WO2018128466A1 - Device and method for encoding or decoding image - Google Patents

Abstract

The present invention suggests a QTBT division structure, which allows blocks having various shapes and can reflect local characteristics of various images more efficiently, and a method for efficiently signaling the division structure. In order to reflect given characteristics of an image, the present invention includes a triangular block division shape, a rectangular block division shape, and a block division shape having concave-convex parts.

Description

Apparatus and method for image encoding or decoding

The present invention relates to image encoding or decoding for efficiently encoding an image. More specifically, the present invention relates to a block partitioning scheme capable of taking into account the characteristics of various images more actively, and a technique of signaling the partitioning information with the partitioning information.

The contents described in this section merely provide background information on the present embodiment and do not constitute a prior art.

1 is a conceptual diagram of an exemplary quadtree block structure for a CTU. According to the HEVC (High Efficiency Video Coding) standard, a coding tree unit (CTU) is divided into a coding unit (CU) using a quadtree structure as a coding tree to reflect various local characteristics in an image. As illustrated in FIG. 1, a CU having the best coding efficiency is selected while repeatedly dividing a CTU having a maximum size of 64x64 in a quadtree manner to at least 4x4. Each CU is further divided into a PU (Prediction Unit). After the PU is determined and the prediction process is performed, the CU is divided into a TU (Transformation Unit) for the residual block. 1 illustrates a rectangular PU divided by a dotted line.

Recently, a quadtree plus binary tree (QTBT) structure has been newly discussed, and attempts have been made to reflect various local characteristics of image data while removing existing CU, PU, and TU concepts.

An object of the present invention is to provide a QTBT partitioning structure that allows various shapes of blocks that can more efficiently reflect local characteristics of various images, and a method for efficiently signaling the partitioning structure.

According to an aspect of the present invention, there is provided a method comprising: receiving a bitstream including a block of encoded image data and segmentation information related to the block of the image data; And determining a QuadTree plus BinaryTree (QTBT) partitioning structure for the block of the image data by using the partitioning information. Herein, the QTBT partition structure is a structure in which a binary tree is rooted from a leaf node of a quadtree, and the binary tree is defined by partition types for splitting a parent node into two child nodes. Types include triangular partition type and rectangular partition type. The method further includes decoding the block of the encoded image data for each leaf node of the QTBT. In the binary tree, child nodes of a parent node divided into a triangular partition type are no longer split, whereas child nodes of a parent node partitioned into a rectangular partition type are allowed to be split into two child nodes again.

According to another aspect of the present invention, there is provided an apparatus for decoding image data including a memory and one or more processors configured to perform the aforementioned method. That is, the one or more processors may include receiving a bitstream including a block of encoded image data and segmentation information related to the block of image data; Determining a QuadTree plus BinaryTree (QTBT) partition structure for the block of the image data by using the split information; And decoding the block of the encoded image data for each leaf node of the QTBT.

According to still another aspect of the present invention, there is provided a method including: receiving a bitstream including a block of encoded image data and segmentation information related to the block of the image data; And determining the QTBT segmentation structure for the block of the image data by using the segmentation information. And decoding the block of the encoded image data for each leaf node of the QTBT. Here, the QTBT splitting structure is a structure in which a binary tree is rooted from a leaf node of a quadtree, and leaf nodes of the quadtree are allowed to be divided into two child nodes, and the two child nodes. Are 凹 shaped blocks and 凸 shaped blocks.

According to another aspect of the invention, receiving a bitstream including a coding tree unit (CTU) of the encoded image data and segmentation information related to the CTU of the image data; Determining a QTBT splitting structure for the CTU using the splitting information; Determining a prediction partition mode for each leaf node of the QTBT using the partitioning information; And decoding the block of the encoded image data according to a prediction partition mode for each leaf node of the QTBT. In the binary tree of the QTBT, a given block can be divided into two rectangles of the same size. The prediction partition mode allows the leaf nodes of the QTBT to be divided and predicted into two triangles of the same size.

1 is a conceptual diagram of an exemplary quadtree block structure for a CTU.

2 is a diagram illustrating a form (a) divided into squares and a divided form (b) divided into a combination of squares and triangles.

3A and 3B illustrate triangular block division shapes.

4 is a view showing a block division form of irregularities.

5 is a block diagram of an example video encoding apparatus in which the techniques of this disclosure may be used.

6 shows an example of a plurality of intra prediction modes.

7 is an exemplary diagram of neighboring blocks of a current block.

