WO2020076034A1 - Prediction method using current picture referencing mode, and image decoding device therefor - Google Patents

Abstract

Disclosed are a prediction method using a current picture referencing mode, and an image decoding device therefor. Provided according to an embodiment of the present invention is a method for predicting a current block, which is a block to be decoded, by using a current picture referencing (intra block copy (ibc)) mode, the method comprising the steps of: decoding, from a bitstream, an enable flag indicating whether the application of the ibc mode is allowed, and type information indicating whether the type of slices is an inter type; depending on the enable flag and the type information, decoding from the bitstream an ibc flag indicating whether a prediction mode for the current block is the ibc mode; when the ibc flag indicates the ibc mode, decoding, from the bitstream, movement information having no index of pictures referred to by the current block; and predicting the current block by using a block indicated by the movement information within a current picture in which the current block is located. Representative drawing: figure 4

Description

Prediction method and video decoding apparatus using current picture reference mode

The present invention relates to encoding and decoding of an image, and to a prediction method for improving the efficiency of encoding and decoding and an image decoding apparatus using the same.

Since video data has a large amount of data compared to audio data or still image data, it requires a lot of hardware resources including memory to store or transmit itself without processing for compression.

Therefore, when storing or transmitting video data, the video data is compressed and stored or transmitted using an encoder, and the decoder receives compressed video data, decompresses and plays the video data. HVC (High Efficiency Video Coding), which improves coding efficiency by about 40% compared to H.264 / AVC, includes H.264 / AVC.

However, since the size, resolution, and frame rate of the image are gradually increasing, and thus the amount of data to be encoded is also increasing, a new compression technique having better encoding efficiency and higher image quality improvement effect than the existing compression technique is required.

In order to meet these demands, the present invention aims to provide an improved image encoding and decoding technology. In particular, one aspect of the present invention is to improve the efficiency of encoding and decoding through various methods for determining a prediction mode of a current block. It's about improving skills.

An aspect of the present invention, as a method of predicting a current block to be decoded in a current picture reference (intra block copy, ibc) mode, enables to indicate whether application of the ibc mode is permitted from a bitstream Decoding type information indicating whether the type of the flag and slice is inter; Decoding an ibc flag indicating whether the prediction mode of the current block is the ibc mode based on the enable flag and the type information from the bitstream; When the ibc flag indicates the ibc mode, decoding motion information not including a reference picture index of the current block from the bitstream; And predicting the current block using a block indicated by the motion information in the current picture in which the current block is located.

Another aspect of the present invention is an enable flag indicating whether application of a current picture reference (intra block copy, ibc) mode is permitted from a bitstream and a type indicating whether the type of slice is inter. Decoding information, decoding the ibc flag indicating whether the prediction mode of the current block is the ibc mode depending on the enable flag and the type information, and when the ibc flag indicates the ibc mode, the current block A decoding unit that decodes motion information not including a reference picture index of; And a prediction unit for predicting the current block by using a block indicated by the motion information in the current picture in which the current block is located.

As described above, according to an embodiment of the present invention, since the number of bits allocated to determine the prediction mode is adaptively adjusted to the frequency of the corresponding prediction mode, bit efficiency can be improved.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of the present disclosure.

2 is a diagram for explaining a method of dividing a block using a QTBTTT structure.

3 is a diagram for describing a plurality of intra prediction modes.

4 is an exemplary block diagram of an image decoding apparatus capable of implementing the techniques of the present disclosure.

5 is a diagram for describing a current picture reference technique.

6 is a diagram for explaining a conventional method of classifying prediction modes.

7 is a flowchart illustrating an example of a prediction mode determination proposed by the present invention.

8 is a flowchart illustrating an example of predicting a current block in a current picture reference mode.

9 to 14 are views for explaining various methods proposed in the present invention.

15 is a flowchart illustrating an embodiment of the present invention for predicting a current block in ibc_BVP mode.

16 to 18 are diagrams for describing BVP candidates included in the BVP candidate list for ibc mode.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. It should be noted that in adding identification numbers to the components of each drawing, the same components have the same reference numerals as possible even though they are displayed on different drawings. In addition, in describing the present invention, when it is determined that detailed descriptions of related well-known structures or functions may obscure the subject matter of the present invention, detailed descriptions thereof will be omitted.

1 is an exemplary block diagram of an image encoding apparatus capable of implementing the techniques of the present disclosure. Hereinafter, an image encoding apparatus and sub-components of the apparatus will be described with reference to FIG. 1.

The image encoding apparatus includes a block division unit 110, a prediction unit 120, a subtractor 130, a transformation unit 140, a quantization unit 145, an encoding unit 150, an inverse quantization unit 160, and an inverse transformation unit ( 165), an adder 170, a filter unit 180 and a memory 190.

Each component of the video encoding apparatus may be implemented in hardware or software, or a combination of hardware and software. Further, the function of each component may be implemented in software, and the microprocessor may be implemented to execute the function of software corresponding to each component.

One image (video) is composed of a plurality of pictures. Each picture is divided into a plurality of regions, and encoding is performed for each region. For example, one picture is divided into one or more tiles or / and slices. Here, one or more tiles may be defined as a tile group. Each tile or / slice is divided into one or more coding tree units (CTUs). And each CTU is divided into one or more coding units (CUs) by a tree structure. Information applied to each CU is encoded as the syntax of the CU, and information commonly applied to CUs included in one CTU is encoded as the syntax of the CTU. In addition, information commonly applied to all blocks in one tile is encoded as the syntax of a tile or encoded as a syntax of a tile group in which a plurality of tiles are collected, and information applied to all blocks constituting one picture is It is encoded in a picture parameter set (PPS) or a picture header. Furthermore, information commonly referred to by a plurality of pictures is encoded in a sequence parameter set (SPS). And, information that is commonly referenced by one or more SPSs is encoded in a video parameter set (VPS).

The block splitter 110 determines the size of a coding tree unit (CTU). Information about the size of the CTU (CTU size) is encoded as a syntax of an SPS or a PPS and transmitted to an image decoding apparatus.

The block dividing unit 110 divides each picture constituting an image into a plurality of coding tree units (CTUs) having a predetermined size, and then repeatedly repeats the CTU using a tree structure. (recursively) split. A leaf node in a tree structure becomes a coding unit (CU), which is a basic unit of encoding.

The tree structure includes a quad tree (QuadTree, QT) in which a parent node (or parent node) is divided into four child nodes (or child nodes) of the same size, or a binary tree (BinaryTree) in which a parent node is divided into two child nodes. , BT), or a ternary tree in which the upper node is divided into three lower nodes in a 1: 2: 1 ratio, or a structure in which two or more of these QT structures, BT structures, and TT structures are mixed. have. For example, a QTBT (QuadTree plus BinaryTree) structure may be used, or a QTBTTT (QuadTree plus BinaryTree TernaryTree) structure may be used. Here, BTTT may be collectively referred to as MTT (Multiple-Type Tree).

2 shows a QTBTTT split tree structure. As shown in FIG. 2, the CTU can be first divided into a QT structure. The quadtree split may be repeated until the size of the splitting block reaches the minimum block size (MinQTSize) of the leaf node allowed in QT. The first flag (QT_split_flag) indicating whether each node of the QT structure is divided into 4 nodes of the lower layer is encoded by the encoder 150 and signaled to the video decoding apparatus. If the leaf node of QT is not larger than the maximum block size (MaxBTSize) of the root node allowed by BT, it may be further divided into any one or more of BT structure or TT structure. In the BT structure and / or the TT structure, a plurality of split directions may exist. For example, there may be two directions in which a block of a corresponding node is horizontally divided and a vertically divided direction. As illustrated in FIG. 2, when MTT splitting is started, a second flag (mtt_split_flag) indicating whether nodes are split, and a flag indicating additional splitting direction (vertical or horizontal) and / or splitting type (Binary or Ternary) The flag indicating) is encoded by the encoding unit 150 and signaled to the video decoding apparatus.

As another example of a tree structure, when a block is split using a QTBTTT structure, information about a CU split flag (split_cu_flag) indicating that the block is split first and a QT split flag (split_qt_flag) indicating whether the split type is QT split is encoded 150 ) And signaled to the video decoding apparatus. If the CU split flag (split_cu_flag) value does not indicate that the partition has not been split, the block of the corresponding node becomes a leaf node in the split tree structure and becomes a coding unit (CU), which is a basic unit of encoding. If the CU split flag (split_cu_flag) value does not indicate that the split is performed, it is determined whether the split type is QT or MTT through the QT split flag (split_qt_flag) value. When the split type is QT, there is no additional information, and when the split type is MTT, additionally, a flag indicating the MTT split direction (vertical or horizontal) (mtt_split_cu_vertical_flag) and / or a flag indicating the MTT split type (Binary or Ternary) (mtt_split_cu_binary_flag) is encoded by the encoding unit 150 and signaled to the video decoding apparatus.

