RU2803065C2 - Method and device for intra-prediction in which prediction block is divided into sub-blocks and prediction in sub-blocks - Google Patents

Abstract

FIELD: video encoding and decoding.

SUBSTANCE: method and apparatus for intra-prediction is proposed, in which a prediction unit is divided into sub-blocks and predicted in sub-blocks. The video decoding method includes: determining whether to divide the current block into a plurality of sub-blocks; when the current block is divided into a plurality of sub-blocks, determining the division direction for the current block between the horizontal and vertical division direction and the number of sub-blocks based on the division information decoded from the bitstream and the width and height of the current block; restoring the current block by sequentially restoring sub-blocks that are indicated according to the split direction and the number of sub-blocks using intra-prediction; and setting a grid of N samples at regular intervals in the horizontal and vertical directions, and performing deblocking filtering among boundaries between sub-blocks in the current block that match the grid boundary.

EFFECT: capability of providing intra-prediction for dividing the prediction unit into sub-blocks in such a way as to place the reconstructed neighbouring samples used to predict the current sample so that it is closer to the current sample, and predict block sub-blocks using the general intra-prediction mode.

10 cl, 2 tbl, 14 dwg

Description

Technical field

[0001] The present invention, in some embodiments, relates to video encoding and decoding. More specifically, the present invention relates to a method and apparatus for intra-prediction in which a prediction unit is divided into sub-blocks and predicted in sub-blocks.

BACKGROUND OF THE ART

[0002] Since video data has a large data volume compared to audio data or still image data, a lot of hardware resources, including memory, are required to store or transmit the data in raw form before subjecting it to the compression process.

[0003] Accordingly, storage or transmission of video data typically involves compressing it using an encoder before the decoder can receive, decompress, and play back the compressed video data. Well-known video compression technologies include the H.264/AVC standard and the High Efficiency Video Coding (HEVC) standard, which improves H.264/AVC coding efficiency by approximately 40%.

[0004] However, the ever-increasing size, resolution, and frame rate of video images, and the resulting increase in the amount of data to be encoded, requires a new and improved compression method with higher encoding efficiency and higher image quality than known compression methods.

[0005] Meanwhile, in intra-prediction, prediction is performed with previously reconstructed samples located adjacent to the current block, where the adjacent sample used for intra-prediction is referred to as a reference sample. Typically, intra-prediction uses a reference sample to best predict all samples in the current block. For example, for a 16x16 block, 256, the values of the samples belonging to the 16x16 block are predicted using their neighboring samples. Since there is spatial correlation in video, the closer the current block sample is to the reference sample, the better the overall prediction results. Accordingly, current block samples adjacent to the reference samples may have accurate prediction values, but those that are far from the reference samples may result in inaccurate prediction values.

The essence of the invention

Technical problem

[0006] The present invention generally seeks to provide an intra-prediction method for dividing a prediction unit into sub-blocks so as to accommodate reconstructed neighboring samples used to predict the current sample to be closer to the current sample, and predicting sub-blocks of blocks using general mode of intra-prediction.

DISCLOSURE OF THE INVENTION

[0007] According to at least one aspect of the present invention, there is provided a video decoding method for reconstructing a current block using intra-prediction, comprising the step of determining whether to divide the current block into a plurality of sub-blocks; a step of determining, when the current block is divided into a plurality of sub-blocks, a division direction for the current block between the horizontal division direction and the vertical division direction, and determining the number of sub-blocks based on the division information decoded from the bitstream, and the width and height of the current block; a step of reconstructing the current block by sequentially reconstructing subblocks specified according to the division direction and the number of subblocks using intra-prediction; and the step of establishing a grid of N samples at equal intervals in the horizontal and vertical directions and performing deblocking filtering among the boundaries between subblocks in the current block, the boundaries being the same as the grid boundary.

[0008] According to another aspect of the present invention, a video decoding apparatus is provided for reconstructing a current block using intra-prediction. The video decoding apparatus includes means for determining whether a current block should be divided into a plurality of sub-blocks, means for determining when the current block is divided into a plurality of sub-blocks, a dividing direction for the current block between a horizontal dividing direction and a vertical dividing direction, and a number of sub-blocks based on the dividing information. decoded from the bit stream and the width and height of the current block, means for reconstructing the current block by sequentially reconstructing sub-blocks that are specified according to the division direction and number of sub-blocks using intra-prediction, and means for setting a grid of N samples at regular intervals. in the horizontal and vertical directions and performing deblocking filtering among the boundaries between subblocks in the current block, the boundaries being the same as the grid boundary.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In FIG. 1 is a diagram illustrating a video encoding apparatus that can implement the methods proposed by the present invention.

[0010] In FIG. 2 is a diagram explaining a block division method using the QTBTTT structure.

[0011] In FIG. 3A is a diagram illustrating a variety of intra-prediction modes.

[0012] In FIG. 3B is a diagram illustrating a variety of intra-prediction modes, including wide-angle intra-prediction modes.

[00013] In FIG. 4 is a diagram illustrating a video decoding apparatus configured to implement the methods proposed by the present invention.

[0014] In FIG. 5A-5C are diagrams illustrating types in which a current block can be divided into a plurality of sub-blocks when the current block is intra-prediction encoded according to at least one embodiment of the present invention.

[0015] In FIG. 6 is a functional block diagram illustrating an exemplary configuration of an intra-prediction unit in a video encoding apparatus according to at least one embodiment of the present invention.

[0016] In FIG. 7 is a flowchart of a method performed by a video encoding apparatus for intra-predictive encoding of a current block of video according to at least one embodiment of the present invention.

[0017] In FIG. 8 is a functional block diagram illustrating an exemplary configuration of an intra-prediction unit in a video encoding apparatus according to at least one embodiment of the present invention.

[0018] In FIG. 9 is a flowchart of a method performed by a video decoding apparatus for decoding a current intra-prediction encoded block from a coded video bit stream, according to at least one embodiment of the present invention.

[0019] In FIG. 10A and 10B are diagrams illustrating a coding block undergoing reconstruction sequentially in units of subblocks when generating a subblock prediction subblock.

IMPLEMENTATION OF THE INVENTION

[0020] In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, like reference numerals preferably refer to like elements even though the elements are shown in different drawings. In addition, for the sake of clarity and brevity, the following description of certain embodiments has omitted detailed descriptions of related known components and functions insofar as they obscure the subject matter of the present invention.

[0021] In FIG. 1 is a diagram illustrating a video encoding apparatus that can implement the methods proposed by the present invention. Next, the form encoding apparatus and subcomponents of the apparatus will be described with reference to FIG. 1.

[0022] The video encoding device may be configured to include an image division block 110, a prediction block 120, a subtraction block 130, a transform block 140, a quantization block 145, a reordering block 150, an entropy encoding block 155, an inverse quantization block 160, a inverse conversion 165, adder 170, filtering unit 180, and memory 190.

[0023] The corresponding components of the video encoding device may be implemented as hardware or software, or a combination of hardware and software. In addition, the function of each component may be implemented in software, and the software function of each component may be implemented to be executed by a microprocessor.

[0024] A video consists of multiple images. Each image is divided into multiple regions, and coding is performed for each region. For example, one image is divided into one or more tiles and/or sections. Here, one or more tiles may be defined as a group of tiles. Each tile and/or section is divided into one or more coding tree units (CTUs). And each CTU is divided into one or more coding units (CU) in a tree structure. Information applied to the corresponding CUs is encoded as CU syntax, and information generally applied to CUs included in a single CTU is encoded as CTU syntax. In addition, information typically applied to all blocks in one section is encoded as section header syntax, and information applied to all blocks constituting one image is encoded in picture parameter set (PPS) or image header. In addition, information typically referenced by multiple images is encoded in a Sequence Parameter Set (SPS). In addition, information typically referenced by one or more SPSs is encoded in a Video Parameter Set (VPS). In the same way, information typically applied to one tile or group of tiles may be encoded as tile header or tile group header syntax.

[0025] The image division unit 110 determines the unit size of the CTU coding tree. CTU size information (CTU size) is encoded as SPS set or PPS set syntax and transmitted to the video decoding device.

[0026] The image division unit 110 divides each image constituting a video into a plurality of CTUs having a predetermined size, and then uses a tree structure to recursively divide the CTUs. The leaf node in the tree structure becomes the CU coding unit, which is the basic coding unit.

[0027] The tree structure for may be a quadtree (QT) in which a top node (or parent node) is divided into four equally sized lower nodes (or child nodes), a binary tree (BT) in which the top node is divided into two bottom nodes, by a ternary tree (TernaryTree (TT)), in which the top node is divided into three bottom nodes with a size ratio of 1:2:1, or a combination of two or more of a QT structure, a BT structure, and a TT structure. For example, a structure including quadtree and binary tree (QTBT) or a structure including quadtree and binary tree ternary (QTBTTT) may be used. Here, BTTT may be collectively referred to as multiple type tree (MTT).

[0028] In FIG. Figure 2 shows the tree structure of the QTBTTT partition. As shown in FIG. 2, CTU can be first divided into QT structure. Quadtree splitting can be repeated until the splitting block size reaches the minimum block size (MinQTSize) of a leaf node allowed in the QT structure. The first flag (QT_split_flag) indicating whether each node of the QT structure is divided into four lower-level nodes is encoded by the entropy encoding unit 155 and transmitted to the video decoding device. If a leaf node of a QT structure does not exceed the maximum block size (MaxBTSize) of the root node allowed in a BT structure, it may be further divided into any one or more BT structures or TT structures. There may be multiple division directions in a BT structure and/or a TT structure. For example, there may be two directions in which the block of the corresponding node is divided horizontally and vertically. As shown in FIG. 2, when MTT splitting begins, a second flag (mtt_split_flag) indicating whether the nodes are split, and, if so, an additional flag indicating the split directions (vertical or horizontal), and/or a flag indicating the split or split type (binary or ternary ) is encoded by entropy encoding unit 155 and transmitted to the video decoding device.

