JP2023168518A - Prediction block generation device, image encoder, image decoder, and program - Google Patents

Abstract

To improve prediction accuracy by properly deciding the weighting coefficient in CIIP.SOLUTION: A prediction block generation device which generates an intra prediction signal and a prescribed prediction signal by predicting a prediction object block obtained by dividing an image by intra prediction and prescribed prediction different from the intra prediction and outputs a prediction signal in the prediction object block by synthesizing the intra prediction signal and the prescribed prediction signal by weighting synthesis, comprises: a mode specification part which specifies an intra prediction mode of intra prediction applied to a peripheral block when there is the peripheral block applied with the intra prediction in the periphery of the prediction object block; and a weighting coefficient decision part which decides a weighting coefficient used for the weighting synthesis on the basis of the intra prediction mode specified by the mode specification part.SELECTED DRAWING: Figure 4

Description

The present invention relates to a predictive block generation device, an image encoding device, an image decoding device, and a program.

BACKGROUND ART Research has been carried out on video encoding methods to compress the amount of data of still images and moving images during transmission and storage. In recent years, ultra-high resolution video such as 8K-SHV has become increasingly popular in video encoding technology, and AVC/H. 264 and HEVC/H. Encoding systems such as H.265 are known.

VVC, a next-generation coding system jointly standardized by MPEG and ITU, uses intra prediction that uses spatial correlation within a frame, and inter prediction that uses correlation between frames ( For example, see Non-Patent Document 1). In these predictions, prediction is performed in units of blocks obtained by dividing an image.

Additionally, VVC is expected to adopt a technology called Combined Inter and Intra Prediction (CIIP). CIIP is a technology that generates inter-predicted blocks and intra-predicted blocks by respectively predicting a prediction target block using inter-prediction and intra-prediction, and outputs a predicted block by combining the inter-predicted blocks and intra-predicted blocks using weighted synthesis. It is. Note that the intra prediction mode for intra prediction in CIIP is fixed to Planar mode.

Information on weighting coefficients used for weighted synthesis in CIIP is not sent from the image encoding device to the image decoding device, and it is determined whether intra prediction is applied to the upper block and left block of the block to be predicted or inter prediction is applied. implicitly determined depending on whether

The specific weighting coefficient is when the weight of the intra prediction block is "Intra" and the weight of the inter prediction block is "Inter".
(a) If intra prediction is used in both, Intra:Inter=3:1
(b) If intra prediction is used in either one, Intra:Inter=2:2
(c) If inter prediction is used in both, Intra:Inter=1:3
It becomes. In other words, the design is such that the weight of the intra-prediction block is large when intra-prediction is applied to the surrounding blocks, and the weight of the inter-prediction block is large when the inter-prediction is applied to the surrounding blocks.

JVET-N1001 Versatile Video Coding (Draft 5)

As described above, the weighting coefficients in CIIP are determined depending on whether intra prediction is applied to surrounding blocks.

However, even if intra prediction is applied to the surrounding blocks, if the intra prediction mode of the surrounding blocks is not Planar prediction, there is a possibility that there is no correlation between the prediction target block and the surrounding blocks, and the patterns and textures may be significantly different. be. In such a case, there is a problem that increasing the weight of the intra-prediction block may have the opposite effect, and the prediction accuracy for the block to be predicted may decrease.

Therefore, an object of the present invention is to provide a predictive block generation device, an image encoding device, an image decoding device, and a program that improve prediction accuracy by appropriately determining weighting coefficients in CIIP.