When QTBT is used as another example of a tree structure, two types of horizontally dividing a block of a corresponding node into two blocks of the same size (ie, symmetric horizontal splitting) and a vertically dividing type (ie, symmetric vertical splitting). Branches can exist. The split flag (split_flag) indicating whether each node of the BT structure is divided into blocks of a lower layer and split type information indicating a split type are encoded by the encoder 150 and transmitted to an image decoding apparatus. On the other hand, there may be further a type of dividing a block of a corresponding node into two blocks having an asymmetric shape. The asymmetric form may include a form of dividing a block of a corresponding node into two rectangular blocks having a size ratio of 1: 3, or a form of dividing a block of a corresponding node in a diagonal direction.

CU may have various sizes according to QTBT or QTBTTT division from CTU. Hereinafter, a block corresponding to a CU (ie, a leaf node of QTBTTT) to be encoded or decoded is referred to as a 'current block'.

The prediction unit 120 predicts the current block to generate a prediction block. The prediction unit 120 includes an intra prediction unit 122 and an inter prediction unit 124.

In general, each of the current blocks in a picture can be predictively coded. In general, prediction of the current block may be performed using intra prediction technology (using data from a picture containing the current block) or inter prediction technology (using data from a picture coded before a picture containing the current block). Can be performed. Inter prediction includes both one-way prediction and two-way prediction.

The intra prediction unit 122 predicts pixels in the current block using pixels (reference pixels) located around the current block in the current picture including the current block. There are multiple intra prediction modes according to the prediction direction. For example, as shown in FIG. 3, a plurality of intra prediction modes may include 65 non-directional modes including a planar mode and a DC mode. Peripheral pixels to be used and expressions are defined differently for each prediction mode.

The intra prediction unit 122 may determine an intra prediction mode to be used to encode the current block. In some examples, the intra prediction unit 122 may encode the current block using various intra prediction modes and select an appropriate intra prediction mode to use from the tested modes. For example, the intra prediction unit 122 calculates rate distortion values using rate-distortion analysis for various tested intra prediction modes, and has the best rate distortion characteristics among the tested modes. The intra prediction mode can also be selected.

The intra prediction unit 122 selects one intra prediction mode from among a plurality of intra prediction modes, and predicts a current block using a neighboring pixel (reference pixel) and an arithmetic expression determined according to the selected intra prediction mode. Information on the selected intra prediction mode is encoded by the encoding unit 150 and transmitted to the image decoding apparatus.

The inter prediction unit 124 generates a prediction block for the current block through a motion compensation process. The block most similar to the current block is searched in the reference picture that is encoded and decoded before the current picture, and a predicted block for the current block is generated using the searched block. Then, a motion vector corresponding to displacement between the current block in the current picture and the prediction block in the reference picture is generated. Generally, motion estimation is performed on luma components, and motion vectors calculated based on luma components are used for both luma components and chroma components. The motion information including information about the reference picture and motion vector used to predict the current block is encoded by the encoder 150 and transmitted to the video decoding apparatus.

The subtractor 130 subtracts the prediction block generated by the intra prediction unit 122 or the inter prediction unit 124 from the current block to generate a residual block.

The transform unit 140 converts the residual signal in the residual block having pixel values in the spatial domain into a transform coefficient in the frequency domain. The transform unit 140 may transform residual signals in the residual block using the entire size of the residual block as a transform unit, or divide the residual block into two subblocks that are a transform region and a non-transformed region, and convert the sub Residual signals can be transformed using only blocks as transform units. Here, the transform region sub-block may be one of two rectangular blocks having a size ratio of 1: 1 on the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_flag), directional (vertical / horizontal) information (cu_sbt_horizontal_flag), and / or location information (cu_sbt_pos_flag) indicating that only the sub-block is converted is encoded by the encoder 150 and signaled to the video decoding apparatus. . In addition, the size of the transform region sub-block may have a size ratio of 1: 3 based on the horizontal axis (or vertical axis). In this case, a flag (cu_sbt_quad_flag) for classifying the split is additionally encoded by the encoder 150 to decode the image. Signaled to the device.

The quantization unit 145 quantizes transform coefficients output from the transform unit 140 and outputs the quantized transform coefficients to the encoder 150.

The encoding unit 150 generates a bitstream by encoding quantized transform coefficients using an encoding method such as CABAC (Context-based Adaptive Binary Arithmetic Code). The encoder 150 encodes information such as a CTU size, a CU split flag, a QT split flag, an MTT split direction, and an MTT split type related to block splitting, so that the video decoding apparatus can split the block in the same way as the video coding apparatus. To make.

Also, the encoder 150 encodes information about a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and intra prediction information (that is, intra prediction mode) according to the prediction type. Information) or inter prediction information (information on reference pictures and motion vectors).

The inverse quantization unit 160 inverse quantizes the quantized transform coefficients output from the quantization unit 145 to generate transform coefficients. The inverse transform unit 165 reconstructs the residual block by transforming transform coefficients output from the inverse quantization unit 160 from the frequency domain to the spatial domain.

The adder 170 restores the current block by adding the reconstructed residual block and the predicted block generated by the predictor 120. The pixels in the reconstructed current block are used as a reference pixel when intra prediction of a next order block.

The filter unit 180 filters the reconstructed pixels to reduce blocking artifacts, ringing artifacts, and blurring artifacts caused by block-based prediction and transformation / quantization. To perform. The filter unit 180 may include a deblocking filter 182 and a sample adaptive offset (SAO) filter 184.

The deblocking filter 180 filters the boundary between the restored blocks to remove blocking artifacts caused by block-level encoding / decoding, and the SAO filter 184 adds additional deblocking filtered images. Filtering is performed. The SAO filter 184 is a filter used to compensate for a difference between a reconstructed pixel and an original pixel caused by lossy coding.

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

4 is an exemplary block diagram of an image decoding apparatus capable of implementing the techniques of the present disclosure. Hereinafter, an image decoding apparatus and sub-components of the apparatus will be described with reference to FIG. 4.

The image decoding apparatus may include a decoding unit 410, an inverse quantization unit 420, an inverse transform unit 430, a prediction unit 440, an adder 450, a filter unit 460, and a memory 470. have.

Similar to the video encoding apparatus of FIG. 1, each component of the video decoding apparatus may be implemented in hardware or software, or a combination of hardware and software. Further, the function of each component may be implemented in software, and the microprocessor may be implemented to execute the function of software corresponding to each component.

The decoder 410 determines a current block to be decoded by decoding a bitstream received from an image encoding apparatus and extracting information related to block partitioning, and prediction information and residual signal information required to restore the current block. To extract.

The decoder 410 extracts information on the CTU size from a Sequence Parameter Set (SPS) or a Picture Parameter Set (PPS) to determine the size of the CTU, and divides the picture into CTUs of the determined size. Then, the CTU is determined as the top layer of the tree structure, that is, the root node, and the CTU is split using the tree structure by extracting the segmentation information for the CTU.

For example, when the CTU is split using the QTBTTT structure, first, the first flag (QT_split_flag) related to the splitting of the QT is extracted, and each node is divided into four nodes of a lower layer. In addition, for the node corresponding to the leaf node of the QT, the second flag (MTT_split_flag) and split direction (vertical / horizontal) and / or split type (binary / ternary) information related to the splitting of the MTT are extracted to extract the corresponding leaf node from the MTT. Divide into structures. Through this, each node below the leaf node of QT is recursively divided into a BT or TT structure.

As another example, when a CTU is split using a QTBTTT structure, a CU split flag (split_cu_flag) indicating whether to split the CU is first extracted, and when the corresponding block is split, a QT split flag (split_qt_flag) is extracted. . If the split type is not QT and MTT, a flag indicating the MTT splitting direction (vertical or horizontal) (mtt_split_cu_vertical_flag) and / or a flag indicating the MTT splitting type (Binary or Ternary) (mtt_split_cu_binary_flag) is additionally extracted. In the splitting process, each node may have 0 or more repetitive MTT splits after 0 or more repetitive QT splits. For example, in the CTU, MTT splitting may occur immediately, or conversely, only multiple QT splitting may occur.

As another example, when the CTU is split using the QTBT structure, the first flag (QT_split_flag) related to the division of the QT is extracted, and each node is divided into four nodes of a lower layer. Then, for a node corresponding to a leaf node of QT, split flag (split_flag) indicating whether to be further divided by BT and split direction information are extracted.

On the other hand, when determining a current block to be decoded through partitioning of a tree structure, the decoder 410 extracts information on a prediction type indicating whether the current block is intra predicted or inter predicted. When the prediction type information indicates intra prediction, the decoder 410 extracts a syntax element for intra prediction information (intra prediction mode) of the current block. When the prediction type information indicates inter prediction, the decoder 410 extracts syntax elements for the inter prediction information, that is, information indicating a motion vector and a reference picture referenced by the motion vector.