[0029] Alternatively, before encoding the first flag (QT_split_flag) indicating whether each node is split into four lower-level nodes, a CU split flag (split_cu_flag) may be encoded indicating whether the node is split or not. When the value of the CU split flag (split_cu_flag) indicates that no split is being performed, the block of the corresponding node becomes the leaf node in the split tree structure and serves a coding unit (CU), which is the basic coding unit. When the value of the CU split flag (split_cu_flag) indicates that a node has been split, the video encoding apparatus starts encoding from the first flag in the manner described above.

[0030] As another example of a tree structure that uses the QTBT structure, there are two types of partitioning, including a type in which the block of the corresponding node is horizontally divided into two blocks of the same size (i.e., symmetrical horizontal partition), and a type , in which it is also divided vertically (i.e., symmetrical vertical division). Encoded by the entropy encoding block 155 and transmitted to the video decoding device is a split flag (split_flag) indicating whether each node of the BT structure is divided into lower-level blocks, and split type information indicating its division type. Meanwhile, there may be an additional type in which the block of the corresponding node is split into two asymmetrically formed blocks. The asymmetrical shape may include a block shape of the corresponding node being divided into two rectangular blocks having an aspect ratio of 1:3, or a block shape of the corresponding node being divided in a diagonal direction.

[0031] The CU may have different sizes depending on the QTBT or QTBTTT structure of the CTU partition. In the following, the block corresponding to the CU to be encoded or decoded (i.e., the QTBTTT end node) is called the “current block”. When using QTBTTT splitting, the current block can be shaped not only as a square, but also as a rectangle.

[0032] Prediction block 120 predicts the current block to generate a prediction block. The prediction block 120 includes an intra-prediction block 122 and an inter-prediction block 124.

[0033] In general, each of the current image blocks may be predictively encoded. Prediction of the current block can usually be performed using an intra-prediction method or an inter-prediction method, with the intra-prediction method using data from the image containing the current block, and the inter-prediction method using data from the image encoded before the image containing the current block . Inter-prediction includes both unidirectional and bidirectional prediction.

[0034] The intra-prediction unit 122 predicts pixels in the current block using neighboring pixels (reference pixels) located around the current block in the current image. There are many intra-prediction modes according to the prediction directions. For example, as shown in FIG. 3A, multiple intra-prediction modes can include 2 omnidirectional modes including planar mode and DC mode, as well as 65 directional modes. The corresponding prediction modes provide various appropriate definitions of neighboring pixels and calculation formulas to be used.

[0035] Additional directional modes can be used to effectively directionally predict a square wave block of current, as shown in FIG. 3B with dotted arrows of intra-prediction modes numbered 67-80 and numbers -1- -14. These may be called "wide-angle intra-prediction modes". Arrows in Fig. 3B indicate the corresponding reference samples used for prediction rather than the direction of prediction. The direction of the prediction is opposite to the direction indicated by the arrow. Wide-angle intra prediction mode is a mode in which prediction is performed in the opposite direction to a specific directional mode without additional bit transmission when the current block is rectangular in shape. In this case, of the wide-angle intra-prediction modes, some of the wide-angle intra-prediction modes available for use in the current block may be determined by the width-to-height ratio of the rectangular current block. For example, wide-angle intra-prediction modes that have an angle of less than 45 degrees (intra-prediction modes numbered 67-80) can be used when the current block is rectangular in shape with a height less than its width. Wide-angle intra-prediction modes having an angle of -135 degrees or greater (intra-prediction modes numbered -1 to -14) can be used when the current block is rectangular in shape with a height greater than its width.

[0036] The intra-prediction block 122 may determine the intra-prediction mode to be used to encode the current block. In some examples, intra-prediction block 122 may encode the current block using multiple intra-prediction modes and select an appropriate intra-prediction mode from the tested modes to use. For example, intra-prediction block 122 may calculate speed distortion values by analyzing the speed-distortion of several tested intra-prediction modes and select the intra-prediction mode that has the best speed-distortion characteristics among the tested modes.

[0037] The intra prediction unit 122 selects one intra prediction mode from a plurality of intra prediction modes and predicts the current block using at least one neighboring pixel (reference pixel) determined according to the selected intra prediction mode and calculation formula. Information about the selected intra-prediction mode is encoded by entropy encoding unit 155 and transmitted to the video decoding device.

[0038] The inter-prediction block 124 generates a prediction block for the current block through a motion compensation process. The inter prediction unit 124 searches for a block most similar to the current block in a reference picture that was encoded and decoded earlier than the current picture, and generates a current block prediction block using the found block. Then, the inter-prediction block 124 generates a motion vector corresponding to the offset between the current block in the current image and the prediction block in the reference image. In general, motion estimation is performed on the luminance component, and a motion vector calculated based on the luminance component is used for both the luminance component and the chrominance component. Motion information including reference image information and motion vector information used for predicting the current block is encoded by the entropy encoding unit 155 and transmitted to the video decoding apparatus.

[0039] Subtraction block 130 generates a residual block by subtracting from the current prediction block generated by intra-prediction block 122 or inter-prediction block 124.

[0040] The conversion unit 140 converts the residual signal in the residual block having pixel values in the spatial domain into transform coefficients in the frequency domain. The transform block 140 may transform the residual signals in the residual block using the entire size of the residual block as a transform block, or divide the residual block into two subblocks that are a transform region and a non-transform region, and transform the residual signals using only a transform region subblock as conversion units. Here, the transform region subblock may be one of two rectangular blocks having a 1:1 aspect ratio along the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_flag) indicating that only one sub-block is converted, direction information (vertical/horizontal) (cu_sbt_horizontal_flag) and/or position information (cu_sbt_pos_flag) are encoded by the entropy encoding unit 155 and transmitted to the video decoding device. Additionally, the transform region subblock size may have an aspect ratio of 1:3 along the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_quad_flag) specifying the corresponding division is further encoded by the entropy encoder 155 and transmitted to the video decoding device.

[0041] Meanwhile, a maximum and/or minimum transformation size can be determined for the transformation. A transform is prohibited from using a transform block that is smaller than the minimum transform size. In addition, when the residual block of the current block is larger than the maximum transformation size, the transformation unit 140 divides the residual block into subblocks having a size equal to or smaller than the maximum transformation size, and performs the transformation using the subblocks as the transformation unit. Here, the maximum and/or minimum transform size may be defined as a fixed size set between the video encoding device and the video decoding device. Alternatively, information about the maximum and/or minimum transform size may be included in the SPS or PPS and transmitted from the video encoding device to the video decoding device.

[0042] The quantization unit 145 quantizes the transform coefficients output from the transform unit 140 and outputs the quantized transform coefficients to the entropy encoding unit 155 .

[0043] Reordering unit 150 may perform reordering of coefficient values using the quantized transform coefficients. Reorderer 150 may use coefficient scanning to transform a two-dimensional matrix of coefficients into a one-dimensional sequence of coefficients. For example, reordering unit 150 may scan DC coefficients to high-frequency domain coefficients through a zigzag scan or a diagonal scan to output a one-dimensional sequence of coefficients. Depending on the size of the transform block and the intra-prediction mode, the zigzag scan used can be replaced by a vertical scan to scan a two-dimensional array of coefficients in the column direction and a horizontal scan to scan the coefficients into a two-dimensional block shape in the row direction. In other words, the scanning method to be used can be selected from zigzag scanning, diagonal scanning, vertical scanning and horizontal scanning according to the transform block size and the intra-prediction mode.

[0044] Entropy encoding block 155 encodes a sequence of one-dimensional quantized transform coefficients output from reordering block 150 using various encoding techniques such as context-sensitive adaptive binary arithmetic code (CABAC), exponential Golomb algorithm, and the like. encoding to generate a bitstream.

[0045] In addition, the entropy encoding unit 155 encodes block division information such as CTU unit size, CU division flag, QT division flag, MTT division type, and MTT division direction, allowing the video decoding apparatus to divide the block in the same manner as and a video encoding device. In addition, the entropy encoding unit 155 encodes prediction type information indicating whether the current block is encoded by intra-prediction or inter-prediction, and decodes, depending on the prediction type, intra-prediction information, that is, intra-prediction mode information or inter-prediction information, i.e., information about reference images and motion vectors.

[0046] The inverse quantization unit 160 inversely quantizes the quantized transform coefficients output from the quantization unit 145 to generate transform coefficients. The inverse transform block 165 converts the transform coefficients output from the inverse quantization block 160 from the frequency domain to the spatial domain to reconstruct the residual block.

[0047] An adder 170 adds the reconstructed residual block and the prediction block generated by the prediction block 120 to reconstruct the current block. The pixels in the reconstructed current block are used as reference pixels for intra-prediction of the next block.

[0048] The filtering unit 180 filters the reconstructed pixels to reduce blocking artifacts, ringing artifacts, blur artifacts, etc. generated due to block-based prediction and transform/quantization. Filtering block 180 may include a deblocking filter 182 and an adaptive sample offset (SAO) filter 184.

[0049] A deblocking filter 180 filters the boundary between reconstructed blocks to remove block artifact caused by block encoding/decoding, and an SAO filter 184 further filters the deblocked filtered image. The SAO filter 184 is a filter used to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy encoding.

[0050] The reconstructed block is filtered through deblocking filter 182 and SAO filter 184 and stored in memory 190. When all blocks in one image are reconstructed, the reconstructed image can be used as a reference image for inter-prediction of blocks in the upcoming image to be encoded.

[0051] In FIG. 4 is a diagram illustrating a video decoding apparatus configured to implement the methods proposed by the present invention. Hereinafter, the video decoding apparatus and components of the apparatus will be described with reference to FIG. 4.

