample.

[422] For example, when the intra prediction mode of the current block is a planar mode or a DC mode, the second prediction sample may be obtained using the upper reference sample and the left reference sample. In this case, the top reference sample may be a reference sample that is vertical with respect to the first prediction sample (e.g., the same x-coordinate reference sample), and the left reference sample may be a reference sample that is horizontal with respect to the first prediction sample (e.g., the same y-coordinate reference sample).

[423] When the intra prediction mode of the current block is the intra prediction mode in the horizontal direction, the second prediction sample may be obtained using the upper reference sample. In this case, the top reference sample may be a reference sample that is vertical with respect to the first prediction sample.

[424] When the intra prediction mode of the current block is the intra prediction mode in the vertical direction, the second prediction sample may be obtained using the left reference sample. In this case, the left reference sample may be a reference sample that is horizontal with respect to the first prediction sample.

[425] When the intra prediction mode of the current block is the diagonal down and left intra prediction mode or the diagonal up and right intra prediction mode, the second prediction sample can be obtained based on the upper left reference sample, the upper reference sample, and the left reference sample. The top left reference point may be the reference point adjacent to the top left corner of the current block (eg, the reference point at position (-1, -1)). The top reference may be a reference diagonally up and to the right of the first prediction sample, and the left reference may be a reference diagonally down and to the left of the first prediction sample.

[426] In summary, when the position of the first prediction sample is (x, y), R(-1, -1) may be set as the top left reference, and R(x+y+1, -1) or R(x, -1) may be set as the top reference. In addition, R(-1, x+y+1) or R(-1, y) may be set as the left reference.

[427] As another example, the position of the left reference or upper reference may be determined in consideration of at least one of the shape of the current block and whether wide-angle intra mode is applied.

[428] In particular, when the intra prediction mode of the current block is a wide-angle intra prediction mode, a reference sample spaced apart from a reference sample located in the diagonal direction of the first prediction sample by an offset amount can be set as a PDPC reference sample. For example, the top reference R(x+y+k+1, -1) and the left reference R(-1, x+y - k+1) may be set as PDPC references.

[429] In this case, the offset k may be determined based on the wide-angle intra prediction mode. Equations 8 and 9 show an example of obtaining an offset based on the wide-angle intra prediction mode.

[430] [Equation 8]

[431] [Equation 9]

[432] The second prediction sample may be determined based on a weighted sum operation of the first prediction sample and the PDPC reference samples. For example, the second prediction sample can be obtained based on Equation 10 shown below.

[433] [Equation 10]

[434] In Equation 10, RL denotes the left reference sample, RT denotes the upper reference sample, and RTL denotes the upper left reference sample. Pred(x, y) denotes the prediction sample at position (x, y). wL denotes a weight value assigned to the left reference, wT denotes a weight value assigned to the upper reference, and wTL denotes a weight value assigned to the upper left reference. The weighting values assigned to the first prediction sample can be obtained by subtracting the weighting values assigned to the reference samples from the maximum value. For convenience of explanation, the weighting value assigned to the PDPC reference sample is referred to as the PDPC weighting value.

[435] The weighting value assigned to each reference sample may be determined based on at least one of the intra prediction mode of the current block and the position of the first prediction sample.

[436] For example, at least one of wL, wT, and wTL may be proportional or inversely related to at least one of the x-coordinate value and the y-coordinate value of the prediction sample. Alternatively, at least one of wL, wT, and wTL may be proportional or inversely related to at least one of the width and height of the current block.

[437] When the intra prediction mode of the current block is the DC mode, the PDPC weighting values may be determined as shown in Equation 11.

[438] [Equation 11]

[439] In Equation 11, x and y denote the position of the first prediction sample.

[440] The variable shift used in the bit shift operation in Equation 11 may be obtained based on the width or height of the current block. For example, the shift variable can be obtained based on equation 12 or 13 shown below.

[441] [Equation 12]

[442] [Equation 13]

)

[443] Alternatively, the variable shift can be obtained taking into account the parameter of the internal direction of the current block.

[444] The number of parameters or parameter types used to obtain the shift variable may be determined differently according to the intra prediction mode of the current block. For example, when the intra prediction mode of the current block is a planar mode, a DC mode, a mode in the vertical direction, or a mode in the horizontal direction, the shift variable can be obtained using the width (width) and height (height) of the current block, as shown in the example of Equation 12 or Equation 13. When the intra prediction mode of the current block is an intra prediction mode having an index that is larger than the intra prediction mode in the vertical direction, the shift variable can be obtained using the height and the inner direction parameter of the current block. When the intra prediction mode of the current block is an intra prediction mode having an index that is smaller than that of the horizontal intra prediction mode, the shift variable can be obtained using the width and the intra direction parameter of the current block.

[445] When the intra prediction mode of the current block is a planar mode, wTL may be set to 0. wL and wT may be obtained based on Equation 14 shown below.

[446] [Equation 14]

[447] When the intra prediction mode of the current block is the intra prediction mode in the horizontal direction, wT may be set to 0, and wTL and wL may be set equally. On the other hand, when the intra prediction mode of the current block is the intra prediction mode in the vertical direction, wL may be set to 0, and wTL and wT may be set in the same way.

[448] When the intra prediction mode of the current block is an up and right intra prediction mode having an index value that is larger than the vertical intra prediction mode, the PDPC weighting values can be obtained as shown in Equation 15.

[449] [Equation 15]

[450] On the other hand, when the intra prediction mode of the current block is a downward and left intra prediction mode having an index value that is smaller than that of the horizontal intra prediction mode, the PDPC weighting values can be obtained as shown in Equation 16.

[451] [Equation 16]

[452] As shown in the embodiment described above, the PDPC weighting values may be determined based on the x and y positions of the prediction sample.

[453] As another example, a weighting value assigned to each of the PDPC reference samples may be determined by a subblock element. Prediction samples included in a subblock may share the same PDPC weighting values.

[454] The size of the sub-block, which is the basic element for determining the weighting value, may be predetermined in the encoder and decoder. For example, a weighting value may be determined for each 2×2 or 4×4 sub-block.