Meanwhile, the decoder 410 extracts information about quantized transform coefficients of the current block as information about the residual signal.

The inverse quantization unit 420 inverse quantizes the quantized transform coefficients, and the inverse transform unit 430 inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to restore residual signals to generate a residual block for the current block. .

In addition, when the inverse transform unit 430 inversely transforms only a partial region (subblock) of a transform block, a flag (cu_sbt_flag) indicating that only a subblock of the transform block is transformed, and vertical / horizontal information (cu_sbt_horizontal_flag) of the subblock ) And / or extracting the location information (cu_sbt_pos_flag) of the sub-blocks, and restoring the residual signals by inverse transforming the transform coefficients of the corresponding sub-blocks from the frequency domain to the spatial domain. By filling, we create the final residual block for the current block.

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

The intra prediction unit 442 determines an intra prediction mode of a current block among a plurality of intra prediction modes from syntax elements for an intra prediction mode extracted from the decoder 410, and according to the intra prediction mode, reference pixels around the current block Use to predict the current block.

The inter prediction unit 444 determines a motion vector of a current block and a reference picture referred to by the motion vector using a syntax element for an intra prediction mode extracted from the decoding unit 410, and uses the motion vector and the reference picture. To predict the current block.

The adder 450 restores the current block by adding the residual block output from the inverse transform unit and the prediction block output from the inter prediction unit or the intra prediction unit. The pixels in the reconstructed current block are used as a reference pixel in intra prediction of a block to be decoded later.

The filter unit 460 may include a deblocking filter 462 and a SAO filter 464. The deblocking filter 462 deblocks the boundary between the reconstructed blocks in order to remove blocking artifacts caused by block-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 blocks filtered through the deblocking filter 462 and the SAO filter 464 are stored in the memory 470. When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter prediction of a block in a picture to be encoded.

The present invention proposes new methods for determining a prediction mode of a block to be coded and / or decoded (current block) and performing prediction on the current block based on the prediction mode.

The prediction mode determined through the present invention can be largely divided into an inter mode, an intra mode, and a current picture referencing (cpr) mode. The cpr mode may be referred to as an ibc (intra block copy) mode. The inter mode may include skip mode, merge mode, and AMVP mode, and cpr mode, i.e., ibc mode, may include ibc_skip mode, ibc_merge mode, and ibc_BVP mode. ibc_skip mode is ibc mode applied to skip mode, ibc_merge mode is ibc mode applied to merge mode, and ibc_BVP mode is ibc mode applied to AMVP mode.

The ibc mode is one of intra prediction methods, and an example of the ibc mode is represented in FIG. 5. As illustrated in FIG. 5, in ibc mode, prediction information of a current block is obtained from another block (reference block) located in the same picture (current picture).

Of the blocks included in the current picture of FIG. 5, a block including a pattern corresponds to a block or region (Coded region) in which decoding is already completed, and a block not including a pattern is a block or region in which decoding is not completed (Not coded yet). Therefore, the reference block from which the prediction information of the current block is obtained corresponds to a block that has already been decoded. The reference block is indicated by a motion vector (MV), and in ibc mode, this motion vector may be referred to as a block vector (BV).

In this ibc mode, prediction information of the current block is obtained from a reference block indicated by BV, while in intra mode, prediction information is obtained from pixels adjacent to the periphery of the current block. Further, in ibc mode, prediction information is obtained from a reference block located in the same picture, while in inter mode, prediction information is obtained from a reference block located in another picture.

In the conventional method of determining the prediction mode, first, a process (S610) of determining the type (slice_type! = I) of the slice including the current block is performed. The slice type may include I-slice (intra slice), P-slice (predictive slice) and B-slice (bi-predictive slice).

I-slice is only available for intra prediction. Therefore, when the current block is included in the I-slice, a process of parsing and decoding information required for intra prediction (S692) is performed. In contrast, P-slices and B-slices are capable of both inter prediction and intra prediction. Therefore, when the current block is not included in the I-slice, additional determination processes for the current block are performed.

First, a process of parsing and decoding a flag (skip_flag) indicating whether the current block is predicted as a skip mode (S620) and a process of determining skip_flag (S630) are performed. When skip_flag is on (skip_flag = 1), the prediction mode of the current block corresponds to skip mode. Accordingly, in order to obtain motion information used for skip mode prediction, a process of parsing and decoding the merge index (merge_index) (S680) is additionally performed.

Alternatively, when skip_flag is off (skip_flag = 0), the prediction mode of the current block may correspond to any one of modes other than skip mode (merge mode, AMVP mode, and intra mode). In order to determine this more accurately, the process of parsing and decoding a flag indicating whether the current block is predicted in the inter mode or the intra mode (the flag indicating whether the current block is predicted as the intra mode, pred_mode_flag) ( S640) and a process of determining pred_mode_flag (S650) is performed.

When pred_mode_flag indicates an inter mode, the prediction mode of the current block may correspond to one of a merge mode and an AMVP mode. In order to determine this more accurately, a flag (merge_flag) indicating whether a current block is predicted as a merge mode is parsed and decoded (S660) and a merge_flag is determined (S670).

When merge_flag is on (merge_flag = 1), the prediction mode of the current block corresponds to the merge mode. Accordingly, a process of parsing and decoding the merge index (merge_index) (S680) is performed. In contrast, when merge_flag is off (merge_flag = 0), the prediction mode of the current block corresponds to the AMVP mode. Therefore, a process of parsing and decoding information required for AMVP prediction (S690) is performed.

Returning to step S650, when pred_mode_flag indicates an intra mode, a process of parsing and decoding information required for intra prediction (S692) is performed.

In the conventional method described with reference to FIG. 6, the ibc mode may be applied based on whether a reference block for the current block is located in the same picture as the current picture. For example, when the prediction mode of the current block is determined to be a skip mode or a merge mode, when a merge candidate's reference picture indicated by merge_idx is the same as the current picture, the current block may be determined and predicted in ibc_skip mode or ibc_merge mode. have.

As another example, when the prediction mode of the current block is determined to be the AMVP mode, when the reference picture index (ref_idx) signaled from the video encoding device indicates the same picture as the current picture, the current block is determined and predicted as the ibc_BVP mode You can.

Whether the ibc mode is on or off may be defined through separate flags (sps_curr_pic_ref_enabled_flag and pps_curr_pic_ref_enabled_flag), and Table 1 and Table 2 below show an example of defining whether the ibc mode is on or off through each of the above flags.

Further, in order to determine whether the reference picture of the merge candidate and the current picture are the same and whether the reference picture index indicates the same picture as the current picture, the current picture must be added to the reference picture list. Equation 1 below shows an example in which the current picture is added to the reference picture list.

The present invention proposes new syntax and semantics for distinguishing prediction modes of the current block. In addition, the present invention proposes syntax and semantics for a current block (predicted) encoded in ibc mode in an image encoding apparatus. Furthermore, the present invention proposes new BVP candidates included in the BVP candidate list for the current block predicted in ibc_BVP mode.

In the present invention, the video encoding apparatus determines the prediction mode of the current block based on whether the preset conditions are satisfied, and signals the video decoding apparatus by including syntax elements indicating whether the preset conditions are satisfied in the bitstream. The video decoding apparatus determines whether the preset conditions are satisfied (S710), and determines the prediction mode of the current block based on the determination result (S720). In addition, the video decoding apparatus predicts the current block based on the determined prediction mode (S730).

The 'preset conditions' refer to a criterion for determining the prediction mode of the current block. The preset conditions include whether the type of the tile group (hereinafter referred to as 'tile group') containing the current block is intra (or whether the tile group type is inter), and whether the ibc mode is active (on). It may include whether or not (application of the ibc mode is allowed) and whether the prediction mode of the current block is the merge mode. Also, the preset conditions may include whether the current block is encoded in an intra mode (or inter mode) and whether the current block prediction mode is an ibc mode.

Whether the type of the tile group is intra may be indicated through type information indicating it. Type information may be implemented with a predefined syntax element (eg, tile_group_type). In this specification, the judgment on the type information may be expressed as 'tile group = inter?'. Here, the tile group may be referred to differently as a tile or a slice. Accordingly, 'whether the type of the tile group is intra' may be differently understood as 'whether the tile type is intra' or 'whether the slice type is intra'.

Whether the application of ibc mode is permitted may be indicated through an enable flag indicating this. The enable flag may be implemented with a predefined syntax element (eg, ibc_enabled_flag). ibc_enabled_flag may be defined in one or more locations among SPS, PPS, tile group header, tile header, and CTU header.

Whether the prediction mode of the current block is a merge mode may be indicated through a syntax element (merge_flag) indicating this. Whether the current block is coded in inter mode (or intra mode) may be indicated through a syntax element (pred_mode_flag) indicating this. Whether the prediction mode of the current block is ibc mode may be indicated through a syntax element (pred_mode_ibc_flag) indicating this.