The prediction block generation device according to the first aspect generates an intra prediction signal and a predetermined prediction signal by respectively predicting a prediction target block obtained by dividing an image by intra prediction and a predetermined prediction different from the intra prediction, and generates an intra prediction signal and a predetermined prediction signal. A prediction block generation device that outputs a prediction signal within the prediction target block by combining an intra prediction signal and the predetermined prediction signal by weighted synthesis, the peripheral block to which intra prediction is applied around the prediction target block. If there is, a mode specifying unit that specifies an intra prediction mode of intra prediction applied to the peripheral block, and a weighting coefficient to be used for the weighted synthesis based on the intra prediction mode specified by the mode specifying unit. A weighting factor determining section. The prediction block generation device according to the embodiment generates an inter prediction block and an intra prediction block by respectively predicting a prediction target block obtained by dividing an image by inter prediction and intra prediction, and generates an inter prediction block and an intra prediction block. A prediction block for the prediction target block is output by combining the blocks using weighted combination. When there is a peripheral block to which intra prediction is applied around the prediction target block, the prediction block generation device includes a mode identifying unit that identifies an intra prediction mode of intra prediction applied to the peripheral block; and a weighting coefficient determination unit that determines a weighting coefficient to be used for the weighted combination based on the intra prediction mode specified by the unit.

The image encoding device according to the second aspect includes the predictive block generation device according to the first aspect.

The image decoding device according to the third aspect includes the predictive block generation device according to the first aspect.

The program according to the fourth aspect causes a computer to function as the predictive block generation device according to the first aspect.

According to the present invention, it is possible to provide a predictive block generation device, an image encoding device, an image decoding device, and a program that improve prediction accuracy by appropriately determining weighting coefficients in CIIP.

FIG. 1 is a diagram showing the configuration of an image encoding device according to an embodiment. FIG. 3 is a diagram showing intra prediction mode candidates according to the embodiment. It is a figure showing Planar mode as an intra prediction mode of intra prediction. FIG. 2 is a diagram showing the configuration of a composition processing section of an image encoding device according to an embodiment. It is a figure showing an upper block and a left block concerning an embodiment. 1 is a diagram showing the configuration of an image decoding device according to an embodiment. FIG. 2 is a diagram showing the configuration of a composition processing section of an image decoding device according to an embodiment. FIG. 3 is a diagram illustrating an example of the operation flow of predictive block generation in the image decoding device according to the embodiment. FIG. 7 is a diagram showing the configuration of a synthesis processing section according to another embodiment.

An image encoding device and an image decoding device according to embodiments will be described with reference to the drawings. The image encoding device and the image decoding device according to the embodiment encode and decode moving images represented by MPEG, respectively. In the description of the drawings below, the same or similar parts are designated by the same or similar symbols.

<Configuration of image encoding device>
First, the configuration of the image encoding device according to this embodiment will be explained. 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 encoding device 1 includes a block division section 100, a subtraction section 110, a transformation/quantization section 120, an entropy encoding section 130, an inverse quantization/inverse transformation section 140, It has a synthesis section 150, a memory 160, and a prediction section 170. In this embodiment, the prediction unit 170 corresponds to a prediction block generation device provided in the image encoding device 1.

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 the division to the subtraction unit 110. The size of the 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 a square, but may be rectangular (non-square). The image block is a unit that is encoded by the image encoding device 1 (that is, a block to be encoded), and is a unit that is decoded by the image decoding device (that is, 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 current block to be encoded output from the block division unit 100 and the prediction block obtained by predicting the current block to be encoded 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 conversion/quantization unit 120.

The transformation/quantization unit 120 performs orthogonal transformation processing and quantization processing on a block-by-block basis. The conversion/quantization unit 120 includes a conversion unit 121 and a quantization unit 122.

The transform unit 121 performs orthogonal transform processing on the prediction residual output from the subtractor 110 to calculate orthogonal transform coefficients, and outputs the calculated orthogonal transform coefficients to the quantizer 122 . The orthogonal transformation refers to, for example, a discrete cosine transform (DCT), a discrete sine transform (DST), a Karhunen-Loeve transform (KLT), or the like.