[455] Alternatively, the size, shape, or number of sub-blocks may be determined according to the size or shape of the current block. For example, regardless of the size of the coding block, the coding block can be divided into four sub-blocks. Alternatively, the coding block may be divided into 4 or 16 sub-blocks according to the size of the coding block.

[456] Alternatively, the size, shape, or number of subblocks may be determined based on the intra prediction mode of the current block. For example, when the intra prediction mode of the current block has a horizontal direction, N columns (or N rows) can be set as one sub-block, while when the intra prediction mode of the current block has a vertical direction, N rows (or N columns) can be set as one sub-block.

[457] Equations 17-19 show examples of determining the PDPC weighting value for a 2×2 subblock. Equation 17 shows the case where the intra prediction mode of the current block is the DC mode.

[458] [Equation 17]

[459] In Equation 17, K may be determined based on the sub-block size.

[460] Equation 18 shows an example in which the intra prediction mode of the current block is an up and right intra prediction mode having an index value that is larger than the intra prediction mode in the vertical direction.

[461] [Equation 18]

[462] Equation 19 shows an example in which the intra prediction mode of the current block is the down and left intra prediction mode having an index value that is less than that of the horizontal direction intra prediction mode.

[463] [Equation 19]

[464] In Equations 17-19, x and y denote the position of a reference sample within a sub-block. The reference sample may be any of the sample located at the top left of the sub-block, the sample located at the center of the sub-block, and the sample located at the bottom right of the sub-block.

[465] Equations 20-22 show examples of determining a PDPC weighting value for a 4x4 subblock. Equation 20 shows an example in which the intra prediction mode of the current block is the DC mode.

[466] [Equation 20]

[467] Equation 21 shows an example in which the intra prediction mode of the current block is an up and right intra prediction mode having an index value that is larger than the intra prediction mode in the vertical direction.

[468] [Equation 21]

[469] Equation 22 shows an example in which the intra prediction mode of the current block is the down and left intra prediction mode having an index value that is smaller than that of the horizontal direction intra prediction mode.

[470] [Equation 22]

[471] In the embodiments described above, it has been described that the PDPC weighting values are determined considering the positions of the prediction samples included in the first prediction sample or subblock. The PDPC weighting values can be determined by further considering the shape of the current block.

[472] For example, in the case of the DC mode, the method for obtaining the PDPC weighting value may vary depending on whether the current block has a non-square shape whose width is larger than the height, or a non-square shape whose height is larger than the width.

[473] Equation 23 shows an example of obtaining a PDPC weighting value when the current block has a non-square shape whose width is greater than the height, and Equation 24 shows an example of obtaining a PDPC weighting value when the current block has a non-square shape whose height is greater than the width.

[474] [Equation 23]

[475] [Equation 24]

[476] When the current block has a non-square shape, the current block can be predicted using the wide-angle intra prediction mode. Thus, even when the wide-angle intra prediction mode is applied, the first prediction sample can be updated by applying PDPC.

[477] When wide-angle intra prediction is applied to the current block, the PDPC weighting value may be determined considering the shape of the coding block.

[478] For example, when the current block has a non-square shape, the width of which is greater than the height according to the position of the first prediction sample, there may be a case in which the upper reference sample located at the upper right of the first prediction sample is closer to the first prediction sample than the left reference sample located at the lower left of the first prediction sample. Accordingly, when correcting the first prediction sample, the weighting value applied to the upper reference sample may be set to be larger than the weighting value applied to the left reference sample.

[479] On the other hand, when the current block has a non-square shape whose height is greater than the width according to the position of the first prediction sample, there may be a case in which the left reference sample located at the lower left of the first prediction sample is closer to the first prediction sample than the upper reference sample located at the upper right of the first prediction sample. Accordingly, when correcting the first prediction sample, the weighting value applied to the left reference sample may be set to be larger than the weighting value applied to the upper reference sample.

[480] Equation 25 shows an example of obtaining a PDPC weighting value when the intra prediction mode of the current block is a wide-angle intra prediction mode having an index greater than 66.

[481] [Equation 25]

[482] Equation 26 shows an example of obtaining a PDPC weighting value when the intra prediction mode of the current block is a wide-angle intra prediction mode having an index that is less than 0.

[483] [Equation 26]

[484] The PDPC weighting value may be determined based on the ratio of the current block. The ratio of the current box represents the ratio of the width and height of the current box and can be determined as shown in Equation 27.

[485] [Equation 27]

[486] According to the intra prediction mode of the current block, the method for obtaining the PDPC weighting value may be determined in various ways.

[487] For example, equations 28 and 29 show an example of obtaining a PDPC weighting value when the intra prediction mode of the current block is the DC mode. In particular, Equation 28 is an example of a case where the current box has a non-square shape whose width is larger than the height, and Equation 29 is an example of a case where the current box has a non-square shape whose height is larger than the width.

[488] [Equation 28]

[489] [Equation 29]

[490] Equation 30 shows an example of obtaining a PDPC weighting value when the intra prediction mode of the current block is a wide-angle intra prediction mode having an index greater than 66.

[491] [Equation 30]

[492] Equation 31 shows an example of obtaining a PDPC weighting value when the intra prediction mode of the current block is a wide-angle intra prediction mode having an index that is less than 0.

[493] [Equation 31]

[494] The resulting afterimage can be obtained by subtracting the prediction video from the original video. In this case, when the residual video is changed to the frequency domain, the subjective video quality is not significantly reduced, although the high frequency components are removed from the frequency components. Accordingly, when the values of the high frequency components are converted to small or the values of the high frequency components are set to 0, there is an effect of increasing the compression efficiency without generating significant visual distortion. Reflecting this characteristic, the current block can be transformed to decompose the residual video into 2D frequency components. The transformation may be performed using a transformation method such as discrete cosine transform (DCT) or discrete sine transform (DST).

[495] The DCT decomposes (or transforms) the residual video into 2D frequency components using a cosine transform, and the DST decomposes (or transforms) the residual video into 2D frequency components using a sine transform. As a result of the conversion of the residual video, the frequency components can be expressed as the base video. For example, when a DCT is performed on an N×N block, N2 base circuit components can be obtained. The size of each of the base circuit components included in the N×N block can be obtained by transformation. According to the conversion method used for this, the base circuit component value may be referred to as a DCT coefficient or a DST coefficient.

