KR20200113173A - Method and Apparatus for Intra Prediction Based on Deriving Prediction Mode - Google Patents

Abstract

Disclosed are an intra prediction method used in a video encoding and decoding apparatus. According to an embodiment of the present invention, provided are an intra prediction apparatus and method which perform derivation of an intra prediction mode of a current block with reference to an intra prediction mode of a previously reconstructed neighboring block, perform intra prediction using the estimated prediction mode, and generate a prediction sample for the current block.

Description

Intra prediction apparatus and method based on prediction mode estimation {Method and Apparatus for Intra Prediction Based on Deriving Prediction Mode}

The present invention relates to an intra prediction method used in a video encoding and decoding apparatus. More specifically, the present invention relates to an intra prediction method for estimating an intra prediction mode of a current block by referring to an intra prediction mode of a previously reconstructed neighboring block.

The content described below merely provides background information related to the present invention and does not constitute the prior art.

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

Accordingly, when moving or transmitting moving picture data, the moving picture data is compressed and stored or transmitted using an encoder, and the decoder receives the compressed moving picture data, decompresses and reproduces the compressed moving picture data. As such video compression technologies, there are H.264/AVC and HEVC (High Efficiency Video Coding), which improves coding efficiency by about 40% compared to H.264/AVC.

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

In the present disclosure, an intra prediction mode of a current block is estimated by referring to an intra prediction mode of a previously reconstructed neighboring block, and intra prediction is performed using the estimated prediction mode to generate a prediction sample for the current block. The main object is to provide an intra prediction apparatus and method.

According to an embodiment of the present invention, there is provided an intra prediction method used by an intra prediction apparatus, the method comprising: decoding mode information indicating use of a prediction estimation mode for a prediction mode block from a bitstream; Estimating an intra prediction mode of each pixel group on a pixel group basis including one or more pixels in the prediction mode block from intra prediction modes of reference pixels at a plurality of pre-restored locations around the prediction mode block; And intra-predicting pixels in each pixel group using intra prediction modes of each pixel group.

According to another embodiment of the present invention, there is provided an entropy decoder for decoding mode information indicating use of a prediction mode for a prediction mode block from a bitstream; A prediction mode estimating unit for estimating an intra prediction mode of each pixel group from intra prediction modes of reference pixels of a plurality of previously restored reference pixels around the prediction mode block in a pixel group unit including one or more pixels in the prediction mode block ; And a prediction sample generator for intra-predicting pixels in each pixel group using intra prediction modes of each pixel group.

As described above, according to the present embodiment, the intra prediction mode of the current block is estimated by referring to the intra prediction mode of the previously reconstructed neighboring block, and intra prediction is performed based on the estimated prediction mode. By providing an intra prediction apparatus and a method for generating a prediction sample for an image, it is possible to improve the compression performance of an image encoding and decoding apparatus.

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 illustrating a plurality of intra prediction modes including wide-angle 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 block diagram of an intra prediction apparatus according to an embodiment of the present invention.
6 is an exemplary diagram of a reference position used for estimation of a prediction mode according to an embodiment of the present invention.
7 is an exemplary diagram for estimation of a prediction mode according to an embodiment of the present invention.
8 is an exemplary diagram for estimation of a prediction mode according to another embodiment of the present invention.
9 is an exemplary diagram of a location of a reconstructed reference sample used to generate an intra prediction sample according to an embodiment of the present invention.
FIG. 10 is an exemplary diagram of a location of a reconstructed reference sample used to generate an intra prediction sample according to another embodiment of the present invention.
11 is an exemplary diagram for intra prediction of a chroma block according to an embodiment of the present invention.
12 is a flowchart of an intra prediction method according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to exemplary drawings. In adding reference numerals to elements of each drawing, it should be noted that the same elements are assigned the same numerals as possible even if they are indicated on different drawings. In addition, in describing the embodiments, if it is determined that a detailed description of a related known configuration or function may obscure the subject matter of the embodiments, the detailed description 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-elements of the apparatus will be described with reference to FIG. 1.

The image encoding apparatus includes a picture segmentation unit 110, a prediction unit 120, a subtractor 130, a transform unit 140, a quantization unit 145, a rearrangement unit 150, an entropy encoding unit 155, an inverse quantization unit. (160), an inverse transform unit 165, an adder 170, a filter unit 180, and a memory 190 may be included.

Each component of the image encoding apparatus may be implemented by hardware or software, or by a combination of hardware and software. In addition, functions of each component may be implemented as software, and a microprocessor may be implemented to execute a 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 CUs (Coding Units) 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 slice is encoded as the syntax of the slice header, and information applied to all blocks constituting one picture is a picture parameter set (PPS) or picture. It is coded in the header. Further, information commonly referred to by a plurality of pictures is encoded in a sequence parameter set (SPS). In addition, information commonly referred to by one or more SPSs is encoded in a video parameter set (VPS). Also, information commonly applied to one tile or tile group may be encoded as syntax of a tile or tile group header.

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

After dividing each picture constituting an image into a plurality of CTUs (Coding Tree Units) having a predetermined size, the picture dividing unit 110 repetitively divides the CTU using a tree structure. (recursively) split. A leaf node in the tree structure becomes a coding unit (CU), which is a basic unit of coding.

As a tree structure, a quad tree (QuadTree, QT) in which an upper node (or parent node) is divided into four lower nodes (or child nodes) of the same size, or a binary tree (BinaryTree) in which an upper node is divided into two lower nodes. , BT), or a ternary tree (TT) in which an 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, by combining BTTT, it may be referred to as MTT (Multiple-Type Tree).