An example of the process of determining the prediction mode of the current block as the ibc_BVP mode by applying all or a part of these preset conditions will be described below.

When the image encoding apparatus transmits the enable flag and the type information for the tile group in the bitstream, the image decoding apparatus (ie, the decoder) decodes the enable flag and type information from the bitstream (S810).

In addition, the image encoding apparatus selectively transmits the ibc flag by including the enable flag, type information, and / or the ibc flag as indicated by the prediction mode of the current block. The decoder 410 decodes the ibc flag depending on the decoded enable flag, type information, and / or the prediction mode of the current block (S820). For example, the image decoding apparatus may decode the ibc flag when the enable flag is on and the type information indicates intra. In addition, the video decoding apparatus decodes the ibc flag when the enable flag is on, the type information indicates inter (type information does not indicate intra), and the prediction mode is inter (prediction mode is not intra). can do.

When the ibc flag indicates the ibc mode, the video encoding apparatus transmits the motion information of the current block by including it in the bitstream, and the video decoding apparatus decodes the motion information included in the bitstream (S830). The reference picture index is not included in the motion information of the current block to be decoded.

The video decoding apparatus (that is, the prediction unit) predicts the current block using a block (reference block) indicated by the decoded motion information (S840). The reference block corresponds to a block located in the same picture (current picture) as the current block.

As described above, in the present invention, it can be determined that the current block is predicted in the ibc mode (ibc_BVP mode) using a separate syntax element (pred_mode_ibc_flag). Therefore, the present invention has a difference from the conventional method of determining that the current block is predicted in the ibc_BVP mode using the reference picture index signaled from the video encoding apparatus.

Due to this difference, the conventional method parses both the BVP index (BVP_idx), the BVD and the reference picture index, whereas the present invention parses only the BVP index and BVD. That is, in the present invention, since the current block can be predicted in the ibc_BVP mode based on only the BVP index and the BVD without signaling for the reference picture index, bit efficiency can be improved.

The embodiments described below may be performed in the same manner in both the image encoding apparatus and the image decoding apparatus, but for convenience of explanation and understanding, the image decoding apparatus will be mainly described. However, the process of parsing and decoding a specific syntax element by the decoder 410 or the video decoding apparatus is preferably understood as being included in the bitstream by the video encoding apparatus encoding the specific syntax element.

Example 1

The first embodiment corresponds to an example in which a prediction mode of a current block is determined based on whether the predetermined conditions are satisfied, and a current block is predicted using the determined prediction mode.

Example 1-1

9, in Example 1-1, whether the application of the ibc mode is allowed, whether the type of the tile group is intra, whether the prediction mode of the current block is a merge mode, and the prediction mode of the current block All or part of whether it is in the ibc mode and whether the current block is encoded by inter prediction may be used.

skip mode, merge mode, ibc_skip mode and ibc_merge mode

When the enable flag and the type information are decoded, the image decoding apparatus may determine whether the application of the ibc mode is allowed or the tile group type is intra using the decoded information (S910).

In step S910, when the enable flag indicates that the application of the ibc mode is permitted or indicates that the type information is not intra (if the application of the ibc mode is not allowed and the tile group type is inter, the application of the ibc mode is allowed. When the tile group type is Intra and the ibc mode is allowed while the tile group type is Inter), the image decoding apparatus parses and decodes merge_flag (S920) and determines merge_flag (S930).

When the merge_flag indicates 'the prediction mode of the current block is a merge mode' in step S930, the prediction mode of the current block may correspond to any one of a skip mode, a merge mode, an ibc_skip mode, and an ibc_merge mode. In this case, the video decoding apparatus may distinguish between the skip / merge mode and the ibc_skip / ibc_merge mode using merge_idx that is parsed and decoded through S940.

When the reference picture of the merge candidate indicated by the decoded merge_idx is the same as the current picture, the prediction mode of the current block corresponds to the ibc_skip / ibc_merge mode. On the other hand, when the reference picture of the merge candidate indicated by the decoded merge_idx is not the same as the current picture, the prediction mode of the current block corresponds to the skip / merge mode.

The distinction between the skip mode and the merge mode and the distinction between the ibc_skip mode and the ibc_merge mode may be determined according to which value of 1 and 0 indicates information (eg, cbf) parsed and decoded through S990.

AMVP mode

The video decoding apparatus determines whether the application of the ibc mode is permitted or the tile group type is intra using the enable flag and type information (S910), and displays information indicating whether the prediction mode of the current block is a merge mode. Parsing and decoding (S920), it can be determined (S930).

If merge_flag does not indicate a merge mode in step S930, the prediction mode of the current block may correspond to any one of AMVP mode, ibc_BVP mode, and intra mode. In order to determine the prediction mode of the current block as one of the AMVP mode, ibc_BVP mode, and intra mode, the video decoding apparatus may parse and decode mode information (pred_mode_flag) (S950) and determine pred_mode_flag (S960).

When pred_mode_flag indicates inter prediction in step S960 (when not indicating intra prediction), the video decoding apparatus uses an enable flag and type information, and a separate syntax indicating that the current block is predicted in ibc mode (pred_mode_ibc_flag) It may be determined whether or not to parse (S970). That is, if the prediction mode is not intra prediction in step S960, the image decoding apparatus may determine whether to parse the pred_mode_ibc_flag using the enable flag and type information (S970).

If the enable flag does not indicate that the application of the ibc mode is allowed in step S970 or the type information indicates intra, the video decoding apparatus may determine the type information again (S980). When the type information indicates inter in step S980, the prediction mode of the current block corresponds to the AMVP mode. Accordingly, the apparatus for decoding an image may parse and decode motion information (ref_idx, mvd, mvp_idx) for predicting the current block in the AMVP mode (S982).

When the S970 process, the S980 process, and the S982 process are combined and described again, the video decoding apparatus parses motion information for predicting the current block in the AMVP mode when the tile group type is inter without applying ibc mode. And decryption.

On the other hand, if the enable flag in step S970 indicates that the application of the ibc mode is allowed and the type information indicates inter (when indicating not intra), the video decoding apparatus parses and decodes pred_mode_ibc_flag (S984), The pred_mode_ibc_flag may be determined (S986). Even if pred_mode_ibc_flag does not indicate ibc mode in step S986, the prediction mode of the current block corresponds to the AMVP mode. Accordingly, the apparatus for decoding an image may parse and decode motion information for predicting the current block in the AMVP mode (S982).

ibc_BVP mode

The image decoding apparatus may determine whether the ibc mode is permitted using the enable flag and type information and whether the tile group type is intra (S970).

When the enable flag in step S970 indicates that the application of the ibc mode is permitted and the type information indicates inter, the image decoding apparatus may parse and decode pred_mode_ibc_flag (S984) and determine pred_mode_ibc_flag (S986). When pred_mode_ibc_flag indicates the ibc mode in step S986, the prediction mode of the current block corresponds to the ibc_BVP mode. Accordingly, the apparatus for decoding an image may parse and decode motion information (bvd, bvp_idx) for predicting the current block in ibc_BVP mode (S988).

If the enable flag in step S970 indicates that the application of the ibc mode is not permitted or the type information indicates intra, the video decoding apparatus may determine the type information again (S980). Even if the type information does not indicate an inter (in the case of indicating an intra) in step S980, the prediction mode of the current block corresponds to the ibc_BVP mode. Accordingly, the apparatus for decoding an image may parse and decode motion information (bvd, bvp_idx) for predicting the current block in ibc_BVP mode (S988).

According to an embodiment, the image decoding apparatus may further perform the processes of parsing and decoding the mode information (pred_mode_flag) before S970 (S950), and determining (S960). In the case of such an embodiment, when it is indicated in step S960 that the prediction mode of the current block is not intra prediction (inter prediction), the video decoding apparatus may perform the above-described S970 process and processes after this S970 process. .

According to an embodiment, the image decoding apparatus may be configured to perform the above-described S910 process, S920 process, and S930 process before the S950 process. In the case of such an embodiment, when merge_flag does not indicate a merge mode in operation S930, operation S950 may be performed.

Intra mode

When the enable flag in step S910 indicates that application of the ibc mode is not allowed and the type information indicates intra, the prediction mode of the current block corresponds to the intra mode. Accordingly, the image decoding apparatus may parse and decode information for predicting the current block in intra mode (S992).

Meanwhile, in step S960, even if the mode information does not indicate inter prediction, the prediction mode of the current block corresponds to the intra mode. Accordingly, the image decoding apparatus may parse and decode information for predicting the current block in intra mode (S992). In the intra mode, cbf is not signaled and is derived to 1 (S994).

The number of bits consumed or allocated to determine the prediction mode for the current block based on Example 1-1 is represented in FIG. 10.

