RU2776871C1 - Method and device for efficient coding of residual blocks - Google Patents

Abstract

FIELD: imaging technology.

SUBSTANCE: invention relates to the field of image encoding. A method for decoding video images and a device for decoding video images are proposed. To effectively encode the residual blocks obtained from block-based motion compensation, the video encoding device and the video decoding device divide the corresponding residual block of the current block into two sub-blocks in the horizontal or vertical direction and encode only one residual sub-block of the two residual sub-blocks.

EFFECT: increase in the efficiency of encoding/decoding of residual blocks.

15 cl, 11 dwg

Description

Technical field

The present invention, described in terms of some embodiments, relates to the encoding and decoding of video images. In particular, the present invention relates to a method and apparatus for efficient encoding of residual blocks.

State of the art

Because video data has a large amount of data compared to audio data or still image data, a lot of hardware resources, including memory, are required to store or transmit the data in its raw form before being subjected to the compression process.

Accordingly, storage or transmission of video data is typically accompanied by compression using an encoder before the decoding unit can receive, decompress and play the compressed video data. Known video compression technologies include the H.264/AVC standard and the High Efficiency Video Coding (HEVC) standard, which improves H.264/AVC encoding efficiency by about 40%.

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

In the video encoding process, the video encoding device generates a residual block by performing prediction of the current block by intra-prediction or inter-prediction, and then subtracting the sample values of the current block from the sample values of the prediction block. The video coding apparatus divides the residual block into one or more transform blocks, applies a transform to one or more transform blocks, and thereby converts the residual values of the transform blocks from the pixel domain to the frequency domain. Depending on the accuracy of the prediction, some areas of the residual block may not have residuals or not many residuals, and it is sometimes very inefficient to blindly divide the residual block into smaller transform blocks.

Disclosure of the essence of the invention

Technical problem solved by the invention

The present invention, described in terms of some embodiments, aims to provide a residual block coding scheme suitable for residual blocks having regions with no residuals or small residuals.

Technical solution

In accordance with at least one aspect of the present invention, there is provided a video image decoding apparatus, including a decoding unit, a prediction unit, an inverse quantization and inverse transform unit, an adder, and a filtering unit. The decoding block is configured to decode from the bitstream a flag indicating whether the residual signals corresponding to only a partial area of the current block have been encoded, and decode from the bitstream information about the transform coefficients for one subblock of two separated subblocks from the current block to restore the transform coefficients, when the flag indicates that residual signals corresponding to only a partial area of the current block have been encoded. The prediction block is configured to predict the current block to generate a prediction block. The inverse quantization and inverse transform block is configured to perform inverse quantization and inverse transformation of the transform coefficients in one sub-block for which the transform coefficient information has been decoded to generate a residual block for the current block. The adder is configured to add the prediction block and the residual block to restore the current block. The filtering unit is configured to set up a grid of N samples at regular intervals in the horizontal and vertical directions, and perform deblocking filtering at a boundary between two sub-blocks in the current block that coincides with the grid boundary.

According to another aspect of the present invention, a method for decoding video images is provided, the method including the steps of (i) decoding from a bit stream a flag indicating whether residual signals corresponding to only a partial area of the current block have been encoded, (ii) recovering transform coefficients by decoding from the stream bits of transform coefficient information for one sub-block of two sub-blocks separated from the current block, when the flag indicates that residual signals corresponding to only a partial area of the current block have been encoded, (iii) predicting the current block to generate a prediction block, (iv) generating a residual block for the current block by performing inverse quantization and inverse transformation of the transform coefficients in one sub-block for which the transform coefficient information has been decoded, (v) recovering the current block by adding the prediction block and the residual block, and (vi) setting up a grid of N samples at equal intervals in the horizontal and vertical directions, and performing deblocking filtering on a boundary between two sub-blocks in the current block that coincides with the grid boundary.

Brief description of the drawings

In FIG. 1 is a diagram illustrating a video coding device that can implement the methods of the present invention.

In FIG. 2 is a diagram explaining a block splitting method using a QTBTTT structure.

In FIG. 3A is a diagram illustrating a plurality of intra prediction modes.

On FIG. 3B is a diagram illustrating a plurality of intra-prediction modes, including wide-angle intra-prediction modes.

On FIG. 4 is a diagram illustrating a video decoding apparatus capable of implementing the techniques proposed by the present invention.

In FIG. 5A-5D show different types of separation of the residual block and subblocks to be encoded.

In FIG. 6 is a diagram for explaining a case of encoding a single sub-block in a relevant residual block of a current block, illustrating positions of adjacent blocks to be referred to for quantization parameter (QP) prediction.

In FIG. 7 shows a diagram of a chrominance block and at least one luminance block that is aligned with the chrominance block.

In FIG. 8 is a diagram of the reconstructed current blocks illustrating their relevant residual blocks undergoing vertical splits and transformations in their left subblocks in order to reveal their inter-block separation boundaries along the deblocking boundary.

In FIG. 9 is a diagram for explaining deblocking filtering performed on a boundary between residual sub-blocks at a residual signal level.

In FIG. 10 is a flowchart of a method performed by a video coding apparatus for inter-prediction coding of a current video block according to at least one embodiment of the present invention.

In FIG. 11 is a flowchart of a method performed by a video decoding apparatus for decoding an inter-prediction encoded current block from an encoded video bitstream according to at least one embodiment of the present invention.

Implementation of the invention

Hereinafter, an embodiment of the present invention will be described in detail with reference to the attached drawings. In the following description, like reference numerals preferably refer to like elements, even though these elements are shown in different drawings. In addition, for the sake of clarity and brevity, in the following description of some embodiments, a detailed description of known components and functions related thereto is omitted when they obscure the subject matter of the present invention.

In FIG. 1 is a diagram illustrating a video encoding device that can implement the methods of the present invention. Next, the video encoding apparatus and components of the apparatus will be described with reference to FIG. one.

The video coding apparatus may be configured to include an image division block 110, a prediction block 120, a subtraction block 130, a transformation block 140, a quantization block 145, a reorder block 150, an entropy encoding block 155, an inverse quantization block 160, an inverse transformation block 165 , adder 170, filter unit 180 and memory 190.

The respective components of the video encoder may be implemented as hardware or software, or as a combination of hardware and software. In addition, the function of each component may be implemented in software, and the software function for each component may be implemented with the possibility of executing the microprocessor.