2 shows a QTBTTT split tree structure. As shown in FIG. 2, the CTU may be first divided into a QT structure. The quadtree division may be repeated until the size of a splitting block reaches the minimum block size (MinQTSize) of a leaf node allowed in QT. A first flag (QT_split_flag) indicating whether each node of the QT structure is divided into four nodes of a lower layer is encoded by the entropy encoder 155 and signaled to the image decoding apparatus. If the leaf node of the QT is not larger than the maximum block size (MaxBTSize) of the root node allowed in BT, it may be further divided into one or more of a BT structure or a TT structure. In the BT structure and/or the TT structure, a plurality of division directions may exist. For example, there may be two directions in which a block of a corresponding node is divided horizontally and a direction vertically divided. As shown in FIG. 2, when MTT splitting starts, a second flag (mtt_split_flag) indicating whether nodes are split, and if split, a flag indicating a split direction (vertical or horizontal) and/or a split type (Binary or Ternary). A flag indicating) is encoded by the entropy encoder 155 and signaled to the image decoding apparatus.

Alternatively, prior to encoding the first flag (QT_split_flag) indicating whether each node is divided into four nodes of a lower layer, a CU split flag (split_cu_flag) indicating whether the node is divided will be encoded. May be. When it is indicated that the value of the CU split flag (split_cu_flag) is not 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. When indicating that the value of the CU split flag (split_cu_flag) is to be split, the video encoding apparatus starts encoding from the first flag in the above-described manner.

When QTBT is used as another example of the tree structure, two types of horizontally splitting a block of the corresponding node into two blocks of the same size (i.e., symmetric horizontal splitting) and a type splitting vertically (i.e., symmetric vertical splitting) Branches can exist. A split flag indicating whether each node of the BT structure is divided into blocks of a lower layer and split type information indicating a type to be divided are encoded by the entropy encoder 155 and transmitted to the image decoding apparatus. Meanwhile, a type of dividing the block of the corresponding node into two blocks having an asymmetric shape may further exist. 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.

The CU can have various sizes according to the QTBT or QTBTTT split from the CTU. Hereinafter, a block corresponding to a CU to be encoded or decoded (ie, a leaf node of QTBTTT) is referred to as a'current block'. According to the adoption of the QTBTTT division, the shape of the current block may be not only square but also rectangular.

The prediction unit 120 predicts the current block and generates 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 is performed using an intra prediction technique (using data from a picture containing the current block) or an inter prediction technique (using data from a picture coded before a picture containing the current block). Can be done. Inter prediction includes both one-way prediction and two-way prediction.

The intra prediction unit 122 predicts pixels in the current block by using pixels (reference pixels) located 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. For example, as shown in FIG. 3A, the plurality of intra prediction modes may include two non-directional modes including a planar mode and a DC mode, and 65 directional modes. Depending on each prediction mode, the surrounding pixels to be used and the calculation expression are defined differently.

For efficient directional prediction for the rectangular-shaped current block, directional modes (67 to 80, intra prediction modes -1 to -14) shown by dotted arrows in FIG. 3B may be additionally used. These may be referred to as "wide angle intra-prediction modes". Arrows in FIG. 3B indicate corresponding reference samples used for prediction, and do not indicate a prediction direction. The prediction direction is opposite to the direction indicated by the arrow. In the wide-angle intra prediction modes, when the current block is a rectangular shape, a specific directional mode is predicted in the opposite direction without additional bit transmission. In this case, among the wide-angle intra prediction modes, some wide-angle intra prediction modes available for the current block may be determined based on a ratio of the width and height of the rectangular current block. For example, wide-angle intra prediction modes with an angle less than 45 degrees (intra prediction modes 67 to 80) can be used when the current block has a rectangular shape with a height smaller than the width, and wide-angle with an angle greater than -135 degrees. The intra prediction modes (intra prediction modes -1 to -14) can be used when the current block has a rectangular shape with a width greater than the height.

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 several 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 several tested intra prediction modes, and has the best rate distortion characteristics among the tested modes. It is also possible to select an intra prediction mode.

The intra prediction unit 122 selects one intra prediction mode from among a plurality of intra prediction modes, and predicts the current block using a neighboring pixel (reference pixel) determined according to the selected intra prediction mode and an equation. Information on the selected intra prediction mode is encoded by the entropy encoder 155 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 inter prediction unit 124 searches for a block most similar to the current block in the coded and decoded reference picture prior to the current picture, and generates a prediction block for the current block using the searched block. Then, 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. In general, motion estimation is performed on a luma component, and a motion vector calculated based on the luma component is used for both the luma component and the chroma component. Motion information including information on a reference picture used to predict the current block and information on a motion vector is encoded by the entropy encoder 155 and transmitted to an image decoding apparatus.

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

The transform unit 140 converts the residual signal in the residual block having pixel values in the spatial domain into transform coefficients in the frequency domain. The transform unit 140 may transform the residual signals in the residual block using the total size of the residual block as a transform unit, or divide the residual block into a plurality of sub-blocks and perform transformation using the sub-block as a transform unit. You may. Alternatively, the residual signals may be transformed by dividing into two subblocks, which are a transform region and a non-transform region, and use only the transform region subblock as a transform unit. Here, the transform region subblock may be one of two rectangular blocks having a size ratio of 1:1 based on the horizontal axis (or vertical axis). In this case, a flag indicating that only the subblock has been transformed (cu_sbt_flag), directional (vertical/horizontal) information (cu_sbt_horizontal_flag), and/or location information (cu_sbt_pos_flag) are encoded by the entropy encoder 155 and signaled to the image decoding apparatus. do. In addition, the size of the transform region subblock may have a size ratio of 1:3 based on the horizontal axis (or vertical axis). Signaled to the decoding device.

Meanwhile, the transform unit 140 may individually transform the residual block in a horizontal direction and a vertical direction. For transformation, various types of transformation functions or transformation matrices can be used. For example, a pair of transform functions for transverse transformation and transformation may be defined as a multiple transform set (MTS). The transform unit 140 may select one transform function pair having the best transform efficiency among MTS and transform the residual blocks in the horizontal and vertical directions, respectively. Information (mts_idx) on the transform function pair selected from the MTS is encoded by the entropy encoder 155 and signaled to the image decoding apparatus. The size of the transform block to which the MTS is applied may be limited within 32×32.