The quantization unit 122 quantizes the orthogonal transform coefficients output from the transform unit 121 using a quantization parameter (Qp) and a quantization matrix, and sends the quantized orthogonal transform coefficients to an entropy encoder 130 and inverse quantization/dequantization. It is output to the inverse transformer 140. Note that the quantization parameter (Qp) is a parameter commonly applied to each orthogonal transform coefficient within a block, and is a parameter that determines the roughness of quantization. The quantization matrix is a matrix having as elements quantization values when quantizing each orthogonal transform coefficient.

The entropy encoding unit 130 performs entropy encoding on the orthogonal transform coefficients output from the quantization unit 122, performs data compression to generate encoded data (bitstream), and performs image encoding on the encoded data. Output to the outside of the device 1. For entropy encoding, a Huffman code, CABAC (Context-based Adaptive Binary Arithmetic Coding), or the like can be used. Note that the entropy encoding unit 130 receives information regarding prediction from the prediction unit 170, and also performs entropy encoding of 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 transformation section 140 includes an inverse quantization section 141 and an inverse transformation section 142.

The dequantization unit 141 performs dequantization processing corresponding to the quantization processing performed by the quantization unit 122. Specifically, the dequantization unit 141 restores orthogonal transformation coefficients by dequantizing the orthogonal transformation coefficients output from the quantization unit 122 using a quantization parameter (Qp) and a quantization matrix. , the restored orthogonal transform coefficients are output to the inverse transform unit 142.

The inverse transform unit 142 performs an inverse orthogonal transform process corresponding to the orthogonal transform process performed by the transform unit 121. For example, if the transform unit 121 performs a discrete cosine transform, the inverse transform unit 142 performs an 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 residual, and combines the restored prediction residual, which is the restored prediction residual, with the synthesis unit 150 Output to.

The combining unit 150 combines the restored prediction residual output from the inverse transform unit 142 with the prediction block output from the prediction unit 170 on a pixel-by-pixel basis. The combining unit 150 decodes (reconfigures) the current block by adding each pixel value of the restored prediction residual and each pixel value of the prediction block, and outputs the decoded block to the memory 160. Note that the decoded block is sometimes called a reconstructed block.

The memory 160 stores the decoded blocks output from the combining unit 150, and accumulates the decoded blocks as decoded images in frame units. The memory 160 outputs the stored decoded blocks or decoded images to the prediction unit 170. Note that a loop filter may be provided between the synthesis section 150 and the memory 160. In this embodiment, the memory 160 further stores information regarding predictions applied to each decoded block (hereinafter referred to as "block prediction information").

The prediction unit 170 performs prediction on a block-by-block basis. The encoding target block handled by the prediction unit 170 is called a "prediction target block." The prediction unit 170 includes an intra prediction unit 171 , an inter prediction unit 172 , a combination processing unit 173 , and a switching unit 174 .

The intra prediction unit 171 performs intra prediction using spatial correlation within a frame. Specifically, the intra prediction unit 171 generates an intra prediction block by referring to decoded pixels around the prediction target block of the intra prediction among the decoded images stored in the memory 160, and generates an intra prediction block. The predicted block is output to the switching unit 174. Generally, the intra prediction unit 171 selects an intra prediction mode to be applied to a prediction target block of intra prediction from among a plurality of intra prediction modes, and predicts the target block using the selected intra prediction mode. Intra prediction section 171 outputs information regarding the selected intra prediction mode to entropy encoding section 130.

FIG. 2 is a diagram showing intra prediction mode candidates according to this embodiment. As shown in FIG. 2, there are 67 intra prediction modes from 0 to 66 as intra prediction mode candidates. Mode "0" of the intra prediction mode is planar prediction, mode "1" of the intra prediction mode is DC prediction, and modes "2" to "66" of the intra prediction mode 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 pixel to be predicted, and the end point of the arrow indicates the position of the reference pixel used to predict the pixel to be predicted. There are two modes: mode "2", which is an intra prediction mode that refers to the lower left direction, and mode "66", which is an intra prediction mode that refers to the upper right direction, as the reference direction parallel to the diagonal line passing through the upper right and lower left vertices of the block. , mode numbers are assigned clockwise from mode "2" to mode "66" for each predetermined angle.