The tile group type of FIG. 10 is an item indicating whether a tile group corresponds to I-type, P-type, or B-type. If the tile group corresponds to the I-type, it is determined to be tile group ≠ inter, and if the tile group corresponds to the P-type or B-type, it is determined to be tile group = inter.

CU type corresponds to an item indicating whether the current block is predicted in inter mode or intra mode, and CU mode indicates whether the current block is in skip mode, merge mode, AMVP mode, ibc_skip mode, ibc_merge mode or ibc_BVP mode. Corresponds to the item indicating whether the mode is predicted.

mode corresponds to an item indicating whether each of merge_flag, pred_mode_flag and pred_mode_ibc_flag is on / off in the entire process of determining the prediction mode of the current block, ref_idx corresponds to an item indicating whether to reference the reference picture index, and cbf is the current block Corresponds to the item indicating whether all of the transform coefficients for have a zero value or whether the transform coefficients have one or more non-zero values.

Total bits correspond to an item indicating the number of bits consumed or allocated to determine the prediction mode of the current block for each prediction mode, and ibc = off represents items consumed in each process when ibc_enabled_flag is off Corresponds to That is, the above-mentioned items excluding the ibc = off item indicate the number of bits on the premise that ibc_enabled_flag is on (assuming that the ibc method is applied).

Hereinafter, the number of bits allocated to determine each prediction mode on the premise of ibc_enabled_flag = 1 will be described first, and then the number of bits allocated to determine each prediction mode on the premise of ibc_enabled_flag = 0 will be described later. .

Assuming that the tile group type is P-type or B-type and the CU type is inter, tile group = inter is further premised. Therefore, when CU mode is skip, merge_flag = 1, ref_idx is not signaled, and cbf = 0, and 2 bits are allocated to determine the skip mode.

When CU mode is merge, merge_flag = 1, ref_idx is not signaled, and cbf = 1, and 2 bits are allocated to determine the merge mode. When the CU mode is AMVP, merge_flag = 0, pred_mode_flag = 1, pred_mode_ibc_flag = 0, ref_idx = 0 and cbf = 0 or 1, and a total of 5 bits are allocated to determine the AMVP mode.

When the tile group type is P-type or B-type and the CU type is intra, a total of 2 bits (merge_flag = 0 and pred_mode_flag = 0) are allocated to determine that the CU mode is intra mode. In this case, cbf is not signaled, but is led to 1.

In addition, a total of 2 bits (merge_flag = 1 and cbf = 0) are allocated to determine that the CU mode is ibc_skip, and a total of 2 bits (merge_flag = 1 and cbf = 1) are allocated to determine that the CU mode is ibc_merge, A total of 4 bits (merge_flag = 0, pred_mode_flag = 1, pred_mode_ibc_flag = 1, cbf = 0 or 1) are allocated to determine that the CU mode is ibc_BVP.

When the tile group type is I-type (when the CU type is intra), in addition to ibc_enabled_flag = 1, tile group ≠ inter is additionally premised. Therefore, a total of 2 bits (merge_flag = 0 and pred_mode_flag = 0) are allocated to determine that the CU type is intra mode.

In addition, a total of 2 bits (merge_flag = 1 and cbf = 0) are allocated to determine that the CU mode is ibc_skip, and a total of 2 bits (merge_flag = 1 and cbf = 1) are allocated to determine that the CU mode is ibc_merge, A total of 3 bits (merge_flag = 0, pred_mode_flag = 1, cbf = 0 or 1) are allocated to determine that CU mode is ibc_BVP.

When the ibc function is off (ibc_enabled_flag = 0), the number of bits consumed or allocated to determine the prediction mode for the current block is expressed in the ibc = off item. Since ibc function is off, Tile group type corresponds to P-type or B-type, CU type corresponds to inter, and pred_mode_ibc_flag = 0 is assumed.

When CU mode is skip, merge_flag = 1, ref_idx is not signaled, and cbf = 0, so a total of 2 bits are allocated to determine the skip mode. When CU mode is merge, merge_flag = 1, ref_idx is not signaled, and cbf = 1, so a total of 2 bits are allocated to determine the merge mode. When the CU mode is AMVP, merge_flag = 0, pred_mode_flag = 1, ref_idx = 0 and cbf = 0 or 1, and a total of 4 bits are allocated to determine the AMVP mode.

Example 1-2

Example 1-2 corresponds to another example of determining a prediction mode of a current block using new syntax and semantics, and predicting a current block based on the determined prediction mode. As shown in FIG. 11, in Embodiment 1-2, some or all of the preset conditions may be applied to determine a prediction mode of the current block.

skip mode, merge mode, ibc_skip mode and ibc_merge mode

The video decoding apparatus may determine whether the application of the ibc mode is permitted or the tile group type is intra using the enable flag and type information (S1110). In step S1110, when the enable flag indicates that the application of the ibc mode is allowed or the type information indicates inter, the image decoding apparatus parses and decodes the merge_flag (S1120) and may determine this (S1130).

If merge_flag indicates a merge mode in step S1130, the video decoding apparatus may distinguish between skip / merge mode and ibc_skip / ibc_merge mode using merge_idx parsed and decoded through step S1140. Specifically, when the reference picture of the merge candidate indicated by the decoded merge_idx is the same as the current picture, the prediction mode of the current block corresponds to the ibc_skip / ibc_merge mode. When the reference picture of the merge candidate indicated by the decoded merge_idx is not the same as the current picture, the prediction mode of the current block corresponds to skip / merge mode.

The distinction between the skip mode and the merge mode and the distinction between the ibc_skip mode and the ibc_merge mode may be determined according to which value of 1 or 0 is indicated by cbf parsed and decoded through the process S1190.

AMVP mode

If merge_flag does not indicate a merge mode in step S1130, the image decoding apparatus may parse and decode mode information (pred_mode_flag) (S1150) and determine pred_mode_flag (S1160).

When pred_mode_flag indicates inter prediction in step S1160, the video decoding apparatus may determine the type information (S1170). When the type information indicates the inter in step S1170, the prediction mode of the current block corresponds to the AMVP mode. Accordingly, the apparatus for decoding an image may parse and decode motion information (ref_idx, mvd, mvp_idx) for predicting the current block in the AMVP mode (S1180).

ibc_BVP mode

The image decoding apparatus can determine whether the ibc mode is applied using the enable flag and type information and whether the tile group type is intra (S1182).

In step S1182, when the enable flag indicates that the application of the ibc mode is allowed and the type information indicates inter, the video decoding apparatus may parse and decode pred_mode_ibc_flag (S1184) and determine pred_mode_ibc_flag (S1186). When pred_mode_ibc_flag indicates ibc mode in step S1186, the prediction mode of the current block corresponds to the ibc_BVP mode. Accordingly, the image decoding apparatus may parse and decode motion information (bvd, bvp_idx) for predicting the current block in ibc_BVP mode (S1188).

Even when the type information indicates intra in step S1170, the prediction mode of the current block corresponds to the ibc_BVP mode. Accordingly, the image decoding apparatus may parse and decode motion information (bvd, bvp_idx) for predicting the current block in ibc_BVP mode (S1188).

According to an embodiment, the image decoding apparatus may further perform the processes of parsing and decoding the mode information (pred_mode_flag) before the process S1182 (S1150) and determining it (S1160). In the case of such an embodiment, the process S1182 may be performed when pred_mode_flag does not indicate inter prediction in step S1160, and the process S1170 may be performed when pred_mode_flag indicates inter prediction in step S1160.

According to an embodiment, the image decoding apparatus may be configured to perform the above-described steps S1110, S1120, and S1130 before S1150. In the case of such an embodiment, when merge_flag does not indicate a merge mode in step S1130, step S1150 may be performed.

Intra mode

When the enable flag in step S1110 indicates that the application of the ibc mode is not allowed and the type information indicates intra, the prediction mode of the current block corresponds to the intra mode. Accordingly, the image decoding apparatus may parse and decode information for predicting the current block in intra mode (S1192).

In addition, in step S1182, even when the enable flag indicates that the application of the ibc mode is not permitted or the type information indicates intra, the prediction mode of the current block corresponds to the intra mode. Accordingly, the image decoding apparatus may parse and decode information for predicting the current block in intra mode (S1192).

Furthermore, even if pred_mode_ibc_flag does not indicate ibc mode in step S1186, the prediction mode of the current block corresponds to the intra mode. Accordingly, the image decoding apparatus may parse and decode information for predicting the current block in intra mode (S1192). In the intra mode, cbf is not signaled and is derived to 1 (S1194).

The number of bits consumed or allocated to determine the prediction mode for the current block based on Example 1-2 is represented in FIG. 12.

The tile group type item, CU type item CU mode item, mode item, ref_idx item, cbf item, Total bits item, and ibc = off item of FIG. 12 have the same meaning as in FIG. 10 described above.

