JP7332385B2 - Intra prediction device, image coding device, image decoding device, and program - Google Patents

Description

The present invention relates to an intra prediction device, an image coding device, an image decoding device, and a program.

2. Description of the Related Art Conventionally, research has been conducted on video coding methods for compressing the data amount of still images and moving images during transmission and storage. In recent years, in video coding technology, ultra-high-resolution video such as 8K-SHV has been spreading, and AVC/H.264 has been developed as a method for transmitting a huge amount of moving images. 264 and HEVC/H. Coding schemes such as H.265 are known.

VVC, a next-generation coding scheme jointly standardized by MPEG and ITU, uses intra prediction using spatial correlation within frames and inter prediction using spatial correlation between frames. (See Non-Patent Document 1).

In intra prediction, the decoded reference pixels around the target block for intra prediction are used, and from among a total of 67 prediction modes consisting of Planar prediction, DC prediction, and 65 directional predictions, the image coding device side , the optimum mode is selected, and the selected information is transmitted to the image decoding device side.

In VVC, when generating predicted images using inter prediction, a technology is implemented to improve prediction accuracy by dividing the target block for inter prediction along diagonal lines and using separate motion prediction for each triangular area obtained by dividing. It is At that time, a flag indicating whether or not to use prediction for each triangular region (hereinafter referred to as "triangulation prediction") and a flag indicating which of the two diagonals should be used for division are sent from the image encoding device. It is transmitted to the image decoding device.

JVET-N1001 Versatile Video Coding (Draft 5)

Triangulation prediction is possible in inter prediction, and triangulation prediction is not used in intra prediction. It is considered effective to do so. However, since intra prediction has a large number of modes, if the intra prediction mode is transmitted from the image encoding device to the image decoding device for each triangular region, there is a drawback that the amount of code to be transmitted increases.

Therefore, an object of the present invention is to provide an intra prediction device, an image coding device, an image decoding device, and a program that enable the use of triangulation prediction in intra prediction while suppressing an increase in the amount of code to be transmitted. do.

An intra prediction device according to a first aspect performs intra prediction on blocks obtained by dividing an image. When dividing the prediction target block of the intra prediction along a diagonal line, the intra prediction device determines a dividing diagonal line to be used for the division from two diagonal lines of the prediction target block, and divides the prediction target block. a determination unit that determines an intra prediction mode to be applied to each of the obtained plurality of triangular regions; and a predicted image for each of the plurality of triangular regions using the intra prediction mode determined by the determination unit, and generated prediction a predicting unit that synthesizes images and outputs an intra-predicted image. Based on the intra prediction modes applied to the decoded blocks around the prediction target block, the determination unit selects at least one of the divided diagonal line and the intra prediction mode to be applied to each of the plurality of triangular regions. Decide on one.

An image coding device according to a second aspect includes the intra prediction device according to the first aspect.

An image decoding device according to a third aspect includes the intra prediction device according to the first aspect.

A program according to a fourth aspect causes a computer to function as the intra prediction device according to the first aspect.

Advantageous Effects of Invention According to the present invention, it is possible to provide an intra prediction device, an image coding device, an image decoding device, and a program that enable triangulation prediction to be used in intra prediction while suppressing an increase in the amount of code to be transmitted.

1 is a diagram showing the configuration of an image encoding device according to an embodiment; FIG. It is a figure which shows the candidate of intra prediction mode which concerns on embodiment. FIG. 4 illustrates triangulation prediction according to an embodiment; It is a figure which shows the structure of the intra prediction part of the image coding apparatus which concerns on embodiment. It is a figure which shows the specific example of the process of the determination part which concerns on embodiment. It is a figure which shows the structure of the image decoding apparatus which concerns on embodiment. It is a figure which shows the structure of the intra prediction part of the image decoding apparatus which concerns on embodiment. It is a figure which shows the example of the operation|movement flow of the intra prediction part which concerns on embodiment. It is a figure which shows the example of a process of the determination part which concerns on other embodiment.

An image encoding device and an image decoding device according to embodiments will be described with reference to the drawings. An image encoding device and an image decoding device according to an embodiment encode and decode a moving image represented by MPEG, respectively. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

<Configuration of image encoding device>
First, the configuration of the image coding apparatus according to this embodiment will be described. FIG. 1 is a diagram showing the configuration of an image encoding device 1 according to this embodiment.

As shown in FIG. 1, the image coding apparatus 1 includes a block division unit 100, a subtraction unit 110, a transform/quantization unit 120, an entropy coding unit 130, an inverse quantization/inverse transform unit 140, It has a synthesizing unit 150 , a memory 160 and a predicting unit 170 .

The block division unit 100 divides an original image, which is an input image in units of frames (or pictures) constituting a moving image, into a plurality of image blocks, and outputs the image blocks obtained by division to the subtraction unit 110 . The size of an image block is, for example, 32×32 pixels, 16×16 pixels, 8×8 pixels, or 4×4 pixels. The shape of the image block is not limited to square and may be rectangular (non-square). An image block is a unit of encoding by the image encoding device 1 (ie, a block to be encoded) and a unit of decoding by the image decoding device (ie, a block to be decoded). Such an image block is sometimes called a CU (Coding Unit).