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

The rearrangement unit 150 may rearrange coefficient values on the quantized residual values.

The rearrangement unit 150 may change a two-dimensional coefficient array into a one-dimensional coefficient sequence through coefficient scanning. For example, the rearrangement unit 150 may scan from a DC coefficient to a coefficient in a high frequency region using a zig-zag scan or a diagonal scan to output a one-dimensional coefficient sequence. . Depending on the size of the transform unit and the intra prediction mode, instead of zig-zag scan, a vertical scan that scans a two-dimensional coefficient array in a column direction or a horizontal scan that scans a two-dimensional block shape coefficient in a row direction may be used. That is, a scan method to be used may be determined from among zig-zag scan, diagonal scan, vertical scan, and horizontal scan according to the size of the transform unit and the intra prediction mode.

The entropy encoding unit 155 uses various encoding methods such as Context-based Adaptive Binary Arithmetic Code (CABAC), Exponential Golomb, and the like, and the quantized transform coefficients of 1D output from the reordering unit 150 are A bitstream is generated by encoding the sequence.

In addition, the entropy encoder 155 encodes information such as a CTU size related to block division, a CU division flag, a QT division flag, an MTT division type, and an MTT division direction, so that the video decoding apparatus performs the same block as the video encoding apparatus. Make it possible to divide. In addition, the entropy encoder 155 encodes information on a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and intra prediction information (ie, intra prediction) according to the prediction type. Mode information) or inter prediction information (reference picture and motion vector information) is encoded.

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 converts transform coefficients output from the inverse quantization unit 160 from the frequency domain to the spatial domain to restore the residual block.

The addition unit 170 restores the current block by adding the restored residual block and the prediction block generated by the prediction unit 120. The pixels in the reconstructed current block are used as reference pixels when intra-predicting the next block.

The filter unit 180 filters reconstructed pixels to reduce blocking artifacts, ringing artifacts, blurring artifacts, etc. that occur due to block-based prediction and transformation/quantization. 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 reconstructed blocks to remove blocking artifacts caused by block-based encoding/decoding, and the SAO filter 184 adds additional information to the deblocking-filtered image. 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 block filtered through the deblocking filter 182 and the SAO filter 184 is stored in the memory 190. When all blocks in one picture are reconstructed, the reconstructed picture may be used as a reference picture for inter prediction of a block in a picture to be encoded later.

4 is an exemplary functional 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 includes an entropy decoding unit 410, a rearrangement unit 415, 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. ) Can be included.

Like the image encoding apparatus of FIG. 1, each component of the image decoding apparatus may be implemented as hardware or software, or may be implemented as a combination of hardware and software. In addition, functions of each component may be implemented as software, and a microprocessor may be implemented to execute a function of software corresponding to each component.

The entropy decoding unit 410 determines the current block to be decoded by decoding the bitstream generated by the image encoding apparatus and extracting information related to block division, and predicting information and residual signals necessary to restore the current block. Extract information, etc.

The entropy decoding unit 410 determines the size of the CTU by extracting information on the CTU size from a sequence parameter set (SPS) or a picture parameter set (PPS), and divides the picture into CTUs of the determined size. Then, the CTU is determined as the uppermost layer of the tree structure, that is, the root node, and the CTU is divided using the tree structure by extracting partition information for the CTU.

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

As another example, when splitting the CTU using the QTBTTT structure, first extract the CU split flag (split_cu_flag) indicating whether to split the CU, and if the corresponding block is split, the first flag (QT_split_flag) is extracted. May be. In the segmentation process, each node may have 0 or more repetitive MTT segmentation after 0 or more repetitive QT segmentation. For example, in the CTU, MTT division may occur immediately, or, conversely, only multiple QT divisions may occur.

As another example, when the CTU is divided using the QTBT structure, each node is divided into four nodes of a lower layer by extracting the first flag (QT_split_flag) related to the division of the QT. In addition, a split flag indicating whether or not the node corresponding to the leaf node of the QT is further split into BT and split direction information are extracted.

Meanwhile, when determining the current block to be decoded through the division of the tree structure, the entropy decoder 410 extracts information on a prediction type indicating whether the current block is intra prediction or inter prediction. When the prediction type information indicates intra prediction, the entropy 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 entropy decoder 410 extracts a syntax element for the inter prediction information, that is, information indicating a motion vector and a reference picture referenced by the motion vector.

Meanwhile, the entropy decoding unit 410 extracts information on quantized transform coefficients of the current block as information on the residual signal.

The rearrangement unit 415, in the reverse order of the coefficient scanning order performed by the image encoding apparatus, reconverts the sequence of one-dimensional quantized transform coefficients entropy-decoded by the entropy decoder 410 into a two-dimensional coefficient array (i.e., Block).

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 performs inverse transform of only a partial region (subblock) of the transform block, a flag indicating that only the subblock of the transform block has been transformed (cu_sbt_flag), and the direction (vertical/horizontal) information of the subblock (cu_sbt_horizontal_flag) ) And/or sub-block location information (cu_sbt_pos_flag), and inversely transforming the transform coefficients of the sub-block from the frequency domain to the spatial domain to restore residual signals, and for regions that are not inverse transformed, the residual signal is “0” value. Fill in to create the final residual block for the current block.

In addition, when MTS is applied, the inverse transform unit 430 determines a transform function or transform matrix to be applied in the horizontal and vertical directions, respectively, using MTS information (mts_idx) signaled from the image encoding apparatus, and uses the determined transform function. Inverse transform is performed on the transform coefficients in the transform block in the horizontal and vertical directions.

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 the current block among a plurality of intra prediction modes from a syntax element for the intra prediction mode extracted from the entropy decoding unit 410, and references around the current block according to the intra prediction mode. Predict the current block using pixels.

The inter prediction unit 444 determines a motion vector of the current block and a reference picture referenced by the motion vector using the syntax element for the inter prediction mode extracted from the entropy decoding unit 410, and determines the motion vector and the reference picture. Is used 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 reference pixels for intra prediction of a block to be decoded later.