A video image consists of a plurality of images. Each image is divided into a plurality of sections, and encoding is performed for each section. For example, one image is divided into one or more fragments and/or sections. Here, one or more fragments can be defined as a group of fragments. Each fragment 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 applicable to corresponding CUs is encoded as CU syntax, and information normally applied to CUs included in one CTU is encoded as CTU syntax. In addition, information generally applicable to all blocks in one section is encoded as section header syntax, and information applicable to all blocks constituting one picture is encoded in a picture parameter set (PPS) or picture header. In addition, information commonly referred to by a plurality of pictures is encoded in a sequence parameter set (SPS). In addition, information typically referred to by one or more SPSs is encoded in a Video Parameter Set (VPS). In the same way, information normally applied to a single fragment or group of fragments can be encoded as fragment header or fragment group header syntax.

The picture splitter 110 determines the size of the CTU coding tree unit. CTU size information (CTU size) is encoded as the syntax of an SPS set or a PPS set and transmitted to the video decoding apparatus.

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

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

In FIG. 2 shows a tree structure of the QTBTTT partition. As shown in FIG. 2, the CTU may first be divided into a QT structure. The splitting of the quadtree may be repeated until the splitting block size reaches the minimum block size (MinQTSize) of the 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 apparatus. If the leaf node of the QT structure does not exceed the maximum size (MaxBTSize) of the root node block allowed in the BT structure, it may be further divided into any one or more BT structures or TT structures. In the BT structure and/or the TT structure, there may be a plurality of separation directions. For example, there may be two directions in which the block of the corresponding node splits horizontally and vertically. As shown in FIG. 2, when the MTT split starts, 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 the entropy encoding unit 155 and transmitted to the video decoding device.

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) indicating whether the node is split or not may be encoded. When the value of the CU's split flag (split_cu_flag) indicates that a node has not been split, that node's block becomes a leaf node in the split tree structure and becomes a coding unit (CU), which is a basic coding unit. When the value of the CU split flag (split_cu_flag) indicates that the node has been split, the video encoding device starts encoding from the first flag in the manner described above.

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 partitioning), and a type in which it is also divided vertically (i.e., symmetrical vertical separation). The entropy encoding block 155 to be encoded and transmitted to the video decoding apparatus is a split flag (split_flag) indicating whether each node of the BT structure is divided into lower-layer blocks, and split type information indicating its split type. Meanwhile, there may be an additional type in which the block of the corresponding node is split into two asymmetrically shaped blocks. The asymmetric shape may include a block shape of the corresponding node being split into two rectangular blocks having an aspect ratio of 1:3, or a block shape of the corresponding node being split in a diagonal direction.

The CU may have different sizes depending on the structure of the QTBT or QTBTTT partition of the CTU. Hereinafter, a block corresponding to a CU to be encoded or decoded (ie, a QTBTTT end node) is referred to as a "current block". When using the QTBTTT division, the current block can be in the form of not only a square, but also a rectangle.

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 .

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, wherein the intra-prediction method uses data from the image containing the current block itself, and the inter-prediction method uses data from the previous image encoded before the image containing current block. Inter prediction includes both unidirectional and bidirectional prediction.

The intra-prediction block 122 predicts pixels in the current block using peripheral pixels (reference pixels) located around the current block in the current image. The different directions of prediction represent several respective modes of intra-prediction. For example, as shown in FIG. 3A, the multiple intra prediction modes may include 2 non-directional modes, including a planar mode and a DC mode, as well as 65 directional modes. The respective prediction modes provide various respective definitions of neighboring pixels and calculation formulas to be used.

For efficient directional prediction of the current rectangular block, additional modes used may be the directional modes shown in FIG. 3B by dashed intra-prediction mode arrows 67-80 and -1 to -14. These may be referred to as "wide-angle intra-prediction modes". The arrows in Fig. 3B indicate the respective reference samples used for prediction rather than the direction of prediction. The direction of prediction is opposite to the direction indicated by the arrow. Wide-angle intra-prediction modes are modes applied when the current block is rectangular in order to perform prediction of a particular directional mode in the reverse direction without additional bit transmission. In this case, among 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 67-80) are available for use in the current block when they have a rectangular shape in which the height is less than the width. Wide-angle intra-prediction modes having an angle of -135 degrees or more (intra-prediction modes numbered from -1 to -14) are available for use in the current block when there is a rectangular shape with a height greater than the width.

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 to use from among the tested modes. For example, intra-prediction block 122 may calculate velocity distortion values by analyzing the rate-distortion of several tested intra-prediction modes and select the intra-prediction mode that has the best rate-distortion performance among the tested modes.

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. The information about the selected intra-prediction mode is encoded by the entropy encoding unit 155 and transmitted to the video decoding device.

The inter-prediction block 124 generates a prediction block for the current block through a motion compensation process. The inter-prediction block 124 searches for a block most similar to the current block in the encoded and decoded reference picture before the current picture, and generates a prediction block of the current block using the found block. Next, inter-prediction block 124 generates a motion vector corresponding to an offset between the current block in the current picture and the prediction block in the reference picture. In general, motion estimation is performed for the luma component, and a motion vector calculated from the luminance component is used for both the luminance component and the chrominance component. Motion information including reference picture information and motion vector information used to predict the current block is encoded by the entropy encoding block 155 and transmitted to the video decoding apparatus.

The subtractor 130 generates a residual block by subtracting from the current block the prediction block generated by the intra prediction block 122 or the inter prediction block 124 .

The transform block 140 divides the residual block into one or more transform blocks, applies a transform to one or more transform blocks, and thus transforms the residual values of the transform blocks from the pixel domain to the frequency domain. In the frequency domain, transformed blocks are referred to as coefficient blocks containing one or more transform coefficient values. A 2D transformation kernel may be used for the transformation, and a 1D transformation kernel may be used for each of the horizontal transformation and the transformation in the vertical direction. Transform kernels may be based on discrete cosine transform (DCT), discrete sine transform (DST), or the like.

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. In addition, the transformation unit 140 may divide the residual block into two subblocks in the horizontal or vertical direction and perform transformation on only one of the two subblocks, as will be described below with reference to Figures 5A to 5D. Accordingly, the size of the transform block may differ from the size of the residual block (and hence the size of the prediction block). In a sub-block in which no transformation is performed, there may be no non-zero sample residuals, or they may be very few. The residual samples of the sub-block in which the transformation is performed are not signaled, and all of them can be considered by the video decoding device as "0". Depending on the directions and ratios of separation, there may be several types of separation. The transform block 140 provides the entropy encoding block 155 with information about the coding mode (or transform mode) of the residual block, such as information indicating whether the transformed residual block is a residual subblock, information indicating the partition type selected for dividing the residual block into subblocks, and information for identifying the sub-block in which the transformation is performed, etc. The entropy encoding block 155 may encode information about the encoding mode (or transformation mode) of the residual block.