The inter prediction unit 172 performs inter prediction using correlation between frames. Specifically, the inter prediction unit 172 uses the decoded image stored in the memory 160 as a reference image, calculates a motion vector by a method such as block matching, predicts the prediction target block for inter prediction, and uses the inter prediction block as a reference image. A prediction block is generated, and the generated inter prediction block is output to the switching unit 174. Here, the inter prediction unit 172 selects the optimal inter prediction method from among inter prediction using multiple reference images (typically, bi-prediction) and inter prediction using one reference image (unidirectional prediction). Inter prediction is performed using the selected inter prediction method. The inter prediction unit 172 outputs information related to inter prediction (motion vectors, etc.) to the entropy encoding unit 130.

In this embodiment, the prediction unit 170 has a CIIP function. In the following, CIIP is assumed to be a function belonging to inter prediction. When applying CIIP to a prediction target block, the prediction unit 170 generates an inter prediction block and an intra prediction block by respectively predicting the CIIP prediction target block by inter prediction and intra prediction, and generates an inter prediction block and an intra prediction block. A predicted block is output by combining using weighted combining. When applying CIIP to a block to be predicted, the prediction unit 170 outputs information indicating that CIIP is applied to this block to the entropy encoding unit 130.

Specifically, when applying CIIP to a prediction target block, the intra prediction unit 171 and the inter prediction unit 172 respectively perform intra prediction and inter prediction on the same prediction target block. Then, the intra prediction unit 171 outputs the intra prediction block to the synthesis processing unit 173, and the inter prediction unit 172 outputs the inter prediction block to the synthesis processing unit 173.

In CIIP, the intra prediction unit 171 applies Planar mode as an intra prediction mode for intra prediction. As shown in FIG. 3, Planar prediction is an intra prediction mode in which a predicted pixel value is generated by interpolation prediction using four reference pixels located on the upper, lower, left and right sides of the starting points of four arrows. Alternatively, in CIIP, the intra prediction unit 171 may apply an intra prediction mode other than Planar mode.

The combination processing unit 173 generates a prediction block by combining the intra prediction block output from the intra prediction unit 171 and the inter prediction block output from the inter prediction unit 172 by weighted combination, and sends the generated prediction block to the switching unit. 174. In this embodiment, it is assumed that the prediction block output by the synthesis processing unit 173 is a type of inter prediction block. Details of the composition processing section 173 will be described later.

The switching unit 174 switches between the inter prediction block output from the inter prediction unit 172 or the synthesis processing unit 173 and the intra prediction block output from the intra prediction unit 171, and selects one of the prediction blocks from the subtraction unit 110 and the synthesis unit. Output to 150.

FIG. 4 is a diagram showing the configuration of the composition processing section 173 of the image encoding device 1 according to the present embodiment.

As shown in FIG. 4, the synthesis processing section 173 includes a mode identification section 173a, a weighting factor determination section 173b, and a weighting synthesis section 173c.

Based on the block prediction information of each decoded block stored in the memory 160, the mode specifying unit 173a determines whether or not the prediction target block has a peripheral block to which intra prediction has been applied (decoded block) around the prediction target block. Identify the intra-prediction mode of the intra-prediction applied to. Furthermore, when there are a plurality of peripheral blocks to which intra prediction is applied around the prediction target block, the mode identifying unit 173a identifies the intra prediction mode of the intra prediction applied to each of the plurality of peripheral blocks.

In this embodiment, an upper block that is an adjacent block above the prediction target block and a left block that is an adjacent block to the left of the prediction target block are used as peripheral blocks. The prediction target block and the surrounding blocks may have different block shapes and block sizes. Therefore, as shown in FIG. 5, the upper block is an adjacent block that includes a pixel adjacent to the upper right pixel of the prediction target block. Further, the left block is an adjacent block including a pixel adjacent to the left side of the lower left pixel of the prediction target block.