8 is a block diagram of an example video decoding apparatus in which the techniques of this disclosure may be used.

9 is a conceptual diagram of partition partitions allowed in BT partitioning according to an embodiment of the present invention.

FIG. 10 is a tree representation of an example of a bit allocation method for four BT divisions illustrated in FIG. 9.

FIG. 11A is a conceptual diagram of an exemplary QTBT splitting structure according to an embodiment of the present invention, and FIG. 11B is a tree structure illustrating the QTBT splitting structure of FIG. 11A.

FIG. 12 is a tree representation of an example of a bit allocation method for the uneven partition illustrated in FIG. 4.

FIG. 13 is a diagram representing an example of a bit allocation method for BT division in which rectangular divisions are allowed.

14A is a conceptual diagram of an exemplary CU partition and a PU partition according to an embodiment of the present invention, and FIG. 14B illustrates the CU partition of FIG. 14A in a tree structure.

15 is a flowchart illustrating an exemplary operation of encoding an image by the image encoding device.

16 is a flowchart illustrating an exemplary operation of decoding an image by the image decoding device.

17 is a flowchart illustrating another exemplary operation of decoding an image by the image decoding device.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. In adding an identification code to the components of each drawing, it should be noted that the same components as possible, even if shown on different drawings have the same reference numerals. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

2 is a diagram illustrating a form (a) divided into squares and a divided form (b) divided into a combination of squares and triangles. As shown in (a) of FIG. 2, even in the conventional quadtree partitioning scheme, by dividing into squares of various sizes, a given characteristic (that is, the position, size, and shape of an object) of the image may be reflected to some extent. However, as illustrated in (b) of FIG. 2, a form divided into a combination of squares and triangles may more efficiently reflect a given characteristic of an image than (a) of FIG. May be advantageous to the process).

3A and 3B illustrate triangular block division shapes. 3A illustrates a form in which a square block is divided into two triangles of equal size, and FIG. 3B illustrates a form in which a rectangular block is divided into two triangles of equal size. The proposed triangular block may be useful when there are diagonal edges in the rectangle, as in the example of FIG. In other words, it is possible to set a triangular region having a similar texture as one block, thereby increasing coding efficiency.

4 is a view showing a block division form of irregularities. 4 shows four shapes in which a square block is divided into irregular shapes. The shapes illustrated in FIG. 4 are distinguished according to the relative position of the block shaped block with respect to the block shaped block. If the image is divided into such a combination of uneven blocks and squares, the given characteristic of the image may be more efficiently reflected.

The present disclosure generally relates to a block partitioning scheme that can more actively consider characteristics of an image, and a technique of signaling the partitioning information. The techniques of this disclosure allow for a more flexible approach to use block partitions of various shapes in addition to square or rectangle in video encoding, thereby providing additional opportunities for improving encoding and / or image quality.

5 is a block diagram of an example video encoding apparatus in which the techniques of this disclosure may be used.

The image encoding apparatus includes a block splitter 510, a predictor 520, a subtractor 530, a transformer 540, a quantizer 545, an encoder 550, an inverse quantizer 560, and an inverse transform unit ( 565, an adder 570, a filter unit 580, and a memory 590. In the image encoding apparatus, each component may be implemented as a hardware chip, or may be implemented in software and implemented so that the microprocessor executes a function of software corresponding to each component.

After dividing each picture constituting an image into a plurality of coding tree units (CTUs), the block dividing unit 510 recursively divides the CTUs using a tree structure. A leaf node in the tree structure becomes a CU (coding unit) which is a basic unit of coding. The tree structure is a quadtree (QT) in which a parent node (or parent node) is divided into four child nodes (or child nodes) of the same size, or such a QT structure and a parent node are divided into two child nodes. A QTBT (QuadTree plus BinaryTree) structure that uses a binary tree structure may be used. That is, QTBT may be used to divide a CTU into a plurality of CUs.

In a QTBT (QuadTree plus BinaryTree) structure, the CTU may be first divided into a QT structure. Quadtree splitting may be repeated until the size of the splitting block reaches the minimum block size (MinQTSize) of the leaf nodes allowed in QT. If the leaf node of the quadtree is not larger than the maximum block size (MaxBTSize) of the root node allowed in BT, it may be further partitioned into the BT structure. In BT, there may be a plurality of partition types. For example, in some examples, a rectangular division type may be used that divides a block of nodes into two rectangles of the same size. In some other examples, a triangular split type that splits into two triangles of the same size may be used in addition to the BT split. In another example, a concave-convex type of dividing a given block into a j-shaped block and a j-shaped block may be used. In the rectangular division type, there may be a horizontal division form and a vertical division form according to the division direction. In the triangular division type, there may be a down-right division form and an up-right division form according to the division direction. As shown in FIG. 4, the uneven division type may have four division forms according to the division direction (that is, according to the relative positions of the U-shaped block and the U-shaped block).