[496] The DCT conversion method is mainly used to convert video in which many non-zero low frequency components are distributed. The DST conversion method is mainly used for videos in which many high frequency components are distributed.

[497] The residual video may be converted using a conversion method other than DCT or DST.

[498] Hereinafter, the transformation of the residual video into two-dimensional frequency components will be called two-dimensional video transformation. In addition, the size of the base circuit components resulting from the transformation is called the transformation factor. 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 factor may indicate the size of the base circuit component generated as a result of the second transform.

[499] A conversion method may be defined for each block. The transform method may be determined based on at least one of the current block predictive coding mode, the current block size, and the current block shape. For example, when the current block is encoded in the intra prediction mode and the size of the current block is smaller than N×N, the transformation may be performed using the DST transformation method. On the other hand, when the above conditions are not satisfied, the conversion can be performed using the DCT conversion method.

[500] 2D video conversion may not be performed for some blocks of residual video. Failure to perform a 2D video conversion may be referred to as a conversion skip. When a transform skip is applied, quantization can be applied to the residual coefficients that have not been transformed.

[501] After converting the current block using DCT or DST, the converted current block can be converted again. In this case, a transform based on the DCT or DST may be defined as the first transform, and re-transforming the block to which the first transform has been applied can be defined as the second transform.

[502] The first transformation may be performed using any of a plurality of candidate transformation bases. For example, the first conversion may be performed using any of DCT2, DCT8, or DCT7.

[503] Different transformation bases may be used for the horizontal direction and the vertical direction. Information indicating a combination of a transformation base in the horizontal direction and a transformation base in the vertical direction may be transmitted via a bitstream.

[504] The elements for performing the first transformation and the second transformation may be different. For example, the first transformation may be performed on an 8x8 block, and the second transformation may be performed on a 4x4 subblock of the transformed 8x8 block. In this case, the transformation coefficients of the residual portions on which the second transformation has not been performed may be set to 0.

[505] Alternatively, the first transformation may be performed on the 4×4 block, and the second transformation may be performed on the 8×8 region containing the transformed 4×4 block.

[506] Information indicating whether the second conversion has been performed may be transmitted via a bitstream.

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

[508] Alternatively, the second transformation may be allowed only when the transformation in the horizontal direction and the transformation in the vertical direction use a predetermined transformation basis. For example, when the DCT2 transformation base is used for the transformation in the horizontal direction and the transformation in the vertical direction, the second transformation may be allowed.

[509] Alternatively, whether the second transform should be performed may be determined based on the number of non-zero transform coefficients of the current block. For example, it may be set not to use the second transform when the number of non-zero transform coefficients of the current block is less than or equal to the threshold, and may be set to use the second transform when the number of non-zero transform coefficients of the current block is greater than the threshold. It may be set to use the second transform only when the current block is encoded with intra prediction.

[510] Based on the shape of the current block, the size or shape of the sub-block on which the second transformation will be performed can be determined.

[511] FIGS. 23 and 24 are views showing the sub-block on which the second transformation will be performed.

[512] When the current block has a square shape, the second transformation may be performed on a sub-block having a size of N×N, from the top left of the current block after the first transformation is performed. For example, when the current block is an 8×8 coding block, a second transformation may be performed on a subblock having a size of 4×4 to the top left of the current block after the first transformation is performed on the current block (see FIG. 23).

[513] When the current block has a non-square shape, the width of which is at least 4 times greater than the height, the second transformation can be performed on a subblock of size (kN)×4 kN) from the top left of the current block after the first transformation is performed. For example, when the current block is 16×4 non-square, the second transformation may be performed on the 2×8 subblock from the top left of the current block after the first transformation is performed on the current block (see FIG. 24(a)).

[514] When the current block has a non-square shape, the height of which is at least 4 times greater than the width, the second transformation can be performed on the (4 kN)×(kN) subblock from the top left of the current block after the first transformation is performed. For example, when the current block is 16×4 non-square, the second transformation may be performed on the 2×8 subblock from the top left of the current block after the first transformation is performed on the current block (see FIG. 24(b)).

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

[516]

[517] Information indicating the conversion type of the current block may be transmitted via a bitstream. The information may be tu_mts_idx index information indicating one of the combinations of a transformation type for the horizontal direction and a transformation type for the vertical direction.

[518] A transformation basis for the vertical direction and a transformation basis for the horizontal direction may be determined based on the conversion candidate types indicated by the index information tu_mts_idx. Tables 7 and 8 show combinations of conversion types according to tu_mts_idx.

[519] [Table 7]

[520] [Table 8]

[521] The type of transformation can be defined as any of the following transformations: DCT2, DST7, DCT8, and skip. Alternatively, a conversion type candidate combination may be composed using only the conversion stems, except for skipping the conversion.

[522] In the case where table 7 is used, when tu_mts_idx is equal to 0, a conversion skip may be applied in the horizontal direction and the vertical direction. When tu_mts_idx is 1, DCT2 can be applied in the horizontal direction and the vertical direction. When tu_mts_idx is 3, DCT8 may be applied in the horizontal direction and DCT7 may be applied in the vertical direction.

[523] In the case where table 8 is used, when tu_mts_idx is 0, DCT2 can be applied in the horizontal direction and the vertical direction. When tu_mts_idx is equal to 1, a transform skip can be applied in the horizontal direction and the vertical direction. When tu_mts_idx is 3, DCT8 may be applied in the horizontal direction and DCT7 may be applied in the vertical direction.

[524] Whether or not the index information should be encoded may be determined based on at least one of the size, shape, and number of non-zero coefficients of the current block. For example, when the number of non-zero coefficients is equal to or less than a threshold value, no index information is transmitted, and a default transform type can be applied to the current block. In this case, the default conversion type may be DST7. Alternatively, the default mode may change according to the size, shape, or intra prediction mode of the current block.

[525] The threshold value may be determined based on the size or shape of the current block. For example, when the size of the current block is less than or equal to 32x32, the threshold may be set to 2, and when the current block is greater than 32x32 (for example, when the current block is a 32x64 or 64x32 coding block), the threshold may be set to 4.