The subtraction unit 110 calculates a prediction residual representing the difference (error) between the encoding target block output from the block dividing unit 100 and the prediction block obtained by predicting the encoding target block by the prediction unit 170 . Specifically, the subtraction unit 110 calculates a prediction residual by subtracting each pixel value of the prediction block from each pixel value of the block, and outputs the calculated prediction residual to the transformation/quantization unit 120 .

The transform/quantization unit 120 performs orthogonal transform processing and quantization processing on a block-by-block basis. The transform/quantization unit 120 has a transform unit 121 and a quantization unit 122 .

Transformation section 121 performs orthogonal transformation processing on the prediction residual output from subtraction section 110 to calculate orthogonal transformation coefficients, and outputs the computed orthogonal transformation coefficients to quantization section 122 . Orthogonal transformation refers to, for example, discrete cosine transform (DCT), discrete sine transform (DST), Karhunen-Loeve transform (KLT), and the like.

Quantization section 122 quantizes the orthogonal transform coefficients output from transform section 121 using a quantization parameter (Qp) and a quantization matrix, and applies the quantized orthogonal transform coefficients to entropy coding section 130 and inverse quantization/ Output to the inverse transformation unit 140 . Note that the quantization parameter (Qp) is a parameter commonly applied to each orthogonal transform coefficient in a block, and is a parameter that determines the coarseness of quantization. A quantization matrix is a matrix having, as elements, quantization values for quantizing each orthogonal transform coefficient.

The entropy coding unit 130 performs entropy coding on the orthogonal transform coefficients output from the quantization unit 122, performs data compression to generate coded data (bitstream), and performs image coding on the coded data. Output to the outside of the device 1 . Huffman code, CABAC (Context-based Adaptive Binary Arithmetic Coding), or the like can be used for entropy coding. The entropy encoding unit 130 also receives information such as a flag and an identifier related to prediction from the prediction unit 170 and entropy-encodes the input information.

The inverse quantization/inverse transform unit 140 performs inverse quantization processing and inverse orthogonal transform processing on a block-by-block basis. The inverse quantization/inverse transform unit 140 has an inverse quantization unit 141 and an inverse transform unit 142 .

The inverse quantization unit 141 performs inverse quantization processing corresponding to the quantization processing performed by the quantization unit 122 . Specifically, the inverse quantization unit 141 restores the orthogonal transform coefficients by inversely quantizing the orthogonal transform coefficients output from the quantizing unit 122 using the quantization parameter (Qp) and the quantization matrix. , and outputs the restored orthogonal transform coefficients to the inverse transform unit 142 .

The inverse transform unit 142 performs inverse orthogonal transform processing corresponding to the orthogonal transform processing performed by the transform unit 121 . For example, when the transform unit 121 performs discrete cosine transform, the inverse transform unit 142 performs inverse discrete cosine transform. The inverse transform unit 142 performs inverse orthogonal transform processing on the orthogonal transform coefficients output from the inverse quantization unit 141 to restore the prediction residuals, and the restored prediction residuals, which are the restored prediction residuals, are synthesized by the synthesis unit 150. output to

The synthesizing unit 150 synthesizes the restored prediction residual output from the inverse transform unit 142 with the prediction block output from the predicting unit 170 on a pixel-by-pixel basis. The synthesizing unit 150 adds each pixel value of the restored prediction residual and each pixel value of the prediction block, decodes (reconstructs) the encoding target block, and outputs the decoded block (reconstructed block) to the memory 160 . .

The memory 160 stores the decoded blocks output from the synthesizing unit 150, and accumulates the decoded blocks as decoded images in units of frames. The memory 160 outputs the stored decoded block or decoded image to the prediction section 170 . Note that a loop filter may be provided between the synthesizing section 150 and the memory 160 .

The prediction unit 170 performs prediction on a block-by-block basis. The prediction unit 170 has an inter prediction unit 171 , an intra prediction unit 172 and a switching unit 173 . In this embodiment, the intra prediction unit 172 corresponds to an intra prediction device provided in the image coding device 1 .

The inter prediction unit 171 uses the decoded image stored in the memory 160 as a reference image, calculates a motion vector by a technique such as block matching, predicts the encoding target block, and generates an inter prediction block. The inter prediction block is output to switching section 173 .

Here, the inter prediction unit 171 selects an optimum inter prediction method from among inter prediction using a plurality of reference images (typically, bi-prediction) and inter prediction using one reference image (unidirectional prediction). Select and perform inter prediction using the selected inter prediction method. The inter prediction unit 171 outputs information (motion vector, etc.) related to inter prediction to the entropy coding unit 130 .

The intra prediction unit 172 generates an intra prediction block by referring to the decoded pixel values around the encoding target block in the decoded image stored in the memory 160, and outputs the generated intra prediction block to the switching unit 173. do.

In general, the intra prediction unit 172 selects a prediction mode to be applied to a prediction target block for intra prediction from among a plurality of intra prediction modes, and uses the selected prediction mode to predict the target block for intra prediction. The intra prediction unit 172 outputs an identifier related to the selected prediction mode to the entropy coding unit 130.