The partition information generated by the block divider 510 by dividing the CTU by the QTBT structure is encoded by the encoder 550 and transmitted to the image decoding apparatus.

Hereinafter, a block corresponding to a CU (that is, a leaf node of QTBT) to be encoded or decoded is called a 'current block'.

The prediction unit 520 generates a prediction block by predicting the current block. The predictor 520 includes an intra predictor 522 and an inter predictor 524.

The intra predictor 522 predicts pixels in the current block by using pixels (reference pixels) positioned around the current block in the current picture including the current block. There are a plurality of intra prediction modes according to the prediction direction, and the peripheral pixels to be used and the equations are defined differently according to each prediction mode. In particular, the intra predictor 522 may determine an intra prediction mode to use to encode the current block. In some examples, intra prediction unit 522 may encode the current block using several intra prediction modes and select an appropriate intra prediction mode to use from the tested modes. For example, intra predictor 522 calculates rate distortion values using rate-distortion analysis for several tested intra prediction modes, and has the best rate distortion characteristics among the tested modes. Intra prediction mode may be selected.

6 shows an example of a plurality of intra prediction modes.

As shown in FIG. 6, the plurality of intra prediction modes may include two non-directional modes (planar mode and DC mode) and 65 directional modes.

The intra predictor 522 selects one intra prediction mode from among the plurality of intra prediction modes, and predicts the current block by using a neighboring pixel (reference pixel) and an operation formula determined according to the selected intra prediction mode. Information on the selected intra prediction mode is encoded by the encoder 550 and transmitted to the image decoding apparatus.

Meanwhile, the intra predictor 522 may efficiently encode intra prediction mode information indicating which mode of the plurality of intra prediction modes is used as the intra prediction mode of the current block. Some of the most probable modes as the intra prediction mode of may be determined as the most probable mode (MPM). In addition, mode information indicating whether the intra prediction mode of the current block is selected from the MPM is generated and transmitted to the encoder 550. In general, when the intra prediction mode of the current block is selected from the MPMs, the first intra identification information for indicating which mode of the MPMs is selected as the intra prediction mode of the current block is transmitted to the encoder. On the other hand, if the intra prediction mode of the current block is not selected from the MPM, the second intra identification information for indicating which mode other than the MPM is selected as the intra prediction mode of the current block is transmitted to the encoder. Alternatively, the intra prediction unit 522 according to an aspect of the present invention instead of explicitly signaling which mode among the MPMs and / or non-MPMs is selected as the intra prediction mode for predicting the current block. Can group the MPMs and / or non-MPMs and signal the index of the group to which the intra mode for predicting the current block belongs.

Hereinafter, a method of constructing the MPM list will be described. Herein, an example of configuring an MPM list with six MPMs is described as an example. However, the present invention is not limited thereto, and the number of MPMs included in the MPM list may be selected within a range of 3 to 10.

First, the MPM list is constructed using the intra prediction mode of neighboring blocks of the current block. The neighboring block may be, for example, all or some of the left block L, the upper block A, the lower left block BL, the upper right block AR, and the upper left block AL of the current block. It may include.

The intra prediction mode of these neighboring blocks is included in the MPM list. In this case, the intra prediction mode of the valid blocks in the order of the left block (L), the top block (A), the bottom left block (BL), the top right block (AR), and the top left block (AL) is included in the MPM list, The candidate is configured by adding a planar mode and a DC mode to the intra prediction modes of the blocks. Alternatively, valid modes in the order of the left block (L), the top block (A), the planar mode, the DC mode, the bottom left block (BL), the top right block (AR), and the top left block (AL) may be added to the MPM list. have. Alternatively, valid modes in the order of the left block (L), the top block (A), the planar mode, the bottom left block (BL), the top right block (AR), the top left block (AL), and the DC mode may be added to the MPM list. have.

The MPM list includes only different intra prediction modes. That is, when a duplicated mode is present, only one of them is included in the MPM list.

If the number of MPMs in the list is smaller than the predetermined number (eg, 6), the MPM may be derived by adding -1 or +1 to the directional modes in the list. In addition, when the number of MPMs in the list is smaller than the predetermined number, the number of insufficient modes is added to the MPM list in the order of vertical mode, horizontal mode, diagonal mode, and the like. You may.