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 . Quantizer 145 may directly quantize the corresponding residual block for a particular block or frame without transformation.

The reordering unit 150 may reorder the coefficient values on the quantized residual samples. Reorderer 150 may use a coefficient scan to transform a two-dimensional coefficient matrix into a one-dimensional coefficient sequence. For example, the reordering unit 150 may scan the DC coefficients to coefficients in the high frequency region by zigzag scanning or diagonal scanning to output a one-dimensional sequence of coefficients. Depending on the transform block size and the intra-prediction mode, the zigzag scan used can be replaced by a vertical scan to scan the 2D coefficient array in the column direction and a horizontal scan to scan the coefficients into a 2D 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.

The entropy encoding unit 155 uses various encoding techniques such as context-dependent adaptive binary arithmetic coding (CABAC), exponential Golomb code, and the like, to encode a sequence of one-dimensional quantized transform coefficients output from the reordering unit 150 to generate a bit stream.

In addition, the entropy encoding unit 155 encodes block division information such as CTU 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 the encoder. video images. 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, ie, information about reference pictures and motion vectors.

An inverse quantizer 160 performs inverse quantization of the quantized transform coefficients output from the quantizer 145 to generate transform coefficients. An inverse transform block 165 converts the transform coefficients output from the inverse quantizer 160 from the frequency domain to the spatial domain to recover the residual block.

Adder 170 adds the recovered residual block and the prediction block generated by predictor 120 to recover the current block. The pixels in the reconstructed current block are used as reference pixels in intra-prediction of the next block.

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

The deblocking filter 180 filters the boundary between reconstructed blocks to remove block artifact caused by block-by-block encoding/decoding, and the SAO filter 184 performs additional filtering of 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 coding.

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

On FIG. 4 is a diagram illustrating a video decoding apparatus capable of implementing the methods of the present invention. Hereinafter, the video decoding apparatus and components of the apparatus will be described with reference to FIG. four.

The video decoder may be configured to include an entropy decoder 410, a reorderer 415, an inverse quantizer 420, an inverse transform 430, a predictor 440, an adder 450, a filter 460, and a memory 470.

As in the video encoding device of FIG. 1, the respective components of the video decoding apparatus may be implemented as hardware or software, or as a combination of hardware and software. In addition, the function of each component may be implemented in software, and the software function for each component may be implemented with the possibility of executing the microprocessor.

The entropy decoding section 410 decodes the bitstream generated by the video encoding apparatus and extracts block separation information to determine the current block to be decoded, and extracts prediction information necessary to reconstruct the current block and residual signal information, etc.

The entropy decoder 410 extracts the CTU size information from the sequence parameter set (SPS) or the picture parameter set (PPS), determines the size of the CTU, and divides the image into CTUs of a given size. Then, the entropy decoding section 410 determines the CTU as the highest level, that is, the root node of the tree structure, and extracts partition information on the CTU, and thereby partitions the CTU using the tree structure.

For example, when splitting a CTU using the QTBTTT structure, the first flag (QT_split_flag) associated with the QT split is first extracted and each node is split into four lower level nodes. For a node corresponding to a QT end node, entropy decoder 410 extracts a second flag (MTT_split_flag) associated with the MTT split and split direction (vertical/horizontal) and/or split type (binary/ternary) information to split this end node into MTT structure. This allows you to recursively split the corresponding nodes below the end node QT into a BT or TT structure.

As another example, when splitting a CTU using the QTBTTT structure, entropy decoding unit 410 may first extract a CU split flag (split_cu_flag) indicating whether the CU is split, and after splitting the corresponding block, it may also extract the first flag. (QT_split_flag). During the splitting process, each node may have zero or more recursive QT splits followed by zero or more recursive MTT splits. For example, a CTU may immediately enter an MTT division or, conversely, have only a few QT divisions.

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

Meanwhile, when the entropy decoding section 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 an intra prediction, the entropy decoding block 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 section 410 extracts a syntax element for inter prediction information, that is, information indicating a motion vector and a reference image referenced by the motion vector.

Meanwhile, the entropy decoding section 410 extracts from the bit stream information about the coding mode of the residual block, such as whether the residual block has been encoded or whether only subblocks of the residual block have been encoded, information indicating the selected partition type for dividing the residual block into subblocks, information identifying encoded residual sub-blocks, quantization parameters, etc. In addition, the entropy decoding section 410 extracts information about the quantized transform coefficients of the current block as information about the residual signal.

The reorderer 415 reorders, in the reverse order of the coefficient scan sequence performed by the video coding apparatus, the one-dimensional quantized transform coefficients that are entropy decoded by the entropy decoder 410 into a two-dimensional coefficient array, i.e. block.

An inverse quantizer 420 performs inverse quantization of the quantized transform coefficients. The inverse transform block 430 inversely transforms, based on the coding mode information of the residual block, the inversely quantized frequency-domain-to-spatial transform coefficients to recover the residual signals, and thereby generate a reconstructed residual block of the current block.

The inverse transform block 430 responds when the residual block coding mode information indicates that the residual block of the current block has been encoded in the video encoder by inversely transforming the inversely quantized transform coefficients using the current block size (thus, the residual block size must be restored) as a transformation unit for generating the restored residual block of the current block.

In addition, the inverse transform section 430 is responsive to when the coding mode information of the residual block indicates that a single sub-block of the residual block has been encoded in the video coding apparatus by performing inverse transform on the inversely quantized transform coefficients using the transformed sub-block size as the transform unit for restoring the residual signals of the transformed sub-block while filling the residual signals of the non-transformed sub-block with values of "0", thereby generating a reconstructed residual block of the current block.

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.

The intra-prediction block 442 determines, among the 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 block 410, and according to the determined intra-prediction mode, it predicts the current block using neighboring reference pixels of the current block.

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 picture referenced by the motion vector, and it uses the motion vector and the reference picture as determined to predict the current block .

An 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 in intra-prediction of the incoming block to be decoded.

The filter block 460 may include a deblocking filter 462 and a SAO filter 464 . Deblocking filter 462 deblocks and filters the boundary between reconstructed blocks to remove block artifact caused by block decoding. The SAO filter 464 performs additional filtering on the reconstructed block after deblocking filtering to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy coding. The reconstructed block is filtered through the deblocking filter 182 and the SAO filter 184 and stored in the memory 190. When all blocks in one picture are reconstructed, the reconstructed picture can be used as a reference picture for inter-prediction of blocks in the nearer picture to be encoded.