FIG. 2 is a diagram showing intra prediction mode candidates according to the present embodiment. Here, intra-prediction mode candidates to be used for luminance blocks among encoding target blocks are shown. As shown in FIG. 2, there are 67 prediction modes from 0 to 66 as intra prediction mode candidates. Prediction mode '0' is Planar prediction, prediction mode '1' is DC prediction, and prediction mode '2' to '66' are directional prediction. In directional prediction, the direction of the arrow indicates the reference direction, the starting point of the arrow indicates the position of the prediction target pixel, and the end point of the arrow indicates the position of the reference pixel used for prediction of this prediction target pixel. As a reference direction parallel to the diagonal line passing through the upper right vertex and the lower left vertex of the block, there are a mode "2" that is a prediction mode that refers to the lower left direction and a mode "66" that is a prediction mode that refers to the upper right direction. A mode number is assigned every predetermined angle clockwise from "2" to mode "66".

The switching unit 173 switches between the inter prediction block output from the inter prediction unit 171 and the intra prediction block output from the intra prediction unit 172 and outputs either prediction block to the subtraction unit 110 and the synthesis unit 150 .

In the image encoding device 1 configured as described above, the intra prediction unit 172 divides the prediction target block for intra prediction along diagonal lines, and applies different intra prediction modes to each of the triangular regions obtained by dividing. It is possible to do split prediction. For example, the intra-prediction unit 172 applies triangulation prediction to a prediction target block that forms a pattern or texture having a triangular shape.

FIG. 3 is a diagram showing triangulation prediction according to this embodiment. In addition, although an example in which the block shape of the prediction target block is square will be mainly described below, the block shape of the prediction target block may be non-square (rectangular).

As shown in FIG. 3, the intra prediction unit 172 determines one diagonal line selected from two diagonal lines in the block to be predicted as the divided diagonal line. FIG. 3A shows an example of determining a diagonal line passing through the upper left vertex and the lower right vertex of the block to be predicted as the dividing diagonal line. FIG. 3(b) shows an example of determining a diagonal line passing through the upper right vertex and the lower left vertex of the block to be predicted as the dividing diagonal line.

In the example shown in FIG. 3A , the intra prediction unit 172 divides the prediction target block into an upper right triangular region (Partition 1) and a lower left triangular region (Partition 2) along a diagonal line passing through the upper left vertex and the lower right vertex, Two predicted images corresponding to the two divided regions are generated, and an intra prediction block is output by synthesizing the two predicted images.

In the example shown in FIG. 3B, the intra prediction unit 172 divides the prediction target block into an upper left triangular region (Partition 1) and a lower right triangular region (Partition 2) along a diagonal line passing through the upper right vertex and the lower left vertex, Two predicted images corresponding to the two divided regions are generated, and an intra prediction block is output by synthesizing the two predicted images.

With such triangulation prediction, it is possible to perform detailed intra prediction according to the pattern, so that the prediction accuracy of intra prediction can be improved. However, when performing such triangulation prediction, the image encoding device 1 may need to transmit (signal) the following three types of additional information to the image decoding device side.

1) "Triangulation prediction flag" indicating whether or not to perform triangulation prediction
2) "Diagonal dividing line identifier" indicating which of the dividing diagonal lines in Figs. 3(a) and 3(b) is to be applied
3) "Intra prediction mode identifier" indicating the intra prediction mode to be applied to each triangular region
In particular, since intra prediction has a large number of modes, if the intra prediction mode identifier is transmitted from the image coding apparatus 1 for each triangular region, the amount of code to be transmitted increases, which can reduce coding efficiency. .

Therefore, in the present embodiment, the intra prediction unit 172 applies the intra prediction mode to each of the divided diagonal lines and the plurality of triangular regions based on the intra prediction mode applied to the decoded blocks around the prediction target block. and at least one of

Here, the intra prediction mode applied to the decoded blocks around the prediction target block is information that can be used by both the image encoding device 1 and the image decoding device. Determining the dividing diagonal line based on such information eliminates the need to transmit the dividing diagonal line identifier. Transmission of mode identifiers becomes unnecessary.

Therefore, even when triangulation prediction is used for intra prediction, it is possible to eliminate the need to transmit at least one of the "division diagonal line identifier" and the "intra prediction mode identifier", thus increasing the amount of code to be transmitted. can be suppressed, and the accuracy of intra prediction can be improved.

In the following, the intra prediction unit 172 determines both the intra prediction mode to be applied to each of the divided diagonal line and the plurality of triangular regions based on the intra prediction mode applied to the decoded blocks around the prediction target block. An example of doing so will be described.

However, the intra prediction unit 172 determines only the dividing diagonal line based on the intra prediction modes applied to the decoded blocks around the prediction target block, and uses different intra prediction modes to apply to each of the plurality of triangular regions. It may be determined based on criteria. Alternatively, the intra prediction unit 172 determines only the intra prediction modes to be applied to each of the plurality of triangular regions based on the intra prediction modes applied to the decoded blocks around the prediction target block, and separates the divided diagonals. can be determined by the criteria of

Next, the configuration of the intra prediction unit 172 of the image encoding device 1 according to this embodiment will be described. FIG. 4 is a diagram showing the configuration of the intra prediction unit 172 of the image encoding device 1. As shown in FIG.