The inter prediction unit 524 searches for the block most similar to the current block in the coded and decoded reference picture before the current picture, and generates a prediction block for the current block using the searched block. A motion vector corresponding to a displacement between the current block in the current picture and the prediction block in the reference picture is generated. The motion information including the information about the reference picture and the motion vector used to predict the current block is encoded by the encoder 550 and transmitted to the image decoding apparatus.

The subtractor 530 generates a residual block by subtracting the prediction block generated by the intra predictor 522 or the inter predictor 524 from the current block.

The converter 540 converts the residual signal in the residual block having pixel values of the spatial domain into a transform coefficient of the frequency domain. The transformer 540 may convert the residual signals in the residual block using the size of the current block as a conversion unit, or divide the residual block into a plurality of smaller subblocks and convert the residual signals in a subblock-sized transform unit. You can also convert. There may be various ways of dividing the residual block into smaller subblocks. For example, it may be divided into sub-blocks of a predetermined same size, or a quadtree (QT) scheme may be used in which the residual block is a root node.

The quantization unit 545 quantizes the transform coefficients output from the transform unit 540, and outputs the quantized transform coefficients to the encoder 550.

The encoder 550 generates a bitstream by encoding the quantized transform coefficients by using an encoding method such as CABAC. In addition, the encoder 550 encodes information such as CTU size, MinQTSize, MaxBTSize, MaxBTDepth, MinBTSize, QT split flag (QT_split_flag), BT split flag (QT_split_flag) related to block division, so that the image decoding apparatus may The block can be divided in the same way as

The encoder 550 encodes information about a prediction type indicating whether a current block is encoded by intra prediction or inter prediction, and encodes intra prediction information or inter prediction information according to the prediction type.

The inverse quantizer 560 inversely quantizes the quantized transform coefficients output from the quantizer 545 to generate transform coefficients. The inverse transformer 565 restores the residual block by converting the transform coefficients output from the inverse quantizer 560 from the frequency domain to the spatial domain.

The adder 570 reconstructs the current block by adding the reconstructed residual block and the predicted block generated by the predictor 520. The pixels in the reconstructed current block are used as reference pixels when intra prediction of the next order of blocks.

The filter unit 580 deblocks and filters the boundary between the reconstructed blocks in order to remove blocking artifacts that occur due to encoding / decoding of blocks. When all the blocks in a picture are reconstructed, the reconstructed picture is used as a reference picture for inter prediction of a block in a picture to be encoded later.

Hereinafter, an image decoding apparatus will be described.

8 is a block diagram of an example video decoding apparatus in which the techniques of this disclosure may be used.

The image decoding apparatus includes a decoder 810, an inverse quantizer 820, an inverse transformer 830, a predictor 840, an adder 850, a filter 860, and a memory 870. Like the image encoding apparatus of FIG. 2, the image decoding apparatus may be implemented by each component as a hardware chip, or may be implemented by software and a microprocessor to execute a function of software corresponding to each component.

The decoder 810 decodes the bitstream received from the image encoding apparatus, extracts information related to block division, determines a current block to be decoded, and includes prediction information and residual signal information necessary for reconstructing the current block. Extract

The decoder 810 extracts information about the CTU size from a high level syntax such as a Sequence Parameter Set (SPS) or a Picture Parameter Set (PPS) to determine the size of the CTU, and determines the size of the picture. Split into CTUs. The CTU is determined as the highest layer of the tree structure, that is, the root node, and the CTU is partitioned using a tree structure (eg, a QTBT structure) by extracting partition information about the CTU.

When the decoder 810 determines the current block (current block) to be decoded by splitting the tree structure, the decoder 810 extracts information about a prediction type indicating whether the current block is intra predicted or inter predicted.

When the prediction type information indicates intra prediction, the decoder 810 extracts a syntax element for intra prediction information (intra prediction mode) of the current block. First, the decoder 810 extracts mode information (ie, MPM flag) indicating whether or not the intra prediction mode of the current block is selected from the MPMs. Also, in general, when the intra mode encoding information indicates that the intra prediction mode of the current block is selected from the MPMs, the first intra identification information for indicating which mode of the MPMs is selected as the intra prediction mode of the current block is extracted. And if the intra mode encoding information indicates that the intra prediction mode of the current block is not selected among the MPMs, a second intra for indicating which mode other than the MPM is selected as the intra prediction mode of the current block. Extract identification information. Alternatively, the intra prediction unit 522 according to an aspect of the present invention may indicate an intra identification information indicating which mode among MPMs and / or non-MPMs is selected as an intra prediction mode for predicting a current block. Instead of extracting, group MPMs and / or non-MPMs and extract intra identification information (eg, group index, etc.) indicating whether an intra mode for predicting the current block belongs.