The mode specifying unit 173a compares the intra prediction mode applied to the intra prediction of the prediction target block and the intra prediction modes of each of the plurality of peripheral blocks (upper block and left block). Specifically, the mode identifying unit 173a identifies the number of mode matches, which is the number that matches the intra prediction mode applied to the intra prediction of the prediction target block, among the intra prediction modes of each of the plurality of peripheral blocks, and The mode matching number is output to the weighting coefficient determination unit 173b.

When the intra prediction mode applied to the prediction target block in CIIP is fixed at Planar mode, the mode specifying unit 173a reads information on the intra prediction modes of the surrounding blocks from the memory 160, and selects the Planar mode among the intra prediction modes of the surrounding blocks. Specify the number of modes as the number of mode matches. In this embodiment, since the peripheral blocks are the upper block and the left block, the number of mode matches is 0, 1, or 2.

On the other hand, when the intra prediction mode applied to the prediction target block in CIIP is variable, the mode specifying unit 173a reads information on the intra prediction mode of the surrounding blocks from the memory 160, and also reads the intra prediction mode information applied to the prediction target block from the memory 160. Mode information is acquired from the intra prediction unit 171. Then, the mode specifying unit 173a specifies the number of intra prediction modes applied to the prediction target block among the intra prediction modes of the surrounding blocks as the number of mode matches. In this embodiment, since the peripheral blocks are the upper block and the left block, the number of mode matches is 0, 1, or 2.

The weighting coefficient determination unit 173b determines a weighting coefficient to be used for weighted combination in CIIP based on the intra prediction mode of the peripheral block identified by the mode identification unit 173a, and outputs the determined weighting coefficient to the weighted combination unit 173c. In the present embodiment, the weighting factor determination unit 173b determines the weighting coefficient based on the number of mode matches output by the mode identifying unit 173a.

For example, as shown in Table 1, the weighting coefficient determining unit 173b determines the weighting coefficients so that as the number of mode matches increases, the weight ratio of the intra-predicted block to the inter-predicted block increases.

Here, the total weight of the intra prediction block and the inter prediction block is set to 4. For example, the weighting coefficient determination unit 173b outputs the weight of the intra prediction block to the weighting synthesis unit 173c as a weighting coefficient wt.

The weighted synthesis unit 173c combines the intra prediction block outputted from the intra prediction unit 171 and the inter prediction block outputted from the inter prediction unit 172 by weighted synthesis based on the weighting coefficient wt outputted from the weighting coefficient determination unit 173b. By doing so, a prediction block is generated, and the generated prediction block is output to the switching unit 174.

Specifically, the weighted synthesis unit 173c synthesizes the intra prediction block and the inter prediction block by weighted synthesis on a pixel basis. For example, when the pixel value of the intra-prediction block is P _intra and the pixel value of the inter-prediction block is P _inter , the weighted synthesis unit 173c calculates the pixel value P _CIIP of the prediction block using the following equation (1).

<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 includes an entropy decoding section 200, an inverse quantization/inverse transformation section 210, a combining section 220, a memory 230, and a prediction section 240. In this embodiment, the prediction unit 240 corresponds to a prediction block generation device provided in the image decoding device 2.

The entropy decoding unit 200 decodes the encoded data generated by the image encoding device 1 and outputs quantized orthogonal transform coefficients to the inverse quantization/inverse transform unit 210. Further, the entropy decoding unit 200 acquires information regarding prediction (intra prediction and inter prediction), and outputs the acquired information to the prediction unit 240. In this embodiment, when CIIP is applied to the block to be decoded, the entropy decoding unit 200 acquires information indicating that CIIP is applied to the block to be decoded, and outputs the acquired information to the prediction unit 240. do.