[0052] The video decoding apparatus may be configured to include an entropy decoding unit 410, a reordering unit 415, an inverse quantization unit 420, an inverse transform unit 430, a prediction unit 440, an adder 450, a filtering unit 460, and a memory 470.

[0053] As with the video encoding apparatus of FIG. 1, corresponding components of the video decoding apparatus may be implemented as hardware or software, or a combination of hardware and software. In addition, the function of each component may be implemented in software, and the software function of each component may be implemented to be executed by a microprocessor.

[0054] The entropy decoding unit 410 decodes the bitstream generated by the video encoding device and extracts block section information to determine the current block to be decoded, and extracts prediction information and residual signal information and the like necessary to reconstruct the current block.

[0055] Entropy decoding unit 410 extracts CTU size information from the Sequence Parameter Set (SPS) or Picture Parameter Set (PPS), determines the CTU size, and divides the image into CTUs of a given size. Then, the entropy decoding unit 410 determines the CTU as the highest level, that is, the root node of the tree structure, and extracts the partitioning information into the CTU and thereby partitions the CTU using the tree structure.

[0056] For example, when splitting a CTU using the QTBTTT structure, the first flag (QT_split_flag) associated with the QT split is first retrieved, and each node is split into four lower-level nodes. For a node corresponding to a QT leaf node, entropy decoding unit 410 extracts a second flag (MTT_split_flag) associated with the MTT split and information about the split direction (vertical/horizontal) and/or split type (binary/ternary) to split the corresponding leaf node to the MTT structure. This allows the corresponding nodes below the QT leaf node to be recursively split into a BT or TT structure.

[0057] As another example, when splitting a CTU using a QTBTTT structure, entropy decoding unit 410 may first retrieve a CU split flag (split_cu_flag) indicating whether the CU is split. When the corresponding block is split, it can extract the first flag (QT_split_flag). In a partitioning process, each node may have zero or more recursive QT partitions followed by zero or more recursive MTT partitions. For example, a CTU may immediately enter an MTT partition or, conversely, have only a few QT partitions.

[0058] As another example, when splitting a CTU using a QTBT structure, the entropy decoding unit 410 extracts the first flag (QT_split_flag) associated with the QT split to split each node into four lower layer nodes. And for the node corresponding to the leaf node QT, the entropy decoding unit 410 extracts a split flag (split_flag) indicating whether this node is further divided into BT and split direction information.

[0059] Meanwhile, when the entropy decoding unit 410 determines the current block to be decoded by dividing the tree structure, it extracts prediction type information indicating whether the current block has been predicted by intra-prediction or inter-prediction. When the prediction type information indicates intra-prediction, the entropy decoding unit 410 extracts a syntax element for the intra-prediction information (intra-prediction mode) of the current block. When the prediction type information indicates inter-prediction, the entropy decoding unit 410 extracts a syntax element for the inter-prediction information, that is, information indicating the motion vector and the reference image referenced by the motion vector.

[0060] In addition, the entropy decoding unit 410 extracts information about the quantized transform coefficients of the current block as residual signal information.

[0061] Reordering unit 415 reverses the coefficient scanning order of the video encoding device, the sequence of one-dimensional quantized transform coefficients entropy decoded by entropy decoding unit 410 into a two-dimensional array of coefficients. (i.e. block).

[0062] An inverse quantization unit 420 performs inverse quantization of the quantized transform coefficients. The inverse transform block 430 deconverts the inverse quantized transform coefficients from the frequency domain to the spatial domain to recover the residual signals and thereby generate a residual block of the current block.

[0063] In addition, when the demapping unit 430 deconverts only a partial region (subblock) of the transform block, it extracts a flag (cu_sbt_flag) indicating that only a subblock of the transform block has been converted, the directionality of the subblock (vertical/horizontal) information (cu_sbt_horizontal_flag ) and/or subblock position information (cu_sbt_pos_flag) and inversely converts the subblock transform coefficients from the frequency domain to the spatial domain to recover the residual signals. At the same time, the deconversion block 430 fills the remaining region that is not deconverted with the value "0" as residual signals, and thereby generates the last residual block for the current block. Meanwhile, conversion is not allowed when using a conversion block with a size smaller than the minimum conversion size. In addition, when the residual block of the current block is larger than the maximum transform size, the inverse transform unit 430 divides the residual block into subblocks having a size equal to or smaller than the maximum transform size, and performs the inverse transform using the subblocks as transform units.

[0064] The prediction block 440 may include an intra-prediction block 442 and an inter-prediction block 444. The intra-prediction block 442 is activated when the prediction type of the current block is intra-prediction, and the inter-prediction block 444 is activated when the prediction type of the current block is inter-prediction.

[0065] The intra-prediction unit 442 determines, from among a plurality of intra-prediction modes, the intra-prediction mode of the current block from the syntax element for the intra-prediction mode extracted by the entropy decoding unit 410, and according to the determined intra-prediction mode, it predicts the current block using adjacent reference pixels of the current block. The intra-prediction mode specified by the syntax element for intra-prediction mode may be a value indicating one of all intra-prediction modes (eg, a total of 67 modes) as described above. In the case where the current block is rectangular, some directional modes out of a total of 67 modes may be replaced by one of the wide-angle intra-prediction modes based on the width-to-height ratio of the current block.

[0066] The inter-prediction block 444 uses the syntax element for the intra-prediction mode extracted by the entropy decoding block 410 to determine the motion vector of the current block and the reference image referenced by the motion vector, and it uses the motion vector and the reference image to predict the current block.

[0067] The adder 450 adds the residual block output from the inverse transform block and the prediction block output from the inter-prediction block or intra-prediction block to reconstruct the current block. The pixels in the reconstructed current block are used as reference pixels when intra-predicting incoming blocks to be decoded.

[0068] Filtering block 460 may include deblocking filter 462 and SAO filter 464. The deblocking filter 462 performs deblocking filtering at the boundary between reconstructed blocks to remove blocking artifact caused by block-by-block decoding. The SAO filter 464 performs additional filtering on the reconstructed block after the deblocking filtering to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy encoding. The reconstructed block is filtered through deblocking filter 462 and SAO filter 464 and stored in memory 470. When all blocks in one image are reconstructed, the reconstructed image can be used as a reference image for inter-prediction of blocks to be encoded in the image.

[0069] The technologies of the embodiments illustrated herein generally relate to intra-predictive coding, that is, encoding and decoding of the current block. Accordingly, certain techniques of the present invention may be performed by intra-prediction unit 122 or intra-prediction unit 442. In some embodiments, intra-prediction block 122 or intra-prediction block 442 performs the methods of the present invention described with reference to FIGS. 5-9. In other embodiments, one or more other blocks of the video encoding device or video decoding device may further participate in performing the methods of the present invention. The following description mainly relates to the decoding technology, in particular to the operation of the video decoding apparatus, while the encoding technology is described briefly since the latter is the inverse of the decoding technology described in detail.

[0070] In intra-prediction, prediction is performed on previously reconstructed samples located adjacent to the current block, where the adjacent sample used for intra-prediction is referred to as a reference sample. Typically, in intra-prediction, all samples in the current block are predicted as a whole using reference samples. For example, for a 16x16 block, 256, the values of the samples belonging to the 16x16 block are predicted using their neighboring samples. Since there is spatial correlation in video, the closer the current block sample is to the reference sample, the better the overall prediction results. Accordingly, in the vertical prediction mode (mode 50 in FIG. 3B) or in the horizontal prediction mode (mode 18 in FIG. 3B), current block samples adjacent to the reference samples may have accurate prediction values, but those that are far from the reference samples , may lead to inaccurate prediction values.

[0071] The intra-coding tool described below relates to dividing a CU depending on its size into a plurality of sub-blocks of equal size in the vertical or horizontal direction, and performing prediction for each sub-block in the same intra-prediction mode. The reconstructed sample values (or predicted sample values) of each sub-block are available for next sub-block prediction, which is iteratively applied to the corresponding sub-blocks. For example, when the current block (CU) is divided into four parallel sub-blocks, the first sub-block can be predicted from the neighboring samples of the current block (CU), the second sub-block can be predicted from its neighboring pixels including the samples of the first sub-block, the third sub-block can be predicted from its neighboring samples, including samples of the second sub-block, and the fourth sub-block can be predicted from neighboring samples, including samples of the third sub-block. Thus, instead of predicting all pixels of the current block (CU) from samples of previously encoded or decoded blocks adjacent to the current block (CU), samples in the current block (CU) can be used to predict other samples in the same current block (CU).

[0072] One advantage of the intra-coding tool proposed according to the invention is that the reconstructed neighboring samples tend to be much closer to the predicted sample than in a conventional intra-prediction scenario. By placing closer to the current sample as a basis for current sample prediction, reconstructed neighboring samples can improve the accuracy of current sample prediction.

[0073] 1. Sub-unit separation and signaling

[0074] In FIG. 5A-5C are diagrams illustrating types in which a current block can be divided into a plurality of sub-blocks when the current block is intra-prediction encoded according to at least one embodiment of the present invention. The minimum block size applicable to the intra-coding tool according to the invention may be 4x8 or 8x4. Additionally, a constraint may be added that all subblocks have a minimum of 16 samples. As shown in FIG. 5A-5C, a 4x8 or 8x4 block is divided into two, and a larger block can be divided into 4 or 8 blocks. The size of the CU for which the intra-encoding tool can be used may be limited to a maximum of 64x64 due to the virtual pipeline data unit (VPDU), which is a VVC processing unit.

[0075] The video encoding device may signal a split flag indicating that the current block has been divided into multiple subblocks and intra-predicted by each subblock. Accordingly, the video decoding apparatus can decode a division flag from the video bit stream and determine whether the current block should be divided based on the division flag. The first value split flag (eg, "0") indicates that the current block has not been split into multiple sub-blocks, and the second value split flag (eg, "1") indicates that the current block has been split into multiple sub-blocks and intra-predicted by each subblock.