As shown in FIG. 4 , the intra prediction section 172 has a determination section 1721 and a prediction section 1722 .

When dividing a prediction target block for intra prediction along a diagonal line, the determination unit 1721 determines a dividing diagonal line to be used for dividing from two diagonal lines of the prediction target block, and determines a plurality of triangles obtained by dividing the prediction target block. Determine the intra-prediction mode to apply to each of the regions. In the present embodiment, the determination unit 1721 determines the intra prediction mode to be applied to each of the divided diagonal lines and the plurality of triangular regions based on the intra prediction modes applied to the decoded blocks around the prediction target block. do.

Here, the functions of the determination unit 1721 can be divided into (a) “input”, (b) “output”, and (c) “processing” as follows.

(a) Input: The determination unit 1721 receives from the memory 160 the intra prediction mode information used in the peripheral blocks (top/left).

(b) Output: The determination unit 1721 outputs information indicating the divided diagonal line (shape information of the triangular area) and the intra prediction mode to be applied to each triangular area.

(c) Processing: When using triangulation prediction in intra prediction, the determination unit 1721 determines the divided diagonal (shape of the triangular region) and each triangle according to the intra prediction mode used in the surrounding blocks (upper/left). Determines the intra-prediction mode to apply to the region.

FIG. 5 is a diagram showing a specific example of processing of the determining unit 1721 according to this embodiment. In FIG. 5 , “A” and “B” are directional prediction modes among intra prediction modes, specifically prediction modes from mode “2” to mode “66”. On the other hand, 'C' and 'D' are non-directional prediction modes among intra prediction modes, specifically, Planar prediction mode as mode '0' and DC prediction mode as mode '1'. Here, "C" is Planar mode and "D" is DC mode.

As shown in FIG. 5, the determination unit 1721 applies intra prediction modes to the upper block, which is the decoded block above the prediction target block, and the left block, which is the decoded block to the left of the prediction target block. The decision is made based on the applied intra-prediction mode. Since the image coding apparatus 1 performs coding processing in raster scan order, the upper block and the left block are used. The determination unit 1721 acquires information on the intra prediction modes of these peripheral blocks from the memory 160 .

Although FIG. 5 shows an example in which each of the upper block and left block is square, at least one of the upper block and left block may be non-square. Also, an example is shown in which the size of each of the upper block and the left block is the same as the size of the block to be encoded. and height. When it is assumed that the upper block and the left block are smaller in size than the target block for encoding, for example, the upper block is an upper adjacent block containing pixels adjacent to the upper rightmost pixel in the target block for prediction, and the left The block may be a left neighboring block containing pixels adjacent to the lower leftmost pixel in the block to be predicted.

Alternatively, the upper block is an upper adjacent block containing pixels adjacent to the upper leftmost pixel in the prediction target block, and the left block is also a left adjacent block containing pixels adjacent to the upper leftmost pixel in the prediction target block. good too.

Alternatively, the upper block is the upper adjacent block with the longest contact length among the blocks adjacent to the upper side of the block to be predicted, and the left block is also the block with the longest contact length among the blocks adjacent to the left side of the block to be predicted. may be the left adjacent block with the longest length.

If the intra prediction mode applied to the upper block and the intra prediction mode applied to the left block are different from each other as illustrated in FIGS. and the diagonal line passing through the lower right vertex is determined as the dividing diagonal line. Then, the determination unit 1721 divides the prediction target block into an upper right triangular area adjacent to the upper block and a lower left triangular area adjacent to the left block.

In the example of FIG. 5A, the upper block is in directional prediction mode "A" and the left block is in directional prediction mode "B", so the intra prediction modes are different from each other. In the example of FIG. 5B, the upper block is in non-directional prediction mode "C" and the left block is in directional prediction mode "B", so the intra prediction modes are different from each other. In the example of FIG. 5(c), the upper block is in the non-directional prediction mode "C" and the left block is in the non-directional prediction mode "D", so the intra prediction modes are different from each other.

As shown in FIGS. 5A to 5C, the determination unit 1721 determines the intra prediction mode applied to the upper block as the intra prediction mode applied to the upper right triangular region, and the intra prediction mode of the left block. Determine the intra prediction mode to be applied to the lower left triangular area.

Specifically, in the example of FIG. 5A , the determination unit 1721 determines to apply the directional prediction mode “A” of the upper block to the upper right triangular region, and applies the directional prediction mode “B” of the left block. Decide to apply to the lower left triangular region. In the example of FIG. 5(b), it is determined to apply the non-directional prediction mode 'C' of the upper block to the upper right triangular area, and to apply the directional prediction mode 'B' of the left block to the lower left triangular area. In the example of FIG. 5C, the determining unit 1721 determines to apply the upper block non-directional prediction mode “C” to the upper right triangular region, and apply the left block non-directional prediction mode “D” to the lower left triangular region. determine that it applies to

In this way, the intra prediction mode applied to the upper block is determined as the intra prediction mode applied to the upper right triangular region, and the intra prediction mode of the left block is determined as the intra prediction mode applied to the lower left triangular region, Since the intra-prediction mode of adjacent blocks with high spatial correlation can be applied to each triangular region, the accuracy of intra-prediction can be improved.