The filter unit 460 may include a deblocking filter 462 and an SAO filter 464. The deblocking filter 462 performs deblocking filtering on the boundary between reconstructed blocks in order to remove blocking artifacts caused by decoding in units of blocks. The SAO filter 464 performs additional filtering on the reconstructed block after deblocking filtering in order to compensate for the difference between the reconstructed pixel and the original pixel caused by lossy coding. The reconstructed block filtered through the deblocking filter 462 and the SAO filter 464 is 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 later.

This embodiment discloses a new intra prediction technique that can be implemented by the video encoding and decoding apparatus described above. In more detail, an intra prediction apparatus and method for derivating an intra prediction mode of a current block with reference to an intra prediction mode of a previously reconstructed neighboring block and performing intra prediction using the estimated prediction mode are provided.

5 is a block diagram of an intra prediction apparatus according to an embodiment of the present invention.

In an embodiment according to the present invention, the intra prediction apparatus 500 estimates a prediction mode by referring to an intra prediction mode of a neighboring block previously restored without transmission of the prediction mode, and uses the estimated prediction mode. Intra prediction is performed on the current block. The intra prediction apparatus 500 includes an entropy decoding unit 410 and an intra prediction unit 442 included in the decoding apparatus.

Since the intra prediction unit 122 included in the encoding apparatus operates similarly to the intra prediction unit 442 included in the decoding apparatus, the intra prediction unit 442 included in the decoding apparatus will be described below.

The intra prediction apparatus 100 according to the present embodiment uses a prediction estimation mode (hereinafter, a “estimation mode”) to improve the efficiency of intra prediction.

The entropy decoding unit 410 decodes information on whether or not the estimation mode is applied to the prediction mode block from the bitstream. Here, the prediction mode block means a block unit in which prediction information including an estimation mode is transmitted. Hereinafter, for convenience of description, the current block represents a prediction mode block.

In order to use the estimation mode, the encoding device may indicate and transmit mode information on whether the estimation mode is used in the bitstream, and the decoding device may determine whether to apply the estimation mode using the corresponding information. The mode information may be information in the form of a flag indicating whether the prediction estimation mode is used. Alternatively, it may be information in the form of an index for indicating one of a plurality of intra prediction modes further including an estimation mode as a new intra prediction mode.

When the estimation mode is applied, the intra prediction unit 442 according to the present embodiment estimates an intra prediction mode for a prediction mode block and a subdivision structure thereof by referring to an intra prediction mode of a previously reconstructed neighboring block. . The intra prediction unit 442 may include all or part of the reference position setting unit 502, the prediction mode estimation unit 504, and the prediction sample generation unit 506.

6 is an exemplary diagram of a reference position used for estimation of a prediction mode according to an embodiment of the present invention.

As shown in FIG. 6, the reference position setting unit 502 estimates a prediction mode block A (M×N, M and N are natural numbers) and a neighboring block (block B) in order to estimate a prediction mode for a subdivision structure. Pixels (pixels a to j) of ~block G) can be used as reference positions.

The reference position setting unit 502 may adaptively set a reference position according to a partition structure of a previously reconstructed block around the prediction mode block. For example, when the top and the left of the prediction mode block A are divided into blocks B to G as shown in FIG. 6, pixels at a predefined position in each block B to G (e.g., at the bottom right of each block Positioned pixels) can be set as a reference position. That is, in the illustration of FIG. 6, the reference position setting unit 502 refers to a predefined position (eg, pixel a, d, g, or additionally, the pixel c in the center of the upper row and the pixel i or h in the center of the left column). Can be used as.

In addition, the reference position setting unit 502 uses a predefined position (eg, one of pixels a, b, j, one of pixels d, e, one of g, f, etc.) in the group of reference positions as a reference position. I can. For example, in the case of the reference position group {a, b, j}, it is determined whether it is a valid reference pixel in the order of a, b, and j, and the first valid position is set as the reference position. Here, the effective reference pixel refers to a pixel in which intra prediction is used, and a pixel in which an intra prediction mode corresponding thereto exists. Also for the reference position group {d, e} or {g, f}, the reference positions can be set in the order of d and e or g and f, respectively.

The reference position setting unit 502 may adaptively set the reference position according to the dimensions of the prediction mode block (the number of horizontal pixels, the number of vertical pixels, the product of the number of horizontal and vertical pixels, etc.). For example, in the case of'number of horizontal pixels> number of vertical pixels', more reference positions may be set at the top, and in the opposite case, more reference positions may be set at the left. A preset number of reference positions may be determined from the predefined positions as described above, and the reference positions may be added at the center of the longer side.

In addition, the reference position setting unit 502 may set the number of reference positions according to the product of the number of horizontal and vertical pixels, and use as many as a set number of predefined positions as the reference positions.

The reference position setting unit 502 may set a reference position at a predetermined position according to an appointment between an encoding/decoding device.

As described above, the reference position setting unit 502 uses at least one of a predetermined position according to a dimension of a prediction mode block, an appointment between an encoding/decoding device, and a block division structure around the prediction mode block. The reference position can be determined.

Meanwhile, alternatively, information on an available reference position may be transmitted from the encoding device to the decoding device. In this case, the reference position setting unit 502 determines a reference position using the received information.

When the estimation mode according to the present embodiment is applied, the intra prediction unit 442 may divide the prediction mode block into pixel group units including one or more pixels. Pixel groups including a plurality of pixels are collectively expressed as a divided block or subblock, but intra prediction may be performed in units of each divided block. Accordingly, the level of the prediction mode block in which the estimation mode is decoded and the block in which intra prediction is performed may not be the same.

Depending on the division structure of the prediction mode block, the shape of the pixel group may be a block shape such as a square, a rectangle, or a triangle, or a block shape in units of lines such as M×1 or 1×N. Meanwhile, the divided pixel groups may have the same size and shape.