Meanwhile, the decoder 810 extracts information about quantized transform coefficients of the current block as information on the residual signal.

The inverse quantization unit 820 inversely quantizes the quantized transform coefficients, and the inverse transform unit 830 inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to generate a residual block for the current block.

The predictor 840 includes an intra predictor 842 and an inter predictor 844. The intra predictor 842 is activated when the intra prediction is the prediction type of the current block, and the inter predictor 844 is activated when the intra prediction is the prediction type of the current block.

The intra predictor 842 determines the intra prediction mode of the current block among the plurality of intra prediction modes from the syntax element for the intra prediction mode extracted from the decoder 810, and references pixels around the current block according to the intra prediction mode. Predict the current block using

In order to determine the intra prediction mode of the current block, the intra predictor 842 constructs an MPM list including a predetermined number of MPMs from neighboring blocks of the current block. The method of constructing the MPM list is the same as that of the intra predictor 522 of FIG. 2.

In general, when the mode information of the intra prediction (ie, the MPM flag) indicates that the intra prediction mode of the current block is selected from the MPMs, the intra prediction unit 842 may indicate the first intra identification information among the MPMs in the MPM list. Select the MPM indicated by the intra prediction mode of the current block. On the other hand, if the mode information indicates that the intra prediction mode of the current block is not selected from the MPM, the intra prediction mode of the current block is determined among the remaining intra prediction modes except the MPMs in the MPM list using the second intra identification information. do.

Alternatively, the intra prediction unit 522 of the image encoding apparatus according to an aspect of the present invention, as described above, an intra prediction mode for which mode among the MPMs and / or non-MPMs predicts the current block. Instead of explicitly signaling whether or not is selected, group the MPMs and / or non-MPMs and signal the index of the group to which the intra mode to predict the current block belongs. In this case, the intra prediction unit 842 of the image decoding apparatus may determine the final intra mode (that is, the intra mode for predicting the current block) by evaluating the intra modes belonging to the corresponding group. For example, in some examples, the intra predictor 842 may generate a reconstructed block for a plurality of intra modes belonging to a group, and evaluate the reconstructed blocks to determine a final intra mode.

The inter predictor 844 determines motion information of the current block using a syntax element for the intra prediction mode extracted from the decoder 810, and predicts the current block using the determined motion information.

The adder 850 reconstructs the current block by adding the residual block output from the inverse transformer and the prediction block output from the inter predictor or the intra predictor. The pixels in the reconstructed current block are utilized as reference pixels in intra prediction of the block to be subsequently decoded.

The filter unit 860 deblocks and filters the boundary between the reconstructed blocks in order to remove blocking artifacts caused by block-by-block decoding, and stores them in the memory 870. When all the blocks in a picture are reconstructed, the reconstructed picture is used as a reference picture for inter prediction of a block in a picture to be decoded later.

Techniques of the present disclosure generally relate to a technique for signaling partition information representing a QTBT block partition structure that allows not only rectangular but also triangular or uneven blocks, and a technique for determining block partitioning from partition information. One aspect of the techniques of the present disclosure may be performed by the encoder 550 of the image encoding apparatus illustrated in FIG. 5 and / or the decoder 810 of the image decoding apparatus illustrated in FIG. 8. In other examples, one or more other units of the image encoding apparatus and / or the image decoding apparatus may additionally or alternatively be responsible for performing the techniques of this disclosure. QTBT block partitioning can be used to partition a CTU into CUs. That is, the root node of the QTBT may be a CTU, and the leaf node of the QTBT may be a CU.

In the QTBT structure, the CTU that is the root node may be first divided into a QT structure. The image encoding apparatus uses a QT split flag (QT_split_flag) to signal whether the root node of the QTBT is split into a QT structure. As shown in Table 1, QT_split_flag = 0 indicates that the root node is not QT split, and QT_split_flag = 1 indicates that the root node is split into four blocks of the same size.