[526] A plurality of lookup tables may be previously stored in the encoder/decoder. In the plurality of lookup tables, at least one of the index value assigned to the conversion type combination candidates, the conversion type combination candidate type, and the number of conversion type combination candidates may be different.

[527] The lookup table for the current block may be selected based on at least one of the size of the current block, the shape of the current block, the predictive coding mode of the current block, the intra prediction mode of the current block, whether a second transform has been applied, and whether a skip transform has been applied to an adjacent block.

[528] For example, when the size of the current block is 4x4 or less, or when the current block is encoded with inter-picture prediction, a lookup table of table 7 can be used, and when the size of the current block is larger than 4x4, or when the current block is encoded with intra prediction, a lookup table of table 8 can be used.

[529] Alternatively, information indicative of any of a plurality of lookup tables may be transmitted via a bitstream. The decoder may select a lookup table for the current block based on the information.

[530] As another example, an index assigned to a candidate combination of transform types can be adaptively determined based on at least one of the size of the current block, the shape of the current block, the predictive coding mode of the current block, the intra prediction mode of the current block, whether a second transform has been applied, and whether a skip transform has been applied to an adjacent block. For example, when the size of the current block is 4×4, the index assigned to the transform skip may have a value that is less than the value of the index assigned to the transform skip when the size of the current block is greater than 4×4. In particular, when the size of the current block is 4x4, index 0 may be assigned to a transformation skip, and when the current block is greater than or equal to 4x4 and less than or equal to 16x16, an index greater than 0 (e.g., index 1) may be assigned to a transformation skip. When the current block is larger than 16×16, a maximum value (eg, 5) may be assigned to the transform skip index.

[531] Alternatively, when the current block is encoded with inter-picture prediction, index 0 may be assigned to a transform skip. When the current block is encoded with intra prediction, an index that is greater than 0 (eg, index 1) may be assigned to a transform skip.

[532] Alternatively, when the current block is a 4x4 block encoded with inter-picture prediction, index 0 may be assigned to a transform skip. On the other hand, when the current block is not encoded with inter-picture prediction or the current block is larger than 4×4, an index with a value greater than 0 (eg, index 1) may be assigned to a transform skip.

[533] Candidate transformation type combinations other than the transformation type combinations listed in Tables 7 and 8 can be defined and used. For example, a transformation type candidate combination can be used in which a transformation skip is applied to any one of a transformation in the horizontal direction and a transformation in the vertical direction, and a transformation basis such as DCT7, DCT8, or DST2 is applied to the other. At this time, whether a transform skip should be used as a transform candidate type for the horizontal direction or the vertical direction may be determined based on at least one of the size (e.g., width and/or height), shape, predictive coding mode, and intra prediction mode of the current block.

[534] Alternatively, information indicating whether a particular conversion candidate type is available may be transmitted via a bitstream. For example, a flag may be passed indicating whether a conversion skip can be used as a conversion candidate type for the horizontal direction and the vertical direction. According to the flag, it can be determined whether a particular conversion type combination candidate is included in the set of conversion type candidate combinations.

[535] Alternatively, whether the specified transformation candidate type applies to the current block may be transmitted via a bitstream. For example, a cu_mts_flag flag may be transmitted indicating whether DCT2 should be applied for the horizontal direction and the vertical direction. When the value of cu_mts_flag is 1, DCT2 can be set as the basis of the transformation for the vertical direction and the horizontal direction. When the value of cu_mts_flag is 0, DCT8 or DST7 can be set as the conversion base for vertical direction and horizontal direction. Alternatively, when the value of cu_mts_flag is 0, tu_mts_idx information indicating any one of a plurality of candidate conversion type combinations may be transmitted.

[536] When the current block has a non-square shape whose width is greater than the height, or a non-square shape whose height is greater than the width, the cu_mts_flag encoding may be omitted, and the value of cu_mts_flag may be regarded as 0.

[537] The number of available candidate transform type combinations may be set differently according to the size, shape, or intra prediction mode of the current block. For example, when the current block is square, three or more candidate transformation type combinations may be used, and when the current block is non-square, two candidate transformation type combinations may be used. Alternatively, when the current block has a square shape, only candidate transformation type combinations whose transformation type for the horizontal direction is different from the transformation type for the vertical direction can be used from among the candidate transformation type combinations.

[538] When there are three or more candidate transformation type combinations that the current block can use, tu_mts_idx index information indicating one of the candidate transformation type combinations may be transmitted. On the other hand, when there are two candidate transformation type combinations that the current block can use, an mts_flag flag indicating either of the candidate transformation type combinations may be transmitted. Table 9 shows a process for encoding information for indicating candidate combinations of transformation types according to the shape of the current block.

[539] [Table 9]

[540] The conversion type candidate combination indices may be permuted (or reordered) according to the shape of the current block. For example, the indices assigned to candidate transformation type combinations when the current block is square may be different from the indices assigned to candidate transformation type combinations when the current block is non-square. For example, when the current block is square, the transform type combination may be selected based on Table 10 shown below, and when the current block is non-square, the transform type combination may be selected based on Table 11 shown below.

[541] [Table 10]

[542] [Table 11]

[543] The transform type may be determined based on the number of non-zero coefficients in the horizontal direction or the number of non-zero coefficients in the vertical direction of the current block. Here, the number of non-zero coefficients in the horizontal direction indicates the number of non-zero coefficients included in the 1×N block (where N is the width of the current block), and the number of non-zero coefficients in the vertical direction indicates the number of non-zero coefficients included in the N×1 block (where N is the height of the current block). When the maximum value of the non-zero coefficient in the horizontal direction is less than or equal to the threshold value, the first transformation type may be applied in the horizontal direction, and when the maximum value of the non-zero coefficient in the horizontal direction is greater than the threshold value, the second transformation type may be applied in the horizontal direction. When the maximum value of the non-zero coefficient in the vertical direction is less than or equal to the threshold value, the first type of transformation may be applied in the vertical direction, and when the maximum value of the non-zero coefficient in the vertical direction is greater than the threshold value, the second type of transformation may be applied in the vertical direction.

[544] Fig. 25 is a view for describing examples of determining the conversion type of the current block.