Hereinafter, the number of bits allocated to determine each prediction mode on the premise of ibc_enabled_flag = 1 will be described first, and then the number of bits allocated to determine each prediction mode on the premise of ibc_enabled_flag = 0 will be described later. .

Assuming that the tile group type is P-type or B-type and the CU type is inter, tile group = inter is further premised. Therefore, when CU mode is skip, merge_flag = 1, ref_idx is not signaled, and cbf = 0, so a total of 2 bits are allocated to determine the skip mode.

When CU mode is merge, merge_flag = 1, ref_idx is not signaled, and cbf = 1, so a total of 2 bits are allocated to determine the merge mode. When the CU mode is AMVP, merge_flag = 0, pred_mode_flag = 1, ref_idx = 0 and cbf = 0 or 1, and a total of 4 bits are allocated to determine the AMVP mode.

When the tile group type is P-type or B-type and the CU type is intra, a total of 3 bits (merge_flag = 0, pred_mode_flag = 0 and pred_mode_ibc_flag = 0) are allocated to determine that the CU type is intra mode. In this case, cbf is not signaled, but is led to 1.

In addition, a total of 2 bits (merge_flag = 1 and cbf = 0) are allocated to determine that the CU mode is ibc_skip, and a total of 2 bits (merge_flag = 1 and cbf = 1) are allocated to determine that the CU mode is ibc_merge, A total of 4 bits (merge_flag = 0, pred_mode_flag = 0, pred_mode_ibc_flag = 1, cbf = 0 or 1) are allocated to determine that the CU mode is ibc_BVP.

When the tile group type is I-type (when the CU type is intra), in addition to ibc_enabled_flag = 1, tile group ≠ inter is additionally premised. Therefore, a total of 2 bits (merge_flag = 0 and pred_mode_flag = 0) are allocated to determine that the CU type is intra mode.

In addition, a total of 2 bits (merge_flag = 1 and cbf = 0) are allocated to determine that the CU mode is ibc_skip, and a total of 2 bits (merge_flag = 1 and cbf = 1) are allocated to determine that the CU mode is ibc_merge, A total of 3 bits (merge_flag = 0, pred_mode_flag = 1, cbf = 0 or 1) are allocated to determine that the CU type is ibc_BVP.

When the ibc function is off (ibc_enabled_flag = 0), the number of bits consumed or allocated to determine the prediction mode for the current block is expressed in the ibc = off item. Since ibc function is off, Tile group type corresponds to P-type or B-type, CU type corresponds to inter, and pred_mode_ibc_flag = 0 is assumed.

When CU mode is skip, merge_flag = 1, ref_idx is not signaled, and cbf = 0, so a total of 2 bits are allocated to determine the skip mode. When CU mode is merge, merge_flag = 1, ref_idx is not signaled, and cbf = 1, so a total of 2 bits are allocated to determine the merge mode. When the CU mode is AMVP, merge_flag = 0, pred_mode_flag = 1, ref_idx = 0 and cbf = 0 or 1, and a total of 4 bits are allocated to determine the AMVP mode.

Example 1-3

Examples 1-3 correspond to another example of determining a prediction mode of a current block using new syntax and semantics, and predicting a current block based on the determined prediction mode. As illustrated in FIG. 13, in Examples 1-3, some or all of the preset conditions may be performed to determine the prediction mode of the current block.

skip mode, merge mode, ibc_skip mode and ibc_merge mode

The image decoding apparatus may determine whether the application of the ibc mode is allowed or the type of the tile group is intra using the enable flag and type information (S1310). When the application of the ibc mode is permitted or the tile group type is inter, the image decoding apparatus parses and decodes the merge_flag (S1320) and can determine this (S1330).

When merge_flag indicates a merge mode in step S1330, the prediction mode of the current block may correspond to any one of skip mode, merge mode, ibc_skip mode, and ibc_merge mode. The video decoding apparatus may distinguish between skip / merge mode and ibc_skip / ibc_merge mode by using merge_idx parsed and decoded through S1340.

The distinction between the skip mode and the merge mode and the distinction between the ibc_skip mode and the ibc_merge mode may be determined according to which of 1 and 0 the cbf parsed and decoded through S1390 indicates.

AMVP mode

If merge_flag does not indicate a merge mode in step S1330, the image decoding apparatus may determine enable flag and type information (S1350). When the enable flag in step S1350 indicates that the application of the ibc mode is allowed and the type information indicates inter, the video decoding apparatus may parse and decode pred_mode_ibc_flag (S1384) and determine pred_mode_ibc_flag (S1386).

If pred_mode_ibc_flag does not indicate ibc mode in step S1386 or the enable flag indicates that application of ibc mode is not permitted in step S1350, or the type information indicates intra, the video decoding apparatus uses mode information (pred_mode_flag). Parsing and decoding (S1360), it can be determined (S1370).

When pred_mode_flag indicates inter prediction in step S1370, the video decoding apparatus may determine type information (S1380). When the type information indicates inter in step S1380, the prediction mode of the current block corresponds to the AMVP mode. Accordingly, the apparatus for decoding an image may parse and decode information (ref_idx, mvd, mvp_idx) for predicting the current block in the AMVP mode (S1382).

ibc_BVP mode

The image decoding apparatus may determine whether the ibc mode is permitted using the enable flag and type information and whether the tile group type is intra (S1350).

When the enable flag in step S1350 indicates that the application of the ibc mode is allowed and the type information indicates inter, the video decoding apparatus may parse and decode pred_mode_ibc_flag (S1384) and determine pred_mode_ibc_flag (S1386). When pred_mode_ibc_flag indicates ibc mode in step S1386, the prediction mode of the current block corresponds to the ibc_BVP mode. Accordingly, the apparatus for decoding an image may parse and decode motion information (bvd, bvp_idx) for predicting the current block in ibc_BVP mode (S1388).

According to the embodiment, when the enable flag in step S1350 indicates that the application of the ibc mode is not permitted or the type information indicates intra, the video decoding apparatus parses and decodes the mode information (pred_mode_flag) (S1360), It can be determined (S1370). When pred_mode_flag indicates inter prediction in step S1370, the video decoding apparatus may determine type information (S1380). When the type information indicates intra in step S1380, the prediction mode of the current block corresponds to the ibc_BVP mode. Accordingly, the apparatus for decoding an image may parse and decode motion information (bvd, bvp_idx) for predicting the current block in ibc_BVP mode (S1388).

According to an embodiment, the image decoding apparatus may be configured to perform the aforementioned S1310 process, S1320 process, and S1330 process before the S1350 process. In the case of such an embodiment, when merge_flag does not indicate a merge mode in step S1330, step S1350 may be performed.

Intra mode

In step S1310, when the enable flag indicates that the application of the ibc mode is not allowed and the type information indicates intra, the prediction mode of the current block corresponds to the intra mode. Therefore, the image decoding apparatus parses and decodes information for predicting the current block in intra mode (S1392).

In addition, even if pred_mode_flag does not indicate inter prediction in step S1370, the prediction mode of the current block corresponds to the intra mode. Therefore, the image decoding apparatus parses and decodes information for predicting the current block in intra mode (S1392). In the intra mode, cbf is not signaled and is led to 1 (S1394).

The number of bits consumed or allocated to determine the prediction mode for the current block based on Examples 1-3 is illustrated in FIG. 14. The tile group type item, CU type item CU mode item, mode item, ref_idx item, cbf item, Total bits item, and ibc = off item of FIG. 14 have the same meanings as those of FIGS. 10 and 12 described above.

Assuming that the tile group type is P-type or B-type and the CU type is inter, tile group = inter is further premised. Therefore, when CU mode is skip, merge_flag = 1, ref_idx is not signaled, cbf = 0, and a total of 2 bits are allocated to determine the skip mode. When CU mode is merge, merge_flag = 1, ref_idx is not signaled, cbf = 1, and a total of 2 bits are allocated to determine the merge mode. When the CU mode is AMVP, merge_flag = 0, pred_mode_ibc_flag = 0, pred_mode_flag = 1, ref_idx = 0 and cbf = 0 or 1, and a total of 5 bits are allocated to determine the AMVP mode.

When the tile group type is P-type or B-type and the CU type is intra, a total of 3 bits (merge_flag = 0, pred_mode_ibc_flag = 0 and pred_mode_flag = 0) are allocated to determine that the CU type is intra mode. In this case, cbf is not signaled, but is led to 1.

In addition, a total of 2 bits (merge_flag = 1 and cbf = 0) are allocated to determine that the CU mode is ibc_skip, and a total of 2 bits (merge_flag = 1 and cbf = 1) are allocated to determine that the CU mode is ibc_merge, A total of 3 bits (merge_flag = 0, pred_mode_ibc_flag = 1, cbf = 0 or 1) are allocated to determine that CU mode is ibc_BVP.