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 transformation section 210 includes an inverse quantization section 211 and an inverse transformation section 212.

The dequantization unit 211 performs dequantization processing corresponding to the quantization processing performed by the quantization unit 122 of the image encoding device 1. The dequantization unit 211 dequantizes the quantized orthogonal transform coefficients output from the entropy decoding unit 200 using the quantization parameter (Qp) and the quantization matrix, thereby dequantizing the orthogonal transform coefficients of the block to be decoded. The restored orthogonal transform coefficients are output to the inverse transform unit 212.

The inverse transform unit 212 performs an inverse orthogonal transform process corresponding to the orthogonal transform process 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 the prediction residual, and combines the restored prediction residual (restored prediction residual) with the synthesis unit 220 Output to.

The combining unit 220 decodes (reconfigures) the original block by combining the prediction residual output from the inverse transform unit 212 and the prediction block output from the prediction unit 240 pixel by pixel. Output the block to memory 230.

The memory 230 stores the decoded blocks output from the combining 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 unit 240. Furthermore, the memory 230 outputs the decoded image in units of frames to the outside of the image decoding device 2 . Note that a loop filter may be provided between the synthesis section 220 and the memory 230. In this embodiment, memory 230 further stores block prediction information regarding predictions applied to each decoded block.

The prediction unit 240 performs prediction on a block-by-block basis. The prediction unit 240 includes an intra prediction unit 241 , an inter prediction unit 242 , a combination processing unit 243 , and a switching unit 244 .

The intra prediction unit 241 performs intra prediction using spatial correlation within a frame. Specifically, the intra prediction unit 241 determines whether the intra prediction is correct among the decoded images stored in the memory 230 based on information regarding intra prediction output from the entropy decoding unit 200 (for example, information on the intra prediction mode). An intra prediction block is generated by referring to decoded pixels around the prediction target block, and the generated intra prediction block is output to the switching unit 244.

The inter prediction unit 242 performs inter prediction using correlation between frames. Specifically, the inter prediction unit 242 performs inter prediction using the decoded image stored in the memory 230 as a reference image based on information regarding inter prediction (for example, motion vector information) output from the entropy decoding unit 200. The prediction target block is predicted to generate an inter prediction block, and the generated inter prediction block is output to the switching unit 244.

In this embodiment, the prediction unit 240 has a CIIP function. When the information output from the entropy decoding unit 200 includes information indicating that CIIP is applied to the prediction target block, the prediction unit 240 predicts the CIIP prediction target block by inter prediction and intra prediction, respectively, and generates an inter prediction block. and an intra prediction block, and outputs the prediction block by combining the inter prediction block and the intra prediction block by weighted combination.

Specifically, when applying CIIP to a prediction target block, the intra prediction unit 241 and the inter prediction unit 242 respectively perform intra prediction and inter prediction on the same prediction target block. Then, the intra prediction unit 241 outputs the intra prediction block to the synthesis processing unit 243, and the inter prediction unit 242 outputs the inter prediction block to the synthesis processing unit 243. In CIIP, the intra prediction unit 241 applies Planar mode as an intra prediction mode for intra prediction. Alternatively, in CIIP, the intra prediction unit 241 may apply an intra prediction mode other than Planar mode.

The combination processing unit 243 generates a prediction block by combining the intra prediction block output from the intra prediction unit 241 and the inter prediction block output from the inter prediction unit 242 by weighted combination, and sends the generated prediction block to the switching unit. 244.

The switching unit 244 switches between the inter prediction block output from the inter prediction unit 242 or the synthesis processing unit 243 and the intra prediction block output from the intra prediction unit 241, and outputs either prediction block to the synthesis unit 220. .

FIG. 7 is a diagram showing the configuration of the composition processing section 243 of the image decoding device 2 according to this embodiment.