In another embodiment of the present invention, a pixel group may consist of only one pixel. In another embodiment, the pixel group may be a prediction mode block. That is, it may be composed of all pixels of the prediction mode block.

In dividing the pixel group from the prediction mode block, the decoding apparatus may estimate information on the division structure from the prediction mode block and neighboring blocks, or may be transmitted from the encoding apparatus.

The decoding apparatus may determine a split structure according to the dimensions of the prediction mode block (the number of horizontal pixels, the number of vertical pixels, a product of the number of horizontal and vertical pixels, etc.). For example, a horizontal division structure of'number of horizontal pixels> number of vertical pixels' may be used, and in the opposite case, a vertical division structure may be used. Also, the decoding apparatus may set the number of pixel groups according to a product of the number of horizontal and vertical pixels.

The decoding device may use pre-determined split information according to an agreement between the encoding/decoding device. For example, the prediction mode block may always be divided into a plurality of subblocks having the same size in a horizontal or vertical direction. The number of subblocks may be determined according to the dimension of the prediction mode block. Alternatively, it may always be divided into subblocks of a fixed size such as 4x4.

The decoding apparatus may use a block division structure around the prediction mode block. For example, when there is a block having a neighboring block having the same size as the prediction mode block, the partition structure of the neighboring block may be used or referred to. As another example, when a plurality of blocks exist on the left side of the prediction mode block as shown in FIG. 7A, the prediction mode block may be divided in the horizontal direction by extending a horizontal boundary line between the blocks. . Likewise, if there are a plurality of blocks above the prediction mode block, the prediction mode block may be divided in the vertical direction by extending a vertical boundary line between the plurality of blocks.

As described above, the intra prediction unit 442 of the video decoding apparatus includes all or all of the division structure predetermined according to the dimension of the prediction mode block, the agreement between the encoding/decoding apparatus, and the block division structure around the prediction mode block, as described above. The partition structure of the prediction mode block may be determined based on some combinations.

In another embodiment of the present invention, information on a split structure of a prediction mode block may be transmitted from an encoding device.

In another embodiment of the present invention, a partition structure may be selected from the list by creating a list of the partition structure of the prediction mode block.

7 is an exemplary diagram for estimation of a prediction mode according to an embodiment of the present invention.

The prediction mode estimating unit 504 estimates a prediction mode for the current block in pixel group units by using reference positions of neighboring blocks.

In the example of FIG. 7, a rectangle indicated by a thick solid line indicates a prediction mode block, and a dotted line indicates a unit in which intra prediction is performed by dividing a prediction mode block, that is, a divided block (a block-shaped pixel group). FIG. 7A illustrates a case where a prediction mode block is horizontally divided into two, and FIG. 7B illustrates a case where a prediction mode block is vertically divided into four equally.

The prediction mode estimating unit 504 may estimate a prediction mode of the prediction mode block using prediction modes indicated by at least two reference positions. In the example of FIG. 7, the prediction mode estimating unit 504 uses prediction modes of three neighboring reference positions to estimate a prediction mode of a prediction mode block.

In the example of FIG. 7, a dotted arrow is a prediction mode of a neighboring block, and a solid arrow is a prediction mode of each divided block estimated from the prediction mode of the neighboring block. Setting of a neighboring reference position and estimation of a prediction mode may be performed in the same manner in an encoding/decoding apparatus.

The prediction mode estimating unit 504 estimates an intra prediction mode of each divided block by using at least one or more of the reference positions based on the position of each divided block in the current block. The intra prediction mode of the divided block is likely to be similar to the intra prediction mode of a nearby reference position. Accordingly, the prediction mode of the corresponding divided block is determined so as to be affected by the reference position at a close distance from the divided block. For example, a weight for each reference position may be determined according to the distance between each divided block and the reference position. The closer the distance is, the larger the weight can be assigned. Here, the position of the divided block may be the position of a center pixel of the divided block.

The prediction mode estimating unit 504 may estimate an intra prediction direction for each divided block by weighting the prediction directions of each reference location based on the weight for each reference location. Alternatively, a prediction mode closest to the weighted sum of all intra prediction modes may be estimated as the prediction mode of the corresponding divided block.

In another embodiment of the present invention, when a pixel group consists of one pixel, the intra prediction mode may be estimated for each pixel in the prediction mode block.

8 is an exemplary diagram for estimation of a prediction mode according to another embodiment of the present invention.

In the example of FIG. 8, squares indicated by thin lines indicate one pixel of a current block that performs intra prediction.

In the example of FIG. 8A, a dotted arrow is a prediction mode of each neighboring pixel, and in the example of FIG. 8B, a neighboring pixel including three dotted arrows is a reference position set for reference. With reference to the set prediction modes of the three reference positions, the prediction mode estimating unit 504 may determine an intra prediction mode for each pixel in the current block as illustrated in FIG. 8B.

The prediction mode estimating unit 504 estimates an intra prediction mode of a corresponding pixel by using at least one or more of the reference positions based on the position of each pixel in the current block. The prediction mode of the corresponding pixel is determined so as to be affected by the reference position at a distance from the divided block. For example, a weight for each reference position may be determined according to the distance between each pixel and the reference position.

The prediction mode estimating unit 504 may determine an intra prediction mode of a corresponding pixel by weighting the prediction directions of each reference location based on a weight for each reference location. Alternatively, a prediction mode closest to the weighted sum of all intra prediction modes may be estimated as the prediction mode of the corresponding pixel.

Meanwhile, if the prediction mode of the set reference position is not useful, the prediction mode estimating unit 504 may replace the prediction mode block with a new position around the prediction mode block. In addition, when the prediction modes of all the reference positions are not useful, the prediction mode for the current block may be determined as one of prediction modes preset between the encoding/decoding apparatuses.

According to the embodiment of the present invention described above, a plurality of division units for a prediction mode block such as one pixel, one line, and a division block may have different prediction modes. It is not required to individually signal information on the intra prediction mode for each division unit.