The techniques of the embodiments illustrated herein generally refer to inter-prediction coding, ie, encoding and decoding the current block. In order to efficiently encode the residual block obtained according to block-based motion compensation, the video encoding apparatus may divide the residual block into two residual sub-blocks in the horizontal or vertical direction, and encode only one residual sub-block between the two residual sub-blocks. In other words, the transformation and quantization process can only be applied to one residual sub-block. Residual values of the other uncoded sub-block are treated as "0" or ignored. Such an encoding tool can be effective in encoding a residual block when some area of it has no residual value or has a small residual value.

The video encoding device may select the optimal coding mode from the first and second coding modes, wherein the first coding mode encodes the residual block, thereby converting the residual signals in the residual block into a transformation block that is equal in size to the prediction block, and the second coding mode separates the residual block. block into two sub-blocks in the horizontal or vertical direction, and encodes only one sub-block, thus converting the residual signals in the residual block into a transformation block that is different in size from the prediction block.

Next, the second mode associated with residual block coding is described in detail. The following description mainly refers to the decoding technology, in particular, to the operation of the video decoding apparatus, and the encoding technology is described briefly, since the latter is the reverse of the decoding technology described in detail. In addition, the terms "subunit(s) of the residual block" and "residual(s) subunit(s)" can be used interchangeably.

1. Separation type and conversion position

In FIG. 5A-5D show various types of splitting or partitioning of the residual block and sub-blocks to be encoded (and thus transformed). The remaining block can be divided into two subblocks. In the illustrated residual blocks 510-580, the sub-blocks that undergo transformation are shaded and labeled "A". A sub-block located on the left or top side in the remainder block may be expressed as being located at "position 0" in the remainder block, and a sub-block located on the right or bottom side in the remainder block may be expressed as being located at "position 1" in the remaining block. The position of the sub-block in the residual block at which the transformation is performed may be referred to as the "transformation position". Therefore, the transformation position indicated as "position 0" may represent a transformation performed on a sub-block located on the left or top side in the residual block, the transformation position indicated as "position 1" may represent a transformation performed on a sub-block. located on the right or bottom in the residual block.

Different types of splitting can be considered according to the splitting direction and the splitting factor. The types of block separation to be considered include the first type in which the separation occurs symmetrically in the horizontal direction, the second type in which the separation occurs symmetrically in the vertical direction, the third type in which the separation occurs asymmetrically in the horizontal direction (for example, in ratio of 1:3 or 3:1), and a fourth type in which the separation occurs asymmetrically in the vertical direction (for example, in a ratio of 1:3 or 3:1).

The block 510 is vertically divided into a left sub-block and a right sub-block, and the transformation is not performed in the right sub-block at position 1, but is performed in the left sub-block at position 0. The block 520 is vertically divided into left and right sub-blocks, and the transformation is not performed in the left sub-block, but is performed in the right sub-block at position 1. The block 530 is horizontally divided into upper and lower sub-blocks, and the transformation is performed in the upper sub-block at position 0 rather than the lower sub-block. Block 540 is horizontally divided into two sub-blocks and the transformation is performed in the lower sub-block at position 1, and not in the upper sub-block.

Block 550 is vertically divided into a left sub-block and a right sub-block with a ratio of 1:3, and the transformation is not performed in the right sub-block at position 1, but is performed in the left sub-block at position 0. Block 560 is vertically divided into left and right sub-blocks with a ratio of 3:1, and the transformation is performed not in the left sub-block but in the right sub-block at position 1. The block 570 is horizontally divided into upper and lower sub-blocks having a ratio of 1:3, and the transformation is performed on the upper sub-block at position 0 rather than in the lower sub-block. Block 540 is divided into two sub-blocks in the horizontal direction, and the transformation is performed in the lower sub-block at position 1 rather than in the upper sub-block.

As with blocks 550-580 shown in FIG. 5C and 5D, when the residual block is split asymmetrically (eg, in a ratio of 1:3 or 3:1), a default may be set to perform transformation on a smaller subblock.

The available split ratios and split direction may be limited according to the size of the residual block to provide 4 or more pixels for the height or width of the sub-block that is being transformed. For example, a first type of horizontally symmetrical separation may be allowed for residual blocks having a width of 8 or more pixels, and a second type of vertically symmetrical separation may be allowed for residual blocks having a height of 8 or more pixels. Similarly, a third type and a fourth type that provide horizontal or vertical asymmetric separation may be allowed for residual blocks having a width or height of 16 or more pixels.

2. Choice of the transformation kernel.

Depending on the splitting direction (horizontal or vertical) of the residual box and its transform position, i.e. the position of the transformed subbox, the transform kernels (horTransform and verTransform) in the horizontal and vertical directions can be selected to be used to transform the subbox.

When a vertical split is applied to a residual block, the kernel to be used to transform the subblock can be implicitly obtained as follows. In the case of blocks 510 and 550, when the sub-block to be transformed is at position 0, then (horTransform, verTransform) = (DCT-8, DST-7). In the case of blocks 520 and 560, when the sub-block to be transformed is at position 1, then (horTransform, verTransform) = (DST-7, DST-7).

When a vertical split is applied to a residual block, the kernel to be used to transform the subblock can be implicitly obtained as follows. In the case of blocks 510 and 550, when the sub-block to be transformed is at position 0, then (horTransform, verTransform) = (DCT-8, DST-7). In the case of blocks 520 and 560, when the sub-block to be transformed is at position 1, then (horTransform, verTransform) = (DST-7, DST-7).

When one of the residual subblocks is larger than 32 pixels, the DCT-2 core can be applied to both horizontal and vertical directions. Furthermore, for a chrominance component residual block, a DCT-2 kernel can always be applied to the transformation of the residual sub-block, regardless of the division direction (horizontal or vertical) of the residual block and its transformation position, i.e. positions of the transformed subblock. In some cases, information may be explicitly transmitted identifying the transformation kernels used for the transformation in the horizontal and vertical directions.

3. Residual coding mode signaling

When the current block is encoded with inter-prediction and the corresponding residual block has at least one non-zero coefficient, a first flag may be explicitly signaled to indicate whether the relevant residual block of the current block is transformed or only one subblock of the residual block is encoded.

Accordingly, the video decoding apparatus, at the time of restoring the residual block of the current block encoded with inter-prediction, may decode the first flag from the bitstream to determine whether the video encoding apparatus has divided the residual block into two subblocks and whether it has coded only one subblock of the two subblocks. .

In some embodiments, the first flag signaling may be omitted depending on the width or height of the current block, or depending on the product of the width and height, the ratio of width to height, and the greater of the width and height. For example, when the width and height of the current block is less than 8 pixels, the video decoding apparatus may skip decoding the first flag and conclude that the entire remaining block of the current block has been converted.