As shown in FIG. 7, the synthesis processing section 243 includes a mode specifying section 243a, a weighting coefficient determining section 243b, and a weighting synthesis section 243c. The mode specifying section 243a, the weighting factor determining section 243b, and the weighting combining section 243c perform the same operations as the mode specifying section 173a, the weighting factor determining section 173b, and the weighting combining section 173c shown in FIG. 4, respectively.

<Operation example of predictive block generation>
Next, an example of the operation flow of predictive block generation according to this embodiment will be described. Although the operation of generating a predictive block is the same in the image encoding device 1 and the image decoding device 2, the operation of generating a predictive block (prediction unit 240) in the image decoding device 2 will be described here.

FIG. 8 is a diagram showing an example of the operation flow of predictive block generation (prediction unit 240) in the image decoding device 2 according to the present embodiment.

As shown in FIG. 8, in step S1, the prediction unit 240 determines whether to apply CIIP to the prediction target block based on the information output from the entropy decoding unit 200.

When applying CIIP to the prediction target block (step S1: YES), in step S2, the intra prediction unit 241 and the inter prediction unit 242 predict the prediction target block by inter prediction and intra prediction, respectively, and generate an inter prediction block and an intra prediction block. Generate a prediction block.

In step S3, the mode specifying unit 243a acquires from the memory 230 information on the intra prediction mode of intra prediction applied to peripheral blocks around the prediction target block. In this embodiment, an upper block that is an adjacent block above the prediction target block and a left block that is an adjacent block to the left of the prediction target block are used as peripheral blocks.

In step S4, the mode specifying unit 243a specifies the number of mode matches, which is the number that matches the intra prediction mode applied to the intra prediction of the prediction target block, among the intra prediction modes of each of the plurality of peripheral blocks.

As described above, when the intra prediction mode applied to the prediction target block in CIIP is fixed at Planar mode, the mode specifying unit 243a reads information on the intra prediction mode of the surrounding block from the memory 230, and uses the intra prediction mode of the surrounding block. The number of Planar modes among the prediction modes is specified as the number of mode matches.

On the other hand, when the intra prediction mode applied to the prediction target block in CIIP is variable, the mode specifying unit 243a reads information on the intra prediction mode of the surrounding blocks from the memory 230, and also reads the intra prediction mode information applied to the prediction target block from the memory 230. Mode information is acquired from the intra prediction unit 241. Then, the mode specifying unit 243a specifies the number of intra prediction modes applied to the prediction target block among the intra prediction modes of the surrounding blocks as the number of mode matches.

In step S5, the weighting coefficient determination unit 243b determines the weighting coefficient to be used for weighted synthesis in CIIP based on Table 1 based on the number of mode matches output by the mode identification unit 243a, and sends the determined weighting coefficient to the weighted synthesis unit 243c. Output.

In step S6, the weighting synthesis unit 243c weights the intra prediction block output from the intra prediction unit 241 and the inter prediction block output from the inter prediction unit 242 based on the weight coefficient output from the weight coefficient determination unit 243b. A prediction block is generated by combining, and the generated prediction block is output.

<Summary of embodiments>
As described above, when applying CIIP to a prediction target block, the synthesis processing unit 173 and the synthesis processing unit 243 according to the present embodiment determine weighting coefficients to be used for weighted synthesis in CIIP based on the intra prediction modes of surrounding blocks. do.

As a result, even if intra prediction is applied to the surrounding blocks, if the intra prediction modes do not match between the prediction target block and the surrounding blocks, the weight of the intra prediction block is not increased, which reduces the prediction accuracy in CIIP. can be suppressed.

In addition, if the intra prediction modes of the prediction target block and the surrounding blocks match, it can be said that the correlation between the prediction target block and the surrounding blocks is high, so by increasing the weight of the intra prediction block, the prediction accuracy in CIIP can be improved.