[0076] The split flag may be output by the video decoding device without explicit signaling, that is, without decoding from the bitstream, but instead depending on the width and height of the current block, the area of the current block, the minimum transform size and/or the maximum transform size allowed to convert the conversion factors.

[0077] In at least one embodiment, when the width and height of the current block are less than the minimum transform size, the split flag may not need to be decoded from the bitstream, but instead should be set to a first value indicating that the current block not divided. In another embodiment, when the current block area (i.e., the number of pixels included in the current block) is smaller than the transform block area (i.e., the number of pixels included in the transform block) defined by the minimum transform size, the split flag may does not need to be decoded from the bitstream, but should instead be set to the first value indicating that the current block is not divided. In yet another embodiment, when the width and height of the current block are greater than the maximum transform size, the split flag cannot be decoded from the bitstream. In this case, we can conclude that the split flag has a second meaning, i.e., that the current block has been divided into many subblocks and intra-predicted by each subblock. Alternatively, one can infer that the split flag has the first value. In other words, when the width and height of the current block are larger than the maximum transform size, when the encoding tool of the present invention, which divides the current block into a plurality of sub-blocks and performs intra-prediction for each sub-block, may not be applied to the current block. In yet another embodiment, when the current block is located on an image (or tile) boundary, the intra-encoding tool of the present invention is not used for the current block, and the split flag is assumed to have the first value. Alternatively, the current block, when located at the boundary of an image (or tile), may accompany the use of the intra-encoding tool of the present invention, and thus the split flag is assumed to have a second value, thereby eliminating the need for additional block CTU splits at the image boundary.

[0078] In addition, when the intra-encoding tool of the present invention is applied to the current block, information about the direction and number of sections of the sub-block can be provided in various ways. For example, the direction and number of sections of a subblock can be determined based on syntax elements (eg, flags) extracted from the bitstream, the size of the current block, the position of the current block, the length (eg, width or height) of one side of the current block, the number of pixels included into the current block, the intra-prediction mode of the current block, the size of the minimum or maximum transformation block, etc.

[0079] In some embodiments, when a current block is divided into a plurality of subblocks, the video decoding apparatus may determine the division direction and the number of subblocks based on the division information decoded from the bit stream and the width and height of the current block.

[0080] In particular, the number of sub-blocks may be determined by the width and height of the current block. For example, as shown in Table 1, when the width and height of the current block are 4x8 or 8x4, the number of subblocks is determined to be 2, and when the width and height of the current block are greater than 4x4 and not equal to 4x8 and 8 ×4, the number of subblocks can be determined to be 4. As another example, as shown in Table 2, when the width and height of the current block are 4x8 or 8x4, the number of subblocks is determined to be 2, and when the width and height of the current block are 8×N to 32×N or N×8 to N×32 (here N>4), the number of sub-blocks can be defined as 4. In addition, the number of sub-blocks can be defined as 8 for the current blocks , the size of which exceeds 32×N and N×32.

[0081] Table 1

Current block size Number of subblocks 4x4 Not divided 4x8 and 8x4 2 Other 4

[0082] Table 2

Current block size Number of subblocks 4x4 Not divided 4x8 and 8x4 2 4x8 and 8x4
32×N and N×32 4 Other 8

[0083] Whether the dividing direction is horizontal or vertical may be determined by the dividing information. Alternatively or in addition, the direction of division can be determined (or inferred) based on the width to height ratio of the current block. For example, the division direction can be defined as horizontal when the width of the current block is greater than its height, and can be defined as vertical when the width of the current block is less than its height.

[0084] Alternatively or additionally, when the current block exists on the boundary of an image (or tile, group of tiles, etc.), the division shape and number of sub-blocks can be output according to the position of the current block.

[0085] Additionally, whether the dividing direction is horizontal or vertical can be determined based on the directionality of the prediction modes included in the intra-prediction mode candidates (ie, the MPM list) defined for the current block. As an example, when relatively horizontal intra-prediction modes, such as modes 3 to 33 shown in FIG. 3B (hereinafter referred to as "horizontally oriented modes") exist or dominate the MPM list, the division direction can be defined as vertical. And when relatively vertical intra-prediction modes, such as modes 35 to 65 shown in FIG. 3B (hereinafter referred to as "vertically oriented modes") exist or dominate the MPM list, the division direction can be defined as horizontal.

[0086] 2. Define intra-prediction mode

[0087] When the intra-encoding tool of the present invention is applied to the current block, the intra-prediction mode defined for the current block may generally be applied to the intra-prediction of sub-blocks of the current block.

[0088] The wide-angle intra-prediction mode can still be used for the current block to which the intra-coding tool of the present invention is applied. In this case, the wide-angle intra-prediction mode may be determined by the ratio between the width and height of the current block, rather than the ratio between the width and height of a subblock separated from the current block.

[0089] The video decoding apparatus may determine the intra-prediction mode of the current block by decoding the intra-prediction mode of the current block from the information bit stream. For example, a video decoding apparatus selects a predetermined number of intra-prediction mode candidates from a plurality of intra-prediction modes, and uses the intra-prediction mode information of the current block to determine from among the intra-prediction mode candidates (i.e., the MPM list), the intra-prediction mode. predictions of the current block.

[0090] Intra-prediction mode candidates can be selected in various ways depending on whether the dividing direction is horizontal or vertical. For example, when the dividing direction is horizontal, vertically oriented modes from among a plurality of intra-prediction modes may be selected as candidates for intra-prediction modes rather than horizontally oriented modes. In addition, when the dividing direction is vertical, horizontally oriented modes from among a plurality of intra-prediction modes may be selected as candidates for intra-prediction modes rather than vertically oriented modes. As another example, when the split direction is horizontal, horizontal modes (eg, mode 18 in FIG. 3B) or horizontally oriented modes may be excluded from the selection of intra-prediction mode candidates, and when the split direction is vertical, vertical modes (eg , 50 in Fig. 3B) or vertically oriented modes may be excluded from the selection of intra-prediction mode candidates.

[0091] 3. Generating an intra-prediction block in units of subblocks

[0092] The video decoding apparatus reconstructs the current block by sequentially reconstructing a plurality of sub-blocks using the intra-prediction mode defined for the current block. For example, a video decoding apparatus may generate an intra-predicted sub-block by predicting, from the reconstructed pixels around the sub-block, a target sub-block that will be currently reconstructed from among a plurality of sub-blocks. The video decoding apparatus can recover transform coefficients by decoding from the bitstream the transform coefficient information corresponding to the target subblock, and can perform inverse quantization and inverse transform of the transform coefficients using the same transform size as the size of the target subblock, thereby generating a residual subblock, having residual signals. The video decoding apparatus may reconstruct the target subblock using the intra-predicted subblock and the residual subblock. In particular, the pixels in the reconstructed subblock can be used to intra-predict the next subblock in the current block. By this process, the subblocks of the current block are processed from the subblock including the top left sample of the current block, to the subblocks in the downward direction sequentially when the dividing direction is horizontal, and to the subblocks in the right direction sequentially when the dividing direction is vertical.

[0093] In some cases, in order to keep the width of the minimum prediction unit for subblocks equal to 4 samples, the dependence of the prediction of the 1xN/2xN subblock on the reconstructed values of the previously decoded 1xN/2xN subblock of the current block cannot be resolved. In other words, when the intra-encoding tool of the present invention is applied to the current block, transformation in 1×N and 2×N units is allowed, but prediction in 1×N and 2×N units may be prohibited. For example, a current 8×N block (N>4) divided in the vertical direction can be divided into four 2×N subblocks. Accordingly, the residual signals of the current block are generated by reconstruction and deconversion in units of 2×N subblocks. However, since prediction is not allowed in 2×N subblock units, the current block is predicted in 4×N subblock units having a width of 4 samples. In other words, the current 8×N block (N>4) divided in the vertical direction can be divided into two 4×N prediction areas and four 2×N prediction areas. In addition, the current 4×N block divided in the vertical direction can be predicted as a 4×N prediction area and divided into four 1×N transform areas. This limitation is due to a typical hardware design feature storing the results of intra-predicted blocks divided into multiple clock cycles in string units, which requires the number of clock cycles used to process 1xN or 2xN blocks so as not to exceed the clock count for 4 blocks ×N.

[0094] 4. In-loop filtration

[0095] The video decoding apparatus may perform in-loop filtering, including deblocking filtering, on the reconstructed current block, and may store the filtered current block in a buffer (e.g., memory 470 in FIG. 4) for use as a reference image for inter-prediction blocks that must be encoded in a prominent image.

[0096] In an exemplary embodiment, the video decoding apparatus establishes a grid of M samples at regular intervals on the CTU or image containing the current block in the horizontal and vertical directions, and performs deblocking filtering on the boundaries that coincide with the grid boundaries among the boundaries between the plurality of sub-blocks in the current block to which the intra-encoding tool of the present invention is applied. Accordingly, deblocking filtering cannot be performed on boundaries between multiple subblocks that do not coincide with the mesh boundary. For example, when performing deblocking filtering in 8x8 units, deblocking filtering can only be performed on the boundary between subblocks coinciding with the boundary of a unit 8x8 grid among the boundaries between 2xN (or Nx2) or 4xN (or N) subblocks ×4) size. Although a grid size of 8x8 units is given as an example, the grid size is not necessarily limited to 8x8. For example, the number M of samples can be expressed in the form 2n (n is a natural number) and can have any value 4, 8, 16, etc.

[0097] In some cases, in-loop filtering may be performed on only part of the boundary between subblocks according to the subblock division direction and the number of partitions. For example, with the current block division in the horizontal direction, only vertical deblocking filtering may be performed, and horizontal deblocking filtering may be omitted. Similarly, with the current block division in the vertical direction, only deblocking filtering in the horizontal direction can be performed, and deblocking filtering in the vertical direction can be omitted.