When only one sub-block of the residual block is encoded, the split type and transformation position of the residual block may be additionally signaled. To the video encoding device, information about the split type and the transform position can be provided in various ways. For example, one syntax element may be used to represent the split type of the residual block, or two flags may be used to represent the split factor and split direction. In addition, one flag may be used to represent a transform position, which is the position of the sub-block to be converted. For example, you can set a flag indicating the position of the transformation to "0" when the transformation is applied to a sub-block located on the left or top side in the remainder block, and set a flag indicating the position of the transformation to "1" when the transformation is applied to subblock located to the right or bottom of the residual block.

The residual block, when split at a ratio of 1:3 or 3:1, can add a constraint that the transformation is invariably performed in a smaller subblock, thus avoiding signaling a flag indicating the position of the transformation.

In addition, depending on the width and height of the residual block, or depending on the product of the width and height, the ratio of width to height, and the larger of the width and height values, it is possible to limit the use of some type of separation or separation direction and/or separation factor, which can eliminate signaling syntax elements representing the same split type or split direction and/or split factor. For example, when the width and height of the residual block is less than 16 pixels, division of the residual block "at a ratio of 1:3 or 3:1" cannot be allowed. Accordingly, the video decoding apparatus can respond to the residual block when the width and height are less than 16 pixels to output a split ratio as 1:1 without decoding a flag indicating a split ratio. In another example, when the width (or height) of the residual block is less than 8 pixels, division of the residual block in the vertical direction (or horizontal direction) cannot be allowed. Accordingly, the video decoding apparatus can respond to a residual block having a width of less than 8 pixels to infer that the residual block is divided in the horizontal direction without decoding flags indicating the division direction. Similarly, the video decoding apparatus may respond to the residual block when it is less than 8 pixels high to infer that the division is performed in the vertical direction. According to another example, the device may respond such that when the width is greater than the height, it is concluded that the separation is in the vertical direction, and when the height is greater than the width, it is inferred that the separation is in the horizontal direction.

The residual block associated with the luminance component may have its single residual subblock exclusively coded, in which case the corresponding residual block associated with the chroma component may also have its single residual subblock exclusively coded. Accordingly, the first flag transmitted at the unit level of the CU may be shared between the luminance component residual block and the chrominance component residual blocks.

The same residual coding mode selected for the luminance component residual block may be applied to the chrominance component residual block co-located with the luminance component residual block. In other words, when the luminance component residual block has only one coded subblock, the chrominance component residual block may similarly have only one coded subblock. In this case, information about the division type of the residual block and the position of the sub-block to be encoded can be shared between the luminance block and the chrominance blocks.

In at least one embodiment of a single tree structure, the same residual coding mode may be applied to the luminance component and the chrominance component, and the same split direction information defined for the luminance component residual block and the position of the sub-block to be encoded may be applied. to the residual blocks of chrominance components. According to another example, in the case of encoding only one sub-block of the chroma component residual block, when only one sub-block of the aligned luminance component residual block is similarly encoded, the same split direction information specified for the luminance component residual block and the position of the sub-block to be encoded, can be applied to the residual blocks of the chrominance component.

4. Recovery of the residual block

Based on the split type and the transform position, the video decoding apparatus can determine the position of the sub-block in the residual block where to decode the corresponding transform coefficient information from the bitstream, as well as the size of the sub-block. The video decoding apparatus may decode the transform coefficient information from the bit stream to recover the transform coefficients of the sub-block corresponding to the transform position. The video decoding apparatus applies an inverse quantization/inverse transform process to the reconstructed transform coefficients to generate residual signals of the sub-block corresponding to the transform position, and sets all residual signals of the other sub-block corresponding to the untransformed position to "0", thereby restoring the residual block of the current block .

Similarly, the video coding apparatus performs transformation and quantization of the residual subblock corresponding to the transform position, entropy encodes the quantized transform coefficients, and applies an inverse quantization/inverse transform process to the quantized transform coefficients to recover the residual subblock corresponding to the transform position, and sets all the residual signals of another subblock, corresponding positions without conversion to "0", thereby restoring the residual block of the current block.

5. Calculation of quantization parameters.

The video encoder may determine a quantization parameter (QP) value for the current block (CU), and determine, based on the QP value and the QP prediction value, a differential quantization parameter (Delta QP or DQP) value for the current block. The video encoder may be configured to signal the DQP value and quantize the current block using the determined QP value. The video encoder may adjust the QP value of the current block, and thus adjust the amount of quantization applied to blocks of coefficients related to the current block.

DQP is defined as the difference between the current QP, i.e. the actual QP used in the current block and the predicted value of the current QP or the predicted QP value. Based on the signaled DQP, the corresponding current QP value can be recovered by adding the DQP to the QP prediction value. In particular, the video coding device outputs the DQP to be calculated by subtracting the QP prediction value from the actual QP of the current block, and the video decoding apparatus outputs the actual QP of the current block to be recovered by adding the received DQP to the QP prediction value.

In some embodiments, the average of the actual QP values for the top block and the left block with respect to the current block may be determined as the QP prediction value of the current block. In some other embodiments, representative values (eg, mean, median, etc.) of the actual QP values for left block, top left block, and top block relative to the current block may be determined as the QP prediction value for the current block.

In some embodiments, only one sub-block of the corresponding residual block of the current block is encoded, with the information about the partitions of the residual block, the split shape or position of the sub-block to encode, etc. being used as the basis for selecting neighboring blocks to refer to. Then, the actual QP values for selecting neighboring blocks may be used as the QP prediction value of the current block, or the actual QP values of the selected neighboring block(s) may be used as the basis for deriving the QP prediction value for the current block.

In FIG. 6 is a diagram explaining the case of encoding one sub-block in the relevant residual block of the current block, illustrating positions of neighboring blocks to be referred to for quantization parameter (QP) prediction.

When the residual block 610 is vertically divided and there is a residual signal only in the left subblock, that is, only the left subblock is encoded, at least one of the QP prediction values of adjacent blocks "a, b, d, e" adjacent to the left subblock can be used. as the basis for calculating the QP prediction value of the current block. For example, the QP prediction value of the current block may be calculated based on the average of the QP values of block "a" and block "b".

When the residual block 620 is vertically divided and there is a residual signal only in the right subblock, that is, only the right subblock is encoded, the QP value of block "c", which is a neighboring block adjacent to the right subblock, can be determined as the QP prediction value of the current block.

In FIG. 7 shows a diagram of a chrominance block and at least one luminance block that is aligned with the chrominance block.