On the other hand, as shown in FIGS. 5D and 5E, the determination unit 1721 determines that the intra prediction mode applied to the upper block and the intra prediction mode applied to the left block are the same. A diagonal line passing through the upper right vertex and the lower left vertex of is determined as the dividing diagonal line. Then, the determination unit 1721 divides the block to be predicted into an upper left triangular area adjacent to both the upper block and the left block and a lower right triangular area adjacent to neither the upper block nor the left block.

In the example of FIG. 5D, the upper block has the directional prediction mode "A" and the left block also has the directional prediction mode "A", so the intra prediction modes are the same. In the example of FIG. 5(e), the upper block is in the non-directional prediction mode "C" and the left block is also in the non-directional prediction mode "C", so the intra prediction modes are the same.

The determination unit 1721 determines the same intra prediction mode applied to the upper block and the left block as the intra prediction mode to be applied to the upper left triangular region, as shown in FIGS. 5(d) and (e). In the example of FIG. 5D, the determining unit 1721 determines to apply the directional prediction mode "A" to the upper left triangular region. In the example of FIG. 5( e ), the determination unit 1721 determines to apply the non-directional prediction mode “C” to the upper left triangular region.

If the same intra-prediction mode is applied to the upper block and the left block, the upper block and the left block are highly correlated, and the upper left triangular region between the upper block and the left block is considered to be highly correlated as well. Therefore, by applying the same intra prediction mode applied to the upper block and the left block to the upper left triangular region, the intra prediction mode of adjacent blocks with high spatial correlation can be applied to the upper left triangular region. accuracy can be improved.

Also, the determination unit 1721 determines the non-directional intra prediction mode as the intra prediction mode to be applied to the lower right triangular region, as shown in FIGS. 5(d) and (e). Specifically, as illustrated in FIG. 5D , when the same intra prediction mode applied to the upper block and the left block is the directional prediction mode, the determination unit 1721 determines the predetermined non-directional prediction mode. We decide to apply prediction mode 'C' to the lower right triangular region.

If the diagonal line passing through the upper right vertex and the lower left vertex of the block to be predicted is the division diagonal, the lower right triangular region is considered to have a low correlation with the intra prediction modes of the upper block and the left block. Therefore, a predetermined non-directional prediction mode is applied to the lower right triangular area.

On the other hand, as shown in FIG. 5(e), the determining unit 1721, when the same intra prediction mode applied to the upper block and the left block is the first non-directional intra prediction mode 'C', the lower right A second non-directional intra prediction mode "D" different from the first non-directional intra prediction mode "C" is determined as the intra prediction mode to be applied to the triangular region.

If the diagonal line passing through the upper right vertex and the lower left vertex of the block to be predicted is the division diagonal, the lower right triangular region is considered to have a low correlation with the intra prediction modes of the upper block and the left block. Therefore, a non-directional prediction mode different from the non-directional prediction modes applied to the upper and left blocks is applied to the lower right triangular region.

In this way, when using triangulation prediction in intra prediction, the determination unit 1721 determines the division diagonal (shape of the triangular region) and each The intra prediction mode to be applied to the triangular region is determined, and information indicating the content of the determination is output to the prediction section 1722 .

The prediction unit 1722 generates a predicted image for each of the plurality of triangular regions using the intra prediction mode determined by the determination unit 1721, synthesizes the generated predicted images, and outputs an intra predicted image. The prediction unit 1722 has a predicted image generation unit 1722a and a predicted image synthesizing unit 1722b.

The functions of the predicted image generation unit 1722a can be divided into three functions of "input", "output", and "processing" as follows.

Input: The predicted image generation unit 1722a receives from the determination unit 1721 information on the dividing diagonal line (shape of the triangular area) and information on the intra prediction mode to be applied to each triangular area. The predicted image generation unit 1722a also receives from the memory 160 reference pixel information used for intra prediction (that is, decoded reference pixel information around the prediction target block).

Output: The predicted image generator 1722a outputs a predicted image of each triangular region.

Processing: Intra-prediction is performed for each triangular region based on information on the dividing diagonal line and information on the intra-prediction mode applied to each triangular region, and a predicted image for each triangular region is generated.

Also, the function of the predicted image synthesizing unit 1722b can be divided into three functions of "input", "output", and "processing" as follows.

Input: The predicted image synthesizing unit 1722b receives two predicted images corresponding to two triangular regions from the predicted image generating unit 1722a.

Output: The predicted image synthesizing unit 1722b outputs the synthesized intra prediction block.

Processing: The predicted image synthesizing unit 1722b synthesizes two predicted images to generate one intra-predicted block. The predicted image synthesizing unit 1722b may perform filter processing on the diagonal portion during such synthesizing.

<Configuration of image decoding device>
Next, the configuration of the image decoding device according to this embodiment will be described. FIG. 6 is a diagram showing the configuration of the image decoding device 2 according to this embodiment.

As shown in FIG. 6 , the image decoding device 2 has an entropy decoding unit 200 , an inverse quantization/inverse transform unit 210 , a synthesizing unit 220 , a memory 230 and a prediction unit 240 .