<Other embodiments>
In the embodiments described above, when applying CIIP to a prediction target block, the combination processing unit 173 and the combination processing unit 243 determine weighting coefficients to be used for weighted combination in CIIP based on the intra prediction modes of neighboring blocks. However, in determining the weighting coefficient, not only the intra prediction mode of the surrounding blocks but also whether the prediction method applied to the surrounding blocks is intra prediction or inter prediction may be considered.

FIG. 9 is a diagram showing the configuration of the synthesis processing section 173 according to another embodiment. Here, the configuration of the composition processing section 173 will be explained as an example, but it is assumed that the composition processing section 243 is also constructed in the same manner.

As shown in FIG. 9, the synthesis processing section 173 further includes a prediction method specifying section 173d that specifies whether the prediction method applied to the peripheral block is intra prediction or inter prediction. For example, the prediction method identifying unit 173d acquires prediction method information indicating whether the applied prediction method is intra prediction or inter prediction for each of the upper block and the left block (see FIG. 5), and acquires the prediction method information indicating whether the applied prediction method is intra prediction or inter prediction. The predicted prediction method information is output to the weighting coefficient determination unit 173b.

The weighting coefficient determination unit 173b determines a weighting coefficient to be used for weighted synthesis in CIIP based on the prediction method of the peripheral block identified by the prediction method identification unit 173d and the intra prediction mode of the peripheral block identified by the mode identification unit 173a. do. For example, the weighting coefficient determination unit 173b determines the weighting coefficients as shown in Table 2.

Here, the total weight of the intra prediction block and the inter prediction block is set to eight. For example, the weighting coefficient determination unit 173b outputs the weight of the intra prediction block to the weighting synthesis unit 173c as a weighting coefficient wt.

Note that 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. Computer-readable media allow programs to be installed on a 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, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

The image encoding device 1 may be configured by a semiconductor integrated circuit (chip set, SoC) by integrating circuits that execute each process performed by the image encoding device 1. The image decoding device 2 may be configured by a semiconductor integrated circuit (chip set, SoC) by integrating circuits that execute each process performed by the image decoding device 2.

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

1: Image encoding device 2: Image decoding device 100: Block division unit 110: Subtraction unit 120: Transformation/quantization unit 121: Transformation unit 122: Quantization unit 130: Entropy encoding unit 140: Inverse quantization/inverse transformation Unit 141: Inverse quantization unit 142: Inverse transformation unit 150: Combination unit 160: Memory 170: Prediction unit 171: Intra prediction unit 172: Inter prediction unit 173: Combination processing unit 173a: Mode identification unit 173b: Weighting coefficient determination unit 173c : Weighted synthesis unit 173d : Prediction method identification unit 174 : Switching unit 200 : Entropy decoding unit 210 : Inverse quantization/inverse transformation unit 211 : Inverse quantization unit 212 : Inverse transformation unit 220 : Combining unit 230 : Memory 240 : Prediction unit 241: Intra prediction section 242: Inter prediction section 243: Combination processing section 243a: Mode specification section 243b: Weighting coefficient determination section 243c: Weighting synthesis section 243d: Prediction method specification section 244: Switching section

Claims (4)

A prediction target block obtained by dividing the image is predicted by intra prediction and a predetermined prediction different from the intra prediction to generate an intra prediction signal and a predetermined prediction signal, and the intra prediction signal and the predetermined prediction signal are weighted and combined. A prediction block generation device that outputs a prediction signal in the prediction target block by combining,
If there is a peripheral block to which intra prediction is applied around the prediction target block, a mode identifying unit that identifies an intra prediction mode of intra prediction applied to the peripheral block;
A predictive block generation device comprising: a weighting coefficient determining unit that determines a weighting coefficient to be used in the weighted combination based on the intra prediction mode identified by the mode identifying unit. An image encoding device comprising the predictive block generation device according to claim 1. An image decoding device comprising the predictive block generation device according to claim 1. A program that causes a computer to function as the predictive block generation device according to claim 1.

Images