Meanwhile, in another embodiment, the prediction mode estimating unit 504 may estimate one intra prediction mode for the prediction mode block from the intra prediction modes of a plurality of reference positions when the pixel group is an entire prediction mode block. have. For example, an intra prediction mode for the entire current block may be estimated by averaging the intra prediction modes (prediction directions) of a plurality of reference positions.

The prediction sample generator 506 according to the present embodiment generates prediction samples by predicting a prediction mode block (current block) in pixel group units according to the intra prediction mode estimated by the prediction mode estimation unit 504.

9 is an exemplary diagram of a location of a reconstructed reference sample used to generate an intra prediction sample according to an embodiment of the present invention.

In the example of FIG. 9, portions indicated by circles represent reference samples included in previously reconstructed blocks referred to in the current block A. The range of the reference sample may be extended according to the usefulness of the reference sample according to the range of the intra prediction mode and the decoding order. In addition, the intra prediction unit 442 may determine prediction ranges M_r and N_r, respectively, according to the sizes M and N of the current block A and the range of the intra prediction mode.

The prediction sample generator 506 may generate a prediction sample from sample values of pre-restored reference samples around the prediction mode block as illustrated in FIG. 9 by using the intra prediction mode estimated for each pixel group. .

In an embodiment in which the intra prediction mode is estimated for each divided block divided from the prediction mode block, the prediction sample generator 506 selects a target pixel to be predicted within the divided block according to the estimated intra prediction mode for the corresponding divided block. Determine reference samples for Then, the target pixel is predicted using the sample values of the determined reference samples.

In the case of another embodiment in which the intra prediction mode is estimated for each pixel in the prediction mode block, the prediction sample generator 506 determines reference samples previously reconstructed using the estimated intra prediction mode for the corresponding pixel, and the determined reference sample The corresponding pixel is predicted using the sample values of.

In another embodiment in which one intra prediction mode is estimated for the entire prediction mode block, the prediction sample generator 506 uses the intra prediction mode of the prediction mode block to predict the target pixel in the prediction mode block. Determine the reconstructed reference samples. Then, the target pixel is predicted using the sample values of the determined reference samples.

FIG. 10 is an exemplary diagram of a location of a reconstructed reference sample used to generate an intra prediction sample according to another embodiment of the present invention.

In an embodiment in which the prediction mode block is divided into K (K is a natural number) divided blocks (dotted rectangles), the prediction sample generator 506 performs intra prediction by using sample values of reference samples as illustrated in FIG. 10. Can be done.

In the example of FIG. 10, a rectangle indicated by a thick line is a position of a reference sample based on a boundary of a prediction mode block, and a rectangle indicated by a thin line is a position of a reference sample based on the boundary of a divided block A.

When performing intra prediction on the divided block A in the prediction mode block, the prediction sample generator 506 generates a prediction sample using sample values of reference samples of the boundary of the prediction mode block or based on the boundary of the divided block A. As a reference sample, the previously reconstructed divided block can be used. Which reference samples to use may be determined by an agreement between encoding/decoding devices. Alternatively, information indicating which reference samples are to be used may be signaled in units of blocks such as each partition block and prediction mode block.

In order to use the reconstructed divided block in the prediction mode block as a reference sample, it is necessary to sequentially reconstruct the divided blocks in the prediction mode block. That is, after the first partitioned block in the prediction mode block is predicted according to a predefined order such as a raster scan order, the first partitioned block is reconstructed by adding residual signals corresponding to the partitioned block. The samples in the reconstructed divided block are used as reference samples for predicting the next divided block adjacent to the reconstructed divided block. For example, in the example of FIG. 10, the decoding apparatus predicts and restores the upper left partitioned block in a prediction mode estimated corresponding thereto (combining with the residual to generate a final reconstructed sample), and then, when restoring the upper left partitioned block. You can use the reconstructed sample within.

In another embodiment, a prediction sample in a divided block predicted first may be used as a reference sample for predicting a next divided block. That is, the prediction sample generator 506 predicts any one of the divided blocks in the prediction mode block according to a predefined order such as a raster scan order. In addition, pixels in the next divided block are predicted using prediction samples (not reconstructed samples generated through addition of the prediction sample and the residual signal) in the predicted divided block.

The intra prediction mode estimation technique described above is It can be used for both luma blocks and chroma blocks. Alternatively, the intra prediction mode for the chroma block may be determined from the intra prediction mode of the luma block using an intra direct mode (DM).

11 is an exemplary diagram for intra prediction of a chroma block according to an embodiment of the present invention.

As illustrated in FIG. 11, the intra prediction mode estimated for each pixel group in the luma block may be set as the intra prediction mode for the pixel group at the same location in the chroma block. The intra prediction unit 442 performs intra prediction for each pixel group in a chroma block by using an intra prediction mode corresponding to the pixel group.

Meanwhile, when resolutions between color components are different, the intra prediction unit 442 may use the intra prediction mode of the luma block sampled according to a specific sampling method as the prediction mode of the chroma block.

12 is a flowchart of an intra prediction method according to an embodiment of the present invention.

The intra prediction apparatus 500 according to the present embodiment decodes mode information indicating the use of the prediction estimation mode for the prediction mode block from the bitstream (S1200). Here, the prediction mode block refers to a block unit through which prediction information including a prediction mode (hereinafter, “estimation mode”) is transmitted. Hereinafter, for convenience of description, the current block represents a prediction mode block.

In order to use the estimation mode, the encoding device may indicate and transmit mode information on whether the estimation mode is used in the bitstream, and the decoding device may determine whether to apply the estimation mode using the corresponding information. The mode information may be information in the form of a flag indicating whether the prediction estimation mode is used. Alternatively, it may be information in the form of an index for indicating one of a plurality of intra prediction modes further including an estimation mode as a new intra prediction mode.

When the estimation mode according to the present embodiment is applied, the intra prediction apparatus 500 may divide the prediction mode block into pixel group units including one or more pixels. Pixel groups including a plurality of pixels are collectively expressed as a divided block or subblock, but intra prediction may be performed in units of each divided block. Accordingly, the level of the prediction mode block in which the estimation mode is decoded and the block in which intra prediction is performed may not be the same.