The entropy decoding unit 200 decodes the encoded data generated by the image encoding device 1 and outputs the quantized orthogonal transform coefficients to the inverse quantization/inverse transform unit 210 . The entropy decoding unit 200 also acquires identifiers related to prediction (intra prediction and inter prediction) and outputs the acquired identifiers to the prediction unit 240 .

In this embodiment, the entropy decoding unit 200 acquires a triangulation prediction flag indicating that triangulation prediction has been applied to a block to which the image encoding device 1 has applied triangulation prediction, and sets the acquired triangulation prediction flag to Output to the prediction unit 240 (intra prediction unit 242).

The inverse quantization/inverse transform unit 210 performs inverse quantization processing and inverse orthogonal transform processing on a block-by-block basis. The inverse quantization/inverse transform unit 210 has an inverse quantization unit 211 and an inverse transform unit 212 .

The inverse quantization unit 211 performs inverse quantization processing corresponding to the quantization processing performed by the quantization unit 122 of the image encoding device 1 . The inverse quantization unit 211 inversely quantizes the quantized orthogonal transform coefficients output from the entropy decoding unit 200 using the quantization parameter (Qp) and the quantization matrix, thereby obtaining the orthogonal transform coefficients of the decoding target block. It restores and outputs the restored orthogonal transform coefficients to the inverse transform unit 212 .

The inverse transform unit 212 performs inverse orthogonal transform processing corresponding to the orthogonal transform processing performed by the transform unit 121 of the image encoding device 1 . The inverse transform unit 212 performs inverse orthogonal transform processing on the orthogonal transform coefficients output from the inverse quantization unit 211 to restore prediction residuals, and the restored prediction residuals (restored prediction residuals) are synthesized by a synthesizing unit 220. output to

The synthesizing unit 220 decodes (reconstructs) the original block by synthesizing the prediction residual output from the inverse transform unit 212 and the prediction block output from the prediction unit 240 on a pixel-by-pixel basis. Output the block to memory 230 .

The memory 230 stores the decoded blocks output from the synthesizing unit 220, and accumulates the decoded blocks as decoded images in units of frames. The memory 230 outputs the decoded block or decoded image to the prediction section 240 . The memory 230 also outputs the decoded image in frame units to the outside of the image decoding device 2 . Note that a loop filter may be provided between the synthesizing section 220 and the memory 230 .

The prediction unit 240 performs prediction on a block-by-block basis. The prediction unit 240 has an inter prediction unit 241 , an intra prediction unit 242 and a switching unit 243 . In this embodiment, the intra prediction unit 242 corresponds to an intra prediction device provided in the image decoding device 2 .

The inter prediction unit 241 predicts the decoding target block by inter prediction using the decoded image stored in the memory 230 as a reference image. The inter prediction unit 241 generates an inter prediction block by performing inter prediction according to the identifier, motion vector, etc. output from the entropy decoding unit 200 and outputs the generated inter prediction block to the switching unit 243 .

In the decoded image stored in the memory 160, the intra prediction unit 242 generates an intra prediction block by referring to the decoded pixel values around the prediction target block for intra prediction (decoding target block), and generates the intra prediction. The block is output to the switching section 243 . The intra prediction unit 242 determines whether or not to apply triangulation prediction to the decoding target block based on the triangulation prediction flag output from the entropy decoding unit 200 .

When triangulation prediction is not applied to the decoding target block, the intra prediction unit 242 determines the intra prediction mode to be applied to the decoding target block based on the intra prediction mode identifier output from the entropy decoding unit 200, and determines the intra prediction mode to be applied to the decoding target block. An intra-prediction block is output by performing intra-prediction in a prediction mode.

On the other hand, when applying triangulation prediction to the block to be decoded, the intra prediction unit 242 divides the divided diagonal line and each of the plurality of triangular regions based on the intra prediction mode applied to the decoded blocks around the block to be predicted. Determines the intra-prediction mode to apply to Then, the intra prediction unit 242 divides the prediction target block into two along the determined dividing diagonal line, generates two predicted images corresponding to the two divided regions according to the determined intra prediction mode, and synthesizes the two predicted images. to output the intra prediction block.

The switching unit 243 switches between the inter prediction block output from the inter prediction unit 241 and the intra prediction block output from the intra prediction unit 242 and outputs one of the prediction blocks to the combining unit 220 .

FIG. 7 is a diagram showing the configuration of the intra prediction unit 242 of the image decoding device 2 according to this embodiment. The intra prediction unit 242 corresponds to an intra prediction device provided in the image decoding device 2 .

As shown in FIG. 7 , the intra prediction section 242 has a determination section 2421 and a prediction section 2422 . The prediction unit 2422 also includes a predicted image generation unit 2422a and a predicted image synthesizing unit 2422b.

The determining unit 2421, the predicted image generating unit 2422a, and the predicted image synthesizing unit 2422b perform the same operations as the determining unit 1721, the predicted image generating unit 1722a, and the predicted image synthesizing unit 1722b shown in FIG. However, the determination unit 2421 receives, from the entropy decoding unit 200, a triangulation prediction flag indicating whether or not to apply triangulation prediction to the block to be decoded in intra prediction. Determines whether to apply split prediction.