[0098] In some embodiments, when the intra-encoding tool of the present invention is applied to the current block, it can be determined whether intra-loop filtering is performed in the units of each sub-block. Accordingly, the video decoding apparatus may check whether in-loop filtering is performed in the units of each sub-block, or may check the same through high-level syntax.

[0099] When performing in-loop filtering for the current block, a method for performing in-loop filtering or a method for calculating in-loop filtering parameters may differ according to criteria calculated based on at least one of information elements, sub-block size, location, depth, QP, etc. P.

[0100] For example, when the intra-encoding tool of the present invention is applied to a current block, a sub-block of the current block may be smaller than a block in which calculation of in-loop filtering parameters, such as parameters for determining filter intensity and a cutoff value for changing a pixel, is performed. In this case, instead of calculating filtering parameters in units of subblocks, filtering parameters can be calculated relative to the current block, and in-loop filtering can be performed in units of each subblock. Alternatively, common filtering parameters may be calculated with respect to every two or more combined sub-blocks, and these sub-blocks may share common filtering parameters.

[0101] As another example, when a block for calculating ALF parameters spans a sub-block boundary, the ALF parameters may be obtained in units such as {N×1, 1×N, N×2, 2×N} to perform ALF. In another example, the present invention can avoid calculating parameters for determining whether to perform deblocking filtering (or filter coefficients) by configuring the deblocking filtering to ever be performed or never performed in the current block. As another example, the present invention depends on whether the boundary of the current subblock overlaps the boundary of the CU (or CTU, or VPDU) to adaptively change the method of performing in-loop filtering or the method of calculating parameters.

[0102] 5. Coded Block Signal Flag

[0103] When the intra-coding tool of the present invention is applied to the current block, a syntax element (eg, coded block flag; CBF) may be signaled for each sub-block, indicating whether at least one non-zero coefficient exists in that sub-block. For example, a CBF equal to "0" may indicate that all coefficients in the corresponding sub-block are zero coefficients, and a CBF equal to "1" may indicate that at least one non-zero coefficient exists in the corresponding sub-block.

[0104] The CBF may be derived based on the number of divided sub-blocks, the size (width or height) of the sub-blocks, intra-prediction mode, block position, QP, the number of pixels included in the sub-block, and the like. For example, at least one CBF for subblocks of the current block is considered to be not equal to "0". Accordingly, when the current block has n subblocks and all CBFs of the previous n-1 subblocks are "0", the CBF of the nth subblock is considered to be "1" and thus the CBFs are not explicitly signaled.

[0105] As another example, when the width or height of the sub-blocks of a given current block is not greater than 2, the intra-encoding tool of the present invention can only be applied when the CBF of each sub-block is not 0. In this case, for example, when the intra-encoding tool of the present invention is applied to the current 8×16 block and divided into 4 2×16 sub-blocks, the CBF of each sub-block is output as “1” and thus is not explicitly signaled. On the other hand, if the current 8×16 block is divided into two 4×16 subblocks, the CBF of each subblock must be explicitly signaled.

[0106] 6. Signaling quantization parameter

[0107] The video encoding apparatus determines a quantization parameter (QP) value for the current block (CU) and determines a delta quantization parameter (DQP) value for the current block based on the QP value and the QP prediction value. The video encoding device may be configured to signal the DQP value and quantize the current block using the specific QP value. The video encoding apparatus may adjust the QP value of the current block and thus adjust the degree of quantization applied to the coefficient blocks related to the current block.

[0108] The DQP is defined as the difference between the current QP (ie, the actual QP used in the current block) and the prediction value of the current QP (ie, the QP prediction value). Based on the signaled DQP, the corresponding current QP value can be recovered by adding the DQP to the QP prediction value. In other words, in the video encoding apparatus, the DQP is calculated by subtracting the QP prediction value from the actual QP of the current block, and in the video decoding apparatus, the actual QP of the current block is recovered by adding the received DQP to the QP prediction value. In some examples, the QP prediction value is determined for the current block as the average of the actual QP values for the top block and the left block.

[0109] The video decoding apparatus may be configured to receive a DQP value for a current quantization block, determine a QP value for the current quantization block based on the received DQP value and a QP prediction value, and inversely quantize the current quantization block by using the determined QP value.

[0110] When the intra-encoding tool of the present invention is applied to the current block, the DQP may be determined with each sub-block as a unit. In this case, the present solution may check a flag to determine whether to use DQP per subblock unit, or may check through high-level syntax whether to use DQP.

[0111] In some examples, when the intra-encoding tool of the present invention is applied to the current block, the same QP may be used for all sub-blocks. Accordingly, the QP value of the current block can be determined using the QPs of the (left and/or top) CUs adjacent to the current block and the transmitted DQP value. Alternatively, the QP value of the current block can be inferred via the passed DQP value and high-level syntax.

[0112] In some other examples, a different DQP may be used for each subblock. In this case, the QP of each sub-block can be determined using the QP determined for the current block and the DQP value of each sub-block. Alternatively, the QP of each subblock may be determined by the DQP between corresponding subblocks, or the QP of the current block may be determined using the QP of a specific subblock.

[0113] In some other examples, the QP of the current block may be signaled, or the QP value to be used may be inferred via high-level syntax.

[0114] FIG. 6 is a functional block diagram illustrating an exemplary configuration of an intra-prediction block in a video encoding apparatus according to at least one embodiment of the present invention, wherein the intra-prediction block supports the intra-coding tool of the present invention. As shown in FIG. 6, the intra-prediction block 600 may include a mode selection block 610, a reference sample construction block 620, a reference sample filtering block 630, and a prediction signal generation block 640.

[0115] Mode selector 610 may determine the intra-prediction mode that will be used to encode the current block. For example, mode selector 610 may encode the current block using different intra-prediction modes, and select the appropriate intra-prediction mode to be used from the modes being tested.

[0116] In some cases, mode selector 610 may signal the intra-prediction mode for the current block using a most likely mode (MPM) process. For example, mode selector 610 may set the intra-prediction modes of neighboring blocks adjacent to the current block, such as the block located at the top of the current block and the block located to the left of the current block, as MPM candidates. When two MPM candidates cannot be found, for example, when no neighboring block has been intra-predicted, or when neighboring blocks have the same intra-mode, mode selector 610 may change the neighboring block's intra-prediction mode to a planar mode. When the number of MPM candidates included in the MPM candidate list is less than the maximum number (e.g., 6), the present solution may insert default modes into the MPM candidate list that are different from previously inserted MPM candidates into the MPM candidate list and directional modes similar to the previously inserted candidates. MPM.

[0117] Information, such as an MPM flag indicating whether the intra-prediction mode of the current block is the same as any of the MPM candidates, may be transmitted via the bit stream. When the intra-prediction mode of the current block is the same as any of the MPM candidates, the mode selector 610 may set the MPM flag to the first value and further signal the MPM index information to identify the matching MPM candidate. Alternatively, mode selector 610 may first signal a flag indicating whether the intra-prediction mode of the current block is a flat mode, and if not, it may signal MPM index information. When the intra prediction mode of the current block does not match any of the MPM candidates, mode selector 610 may set the MPM flag to a second value and may signal the residual mode information via a bit stream to indicate which of the remaining intra prediction modes matches the mode and intra -predictions of the current block.

[0118] The mode selector 610 may select the intra-coding tool of the present invention that predicts the current block sequentially in units of sub-blocks. In this case, the mode selector 610 may perform distortion factor analysis to determine the direction in which the current block is divided into subblocks. In other words, the mode selector 610 can determine whether the current block should be divided into a plurality of sub-blocks in the horizontal direction or into a plurality of sub-blocks in the vertical direction.

[0119] When the current block is predicted without being divided into multiple sub-blocks, the mode selector 610 may set the division flag to a first value, for example, "0", indicating whether the current block is divided or not. When the current block is predicted after being divided into a plurality of sub-blocks, the mode selector 610 may set a division flag indicating whether the current block is divided into a second value, for example, "1". Mode selector 610 may pass a split flag to, for example, entropy decoder 155 of FIG. 1 to signal the split flag.

[0120] In some cases, mode selector 610 may be restricted from using the intra-encoding tool of the present solution described above if predetermined criteria are not met. For example, whether the intra-encoding tool of the present invention can be used can be determined depending on the position of the current block, the width and height of the current block, the area of the current block, the minimum transform size, the maximum transform size and the like. In this case, the present solution may not specify a split flag indicating whether its intra-encoding tool should be used. This means that the split flag is not included in the bit stream.

[0121] For example, when the current block is smaller than a preset size (eg, 4x8 or 8x4, etc.), the mode selector 610 may not use the intra-coding tool of the present invention. As another example, the intra-coding tool of the present invention is not applied and the split flag is not signaled when the width and height of the current block is smaller than the minimum transform size, or when the area of the current block (i.e., the number of pixels included in the current block) less than the area of the transform unit (i.e., the number of pixels included in the transform unit), determined by the minimum transform size. In this case, the video decoding apparatus defines the division flag as a value indicating that the current block is not divided. As another example, the split flag signaling may be omitted when the width and height of the current block are greater than the maximum transform size. In this case, the video decoding apparatus may be implemented to output a split flag as a value indicating that the current block is divided into multiple sub-blocks and intra-predicted by each sub-block. Alternatively, the video decoding apparatus may infer that the division flag is a value indicating that the current block is not divided into subblocks.

[0122] When the intra-encoding tool of the present invention is applied to the current block, the direction and number of sections of the sub-block can be determined based on the size of the current block, the position of the current block, the length of one side (i.e., width or height) of the current block, the number of pixels included in the current block, the intra-prediction mode of the current block, the size of the minimum or maximum transformation block, etc.

[0123] Information about the direction and number of subblock sections may be provided in various ways. For example, mode selector 610 may use one or more syntax elements, such as a 1-bit flag, to signal the direction and number of sections of a subblock.