[545] For example, when the current block is encoded with intra prediction, and the maximum value of the non-zero coefficient in the horizontal direction of the current block is 2 or less (see FIG. 25(a)), the transform type in the horizontal direction can be determined as DST7.

[546] When the current block is encoded with intra prediction, and the maximum value of the non-zero coefficient in the vertical direction of the current block is greater than 2 (see FIG. 25(b)), DCT2 or DCT8 may be determined as the transform type in the vertical direction.

[547]

[548] Information indicating whether to explicitly determine the conversion type of the current block based on the information transmitted from the bitstream may be transmitted by the bitstream. For example, sps_explicit_intra_mts_flag information indicating whether explicit definition of a transform type for an intra prediction encoded block and/or sps_explicit_inter_mts_flag information indicating whether explicit definition of a transformation type for an inter-picture encoded block is allowed can be transmitted at the sequence level.

[549] When it is allowed to explicitly define the transformation type, the transformation type of the current block may be determined based on the tu_mts_idx index information transmitted from the bitstream. On the other hand, when explicitly determining the type of transformation is not allowed, the type of transformation can be determined based on at least one of the size of the current block, the shape of the current block, whether the transformation of a sub-block element is allowed, and the position of the sub-block containing a non-zero transformation coefficient. For example, the transformation type in the horizontal direction of the current block may be determined based on the width of the current block, and the transformation type in the vertical direction of the current block may be determined based on the height of the current block. For example, when the width of the current block is less than 4 or greater than 16, the transformation type in the horizontal direction may be determined as DCT2. Otherwise, the conversion type in the horizontal direction can be defined as DST7. When the height of the current block is less than 4 or greater than 16, the transformation type in the vertical direction can be specified as DCT2. Otherwise, the conversion type in the vertical direction can be defined as DST7. Here, in order to determine the transform type in the horizontal direction and the transform type in the vertical direction, threshold values comparable to the width and height may be determined based on at least one of the size, shape, and intra prediction mode of the current block.

[550] Alternatively, when the current block has a square shape whose height and width are the same, the transformation type in the horizontal direction and the transformation type in the vertical direction are set to be the same, while when the current block has a non-square shape whose height and width are different, the transformation type in the horizontal direction and the transformation type in the vertical direction can be set to be different from each other. For example, when the width of the current block is larger than the height, the transformation type in the horizontal direction may be determined as DST7, and the transformation type in the vertical direction may be determined as DCT2. When the height of the current block is larger than the width, the transformation type in the vertical direction may be determined as DST7, and the transformation type in the horizontal direction may be determined as DCT2.

[551] The number and/or type of conversion candidate types or the number and/or type of conversion type candidate combinations may vary according to whether explicit definition of the conversion type is allowed. For example, when explicitly specifying a conversion type is allowed, DCT2, DST7, and DCT8 can be used as candidate conversion types. Accordingly, each of the horizontal direction conversion type and the vertical direction conversion type can be set to DCT2, DST8, or DCT8. When an explicit definition of a conversion type is not allowed, only DCT2 and DST7 can be used as candidate conversion types. Accordingly, each of the horizontal direction conversion type and the vertical direction conversion type can be defined as DCT2 or DST7.

[552] A coding block or a transformation block is partitioned into a plurality of sub-blocks, and a transformation may be performed on each of the plurality of sub-blocks. For example, when the subdivision intra prediction coding method described above is applied to a coding block, the coding block is partitioned into a plurality of subblocks, and a transformation can be performed on each of the plurality of subblocks.

[553] The sub-block conversion types may be the same. For example, when a transform type is determined for the first sub-block of a plurality of sub-blocks, the first sub-block transform type may also be applied to other sub-blocks. Alternatively, a transform type for a coding block is determined, and a transform type of the coding block may be defined as a sub-block transform type.

[554] As another example, conversion types from a plurality of sub-blocks may be individually determined. The transformation type of each sub-block may be determined based on the information transmitted for each sub-block. For example, index information tu_mts_idx may be transmitted for each sub-block. The index information tu_mts_idx may indicate any of a plurality of combinations of a transform type for the horizontal direction and a transform type for the vertical direction. According to the value of tu_mts_idx, the transformation type in the horizontal direction and the transformation type in the vertical direction can be defined as DCT2, DST7, or DCT8. Based on the index information tu_mts_idx, it can be determined whether the transformation type in the horizontal direction and the transformation type in the vertical direction are the same.

[555] Information indicating whether the current sub-block uses a transform type that is the same as the previous sub-block's transform type may be transmitted. When the information indicates that a transform type is used that is the same as that of the previous sub-block, the encoding of the tu_mts_idx index information for the current sub-block may be skipped, and the transform type of the previous sub-block may be applied to the current sub-block. On the other hand, when the information indicates that a transform type is used that is different from that of the previous sub-block, the tu_mts_idx index information for the current sub-block may be encoded. In this case, the index information of the current sub-block may indicate any of the remaining combinations of transformation types except for the combination of transformation types indicated by the index information of the previous sub-block.

[556] Alternatively, it may be set to not allow explicit definition of the transform type when a coding block is split into multiple sub-blocks. When explicit definition of the type of transformation is allowed, the type of transformation may be determined based on information about the indexes tu_mts_idx. On the other hand, when explicit definition of the type of transformation is not allowed, the type of transformation can be determined considering at least one of the size, shape, and position of the sub-block containing the non-zero coefficient.

[557] FIG. 26 is a view showing an example of determining a sub-block transformation type.

[558] FIG. 26 shows an example in which the height to width ratio of the subblock is 1:2 or 2:1.

[559] A transformation type in the horizontal direction and a transformation type in the vertical direction may be determined based on the width and height of each sub-block. For example, as shown in the examples in FIGS. 26(a) and 26(b), when the sub-block width is smaller than the threshold value, the first transform type (eg, DCT2) can be used as the transform type in the horizontal direction. On the other hand, when the sub-block width is greater than or equal to the threshold value, the second transform type (eg, DST7) can be used as the transform type in the horizontal direction.

[560] In addition, when the sub-block height is less than the threshold value, the first transform type (eg, DCT2) can be used as the transform type in the vertical direction. On the other hand, when the sub-block width is greater than or equal to the threshold value, the second transform type (eg, DST7) can be used as the transform type in the vertical direction.