Depending on the division structure of the prediction mode block, the shape of the pixel group may be a block shape such as a square, a rectangle, or a triangle, or a block shape in units of lines such as M×1 or 1×N. Meanwhile, the divided pixel groups may have the same size and shape.

In another embodiment of the present invention, a pixel group may consist of only one pixel. In another embodiment, the pixel group may be a prediction mode block. That is, it may be composed of all pixels of the prediction mode block.

The intra prediction apparatus 500 sets a plurality of reference positions from a previously reconstructed block around the prediction mode block in a pixel group unit including one or more pixels in the prediction mode block (S1202).

The intra prediction apparatus 500 may determine a reference location using at least one of a predetermined location according to a dimension of a prediction mode block, an appointment between an encoding/decoding apparatus, and a block splitting structure around the prediction mode block.

Meanwhile, alternatively, information on an available reference position may be transmitted from the encoding device to the decoding device. In this case, the intra prediction apparatus 500 determines a reference position using the received information.

The intra prediction apparatus 500 estimates an intra prediction mode of each pixel group from intra prediction modes of a plurality of reference positions (S1204).

The intra prediction apparatus 500 estimates an intra prediction mode of each divided block by using at least one or more of the reference positions based on the position of each divided block in the current block. That is, the prediction mode of the partitioned block is determined so as to be affected by the reference position at a close distance from the partitioned block. For example, a weight for each reference position may be determined according to the distance between each divided block and the reference position. The closer the distance is, the larger the weight can be assigned.

The intra prediction apparatus 500 may estimate an intra prediction direction for each divided block by weighting the prediction directions of each reference location based on a weight for each reference location. Alternatively, a prediction mode closest to the weighted sum of all intra prediction modes may be estimated as the prediction mode of the corresponding divided block.

Meanwhile, when the prediction mode of the reference position is not useful, the intra prediction apparatus 500 may replace the prediction mode block with a new position around the prediction mode block. In addition, when the prediction modes of all the reference positions are not useful, the prediction mode for the current block may be determined as one of prediction modes preset between the encoding/decoding apparatuses.

Setting of a neighboring reference position and estimation of a prediction mode may be performed in the same manner in an encoding/decoding apparatus.

The intra prediction apparatus 500 may estimate the intra prediction mode of the current block in the same manner as the neighboring blocks. The intra prediction apparatus 500 first selects a plurality of directions from neighboring blocks and then selects one of the modes as the intra prediction mode of the current block, or calculates the intra prediction mode of the current block from the prediction modes of the plurality of neighboring blocks. I can.

The intra prediction apparatus 500 performs intra prediction on pixels in each pixel group, using intra prediction modes of each pixel group (S1206).

The intra prediction apparatus 500 may generate a prediction sample from sample values of previously reconstructed reference samples around the prediction mode block by using the intra prediction mode estimated for each pixel group.

In an embodiment in which the intra prediction mode is estimated for each divided block divided from the prediction mode block, the prediction sample generator 506 selects a target pixel to be predicted within the divided block according to the estimated intra prediction mode for the corresponding divided block. Determine reference samples for Then, the target pixel is predicted using the sample values of the determined reference samples.

In order to use the reconstructed divided block in the prediction mode block as a reference sample, it is necessary to sequentially reconstruct the divided blocks in the prediction mode block. That is, after the first partitioned block in the prediction mode block is predicted according to a predefined order such as a raster scan order, the first partitioned block is reconstructed by adding residual signals corresponding to the partitioned block. Samples in the reconstructed divided block may be used as a reference sample for predicting a next divided block adjacent to the reconstructed divided block.

As described above, according to the present embodiment, the intra prediction mode of the current block is estimated by referring to the intra prediction mode of the previously reconstructed neighboring block, and intra prediction is performed based on the estimated prediction mode. By providing an intra prediction apparatus and a method for generating a prediction sample for an image, it is possible to improve the compression performance of an image encoding and decoding apparatus.

In general, when a natural image is divided into blocks for intra prediction, one block and its neighboring blocks have similar image characteristics. Therefore, the intra prediction mode can be similar. In consideration of these characteristics, there is an intra prediction method using a Most Probable Mode (MPM) list generated based on prediction modes of left and upper adjacent blocks based on the current block.

The encoding apparatus first transmits an MPM flag indicating whether the prediction mode of the current block is generated from the MPM list. When the prediction mode of the current block is included in the MPM list, the encoding apparatus transmits an MPM index indicating the intra prediction mode of the current block among intra prediction modes in the MPM list to the decoding apparatus. Using the received index, the decoding apparatus may select a prediction mode from the MPM list and then perform intra prediction on the current block. Meanwhile, when the prediction mode of the current block is not included in the MPM list, the encoding device may transmit residual mode information indicating the prediction mode of the current block among residual prediction modes excluding the prediction mode included in the MPM list to the decoding device. .

In another embodiment of the present invention, a method of determining an intra prediction mode of a prediction mode block using a Most Probable Mode (MPM) is disclosed. The intra prediction unit 442 generates an MPM list based on the prediction mode block. That is, an MPM list is generated using intra prediction modes of neighboring blocks (eg, left and upper neighboring blocks) of the prediction mode block.

Meanwhile, the intra prediction unit 442 divides the prediction mode block into a plurality of subblocks. The splitting method may be the same as described above in the prediction estimation mode. In addition, the MPM list generated based on the prediction mode block is shared for all a plurality of subblocks in the prediction mode block. That is, the same MPM list is used for a plurality of subblocks.