When the tile group type is I-type (when the CU type is intra), in addition to ibc_enabled_flag = 1, tile group ≠ inter is additionally premised. Therefore, a total of 2 bits (merge_flag = 0 and pred_mode_flag = 0) are allocated to determine that the CU type is intra mode.

In addition, a total of 2 bits (merge_flag = 1 and cbf = 0) are allocated to determine that the CU mode is ibc_skip, and a total of 2 bits (merge_flag = 1 and cbf = 1) are allocated to determine that the CU mode is ibc_merge, A total of 3 bits (merge_flag = 0, pred_mode_flag = 1, cbf = 0 or 1) are allocated to determine that CU mode is ibc_BVP.

When the ibc function is off (ibc_enabled_flag = 0), the number of bits consumed or allocated to determine the prediction mode for the current block is expressed in the ibc = off item. Since ibc function is off, Tile group type corresponds to P-type or B-type, CU type corresponds to inter, and pred_mode_ibc_flag = 0 is assumed.

When CU mode is skip, merge_flag = 1, ref_idx is not signaled, cbf = 0, and a total of 2 bits are allocated to determine the skip mode. When CU mode is merge, merge_flag = 1, ref_idx is not signaled, cbf = 1, and a total of 2 bits are allocated to determine the merge mode. When the CU mode is AMVP, merge_flag = 0, pred_mode_flag = 1, ref_idx = 0 and cbf = 0 or 1, and a total of 4 bits are allocated to determine the AMVP mode.

Example 2

Hereinafter, various embodiments of the present invention for a method of constructing a prediction block vector candidate list (BVP candidate list) used in the ibc mode will be described with reference to FIGS. 15 to 18.

As described above, the present invention may be configured to indicate that the prediction mode of the current block corresponds to the ibc mode (any of ibc_skip mode, ibc_merge mode, and ibc_BVP mode) by explicitly signaling pred_mode_ibc_flag.

When the prediction mode of the current block corresponds to the ibc_BVP mode, the image decoding apparatus configures a BVP candidate list consisting of one or more prediction block vector predictor (BVP) candidates (S1510). In addition, the video decoding apparatus selects a BVP candidate corresponding to the BVP index (included in the motion information) signaled from the video encoding apparatus from the BVP candidate list (S1520). Subsequently, the image decoding apparatus derives a block vector (BV) for the current block by summing the selected BVP candidates (selected BVPs) and the BVD signal (included in the motion information) from the image encoding apparatus (S1530), and deriving The current block may be predicted by obtaining prediction information from the reference block in the current picture indicated by the BV (S1540).

Example 2-1

The BVP candidate list constructed through Example 2-1 includes: 1) BV of a block predicted in ibc mode among one or more blocks spatially adjacent to the current block (spatial neighboring block); 2) one or more temporally adjacent to the current block. Among blocks (temporary neighboring blocks), a BV of a block predicted in ibc mode and 3) a preset BV may be included as BVP candidates. That is, the BVP candidates included in the BVP candidate list may include BVs of spatial neighboring blocks predicted in ibc mode, BVs of temporal neighboring blocks predicted in ibc mode, and preset BVs.

As shown in FIG. 16, in the spatially adjacent block, one or more of blocks A0, A1, and A2 located on the left side of the current block and / or blocks B0 located above the current block B1, B2) may be included, and a block AB located in the upper left of the current block may be further included. Here, the block AB located in the upper left of the current block may be treated as a block located to the left of the current block, or may be treated as a block located above the current block.

Blocks located on the left side of the current block include a block A1 located at the bottom and / or a block A0 located at the bottom based on the height direction H of the current block, or a block A2 located at the center. It may be further included. Blocks located above the current block include a block B1 located at the right and / or a block B0 located at the right end based on the width direction W of the current block, or a block B2 located at the center It may be further included.

If the spatial neighboring blocks are re-expressed based on a pixel, A1 may be a block including a pixel located at the bottom left of the current block as its right-most pixel, and A2 positioned at the left-most center of the current block. It may be a block including a pixel as its rightmost pixel. B1 may be a block including the rightmost pixel of the current block as its rightmost pixel, and B2 may be a block including the pixel located at the uppermost center of the current block as its rightmost pixel. AB may be a block including the leftmost pixel of the current block as its rightmost pixel, A0 may be a block including the leftmost pixel of the current block as its rightmost pixel, and B0 is a current block It may be a block including the rightmost pixel of the rightmost pixel of its own.

The video decoding apparatus searches for one or more blocks among blocks located on the left side of the current block and / or one or more blocks among blocks positioned above the current block and / or blocks located in the upper left of the current block according to a preset order. One or more BVP candidates may be derived, and the BVP candidate list may be constructed by including the derived BVP candidates. For example, the image decoding apparatus searches for a block A1 located on the left side of the current block and a block B1 located on the upper side in a predetermined order to derive BVP candidates, and includes the derived BVP candidates to list the BVP candidates. Can be configured.

Also, the apparatus for decoding an image may derive one or more BVP candidates by searching blocks A0, A1, and / or A2 and / or AB located on the left side of the current block in a preset order. Furthermore, the image decoding apparatus may derive one or more BVP candidates by searching for blocks B0, B1 and / or B2 and / or AB located above the current block in a preset order.

As illustrated in FIG. 17, the temporal neighboring block may refer to one or more blocks adjacent to this col_block based on a collocated block (col_block) located in a collocated picture (col_picture). Here, the col_picture may be specified in advance, such as a picture located at the first position (index of 0) of the reference picture list (L0 or L1). The col_block is located in the col_picture, but may be specified in advance, such as a block located in the same position as the current picture in the current block.

As shown in FIG. 17, the temporal adjacent blocks include a block BR located at the lower right of the col_ block, a block CT located at the center of the col_ block, and a block TR located at the upper right of the col_ block, and A block BL located at the bottom left of the col_block may be included.

Re-expressing the positions of temporal adjacent blocks based on a pixel, BR may be a block including a pixel located at the bottom right of the current block as its leftmost pixel, and CT indicates a pixel located at the center of the current block. It may be a block included as its leftmost pixel. TR may be a block including a pixel located at the top right of the current block as its leftmost pixel, and BL may be a block including a pixel located at the bottom left of the current block as its leftmost pixel. .

The video decoding apparatus may search temporal temporal blocks according to a preset order to derive one or more BVP candidates, and construct the BVP candidate list by including the derived BVP candidates.

The preset BV may correspond to a BV indicating a position moved to the upper left by the height and width of the current block. For example, when the width of the current block is W and the height of the current block is H, the preset BV may be (-W, -H). In addition, the preset BV may be (-W * k, -H * k) in which the size of the BV is changed using an arbitrary constant k. The preset BV may be referred to as a default BV in terms of being preset, rather than being acquired through a search process.

The BVs described through Embodiment 2-1 may indicate a relative position based on the CTU including the current block or a relative position based on the current block. As shown in FIG. 18, based on the upper leftmost pixel B of the current block, the BVs described through Example 2-1 are relative positions after setting this pixel B as a zero vector. It may be a vector indicating. Also, based on the leftmost pixel A of the CTU including the current block, the BVs described through Example 2-1 may be a vector indicating a relative position after setting the pixel A to a zero vector. have.

The video decoding apparatus may (optionally) express BVs based on either the CTU including the current block or the current block. By expressing BVs based on the current block or by expressing BVs based on the CTU including the current block (optionally applying a criterion for expressing BVs), it is possible to efficiently set a search range for searching BVP candidates. do. Accordingly, the present invention can effectively reduce the amount of memory consumed for BVP candidate search, as well as the number of bits consumed to represent BV.

Example 2-2

In Example 2-2, a history-based BV is proposed that can replace BV of temporal adjacent blocks. The BVP candidate list constructed through Example 2-2 may include BVs of blocks predicted (predicted) in ibc mode. That is, the BVP candidate list of Example 2-2 may include BVs of blocks predicted in ibc mode among blocks that have already been decoded (predicted) before the current block is decoded.

In order to use the BV of blocks whose prediction is completed in ibc mode for prediction of the current block, a configuration is required to store the BV of blocks whose prediction is completed in ibc mode. In the present invention, this 'storing configuration' will be referred to as 'record' or HBV (history-based BV) for ibc mode. In addition, BVs (BVs of blocks whose prediction is completed in ibc mode) stored in the HBV may constitute a list, and this list may be referred to as a history-based block vector predictor (HBVP) candidate list.

HBV may have a FIFO (first in first out) structure capable of storing one or more BVs. When a separate BVP candidate list is configured for each independent processing unit for parallel processing such as a tile group, the BV stored first in the HBV may correspond to a zero vector.

When the BV of blocks whose prediction is completed in ibc mode is sequentially (FIFO) stored in HBV according to the prediction order (decoding order), when the specific block (current block) is to be predicted in ibc mode, the last BV stored in HBV From then, one or more BVs may be selected by searching sequentially (in the reverse order of the stored order or in the reverse order of the decoding order), and then the selected BVs may be included in the BVP candidate list.