The QP value for the chrominance block may be determined based on the determined QP value for the corresponding luminance block(s). The QP prediction value of the chrominance block may be determined based on the QP value of the luma block at the same location. As an example, the QP value of the luminance block "a" located in the upper left corner of the current block may be used as the QP prediction value for the residual chroma component block. Alternatively, the chrominance component residual block QP prediction value used may be the most frequent value, the maximum value, the minimum value, the average value, or the average value among the QP values of the luma blocks "a to i".

When encoding one subblock in a chrominance component residual block, the chrominance block QP prediction value used may be a luma block QP value selected based on a larger value (alternatively a smaller value) among the residual block split direction, subblock position for encoding, subblock size, horizontal to vertical ratio subblock, as well as the width or height of the subblock. In at least one embodiment, the QP prediction value of the chroma component block used is the QP value of one of the "d" block and the "i" block, which are the luminance blocks corresponding to the A subblock encoded in the chroma component, the residual block, or the mean of the values QP of block "d" and block "i".

6. In-loop filtration

The video encoder and the video decoder may perform in-loop filtering, including deblocking filtering on the reconstructed current block, and store the filtered current block in a buffer (e.g., memory 190 in FIG. 1 and memory 470 in FIG. 4) for future use. as a reference picture for inter-prediction of incoming blocks in the encoded picture.

The deblocking filter is applied to the pixels at the block boundary to reduce block artifacts caused by the boundary between blocks in the reconstructed image. Deblocking filtering is performed on the vertical border and the horizontal border. Filtering, first performed on the vertical boundary, can serve as input for subsequent filtering of the horizontal boundary.

In FIG. 8 is a diagram of the reconstructed current blocks (810, 820) illustrating their respective residual blocks undergoing vertical splits and transforms in their left subblocks (i.e., transform position is 0) to show their inter-subblock split boundaries and deblocking boundary.

The video encoder and the video decoder may determine whether or not to apply deblocking filtering to the current block based on whether a 4x4 (or 8x8) deblocking boundary matches a boundary between sub-blocks of the residual block. For example, the video decoding apparatus may set up a grid of N samples at regular intervals in the horizontal and vertical directions, and perform deblocking filtering only when the boundary between two sub-blocks in the current block matches the grid boundary. Accordingly, deblocking filtering cannot be performed on boundaries between sub-blocks that do not coincide with a grid boundary. Here N can be set to 2n (n is a natural number). Alternatively, the video encoder and the video decoder may determine whether to apply deblocking filtering to the current block based on pixels included in multiple columns or rows included in the current block. A grid in different units can be used depending on whether the current block is a luma block or a chrominance block. For example, the grid may be set to 4x4 units for the luminance block, and the grid may be set to 8x8 units for the chrominance block.

In some embodiments, deblocking filtering may be performed at the reconstructed residual signal level. In FIG. 9 is a diagram for explaining deblocking filtering performed on a boundary between residual sub-blocks at a residual signal level. On ifg. 9 shows a 4×8 residual block that undergoes a horizontal split and transformation in its lower 4×4 subblock (ie, the transformation position is 1). After the residual signals corresponding to the lower sub-block are restored and the residual signals of the upper sub-block are filled with "0" to complete the restored residual block, deblocking filtering can be performed on the residual block. The embodiment of FIG. 9 illustrates a one-dimensional mean filter having the parameter [1 2 1] applied to the boundary between two sub-blocks.

When applying the deblocking filter to the current block, a strong filter or a weak filter can be selected according to the required strength of the deblocking filtering. In addition, you can consider using various conventional filters in common image processing methods such as mean value filter, median value filter, and two-sided filter.

With regard to filter selection, the video decoding device may be informed by the video encoding device of the filter to be used before selecting a filter to use in the residual deblocking filtering. For example, the filter index to be used may be reported among a plurality of predefined filters. Alternatively, one predefined filter can be used.

Once a filter is selected, in embodiments, filtering parameters related to the selected filter are calculated, in particular, parameters that determine the filter intensity and cutoff values for pixel changes, and based on the calculated filtering parameters, filtering is performed on the residual sample boundary.

For the filter parameters, location information of a neighboring coding block, such as a previous frame, a neighboring block, a group of neighboring fragments, a neighboring fragment, etc., can be transmitted, and the filter parameters of the neighboring decoding block corresponding to the location for the current block can be used as it is. is, or the filter parameters for the current block are restored from the values of neighboring parameters and additional signaled difference values.

In FIG. 10 is a flowchart of a method performed by a video coding apparatus for inter-prediction coding of a current video block according to at least one embodiment of the present invention.

In step S1010, the video encoding apparatus may generate a prediction block by inter-prediction of the current encoded video data block, and it may generate a residual block by subtracting the prediction block from the current video data block.

In step S1020, the video encoding device may determine the residual coding mode for the residual block of the current block. In particular, the video encoder may choose whether to encode the residual block of the current block, or to encode only one sub-block, which is a partial area of the residual block. This selection may be based on a rate-distortion test.

In step S1030, the video encoder may encode information about the residual coding mode selected for the corresponding residual block of the current block.

The residual coding mode information may include a first flag indicating whether the residual block or only one subblock of the residual block is encoded.

When only one sub-block of the residual block is encoded, the video coding apparatus may further encode information indicative of a partition type for dividing the residual block into two sub-blocks. Different types of splitting can be considered according to the splitting direction and the splitting factor. For example, an inter-prediction coding method may use partition types including a first type that provides a horizontally symmetrical split into two sub-blocks, a second type that provides a vertically symmetrical split into two sub-blocks, a third type that provides a horizontal asymmetric split into two sub-blocks . (for example, with a ratio of 1:3 or 3:1), and a fourth type, which provides an asymmetric vertical division into two sub-blocks (for example, with a ratio of 1:3 or 3:1). One or more syntax elements may be used to signal the split type (or split direction and split factor) for the corresponding residual block of the current block.

Depending on the width and height of the corresponding residual block of the current block, and thus depending on the width and height of the prediction block, the video encoder may restrict the use of certain split directions, split ratios, and/or split types, and thus it may skip signaling syntax elements expressing the split direction, split factor, and/or split type depending on the width and height of the residual block.

In at least one embodiment, when the width and height of the residual block is less than 16 pixels, division of the residual block "at a ratio of 1:3 or 3:1" cannot be allowed. Accordingly, when the width and height of the residual block is less than 16 pixels, the video decoder may conclude that the split ratio may be 1:1, which may be taken into account by the video encoder to skip signaling syntax elements (e.g., 1-bit flag) expressing the direction of separation. In another embodiment, when the width of the current box is less than 8 pixels, vertical splitting of the current box may be disabled. When the height of the current block is less than 8 pixels, horizontal splitting of the current block may be disabled. Accordingly, when the width (or height) of the residual block is less than 8 pixels, the current block can be divided at a ratio of 1:1 in the vertical (or horizontal) direction by the video decoding device, which allows the video encoding device to skip the signaling of syntax elements (e.g., 1-bit flag) expressing the direction of separation.