[0124] In particular, the number of sub-blocks may be determined by the width and height of the current block. For example, when the width and height of the current block are 4x8 or 8x4, the number of subblocks can be defined as 2, and when the width and height of the current block are greater than 4x4 and not equal to 4x8 and 8x4, the number of sub-blocks can be defined as 4. As another example, when the width and height of the current block are 4×8 or 8×4, the number of sub-blocks can be defined as 2, and when the width and height of the current block are between 8×N to 32×N or from N×8 to Nx32 (here N>4), the number of sub-blocks can be defined as 4, and the number of sub-blocks can be defined as 8 for current blocks whose size is greater than 32xN and Nx32.

[0125] Whether the dividing direction is horizontal or vertical may be determined by the dividing information. Alternatively or additionally, the direction of division can be determined (or inferred) based on the width to height ratio of the current block. For example, a split direction can be defined as a horizontal split when the current block's width is greater than its height, and can be defined as a vertical split when the current block's width is less than its height. Alternatively or additionally, when the current block exists on the boundary of an image (or tile, group of tiles, etc.), the shape and number of sections of the sub-block can be inferred according to the position of the current block. Additionally, whether the dividing direction is horizontal or vertical can be determined based on the directionality of the prediction modes included in the intra-prediction mode candidates (ie, the MPM list) defined for the current block. This may free the bitstream from signaling one or more syntax elements indicating information about the shape and/or number of sections of the subblock.

[0126] Reference sample builder 620 may check for available neighboring samples and use the available samples to construct reference samples to be used for prediction. When there is no sample available, or when intra-prediction is not performed using neighboring samples, the reference sample builder 620 may arbitrarily construct the reference sample.

[0127] The reference sample filtering unit 630 may determine whether to perform filtering. Whether to perform filtering may be determined based on information about at least one of the size, depth, QP, and mode of the current block. When it is necessary to perform filtering, the reference sample filtering unit 630 may select a filter to perform the filtering. In this case, information about what filtering to perform can be carried in the bit stream.

[0128] The prediction signal generating unit 640 may generate a prediction sub-block by predicting a sub-block to be encoded among a plurality of sub-blocks from previously reconstructed pixels around the sub-block. The prediction signal generating unit 640 may use the intra-prediction mode defined for the current block when performing intra-prediction on a plurality of sub-blocks. The prediction subblock can then be subtracted from the corresponding subblock of the current block to generate a residual subblock. The residual subblock can be reconstructed by a transform/quantization process and an inverse quantization/inverse transform process. The reconstructed residual subblock is added to the prediction subblock generated by the prediction signal generating unit 640 to generate the reconstructed subblock. Specifically, when predicting the next subblock, the prediction signal generation unit 640 may use the reconstructed pixels of the previous subblock and the reconstructed pixels of the previously reconstructed CU.

[0129] In FIG. 7 is a flowchart of a method performed by a video encoding apparatus for intra-predictive encoding of a current block of video according to at least one embodiment of the present invention.

[0130] In step S710, the video encoding apparatus may determine an intra-prediction mode to be used for encoding the current block. In addition, the video encoding device can determine whether to apply the intra encoding tool of the present invention, and, if so, determine the dividing direction of the current block between the horizontal direction and the vertical direction.

[0131] In step S720, the video encoding apparatus may encode an intra-prediction mode of the current block and syntax elements indicating whether the current block is to be predicted after being divided into a plurality of sub-blocks. The video encoding device may use a most probable mode (MPM) process to signal the intra-prediction mode for the current block. In addition, the video encoding device may signal a split flag indicating whether the current block is predicted after being divided into a plurality of sub-blocks.

[0132] In some cases, a video encoding device may be prohibited from using the intra-encoding tool of the present invention if predetermined criteria are not met. For example, whether the intra-encoding tool of the present invention can be used or not can be determined depending on the position of the current block, the width and height of the current block, the area of the current block, the minimum transformation size, the maximum transformation size and the like. In this case, the present solution may omit split flag signaling indicating whether to use the intra-coding tool of the present invention in the bitstream.

[0133] When the intra-encoding tool of the present invention is applied to the current block, the direction and number of sections of the sub-block can be determined based on the size of the current block, the position of the current block, and the length of one side (i.e., width or height) of the current block, the number pixels included in the current block, the intra-prediction mode of the current block, the size of the minimum or maximum transform block, etc.

[0134] Information about the direction and number of subblock sections may be provided in various ways. For example, a video encoding device may use one or more syntax elements, such as a 1-bit flag, to signal division information, such as the direction and/or number of divisions of a subblock.

[0135] In particular, the number of sub-blocks may be determined by the width and height of the current block. For example, when the width and height of the current block are 4x8 or 8x4, the number of subblocks can be defined as 2, and when the width and height of the current block are greater than 4x4 and not equal to 4x8 and 8x4, the number of subblocks can be defined as 4.

[0136] The video encoding device may explicitly signal a flag indicating the direction of division of the subblock, for example, whether the direction is horizontal or vertical. Alternatively or additionally, the direction of division can be determined (or inferred) based on the width to height ratio of the current block. For example, a split direction can be defined as a horizontal split when the current block's width is greater than its height, and can be defined as a vertical split when the current block's width is less than its height. In this case, the signaling of the flag indicating the direction of separation may be omitted.

[0137] In step S730, when the intra-encoding tool of the present invention is applied to the current block, the video encoding device can sequentially encode a plurality of sub-blocks using the intra-prediction mode determined for the current block.

[0138] For example, a video encoding apparatus may generate a prediction sub-block by predicting a target sub-block to be encoded among a plurality of sub-blocks from previously reconstructed pixels around the target sub-block (S732). The video encoding apparatus may generate a residual subblock from the target subblock and the prediction subblock (S734). The video encoding apparatus may transform and quantize the residual subblock using the same transform size as the target subblock (S736). The video encoding apparatus may entropy encode the quantized transform coefficient (S738). In addition, the video encoding apparatus may reconstruct the residual subblock by applying an inverse quantization/inverse transform process to the quantized transform coefficient, and may add the reconstructed residual subblock to the prediction subblock to generate the reconstructed subblock (S738). In particular, the pixels in the reconstructed subblock can be used to intra-predict the next subblock in the current block. Through this process, the current block is processed sequentially, starting from the sub-block, including the top-left example of the current block, in a downward direction in a horizontal split, and in a right direction in a vertical split.

[0139] In step S740, the video encoding apparatus may perform deblocking filtering and other processes on the reconstructed current block, and may store the filtered current block in a buffer (eg, memory 190 of FIG. 1) for use as a reference image for inter-prediction of unfinished blocks to be encoded in the image. The video encoding apparatus may establish a grid of N samples at regular intervals in the horizontal and vertical directions and perform deblocking filtering on boundaries that coincide with the grid boundary from among the boundaries between a plurality of sub-blocks in the current block.

[0140] FIG. 8 is a functional block diagram illustrating an exemplary configuration of an intra prediction unit in a video decoding apparatus according to at least one embodiment of the present invention, wherein the intra prediction unit supports the intra encoding tool of the present invention. As shown in FIG. 8, the intra-prediction block 800 may include a mode determination block 810, a reference sample construction block 820, a reference sample filtering block 830, and a prediction signal generation block 840.

[0141] The mode determination unit 810 may determine the intra-prediction mode of the current block by decoding the intra-prediction mode of the current block from the information bitstream. For example, the mode determination unit 810 may select a predetermined number of intra-prediction mode candidates from a plurality of intra-prediction modes, and use the intra-prediction mode information of the current block to determine the intra-prediction mode of the current block from among the intra-prediction mode candidates.

[0142] The mode determination unit 810 may also determine whether to divide the current intra-prediction encoded block into a plurality of sub-blocks. In particular, the mode determination unit 810 may divide the current block into sub-blocks of the same size and determine whether to perform intra-prediction for the corresponding sub-blocks using the same intra-prediction mode as the intra-prediction mode of the current block.

[0143] For example, the mode determination unit 810 may decode from the bit stream a split flag indicating whether the current block should be split, and determine whether the current block should be split into a plurality of sub-blocks based on the split flag. The first value, eg "0" of the split flag, indicates that the current block is not divided into sub-blocks, and the second value, eg, "1" of the split flag, indicates that the current block has been split into sub-blocks and has been intra-predicted by each sub-block.

[0144] The split flag may be output by the video decoding device without explicit signaling, that is, without decoding from the bitstream, but instead depending on the width and height of the current block, the area of the current block, the minimum transform size and/or the maximum transform size allowed to convert the conversion factors. Accordingly, the mode determination unit 810 may derive the value of the division flag based on the width and height of the current block, the area of the current block, and the minimum and maximum transform sizes allowed for transform coefficient conversion.

[0145] In at least one embodiment, when the width and height of the current block is less than the minimum transform size, the split flag may not need to be decoded from the bitstream, but instead must be set to a value indicating that the current block is not is divided. In another embodiment, when the current block area (i.e., the number of pixels included in the current block) is smaller than the transform block area (i.e., the number of pixels included in the transform block) defined by the minimum transform size, the split flag may does not need to be decoded from the bitstream, but should instead be set to a value indicating that the current block is not divided. In yet another embodiment, when the width and height of the current block are greater than the maximum transform size, the split flag may not need to be decoded from the bitstream, but instead the split flag can be inferred to have a second value (e.g., '1') , i.e., the current block has been divided into many subblocks and intra-predicted by each subblock. Alternatively, conversely, one can infer that the split flag has the first value (for example, "0"), that is, that the encoding tool of the present solution is not applicable, retaining its process of dividing the current block into many sub-blocks and intra-predicting the corresponding sub-blocks .