[561] Here, the threshold may be a natural number such as 2, 4, or 8. The threshold may be variably determined based on at least one of the size, shape, intra prediction mode, and coding block predictive coding mode. Alternatively, the information for determining the threshold value may be transmitted via a bit stream.

[562] In the example described above, although the case of comparing the sub-block width and height with one threshold value is shown as an example, the transform type can be determined by comparing the sub-block width and height with two threshold values. For example, when the sub-block width is smaller than the first threshold or larger than the second threshold, the transform type in the horizontal direction may be determined as DCT2. Otherwise, the conversion type in the horizontal direction can be defined as DST7. Further, when the sub-block height is smaller than the first threshold value or larger than the second threshold value, the transform type in the vertical direction may be determined as DCT2. Otherwise, the conversion type in the vertical direction can be defined as DST7. The second threshold is a natural number that is greater than the first threshold, and the first threshold may be a natural number such as 2, 4, or 8, and the second threshold may be a natural number, such as 8, 16, or 32.

[563] As another example, when the sub-block has a square shape whose height and width are the same, the transformation type in the horizontal direction and the transformation type in the vertical direction can be set to be the same, while when the sub-block has a non-square shape whose height and width are different, the transformation type in the horizontal direction and the transformation type in the vertical direction can be set to be different from each other. For example, when the width of the sub-block is larger than the height, the transformation type in the horizontal direction may be determined as DST7, and the transformation type in the vertical direction may be determined as DCT2. When the height of the sub-block is larger than the width, the transformation type in the vertical direction may be determined as DST7, and the transformation type in the horizontal direction may be determined as DCT2.

[564] The values of the residual coefficients included in at least one of the plurality of sub-blocks may be set to 0. Here, the residual coefficient refers to a transform coefficient generated by a transform, a transform skip coefficient generated by a transform skip, or a quantized coefficient generated by quantizing a transform coefficient or coefficient. For example, the values of the residual coefficients included in a subblock spaced from a coding block boundary by a predetermined distance or more may be set to 0.

[565] FIG. 27 is a view for describing an example in which the subblock residual coefficients are set to 0.

[566] In the example shown in FIG. 27, the coded block flag (CBF) indicates whether there is a non-zero residual coefficient in the subblock. When the CBF value is 0, it indicates that there is no non-zero residual coefficient in the sub-block, and when the CBF value is 1, it indicates that there is a non-zero residual coefficient in the sub-block.

[567] When the distance from the coding block boundary to the subblock is greater than or equal to the threshold value, the residual coefficients included in the subblock may be set to 0. In this case, the distance from the coding block boundary to the subblock may be obtained based on the first sample located on the coding block boundary and the second sample included in the subblock. For example, the first sample may be the sample located in the upper left corner of the coding block, the sample located in the lower left corner, the sample located in the left middle, the sample located in the upper right corner, the sample located in the lower right corner, the sample located in the right middle, the sample located in the upper middle, and the sample located in the lower middle. The second sample may be the sample located in the top left corner of the subblock, the sample located in the lower left corner, the sample located in the left middle, the sample located in the upper right corner, the sample located in the lower right corner, the sample located in the right middle, the sample located in the upper middle, and the sample located in the lower middle.

[568] The threshold value may be determined based on at least one of the size and shape of the coding block, the number of subblocks included in the coding block, and the size of the subblock. Alternatively, the information for determining the threshold value may be transmitted via a bitstream.

[569] For example, when splitting in the vertical direction is applied to the current block, the residual coefficients of the subblocks whose distance from the left border of the coding block is equal to or greater than the threshold value can be set to 0. When the coding block size is 64 and the threshold value is 32, as shown in the example of FIG. left border of the coding block may be set to 0.

[570] Alternatively, when splitting in the horizontal direction is applied to the current block, the residual coefficients of the sub-blocks whose distance from the upper boundary of the coding block is equal to or greater than the threshold value may be set to 0. When the coding block size is 64 and the threshold value is 32, as shown in the example in FIG. from the upper bound of the coding block, may be set to 0.

[571] Unlike the example shown in the figures, the residual coefficients included in sub-blocks whose distance from the coding block boundary is less than the threshold value can be set to 0.

[572] Alternatively, the residual coefficients of the remaining subblocks, except for the subblock located at the preset position, of the plurality of subblocks may be set to 0. For example, when splitting in the vertical direction is applied to a coding block, the residual coefficients of the remaining subblocks, except for the leftmost or rightmost subblock, of the plurality of subblocks may be set to 0. Alternatively, when partitioning in the horizontal direction is applied to a coding block, the residual coefficients of the remaining subblocks, except for a sub-block located above or below, of the plurality of sub-blocks can be set to 0.

[573] Information indicating whether there is a non-zero coefficient, such as CBF encoding, may be omitted for sub-blocks. When CBF encoding is omitted, then whether a non-zero residual coefficient is included in each sub-block may be determined considering the distance between the coding block boundary and the sub-block or sub-block position. For example, in the example shown in FIG. 27, the CBF values of sub-block 0 and sub-block 1 (sub-CU0, sub-CU1) can be obtained as 1, and the CBF values of sub-block 2 and sub-block 3 (sub-CU2, sub-CU3) can be obtained as 0.

[574] Transformation and/or quantization may be performed on sub-blocks containing a non-zero coefficient, while transformation and quantization may be omitted for sub-blocks that do not contain a non-zero coefficient.

[575] As another example, information indicating that a transformation has been performed on only a partial portion of an encoding block or a transform block may be encoded and transmitted. The information may be cu_sbt_flag of a 1-bit flag. When the flag is 1, it indicates that the transformation is performed on only some of the plurality of subblocks generated by splitting the coding block or transform block, and when the flag is 0, it indicates that the transformation is performed without splitting the coding block or transform block into subblocks.

[576] A method of performing transformation on only a partial portion of a coding block can be allowed only when the intra subdivision coding method is applied to the coding block. Accordingly, cu_sbt_flag can be encoded and transmitted only when the intra subdivision coding method is applied to a coding block. When the value of cu_sbt_flag is 1, transformation is performed on only some sub-blocks of the plurality of sub-blocks generated by splitting a coding block or a transformation block, and the residual coefficients of the remaining sub-blocks may be set to 0. When the value of cu_sbt_flag is equal to 1, transformation may be performed on all sub-blocks.