As an example, the intra prediction mode of each subblock in the prediction mode block may be determined from the MPM list. In this case, the MPM index for each subblock may be signaled from the encoding device to the decoding device. The intra prediction unit 442 of the decoding apparatus may determine an intra prediction mode of a corresponding subblock from the shared MPM list through the received MPM index. In the prediction mode block, the intra prediction mode determined for the subblock that is first predicted may not be used as the intra prediction mode of the next subblock. To this end, the intra prediction mode for the subblock predicted first may be deleted from the MPM list. Through this method, it is possible to reduce the total amount of bits required to signal the MPM index for all subblocks in the prediction mode block.

As another example, information about an intra prediction mode (MPM flag and MPM index or residual mode information according to the MPM flag) for each subblock in the prediction mode block may be signaled from the encoding device to the decoding device. The intra prediction unit 442 of the decoding apparatus determines an intra prediction mode of each subblock using the received information. In this case, the intra prediction mode determined for the subblock that is first predicted in the subblock prediction mode block predicted first may not be used as the intra prediction mode of the next subblock. To this end, the intra prediction mode determined for the first predicted subblock may be deleted from the MPM list or the residual prediction mode list. Accordingly, it is possible to reduce the total amount of bits required to signal the MPM index and residual mode information for all subblocks in the prediction mode block.

Each flow chart according to the present embodiment describes that each process is sequentially executed, but is not limited thereto. In other words, since it is possible to change and execute the processes described in the flow chart or execute one or more processes in parallel, the flow chart is not limited to a time series order.

Meanwhile, various functions or methods described in the present disclosure may be implemented as instructions stored in a non-transitory recording medium that can be read and executed by one or more processors. The non-transitory recording medium includes, for example, all kinds of recording devices in which data is stored in a form readable by a computer system. For example, the non-transitory recording medium includes a storage medium such as an erasable programmable read only memory (EPROM), a flash drive, an optical drive, a magnetic hard drive, and a solid state drive (SSD).

The above description is merely illustrative of the technical idea of the present embodiment, and those of ordinary skill in the technical field to which the present embodiment belongs will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present exemplary embodiments are not intended to limit the technical idea of the present exemplary embodiment, but are illustrative, and the scope of the technical idea of the present exemplary embodiment is not limited by these exemplary embodiments. The scope of protection of this 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.

120, 440: prediction unit 130: subtractor
170, 450: adder 180, 460: filter unit
442: intra prediction unit
500: intra prediction device
502: reference position setting unit 504: prediction mode estimation unit
506: prediction sample generation unit

Claims (17)

In the intra prediction method used by the intra prediction device,
Decoding mode information indicating use of the prediction mode for the prediction mode block from the bitstream;
Estimating an intra prediction mode of each pixel group on a pixel group basis including one or more pixels in the prediction mode block from intra prediction modes of reference pixels at a plurality of pre-restored locations around the prediction mode block; And
Intra-predicting pixels in each pixel group using intra prediction modes of each pixel group
Intra prediction method comprising a. The method of claim 1,
And setting positions of reference pixels for the pixel group from a previously reconstructed block around the prediction mode block. The method of claim 2,
The positions of the reference pixels are,
Determined based on all or part of a method of determining using the dimension of the prediction mode block, a method of setting it at a predetermined position according to a pre-arrangement, and a method of determining using a block division structure around the prediction mode block Intra prediction method, characterized in that. The method of claim 1,
The mode information is a flag indicating whether the prediction estimation mode is used, or an index indicating the prediction estimation mode among a plurality of intra prediction modes including the prediction estimation mode. The method of claim 1,
The intra prediction mode of each pixel group is estimated from one or more intra prediction modes of the reference pixels based on a position of each pixel group in the prediction mode block. The method of claim 5,
For each pixel group, weights are assigned to intra prediction modes of the reference pixels according to distances from the reference pixels, and intra prediction modes of the reference pixels are weighted sum, and the respective pixel groups Intra prediction method, characterized in that estimating the intra prediction mode of. The method of claim 1,
The intra prediction method, wherein each pixel group is composed of one pixel. The method of claim 1,
Each of the pixel groups,
Intra prediction method, characterized in that the subblocks are divided in at least one of a horizontal or vertical direction from the prediction mode block and include a plurality of pixels. The method of claim 8,
The intra prediction method, wherein the plurality of subblocks are divided into the same shape and size. The method of claim 8,
The prediction mode block,
Intra prediction method, characterized in that the subblocks are divided based on at least one of a dimension of the prediction mode block, a predefined method, and a block division type around the prediction mode block. The method of claim 1,
And decoding information on the division structure of the prediction mode block from the bitstream, and generating the pixel groups using the information on the division structure. The method of claim 1,
The intra prediction step,
And generating prediction samples for pixels of each pixel group by using previously reconstructed pixels adjacent to the prediction mode block. The method of claim 1,
The intra prediction step,
Including the step of sequentially restoring the pixel groups included in the prediction mode block,
Wherein the reconstructed pixels in the pixel group reconstructed first in the prediction mode block are used for intra prediction of a pixel group adjacent to the reconstructed pixel group. The method of claim 1,
The intra prediction step,
Intra-predicting the pixel groups included in the prediction mode block sequentially,
And the prediction pixels in the pixel group predicted first in the prediction mode block are used to intra predict a pixel group adjacent to the reconstructed pixel group. An entropy decoder for decoding mode information indicating use of the prediction mode for the prediction mode block from the bitstream;
A prediction mode estimating unit for estimating an intra prediction mode of each pixel group from intra prediction modes of reference pixels of a plurality of previously restored reference pixels around the prediction mode block in a pixel group unit including one or more pixels in the prediction mode block ; And
A prediction sample generator for intra prediction of pixels in each pixel group using intra prediction modes of each pixel group
Intra prediction apparatus comprising a. The method of claim 15,
And a reference position setting unit configured to set positions of reference pixels for the pixel group from the reconstructed blocks around the prediction mode block. The method of claim 15,
A division structure for dividing the prediction mode block into the pixel groups,
It is determined based on at least one of a dimension of the prediction mode block, a predefined method, and a block division structure around the prediction mode block, or
Intra prediction apparatus, characterized in that it is determined based on information decoded from the bitstream by the entropy decoding unit.

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