[0146] When the encoding tool of the present invention is applied to the current block, the mode determination unit 810 can determine the direction and number of sections of the subblock. A mode determination unit 810 may extract one or more syntax elements from the bitstream to determine the direction and number of sections of the subblock. For example, whether the dividing direction is horizontal or vertical can be explicitly signaled using a syntax element such as a 1-bit flag. Accordingly, mode determination unit 810 may extract from the bit stream a syntax element indicating the dividing direction of the current block.

[0147] Alternatively or additionally, the direction and number of subblock sections may be determined or inferred based on the size of the current block, the position of the current block, the length of one side (i.e., width or height) of the current block, the number of pixels included in the current block, the intra mode -prediction of the current block, the size of the minimum or maximum transformation block, etc.

[0148] For example, the dividing direction may be determined (or inferred) based on the width-to-height ratio of the current block. For example, a split direction can be defined as a horizontal split when the current block's width is greater than its height, and can be defined as a vertical split when the current block's width is less than its height. Alternatively or additionally, when the current block exists on the boundary of an image (or tile, group of tiles, etc.), the shape and number of sections of the sub-block can be inferred according to the position of the current block. Additionally, whether the dividing direction is horizontal or vertical can be determined based on the directionality of the prediction modes included in the intra-prediction mode candidates (ie, the MPM list) defined for the current block. This may free the bitstream from signaling one or more syntax elements indicating information about the shape and/or number of sections of the subblock.

[0149] The number of sub-blocks may be determined based on the size of the current block, the position of the current block, the length of one side (i.e., width or height) of the current block, the number of pixels included in the current block, the intra-prediction mode of the current block, the size of the minimum or maximum conversion block, etc.

[0150] In some cases, the number of subblocks may be determined by the width and height of the current block. For example, when the width and height of the current block are 4x8 or 8x4, the number of subblocks can be defined as 2, and when the width and height of the current block are greater than 4x4 and not equal to 4x8 and 8x4, the number of sub-blocks can be defined as 4. As another example, when the width and height of the current block are 4×8 or 8×4, the number of sub-blocks can be defined as 2, and when the width and height of the current block are between 8×N to 32×N or from N×8 to Nx32 (here N>4), the number of sub-blocks can be defined as 4, and the number of sub-blocks can be defined as 8 for current blocks whose size is greater than 32xN and Nx32.

[0151] The reference sample builder 820 may check for available neighboring samples and use the available samples to construct reference samples to be used for prediction. When there is no sample available, or when intra-prediction using neighboring samples is not performed, the reference sample builder 820 may arbitrarily construct the reference sample.

[0152] The reference sample filtering unit 830 determines whether to perform filtering. Whether to perform filtering may be determined based on information about at least one of the size, depth, QP, and mode of the current block. When it is necessary to perform filtering, the reference sample filtering unit 830 may select a filter to perform the filtering. In this case, information about what filtering to perform can be extracted from the bitstream.

[0153] The prediction signal generation unit 840 may generate an intra-predicted sub-block by predicting a sub-block currently to be reconstructed from among a plurality of sub-blocks from previously reconstructed pixels around the sub-block. Specifically, when predicting the next subblock, the prediction signal generation unit 840 may use the reconstructed signal of the previous subblock and the reconstructed signal of the previously reconstructed CU. To generate a reconstructed subblock, the intra-predicted subblock can be summed with the reconstructed residual subblock from the bitstream.

[0154] In FIG. 9 is a flow diagram of a method performed by a video decoding apparatus for decoding a current intra-prediction encoded block from a coded video bitstream, according to at least one embodiment of the present invention.

[0155] In step S910, the video decoding apparatus determines whether the current intra-prediction encoded block should be divided into a plurality of sub-blocks. Specifically, the video decoding apparatus divides the current block into equal-sized subblocks and determines whether to perform intra-prediction for the corresponding sub-blocks using the same intra-prediction mode as the intra-prediction mode of the current block.

[0156] For example, a video decoding apparatus may decode from the bit stream a split flag indicating whether the current block should be split, and determine whether the current block should be split based on the split flag. The first value (eg, "0") of the split flag may indicate that the current block has not been split into multiple subblocks, and the second value (eg, "1") of the split flag may indicate that the current block has been split into multiple subblocks and was intra-predicted by each subblock.

[0157] The split flag may be output by the video decoding device without explicit signaling, that is, without decoding from the bitstream, but instead depending on the width and height of the current block, the area of the current block, the minimum transform size, and the maximum transform size allowed for the transform conversion factors. Accordingly, the video decoding apparatus may derive a split flag value based on the width and height of the current block, the area of the current block, and the minimum and maximum transform sizes allowed for transform transform coefficients.

[0158] In step S920, the video decoding apparatus may respond to the fact that the current block is divided into a plurality of sub-blocks, to determine the division direction for the current block between the horizontal division direction and the vertical division direction and the number of sub-blocks based on the divided information decoded from the bit stream and the width and height of the current block.

[0159] Whether the dividing direction is horizontal or vertical may be determined by the dividing information. Alternatively or additionally, the dividing direction can be determined based on the width to height ratio of the current block. For example, a split direction can be defined as a horizontal split when the current block's width is greater than its height, and can be defined as a vertical split when the current block's width is less than its height.

[0160] The number of sub-blocks may be determined by the width and height of the current block. For example, when the width and height of the current block are 4x8 or 8x4, the number of subblocks can be defined as 2, and when the width and height of the current block are greater than 4x4 and not equal to 4x8 and 8x4, the number of subblocks can be defined as 4.

[0161] In step S930, the video decoding apparatus reconstructs the current block by sequentially reconstructing a plurality of sub-blocks divided according to the dividing direction and the number of sub-blocks through intra-prediction.

[0162] For example, a video decoding apparatus may generate an intra-predicted sub-block by predicting a target sub-block to be encoded from among a plurality of sub-blocks from previously reconstructed pixels around the target sub-block (S932). The video decoding apparatus may decode transform coefficient information corresponding to the target subblock from the bit stream to recover transform coefficients (S934), and inversely quantize and inversely transform the transform coefficients using the same transform size as the target subblock to generate a residual subblock , having residual signals (S939). The video decoding apparatus may reconstruct the target subblock using the intra-predicted subblock and the residual subblock (S938). The pixels in the reconstructed sub-block can be used to intra-predict the next sub-block in the current block.

[0163] Additionally, at or before step S930, the video decoding apparatus may decode intra-prediction mode information of the current block from the bitstream to determine the intra-prediction mode of the current block. For example, a video decoding apparatus may select a predetermined number of intra-prediction mode candidates (ie, MPM candidates) from a plurality of intra-prediction modes, and use the intra-prediction mode information of the current block to determine the intra-prediction mode of the current block from among the MPM candidates. Intra-prediction mode candidates can be selected in different ways according to whether the split direction is horizontal or vertical. For example, when the dividing direction is horizontal, vertically oriented modes may be selected as MPM candidates from among a plurality of intra-prediction modes instead of horizontally oriented modes. In addition, when the dividing direction is vertical, modes with horizontal orientation may be selected as MPM candidates from among a plurality of intra-prediction modes instead of modes with vertical orientation.

[0164] In addition, at or before step S930, the video decoding apparatus may decode from the bit stream a sub-block flag indicating whether a non-zero transform coefficient exists in the target sub-block based on the position of the target sub-block in the current block and the number of sub-blocks. In this case, the video decoding apparatus can recover transform coefficients corresponding to the target sub-block from the bit stream when the sub-block flag indicates that a non-zero transform coefficient exists in the target sub-block. If the subblock flag is not decoded from the bitstream, the video decoding apparatus may set the subblock flag to a value indicating that a non-zero transform coefficient exists in the subblock.

[0165] In step S940, the video encoding apparatus may perform deblocking filtering and other processes on the reconstructed current block, and may store the filtered current block in a buffer (eg, memory 470 of FIG. 4) for use as part of a reference picture for inter-prediction incomplete blocks to be encoded in the image. The video encoding apparatus may establish a grid of N samples at regular intervals in the horizontal and vertical directions and perform deblocking filtering on boundaries that coincide with the grid boundary from among the boundaries between a plurality of sub-blocks in the current block.

[0166] Meanwhile, when a block (CU) is encoded sequentially in units of sub-blocks according to the intra-coding tool described above, both intra-prediction and inter-prediction can be performed when generating a prediction signal (to be added to the corresponding residual signal) of the sub-block. Fig. 10A and 10B are diagrams illustrating a coding block in which a first subblock is recovered first, and a second subblock that is in the process of recovery, when generating a prediction subblock of the second subblock.

[0167] As shown in FIG. 10A, where the first subblock has been restored and the second subblock of the coding unit (CU) is in the process of recovery, a weighted sum (or weighted average) is performed on the prediction subblock 1010 from intra prediction of the second subblock to intra prediction mode and the prediction subblock 1020 from inter -prediction of the second sub-block, thereby generating a final prediction sub-block 1030 (to be added to the corresponding residual signal) of the second sub-block. Here, for inter-prediction in sub-block units, motion information may be transmitted in sub-block units individually, or motion information transmitted for a coding unit (CU) can be generally used for all sub-blocks of the CU.

[0168] When the CU is reconstructed sequentially in units of subblocks, the prediction block 1060 from the inter-prediction of the CU can be used in the process of recovering the corresponding subblocks. As shown in FIG. 10B, where the first subblock has been reconstructed and the second subblock of the coding unit (CU) is in the process of recovery, a weighted sum (or weighted average) is performed on (1) a prediction subblock that corresponds to the second subblock and is extracted from prediction block 1060, and (2 ) of the prediction subblock 1010, which is generated from the intra-prediction of the second subblock, thereby generating the final second subblock prediction subblock 1030. The CU prediction block 1060 may be generated before the final prediction subblock is generated for the first subblock and stored in a buffer before the final prediction subblock is generated for the fourth subblock.