[577] Alternatively, when the subdivision intra-coding method is applied to a coding block, the cu_sbt_flag encoding may be skipped, and the value of cu_sbt_flag may be set to 1.

[578] As another example, only when the coding block predictive coding mode is inter-picture prediction or current picture anchoring, a method for performing transformation on only a partial portion of the coding block can be allowed. When a coding block is encoded by inter-picture prediction or by reference to a current picture, information indicating whether a transformation has been performed on only a partial section of the coding block may be encoded and transmitted. When the transformation is performed on only a partial portion of a coding block, information indicating the partition type of the coding block may be encoded and transmitted. The information indicating the partitioning type of the coding block may include at least one of information indicating whether the coding block is divided into four subblocks, information indicating the splitting direction of the coding block, and information indicating the number of subblocks. For example, when cu_sbt_flag is 1, a cu_sbt_quadtree_flag flag may be transmitted indicating whether the coding block is split into four subblocks. When cu_sbt_quadtree_flag is equal to 1, this indicates that the coding block is divided into four sub-blocks. For example, a coding block may be divided into four subblocks using three vertical lines or three horizontal lines, or a coding block may be divided into four subblocks using one vertical line and one horizontal line. When cu_sbt_quadtree_flag is 0, this indicates that the coding block is split into two sub-blocks. For example, a coding block may be split into two sub-blocks using one vertical line and one horizontal line.

[579] In addition, a flag indicating the splitting direction of a coding block may be transmitted via a bitstream. For example, a cu_sbt_horizontal_flag flag indicating whether splitting in the horizontal direction is applied to the coding block may be encoded and transmitted. When the value of cu_sbt_horizontal_flag is 1, it indicates that the split in the horizontal direction is applied to the coding block, and when the value of cu_sbt_horizontal_flag is 0, it indicates that the split in the vertical direction is applied to the coding block.

[580] Information indicating the position of a sub-block in which there is no non-zero coefficient, or a sub-block in respect of which no transformation is performed, can be transmitted via a bitstream. Based on the information, a sub-block on which transformation and/or quantization is performed and a sub-block on which transformation and/or quantization is omitted can be determined.

[581] FIG. 28 is a view showing an example in which the position of a sub-block on which transformation and/or quantization has been performed is indicated based on information transmitted by the bitstream.

[582] An sbt_upleft_flag flag may be transmitted indicating whether there is a non-zero coefficient at a particular position or in the first subblock. When the value of sbt_upleft_flag is 1, it indicates that the transformation and/or quantization is performed on the subblock located above or to the left of the coding block, and the transformation and/or quantization is not performed on the subblock located to the right or below the coding block. When the value of sbt_upleft_flag is 0, it indicates that the transformation and/or quantization is performed on the subblock located above or to the left of the coding block, and the transformation and/or quantization is not performed on the subblock located to the right or below the coding block.

[583] When a coding block is split into four subblocks, sbt_upleft_flag may indicate that transformation and/or quantization is performed on N subblocks. For example, when the value of sbt_upleft_flag is 1, it indicates that transformation and/or quantization is performed on two sub-blocks from the top or left, and when the value of sbt_upleft_flag is 0, it indicates that transformation and/or quantization is performed on two sub-blocks from the right or bottom.

[584] Unlike the example shown in the figure, the value of N can be set to 1 or 3.

[585] Residual subblock coefficients on which no transform and/or quantization is performed may be set to 0.

[586] The transformation type of the sub-block may be determined based on the splitting direction of the coding block and the position of the sub-block. For example, when a coding block is split in the vertical direction and a transformation is performed on a sub-block located on the left of the sub-blocks, the transformation type in the horizontal direction and the transformation type in the vertical direction may be set to be different. For example, the transformation type in the horizontal direction may be set to DCT8, and the transformation type in the vertical direction may be set to DST7. On the other hand, when a coding block is split in the vertical direction and a transformation is performed on a subblock located on the right of the subblocks, the transformation type in the horizontal direction and the transformation type in the vertical direction of the subblock can be set equally. For example, the conversion type in the horizontal direction and the conversion type in the vertical direction can be set to DST7.

[587] Alternatively, when a coding block is split in the horizontal direction, and the transformation is performed on the topmost subblock of the subblocks, the transformation type in the horizontal direction and the transformation type in the vertical direction may be set to be different. For example, the transformation type in the horizontal direction may be set to DST7, and the transformation type in the vertical direction may be set to DCT8. On the other hand, when a coding block is split in the horizontal direction and a transformation is performed on a sub-block located at the bottom of the sub-blocks, the transformation type in the horizontal direction and the transformation type in the vertical direction of the sub-block can be set equally. For example, the conversion type in the horizontal direction and the conversion type in the vertical direction can be set to DST7.

[588] Information indicating whether there is a non-zero coefficient, such as CBF encoding, may be omitted for subblocks. When CBF encoding is omitted, then whether a non-zero residual coefficient is included in each sub-block may be determined based on the position of the block on which the transformation is performed. For example, when the sbt_upleft_flag value is 0, the CBF values of the left or top subblocks can be obtained as 0, and the CBF value of the right or bottom subblocks can be obtained as 1. Alternatively, when the sbt_upleft_flag value is 1, the CBF value of the left or top subblocks can be obtained as 1, and the CBF value of the right or bottom subblocks can be obtained as received as 0.

[589] The restored count of the sub-block on which the transformation is performed can be obtained from the sum of the prediction count and the residual count. On the other hand, in a sub-block for which a transformation is skipped, the prediction count may be set as a recovered count. A constant value can be obtained with a quantization parameter, and the quantization parameter can be defined as a value from 1 to 63.

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

[591]

[592] When a reconstructed block of the current block is obtained, the loss of information occurring in the quantization and encoding process can be reduced by loop filtering. An in-loop filter may comprise at least one of a de-blocking filter, a sample-adaptive offset (SAO) filter, and an adaptive loop filter (ALF). Further, the reconstructed block before applying the filter in the loop is called the first reconstructed block, and the reconstructed block after applying the filter in the loop is called the second reconstructed block.