QT split flag	Value
No split	0
split	One

The QT division of each node may be repeated recursively. BT partitioning may be performed on blocks that are not QT partitioned (ie, leaf nodes of QT). The BT partition proposed in the present disclosure may have a plurality of partition types. For example, in some examples, a rectangular division type may be used that divides a block of nodes into two rectangles of the same size. In some other examples, a triangular split type that splits into two triangles of the same size may be used in addition to the BT split. In another example, a concave-convex type of dividing a given block into a j-shaped block and a j-shaped block may be used.

Hereinafter, some embodiments regarding partition types allowed in BT partitioning and a method of signaling the same will be described.

First Embodiment (BT Division—Combination of Rectangular Division and Triangle Division)

9 is a conceptual diagram of partition partitions allowed in BT partitioning according to an embodiment of the present invention.

In the present embodiment, BT division and triangular division are used for BT division. Rectangular division is to divide a given block (square or rectangular) into two rectangles of the same size, and triangular division is to divide a given block (square or rectangular) into two triangles of the same size. (A) and (b) in FIG. 9 are examples of two kinds of rectangular division, and (c) and (d) are examples of two kinds of triangular division. The rectangular division is divided into a horizontal form and a vertical form according to the division direction, and the triangular division is divided into a down-right form and an up-right form according to the division direction. Therefore, in the present embodiment, BT divisions are divided into four types according to shape and direction.

Although FIG. 9 illustrates a square block divided into two rectangles or two triangles, a rectangular block divided into two rectangles or two triangles is also possible. Thus, the rectangular block can be further divided into two rectangles or two triangles. Triangle blocks, on the other hand, are no longer split.

FIG. 10 is a tree representation of an example of a bit allocation method for four BT divisions illustrated in FIG. 9.

Referring to FIG. 10, one bit is allocated to indicate whether a BT division is selected, and in the case where the BT division is selected, a type of BT division (i.e., triangle division or rectangular division is selected). One bit and one bit for indicating a division direction are additionally allocated, thus representing a BT partition shape for a given block with a total of three bits.

A summary of the bits allocated to each BT partitions is shown in Table 2. As shown in Table 2, the first bin of the BT split flag indicates whether the block is BT split, the second bin indicates the type of BT split (ie, rectangular or triangular split), and the third bin. The bin indicates the division direction of the BT division (ie, the direction of the rectangular division or the direction of the triangular division).

BT split flag	Value
No split	0
Split rectangle (horizontal)	100
Split rectangle (vertical)	101
Split triangle (down-right)	110
Split triangle (up-right)	111

FIG. 11A is a conceptual diagram of an exemplary QTBT splitting structure according to an embodiment of the present invention, and FIG. 11B is a tree structure illustrating the QTBT splitting structure of FIG. 11A. In FIG. 11B, black circles indicate leaf nodes of the QTBT splitting structure, and white circles indicate nodes that are QT splitting or BT splitting. In addition, the bits indicated in each node mean the QT partition flag and the BT partition flag based on Tables 1 and 2. Of the bits assigned to each node, the underlined bits are QT split flags and the remaining bits are BT split flags. Note that in FIG. 11B, the bit nodes “0” are not assigned to child nodes of nodes to which “ 110 ” and “ 111 ” are assigned italics. As mentioned above, the triangular block corresponds to a leaf node that is no longer split, so once a given node is triangulated, there is no need to signal that it is no longer BT split for its child nodes.

Alternatively, it may have child nodes when divided into triangular blocks. In this case, the child node may have a shape in which the triangle block, which is the parent node, is bisected into triangles again. The triangle blocks, which are the two parent nodes, each independently determine the triangle split. The partition flag may be displayed as "0" if the partition flag is not divided and "1" if the partition flag is partitioned.

Second embodiment (combination of BT division-uneven division)

In the present embodiment, partitions of the concave-convex shape illustrated in FIG. 4 are used for BT partitioning. Uneven partitions are divided into four types according to their division direction (that is, according to the relative position of the block in the shape of the block in the shape of the block).

FIG. 12 is a tree representation of an example of a bit allocation method for the uneven partition illustrated in FIG. 4. Referring to FIG. 12, one bit is allocated to indicate whether a BT division is selected, and two bits are additionally allocated to indicate which uneven division is selected when the BT division is selected. In this way, the bits allocated to the respective partition patterns are summarized in Table 3 below. As shown in Table 3, the first bin of the BT split flag indicates whether the block is BT split, and the second bin and the third bin indicate which uneven split is applied.

BT split flag	Value
No split	0
Split rectangle (horizontal)	100
Split down-type	101
Split left-type	110
Split right-type	111

In this embodiment, once the square (or rectangular) block is divided into an uneven shape, the divided blocks are no longer BT divided. Therefore, it is not necessary to signal the BT split flag for child nodes of the BT split node.