[0169] Accordingly, in some embodiments, when the above-described intra-encoding tool is applied to a current block, the video decoding apparatus may reconstruct the current block sequentially in units of sub-blocks so as to process the target sub-block to be reconstructed by: generating its intra-predicted subblock and inter-predicted subblock; performing a weighted average on the two prediction subblocks to generate a final prediction subblock for the target subblock; and adding the final prediction subblock to the residual subblock decoded from the bitstream. This can restore the target subblock.

[0170] It should be understood that the above description presents illustrative embodiments that may be implemented in various other ways. The functions described in some embodiments may be implemented by hardware, software, firmware, and/or a combination thereof. It should also be understood that the functional components described herein are labeled "...block" to emphasize their ability to be implemented independently.

[0171] Meanwhile, various methods or functions described herein may be implemented as instructions stored on a non-volatile storage medium that can be read and executed by one or more processors. Non-transitory recording medium includes, for example, all types of recording devices in which data is stored in a form readable by a computer system. For example, non-transitory storage media may include, but are not limited to, storage media such as an erasable programmable read-only memory (EPROM), a flash drive, an optical drive, a magnetic hard disk, and a solid-state drive (SSD).

[0172] Although exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible without departing from the spirit and scope of the claimed invention. Therefore, exemplary embodiments of the present invention have been described for brevity and clarity. The scope of the technical idea of the present embodiments is not limited to the illustrations. Accordingly, it is clear to an ordinary specialist that the scope of the claimed invention is limited not by the embodiments that were directly described above, but by the claims and their equivalents.

CROSS REFERENCE TO RELATED STATEMENT

This application claims priority to Korean Patent Application No. 10-2019-0028356, filed March 12, 2019, the disclosure of which is incorporated herein by reference in its entirety.

Claims (70)

1. A video decoding device for reconstructing the current block using intra-prediction, containing: memory; a processor coupled to memory and configured to: decoding, from the bit stream, a split flag indicating whether to divide the current block into a plurality of sub-blocks, wherein decoding the split flag depends on the width and height of the current block, the area of the current block, and the minimum transform size and maximum transform size that are allowed for transform coefficients transformations; determining, based on the division flag, whether to divide the current block into a plurality of subblocks; determining when a current block is divided into a plurality of sub-blocks, a dividing direction for the current block between a horizontal dividing direction and a vertical dividing direction based on the dividing information decoded from the bit stream, and determining the number of sub-blocks based on the width and height of the current block; restoring the current block by sequentially restoring sub-blocks specified according to the division direction and the number of sub-blocks using intra-prediction; And setting a grid of N samples at equal intervals in the horizontal and vertical directions and performing deblocking filtering, among the boundaries between the reconstructed subblocks in the current block, boundaries that coincide with the grid boundary, wherein, when the area of the current block is smaller than the area of the transformation unit specified by the minimum transformation size, the division flag is not decoded from the bit stream and is set to a value indicating that the current block should not be divided, wherein, when at least one of the width and height of the current block is greater than the maximum transform size, the division flag is not decoded from the bit stream and is set to a value indicating that the current block should not be divided, wherein the processor is further configured to decode intra-prediction mode information of the current block from the bit stream to determine the intra-prediction mode of the current block, wherein intra-prediction of each of the sub-blocks is performed based on the intra-prediction mode of the current block. 2. The device according to claim 1, in which restoring the current block includes the following steps: predicting a target sub-block currently to be restored from among the sub-blocks of previously restored pixels around the target sub-block to generate an intra-predicted sub-block; creating a residual subblock having residual signals by decoding, from the bitstream, transform coefficient information corresponding to the target subblock to recover the transform coefficients, and perform inverse quantization and inverse transform of the transform coefficients using a transform size equivalent to the target subblock; And reconstructing the target subblock using the intra-predicted subblock and the residual subblock, wherein the pixels in the reconstructed target sub-block are used for intra-prediction of the subsequent sub-block in the current block. 3. The apparatus of claim 2, wherein decoding the transform coefficient information corresponding to the target subblock includes the following steps: decoding, from the bit stream, a sub-block flag indicating whether a non-zero transform coefficient exists in the target sub-block, based on the position of the target sub-block in the current block and the number of sub-blocks; And recovering transform coefficients corresponding to the target subblock from the bit stream when the subblock flag indicates that a non-zero transform coefficient exists in the target subblock. 4. The apparatus of claim 3, wherein if the subblock flag is not decoded from the bit stream, the subblock flag is set to a value indicating that a non-zero conversion coefficient exists in the subblock. 5. The device according to claim 1, in which determining the intra-prediction mode of the current block includes the following steps: selecting a predetermined number of intra-prediction mode candidates from a plurality of available intra-prediction modes; And determining the intra-prediction mode of the current block from among the intra-prediction mode candidates using the intra-prediction mode information of the current block, wherein, intra-prediction mode candidates are selected in different ways depending on whether the dividing direction is a horizontal dividing direction or a vertical dividing direction. 6. The device according to claim 5, in which, when the dividing direction is horizontal, from among the plurality of available intra-prediction modes, modes with vertical orientation are selected as intra-prediction mode candidates instead of modes with horizontal orientation; And, when the dividing direction is vertical, from among the plurality of available intra-prediction modes, modes with horizontal orientation are selected as intra-prediction mode candidates instead of modes with vertical orientation. 7. The device according to claim 6, in which restoring the current block includes the following steps: determining a motion vector of the target sub-block and generating an inter-predicted sub-block for the target sub-block using the motion vector; And generating a prediction sub-block for a target sub-block by calculating a weighted average of the intra-predicted sub-block and the inter-predicted sub-block, wherein the target subblock is reconstructed by adding the prediction subblock and the residual subblock. 8. A video encoding device for reconstructing the current block using intra-prediction, comprising: memory; a processor coupled to memory and configured to: determining whether to divide the current block into a plurality of sub-blocks based on the width and height of the current block, the area of the current block, and the minimum transform size and maximum transform size that are allowed for transforming transform coefficients; encoding, into the bit stream, a split flag indicating whether to divide the current block into a plurality of sub-blocks; determining when the current block is divided into a plurality of sub-blocks, a division direction for the current block between a horizontal division direction and a vertical division direction, and determining the number of sub-blocks based on the width and height of the current block; encoding, into a bit stream, partition information indicating the direction of partition; encoding the current block by sequentially encoding and reconstructing subblocks using intra-prediction; setting a grid of N samples at equal intervals in the horizontal and vertical directions and performing deblocking filtering, among the boundaries between the reconstructed subblocks in the current block, boundaries that coincide with the grid boundary, wherein, when the area of the current block is smaller than the area of the transform unit specified by the minimum transform size, the processor is further configured not to encode the split flag into the bit stream and to determine that the current block should not be split, wherein, when at least one of the width and height of the current block is greater than the maximum transform size, the processor is further configured not to encode the split flag into the bitstream and to determine that the current block should not be split, wherein the processor is further configured to determine the intra-prediction mode of the current block, wherein intra-prediction of each of the sub-blocks is performed based on the intra-prediction mode of the current block. 9. A non-transitory computer-readable medium storing instructions implemented in a processor to perform intra-prediction encoding, the method comprising the following steps: decoding, from the bit stream, a split flag indicating whether to split the current block into a plurality of sub-blocks, wherein decoding the split flag depends on the width and height of the current block, the area of the current block, and the minimum transform size and maximum transform size that are allowed for transform coefficients transformations; determining, based on the division flag, whether to divide the current block into a plurality of subblocks; when the current block is divided into a plurality of sub-blocks, determining a division direction for the current block between the horizontal division direction and the vertical division direction based on the division information decoded from the bit stream, and determining the number of sub-blocks based on the width and height of the current block; recovering the current block by sequentially recovering subblocks in the current block using intra-prediction; And establish a grid of N samples at equal intervals in the horizontal and vertical directions and perform deblocking filtering, among the boundaries between the reconstructed subblocks in the current block, boundaries that coincide with the grid boundary, wherein, when the area of the current block is smaller than the area of the transformation unit specified by the minimum transformation size, the division flag is not decoded from the bit stream and is set to a value indicating that the current block should not be divided, wherein, when at least one of the width and height of the current block is greater than the maximum transform size, the division flag is not decoded from the bit stream and is set to a value indicating that the current block should not be divided, wherein the processor is further configured to decode intra-prediction mode information of the current block from the bit stream to determine the intra-prediction mode of the current block, wherein intra-prediction of each of the sub-blocks is performed based on the intra-prediction mode of the current block. 10. A method for storing a bit stream of encoded video data, the method comprising: encoding the video data into a bitstream by performing an encoding process; And storing the bitstream in a non-transitory machine-readable medium, the encoding process includes: determining whether to divide the current block into a plurality of sub-blocks based on the width and height of the current block, the area of the current block, and the minimum transformation size and maximum transformation size allowed for the transformation of transform coefficients; encoding into the bit stream a split flag indicating whether to divide the current block into a plurality of sub-blocks; when the current block is divided into a plurality of sub-blocks, determining a division direction for the current block between the horizontal division direction and the vertical division direction, and determining the number of sub-blocks based on the width and height of the current block; encoding into the bit stream dividing information specifying the dividing direction; encoding the current block by sequentially encoding and reconstructing subblocks using intra-prediction; And setting a grid of N samples at equal intervals in the horizontal and vertical directions and performing deblocking filtering, among the boundaries between the reconstructed subblocks in the current block, boundaries that coincide with the grid boundary, wherein, when the area of the current block is smaller than the area of the transform unit specified by the minimum transform size, the processor is further configured not to encode the split flag into the bitstream and to determine that the current block should not be split, wherein, when at least one of the width and height of the current block is greater than the maximum transform size, the processor is further configured not to encode the division flag into the bitstream and to determine that the current block should not be divided, wherein, when the intra-prediction mode of the current block is determined, intra-prediction of each of the sub-blocks is performed based on the intra-prediction mode of the current block.