[593] The second recovered block may be obtained by applying at least one of the deblocking filter, SAO, and ALF to the first recovered block. In this case, SAO or ALF can be applied after the deblocking filter has been applied.

[594] The de-block filter is designed to reduce video degradation (block artifact) at a block boundary that occurs when quantization is performed on individual blocks. To apply a deblocking filter, a block quality score (BS) between the first reconstructed block and an adjacent reconstructed block can be determined.

[595] FIG. 29 is a flowchart showing a block quality determination process.

[596] In the example shown in FIG. 29, P denotes the first reconstructed block, and Q denotes an adjacent reconstructed block. In this case, the adjacent reconstructed block may be a block adjacent to the left side or top side of the current block.

[597] In the example shown in FIG. 29, the block quality score is determined considering the P and Q predictive coding modes, whether a non-zero transform coefficient is included, whether inter-picture prediction is performed using the same reference picture, and whether the motion vector difference value is greater than or equal to a threshold value.

[598] Whether a deblocking filter should be applied can be determined based on the block quality. For example, when the block quality score is 0, filtering may not be performed.

[599] SAO is designed to reduce the ring phenomenon (ring artifact) that occurs when quantization is performed in the frequency domain. SAO may be performed by adding or subtracting an offset determined from the schema of the first reconstructed video. The method for determining the offset includes edge offset (EO) or band offset (BO). EO denotes a method for determining the current sample offset according to the surrounding pixel pattern. BO refers to the way in which a conventional offset is applied to a set of pixels that have similar brightness values in a region. In particular, the brightness of pixels can be divided into 32 equal sections, and pixels having similar brightness values can be set as one set. For example, four adjacent bands of 32 bands can be set as one group, and the same offset value can be applied to the samples belonging to the four bands.

[600] ALF is a method for generating a second reconstructed video by applying a filter having a predetermined size/shape to a first reconstructed video or a reconstructed video to which a deblocking filter has been applied. Equation 32 shows an example of ALF application.

[601] [Equation 32]

[602] Any of the predefined candidate filters may be selected by an image element, a code tree element, a coding block, a prediction block, or a transformation block. Each of the candidate filters may differ in either size or shape.

[603] FIG. 30 is a view showing predefined candidate filters.

[604] As shown in the example of FIG. 30, at least one of 5×5, 7×7, and 9×9 diamond shapes can be selected.

[605] Only a 5x5 diamond shape can be used for the chrominance component.

[606]

[607] The application of the embodiments described above focused on a decoding process or an encoding process to an encoding process or a decoding process is included within the scope of the present invention. Changing the embodiments described in a predetermined order in an order other than the order described is also included within the scope of the present invention.

[608] Although the above embodiments have been described based on a number of steps or flowcharts, this does not limit the order of execution in time of the present invention, and they can be performed simultaneously or in a different order if necessary. In addition, each of the components (e.g., elements, modules, or the like) constituting the block diagram in the embodiments described above may be implemented as a hardware device or software, or multiple components may be combined to be implemented as a single hardware device or software. The embodiments described above may be implemented in the form of program instructions that may be executed by various computer components and stored in a computer-readable storage medium. The computer-readable storage medium may contain program instructions, data files, data structures, and the like. independently or in combination. A computer-readable storage medium includes, for example, magnetic media such as hard disk, floppy disk and magnetic tape, optical storage media such as CD-ROM and DVD, magneto-optical storage media such as floppy optical disk, and hardware devices specifically configured to store and execute program instructions 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.

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

Claims (24)

1. Video decoding method, including: determination of the line of reference readings of the current block; determining whether there is a candidate intra prediction mode that is the same as the intra prediction mode of the current block; obtaining an intra prediction mode of the current block based on the determination; And performing intra prediction on the current block based on the reference sample line and the intra prediction mode, wherein at least one of the candidate intra prediction modes is obtained by adding or subtracting an offset to a maximum value from the top neighbor intra prediction mode of the current block and the left neighbor intra prediction mode of the current block; And a transformation type in the horizontal direction of the sub-block is determined based on the width of the sub-block, and a transformation type in the vertical direction of the sub-block is determined based on the height of the sub-block. 2. The method according to claim 1, characterized in that at least one of the candidate intra prediction modes is obtained by adding 2 to or subtracting from the maximum value when the difference between the intra prediction mode of the top neighbor block and the intra prediction mode of the left neighbor block is 64. 3. The method according to claim. 1, characterized in that it further includes the step of determining whether the current block should be split into a plurality of subblocks, while, when the current block is divided into a plurality of subblocks, the plurality of subblocks share one intra prediction mode, wherein the transformation type in the horizontal direction and the transformation type in the vertical direction of the sub-block are determined based on the shape of the sub-block. 4. The method of claim 3, wherein the inverse transformation is omitted for some of the plurality of sub-blocks. 5. Video encoding method, including: determination of the line of reference readings of the current block; determining whether there is a candidate intra prediction mode that is the same as the intra prediction mode of the current block; obtaining an intra prediction mode of the current block based on the determination; And performing intra prediction on the current block based on the reference sample line and the intra prediction mode, wherein at least one of the candidate intra prediction modes is obtained by adding or subtracting an offset to a maximum value from the top neighbor intra prediction mode of the current block and the left neighbor intra prediction mode of the current block; And a transformation type in the horizontal direction of the sub-block is determined based on the width of the sub-block, and a transformation type in the vertical direction of the sub-block is determined based on the height of the sub-block. 6. The method according to claim 5, characterized in that at least one of the candidate intra prediction modes is obtained by adding 2 to or subtracting from the maximum value when the difference between the intra prediction mode of the top neighbor block and the intra prediction mode of the left neighbor block is 64. 7. The method of claim 5, further comprising the step of determining whether the current block should be split into a plurality of subblocks, wherein, when the current block is divided into a plurality of subblocks, the plurality of subblocks share one intra prediction mode, wherein the transformation type in the horizontal direction and the transformation type in the vertical direction of the sub-block are determined based on the shape of the sub-block. 8. The method of claim 7, wherein the transformation is omitted for some of the plurality of sub-blocks.