Third Embodiment (Triangle Division Allowed in PU)

The technique proposed in this embodiment uses the rectangular division illustrated in FIGS. 9A and 9B for BT division in the QTBT division structure of the CTU for determining a coding unit (CU), and uses a PU (Prediction Unit). The triangular division illustrated in (c) and (d) of FIG. That is, if the first embodiment allows a triangular CU, this embodiment allows a triangular PU. Here, the triangular PU may be described as a partition mode for prediction of a corresponding CU.

FIG. 13 is a diagram representing an example of a bit allocation method for BT division in which rectangular divisions are allowed. Referring to FIG. 13, one bit is allocated to indicate whether the BT division is selected, and in the case where the BT division is selected, one bit for additionally indicating the direction of the BT division (ie, the direction of the rectangular division) is additionally allocated. do. Therefore, it is possible to express the BT partition shape for a given block with 2 bits in total. A summary of the bits allocated to each BT partitions is shown in Table 4. As shown in Table 4, the first bin of the BT split flag indicates whether the block is BT split, and the second bin indicates the split direction of the BT split (ie, the direction of the rectangular split).

BT split flag	Value
No split	0
Split horizontal	10
Split vertical	11

14A is a conceptual diagram of an exemplary CU partition and a PU partition according to an embodiment of the present invention, and FIG. 14B illustrates the CU partition of FIG. 14A in a tree structure. In FIG. 14A, solid lines represent CU divisions of the QTBT division structure, and dotted lines represent PU divisions. In FIG. 14B, black circles indicate leaf nodes of the QTBT splitting structure, and white circles indicate nodes that are QT splitting or BT splitting. In addition, the bits indicated in each node mean the QT partition flag based on Table 1 and the BT partition flags based on Table 4.

When the CU partition is determined, the image encoding apparatus should signal PU partition information (or mode type) for the corresponding CU. Mode type signaling is performed for all CUs corresponding to the leaf nodes of FIG. 14B. Information on the mode type for one CU may be displayed as shown in Table 5.

BT split flag	Value
Quadrangle	0
Triangle (down-right)	10
Triangle (up-right)	11

15 is a flowchart illustrating an exemplary operation of encoding an image by the image encoding device.

In the example of FIG. 15, the image encoding apparatus determines a QTBT splitting structure for encoding a block of image data (S1510). The QTBT block partitioning structure is a structure in which a binary tree is rooted from a leaf node of a quadtree. In some examples, the binary tree is defined by a plurality of partition types that split a parent node into two child nodes. The division types may include a triangular division type and a rectangular division type. In a binary tree, nodes that are split into triangular split types are no longer split. In the binary tree, nodes that are split into rectangular partition types are again allowed to split into two child nodes. In some other examples, the leaf nodes of the quadtree are allowed to be split into two child nodes, where the two child nodes may be j-shaped blocks and j-shaped blocks. In this case, the child nodes may no longer be divided.

The image encoding apparatus generates an encoded bitstream including the block of the image data and the segmentation information representing the determined QTBT segmentation structure based on the determined QTBT segmentation structure (S1520).

16 is a flowchart illustrating an exemplary operation of decoding an image by the image decoding device.

In the example of FIG. 16, the image decoding apparatus receives a bitstream including a block of encoded image data and segmentation information related to the block of the image data (S1610).

The image decoding apparatus determines the QTBT segmentation structure for the block of the image data by using the segmentation information (S1620). The QTBT splitting structure is a structure in which a binary tree is rooted from a leaf node of a quadtree. In some examples, the binary tree is defined by a plurality of partition types that split a parent node into two child nodes. The division types may include a triangular division type and a rectangular division type. In a binary tree, nodes that are split into triangular split types are no longer split. In the binary tree, nodes that are split into rectangular partition types are again allowed to split into two child nodes. In some other examples, the leaf nodes of the quadtree are allowed to be split into two child nodes, where the two child nodes may be j-shaped blocks and j-shaped blocks. In this case, the child nodes may no longer be divided.

The image decoding apparatus decodes the block of the encoded image data for each leaf node of the QTBT (S1630).

17 is a flowchart illustrating another exemplary operation of decoding an image by the image decoding device.

In the example of FIG. 17, the image decoding apparatus receives a bitstream including a coding tree unit (CTU) of encoded image data and segmentation information related to the CTU of the image data (S1710).