BVs selected from HBV may replace 'temporal BV' and / or 'pre-established BV' among the BVs included in the BVP candidate list. That is, the BVP candidate list construction process implemented through Example 2-2 includes' spatial BV construction process → BV configuration process selected from HBV ',' spatial BV construction process → BV configuration process selected from HBV → preset BV configuration Process' and 'spatial BV construction process → temporal BV construction process → BV construction process selected from HBV' can be implemented in various orders.

Here, 'temporal BV' means BV of adjacent blocks predicted in ibc mode among temporal neighboring blocks, and 'spatial BV' means BV of adjacent blocks predicted in ibc mode among spatial neighboring blocks. Accordingly, the video decoding apparatus may select an appropriate number of BVs from HBVs according to the type of BV to be replaced (temporal BV and / or preset BV). In addition, 'the BV configuration process selected from HBV' may be performed when the number of BVP candidates included in the BVP candidate list is less than the maximum number that can be included in the BVP candidate list through the BV configuration process (s) previously performed. .

Example 2-3

In Example 2-3, a zero BV is proposed that can replace the preset BV.

The process of constructing the BVP candidate list implemented through Examples 2-3 includes 'spatial BV constructing process → temporal BV constructing process → zero BV constructing process' and 'spatial BV constructing process → selected BV constructing process from HBV → zero BV constructing process' 'It can be implemented in various order.

The 'zero BV configuration process' may be performed when the number of BVP candidates included in the BVP candidate list is less than the maximum number that can be included in the BVP candidate list through the previously performed BV configuration process (es).

The above description is merely illustrative of the technical spirit of the present embodiment, and those skilled in the art to which this embodiment belongs may be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Therefore, the present embodiments are not intended to limit the technical spirit of the present embodiment, but to explain, and the scope of the technical spirit of the present embodiment is not limited by these embodiments. The protection scope of the present embodiment should be interpreted by the claims below, and all technical spirits within the equivalent range should be interpreted as being included in the scope of the present embodiment.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is filed in Korea on October 8, 2018, Patent Application No. 10-2018-0119881, filed in Korea on June 10, 2019, the entire contents of which are incorporated herein by reference. Priority is claimed on Patent Application No. 10-2019-0067724.

Claims (20)

1. As a method of predicting the current block to be decoded in the current picture reference (intra block copy, ibc) mode,

   Decoding, from a bitstream, an enable flag indicating whether application of the ibc mode is allowed and type information indicating whether a type of slice is inter;

   Decoding an ibc flag indicating whether the prediction mode of the current block is the ibc mode based on the enable flag and the type information from the bitstream;

   When the ibc flag indicates the ibc mode, decoding motion information not including a reference picture index of the current block from the bitstream; And

   And predicting the current block using a block indicated by the motion information in the current picture in which the current block is located.
2. According to claim 1,

   The ibc flag,

   A prediction method using the current picture reference mode, characterized in that the enable flag is decoded when the ibc mode is allowed to be applied and the type information indicates an inter.
3. According to claim 2,

   Before decoding the ibc flag, further comprising decoding mode information indicating whether the current block has been encoded by intra prediction from the bitstream,

   The enable flag and the type information,

   A prediction method using a current picture reference mode, characterized in that it is determined when the mode information indicates inter prediction.
4. According to claim 3,

   The motion information,

   A prediction method using the current picture reference mode, characterized in that the enable flag is decoded when the ibc mode is applied and the type information is not inter.
5. According to claim 2,

   Before decoding the ibc flag, further comprising decoding mode information indicating whether the current block has been encoded by intra prediction from the bitstream,

   The enable flag and the type information,

   A prediction method using a current picture reference mode, characterized in that it is determined when the mode information indicates intra prediction.
6. The method of claim 5,

   The motion information,

   A prediction method using a current picture reference mode, characterized in that the mode information is decoded when it indicates inter prediction and the type information is not inter.
7. According to claim 1,

   The predicting step,

   Selecting a BVP candidate corresponding to a BVP index included in the motion information from a list of BVP candidates including one or more prediction block vector predictor (BVP) candidates;

   Deriving a block vector (BV) of the current block using a differential block vector difference (BVD) included in the motion information and the selected BVP candidate; And

   And predicting the current block by using the block indicated by the derived BV in the current picture,

   The BVP candidate list,

   And a BV of a block predicted by the ibc mode among one or more spatial neighboring blocks for the current block, a BV of one or more blocks predicted by the ibc mode, and one or more zero BVs as the BVP candidates. A prediction method using the current picture reference mode.
8. The method of claim 7,

   The spatial adjacent block,

   It includes a left block located on the left and an upper block located on the upper side based on the current block,

   The left block,

   Based on the height direction of the current block, includes a block located at the bottom,

   The upper block,

   A prediction method using a current picture reference mode, comprising a block located on the right side based on the width direction of the current block.
9. The method of claim 7,

   The BV of the block for which prediction is completed in the ibc mode,

   The prediction method using the current picture reference mode, characterized in that BVs of blocks whose prediction is completed in the ibc mode are included in the BVP candidate list after being sorted in reverse order from a candidate list stored in a prediction order.
10. From the bitstream, an enable flag indicating whether the application of the current picture reference (intra block copy, ibc) mode is allowed, and type information indicating whether the type of the slice is inter, decode the type information, and enable the The ibc flag indicating whether the prediction mode of the current block is the ibc mode is decoded depending on the flag and the type information, and when the ibc flag indicates the ibc mode, the reference picture index of the current block is not included. A decoder for decoding motion information; And

    And a prediction unit for predicting the current block using a block indicated by the motion information in the current picture in which the current block is located.
11. The method of claim 10,

    The ibc flag,

    And when the enable flag indicates that application of the ibc mode is allowed and the type information indicates inter, the video decoding apparatus.
12. The method of claim 11,

    The decoding unit,

    Before decoding the ibc flag, mode information indicating whether the current block is encoded by intra prediction is decoded,

    The enable flag and the type information,

    An image decoding apparatus characterized in that it is determined when the mode information indicates inter prediction.
13. The method of claim 12,

    The decoding unit,

    And decoding the motion information when the enable flag indicates that the application of the ibc mode is allowed and the type information is not inter.
14. The method of claim 11,

    The decoding unit,

    Before decoding the ibc flag, mode information indicating whether the current block is encoded by intra prediction is decoded,

    The enable flag and the type information,

    An image decoding apparatus characterized in that it is determined when the mode information indicates intra prediction.
15. The method of claim 14,

    The decoding unit,

    And decoding the motion information when the mode information indicates inter prediction and the type information is not inter.
16. The method of claim 10,

    The prediction unit,

    A BVP candidate corresponding to the BVP index included in the motion information is selected from a list of BVP candidates including one or more prediction block vector predictor (BVP) candidates, and a block vector difference included in the motion information , BVD) and the selected BVP candidate to derive a block vector (BV) of the current block, and predict the current block using a block indicated by the derived BV in the current picture, ,

    The BVP candidate list,

    The decoding of an image comprising the BV of a block predicted by the ibc mode among the one or more spatial neighboring blocks for the current block, and a BV and a zero BV of a block predicted by the ibc mode as the BVP candidates. Device.
17. The method of claim 16,

    The spatial adjacent block,

    It includes a left block located on the left and an upper block located on the upper side based on the current block,

    The left block,

    Based on the height direction of the current block, includes a block located at the bottom,

    The upper block,

    And a block located on the right side based on the width direction of the current block.
18. The method of claim 16,

    The BV of the block for which prediction is completed in the ibc mode,

    The BV of the blocks whose prediction is completed in the ibc mode is selected from a candidate list stored in a prediction order, in reverse order, and included in the BVP candidate list.
19. As a method performed in the video encoding device,

    Encoding an enable flag indicating whether application of the current picture reference (intra block copy, ibc) mode is permitted and type information indicating whether a slice type is inter;

    Encoding an ibc flag indicating whether the prediction mode of the current block is the ibc mode, depending on the enable flag and the type information; And

    When the ibc flag indicates the ibc mode, encoding motion information not including a reference picture index of the current block,

    The motion information,

    A prediction method using a current picture reference mode, characterized in that a block to be used for prediction of the current block is indicated within a current picture in which the current block is located.
20. As a video encoding device,

    The enable flag indicating whether the application of the current picture reference (intra block copy, ibc) mode is allowed and the type information indicating whether the type of the slice is inter, encodes the enable flag and the type Depending on information, an ibc flag indicating whether the prediction mode of the current block is the ibc mode is encoded, and when the ibc flag indicates the ibc mode, motion information not including a reference picture index of the current block is encoded. It includes an encoding unit for encoding,

    The motion information,

    And a block to be used for prediction of the current block in the current picture in which the current block is located.

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