<Example of intra prediction operation flow>
Next, an operation flow example of intra prediction according to the present embodiment will be described. Although the intra prediction operation is the same in the image encoding device 1 and the image decoding device 2, the intra prediction operation (the intra prediction unit 242) in the image decoding device 2 will be described here.

FIG. 8 is a diagram illustrating an operation flow example of the intra prediction unit 242. As illustrated in FIG. The intra prediction unit 242 performs the operation shown in FIG. 8 when a triangulation prediction flag indicating that triangulation prediction is to be applied to the decoding target block in intra prediction is input from the entropy decoding unit 200 .

As shown in FIG. 8, in step S1, the determination unit 2421 refers to the memory 230 and determines whether the intra prediction mode applied to the upper block and the intra prediction mode applied to the left block are the same. judge.

When the intra prediction mode applied to the upper block and the intra prediction mode applied to the left block are different from each other (step S1: NO), in step S2, the determination unit 2421 determines the upper left vertex and lower right vertex of the block to be predicted. A diagonal line passing through is determined as a dividing diagonal line, and the block to be predicted is divided into an upper right triangular area adjacent to the upper block and a lower left triangular area adjacent to the left block (see FIG. 3(a)). In step S3, the determining unit 2421 determines to apply the intra prediction mode applied to the upper block to the upper right triangular region, and to apply the intra prediction mode of the left block to the lower left triangular region.

On the other hand, when the intra prediction mode applied to the upper block and the intra prediction mode applied to the left block are the same (step S1: YES), in step S6, the determination unit 2421 determines the upper right vertex of the prediction target block and A diagonal line passing through the lower left vertex is determined as a dividing diagonal line, and the block to be predicted is divided into an upper left triangular region adjacent to both the upper block and the left block and a lower right triangular region adjacent to neither the upper block nor the left block. (See FIG. 3(b)).

In this case, in step S7, the determining unit 2421 determines whether or not the same intra prediction mode applied to the upper block and the left block is the directional prediction mode.

If the same intra prediction mode applied to the upper block and the left block is the directional prediction mode (step S7: YES), in step S8, the determination unit 2421 determines the same intra prediction mode applied to the upper block and the left block. A prediction mode is determined to be applied to the upper left triangular region and a predetermined non-directional prediction mode is determined to be applied to the lower right triangular region.

On the other hand, if the same intra prediction mode applied to the upper block and the left block is the non-directional prediction mode (step S7: NO), in step S9, the determining unit 2421 It is determined to apply the same intra-prediction mode to the upper left triangular region and to apply a non-directional intra prediction mode different from the same intra prediction mode (non-directional prediction mode) to the lower right triangular region. For example, the determining unit 2421 determines to apply the planar prediction mode to the lower right triangular region when the same intra prediction mode applied to the upper block and the left block is the DC prediction mode. Also, when the same intra prediction mode applied to the upper block and the left block is the planar prediction mode, the decision unit 2421 decides to apply the DC prediction mode to the lower right triangular region.

After that, in step S4, the predicted image generation unit 2422a generates a predicted image of each triangular region using the intra prediction mode determined by the determination unit 2421 while referring to the memory 230. FIG. In step S5, the predicted image synthesizing unit 2422b synthesizes the predicted images generated by the predicted image generating unit 2422a and outputs an intra predicted image.

<Other embodiments>
In the above-described embodiment, when the same intra prediction mode is applied to the upper block and the left block, the determination unit 1721 and the determination unit 2421 apply the non-directional prediction mode to the lower right triangular region of the prediction target block. had decided.

However, in such a case, the determination unit 1721 and the determination unit 2421, as shown in FIG. 9, the intra prediction mode applied to the upper right block, which is the decoded block on the upper right of the prediction target block, and the prediction target block The intra-prediction mode to be applied to the lower-right triangular region is determined based on at least one of the intra-prediction mode applied to the lower-left block, which is the decoded block at the lower-left of the .

9A shows an example in which the same directional prediction mode 'A' is applied to the upper block and the left block, and FIG. 9B shows an example in which the same non-directional prediction mode 'C' is applied to the upper block and the left block. ” shows an example applied. Note that the upper right block is a decoded block adjacent to the right side of the upper block, and the lower left block is a decoded block adjacent to the lower side of the left block.

For example, the determination unit 1721 and the determination unit 2421 may determine to apply the same intra prediction mode to the lower right triangular region when the same intra prediction mode is applied to the upper right block and the lower left block. The determining unit 1721 and the determining unit 2421 may determine to apply the intra prediction mode applied to the upper right block to the lower right triangular region when different intra prediction modes are applied to the upper right block and the lower left block.

In the above-described embodiments, triangulation prediction may also be applied to the upper block and the left block of the prediction target block. In this case, even if the prediction mode of the triangular area containing the side that is in contact with the prediction target block among the adjacent blocks (upper block or left block) to which triangulation prediction is applied is regarded as the prediction mode of the adjacent block. good. Alternatively, adjacent blocks to which triangulation prediction is applied may be uniformly regarded as blocks using a specific prediction mode. Examples of the specific prediction modes mentioned above include Planar prediction mode and DC prediction mode.