In addition, the video encoder may explicitly signal a flag to identify a sub-block of two sub-blocks classified according to the partition type to be encoded (and thus be transformed). In some embodiments, the video encoder may respond when the split type of the current block is the third type or the fourth type, that is, when the current block is asymmetrically split in the horizontal or vertical direction, to immediately decide whether a smaller subblock of two blocks, while skipping flag signaling to identify the subblock to be encoded.

In steps S1040 to S1050, the video encoder encodes the residual block or one subblock of the residual block according to the residual coding mode selected for the corresponding residual block of the current block. When the residual block encoding is selected, the video coding apparatus can perform transformation and quantization of the residual block in a transformation unit equal in size to the residual block, and entropy encode the quantized transform coefficients. When encoding of only one sub-block of the residual block is selected, the video coding apparatus can perform transformation and quantization of the sub-block corresponding to the transformation position and entropy-code the quantized transformation coefficients. Residual signals of other sub-blocks corresponding to untransformed positions are considered to be 0, which eliminates the need to convert coefficient information.

In step S1060, the video encoding apparatus may apply an inverse quantization/inverse transform process to the quantized transform coefficients to recover the residual signals corresponding to the transform positions, and set all residual signals of other sub-blocks corresponding to the untransformed positions to 0, thereby restoring the residual block for current block. The video encoder may add the reconstructed residual block to the prediction block to generate the reconstructed current block.

In step S1070, the video encoder may perform deblocking filtering on at least the reconstructed current block and store the filtered current block in a buffer, such as memory 190 in FIG. 1 to be used as a reference picture for inter-prediction of incoming blocks in the encoded picture. In particular, the video encoder may grid N samples at regular intervals in the horizontal and vertical directions, and determine whether to apply deblocking filtering to the current block based on whether the boundary between sub-blocks of the residual block coincides with the grid boundary. The video encoder can only perform deblocking filtering when the boundary between two residual sub-blocks in the current block matches the grid boundary. In other words, deblocking filtering can only be performed when a 4×4 (or 8×8) deblocking boundary matches the boundary between the residual sub-blocks.

In FIG. 11 is a flowchart of a method performed by a video decoding apparatus for decoding a current block encoded with inter prediction from an encoded video bitstream according to at least one embodiment of the present invention.

In step S1110, the video decoding apparatus, such as the entropy decoding unit of FIG. 4 can decode the residual coding mode information of the corresponding residual block of the current block.

For example, the video decoder may decode from the bitstream a first flag indicating whether a relevant residual block of the current block or only one subblock of the residual block has been encoded. The first flag having a first value (eg, "0") may indicate that the residual block has been converted, and the first flag having a second value (eg, "1") may indicate that only one sub-block of the residual block has been converted.

When the first flag indicates that only one sub-block of the residual block has been converted, the video decoding apparatus may further decode one or more syntax elements representing the split type (split direction and/or split ratio) of the residual block from the bitstream and may determine the split type of the residual block. , at least in part, based on the decoded one or more syntax elements. Different types of splitting can be considered according to the splitting direction and the splitting factor. For example, the partition types may include a first type that provides a horizontally symmetrical split into two subblocks, a second type that provides a vertically symmetrical split into two subblocks, a third type that provides a horizontal asymmetric split into two subblocks. (for example, with a ratio of 1:3 or 3:1), and a fourth type, which provides an asymmetric vertical division into two sub-blocks (for example, with a ratio of 1:3 or 3:1).

When determining the split type, the width and height of the current block may be further taken into account, along with information indicating the split type. The use of some split types (or split direction and/or split factor) may be restricted depending on the width and height of the current box, which may preclude signaling syntax elements expressing the same split types (or split direction and/or split ratio) .

In at least one embodiment, the device may respond when the current block's width and height are less than 16 pixels by disallowing the current block to be split "at a ratio of 1:3 or 3:1". Accordingly, when the width and height of the residual block is less than 16 pixels, the video decoding apparatus can simply infer that the split ratio is 1:1 without having to decode a syntax element indicating the split direction, such as a 1-bit flag.

According to another embodiment, the device may respond when the width (or height) of the current box is less than 8 pixels by preventing the current box from being split in the vertical direction (or horizontal direction). Therefore, when the width of the residual block is less than 8 pixels, the video decoding apparatus can simply infer the split direction as the horizontal direction without having to decode the syntax element indicating the split direction. In the same way, when the height of the residual block is less than 8 pixels, the video decoding apparatus can simply infer the split direction as a vertical direction without having to decode the syntax element indicating the direction.

In order to identify the subblock from which the transform coefficient information is to be decoded, the video decoding apparatus may further decode from the bitstream a syntax element (eg, a 1-bit flag) indicating the position of the encoded subblock, and thus the position of the subblock at which the conversion done. In some embodiments, the video decoder may respond when the split type of the current block is the third or fourth type by immediately inferring that the transformation has undergone a smaller subblock of two blocks, skipping decoding the syntax element to indicate the subblock position where it was performed. transformation.

In steps S1120 to S1130, the video decoding apparatus may reconstruct the relevant residual block of the current block based on the decoded residual coding mode information.

When the first flag indicates that the corresponding residual block of the current block has been encoded, the video decoding apparatus may decode transform coefficient information for the residual block from the bitstream to recover the transform coefficients. Thereafter, the video decoding apparatus performs inverse quantization of the transform coefficients and inversely transforms the quantized transform coefficients in a transform unit equal in size to the residual block, thereby recovering the residual block of the current block.

When the first flag indicates that only one subblock of the residual block has been encoded, the video decoding apparatus may decode transform coefficient information for the subblock corresponding to the transform position from the bit stream to recover the transform coefficients. Thereafter, the video decoding apparatus performs inverse quantization and inverse transformation of the transform coefficients to generate residual signals for the subblock corresponding to the transform position, and sets all residual signals of the other subblock corresponding to the untransformed position to 0, thereby restoring the residual block of the current block.

In step S1140, the video decoding apparatus may generate a prediction block by inter-prediction of the current block, and may reconstruct the current block by summing the prediction block and the residual block.