The image decoding apparatus determines the QTBT segmentation structure for the CTU by using the segmentation information (S1720). The QTBT splitting structure is a structure in which a binary tree is rooted from a leaf node of a quadtree. In the binary tree, a given block is divided into two rectangles of the same size. Nodes split into a rectangular partition type are allowed to split into two child nodes again. Thus, leaf nodes (ie CUs) of QTBT may be square or rectangular in shape.

The image decoding apparatus determines the prediction partition mode for each leaf node of the QTBT by using the split information (S1730). The prediction partition mode allows the leaf nodes of the QTBT to be divided and predicted into two triangles of the same size. Thus, the PU may be square, rectangular or triangular in shape.

The image decoding apparatus decodes the block of the encoded image data according to the prediction partition mode for each leaf node of the QTBT (S1740).

The above description is merely illustrative of the technical idea of the present embodiment, and those skilled in the art to which the present embodiment belongs may make various modifications and changes without departing from the essential characteristics of the present embodiment. Therefore, the present embodiments are not intended to limit the technical idea of the present embodiment but to describe the present invention, and the scope of the technical idea of the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present embodiment.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is incorporated by reference in Korean Patent Application No. 10-2017-0003156, filed on Jan. 09, 2017, and Jan. 04, 2018, which is hereby incorporated by reference in its entirety. Priority is claimed on number 10-2018-0001062.

Claims (10)

1. In the method for decoding video data,

   Receiving a bitstream including a block of encoded image data and segmentation information related to the block of image data;

   Determining a QuadTree plus BinaryTree (QTBT) partition structure for the block of the image data using the partition information, wherein the QTBT partition structure is a binary tree rooted from a leaf node of a quadtree. The binary tree is defined by partition types for dividing a parent node into two child nodes, the partition types including a triangle partition type and a rectangular partition type; And

   Decoding the block of the encoded image data for each leaf node of the QTBT

   Image decoding method comprising a.
2. The method of claim 1,

   In the binary tree, child nodes of nodes divided into triangular partition types are no longer partitioned.
3. The method of claim 1,

   The child decoding method of the binary tree, characterized in that the child nodes of the node divided into the rectangular partition type is allowed to be divided into two child nodes again.
4. The method of claim 1,

   The triangular division type,

   And a down-right segmentation form and an up-right segmentation form according to the segmentation direction.
5. The method of claim 1,

   The rectangular division type is

   The image decoding method according to the division direction, characterized in that divided into a horizontal (vertical) form and a vertical (vertical) divided form.
6. An apparatus for decoding video data,

   Memory; And

   Includes one or more processors,

   The one or more processors,

   Receiving a bitstream including a block of encoded image data and segmentation information related to the block of image data;

   Determining a QuadTree plus BinaryTree (QTBT) partition structure for the block of the image data using the partition information, wherein the QTBT partition structure is a binary tree rooted from a leaf node of a quadtree. The binary tree is defined by partition types for dividing a parent node into two child nodes, the partition types including a triangle partition type and a rectangular partition type; And

   And decoding the block of the encoded image data for each leaf node of the QTBT.
7. The method of claim 6,

   In the binary tree, child nodes of nodes divided into triangular partition types are no longer partitioned.
8. The method of claim 6,

   The child decoding method of the binary tree, characterized in that the child nodes of the node divided into the rectangular partition type is allowed to be divided into two child nodes again.
9. In the video data decoding method,

   Receiving a bitstream including a block of encoded image data and segmentation information related to the block of image data;

   Determining a QTBT splitting structure for the block of the image data using the splitting information, wherein the QTBT splitting structure is a structure in which a binary tree is rooted from a leaf node of a quadtree. Leaf nodes of the quadtree are allowed to be divided into two child nodes, wherein the two child nodes are 凹 -shaped blocks and 凸 -shaped blocks; And

   Decoding the block of the encoded image data for each leaf node of the QTBT

   The image data decoding method comprising a.
10. In the video data decoding method,

    Receiving a bitstream including a coding tree unit (CTU) of encoded image data and segmentation information related to the CTU of the image data;

    Determining a QTBT splitting structure for the CTU using the splitting information, wherein the QTBT splitting structure is a structure in which a binary tree is rooted from a leaf node of a quadtree;

    Using the partitioning information, determining a prediction partition mode for each leaf node of the QTBT, wherein the prediction partition mode allows the leaf nodes of the QTBT to be split and predicted into two triangles of the same size; And

    Decoding a block of the encoded image data according to a prediction partition mode for each leaf node of the QTBT

    Image decoding method comprising a.

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