A program that causes a computer to execute each process performed by the image encoding device 1 may be provided. A program that causes a computer to execute each process performed by the image decoding device 2 may be provided. The program may be recorded on a computer readable medium. A computer readable medium allows the installation of the program on the computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be, for example, a recording medium such as CD-ROM or DVD-ROM.

A circuit for executing each process performed by the image encoding device 1 may be integrated, and the image encoding device 1 may be configured by a semiconductor integrated circuit (chipset, SoC). A circuit for executing each process performed by the image decoding device 2 may be integrated, and the image decoding device 2 may be configured by a semiconductor integrated circuit (chipset, SoC).

Although the embodiments have been described in detail with reference to the drawings, the specific configuration is not limited to the above, and various design changes can be made without departing from the spirit of the invention.

1: image coding device 2: image decoding device 100: block division unit 110: subtraction unit 120: transformation/quantization unit 121: transformation unit 122: quantization unit 130: entropy coding unit 140: inverse quantization/inverse transformation Unit 141 : Inverse quantization unit 142 : Inverse transform unit 150 : Synthesis unit 160 : Memory 170 : Prediction unit 171 : Inter prediction unit 172 : Intra prediction unit 173 : Switching unit 200 : Entropy decoding unit 210 : Inverse quantization/inverse transform Unit 211 : Inverse quantization unit 212 : Inverse transform unit 220 : Synthesis unit 230 : Memory 240 : Prediction unit 241 : Inter prediction unit 242 : Intra prediction unit 243 : Switching unit 1721 : Determination unit 1722 : Prediction unit 1722a : Predicted image generation Unit 1722b: predicted image synthesizing unit 2421: determining unit 2422: predicting unit 2422a: predicted image generating unit 2422b: predicted image synthesizing unit

Claims (12)

An intra prediction device that performs intra prediction on blocks obtained by dividing an image,
When dividing the prediction target block for intra prediction along a diagonal line, a dividing diagonal line used for the division is determined from two diagonal lines of the prediction target block, and a plurality of triangular regions obtained by dividing the prediction target block. a determination unit that determines an intra prediction mode to be applied to each of the
a prediction unit that generates a predicted image for each of the plurality of triangular regions using the intra prediction mode determined by the determination unit, synthesizes the generated predicted images, and outputs an intra predicted image;
Based on the intra prediction modes applied to the decoded blocks around the prediction target block, the determination unit selects at least one of the divided diagonal line and the intra prediction mode to be applied to each of the plurality of triangular regions. An intra prediction device characterized by determining one. The determination unit includes an intra-prediction mode applied to an upper block that is a decoded block above the prediction target block and an intra-prediction applied to a left block that is a decoded block to the left of the prediction target block. 2. The intra-prediction device of claim 1, wherein the determination is made based on a mode. When the intra-prediction mode applied to the upper block and the intra-prediction mode applied to the left block are different from each other, the determining unit divides a diagonal line passing through the upper left vertex and the lower right vertex of the prediction target block into the divided diagonal line. 3. The intra prediction device according to claim 2, characterized in that it is determined as . the plurality of triangular areas comprise an upper right triangular area adjacent to the upper block and a lower left triangular area adjacent to the left block;
The determination unit determines the intra prediction mode applied to the upper block as an intra prediction mode to be applied to the upper right triangular region, and determines the intra prediction mode of the left block as an intra prediction mode to be applied to the lower left triangular region. 4. The intra-prediction device according to claim 3, characterized in that it determines. When the intra prediction mode applied to the upper block and the intra prediction mode applied to the left block are the same, the determining unit divides a diagonal line passing through the upper right vertex and the lower left vertex of the prediction target block into the divided diagonal line. 3. The intra prediction device according to claim 2, characterized in that it is determined as . the plurality of triangular areas are composed of an upper left triangular area adjacent to both the upper block and the left block and a lower right triangular area adjacent to neither the upper block nor the left block;
The intra prediction apparatus of claim 5, wherein the determining unit determines the same intra prediction mode applied to the upper block and the left block as an intra prediction mode to be applied to the upper left triangular region. . 7. The intra prediction apparatus of claim 6, wherein the determining unit determines a non-directional intra prediction mode as an intra prediction mode to be applied to the lower right triangular region. When the same intra-prediction mode is a first non-directional intra-prediction mode, the determining unit selects an intra-prediction mode to be applied to the lower right triangular region as the first non-directional intra-prediction mode. 8. The intra prediction device according to claim 7, wherein a different second non-directional intra prediction mode is determined. The determination unit determines an intra prediction mode applied to an upper right block that is a decoded block located to the upper right of the prediction target block, and an intra prediction mode that is applied to a lower left block that is a decoded block located to the lower left of the prediction target block. 7. The intra prediction device according to claim 6, wherein the intra prediction mode to be applied to the lower right triangular region is determined based on at least one of a mode and a mode. An image encoding device comprising the intra prediction device according to any one of claims 1 to 9. An image decoding device comprising the intra prediction device according to any one of claims 1 to 9. A program that causes a computer to function as the intra prediction device according to any one of claims 1 to 9.

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