In step S1150, the video decoding apparatus may perform deblocking filtering on at least the reconstructed current block, and store the filtered current block in a buffer, etc., for example, in the memory 470 of FIG. 4 for use as a reference picture for inter-prediction of incoming blocks in the encoded picture. The video decoding apparatus may set up a grid of N samples at regular intervals in the horizontal and vertical directions, and determine based on the boundary of the set grid whether to apply deblocking filtering to the current block. For example, deblocking filtering may be applied to a boundary between the current block and other blocks that have already been decoded when that boundary matches a grid boundary. In addition, deblocking filtering can be applied to a boundary between sub-blocks of a residual block when that boundary matches a grid boundary. A grid in different units can be used depending on whether the current block is a luma block or a chrominance block. For example, the grid may be set to 4x4 units for the luminance block, and the grid may be set to 8x8 units for the chrominance block.

It should be understood that the above description provides exemplary embodiments that may be implemented in various other ways. The functions described in some embodiments may be implemented using hardware, software, firmware, and/or combinations thereof. It should also be understood that the functional components described in the present description are marked as "... block" to emphasize the possibility of their stand-alone implementation.

Meanwhile, various methods or functions described herein may be implemented as instructions stored in a non-volatile storage medium that can be read and executed by one or more processors. A non-volatile 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, a non-volatile storage medium may include, among other things, 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).

While the 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, for brevity and clarity, exemplary embodiments of the present invention have been described. The scope of the technical idea of the present embodiments is not limited to the illustrations. Accordingly, one of ordinary skill in the art will appreciate that the scope of the claimed invention is not limited by the embodiments that have been directly described above, but by the claims and their equivalents.

Link to related application

This application claims priority from Korean Patent Application No. 10-2019-0028364, filed March 12, 2019, the disclosure of which is incorporated herein by reference in its entirety.

Claims (50)

1. A video decoding device, comprising: decoding unit configured to decoding from the bit stream a flag indicating whether residual signals corresponding to only a partial area of the current block have been encoded, and decoding transform coefficient information for one sub-block of two sub-blocks extracted from the current block from the bitstream to recover transform coefficients when the flag indicates that residual signals corresponding to only a partial area of the current block have been encoded; a prediction block configured to predict the current block to generate the prediction block; an inverse quantization and inverse transform unit, configured to perform inverse quantization and inverse transformation of the transform coefficients in one sub-block, for which the transform coefficient information has been decoded, to generate a residual block for the current block; an adder configured to add the prediction block and the residual block to recover the current block; and a filtering unit configured to set a grid of N samples at equal intervals in the horizontal and vertical directions and perform deblocking filtering on a boundary between two sub-blocks in the current block that coincides with the grid boundary. 2. The apparatus of claim 1, wherein the inverse quantization and inverse transform block is further configured to generate a residual block for the current block by performing inverse quantization and inverse transformation of the transform coefficients in one subblock for which the transform coefficient information has been decoded to generate residuals. signals for one subblock of the two subblocks, and by setting the residual signals for the other subblock of the two subblocks to zero. 3. The device according to claim 1, wherein the decoding unit is further configured to decoding from the bit stream one or more syntax elements indicating the split type of the current block, determining a split type for the current box to be split into two sub-boxes, depending on one or more syntax elements indicating the split type of the current box, as well as the width and height of the current box, and decoding the transform coefficient information corresponding to only one sub-block of the two sub-blocks, which is determined according to the partition type. 4. The apparatus of claim 3, wherein the partition type for the current block includes: the first type, in which the current block is symmetrically divided in the horizontal direction; the second type, in which the current block is symmetrically divided in the vertical direction; the third type, in which the current block is asymmetrically divided in the horizontal direction; and the fourth type, in which the current block is asymmetrically divided in the vertical direction. 5. The apparatus of claim 4, wherein the decoding unit is further configured to decode the transform coefficient information for only a relatively small subblock of the two subblocks when the division type is the third type or the fourth type. 6. The apparatus of claim 1, wherein the current block is a chrominance block composed of chrominance components. 7. The device according to claim 1, in which N is 8. 8. The device according to claim 1, further comprising: a residual filtering block configured to filter a boundary between two sub-blocks in the residual block generated by the inverse quantization and inverse transform block. 9. The apparatus of claim 1, wherein the decoding block is further configured to decode a differential quantization parameter for the current block, and wherein the block of inverse quantization and inverse transformation is additionally configured to obtaining a quantization parameter prediction value from the quantization parameter of at least one adjacent block adjacent to one sub-block for which transform coefficient information has been decoded, and performing inverse quantization using the prediction value of the quantization parameter and the differential quantization parameter of the transform coefficients in one sub-block for which the transform coefficient information has been decoded. 10. The device according to claim 6, in which the inverse quantization and inverse transform unit is configured to obtaining a chrominance block quantization parameter from the quantization parameter of at least one luminance block aligned with the chrominance block, and performing inverse quantization using a chrominance block quantization parameter. 11. Method for decoding video images, including: decoding from the bit stream a flag indicating whether residual signals corresponding to only a partial region of the current block have been encoded, and restoring transform coefficients by decoding transform coefficient information for one sub-block of two sub-blocks extracted from the current block from the bit stream, when the flag indicates that residual signals corresponding to only a partial area of the current block have been encoded; predicting the current block to generate a prediction block; generating a residual block for the current block by performing inverse quantization and inverse transformation of the transform coefficients in one sub-block for which the transform coefficient information has been decoded; restoring the current block by adding the prediction block and the residual block; and setting a grid of N samples at equal intervals in the horizontal and vertical directions; and performing deblocking filtering on a boundary between two sub-blocks in the current block that coincides with the grid boundary. 12. The method of claim 11, wherein restoring the transform coefficients includes: generating a residual block for the current block by performing inverse quantization and inverse transformation of transform coefficients in one sub-block for which transform coefficient information has been decoded to generate residual signals for one sub-block of two sub-blocks, and by setting the residual signals of another sub-block of two sub-blocks to be zero. 13. The method of claim 11, wherein restoring the transform coefficients includes: decoding from the bit stream one or more syntax elements indicating the split type of the current block, determining the split type for the current box to be split into two sub-boxes, depending on one or more syntax elements indicating the split type of the current box and the width and height of the current box, and decoding the transform coefficient information corresponding to only one sub-block of the two sub-blocks, which is determined according to the partition type. 14. The method of claim 13, wherein the split type for the current block includes: the first type, in which the current block is symmetrically divided in the horizontal direction; the second type, in which the current block is symmetrically divided in the vertical direction; the third type, in which the current block is asymmetrically divided in the horizontal direction; and the fourth type, in which the current block is asymmetrically divided in the vertical direction. 15. The method of claim 14, wherein decoding the transform coefficient information includes: decoding the transform coefficient information only for a relatively small subblock of the two subblocks when the partition type is the third type or the fourth type.

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